North American XB-70 Valkyrie

When it was rolled out on 11 May 1964, the first prototype of North American’s XB-70 six-engine Mach 3 strategic bomber was the most expensive, most powerful, longest, and heaviest aeroplane ever built. It had six engines housed in a box structure beneath the delta wing, In flight, the wingtips could be lowered up to 65 degrees to contain
the airflow under I he wing, a feature found in no other large aircraft .Flying at three times the speed of sound, the airframe temperatures were expected to exceed 330°C, so almost 70 per cent of the Valkyrie’s structure was made
of heat – resistant stainless steel.
The aircraft was originally intended to replace the Boeing B-52, but long before the first prototype appeared, plans to put the XB-70 into production had heen cancelled. It seemed that missiles were in fashion and large, high-flying nuclear bombers were out.
The Valkyrie found a niche, however, as an experimental aircraft. After early structural problems were overcome, it performed well.
In October 1965 the second and last XB-70 maintained Mach 3.08 for 33 minutes, crossing eight US states. This aircraft was then lost in an in-flight collision with an F-104 when flying information for a photo-shoot on 8 June 1966. The surviving XB-70 continued research flights until February 1969.