Optimal flapping wing shape and kinematics are different for different flight velocities: an analysis on local relative wind

Abstract

Different species of insects and birds fly differently. Their wing forms and wing motion are different. Understanding the purpose of this difference will lead to successful development of flapping wing vehicles for different purposes. This paper discusses the influence of one of the important factors which affects the aerodynamic performance of a flapping wing: the local instantaneous relative wind. Its distribution along the span of a flapping wing has been analyzed for the practical flight range of advance ratios ranging from 0 to 1.5 and stroke plane orientations ranging from 0 to 90°. In this domain, the variation of spanwise distributions of magnitude and direction of relative wind are presented separately for downstroke and upstroke of a flapping cycle. Accordingly, qualitative suggestions are given for wing planform design, orientation and twist of the wing, and actuation of wing for effective utilization of the relative wind and obtaining the necessary force distributions for different flight phases. The formulation presented will be helpful for experimenting flapping wings in hovering and forward flight; especially for setting the wing twist for a required angle of attack distribution and designing the flapping kinematics in upstroke and downstroke.