Engineer debunks theory of flight

AN ENGINEER has debunked one of the most common myths in science - why aircraft fly.

Aeroplanes fly because their wings cause the air pressure underneath to be greater than that above, lifting them into the air. For years engineers have been frustrated by a theory that wrongly explained the change in pressure.

The myth is common in textbooks, and even Einstein was rumoured to have subscribed to it.

A Cambridge scientist was so fed up with it that he created a minute-long video to lay it to rest. The video, published on YouTube by Professor Holger Babinsky, seeks to explain in simple terms why the theory goes against the laws of physics.

According to the myth, the pressure change happens because 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.

The true explanation is nothing to do with the distance the air has to travel. 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.

Professor Babinsky explains that, although lift is caused by a pressure change between the top and bottom surfaces, it's due to the change in the shape of the air flow, rather than its speed. ''This is why a flat surface like a sail is able to cause lift,'' he says. ''In this case, the distance on each side is the same but it is slightly curved when it's rigged, acting like an aerofoil.''

Professor Babinsky filmed smoke passing across a wing. If traditional wisdom had been correct the smoke above and below should have reached the back at the same time. Actually, the plume above the wing reached the back much sooner.