From C.M. Davies
Timothy Jenson (Letters, 6 January) seems to have got his vortices in a twist, or at least to have confused action and reaction.
He is quite correct to note that in normal flight an aircraft wing produces a downwash, and that the reaction to the force acting downwards on the airflow is equal to the lift on the wing. He is incorrect to dismiss as a myth the idea that the lift corresponds to pressure variations. The reduction in pressure above the wing, together with a slightly smaller increase in pressure below the wing, are measurable quantities which are found to account for the magnitude of the lift.
The pressure variations involved are quite modest – it has been said that the suction acting on the upper wing surface of an airliner at takeoff is approximately equal to that which a three-year-old child can achieve through a drinking straw.
