ANALYSIS OF BEARINGLESS MAIN ROTOR AEROELASTICITY USING AN IMPROVED TIME-DOMAIN NONLINEAR ELASTOMERIC DAMPER MODEL

An elastomeric damper model comprising a nonlinear spring and a Kelvin chain is augmented to represent experimentally observed degradation i n G '' (damping) at very low dynamic amplitudes, and occurrence of lim it cycle oscillations (jitter) due to applied perturbations. The dampe r model is described in the time domain by a nonlinear differential eq uation. Integration into a bearingless rotor comprehensive analysis re sults in the addition of damper states to the rotor/fuselage state vec tor, and augmentation of the baseline modal mass, damping and stiffnes s matrices, and load vector. The influence of the damper is examined o n bearingless rotor aeroelastic behavior, including aeromechanical sta bility in forward flight. Damper stiffness results in a significant va riation of second lag frequency with advance ratio. The nonlinear char acterization of the damper results in greater stability augmentation o f the lag mode at low advance ratios than at higher advance ratios.