Abstract: In the traditonal flapping-wing aircraft model, most of the wings are two-dimensional rigid wings, and the upswing and downwing processes are completely symmetrical. In order to further improve the aerodynamic characteristics of the flapping-wing aircraft, this paper uses the idea of approximate flexibility to establish the multi-stage wing to achieve the approximate flexibility effect. At the same time, the rapid return characteristic is added to prolong the down-flapping time. And a three-dimensional model of “flutter-twist-bend folding” is proposed by adding the bending-folding motion on the basis of the original movement and twisting motion. The model is imported into Xflow to change the motion parameters of the flapping-wing aircraft model, and the aerodynamic simulation of the flapping-wing aircraft model is carried out. Therefore, the non-linear relationship between the lift coefficient and the trust coefficient of the multi-stage wing and the MDOF (multiple degree of freedom) of the flapping-wing aircraft and the flow velocity, the flapping frequency, the wing initial angle of attack and the inner wing flutter amplitude is obtained.

Key words: bird-like flapping-wing aircraft, multi-stage wing, multiple degree of freedom (MDOF), approximate flexibility, aerodynamic characteristics