Animal wings are lightweight and flexible; hence, during flapping flight their shapes change. It has been known that such dynamic wing morphing reduces aerodynamic cost in insects, but the consequences in vertebrate flyers, particularly birds, are not well understood. We have developed a method to reconstruct a three-dimensional wing model of a bird from the wing outline and the feather shafts (rachides). The morphological and kinematic parameters can be obtained using the wing model, and the numerical or mechanical simulations may also be carried out. To test the effectiveness of the method, we recorded the hovering flight of a hummingbird (Amazilia amazilia) using high-speed cameras and reconstructed the right wing. The wing shape varied substantially within a stroke cycle. Specifically, the maximum and minimum wing areas differed by 18%, presumably due to feather sliding; the wing was bent near the wrist joint, towards the upward direction and opposite to the stroke direction; positive upward camber and the ‘washout’ twist (monotonic decrease in the angle of incidence from the proximal to distal wing) were observed during both half-strokes; the spanwise distribution of the twist was uniform during downstroke, but an abrupt increase near the wrist joint was found during upstroke.
Hummingbirds are promising reference for small flying robots in terms of their excellent ability to hover. Wing kinematics and shape of a hovering hummingbird were measured with four high-speed video cameras. Four types of wing models consisting of carbon fiber rods and polymer membranes with the same planform as the hummingbird wing were fabricated. 1-degree-of-freedom (DOF) flapping experiments with the wing models were performed, where the wing deformation and vertical force (hereafter called 'lift') were measured. The model wings demonstrated similar feathering deformation as that of the hummingbird in the upstroke. In addition, the model wing with a loosened membrane which caused larger feathering deformation produced lift enough to support the weight of the hummingbird. The results suggest that hovering hummingbirds could be modeled as a pair of 1-DOF flapping wings with a thin membrane which passively feathers.
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