An owl glides by on silent wings. Many holiday travelers probably wish airplanes could do the same.
"On airplanes, the back edge of the wing is where you get most of the noise," Justin Jaworski, a mathematician at the University of Cambridge in the United Kingdom, told TechNewsDaily. "My work is looking at developing theoretical models to explain trailing-edge noise."
Most recently, he and his colleague Nigel Peake showed, mathematically, that the noise from airplane wings could be reduced tenfold if their designers took a few cues from the feathers that fringe the trailing edge of an owl's wings.
In their latest research, Jaworski and Peake found that owl wings are especially quiet in part because their trailing-edge feathers are flexible and porous, allowing some air through. Plane wings, of course, are hard and solid. But the pair found that if the edge of a plane's wings were perforated in a particular way, "the theory says you should be able to reduce noise as if there were not an edge there at all," Jaworski said.
Makers of real planes might have a difficult time taking that suggestion. Holes in the wings might reduce a plane's aerodynamics too much for the companies' liking, Jaworski said. Also, flexible trailing edges might flap in the wind, which would also reduce aerodynamics. These are issues that other engineers would work out in later stages of research, Jaworski said. He collaborates with experimental researchers to uncover the engineering trade-offs in his ideas.
In any case, the findings are still in their earliest stages, and it might take two or three years before the ideas for a quieter airplane wing are tested with a small model in a wind tunnel, Jaworski said. After wind tunnel tests, even more research would go into seeing whether the ideas would be cost-effective in real planes.
Meanwhile, the Cambridge researchers continue to refine their model and study owl wings for further secrets into their quiet flight, Jaworski said.
On the theory side, the next step is to study other features of owl wings that are not common to noisier flapping birds such as pigeons. "We're really excited about looking at this downy material on top," Jaworski said, referring to a unique, soft covering owl wings have. He said the down covering is difficult to model mathematically, no one has studied it before, and it may be especially important to quiet flight.
Jaworski presented his and Peake's research Nov. 18 in San Diego at a conference hosted by the American Physical Society.