Abstract: An improved nonlinear VKS model of an elastomeric lag damper based on complex modulus is presented in order to predict its nonlinear characteristics with respect to dynamic amplitude undergoing single and dual frequency excitations. The regressive lag modal damping with respect to advance ratio is resolved by Floquet transform matrix technology. Compared with hovering flight conditions, the complex modulus of elastomeric lag damper is significantly reduced in forward flight arising from the damper undergoing dual frequency motion. For light and heavy load conditions, the loss mode have about, respectively, 50% and 60% decrements in forward flight in comparison with hovering flight. Consequently, as helicopter flies from hovering to forward flight, the regressive lag modal damping has about 30% decrement for light load condition and about 37% decrement for heavy load condition.

Key words: helicopter, air resonance, elastomeric lag damper, nonlinear characteristic