North American XB-70 Valkyrie

XB-70 Valkyrie was a prototype of plane bomber American Supersonique of the end of the year 1950. It was conceived by the firm North American, only two specimens were built, of which one which was destroyed at the time of an accident.

Historical context

In the context of the Cold war of the beginning of the year 1950, the doctrines of armament were founded on the use of strategic bombers with long operating range, able to affix a nuclear striking on the enemy ground by a non-stop flight since the territory of the the United States. The first apparatus qualified for this task was the Boeing B-52 Stratofortress, which accomplished its first flight in 1952. Nevertheless, the rapids progress carried out by the hunters and the ground-to-air missiles Soviet made null and void this tactical strategy: too much slow and not flying rather high, the B-52 had become an easy prey.

A new strategy was then elaborate: outward journey and return at high-altitude and low speed (to save the fuel) and penetration of the hostile territory with Mach 2 (to avoid an interception). This strategic vision first of all gave rise to the B-58 Hustler which, although innovating and powerful, did not fulfill the requirements formulated by the Strategic Air Command (SAC): it was in particular too weak in term of range operating, too expensive to maintain, not reliable enough and finally too small to have a capacity of sufficient striking.

A new schedule of conditions was thus published by the SAC in March 1953 describing a strategic bomber with long range operating, and was equipped with the best possible performances in term of ceiling and operating range.

Genesis of the project

The majority of the manufacturers proposed a project but the difference between the required performances and the technology of the moment led them to imagine solutions too much innovating to consider implementation a short-term (composites bomber + hunter " parasite" , nuclear engines, drones, etc)

This period of uncertainty ended on September 18th, 1957, when the US Air Force formulated its final schedule of conditions. It henceforth specified a cruising speed of Mach 3, an operational ceiling of 22.860 meters and a minimal autonomy of 9.650 km. Meanwhile, technology had evolved/moved, in particular on the level of the turbojets, and the market had been clarified: only Boeing and North American remained in string.

December 23rd, North American was declared victorious. the US Air Force hoped to have 30 operational apparatuses with the end of the year 1965. The complexity of the project led North American to select many subcontractors, among whom:

Boeing (wings)
Lockheed (certain elements of the fuselage)
Westinghouse (electronic defense system)
IBM (avionics of navigation and bombardment)
General Electric (radar and avionics of propulsion)
Chance-Vought (empennage and ailerons)

In fact, the XB-70 (official designation since February 6th, 1958) comprised several important technological innovations:

Entered of air with variable geometry ordered automatically
Empennage duck (intended to reduce the trail)
mobile Salmons: the XB-70 was one of the first aircraft whose construction drew part of the Loi from the surfaces, not in the drain of flows of air around the fuselage (as for the F-102, for example) but by modifying in flight the curve of its aerofoil. To high-speeds (Mach 2+), the XB-70 lowered its wing tips downwards, and thus arrived to " chevaucher" its own shock wave. This process made it possible to decrease in a significant way the trail and to increase by this fact the passable distance.

The bomber was equipped with ejector capsules of survival, which allowed the pilots and their copilots to eject itself at high speed.

Development - first version

The first specimen of the XB-70 left the workshops the May 11th, 1964 to Palmdale. It was able to fly at Mach 2,3, sufficient speed so that the heat caused by the friction of the air is the source of engineering problems: its painting of coating was scaled, and of the fuel leaks appeared because of the deformation of the tanks. It took off on September 21st 1967, controlled by the colonel Joe Cotton.

Second version

The second version was equipped with a radar assembled in the front radome, as well as elements of avionics moreover. Like the first version, before plane, in front of the cockpit, was painted in black, so that the rays of the sun are absorbed by the color, rather than to dazzle the pilot and the copilot during the flights with high-altitude. This technique is also used in the sports, like American football.

The accident

June 8th, 1966, the second prototype left Edwards AFB to take measurements of supersonic bangs. Moreover, this test allowed General Electric, manufacturer the engines of the XB-70, to carry out advertizing photographs of the plane with a F-4B Phantom II, a F-104N Starfighter, a F-5A Freedom Fighter and a T-38 Talon, all propelled with engines of General Electric. But F-104, taken in the movements of air caused by the XB-70, struck it, destroying the vertical stabilizer right. After still a minute of flight, the bomber became unverifiable, then was crushed. The pilot of the XB-70 ejecta in time but his copilot did not manage to eject himself and perishes, just as the pilot of F-104, Joseph Albert Walker.

End of the program

The loss of one of the prototypes was the death warrant of the program. This flight having been an advertizing flight, many journalists were pilot accident of this extremely expensive machine. Moreover, the plane was almost obsolete as of its first flight: the capacity of the Russian army to destroy in flight of the enemy planes using ground-to-air missiles (causes destruction of the U-2 of Gary Powers in 1960) caused a new change of orientation of strategy, supporting the search for furtive planes rather than fast, as well as the development of intercontinental ballistic missiles.

The first protoype is exposed to the US Air Force Museum.

The program of the XB-70, in spite of the failure, strongly influenced the Soviet Union, which decided to conceive a hunter able to come to end of bombers trisonic like the Valkyrie: this one was the MIG-25 “Foxbat”, which remains the fastest plane in service.

Sources

Atlas of the planes of the extreme , Edition Atlas , 2003.

See too

history of the French XB-70
001 - Flight off the Valkyrie
Site of Boeing - Card on the Valkyrie
Valkyrie on Area51Specialprojects
on LaunchComplex
List of the military aircrafts

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