April 9, 2009 -- Flying, flapping robots could soon get an upgrade, thanks to new research that reveals the deceptively simple mechanism used by bats, birds and bugs to turn in flight.
"Why are animals so much better at maneuvering and recovering from perturbations than our human-designed flight systems?" asked Tyson Hedrick, a professor of biology at the University of North Carolina and an author of the study, which appears in the current issue of Science.
"From fruit flies through hummingbirds to larger birds and bats, we tried to uncover the fundamental aspects of turning in flight," he said.
The study is the first to examine how various flying creatures can turn in midair without crashing to the ground. Previous studies of animal flight have mostly focused on how they manage to stay aloft at all.
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Experiments to test bird flight are simpler than those for studying turns, since scientists can stick birds in wind tunnels or super-glue insects to anchored bits of string. Catching a free-flying bird, bat or bug in the middle of a turn is significantly harder, but not impossible, as the scientists showed.
Detailed photographic images showed the scientists that it is easier for animals to turn than they previously though. To turn left, all a bird has to do is flap its right wing a little bit harder than the left wing.
To end the turn, the bird simply returns to flapping its wings in unison.
"Flapping is a rapid and powerful activity that offers a potent means for rapid movement control and recovery," said Bret Tobalske, a professor at the University of Montana who was not involved in the research but wrote an accompanying commentary in Science.
Tobalske used the example of the cheap plastic helicopters found in hobby stores. They work great indoors, but even a mild gust of wind outdoors sends them crashing to Earth.
A bird, or a robot with flapping wings, would be inherently more stable against perturbations in the environment.
"The idea is that just by simply getting something to oscillate it offers increased stability," said Tobalske.
Xinyan Deng, another co-author of the new study, and her colleagues at the University of Delaware are using the high-speed photography to create flapping robots that bring humans a little closer to the speed and maneuverability of these animal aces.
The first robot sits in a container of mineral oil, flapping its wings to "fly" in the liquid.
The other robots are 10 to 15 centimeters from wingtip to wingtip and are designed to be true flyers, eventually. So far Deng has gotten the robots to flap their wings, but has yet to achieve lift.
A wing-flapping robot would have many advantages over fixed-wing aircraft, said Deng. Wing-flapping robots, like their organic counterparts, would be easier to control and could operate in a much smaller area.
The new research also shows that wing-flapping aircraft would have an inherent stability that scientists previously didn't expect.
"Usually if you have increased stability that means you have decreased mobility," and vice versa, said Deng. "Here it looks like you get a little bit of both."
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