Fig. 7. Stable attachment of the leading edge vortex. As the flapping wing translates, a span-wise velocity gradient interacts with the leading edge vortex, causing the axial flow to spiral towards the tip. The axial flow transports momentum out of the vortex, thus keeping it stably attached. The vortex detaches at about three-quarters of the distance to the wing tip and is shed into the wake. Thick black arrows indicate downwash due to the vortex system generated by the wing in its surrounding fluid. Figure adapted from VandenBerg and Ellington (1997).

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