Meeting Abstract

104.2  Tuesday, Jan. 7 08:15  Passive wing deformation of hovering hummingbirds TANAKA, H*; SUGA, K; MAEDA, M; KITAMURA, I; LIU, H; Chiba University; Chiba University; Chiba University; Chiba University; Chiba University htanaka@chiba-u.jp

Hummingbirds are known as the only birds which are capable of sustained hovering flight. Unlike the other birds, their upper and lower arm bones are very short and the wings do not fold at the elbow during flight. Since most of the wing surface is composed of flight feathers without muscles, the wing is assumed to passively deform due to aerodynamic and inertia forces. Moreover, overlapping of the sliding feathers could change the wing area. Those wing deformations should affect aerodynamic performance. Here we measured the wing shape of a hovering hummingbird, Amazilia amazilia, with multiple high-speed video cameras. We also fabricated flexible wings consisting of carbon fiber frames and thin polymer films with the same planar shape as the hummingbird wing. The synthetic wings were tested with an electric-powered tethered 1-DOF (degree of freedom) flapping mechanism to observe the passive deformation. It was found that the synthetic wings twisted in a similar way to the up-stroking real wing, indicating that the hummingbird wings passively twist during upstroke. The wing area of the real wing changed by around 20% of the maximum value during a single flapping cycle, which was caused by spreading motions of the flight feathers. Measured lift of the synthetic wing with a relaxed film which produced larger twist matched the weight of the measured hummingbird. Those results suggest that the passive twist of the wing surface and variation of the wing area should be taken into account in the study of aerodynamics and flight performance of hovering hummingbirds.