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The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep penetration bomber for the United States Air Force's Strategic Air Command. Designed in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly at beyond Mach 3 at an altitude of , which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.

Two XB-70 prototypes were built for the U.S. Air Force. The aircraft program's high development costs, and changes in the technological environment with the introduction of effective high-altitude anti-aircraft missiles, led to the cancellation of the B-70 program in 1961. Although the proposed fleet of operational B-70 bombers was never built, the XB-70A aircraft were used in supersonic test flights from 1964 to 1969, performing research for the design of large supersonic aircraft. One prototype crashed following a midair collision in 1966; the other is on display at the National Museum of the United States Air Forcemarker in Ohio.


Early studies

Boeing Aircraft Corporation's MX-2145 Project with Rand Corporation that started in January 1954 explored what sort of aircraft would be needed to deliver the very-high-yield nuclear weapons then under construction. Long range and high payload were obvious requirements, but they also concluded that after a bombing run it would need supersonic speed to avoid the nuclear blast.

Jet engines of the time had very poor fuel efficiency; an aircraft capable of carrying a reasonable bomb load all the way to the Soviet Unionmarker from the continental United States had to be very large. One example was the B-52 Stratofortress, a strictly subsonic design. An aircraft able to fly the same types of missions as the B-52 and have supersonic performance would have to carry much more fuel for supersonic flight portion. The aircraft industry was exploring different ways of solving this problem.

There was considerable interest in the use of nuclear powered aircraft in the bomber role in 1947. Nuclear engines used the heat generated by a nuclear reactor in place of jet fuel, giving an aircraft virtually unlimited cruising range. In addition to solving the range issue, these aircraft could be flown to holding areas away from the airbases and kept in the air for extended periods of time, making them immune to sneak attack. Accordingly, Boeing developed plans for a nuclear powered bomber equipped with afterburners that used chemical fuel. Lockheed and Convair proposed similar designs.

Another possibility was the use of boron-enriched "zip fuels", which improved the energy density of the fuel by about 40%. Various US government agencies had been experimenting with zip fuels for some time, and they believed that once the problems were solved zip fuel would become almost universal for high-speed aircraft. Although the advantages of a zip-fueled aircraft would not be as great as those of a nuclear powered one, it would offer a real performance increase and was a relatively straightforward development of existing engines and fuels.

First attempts

In October 1954, the Air Force issued General Operational Requirement No. 38 for a new bomber with the intercontinental range of the B-52 and the Mach 2 maximum speed of the B-58 Hustler. The new bomber was expected to enter service in 1963. March 1955's follow-on GOR.81 was more specific, calling for a nuclear-powered bomber with a combat radius of 11,000 nmi (12,650 mi, 20,375 km), capable of flying up to 1,000 mi (1,600 km) at a speed greater than Mach 2 at altitudes greater than 60,000 ft (18,300 m) with a 20,000 lb (9,100 kg) payload. The payload was revised upward to 25,000 lb (11,350 kg) in GOR.82 later that month.

The Air Research and Development Command (ARDC) decided to separate the two approaches, and issued a requirement for "Weapon System 110A", which asked for a chemical fuel bomber with Mach 0.9 cruising speed and "maximum possible" speed during a 1,000 nmi (1,609 km) entrance and exit from the target. The requirement also called for a 50,000 lb (22,670 kg) payload and a combat radius of 4,000 nmi (4,600 mi, 7,400 km). The nuclear approach became "Weapon System 125A", while the ICBM work was organized under "Weapon System 107A".

In early 1955, the Air Force issued GOR.96, which called for an intercontinental reconnaissance system (WS-110L) with the same general requirements as WS-110A. In 1956, the separate WS-110L reconnaissance requirement was combined with the WS-110A bomber requirement to become Weapon System 110A/L. In February 1958, the former WS-110L ("RB-70") reconnaissance mission was canceled due to better alternatives, and the nuclear-powered bomber work had been dropped "soon after" 8 November 1955, due to cost issues.

On 21 June 1955, the Deputy Chief of Staff directed WS-110A development to proceed.B-70 Aircraft Report, Vol. I., pp. I-34–I-38. Six contractors were selected to bid on WS-110A studies; Boeing and North American Aviation (NAA) submitted proposals. On 8 November 1955, the Air Force issued letter contracts to both Boeing and North American for Phase 1 development. The contracts called for models, design reports, wind tunnel tests, plus a mock-up.

In mid-1956, initial designs were presented by the two companies. Zip fuel was to be used in the afterburners to improve range by 10% to 15% over conventional fuel. Both designs featured huge wingtip fuel tanks that could be jettisoned when their fuel was depleted before a supersonic dash to the target. On both Boeing and North American designs, the entire outer portion of the wings was jettisoned with the fuel wing tanks.

