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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.''
