Forum 79 Proceedings

The Vertical Flight Society thanks Toray for sponsorship of the Forum 79 proceedings!

Find Proceedings by clicking one of the sorting functions below. You can also use the Quick Search box to quickly locate titles and authors.

Attended the Forum? Log in at the top of this page or at My VFS for links to download papers and interfaces!

Sort by session | Sort by author | Sort by title

39th Student Design Competition Graduate Winner: RPI Oliwhoper eVTOL Air Taxi for Passengers with Reduced Mobility (Paper 1410)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Richard Healy, Alexander Stillman

The successful implementation of eVTOLaircraft as a viable mode of future transportation hinges on the inclusion of all passengers, including those with disabilities either visible or hidden. To this end, the graduate design team from Rensselaer Polytechnic Institute propose Oliwhoper, a lift + cruise multicopter universally designed for all passengers. Oliwhoper takes on a universal design approach, where accommodations for those with disabilities are used to enhance the ride experience for everyone. A spacious cabin with carefully designed lighting, hand-holds and audio cues makes it easy for anyone with mobility, visual or auditory challenges to safely and easily ride in comfort. These vehicle design features make Oliwhoper accessible to passengers with reduced mobility, allowing for operators to flexibly service customers in a variety of locations, without the need for specialized ground equipment. Operators will also enjoy Oliwhoper's efficient lift + cruise design which maximizes the performance advantages of distributed electric propulsion, while maintaining the redundancy and control authority expected from modern aircraft.

39th Student Design Competition Undergraduate Winner: UMD Blitzen eVTOL Air Taxi for Passengers with Reduced Mobility (Paper 1409)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Vivek Uppoor

The UMD team was tasked with designing an electric vertical takeoff and landing (eVTOL) air taxi for accommodating passengers with varying disabilities. Blitzen's name is inspired by the German word 'Blitz', which translates to lightning, as well as the name of the mythical flying reindeer. With Blitzen, everyone can enjoy the future of lightning-fast, comfortable, and convenient transportation. Blitzen follows an energy-efficient lift and thrust compounding single main rotor (SMR) design with a fixed wing and swiveling rotorprop that provides anti-torque in hover and forward thrust in cruise. Its spacious cabin provides several disability accommodations, including wheelchair accessibility, storage for large medical devices and resources for those with impaired hearing. A compact wide-screen avionics suite minimizes pilot workload. Outside the cockpit and cabin, all of Blitzen's systems are designed to prioritize safety and comfort without compromising vehicle performance.

46 Years of Flight Test: Sikorsky's Development Flight Center (Paper 127)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Adam Posset, John Herter, Phil Alldridge

Sikorsky's Development Flight Center (DFC) began operations in March of 1977, just days before the first flight of the S-76® commercial utility helicopter. Since then, the facility has witnessed a significant number of 'first flights', with development and production programs spanning from small, unmanned, air vehicles (UAV) through to the massive CH-53K heavy lift helicopter, culminating in the recent S-97 RAIDER® and Sikorsky-Boeing SB<1 DEFIANT® programs for the U.S. Army's Future Vertical Lift (FVL) program. This paper will walk the reader through the construction of this unique flight test facility located in the midst of the Florida wetlands, and will highlight some of the major, and often innovative, test programs performed over the last 46 years.

4th Rotor Hub Flow Prediction Workshop Experimental Data Campaigns and Computational Analyses (Paper 1239)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Sven Schmitz, David Reich, Nicholas Jaffa

The rotor hub flow prediction workshops are held bi-annually at Penn State's Vertical Lift Research Center of Excellence (VLRCOE) to support academia, industry, and government in validating state-of-the-art computational fluid dynamics (CFD) tools. Initiated with support from VLRCOE, the National Rotorcraft Technology Center (NRTC), and the Fluid Dynamics Research Consortium (FDRC) at Penn State, these workshops have been compelling examples of productive exchanges between experimentalists and computational researchers and have had positive impact on both planning new experiments and subsequent computational grid and method development. There is continued interest in these comparisons as rotor hub flows are characterized by complex turbulent flow fields, while at the same time being a primary contributor to helicopter parasite drag. High-Reynolds number testing of rotor hub flows is necessary as high-Reynolds turbulent coherent structures remain strong for long distances downstream of the hub and up to the long-age wake where they interact with the empennage and tail. Basic research conducted at Penn State's water tunnel facilities has provided such unique high Reynolds-scale data of rotor hub wakes, providing new data for physical understanding and CFD validation. This paper summarizes the experimental data campaigns and 'blind comparison' computational results presented at the fourth rotor hub flow prediction workshop.

A Comparison of Rotor Disk Modeling and Blade-Resolved CFD Simulations for NASA's Tiltwing Air Taxi (Paper 104)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
David Garcia Perez, Patricia Ventura Diaz, Jasim Ahmad, Seokkwan Yoon

A multi-fidelity computational fluid dynamics analysis is carried out for NASA's tiltwing air taxi concept operating in airplane and helicopter mode. High-fidelity simulations are computationally expensive due to individual rotor blade modeling in a time-dependent computational domain with rotating grids. The mid-fidelity rotor disk option, in its source term implementation, is explored as a more affordable alternative. Computations are performed with NASA's OVERFLOW flow solver loosely-coupled with the comprehensive code CAMRAD II for appropriate rotor trim. Detailed comparisons are shown for the trim solution, airloads, wake geometry, and rotor performance. While the rotor disk model is able to capture the flow field with satisfactory agreement in airplane mode, it faces difficulties in helicopter mode due to the three-dimensional effects of the wake. Although this study is limited to a specific vehicle geometry, it is expected that the results are somewhat generalizable to the analysis of multirotor configurations.

A Comparison of Traditional and Vuichard Vortex Ring State Recovery Techniques Using On-line Simulation (Paper 1231)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Eleni Sotiropoulos-Georgiopoulos, Alexia Payan, Charles Johnson, Dimitri Mavris

From 2008 to 2021, 48 helicopter accidents have involved Vortex Ring State (VRS) encounters in the United States. Vortex Ring State is still a misunderstood phenomenon, which is challenging to identify and recover from. Currently, two competing recovery techniques are taught to pilots: the Traditional and the Vuichard recoveries. This paper presents initial steps in comparing these techniques. A first approach relies on online scenario-based simulations in an S76 flight simulator to determine pilots' decision-making process during a VRS encounter and their ability to recover. These scenarios are designed based on an analysis of VRS accident reports from the 13 biggest helicopter-operating countries.

A Computational Investigation of Canted Side-by-Side Rotors in Ground Effect (Paper 1295)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Richard Healy, Farhan Gandhi

This study investigates the interactional aerodynamics of canted side-by-side rotors hovering in ground effect. The 5.5 ft diameter 3-bladed fixed-pitched rotors are simulated using CFD at a targeted 5 psf disk loading. Simulations are performed using the commercial Navier Stokes solver AcuSolve with a delayed detached eddy simulation (DDES) model. Side-by-side rotors are simulated at a height above the ground equal to one rotor radius (z/R = 1.0) and with 2.5R hub-hub spacing. In addition to an uncanted case, side-by-side rotors are simulated in ground effect (IGE) with 10° differential lateral cant, 10° inwards cant, and 10° outwards cant. Between the uncanted side-by-side rotors IGE, a highly turbulent mixing region is identified where the wakes of each rotor collide and fountain up. As blades traverse the highly turbulent flow, strong vibratory loading is induced and a thrust loss is observed over the outboard blade sections. The associated unsteady vertical loading for uncanted, laterally canted, and canted outwards rotors is similar, ranging from 10% - 16% peak-to-peak whereas canted inwards rotors show increased vibratory loading at 22% peak-to-peak. Integrated thrust for uncanted rotors IGE is 4.3% more than if out of ground effect (OGE), though when laterally canted or canted outwards, thrust generation is reduced to within 1% of isolated OGE rotors. Canted inwards rotors produce even less thrust, generating 15.2% less thrust than isolated OGE rotors. Overall, canting side-by-side rotors IGE incurs thrust production and vibration penalties. If canting is required for improved control authority, laterally canted rotors generate the most thrust while canted outwards rotors generate the least vibratory loading.

A Digital Twin Framework for Structural Health Monitoring Enhanced by Physics-Based Reduced Order Modeling and Stochastic Time Series Models (Paper 1381)
Full registrant at Forum? Log in for link!
HUMS II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Fotis Kopsaftopoulos, Peiyuan Zhou, Yiming Zhou, Brian Ju

In this work, a hybrid digital twin (DT) framework for structural health monitoring (SHM) of rotorcraft structures is proposed. This framework integrates both ultrasonic-guided wave-based and vibration-based SHM schemes for tackling damage detection, identification and quantification under uncertainty. To achieve that, two novel data-driven reduced-order models (ROMs) are introduced to approximate high-frequency (ultrasonic) guided-wave dynamics and low-frequency vibration dynamics, respectively. For the high-frequency DT (HFDT), a novel scheme taking direct guided wave signals as inputs is proposed for damage detection and quantification task. In the training phase, a Convolutional AutoEncoder (CAE) is trained to achieve accurate ultrasonic wave signal reconstruction. In the online monitoring phase, the latent space representations of inputs can be extracted in an automated manner through the encoder. The extracted features are then combined with a feed forward neural network (FFNN) and Gaussian process (GP) models to provide damage level estimates in a deterministic and probabilistic manner, respectively. For the low-frequency DT (LFDT), the cornerstone of the proposed approach is the stochastic functionally pooled (FP) time series family of models. The FP model structure makes use of functional data pooling techniques for combining and optimally treating as one entity the data obtained from various structural states, and statistical techniques for model estimation. Damage detection and quantification are treated as an inverse problem and appropriate optimization techniques. To address the LFDT requirement for training data under various structural states, a Bayesian inversion physics-based finite element model (FEM) framework is postulated that enables the FEM updating and calibration via the use of experimental data. To demonstrate the applicability and evaluation of the proposed DT platform, two case studies are performed: (i) HFDT/ROM of guided-wave in Airbus H125 main rotor blade for SHM purposes and a (ii) LFDT/ROM of an Airbus H125 main rotor blade updated via vibrational data.

A Framework to Enhance the Mitigation of Loss of Tail Rotor Effectiveness (Paper 1363)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Paola Zanella, J.V.R. Prasad, Charles Johnson, Dimitri Mavris

Loss of tail rotor effectiveness (LTE), also known as unanticipated yaw, has been recognized as a major contributing factor in several helicopter accidents where directional control is lost. Through the Helicopter Flight Data Monitoring (HFDM) program, pilots receive constant flight evaluation reports to support LTE risk mitigation. Nevertheless, the existing LTE safety metric presents several pitfalls that hinder the reliability of the detection of violations of boundaries for flight safety. This paper presents a new framework in the development and evaluation of an expanded safety metric to enhance the detection of proximity to LTE within the HFDM program. The new metric combines three different underlying phenomena that can lead to an LTE event, i.e., loss of weathercock stability, running out of pedal (tail rotor collective) for trim, and tail rotor vortex ring state. A parametric surrogate model for the detection of proximity to an LTE event is formulated by combining results from physics-based simulations with machine learning techniques. The new framework allows for operator fine-tuning of proximity to LTE boundaries, and hence, it provides flexibility in risk management from post-flight analyses. Finally, the framework is compared against the method currently used within the HFDM program, confirming its enhanced detection of the proximity to LTE.

A Holistic Comparison of a Trailing Edge Rib Demonstrator made with Three Different PEEK Thermoplastic Composite Form Factors: Unidirectional, Fabric and Braid (Paper 1170)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Alfonso Lopez, Joe Spangler, Supun Kariyawasam, Waruna Seneviratne, Richard Postera, David Leach, Brennan Carroll, Billy Wood

This study investigates the forming quality and mechanical performance of a trailing edge rib made with three different carbon fiber PEEK form factors, tape, fabric, and braid. It was found tape ribs developed the most severe level of wrinkling and waviness leading to premature ILT failure in the flange. This contrasted with braid and fabric ribs, which failed in compression buckling and had almost three times the deformation before ultimate failure. Moreover, the reinforcement form factor, combined with a high elongation to break matrix like PEEK, was found to have a significant effect on crack propagation and toughness leading to the different failure modes. The trade-offs between tape, fabric and braid form factors are similar to those with thermosets, but seemingly exaggerated, considering fabrics and braids displayed a large amount of plastic deformation while PEEK tape laminates displayed failure progression similar to thermoset composites. These findings have important implications for the design and optimization of thermoplastic composites in new aerial mobility vehicles expected to operate at higher frequency in environments with more varied damage hazard potential.

A Method to Compare Virtual and Live Critical Azimuth Results for a V-22 (Paper 1159)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Zachary Smith, Robert Brymer, Jonathan Dronfield, Eddie Ball, Tyler Fean, Ryan Paul

Virtual V-22 critical azimuth data was collected in the Manned Flight Simulator at Naval Air Station Patuxent River using a new developmental un-validated blade-element-model. The virtual data was compared to live data that had mirrored test conditions as a way to create a process for model validation. Pilot ratings and comments enabled assessment of the relative workloads between the live and simulated test points. In the future, this quantitative and qualitative data will be one of the building blocks to help with simulation validation for multiple type/model/series aircrafts. The process is defined here and initial comparisons with the un-validated model return promising results.

A Model-Based Design Framework for Electric VTOL Aircraft (Paper 1372)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Vishnu Saj, Farid Saemi, Tasfia Kamal, Yen-Cheng Wang, Harsh Sapra, Atanu Halder, Moble Benedict, Sage Kokjohn, Constandinos Mitsingas

The paper presents the development of a multi-disciplinary modeling framework to predict the system-level performance of a diverse range of electric vertical takeoff and landing (eVTOL) aircraft. A key feature of this framework is its modular architecture where the various components are modeled separately and then integrated together based on the aircraft configuration. This modular approach enables the user to analyze various conventional as well as unconventional aircraft architectures by selecting and arranging different pre-existing component models within the framework. The framework comprises four key modules: control system, powertrain, aerodynamics, and flight dynamics, each representing a specific aspect of the system. These modules are further broken down into component/subsystem models, utilizing a combination of physics-based and semi-empirical modeling techniques. The subsystem models are validated using existing experimental data. The framework's modularity is demonstrated by modeling three different multirotor configurations for a given mission while predicting the performance of each subsystem. The proposed framework provides a powerful tool for eVTOL aircraft designers and engineers to predict the aircraft's performance and improve their design.

A Modular Open Systems Approach (MOSA) for Assured Autonomy Certification for Autonomous and Semi-autonomous Air Vehicles (Paper 75)
Full registrant at Forum? Log in for link!
Systems Engineering I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Daniel Schrage

A Modular Open Systems Approach (MOSA) is an integrated business and technical strategy for assessing and implementing open systems in the Department of Defense (DoD) and beyond. An open system is a system that employs modular design tenets, uses widely supported and consensus-based standards for its keyinterfaces, and is subject to Validation and Verification, including Test and Evaluation, to ensure the openness of its key interfaces. The Army PEO Aviation MOSA Implementation Guide defines MOSA as follows:

A Parametric Investigation of Rotor-Rotor Interaction Noise Generation (Paper 1255)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Robert Rau, Eric Greenwood

An extensive parametric study of a two rotor system configurations is conducted to investigate the effect of rotor placement on noise generation, with the aim of providing preliminary design information to multirotor aircraft designers. A computationally efficient wake method called OpenCOPTER is used to conduct the aerodynamic simulations and PSU-WOPWOP is used to predict the rotor sound power level over an acoustic hemisphere. An extensive parameter sweep is explored consisting of several different rotor placements and operating conditions. Aerodynamic interactions between the rotors are found to result in significant rotor-rotor interaction noise when the downstream rotor is placed in two different regions behind the upstream rotor. The rotor-rotor interaction noise also varies as the rotors are offset laterally. Even for conditions where rotor-rotor interaction noise does not occur, aerodynamic interactions between the rotors can affect how rotors interact with their own wake. Positioning the downstream rotor above, but relatively close to, the upstream rotor is shown to result in a robust reduction in noise across the entire operating envelope.

A Piloted Simulation Study to Investigate the Relationship between Handling Qualities and Workload (Paper 1313)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
David Klyde, Amanda Lampton, Dakota Musso, Samuel Brand, David Mitchell, Aaron Winder, Amir Meghdadi, Matthew Rhinehart

In application, ADS-33E-PRF provides the means to effectively predict rotorcraft handling qualities via validated criteria and demonstrate actual handling qualities in flight test using mission task elements (MTE). With decades of successful outcomes achieved by integrated industry and government test teams, international users, and researchers, this approach provides an effective means to evaluate handling qualities of advanced rotorcraft designs. The requirement for at least three test pilot evaluators of each MTE expands the flight hours required for test and hence increases costs. To reduce flight hours required, while maintaining process effectiveness, the Naval Air Warfare Center Aircraft Division (NAWCAD) is interested in better understanding the relationship between pilot workload and assigned handling qualities ratings such that predictive tools, if proven effective, can reduce this burden. To meet this challenge, Systems Technology, Inc. (STI), Charles River Analytics, Inc. (CRA), Mitchell Aerospace Research, and Advanced Brain Monitoring, Inc. joined with NAWCAD to explore through piloted simulation the relationship between physiological measures of pilot workload and assigned pilot ratings as experienced test pilots conducted handling qualities evaluations using three exemplar MTEs. This paper describes the piloted simulation study and summarizes initial results.

A Reinforcement Learning Approach to Control of a Quadrotor Biplane Tailsitter for Adaptive Landing Maneuvers (Paper 1208)
Full registrant at Forum? Log in for link!
Systems Engineering II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Jae Woo Kim, Kristoff McIntosh, Elena Shrestha, Jean-Paul Reddinger, Sandipan Mishra

This paper presents a reinforcement learning (RL) based trajectory planning and control architecture for autonomous landing maneuvers of a quadrotor biplane tailsitter (QRBP). The RL controller replaces a gradient-descent based optimal trajectory planner and outer loop position controller of a standard QRBP control system, while retaining the inner loop for regulating attitude dynamics. The RL agents are trained in a simulated environment, using a curriculum learning approach for training an RL agent capable of landing on a moving Unmanned Ground Vehicle (UGV) with changing velocity. The RL architecture is capable of generating landing trajectories onto a moving ground vehicle, with computational costs suitable for real-time implementation. Further, the RL guidance architecture successfully completes the landing mission more consistently compared to a gradient-descent based guidance architecture when there is uncertainty in the path of the UGV.

A SW V&V Practitioner's Perspective on EASA's Guidance for ML Applications (Paper 70)
Full registrant at Forum? Log in for link!
Avionics and Systems I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Robert Mulryan, Daniel Barbour, Filipe Altoe

The development of autonomous electric vertical take-off and landing (eVTOL) aircraft to serve the commercial market for Advanced Air Mobility (AAM) is expected to accelerate the introduction of Machine Learning (ML) based systems into the national and international airspace. Facing this prospect, aerospace advisory groups, the European Organisation for Civil Aviation Equipment (EUROCAE) and SAE International, established working groups in 2019 to begin studying the challenges associated with certifying the use of these new technologies. In 2021, leveraging off these studies, the European Union Aviation Safety Agency (EASA) published 'EASA Concept Paper: First usable guidance for Level 1 machine learning applications.' Previously, Radio Technical Commission for Aeronautics' (RTCA) document DO-178C and EUROCAE's ED-12C (Software Considerations in Airborne Systems and Equipment Certification) standards have been the true north for serious practitioners of Software Verification and Validation (V&V) activities performed for the aerospace industry. This whitepaper presents a commentary on initial concerns expressed by the community on how the implementation of ML solutions could affect overall verification and validation of aerospace applications. It focuses the evaluation on the initial recommendations presented in section 3 of the concept paper, titled 'Learning Assurance'.

A Summary of Test Results from a NASA Lift + Cruise eVTOL Crash Test (Paper 1390)
Full registrant at Forum? Log in for link!
Crash Safety (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Justin Littell, Jacob Putnam

On November 9, 2022, the National Aeronautics and Space Administration (NASA) conducted a full-scale crash test of the NASA Lift+Cruise (LPC) reference vehicle at the NASA Langley Research Center (LaRC) Landing and Impact Research Facility (LandIR) under combined vertical and horizontal impact conditions to simulate a severe but survivable crash. The LPC test article is a carbon-composite skin/frame structure design, developed and fabricated for the cabin section only. The test utilized various configurations of seats and Anthropomorphic Test Devices (ATDs, a.k.a. crash test dummies) intended to encompass a variety of occupant conditions. In addition, an in-house developed energy absorbing subfloor was utilized for the evaluation of load attenuation.

Accelerating Full Scale Fatigue Testing (Paper 1222)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
William Bradshaw, Pavan Vaddadi

This paper will discuss the use of Model Predictive Control (MPC) to increase the speed and accuracy of airframe fatigue testing. This will save time and cost while providing a very high fidelity test that will greatly reduce future fleet problems. Additionally accelerating fatigue testing allows for more realistic test load spectrum to be utilized, with reduced amounts of spectrum truncation and artificial load increases. A new load control system under development by Dayton T Brown, Inc. (DTB) utilizes Model Predictive Control (MPC) rather than Proportional Integral Derivative (PID) load control to compute test actuator loads. MPC utilizes a model of the test system, a Digital Twin, to determine the best path forward to reduce loading errors and increase test load application rate.

Acoustic Predictions for Side-by-Side Rotor with Ground Effect (Paper 1206)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jared Sagaga, Seongkyu Lee

Influence of the ground plane on the performance, aerodynamics, and aeroacoustics of NASA's side-by-side Urban Air Mobility (UAM) reference vehicle rotors in hover is investigated using high-fidelity computational fluid dynamics (CFD) and aeroacoustics simulations. CFD simulations are carried out with Helios, while acoustics calculations are conducted using PSU-WOPWOP. Two overlap cases, each at two different rotor heights, are considered. The results demonstrate a significant influence of the ground plane on rotor performance, with the figure of merit (FM) increasing as the distance between the rotors and the ground is reduced. The 0% overlap configuration shows an increase in blade sectional thrust, pressure fluctuations, and resulting noise levels compared to the 25% overlap configuration, primarily due to lower induced velocity as a result of having no rotor overlap, allowing upwash to reach the rotor disk plane. Aerodynamic interactions intensify with the presence of the ground plane and become more pronounced as the rotor-ground distance decreases. The 25% overlap configuration is found to provide a noise reduction benefit of 3-4 dBA near the ground compared to the 0\% overlap configuration. Furthermore, a considerable difference is observed in the noise directivity between A-weighted and unweighted OASPL. A-weighting notably reduces regions of acoustic interference.

Active Reduction of Unsteady Rotor Noise via Redundant Control Allocation (Paper 81)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Batin Bugday, Umberto Saetti

This paper demonstrates the development and implementation of active noise abatement flight control laws that make use of redundant control allocation. A periodic equilibrium of the coupled rotorcraft flight dynamics and acoustics is first found at a desired flight condition using a modified harmonic balance trim solution method. Next, the nonlinear time-periodic dynamics are linearized about that periodic equilibrium and transformed into an equivalent higher-order linear time-invariant system in harmonic decomposition form. Composite aeroacoustic measures are included as an output of this system. To speed up runtime and make control design tractable, the order of these harmonic decomposition models is reduced via residualization to an 8-state model where the states are representative of the rigid-body dynamics of the aircraft. This 8-state model is shown to provide accurate acoustic response predictions for small-amplitude pilot inputs and to abate runtime by a factor of approximately $10^5$, thus enabling acoustic predictions in generalized maneuvering flight that are significantly faster than real-time. The 8-state model is subsequently used to synthesize an Explicit Model Following (EMF) control law with pseudo-inverse allocation to redundant control surfaces. In this study, the redundant control surfaces taken into consideration were an active horizontal stabilizer (or stabilator). Results demonstrate that while affinity in the controls yields little potential for noise abatement, the use of redundant control surfaces is an effective method for active reduction of unsteady rotor noise. In fact, redundant control allocation was shown to be increasingly effective with increasing aggressiveness in maneuvers. Within the context of future-generation rotorcraft, noise abatement through redundant control allocation will be particularly effective for Future Vertical Lift (FVL) configurations featuring high levels of control redundancy and capable of aggressive maneuvering flight.

Active Twist and Passive Rotors in Hover and Level Flight (Paper 1220)
Full registrant at Forum? Log in for link!
Modeling and Simulation I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Rinaldo Steininger, George Barakos

The effect of blade twist on rotor performance is investigated using the Hover Validation Acoustic Baseline (HVAB) and Smart Twisting Active Rotor (STAR) rotors. This is a numerical study conducted using computational fluid dynamics and aeroelastic simulations. The main tool is the Helicopter Multi Block 3 CFD solver of Glasgow. Hover loads are analysed for rigid and elastic cases using a nominal and a higher twist rate. The increased twist did not affect the rotor thrust but increased the hover efficiency. In forward flight, at high-advance ratio, the effect of blade twist was also investigated using aeroelastic computations. A 2-per-rev active twist input was also investigated. Higher blade twist increased vibration in all cases, and reduced performance at high disk loading. The active twist system could achieve increased rotor efficiency and reduced vibration at the studied conditions.

Aerodynamic and Aeroacoustic Analysis of a Quadrotor Biplane Tailsitter in Forward Flight (Paper 1308)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Dilhara Jayasundara, James Baeder

Unmanned aerial vehicles (UAV) with vertical take-off and landing capability have made significant progress in recent decades, especially with the emergence of advanced air mobility. One of the main issues these aircraft face that has challenged their commercial applicability is the high noise footprint. The aim of this study is to understand the complex aerodynamic interactions in such aircraft that lead to high noise emissions. For this purpose, a quadrotor biplane tailsitter was analyzed in forward flight conditions using computational fluid dynamics (CFD) focusing on the rotor-wing unsteady aerodynamic interaction, and its implications on the acoustic footprint of the aircraft. The aircraft was trimmed using the CFD data and blade element momentum theory estimates. The resulting surface pressure distribution was used to calculate the tonal and broadband noise footprints using the Ffowcs Williams - Hawkings equation and the Brooks, Pope, and Marcolini (BPM) semi-empirical model, respectively. The aircraft was analyzed with different rotor phasing arrangements to understand its effect on the noise footprint. The rotor-rotor interactions were found to be minimal due to the freestream. The rotor-airframe interaction leads to a substantial increase in aircraft noise. Rotor synchrophasing proved to be effective in controlling the aircraft noise footprint.

Aeroelastic Behavior of a Rotating Semi-elastic Double-swept Rotor Blade under Climb Conditions at the Rotor Test Facility Gottingen (Paper 1297)
Full registrant at Forum? Log in for link!
Test and Evaluation II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Martin Müller, Christian Wolf, Armin Weiss, Johannes Braukmann

The study presents the aeroelastic behavior of a double-swept rotor blade, that was investigated under climb conditions on a four-bladed rotor in the rotor test facility at the German Aerospace Center in Gottingen. The results of two measurement campaigns are combined to obtain a detailed insight in the coupling of blade deformation, integral loads, aerodynamic behavior and blade tip vortex. Especially the interaction between stall onset and blade tip vortex is in focus of the investigation. The first measurement campaign considered the underlying aerodynamics, integral blade loads and blade deformation by means of unsteady pressure-sensitive paint (iPSP), strain gauges at the blade root and blade tip marker. The blade tip vortex behavior was characterized in a second measurement campaign with particle image velocimetry (PIV). Different pitch settings were investigated at a rotation frequency of f rot = 23.6 Hz, that corresponds to blade tip Mach and Reynolds numbers of Mtip = 0.282 - 0.285 and Retip = 5.84 - 5.95 x 105. The results reveal a detailed insight into a two-step stall behavior and its impact on blade flapping and torsion. The iPSP and PIV data indicates an interaction between stall onset at the blade tip and a simultaneous inward motion of the blade tip vortex caused by the backward-swept part of the blade.

Aeroelastic Design of a High Speed Highly Efficient Rotor (Paper 1275)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Chris Sutton, Claude Matalanis, Ramin Modarres, Byung-Young Min, Vera Klimchenko, Brian Wake

The aeroelastic design of a high speed highly efficient rotor, from conceptual layout to detailed design, is presented. The overall strategy is described along with details and a demonstration case on the conceptual design optimization strategy. In Phase I, rapid design iterations were performed using lower order quick turnaround tools to establish basic design aspects such as rotor head sizing and stiffnesses. In Phase II, higher order tools are implemented along with a more realistic structural representation of the head and blades. The outcome is a robust preliminary design to be analyzed with CFD-CSD and tuned further in detailed design without requiring major rework. Finally, dynamic tailoring performed on the blade during final design is presented. This was done to maintain or improve frequency placements and vibration levels as relatively small, surgical changes were made to the blade detailed design (ply thicknesses, orientations, blade weights, etc.) to satisfy strength, life, and manufacturability requirements. This work highlights the importance of upfront aeromechanics optimization to establish a robust early conceptual design, and high-fidelity analysis through final design to maintain desired characteristics.

Aeromechanical and Aeroelastic Effects of the Blade Structural Design of a Coaxial Rotor by the Physically Coupled Mid-Fidelity Aerodynamics (Paper 1246)
Full registrant at Forum? Log in for link!
Dynamics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Byeonguk Im, Hyunjae Lee, Kunhyuk Kong, Gwangin Ko, SangJoon Shin

A physically coupled mid-fidelity aeromechanical and aeroelastic analysis is used to investigate the effects for a compound coaxial rotorcraft rigid blade structural design in terms of the dimensionless parameter such as Lock number, advance ratio, and lift-offset. A rigid compound coaxial rotorcraft X2 technology demonstrator is represented by the comprehensive rotorcraft analysis CAMRAD II, where the physical components of the main rotor, pusher propeller, fuselage and empennage are analyzed using the generalized free wake and vortex theory. The aerodynamic coefficients are computed by MSES and DATCOM+, and rotor cross-section properties are designed using VABS. Three blade design candidates are created for different Lock number, and systematic trim analyses are conducted by the different lift-offset and advance ratio sweep. Results are presented on how each component load affects the vehicle trim state, and an investigation of the new design bounds for Lock number to define a rigid coaxial rotor.

Aeroservoelastic Flight Dynamics and Control of Lift Plus Cruise Electric Vertical Take-Off and Landing Vehicle in Forward Flight (Paper 1285)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Nhan Nguyen, Benjamin Webb, Juntao Xiong

This paper presents an aeroservoelastic modeling approach for NASA Lift+Cruise electric vertical take-off and land- ing (eVTOL) aircraft in forward flight. A trim analysis for forward flight is performed in CHARM. A mode shape extraction is performed to construct the mode shapes and elastic axes from a NASTRAN model of the Lift+Cruise vehicle. An aeroelastic model is developed using Theodorsen's theory to capture unsteady aerodynamics. The aeroe- lastic model is coupled to a rigid-body flight dynamic model of the Lift+Cruise vehicle. A closed-loop servo-actuator model is developed for each of the control surfaces and collective pitch of the push fan. A linearized aeroservoelastic state-space model is formulated by coupling the aeroelastic model, flight dynamic model, and servo-actuator models together. An altitude command longitudinal flight controller and a stabilizing lateral-directional flight controller to stabilize the unstable spiral mode are designed using the LQR method.

Airbus Helicopters Takes Technical Support to New Heights using AI-powered search platform (Paper 1199)
Full registrant at Forum? Log in for link!
Product Support (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Frederic Antoine

To maintain and operate their helicopters, customers may need Airbus Helicopters technical support. The increase of technical requests addressed by the customers is in relation with the increase of the global fleet. But the sizing of Airbus Helicopters technical support teams cannot be increased the same way. The project was to analyze how the current Artificial Intelligence features could help Airbus Helicopters to be more efficient to manage its customers' technical requests. A search application was developed using Natural Language Processing technology to search more rapidly and more efficiently by finding results in the technical documentation available to customers and technical support teams or by finding similar cases already treated. The result is an important gain in search time, as well as an increase of customers and technical support autonomy. Based on these technical requests, Airbus Helicopters technical support is also gathering the return of experience of the in-service behavior of the global fleet. Thanks to the Machine Learning technology, an automatic classification of technical requests is set up to determine if a request is relevant for return of experience or not. These AI technologies permit to reduce the low-added valued tasks - search for information, to allow Airbus Helicopters teams to have more time to focus on high-added valued tasks - technical analysis.

An Airport and Vertiport/Aircraft Compatibility Approach of Electric Vertical Takeoff & Landing Aircraft Design (Paper 1258)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Gaël Le Bris, Loup-Giang Nguyen

Most ongoing electric vertical takeoff and landing (eVTOL) aircraft projects focus on the development of products that meet the needs of urban air mobility (UAM). The use cases that eVTOL aircraft could fulfill include intra-urban passenger mobility, cargo delivery, and emergency medical services (EMS). As UAM intends to provide point-to-point mobility service, it will need to leverage heliport facilities and create new vertiports on existing city real estate (e.g., high-rise building and parking garage rooftops). In order to achieve this, eVTOL aircraft design shall be, as far as practicable, compatible with the infrastructure available. The various aspects of eVTOL/vertiport and airport compatibility were investigated, and a list of criteria was established. The paper describes how key eVTOL design features interact with aviation facilities, and how and why careful aircraft design taking the ground infrastructure into consideration is important to maximize compatibility and facilitate UAM implementation by minimizing the need for costly and impactful capital investments. Considerations should be given to several features, including but not limited to the general aircraft configuration, passenger accessibility, electric and hybrid propulsion systems, and the charging and refueling systems. The review of existing heliport/vertiport facilities representing the diversity of the ground infrastructure in selected large metropolitan areas against over 100 eVTOL concepts and original designs provide an insight of the challenges ahead. The assessment of aviation risks expands the aircraft/airport compatibility conversation to fostering operational safety and efficiency 'by design'. Finally, the role of standardization in further reducing compatibility issues through industry standards and best practices in aircraft design, airport/vertiport design, and aircraft/airport operations is also discussed.

An Analytic Method to Predict Rotor Blade Wake Interaction Noise (Paper 1260)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Sicheng Kevin Li

This paper presents a low-fidelity and analytical method for predicting rotor blade-wake interaction (BWI) noise. The method analyzes the rotor wake geometry, potential blade-vortex interaction (BVI) locus, rotor inflow distribution, rotor trim settings, leading-edge noise model, and turbulence development of the rotor tip vortices. The predictions of rotor BWI noise are validated against experiments on three rotor conditions with varying tip-path-plane angles of attack. Good agreement is found in the frequency range where BWI noise dominates. The results show that BWI noise is mainly contributed by the forward region of the disk, where vortices experience minimal interference from the blade prior to BWI noise generation. The study also shows that the low-fidelity wake model effectively captures the effects of tip-path-plane angle variation. The higher αTPP rotor gives much smaller noise levels due to the further distance between the vortex and the blade in the third disk quadrant. The predictions of BWI noise on an eVTOL-scale rotor indicate that BWI is the dominant broadband noise source for the sensitive frequencies of human hearing.

An Assessment Framework for the Maturity of Simulation-Based Verification (Paper 24)
Full registrant at Forum? Log in for link!
Systems Engineering I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Benjamin Stirgwolt, Stephanie Keomany

Simulation-based verification is a term that promises to reduce lengthy and costly ground and flight tests of aircraft, using high-fidelity physics-based simulations instead of testing physical assets. There has been considerable research into building more robust aircraft models that accurately depict the physics of an operational aircraft. The focus has been on the 'simulation-based' portion of the phrase 'simulation-based verification.' However, to achieve the full benefit of simulation-based verification, the focus needs to include how these physics-based simulations can be incorporated into an organization's requirements verification activities, which are traditionally the responsibility of the systems engineering organization. Over the last decade, systems engineering has been transforming into a 'model-based' discipline, where all systems engineering data is contained in a model of the system, including requirements and their properties. With a drive toward simulation-based verification, there is a need to incorporate the results of simulation-based verification into the system architecture model that contains the system's requirements. By integrating physics-based simulation into the system architecture models, organizations can build a robust verification story and to automate the requirements verification process. However, an organization does not simply transform from a traditional, physical test-based organization into a simulation-based organization; it is an evolutionary process. This paper describes a framework for assessing the maturity of an organization's simulation-based verification capabilities, with the highest level of maturity having physics-based simulation integrated into the model-based systems engineering verification process.

