Hughes XH-17

The Hughes XH-17 Flying Crane was the first helicopter project of the helicopter division of Hughes Aircraft and a one-off heavy-lift research machine. Hughes bought the design from Kellett in August 1947 and began developing it in 1948; it was tested at Culver City, California from 1952 and flew in 1953 at a gross weight above 50,000 pounds. Its two-bladed rotor, roughly 130 to 134 feet across, still holds the record as the largest rotor system ever flown. Two General Electric J35 turbojets acted as gas generators, sending bleed air through the hollow blades to tip jets where fuel was injected, so the rotor turned at only 88 revolutions a minute and needed just a small tail rotor. The inefficient drive limited range to about 40 miles, only one was built, and a larger derivative, the XH-28, was cancelled after a wooden mockup.