Meeting Abstract

69.6  Jan. 7  Compliant wings and the evolution of gliding in vertebrates BISHOP, K.L.*; SWARTZ, S.M.; BREUER, K.; TIAN, X.; Duke University; Brown University; Brown University; Brown University klb23@duke.edu

Gliding flight is often regarded as a simple, primitive form of locomotion and has consequently attracted little scientific attention as a form of locomotion in its own right. However, gliding has evolved independently at least twelve times in vertebrates, including representatives in each vertebrate class. Studies of the performance of gliding vertebrates indicate that many of them achieve shallow glides and can travel substantial distances. Kinematic studies have shown that gliding mammals use extremely high angles of attack, beyond the angles at which airplane wings would typically stall, yet generate much higher lift coefficients than expected for stalled wings. Part of the explanation for this lies in lift-enhancing properties of low aspect ratio wings, but another part lies in the properties of flexible, extensible membrane wings. To investigate the relative performance of flexible and rigid wings, we measured aerodynamic forces produced by physical models of wings in a wind tunnel. In addition, we used high-resolution video of membrane wings to measure deflections across the wing surface under aerodynamic loading. Membrane wings generated higher lift coefficients than rigid wings at all angles of attack. Moreover, flexible wings had a “softer” stall, with lift decreasing with increasing angle of attack beyond the stall angle at a lower rate than in rigid wings. Imaging results show that the amplitude of wing deformations increases and that wing camber decreases around the stall angle, both of which may contribute to the �soft� stall. We suggest that compliant skin is exceptionally well suited to a role as a lift generating surface and may render more likely the repeated evolution of gliding in vertebrates.