Impact of Design and Operational Parameters on Helicopter Vertical Bounce

Abstract

Vertical bounce is a rotorcraft aeroelastic instability triggered by the feedback interaction between two significantly damped vibration modes: the rotor collective flap mode and the biodynamic vertical oscillation of the pilot's left arm holding the collective lever in the cockpit. The instability can endanger the safety of flight and in some cases led to catastrophic events. This work develops simple yet complete models that allow us to better understand the dependency of the phenomenon on parameters like the flight condition, the characteristics of the aircraft, and the properties of the pilot's biodynamic feedthrough. The stability analyses presented demonstrate that the landing gear dynamics may amplify the vertical oscillations driven by the pilot's biodynamic response when considering on-ground conditions, reducing the stability margins of the pilot–vehicle system. The detailed sensitivity analysis allows inferring indications to develop future rotorcraft that could be less prone to this adverse rotorcraft–pilot coupling phenomenon.