Owl wings could bring quieter aircraft

The ability of owls to to fly silently in search of prey could lead to quieter passenger aircraft, researchers at the University of Cambridge in England say. Owls rely on the special shape of some wing feathers to reduce noise so they can hunt stealthily, and the researchers are analyzing the birds' wing structure to better understand how it mitigates noise so they can apply that information to the design of aircraft. "Many owl species have developed specialized plumage to effectively eliminate the aerodynamic noise from their wings, which allows them to hunt and capture their prey using their ears alone," Cambridge researcher Justin Jaworski said. "No one knows exactly how owls achieve this acoustic stealth, and the reasons for this feat are largely speculative based on comparisons of owl feathers and physiology to other not-so-quiet birds such as pigeons." All wings, whether in nature or on aircraft, create noise as turbulent eddies created as they move through the air hit the trailing edge, where they are amplified and scattered as sound. Conventional aircraft, which have hard trailing edges, are particularly noisy in this regard, researchers said. Scientists are looking at three features of owl wings: a comb of stiff feathers along the leading edge of the wing; a soft downy material on top of the wing; and a flexible fringe at the trailing edge of the wing. Using mathematical models, they found a wing trailing edge with elastic and porous properties could be tuned to mitigate noise. "This implied that the dominant noise source for conventional wings could be eliminated," researcher Nigel Peake said. The scientists presented their findings Sunday at a meeting of the American Physical Society's Division of Fluid Dynamics in San Diego.