Analysis on controllability and stability of quad-tilt-rotor aircraft in helicopter mode

The controllability and stability of quad-tilt-rotor aircraft in helicopter mode are modeled and analyzed, which will provide a theoretical guidance for the subsequent control system design. First of all, the flight dynamics model is established considering rotor-wing interference and verified with relevant experiments. Then, a control strategy for helicopter mode is proposed with trim characteristic analysis. Finally, corresponding control efficiency and cross coupling are calculated and analyzed along with characteristics of the stability derivatives and eigenvalues. The results show that the value of heading control efficiency is much smaller than that of other channels. The longitudinal force and pitch moment caused by vertical control input increase with the increase of the velocity. Yawing moment caused by lateral control input shows similar variations. The velocity stability becomes worse with the increase of the velocity. The stability of all other modes is augmented as velocity increases except the spiral mode