Hughes XH-17 - Design and Development

Design and Development

The XH-17 was a heavy-lift rotorcraft that was designed to lift loads in excess of 15 metric tons. To speed construction, parts of the XH-17 were scavenged from other aircraft. The front wheels came from a B-25 Mitchell and the rear wheels from a C-54 Skymaster. The fuel tank was a bomb bay-mounted unit from a B-29 Superfortress. The cockpit was from a Waco CG-15 and the tail rotor from a Sikorsky H-19 was used for yaw control.

In the late 1940s, Hughes developed an interest in helicopters. In August 1947, helicopter manufacturer Kellett sold his design for the giant XH-17 Sky Crane to Hughes, who commissioned the development of the XH-17 Flying Crane research vehicle. In 1948 the XH-17 began to take shape. The giant helicopter was tested in Culver City, California over a three-year period beginning in 1952. The XH-17 flew in 1953 at a gross weight in excess of 50,000 pounds (23,000 kg). It still holds the record for flying with the world's largest rotor system. Only one unit was built, since the aircraft was too cumbersome and inefficient to warrant further development.

The propulsion system was unusual. Two General Electric J35 turbojet engines were used, sending bleed air up through the rotor hub. The blades were hollow, and the hot compressed air traveled through the blades to tip jets where fuel was injected. In flight the rotors spun at a sedate 88 rpm. Since the rotor was driven at the tips rather than the hub, little torque compensation was required. Thus, the XH-17 had a very small tail rotor compared to its main rotor. This drive system was inefficient, limiting the test aircraft to a range of only 40 miles (64 km).

The XH-28 was a derivative, with a maximum weight of 104,000 pounds (47,000 kg). Though a wooden mockup of the design was made, the program was cancelled and none were built.