Modeling the influence of inter-blade connections and variable rotor speed on the aeromechanical stability of a helicopter

A method of modeling the effect of inter-blade connections and variable rotor speed on the aeromechanical stability of helicopters is presented. The model incorporates twelve degrees of freedom. The new effects that are investigated in the present study result in a system of equations of motion that the usual Multiblade Coordinate Transformation (MCT) cannot deal with. Therefore, suitable coordinate transformations are defined: The Modified Multiblade Coordinate Transformation (MMCT) and the Extended Multiblade Coordinate Transformation (EMCT). These transformations are derived and their implementation is presented. A large part of the derivation is carried out using a symbolic algebra software. An eigenvalue analysis of the final linearized transformed equations defines the aeromechanical stability. Finally some preliminary results are presented that help in validating the model and pointing out the importance inter-blade connections and variable rotor speed can have on the dynamics of the system.