Img/2012/1/25/fly-small.jpgLondon: A scientist at Cambridge University has debunked the long-held myth about how aircraft stay aloft.Aeroplanes can fly as their wings cause the air pressure underneath to be greater than that above, lifting them into the air. But, engineers have for years been frustrated by a theory which wrongly explains what causes the pressure change, a myth commonly found in school textbooks and flight manuals.
But, Prof Holger Babinsky of Cambridge University`s engineering department has now created a minute-long video, posted on `YouTube` website, to lay to rest the myth once and for all, `The Daily Telegraph` reported.
According to conventional wisdom, the pressure change happens as the air on the curved upper surface of the wing has further to travel than that below the flat underneath surface, meaning it must travel faster to arrive at the other side of the wing at the same time.
Prof Babinsky says the myth goes against the laws of physics and the real explanation has nothing to do with the distance the air has to travel.
According to him, the curvature of the wing causes the change in air pressure because it pulls some of the air upwards, which reduces pressure, and forces the rest beneath it, creating higher pressure.
A law known as the Bernoulli equation means that when pressure is lower, air moves faster -- so the air stream above the wing does move more quickly than the one below, but this is not what causes the difference in pressure.
Prof Babinsky proved his theory by filming smoke passing across a wing.
If traditional wisdom had been correct the smoke above and below the wing should have reached the front edge at the same time. The video demonstrates that the explanation is fundamentally flawed because the plume above the wing reached the edge much sooner than the plume below, he says.
If the distance the air had to travel was causing the pressure to change, then a boat`s sail -- where the air travels the same distance on the inside and outside of the curve -- would not work, Prof Babinsky said.
He added: "I don`t know when the explanation first surfaced but it`s been around for decades. There is no law in physics which states when streams of particles start at the leading edge of the wing they should reach the tailing edge at the same time."
First Published: Wednesday, January 25, 2012, 13:51