Robust Aeroservoelastic Stability of Helicopters: Application To The Air/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, wear. The robustness of stability analysis is fundamental to determine the amount of freedoma 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 MIMO systems. The proposed method is applied to the air/ground resonance problem, cast in a form that isolates a closed loop containing the lead-lag damper, which is considered the uncertain component. The problem is solved considering 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.