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Fig. 11. Smoke flow over hawkmoth wings at {alpha}=0° (A) and {alpha}=35° (B) revolving steadily at 0.1 Hz. Smoke was released from various positions (marked with white arrows) on the leading edge and upper surface of the wings. At very low angles of attack, the smoke describes an approximately circular path as the wing revolves underneath. At higher angles of attack, a spiral leading-edge vortex and strong spanwise flow are visible. {alpha}, geometric angle of attack.