AEROELASTIC RESPONSE AND STABILITY OF HELICOPTERS WITH ELASTOMERIC LAG DAMPERS

An analytical model capable of studying the aeroelastic response and s tability of helicopter rotor systems incorporating elastomeric dampers has been developed. The rotor is idealized as a rigid blade with flap , lag, torsion, and damper degrees of freedom. The elastomeric damper is modeled using a recently developed time-domain finite element techn ique based on the method of Anelastic Displacement Fields (ADF). The d amper model preserves the strain-dependent nonlinear behavior, charact eristic of elastomeric materials. The potential of the new approach is explored through a single element model of an elastomeric lag damper in simple shear. The blade degrees of freedom are augmented by the dam per degrees of freedom. The blade and damper responses are discretized about the azimuth using a finite-difference formulation. The nonlinea r coupled blade and damper equations are solved by the Newton-Raphson iteration process. Linearized stability of the rotor system is evaluat ed using an eigenvalue analysis based on Floquet theory. Results are p resented for both soft-inplane and stiff-inplane configurations. The n onlinear behavior of the elastomeric damper is seen to have a signific ant effect on lag mode stability in hover and forward flight. The deta ils of damper response in forward night vary significantly with blade loading and advance ratio; damping appears to increase with dynamic la g amplitude. This work provides a framework for continuing research on elastomeric dampers and their effects on rotor performance and stabil ity.