How does an airplane wing create “lift”?

Aerodynamics Read more from
Chapter Fluids

The explanation behind this question is not meteorological, but physical. In major cities, there are skyscrapers and other tall buildings that obstruct the flow of wind. In order to flow past these large obstacles, the wind speed increases in the narrow corridors of the streets and avenues. The same effect can also be found in tunnels and outdoor “breezeways.” It is the continuity of the fluid that increases its speed through the narrow corridors of streets and avenues that makes the city such a windy place.

The upward force on an airplane wing caused by the air moving past it is called lift. According to Newton’s Third Law, if the air exerts an upward force on the wing, then the wing must exert a downward force on the air. There are three causes of this downward force. The first is the tilt, or angle of attack of the wing. The tilt deflects the airflow downward. The second is the Bernoulli Principle. Because of the shape of the wing, the speed of the air on the top surface of the wing is faster than at the lower surface, and so the pressure is lower. Thus the downward force on the wing is reduced. The third reason is the fact that air “sticks” to the surface of the wing. The air coming off the upper surface is moving downward. This exerts an additional downward force on the air. The downward forces produce the lift needed to keep the plane airborne.


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