Meeting Abstract

21.6  Sunday, Jan. 4  Wing stiffness affects mean advective flows of Manduca sexta, with wing overlap a potential contributor MOUNTCASTLE, A.M.*; TULL, C.; DANIEL, T.L.; University of Washington mtcastle@u.washington.edu

Many insects have wings that bend and twist during flight, often with dramatic deformations. The pattern and extent of deformation are dependent on wing flexural stiffness and the boundary conditions that govern actuation. Prior work has shown that the extent of deformation during hovering in Manduca can vary between strokes. The aerodynamic consequences of wing compliance, however, remain largely unknown. In this study, we examined the effects of wing stiffness on the overall induced flow in the wings of the hawkmoth, Manduca sexta. We subjected moth wings to robotic actuation in their dominant plane of rotation at the natural wing beat frequency of 25 Hz. We used digital particle image velocimetry at high temporal resolution (2,100 fps) to assess the influence of wing stiffness on the mean advective flows of three wings, each tested in a fresh, flexible state and a desiccated, stiff state (overall spanwise flexural stiffness increased 2-2.5x). We find that flexible wings yield mean advective flows with total magnitudes 2-4x those of their stiff wing counterparts, and vertical (lift-favorable) components that are 7-31x those of stiff wings. If flight forces are sensitive to wing deformation, then any mechanism that alters deformation is a potential source of flight control. We show that the overlap between forewing and hindwing can vary by 15% during ventral stroke reversals in Manduca. Flexural stiffness tests on extracted wing pairs reveal that overall spanwise stiffness can increase by a factor of 1.3 for a similar change from min. to max. wing overlap. Our results show that wing compliance may play a critical role in the production of insect flight forces, and suggest the possibility that wing overlap may affect compliance.