Wing flexibility and design for animal flight
Combes, Stacey A. (Stacey Anne), 1971-
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The wings of flying animals change shape dramatically during flight, yet the control and effects of these shape changes have received little attention. In Chapter 1, I discuss the potential effects of wing flexibility and dynamic shape changes in flying vertebrates (who can actively control wing shape) and in insects (whose wings deform passively).In Chapter 2 (Combes and Daniel, 2001), we use an unsteady potential flow analysis to explore how unsteady motion and wing flexion affect flight performance. We compare our model predictions to aquatic flight in the ratfish Hydrolagus colliei, and assess the performance of various wing shapes. We find that wing flexibility increases efficiency and interacts with flapping frequency and wing shape to generate local performance optima.In Chapter 3, I explore how insect wing architecture contributes to the control of wing deformations by measuring flexural stiffness (which incorporates both material and structural features) and quantifying patterns of supporting veins in 16 insect species. I find that average spanwise and chordwise stiffness scale strongly with wing size, and that spanwise stiffness is significantly larger than chordwise stiffness. Independent contrasts of stiffness residuals are uncorrelated with contrasts of wing venation traits, but a finite element model of a wing reveals that leading edge veins may generate the spanwise-chordwise anisotropy measured in real wings.In Chapter 4, I estimate spatial variation in flexural stiffness in the wings of a hawkmoth (Manduca sexta) and a dragonfly ( Aeshna multicolor). In both species, stiffness declines sharply (approximately exponentially) from wing base to tip and from the leading to the trailing edge. Finite element models suggest that this pattern of stiffness transfers bending to the edges of the wing.In Chapter 5, I explore the relative contributions of fluid-dynamic and inertial-elastic forces to passive wing deformations by comparing bending in fresh Manduca wings flapped in normal air versus helium (15% air density). I find that a substantial reduction in air density produces only slight changes in bending patterns, and that a simple damped finite element model may be able to predict patterns of wing deformation independent of calculations of aerodynamic force production.
- Biology