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North American XB-70 Valkyrie

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Developed to USAF General Operational Requirement 38 for an intercontinental bomber to replace the Boeing B-52,

At one time the order was cut back to a single prototype containing no military equipment. In 1960 the US Government decided to order 12 fully operational B-70s. In March 1961, the contract awarded on 4 October 1961 was again cut back to three aeroplanes, intended mainly for research, although the third was later cancelled.

The North American XB-70 Valkyrie first flew in prototype form on 21 September 1964. When the first prototype flew it was simultaneously the longest (56.4 m/185 ft), fastest (Mach 3+), most powerful and costliest aircraft ever built, US$2000 million, and weighing 305-tonne (300-ton).

A delta-winged canard design, the airframe made extensive use of contemporary ‘exotic’ alloys to overcome the problems associated with kinetic heating. The wings were swept back at 65 degrees 34 minutes on the leading edge, and were covered with brazed stainless steel honeycomb panels welded together to produce an extremely strong yet heat-resistant whole. Similar construction was used for the huge rectangular moveable engine duct under the centreline, the twin vertical tail surfaces (30 ft high) and part of the fuselage. The advanced aerodynamics of this elegant yet menacing warplane were based on a large delta wing from whose centre grew a slim forward fuselage complete with canard foreplanes.

 

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The powerplant comprised six 31,000-lb (14.062-kg) thrust General Electric YJ93-GE-3 afterburning turbojets in a 30 ft long ducted arrangement under virtually the full chord of the delta wing. To slow entering airstream from Mach 3 to less than Mach 1 the designers created a series of shock patterns which employ the vertical splitter, then additional breaks within the splitter duct. Finally hydraulically operated panels vary final throat area to meet varying conditions.
 
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The wings outer portions were arranged to hinge downward in flight under hydraulic power to improve stability and maneuverability. An anhedral angle of 25 degrees was used for low-altitude supersonic flight, increasing to 65 degrees for high-altitude flight at Mach 3. Six power hinge actuators on each lower outer surfaces during high speed flight. Each hinge has hundreds of closely meshed gears of hard H-11 steel.
 
 NA-XB-70-05
 
Control was provided by a combination of flaps on the canard foreplanes, no fewer than 12 wide-chord elevons across much of the trailing edge of the wings outboard of the variable-geometry engine exhausts, and large rudders on each of the vertical surfaces. The canard slab surfaces provide trim control while keeping drag low, their rear section deflecting down as flaps. Control of so complex an aerodynamic platform moving at high supersonic speeds was effected with the aid of a three-axis stability-augmentation system.
 
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The landing gear consists of 2 tons of wheels, tires and brakes. A brake control device employs a fifth wheel on the main gear, comparing the amount of slippage between braked wheels and the fifth wheel with coefficient of friction between tires and runway surface, predicts skid point, and automatically regulates
 
 NA-XB-70-07
 
The windshield moves along with a variable-position nose ramp. During subsonic operation the forward edge of the windshield can be lowered for better visibility. Dark spos above the cockpit area and on the canard surfaces are crane lift points.

 

The first prototype was flown by Alvin S. White and Colonel Joseph F. Cotton on 21 September 1964. The first flight had been so long postponed and the entire project downgraded to only two prototypes. By the flight, the first US had spent $1.34 billion on its development. $92 million was then allocated to see the two prototypes through the flight program. Both XB-70’s were programmed for a 180 hr flight test schedule, including experiments for NASA. It first achieved its design speed of Mach 3 on 14 October 1965.

 

NA-XB-70

 

NASA’s Flight Research Center spent $2,000,000 on instrumentation on the No.1 aircraft. Areas of study included flutter of skin panels and internal noise levels; heating of structures in such areas as windshield, fuel tanks and crew compartment. 


The improved second prototype flew on 17 July 1965, but was lost in a mid-air collision on 8 June 1966. The surviving aircraft carried out a number of test programmes, including work in connection with the US supersonic transport programme, but on 4 February 1969 it was flown to retirement at the US Air Force Museum, Wright Patterson AFB, Dayton, Ohio.

 

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Even before the fist prototype flew, however, technological developments in air defence had made the XB-70 obsolete. In 1963 the U.S. government ended the XB-70 development programme and turned the prototypes over for research purposes although one of the XB-70s was lost on 8 June 1966. The surviving XB-70 is now a museum piece.

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Gallery


Engines: 6 x General Electric YJ93-GE-3 afterburning turbojets, 31,000-lb (14.062-kg)
Wing span: 105 ft 0 in (32 m)
Length: 196 ft 0 in (59.74 m)
Max TO wt: 530,000 lb (240,400 kg)
Max level speed: M3 / 3218 km/h / 2000 mph
Height: 9.1 m / 29 ft 10 in
Wing area: 565.0 sq.m / 6081.60 sq ft
Ceiling: 21336 m / 70000 ft
Range w/max.fuel: 12000 km / 7457 miles
Crew: 2

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North American XB-70 Valkyrie

 

 


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