Control of ground resonance in helicopters using semi active damping

Ground resonance is an aero-mechanical instability that occurs in soft in-plane rotors where there is a coalescence of low frequency lead-lag motions of the blade with that of the frequencies of the fuselage, when on ground. Such a coalescence results in violent oscillations of the fuselage and can prove catastrophic to the helicopter if not reduced in time. The present work focuses on a nonlinear control strategy to alleviate ground resonance in helicopters. In this work, a magnetorheological (MR) fluid based semi active damper is proposed. Nonlinear dynamic inversion based control law is designed to monitor the voltage of the MR damper directly based on the feedback from the blades. The damper dynamics is integrated into the classical ground resonance model and its performance is assessed to control the unstable rotor.