COMBES, S.A.*; TRIMBLE, A.C.; DANIEL, T.L.: Spatial profiles of wing stiffness in hawkmoths and dragonflies

Insect flight performance depends strongly on the dynamic geometry of wings. The curvature of the trailing edge, in particular, is a crucial determinant of aerodynamic force generation. In insects, wing curvature results from the instantaneous interaction between aerodynamic forces and bending stiffness. If bending stiffness varies spatially, then regional flow control is possible, suggesting a passive mechanism of stability. To examine this structural heterogeneity and its consequences for flight aerodynamics, we characterize spatial variation of wing flexural stiffness in both the spanwise and chordwise direction of insect wings. We measure the surface shape of wings by multiple laser ranging techniques, and then calculate flexural stiffness along the wing by comparing the surface shape of wings before and after loading the tip with a known force. We compare the spatial distribution of wing stiffness in the hawkmoth, Manduca sexta, and an aeshnid dragonfly, Aeshna multicolor. These insects, both excellent fliers, differ greatly in wing shape and venation pattern. Despite such morphological differences, we find that the profile of flexural stiffness in the spanwise direction is remarkably similar in both species, with a peak in stiffness located between 1/3 and 1/2 of wing span, and a sharp drop in stiffness (~2 fold) past this point. In contrast, chordwise stiffness differs in the two species; in Manduca, stiffness falls sharply towards the trailing edge, while the dragonfly does not display this abrupt drop. Thus, trailing edge curvature and chordwise flow may differ significantly in these species.