The Hiller X-18 was an experimental cargo transport aircraft designed to be the first testbed for tiltwing and V/STOL (vertical/short takeoff and landing) technology.

The Westinghouse turbojet engine had its exhaust diverted upwards and downwards at the tail to give the plane pitch control at low speeds.

A number of problems plagued the X-18 including being susceptible to wind gusts when the wing rotated, acting like a sail.

On the 20th and final flight in July 1961, the X-18 had a propeller pitch control problem when attempting to convert to a hover at 10,000 ft (3,000 m) and went into a spin.

One engine run was successfully conducted to the full 15-foot (4.6 m) wheel height on the VTOL Test Stand.