Layman's guess: wings push air down, air pushes wings up.
An everyday experiment is sticking your flat hand out the window of a moving car. With slight wrist rotations, you'll find even slight deviations from neutral (parallel to the ground) cause your "wing" to rise or fall, with a force that seems proportional to the angle.
We can hypothesize that a symmetric wing, with zero angle of attack, should experience no lift:
There is a pressure difference with an asymmetric airfoil, and that results in air being directed downward with a resulting upward reaction force. F=ma still holds, the lift force is equal to the mass × acceleration of the air downwards, likewise momentum is conserved as the momentum of the plane up equals that of the air going down.
All of the lift can be explained by Newton's laws, but explaining why the air moves down in the first place can't be explained by Newton's laws.
I checked the top hit [1] for googling "how do wings really generate lift"
which, being a NASA webpage, instilled some confidence they would have the correct explanation. But alas:
> Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air.
Then I read [2] which corrects that view:
> “What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes – lower pressure on the upper surface and higher pressure on the lower surface,” clarified Babinsky, from the Department of Engineering. “This is why a flat surface like a sail is able to cause lift – here the distance on each side is the same but it is slightly curved when it is rigged and so it acts as an aerofoil. In other words, it’s the curvature that creates lift, not the distance.”
This is still not very satisfying, as it fails to show HOW curvature causes lift. Maybe there is no simple explanation...
That's incomplete though; an asymmetric airfoil with 0° angle of attack does generate lift. The problem is the "equal times" -- the times are not "equal", but the air passing over the curved side does go faster.
> Cambered airfoils generate lift at zero angle of attack. When the chord line is horizontal, the trailing edge has a downward direction and since the air follows the trailing edge it is deflected downward.
