DICKINSON, M.; BIRCH, J.; FRY, S.; SANE, S.: Deconstructing the Aerodynamics of Insect Flight.

The purpose of this paper is to review recent research that has identified and isolated a series of different aerodynamic mechanisms that collectively account for the forces produced by flapping wings. These force components include: wing and added mass inertia, dynamic stall, rotational force, and wake capture. The genesis of all these forces is linked to the reciprocating back and forth motion of flapping wings. Wing and added mass inertia result from the acceleration of the wing and surrounding air during stroke reversals. Although the peak inertial forces can be quite large, they are brief and tend to cancel out when averaged over a complete stroke cycle. Dynamic stall occurs because the wings sweep through both the downstroke and upstroke at high angles of attack. Under these conditions, flow separates at the leading edge forming a stable vortex that generates an elevated pressure force. Rotational forces result as the wings rapidly flip in preparation for the next stroke. These forces can either enhance or attenuate lift and drag, depending on the precise timing of wing rotation. After the wings reverse direction, the forces they create are greatly influenced by the wake generated during previous strokes. Immediately following stroke reversal, force production is augmented by the transient increase in fluid velocity due to the lingering presence of the leading edge vortex shed at the end of the prior stroke. Towards the middle of the stroke, however, forces are attenuated because the downwash of the wake lowers the effective angle of attack. The identification of these separate mechanisms is important, not simply because they can collectively explain how an insect generates enough force to remain in the air, but because they represent the aerodynamic palette with which insects produce their complex flight maneuvers.