An Assessment of FVL Readiness of Certifiable MOSA Ethernet Digital Backbone Solutions (Paper 109)
Full registrant at Forum? Log in for link!
Avionics and Systems I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Daniel Finnegan, Alvaro Soares, Wolfram Zischka

Modern aircraft employ an ever-growing array of sensors, probes, displays, and other high-integrity avionics. This has grown to the point where legacy networking technologies like MIL-STD-1553 and ARINC-429 are no longer sufficient. At the same time, a growing emphasis on Modular Open Standards Approach (MOSA) in defense acquisitions has moved toward favoring more open standards. This presents an opportunity to leverage ubiquitous, high-bandwidth, and flexible Ethernet into an avionics context. The US Army Future Vertical Lift (FVL) initiative presents a key opportunity to realize the advantages of Ethernet for avionics networking by using it as the basis for an avionics Digital Backbone. This paper will evaluate the Certification Readiness, Maturity, and MOSA-Conformance of the Ethernet technologies likely to be featured on FVL aircraft: IEEE 802.3 Best-Effort (BE) Ethernet, Time-Triggered Ethernet (TTE), and IEEE 802.1 Time Sensitive Networking (TSN). All the listed technologies are open Ethernet standards, allowing the system architect to deploy them as needed based on the specific use case and program requirements. This evaluation assesses these three Ethernet technologies on aspects necessary to safely manage flight-critical data over a real-time network, including native fault tolerance, determinism, software dependency, and certifiability. The paper also assesses the technological maturity of each technology in relation to the planned timeline for FVL and evaluates how evolution of the technologies could impact MOSA-conformance. This paper will ultimately recommend a mixed network of a Time-Triggered Ethernet Digital Backbone for high-criticality Air Vehicle System traffic with Best-Effort Ethernet or Time-Sensitive Networking for lower-criticality Mission System traffic.

An Emergency Landing Spot Detection Algorithm Based on Semantic Segmentation and Safety Evaluation (Paper 1304)
Full registrant at Forum? Log in for link!
Crash Safety (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Ting Wang, Senwei Xiang, Zehua Men, Minxiang Ye, Yifei Zhang, Anhuan Xie

Due to emergencies such as GPS failures and hardware malfunctions, the UAVs may need to terminate their flight to prevent further damage. In this work, we propose an emergency landing spot detection algorithm that classifies terrain under the UAVs and identifies an optimal landing spot by safety evaluation. First, a knowledge distillation strategy is introduced for training a real-time semantic segmentation network DDRNet-23-slim with high accuracy. Next, the segmentation map is converted into a binary map and suitable landing areas are identified through morphology operations. Thin operation is then applied to represent the landing areas and the safety score at each point in the skeleton is estimated by the safety degree. Duplicate points are removed using a NMS algorithm, and a list of K points with top safety scores is generated and the optimum spot is then selected from this list. Both segmentation performance and safety gain of the optimum spot have been evaluated in our ZJLabid dataset. Experiment results prove that the proposed algorithm can effectively detect suitable landing spots and achieve a reliable and safe landing.

An Experimental Investigation of eVTOL Flight State Variance on Noise (Paper 1249)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Vitor Tumelero Valente, Eric Johnson, Eric Greenwood

Experimental data collected for a custom multirotor aircraft are used to perform an analysis to relate the variability of noise levels measured on the ground to the state vector of the vehicle in hover. Data from a total of sixty-nine hover points are used to correlate the aircraft state to A-weighted Sound Pressure Levels measured at a microphone located directly underneath the aircraft. A spherical spreading normalization is applied to the data to allow data collected from different altitudes to be compared to one another. Noise levels are found to increase as vehicle attitude (orientation) and attitude rates diverge from the trim condition. The noise was found to be most sensitive to changes in yaw or yaw rate. Conversely, the noise was found to decrease as the commanded thrust of the vehicle increased. Additional analysis indicates that the mean A-weighted Sound Pressure Level increases when the variability of the vehicle flight condition is increased.

An Overview of the Proprotor Performance Test in the 14- by 22-Foot Subsonic Tunnel (Paper 140)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Nikolas Zawodny, Kyle Pascioni, Christopher Thurman

This work experimentally investigates the aerodynamic behavior of proprotors across a wide range of angles of attack. These flight conditions are intended to be representative of Urban Air Mobility (UAM) vehicle platforms that utilize articulating propulsors to transition from a vertical takeoff and landing (VTOL) phase typical of a conventional rotorcraft to an axial mode of forward flight typical of a fixed-wing aircraft. These data are used to identify the potential limits of lower-fidelity aerodynamic modeling tools, as well as to inform future acoustic phases of testing. Tests were conducted on two proprotor designs in the NASA Langley 14- by 22-Foot Subsonic Tunnel using an articulating propeller test stand. Hover results identified unique flow physics on one of the proprotors, including severe outboard flow separation and perpendicular blade-vortex interactions on the outboard portions of the blades. Transition and forward flight conditions yielded informative trends in terms of both on- and off-axis forces and moments against which low-fidelity prediction models were compared.

Analysis of Aerial Firefighting with Rotorcraft Platforms (Paper 1298)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Shawn Melhorn, Monica Gil, Jordan Gorelick

Wildfires are an annual torment in many parts of the world. They can spread very quickly and destroy forests, wildlife, buildings, infrastructure, and homes, as well as risk human life before they are able to be controlled. Because of the rapid response time that is necessary to extinguish a wildfire before it becomes too large, the quantity and speed of water delivery are extremely important - helicopters are a great tool for accomplishing this goal. They can fly directly to the fire and refill their water supply from smaller, more remote water sources than other aerial platform options require. There are several water tank options to transport and drop water on the fire from a helicopter. This paper focuses on four of these options: an external rigid tank, an accordion tank, a Bambi Bucket® 1, and an internal tank in addition to the outlining some of the options for remote water sourcing. Each of these tank types have various advantages and disadvantages which are discussed using models developed for evaluating helicopter firefighting applications.

Analysis of Flap-Lag Aeroelastic Stability at High Advance Ratios (Paper 1155)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Spencer Fishman, Inderjit Chopra

The aeroelastic stability of rotor blades in the flap and lag degrees of freedom is analyzed in preparation for high advance ratio wind tunnel testing of Mach-scaled rotors. A wide range of advance ratios (0 ≤ μ ≤ 3) and Lock numbers (0 ≤ g ≤ 18) are evaluated for articulated and hingeless rotor configurations. Linearized equations of motion are derived in the rotating frame. Periodic coefficients, reverse flow, pitch coupling, and collective inputs are considered. Floquet Theory is used to evaluate the stability of the equations of motion in response to perturbations from the trimmed state. Results are compared to past analyses and expanded to higher advance ratios. Damping and frequency response behavior are evaluated, and rotor stability boundaries are presented.

Analyzing Mechanical Systems Using 3DX Design Tables, Kinematic Simulations, and Dynamic Simulations (Paper 73)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jack Faysash

This paper discusses the mechanism design and analysis methodology used within the Airframe and Mechanical Systems (AF&MS) design organization at Sikorsky, a Lockheed Martin Company. The paper also highlights tools offered by 3DEXPERIENCE (3DX) that allow the engineer to more efficiently design and analyze mechanisms. The methodology used by AF&MS utilizes design tables to drive the analysis of complex mechanisms through thousands of unique positions as well as to quickly iterate through design changes. This paper showcases the methodology and tools used through the example of a brake mechanism designed and analyzed by the author. The example goes step by step through determining requirements, initializing the design, and running the mechanism simulation. The paper will close with a second example summarizing the methodology and tools used.

Army Aviation Reusable Operating Environment Component Certification (Paper 1350)
Full registrant at Forum? Log in for link!
Avionics and Systems I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
David Walsh, Tony Adams, Mark Brown, Will Keegan, Scott Dennis, Harold Carter, Alan Hammond, Chip Downing

The Program Executive Office (PEO) Aviation (AVN) Enterprise has identified a Major System Component (MSC) titled, 'Aviation Mission Computing Environment' (AMCE) and is developing its Component Specification Model (CSM). The AMCE CSM consists of configurable processing, Software Operating Environment (SOE), and software loading requirements. The PEO AVN Enterprise has determined that the resulting MSC developed by a supplier meeting the AMCE CSM shall 'acilitate incremental deployment of capabilities'. This paper first intends to draw attention to specific MOSA related benefits we hope to achieve in our industry and call out the key impediments to productivity in our standards and software development tools. We then propose definitions of software modules, operating system properties and key interface standards for two distinct SOEs for the AMCE CSM: a mission system SOE, and a safety critical SOE intended to address the Army Aviation Airworthiness Release (AWR) viewpoint and associated software levels of reuse.

Assembly and Testing of a High Reduction Ratio Pericyclic Drive (Paper 1341)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jeremy McGovern, Edward Smith, Hans DeSmidt, Robert Bill, Matthew Wagner, Mark Stevens

In this work, the procedure for experimental validation of a pericyclic transmission is described. From its conception in 1970's, the nutating (now pericyclic) mechanical transmission has undergone several years of rigorous analysis in hopes of addressing common drivetrain considerations of noise, maintenance, and power density. These analytical studies have led to the fabrication of a 50 HP 32:1 reduction ratio prototype, meant to demonstrate whether it can achieve the theoretical design goals. The final analyses will be detailed characterizations of the system's torque transmission, thermal efficiency, and vibration under dynamic load. This paper outlines the successful assembly and alignment procedures, validated by contact pattern and tooth strain, as well as the experimental layout for the dynamic testing of a pericyclic transmission.

Assessing the Effect of Lift Position on Helicopter Recovery to a Twin-Island Aircraft Carrier using Piloted Flight Simulation (Paper 1191)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Neale Watson, Ieuan Owen, Mark White

This paper describes an investigation of the air flow over the flight deck of a twin-island aircraft carrier with the ship's lifts in a raised and lowered position, and the subsequent effect on the helicopter and on pilot workload. Computational Fluid Dynamics was used to model the unsteady flow over the flight deck in a 40 kt wind approaching from 60°starboard. The turbulence intensity and velocity flow field produced over the flight deck for each lift configuration was analyzed and compared. The unsteady air flow computed for each lift position was combined with a flight dynamics model of a helicopter configured to represent a SH-60B Seahawk an integrated with a full-motion flight simulator. To analyze the effect of the two airwakes on the helicopter and on pilot workload, a series of simulated flight trials were conducted in which the pilot performed landings to the flight deck of the aircraft carrier. The results show that while the lift configuration does affect the air flow over the flight deck, the effect on pilot workload is dependent on the location on the flight deck the pilot is landing to.

Assessment of Numerical Approaches for Modelling Tilt-Rotor Ground Effect stability in Hover and Near Hover Conditions (Paper 62)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Federico Porcacchia, Fabio Riccardi, Andrea Mancini, Matteo Pecoraro, Andrea Ragazzi, Luca Vigano

The paper proposes a process which, starting from the outcomes of dedicated CFD high fidelity simulations, is able to synthetize accurate ground effect modeling for complex rotorcraft configurations (specifically addressing tilt-rotor case), suitable both for real time pilot in the loop and design/configuration trade-off analyses. The effect of complex aerodynamic interactions between the rotor wakes, nacelles, fuselage, wing, and ground may consistently alter the rotorcraft dynamic response. In this regard, specific design choices as shape and dimensions of movable nacelle parts, rotor blades twist and thickness, wing and tail geometry may have consistent impact on the nature of the rotorcraft aeromechanic response, especially for near-ground operations, with consequent need to capture such phenomena at early stage of design. This picture is even more complex in case of Fly-By-Wire configurations where control laws, generally synthetized out of ground effect, should guarantee their effectiveness in ground effect as well. Specifically, the paper addresses the development of a ground effect modeling based on the outcomes of high fidelity aerodynamics (addressing Next Generation Civil Tiltrotor Technology Demonstrator NGCTR-TD) in the framework of FLIGHTLAB tool. Then, the effects of proposed modeling strategies on the bare aircraft and closed loop system are assessed in terms of the rotorcraft trim conditions and stability features. Investigation of the complete workflow toolchain, starting from aerodynamics modelling up to physical trends and control laws impact analysis provided the opportunity to consolidate an industrial based optimized approach, that carefully merge feasibility/time consumption/accuracy requirements, thanks to which both pilot in the loop simulation and design trade-off analysis are accomplished together, increasing the level of safety of flight for novel rotorcraft configuration.

Assessment of Objective Functions for Rotor Performance in Multi-Objective Rotor Blade Optimization (Paper 1225)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Luke Allen, Joon Lim, Robert Haehnel, Ian Dettwiller

The Aerodynamic Shape Optimizer for Rotor Blades (ADSORB) framework was used to perform four case studies optimizing the UH-60A blade airfoils along the blade span. The framework is built within Galaxy Simulation Builder. It uses CFD to generate data and construct a surrogate model for airfoil coefficient predictions. Dakota and a multiobjective genetic algorithm are then used to optimize the blade airfoils for four distinct segments of the blade. RCAS was then used to predict the rotor power in hover and forward flight (advance ratio 0.3), as well as the rotor L/DE in a high load forward flight condition (CT/σ ≈ 0.13). Each case study compared different combinations of objective functions to determine the most desirable traits. Ultimately, a design was found that increased the high load L/DE by 6.7%, while decreasing the hover and forward flight rotor power by 2.0% and 2.7%, respectively.

Automated Fiber Placement Double in-situ Manufacturing Technology of Thermoplastic Composites Components (Paper 1211)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Marcin Głodzik, Aleksander Banaś, Radosław Wojtuszewski, Konrad Farbaniec, Jarosław Sienicki, Tomasz Gałaczyński, Wojciech Krauze

Presented idea describes the manufacturing approach to low-cost production and assembly of a composite part in one operation with the use of AFP (Automated Fiber Placement) technology. The proposal illustrates production of the floor panel dedicated to helicopters and airplanes. Traditionally, stiffeners are joined to the composite skin after it has been manufactured, most often in a different fixture, position, and other process. The present idea takes full advantage of the AFP method, which makes it possible these separate processes to be combined in one operation, allowing the hybridization of the fiber placement skins with the joining of the stiffeners. The article presents then design, tooling and manufacturing principals of a such innovative hybrid approach in a building of complex aircraft composite components.

Autorotation Modeling, Simulation, and Analysis of a Generic Lift-Offset Coaxial Compound Rotorcraft (Paper 152)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Ashwani Padthe, Mark Lopez, Tom Berger, Emily Glover

Lift-offset coaxial compound rotorcraft designs have been proposed for the U.S. Army Future Vertical Lift (FVL) programs. Without a need for the tail rotor and equipped with a pusher-propeller, the coaxial compound configuration is capable of achieving high airspeeds and perform maneuvers not feasible for the conventional rotorcraft. To facilitate an independent assessment of the lift-offset coaxial configuration by the U.S. Army, a physics-based flight dynamic model of a 14,000 lbs gross weight configuration was developed using open source data and implemented into the HeliUM-A comprehensive analysis code. This paper evaluates the coaxial configuration for autorotation performance in case of an engine failure. The HeliUM-A code is enhanced to simulate a steady descending autorotative trim condition with and without the pusher-propller declutched from the main rotor. Minimum descent angle and sink rate occur at approximately 70-80 kts airspeed. The declutched case with pusher-propeller speed reduced by 75% yields the lowest sink rate and descent angle. Flight dynamics responses in steady descending autorotation are analyzed with the yaw rate response showing significant differences compared to a steady level flight condition.

BOS and Hot-Film Analysis of a CH-53G Helicopter Wake in Ground Effect (Paper 1354)
Full registrant at Forum? Log in for link!
Test and Evaluation II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Johannes N. Braukmann, Clemens Schwarz, C. Christian Wolf, Elizabeth Buron, Stefan Koch, Gerrit Buske, Anthony D. Gardner

Constant temperature anemometry and background-oriented schlieren (BOS) measurements on a CH-53G helicopter (take off mass) are used to investigate the rotor wake including the vortex breakdown to statistical turbulence. Hovering flights at a range of hub heights 0:50 < h < 0:83 were investigated. The position of the rotorcraft was optically tracked using markers affixed to the fuselage. A complete breakdown of the tip vortices was noted within 0:3R of the rotor plane, in stark qualitative contrast to small scale experiments which show the tip vortices persisting to the ground plane. The large (37m2) BOS field of view showed a small effect of vortex pairing and blade vortex interaction, which was overshadowed by the rapid wake breakdown. Vortex pairing was found to result from varying vortex convection velocities rather than from differences in the vortex spacing due to the blade track.

Blade Shape Optimization of Rotors using Neural Networks (Paper 1277)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Bharath Govindarajan, Hrithwik Shalu, Ananth Sridharan, Rajneesh Singh

This paper presents a methodology for using a neural network to predict airfoil behavior, for rapid airfoil design as well as prop-rotor blade and airfoil shape optimization. To train the neural network, reference airfoil shapes were obtained from the roughly 1600 airfoils in the UIUC airfoil database. The Class Shape Transformation approach is used to parameterize airfoil upper and lower surface geometries, using Chebyshev polynomials as shape functions. Three separate neural networks were trained, one each for lift, drag, and pitching moment. 'Truth' data is generated by conducting angle of attack sweeps with XFOIL on the various airfoils in the UIUC database. After training the neural network, isolated airfoil shape optimization was performed using the NSGA2 algorithm, targeting minimum average drag over an operating lift coefficient range for 10%, 12% and 16% thick airfoils. Additionally, prop-rotor aerodynamic optimization was carried out by designating airfoil shape parameters, blade twist distribution and blade chord distribution as simultaneous design variables for two objectives: hover figure of merit and cruise-mode propeller efficiency. A Blade Element Momentum Theory is used to predict rotor performance, using airfoil tables generated by the neural network. Pareto frontiers and an analysis of the resulting designs is presented. Using a neural network is advantageous for both applications, because it results in a roughly 40-fold speed-up over the XFOIL, while effectively decoupling the computational cost of shape optimization from that of the physics-based model generating truth data.

Bolt Hole Corrosion and Fatigue Damage Repair in Hybrid Vertical Lift Structure (Paper 1368)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Jude Restis, Matthew Kokaly, Michael Dubberly, Dale Manning

Cold expansion has been successfully used in aerospace structures, including vertical lift airframes to repair and prevent fatigue damage for more than 50 years. In 2022 PartWorks described an innovative program that would be performed for the United States Air Force using a new process, that included cold expansion, to repair corroded fastener holes (U.S. Patent 11,255,371). This paper will focus on the test results of that development and demonstration program for the United States Air Force (Air Force Research Lab/AFRL) for repairs to bolt holes on aerospace structures with metal/carbon-fiber composite skins. Locations in aerospace structures that combine composites and metallic for vertical lift or fixed wing have demonstrated greater levels of corrosion when compared to all-metal structural skin due to galvanic corrosion between metal and carbon fiber composites. Existing repair methods for these metal/carbon fiber composite skin bolt hole/fastener sites often involve extensive removal of corrosion, non-standard or oversized holes, and extensive modeling/validation to prove repair effectiveness. Existing repairs can also lead to premature structural component replacement. This project evaluated a new repair method that uses cold expansion with thin wall bushings and/or a rivetless nut plate (RNP) to restore fatigue life to the metal bolt hole if damage is missed or potentially without having to remove all the damage/corrosion.

Boosting Certification Process Efficiency thanks to Regulation Ontologies And Inference Engine (Paper 96)
Full registrant at Forum? Log in for link!
Systems Engineering I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Patrice Micouin, Olivier Jeunehomme

Airworthiness of Rotorcraft products is established through the certification activity that can be seen as a demonstration process based on rules given in the Certification Specifications and associated Acceptable Means of Compliance. After a presentation of our goals, a delimitation of the field of interest, including certification specifications and acceptable means of compliance and its semantic analysis in the form of taxa, networks and discriminants, we introduce the concepts of rotorcraft breakdown structures, configuration parameters and skill areas forming the underlying ontology behind the certification specifications. Then, we present a parameterized model of rotorcraft breakdown structure in the form of an inference engine. The paper shows how this inference engine can support system designers taking into account, at the right times, the applicable certification requirements and the procedures and standards, acceptable by the authorities for the demonstrations of compliance they have to establish and how it can support certification engineers preparing a certification program and verifying compliance demonstrations performed by system designers. Before concluding and presenting foreseen future works, we present a simple use case intended to illustrate our work.

CFD Thermal Analysis of an AH-64 Engine Bay (Paper 39)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Brian Casaday, Justine Tang

The Boeing AH-64 Apache is upgrading its twin GE T700-701D engines to the GE T901 engines in order to enhance the aircraft's capabilities. The engine nacelle is cooled with an exhaust eductor, and the integration of the new engines needs to be analyzed to ensure that temperature requirements are satisfied. A CFD model was developed to predict temperatures throughout the nacelle for both the port and starboard engines. This model incorporates surface-to-surface radiation and over a dozen inflow or outflow boundary conditions. Several sensitivities were analyzed in CFD, including a turbulence model and wall function comparison, and sensitivities to gravity, radiation, external airflow, and multiple other boundary condition assumptions. These sensitivities provide valuable information as to which parameters are necessary for accurately predicting component temperatures in these types of analyses. Future testing will be used to validate the results.

CH-53K Maneuvering Envelope Expansion Challenges (Paper 57)
Full registrant at Forum? Log in for link!
Test and Evaluation I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
John Rucci, Robert A. Pupalaikis, Glen A. Knaust, Sean Maloney, Alex Faynberg, Don Ream, Steven Spoldi, Rich Lamb, Laura Slingerland, Kenneth Cahill

The CH-53K® heavy-lift helicopter, contracted under the Heavy Lift Replacement Program, is nearing the end of development, and was recently approved for Full Rate Production (FRP). The CH-53K features a full authority Fly-By-Wire (FBW) flight control system with Model Following Control Law architecture, chosen to address several overarching requirements including Level 1 Handling Qualities in accordance with ADS-33E-PRF. Early system identification of the air vehicle and tuning of the Flight Control System (FCS) allowed for an incremental expansion in airspeed, altitude, and maneuvering envelope. During the maneuver envelope expansion forward cyclic control margin (B1s) became a limiting factor. The reduced margin was noted during aft CG configurations when expanding load factor. Control margin limits and Do Not Exceed (DNE) criteria were established for safe expansion early in the test planning process. These criteria were based on best practices, specifications, desktop, and simulation models as well as engineering judgment prior to first flight. Some influence of the criteria likely derived from the defunct MIL-H-8501A Military Specification ‘General Requirements for Helicopter Flying and Ground Handling Qualities,’ with a notable absence of quantitative criteria in ADS-33E-PRF. As the full authority FBW control system was demanded to work within a smaller forward portion of the control authority envelope for mission-representative aft CG configurations, the DNE criteria challenged the long-standing general guidelines regarding control margins. Furthermore, control margin DNE's were experienced primarily during maneuver recovery—not through pilot input but via a closed loop response to the Model Following architecture and had the potential to restrict unnecessarily the boundaries of the Operational and Service Flight Envelope (OFE/SFE). Challenged with the task of envelope expansion, the Integrated Test Team (ITT) comprising contractor and government flight test engineers and pilots, worked to refine flight test technique and continuation criteria to validate the maneuvering requirements of the Air Vehicle Specification (AVS). Ultimately, the ITT developed a criterion for expansion of a modern FBW system to demonstrate the full capability in all corners of the envelope and deliver a superbly flying aircraft to the end customer, the United States Marine Corps (USMC).

CH-53K® Supplemental Engine Feed System (Paper 1326)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Christopher Foti, Daniel Shields, Robert Morrissette, Esther Lee, Robert Eby

The CH-53K® fuel system employs a unique on-demand Supplemental Engine Feed System (SEFS), which provides regulated pressure to the engine without the use of software or electronic controls. The system balances the engines' need for intermittent fuel boost with the survivability restrictions of a positively pressurized fuel system. Under normal aircraft maneuvering and loading, SEFS provides boost equivalent to a full tank of fuel such that the engine pumps can provide a consistent level of suction even when fuel levels are low. However, with higher airframe g-loading created by certain maneuvers, a second stage activates and further increases pressure boost to prevent any interruption of fuel flow. Upon completion of a high-g maneuver, the SEFS automatically returns to its constant boost mode. SEFS underwent the full developmental lifecycle, beginning as an analytical exercise before progressing through ground testing and in-flight verification.

Characterization of a Blade-Tip-Propeller Driven Rotor (Paper 1188)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Robert Brown, Inderjit Chopra

A blade-tip-propeller driven rotor utilizes small electric motors and propellers attached at the blade tip to spin the main rotor. Potential applications of this technology are for high performance, mechanically simple, vertical takeoff and landing unmanned aerial vehicles. This paper presents a method of systematically characterizing the performance of an isolated propeller, isolated rotor, as well as the combined blade-tip-propeller driven rotor configuration. A series of wind tunnel tests were performed to experimentally obtain the isolated propeller performance at axial wind speeds up to 25 m/s and propeller tip speeds up to 100 m/s. Next, a novel method of rotor blade manufacturing was developed that involved laying multiple high powered wires inside the blade to provide electrical power to the motor at the blade tip. This process was utilized to fabricate a 5.5 feet (1.68 meter) diameter blade-tip-propeller driven rotor system that was tested in hover. Finally, a mathematical model was created for the blade-tip-propeller configuration and the predictions were compared to experimental results from the hover test stand model. The power loading of an isolated rotor and the new blade-tip-propeller configuration were compared, which identified several key areas of improvement.

Characterization of the Response of a Single Rotor in Hover to Dynamic Collective Pitch (Paper 1355)
Full registrant at Forum? Log in for link!
Test and Evaluation I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Patrick Mortimer, Daniel Yu, Jayant Sirohi, Jimmy Ho, Mark Lopez, Ashwani Padthe

The flow fields of a 2m-diameter two-bladed single rotor were measured using particle image velocimetry, and computed using a coupled RCAS-VVPM analysis. Dynamic collective pitch inputs were introduced in terms of stepped sines with an amplitude of 1◦ , and frequencies of 0.0/rev, 0.2/rev, 0.3/rev, 0.4/rev, 0.6/rev, and 0.7/rev. Phase-resolved particle image velocimetry measurements were performed to capture the flow field response to the dynamic pitch inputs at an azimuthal location of ψb = 90◦. Flow field information was acquired at specific measurement locations in order to capture the dynamic effects at the azimuthal plane of interest. A total of ten measurement locations were captured for each excitation frequency. At each measurement location 200 instantaneous flow realizations were captured. The goal of this study was to develop an experimental and numerical procedure to investigate the wake and loads of a single isolated rotor in hover in response to stepped sine pitch inputs at a nominal collective pitch angle of θ0 = 8◦ and nominal blade loading of CT/σ = 0.08. The change in rotor thrust ranged from ΔCT = 13.5% to 22% over the range of actuation frequencies tested. The corresponding change in rotor power ranged from ΔCP = 2.3% to 6.7%. Frequency analysis performed at multiple radial locations along the rotor blade showed a gradual increase radially in the axial velocity magnitude for all excitation frequencies. The largest axial velocity magnitude corresponded to an actuation frequency of f = 0.2/rev for all radial locations. The numerical results showed a consistent under-prediction at all outboard radial locations, but showed closer agreement to the measured data at inboard radial locations.

Cheeseman Best Paper: Are eVTOL Aircraft Inherently More Susceptible to the Vortex Ring State than Conventional Helicopters? (Paper 1408)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Richard E. Brown

There is currently extensive interest worldwide in developing small, lightweight, electrically-powered, multi-rotor vertical takeoff and landing aircraft. The aim is to use these new vehicles to carry a small number of passengers on short-range intra-urban missions, for instance as part of a passenger ferry service between an airport and a downtown commuter hub. The concern is that these aircraft might have certain characteristic design features that, in combination with the environmental conditions that they will experience, will render them particularly susceptible to a potentially hazardous operating regime, known as the Vortex Ring State, especially during their descent and landing. This paper extends our classical understanding of the basic physics that underpins the Vortex Ring State in order to assess the likely impact of this phenomenon on the safety and operational characteristics of this new class of vehicle.

Coaxial Hub Drag Correlation with Water-tunnel Model using Two Flow Solvers (Paper 1226)
Full registrant at Forum? Log in for link!
Aerodynamics IV (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Byung-Young Min, Kalki Sharma, Charles Berezin, Peter Lorber, Brian E. Wake

Current paper summarizes a correlation study of two flow solvers (CREATE-AV™ Helios and STAR-CCM+), routinely used at Sikorsky, with the spinning coaxial hub drag and flow field measurements conducted by Penn State University at the 12' diameter water tunnel. The Helios modeling approach was aiming for a high fidelity accurate simulation, whereas the STAR-CCM+ modeling approach was aiming for a fast turn-around time with reasonable solution accuracy with a relatively coarse mesh and simplification. The two solvers generally agreed well with the test data within reasonable accuracy and captured the drag trend between two shaft fairing configurations. Impact of turbulence model selection (Spalart-Allmaras Detached Eddy Simulation and Spalart-Allmaras Reynolds-Averaged-Navier-Stokes model) has been demonstrated. The RANS model generally delayed separation and resulted in lower drag. The STAR-CCM+ runs simulated both air and water at matching Reynolds number and showed good agreement between the drag results for the two mediums. Also, the importance of accurate representation of geometric details including gaps, shafts, and holes is highlighted.

Comparison and Analysis of a Tiltrotor UAM Configuration by Using NDARC (Paper 1185)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Chihyun Ahn, SunHoo Park, Yooho Chang, Minho Hwang, Wonseok Cha, SangJoon Shin

For its high-speed cruise flight performance and vertical take-off and lift (VTOL) capability, tiltrotor configurations are being looked upon as the most reliable among the proposed eVTOLs. However, since UAM aircraft development is mainly led by industries, there are few studies that deal with the effect of rotor configuration as a major parameter within design of eVTOL. Therefore, this study aims to identify the effect of change in rotor configurations on eVTOL tiltrotor weight composition and mission performance, at conceptual design level. NASA Design and Analysis of Rotorcraft (NDARC), a rapid multi-disciplinary conceptual design program, will be utilized for the procedure. Three configurations based on NASA reference tiltrotor models will be presented, and optimal configuration in terms of weight and performance will be determined. In order to identify the reliability of such results, wing-nacelle structural analysis model will be constructed based on existing literature. By undergoing static structural and modal analyses, the model will be verified to be utilized for whirl flutter analysis.

Comparison of Reality versus Integrated Reality during In-Flight Maritime Helicopter Hover Manoeuvres (Paper 1347)
Full registrant at Forum? Log in for link!
Crew Stations I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Andrew Law, Perry Comeau, Alanna Wall, Sion Jennings, Gregory Craig, Sukriti Kumar, Kris Ellis, Arthur Gubbels

The National Research Council of Canada (NRC) recently developed an Integrated Reality In-flight Simulator (IRIS) allowing helicopter pilots to fly the NRC's Bell 412 helicopter while wearing a virtual reality headset and experiencing real-world multi-sensory cues. The first IRIS prototype simulated maritime helicopter ship-deck landing operations to augment current flight test and flight training methods. Two NRC test pilots evaluated the IRIS prototype using a customized mission task element (MTE) that represented maritime helicopter hover manoeuvres under three different Visual Cueing Environments (VCEs). Pilot performance and workload was evaluated in each cueing environment along with the effect of simulated airwake turbulence. Both pilots successfully completed the MTE using the Reality Field VCE with moderate workload, but found the Integrated Reality (IR) Field VCE to be higher workload due to poor VR resolution of subtle cues required for longitudinal positioning. By comparison, the pilots successfully completed the MTE using the IR Ship VCE with similar performance levels to the Reality Field. This evaluation demonstrated that the IRIS prototype is suitable for in-flight simulation of shipboard helicopter manoeuvres.

Comparison of Tail Rotor Performance with a Slotted, Natural-Laminar-Flow Airfoil (Paper 1271)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Christopher Axten, Mark Maughmer

The slotted, natural-laminar-flow (SNLF) airfoil is a low-drag, high-lift airfoil concept that has been explored for commercial and general aviation applications. This work seeks to determine the performance benefits of using an SNLF airfoil on the tail rotor of a small helicopter. Blade element momentum theory (BEMT) and Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) results for a rotor in hover are compared, including with an SNLF rotor that has the rotational speed reduced to generate the same amount of thrust as the baseline rotor. The BEMT analysis uses polar data generated from two-dimensional RANS CFD with methods and grids validated against wind tunnel data taken from high-quality facilities. Sectional data for the baseline and SNLF airfoils are presented and discussed, such as the higher maximum lift coefficient of the SNLF airfoil and subsonic and transonic Mach numbers and the SNLF airfoils' performance with high levels of freestream turbulence. Skin friction coefficient contours from the rotor CFD indicate the blade operates as intended and show regions of high skin friction on the tip closure geometry, highlighting a region of potential improvement. Integrated results, such as dimensionless and dimensional thrust and power, demonstrate that the SNLF rotor with a reduced rotational speed outperforms the baseline blade in terms of power requirements; however, the magnitude of the gain is substantially different between the BEMT and rotor RANS CFD. Lastly, BEMT results with various freestream turbulence levels and completely turbulent boundary layers indicate that the reduced rotational speed SNLF rotor requires the same amount of power as the fully turbulent baseline.

Comprehensive Simulation with Coupled Airframe-Propulsion Dynamics in Support of eVTOL Design (Paper 1210)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Felix Brenner, Jan Goericke, Matt Hasbun

A major consideration in the design and development of rotorcraft vehicles to support Urban Air Mobility (UAM) is meeting their mission endurance requirements. This is especially true of Electric Vertical Take-Off and Landing (eVTOL) configurations, with modern batteries providing significantly less energy storage density compared to traditional fossil fuel or hybrid-electric power sources. This constraint on available energy requires careful design of the entire propulsion system, from batteries to rotors, to maximize efficiency. Additionally, integrated full vehicle and propulsion system simulation and optimization of mission power requirements may be used early in the design to mitigate the risks associated with limited energy storage. This optimization can reduce the total weight of the components of the electric propulsion system including the sizing of the appropriate heat dissipation components. This study explores the coupling of a comprehensive flight dynamics model with a physics-based electric propulsion system in support of conceptual and preliminary aircraft design. The coupled simulation models are exposed wind profiles during the eVTOL hover stationkeeping to investigate the transient effects on aircraft response, effectiveness of the electric propulsion system, battery discharge, and heat dissipation.

Computational Analysis of Coaxial Rotor Hub and Sail Fairing Wake (Paper 1353)
Full registrant at Forum? Log in for link!
Aerodynamics IV (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Neal Deore, Forrest J. Mobley, James G. Coder

A computational study is conducted for coaxial rotor hubs with a sail fairing to characterize its downstream wake and surface forces. The flow conditions and grids are based on experimental tests performed at the Penn State Applied Research Lab (ARL) Water Tunnel at appropriate Reynolds numbers. Grid development for the rotor hubs and sail fairing is done using Pointwise v18.0R1 and Chimera Grid Tools. Simulations are performed using NASA's OVERFLOW 2.4b Reynolds Averaged Navier-Stokes solver. The drag forces on the rotor hubs are computed and compared to previous computational studies and experimental results. The drag forces are similar to previous computational studies but still do not match experimental results. The streamwise, spanwise, and vertical velocity components of the wake have been visualized, analyzed, and compared to experimental results. Further work is needed to analyze frequency content and Reynolds stresses.

Computational Fluid Dynamics Simulation for Additive Friction Stir Deposition of Aluminum Alloy (Paper 1349)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jim Lua, Xuxiao Li, Manoj R. Rajanna, Alan Timmons, Gabriel Murray, Nam Phan, Richard Eberheim

Additive friction stir deposition (AFSD) is a novel additive manufacturing (AM) technology in which solid-state, friction-stirred metal is deposited layer-by-layer to build three-dimensional parts. Unlike the mainstream fusion-based AM methods, AFSD does not cause metal melting and solidification. Therefore, AFSD can eliminate defects such as lack-of-fusion, key-holing, and large residual stress. Currently, the understanding of AFSD is based on the friction stir welding (FSW) process that has been widely studied for the past two decades. However, the material feeding and spreading in AFSD is essentially different from FSW and can complicate the thermal field and material flow. In this work, a computational fluid dynamics (CFD) model is created to simulate the temperature and fluid flow for AFSD of aluminum 7050 alloys. The predicted temperature is validated against both literature and thermocouple measurements. The current work lays the foundation for a quantitative understanding of AFSD process physics and the simulation-guided process design to tailor the thermal-mechanical field.

