A backpack helicopter is a helicopter motor and rotor and controls assembly that can be strapped to a person's back, so he can walk about on the ground wearing it, and can use it to fly. It uses a harness like a parachute harness and should have a strap between the legs (so the pilot does not fall out of the harness during flight). Some designs may use a ducted fan design to increase upward thrust. Several inventors have tried to make backpack helicopters, with mixed results. (source)