Before the advent of stealth technology, the variable that mattered more than any other in terms of tactical aircraft survivability and lethality was speed. So in 1955 the U.S. Air Force issued a request for a high-altitude, long-range bomber that could go Mach 3 while carrying either a conventional or nuclear payload. After a few trips to the drawing board and some mods to the Air Force's requirements, North American Aviation was awarded a developmental contract based on their submission.
The Valkyrie XB-70 (U.S. Air Force photo)
Enter the B-70 Valkyrie, a revolutionary scream-machine that was nearly four times as fast as the legacy B-52s it was designed to replace. The Valkyrie was huge -- 185 feet long and 30 feet tall with a maximum takeoff weight at a whopping 542,000 pounds. The bomber was powered by six General Electric J-93GE turbojet engines that could each deliver 30,000 pounds of thrust in full afterburner. But it's massive size and power was belied by sleek lines that made it arguably the most aesthetically-pleasing aircraft ever built.
The B-70 had a crew of four -- a pilot, co-pilot, bombardier, and defense systems operator each seated in comfortable cocoons with clamshell doors. In the event of an emergency each cocoon could rocket away from the aircraft individually.
The Valkyrie used "compression lift" -- a phenomenon that occurs when a conical body (the fuselage) under the center of a wing pushes air to the sides, which increases pressure and therefore lift -- to travel upwards of 7,500 nautical miles supersonic. At takeoff the wingtips were straight, but a high speeds they'd angle down as much as 65 degrees to create the necessary compression.
The bomber had a number of unorthodox moving parts including movable canards on the nose and a ramp in front of the windscreen that would raise at high speed to create a more aerodynamic airframe (and it also gave the pilot very poor visibility in that regime).
Mach 3 creates a lot of air friction, and friction creates heat, so the Valkyrie was built with honeycomb stainless steel and (sparingly, like 9 percent) titanium, which was expensive and in short supply back in those days.
North American was funded to built a single test aircraft -- designated the XB-70 -- at a cost of $750 million. The inaugural test flight was delayed by maintenance and other technical issues by three years. All of the Valkyrie's revolutionary subsystems came with their own problems -- honeycomb structures broke, hydraulic systems hemorrhaged fluid, and control surfaces didn't fit right.
At the same time the tactical world began to change. Better ICBMs made Air Force planners wonder whether they needed long-range bombers at all. And the introduction of the Soviet-made SA-2 surface-to-air missile rendered even the speedy B-70 vulnerable. Based on these factors as well as the projected cost of the Valkyrie, the Eisenhower administration grew sour on the program. The Air Force reduced the program funding to a single asset that would be used for experimental research testing only.
But the presidential election of 1960 changed the landscape. President Kennedy believed the Valkyrie was important in the arms race. The program budget was upped by $265 million and the test plan was reworked to include warfare capabilities and not just research.
A year later the Kennedy administration understood the Eisenhower administration's issues with the airplane, and the Valkyrie was once again relegated to a research program -- however the requirement was reworded with the caveat that if the Air Force requirement necessitated the need for the B-70 the program would be quickly modified to also test for combat operational capabilities.
The Valkyrie's maiden flight occurred on May 11, 1964 out of Edwards Air Force Base. The plan was to take the airplane supersonic on the first flight, but a landing gear problem kept them subsonic. The XB-70 also had a minor hydraulic fire but managed to land safely.
The airplane finally went supersonic on it's third test flight and eventually broke a number of speed records including 70 sustained minutes of supersonic flight, 50 of them at greater than Mach 2.
But the test team also discovered that extended supersonic flight punished the airframe beyond its existing design limits, and they had to modify parts of the intake system and fuselage as the test plan went forward.
The first XB-70 reached Mach 3 only once -- on it's 18th test flight on October 14, 1965 -- and that speed did substantial damage to the leading edge of one of the wings. (Luckily nothing was sucked into the intakes.) After that the airplane was limited to no greater than Mach 2.5.
A second XB-70 was built after comprehensive wind tunnel testing that yielded a modified design of the intake system, the hydraulics, and the wings. The new design made the airplane more stable, especially at high speeds. On May 19, 1966 the second Valkyrie flew Mach 3 for 33 minutes.
But test problems persisted. One flight forced test pilot Joe Cotton to jump a circuit breaker with a paper clip to get the landing gear to come down. (Basically, a $750 million airplane was saved with a 39 cent paperclip.)
Then one of the contractors pushed the notion of a "family photo," an idea that proved to be the true beginning of the end for the Valkyrie. General Electric wanted to use a private Learjet to shoot both film and still photos of the XB-70 flying in formation with a T-38, F-4, F-104, and an F-5 -- all GE-powered jets.
The requisite approvals were obtained, and on June 8, 1966 the four Air Force test jets launched to rendezvous with the XB-70 at the end of a test event. The five-jet formation flew around the Edwards AFB airspace for about 40 minutes without incident while the Learjet got the desired footage and photos. But as the formation was breaking up to return to base, disaster struck.
The F-104 drifted left until its left wing hit the XB-70's right wing. At that point the Starfighter flipped over and rolled inverted over the top of the Valkyrie, striking the vertical stabilizers and left wing of the bomber. The F-104 exploded, destroying the Valkyrie's rudders and damaging its left wing. With the loss of both rudders and damage to the wings, the Valkyrie entered an uncontrollable spin and crashed into the ground north of Barstow, California. NASA Chief Test Pilot Joe Walker (who was flying the F-104) and Carl Cross (the XB-70's co-pilot who was on his first Valkyrie flight) were killed. Al White (XB-70 pilot) ejected, sustaining serious injuries, including one arm crushed by the closing clamshell-like escape crew capsule moments prior to ejection.
The investigation concluded that Walker was unable to properly perceive his motion relative to the Valkyrie, leading to his aircraft drifting into contact with the XB-70's wing. The accident investigation also pointed to the wake vortex off the XB-70's right wingtip as the reason for the F-104's sudden roll over and into the bomber. There was also a lot of CYA and finger-pointing among Air Force leadership regarding who had actually approved the "family photo," and ultimately the punishment for improperly vetting the event fell to the lowest levels of the chain of command.
Although the remaining Valkyrie continued to fly test events, the mishap crushed any chance of the airplane being used as an operational asset. On February 4, 1969 the XB-70 flew to Wright-Patterson AFB to be made into an exhibit at the National Museum of the United States Air Force -- the final flight for a powerful and visually stunning airplane the likes of which will never be seen again.
Here's a video that shows the Valkyrie in action: