The Aerodynamics of Flapping Animal Flight

Our understanding of the aerodynamics of flapping animal flightis largely based on the quasi-steady assumption: the instantaneousaerodynamic forces on a flapping wing are assumed to be identicalwith those which the wing would experience in steady motionat the same instantaneous speed and angle of attack. Researchup to a decade ago showed that the assumption was sufficientto explain the flight of the vast majority of animals, but didnot rule out the possibility that alternative aerodynamic mechanismswere employed instead. Results are presented here for four hoveringanimals for which the quasi-steady explanation fails. Theseanimals apparently use lift mechanisms that rely on vorticesshed during the rotational motion of the wing at either endof the wingbeat. The postulated rotational lift mechanisms shouldalso apply to other hovering animals, even though the quasi-steadyassumption could explain their flight. Measurements of the wingforces produced by locusts cast doubt on the validity of thequasi-steady assumption for fast forward flight as well.