Computational Study of Vortex-Induced Separation for a 5-Bladed Rotor (Paper 85)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Christopher Thurman, Nikolas Zawodny, Kyle Pascioni

This work computationally investigated the rotor blade vortex-induced separation recently observed during an aerodynamic rotor test campaign in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Two separate approaches (i.e., airfoil modification and blade tip modification) were studied to mitigate the vortex-induced separation. Mid-fidelity tools based on blade element momentum theory were shown to mispredict the rotor inflow and were also shown to not capture the vortex-induced separation caused by perpendicular blade-vortex interaction. This misprediction was exploited to isolate the aerodynamic thrust deficit caused by the vortex-induced separation (20%) from the thrust deficit due to inflow variation (31%). High-fidelity tools were shown to reasonably predict aerodynamic forces within 13% and flow separation when compared to experimental results. The modified airfoil variant of the baseline rotor effectively mitigated the vortex-induced separation, while the blade tip modified variant still showed separation, though the size and strength of the vortex was reduced. Acoustic predictions were underpredicted by 10B from preliminary measurements taken in the untreated wind tunnel. Broadband noise contributions from different rotor blade sections showed that self-noise due to flow separation and other turbulent boundary layer mechanisms was the dominant noise source for all three rotor cases, followed by blade-wake interaction noise caused by perpendicular blade-vortex interactions.

Computational Study on the Aerodynamic and Acoustic Rotorprop Test in the NFAC 40- by 80-Foot Wind Tunnel (Paper 1165)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Zhongqi (Henry) Jia, Joon Lim, Rohit Jain

This paper focuses on the validation and investigation of interactional acoustics of a modern wing and pusher propeller configuration, which was tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel and the Army 7- by 10-Foot Wind Tunnel at NASA Ames Research Center. Isolated propeller and wing-propeller configurations were simulated in this work. The CFD simulations were carried out using the High Performance Computing Modernization Program (HPCMP) multi-disciplinary rotorcraft simulation tool CREATE™-AV Helios, and the acoustics were simulated using the noise prediction software PSU-WOPWOP. The propeller-wing case showed a 2/rev abrupt change of sectional airloads when blade cuts through the flowfield convected from the wing in the upstream, resulting in impulsive acoustic pressure pulses. Acoustics prediction for the propeller-wing case showed good agreement with the measured data. However, the isolated propeller case showed large discrepancies between predictions and measurements. The overall sound pressure level comparison between the isolated propeller and wing-propeller cases suggested that the wing and propeller interaction could significantly increase the propeller noise by up to 17 dB.

Concept of Operations in Aviation Industry - A Procedure Based Approach for Developing Novel Aerial Systems (Paper 1284)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Markus Maly, Julius Hoffelner, Christoph Krammer, Maximilian Wechner, Jerg Jaisle, Florian Holzapfel

In the last decades, Unmanned Aerial Systems (UAS) have been used extensively for various purposes. Consideringthe advantages of UAS compared to conventional manned aircraft, such as lower manufacturing and operating costs, UAS are creating a new industry with sizable economic potential. In this article, we introduce a novel procedure-based approach for developing a Concept of Operations (ConOps) document that integrates best practices from the aviation industry. A ConOps document should be defined to develop and operate a UAS safely. Since different guidelines are available that attend to different ConOps content, there needs to be a transparent process definition of how to generate a ConOps. In previous works, we developed and published a procedure-based methodology for aircraft design, initially intended for the development of optionally piloted vehicles.The ConOps process in this paper builds upon the existing aircraft development process and follows aviation standards, for example, SAE ARP4754A. Hence, ensuring maximum traceability, conformity, and integration with existing aviation guidelines is achievable while keeping flexibility as high as possible and supporting an agile development process. This novel process is independent of the mission goals and can be applied to manned, unmanned, and optionally piloted aircraft. The first insights from our practical experience in applying the new process are also presented.

Concerns with Using Machine Learning in Airworthiness Applications (Paper 65)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jason Rupert, H. Glenn Carter, Alexander Chan, Chris Vinegar

Machine Learning is seeing accelerating growth in its use across a wide swath of applications ranging from wall mounted thermostats to automobiles. Even the historically conservative aviation industry is beginning to explore the use of machine learning in benign applications, e.g., predictive health monitoring, and beyond, including plans for flight critical applications such as navigation solutions. With the potential push of machine learning into flight critical applications, airworthiness practitioners concerned with software should ask: are there concerns with using machine learning in flight critical airworthiness applications? The goal of this paper is to answer this question with a resounding 'yes', by identifying some specific concerns. These concerns include data-driven development, uncertain (statistical/probabilistic) output, and extending to functional behavior, repeatability, non-rigorous development, and specific deployment environments. Beyond just identifying the concerns, this paper proposes approaches to build justified confidence in the use of machine learning in flight critical applications through combined evaluation of performance assurance, development assurance, and mitigations.

Concerns with using Python in Machine Learning Flight Critical Applications (Paper 1343)
Full registrant at Forum? Log in for link!
Avionics and Systems I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Jason Rupert, H. Glenn Carter, Alexander Chan, Chris Vinegar

Python is a programming language that is proving irresistible to the Machine Learning development community. The characteristics that make it irresistible may not be well suited for flight critical applications, e.g., Python is an interpreted programming language reliant upon a virtual machine to execute bytecode. Programming languages used in flight critical applications have higher assurance expectations than non-flight critical applications. For aviation applications, Python may be appropriate for the development of Machine Learning models, but Python does not appear to be appropriate for the implementation of those Machine Learning models for deployment on flight critical applications. This paper explores concerns for using Python in those applications and offers potential courses of action to alleviate these concerns: (1) certify/qualify/mature Python, (2) transition from development in Python to implementation in a certified/qualified/maturity programming language, or (3) development and implementation in an environment with certification/qualification/maturity pedigree.

Control Power Margin as a Certification Consideration for Distributed Electric Propulsion (DEP) Aircraft (Paper 1182)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Robert McKillip, Daniel Wachspress, R. John Hansman, David Sizoo, Traci Stadtmueller, Dan Dellmyer

On-going work in examining the potential use of on-board calculation of remaining control power margin (RCP) for distributed electric propulsion (DEP) aircraft is described, where that metric may be an indicator of the capability of the vehicle to accommodate operational disturbances and avoid loss of control (LOC) events. Analysis and simulation modeling for the DEP vehicle is using CDI's CHARM (Comprehensive Heirarchical Aeromechanics Rotorcraft Model) code for representing the highly interactional aerodynamic environment for these aircraft, with the RCP algorithm development tested in both simulation and scaled flight experiments of representative DEP configurations

Correlation of Tiltrotor Aeroelastic Stability Wind Tunnel Test (Paper 1279)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Hao Kang, Andrew Kreshock, Robert Thornburgh, Matt Floros, Hyeonsoo Yeo, Jinwei Shen

This paper presents a correlation study of detailed finite element modeling with component vibration tests and comprehensive analysis modeling with whirl flutter experimental data for the TiltRotor Aeroelastic Stability Testbed (TRAST). TRAST is a semi-span tiltrotor model system that has been developed to investigate tiltrotor whirl flutter phenomena and to provide experimental data for rotorcraft analysis validations. Two comprehensive rotorcraft analysis codes, CAMRAD II and RCAS, were used for the whirl flutter correlation study. To ensure that real structures are represented accurately by the comprehensive analysis codes, detailed NASTRAN models using 2D/3D shell and solid elements were developed and refined based on vibration tests of the TRAST components. The 2D/3D NASTRAN model was simplified to a 1-D model consisting solely of beam and other 1-D elements. Using the components and the properties of the 1-D model, structural models for the comprehensive analyses were developed and validated against the vibration test data. Models for whirl flutter analysis were developed based on the validated structural models and compared to the whirl flutter experimental data. Sensitivity of the TRAST whirl flutter prediction to modeling details is discussed.

Coupled Experimental and Offline Simulation Study of a Helicopter Rotor in a Frigate Airwake with Active Flow Control (Paper 113)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Elvina Derhille, Quentin Gallas, Luc Bordier, Simon Verley, Laurent Keirsbulck

The operation of helicopters from small naval vessels like frigate present a demanding challenge for pilots. This paper studies the effect of active flow control system located along the sides of the hangar edges on the unsteady aerodynamic loads of a scaled rotor model operating along a stern approach. The flowfield above the helideck is experimentally measured using stereo particle image velocimetry. These data are compared to ship airwake computations to assess the flow prediction capabilities. The ship airwake in headwind and G20 conditions without and with blowing are implemented into the Airbus Helicopters HOST simulation code based on the one-way coupling approach. The output data are equilibrium monitoring curves of the four commands states. The deviations induced by blowing are in the order of 1% to 25% and it allows at bringing the commands back to the uncontrolled airwake case.

Deep Learning Based Framework for Multicopter Sensor Data Imputation (Paper 1329)
Full registrant at Forum? Log in for link!
HUMS I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Gaurav Makkar, Farhan Gandhi

The study presented in this paper introduces a novel approach for imputing missing sensor data in multicopters, which enables enhanced safety and reliability by leveraging the multitude of sensors on these aerial vehicles. The proposed approach is based on two deep learning techniques, namely Autoencoders (AE) and Long Short-Term Memory (LSTM) networks. The effectiveness of this approach is evaluated using flight test data from a 2.5 kg hexacopter, and three different scenarios of missing data are considered. To validate the performance of the proposed approach, it is compared against two commonly used imputation techniques: k-Nearest Neighbor (KNN) imputation and Random Forest imputation. The results indicate that the proposed approach outperforms both KNN and Random Forest in terms of the accuracy of imputation. The network has an error of less than 10% when processing signals with six missing sensor readings for a duration of 10 seconds. In contrast, KNN and Random Forest algorithms have an average error of 18% and 26%, respectively. Moreover, the trained model can handle missing data with varying degrees of sparsity, which makes it a more robust and flexible solution. The study also investigates the impact of using initial estimates provided by the Kalman Filter for training the deep learning models. It is observed that incorporating these estimates does not result in any improvement in the imputation accuracy. This suggests that the proposed approach is able to learn the underlying patterns in the data without the need for additional information from the Kalman Filter. Overall, the results of this study demonstrate the potential of deep learning techniques for imputing missing sensor data in multicopters. The proposed approach offers a more accurate and efficient solution than the traditional imputation techniques, and can handle varying degrees of data sparsity. The findings of this study have important implications for the design and operation of multicopters, and could result in enhanced performance and operational effectiveness of these aerial vehicles.

Defects Detection in Rotor Composite Parts using AI (Paper 128)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Nicolas Griselin, Pierre Barbier

During the manufacturing process of rotor composite parts, each part is systematically controlled using a Radiographic Testing (RT) approach. This is a non-destructive testing (NDT) method, which uses x-rays to examine the internal structure of manufactured components identifying any flaws or defects within the material. This paper describes a three steps approach to detect defects in radiographies of composite parts using Artificial Intelligence (Convolutional Neural Network and Computer Vision analysis).

Design Exploration for Aerodynamic Performance of Hovering Stacked Rotor (Paper 52)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Yoonpyo Hong, Dawoon Lee, Sunwoong Yang, Hyojin Kook, Kwanjung Yee

This study analyzed the aerodynamic performance and the underlying physics of various stacked rotor configurations under hovering conditions using a high-fidelity numerical solver. Three design variables, namely index angle, stacked distance, and pitch angle difference, were adopted to define the stacked rotor configurations. Accordingly, two dominant physical phenomena were captured by high-resolution simulations: the inflow effect and the wake interference effect. In particular, the blade-vortex interaction at the lower blade plays a crucial role in increasing the overall aerodynamic performance by generating upwash that increases the local power loading of the lower blade. Unsteady simulations demonstrated that the blade-vortex interaction of the stacked rotor generates a significantly lower peak-to-peak thrust value compared to the counter-rotating coaxial rotor, which may result in a much lower aeroacoustic noise level. Finally, design optimization to maximize inflow and wake effects was performed leveraging neural networks, successfully extracting design rules that can guide future preliminary design studies.

Design and Testing of a 35 kW Hybrid Power Genset (Paper 1230)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Michael Ricci, Jason Hu, Jack Brewer

Hybrid electric propulsion is a promising technology to achieve excellent overall vehicle performance. Electric propulsion enables new types and configurations of rotorcraft, but the poor energy density of batteries has limited the overall performance of electrically propelled aircraft. A hybrid architecture can take advantage of the high energy density of chemical/liquid fuels; but also utilize the advantages of electric propulsion technology. This advantage of a hybrid system can only be realized if the hybrid system can be implemented with sufficient energy conversion efficiency and low enough mass. If not done in a highly optimized way, the complexity of the hybrid system can lead to it being too heavy and too inefficient - the worst of both worlds instead of the best of both worlds. LaunchPoint EPS will present design details and test results of our flightweight 35 kW hybrid electric genset system. Overall estimated vehicle mass breakdowns and estimates of vehicle performance range-payload diagrams extrapolated from genset test data will be presented. Mass breakdowns for the hybrid propulsion system will be presented showing the complexity and potential for 'ass-creep'in the aircraft weight budget. Dynamic transient performance requirements and results for the hybrid propulsion system will be presented. Lessons learned on testing and commercializing a 35 kW flight weight genset will be presented.

Design of High Power Density Direct-Drive E-machine for an eVTOL Application (Paper 1163)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Hanafy Mahmoud, Phillip Scott, Travis Histed

Electric powered vertical take-off and landing (eVTOL) vehicles are in development for urban air mobility, as they have zero emissions and support a reduction of traffic congestion. A long-range eVTOL aircraft requires a propulsion unit with challenging requirements for power and torque densities, efficiency, reliability, safety, and environmental sustainability. This paper deals with designing an efficient high-TRL direct-drive electric machine (E-machine) with high power and torque density for the propulsion unit. As an example, City Airbus eVTOL's requirements have been considered as a baseline. The work-flow proposed demonstrates the feasibility of designs that push both active power density and torque density of the studied E-machine to more than the twice that of the current system. The proposed approach includes investigations of the optimum slot/pole combination, air-gap length, number of three-phase groups and advanced materials. Furthermore, a fast multi-objective optimization approach based on a meta-model of optimized prognosis (MOP) has been applied.

Design of a Lift+Cruise eVTOL Aircraft reflecting the Geometry and Structural Details regarding Battery Locations (Paper 151)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
WonSeok Cha, SunHoo Park, MinHo Hwang, YooHo Chang, ChiHyun Ahn, SangJoon Shin

The concept of Advanced Air Mobility (AAM) has gained significant attention in recent years, leading to the development of many conceptual and external designs. However, there has been limited academic investigation into the phases after conceptual design, such as preliminary and detailed design, with structural design being a critical component. This paper focuses on the conceptual and preliminary structural design of a lift+cruise eVTOL aircraft, considering battery locations. The conceptual design phase introduces a flexible and rapid design framework that reflects variations in geometry, and the structural design is conducted using simplified form structures to maintain a short design cycle. Structural robustness is evaluated through modal and static structural analysis, with a few manual iterations to meet constraints. The research investigates two battery locations, the fuselage and main wing, and provides weight breakdown data for the designed present lift+cruise eVTOL model.

Design, Fabrication, and Testing of Stiffened Composite Panels with Acoustically Tailored Stiffeners (Paper 1293)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Avery Brown, Anna Moorehouse, Charles Bakis, Edward Smith, Ben Beck, Micah Shepherd

Carbon fiber reinforced epoxy composites are being increasingly used for load bearing structural elements in large transport rotorcraft. However, due to the increased stiffness-to-density ratio of composites, problems associated with vibration and interior noise can be exacerbated by the use of composites in airframes. The current investigation explores the potential of optimized composite meta-structures to reduce vibration and interior noise in rotorcraft. The approach involves designing a taper into the thickness of blade stiffeners which, when combined with a limited amount of absorbing material in the thinned region, creates what is known as an 'acoustic black hole' (ABH) in the stiffener. It is hypothesized that optimally designed ABH stiffeners can reduce broadband vibrations in stiffened panels. An optimization routine has been developed to determine the tradeoffs between vibration, mass, and buckling load due to compression parallel to the stiffeners. The tradeoffs are visualized using a 3-D Pareto front that helps the designer decide on the optimal design. Carbon/epoxy panels were made using vacuum-bag-oven processing with out-of-autoclave prepreg and verified to be of good quality. Panel vibration, buckling onset, and post-buckling load-deflection behavior were simulated using finite elements and measured using model testing and compression testing. Based on preliminary results, ABH-tapered stiffened panels have the ability to reduce radiated noise without a significant penalty in the mass and compressive load-bearing capability.

Developing and Applying Means of Compliance For a Powered Lift Aircraft (Paper 1234)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Luca Belluomini, Joseph M. Schaeffer, Damian Rogers

The paper discusses the certification basis for the AW609 Tiltrotor, a next-generation aircraft that combines the vertical takeoff and landing capabilities of a helicopter with the speed and range of an airplane. The paper describes the development of the certification basis, which is based on a mix of new tiltrotor requirements and existing regulations from Parts 23, 25, and 29 of the Federal Aviation Regulations (FAR). The paper also discusses the specific safety requirements that were developed for the AW609, and how these requirements were met through the use of advanced flight control systems. The paper concludes by stating that the AW609 certification basis is a mature process that is undergoing final reviews and approvals for public release in 2023. The paper also states that the AW609 is an example of an highly integrated PL aircraft that alleviates crew workload with unique capabilities, like thrust power management system, full time rotor speed governor, automatic nacelle control, and 'envelope protection'.

Development and Performance Evaluation of a Multi-Rotor eVTOL Using RPM, Collective, and Cyclic Control in Failure State (Paper 1377)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Riccardo Roiati, Richard Anderson, Kyle Collins, Vivek Saini, Patric Hruswicki, Nishant Sharma, Syed Zuhair Ali Razvi, Shivansh Agrawal, Xinyu Yang, Sahil Ghate

The Eagle Flight Research Center (EFRC) at Embry Riddle Aeronautical University (ERAU) is investigating the risks and failure modes of Distributed Electric Propulsion (DEP) employed in novel Advanced Air Mobility (AAM) aircraft designs. To certify these aircraft for private and commercial operations, a greater understanding of how the vehicle is controlled in both nominal and off nominal or degraded modes is required. The EFRC team has designed and built a test stand to characterize the capabilities of a single DEP unit as well as 2 full-scale quadcopter AAM vehicles with RPM, collective and cyclic control. Extensive testing and simulation results showed that in order to operate and stabilize a quadcopter in a rotor out condition both collective and cyclic control must be utilized.

Development of Control Laws for a Large Multi-Rotor eVTOL Using RPM, Collective, and Cyclic Control Allocation Methods (Paper 1383)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Syed Zuhair Ali Razvi, Richard Anderson, Kyle Collins, Riccardo Roiati, Shivansh Agrawal, Patric Hruswicki, Nishant Sharma, Vivek Saini, Xinyu Yang

The Eagle Flight Research Center (EFRC) at Embry-Riddle Aeronautical University (ERAU) is investigating the handling qualities of partial and full rotor failure modes of a multi-rotor employing distributed electric propulsion (DEP) systems in Advance Air Mobility (AAM) aircraft vehicles. The handling characteristics for the operation of these vehicles in private and commercial industries require a deeper understanding of their dynamics and controllability under rotor failure conditions. The objective of the research performed at the EFRC centers around designing and testing different thrust and moment control allocation methods for an electric Vertical Take-Off and Landing (eVTOL) vehicle, in addition to assessing their performance in both nominal and failure modes of operation. This paper focuses on developing the vehicle dynamic models and various Control Law (CLAW) architectures for a full-scale quadrotor testbed vehicle with RPM, collective, and cyclic blade pitch control allocation. The study uses simulation and flight-test data to evaluate the theoretical and experimental concepts proposed for the testbed vehicle. The performance of the developed control laws is compared in simulation and flight tests to conclude that collective plus cyclic control provides better response time in yaw control and it is the only control law that makes it possible to operate the vehicle during a rotor out condition

Development of Parametric Rotor Control Equivalent Turbulence Input (RCETI) Models for Rotorcraft (Paper 1265)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Mahmoud Hayajnh, J. V. R. Prasad

This paper presents an extension of previous research that aims to generalize the hover/low-speed Control Equivalent Turbulence Inputs (CETI) models for different helicopter configurations. The rotor hub-loads are utilized as the outputs to which the turbulence-related spectra are matched in order to achieve this generalization. Additionally, the rotor swash-plate deflections are considered as inputs to create what is referred to herein as the Rotor Control Equivalent Turbulence Inputs (RCETI) model. The development of the RCETI model, which aims to produce rotor loads spectra similar to those generated by vertical turbulence, is conducted using a representative model of the UH-60 helicopter in FLIGHTLAB®. The analysis is performed as a Multiple-Input Multiple-Output (MIMO) case, and the results are compared to the Single-Input Single-Output (SISO) cases. Furthermore, the effect of altering the rotor parameters on the RCETI model is studied and presented in the paper.

Development of a Coupled Torsional Dynamics and Gear Contact Model to Predict Peak Loads in a Tiltrotor Drive System (Paper 102)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Nathaniel Albuck, Tanmay Mathur, Ahmad Haidar

The tiltrotor drive system is a complex and coupled system with different torsional dynamics compared to conventional rotorcraft. It is designed to guarantee safety and reliability and tested for the effects of its dynamics and loads on component sizing. The epicyclic gearing system, the final reduction stage in most aircraft gearboxes, is most impacted by such dynamics. The components of this subsystem must withstand all peak loads due to novel control strategies and torsional dynamics. In this paper, a gear contact analysis model is coupled with a validated torsional dynamics model of a tiltrotor interconnected drive system. The coupled model predicts component-level design loads in the interconnected drive system originating from its torsional dynamic behavior. An accurate gear macro and micro geometry is generated in the gear contact model which is used to derive the time varying mesh stiffnesses at the sub-component interfaces. The variable mesh stiffnesses are applied in the gear dynamic model to simulate the dynamic responses of the gear system under load. Finally, a dynamic overload factor relating the peak dynamic and static loads is analytically assessed, and it is shown to exceed conventional predictions in the case of an asymmetrically loaded interconnected drive system. This dynamic factor can be implemented to inform design decisions during the development of future multi-rotor VTOL aircrafts to mitigate component damage and, in turn, increase the safety and extend the lifespan of critical components.

Development of a Datadriven Model for Prediction of Vibrational Discomfort in Helicopters (Paper 1171)
Full registrant at Forum? Log in for link!
Dynamics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Tim Burkhardt, Süleyman Özkurt, Fabian Schimpf, Walter Fichter

Ensuring passenger comfort is an essential task of manned aviation. To describe the discomfort as a result of the entire vibration environment of a helicopter, an evaluation procedure is required. Currently, the most comprehensive approach to evaluate discomfort caused by whole-body vibration is described in ISO2631-1. Since ISO2631-1 is based on uniaxial and sinusoidal laboratory experiments, the discomfort evaluation of complex helicopter vibrations is not correctly reflected. This paper describes the systematic creation of an evaluation procedure for discomfort caused by whole-body vibration. Based on a study in a realistic helicopter environment, a data-driven evaluation procedure is derived that can also be applied to other experimental campaigns. Two possibilities for the structure of the evaluation procedure are presented. One is derived by optimizing the metric to the measured data. Therefore, a larger computation time is required. With the other structure, the calculation time is reduced by some simplifications. The calculation procedure is similar to that of ISO2631-1. The procedure determined in this way can be used, among other things, for future flight controller design. The newly developed model provides more accurate predictions of discomfort than the previous standard for helicopter applications.

Development of a Machine-Learned Cruise Guide Indicator for Rotorcraft (Paper 1203)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Mathew Boyer, Wesley Brewer, Jeff Finckenor, Chris Brackbill, Daniel Martinez-Gonzalez, Andrew Wissink

This paper presents a machine-learned virtual cruise guide indicator (vCGI) for Chinook helicopters. Two temporal neural networks were trained and evaluated on measured data from 55 flight tests, one for the fore rotor and another for the aft rotor, to predict a vCGI value, which protects 23 components from fatigue damage during steady-state conditions. Three different classes of machine learning architectures were evaluated for prediction of the vCGI from time sequences: a temporal convolutional neural network with 1D dilated causal convolutions, a long short-term memory recurrent neural network, and an attention-based transformer architecture. The final average model accuracy on unseen flight data is currently greater than 93% for CGI values which could result in fatigue damage and 90% for normal operation CGI values. Model accuracy was improved through a series of advancements in: (1) selection of optimal training data using temporal collective variables and unsupervised learning, (2) dataset augmentation with maximum-entropy temporal collective variables, and (3) implementation of a mixture-of-experts classification-regression approach using an adversarial classification approach to assign maneuver labels. The results are presented for each advancement in model development along with lessons learned in training machine learning models on real-world, time-dependent rotorcraft data.

Development of an Air-launched Tail-Sitter Unmanned Aerial Vehicle (Paper 133)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jiaze Cai, Hunter Denton, Moble Benedict

This paper describes the development and flight testing of the first-ever air-launched tail-sitter UAV platform. Integrated with VTOL capability, the platform can be launched from various platforms, perform long-endurance loiter tasks and low-speed or hover flight, and land vertically in limited spaces. This work covers the experimental exploration of possible rotatable-fin designs, which then converge to a coaxial thrust vectoring design. A platform featuring a coaxial propeller and a thrust-vectoring mechanism is combined with a conventional fixed-wing design to accomplish both vertical and horizontal flights. An innovative bird-wing-inspired wing folding mechanism is also proposed in this work. A control strategy capable of handling both vertical and horizontal flight has been proposed. A cascaded feedback control strategy was implemented on a 1.7-gram custom-designed autopilot to stabilize the vehicle attitude. The proposed platform uses the coaxial rotors and the thrust-vectoring mechanism to accomplish the control in pitch, roll, and yaw for both vertical and horizontal flight. An indoor flight test with aggressive pilot inputs was successfully performed to demonstrate the controllability of the aircraft. Additionally, transition flight testing has successfully demonstrated the vehicle's capability of transition flight using the proposed thrust-vectoring mechanism.

Development of an Operational Analysis Tool for Urban Air Mobility (Paper 1360)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Marilyn Smith, Aaron Crawford, Kyle Carozza

The current interest in autonomous urban/advanced air mobility (U/AAM) capabilities raises important questions regarding the safety, maintenance, cost, and life cycles of UAM vehicles to produce a business case, in particular as operations will be in significantly different environments. Accurately estimating a vehicle's aerodynamic and structural behavior, combined with a knowledge of material properties and operational sensor data, permits the prediction of vehicle fatigue throughout its life cycle. This should result to less scheduled maintenance, less time out of operation, and therefore a lower overall operational cost. Under NASA University Leadership Initiative (ULI) funding, Georgia Tech and their partners are addressing this problem through the development of an Operation Analysis Tool (OAT) for U/AAM platforms of varying size and configuration. The OAT seeks to provide a framework for real-time analysis of UAM vehicles in various flight conditions allowing for rapid prediction of structural responses and other safety-related events. The current version of the tool, along with planned improvements are described in this paper.

Development of the Langley Rotor Test Stand (Paper 1157)
Full registrant at Forum? Log in for link!
Test and Evaluation II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Austin Overmeyer, Lynn Rawlinson, Stephen O'Grady

A new Mach-scaled single main rotor test stand, the Langley Rotor Test Stand, was designed, fabricated and tested at NASA Langley by the U.S. Army Aviation and Missile Command. This paper provides a description of the test stand, summarizes the acceptance testing and provides recommendations for future improvements. The objective of the test stand was to modernize the U.S Army's testing capabilities to meet both the short term and long term goals of the Future Vertical Lift (FVL) program and basic research needs. The test stand provides a backbone for various rotor and fuselage configurations at a 20-40% scale to study interactional aerodynamics in the wind tunnel. The test stand was purpose built for forward flight testing in the NASA Langley 14- by 22-Foot Subsonic Tunnel, but is easily portable for testing in other hover facilities and/or wind tunnels.

Development, Simulation, and Flight Testing of Damage Tolerant Control Laws for the ADAPT Winged Compound Helicopter Scaled Demonstrator (Paper 143)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Samuel Nadell, Tom Berger, Alex DiJoseph, Eric Huang

Damage tolerant control (DTC) laws were developed for the Adaptive Digital Automated Pilotage Technology (ADAPT) Winged Compound Helicopter Scaled Demonstrator, a 10% scale version of the Piasecki X-49A, and tested in simulation and flight. The damage scenarios considered include failures of the aircraft's eight redundant actuators: left, right, and aft swashplate servos; Vectored Thrust Ducted Propeller (VTDP) RPM; rudder; left and right flaperons; and elevator. A pseudo-inverse control allocation scheme was used to reallocate control to the remaining actuators based on detection of a failed actuator. The paper covers discussion of the vehicle configuration, flight dynamics, control design, piloted simulation study to evaluate aircraft survivability and failure severity, and flight testing. The results show that DTC improved aircraft survivability and reduced failure severity, as measured by Sullivan Survivability and Integrated Failure Evaluation Scheme ratings, for three of the five damage scenarios tested in the piloted simulation study. Most notably, DTC enabled recovery after a left swashplate servo hardover that was unrecoverable with DTC off. DTC for this damage scenario was successfully tested in flight.

Drag Prediction of the Coaxial PSU-Hub using Helios (Paper 1352)
Full registrant at Forum? Log in for link!
Aerodynamics IV (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Dylan Jude, Aaron Crawford, Rohit Jain

The rotor hub on a traditional helicopter accounts for a significant portion of the overall aircraft drag. On-going experimental research from Pennsylvania State University (PSU) investigates drag from different rotor hub models using a water tunnel with the goal of better understanding sources of hub drag. The experimental work is being performed in tandem with high-fidelity CFD simulations from different groups from government, industry, and academia. This work presents a CFD study on the drag of the coaxial hubs and the components that included stand, sail fairing, and shafts. The HPCMP CREATE-AV Helios CFD framework is used for all simulations. The drag of the components are all compared in a drag build-up study. First, the hubs are run in isolation. Second, the stand/sail is also run in isolation. Third, the hubs and stand/sail are run together. Finally, all hubs, shafts, and stand/sail are combined. Calculations are performed primarily using kCFD within Helios. Comparisons are also made to results using FUN3D as the near-body solver in Helios. Simulations from previous work assumed the shaft influence would be negligible. However, results from this work suggests the presence of the shafts significantly affects the overall drag of the assembly.

Dynamic Shock Load Analysis of an eVTOL Aircraft Transmission System (Paper 1151)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Dexin Wang, Jennifer Peeples, Andrew Johnston, Giorgio Valente, Younes Riache, Hanafy Mahmoud

Electric Vertical Take-Off and Landing (eVTOL) aircraft are considered as a solution to support urban transportation, including cargo delivery (Unmanned Aerial Vehicles, UAVs) and passenger travel (Urban Air Mobility, UAM). Over the last few years many different concepts have been derived and tested to varying levels of maturity. The race for the most efficient, safe and reliable system solution ongoing, with many new challenges in the propulsion system and energy storage technology and design space, including specifically the power electronics, electrical machine (e-machine) and transmission design and verification.This paper presents an integrated '3in1' eVTOL e-Propulsion concept that has been developed utilizing a novel, integrated, model-based system engineering (MBSE) workflow that is enabled via newly developed model-translation capabilities and software interfaces. It starts with the design of the drivetrain based on a steady-state approach with low computational effort, which is then rapidly translated into a multibody model and directly coupled to a high-fidelity behavioral model of the e-machine, the inverter and control system, to represent reaction loads with even higher fidelity. The resulting holistic model can be used for assessing performance, efficiency and robustness, including various foreseeable dynamic loads such as turbulence. It was found that this workflow was valuable in supporting the risk-reduction exercise during the development of a complex aerospace propulsion system, promoting reliability and safety engineering methodology from the outset.

Dynamic Simulation of a Rotorcraft Main Transmission with Continuous Variable Ratio (Paper 1331)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Michael Weigand, Florian Donner, Thomas Scheu, Agnes Poks

The 'VARI-SPEED II' project involves TU Munich, TU Wien, Zoerkler Gears, and Advanced Drivetrain Technologies GmbH developing a drivetrain that allows variable speed of a helicopter's main rotor. This is beneficial for different speed requirements, reduced noise, and higher efficiency. Various researchers have investigated the benefits and suitable technologies for varying main rotor speed. Calculation formulas were established to find the ratio distribution of gear stages with the lowest total mass of the drivetrain, and electric variators are potential solutions. The architecture with two compound splits before the bevel gear stage was chosen for the dynamic simulation of the drivetrain due to its favorable design considerations. In the 'VARI-SPEED II' project, control of the variable speed drivetrain is crucial for achieving the desired variable main rotor speed. To achieve optimal control, a fuzzy model predictive control (FMPC) approach has been proposed. The FMPC has several advantages, including the ability to handle nonlinearities and uncertainties. Furthermore, the FMPC is real-time capital and of and can adapt to changing operating conditions.

Effect of Rotor Blade Elasticity on UAM Quadrotor Acoustics (Paper 66)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Sesi Kottapalli, Christopher Silva, D. Douglas Boyd, Jr.

The 6-passenger quadrotor concept vehicle designed under the NASA Revolutionary Vertical Lift Technology (RVLT) Project is considered for acoustic analysis. The tip speed is 550 ft/sec, with three blades per rotor (550/3). Originally, the blades were rigid, uniform spanwise, and with flap and pitch degrees of freedom. The blade model has since been updated: a lag hinge was added, and nonuniformities and elastic properties were introduced. Four blade models are considered: 1) original model, rigid uniform flap-pitch; 2) rigid uniform flap-lag-pitch; 3) rigid nonuniform flap-lag-pitch; and 4) elastic nonuniform flap-lag-torsion. Predictions are made for three flight conditions (approach, flyover, and takeoff) using the four blade models. The RVLT Toolchain is exercised using CAMRAD II and pyaaron/AARON/ANOPP2. Quadrotor trim and performance, 0.75R vertical blade loading for all four rotors, and noise sources are analyzed. Also, the contributions of the front and rear rotor pairs to noise are studied. In approach and flyover, a 2 dBA loading noise difference (delta) is predicted between blade models 1 and 4 (delta for takeoff is smaller, 1 dBA). Most of this noise delta is due to the lag hinge and nonuniformities, which is consistent with the results of a 2022 study that had considered only the approach condition; the current results extend this conclusion to flyover and takeoff also. The insensitivity of quadrotor noise to blade elasticity is currently attributed to the high blade torsional stiffness (frequency 6.41 per rev) and the small blade radius (9 ft) of the 550/3 design. Suggestions for potential follow-on work are given.

Effects of Anhedral Tip on Forward Flight Performance (Paper 149)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Christopher Nelson, Chong Zhou, Shivani Shankar, Lakshmi Sankar

The effect of blade tip planform on rotor aerodynamics in hover and forward flight is investigated. This work is based a set of test data for several advanced planforms, with the S-76 rotor serving as the baseline. Two complementary numerical modeling approaches - a hybrid Navier-Stokes/free wake approach, and a wake capturing approach - are used to study the rotor aerodynamics in hover and forward flight. The present studies indicate that the rotor hover performance, as measured by the required power for a specified thrust setting, improves when anhedral is introduced. Anhedral rotors are seen to produce a smother blade loading and a more uniform inflow, which is expected to result in reduced induced power for a given thrust loading. In forward flight, the anhedral tip behaves similarly to the baseline swept tapered tip, and the benefits of the anhedral tip are less pronounced due to the decreasing contribution of induced power to the total power consumption.

Effects of Light Rain on Coaxial and Tandem Rotor Performance in Hover (Paper 86)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Aishwerya Singh Gahlot, Lakshmi Sankar, Po-Wei Chen

With the advent of the new generation of eVTOL helicopters and UAS systems, there has been an increased interest in designing and modeling compact multi-rotor systems that provide the required lift and thrust forces, and control moments. These systems would be expected to be available and operate in adverse weather that includes light rain in warm and cold weather. Towards this need, an existing hybrid Navier-Stokes/free wake model has been enhanced to tightly couple the transport of water droplets with the aerodynamic flow, taking into consideration the drag force exerted by the airstream on the water droplets, and the reaction forces exerted by the droplets on the air flow. In this study, this coupled solver is used to model the effects of rain on coaxial and tandem rotors operating in hover. A coaxial rotor tested by Harrington and a tandem rotor tested by Sweet are considered. The aerodynamic performance (thrust and power coefficients, and the figure of merit) are presented as a function of the rotor collective pitch and compared with computational and experimental data in the absence of rain. The incremental effects of rain on the rotor thrust and power are quantified.

