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Bat Flapping




http://www.nature.com/news/2008/080228/full/news.2008.633.html

Bats have a clever aerodynamic trick to make flying easier, researchers have found: the sharp edge at the front of their wings cuts through the air in such a way as to create a vortex on top of the wing, producing up to 40% of the lift needed to stay aloft.
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Hedenstrm and his team showed that the down-stroke of a bat's wing moves forward as well as down, and is tilted at a sharp angle just like that of an insect in flight. This produces a powerful lifting vortex. The swirling air closely follows the surface of the wing during the down-stroke: that's a good thing, because if the vortex moved away from the wing, a slow-flying bat would stall, dropping out of the sky. To keep the vortex close to the wing takes some delicate wing movement. The bats control their wing curvature in a very subtle way, says Hedenstrm.
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