OWLS are the original stealth aircraft, dropping silently, talons at the
ready, onto their prey. That鈥檚 why engineers working with military and defence
agencies will be all ears later this month during a meeting of the European
Acoustics Association to be held at the Technical University of Berlin.
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鈥檚 flight. This could give designers tips for reducing noise in future
stealth aircraft.
The prey of owls鈥攔ats, mice and voles鈥攐ften has excellent
hearing, so they can鈥檛 afford to fly as noisily as other birds. 鈥淭he owl has to
be able to fly silently to have a good dinner,鈥� says Lilley, who also works at
NASA鈥檚 Langley Research Center in Hampton, Virginia.
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To do this, the owl has evolved feathers that are different from those of
other birds. 鈥淭he flight feathers of most birds have a fairly sharp, clean
edge,鈥� says Gerry Carr, a biomechanist at the University of Victoria in British
Columbia, Canada. 鈥淏ut the leading edges of the flight feathers of an owl
coupled with the outer third of the hand section of the wing鈥檚 trailing edges
are characterised by soft, feathery `fringes鈥� which have the effect of muffling
the flow of air as it passes over the wing.鈥�
Just how these fringes reduce noise was unclear, so Lilley used computer
simulations to work out what they did. 鈥淭he devices at the trailing edge are
acting like some sort of pressure release,鈥� he told 快猫短视频. 鈥淭he
various gaps in the trailing edge allow pressure relief, and as a result, the
noise generation of the turbulent flow decreases.鈥�
鈥淚t鈥檚 plausible that the owl will yield secrets engineers can use,鈥� 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.