Effects of Linked vs. Unlinked Cyclic Controllers on Crew Coordination (Paper 145)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Tom Berger, Brandon Dotson, Anthony Gong, Jeffery Lusardi, M. Hossein Mansur, Carl Ott, Wesley Ogden, Matthew Miller

With the move towards fly-by-wire flight control systems for rotorcraft, pilot inceptors are no longer physically connected to the mechanical hardware of the aircraft. This has allowed the move to smaller, lighter, side-mounted controllers, which typically lack a mechanical connection between the pilots' inceptors. Such controllers can be electronically linked using active inceptors, however this adds cost and weight over passive inceptors. The objective of the work presented in this paper is to assess the impact of linked versus unlinked cyclics on Army helicopter aircrew coordination. To do this, a piloted simulation was conducted in the NASA Ames Vertical Motion Simulator using both Mission Task Element type maneuvers, as well as more operationally relevant mission vignettes. The simulator was configured with two side-by-side pilot stations with sidestick controllers which could be configured to operate in either a linked or unlinked configuration. During each task, a control transfer from the pilot flying to the pilot not-flying was either forced or induced, and subsequently the pilots were asked to answer a series of questions and rating scales related to predictability, awareness, and acceptance. Results of the study showed that in all cases, pilots preferred the linked cyclic controller configuration, which received better predictability, awareness, and acceptance ratings. In addition, the linked cyclic controller configuration had shorter-duration simultaneous input events (both pilots moving their inceptors to control the aircraft at the same time) compared to the unlinked cyclic controller configuration.

Effects of Sloped Terrain on In-Ground-Effect Hover Performance for an Isolated Rotor (Paper 1259)
Full registrant at Forum? Log in for link!
Test and Evaluation II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jack Prewitt, Joseph Milluzzo, John Tritschler

The present work reports the results of an investigation into the performance effects of hovering over sloped terrain for a laboratory-scale rotor. A pair of 1 : 13.24 scale OH-58C rotor blades were operated over a six-axis ground plane which could vary in angle, and rotor performance measurements were collected using a six-axis load cell. The design of the experiment included variation of the ground plane angle, collective blade pitch angle, and rotor height above the ground. The results showed that sloped terrain had a measurable performance degradation for all tested hover regimes, which was found to be greatest at combinations of low rotor hub heights and low blade loading coefficients with degradations up to 9.3% when compared to hover over level terrain. In certain flight regimes, hover over sloped terrain required up to 2.6% more power than hover out-of-ground effect. An increase in blade loading coefficient was seen to improve hover performance over sloped terrain by up to 4.5% rather than degrade performance, which is typically seen when hovering over level terrain. Finally, a model of hover over sloped terrain using a semi-empirical model is presented and discussed.

Employment of Simulation for the Flight Certification of Rotorcraft (Paper 1193)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Giuseppe Quaranta, Stefan van't Hoff, Linghai Lu, Gareth Padfield, Philipp Podzus, Mark White

The aim of this paper is to provide guidance on the employment of flight simulation to demonstrate, either directly or indirectly, compliance with the flight-related requirements within the certification standards for small or large rotorcraft. Herein are presented the approaches that are suggested in the guidelines for rotorcraft certification by simulation developed by the RoCS project to tackle the topic of the credibility of simulation.

Engine Usage Analysis using Unsupervised Machine Learning (Paper 115)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Stephane Cerqueira, Herve Morel

During operation, Helicopter Gas Turbine undergo various types of degradation due to high temperatures and mechanical loading. Its life assessment and associated maintenance concepts are oftenly based on counters of type of cycles or running hours. In the present article, a methodology for analyzing engine usage is exposed thanks to big data and subsequent Machine Learning capability. Attention is focused on Flight Code Recognition and its value while having a close look at the damage experienced, in flight, by engines. The specific case of the creep counter is discussed and illustrated through real examples of typical helicopter missions. It allows demonstrating the benefits of such approach while defining the maintenance model or providing recommendations in preventing unexpected engine removal prior to TBO. Finally, the limitations of the present model are listed and a way to formalize an universal model, where the steady and transient phases are treated separately, is presented.

Enhanced Flight Dynamics Models with Aerodynamic Interference for Real-Time Simulation of VTOL Concept Vehicles (Paper 148)
Full registrant at Forum? Log in for link!
Modeling and Simulation I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Matthew Gladfelter, Chengjian He, Hossein Saberi, Carlos Malpica, Wayne Johnson, Christopher Silva

In an effort to establish common models to support the Advanced Air Mobility (AAM) community, NASA has designed a fleet of VTOL configuration reference models. Advanced Rotorcraft Technologies (ART) in cooperation with the NASA Ames Aeromechanics branch has developed FLIGHTLAB simulation models for several of these AAM VTOL concept vehicles. These simulation models are real-time capable while maintaining accurate flight dynamic characteristics with enhanced interference simulation by extracting important modeling parameters from Viscous Vortex Particle Method (VVPM). The focus of the paper is threefold. First, it introduces the simulation models developed and describes their modeling characteriestics important to control and flight dynamics simulation. Second, the method for deriving the interference coefficients between model components such as rotors and wings is outlined. Implementation of the method for the lift+cruise and tiltwing models are discussed in detail. Third, the accuracy of the interference enhancement is assessed, with emphasis placed on the impacts to trim and flight dynamic characteristics. The interference enhancement method is further used to evaluate configuration design decisions by quantifying perfomance aspects of interference. This research effort culmintated in simulation models for the AAM VTOL concept vehicles, with proper interference and real-time capability.

Enhancing UAS Sensor Operators' Performance in Constrained Network Environments (Paper 1173)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Benjamin Purman, Daryn Dever, Bridget Furlong, Matthew Nulle

Unmanned aerial systems (UASs) are currently utilized to for a wide range of intelligence, surveillance, and reconnaissance (ISR) tasks, but typically require a realtime video connection. Our paper examines the effectiveness of Forward Observer, an architecture which mitigates these networking limitations for UAS sensor operators. Forward Observer is designed around the notion of 'bursty' data products. Bursty data products are compressed image files that summarize events in UAS video stream data. To generate these products, Forward Observer incorporates on-board analytics (e.g., object detection, semantic labeling) to identify content of interest, and it incorporates recommendation algorithms to prioritize content to send to the operator. To examine Forward Observer's effectiveness, experienced sensor operators engaged in an ISR task under three conditions: (1) immediate access to bursty data products; (2) limited bandwidth for bursty data product transmission; and (3) Forward Observer capabilities in a limited bandwidth. Results found that, with Forward Observer, participants had greater time on task efficiency, the amount of data needed was significantly less, and confidence generally increased after approximately six minutes in the ISR task. Implications of these results show that Forward Observer's bursty data products and on-board analytics and prioritization capabilities positively contribute to sensor operators' ISR task efficiency and success.

Estimation of Confidence Margins for Direct Load Recognition (DLR) using Supervised and Unsupervised Machine Learning (Paper 1174)
Full registrant at Forum? Log in for link!
HUMS II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Jeremy Jouve, Caroline Des-Cistia-Gallimard, Konstanca Nikolajevic, Herve Morel

One of the key challenges of any helicopter manufacturer lies in the competiveness of its products compared to its competitors. Operating costs is clearly one of them. Taking into account the complexity to maintain in operational and airworthy conditions a helicopter, substantial gains are achievable through the optimization of the Direct Maintenance Cost (DMC). Over the last decades, significant improvements have been made on mandatory enablers of such technologies, as for example Data Based Models (DBM), Predictive Maintenance (PM) or Conditions (Usage) Based Maintenance (CBM). More and more complex approaches were elaborated, getting always closer from true helicopter behavior, but certification has often been a hindrance to development, as infallible evidences are difficult to build. Thus, instead of pushing for additional improvement to gain limited performances, this paper presents an alternative way, taking uncertainties as an intrinsic component of the prediction. Similarly to fatigue metallic, choice is made to live with uncertainties, but to confine them thanks to statistics approaches based on the estimation of confidence intervals around a prediction. Through the paper, three methods have been explored, Euclidean proximity (K-Nearest Neighbors ,KNN), unsupervised learning (Self-Organizing Map) and supervised learning (Conformal Prediction). This broad, largescale exploratory analysis, has demonstrated that reasonable intervals, which would not prevent any gain from a Condition Based Maintenance approach, can be defined and shall be now compared with certification authority's preliminary targets.

Estimation of Probability of Exceeding SC-VTOL Performance Requirements During Automatic Landing Using Subset Simulation (Paper 80)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Christoph Krammer, Florian Holzapfel

With the rising interest in urban air mobility, new regulations are released to enable the certification of electric Vertical Take-off and Landing (eVTOL) vehicles. These novel performance requirements pose both technical challenges and opportunities for new design approaches. In this paper, we apply a Markov chain Monte Carlo method called subset simulation to the flight dynamic model of a prototype eVTOL vehicle to estimate the probability of violating performance and operational criteria. These requirements are derived from the means of compliance for the EASA 'Special Condition for small-category VTOL aircraft'; and 'Prototype Technical Design Specifications for Vertiports,' with additional aspects from the EASA 'Certification Specifications for All Weather Operations' transferred to eVTOL aircraft. The simulations are conducted with a closed-loop experimental flight guidance and control system for automatic landing in combination with varying parameters in the environmental and aircraft models. The computation time to estimate the failure probabilities is reduced compared to pure Monte Carlo methods by utilizing a subset simulation framework. Initial results show the sensitivity of exceeding limit thresholds to the parameters varied in the flight dynamic model.

Evaluation of Acoustic Propagation in Layered Media using Wave Confinement (Paper 64)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Subhashini Chitta, Mary Houston, James Stephenson, John Steinhoff

A comprehensive method for propagation of sound in layered media is discussed that involves dividing the domain into two regions, source field and far field. The source field is provided using experimentally collected data from full-scale rotorcraft acoustic flight tests, which consists of short waveforms that cannot be directly simulated on the grid without numerical errors. Instead, grid based computational waves are used to carry the details of these waveforms, including amplitude, arrival time and location of origin on source sphere. This is done by solving the scalar wave equation using the Wave Confinement (WC) method, which involves adding an extra term to produce converged solutions. WC is used to study wave propagation in two different atmospheric conditions, and the results are compared to the flight test data. Overall, WC can accurately capture the propagation effects, and there is a good agreement with the flight test data.

Evaluation of Autonomous Ship Landing Systems at the Maneuvering and Seakeeping Basin (Paper 1333)
Full registrant at Forum? Log in for link!
Unmanned VTOL I (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Christopher Hendrick, Emma Jaques, Jack Langelaan, Anish Sydney, Joseph Horn

This paper presents the results of an extensive model-scale experimental evaluation of autonomous ship landing guidance and control modes, with flight tests performed in the Maneuvering and Seakeeping (MASK) Basin at the U.S. Naval Surface Warfare Center Carderock Division. The experiments were performed using a commodities-based multirotor UAV operating from a 20-foot-long model scale ship subject to scaled wave conditions. During testing, two separate guidance algorithms were evaluated: a quadratic programming (QP) based landing algorithm that plans the trajectory to a forecasted deck state, and a simpler 'baseline' method that tracks deck motions while closing the distance between the aircraft and deck at a constant rate. Both algorithms commanded a Froude scaled explicit model following control law, and the control laws were used to progressively degrade aircraft tracking bandwidths. The results showed the QP algorithm to be capable of good performance despite poor long term deck state predictions, though several landings with the QP algorithm did terminate with significant velocity and attitude errors. In these cases, however, it is shown that the major factor contributing to degraded performance was not poor deck predictions, giving confidence in the feasibility of incorporating deck predictions directly in path planning. The results also showed that the predictive capabilities of the QP algorithm allowed more direct landing paths to be planned when compared to the baseline algorithm, and also allowed the QP algorithm to land with lower tracking bandwidths. The baseline guidance algorithm, on the other hand, proved to be both simple and reliable when the UAV was in high bandwidth configurations but is sensitive to increased lag in the system.

Evaluation of High- and Mid-Fidelity Computational Fluid Dynamics for Complex Ship Airwake Analysis with New Experimental Data (Paper 56)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Brenden Oates, Erk Kurban, Marilyn Smith, Juergen Rauleder

Safe flight with maneuvers of rotorcraft systems in the near vicinity of Naval ships poses a number of challenges due to the complex, unsteady wake shedding from the ship surface. To prepare pilots to operate in these conditions, it is desired to ensure accurate ship airwake simulation capabilities that provide an understanding of the flow field and are sufficiently cost-effective so that they can be applied in flight simulators to enhance pilot training and safety. While the simple frigate shape (SFS2) geometry has been extensively studied, assessments of the flow environment with respect to practical usage in flight simulations have experienced fewer analyses. A high-fidelity, conventional unsteady unstructured Reynolds-Averaged Navier--Stokes CFD solver (FUN3D) and novel time-resolved particle image velocimetry measurements are evaluated with Lattice-Boltzmann Method (LBM) simulations to understand LBM's potential for real-time flight simulations. LBM predictions are overall relatively comparable to FUN3D and PIV, albeit with some loss in magnitude and detail, but at computational time savings of several orders of magnitude to unstructured CFD. Ship orientations with yaw experiencing winds have more differences between LBM and FUN3D than non-yawed orientations.

Evaluation of an Automatic System for Cockpit Integration Testing (Paper 72)
Full registrant at Forum? Log in for link!
Avionics and Systems II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
David Frisini, Vincenzo Taumaturgo, Giorgia Giulianini, Marco Romano, Nicola Zonzini, Glauco Rinaldi

The purpose of this paper is to report the results of the evaluation conducted on ARTO, an automated system designed to perform integration tests that require interaction with the cockpit. The system has two key elements, the robotic manipulator that acts on the cockpit panels and displays, and the Computer Vision that collects the visual information. The methodology followed during the activity addressed different technical processes of system engineering, starting from the architectural design of the system up to the validation in a representative testing environment. For the validation environment of ARTO, TXT E-Tech, and Leonardo Helicopters have chosen the LHD Next-Gen Civil Tiltrotor-Technology Demonstrator (NGCTR-TD) Avionics Full Scale Integration Rig (FSIR). The results collected during this activity comprehend several KPIs chosen because significant in terms of accuracy and test operation efficiency.

Experimental Aerodynamics Validation of a Tiltrotor Platform within Next Generation Tiltrotor Technology Demonstrator Project (Paper 1212)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Carlo Cassinelli, Pierre Abdel Nour, Gianni Bernini, Gabriele Campanardi, Maria Ludovica Dall'Aglio, Cristian Lilliu, Matteo Pecoraro, Gaetano Preatoni

This paper aims to present the evolution of a comprehensive and lean approach used to validate an aircraft design against given aerodynamics requirements. The architecture is a tiltrotor developed under Clean Sky 2 JU FRC (CS2 FRC) program by Leonardo Helicopters Division (LHD): Next Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD). Against previous tiltrotors, this configuration encompasses some key aerodynamics differences: a v-shaped tail, partially movable nacelle with fixed engine and an efficient wing with the ability to carry a significant fuel fraction. Undergoing significant modifications, a validation of the aerodynamics phenomena typical of a tiltrotor is necessary. At first, a deep explanation of the phenomena and their 3D interactions is given, then the corresponding experimental campaigns are explained in terms of the critical decisions toward a lean approach and finally the key results are presented together with a global review of the entire campaigns and the value of the validation against reliable experiments.

Experimental Demonstration of the Lifting Capability of a Towed Payload Using Multiple Fixed-wing UAVs (Paper 1270)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Samuel Quenneville, Francis Therien, Jessy Verrette, David Rancourt, Alex Walsh, Jean-Philippe Lucking Bigue, Philippe Feyel

This paper presents an experimental demonstration of the Giant Rotor System (GRS), a heavy-lifting aircraft concept based on the Electric Power Reconfigurable Rotor (EPR²) concept and subsequent studies. The GRS is the first system to successfully demonstrate, under real outdoor flight conditions, the lifting of a payload with two off-the-shelf tethered fixed-wing unmanned aerial vehicles (UAVs). The non-optimized system demonstrated hover flight and slow vertical lifting (less than 1 m/s) capabilities while lifting a 20 kg payload with two 3.2 kg UAVs and a total of 2.1 kW. The lifting efficiency achieved by the GRS is approximately 4 times better than that of any conventional rotorcraft or heavy-lift VTOL system. The results of this study are promising and bring us closer to the reality of using available commercial airplanes for vertical lifting applications. The experimental setup, the control scheme, the flight test results, and a comparison of the GRS performance to that of conventional rotorcraft are described in this paper.

Experimental Investigation of Quadrotor Aerodynamics with Computational Cross-Validation (Paper 1310)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Anna A. Kostek, Johannes N. Braukmann, Felix Lößle, Sebastian Miesner, Antonio Visingardi, Ronan Boisard, Vasilis Riziotis, Manuel Keßler, Anthony D. Gardner

The influence of interactional effects on quadrotor performance in forward flight was evaluated taking into account square and diamond configurations, forward and backward tilt angles and a range of hub spacings including overlapping blades. The analysis was based on the wind-tunnel measurements and simulations from five computational methods with different fidelity levels. The outcome indicates that the efficiency of a diamond configuration improves in comparison with isolated rotors for non-overlapping rotor spacings, while the interactions in square alignments are detrimental for all analysed test cases. The computational results showed good agreement with the measurement data for the forward rotor plane tilt, however for the increased rotor-wake interactions at a backward tilt angle the spread between the calculated values, especially for torque, could be observed with the general trends maintained. The study proves the diamond configuration with 1.2 D rotor spacing and tip-to-tip rotor phasing to be most favourable in analysed conditions in terms of both aerodynamic performance and acoustic signature.

Experimental Testing of Advanced Generalized Predictive Control for Stability Augmentation and Vibration Reduction of Tiltrotor Aircraft (Paper 1324)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Thomas Ivanco, Andrew Kreshock, Robert Thornburgh, Matthew Wilbur, Brett Newman

Generalized Predictive Control (GPC) is an advanced form of an adaptive control algorithm that uses experimentally acquired data to determine the input-output relationship of complex systems through a process called system identification (system ID). GPC has historically been applied to wind tunnel tests of dynamically-scaled tiltrotor aircraft for stability augmentation and vibration reduction since the complex nature of these dynamic systems does not lend itself well to traditional control theory. Advanced GPC (AGPC) improves upon traditional GPC by enabling self-adaptation as conditions change from those used to acquire the system ID and controller performance would normally erode. The present research expands upon previous analytical development and demonstration of AGPC with experimental demonstration. To support AGPC, this present work also identifies and describes figures of merit that define a good working controller and quantifies the uniqueness of the control inputs and quality of the system ID parameters. The present research demonstrates that AGPC consistently performs better than traditional GPC and can successfully adapt to changing conditions.

Experimental and Computational Investigation of a Stacked Rotor With Unequal Radii (Paper 1328)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Chloe Johnson, Vasha Sedlacek, Jayant Sirohi, George Jacobellis

The loads and acoustics of a coaxial, co-rotating, or stacked, rotor with unequal upper and lower rotor radii were explored through measurements and simulations. The upper and lower rotor radii were both set to the nominal radius of 1.108 m, as well as the upper rotor radius to 90% nominal radius and the lower rotor radius to 90% nominal radius, with an axial spacing of 5.27% nominal radius. Simulations of the rotor system were made using the Rotorcraft Comprehensive Analysis System (RCAS) viscous vortex particle method and acoustic predictions were made coupling RCAS with the PSU-WOPWOP and ANOPP2. The simulations were validated with the NASA ideal twist rotor. The most accurate simulations of the stacked rotor were observed using PSU-WOPWOP's tonal noise predictions and the Brooks, Pope, and Marcolini method implemented in ANOPP2 with a maximum sectional Reynolds number to apply untripped conditions. Flow visualization and blade tip vortex tracking revealed that vortex interactions on the upper surface of the lower rotor blade resulted in adverse broadband noise generation. Therefore, the radius of one rotor was decreased to avoid tip vortex interactions, and subsequent measurements and simulations were made at constant thrust conditions of 150 lbf. Total rotor noise was reduced by 4.5 dB with minimal power increases by shortening the lower rotor to 90% nominal radius. This noise reduction was not captured by the simulations, as the vortex interaction with the rotor blade's boundary layer is not incorporated in current broadband models.

Experimental and Numerical Investigation of Isolated Swept Rotors for UAVs (Paper 1184)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Naina Pisharoti, Jeremiah Whelchel, W. Nathan Alexander, Stefano Brizzolara

An in-depth investigation into the effects of sweep on the aerodynamic and aeroacoustic performance of a rotor is carried out in this study. Dynamically similar swept and unswept rotor designs were tested and compared at the Virginia Tech Open Jet Wind tunnel for varying rotational rates and inflow speeds. It was observed that introducing sweep did not compromise the aerodynamic performance. Noise measurements indicated that the swept rotor has a lower noise signature in the mid-frequency range (~0.5-5 kHz). Further, the broadband and tonal components were separately studied and it was observed that the noise reduction in the swept rotor is largely due to reduced broadband noise. Additionally, a URANS CFD analysis was carried out using the SSG/LRR-omega-gamma transition turbulence model to further understand near-wall flow and wake characteristics. A qualitative analysis of the flow suggested that the swept rotor exhibited lower levels of blade wake interaction compared to the unswept geometry.

Exploration of Feature-Based Algorithm for Autonomous Ship-Deck Landing under Visually Degraded Conditions (Paper 1180)
Full registrant at Forum? Log in for link!
Unmanned VTOL I (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Victoria Britcher, Abhishek Shastry, Inderjit Chopra

The objective of this paper is to experimentally validate our 2D, feature-based vision algorithm for tracking stochastic ship deck motion. Two main advancements are described in this work. First, the feature-based algorithm is computationally intensive and therefore requires a larger, more powerful flight computer to run in real-time. To accommodate this computer, a larger quadrotor UAV is developed. Second, the new quadrotor with the upgraded flight computer is used to experimentally evaluate the performance of the feature-based algorithm for estimating stochastic ship-deck motion generated by a Stewart platform. Additional open-loop tests were conducted, with the quadrotor held by hand above the landing pad, to analyze performance under visually degraded conditions. The results were validated against Vicon ground-truth data. From these results, it was found that the algorithm can accurately estimate the pose of the stochastically moving ship-deck under ideal visual conditions. However, in visually degraded conditions, the performance of the algorithm worsens, and provides unsatisfactory results under significant occlusion. A small time lag is also present in the pose estimation, due to the large computational time of the algorithm.

Extended Use of Strategic Air Mobility in Cambodia Could have Won the Vietnam War in 1970 (Paper 1176)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Daniel Schrage

The purpose of this paper is partially to trace the evolution of air mobility in the U.S. Army and how it was utilized in the Vietnam War in 1970. The integration of aircraft into the organic structure of the ground forces is as radical a change as the move from the horse to the truck. In the Vietnam War the process was only beginning. Because this change is not the product of one man or one small group of men but rather a fortunate confluence of technology, tactics, and imagination, proper credit to every responsible individual is impossible. I have tried to utilize my experiences in South Vietnam and Cambodia to describe how air mobility was utilized.

External Airframe Loads Development for Full-Scale Helicopter Fatigue Test Application (Paper 74)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jeffery Brenna, Robert McGinty

This paper presents the development and evaluation of helicopter airframe loads for application to a full-scale fatigue test demonstration. The loads development method utilizes flight strain survey data and an airframe-representative finite element model to relate structural loading to strains. A previously developed approach has been modified to meet the requirements to simulate structural loading from flight conditions on a fixed load frame. A comparative stress-life fatigue analysis using measured flight data and predicted spectra to quantify fatigue prediction accuracy is also presented. A theoretical evaluation found a 10% error in strain prediction could result in up to 74% error in fatigue damage prediction. The practical evaluation using the predicted stress spectra found a wide spread of prediction accuracy. 77% of all predictions are under-predicted, typically in regions of low measured strain. The best predictions, in regions of highest measured strains, were within measurements by a factor of 1.5. These predictions exceed expectations, well within an acceptable level of error, however universal correlation in fatigue prediction is desired.

Factory Planning through Modeling and Simulation (Paper 1183)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Devon Keane

The application of 3D modeling and simulation has advanced our capabilities to be more agile, collaborative, and efficient through a lean six-sigma approach. As our aircraft grow more complex, so does our factory and our manufacturing processes that are contained within. There is an inherent need to be agile throughout all our processes, from design, to assembly, and ultimately throughout aircraft sustainment. The progression in areas such as model based definition, discrete event process models, and extended reality technologies (such as Virtual Reality, Augmented Reality, and Immersive Reality) are all key enablers to be able to adapt as both our production and our customer demands grows. Now more than ever, a digital representation of our manufacturing work cells is critical to success and will allow us to maintain a competitive edge.

Feasibility Study on the Tender eVTOL Vehicle (TeV) for Range Extension (Paper 1280)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Yu Ito, Takaaki Adachi

his study examines the utility of introducing an air-to-air power transfer (AAPT) tender vehicle (TeV) to recharge the main mission eVTOL (MeV) aircraft and extend its range without reducing the payload. After discussing how to conduct AAPT and setting numerical models of the aircrafts through referring to preceding studies, a simple simulation from the perspective of power (kW) and energy (kWh) is made to find the desirable configuration to be applied to the TeV. The result shows that by adopting slowed rotor helicopter configuration, the TeV may extend the range of the MeV for another 150+% by consuming only 70% of the energy the MeV requires. It is also found that the effect of the TeV is higher when the MeV requires more power at hovering than at cruise, so that energy available while at cruise can result in more range, compared to those recharged on ground. Future evolution in increasing the power battery will enhance the utility of the TeV.

Field Repair of Advanced Multifunctional Composite Structure (Paper 1398)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Lisa Chiu, Mark Robeson, Dennis McCarthy, Andy Lee, Manny Urcia

Rotorcraft structures fabricated from composites enable lightweight multifunctional design solutions that provide enhanced structural performance, enable transparent conformal apertures, and improve durability and damage tolerance. The designs are enabled by utilizing the unique properties of X-Cor™ fiber-reinforced, heat-formed core sandwich panels. The development and demonstration of suitable repairs is a critical aspect of fielding composite rotorcraft structure. Contained herein is a discussion of the methodology, analysis, and execution of the repair of composite rotorcraft structures that utilize the X-Cor™ material system. The discussion includes two case studies: 1- the repair of a prototype composite tailboom for restoration of structural capability, as well as 2- the repair of a multifunctional structural aperture for embedded antenna, where both structural and electrical performance are restored. Results, challenges, and lessons learned will be discussed.

Finite Element Analysis and Test of a Sharp Radius on the Shank of a Ring Locked Stud (Paper 138)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
David Binney, Lin Liu

This paper is an expansion on a prior paper in which the authors detailed an analytical approach to determining the effect of a sharp radius on the fatigue life of a ring locked stud. Fatigue testing of several studs has since been completed and the test results are compared with analytical predictions. Using the stresses determined by a validated finite element (FE) model, three methods of life calculation, stress life, strain life, and the theory of critical distances (TCD) point method, are evaluated in light of the test results. The stress life method is found to be inapplicable since there is no reliable Kdata for the high Klevels in question. Strain life results are conservative relative to the test. The TCD may provide more accurate life results without the conservatism of strain life, but current test results do not support its use. The idea that small non-propagating cracks may exist at the sharp radius, below some threshold of alternating stress, is also discussed. In addition, the test program revealed that the installation depth of studs can potentially affect their fatigue strength.

Flight Dynamics and Control of the Butterfly eVTOL Aircraft in Hover (Paper 1323)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Puneet Singh

The Butterfly eVTOL aircraft configuration includes four tilting propellers based on Optimum Speed Tilt Rotor technology. The propellers have the ability to operate over a wide range of rotor speeds and therefore generate thrust efficiently in all design flight conditions. Individual blade control actuators are used to provide cyclic inputs and generate hub mast moments. The combined features of variable RPM and mast moment control gives the Butterfly the unique ability to operate with sufficient control margins even with two operational propellers. This paper describes the control methodology to stabilize and operate the aircraft in both the normal and multiple failed propeller conditions. The propeller performance and control response is validated with experiments. The effect of the control methodology and propeller performance on the center of gravity envelope is analyzed. A simple feedback control scheme is applied to demonstrate the efficacy of the control methodology in normal and failure modes.

Flight Dynamics, Control, and Testing of a Coaxial Helicopter UAV with Folding Rotor Blades (Paper 141)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Anthony Gong, Mark Tischler, Ohad Shalev-Eggert

Air launched effects refer to unmanned aerial vehicles deployed from another aircraft. These unmanned aircraft can perform intelligence gathering, surveillance, and reconnaissance in contested areas in place of or prior to the arrival of manned aircraft. A potential air launched effects candidate is the Unmanned Generic Coaxial Rotorcraft which has a cylindrical fuselage, folding rotor blades, and the capability to hover. A series of flight tests were conducted to collect test data for system identification. A bare-airframe flight dynamics model of the vehicle was identified using frequency domain methods and verified in the time domain with doublets. The existing vehicle's PX4 inner-loop flight control system was modeled in Simulink®, combined with the identified hover model, and validated against flight test data. The analysis model was then used to perform multi-objective optimization of the flight control system gains using a comprehensive set of specifications. The optimized control system is shown to have improved tracking and disturbance rejection performance over the baseline in simulation while meeting all desired specifications.

Flight Testing of Automated Rotor Track and Balance using Active Trim Tab and Pitch Control Rod Technologies (Paper 1168)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Preston Bates, Ray Vanacore, Patrick Reilly, James DiOttavio

An innovative prototype in-flight automated rotor track and balance (RTB) system using advanced algorithms to command active rotor blade trim tabs and pitch control rods was demonstrated in a full-scale UH-60M flight test conducted by the U.S. Army. The primary technical objective was to reduce main rotor one per revolution (1P or 1/Rev) vibrations and maintain them at or below vibration acceptance levels throughout the entire flight envelope and achieve this in the presence of blade anomalies that create rotor imbalances. A secondary objective was to minimize higher harmonic vibration at two per revolution (2P or 2/Rev) and three per revolution (3P or 3/Rev) frequencies, without negatively impacting 1P. The flight test demonstration showed the system successfully met the desired performance objectives with the necessary characteristics to operate safely under normal flight conditions.

Flight Testing of Optimal Blade for a High-Speed Helicopter (Paper 1374)
Full registrant at Forum? Log in for link!
Test and Evaluation I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Keita Kimura, Masahiko Sugiura, Hideaki Sugawara, Yasutada Tanabe

In this paper, flight demonstration of the feasibility of an optimal rotor blade designed by JAXA for high-speed helicopters and the single-rotor lift-offset technology using flap differentials on the fixed-wing is reported, conducted using a 1/7 scale model helicopter named HARIOS. Flight speed of the model helicopter was measured by equipping a pitot tube and static pressure ports, and the power consumption during forward flight was obtained by summing the power consumption of various motors. These results were then compared. Although the flight demonstration was limited to an advance ratio of 0.4, it was observed that the acceleration of the aircraft increased when equipped with JAXA's optimal blade, and a significant reduction in power consumption occurred when applying the lift-offset technique. This marks a milestone in the test-flight verification for the two technologies, which had previously been investigated through wind tunnel tests and Computational Fluid Dynamics (CFD) simulations. With this flight demonstration, a significant step towards validating the effectiveness of the JAXA optimal rotor blade design and single-rotor lift-offset technology has been taken.

Floquet Instability in Periodically Reversing Flows (Paper 22)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jake Welsh, David Peters

Current 3-D finite-state wake models are incapable of simulating a maneuver in which the sign of the free-stream velocity changes direction and the rotor enters its own wake - as might occur in the case of a helicopter which ascends and then descends. It is the purpose of this work to create a 2-D finite-state wake model which is capable of handling changes in free-stream direction as a precursor to development of a 3-D model that can do the same. The 2-D finite-state model used for reentry modifications is an existing model created by Peters, Johnson, and Karunamoorthy. By the addition of a parameter which changes the sign of the free-stream accordingly, a model capable of handling forward and backward flight is developed and tested. Upon testing of the model for an oscillatory free-stream which changes direction, it was discovered that the presence of a singularity causes the system to become unstable. This behavior was determined to be due to a Floquet instability which occurs in periodic free-streams that reverse direction.

Flowfield Effects on the Flight Dynamics and Control Response of Rotorcraft Operating in Close Proximity (Paper 1366)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Ondrej Juhasz

Requirements in future rotorcraft operations will likely place several aircraft in close-proximity to one another. Flowfield interference impacts on a secondary rotorcraft operating in the wake of a primary helicopter are investigated. Of primary concern is the degradation in the flight dynamics and control performance of the secondary helicopter. A free-vortex based wake is used to trim a primary helicopter and generate a flowfield. The secondary helicopter uses a finite-state inflow model, with one way coupling to the flowfield of the primary. The trim swashplate deflections and linear responses are compared at various positions of the secondary helicopter with respect to the primary. The results show that while the trim swashplate positions vary greatly between the different cases, the linear response remains unchanged. Next, a flapping controller is developed and a time marching simulation of the secondary rotorcraft traversing the wake of the primary shows actuator usage requirements for various air speeds. The faster the secondary helicopter traverses the wake, the larger the swashplate displacement required. The swashplate limits were not reached for either scenario evaluated.

Flying Qualities Analysis and Piloted Simulation Testing of a Lift+Cruise Vehicle with Propulsion Failures in Hover and Low-Speed Conditions (Paper 1286)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
George Altamirano, Justin Matt, John Foster, Peter Suh, Curtis Hanson, Carlos Malpica, Stefan Schuet

The recent emergence of electric-Vertical Take-Off and Landing (eVTOL) vehicles for Urban Air Mobility (UAM) applications has resulted in a wide variety of configurations with unique stability and control characteristics. NASA is currently conducting research to develop conceptual design tools to accelerate public acceptance of these vehicles which includes requirements for safety during failure scenarios. This paper summarizes progress toward a toolbox for predicting flying qualities of eVTOL vehicles during critical propulsion failures that could impact the allowable design of the vehicle geometry or control system. Key topics include unique vulnerabilities of eVTOL/multirotor vehicles to propulsion failures, relevant flying qualities design metrics, and simulation modeling requirements for assessing flying qualities degradation due to failures. Results of a piloted simulation study conducted in the NASA Ames Vertical Motion Simulator (VMS) are presented. The VMS experiment was designed to assess and validate key handling qualities and safety design metrics for propulsion failures. These results show the correlation between control system design requirements and the degradation in handling qualities for various propulsion failures.

Flyover Noise Computations of the Joby Aviation Aircraft (Paper 1345)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Austin Thai, Jeremy Bain, Gregor Mikic, Alex Stoll

Joby Aviation is developing a six propeller, all electric vertical takeoff and landing aircraft. The aircraft is designed to operate near high population areas such as residences and workplaces, so it is imperative that the acoustic emissions of the aircraft are minimized for community acceptance. The aircraft design process incorporated the usage of high-fidelity computational aeroacoustics methods. Acoustic flight tests of the Joby aircraft were conducted by the National Aeronautics and Space Administration as part of the Advanced Air Mobility National Campaign and confirmed the revolutionary low noise footprint. The measured noise levels were compared with high-fidelity computational aeroacoustics predictions for two steady, level flight conditions. The results provide insight into the noise sources of the aircraft in these flight conditions. Airframe noise was predicted to be dominant for both flight conditions in the A-weighted spectrum due to the low propeller loading. Modeling efforts were made to account for acoustic shielding and airframe broadband noise and resulted in an improvement in the predictions, although the true noise sources are to be confirmed with further investigation.

Forward Flight and MTE Simulation of a UAM-Scale Quadcopter with Hybrid RPM and Pitch Control (Paper 147)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Ariel Walter, Robert Niemiec, Farhan Gandhi, Tom Berger

The handling qualities of a 1200-lb gross weight, UAM-scale quadcopter with both variable rotor speed and collective pitch control are examined in simulation. With these redundant controls, the forward flight trim space is analyzed and three trim modes are defined, where power consumption can be increased to improve mobility with pitch control inputs. Explicit model following control laws are optimized using CONDUIT to meet ADS-33E-PRF handling qualities specifications in hover, with design margin optimization on each axis. Three control strategies are compared for heave, roll, and pitch control: pure RPM-control, pure pitch-control, and hybrid-control using a complementary filter (allowing pitch inputs to be used for maneuvers and changes in RPM to be used for trim). Hybrid trim control is also defined to maintain pitch actuator margin from stall in forward flight trim conditions. Based on standard handling qualities metrics, the hover control laws are found to be robust enough to provide adequate performance in forward flight at cruise speed. The lateral/longitudinal performance of the trim modes and control strategies are then compared through simulation of the ADS-33E-PRF Mission Task Element (MTE): lateral reposition. Outer loop control design is performed in order to simulate pilot inputs during the maneuver and provide aggressive acceleration with minimal oscillation about the end point. Based on results from simulation of a lateral reposition maneuver, two of the three trim modes considered were able to complete the maneuver with satisfactory handling qualities.

