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17 April 2014 12:48 pm ,
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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
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Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
- About Us
Bats Best Birds at Slow Flight
10 May 2007 (All day)
Birds get all the credit for aerial virtuosity. But bats have some fancy tricks as well, especially at low speeds. Researchers have found a possible reason why: Bats cultivate a unique pattern of turbulence behind their wings. The findings could one day be used to design new flying machines, such as unmanned micro-air vehicles.
At fast speeds, bats and birds fly in much the same way. But at slower speeds, they take different approaches. The reason is anatomical. Birds can separate their feathers on the upstroke to minimize drag and maximize lift. But bats have an elastic membrane for their skin, so they do another trick to keep aloft: They flick their wings backwards and almost upside down.
Turbulence impacts performance at slow speeds, too. In previous studies, biologist Anders Hedenstrom of Lund University in Sweden and colleagues had measured vortices produced by a thrush nightingale and a robin and found their wings create a single vortex, or swirl of turbulent air, as they fly. Next, they decided to assess the wake in bats. The researchers put two nectar-feeding bats into a low-turbulence wind tunnel. As the researchers report in tomorrow's Science, the aerodynamic wakes for bats are much more complicated than previous studies suggested. In contrast to birds, bats form one vortex behind each wing, a "totally unexpected" find, says Hedenstrom.
What accounts for the difference? Hedenstrom guesses it could be because nectar-feeding bats don't have tails, which connect vortices in birds. Isolated wake loops might enhance maneuverability, he says, because the wings are more aerodynamically independent.
The results provide interesting and complex information about the individual vortex structures, a phenomenon never witnessed before, says zoologist Ulla Lindhe Norberg of Göteborg University in Sweden. The research also has broader implications for flight, says biologist Bret Tobalske of the University of Portland in Oregon. It appears to indicate that the bat wing--with lift produced during the upstroke thanks to a flexible membrane--is a more efficient design for slow flight compared with a feathered wing, he says, which could be of interest to developers of miniature autonomous flying vehicles.