The purpose of this investigation is to clarify the generation mechanism for the aerodynamic force from the flapping wings of insects. In this investigation, a quantitative analysis of vortex field around a dragonfly and an instantaneous aerodynamic force were measured directly using a dynamic PIV and a micro-load cell system. The experimental result showed that the feathering angle of the wing was kept at small value, which generated the leading-edge vortices in downstroke process. The negative pressure field of the leading-edge vortices makes large aerodynamic force in the downstroke process. In the upstroke process, the angle of attack of the flapping wing was smaller than that of the downstroke process. As a result, vortices were not generated, and then the negative aerodynamic force was reduced. These results revealed that the constant feathering angles of both processes play an important role in the aerodynamic force generated by the flapping wings of insects. Moreover, it indicated that the control of the feathering motion is key technology for the development of flapping-Micro Air Vehicles.