Frequency Domain System Identification of a Small Autonomous Helicopter Using CIFER (Paper 1192)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jacobo Pastor Fernández-Posse López, David Pérez-Piñar López, Michael Allen

This paper presents the flight-testing method for system identification used during the LUA autonomous helicopter development and the computed on-axis dynamic model derived from the flight test data. The applied flight-testing method achieved excellent results with very low cross-control correlation, which was verified by comparing the SISO and MISO frequency response. A simple, yet accurate, on-axis dynamic model was derived for the hover condition using the higher-order hybrid model formulation, demonstrating that the vehicle response is dominated by the coupled rotor/fuselage dynamics. A short analysis of the LUA and similar size helicopters dynamic modes is completed, finding that their responses are dominated by the rotor dynamics, which might be a common trait among small-scale helicopters due to design choices in low-weight aircraft.

From Aerodyne to Vectodyne: The Quest for the Optimal, High Speed VTOL Transport Design (Paper 13)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
C. Sundiata Cowels

Vertol Aircraft Corporation's Vectodyne concept (based on the theories of re-known aerospace engineer Dr. Alexander Lippisch and other lesser known inventors) was a tubular wing, dual contra-rotating, propeller driven aircraft design that never left the drawing board. It was created in answer to a 1956 U.S. Army request for unconventional VTOL Tactical Transport weight and performance proposals that would offer direction in the development of a new type of cargo aircraft that would potentially be deployed within the 1962-1965 timeframe. This paper will address the aerodyne origins of the Vectodyne, its strengths, weaknesses and dismissal, and finishing with the vindication flight of the propulsive technology behind its design via a single engine surveillance drone, ending with the question, "After fifty years of false starts, is the Vectodyne a viable concept with today's technology?"

Fuel Cell Sizing for a UAV with Intermeshing Rotors using a Genetic Algorithm for NDARC Rotor Performance Calibration (Paper 53)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Victor Zappek, Ilkay Yavrucuk

Hydrogen fuel cell driven electric vertical flight is a current area of research and an alternative to battery based electric flight. This paper presents the models and methods used to size the hydrogen power plant and tanks of an unmanned helicopter named AREA. The battery electric power system of AREA will be converted to hydrogen power in the future. The goal of the conversion is to increase the flight time from the current 25 minutes to more than one hour. The design is performed using the NDARC preliminary design software. AREA uses intermeshing rotors. First, the necessary settings are found to model intermeshing rotors in NDARC, as this rotor concept is not natively supported by NDARC. Second, the rotor performance model is calibrated based on CAMRAD II simulations and flight test data. For this purpose, an automated calibration tool is developed using a genetic algorithm for robust calibration results. Third, the hydrogen system components are modeled and sized for the planned 60 min cruise test mission at maximum endurance speed. The results show that the nominal fuel cell power should be 3.8 kW and 280 g of hydrogen are required. The sized hydrogen system weighs approximately 20 kg.

Full Scale Gear Tooth Bending Fatigue Tests Obtained Early in the Development of a Rotorcraft Transmission (Paper 1397)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Peter Palcic, David Binney, Yuriy Gmirya, Wei Hu, Erin Carter

A new gear testing method is introduced to reduce development cost and time. It allows component-level testing of individual gear meshes and new gear designs. Instrumented gear sets are tested at full load while the rest of gearbox components are still being built. Since the fatigue strength of the gears is determined earlier in the development cycle, design deficiencies are identified and understood earlier. In this new method, an individual gear mesh installed in a stiff facility housing is used to mimic the contact pattern and bending stress demonstrated by the same mesh in an actual aircraft housing. Analytical gear models are used to identify the displacement difference between the stiff test facility and the aircraft housing. The test stand is designed so it can be adjusted accurately to provide gear and pinion positions that are representative of the deflected positions under load in the aircraft housing. A spiral bevel mesh and a split torque double helical reduction stage with multiple meshes are evaluated using the developed method. The contact pattern and strain survey results of the gear meshes are correlated with predicted results.

Full-Aircraft CH-53K Hover Simulations with HELIOS (Paper 132)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Brian Wake, Vera Klimchenko, Byung-Young Min, Jinggen Zhao, Jeewoong Kim

The CH-53K® King Stallion™ is the most advanced heavy lift helicopter developed by Sikorsky, a Lockheed Martin Company, to address the requirements of the United States Marine Corps. The aircraft was designed to support missions with a maximum design gross weight of 88000 lbs and can carry external loads up to 36000 lb. Full-aircraft HELIOS calculations were performed for a CH-53K King Stallion including main rotor, tail-rotor, fuselage and detailed hub. Calculations were performed for various configurations, with main-rotor removed, tail-rotor removed, and isolated main and tail rotors to evaluate the multiple interactional effects. Comparisons of the total power show excellent agreement with the flight-test measurements.

Full-Body Haptic Cueing Algorithms for Augmented Pilot Perception in Degraded/Denied Visual Environments (Paper 83)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Michael Morcos, Spencer Fishman, Alessandro Cocco, Umberto Saetti, Edward Bachelder, Martine Godfroy, Tom Berger

This paper demonstrates the development, implementation, and testing of full-body haptic cueing algorithms for augmented pilot perception. Full-body haptics is in the form of localized electrical muscle stimulation (EMS) is achieved via a commercial, off-the-shelf product called TESLASUIT. Cueing algorithms are developed for roll-axis compensatory tracking tasks where the pilot acts on the displayed error between a desired input and the comparable vehicle output motion to produce a control action. The error is displayed to the pilot using three different cueing modalities: visual, haptic, and combined visual and haptic. For the visual and combined visual and haptic modalities, visual cues are also considered in degraded visual environments (DVE). Full-body haptic cueing algorithms that are based on a proportional-derivative (PD) compensation strategy on the tracking error are found to provide satisfactory pilot vehicle system (PVS) performance for the task in consideration when using haptic feedback only (no visual cues) and to improve PVS performance in DVE when using combined visual and haptic feedback. These results indicate that the use of secondary sensory cues such as full-body haptics to augment the pilot perception can lead to improved/partially-restored PVS performance when primary sensory cues like vision are impaired or denied.

Fundamental Test of a Hovering Rotor: Comprehensive Measurements for CFD Validation (Paper 1166)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Thomas Norman, James Heineck, Edward Schairer, Norman Schaeffler, Lauren Wagner, Gloria Yamauchi, Austin Overmeyer, Manikandan Ramasamy, Christopher Cameron, Michelle Dominguez, Alex Sheikman

A model-scale hover test of a 4-bladed, 11.08-ft diameter rotor was recently completed inside the National Full-Scale Aerodynamics Complex 80- by 120-Foot Wind Tunnel test section. The primary objective of the test was to acquire key experimental data for a hovering rotor of sufficient quality and quantity to allow validation of state-of-the-art analysis codes. A comprehensive measurement set has been acquired, including rotor performance, blade airloads, flow transition locations, blade deflections, and wake geometry for a range of tip Mach numbers and collective settings. The present paper provides an overview of the test, including detailed descriptions of the hardware, instrumentation, and measurement systems. In addition, the specific test objectives, approach, and sample results are presented. The full test database, as well as detailed rotor geometry information, will ultimately be shared openly on a NASA-sponsored website to serve as a benchmark validation dataset.

Fundamental Understanding of Hybrid-Electric Power (Paper 1296)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Matt Arace, Anubhav Datta

A 3.43 kW 4-stroke piston engine is coupled to a generator and a rectifier to acquire basic data on power generation for hybrid-electric aircraft. Isolated engine, generator, and coupled engine-generator efficiencies are characterized. A semi-empirical 4-stroke engine model is developed. The model is calibrated with the test data. It is found that steadystate performance of a 4-stroke engine can be well predicted. The pumping power required for intake and exhaust of each cycle is a key factor that separates 4-stroke from 2-stroke engines but it can be accurately modeled. The key conclusions are that the specific fuel consumption is a strong function of output current and voltage separately, not power alone, and isolated engine specific fuel consumption and generator efficiency are not adequate metrics on their own. The designer must understand and model the integrated system. The semi-empirical model developed here for fuel consumption may be used to guide the design of future small hybrid-electric VTOL uncrewed aerial vehicles.

Gaze Movements of Helicopter Pilots during real and simulated Take-Off and Landing Maneuvers (Paper 1276)
Full registrant at Forum? Log in for link!
Crew Stations I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Daniel H. Greiwe, Maik Friedrich

Most accidents and serious incidents of commercial air transport helicopters occur during standard flight phases, whereby a main cause are pilots' situational awareness. Enabling pilots to better assess their situational awareness can make an important contribution in reducing the risk of fatal accidents. One approach is to examine pilot's gaze behavior with the help of eye tracking. This paper reports the results of eye tracking measurement during real flight and simulator studies of a standard mission profile. The general gaze behavior is characterized by a dominant, external view and the airspeed and altitude indicator as the most important flight instruments. A real-world applicability of gaze data obtained in the simulator could be shown.

Generic Tilt-Rotor Simulation Model with Coupled Flight Dynamics, State-Variable Aeromechanics, and Aeroacoustics (Paper 82)
Full registrant at Forum? Log in for link!
Modeling and Simulation I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Umberto Saetti, Batin Bugday

This paper describes the development, implementation, and validation of a generic tilt-rotor simulation model with coupled flight dynamics, state-variable aeromechanics, and aeroacoustic. A major novelty of this work lies in the integration of the flight dynamics with a state-space free-vortex wake code that adopts a near-wake vortex-lattice model. This way, the flight dynamics are augmented by the vortex wake dynamics so that the coupled flight and wake dynamics is self-contained and inherently linearizable. The model is implemented for a Bell XV-15 tiltrotor and validated against U.S. Army/NASA XV-15 flight-test data and other data in the literature. Flight control design is performed to provide desired stability, performance, handling-quality properties and to allow for a fully-autonomous transition between hover in helicopter mode and high-speed flight in aircraft mode. The simulation model has clear applications in the development and testing of advanced flight control laws, aeromechanics analysis, and in the prediction of aerodynamically-generated noise in generalized maneuvering flight.

Hamiltonian and Port-Hamiltonian Mechanics as A Possible Alternative for Helicopter Flight Dynamics Representation (Paper 1318)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Marilena Pavel

In the case of complicated, non-linear problems where simulations in the time-domain are needed to understand systems' behavior, Hamiltonian formulation can be used to obtain insight into system evolution in time. Hamiltonian dynamics has two advantages: 1) there is no need to write down the complete equations of motion explicity and thus help to solve the problem much quicker and 2) it can help understanding and designing controllers using the energy flow, Hamiltonian phase space and port-Hamiltonian representation for system evolution. The present paper highlights the importance of using the Hamiltonian dynamics for helicopter flight dynamics, exemplifying it for the helicopter pitch motion and for a 6-DOF nonlinear model. The paper shows that, using Hamiltonian formulation, one can define energy stagnations areas in the Hamiltonian phase plane and dissipative non-passive terms in the equations of motion that need to be restrained when designing a helicopter controller. The extension of the Hamiltonian to the port-Hamiltonian formulation can be used to design nonlinear controllers robust to system nonlinearities.

Handling Qualities of Multirotor RPM-Controlled Electric-Vertical Take-Off and Landing (eVTOL) Aircraft for Urban Air Mobility (UAM) (Paper 1306)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Carlos Malpica, Shannah Withrow-Maser, Jeremy Aires, Stefan Schuet, Peter Suh, Kyle Barnes, Curt Hanson, Allen Ruan, George Altamirano, John Foster

A paradigm shift in rotorcraft design is being led by the prospect of propulsive forces being distributed across multiple rotors, such that each rotor can be directly driven by a dedicated electric motor. Crucially, some designers attempt to utilize these direct-drive mechanisms as the sole form of primary flight control. The feasibility of this design choice remains to be proven at the scales required for passenger transport. The paper presents a preliminary handling qualities analysis, for a six-passenger (1,200 lb payload) electric Hexacopter conceptual design, which shows that Level 1 handling qualities for limited agility operations are possible, provided that electric powertrains can deliver transient peak torques twice as high as the rated continuous torque of the conceptual design. Preliminary predictions are then substantiated by the results from a piloted handling qualities evaluation conducted in the NASA-Ames Vertical Motion Simulator (VMS). Three eVTOL configurations (a quadrotor, a hexacopter and a lift+cruise) with flight control laws implementing different levels of stability augmentation (Attitude Command-Attitude Hold and Translational Rate Command response types) were evaluated in four low speed and hover tasks requiring various levels of agility and precision.

Helicopter Aerodynamic Loading in the Airwake of a Moving Ship (Paper 1250)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Nicholas Fernandez, Alanna Wall, Ieuan Owen, Richard Lee, Weixing Yuan, Mark White

This paper presents an analysis of the unsteady aerodynamic loading of a helicopter immersed in the airwake of a generic destroyer undergoing several ship motion types: static, sinusoidal pitching, regular 2-DOF, and realistic irregular 3-DOF ship motions. The study was a collaborative effort between the National Research Council Canada and the University of Liverpool, where each organization have applied their respective modeling approach (whether by simulation or experiment). It was shown that whilst there were only marginal differences in the mean helicopter loads for each motion type, the effects of ship motion are more apparent in the RMS loads, and the instantaneous load and air-velocity spectra. Dominant peaks in the thrust load spectra, as well as subsequent second and third harmonics, are shown at the ship motion frequency for sinusoidal pitching and regular 2-DOF ship motions, which have been attributed to the interaction between the turning rotor and the moving ship. This analysis provides a foundation for understanding the relationships between ship airwake and helicopter loading, and for extending that understanding to impacts on flight operations.

Helicopter In-Flight Eye Tracking: System Integration Aspects and First Results (Paper 1273)
Full registrant at Forum? Log in for link!
Crew Stations I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Malte-Joern Maibach, Daniel Greiwe, Mario Muellhaeuser

In modern helicopters highly accurate flight state data is available through precise sensors and complex fusion algorithms in the aircraft. This data is used by the avionic systems and transported to the pilot through sophisticated human machine interfaces (HMI). Especially in helicopters, the pilot is in most flight phases directly involved in the control of the aircraft and uses the information provided by the HMI. However, in most civil aircraft no sensor systems exist to get an insight about the pilots physiological state. Even in experimental helicopters there is no real-time information about the pilots mental state and this information is typically gathered through questionnaires in the debriefing. One way to close this gap is to use physiological measurement systems such as eye tracking. In our work we integrated an eye tracking system into the experimental system of DLR's research simulator AVES and the research helicopter ACT/FHS. In this paper we describe the first steps, which include the selection of the systems, technical aspects of the hardware and software integration process and first experiments in DLR's Bo 105 helicopter and DLR's AVES simulator. Details of our developed toolchain for the live data conditioning are given and first results of combined helicopter state and eye tracking data are presented. In the end we give an outlook on the next integration steps, which include the combination with a high-fidelity head tracking system.

Helicopter Rotor Wake Investigations on a Wind Tunnel Model with Varying Blade Stub Lengths (Paper 1178)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Ulrich Hartmann, Christian Breitsamter

Experimental and numerical investigations have been performed on a helicopter wind tunnel model for three rotor heads with different blade stub lengths. This investigation analyzes the origin and the development of the wake structures occurring from the various blade stub lengths and their interaction with the tail section of the helicopter to judge the influence of the blade stub spanwise dimension on drag, lift and pitching moment characteristics. Therefore, aerodynamic forces and moments and the wake flow fields are analyzed by experimental and numerical simulations. The origin of the distinct structures is identified by the numerical simulations. Specific cross flow planes in the wake captured experimentally the flow field and allowed a comparison with the numerical results. The numerical investigations are based on the unsteady Reynolds-averaged Navier-Stokes equations. The turbulence is modeled by the scale-adaptive simulation method and the rotation of the rotor head is modeled by the sliding mesh approach. The flow field of the experiment and the simulation showed good agreement and a detailed analysis of the dominant vortices propagating downstream is performed.

Henrich Focke's Lectures at the German Academy of Aeronautical Research 1937 - 1943 (Paper 4)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Berend G. van der Wall, Franklin D. Harris

In the years 1937, 1942, and 1943 Henrich Focke gave three lectures at the German Academy of Aeronautical Research. The first lecture was about autogiro and helicopter problems in general and specifically the development of the Fw 61. The second lecture dealt with the prospect of rotating wing aircraft and some tests and use of the Fa 223 and the third lecture was about research and development of the Fa 223. The first lecture had been translated into English soon after its publication, but the translation lacked precision. The latter two lectures were classified as secret during wartime, and to both author's knowledge were not translated. A revision of the translation of the first lecture and a first-time translation of the other two has been published recently. The paper presents key aspects of the three lectures and the corresponding discussions and shows that Focke's development program already anticipated many of today's rotorcraft industry efforts.

High Fidelity Aerodynamic and Aeroacoustic Simulations of Multicopter Rotors with Anhedral during Hover and Forward Flight (Paper 1214)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Moritz Muth, Manuel Keßler, Ewald Krämer

High fidelity CFD simulations of rotors with different anhedral tip angles are performed in isolated and tandem configurations at two different flight scenarios. The studied cases are hover, as well as a 25 m/s forward flight. Additionally, the convection of emitted noise of the rotors is simulated by using a Ffowcs Williams & Hawkings based CAA code. For comparison of the acoustic characteristics each rotor is simulated with the same RPM and pitch angle. Futhermore a flight mechanic trim is performed using the flight mechanic tool VFAST to compare selected anhedral rotors at the same thrust level. A NACA0012 rotor was used as a baseline rotor and all tip geometry changes are applied to this rotor blade. In hover, the isolated anhedral rotors show a drop in the Figure of Merit (FM) compared to the baseline rotor. Meanwhile the noise emission in the rotor plane increases, while the noise emission below the rotor plane decreased with rising anhedral angles. In contrast, the tandem configuration in hover showed increase FM due to changed inflow conditions. Further no clear acoustic benefits were found, with higher noise emission in the rotor plane. For the 25 m/s forward flight the efficiency of the anhedral rotors is increased, while the noise emission is also increased. This behavior was found for both the isolated and tandem rotors.

High Speed Whirl Flutter Tests of the Maryland Tiltrotor Rig (Paper 119)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Akinola Akinwale, Anubhav Datta

A 4.5-ft diameter proprotor was tested on the Maryland Tiltrotor Rig (MTR) in free-wheeling airplane mode reaching unprecedented speeds of up to 200 knots. Data was acquired at two wind-tunnels --- Navy Carderock tunnel and the Glenn L. Martin tunnel and for two hub configurations --- gimbal free and gimbal locked. The data consisted of frequency and damping of beam, chord, and torsion motions of the wing-pylon system at a Froude-scale RPM of 1050. The roots were extracted with two methods --- Moving-Block and Prony. The tests shed light on the nature of roots in high-speed tiltrotor flight. The key conclusions were: 1) the beam and chord damping always remained low to around 1-2%, 2) torsion damping was higher around 3-6%, 3) the gimbal-locked condition increased chord and torsion significantly and also changed their trends with speed, 4) the model remained flutter-free up to 200 knots, and 5) the chord damping showed signs of a sudden drop after 175 knots.

High-Fidelity Structured Mesh Models for As-Manufactured Composite Laminates (Paper 1292)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Yuri Nikishkov, Guillaume Seon, Andrew Makeev

High-resolution X-Ray computed tomography have demonstrated a unique ability to accurately detect and quantify critical subsurface irregularities, such as voids, waviness, and service damage in composites. While significant progress has been made in the respective areas of characterization and failure predictions, integrating 3D material characterization and non-destructive inspection of composites at the coupon scale into a comprehensive methodology applicable to failure prognosis of composite structures has yet to be developed. Such integration is especially important for the additively manufactured continuous fiber-reinforced thermoplastics that are often built with specific microstructural irregularities, such as voids, ply and fiber waviness, geometric errors, and variability of individual layers. The objective of this work is to provide a comprehensive description of novel modeling techniques used for the automated generation of structured mesh FE models for composite laminates that include as-designed and as-manufactured conditions while maintaining high-fidelity definition of model properties needed for the accurate predictions of structural performance.

High-Speed Stability Predictions of Maryland Tiltrotor Rig and Parametric Study (Paper 150)
Full registrant at Forum? Log in for link!
Dynamics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Seyhan Gul, Hyeonsoo Yeo

High-speed stability of Maryland Tiltrotor Rig (MTR) was studied. An RCAS model was built in addition to the UMARC-II model from previous work. Trim collective for freewheeling and stability predictions were compared with the test data up to 100 knots collected in the NAVY Carderock wind tunnel. RCAS and UMARC-II predictions showed good agreement with each other and the test data. Predictions show that MTR is stable up to 215 knots (490-knots full-scale flight) although the wing is only 18% thick (current technology is 23%). A parametric study was carried out to shed light on the high stability behavior. Impact of wing stiffness, pitch-flap coupling (delta3 angle), lag stiffness, rotor chord, number of blades, pylon mass, pylon center of gravity (c.g.), pylon location, and rotor speed were studied. MTR's pylon c.g. is behind the wing elastic axis, unlike many full-scale tiltrotor aircraft. It was found that this significantly improved stability. Full-scale aircraft stability can also be improved by moving the pylon c.g. backward if wing beam is the least stable mode. A combination of forward pylon c.g., reduced rotor speed, and increased rotor chord reduced the instability speed by more than 55 knots to near 160 knots, helping researchers obtain high-quality test data in the Glenn L. Martin wind tunnel.

Hover Performance of an OH-58C in Confined Areas (Paper 1380)
Full registrant at Forum? Log in for link!
Test and Evaluation I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Dylan Black, Cole Shenk, John Tritschler, John Holder, Joseph Milluzzo

Flight test performance of an OH-58C helicopter hovering in confined areas is discussed using a combination of pilot-recorded data cards and instrumentation data time histories. The test includes an investigation of the effects of wall height and blade loading on hover performance in close proximity to a three-walled structure forming a confined space. Hover performance for a range of altitudes far from the confined area, at the edge of the confined area, and at the center of the confined area are discussed. Significant performance penalties (i.e., up to 20% greater than the power required to hover out of ground effect) were observed at various positions within the confined space. Additionally, the pilots reported uncommanded vehicle excursions at some positions within the confined area, necessitating increased control inceptor activity. These observations are indicative of aerodynamic interactions that affect helicopter performance and have implications for the consideration of instrumentation data.

How to Integrate the Management of Operating Procedures and Crew Training into UAS Development (Paper 11)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Kevin Schmiechen, Julius Hoffelner, Florian Holzapfel

Already for the prototyping phase of Unmanned Aircraft System (UAS) development, operating procedures need to be defined and approved by the authorities to conduct flight tests. Especially in this early phase, where the specification and implementation details of the UAS are regularly updated, the operating procedures need to be aligned accordingly. Furthermore, the crew needs to be trained in theoretical and practical courses for these changing procedures to be well prepared for the operation of the aircraft system. In this paper, we show how we integrated the management of operating procedures and crew training into our UAS development process. We describe the development of the procedures and training material, their release management, and the traceability to the related system development artifacts. We also show how we implemented the execution and logging of procedure validation and crew training. Based on automatic reports, we can monitor the validation status as well as the training status of the crew, identify missing validation, and determine when retraining is required. The process and its implementation are demonstrated with exemplary data from our ongoing work.

Identification of Nonlinear Corrections to Multicopter Flight Simulation Model Using Machine Learning (Paper 1195)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Gaurav Makkar, Robert Niemiec, Farhan Gandhi

This study presents a novel methodology for identifying nonlinear corrections to improve the accuracy of a physics-based simulation model of a hexacopter using flight test data. Two distinct models are employed to capture the dynamics of the hexacopter in hover: one model is identified from flight data, and the other utilizes a physics-based blade element model with a 10-state Peter-He inflow. An input filter is extracted based on the difference between the flight test data and frequency response from the physics-based model to make corrections. This improves the predictions over the entire frequency range. For time domain analysis, the nonlinear corrections are identified by analyzing correlations between different flight variables and utilizing a filtered dataset with high normalized correlation. Regularized version of partial least squares is applied for identifying the correction terms. The performance of the updated linearized model is compared with the physics-based model and system ID model in the time domain for all four axes. It was observed that for low amplitude maneuvers, the corrected model is comparable to the model identified from flight test data and sometimes slightly better (2-5%). Predictions obtained using the corrected model exhibit superior performance to those generated by the physics-based model, particularly in the vicinity of peak values (8%-14%). For large amplitude maneuvers, the distinction is even more pronounced, with the model with nonlinear corrections surpassing all other models in terms of accuracy. Notably, while the physics-based model predictions exhibit an average error of 32% when compared to the flight test data, and the model identified using flight test data generated predictions with an average error of 22%, the model with nonlinear corrections yielded predictions with an average error of less than 10%.

Impact of Rotor-Rotor and Rotor-Body Aerodynamic Interactions on Quadrotor Vehicle Performance (Paper 1317)
Full registrant at Forum? Log in for link!
Test and Evaluation II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Sage Herz, Abraham Atte, Dhuree Seth, Juergen Rauleder, Matthew McCrink

Rotor-rotor and rotor-body interactions can have a first-order impact on multirotor vehicle performance. Identification of these performance impacts has previously been limited to numerical analysis and controlled environment testing, and they are largely unknown for full-scale multirotor flight vehicles. To capture these interactional effects, the work presented in this paper used a series of wind tunnel and flight test experiments of a quadrotor vehicle at multiple speeds and sideslip angles to estimate these rotor-rotor and rotor-body interactions. Performance data was measured for individual rotors and for the overall vehicle at flight speeds ranging from 5 to 15 m/s. Results indicated that aft rotor performance decreased by 4.8% in the cross configuration with the fuselage. In the plus configuration, the fuselage resulted in a 3.8% decrease in the aft rotor thrust coefficient. Rotor performance between cross and plus configurations was measured in a series of flight tests, where the plus configuration had a higher overall thrust coefficient than the cross configuration. Inwardly rotating rotors resulted in a 5.0% increase in thrust coefficient compared to outwardly rotating rotors. Measured trends in rotor performance between the cross and plus configurations were highly nonlinear with respect to sideslip angle and vehicle velocity.

Implications of Sustainable Aviation Fuel for the Rotorcraft Industry (Paper 1189)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Robert Andrejczyk

International governments and the airline industry have set goals to progressively replace aviation fossil fuels with sustainable aviation fuel (SAF). SAF is presently less than 0.1 % of the global aviation fuel supply but projected to be greater than 50% by 2050. SAF is kerosene synthetically produced from sustainable agriculture and recycled waste. SAF has lower contrail-forming particulates and has substantial benefit of lifecycle COreduction from using sustainable feedstocks rather than petroleum. The rotorcraft industry consumes less than 1% of the global aviation fuel supply and is not driving the transition to SAF but will need to have compatibility with SAF. The American Society of Testing and Materials (ASTM) has developed a process in conjunction with the FAA and original equipment manufacturers (OEMs) whereby SAF blends are approved as drop-in equivalent to ASTM D1655 Jet A/A1 fuel and can then be seamlessly distributed and utilized under existing aircraft approvals for Jet A/A1. SAF candidates are comprehensively evaluated by an OEM task group. Global aviation industry, certification agencies, and military are harmonizing around this approach. The FAA has encouraged rotorcraft manufacturers to monitor OEM task group proceedings and provide input for concerns to rotorcraft. A unique rotorcraft concern regarding suction lift fuel systems is explained as an example.

In-flight Measurements and Validation of Electric Powertrain Models (Paper 1358)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Farid Saemi, Owen Dunston, Moble Benedict, Constandinos Mitsingas

Small electric drones are popular vehicles for consumers and researchers. However, literature contains little data on in-flight aerodynamic loads that could validate aerodynamic or electric powertrain design tools. We developed a specially instrumented quadcopter to directly measure and record rotor torque and rotational speed during flight. We used this data to validate powertrain efficiency models for the motor, motor controller, and battery. The validated models predicted the time histories for battery discharge, controller current, and combined motor+controller efficiency within 5%, 20%, and 25% of experimental flight data respectively. The validated models can help engineers explore drone concepts without costly experiments and reduce program development costs. The novel flight data can help researchers validate other models, such as vehicle aerodynamic performance models. The modular instrumentation can help engineers measure analog signals onboard a flying vehicle for other applications, such as the wing loading on a fixed-wing drone.

Increasing Agility through AMESim to Iteratively Simulate, Analyze and Design Helicopter Brake Systems (Paper 1197)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Kaila Spiller, Kevin Debacher

This paper outlines the use of a numerical physics simulation software, AMESim, to increase agility in designing a helicopter brakes system. The paper emphasizes details of each simulation iteration per design phase. It will be shown that the simulation accelerates design decisions, verifies system level functionality, and improves prediction accuracy as reflected in system testing. The paper will illustrate how the software aided engineering decisions and risk reductions at each project milestone, which led to a successful system design that met all requirements.

Increasing Damping Properties of Helicopter Composite Substructures using Flax Fiber Hybridization (Paper 1332)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Jonas John, Lukas Gaugelhofer, Manfred Hajek, Ilkay Yavrucuk

Helicopter and VTOL structures are heavily influenced by vibrations and complex interaction effects. One possible solution to minimize design risks and to enhance cabin comfort is to increase the damping in the vehicle's structure, for which natural flax fibers offer a promising approach. The presented study investigated the hybridization of conventional composites with flax fibers of sub-structural components, including double-T beams and airfoil structures. The frequency dependent dynamic properties of the structures, damping and stiffness, are measured using experimental modal analysis. Local flax rib reinforcements on shells showed a significant increase in stiffness-damping factor but did not improve damping in flax laminates. According to the investigation, hybridization of conventional composites can lead to a significant increase in damping for both, double-T beams and airfoils. The damping can be increased by three to four times, and there can be a significant improvement in the damping-to-stiffness factor.

Influence of Rotorcraft Gearbox Lubricants on the Relative Adhesive Wear of Rolling Element Bearing Material Pairs (Paper 122)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Carl Hager, Bob Sadinski, Gretchen Hullenbaugh

The combined adhesive wear resistance of both all-steel and hybrid (Si3N4 and steel) interfaces lubricated by rotorcraft gearbox lubricants was evaluated. Bench-level tribological tests were utilized to rank selected material and lubricant combinations. Material pairings of M50 balls with M50 cylinders, and Si3N4 balls with M50NiL cylinders, were selected for the comparison. This work includes three fully formulated aerospace oils: 1. a MIL-PRF-32538 9 cSt polyol ester, 2. an unclassified ISO VG 68 synthetic hydrocarbon, and 3. a DOD-PRF-85734 5 cSt polyol ester. The results offer a relative comparison of rotorcraft gear oil formulations and their efficacy in reducing the onset of adhesive wear in both all-steel and hybrid interfaces.

Influence of Temperature and Humidity on Flax Fiber-Reinforced Composites for Helicopter Structures Using Protective Coatings (Paper 1256)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Lukas Gaugelhofer, Jonas John, Manfred Hajek, Ilkay Yavrucuk

With the aim of investigating whether sustainable and environmentally friendly flax fiber reinforced composites can meet the high technical requirements of aeronautical structures, this paper presents the influence of temperature and humidity on their structural-mechanical properties using protective coatings. Four coatings, two of which are partially bio-based, are tested on unidirectional flax fibers reinforced with bio-epoxy and polyfurfuryl alcohol resin. To simulate environmental conditions, coated and uncoated test panels are conditioned for two weeks in a climatic chamber at different temperature and humidity levels before their tensile specimens are tested and evaluated for moisture absorption, tensile strength, Young's modulus and fracture strain. The results show that higher temperatures lead to an increased moisture absorption rate and a lower maximum uptake. Higher relative humidity results in an increased maximum moisture uptake. A fossil-based coating could significantly reduce and retard moisture uptake at 30° C and 95 % relative humidity.

Influence of the Perception, Observer Position, and Broadband Self-Noise on Low-Fidelity UAM Vehicle Perception-Influenced-Design (PID) Optimization (Paper 63)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Leonard Lopes, Daniel Ingraham

This paper will present an approach in design optimization of a proprotor in a forward flight condition with several acoustic objective functions that simulate community response. An adjoint-capable blade element momentum theory (BEMT), implemented in CCBlade.jl, will be used to compute the blade forces and inflow properties required to compute tonal and broadband noise using the second-generation Aircraft NOise Prediction Program (ANOPP2). The influence of broadband noise, observer location, and choice of perception constraint on optimized values of rotation rate, chord distribution, and twist angle will be shown. It is determined that broadband self-noise is an influential source noise mechanism in the design optimization when frequency weighting is used to predict the noise at an out-of-plane observer position.

Infrared Thermography Measurements over an eVTOL Full-Scale Wing Section Equipped with Propellers Mounted on a Boom (Paper 1162)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Luca Riccobene, Alex Zanotti, Donato Grassi, Johannes N. Braukmann, Mike Kerho, Giovanni Droandi

The present paper describes the results of an experimental wind tunnel test campaign aimed at investigating and characterizing the complicated aerodynamic flow patterns around a wing section equipped with propellers mounted on a boom. The investigated configuration is meant to be representative of a full-scale eVTOL aircraft in cruise flight condition. The Infrared Thermography technique enabled a quantitative evaluation of the amount of laminar flow for the baseline airfoil section and also for the wing airfoil under the influence of the propeller at different thrust conditions.

Initial Whirl-Flutter Characterization of the TiltRotor Aeroelastic Stability Testbed (Paper 137)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Andrew Kreshock, Robert Thornburgh, Matthew Wilbur, Martin Sekula, David Piatak, Hao Kang

This paper discusses the initial wind tunnel test of the TiltRotor Aeroelastic Stability Testbed (TRAST). TRAST is a generic tiltrotor testbed developed in collaboration between NASA and the Army. Ultimately, this test was a checkout of the model systems, functionality and familiarization, but also obtained subcritical whirl-flutter data in the terms of frequency and damping. Flutter data include two main configurations with different pitch spring stiffness, referred to as 4k and 8k, that were tested at various rotor speeds and airspeeds at the NASA Langley Transonic Dynamics Tunnel. The test included two modes of drivetrain operation: powered and windmilling. However, powered mode of operation was only conducted with the 8k pitch spring. This test reinforced the traditional knowledge of whirl-flutter trends such as flutter speed would decrease with an increase in rotor speed. The critical mode consistently being the wing vertical bending mode. The chord mode as expected was not affected by the pitch spring and was likely to go unstable at a tunnel airspeed slightly beyond the wing vertical bending mode. There were also test specific challenges such as the TRAST modal damping was more sensitive to temperature and amplitude motor than was expected. This test gathered valuable data on the baseline characterization of TRAST, how to improve the model and test practices for future wind tunnel testing. Additionally, a new more automated method for experimental subcritical damping determination based on the Stockwell transform has been demonstrated that may lead to more consistent whirl-flutter stability boundaries.

Integrated Reality In-flight Simulation (IRIS): The Developmental Challenges (Paper 1200)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Perry Comeau, Alanna Wall, Kris Ellis, Arthur W. Gubbels

The National Research Council Canada (NRC) and Defence Research and Development Canada (DRDC) have developed modelling and simulation tools intended to de-risk, increase efficiency and standardize Ship Helicopter Operating Limitations (SHOL) testing through the use of modelling and simulation. The Integrated Reality In-Flight Simulation (IRIS) tool is a novel simulator platform where an evaluation pilot (EP) flies a variable stability aircraft while wearing a virtual reality (VR) headset with many elements of the shipboard environment carefully reproduced including the injection of real time turbulence models established from wind tunnel trials. The turbulence and other environmental effects on the aircraft motion are coupled directly into the aircraft in real time, thereby retaining accurate critical proprioceptive and vestibular cueing for the pilot. NRC has recently completed flight test evaluations of the prototype concept. Pilot comments from initial testing indicated that the system required little adaptation, presented no noticeable lag, no attributable propensity to cause motion sickness, and that the turbulence felt realistic.The testing indicated that typical VR deficiencies such as resolution and field of view are not as impactful during close-in shipboard operations, making this application very effective.

Intelligent Wind Estimation for Chemical Source Localization (Paper 1330)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jared Cooper, Jeremy Hopwood, Craig Woolsey, Stephan De Wekker, Michael DeVore

This paper presents a methodology to sense ambient wind conditions to assist in localizing the source of a released agent using small unmanned aerial systems (sUAS). The technology and methods to detect, localize, and model release and dispersion of chemical, biological, radiological, or nuclear (CBRN) agents have been enhanced by integrating cross-disciplinary solutions using advances from sensor design, intelligent signal processing, control systems, vehicle design, chemical modeling, and atmospheric modeling. The miniaturization of sensors and sUAS has enabled the application of sUAS with a chemical sensor payload to detect and localize the source of CBRN agents. In many instances, this chemotaxis operation can be performed faster and more accurately with the addition of atmospheric information, such as ambient wind condition. The paper provides an overview of chemical source localization and current challenges which motivated this work, including operation in complex settings and turbulence. Analysis of these challenges from an atmospheric science perspective is summarized along with strategies to obtain accurate and useful wind estimates that assist in localizing the source quickly and efficiently. A description of the wind estimation approach, based on Bayesian estimation, is provided along with results from simulation studies utilizing realistic vehicle dynamics, wind, turbulence, and chemical plume models.

