A growing body of evidence indicates that a majority of insects experience some degree of wing deformation during flight. With no musculature distal to the wing base, the instantaneous shape of an insect wing is dictated by the interaction of aerodynamic forces with the inertial and elastic forces that arise from periodic accelerations of the wing. Passive wing deformation is an unavoidable feature of flapping flight for many insects due to the inertial loads that accompany rapid stroke reversals—loads that well exceed the mean aerodynamic force. Although wing compliance has been implicated in a few lift-enhancing mechanisms (e.g., favorable camber), the direct aerodynamic consequences of wing deformation remain generally unresolved. In this paper, we present new experimental data on how wing compliance may affect the overall induced flow in the hawkmoth, Manduca sexta. Real moth wings were subjected to robotic actuation in their dominant plane of rotation at a natural wing beat frequency of 25 Hz. We used digital particle image velocimetry at exceptionally high temporal resolution (2,100 fps) to assess the influence of wing compliance on the mean advective flows, relying on a natural variation in wing stiffness to alter the amount of emergent deformation (freshly extracted wings are flexible and exhibit greater compliance than those that are desiccated). We find that flexible wings yield mean advective flows with substantially greater magnitudes and orientations more beneficial to lift than those of stiff wings. Our results confirm that wing compliance plays a critical role in the production of flight forces.
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The authors would like to thank Dr. Dana Dabiri (University of Washington) for his assistance with PIV methods, and two anonymous reviewers for providing helpful comments on this paper. This work was supported by DARPA and the Komen Endowed Chair to T.D., and a National Science Foundation Graduate Research Fellowship to A.M.
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Mountcastle, A.M., Daniel, T.L. Aerodynamic and functional consequences of wing compliance. Exp Fluids 46, 873 (2009). https://doi.org/10.1007/s00348-008-0607-0
- Particle Image Velocimetry
- Flexural Stiffness
- Digital Particle Image Velocimetry
- Stroke Plane
- Wing Kinematic