User:Born2flie/Lockheed XH-51

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Main article: Lockheed XH-51
XH-51

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
NASA
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.

Contents

[edit] History

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.

[edit] Survivors

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

[edit] References

Notes
  1. ^ Ed. Connor, R. "Lockheed CL-475". Smithsonian National Air & Space Museum. Accessed 3 September 2007 <http://www.nasm.si.edu/aircraft/lockheed_cl475.htm>.
  2. ^ Hirschberg, Michael J. and David K. Daley. "Lockheed", US and Russian Helicopter Development In the 20th Century. American Helicopter Society, International. Accessed 16 November 2007 <http://www.vtol.org/History.htm>.
  3. ^ a b (Badrocke and Gunston 1998)
  4. ^ Rotary Wing Collection. United States Army Aviation Museum.
Bibliography
  • Badrocke, Michael and Bill Gunston. Lockheed Aircraft Cutaways the History of Lockheed Martin. London: Osprey Aviation. 1998. ISBN 978-1-855-32775-7

[edit] External links