Uplifting sounds

An Australian aerospace engineer has developed a technique that he claimed can boost aircraft lift by using sound to control air flow over wings.

The discovery would allow UAVs and light aircraft to benefit from smaller, more efficient wings that reduce weight and fuel consumption without increasing the chance of the plane stalling, according to its developer.

Ian Salmon, an aircraft development engineer within the Fleet Development arm of Qantas Airways, fitted a wing with flexible plastic panels.

These vibrate when an electric current is passed through them, producing barely audible sound.

At certain frequencies the air passing over the wing can be made to remain more closely aligned to it, increasing efficiency and giving a boost in lift of up to 22 per cent compared to a traditional wing, said Salmon.

Previous attempts to use sound to control lift consisted of directing sound at a model in a wind tunnel. However, the noise level required was often painfully high.

‘This technique may be useful whenever an aircraft wing is required to produce either more lift than is otherwise possible, or to produce the same lift at a lower air speed,’ said Salmon.

‘This is achieved by allowing the wing to operate at a greater angle of attack — the angle of the wing to the relative air flow — without stalling.

‘The radiation of sound of specific frequencies from the wing surface encourages the continued attachment of the airflow and delays the stall.’

The system would prevent crashes when the airspeed of an aircraft is accidentally allowed to decay to a point where the plane would normally stall, providing an additional safety margin before stalling occurs.

This would be particularly useful in the case of remote-controlled UAVs, where there may be operator errors.

It would also protect the light aircraft or UAV if horizontal or vertical wind gusts suddenly increased the wing’s angle of attack beyond the normal stalling angle.

At present, small aircraft have wings sized according to stall speed requirements. However, at normal cruising speed the wings are larger and less efficient than they could be.

Salmon’s technique would allow smaller wings to provide increased efficiency at cruise conditions, yet provide the same stalling speed as larger wings, he said.

However, the system is unlikely to be useful for large transport aircraft such as commercial jet liners, as stalling is not considered a major issue for these craft because various lift-enhancement devices already exist. The method also becomes less effective as the size and speed of the wing increase.