Why do Airplanes Fly?

In many physics textbooks, the explanation for lift on a flying airplane is that the top of a plane’s wing is longer than the bottom, and so air must travel faster across the top than the bottom, and therefore the pressure is lower above the wing than below. (This difference in pressure caused by different speeds of a moving fluid is a consequence of Bernoulli’s principle.)
However, the problem with this explanation is that some planes nevertheless manage to fly upside-down! How could these planes fly both right-side up and upside-down? Could the top of the wing and the bottom of the wing both be shorter than the other when depending on the plane’s orientation? This is absurd, and so there must be something wrong with the explanation.
For the correct explanation (briefly, the angle of attack of the wings provides overwhelmingly more lift than any lift produced because of asymmetry in the cross-section of the wing), check out the following references:


About Santo D'Agostino

I have taught mathematics and physics since the mid 1980s. I have also been a textbook writer/editor since then. Currently I am working independently on a number of writing and education projects while teaching physics at my local university. I love math and physics, and love teaching and writing about them. My blog also discusses education, science, environment, etc. https://qedinsight.wordpress.com Further resources, and online tutoring, can be found at my other site http://www.qedinfinity.com
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4 Responses to Why do Airplanes Fly?

  1. Peter Brown says:

    The angle of attack is much more important in high powered jet aircraft because the thrust from their engines compensates for the added air resistance. On low powered, propeller driven aircraft the aerofoil section is much more important. At low landing speeds, jets have to increase their wing area to provide sufficient lift for control. During WW2, the German Fiesler ‘Storch’ had the ability to massively increase its aerofoil section for low speed flying to the point that the plane could actually be flying backwards in a strong head wind.

  2. Lawson says:

    My intuition as a kid was always along these lines because of exactly the analogy of sticking your hand out a car window. Glad to hear that I wasn’t completely wrong after-all..

    Glad to see you posting again!

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