North American Aviation’s B-70 was a nuclear-armed bomber designed for the United States Air Force’s Strategic Air Command in the 1950s. The Valkyrie was a large six-engined aircraft able to fly at Mach 3 at high altitudes.

Although the proposed full fleet of operational B-70 bombers was never built, two prototype XB-70s flew in flight tests in the 1960s, performing research on the design of large supersonic aircraft.

The Valkyrie was designed to be a large, high-altitude bomber with six engines to fly at Mach 3. It was configured as a canard delta wing, and built largely of stainless steel, sandwiched honeycomb panels, and titanium. It was designed to make use of a phenomenon called “compression lift”, achieved when the shock wave generated by the airplane flying at supersonic speeds is trapped underneath the wings, supporting part of the aircraft’s weight.

Under the center of the wing, the Valkyrie featured a prominent wedge at the center of the engine inlets, designed to produce a strong shock wave. By acting upwards upon the wings, this shock wave would allow the aircraft to recover energy from its own wake. At high speeds, compression lift increased the lift of the wings by thirty percent, with no increase in drag. 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, rather than simply flowing out past the wingtips.

In November 1959, during a meeting concerning the military programs of the coming year, President Eisenhower told the Air Force Chief of Staff that the “B-70 left him cold in terms of making military sense.” General White conceded there were important questions involved and that the aircraft was very different from anything previously developed. He said the B-70 must overcome the terrific heat generated by high speed and high altitude and that the shape of the aircraft’s wings and fuselage must be studied. However, to eliminate such unconventional aircraft would be going too fast and too far. Hardly impressed with the many pro-B-70 arguments put forth, the President stressed that the B-70, if allowed to reach production, would not be available for 8 or 10 years, when the major strategic retaliatory weapon would be the missile. The President finally agreed to take another look at the B-70 proposition, but in the same breath pointed out that speaking of bombers in the missile age was like talking about bows and arrows in the era of gunpowder.

The Air Force announced on 29 December that the B-70 program was reoriented to produce a prototype vehicle only and that the development of most sub-systems was canceled.

The first flight of the XB-70A Valkyrie occurred on 21 September 1964, nearly 4 years later than the date scheduled in 1958 (right after North American had won the contract). The 2-member crew-Alvin White, North American Chief Test Pilot, and Col. Joseph F Cotton, USAF B-70 Chief ‘lest Pilot-landed successfully at Edwards AFB. Nevertheless, the plane had to undergo additional ground tests before entering an extensive flight testing program at Edwards.

The striking features of the experimental B-70 centered on the configuration and composition of its airframe, with its semi-monocoque fuselage of steel and titanium. Also, the bomber’s external skin was composed of brazed stainless steel honeycomb sandwich, wide use having been made of titanium alloys. The XB-70′s flying controls comprised elevons on the trailing edges of the cantilever delta wings and twin vertical fins and rudders. The large canard foreplane was adjustable to achieve “trim” (balance in flight or landing, etc.). Its trailing edge flaps enabled it to droop the elevons to act as flaps, making it possible for the XB-70 to take off from and land on existing B-52 airstrips.

Continued technical difficulties delayed the XB-70′s testing program. For the same. reasons, completion of the second experimental B-70 took longer than expected, and the bomber did not fly before July 1965. Less than a year later, on 19 May 1966, the second XB-70A flew for 32 minutes at the sustained speed of mach 3. Unfortunately, tragedy closely followed this remarkable achievement. On 8 June, the plane was lost in a mid-air collision with a Lockheed F-104 fighter. The loss, occurring at approximately 25,000 feet, near Barstow, California, , reduced the XB-70A program to a single vehicle.