When i was flying as A Flight Engineer on Chinnoks, I discoved by accident, with the rear ramp down at 140 knots you could pour about half a coffee cup of water out the left hand side at the rear and it would swirl in a hover (like a mini tornado) about 4 feet above the ramp! It was so cool! (The things you discover on long filght in the artic!!!)Another example of lift or actually killing of lift is when people secure their small airplanes in remote areas without hangars when extreme winds are expected. They will strap 2X4s along the top of the wings (lengthwise) on the Cessna singles right above the main spars where the leading edge skin and main top skins join. Oh, one other example for the NASCAR fans on the board. The spoiler that flips up out of the top when the car get around backwards that keeps the car on the ground. What is it doing "Killing lift"!
Same principal as the rumble strip on the helmet.