Abstract:
A joint acoustic flight test was conducted by NASA Langley Research Center and the U.S. Army Combat Capabilities Development Command Aviation & Missile Center, with the goal of investigating new methods for acoustic data collection. The impetus for the effort is the anticipated growth of Urban Air Mobility and Future Vertical Lift vehicles. Many of these vehicles are expected to have distributed propulsion systems that may result in unsteady vehicle state conditions even during steady flight. This work examines the acoustic measurements collected during purposefully unsteady maneuvers performed by an MD530F helicopter. A snapshot microphone array design was deployed for this test to capture the acoustic signature on the ground from the helicopter under maneuver conditions. An analysis of the acoustic emissions indicated the presence of blade-vortex interactions, not only during the rolls towards the advancing side of the main rotor, but also rolls towards the retreating side and during pitch-up maneuvers. The strength of the interaction noise was found to be strongly dependent on the acceleration of the vehicle.