Aerodynamic Characteristics Of Flexible Flapping-wing Micro Aerial Vehicle

Compared with the traditional fixed-wing and rotary-wing micro aerial vehicles, the main characteristic of flapping-wing micro aerial vehicle (FMAV) is that the lift and thrust are produced at the same time. FMAV can complete distance flight with very little energy, at the same time with high efficiency, high mobility, low noise, no need special sites to take off or land. All the biology that could fly in the nature adopt flapping-wing flight mode without exception. Therefore, it has a wide application foreground to development FMAV, such as environmental monitoring, battlefield reconnaissance, battlefield attack, communications relay, the exploration of Mars, and so on, all of the new achievements in this fields are very concerned by every countries.In the biosphere, the movement of flapping-wing is extremely complex, and much debate is existed in the effect of flexible wing on the aerodynamics at present. In this paper, a membrane FMAV designed by Nanjing University of Aeronautics and Astronautics was studied, the main work is as follows:Firstly, the flight mechanism of birds and insects was analyzed based on the structure of their wings, the foundation of theory and bionics are provided for the FMAV.Secondly, new formulations of lift and thrust were derived based on the three-dimension unsteady vortex lattice method. The formulations that based on vector analysis and considered the factor of the induced drag can estimate adequately the lift and thrust of flapping-wing through comparing with the experimental data.Thirdly, the effect of instantaneous shape velocity ?η/?t on aerodynamics was analyzed. Because the deformations were existed in the flexible structural flapping-wing during flapping process, in order to approach the real flapping situation, an expression of ?η/?t was proposed and its effect to lift and thrust of flapping-wing was calculated. It is found through the calculation that, as ?η/?t increases, the positive peak value and negative peak value of Cl and Ct increase, and the average lift and thrust increase too. It indicates that the structural parameters of flapping-Wing also affect the aerodynamic performance.Fourthly, the inertial force and aerodynamics of membrane FMAV in one cycle were compared, and found their ratio is about 2. The boundary condition of fixed support in body-fixed coordinate system was put forward, and the finite element method was used to calculate the deformations that respectively caused by inertial force and aerodynamics. A conclusion can be found that the deformation caused by the aerodynamics should not be overlooked. The maximum positive deformation caused by the composition of inertial forces and aerodynamics occurs at the start phase of downstroke, and the maximum negative deformation occurs at the start phase of upstroke. The study provides a foundation of mechanic analysis for the design of membrane FMAV.Last, the unsteady lift and thrust were calculated of flexible FMAV. The result of calculation is reliable through comparing with the experimental data. Compared with rigid flapping-wing, membrane flapping-wing affects the lift little, but increases the thrust because the positive peak value of thrust increases greatly. Thus the aerodynamic performance of flapping-wing aerial vehicles is improved. The study can possess the guide acting for the design of flexible membrane FMAV.