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Lockheed XH-51

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XH-51A following its conversion into a compound rotorcraft testbed
Type Helicopter, compound helicopter
Manufacturer Lockheed
Maiden flight 2 November 1962
Status Retired
Primary users United States Army
Produced 1962-64
Number built 3
Developed from Lockheed Model 86

The Lockheed XH-51 was an experimental helicopter design by Lockheed utilizing a rigid rotor. Lockheed's design, Model 186, was selected for a US military requirement for a high-speed, research helicopter.


The rigid rotor concept had been in use by Lockheed in an earlier helicopter, the CL-475, since 1949.[1] The choice of a rigid rotor meant that the helicopter was more agile than it would have been with a flapping rotor. The CL-475 competed against the Hughes 269 in the Army's early quest for a Light Observation Helicopter and Lockheed tested the commercial market waters without success. However, in February of 1962, Lockheed's Model 186, a new design based on the CL-475's successful rigid rotor, was selected as the winner for a joint Army-Navy program to evaluate the rigid rotor for high-speed flight capability.

Two four-seat, three-bladed XH-51As were ordered and built for the program. Powered by the Pratt & Whitney Canada PT6B-9 (550-shp) turboshaft engine, the first helicopter first flew on 2 November 1962. As the aircraft began testing, the original three-bladed, rigid rotor system developed instability at higher speed ranges. Lockheed solved the problem by modifying the aircraft with a four-bladed rotor system. The second XH-51A was subsequently converted into a compound helicopter using stub wings (16.1 ft span), a 2,900 hp Pratt & Whitney J60-2 turbojet engine mounted on the left wing, and the same four-bladed rotor system to increase performance. The XH-51A Compound first flew on 10 April 1965,[2] and on 29 November 1967 achieved a speed of 263.0 knots (302.6 mph, 486.9 km/h).[3]

In June 1964, NASA ordered a five-seat, three-bladed variant, the XH-51N (NASA 531) as a helicopter test vehicle.[3]

Lockheed built two demonstrator aircraft, designated the Lockheed Model 286, to market to the public (registration numbers N286L and N265LC). These aircraft had the five-seat configuration of the XH-51N with the four-bladed rotor system of the XH-51A. The Model 286 was certificated for civil operation by the FAA on 30 June 1966 but Lockheed never sold any aircraft.


The two XH-51A examples (Serial Numbers 61-51262 and 61-51263) are stored at Fort Rucker's Army Aviation Museum.[4]

Specifications (XH-51A)

Data from Janes's All The World's Aircraft 1969-70 [5]

General characteristics

  • Length: 40 ft 9 in (12.40 m)
  • Rotor diameter: 35 ft 0 in (10.67 m)
  • Height: 8 ft 2½ in (2.50 m)
  • Disc area: 962 ft² (89.4 m²)
  • Empty weight: 2,790 lb (1,265 kg)
  • Max takeoff weight: 4,100 lb (1,864 kg)
  • Powerplant:Pratt and Whitney PT-6B-9 turboshaft, 550 hp (410 kW)


See also

Related development

Related lists


  1. Lockheed CL-475. Smithsonian National Air & Space Museum. Retrieved on 2007-09-03.
  2. Michael J. Hirschberg; David K. Daley. US and Russian Helicopter Development In the 20th Century. Retrieved on 2007-09-16.
  3. 3.0 3.1 Badrocke, Michael; Bill Gunston (1998). Lockheed aircraft cutaways the history of Lockheed Martin. London: Osprey Aviation. ISBN 9781855327757. 
  4. Rotary Wing Collection. United States Army Aviation Museum.
  5. Taylor, J.W.R. (ed.) (1969). Jane's All The World's Aircraft 1969-70. London: Jane's, 359-360. 

External links

Template:USAF helicopters

This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "Lockheed XH-51".