The effect of nonlinear elastomeric lag damper characteristics on helicopter rotor dynamics

Many helicopters use elastomeric lag dampers to prevent ground resonance and aeromechanical instability in hover and forward flight. Recent experimental results have shown that when the damper motion occurs at two superimposed frequencies, which is characteristic of operation in forward flight, the damper properties are not well-predicted by a superposition of the damper properties at each of the motion frequencies. This paper presents experimental data obtained with an elastomeric damper while it was undergoing single- and dual-frequency motion. The effect of the nonlinear dual-frequency damper characteristics on predicted rotor aeromechanical stability in forward-flight operation in a wind tunnel was evaluated using the comprehensive rotorcraft analysis program called CAMRAD.