The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep-penetration strategic bomber for the United States Air Force's (USAF) Strategic Air Command. Designed by North American Aviation in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly Mach 3+ at an altitude of 70,000 feet (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.
The introduction of effective high-altitude surface-to-air missiles (SAMs), the program's high development costs, and changes in the technological environment with the introduction of intercontinental ballistic missile (ICBM)s led to the cancellation of the B-70 program in 1961. Although the proposed fleet of operational B-70 bombers was canceled, two prototype aircraft were built as the XB-70A and used in supersonic test flights from 1964 to 1969. One prototype crashed following a midair collision in 1966; the other is on display at the National Museum of the United States Air Force in Ohio.
General characteristics
- Crew: 2
- Length: 189 ft 0 in (57.6 m)
- Wingspan: 105 ft 0 in (32 m)
- Height: 30 ft 0 in (9.1 m)
- Wing area: 6,297 ft² (585 m²)
- Airfoil: Hexagonal; 0.30 Hex modified root, 0.70 Hex modified tip
- Empty weight: 128,000 lb (58,100 kg)
- Loaded weight: 534,700 lb (242,500 kg)
- Max takeoff weight: 550,000 lb (250,000 kg)
- Powerplant: 6 × General Electric YJ93-GE-3 afterburning turbojet
- Dry thrust: 19,900 lbf (84 kN) each
- Thrust with afterburner: 28,800 lbf (128 kN) each
- Internal fuel capacity: 300,000 lb (136,100 kg) or 46,745 US gallons (177,000 L)
Performance
- Maximum speed: Mach 3.1 (2,056 mph, 3,309 km/h)
- Cruise speed: Mach 3.0 (2,000 mph, 3,200 km/h)
- Range: 3,725 nmi (4,288 mi, 6,900 km) on combat mission
- Service ceiling: 77,350 ft (23,600 m)
- Wing loading: 84.93 lb/ft² (414.7 kg/m²)
- lift-to-drag: about 6 at Mach 2
- Thrust/weight: 0.314
The XB-70 Valkyrie was designed to be a high-altitude bomber-sized Mach 3 aircraft 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 Navaho, as well as a modified form of the SM-64 Navaho's all-inertial guidance system.
The XB-70 used compression lift, which was generated from a prominent wedge at the center of the engine inlets that created a shock wave below the aircraft. The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave (the airflow at the XB-70 wing's leading edge was subsonic). The compression lift increased the lift by five percent. Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees. This increased the aircraft's directional stability at supersonic speeds, shifted the center of lift to a more favorable position at high speeds, and strengthened the compression lift effect. With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings.
The XB-70 was equipped with six General Electric YJ93-GE-3 turbojet engines, designed to use JP-6 jet fuel. The engine was stated to be in the "30,000-pound class", but actually produced 28,000 lbf (124.6 kN) with afterburner and 19,900 lbf (88 kN) without afterburner. The Valkyrie used fuel for cooling; it was pumped through heat exchangers before reaching the engines. To reduce the likelihood of auto ignition, nitrogen was injected into the JP-6 during refueling, and the "fuel pressurization and inerting system" vaporized a 700 lb (320 kg) supply of liquid nitrogen to fill the fuel tank vent space and maintain tank pressure.
