3D "flying" is overpowering an aircraft to the point where it really doesn't even need to fly, i.e. generate lift. Ostensibly this is so one can back a plane down to where it's tail touches the ground and then drive it back up. Based on the answer above 4D is doing the same thing but nose down with a reverse thrust prop until the spinner touches the ground. Sane people would ask "what's the point?" Some people also play Russian roulette - sane people also ask "why?" about that. But then...