Let's try for an intuitive approach using a flat plate (your hand, for
example). Imagine sticking your hand out the window of a moving car
and "flying" it through the air as most of us have probably done as a
kid until our parents yelled at us.

If you hand is more or less parallel to the ground, you have wind
resistance (drag), but no lift. Tilt you hand slightly upwards and
now the wind strikes the bottom of your palm and forces it upwards
(lift). The reason lift is created is that your hand is deflecting
molecules of air downwards (change in momentum), and the resultant
force is upwards. It's simple Newtonian mechanics.


.........nah........it's water skiing, which has nothing to do with airfoils
(but does illustrate how the flaps help an airfoil at low speeds).

High v, low p on top
Low v, hi p on bottom (relative)

lift

QED

cheers

oz, flight test engineer, Edwards, 1968-71