The North American Aviation XB-70 Valkyrie was the prototype version of the planned B-70 nuclear-armed, deep-penetration supersonic strategic bomber for the United States Air Force Strategic Air Command.
The Valkyrie was designed to be a high-altitude Mach 3 bomber with six engines.
Harrison Storms shaped the aircraft with a canard surface and a delta wing, which was built largely of stainless steel, sandwiched honeycomb panels, and titanium.
The XB-70 was designed to use supersonic technologies developed for the Mach 3 SM-64 Navaho, as well as a modified form of the Navaho’s inertial guidance system.
The XB-70 used compression lift, which resulted from a shock wave generated by the leading edge of the engine intake splitter below the apex of the wing.
At Mach 3 cruising speed, the shock wave is bent back about 65 degrees and the wing is superimposed on the shock system which has a pressure 40 pounds per square foot higher under the aircraft than in front of the shock.
The compression lift provided five percent of the total lift.
Camber was added to the wing leading edge inboard of the folding tips to improve subsonic handling and reduce supersonic drag.
The outer portions of the wings were hinged to pivot downward by 65 degrees, acting as a type of variable-geometry wingtip device.
This increased the aircraft’s directional stability at supersonic speeds, shifted the centre of pressure to a more favourable position at high speeds, and caused the shock originating at the intake splitter to reflect from the vertical tip surface giving additional compression lift.
Like a number of other delta-wing aircraft designed for supersonic speeds (Concorde, Tu-144, FD2), the Valkyrie needed a feature to improve the pilot’s view during nose-high low-speed flight and on the ground.
An outer windshield and ramp, which could be lowered, was provided enabling viewing through the fixed cockpit windshield.
With the ramp raised into its high-speed position, the forebody was more streamlined.
Rain removal and windshield anti-ice was accomplished by utilizing 600 °F (316 °C) bleed air from the engines.
The lower forward section included a radar bay, and production machines were to be equipped with a refuelling receptacle on the upper surface of the forward fuselage.
The XB-70 was equipped with six General Electric YJ93-GE-3 turbojet engines, which used JP-6 jet fuel, specially formulated for the mission requirements.
The engine was stated to be in the “30,000-pound class”, but actually produced 28,000 lbf (120 kN) with afterburner and 19,900 lbf (89 kN) without afterburner.
The Valkyrie used fuel for cooling; it was pumped through heat exchangers before reaching the engines.
To reduce the likelihood of autoignition, nitrogen was injected into the JP-6 during refuelling, and the “fuel pressurization and inerting system” vaporized a 700 pounds (320 kg) supply of liquid nitrogen to fill the fuel tank vent space and maintain tank pressure.
Variants
XB-70A
Prototype of B-70, Two were built.
AV-1
NAA Model Number NA-278, USAF S/N 62-0001, completed 83 flights spanning 160 hours and 16 minutes.
AV-2
NAA Model Number NA-278, USAF S/N 62-0207, flew 46 times over 92 hours and 22 minutes, before it crashed in June 1966.
XB-70B
AV-3
NAA Model Number NA-274, USAF S/N 62-0208, was originally to be the first YB-70A in March 1961.
This advanced prototype was cancelled during early manufacture.
YB-70
Planned preproduction version with improvements based on XB-70s.
B-70A
Planned bomber production version of Valkyrie.
A fleet of up to 65 operational bombers was planned.
RS-70
Proposed reconnaissance-strike version with a crew of four and in-flight refuelling capability.
Specifications
Crew
2
Length
185 ft 0 in (56.39 m)
Wingspan
105 ft 0 in (32.00 m)
Height
30 ft 0 in (9.14 m)
Wing area
6,297 sq ft (585.0 m2)
Airfoil
Hexagonal
0.30 Hex modified root
0.70 Hex modified tip
Empty weight
253,600 lb (115,031 kg)
Gross weight
534,700 lb (242,536 kg)
Max take-off weight
542,000 lb (245,847 kg)
Fuel capacity
300,000 pounds (140,000 kg) / 46,745 US gal (38,923 imp gal; 176,950 l)
Powerplant
6 × General Electric YJ93-GE-3 afterburning turbojet,
.