Nonlinear Aeroelastic Coupled Trim Analysis of a Twin Cyclocopter in Forward Flight

The paper discusses the development of a nonlinear aeroelastic coupled trim model of a twin cyclocopter in forward flight. The twin cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs [mean and differential revolutions per minute (RPM), mean and differential phase offset of cycloidal rotors, RPMs of nose rotor] are needed to balance three moments and two forces on a cyclocopter in forward flight while forces along the lateral direction remain balanced at all stages. Alternatively, the mean and differential pitch amplitude of cycloidal rotors can be used as control inputs while keeping the RPMs of cycloidal rotors constant. In this coupled trim procedure, blade aeroelastic response equations and vehicle trim equations are solved together by simultaneously updating control inputs and blade response. The present model is validated with previously published data by the authors on the performance of a trimmed cycloidal rotor at different forward speeds. Once systematically validated, the model is used to understand the trim behavior of a micro-air-vehicle-scale twin cyclocopter in forward flight. One major conclusion from this study is that the center of gravity of the vehicle is desired to be as close to the cycloidal rotor as possible in order to decrease the required power.