Rotor cross-tilt optimization for yaw control improvement of multi-rotor eVTOL aircraft

Manned multi-rotor electric Vertical Takeoff and Landing (eVTOL) aircraft is prone to actuator saturation due to its weak yaw control efficiency. To address this inherent problem, a rotor cross-tilt configuration is applied in this paper, with an optimization method proposed to improve the overall control efficiency of the vehicle. First, a flight dynamics model of a 500-kg manned multi-rotor eVTOL aircraft is established. The accuracy of the co-axial rotor model is verified using a single arm test bench, and the accuracy of the flight dynamics model is verified by the flight test data. Then, an optimization method is designed based on the flight dynamics model to calculate an optimal rotor cross-tilt mounting angle, which not only improves the yaw control efficiency, but also basically maintains the efficiency of other control channels. The ideal rotor cross-tilt mounting angle for the prototype is determined by comprehensively considering the optimal results with different payloads, forward flight speeds, and rotor mounting angle errors. Finally, the feasibility of the rotor cross-tilt mounting angle is proved by analyzing the control derivatives of the flight dynamics model, the test data of a ground three Degree-of-Freedom (3DOF) platform, and the actual flight data of the prototype. The results show that a fixed rotor cross-tilt mounting angle can achieve ideal yaw control effectiveness, improving yaw angle tracking and hold ability, increasing endurance time, and achieving good yaw control performance with different payloads and forward speeds.