Insects aren't airplanes. If they flew like airplanes, they would fall right out of the sky because their wings are much too small. But since they flap their wings, they can generate a "leading-edge vortex', a rotating clement of fluid along the front of the wing that dramatically increases lift briefly and helps keep them aloft. A recent debate has focused on how and when the leading-edge vortex forms and what it docs once formed. Gregory Lewin and Hossein Haj-Hariri have added more complications to the argument in their computational study of small flapping wings, published in J. Fluid Mech- They describe how the leading-edge vortex can interact with other wing vortices to produce forces that differ on the up- and downstroke. even when the wing movements are symmetrical.
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