Originally Posted by
ryan1234
Crazy as it sounds, I agree with shdw in this case. Lift generally is 90 degrees from the relative wind, not really gravity (remember this is how you turn). Anytime the vortex is disrupted the loss of induced drag results. The aircraft by the cliff would be increasing AOA as thrust energy was reduced - as long as you had enough energy to maintain a non critical AOA (which should be a lot!) you could "feel" the "ground effect". Guess we could try it and find out.
Alright. Draw a simple diagram of an airplane in straight and level flight with all four forces: thrust, lift, weight and drag. To compare it, draw now this same airplane flying along this cliff straight up (90 degrees in relation to the horizon). Do you see any differences?
You are right to say "lift" is 90 degrees from the relative wind - BUT - does it apply to us in our case? Are we really generating lift? Just like straight and level - you maintain straight level because you have a balance of two forces: Lift and Weight.
If you fly now straight up, the weight vector is pointing right to the center of the Earth. If we did generate any lift even a small amount, we would then in this case fly away from the cliff. There is just no force to counteract it. So how can we fly parallel to this cliff? By simply flying the angle of attack (ie no lift line) that will generate no lift. If no lift is generated, ground effect is impossible.