Imagine that you are floating in space, and that the vacuum around you is perfect. Imagine further that you have, right beside you, a large rock, with exactly the same mass as you (including your spacesuit). What would happen if you were to push the rock away from you as hard as you can? You and the rock would move apart in opposite directions. You would each have the same speed, relative to your initial speed.

The exhaust of a rocket is no different from that rock. It has mass, and is being pushed away at high speed. The rocket is accelerated by the resulting force, even in a perfect vacuum.

Back to airfoils & wings. A wing creates lift when the pressure on the top is lower than the pressure on the bottom. It is not correct to say that a wing also creates lift because it deflects the air downward. A wing with the same pressure on the top and bottom surfaces will not deflect air downward. We can't separate the lift generated by a wing into these two separate components. The old debate about "deflection" vs. "pressure difference" is nonsensical.


banktoturn