By Emma Young
”Singing” wings could reduce the number of fatal small plane crashes, Australian research suggests, and may even lead to a new generation of smaller-winged, more fuel-efficient aircraft. The new technology uses a sound-emitting plastic coating to help control the flow of air over the wings, reducing the chance of the aircraft stalling—experiencing a sudden loss of lift—in mid-air.
US Federal Aviation Administration data shows that about one-quarter of fatalities involving planes with eight seats or fewer are due to crashes following a stall, which can happen when the plane turns too tightly or flies too slowly.
"The air can no longer remain attached to the wing and it tends to break off in large sheets," says Ian Salmon, an engineer with Qantas Airways in Sydney, who conducted the research while at the University of New South Wales, also in Sydney. But Salmon has found that certain frequencies of sound help air stay attached to the wing.
In wind tunnel tests, Salmon stuck sections of plastic piezo-electric film to wing segments. This film vibrates when an electrical signal is applied, producing sound. Tests using a barely audible sinusoidal tone of about 400 hertz showed a 22% increase in lift, compared with a standard wing. This could translate into a few extra seconds of time for a pilot to boost a plane's speed before it stalls, says Salmon.
The simple tones worked best, though Salmon did experiment: "I can say that songs by the band Spiderbait are more effective than Radiohead's."
Small planes are fitted with devices to sound the alarm when their speed drops dangerously low, but given the fatality data, it is clear these warnings do not always succeed, he adds. But the technique could have other advantages.
The size of a small plane's wings is determined by the need to avoid stalls during take-off and landing. "So if you use this device to improve lift at low speed, you can potentially decrease wing size," says Salmon, thereby reducing the plane's weight and its fuel requirements.
The beneficial effect of sound would be significantly less in much larger, faster planes, which fly in conditions in which the air's viscosity has less of an impact on air behaviour around the wings, Salmon explains.But he thinks the system could effectively boost lift for anything with about eight seats or less, right down to un-crewed fly-sized vehicles.
Salmon presented his work in Melbourne, Australia on Tuesday, as part of the Fresh Science initiative, which promotes the research of young Australian scientists during the country's national Science Week.
—NewScientist.com news service