Abstract
Flapping-wing small flying robots inspired from natural flyers have a potential for high maneuverability and high aerodynamic performance in low-Reynolds-number flow regime. To generate sufficient aerodynamic force in hovering flight, the wings should not only flap but also feather (i.e. rotate around the spanwise axis of the wing) in order to maintain appropriate angle of attack. In this study, we investigated effect of passive feathering at the wing base on aerodynamic thrust and efficiency. In particular, various pre-determined limits of passive feathering angle were tested for three different aspect ratios of the wings. The time-averaged thrust, power consumption, and efficiency were measured using a hummingbird-sized electric flapping mechanism. It was found that the low-aspect-ratio wing without the passive feathering generated the largest thrust, but the power consumption was the worst too. On the other hand, the high-aspect-ratio wing like a hummingbird wing with passive feathering achieved relatively large thrust and the smallest power consumption, that is, the best efficiency. This result suggested that passive feathering at the wing base drastically improves efficiency with the minimum loss of the thrust.
