A majestic eagle owl stretching its six-foot wingspan as it soared over the 14th century Bolton Castle, in Wensleydale, North Yorks. (Photo courtesy: SWNS)
LONDON — The sound of airplanes soaring overhead can not only be distracting and frustrating for people on the ground, studies have shown it can also be detrimental to health. Could the wisest of birds be the key to one day quieting our busy skies? Scientists believe the secret to reducing airplane noise could be found in owl feathers.
The method by which owls swoop silently on their prey has been probed by scientists who can now apply it to aeronautics. Engineers have built a model and believe micro-structured finlets on the tips of their feathers are the key to why owls are so silent. Measurements have shown the flapping of a barn owl's wings, whose wingspan can reach more than six feet, is below the threshold of human hearing until the bird is about three feet away.
Researchers at City, University of London, used 3D geometry data to study the aerodynamic effects of the finlets in a water tunnel to discover how they work. They show that the structures are able to turn the flow direction near the aerodynamic wall and keep the flow for longer and with greater stability, avoiding turbulence.
The effect is known to stabilize the flow over the feathers, so as to create little to no noise when owls flap their wings and glide. In future tests the team will test the model in a wind tunnel for further acoustic tests, which will hopefully inspire future wing designs for aircrafts and reduce noise.
Airplane noise is more harmful than you might realize
Airplane noise is considered to be dangerously loud, with noise levels in the cabin at take-off and landing reaching 105 decibels, similar to a chainsaw at close proximity. At cruising altitudes, noise drops to around 85 dB, the equivalent to heavy traffic.
Sounds at or below 70 dBA are generally considered safe. Any sound at or above 85 dBA is more likely to damage hearing over time.
“We were surprised that instead of producing vortices, the finlets act as thin guide vanes due to their special 3D curvature,” says professor Christoph Breucker, the university's Chair on Aeronautical Engineering, in a statement. “The regular array of such finlets over the wing span therefore turns the flow direction near the wall in a smooth and coherent manner.”
The research was published in the Institute of Physics journal, Bioinspiration and Biomimetics.
SWNS writer Joe Morgan contributed to this report.
Anything that displaces air makes a sound . Just because no one hears it doesent mean it doesent exist .