A wind tunnel test and numerical simulation on a flapping wing with a passive non-symmetrical wing flexure

Because of the potential use of micro air vehicles, the flapping wing mechanism has generated a great deal of interest. To understand the effect of the flexure of bird wings, a mathematical model of a patented flapping wing with a wing flexure is built and then investigated systematically by a wind tunnel experiment and numerical computation. In the computation the deflection angle of the outer wing is decided by the unsteady aerodynamic forces, the elastic moment and the inertia force. The experiment and computation results indicate that the wing flexure can increase the average lift of the flapping wing. Within a certain range, the larger the flapping frequency of the inner wing is, the greater the average lift coefficient will be. But the average drag coefficient is weakly dependent on the inner wing flapping frequency. The flapping wing with a wing flexure consumes less energy than that without a wing flexure in a flapping cycle. The force curves may account clearly for the differences of aerodynamics between a flapping wing with and without a wing flexure. Therefore it is very important to consider adopting a wing flexure in flapping wing design.