Interactional Aerodynamic Assessment of a Quad-Rotor Tail Sitter using CFD (Paper 1156)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Richard Healy, Matthew Floros, Phuriwat Anusonti-Inthra

Efforts towards enhanced Unamnned Aerial System (UAS) efficiency has lead to the development of the Quadrotor Biplane Tailsitter (QBiT) configuration that employs variable blade pitch to control the aircraft. To reduce the overall system complexity, an alternative control system using fixed-pitch/variable-RPM trim is explored, with the rotors' relative positions/tilt to the wing varied to provide improved rotor efficiency in cruise. Medium-fidelity aerodynamic models of the baseline and modified QBiT reveal that the power required for high-speed level flight (40 - 70 kts) with fixed-pitch rotors tilted 60° nose-up is comparable to that for the baseline variable-pitch rotor configuration. The modified Quad Rotor Tail Sitter (modified QRTS) configurations are also simulated using a high-fidelity CFD software, revealing that wing-rotor aerodynamic interactions are responsible for up to 34.5% thrust deficit on the aft rotors due to wing-induced downwash. This thrust deficit contributes to a 5.4--6.3% lower overall system efficiency measured by L/De (compared to a system without aerodynamic interaction). When trimmed using CFD-CSD loose coupling, this reduced efficiency in part makes the modified QRTS power only 26.9% lower than a fixed blade pitch QBiT (compared to the 60.2% reduction predicted by comprehensive analysis). Interactional aerodynamic penalties can be mitigated somewhat by adjusting the mounting position of the rotors with wing lift increasing when aft rotors are positioned behind the wing. At a high flight speed (50 kts), interactional aerodynamic penalties are extended, with greater aft rotor thrust deficit and wing lift penalty causing a 7.2 - 7.9% drop in L/De (compared to isolated rotors and wings). Overall, the modified QRTS (with fixed-pitch/RPM control and optimal rotor tilt/position) shows an increased aerodynamic efficiency over the baseline QBiT (with variable-pitch control) due to a reduction in axial rotor flow despite interactional aerodynamic penalties.

Investigation of Coaxial Rotor Performance for a Gun-launched Micro Air Vehicle (Paper 94)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Hunter Denton, Moble Benedict

This paper presents an experimental parametric study to maximize the hover efficiency of a coaxial rotor system for a micro air vehicle (MAV) that could be launched from a 40 mm grenade launcher. Towards this, isolated rotor experiments were first conducted to optimize the performance of a single rotor at low Reynolds numbers (Re) through varying parameters including blade pitch angle, thickness-to-chord ratio (t/c), chord length, and Reynolds number. Results showed that t/c had minimal impact on the figure of merit FM) below 4%, while increasing blade chord length significantly improved hover efficiency until a chord length of 16.6 mm (solidity = 0.10). The optimal pitch angle for the isolated rotor was around 16 degrees, and the maximum FM was 0.59 at Re = 70,000. Coaxial rotor experiments were performed using the optimal isolated rotor as the baseline. The vertical separation between the upper and lower rotors had negligible impact on performance for a separation distance range from 0.5R to 3R. However, below a separation distance of 0.5R, the thrust and FM of the lower rotor increased and that of the upper rotor decreased. The highest FM obtained for the coaxial rotor was around 0.60 at Re = 30,000, which remained relatively constant across all vertical separations tested. The coaxial rotor system produced almost 1.66 times the thrust of an isolated single rotor. When compared at the same disk loading, the power loading (thrust/power) for the coaxial rotor was similar to that of an isolated single rotor. A comprehensive analysis (RCAS) was used to model the MAV-scale isolated rotor in hover and the analytical predictions agreed well with the experiments. In order to generate the airfoil lookup table for the RCAS model, water tunnel experiments were conducted at Re = 44,000 using a scaled-up wing with the exact same circular-cambered plate airfoil used in the coaxial rotor blades.

Investigation of departure transition noise for lift-plus-cruise eVTOL aircraft (Paper 3)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Bhaskar Mukherjee, Andrew Jue, Jean-Pierre Theron, Kenneth Brentner, Eric Greenwood, Joseph Horn

This paper investigates the acoustics and performance during departure transition maneuvers for an eVTOL aircraft design of lift-plus-cruise configuration. A variable pitch lift rotor thrust control scheme with an airspeed-dependent schedule of rotor RPMs was used to fly the transition maneuvers. Parametric sweeps at different flight speeds were used to develop a schedule that would meet the goals of low noise and low power consumption. The aircraft forces and moments were studied throughout the departure transition maneuver and significant, unsymmetrical rotor-wing interaction occurred in the range of 40 - 70 knots. A change in the control mixer was found to reduce the impact of rotor-wing interactions on motor power consumption, improving the power margin and safety of the aircraft. Three departure transition maneuvers were studied to compare the power and energy required and the acoustic impact. First, a level acceleration maneuver prioritized airspeed gain; second, an axial climb maneuver prioritized altitude gain; and third a continuous climb maneuver was a combination of both strategies, as it accelerated and climbed at the same rate as the other two maneuvers. In general, it was observed that transitioning to wing-borne flight as quickly as possible reduced both acoustic impact and energy consumption during the departure maneuvers.

Landing Phase Analysis of the NRC Bell 412 Advanced Systems Research Aircraft in Supervised-Autonomous Flight Systems Configuration (Paper 1386)
Full registrant at Forum? Log in for link!
Test and Evaluation I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Marc Alexander, Greg Craig, Iryna Borshchova, Derek Gowanlock, Arthur Gubbels, Kris Ellis, Awantha Jayasiri, Tomas Naprstek, Bryan Carrothers, Sion Jennings, Perry Comeau

The National Research Council of Canada (NRC) Flight Research Laboratory (FRL) is advancing research under its Canadian Vertical Lift Autonomy Demonstration (CVLAD) program. Modular architecture hosted on the NRC Bell 412 Advanced Systems Research Aircraft (ASRA) enables pilot supervised autonomous flight via customized multi-display guidance-cueing. The capability exploits ASRA's full-authority control and safety systems, inertial-radar navigation, state-based digital supervision and is supported by open-source mission planning and digital-twin simulation. To date, ground interfacing (takeoff, landing) trials have been executed in proximity to NRC facilities in Ottawa (Canada) with rich test site variability (surfaces, slopes, obstacles, seasonal variations). Applied knowledge has been generated for autonomous mission execution in broad weather, low-speed, low-altitude, and low obstacle-standoff conditions critical in the vertical lift flight autonomy research domain.

Launch and Recovery of Traditional VTOL UAVs by Quiescent Period Prediction (QPP); the development of QPP for All Weather Operations (AWOPS) (Paper 16)
Full registrant at Forum? Log in for link!
Unmanned VTOL I (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Bernard Ferrier, CDR Robert Taylor, Michael Belmont, Jacqueline Christmas, CDR John Paul Kish

For most of the traditional VTOL UASs, the precise measurement of these environmental data is essential for air vehicle safe launch and recovery events. Physics limits the speed by which the deck can be raised from rest to a dangerous position. It is helpful to identify the quieter, more quiescent periods in deck motion. However, the time needed to set-up and land UASs are often longer than these quiescent windows may persist, assuming a quiescent window can be identified in the first place. Without precise measurement of deck motion or sufficient advanced notice of the onset of quieter motions, cycle after cycle of ship's motions whilst the vehicle attempts stabilize for recovery. The aim of Quiescent Period Prediction (QPP) is to provide ship motion conditions and motion predictions with sufficient forecasted time (over a minute) to launch, recover and complete other motion sensitive tasks regardless of the seaway. The fundamental concept is to measure remote sea surface profiles to predict the future wave forces acting upon a vessel. QPP operates within a federated architecture system containing measurement instruments such as a Wave Radar system used to map remote sea surfaces several hundred meters in advance of the ship. This enables the computation of future wave forces acting on the vessel.This article describes the development of the QPP System concentrating on test procedures, timely seaway mapping and ship motion characteristics to complete specific motion sensitive task. The objective is to expand ship operating deck limits to approximately Sea State 6+.

Let's Not Forget our VTOL Forebears and Historical Aircraft (Paper 1348)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Kaydon Stanzione, Daniel Schrage

Going back to the days of Leonardo DaVinci, and perhaps earlier, there has been significant interest in being able to fly vertically and hover. These tasks require innovation, engineering, and scientific knowhow in many disciplines and then blending them together to create a Vertical Takeoff and Landing (VTOL) flying machine. Vertical flight enthusiasts recognize just a few of the names of great inventors that set the foundation for our great VTOL industry today. However, there are many individuals whose names are either forgotten or were never in the limelight of VTOL aircraft developed over the past 80 years. A VTOL machine is an ingenious contraption of innovation in mechanical systems, materials, aerodynamics, flight controls, and structures. Over time add to these inventions the advancements in integrated modular avionics, electronics, electro-mechanical actuators, computers, mathematics, vibration suppression, and fiber optics to name a few. However, the most important contribution to our VTOL advancements is from people. Not just technically trained people, but inventors, pilots, managers, professors and the investors willing to direct personal, public, and corporate funds to the Research, Development, Testing and Engineering necessary to build a VTOL aircraft. This paper presents concepts to fill-in our history leveraging a crowd-sourcing model.

Leveraging Advanced Engineering Visualization for Human Factors Analysis on Future Vertical Lift Development Programs (Paper 68)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Kirk Layman, Douglas Fischer, George Tamasi

This paper will discuss a Model Based Systems Engineering (MBSE) approach that leverages virtual reality, and augmented reality to shape and optimize design for cockpit, cabin, and maintenance interfaces during the initial design development. The Boeing Company is leveraging these new technologies to improve system design, usability, production performance, training, and safety. Use of this method in the design lifecycle ensures compliance with operational requirements, creates an accurate and detailed maintenance plan and influences engineering to optimize usability and deliver a maintainable product. This technique allows engineers to identify non-compliances promptly in the design process and iterate the design in real-time with user participation to satisfy the customer and operator requirements. This improves initial quality, eliminates production rework and prevents downstream program costs and delays by revealing design deficiencies earlier than previously achievable

Lichten Award Paper: Individual Blade Pitch Control (IBC) for Vibration Reduction of Lift-Offset Coaxial Rotor Vehicles with Auxiliary Propulsion (Paper 69)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Jessica Beyer, Edward Smith, Sven Schmitz, Jianhua Zhang

The present study investigates the vibration reduction potential of single harmonic individual blade pitch control (IBC) applied to a lift-offset coaxial main rotor. An open-loop phase sweep is conducted using comprehensive aeroelastic simulations of the XH-59A rotor to quantify the effects of IBC on the hub vibration index and the rotor effective lift-to-drag ratio. Applying 4/rev, 1 degree amplitude IBC at 0 degree phase to both rotors decreased the hub vibration index by 64% at 200 knots and only decreased the rotor lift-to-drag ratio by 2%. Single harmonic IBC retained effective hub vibration index reduction with varying flight speed, including a 56% decrease at 160 knots and a 69% decrease at 240 knots. Higher amplitude IBC inputs were more effective at higher forward flight speeds. The vibration reduction of single harmonic IBC with 2 degree pitch amplitude increased from 24% to 69% when the forward flight speed increased from 160 to 240 knots. Application of a closed-loop control algorithm using multiple-harmonic IBC achieved an 84% decrease in the hub vibration index with only a 2% decrease in the rotor effective lift-to-drag ratio.

Lichten Runner-up Paper: Correlation and Accuracy Quantification of Proprotor Loads between Predictions of Comprehensive Aeroelastic Software and Experimental Data (Paper 91)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Giuseppe Bucciaglia, Andrea Duina, Davide Prederi

Nowadays, numerical modelling and simulation are essential in the development and certification of new aircrafts in order to increase safety and lower costs. Modelling and simulation activities can be divided in three main phases: model building, model correlation and model usage. In this paper, the focus is on model correlation; in particular, for what concerns the estimation of rotor loads using the LHD in-house comprehensive code, i.e. GyroX. The work presents a summary of an extensive correlation activity performed on the AW609 proprotor and it highlights the modelling key ingredients to consider for accurate load prediction across the conversion corridor. Precisely, the choice of the rotor aerodynamic model, the effects of hub center accelerations and the wing interference are addressed in the correlation process. Furthermore, a metric, i.e. CEPS, is proposed and used to quantify the correlation error between analytical predictions and experimental data coming from flight tests in order to have a better and immediate comparison between the different model set-ups.

Main Rotor Gearbox Oil Cooling System Design (Paper 112)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
David Gore, John Kerr

This paper details the design process for a Main Rotor Gearbox Oil Cooling System and recommends techniques to optimise future designs. It covers the drive methods which must be considered in the design, along with the optimum heat exchanger and airflow path arrangements to meet the design requirements. This paper also describes the different type of fan which can be used, and the relative merits. The cooling system design is dictated by the specification, and the impact of certain requirements - temperature, fan seizure performance, containment, bearing selection and lubrication - are covered in detail. The typical qualification testing suite for a Main Rotor Gearbox Oil Cooling System is also provided, along with predicted areas of future developments in this sector of the aerospace industry.

Mars Sample Recovery Helicopter: Rotorcraft to Retrieve the First Samples from the Martian Surface (Paper 1359)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Shannah Withrow-Maser, Wayne Johnson, Theodore Tzanetos, Havard Grip, Witold Koning, Natasha Schatzman, Larry Young, Athena Chan, Allen Ruan, Haley Cummings, Brian Allan, Larry Meyn, Carlos Malpica, Benjamin Pipenberg, Matthew Keennon

The Mars Sample Return Mission (MSR) will carry the next set of Mars helicopters, Sample Recovery Helicopters (SRHs), to the Martian surface. After successfully demonstrating extraterrestrial flight in 2021, Ingenuity has acted as a "scout" for the Perseverance rover while the rover gathers samples of Martian soil. In 2028, the MSR mission will launch a lander and two Ingenuity-sized SRHs to retrieve these samples. These will be the first samples of the Martian surface delivered to Earth. The SRH project will maintain heritage from Ingenuity's design when possible. However, several key changes must be made, including a ground mobility system, a robotic arm for tube manipulation, and the ability to carry the weight of a science payload (the sample tubes). In addition, the onboard software and cameras will be upgraded, and the rotor radius will be increased. Furthermore, new rotor performance and flight dynamics models and thorough characterization of vehicle limits will be required. The new vehicle design will be described, as well as validation and verification efforts to date. Note: The decision to implement Mars Sample Return will not be finalized until NASA's completion of the National Environmental Policy Act (NEPA) process.

Method for Predicting Multi-Axis Task Performance and Handling Qualities Rating for a Coaxial-Compound and Tiltrotor Rotorcraft with Validating Data (Paper 45)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Edward Bachelder, Tom Berger, Bimal Aponso, Jeff Lusardi

The Cooper-Harper scale provides a structured approach for assessing handling qualities. It ties performance and relative pilot workload to the Handling Qualities Rating (HQR) of a task such that neither one, in isolation, is used to assess handling qualities. Prior work demonstrated that the Spare Capacity OPerator Estimator (SCOPE), whose elements derive from tracking error and pilot control motion, could predict HQR and performance for a single-axis task by applying a model of pilot control and an objective function driving pilot behavior to establish reference workload associated with Level 1 and Level 2 handling qualities. Level 1 workload is generated using elementary vehicle dynamics for executing the task. Level 2 workload is generated using vehicle dynamics that are degraded to produce a response coinciding with the adequate performance criteria. This method of workload calibration avoids using training data collected from pilots. The work presented in this paper extends SCOPE's single-axis predictive capabilities to multi-axis coupled control using the same perceptual principles used in SCOPE, where individual stimuli are perceived collectively as the product of their logarithms. SCOPE's predictive performance and HQR estimates were tested using data from a high-fidelity piloted simulation study for a variety of evaluation tasks using two representative Future Vertical Lift rotorcraft configurations (a lift offset coaxial helicopter with a pusher propeller and a tiltrotor). The SCOPE derived estimates compared favorably with the pilot performance and ratings from the simulation study.

Micro-Mechanics Based Gear Tooth Contact Fatigue Analysis (Paper 130)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Biqiang (Johnny) Xu, Bruce Hansen

Microstructure-based component life prediction (CLP) tool is validated through gear contact fatigue test and used to create contact fatigue S-N curve. Trade off study of different micro-material structures, grain size, surface roughness, and residual stress, is conducted to understand the impact on fatigue life. The results can be used as gear material design guidance to save expensive cost of fatigue test.

Microstructurally Tailored Materials Improving Structural Performance (Paper 1382)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Sarvenaz Ghaffari, Guillaume Seon, Andrew Makeev

High-modulus (HM) carbon fiber-reinforced polymers (CFRPs) have attracted strong demand by the rotorcraft industry as such materials can potentially enable lightweight airframes and rotor components with significant weight savings. However, low fiber-direction compressive strength, compared to intermediate-modulus (IM) CFRPs currently used in primary structures, has been a well-recognized weakness of HM CFRPs, prohibiting their implementation in rotorcraft platforms. Microstructural tailoring provides an innovative means for breaking through the fiber-direction compressive strength barrier of the HM CFRPs. Microbuckling, the fiber-direction compressive failure mechanism of the subject HM and IM CFRPs, is driven by fiber-matrix interface shear strength. Assessment of the interface properties using in-situ SEM-based experiments reveal substantial difference in surface topology between IM and HM fibers, which is related to higher interface strength in HM fibers. This instigates a microstructural tailoring approach of reinforcing material surrounding HM fibers with IM fibers to improve microstructural stability. A manufacturing system has been developed, and promising results enabling HM CFRPs with adequate fiber-direction compressive strength have been achieved through hybridization of IM and HM fibers at the filament level in HM CFRP toughened with nano-silica. A new material achieving compressive strength of IM CFRPs but with >30% higher modulus has been developed.

Model-Scale Investigation of Tiltrotor Low-speed Obstacle-Induced Downwash Recirculation (Paper 46)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Mark Silva, Scott Hromisin, Michael Corbett, Nathan Graybeal, Steven Cato, John Ralston, Richard Prevost, Callum Gray

A model scale investigation of tiltrotor/obstacle aerodynamic interactions under zero wind conditions was conducted in the winter of 2022 by Bihrle Applied Research, Inc. (BAR) and LaVision, Inc. on behalf of NAVAIR. The test was conducted at 6% scale in a closed test hall with a full-span tiltrotor and an obstacle representing the aft portion of an amphibious class ship. The test objectives were to quantify the impact of recirculation on aircraft performance and trim as a function of aircraft position and orientation relative to the obstacle, and to acquire velocity flow field measurements for analysis validation and empirical model development. Principal data acquired include the force and moment reaction of the aircraft rotors and airframe, dynamic surface pressures on the obstacle, and particle tracking velocimetry (PTV) measurements of the flow field. This paper provides an overview of the test approach and execution and a presentation of selected results illustrating the variation of recirculation impacts with position and orientation relative to the ship obstacle.

Modeling Turboshaft Engines for the Revolutionary Vertical Lift Technology Project, Expanded (Paper 111)
Full registrant at Forum? Log in for link!
Propulsion I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Jeffryes Chapman, J. Michael Vegh, Gerardo Nunez, Christopher A. Snyder

Turboshaft engine performance and weight models were developed to support conceptual propulsion and vehicle mission design and performance under the Revolutionary Vertical Lift Technology (RVLT) Project in 2019 by Snyder.T hese models were developed using open data sources, assuming present and future technology levels, and range from 650 to 5,000 output shaft horsepower (485 to 3,730 kW). This paper expands on the previous research, extending the power ranges from 200 to 15000 output shaft horsepower (150 to 11,200 kW) Documenting the methodology, assumptions, and resulting performance realizes important benefits for NASA and the aviation community.

Modeling and Flight Dynamics Analysis of Rotor-on-Wing Interference Effects of a Winged Single Main Rotor (Paper 146)
Full registrant at Forum? Log in for link!
Modeling and Simulation I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Emily Glover, Mark Lopez, Ashwani Padthe, Tom Berger

The U.S. Army is considering a single main rotor helicopter with a wing for Future Vertical Lift (FVL) Capability Set 1 (CS-1). Previous work has been done to design a blade element flight dynamics model of a generic winged single main rotor helicopter. To increase the fidelity of the model, a rotor-on-wing interference model was developed to determine how the interference impacts trim and flight dynamics of the winged single main rotor configuration throughout the flight envelope. The model leverages preexisting models to determine the rotor wake location and radius as well as the download on the wing at low speeds. Once the wake moves off of the wing, the model applies download observed in CFD, wind tunnel tests, and flight tests to both wings. Finally, differential lift is applied to the wing as the reverse flow region forms. The differences in trim and flight dynamics of the rotor-on-wing interference model compared to the no interference model at different wing locations and lift share ratios are important to understand when designing control systems, power required for trim and dynamic maneuvers, and actuator throw. It was found that the control system designed for the generic winged single main rotor does not need to be adjusted for rotor-on-wing interference. Therefore rotor-on-wing interference models that focus on trim are sufficient.

Modeling of Helicopter Pilot Behavior through Methods of Artificial Intelligence (Paper 1314)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Najrane Heni, Benjamin Rothaupt, Walter Fichter

Machine Learning algorithms are used in this paper to synthesize models for an ultralight coaxial helicopter pilot controlling the roll- and pitch motion during stationary hover. Different topologies of neural networks modeling the pilot are evolved with a neuroevolutionary algorithm, and trained via a data-driven approach using datasets that are collected from both real hover sequences and piloted flight simulations. The models are validated using flight test data and evaluated in a closed loop simulation alongside helicopter and turbulence models. Results demonstrate the models capability to stabilize the helicopter during hover and thus, to imitate human pilot behavior.

Multi-fidelity Aeroacoustic Prediction of an eVTOL Rotor (Paper 26)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Gabriel Reboul, Danny Lewis, Mikel Balmaseda, Joelle Bailly, Fabrice Falissard, Frederic Guntzer, Caroline Lienard

The rising interest in urban air mobility has brought new challenges in terms of noise pollution. Developing dedicated methods to accurately predict the noise generated by such aircraft configurations is thus a cornerstone to be able to meet the noise emission requirements in an urban environment. This work presents three numerical approaches, with different levels of fidelity, which aim at predicting the noise produced by such configuration: a lifting-line code with free wake, an innovative intermediate approach based on a Reynolds-averaged Navier-Stokes/Blade Element Theory (RANS/BET) coupling, and an Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. These methods are assessed on a rotor representative of those installed on an electric Vertical Take-Off and Landing (eVTOL) aircraft. A thorough comparison of the aerodynamic features and the noise predicted by each approach is presented for two challenging operating conditions, namely hover and edgewise flight. Their capacity to account for the effect of a supporting arm is also assessed. Only the URANS method is able to accurately predict the blade-vortex interactions that characterize both operating conditions as well as installation effects due to the supporting arm. The RANS/BET method has limitation in the capture of blade-vortex interaction while the lifting-line approach fails to predict accurately the installation effect. Nevertheless, those two proposed alternative approaches allow to significantly reduce the CPU and manpower costs inherent to the use of a URANS simulation with discrepancies in terms of mean and maximum levels lower than 3 dB in all the considered configurations.

Multiaxial Fatigue Damage Evaluation of Bonded Repair and Efficient Performance Evaluation of a Composite Wing Section (Paper 1164)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jim Lua, Xiaodong Cui, Anand Karuppiah, Supun Kariyawasam, Caleb Saathoff

Technology gaps exist for design and certification of bonded repair of large composite structures under multiaxial loading. They are 1) consideration of delamination failure without including the matrix cracking-induced stress concentration at a ply interface; 2) use of test data from a simple geometry for the failure prediction of a complex repaired configuration with a multiaxial stress state and spatial variation of the local stress ratio; 3) pre-assumed failure modes without including the multiaxial stress state-driven damage initiation and progression; and 4) lack of a rational modeling approach for the damage evaluation of a full-scale structure to balance the computational efficiency and solution accuracy. Our primary goal of this study is to extend our modeling capability for a bonded composite structure subjected to multiaxial loading and to demonstrate a global-local modeling capability for the high-fidelity damage evaluation at a critical location of a full-scale composite wing section. Multiaxial tests for a scarf repaired component are performed via the bi-axial cruciform apparatus while a capability demonstration is conducted using the strain survey test of a full-scale wing section via the developed test rig. After verification of the global response prediction, the developed global-local modeling strategy is used to evaluate the damage progression at a critical location with a detected initial defect.

NATO Generic Destroyer Moving-Ship Airwake Validation and Rotor-Ship Dynamic Interface Computations using Immersed Boundary Lattice-Boltzmann Method (Paper 1342)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Shreyas G. Ashok, Juergen Rauleder

During rotorcraft ship-deck landing operations, complex interactional aerodynamic phenomena occur between the rotor and ship airwakes, and these phenomena are not fully understood. Many traditional ship - rotorcraft interactional simulation approaches use a one-way coupling, where the ship airwake is superimposed on the rotor, modifying its inflow. However, because the rotor wake does not alter the ship airwake in such a simulation, one-way coupling may not capture all relevant phenomena, especially when ship motion is accounted for; two-way fully-coupled simulations may be needed. In this study, the NATO Generic Destroyer, a shared, representative ship geometry created for collaborative studies, was investigated numerically, and the ship airwake results validated by wind tunnel measurements using discrete velocity probes on the landing deck. Lattice - Boltzmann Method (LBM) simulations of the standalone ship airwake and one- and two-way coupled ship-rotorcraft interactional simulations were conducted using a Graphics Processing Unit (GPU) accelerated solver. The ship surface was represented using a novel Grad immersed boundary approach. Using this boundary condition, effects of ship motion were included in the simulations. Ship airwake results showed good agreement with the experiment and excellent computational performance; simulations took less than four hours to run on a single GPU node. Through ship-rotorcraft interactional simulations, it was determined that one-way and two-way coupling strategies resulted in different frequency profiles of unsteady induced inflow velocity variations, with considerable differences in the closed-loop pilot response range.

Numerical and Experimental Assessment of Parameters Influencing the Development of Secondary Vortex Structures in Rotor Wakes (Paper 1365)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Andrew Bodling, Clemens Schwarz, Christian Wolf, Anthony Gardner

A common phenomenon in modern high-fidelity CFD simulations is the breakdown of the primary vortex system in hover due to secondary vortex braids. In the current work, the development of secondary vortex structures in the wake of a two-bladed rotor was investigated by combining stereoscopic particle image velocimetry measurements in different measurement planes and high-fidelity simulations. An analysis was performed to investigate how various numerical inputs including sub-iteration convergence, numerical dissipation, blade pitch offset, grid-resolution, and rotor thrust affect the primary and secondary vortex characteristics. A parametric study on near- and off-body solver sub-iteration convergence demonstrated that the primary and secondary vortex characteristics converge as the sub-iteration convergence of both solvers increase. The breakdown of the primary vortex was shown to be directly linked to the number of secondary vortices. Dissimilarities in the blade pitch angle, which could not be avoided in the experiment, were modeled by intentionally using an offset in the blade pitch angle of the two blades. It was shown that as blade pitch angle offset increases, vortex pairing becomes more distinct. When vortex pairing occurred in both the experiment and simulation, the decay of secondary vortices in the experiment and simulation agreed best. Grid resolution was decreased from 5% chord to 3% chord, and the finer mesh simulation with higher sub-iteration convergence agreed best with the measured primary and secondary vortex characteristics. Differences in the measured and predicted number of secondary vortices for the lower thrust case was attributed to differences in tip vortex breakdown in the experiment and simulation.

Onboard Acoustic Prediction Method for VTOL Aircraft (Paper 1307)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Mrunali Botre, Daniel Wachspress, Eric Greenwood, Kenneth Brentner

A novel method is presented in which a mid-fidelity, physics-based rotorcraft aeroacoustic model is calibrated to closely match flight test integrated acoustics metrics and subsequently shown to be able to accurately predict acoustic pressure time-history and narrowband spectra.

Optimal Operation of Rotor-Wing Assemblies on eVTOL Aircraft (Paper 1319)
Full registrant at Forum? Log in for link!
Aircraft Design II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Jonah Whitt, Farhan Gandhi

eVTOL aircraft with tilting rotors and fixed wings for cruise lift have control redundancy leading to the possibility of optimal operation over the range of airspeeds. In this study, a single rotor-wing unit is considered to examine how a combination of rotor RPM, rotor root pitch, rotor cant, and wing angle of attack can minimize the power requirement, while ensuring that the rotor-wing unit provides the necessary lifting and propulsive forces. Analysis is conducted for both a UAV-scale rotor-wing unit producing 5 lbs lift as well as a manned-UAM scale unit producing 550 lbs lift. For both cases, the power requirements are highest in hover, reduce rapidly as airspeed increases, and then increase slowly at speeds greater than maximum endurance speed. For minimum power operation, the rotors are oriented mostly up at low speed with a relatively low root pitch setting of 25-30 deg, and fully forward (operating as axial propellers) at speeds greater than maximum endurance speed, with the root pitch increasing significantly to account for axial flow through the rotor. At speeds right before the rotor starts tilting downward, the wing lift-share is ~25%, increasing to ~83% at maximum endurance speed, and 100% at higher cruise speeds. If the rotor solidity is low (similar to a UAV-scale propeller, and not high as seen on manned-UAM scale eVTOL rotors), it is feasible to use a fixed pitch rotor set at optimal low-speed values. For such low-solidity fixed-pitch rotors, the power penalty at cruising speeds may be acceptable, but the rotors must operate in a tilted position, rather than oriented fully forward like axial propellers.

Optimizing Automatic Flight Condition Recognition through a Multi-Strategy Machine-Learning Based Approach (Paper 1274)
Full registrant at Forum? Log in for link!
Systems Engineering I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Eugenia Villa, Francesco Zinnari, Giovanni Coral, Gabriele Cazzulani, Mara Tanelli, Andrea Baldi, Ugo Mariani, Daniele Mezzazanica

Flight Condition Recognition (FCR) is essential in the usage monitoring of helicopters, as maneuver instances determine the usage spectrum, and thus the assessment of the original usage assumptions, adopted at design time for the definition of the retirement life of its components.Automated FCR capabilities, exploiting algorithms to detect the aircraft maneuvers by appropriate processing of on-board sensors measurements, allow us to reconstruct the usage spectrum, supporting the definition of improved maintenance manuals, with replacement times and inspection intervals tailored to the helicopters actual usage, thus enabling Condition-Based Maintenance (CBM) schemes. However, designing an efficient automatic FCR system is a challenging task, due to the complex machine dynamics characterizing the different flight regimes. In this work, we show how to optimize a machine-learning based approach to FCR design by exploiting a multi-strategy time-series segmentation framework, which combines two supervised learning approaches that leverage sliding windows and stacking ensembles to produce reliable estimates of the flown regimes. The approach is validated on an experimental dataset of nearly 500 labeled flights from two helicopter models, demonstrating its effectiveness in predicting the different maneuver types, and its improvement over a single-strategy approach.

Performance Exploration of Vertical Payload Lifting Using a Single Circling Tethered Fixed-Wing Aircraft (Paper 1235)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Maxime Doguet, Mathieu Bouchard, David Rancourt

Since the beginning of the 2000s, concepts for transporting payload with multiple tethered aircraft have been proposed to balance the lateral loads on a stationary payload. An alternative, initially developed in the 1940s considered a single aircraft and long tether to minimize the lateral motion of the payload during the circling motion of the aircraft in hover. To shorten the tether and reduce the drag losses associated, a concept with a single aircraft and an active stabilization system on the payload is proposed. This paper demonstrates that a single Pipistrel Sinus can vertically lift a stabilized underslung payload of 660 lb (300 kg) at 6,000 ft (1,800 m) under temperature conditions of 95 deg F (35 deg C) with less than 47 hp (35 kW) and a reduction of 70% of the tether length compared to a non-stabilized payload.

Physics Based Flight Dynamic Modeling for Biplane Tailsitter During Forward Transition (Paper 1244)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Shubhanshu Gupta, Aadhithya S, Abhishek Abhishek, Mangal Kothari

This paper describes the aerodynamic and flight dynamic modeling of a biplane tailsitter Unmanned Aerial Vehicle (UAV) that is capable of vertical takeoff and landing (VTOL) and high efficiency cruise flight. The conventional quasi-steady aerodynamic model is enhanced incrementally while discussing the limitations of the models. The effect of model refinement on the forward transition trajectory is studied as it involves most of unsteady effects due to the aggressive nature of forward transition maneuver in which the UAV pitches by 90 degrees. An octarotor biplane tailsitter vehicle is fabricated and instrumented to collect flight test parameters for the transition flight. The states of the UAV during the transition flight are recorded onboard using the autopilot and are subsequently used to validate the simulation. The use of unsteady aerodynamic model helps improve the predicted flight trajectory.

Physics-based Model Identification of a Lead-lag Damper with Wearing (Paper 1190)
Full registrant at Forum? Log in for link!
Dynamics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Michele Zilletti, Federico Pellegrino, Ermanno Fosco

In this paper, the identification of a time-domain numerical model of a lead-lag damper assembly consisting of a damper body connected to a link is discussed. Lead-lag dampers are fundamental components to guarantee the stability of helicopters as they increase the damping of the blade lead-lag motion. Thus, an accurate model of their dynamics is essential to predict complex phenomena such as instabilities, limit cycles, etc. It has been also observed that a significant contribution to the dynamical behavior of the rotor is not only given by the response of the damper itself but also by the presence of other components used in the installation. For example, an important role is played by the link connecting the damper body to the rotor blade not only in nominal conditions but also in the presence of possible wearing of the link joints (e.g. elastomeric material damage, free-play, etc.). This work discusses a data-driven approach used to identify a physics-based damper assembly model. Furthermore, the loss of performance due to the wearing of the damper link joints is modeled and analyzed.

Pilot Modeling and Sensitivity Analysis for Rotorcraf-Pilot Couplings Robust Design (Paper 1327)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Pierfilippo Mancini, Andrea Zanoni, Vincenzo Muscarello, Giuseppe Quaranta

To better understand the underlying physics of rotorcraft-pilot coupling events on the collective control chain, a hybrid modeling approach is proposed for the biomechanical response of the pilot's body. A condensed modal representation of the two most relevant mode shapes, obtained from multibody simulations, is employed alongside a physical representation of the loading factors. The enhanced pilot model response in the closed-loop system is compared to the established, one degree of freedom approach by coupling the pilot model to a simplified representation of the helicopter vertical dynamics, comprising the effects of the heave and collective flap degrees of freedom. The stability of the close-loop system is evaluated on the loop transfer function through the gain and phase margins. It is found that the added dynamics, even though it is not evident in the experimental biodynamic feedthrough transfer functions, has a non-negligible effect on the closed-loop stability of the pilot-vehicle system. The effect of the landing gear dynamics and of non-minimal muscular activation contribution on the closed-loop stability is also assessed.

Piloted Simulation Evaluation of Damage Tolerant Control for a Coaxial Compound Helicopter (Paper 144)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Tom Berger, Anthony Gong, Derek Bridges, Nicholas Kuhn, D. Grey Hagwood, Joseph Horn

Advanced rotorcraft configurations currently being considered for Future Vertical Lift and Advanced Air Mobility applications typically feature redundant control effectors, which bring new opportunities for control design, including the ability to re-allocate control in response to failure or damage. This paper presents the design of damage tolerant control (DTC) for a generic utility-class lift-offset coaxial compound helicopter using weighted pseudo-inverse control allocation. Consideration was given to tip clearance between the upper and lower rotors of the coaxial configuration in the design of DTC. The damage tolerant control was then integrated into full flight envelope control laws, and tested in a piloted simulation using several mission task elements and one operational scenario. Results showed that DTC significantly reduced aircraft coupling in the presence of stuck actuators and maintained sufficient rotor tip separation even during aggressive maneuvers. Furthermore, for all damage cases tested, DTC received better or similar ratings than the baseline case. This work was done in support of the Adaptive Digital Automated Pilotage Technology (ADAPT) program which aims to develop a flight control software package to take advantage of redundant controls to improve safety, survivability, and performance for advanced vertical takeoff and landing capable aircraft.

