How bats fly out of hell

Flying like a bat out of hell is supposed to mean sudden, fast and wild.But how do bats fly? It turns out they have some unique tricks:

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.

"It explains how these animals are able to fly at very slow speed," says Anders Hedenström from Lund University in Sweden, who led the research -- published in Science 1 -- that showed the effect with a live bat.

The phenomenon of a 'leading-edge vortex' is known to help insects to fly; this discovery helped to work out how the bumble bee manages to stay airborne. But it hasn't been definitively seen before in a non-insect with live animals. (Nature)

I'm sure you believe this much, right? But seeing is believing, and now you can see it, too. Because the Lund group made some really nice videos of a bat feeding on nectar -- in a wind tunnel. By filling the tunnel with fog and illuminating it with a pulsing laser they could see how air was moving around animal's wings.

Hedenström 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 Hedenström.

Not all secrets of bat flight have been revealed but this is a big step forward. And you can see the bat fly (although not the vortices) in this online video. These little bastards are pretty neat aviators: take a look.


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One hopes we can continue to speak about bats in the present tense. They are, of course, dying in great numbers from an as yet unknown cause, in parts of Northeastern U.S.

Beautiful video, though. I do love the little critters, even when they get into the house.