Lockheed XH-51

Le Lockheed XH-51 sur Wikipedia.en

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The Lockheed XH-51 (CL-595, Model 186) was a three-bladed, single-engine experimental [Vous devez être inscrit et connecté pour voir ce lien] designed by Lockheed-California, a division of [Vous devez être inscrit et connecté pour voir ce lien], utilizing a rigid rotor and retractable skid landing gear .

The XH-51 was selected as the test vehicle for a joint research program conducted by the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] to explore rigid rotor technology.

History

Lockheed began developing its [Vous devez être inscrit et connecté pour voir ce lien] concept with the [Vous devez être inscrit et connecté pour voir ce lien] helicopter design in 1959.

The choice of a rigid rotor meant that the helicopter was more agile than it would have been with a flapping rotor.

The performance of the CL-475 encouraged Lockheed to seek further development.

Lockheed submitted the CL-475 to the Army as a candidate to replace the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] helicopters.

Lockheed also tested the commercial market waters without success.

However, in February 1962, Lockheed's Model 186, a new design based on the CL-475 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 550 shp (410 kW) [Vous devez être inscrit et connecté pour voir ce lien] turboshaft engine, XH-51A (serial number 61-51262) first flew on 2 November 1962.

As flight testing progressed, the original three-bladed, rigid rotor system demonstrated instability at higher speed ranges.

Lockheed engineers solved the problem by modifying the aircraft with a four-bladed rotor system.

In 1963, the Army's Technology Research and Evaluation Command (TRECOM) contracted with Lockheed to modify one of the XH-51 aircraft into a compound helicopter.
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The second XH-51A (serial number 61-51263) was subsequently converted by adding wings with a span of 16.1 ft (4.9 m), and a 2,500 hp (1,864 kW) [Vous devez être inscrit et connecté pour voir ce lien] engine mounted on the left wing to increase performance.

The XH-51A Compound first flew without powering up the turbojet on 21 September 1964, while tests were conducted for balance and handling.

The aircraft's first flight as a true compound helicopter took place on 10 April 1965. and on 29 November 1967 achieved a speed of 263 knots (302.6 mph, 486.9 km/h).

In June 1964, NASA ordered a five-seat, three-bladed variant, the XH-51N (NASA 531) as a helicopter test vehicle.^{[Vous devez être inscrit et connecté pour voir ce lien]
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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.

Lockheed used the aircraft for several years as executive transports.

The aircraft were eventually sold to a collector and later destroyed by fire in 1988.
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The rigid rotor with a pusher tail prop distinguised the [Vous devez être inscrit et connecté pour voir ce lien] attack helicopter.

It was developed as the winning design for the 1964 AAFSS competition, with first flight in 1967.

However its intended role in the Vietnam war would be filled by the "interim" Bell AH-1 Cobra, as the complex design was plagued by various technical problems until its cancellation in 1972, and Lockheed's high hopes for the rotary wing aircraft market were never to materialize.

Variants


XH-51A

four place, three-bladed rotor

XH-51A Compound

modified with a four-bladed rotor and stub wings and an auxiliary 2,900 hp Pratt & Whitney J60-2 engine.

Compound

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XH-51N

five place, three-bladed rotor for NASA test purposes.

Model 286


five place civilian or military light helicopter offered for sale, none were sold.

Un N qui ne semble pas pouvoir accueillir 5 personnes

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Specifications (XH-51A)

Data from Janes's All The World's Aircraft 1969-70 ^{[Vous devez être inscrit et connecté pour voir ce lien]}

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)
  
• [Vous devez être inscrit et connecté pour voir ce lien]: 2,790 lb (1,265 kg)
  
• [Vous devez être inscrit et connecté pour voir ce lien]: 4,100 lb (1,864 kg)
  
• Powerplant: 1× [Vous devez être inscrit et connecté pour voir ce lien]B-9 [Vous devez être inscrit et connecté pour voir ce lien], 550 hp (410 kW)
  

XH-51A Compound

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