Owls could hold the key to developing ‘stealth’ passenger jets, according to new research.
Being woken up at the crack of dawn by noisy airplanes could become a thing of the past thanks to scientists who are trying to replicate the ability of the birds to fly silently in search of prey.
Owls rely on specialized plumage to reduce sound so they can hunt with stealth and scientists are studying the wing structure in a bid to design better conventional aircraft.
A long-eared owl in flight. Scientists are studying the wing structures that enable the nocturnal hunters to fly silently in the hope of replicating them to produce quieter passenger aircraft
Dr Justin Jaworski, of the University of Cambridge, said: ‘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.’
All wings, either natural or engineered, create turbulent eddies as they cut through the air. When these hit the trailing edge of the wing, they are amplified and scattered as sound.
Conventional aircraft, which have hard trailing edges, are particularly noisy in this regard.
But owls possess distinct physical attributes that contribute to their silent flight including a comb of stiff feathers along the leading edge of the wing, a soft downy material on top and a flexible fringe at the trailing edge.
It is not known whether it is a single attribute or the combination of all three that are the root cause of the noise reduction.
The researchers attempted to unravel this mystery by developing a theoretical basis for the owl’s ability to mitigate sound from the trailing edge of its wing, which is typically an airfoil’s dominant noise source.
Earlier owl experiments suggest their wing noise is much less dependent on air speed and that there is a large reduction of high frequency noise across a range where human ears are most sensitive.
A Ryanair plane lands at Dublin Airport. Conventional aircraft, which have hard trailing edges, are particularly noisy as the hard trailing edges of their wings create turbulent eddies in the air
Using mathematical models, the researchers demonstrated elastic and porous properties of a trailing edge could be tuned so aerodynamic noise would depend on the flight speed as if there were no edge at all.
Professor Nigel Peake, who presented the study at a meeting of the American Physical Society in San Diego, added: ‘This implied the dominant noise source for conventional wings could be eliminated.
‘The noise signature from the wing could then be dictated by otherwise minor noise mechanisms such as the roughness of the wing surface.’
Attribution: Damien Gayle