" The cross-section of a helicopter blade, according to Sarah, is more or less the same as the wing of an aeroplane. Its shape creates a pressure differential in the air passing over its upper and lower surfaces, producing a consequent lift. It differs from an aeroplane wing, however, in that when a helicopter moves forward, air starts passing over the blade that’s coming forward faster than it passes over the blade that’s going backwards. This produces unequal lift on the two sides of the helicopter, and the faster it goes, the more unequal the lift becomes. Eventually the ‘retreating’ blade stops producing any lift at all, and the helicopter flips on to its back and drops out of the sky. This, according to Sarah, was a negative aspect. "

― Hugh Laurie , The Gun Seller