I've been recently looking for answers to this question on the internet but the jungle of propellers, fans and electric motors didn't quite get me an answer. How would I have to design an electric engine to produce as much thrust as possible on an area as small as possible, so the thrust/area ratio should be high. Also, assume there's enough power available. Would I use propeller and if so, how many blades? Would I use a fan like the turbofan of a jet engine?
With the optimal solution, which thrust do you think a 500 mm prop/fan could produce?