Researchers Unlock Secret of How Bats Fly

Scientists who study bats have never understood exactly how these winged mammals can stop and hover in mid-air without falling to the ground. Now they have their answer, according to a study in the journal, Science.

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RENE MONTAGNE, host:

We know a lot of things about the little mouse-like mammals called bats. We know they're nocturnal and that they listen to the echoes of their high-pitched sounds to locate prey and other objects.

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MONTAGNE: They've also inspired a well-known superhero.

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Unknown Group: (Singing) Batman. Batman.

MONTAGNE: OK. You can bring down the theme. Let's go back to the real bats. Scientists may now have the answer to a nagging question about one of the world's most maneuverable flying animals. How do soaring bats stop in mid-air as quickly as they do without falling from the sky like rocks? Researchers say this discovery could help them learn how to build speedy flying robots that can stop and turn on a dime.

NPR's John Nielsen has more.

JOHN NIELSEN: In the movies, flying robots sometimes look like mutant helicopters or flying saucers. But Geoff Spedding, an aerospace engineer at the University of Southern California, says it might be time to start re-imagining these machines as smallish things that move around on artificial bat wings.

Mr. GEOFF SPEDDING (Aerospace Engineer, University of Southern California): Maybe if they need to be highly maneuverable and readily controllable in confined spaces, maybe they should be wing flappers rather than propeller driven or helicopter-type things.

NIELSEN: Spedding says he came to that conclusion after he and some colleagues put a group of nectar eating bats into a high tech wind tunnel in the town of Lund in Sweden. The tunnel was filled with heavy fog and lit up by lasers, but the bats didn't seem to mind.

Mr. SPEDDING: Bats learn to hang out in a nice calm dark section of the wind tunnel, and then they feed at the feeder, execute a very stereotypical u-turn and then go back to their perches, all day long.

NIELSEN: The fog lit by the lasers showed the scientists exactly how the bats kept themselves up in the air when they were hovering in front of the tiny food trays. What Spedding and his colleagues saw was that as a bat's wing flapped downwards, a small but potent vortex formed in the air above the leading edge of the wing.

Mr. SPEDDING: I like to think of it as a tame tornado, if you like. And the high speeds associated with this swirling motion are responsible for generating suction on top of the wing. And that translates to lift.

NIELSEN: Lift that makes it possible for bats to stop and twist and turn almost as well as some of the flying bugs they like to eat. Lift that may just make these bats the perfect model for the flying robots of tomorrow.

Now, scientist have known for years that flying insects make much smaller versions of these tame tornadoes when they move their wings. That's how all those clunky-looking bumblebees have managed to stay airborne, for example. But until now, a lot of scientists have thought that bats were just too big to do the same thing.

Coauthor Anders Hedenstrom of Lund University in Sweden says the secret is probably the incredible flexibility of a bat's wing, which is basically a super modified hand.

Mr. ANDERS HEDENSTROM (Lund University, Sweden): We think that they are actively controlling this vortex so it remains attached on top of the wing, because if it breaks away from the wing, it doesn't work in adding any lift any longer.

NIELSEN: Hedenstrom and Spedding report on the bat wing vortex in the latest issue of the journal Science. But don't expect to see those flapping robots hit the market anytime soon. Researchers are still trying to figure out exactly what a bat wing does to make and hold onto those tame tornadoes.

John Nielsen, NPR News, Washington.

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