These pressure differences push the wing upwards. The circulation process controls the speed of the overall flow. The energy for the circulation comes from the aircraft's engine or, in the case of a glider, from gravity. It's all one interconnected system. Unless the overall result of that system is for air to end up lower than it was before the plane flew by, there will be no lift.
Wings move air downward, and react by being pushed upward.
That's what makes lift. All the rest is just interesting details. Return to AVweb welcome page . The AVweb Group. All rights reserved.