Analysis Methods for Ground Resonance in Partial Ground Contact

Abstract

Soft-in-plane rotor systems are susceptible to a self-induced vibration phenomenon called ground resonance. This dynamic instability results from lag motions of the rotor blades coupling with airframe degrees of freedom while the helicopter is in ground contact. As an addition to previous studies of nonlinear landing gear effects, this work presents the Matrix Pencil Method as a useful additional tool for signal analysis of perturbed nonlinear systems. Contrary to simple logarithmic decrements of decaying time-series, the Matrix Pencil Method allows additional insight into the underlying structure. This makes the method interesting for ground resonance. Additionally, the Lyapunov Exponent Method is introduced to highlight and analyze nonlinear effects in helicopter substitute models.