Abstract: Throughout the previous studies, none of them are involved in analysing the downwash flow effect on the control surface of the Flapping Wing Rotor (FWR). An overset CFD numerical model is built up and validated to study the downwash flow’s effect on the stability of the FWR. After simulation, a cone like self-lock region which acts as the critical condition determining the stability of FWR is found. Only when the flow’s resultant velocity acting on the control surface lies in the stable region, the FWR can keep stable. The size of the cone like self-lock stable region can be enlarged by increasing the maximum feasible deflection angle constrained by mechanical design or enhancing the equivalent downwash flow velocity. Among all the simulated cases, when J?=?2.67 (f=5 Hz, \dot {\psi }=5 r/s), the largest average equivalent downwash flow velocities are found. On the other hand, the recovery torque could be enhanced due to the increase of the arm of the lateral force. According to these simulation results, a 43 g FWR model with two control surfaces and two stabilizers is then designed. A series of flight tests is then conducted to help confirm the conclusion of the mechanism research in this work. Overall, this study points out several strategies to increase the flight stability of the FWR and finally realizes the stable climb flight and mild descent flight of the FWR.

Key words: Flapping wing rotor')">Flapping wing rotor, Downwash flow, Self-lock stable region