This Saturday marks the 60th anniversary of the XB-70 exceeding Mach I for the first time!
In 1954, the US Air Force issued a General Operational Requirement calling for a strategic bomber to replace the Boeing B52—which had not yet even become operational. After further studies and refinement over the ensuing months, Weapons System 110A emerged, specifying a large payload, intercontinental range, subsonic cruise, “maximum possible” speed during a lengthy “penetration dash,” and an operational date of 1963. Only Boeing and North American Aviation elected to take on this considerable challenge. It was just seven years after the tiny, rocket-powered X1 first “broke the sound barrier,” but now the Air Force wanted to fly a massive bomber across the world, at a minimum of 60,000 feet, going two or three times as fast as Chuck Yeager did. Even current fighters could not hit these performance requirements, regardless of range. To further complicate the design, the contract also called for a reconnaissance version of the plane to be developed simultaneously.
The radical specifications resulted in initially radical designs from Boeing and North American. Both concepts used disposable fuel tanks and weighed threequarters of a million pounds (for comparison, a B52 is less than 200,000 pounds). Realizing the folly of this approach, the Air Force permitted more technology/performance tradeoffs and, in 1957, selected North American’s new design, dubbed the XB70, as the winner. It featured a massive delta wing, six engines that propelled it beyond Mach 3, and an extended “swan neck” front fuselage that was graced by canards (small control wings) on either side.
But from the fall of 1957 into 1958, global events outpaced the program. The Soviets had launched Sputnik, the world’s first artificial satellite, and the US had drastically accelerated its Intercontinental Ballistic Missile (ICBM) programs. The ICBMs topped with nuclear warheads could hit the Soviet Union faster (and more cheaply), were nearly invulnerable to interception, and would be ready sooner than massive and expensive bombers like the XB70. The resulting debate was heavily swayed by the ICBM, the potential vulnerability of even highspeed aircraft to interception or surface to air missiles, and by the cancellation of a related fighter program that used many of the same systems, thereby sharing development costs. After several fits and starts, the XB70 program was reduced to just two airframes as prototype/research demonstrators.
The first XB70 Valkyrie rolled out of the North American plant at Palmdale, California, on 11 May 1964, and made its first flight on 21 September, concluding at the adjacent Edwards AFB for the rest of the test program. The pilots had planned to take the Valkyrie past Mach 1 on that maiden voyage, but its landing gear got stuck in the lowered position. A second attempt had a hydraulic failure and saw a “large amount” of paint peel from the aircraft (below). Finally, on 12 October 1964, the XB70 exceeded the speed of sound for the first time. The remaining test program experienced a fair share of difficulties, culminating in a midair collision that destroyed the second prototype. NASA briefly flew the remaining airplane for further research, until it made its final journey—to Wright-Patterson AFB for display at the National Museum of the USAF. (Photos: NMUSAF)
B-58 Hustler: Length: 96 ft 9.4 in, Wingspan: 56 ft 9.9 in
XB-70 Valkyrie: Length: 186 ft, Wingspan: 105 ft