Helicopter aeroelastic response and stability using a refined time domain elastomeric damper model

A new nonlinear time domain elastomeric damper model is developed for use with helicopter rotor analyses. A methodology is developed for integrating the new time domain damper model with a helicopter rotor aeroelastic response and stability analysis. Damper finite element equations are coupled with rotor blade equations of motion and analyzed simultaneously. Analytical tools are developed for determining steady state response, stability, and transient response of the combined system. The new damper model is shown to be an improvement over traditional complex modulus models and first generation time domain models. In hover, the new model exhibits significant low amplitude nonlinearity: as the amplitude decreases, the lag frequency increases by 60% and the damping decreases by 85%. In forward flight, the model shows a decrease in damping of approximately 50% due to 'dual-frequency' motion. Damper response and loads are also examined. For certain flight conditions, the damper loads predictions of various models differ significantly. A complex modulus model predicts a 90% higher peak dynamic dampler load than the current model. A baseline ('first generation') time domain predicts 40% lower peak damper load. Basic damper sizing (design) issues are also examined. For an increase in damper area while maintaining the design dynamic lag stiffness, the current damper model predicts an increase in static lag angle. A complex modulus model does not capture this effect. A reduced damper operating strain range increases damping in forward flight, but reduces low-amplitude damping in hover, and can only be achieved by significantly increasing the damper size.