Robust Stability Analysis of Adverse Aeroelastic Roll/Lateral Rotorcraft–Pilot Couplings

This paper investigates the roll/lateral rotorcraft–pilot coupling, a phenomenon caused by the interaction between the pilot's involuntary biodynamic response on the cyclic stick and the aeroelastic response of the helicopter. Such interaction falls under a class of events, denominated pilot augmented oscillations, that may significantly affect helicopters. This phenomenon was experienced during a piloted flight simulation campaign performed in a flight simulator. An analytical model of the coupled rotorcraft–pilot problem is developed and validated. This model is used to understand the physics that govern this instability and the most influential parameters. The model is subsequently used to perform several sensitivity analyses with respect to basic helicopter design parameters. The stability of helicopters with soft in-plane hingeless main rotor design showed significant sensitivity to the amount of damping in the regressive lead–lag mode. Such a mode may interact with the pilot since it can transmit lateral vibrations to the airframe in the vicinity of the pilot's fundamental biodynamic feedthrough frequency. Furthermore, it is shown that an increase in main rotor loading may reduce the stability margins. The results of the sensitivity analysis give the rotorcraft designer the capability to infer how rotor design may be prone to rotorcraft–pilot coupling and what mitigation actions can be taken.