The Flying Crane, Hughes XH-17.

The Hughes XH-17 “Flying Crane“ was the first helicopter project for the helicopter division of Hughes Aircraft Company. The XH-17, which had a two-bladed main rotor system with a diameter of 134 feet, still holds the world record for flying with the largest rotor system. Two General Electric J35 turbojet engines were used, sending bleed air up through the rotor hub. In flight, the main rotor spun at a sedate 88 revolutions per minute, less than half the speed of typical helicopter rotors. Since the rotor was driven at the tips rather than the hub, little torque compensation was required, mostly due to friction in the main rotor bearing. Thus, the XH-17 had a very small tail rotor compared to its main rotor. Powerplant: 2 General Electric 7E-TG-180-XR-17A gas generators, 3,480 hp each combined predicted gas poer output, with rotor turning at 88 rpm.