Effect of Rotor Wake Distortion on the Stability of Flapping Dynamics

In this paper, the coupled rotor inflow-wake distortion-flapping dynamics is investigated through coupling a rotor dynamic wake distortion model, the augmented Pitt-Peters dynamic inflow model for maneuvering flight and a rigid blade flapping model. The effect of rotor dynamic wake distortion on the stability of flapping dynamics is studied. It is shown that while a quasi-steady wake distortion model tends to destabilize the high frequency progressive flapping mode, the dynamic wake distortion model keeps the progressive flapping mode stable for the range of values for the wake curvature parameter considered in this study. The augmented Pitt-Peters dynamic inflow model, combined with the dynamic wake distortion model, is implemented in the RIPTIDE flight simulation environment at the Georgia Institute of Technology. Pilot-in-the-loop simulation results are presented to illustrate the impact of wake distortion dynamics on the off-axis response behavior of a helicopter.