Piloted Simulation Evaluation of Maneuver Optimization Control for a Coaxial Compound Helicopter (Paper 1240)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Joseph Horn, Ryan Perry, Derek Bridges, Nicholas Kuhn, Grey Hagwood, Tom Berger, Anthony Gong

The Adaptive Digital Automated Pilotage Technology (ADAPT™) flight control software package aims to take advantage of redundant controls to improve safety, survivability, and performance for advanced rotorcraft. Vehicle Maneuver Optimization (VMO) is one component of the ADAPT™architecture, VMO uses feedforward control to increase aircraft maneuverability. The VMO algorithm takes advantage of the control null space of over-actuated aircraft to optimize their quasi-steady trim. In this study, the system is applied to a coaxial compound helicopter and evaluated in piloted simulations at the NASA Ames Vertical Motion Simulator and at the Penn State Rotorcraft Simulator. Handling Qualities Ratings indicated that VMO enhanced handling qualities in aggressive MTEs involving turns, as seen in a Break Turn MTE and a customized Maximum Performance Turn MTE. Simulation results also showed that VMO achieved significant power reductions in these maneuvers. VMO was found to degrade handling qualities for some other MTEs, notably in some of the precision tracking MTEs and the High Speed Accel / Decel MTE. While VMO is not intended for use in precision tracking tasks, some improvements are warranted so that VMO can be used to maximize performance in accelerations without degradation in handling qualities. The benefits of VMO in turn maneuvers, both in terms of performance and handling qualities, are achievable in conjunction with both the inner- and outer-loop control laws of the coaxial compound helicopter.

Prediction of Coaxial Rotor Hub Flow Using Mercury Framework (Paper 1196)
Full registrant at Forum? Log in for link!
Aerodynamics IV (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Yong Su Jung, Bumseok Lee, James Baeder

The rotor hub is one of the primary sources of high-speed rotorcraft parasite drag. To better understand the flow physics of the rotor hubs, counter-rotating coaxial rotor hub flows were simulated, followed by the experiment at the Penn State University. For the simulations, the Mercury computational fluid dynamics (CFD) framework employs an unstructured/Cartesian multi-mesh paradigm and Spalart-Allmaras delayed detached eddy simulation (SA-DDES) turbulent modeling. The coaxial hub flow physics was studied at two advance ratios by building up the hub components. The interference between the hub and the fairing components induced higher mean hub drag and unsteady harmonics in both hub and fairing drags. Different advance ratios affected hub wake structures and velocity fields at near- and mid-wake distances. Finally, the complete hub model in the water tunnel was simulated at the advance ratio of 0.25. The mean and unsteady drag predictions were compared with the experiment as well as the mean wake velocity fields. Additionally, the effect of hub shafts on the hub drags and wake velocity fields was studied. These efforts were based on the fourth Rotor Hub Flow Prediction Workshop in 2022.

Prediction of Interactional Aerodynamic Noise of Propellers and Wing Using High-Fidelity CFD (Paper 1264)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Nikos Trembois, Ethan Brown, Seongkyu Lee, Tyler Ramsarran, Kenneth Brentner

This study aims to enhance the understanding of the upstream-downstream interaction between propellers and wings in terms of their acoustic impact using high-fidelity simulations. The research focuses on a propeller placed upstream of a wing, with the wing positioned at various horizontal and vertical offsets to evaluate the sensitivity of noise to wing placement. The isolated propeller thrust is found to match well with the experimental data. However, when the wing is present, the thrust is over-predicted compared to the experimental data. The pressure coefficient and its root-mean-square (RMS) values are used to evaluate the wing aerodynamics. The RMS of the pressure coefficient reveals significant unsteady loading near the wing leading edge due to the interactional effect between the propeller and the wing. In terms of noise prediction, the isolated propeller noise is well predicted in both high-fidelity and medium-fidelity simulations. When the wing is present, the wing loading noise exceeds the propeller loading noise. Finally, the directivity of the noise is compared with experimental data for the propeller and wing configuration. The predictions do not agree as well with the experimental data as desired, possibly due to the over-prediction of propeller thrust, the associated inaccuracies in the phase of the wing noise, and the acoustic shielding by the wing.

Prediction of the Laminar-to-Turbulent Transition Position on a Helicopter Rotor Blade with Cyclic Pitch Variation (Paper 1152)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
François Richez, Rohit Jain

This work aims at assessing different laminar-to-turbulent transition models with different CFD codes for unsteady cases of a helicopter rotor with cyclic pitch variation. ONERA evaluates with elsA code the semi-empirical transition criteria-based approach and the Langtry-Menter model, while US Army investigates two versions of the Langtry-Menter model available in the Helios/Overflow code. The experimental transition position measurements provided by DLR show a complex hysteretic behavior of the transition front motion. The simulations show that Langtry-Menter model can reproduce this hysteresis with a satisfactory agreement, if spatial accuracy is maximized using refined meshes and minimized numerical dissipation. The numerical results are then used to identify the transition mechanisms involved and the unsteady effects at the origin of hysteresis.

Process of Implementation and Certification of the First Parts Manufactured in Selective Laser Sintering Technology, on the Example of PZL Mielec a Lockheed Martin Company (Paper 1209)
Full registrant at Forum? Log in for link!
Manufacturing Technology (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Aleksander Banaś, Radosław Wojtuszewski, Tomasz Gałaczynski, Marcin Głodzik

The article presents material and functional tests carried out to implement the first part made in the Selective Laser Sintering (SLS) technology on the aircraft. The tests were done based on guidelines fromaviation regulations and internal standards of PZL Mielec and Lockheed Martin Company.

Project Ivory Soap and the Largest Helicopter Rescue Operation of WWII (Paper 41)
Full registrant at Forum? Log in for link!
History honoring Franklin Harris (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Paul Fardink

Until recently, Operation Ivory Soap, a secret World War II collaboration between the United States Army, Navy, and Merchant Marines, to reconfigure six Liberty Ships into floating maintenance shops for repairing damaged aircraft in the Pacific, remained in obscurity. Sikorsky R-4B and R-6A helicopters were based on these ships to ferry mechanics and parts wherever needed. This secret project proceeded as planned until an emergency request for medical evacuation of wounded soldiers came in June 1945. Until then, the newly-developed helicopter had rarely been used for aeromedical rescue and never in hostile action. Nonetheless, the incredibly brave and resourceful Ivory Soap pilots, flying without radios, medical training, or specialized transport equipment, saved as many as ninety-four seriously-injured troops in the Philippines - and forever revolutionized the value of the helicopter in combat. Sadly, the pilots' stories of valor lay buried in forgotten piles of once-classified documents for decades. But no longer....

Quantifying Taskload and Workload with Instantaneous Power Spectrum: An Initial Assessment of 3D Conformal Cueing in Rotorcraft Shipboard Landings (Paper 1309)
Full registrant at Forum? Log in for link!
Crew Stations I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Kevin Zander, Robert Alstrom, Rahul Tauro-Padival, Jonnalagadda Prasad, Karen Feigh

The authors present a novel taskload metric, Instantaneous Power Spectrum (IPS), and use the IPS to investigate the taskload of pilots conducting helicopter shipboard operations with and without cueing sets. A brief review of the most relevant studies on the application of time-frequency analysis to flight dynamics is provided to situate the reader. The authors derive the IPS from classical time-frequency analysis methods and modify it using foundational rotorcraft inceptor theory. The accuracy of IPS as a taskload metric is assessed by analyzing a small set of helicopter shipboard landing scenarios with and without the assistance of 3D Conformal Pilot Cueing. The goal of the study is to explore the relationship of power in crossover (0.5-1.0 Hz) and stabilization (1.0-2.5 Hz) frequency bands to the taskload experienced by the pilot. These initial results indicate that the IPS is comparable to the well-established time-varying power frequency and provides detailed insight into pilot taskload during maneuvers.

Quantitative Risk Assessment of Component Retirement Time Reduction (Paper 1320)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
John Hewitt, Loan (Joan) Pham

In order to ensure safety and compliance with airworthiness regulations, demonstration of fatigue service life by testing and analysis is typically required for mechanical components on vertical flight aircraft. The resulting service lives often result in establishment of component retirement times that are approved by the airworthiness certification or military qualification authority. In some cases, reduction of the original component retirement times becomes necessary, even if no failures have occurred in operation. This may result from the application of newer fatigue service life testing and analysis methods to components that were developed many decades ago, or discovery that the components in operation differ from the analyzed designs. Quantitative Risk Assessment is typically used as a means of assessing and managing fleet risk for components that have failed or if signs of potential failure have been observed on components in operation. However, if a reduction in component retirement life becomes necessary, a new method of applying Quantitative Risk Assessment can assess fleet risk and possibly be applied to reduce risk before any field failures have occurred.

Rapid Methods for the Aeroelastic Analysis of VTOL Blades in Hover Flight (Paper 1218)
Full registrant at Forum? Log in for link!
Dynamics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Mikel Balmaseda Aguirre, Luis Bernardos, Théo Flament, Miguel Garcia Bravo

This work concerns the numerical steady aeroelastic modelling of Vertical Take-off and Landing (VTOL) blades. The originality of this work is the use of rapid methods to represent both the structure and the aerodynamics. The structure is modelled with projection based reduced-order models (ROMs), which are widely used in turbomachinery and are well adapted to VTOL blades analyses. In order to cover a large number of rotating velocities the structural ROM is parametrised as a function of the rotating velocity in terms of the stiffness and the pre-stressed state due to rotation. The aerodynamics is modelled with the Blade Element Momentum Theory (BEMT) and the Vortex Particle Method (VPM). In this article, the underlying concepts of the aeroelastic coupling implementation using the parametrised ROM and the rapid aerodynamic models are introduced. Then such concepts are applied to the design of a blade. The influence of the structural mesh discretisation, the validation of the proposed parametric model and the aeroelastic coupling analysis are performed both for small displacements and for nonlinear large displacements.

Realistic Manipulations in Mixed Reality: Application to the Aeronautical Maintenance Review (Paper 1177)
Full registrant at Forum? Log in for link!
Product Support (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Eva Di Noia, Marie-Line Bergeonneau, Daniel Mestre, Remy Casanova

The main objective of this study is to improve maintenance activities using mixed reality. Co-design work with Support Engineers was undertaken to develop a mixed reality solution that corresponded to the different needs of task sequencing feasibility. Multiple versions of the solution were tested using Microsoft HoloLens hardware to achieve continuous improvement. The study compared the two latest versions of the solution: the CAD version and the PHYS version. The CAD version was an immersive version inspired by CATIA CAD software, while the PHYS version implemented a realistic approach to parts handling (including gravity, continuous presence, and spatial organization of physical parts on a real table). Support Engineers carried out an experiment, performing a disassembly/assembly task using both versions of the solution. Results showed that the overall workload was significantly reduced, along with task completion time, using the PHYS solution. The PHYS version was also judged to be more usable than the CAD version. Adding 'pseudo-natural' manipulation of virtual objects to a maintenance task simulation better suits the needs of Support Engineers.

Reliability Prediction with no Observed Field Failure but with Known Design Lives (Paper 1362)
Full registrant at Forum? Log in for link!
Systems Engineering II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Joan Pham, John Hewitt

To minimize direct maintenance cost while also ensuring optimum system safety and availability, rotorcraft fleet management decision making must be based on accurate forecasts of component reliability and proper maintenance policy. However, component reliability predictions such as Mean Time to Failure (MTTF), hazard function, and reliability curve are typically performed based on MIL-HDBK-217 that is adjusted for field data once failures have been observed. MIL-HDBK-217 includes a series of empirically based hazard rate models with a fundamental assumption of exponential statistical distribution i.e., constant hazard rate. This assumption is not accurate for mechanical components that might have a non-constant hazard function. Furthermore, fleet management decision making is required during the development process before there is any field experience. This paradigm could change if component reliability predictions can be performed early when no field failures have occurred. Through this approach of performing a component reliability prediction with no field failures but with known design lives, rotorcraft reliability metrics can be more predictive thus better reliability prediction and maintenance policies can be determined early.

Rotor Cross-Tilt Optimization of Manned Multi-rotor eVTOL Aircraft for Yaw Control Efficiency (Paper 120)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Xufei Yan, Jiandong Cai, Bin Lou, Yiren Hu, Anhuan Xie, Shiqiang Zhu, Libo Cheng, Xiaobo Wang

This paper proposed a rotor cross-tilt optimization method of manned multi-rotor eVTOL aircraft for yaw control efficiency improvement. Firstly, the flight dynamics model of a 500kg low-altitude manned multi-rotor eVTOL aircraft is established, and the accuracy of the model is verified by single arm test platform and flight test data. Then, a rotor cross-tilt optimization method which simultaneously completes the trim and optimization calculation, is designed to maximize the overall control efficiency under different loads, forward flight speeds and rotor mounting angle errors. The manipulation derivative is applied to analyze the influence of the optimal rotor tilt angle on the control efficiency of each control channel. Finally, the feasibility of the optimization method is verified by comparing the ground(3DOF test platform) and flight test data of the prototype before and after optimization. Results show that the control efficiency of yaw channel is improved while the control efficiency of other control channels are basically maintained, so as to achieve the overall optimal control performance. In addition, the endurance time of the prototype is also improved, and the greater the load, the more obvious the improvement.

Rotor Loads Prediction on UH-60A Flight Test using Loose Fluid/Structure Coupling (Paper 28)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Rocco Moretti, Hyeonsoo Yeo, François Richez, Biel Ortun

This work exploits the high-quality UH-60A flight test campaign for comparison with concurrent simulations at the U.S. Army and ONERA. Rotor airloads and structural loads are predicted by coupling Computational Fluid Dynamics (CFD) with rotorcraft comprehensive analysis (CA). A high-speed test point is examined. Comparisons are shown for airloads, structural loads and rotor controls. Agreement with test data is improved when the flexibility of the pitch link is considered. Results show good agreement between the two partners predictions and with test data.

S-97 RAIDER® Maneuvering Loads Flight Test and Simulation Correlation (Paper 136)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Jinggen Zhao, Mark Wilson, William Welsh

This paper demonstrates the recent success of applying advanced digital modeling and simulation tools to simulate challenging transient maneuver flight conditions and shows the resulting correlation with flight test. To understand and improve the predictive capabilities for advanced rotorcraft configurations such as the coaxial aircraft, a multi-year effort has been pursued to develop a coupled full aircraft Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) methodology for both steady and transient maneuver flight conditions. The CFD-CSD full-aircraft transient maneuver simulation methodology developed was applied to simulate S-97 RAIDER® aircraft for both a low-speed level-body acceleration (using only the propulsor to accelerate the aircraft) and a 2.0g pull-up maneuver. In-depth studies were carried out to gain insights into flight test observations and to identify important modeling feature enhancements to better simulate the complex aerodynamic and structural couplings between the rotor and airframe systems. Overall, the simulation results at these transient maneuver conditions demonstrated reasonably good correlation with the corresponding flight test data. This study shows that usage of the current state-of-the-art methodology, when carefully validated and applied, can capture the complex coaxial rotor physics due to fluid and structure interaction with sufficient accuracy to support designs.

S-97 RAIDER® Propulsor Flight Loads and Validation (Paper 92)
Full registrant at Forum? Log in for link!
Dynamics I (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Daniel Schuster

The S-97 RAIDER® helicopter uses a pusher propeller to provide forward and reverse thrust capability to Sikorsky's X2 Technology™ design. Due to the propeller's aft mounting location on the aircraft it experiences aerodynamic interactions with both the airframe wake and main rotor wake across the flight envelope. This paper details the inclusion of an aerodynamic interference flow field near the propulsor disk plane in a CSD (Computational Structural Dynamics) propulsor model used to predict blade loads. The interference flow field uses either wind tunnel measurement or CFD (Computational Fluid Dynamics) to define the aerodynamic flow near the propeller plane. The predicted blade loads were compared with flight test data at a variety of steady flight conditions and overall good agreement is found between simulation and test. The simulation methodology is also expanded to simulate transient hover and acceleration conditions using a quasi-steady trim approach at multiple discrete time points of the maneuver. Overall good correlation of the measured blade maximum, minimum, and vibratory loads are achieved.

Safety and Product Robustness in the Air Vehicle Design Process (Paper 5)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Barton Hainsworth, Peter Barner, Ide Ehigiato

This paper discusses the application of the Design Failure Modes and Effects (DFMEA) process as applied within the Airframe and Mechanical Systems (AF&MS) design organization at Sikorsky Aircraft, a Lockheed Martin Company. The DFMEA process, an adaptation of the SAE J1739 Surface Vehicle FMEA standard, is tailored to meet the helicopter airframe design application for DFMEA and is further modified for a bottoms-up abbreviated Design Failure Modes and Effects method, the A-DFMEA, which is a design engineer conducted assessment versus the top down DFMEA team approach. While this method may have certain shortfalls in that only a single individual is conducting the preliminary assessment, it does have the benefit of increasing the design engineer's awareness and focus on potential areas of concern such as various failure modes by component type which can be addressed early in the design or monitored as the design matures through the product design/development cycle. The paper will present a process flow, risk assessment scoring methodology as well as DFMEA and A-DFMEA scoring worksheet, remedial actions, and mitigations from those results. Lastly, a discussion of how those results enter into the digital thread and data archiving are presented.

Scalable Collision Avoidance in High-Density Airspaces (Paper 25)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Bianca Gonzalez, Jack Langelaan, Alan Wagner, Muhammad Junayed Hasan Zahed

Human-piloted, remotely piloted, and autonomous aircraft are likely to share the air space in the near future. Furthermore, the density of air traffic is likely to increase as urban air mobility and air package delivery operations become more prevalent. This paper discusses a collision avoidance approach based on velocity potentials: it is scalable to large numbers of aircraft and is highly likely to be easily interpretable for human pilots, passengers, and bystanders. This paper describes the velocity potential approach for three dimensional collision avoidance and uses Monte Carlo simulations to examine (1) the effect of number of aircraft in the airspace; (2) the number of aircraft that are actively tracked for collision avoidance; (3) the elementary potentials used for collision avoidance.

Simulated Flight Trial Assessment of Novel Autorotation Cueing Methods using a Head Down Display (Paper 1281)
Full registrant at Forum? Log in for link!
Crew Stations I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Mushfiqul Alam, Mike Jump, Jonathan Rogers

Autorotation is an emergency maneuver executed by helicopter pilots usually following a loss of power, mechanical or system failure. The pilot is required to perform several tasks simultaneously and the timing of each of these must be precisely controlled. Workload can be high throughout the maneuver and the consequences of getting things wrong can be serious, if not fatal. Following on from a series of studies that investigated the use of both head-up displays and haptic cueing methods to assist pilots to fly the maneuver more safely and consistently, this paper presents a pilot-in-the-loop flight simulation study to explore the use of pilot cues provided on a head-down display. These provided pitch angle (and hence airspeed) cueing to the pilot. The cueing symbology was tested for a straight-in autorotation approach for a number of different visual environments and the results compared to equivalent cases where no cueing was present. The cues were assessed both subjectively, via pilots providing Bedford Pilot Workload Ratings, as well as objectively, via analysis of the flight path performance achieved. The subjective evaluation showed that cues using the head-down display were useful in terms of pilot workload reduction, particularly for the degraded visual environment scenario tested. The objective assessment revealed that pilots were able to establish the steady state descent more quickly and maintain forward airspeed within the specified bounds more reliably with the aid of the cues.

Simulation and Analysis of NASA Lift Plus Cruise eVTOL Crash Test (Paper 1340)
Full registrant at Forum? Log in for link!
Crash Safety (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Jacob Putnam, Justin Littell

The National Aeronautics and Space Administration (NASA) conducted a full-scale crash test of a representative electric vertical take-off and landing (eVTOL) fuselage in November 2022. The test article was a carbon-composite fuselage cabin section of the six-passenger lift plus cruise (LPC) eVTOL design concept which was created by NASA researchers to advance understanding of eVTOL propulsion, noise, and safety. The fuselage cabin section was impacted onto a concrete surface with a combined horizontal and vertical velocity approximating a severe but survivable crash landing. This test was conducted to generate data to help inform eVTOL crashworthiness regulation development, evaluate the use of energy absorbing (EA) concepts within vehicle design, and quantify the predictive accuracy finite element (FE) modelling techniques used in crashworthiness predictions. The response of the eVTOL representative fuselage when subjected to dynamic impact loading was evaluated through structural instrumentation, anthropometric test devices (ATDs), and high-speed photogrammetry. The development of a representative FE model of the test article and comparison between model to test results is described within this manuscript to quantify the capability of these tools to predict crashworthiness of the carbon-composite eVTOL airframe.

Simulation of the Rotorwash Induced by a Quadrotor Urban Air Taxi in Ground Effect (Paper 58)
Full registrant at Forum? Log in for link!
Aerodynamics III (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Denis-Gabriel Caprace, Patricia Ventura Diaz, Seokkwan Yoon

A rotorcraft hovering near the ground causes downwash and outwash. The impact of these induced velocities on urban air mobility operations has not been extensively quantified. This paper explores the opportunity of using CFD to perform dedicated studies on the aerodynamics of rotorcraft in ground effect (IGE). For this purpose, we compare load and flow predictions obtained with the high-fidelity CFD solver OVERFLOW and with a medium-fidelity vortex particle-mesh (VPM) method, for a single rotor IGE. We show that the computational cost of high-fidelity simulation makes it impractical to sweep through a large number of configurations or operating conditions. However, a small set of cases can be used to verify a medium-fidelity tool. The latter provides a better trade-off between 'accuracy' and computational intensity, which enables numerous, longer simulations at a more affordable cost. As an example, the outwash flow is computed for two different designs of a quadrotor air taxi in hover and reveals the existence of increased velocities between the rotors. This work illustrates how CFD can help identify dangerous areas for passengers and ground personnel when they approach the vehicle.

Simulation-Assisted, Weather-Aware Urban Air Mobility System Planning (Paper 1160)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Michael Yablonski, Alexander Klein

The emergence of Urban Air Mobility (UAM) as a novel mode of transportation presents new challenges to government and commercial stakeholders: new vehicle types are being introduced for which supporting infrastructure, such as new routes and vertiports, needs to be designed and put in place, often in the vicinity of airports; community concerns need to be addressed; and inclement weather is a potential disruptive factor. In this new UAM paradigm, simulation modeling is an indispensable tool for aviation planners in identifying optimal solutions to these challenges. AvMet and Kimley-Horn have developed an efficient process for UAM simulation study planning and execution, facilitating rapid turnaround through collaborative model development. This streamlined process, from UAM airspace design and flight schedule development to fast-time simulation modeling, to advanced 3D visualization, can greatly reduce the study completion time and allow for a variety of UAM scenario alternatives to be explored, evaluated from a cost-benefit perspective, and presented to stakeholders. A key component of this process is AvMet's state-of-the-art UAM Simulation Model (USM). In this paper, we provide UAM scenario setup examples and simulation results utilizing the USM, as well as describing the study planning and modeling process.

Simulator-Based Evaluation of Visual Pilot Assistance for Coaxial Ultralight Helicopters (Paper 1312)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Benjamin Rothaupt, Manuel Spülbeck, Walter Fichter

This paper presents a flight simulator study that examines whether a display inside the cockpit can aid helicopter pilots with little to no experience in completing basic maneuvers. The study participants have no prior experience as helicopter pilots. The flight simulation uses a dynamic model of a coaxial ultralight helicopter horizontal motion that includes a stability augmentation system. A virtual reality headset is used to give the participants a realistic sense of perspective. The benchmark task includes decelerating into hover and hovering above a target for a given time. Three cueing configurations are compared. One includes visual cues on the ground that mark the hover target position. The two others add either a heads down display or a heads up display inside the cockpit, which visualize the relative target position and a prediction of the helicopter motion. With the proposed displays available inside the cockpit, participants tend to reach the target faster and more consistently. Hover performance is not improved by an additional display as the pilots mostly rely on visual cues on the ground during hover. In summary, both log data and pilot feedback suggest that the proposed displays are primarily beneficial in flight phases where the helicopter moves.

Sinusoidal Gust Response of RC Propellers in Tandem Configuration (Paper 1154)
Full registrant at Forum? Log in for link!
Aerodynamics II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Jielong Cai, Sidaard Gunasekaran

The study of the fixed-pitch small-scale propeller under sinusoidally time-varying freestream is extended to a tandem propeller configuration. The changes in thrust and pitching moment of both the front and back propeller were characterized when encountering the sinusoidal gust in edgewise flight conditions. The propeller's steady freestream performance obtained in the previous study was used to predict response under sinusoidal time-varying freestream in edgewise flight. Below a reduced frequency of 0.2, the propeller response agrees with the prediction model, suggesting a linear superposition and quasi-steady dynamics for the propellers. At a higher reduced frequency, a reduction in mean thrust and pitching moment was measured. A phase lag in the propeller response was also observed indicating an unsteady response of the propeller. When placing the propeller in close proximity to each other, additional variations in the back propeller's performance were also observed at higher reduced frequencies, creating additional instability in the system.

SmartHangars and SAE International Aircraft Charging Standards (Paper 1283)
Full registrant at Forum? Log in for link!
Product Support (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Joshua Portlock, Richard Watson

Electro.Aero has been supporting the emerging electric aviation industry for nearly a decade, including the development of chargers, electrical management systems, battery management systems and electric propulsion systems to numerous electric aircraft development projects. During that time, it was identified that the industry needed standardization, especially regarding the charging coupler, so the SAE AE-7D committee was founded by Joshua Portlock in 2018 to help standardize electric aircraft charging and energy management. While the charging coupler standard was proving to be of high priority to the industry, there has also been a noticeable trend that typical airport hangars do not have sufficient electrical power to charge the growing power demands of future electric vertical take-off and landing (eVTOL) aircraft. Therefore, SmartHangar technology was developed, whereby the limited grid connectivity is supplemented by solar and stationary battery energy storage systems to help deliver the peak power demands of electric aviation charging, whilst also helping airports and vertiports transition to more self-sufficient sustainable energy.

Software testing is boring, until it’s not... (Paper 1201)
Full registrant at Forum? Log in for link!
Avionics and Systems II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Dustin Flaum

Software regression testing is unavoidable for any modern aircraft, but is especially critical for highly complex multi-mission helicopters. Regression testing is every test pilot's least favorite flight, it is cumbersome, monotonous, and boring, until it's not... This paper presents the challenges and lessons learned during software flight test through a case study of a seemingly benign software bug that brought an entire test program to a halt. Also highlighted is the importance of mission relation when conducting software test and covers techniques on how to build that relation into the test structure to produce actionable results. Some of the challenges discussed include managing complex configurations and testing for intermittent software issues. The MH-60R Seahawk program discussed in this case study has maintained a state-of-the-art multi-mission helicopter through brute force and large development efforts. With the increasing pace of technological advancement, this strategy will be impossible to sustain for the Future Vertical Lift platform. This paper goes on to discuss how the lessons learned from recent software flight test must influence the design of the next generation of military helicopters. The lessons learned during today's flight test will help answer the critical question, how do you design a state-of-the-art aircraft now that will remain state-of-the-art throughout its entire lifecycle?

Structural Analysis of a Rotorcraft Blade Design Using iVABS (Paper 1217)
Full registrant at Forum? Log in for link!
Structures and Materials II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Robert Haehnel, Joon Lim, Yonghu Wenren, Su Tain, Wenbin Yu

In this paper we introduce integrated VABS (iVABS) a tool to aid in the design of composite slender structures. iVABS can be used as an inverse tool to determine cross-section design given structural properties, such as torsional and bending stiffnesses, and inertial constraints (i.e., mass per unit length). In this work we explore using iVABS for designing the structural elements of a composite blade. We use a modified UH-60A blade; the updated outer mold line used in this study is a blade design presented by Allen et al. (ref. 1). In this effort we endeavor to develop a composite blade design that matches the torsional, chordwise and flap stiffnesses, blade mass per unit length, and shear center and center of gravity offsets properties of the UH-60A blade, while meeting strength constraints for the blade. In this initial effort we found that meeting the strength constraints and matching the target blade properties was challenging to do simultaneously with iVABS. Further work is needed to refine the optimization problem, chosen design variables, and cross-section templates to improve the final blade design. Regardless, this work demonstrates the power and flexibility of iVABS to quickly explore the design space. In the hands of an experienced design engineer iVABS could be a powerful tool to reduce design cycle times and develop innovative blade structural designs.

Studying the Effect of Sensor Visualization and Graphical Augmentation on Obstacle Detection Time in the Low Altitude Flight Environment (Paper 37)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Paul Flanigen, Michael Wilson, Nadine Sarter, Ella Atkins

Obstacle strikes are only behind controlled flight into terrain as the known cause of fatal civilian helicopter accidents. Failing to notice obstacles is also a leading cause of military rotor craft mishaps. This can be explained, in part, by the fact that aircrews must quickly notice and locate a wide variety of hazards, including vertical obstacles while performing various other flight-related tasks. This need for divided attention calls for the development of better bottom-up support for obstacle detection through display design. To this end, the present study will employ a within-subjects design to assess the efficacy of visualization types (unaided, image intensification, or thermal imaging) and obstacle augmentation approaches (none, a priori circles, or active sensor boxes around the obstacle) for aiding hazard awareness and avoidance. Performance and eye tracking data, verbal behavior, and qualitative feedback will be collected to assess pilots' ability to balance vital aircraft state awareness with timely perception of obstacles in the low altitude flight environment. Ultimately, the results from this study will contribute to the literature in visual attention and interface design, potentially increasing safety during helicopter flight operations.

Successive Optimization of Airfoils, Planform and Twist for Aerodynamic Performance of Helicopter Rotor Blades (Paper 1316)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Gunther Wilke

The design of new helicopter rotor blades is a challenging task. The individual blade sections undergo very different flow conditions during the various flight regimes of the helicopter. In forward flight, the advancing side operates in a transonic regime where potentially shock waves can occur, while on the retreating side little flow velocities at high angle of attacks are seen up to reverse flow. In hover, the oncoming tip vortex of the previous blade drastically influences the inflow on the rotor. This paper joins the classical blade shape design with numerical optimization techniques. Opposing to the direct solution process of directly modifying the blade shape, the rotor blade is conventionally considered as a set of airfoils, a planform and a twist distribution. First, rotor airfoils are found through numerical optimization and then placed on the reference rotor. The planform and twist of this rotor are then also numerical optimized. The obtained trade-off blade for hover and forward flight drastically improved the performance over the reference HART-II blade (11% in forward flight, 5% in hover flight). In order to arrive at industrial relevant blades, further work including more disciplines becomes necessary.

Surrogate-model based Optimization Framework for the Structural Design of Helicopter Rotor Blades subject to Dynamics and Failure Criteria (Paper 1291)
Full registrant at Forum? Log in for link!
Aircraft Design I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Rohin Kumar Majeti, Franziska Becker

Helicopter rotor hub vibratory loads can be alleviated through careful design of the rotor blade inner structure. Large design space and the nonlinear nature of the problem are major obstacles that need to be overcome. Apart from that, the need for high-fidelity solutions lead to high computational times. An automated surrogate-model based design optimization process using commercially available software as well as codes developed within DLR has been described in this paper. Minimal human interference and overall process efficiency is the goal of this work. Latin Hypercube Sampling function for the design of experiments, Kriging function for surrogate modeling and particle swarm optimization algorithm make up the framework. The rotor blade inner structure parameters constitute the design variables while the natural frequencies and vibration index are taken as objective functions. Results show that through careful design of the inner structure, it is possible to obtain a rotor with lower hub vibratory loads. For the optimization process, it must be ensured that sufficient number of sampling points are taken for building accurate surrogate models and the problem definition should be neither under-constrained nor over-constrained.

System Identification of a Compound Intermeshing Rotor UAV (Paper 60)
Full registrant at Forum? Log in for link!
Modeling and Simulation III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Johannes Wartmann, Susanne Seher-Weiß, Philippe Petit, Alexej Dikarew, Andreas Voigt, Kristian Fettig

Within the FaUSt (Fast Unmanned Scout) project, an existing UAV with intermeshing rotors was enhanced by two electric pusher propellers to extend the speed range for future manned-unmanned teaming research. The modeling of such a compound UAV has not yet been covered in the literature. To extract models for simulation and flight control design, dedicated flight tests were performed using a multi-axis binary noise signal for system identification with activated base flight control system. Two different system identification methods are applied to estimate bare-airframe models of the modified UAV at hover condition: one in the time domain, the other in the frequency domain. The time domain method can inherently be applied to correlated closed-loop data, while input correlations have to be accounted for when using the frequency domain method. The resulting models are analyzed in both time and frequency domain and the model eigenvalues and modes are compared in detail. The results indicate that the time-domain model matches low frequency modes of the vehicle more accurately, but both models show good model performance.

System Simulation at Airbus Helicopters: From Early Validation to Formal Certification (Paper 1227)
Full registrant at Forum? Log in for link!
Systems Engineering II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Nicolas Brisset, Andrew Duffy

Over the last 15 years, Airbus Helicopters has been investing significantly into avionics simulation, in order to leverage its potential all the way from early design validation to integration, testing, verification and recently even certification. One key feature in making simulation a backbone of development activities is digital continuity and the aggregation of the work produced by a large community all along the product lifecycle, with the right sequencing: typically investing early in simulation rather than waiting late until the final development steps to produce a training simulation that will not benefit development. This paper explores the various benefits brought by the approach, putting it into perspective with recent MBSE developments. It also explains recent efforts Airbus Helicopters has been undertaking towards using avionics simulation as a formal Means of Compliance for certification activities, and it underlines some key challenges avionics simulation must address in order to remain relevant in the next years.

Systems Engineering - The Art Of Requirements (Paper 1322)
Full registrant at Forum? Log in for link!
Systems Engineering I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Brad Pelletier

There is an art in requirements that will lead to a product that is completed on budget, on schedule and certified by the FAA. The particular way that requirements are determined, the way that they are worded, the way they are put down on the page all blend to give you the picture of the final product to be developed. The beauty in the process of requirements development is the versatility that the world of requirements has on the vertical flight industry. Requirements are used for manufacturers of small simple products to manufacturers of extremely high complex systems, to include simple or complex software definition, like Artificial Inelegance (AI). Requirements can be documented in multiple ways to include Word, Excel, Dynamic Object Oriented Requirements System (DOORS), or more modern ways like Model Based Systems Engineering (MBSE). This paper is a brief overview of the need for requirements, where requirements fit into the product design lifecycle, and how to develop requirements. The paper will conclude with a brief explanation of how to word good requirements that are verifiable or can be properly validated.

Test and Evaluation of Image-Based Navigation for Shipboard Landing on the MQ-8C Fire Scout Unmanned Aircraft System (Paper 88)
Full registrant at Forum? Log in for link!
Unmanned VTOL I (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Doug Duehring, Brendan Egan, Avinash Gandhe

From August 2022 to January 2023, Air Test and Evaluation Squadron Two Four (UX-24), the U.S. Navy's UAS test squadron, conducted ground and flight tests of the Image-Based Navigation for Shipboard Landing (INAV-SL) system on the MQ-8C Fire Scout UAS. The three-camera INAV-SL system was designed to optically detect standard flight deck markings and calculate relative position and orientation of the MQ-8C. The INAV-SL system was configured to collect data for comparison to the current landing system. No commands were input into the air vehicle's control feedback loop. A variety of approaches were conducted to fixed flight deck markings on an airfield taxiway and to the USS Jackson, an Independence class Littoral Combat Ship based out of San Diego, CA. The system demonstrated the ability to optically acquire and track the flight deck during approach and landing phases of flight with typical error of less than 2 ft.

Testing of a Fiber-Optical Sensor System for Rotor Blade HUMS (Paper 33)
Full registrant at Forum? Log in for link!
HUMS I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Florian Berghammer, Benedikt Sosa, Verena Heuschneider, Ilkay Yavrucuk, Manfred Hajek

As a prerequisite for the development of HUMS (Health and Usage Monitoring Systems) using blade displacement and sectional force estimation in forward flight, rotor blades are instrumented with fiber-optical sensors at the Institute for Helicopter Technologies and VTOL at the Technical University of Munich. Utilizing a total number of 60 directional strain measurements it is possible to reproduce the strain field of five sections along the uniform airfoil section. Knowing the exact location of the integrated sensors is crucial for shape reconstruction and may vary in reality due to a number of uncertainties occurring in chordwise and thickness direction of the airfoil profile during fabrication. Thermographic scan methods and computed tomography scans are investigated in order to determine the sensor locations inside the blade and to reproduce a 3D model of the integrated sensor system. Improvements can be seen when comparing results from static deformation tests using the sensor positioning from the layout and the real sensor positions investigated in computed tomography. In addition sectional stiffness terms are derived from strain measurements in combination with loadcell data. With the scope of state observation on the MERIT (Munich Experimental Rotor Investigation Testbed) test rig at the TU Munich a measurement environment is established using an optical data transmission to extract strain signals from the rotating system. First investigations show the potential of optical strain measurements in the rotating systems for a variety of applications.

