Actually, multi-propeller.
Giving the same total power, the same tip speeds, the same total propeller disk area, and similarly well-designed propellers, how does a single propeller compare to two propellers, in terms of efficiency. There will be Reynolds number effects, of course... anything else?
Giving the same total power, the same tip speeds, the same total propeller disk area, and similarly well-designed propellers, how does a single propeller compare to two propellers, in terms of efficiency. There will be Reynolds number effects, of course... anything else?