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Title:

“How do wings work?”, Holger Babinsky, Physics Education Vol. 38 p 497-503, 2003

 Introduction:

This paper clarifies how wings work for general levitation. It also shows that the typical explanation with Bernoulli’s equation is misleading. The keys are following: The curved surface of a wing and the angle of attack play a critical role for levitation. It is not necessary to use different distances of the upper and lower surfaces of an aerofoil to expound the lift.

 Summary:

The typical explanation of how an airplane is lifted is: The upper and lower streamlines get together at the tailing edge simultaneously although the upper surface has more distance. Therefore, the upper stream is faster than lower. From Bernoulli’s equation, the faster the stream gets, the lower the pressure becomes. The lower region has higher pressure; thus, the lifting force works upward on the aerofoil. This has been believed as the right explanation; however, it turns out to be fallacy.

 In fact, the typical explanation with Bernoulli’s theorem cannot show how aircraft manage to fly upside down. From the simulation and experiment, several factors are proven:

1. Even though the upper and lower surfaces have the same length, the pressure difference can be created to levitate.
2. When lift is generated, the upper streamline reaches actually faster than lower one. Namely, they do NOT arrive at the tailing edge at the same time.
3. A curved surface, however, creates pressure gradients (differences) in terms of stream lines for the lift.
4. The thickness of aerofoil does not influence the flow pattern of streamlines, but some specific shape, such as bird’s wings, could create more effective pressure gradients for the levitation.

 In conclusion, the correct explanation is given as follows: A curved aerofoil creates pressure gradients along with the streamlines. In addition, changing the angle of attack alters the pressure gradients around the aerofoil to control the lift points, up or down. (It could make a stalled flow.)