Hiller X-18

(Redirected from X-18)

The X-18 was an experimental cargo transport aircraft designed to be the first testbed for tiltwing and STOVL (short take off and vertical landing) technology.

The Hiller X-18, roatating its tiltwings

Ground testing the X-18 tiltwing

The X-18 showing its elaborate engine configuration

The X-18 with partially rotated tiltwings

Development

Design work started in 1955 by Stanley Hiller Jr and Hiller Aircraft Corporation received a manufacturing contract and funding from the U.S. Air Force to build the only X-18 ever produced.

To speed up construction and conserve money the plane was constructed from scavenged parts including a Chase C-122 Avitruc fuselage and the turboprops came from the Lockheed XFV-1 and Convair XFY-1 Pogo experimental airplanes program. The tri-bladed counter-rotating propellers were a giant 16 ft (4.8 m) 4.8 m across. The Westinghouse turbojet engine had its exhaust diverted upwards and downwards at the tail to give the plane pitch control at low speeds.

Service history

The first test flight wasn't until November 24, 1959, ultimately recording 20 flights out of Edwards AFB. A number of problems plagued the X-18 including being susceptible to wind gusts when the wing rotated, acting like a sail. In addition the turboprop engines were not cross-linked, so the failure of one engine meant the airplane would crash.

On the 20th and final flight in July 1961, the X-18 had a propeller pitch control problem when attempting to hover at 10,000 ft and went into a spin. The crew regained control and landed but the X-18 never flew again, however ground testing of the tiltwing concepts continued. Eventually a test stand the plane was mounted on failed and the plane was severely damaged in the fall. The program was cancelled January 18, 1964 and the X-18 was cut up for scrap.

Specifications (X-18)

General characteristics

Crew: 2–3
Capacity:
Length: 63 ft 0 in (19.2 m)
Wingspan: 48 ft 0 in (14.6 m)
Height: 24 ft 7 in (7.5 m)
Wing area: ft² m²
Empty: 26,786 lb (12,150 kg)
Loaded: lb ( kg)
Maximum takeoff: 33,000 lb (14,850 kg)
Powerplant:
- 2x Allison T40-A-14 turboprop, 5,500 hp (4,100 kW) each
- 1x Westinghouse J34 turbojet for pitch control, 3,400 lbf (15.2 kN) thrust

Performance

Maximum speed: 253 mph (407 km/h)
Range: miles ( km)
Service ceiling: 35,300 ft (10,800 m)
Rate of climb: ft/min ( m/min)
Wing loading: lb/ft² ( kg/m²)
Power/mass: