In terms of rotor length, the smallest helicopter is the GEN H-4 made by Gen Corporation (Japan) with a rotor length of only 4 m (13 ft).
Ride in it, if you dare. Constructed by Gen Corporation of Japan with a rotor length of a paltry 13 feet (that is less than twice the length of Zeus, the tallest living dog according to Guinness), the GEN H-4 is the smallest helicopter around. With a single seat, one piece of landing gear and a power unit, the entire contraption weighs only 154 pounds, about as much as the person flying it. Unlike more traditional helicopters, it has two sets of coaxial, counter-rotating rotors, which eliminate the need for a tail rotor for balancing. Just bring your own visor, because this beauty doesn’t have a windshield.