The North American Aviation XB-70 Valkyrie was the prototype version of the planned B-70 nuclear-armed, deep-penetration strategic bomber for the United States Air Force Strategic Air Command.
Designed in the late 1950s by North American Aviation, the six-engined Valkyrie was capable of cruising for thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m). 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.
North American improved on the basic concept by adding a set of drooping wing tip panels that were lowered at high speed. This helped trap the shock wave under the wing between the downturned wing tips. It also added more vertical surface to the aircraft to maintain directional stability at high speeds. When the wing tips were drooped, the surface area at the rear of the wings was lessened, moving the lift forward and reducing trim drag.
The buildup of heat due to skin friction during sustained supersonic flight had to be addressed. During a Mach 3 cruise, the aircraft would reach an average of 450 °F (230 °C), with leading edges reaching 630 °F (330 °C), and up to 1,000 °F (540 °C) in engine compartments. NAA proposed building their design out of sandwich panels, with each panel consisting of two thin sheets of Stainless Steel brazed to opposite faces of a honeycomb-shaped foil core.
The USAF eventually gave up fighting for its production and the B-70 program was canceled in 1961. Development was then turned over to a research program to study the effects of long-duration high-speed flight. As such, two prototype aircraft, designated XB-70A, were built; these aircraft were used for supersonic test-flights during 1964–69. In 1966, one prototype crashed after colliding with a smaller aircraft while flying in close formation; the remaining Valkyrie bomber is in the National Museum of the United States Air Force near Dayton, Ohio.
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