ANALYTICAL MODEL FOR A NONLINEAR ELASTOMERIC LAG DAMPER AND ITS EFFECT ON AEROMECHANICAL STABILITY IN HOVER

A new nonlinear elastomeric damper model, based on a combination of linear and nonlinear springs and dashpots, is developed, The damper is characterized completely by a nonlinear constitutive differential equation, Since this ''differential equation approach'' is not based on the frequency- and amplitude-dependent complex modulus components, it can conveniently be used in a variety of operating conditions, including multi-frequency excitations, varying rotor speeds, and different steady-lag angles, A methodology is developed for the inclusion of such a damper model into a rotor analysis scheme, For aeromechanical stability analysis, the damper perturbation equation is solved along with the blade and fuselage equations, with damper-force appearing as an independent state, The elastomeric damper has a stabilizing influence on ground resonance and hover air resonance regressive lag modes, The eigensolution damping estimates overpredict the damping when the system is subjected to larger perturbations. Steady lag angle has a significant influence on the elastomeric damper behavior and can change the regressive lag mode damping by 50% for ground resonance and 80% for air resonance in hover.