Deformation and Performance Measurements of MAV Flapping Wings

Abstract

If bumblebees and hummingbirds could speak to us, could they tell us how they fly? Probably not. “How they fly” has been a fascinating question to biologists and aerodynamicists. Recently, attention is directed to micro air vehicle (MAV) research, which is aimed to develop sub 150 mm wingspan aircraft for reconnaissance and surveillance. The hummingbird poses as a perfect emulation target: they can dash like a jet fighter, hover like a helicopter, and they are on the MAV length scale. Warrick et al.¹ examined the aerodynamics of hummingbird hovering with digital particle image correlation to capture the airflow structure. The authors found that the hummingbird’s upstroke and downstroke are not symmetrical in producing lift (thrust): the downstroke responsible for about 75% of the body weight and the upstroke about 25%. This is very different from insects, which have a more symmetrical load distribution. The differences are results of wing kinematics and structure. If a robotic hummingbird or insect is to be developed, understanding the causal relationship between kinematics, deformation and aerodynamics is essential. On the other hand, Tobalske et al.² documented the kinematics of hummingbirds in forward flight at different speeds. The authors used a few parameters to described wing trajectories and angles. However such description may be considered insufficient for reconstructing the same kinematics. Therefore, in order to facilitate the research of flapping wing MAVs, an experimental method that can describe the complete wing kinematics and deformation, and correlate with aerodynamic loads, is called for. This paper presents an experimental technique for studying hummingbird-size flapping wings in MAV research. A sophisticated experimental setup featuring a customized digital image correlation system is described; several anisotropic flexible membranous wings are tested and post processed results are presented.