Hummingbird-inspired flapping wings composed of multiple flight feathers

Hummingbirds can hover by flapping their wings composed of multiple flight feathers and wings consisting of multiple separate flight feathers are considered robust against collision. However, most of hummingbird-inspired wings developed so far were composed of one membrane and the feathers are not separate. Therefore, in-plane deformation of a hummingbird-inspired wing would be difficult, and the wing would not be easily twisted like a real hummingbird, causing large angle of attack and low efficacy. In this study, we propose a hummingbird-inspired wing composed of multiple separate flight feathers and discuss the difference from one composed of one membrane from the viewpoint of efficacy and angle of attack. First, we fabricated a wing with 8 flight feathers and one composed of one membrane for comparison. Then, we conducted flapping tests for the two wings and measured time-averaged efficacy and angle of attack at 57% wing chord. As a result, there was no difference of time-averaged efficacy between the two wings. However, angle of attack at 57% chord was different between the two wings. A wing with 8 flight feathers maintained lower angle of attack during first half of downstroke and upstroke because of wing twist. However, during last half of each stroke, the angle of attack for a wing with 8 flight feathers was larger. This may be caused by elevation of a wing. By preventing wing elevation, we would be able to realize a wing composed of multiple flight feathers more efficient than one composed of one membrane.