Aeroelastic Rotorcraft–Pilot Couplings in Tiltrotor Aircraft

Abstract

This work investigates rotorcraft–pilot coupling phenomena in tiltrotor aircraft. A detailed tiltrotor model, representative of the Bell XV-15, has been built. Biomechanical models of the pilot, acting on the power lever and on the center stick, are included in feedback loop to define the pilot–vehicle system. Pilot-assisted oscillation phenomena are investigated on the overall conversion corridor using Nyquist’s criterion. Pilot-in-the-loop analyses demonstrate that a critical parameter is detected in the vertical tail geometry. For an asymmetric deflection of the flaperons, the wing’s wake impacts on the vertical tail, producing a side force. The pulsating tail-side force makes the fuselage yaw and excites the asymmetric wing chord mode coupled with the lateral pilot’s biomechanics, leading to a reduction, and in some cases to a loss, of stability. No possibility of unstable events is detected in the longitudinal direction. Conversely, a resonance between the pilot’s biomechanics and the aircraft poorly damped symmetric wing bending mode is predicted along the vertical axis. The vertical bounce instability is found along the whole conversion corridor, although the source of excitation changes according to the nacelle angle. Means of prevention are implemented and discussed.