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 in G″ (damping) at very low dynamic amplitudes, and occurrence of limit cycle oscillations (jitter) due to applied perturbations. The damper model is described in the time domain by a nonlinear differential equation. Integration into a bearingless rotor comprehensive analysis results in the addition of damper states to the rotor/fuselage state vector, and augmentation of the baseline modal mass, damping and stiffness matrices, and load vector.The influence of the damper is examined on bearingless rotor aeroelastic behavior, including aeromechanical stability in forward flight. Damper stiffness results in a significant variation of second lag frequency with advance ratio. The nonlinear characterization of the damper results in greater stability augmentation of the lag mode at low advance ratios than at higher advance ratios.