CNN - Owls teach scientists to fly silently

Owl feathers are different from those of other birds, allowing them to swoop down quietly on their keen-hearing prey

March 5, 1999
Web posted at: 3:45 PM EST

Engineers working with military and defense agencies will be taking advice from the birds at a meeting of the European Acoustics Association later this month at the Technical University of Berlin.

In an attempt to build models for future stealth aircraft, engineers are looking at the original stealth model: the owl. Owls move swiftly and drop silently onto their prey -- features aircraft engineers are trying to emulate.

At the meeting, Geoffrey Lilley, an acoustics expert at the University of Southampton, will describe how the trailing edge of owl feathers helps to stifle the sound of the bird's flight. This could give designers tips for reducing noise in future aircraft.

Rats, mice and voles -- which make up most of an owl's diet -- often have excellent hearing, so owls can't afford to fly as noisily as other birds, according to an article in New Scientist Magazine. "The owl has to be able to fly silently to have a good dinner," says Lilley, who also works at NASA's Langley Research Center in Hampton, Va.

"The flight feathers of most birds have a fairly sharp, clean edge," says Gerry Carr, a biomechanist at the University of Victoria in British Columbia, Canada. "But the leading edges of the flight feathers of an owl coupled with the outer third of the hand section of the wing's trailing edges are characterized by soft, feathery 'fringes' which have the effect of muffling the flow of air as it passes over the wing."

Just how these fringes reduce noise was unclear, so Lilley used computer simulations to work out what they did. "The devices at the trailing edge are acting like some sort of pressure release," he told New Scientist. "The various gaps in the trailing edge allow pressure relief, and as a result, the noise generation of the turbulent flow decreases."

"It's plausible that the owl will yield secrets engineers can use," says Jeremy Rayner, a bird flight expert at the University of Bristol. He notes that engineers have already used bird-like designs to improve the efficiency and reduce the noise of helicopter blades.

For more information, contact Claire Bowles, New Scientist Magazine, email: .

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