The Battery Cooling Design and Simulation Study in Multirotor eVTOL Aircraft (Paper 118)
Full registrant at Forum? Log in for link!
eVTOL III honoring Alex Stoll (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Lintao Shao, Anhuan Xie, Jiandong Cai, Yunzheng Zhu, Shiqiang Zhu

High-specific energy Li-ion batteries are widely used in eVTOL aircraft and usually rapidly heat up during flight. Therefore, proper and efficient cooling strategies should be adopted during eVTOL design in order to prevent overheating. This paper collected and compared the battery cooling strategies adopted by different eVTOL aircraft manufacturers based on published patents. The choice of battery cooling strategies could be influenced by aircraft configurations. The ZJCopter eVTOL aircraft developed by Zhejiang Lab adopted the PCM cooling method as a fast-cooling and lightweight battery cooling strategy. The effectiveness of this cooling method was demonstrated by comparing it with air cooling method through simulation, which showed that the PCM cooling method can reduce the average and maximum temperatures of the battery. Moreover, increasing the heat transfer area and thickness of the PCM layers could improve the cooling effect even further.

The Effect of Phase Offset Angle for Coaxial Co-Rotating Rotors (Paper 17)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Raja Akif Raja Zahirudin, Vitor Valente, Eric McThane, Aaron Hafner, Zach Birbeck, Sihong Yan, Eric Greenwood, Jose Palacios

The aerodynamic performance and noise generation of stacked co-rotating rotor systems are investigated in this paper. A test apparatus is employed which allows the rotor blade pitch and the separation distance between the two bladed rotors to be varied. Instrumented motors and a novel phase control system are used to vary the azimithal phase offset between the upper and lower rotors. This configuration also allows the upper and lower rotor thrust and torque to be measured independently. The phase offset is shown to have a strong effect on tonal noise generation at all separation distances, with the lowest noise achieved when the blades rotate out of phase with one another. The broadband noise also varies with phase offset; at close separation distances, the lowest noise broadband noise levels occur when the lower rotor leads the upper rotor. However, the phase offset for minimum broadband noise levels shifts linearly toward the upper rotor leading as the separation distance is increased. At a separation distance of 0.65 rotor radii, the phase offset is no longer effective in controlling broadband noise due to an apparent break down of the upper rotor wake. In general, the phase offset for lowest broadband noise is associated with the offset for the highest power loading for any separation distance. The power loading of the rotor system does not change in low speed edgewise flight, but both tonal and broadband noise increase and phase control is no longer effective in reducing broadband noise. Stacked rotor configurations with several different blade pitch settings are also compared to co-planar (conventional) two and four bladed rotors operating at the same total rotor system thrust. The stacked configurations all demonstrate a higher aerodynamic efficiency than the co-planar configurations, with the most efficient stacked configuration have the lower rotor blade pitch increased to balance the thrust across the upper and lower rotors. With these pitch settings, the broadband noise no longer varies significantly with phase offset angle. While this configuration also has the lowest noise levels of any stacked rotor configuration, the broadband noise is not significantly different than a four bladed co-planar design and the tonal noise levels are slightly higher.

The Effects of Rotor-Rotor and Rotor-Wing Interactions on eVTOL Aeroacoustics (Paper 1300)
Full registrant at Forum? Log in for link!
Acoustics II (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Brendan Smith, Ulhas Udaya Hebbar, Farhan Gandhi

This study examines the effect of aerodynamic interactions on a two-rotor pair in cruise, and a propeller acting in the presence of a wing. The two-rotor system with a forward and an aft rotor in-line is considered at different disk loadings (6, 8, 12 lb/ft² for a fixed cruise speed and different cruise speeds (20, 40, 60 knots) for a fixed disk loading. Loads for these rotors are generated using the CFD solver AcuSolve to capture the aerodynamic interactions on the rear rotor due to the front rotor. These loads are used as inputs to an acoustic solver (PSU-WOPWOP, ANOPP2) to predict noise at observers in the rotor plane, with noise compared to that from isolated rotors in the absence of aerodynamic interactions, to quantify the interaction effects. The rotor wing case, with the rotor in front of the wing operating in axial propeller mode, is simulated at 24 knots cruise and 8 degree wing angle of attack. Loads for the rotor with a wing and a rotor acting in isolation are generated using the CFD solver AcuSolve. These loads are used as inputs to an acoustic solver, with observers placed in the plane of the rotor, in the plane containing the wing chord cut through the rotor hub, and a vertical plane through the hub in the wind direction. The two-rotor system simulation results show that the presence of aerodynamic interactions on the rear rotor results in changes in noise levels of less than 2 dB in the plane of the rotors. The rotor wing results show that the aerodynamic interactions increase the overall noise by up to 8 dB, with the largest increase being above and behind the prop-rotor.

The Impact of Control Augmentation and Stability Augmentation System Parameters on Kinetosis of Rotorcraft Passengers (Paper 1215)
Full registrant at Forum? Log in for link!
Handling Qualities II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Süleyman Özkurt, Tim Burkhardt, Fabian Schimpf, Walter Fichter

Kinetosis is provoked by low-frequency vibrations below 0.5 Hz. The severity of kinetosis increases with increased vibrational magnitudes within the mentioned frequency range. In rotorcraft, these frequency range intersects with the bandwidth of automatic flight control systems. The counterreactions of the automatic flight control system to atmospheric disturbances lead to vibrations within its bandwidth. The magnitude of these vibrations depends on the disturbance rejection properties of the implemented flight control system. Consequently, it is assumed that the severity of kinetosis depends on the design parameters of the flight control system. To confirm this assumption, a controller to stabilize the helicopter and track commanded attitude angles is proposed. The parameters of the controller are permutated to analyze their impact on kinetosis under turbulent atmospheric conditions. Further, a mathematical kinetosis model is adapted to experimental results obtained from helicopter vibrations. This modified model is used to evaluate the accelerations and angular velocities of the closed-loop helicopter regarding kinetosis. The results of this work show that the disturbance rejection properties, hence the control parameters, affect the vibration magnitudes. Therefore, the extent of kinetosis is driven by the control parameters of the stabilization and control augmentation system.

The RASCAL Vehicle: a Functional View of the Modern Airborne Laboratory (Paper 1402)
Full registrant at Forum? Log in for link!
Avionics and Systems II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Fernando Dones, Carl Ott, Matthew Yu, John Glodowski, Mark Spano, Anthony Emma, Eric Katzen, Franco Ruiz, M. Patrick Hickman

Fernando Dones is Boeing Technical Fellow and a recognized expert on Flight Controls Systems and Fly-by-Wire technology across the aerospace industry. His expertise was developed over a 42 year career making technical leadership contributions on programs such as Advanced Digital/Optical Control System (ADOCS), CH-47, BellBoeing 609, Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL), EMARSS, a variety of other Programs, and Adaptive Vehicle Management System, and designed the Vehicle Management System architecture of the DARPA CRANE vehicle. His contributions to these programs include systems architectures, redundancy management algorithms, FCS actuator servo loop approaches with safety monitors, and software architectures optimized for system safety and handling quality performance. His broad practical experience complemented by deep technical understanding and ability to explain complex concepts make him a highly sought technical advisor and a celebrated mentor. Carl Ott is an Experimental Test Pilot in the U.S. Army DEVCOM Aviation and Missile Center, Technology Development Directorate at Fort Eustis, VA. He retired from active duty in 2019 after 26 years of service. His prior assignments include Chief of Flight Test for the Aviation Applied Technology Directorate, Chief of Flight Projects for the Aeroflightdynamics Directorate, Forward Operational Assessment Officer at Bagram Airfield, Afghanistan, and the Army Test Lead for the UH-60M Upgrade program with the Aviation Technical Test Center. He received a Bachelor's of Mechanical Engineering from the United States Military Academy and a Master's of Aerospace Engineering from the University of Washington. Mr. Ott is a distinguished graduated from the US Naval Test Pilot School class 131, a Master Aviator with over 900 hours of experimental flight test, and is the recipient of the 2013 U.S. Army Research and Development Achievement Award.

The Stopped Rotor - A New Look at an Old Idea (Paper 78)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Gerald Brown, Vivek Ahuja

This paper reviews and reassesses the Stopped Rotor Concept. It briefly describes a number of historical Stopped Rotor experiments, discusses the problems they encountered, the limitations imposed by old technologies, and why they were not successful. It sheds some light on the rationale, during that time, for not pursuing further research in those design concepts. While it has been well understood for decades that a low disc-loading rotor is the most efficient vertical take-off and landing (VTOL) element, and high aspect ratio wings are the most efficient cruise elements, those experiments demonstrated how difficult it has been to combine those two efficient elements in a single aircraft. A new design is presented which revisits the Stopped Rotor Concept and shows that with modern technologies, materials, and analysis tools it is now possible to design and build an aircraft that uses low disc-loading rotor blades not only for efficient VTOL but also for efficient cruise.

Time and Frequency Analysis of a Speed-Controlled Rotor in Hover (Paper 1339)
Full registrant at Forum? Log in for link!
eVTOL I honoring Alex Stoll (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Matthew Asper, Jayant Sirohi

As electric propulsion technologies advance, rotor speed control is becoming viable for manned VTOL aircraft primary propulsion. These control methodologies are an area that still needs to be explored, especially for high Reynolds number conditions. For this reason, a 2 meter diameter, speed-controlled rotor system was tested in hover. The rotor was driven by an electric motor, and step and sine inputs of 3% of the nominal speed were commanded at blade loadings up to CT /σ = 0.11 to determine the time and frequency response of rotor thrust and torque. Sine inputs were tested at frequencies up to 25% of the rotor speed. The data was used to validate an integrated aerodynamic and powertrain model of a speed-controlled rotor. A dynamic inflow model with blade element momentum theory predicted the aerodynamic loads, and an electromechanical model was used to account for the motor and control dynamics. Findings showed that there was good agreement between measured and predicted motor speed, thrust, and torque time response. Experimental results showed a faster response in the measured thrust and a lower peak torque versus the model. The model was able to capture the correct trends in magnitude and phase for motor speed, thrust and torque for all conditions tested. Inertial torque dominated the peak torque response, resulting in a linear increase with frequency of the input speed variation, whereas aerodynamic torque added damping and resulted in a negative offset in phase. Discrepancies between the model and the experiment may be due to the algorithms programmed into the motor controller, which were not modeled. The results of this study will be useful for informing engineers looking to design for rotor speed control.

Towards A Regulation Based Functional Hazard Assessment for Safety & Certification Requirements of Hydrogen-Hybrid eVTOLs (Paper 6)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Colin Bosch, Lukas Bertsch, Ilkay Yavrucuk

The multitude of new eVTOL projects provides not only revolutionary configurations, but also the chance to consider cleaner energy sources for providing power. At the same time, regulations for these systems have not been defined in detail. Nevertheless, the use of classical safety assessment standards could assist in preliminary safety and reliability investigations. This work describes an approach to be used to facilitate the creation of functional safety requirements for hydrogen-hybrid architectures for eVTOLs. In a first step, we present an overview of current EU safety regulations to introduce the accepted Target Level of Safety (TLS) which is then followed by a systematic method to describe how a Functional Hazard Assessment (FHA) can be tailored for both manned and unmanned use cases. We apply this process to the power systems of two different VTOL case studies (manned VTOL and UAV), discuss examples of the created FHAs and comment on the shortcomings and benefits of this method.

Towards Accurate Broadband Noise Predictions Using CFD (Paper 1243)
Full registrant at Forum? Log in for link!
Acoustics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Jordon Won, Seongkyu Lee, Nikos Trembois

Rotor broadband noise can be predicted using various numerical and analytical methods. This paper explores the application of computational fluid dynamics (CFD) combined with Lee's wall pressure spectrum and Amiet's trailing edge noise model to predict broadband noise, comparing the results to different experiments. A simple, ideally twisted rotor blade with the NACA 0012 airfoil in hover is employed to establish the appropriate methodology for integrating CFD with other models. Two approaches are utilized: the first is a direct input approach, where flow data from the CFD solution is directly input into the models, while the second approach employs CFD to inform XFOIL inputs, which subsequently provide inputs for the wall pressure spectrum and acoustic model. The CFD/XFOIL approach demonstrates better agreement with experimental measurements and is less sensitive to CFD pre- and post-processing setups. The Straight Up Imagining (SUI) Endurance rotor is also validated for forward flight, followed by the prediction of broadband noise generated by a propeller and wing configuration. Observed trends during the validations and predictions suggest that airfoil selection and blade geometry play a more significant role in the magnitude of trailing edge noise than thrust.

Towards CFD Simulations of Transient Tiltrotor Conversion Maneuvers (Paper 1287)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Steven Tran, Hyeonsoo Yeo, Andrew Wissink, Joon Lim

This paper details the progress made towards using Computational Fluid Dynamics/Comprehensive Analysis (CFD/CA) coupled simulations to model transient tiltrotor conversion maneuvers from hover to cruise. Recently the availability of Helios' mid-fidelity tool ROAM has enabled Cartesian-based CFD simulations of full aircraft in reasonable compute times. In this work, ROAM is tightly coupled to RCAS which allows for transient conversion maneuvers to be dynamically computed based on realistic aerodynamic loads. Both a 30 second and 45 second conversion maneuver are analyzed using this method. Quasi-steady comparisons between ROAM and traditional high-fidelity CFD tools Overflow and Fun3D demonstrate that though ROAM underestimates rotor power, it predicts more realistic loads than an RCAS standalone model using dynamic inflow. This is due to ROAM's ability to capture blade/vortex interactions and rotor/wing interactional aerodynamics, which in turn led to more realistic structural load predictions during both the quasi-steady and transient conversion maneuver simulations. Furthermore, ROAM is up to 52x faster than traditional high-fidelity methods.

Towards Flight Envelope Protection for the NASA Tiltwing eVTOL Flight Mode Transition using Hamilton-Jacobi Reachability (Paper 1376)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Ting-Wei Hsu, Jason Choi, Divyang Amin, Claire Tomlin, Shaun McWherter, Michael Piedmonte

This paper presents a collaborative research effort between authors from Bechamo LLC, UC Berkeley, and NASA to establish a framework for applying Hamilton-Jacobi Reachability Analysis to the full 6-DOF dynamics of the NASA Tiltwing vehicle, verifying the safe flight envelope during the flight mode transition between hover and cruise flight, which prevents loss of control of the vehicle and ensures recoverability to safe trim conditions. This involved first verifying the nominal flight mode transition path as a series of trim points, defining the safe flight envelope using reachability, and decomposing the system dynamics into longitudinal and lateral subsystems. Our formulation guarantees the computed envelope's robustness against modeling errors and uncertainty, and the usage of state decomposition significantly improved the tractability of the reachability computation. The framework's success is validated through 6-DOF Monte Carlo nonlinear simulation of vehicle dynamics, demonstrating that the vehicle states within the flight envelope can successfully recover to trim states and continue a safe flight mode transition.

Towards an Agile Crew Training Program of a Remotely Piloted eVTOL Aircraft in Context of Flight Test Operation (Paper 1301)
Full registrant at Forum? Log in for link!
Safety (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Julius Hoffelner, Markus Maly, Kevin Schmiechen, Jacquelyn Banas, Florian Holzapfel

The paper discusses an approach for a modular training program that is adapted but not limited to flight test operations of a remotely piloted electrical vertical takeoff and landing (eVTOL) aircraft. The basis of this crew training program is built on an analysis of the legal framework, aviation safety in respect of airmanship and situational awareness, training methods, and agile project environment. A key role is the inclusion of aviation safety, with particular attention to operation-based subject good airmanship. The needs arising from testing and agile project development are considered. The training program is adapted to a Concept of Operations (ConOps) for an unmanned aerial system (UAS) of several hundred kilograms. The results in the form of a modular training program are described.

Towards an Evaluation Process for Regime Recognition Approaches: Addressing Variability in Labeling Training Data (Paper 1167)
Full registrant at Forum? Log in for link!
HUMS II (Thurs. May 18, 2023 - 10:15 AM to 12:15 PM)
Catherine Cheung, Emma Seabrook

Regime recognition is an important tool for monitoring aircraft usage. Algorithms for this task are normally trained and tested on flight load survey data. In many instances, significant portions of the flight data are not used because of labeling uncertainties. Flight test data is expensive to generate, but machine learning-based solutions rely on copious amounts of training data, so the idea of discarding data is unappealing. This paper presents a process to consistently and systematically label flight data with common helicopter regimes that would reduce the amount of unlabeled flight test data. The approach makes use of regime descriptions and parameter time histories to assign labels, which are then verified using flight path and flight test card information. Although the implementation of the approach is challenging, the initial results from Bell 206 test flights demonstrate that this approach can significantly reduce the amount of unlabeled flight data, enabling much more usable data for training algorithms.

Understanding UAS Operator and Aviation Authority Challenges with the SORA Process for UAS Operational Approval in DACH Nations (Paper 12)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Jacquelyn Banas, Matthias Vyshnevskyy, Florian Holzapfel, René Wagnor, Joschka Höfling

The new SORA process for authorization of unmanned flight operations has quickly become an important method and major challenge for UAS operations in and around Europe, particularly in the German-speaking DACH nations. Under the SORA process, UAS operators often experience significantly higher application workloads, costs, and time until authorization. Through a targeted set of industry outreach and data gathering initiatives, the UAV DACH SORA Focus Group sought to understand the challenges faced on all sides of the SORA process. Findings show that SORA applicants are typically very small groups with diverse experience levels, missions, and aircraft - often not from aircraft safety/certification backgrounds. On average, DACH applicants needed nearly six months for full UAS operational approval, and this long time was rated as the most painful element in the SORA process. UAS operators overall support the methodology and vision of the SORA process. With increased clarity in rules and expectations, standardization across regions, availability of aids and training materials, and additional PDRAs and STSs, the SORA process could run much more efficiently and better support the growing complexity of DACH-region UAS operations.

Unmanned Aerial System Handling Qualities Framework Applicability to Heavy Gross Weight Mission-Configured UAS (Paper 106)
Full registrant at Forum? Log in for link!
Handling Qualities I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Christina Ivler, William Geyer, Adam Pua, Connor Possedi

Unmanned Aerial Systems (UAS) are becoming more prominent across both commercial and military applications, and the need to define handling qualities requirements for assessing vertical lift UAS ability to meet mission demands is essential. The UAS handling qualities requirement must be scalable and apply to the wide range of airframe configurations across their operational flight envelopes, due to the increasing variety of unmanned or optionally manned systems. Flying and handling qualities criteria are well defined in ADS-33E-PRF for manned vertical lift aircraft, where the predictive requirements and mission task elements have proven effective on a wide range of aircraft with varying configurations, sizes and loading configurations. A similar robustness is needed in an effective vertical lift UAS handling qualities framework. This paper builds upon previous work towards a scalable vertical lift UAS handling qualities framework by evaluating the robustness of this framework on a representative range of Group 1 UAS in various sizes, configurations, and loading conditions. Two group 1 UAS, a hexacopter (1.8 ft hub-to-hub) and a single main rotor Synergy 626 (4.6 ft rotor diameter) were extensively evaluated with the framework, using two mission task elements each, evaluated across a range of mission and empty weight configurations, with low and high aggressiveness. A third Group 1 UAS, a coaxial (8 propeller) quadcopter (1.83 ft hub-to-hub), was evaluated with the framework in a mission weight configuration at nominal aggressiveness. The key outcomes of the work are updated time-to-complete specifications that are more consistent with waypoint navigation, validation of MTE courses and performance specifications at alternate loading conditions, and validation of the robustness of the Froude-scaled ADS-33E-PRF Level 1 attitude bandwidth and disturbance rejections bandwidth metrics as predictive requirements.

Unsteady Loading Noise Measurements and Predictions for eVTOL Rotors (Paper 1228)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
James Goldschmidt, Lawrence Ukeiley

The induced velocity field of three different sub-scale eVTOL rotors were measured using a newly implemented stereoscopic particle image velocimetry (sPIV) system in the UF Anechoic Wind Tunnel Facility. The measurements were performed in the test section of the open jet wind tunnel for hover and edgewise flight conditions with advance ratios ranging from 0.065 to 0.268. The ensemble averaged sPIV measurements showed that an increase in advance ratio leads to a skewing of the maximum induced velocity towards the advancing side of the rotor disk and an increased area of upwash velocity at the front of the rotor disk. The results were further compared to the induced velocity field modeled with Peters-He Generalized Dynamic wake model. The modeled induced velocity was shown to be in poor agreement to the measured velocity field pointing to the limitations of the cylindrical wake assumption for a fixed pitch rotor in edgewise flight. The measured velocity field was utilized in both blade element theory and Sears unsteady airfoil theory to estimate the unsteady rotor blade forces. These forces were then utilized in an analytical noise model to predict unsteady loading noise and the results showed good agreement to measured sound pressure levels.

Use of Hunting Tooth for Gear Fault Detection (Paper 108)
Full registrant at Forum? Log in for link!
HUMS I (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Eric Bechhoefer

This paper looks at the use of the hunting tooth (HT) time synchronous average (TSA) to improve fault detection on gears. HT analysis is based on the period at which two damaged teeth mesh. The HT frequency tends to be low, requiring a long acquisition in order to calculate the TSA. Because of the long acquisition, the HT TSA may improve the signal-to-noise of some gear fault pairs, such as seen in the epicyclic gearbox planet/ring gear mesh. This study develops two CIs based on the HT TSA from two different data sets. The first data set has been used to quantify the performance of gear algorithms using statistical separability. The second data set is from an OH-58 gearbox that was seeded with a damaged planet gear. Planet gears are typically difficult to analyze as if only one planet has damage, and the fault may be masked by the other good planets, making early fault detection difficult. The proposed CI showed good fault detection and trends for both data sets and was superior for the epicyclic gearbox. The performance of the HT TSA and new CIs is quantified relative to other gear CIs.

Using Intelligent Design to Increase Redundancy Without Sacrificing Efficiency Through Adoption of Passive Lubrication in Reduction Drives (Paper 1405)
Full registrant at Forum? Log in for link!
Propulsion II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Rob Peacey, Lee Rogers

The eVTOL world is generally sceptical of using a transmission in their designs, this is largely due to the misconception that vertical flight requires a complex helicopter-style gearbox. Various styles of reduction drives have been used since the dawn of powered flight and are a viable and reliable option for an eVTOL system. Transmissions will be a key component of eVTOL propulsion systems moving forward. Their ability to match power dense motors to efficient propellers in a compact package space are unparalleled. A key aspect to the reliability and efficient operation is a robust and suitable lubrication system. Gears and bearings cannot operate effectively without this lubrication, which does not have to be complicated or inefficient. DSD will cover the process required to intelligently design a reduction gearbox lubrication system to remain passive, be efficient and robust, eliminating unnecessary complexity for improved reliability.

Validated Technologies to Maintain Spatial Orientation (Paper 1356)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Bruce Mortimer, Jon French, Braden McGrath, Angus Rupert

Maintenance of spatial orientation (SO) is critical for safe military and civilian flight. This work describes the validation of a vibrotactile array that is used to provide continuous orientation information to pilots during flight. Continuous tactile orientation information has the potential to improve the maintenance of SO under conditions of pilot distraction and/or during degraded visual environments. This work summarizes a series of experiments where participants reported their perceived orientation during test flight maneuvers, while under various controlled, sensory reference conditions. During maneuvers where visual, tactile cueing, or information from both combined, all participants maintained spatial orientation. The test flight data were then used to extend a human gravito-inertial orientation biomathematical model that is capable of predicting pilot perceptions resulting from the integration of orientation/motion cues provided by visual, auditory, vestibular, and somatosensory senses.

Validation of a Flexible and Highly Scalable Mid-fidelity Aerodynamic Solver with Wind-tunnel Testing (Paper 1213)
Full registrant at Forum? Log in for link!
Modeling and Simulation I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Enrico Sabatino, Davide Prederi, Fabrizio Petri, Antonio Sciarappa, Carlo Cassinelli, Gregorio Frassoldati

The design process of new VTOL vehicles is a challenging task that demands the synergy of many disciplines, such as flight mechanics, aerodynamics, structural dynamics, loads and aeroelasticity. Within this frame of reference, GyroX is an in-house aeroelastic simulation software developed by Leonardo Helicopters meant to integrate all of the previous disciplines. It hence aims to provide a fast and reliable numerical tool for aeroelastic and aeromechanical simulations of complex rotorcraft configurations. Indeed, GyroX gathers more than 25 years of experience in rotorcraft simulations and lays the way towards a multi-comprehensive tool for aircraft design and analysis.The purpose of this work is to present the tool and to assess the accuracy of a set of aerodynamic mid-fidelity numerical methods available in GyroX, with respect to rotor performances obtained during wind tunnel test campaigns.

Validation of a Motion Sickness Prediction Model via Flight Tests on DLR's Bo-105 Helicopter (Paper 97)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Philippe Petit

In previous work, a motion sickness prediction model aimed at vertical lift applications was developed. To validate this model, flight tests with a MBB Bo-105 Helicopter owned and operated by the DLR were conducted. In total, 32 test subjects were flown in 16 sorties on 30 minute sinusoidal flight paths of various frequencies. The test design and implementation included the development of a suitable measurement flight instrumentation, auditive cueing systems for accurate following of the test trajectory and questionnaires for recording motion sickness during flight. The results are analyzed and it is shown that the previously developed motion sickness prediction model agrees well with the motion sickness observed during flight in the case of medium motion sickness

Verification and Optimisation of Distributed Propulsion Using High-Fidelity CFD Method (Paper 1221)
Full registrant at Forum? Log in for link!
Aerodynamics I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Geng Qiao, George N. Barakos

This work presents CFD verifications and comparisons related to distributed propulsion concepts. The work started with validation studies using experimental data from the NASAWorkshop for Integrated Propeller Prediction (WIPP) and the folding conformal high lift propeller (HLP) projects. The highfidelity CFD results from HMB3 for isolated and installed configurations at different forward flight speeds were compared with experiments. Expanding from that, the second part of the paper examined several configurations of propellers similar to the ones used in modern eVTOL designs to identify performance differences for propellers located at different positions around a lifting wing. Results from different methods show that distributed propellers with a small radius have much stronger interference with the lifting wing compared to the tip-mounted propeller. The interference also depends on the location of the propellers, with propellers placed ahead of the leading edge showing slightly better performance than propellers placed on top of the wing. However, both methods indicate that the wing's performance improved significantly after optimizing the propeller from a traditional tractor configuration to a novel overwing configuration. More specifically, the fully resolved results show that the wing lift-to-drag ratio has totally increased by 69%.

Verifying the Fidelity of the Acceleration in Surge and the Rotational Velocity in Yaw Directions for a Flight Simulation Platform (Paper 54)
Full registrant at Forum? Log in for link!
Crew Stations II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Spencer Miller, Davide Piovesan, Xiaoxu Ji

Flight simulators are training devices that are meant to assist the pilot in learning the mechanics and feel of flying an aircraft without actually leaving the ground. The Stewart platform is a six degree of freedom platform capable of simulation precise movements as well as vibrations. In this paper the fidelity of a Stewart platform will be tested in the surge direction as well as yaw rotation. The fidelity of the platform will be tested to ensure accuracy when being used as a flight simulator to train future pilots before they leave the ground in an aircraft to further prevent potential accidents. The movements for verification will be generated using MATLAB and used as an input to the platform which will collect the movements with a 6 axis inertial movement unit. The results show that the fidelity of the Stewart platform satisfies the standards to be used as a flight simulator training device.

Vertiport Passenger Security Standard (VPSS) (Paper 124)
Full registrant at Forum? Log in for link!
Operations (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Grant Young, Isam Saleh

This technical paper will propose solutions for developing and implementing biometric driven screening processes for both passengers and employees utilizing or working in Vertiport secured areas. We will explore how biometric-based Vertiport Passenger Security can overcome the limitations of existing airport screening processes by improving accuracy, reducing wait times, and enhancing the overall passenger experience. No definitive policies or procedures have been developed to date by regulators.

Vibratory Loads/Stress Analysis and Fatigue Alleviation with Rotorcraft Comprehensive Modeling Tool (Paper 1179)
Full registrant at Forum? Log in for link!
Structures and Materials I (Tues. May 16, 2023 - 8:00 AM to 12:00 PM)
Dooyong Lee, Chengjian He, Mulugeta Haile

The primary cause of rotorcraft component fatigue is the vibratory loads from the rotors. Rotorcraft constantly experience time varying loads even in steady state flight. The source of excitation is the unsteady airloads due to the combined effect of rotor rotation and flight speed. In aggressive flight maneuvers, critical loads are experienced, which may induce large structural stress response and, hence, severely impact the fatigue life of certain critical structural components (e.g., swashplate control pitch link, rotor blades, etc). This paper addresses the application of the FLIGHTLAB high fidelity comprehensive modeling and analysis tool to rotorcraft vibratory loads and stress analysis and active control methods for fatigue alleviation. Through this study, a fatigue reduction controller was designed. The prototyped controller was integrated with FLIGHTLAB and the effectiveness of the control method for fatigue reduction was tested and evaluated for selected critical rotor components (e.g., blade, hub, and pitch link) and flight maneuver conditions.

Visual Localization for Autonomous eVTOL Based on Semantic Map (Paper 1267)
Full registrant at Forum? Log in for link!
Unmanned VTOL II (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Senwei Xiang, Ting Wang, Minxiang Ye, Weimin Yang, Yifei Zhang, Anhuan Xie

The emerging concept of urban air mobility (UAM) and advanced air mobility (AAM) has made autonomous electric vertical takeoff and landing (eVTOL) aircraft a focal point for both academic research and commercial application. Achieving localization without the use of global navigation satellite systems (GNSS) is crucial to achieve full autonomy. In this paper, we present our exploration and progress on visual localization for autonomous eVTOL using semantic maps. By extracting semantic features from bottom-view images of the ground, we can create robust representations of flight routes that enable reliable and accurate localization even in dynamic environments. Taking inspiration from high-precision maps used in self-driving cars, we have designed a three-stage method that leverages massive flight data collected by eVTOLs during regular flights. Through on-board mapping and on-cloud merging, we can build up-to-date semantic maps of flight routes, which is further used for onboard localization. Real-world experiments conducted on an eVTOL prototype named ZJ-Copter show the localization accuracy is less than 2 meters over a flight distance of approximately 2.0 kilometers. We believe that our method has the potential to serve as an alternative localization solution for autonomous eVTOLs.

Watching Weight: Autorotation Insights for a winged Single Main Rotor (wSMR) (Paper 134)
Full registrant at Forum? Log in for link!
Modeling and Simulation II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Mark Lopez, Tom Berger, Ashwani Padthe, Emily Glover

A single main rotor helicopter with a wing is one proposed design for the U.S. Army Future Vertical Lift (FVL) Capability Set 1 (CS-1). The wing is intended to share lift and offload the main rotor, increasing the achievable speeds; however those features come with tradeoffs particularly in autorotation. This work studies single main rotor configurations in autorotation conditions using a range of approaches: simple analytical models, more complex medium-fidelity physics-based flight dynamics modeling, and also examination of flight test data. The analyses are then leveraged to examine the effects of adding a wing to a single main rotor configuration and the tradeoffs for autorotation versus nominal operating conditions. Overall the results show that adding a wing tends to increase the rate of descent for autorotation.

Wind Tunnel Testing and Aeromechanics Predictions on Slowed Mach-scaled Thrust Compounding Rotorcraft with a Trailing Propeller (Paper 1194)
Full registrant at Forum? Log in for link!
Dynamics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
Noam Kaplan, Mrinalgouda Patil, Inderjit Chopra, Anubhav Datta

A thrust compounded helicopter - a main rotor with a trailing propeller was tested in the Glenn L. Martin Wind Tunnel (GLMWT) to evaluate its performance under different flight conditions. The main rotor rig consists of a hingeless hub with four fully instrumented NACA 0012 blades and a modified Robin fuselage. The propeller rig consists of a rigid Sensenich L26H propeller with four blades. Tunnel tests were carried out for the isolated propeller, and thrust compounded rotor configurations. The isolated propeller tests were conducted with and without the fuselage installed ahead of it to understand the effects of the fuselage on propeller performance. The thrust compound configuration was tested at three different main rotor shaft tilt angles (αs): -4°, 0°, and 4°, advance ratios (µ) from 0.3 to 0.6, and multiple lift (CL/σ) and propulsive (CX/σ) trim targets. Main rotor hub loads, oscillatory blade structural loads, and propeller hub loads were measured for all the tests. The test data was verified with a full vehicle aeromechanical analysis using the University of Maryland Advanced Rotorcraft Code (UMARC). The thrust compound configuration with the main rotor shaft tilt of -4° (rearward tilt) provided the best performance. Thrust compounding with rearward shaft tilt (-4°) resulted in a 50% increase in the maximum aircraft lift-to-drag ratio compared to a single rotor helicopter. Half peak-to-peak hub vibratory loads and blade bending loads decreased with thrust compounding. It was observed that for the same lift target (CL/σ), thrust compounding achieved 20% higher flight speeds than a single rotor.

Wind-Tunnel Performance Investigation of an Electric Medium-Sized Variable-RPM Rotor (Paper 1224)
Full registrant at Forum? Log in for link!
Advanced Vertical Flight II (Wed. May 17, 2023 - 8:00 AM to 12:15 PM)
Matthew Floros, Radu Teodorescu, Peter Ryseck, Inderjit Chopra

This paper describes isolated rotor and fuselage testing in the Glenn L. Martin Wind Tunnel at the University of Maryland, College Park. The multi-part test included both steady and transient rotor testing and fuselage aerodynamics testing. A T-Motor 28x9.2 rotor was tested under steady conditions from hover to 35 m/sec wind speeds over a 180-degree range of flow angles from -90 degrees or axial climb to +90 degrees or axial descent. Four steady rotor speeds were tested, 1600, 2300, 3100, and 3900 RPM. Transient rotor data was collected at 15 m/sec tunnel speed with chirp inputs to rotor speed. The aerodynamics of a coaxial quadrotor unmanned aerial vehicle fuselage were also tested. Thrust and torque from the steady isolated rotor testing is presented as sweeps of rotor angle of attack at fixed wind tunnel speeds and sweeps of wind tunnel speed at fixed rotor angles of attack.

eVTOL Modeling Framework for Future Level-D Training Simulators (Paper 135)
Full registrant at Forum? Log in for link!
eVTOL II honoring Alex Stoll (Wed. May 17, 2023 - 1:45 PM to 6:00 PM)
Vincent Myrand-Lapierre, Carlo Ferlisi, Julien Guay, Jaclyn Milne

This paper presents an adapted aerodynamics modeling framework that will be used to develop future Level-D flight training simulators for electric Vertical Takeoff and Landing (eVTOL) aircraft. It enables physics-based multi-rotor models to simulate accurate stability and control characteristics defined by aircraft requirements or determined from system identification techniques using flight test data. For this study, parameter estimation in the frequency domain is used to generate linear state-space 6 degrees of freedom (6-DoF) quasi-steady models from a non-linear physics-based simulation model. A common model structure is formulated to handle the two principal flight configurations, wing-borne and thrust-borne flight, and the transitions between the two. As with fixed wing and rotary wing flight simulators, eVTOL simulators are expected to be qualified using updated Qualification Test Guide (QTG) requirements prior to providing pilot training for these vehicles. This paper focuses on how CAE's modeling framework can be used to develop a platform-agnostic real-time aircraft performance and handling model for pilot training.

eVTOL Rotor Performance and Acoustic Noise Study Using Unified Comprehensive Modeling and Acoustic Analysis (Paper 100)
Full registrant at Forum? Log in for link!
Acoustics III (Thurs. May 18, 2023 - 1:30 PM to 5:30 PM)
SeungJoon Yang, Christopher Ware, Jagdeep Batther, Chengjian He, Dilhara Jayasundara, James Baeder, John Gerdes

A study of eVTOL AAM (Advanced Air Mobility) flight performance characteristics and acoustic signature is performed using a seamless unified comprehensive rotorcraft modeling and acoustic analysis toolkit. This toolkit includes a rotor design optimization function within the framework to support eVTOL modeling, analysis, and design. Parametric studies of both isolated rotor and multi-rotor configurations were conducted featuring design optimization that considered both the rotor performance and the acoustic signature. The utility usage with a dual-rotor configuration is included to validate the prediction accuracy and capabilities of the toolkit for multi-rotor configurations. The tool has been further validated using acoustic test data for an generic eVTOL hexa tiltrotor fly-over. Good correlation of the variation trend between the measured flight test data and the simulation results was seen. Simulation of a full eVTOL air vehicle using the multi-objective optimized rotor design was also performed to demonstrate the usage of the unified tool.