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Flexible and coupled structural systems during avian wing morphing Wong, Jasmin

Abstract

Birds are incredibly successful animals that can be found on every continent on this planet across a large range of habitats and atmospheric conditions. This success can be attributed, in part, to wing morphing, passive or active changes in wing shape, during flight to enable good flight performance during changing environmental conditions or behavioural needs. The morphing wings that facilitate this adaptive flight ability is a structural system with a variety of flexible biological components. It is currently unknown how the structure of one of these components, the flight feathers, and their interaction with neighbouring feathers and active musculoskeletal components can affect aerodynamic performance. First, we used geometric morphometrics on feather specimens from multiple species to quantify shape variation and then used a computational aerodynamic toolkit to evaluate the aerodynamic performance of each feather shape. We found that the lift slope explained more feather shape variation than the feather’s location on the wing, the feather type, or phylogenetic relatedness. Second, we did dynamic mechanical analysis testing on a feather in the distal wing (P9) near the leading edge and a feather in the proximal wing (P1) near the wrist joint in an extended and folded wing with and without neighbouring feathers present. We found that wing folding slightly decreases feather-anchoring tissue stiffness, but this is overcome by an increase in stiffness in the proximal wing via feather-feather interaction. Damping was consistently high within a wing and independent of wing shape. Finally, we used computational fluid-structure interaction simulations to evaluate the effect of varying stiffness during wing morphing on aerostructural responses and flight performance. We found that aerodynamic performance can be improved by the synchronization between structural deformations and flow vortices, and that as a bird folds its wings for higher speed glides, the increase in stiffness through feather-feather interaction resulted in greater lift production. Taken together, we propose that the avian wing structural system allows for the coupling of passive flight feathers to a simple active musculoskeletal system for aerostructural flow control and performance enhancement over a large range of flight speeds. Supplementary material(s) available at: http://hdl.handle.net/2429/81486

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