Lead-Lag Damper Robustness Analysis for Helicopter Ground Resonance

Aeroelastic stability is a key issue that drives the design of modern rotorcraft. Rotary wing vehicles may present significant parameter variability and uncertainty related to environment, operating conditions, and wear. The capability for analyzing the robustness of the stability is fundamental to determine the amount of freedom a designer has in defining the key properties in specific rotorcraft problems dominated by stability. This paper discusses robust stability analysis, focusing on the generalization of the computation of frequency-dependent stability margins for multi-input/multi-output systems. The proposed method is applied to the ground resonance problem, cast in a form that isolatesaclosed loop containing the lead-lag damper, whichis considered the uncertain component. The problem is solved for linear and nonlinear models of the damper, illustrating how stability requirements can be used to determine uncertainty bounds on the stiffness and damping properties of the damper.