North American Aviation XB-70 Valkyrie

North American Aviation XB-70 Valkyrie was the prototype of the B-70 nuclear-armed, deep-penetration strategic bomber for the United States Air Force Strategic Air Command. In the late 1950s, North American Aviation designed the Valkyrie bomber as a large, six-engined aircraft capable of reaching Mach 3+ while flying at 70,000 feet (21,000 m). At these speeds, it was expected that the B-70 would be almost immune to interceptor aircraft, the only effective weapon against bomber aircraft at the time. The bomber would spend only a few minutes over a particular radar station, flying out of its range before the controllers could position their fighters in a suitable location for an interception. Its high speed also made the aircraft difficult to see on the radar displays and its high altitude flight could not be matched by any contemporary Soviet fighter.

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 Navaho, as well as a modified form of the SM-64 Navaho's all-inertial guidance system. The XB-70 used compression lift, which arose from a shock wave generated by the sharp leading edge of the central engine intake splitter plate below the wing.At Mach 3 cruising speed, the shock wave attached along the wing leading edge, preventing the high pressure behind the shock front from leaking up over the wing.

The compression lift provided five percent of the total lift.The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave. Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees, acting almost as a type of variable-geometry wingtip device. 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.

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 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