Validation of Variable Rotor Speed Trim Using Computational Fluid Dynamics

Abstract

A multirotor trim algorithm is developed and validated using the HPCMP CREATE™-AV Helios rotorcraft analysis and simulation framework. Validation data were sourced from experiments in which a quadrotor with fixed-pitch rotors was trimmed for steady hover and forward flight in the NASA Langley Low-Speed Aeroacoustic Wind Tunnel. For each flight condition, the aircraft attitudes were fixed so that the only control variables were the rotation rates of the four rotors, which were varied until the residual loads were minimal. The resultant trim states were first replicated in the computational framework to verify the aerodynamic solver. Then, the trim algorithm was validated in Helios by constraining the aircraft attitudes and searching for the rotor speeds that minimized the residual loads. The analysis demonstrated excellent agreement between the predicted and measured trim states. Finally, free-flight trim cases were simulated to quantify the effect of the trim constraints and verify the experimentally trimmed flight conditions. The predicted free-flight trim state showed reasonable agreement to the constrained case, with negligible change in the residual loads, indicating trim was achieved in both the experiments and the simulations.