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The B-70 Valkyrie supersonic heavy bomber was one of the most elegant planes ever take to the skies. It was not only a remarkable looking aircraft but also the most advance flying platform of its time. Its elegant design and airborne avionic systems were decades ahead of its peers. Just the sight of a Valkyrie flying sent chills down the collective spines of military leaders in both America and the Soviet Union. But, as with most revolutionary weapons platforms, the B-70 was also an aircraft without a dedicated mission profile. In an ironic twist of fate, the B-70, once conceived and designed with the intention of penetrating the most complex of Soviet’s air defensive systems as well as their most advance fighters, in the end was terminated by advances in those same systems, specifically the Soviet’s surface to air missile (SAM) systems. The new Soviet SAMs made the Valkyrie’s great advantage, sheer speed, somewhat irrelevant.

Conceived to replace the United States Air Force’s fleet of Boeing’s B-52 heavy bombers, the XB-70 program commenced at earnest in the spring of 1955. The Air Force, fresh out of the complex and highly technical B-58 program, wanted the new bomber to be incorporated with the latest of the so called “next generation” technology packages available. It was towards this end, that the Air Force was willing to give total weapon system design responsibility to the winner of the contract. During the design phase, two companies emerged as the leading contenders for the contract to build the most advance aircraft in the world: Boeing and North America. After a relative short test design stage, North America was awarded a developmental contract. Work commenced on the project late in 1958 and in 1964, the first of two ordered prototype performed its maiden flight.The XB-70 was indeed an elegant flying machine.

One that concealed its true nature: the nuclear showering of targets deep inside the Soviet Union. This amazing aircraft had a fuselage length of 196 feet with a high of 31 feet. It is estimated maximum gross operational weight was of 521,000 pounds. The bomber was manned by a crew of four: a pilot, copilot, and bombardier and, a defensive weapon systems operator. The aircraft was fitted with a thin delta wing structure that spanned 105 feet. Six massive General Electric YJ-93 engines capable of producing 30,000 pounds of thrust each with afterburners. They were located in a side-by-side configuration on a large pod underneath the airframe. Two rectangular inlets ducts provided the engines with a two dimensional airflow profile. The aircraft’s fuel tanks where housed on the delta wing structure. The high drag ratio of the B-70 while flying at Mach 3, required a total fuel load comparable to that of a B-52. This in turn limited the operational range of the bomber to around 5,000 nautical miles. The wing structure was swept at an angle of 65.5 degrees, and the wing tips were folded down hydraulically 25 to 65 degrees to improve the aircraft’s stability while performing at speeds of Mach 3. While flying at this speed envelop, the XB-70 was designed to “ride” in its own shock wave. A large canard fore-plane (28 feet, 10 inches) installed near the front of the fuselage was utilized for stability moderation. Two large vertical tail units, each of them possessing hydraulic-moving sections, were fitted on the aft of the airframe. The Valkyrie was made completely out of titanium and brazed stainless steel materials. These composite materials were incorporated to enable the aircraft to withstand the heating during the sustained high Mach portions of the bomber’s flight. The aircraft’s fuselage was painted with a nuclear blast reflecting white-looking paint cover which did not stand up well to the Mach 3 kinetic heating. The aircraft did not have any defensive armament system and could only carry its ordinance inside due to its speed profile. The B-70’s had a massive payload capacity. Up to 50,600 pounds of free fall nuclear bombs could be stored inside the aircraft’s bomb bay.

As the first series of trials began, the aircraft started to demonstrate that it could accomplish almost all of the Air Force’s mission requirements, including the most important one: the achievement and sustaining of flying operations at three times the speed of sound. While the Valkyrie was enduring its test trial stages, one aspect that eventually would lead to the cancellation of the entire program, surfaced. At high altitude, an aircraft operating at Mach 3 speeds could not manoeuvre well enough to evade even the Soviet’s second generation SAM missiles of the early 1960s. Also, the aircraft’s straight and level trajectory profile, which Mach 3 speed requires, would have provided the Soviets with nearly pint-point information on the B-70’s projected directional path, enabling their fighters to intercept the bomber’s path instead of the aircraft itself. There was also another unexpected situation that arose out of the bomber’s speed profile: the Valkyrie radar cross section signature was huge. This was due to the technology, airframe material and avionics package, implemented on the aircraft in order to make sustainable Mach 3 operational speeds feasible. The trials also revealed the aircraft’s poor low level operational capability. The B-70 was not adaptable to low level penetration because its thin delta wing structure did not provided the bomber with the necessary in-flight modifications for sustained low level operations. As the trials continued, it was becoming apparently to engineers at North America that the XB-70 did not posses the necessary characteristics to perform as a stable bombing platform. Thus the aircraft’s profile was changed from a deep penetration heavy bomber, to a reconnaissance and strike platform. This change in profile actually occurred while the aircraft was still in its development stages in late 1959.
 

Technical Info:

In mid 1961, the Kennedy Administration officially removed the program from its active operational status to a purely research project. The high cost of the aircraft program, between 500 - and $700 million at the time, and its perceived vulnerability to the latest Soviet SAM batteries, were cited as the cause of the shifting in the program status. Eventually, two units were built by North American. The first plane took to the air in 1964. The second prototype followed the next year. Initial testing showed the brilliance of the aircraft’s aerodynamic design. During its test flight, the B-70 consistently demonstrated its ability achieve and sustain speeds above the 1,988mph threshold. But the trials also demonstrated the plane’s vulnerability. At the same time, the US Air Force began to shift its nuclear deterrence resources from manned bombers and nuclear capable strike aircrafts to the relative easy to develop and maintain Inter Continental Ballistic Missile force which had began to eat more and more of the Air Force’s budgetary pie.

The end of the Valkyrie program came swiftily. On the morning of June 8th, 1966, the first prototype was flying an experimental mission with a formation of NASA operated aircraft consisting of an F-4, F-5, T-38, and F-104 Starfighter, piloted by the experience Joe Walker. The purpose of this flight was for a photoshoot. With the photoshoot complete, the F-104 rolled inverted, passed over the top of the Valkyrie, struck it and exploded, destroying the Valkyrie's rudders and damaging its left wing. The Valkyrie entered a spin and crashed into the ground. The XB-70 was able to fly for a few short seconds before it spiralled out of control until it crashed deep inside California’s Mojave Desert. Only one man survived the accident. Following the incident, what was left of political support for the program promptly evaporated.

The program was officially cancelled in the spring of 1969. A undistinguished ending for such an elegant and advance flying platform, but an end that was scripted the minute the aircraft’s plan was on North American’s drawing board.
 

Ref :

The World Encyclopedia of Bombers, Francis Crosby, Herms House 2004
Behind Valkyrie: The Amazing Story of the XB-70, Martin Cooper, Penguin Books, 1978
Concept Aircraft: Prototypes, X-planes and Experimental Aircraft, Edit Jim Winchester, Thunder Bay Press, 2005