Abstract:
Active control systems for external load operations have been an area of interest in research and development in recent years because of their potential to improve load damping and precision placement. However, the damping performance of these systems can be sensitive to the sling length, and therefore knowledge of sling length can improve the performance for active control of external loads. It would be advantageous to enable accurate real-time identification of the sling length from measurements of the external load motion. This reduces complexity of the active external load control system, as compared to directly measuring or inputting the sling length, because it does not require any operator input or communications with other systems (such as the helicopter or hoist). This paper is focused on development and validation of sling length estimation methods using collocated inertial measurement units that are fixed to the load. These methods are validated against data collected onboard the Load Stabilization System, an active external load control device, which is being developed by Vita Inclinata Technologies. A selection of real-time time-domain and frequency-domain system identification techniques were adapted for use in sling length identification. These methods were then compared against flight and simulation data. The results show that batch frequency domain methods were most effective in real time system identification of sling length.