Comparison of Albatross and Hummingbirds Wings at Low Reynolds Number

Abstract

This paper presents a part of our ongoing development of a bird-like type flapping wing micro-aerial vehicle. We attempt to mimic both the long-distance bird, such as albatross, as well as, the short-hop bird, such as hummingbird. The flapping mechanisms and flow physics of these two types are significantly different, especially, during start-up. Hence, detailed studies of the flow physics is necessary.  We investigate the effect of flapping either about the spanwise axis or aobut the chord wise axis, of both wings to examine the difference in start-up lift and thrust. With similar pitching patterns, angular velocities and amplitudes, the flapping motion of the albatross generates the large start-up vortices which attribute for the high lift and thrust to drag ratio (L/D) and that suitable for long-distance flight. The flapping motion of the humming bird about the spanwise axis of the wing produces smaller vortices, but with better control of the flow structure (more quiescent). Moreover, the spanwise flapping motion provides continous lift in every plunging cycles. To achieve effective MAV, one should use the combinations of both spanwise and chordwise motions to effectively provide thrust, lift and directional control.