June 2007, Volume 5, Issue 6

Bats in the News

The Secrets of Bat Flight

Most people assume that bats fly much as birds do, by flapping fairly rigid, airplane-style wings. Now, BBC News reports, scientists using a computerized imaging system to study bats in wind tunnels have demonstrated that bats and birds have very little in common when it comes to flying.

The research team, led by Anders Hedenström of Lund University in Sweden, studied Pallas’ long-tongued nectar bats (Glossophaga soricina) in flight in a small wind tunnel. Hedenström has spent more than a decade studying the flight patterns of birds.
Following his experiments, Hedenström told the BBC, “There is nothing else that is similar to a bat in flight because their wings are so flexible.” Bats evolved flight independently from birds, BBC Environment Correspondent Richard Black said, and their wings work differently.
The most striking aspect is that on the upstroke, a bat’s wings turn upside down to generate more lift, Black reported. “This is completely different from birds,” Hedenström said.
The research results were reported in the journal Science.
Scientists placed the nectar-eating bats on a net inside the wind tunnel, where they occasionally flew to feeding tubes filled with water and honey.
The tunnel, buffeted by an artificial wind, was filled with a fog of minute water droplets and swept by a pulsed laser, which, Hedenström said, “illuminated areas of the tunnel [as] we captured pairs of images.” A computer program scanned the images for clusters of water droplets that it tracks from one snapshot to the next to identify detailed movement of the wings.
The research team believes, according to the BBC, that this method reveals bats’ flying secrets with much greater precision and detail than ever before.
The key element seems to be the wing inversion. At first glance, it seems logical that the wing’s upward stroke would push the animal downward, the BBC said. But bats maintain lift by turning the wing over and moving it backwards during the upstroke.
Birds use a completely different strategy to get around the same problem. They separate and turn their feathers so they can pass through air more freely as the wing moves upwards.
In the Science paper, the researchers suggest their study might help develop small, highly maneuverable robotic aircraft that fly with flapping wings.
Geoffrey Spedding, an aerospace engineer at the University of Southern California who collaborated on the research, told the BBC: “Bats are agile hunters, capable of plotting and executing complex maneuvers through cluttered environments.
“These are the traits we’d like our unmanned air vehicles to have because there are so many complex rural and urban environments in which we could use them.”

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