Wings that sing

Sound could stop light planes from stalling

Sound can be used to control the flow of air over an aircraft’s wing greatly boosting its lift, according to a Sydney aerospace engineer who is working on applying this idea to a new generation of light aircraft.

Ian Salmon has developed a technique whereby a wing is covered with flexible plastic panels which vibrate when an electric current is passed through them, and produce sound. At a carefully selected frequency, the air passing over the wing can be made to remain more closely attached, increasing the wing’s efficiency.

Salmon has already demonstrated a boost in lift of up to 22 per cent compared with a conventional wing. His technique would therefore allow a smaller wing to be used on aircraft, resulting in lighter weight and reduced fuel consumption. “Such innovative approaches are needed in this age of greenhouse gas awareness, and rising fuel prices,” he says.

While the theory behind Salmon’s technique is not new, his method of applying sound directly to the wing during flight is. Previous studies used large speakers pointing at a model in a wind tunnel, he says. The results were encouraging, but the sound levels were often painful.

“This new method grew from the desire to carry a lightweight sound source on the aircraft, and to apply sound exactly where it was needed, rather than spraying it everywhere. Obviously one thing we did not want to do was to make aircraft noisier.”

Salmon’s approach seems to have paid off. Useful gains have been measured even at barely audible volumes, showing that the amount of energy required is very small.

It’s unlikely, however, that his method will be used on large commercial jets. “The beneficial effects are far more pronounced for small, slow aircraft which fly in conditions where the air’s viscosity, or ‘stickiness’ has more influence on the air’s behaviour.”

Although the kind of sound which is most effective in manipulating airflow is a single-frequency tone, other forms, including music, have shown some effect. “While I’ve not tested a large selection of music, I can say that Spiderbait is more effective than Radiohead,” Salmon says.

Ian is one of 13 Fresh Scientists presenting their research to the public for the first time thanks to Fresh Science, a national program hosted by the State Library of Victoria. One of the Fresh Scientists will win a trip to the UK courtesy of the British Council to present his or her work to the Royal Institution.

Ian Salmon works as an Aircraft Development Engineer for Qantas Airways. The research was undertaken at the University of New South Wales as part of a BE Thesis under the supervision of Associate Professor N.A.Ahmed.