AbstractAn experimental study was conducted to assess the aerodynamic benefits of flapping flight compared with fixed-wing soaring flight for the development of flapping-wing Micro-Air-Vehicles (MAVs). The time-averaged aerodynamic performances (i.e. mean lift and thrust/drag) of two flexible membrane wings with different skin flexibility (i.e., a flexible nylon wing and a very flexible latex wing) were compared with that of a conventional rigid wing to evaluate the effects of skin flexibility of the tested wings on their aerodynamic performances for flapping flight applications. The measurement results revealed clearly that, for all the tested wings, flapping motion would bring significant aerodynamic benefits when the flapping flight is in unsteady state regime with advance ratio (i.e., the ratio of forward flight speed to wingtip velocity) of the flapping flight being smaller than 1.0. The aerodynamic benefits of flapping flight were found to decay rapidly as the advance ratio increases. The skin flexibility of the tested wings was found to have considerable effects on their aerodynamic performances for both soaring and flapping flights: The flexible membrane wings were found to have better overall aerodynamic performance (i.e., lift-to-drag ratio) over the rigid wing for soaring flight, especially for high speed soaring flight or at relatively high angle of attack. The rigid wing was found to have better lift production performance for flapping flight in general. The latex wing, which is the most flexible among the three tested wings, was found to have the best thrust generation performance for flapping flight. The less flexible nylon wing, which has the best overall aerodynamic performance for soaring flight, was found to be the worst for flapping flight applications.