The massive XB-70 Valkyrie is the largest and heaviest airplane ever to fly at Mach 3.
The North American XB-70 Valkyrie was the most ambitious super-bomber project of the Cold War. The massive six-engine bomber was slated to be the ultimate American high-altitude, high-speed, deep-penetration manned nuclear bomber designed to fly high and fast, so has to be safe from Soviet interceptors.
Two Valkyrie prototypes were been built at North American Aviation before the Kennedy Administration cancelled the program as a consequence of the doubts that surrounded the future of manned bombers believed to be obsolete platforms. The threat posed by Soviet SAMs (Surface-to-Air Missiles) put the near-invulnerability of the strategic bomber at high altitudes in doubt. In low-level penetration role, the B-70 offered little performance improvement over the B-52 it was designed to replace (!) and it was much more expensive with shorter range.
Some fascinating variants of the aircraft were proposed. Some envisaged the B-70 carrying an Alert Pod, or flying as a Supersonic Refueler or as a Recoverable Booster Space System (RBSS). You can find all the details about these crazy concepts in this story we have posted last year.
The B-70 program was canceled in 1961 and development continued as part of a research program to study the effects of long-duration high-speed flight with the two XB-70A.
XB-70A number 1 (62-001) made its first flight from Palmdale to Edwards Air Force Base, CA, on Sept. 21, 1964. The second XB-70A (62-207) made its first flight on Jul. 17, 1965. The latter differed from the first prototype for being built with an added 5 degrees of dihedral on the wings as suggested by the NASA Ames Research Center, Moffett Field, CA, wind-tunnel studies.
While the 62-001 made only one flight above Mach 3, because of poor directional stability experienced past Mach 2.5, the second XB-70, achieved Mach 3 for the first time on Jan. 3, 1966 and successfully completed a total of nine Mach 3 flights by June on the same year.
A joint agreement signed between NASA and the Air Force planned to use the second XB-70A prototype for high-speed research flights in support of the American supersonic transport (SST) program.
However, on June 8, 1966, the XB-70 62-207 was involved in one of the most famous and tragic accidents in military aviation when it collided with a civilian registered F-104N while flying in formation as part of a General Electric company publicity photo shoot over Barstow, California, outside the Edwards Air Force Base test range in the Mojave Desert. The aircraft were flying in formation with a T-38 Talon, an F-4B Phantom II, and a YF-5A Freedom Fighter.
As explained in a previous post here at The Aviationist:
Towards the end of the photo shooting NASA registered F-104N Starfighter, piloted by famous test pilot Joe Walker, got too close to the right wing of the XB-70, collided, sheared off the twin vertical stabilizers of the big XB-70 and exploded as it cartwheeled behind the Valkyrie. North American test pilot Al White ejected from the XB-70 in his escape capsule, but received serious injuries in the process. Co-pilot Maj. Carl Cross, who was making his first flight in the XB-70, was unable to eject and died in the crash.
The root cause of the incident was found to be wake turbulence: wake vortices spinning off the XB-70’s wingtip caused Walker’s F-104N to roll, colliding with the right wingtip of the huge XB-70 and breaking apart. As explained in details in this post, wingtip vortices form because of the difference in pressure between the upper and lower surfaces of a wing. When the air leaves the trailing edge of the wing, the air stream from the upper surface is inclined to that from the lower surface, and helical paths, or vortices, result. The vortex is strongest at the tips and decreasing rapidly to zero nearing midspan: at a short distance from the trailing edge downstream, the vortices roll up and combine into two distinct cylindrical vortices that constitute the “tip vortices.
Although research activities continued with the first prototype with a first NASA flight on April 25, 1967, the last one was on Feb. 4, 1969.
The only remaining XB-70 Valkyrie super bomber in on display at the National Museum of the U.S. Air Force at Wright-Patterson AFB in Dayton, Ohio. In October last year, it had to briefly moved outside for display maintenance. Here you can watch a video of the monumental move.