[rcxdude]

Because the pressure on the top is lower :) (this is half-serious: the whole problem with these explanations is that cause and effect for all of these variables is not straightforward: you can see from the navier-stokes equations they are all dependent on each other).

[tomsto]

Kind of. Actually the real ‘cause’ in my understanding is 1) the curved geometry of the suction (upper) side of the aerofoil and 2) the fact that the flow remains attached to it. Everything else - you can actually approximate the curved surface to a circle and apply equations of circular motion to a parcel of air to satisfy yourself with why the flow is accelerating. And Newton’s 3rd law explains how lift is generated on the wing. In my view there’s no need to use Navier-Stokes to explain how an aerofoil works, if you simplify the geometry to make a special case.

Most of the lift comes from the suction side.

Actually, if you really want to test an explanation, try to apply the same reasoning to explain how a sailing boat can sail upwind (or at least up to about 45 degrees off).

[shadowgovt]

The devil is in that last detail. "Flow stays attached" is a description of the properties of the flow, not an explanation for what causes attached flow or why attached flow matters. It's semicircular reasoning to say that the plane gets lift because the flow stays attached... Attached flow and lift are correlated, but they may be two phenomena caused by the same underlying property.