Ducted fan flight works basically like this: You have a horizontal fan in a short vertical tube, sucking air downward. Around the top end of this tube is a sort of shelf that protrudes outward. A pressure differential is created because the air rushing over the top of the shelf, being sucked in by the fan, exerts less pressure on the shelf than the stationary air below the shelf, so lifting thrust is generated.
I’ve seen pictures in old books of men flying in such machines. But what ever happened to the idea, and why was it abandoned? I can think of one excellent reason, which is that in case of engine failure you’d drop like a rock. Other powered aircraft offer a better chance of surviving a crash, as an airplane has some glide ratio even without engine power, and a helicopter can survive a crash by autorotation.