C

Delayed Stall

Delayed Stall

KV wing x ^rotation

Rotational Lift

Wake Capture

FIGURE 1 Summary of aerodynamic mechanisms used by insects. (A) Under hovering or near-hovering conditions, insects flap their wings back and forth at a high angle of attack during each stroke. The wing path is shown by the dotted line; white arrows indicate wing motion. Between strokes, the wing rapidly rotates so that the dorsal surface faces up during the downstroke, while the ventral portion faces up during the upstroke. The total aerodynamic force (thick arrow) acts perpendicular to the surface of the wing and may be decomposed into orthogonal lift and drag components (thin arrows). (B) Diagram of wing motion indicating magnitude and orientation of the total aerodynamic force vector (black arrows) generated throughout the stroke. Gray lines indicate instantaneous position of the wing at temporally equidistant points during each stroke. Small circles indicate the leading edge of the wing. Time moves left to right during downstroke and right to left during upstroke. (C) Drawings indicate air flow around wing and resulting forces at points within the wing stroke (as indicated in B). Delayed stall (1) results from the formation of a leading edge vortex on the wing. Rotational lift (2 and 3) results from the rapid rotation of the wing at the end of the stroke. Wake capture (4 and 5) results from the collision of the wing with the wake shed during the previous stroke.

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