Aeromechanical Stability and Response of Helicopters with Interblade Elastomeric Dampers

A model of a helicopter with an interblade damper rotor system is developed. The model includes rigid blade flap-lag-torsion motions, all possible kinematic damper attachment offsets from the blade hinge, a nonlinear elastomeric damper model, and fuselage pitch and roll motions. The damper attachment offsets are necessary to correctly model the damper 1/rev motion and loads. A baseline rotor analytical model is modified by attaching traditional blade-to-hub dampers from blade-to-blade and reducing their size. The ground resonance behavior of the interblade damper system is studied and comparisons are made between the current damper kinematics model, and a model used in previous research that included only spanwise attachment offsets. The interblade configuration is shown to be stable from ground resonance even with the reduction in damper size. In the on-ground condition, the difference between the damper kinematics models is insignificant because the damper 1/rev motion is not a factor. In forward flight, there is a 2% to 3% increase in predicted regressing lag mode damping for the current kinematics model compared to the previous model. This increased damping is due to the decreased “dual-frequency” effect on the damper – a direct result of the decreased 1/rev damper motion resulting from the appropriate selection and modeling of the damper attachment offsets.