One common explanation for airplane lift is that air pressure over the wing both moves faster and has lower pressure, a la Bernoulli. A very different explanation is that air is deflected downward by the lower wing surface, thus creating upward thrust. Probably both effects count, and it should be possible to gauge their relative contribution. One can measure, with sensors, the top-to-bottom pressure difference at many points in a real wing in flight. Integrating over the wing, is the total force equal to the weight of the plane? Surely, after 118 years of light, this has been done -- hasn't it??

  • $\begingroup$ Of course it has been done. It's a standard wind tunnel lab experiment in any university aerodynamics course. $\endgroup$
    – alephzero
    Commented Apr 30, 2021 at 22:31
  • $\begingroup$ Both of them are not separate effects. You cannot have one and not the other . So it does not make sense to talk about their relative contribution. Each of them can be used to explain lift and calculations using any of the effect will give you the total amount of lift $\endgroup$ Commented May 1, 2021 at 6:22

1 Answer 1


The two effects are actually the same effect so there is no "relative constribution".

As has been explained many times on the site, the air being deflected downwards means that the wing gives momentum to the air and by Newtons's third law the air pushes the wing up so the pressure below the wing is higher than that below. The high pressure slows the air down so the velocity below the wing is lower that that above the wing. The air being pushed down also leaves a partial vacuum above the wing so the pressure there is lower and the air speeds up as it enters the low pressure region because is being pushed by the higher pressure behind. Bernouli and deflection are therefore just two different ways of doing the momentum balance accounts.


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