The Air Force evaluated their designs and then in September 1956 deemed them too large and complicated. The huge fuel load resulted in takeoff weights of , making them too large and complicated for safe operation from existing runways and for fitting in existing hangars. Curtis LeMay was not enthusiastic about the NAA design, claiming "Hell, this isn't an airplane, it's a three-ship formation." NAA and Boeing's study contracts were extended to further develop their bomber designs. In October 1956, the USAF directed WS-110A Phase 1 development be discontinued due to the design weight and the wing design, and the two contractors were to continue development at a decreased level.

By March 1957, engine development and wind tunnel testing had progressed so that supersonic speed for an entire flight appeared possible. The project decided that the aircraft would fly at speeds up to Mach 3 for the entire mission, instead of a combination of subsonic cruise and supersonic dash of the aircraft designs in the previous year. Zip fuel was to be burned in the engine's afterburner to increase range.

NAA's final WS-110A proposal, built as the XB-70

The buildup of heat due to skin friction during sustained supersonic flight had to be addressed. The traditional aircraft material, duralumin, goes "plastic" at a few hundred degrees, limiting its use to speeds below Mach 2.3. Additionally, jet engines need their feed air to be subsonic, which is supplied through the use of intake systems that slow the air as it travels towards the engine. This process creates drag, significantly reducing performance; minimizing this drag is critical for cruise performance.

New designs

Both North American and Boeing returned new designs with very long fuselages and large delta wings. They differed primarily in engine layout; the NAA design arranged its six engines in a semi-circular duct under the rear fuselage, while the Boeing design used separate podded engines located individually on pylons below the wing.

North American had scoured the literature to find any additional advantage. One possibility that turned up was an obscure piece of research known as compression lift, which used the shock wave generated by the nose or other sharp points on the aircraft as a source of high pressure air. By carefully positioning the wing in relation to the shock, the shock's high pressure could be captured on the bottom of the wing and generate additional lift. Since the energy put into forming the shock wave has already been spent simply flying through the air, the lift generated in this fashion is essentially free. To take maximum advantage of this effect, they redesigned the entire underside of the aircraft to feature a large triangular intake area far forward of the engines, better positioning the shock in relation to the wing. The semi-circular duct disappeared and the engines were re-arranged to lie side-by-side in a line. Fuel tanks were repositioned from the fuselage into a number of smaller tanks wrapped around the ducting, and the rudder switched to a twin-fin design.

North American improved the design with a set of drooping wing tip panels that were lowered at high speeds. This not only helped trap the shock wave under the wing, between the downturned wing tips, but also added more vertical surface to the aircraft, which was important in helping offset a general decrease in directional stability all aircraft encounter at high speeds. Other designs had generally used fixed surfaces for this, ending up over-stable at slower speeds, or alternately used dedicated movable surfaces as on the Republic XF-103. NAA's solution had an additional advantage, however, as it decreased the surface area of the rear of the wing when they were moved into their high speed position. This helped alleviate a more minor problem, the shift in center of pressure as speeds changed. Under normal conditions the "average lift point", or center of pressure, moves rearward with increasing speeds, causing an increasing nose-down trim. By dropping the wingtips, the horizontal surface of the wing was reduced at the rear, leaving more surface forward, offsetting this effect.

During a Mach 3 cruise the aircraft would reach an average of 450˚ F, although there were portions as high as 650˚ F. NAA proposed building their design out of a honeycomb stainless steel material, consisting of two thin sheets of steel brazed to a honeycomb-shaped foil in the middle. Expensive Titanium would be used only in high-temperature areas like the leading edge of the horizontal stabilizer, and the nose.B-70 Aircraft Report, Vol. III., pp. II-31, III-141, III-210. For cooling, the XB-70 pumped fuel en route to the engines through heat exchangers.B-70 Aircraft Report, Vol. III., pp. III-496 to III-498.

On 30 August 1957, the Air Force decided that enough data was available on the NAA and Boeing designs that a competition could begin. On 18 September, the Air Force issued operational requirements which called for a cruising speed of Mach 3.0 to 3.2, an over-target altitude of 70,000-75,000 ft (21,300-22,700 m), a range of up to 10,500 mi (16,900 km), and a gross weight not to exceed 490,000 lb (222,000 kg). The aircraft would have to use all of the hangars, runways and handling procedures used with the B-52. On 23 December 1957, the North American proposal was declared the winner of the competition, and on 24 January 1958, a contract was issued for Phase 1 development. In February 1958, the proposed bomber was assigned the number B-70, with the prototypes receiving the "X" experimental prototype designation. The name "Valkyrie" was the winning submission in spring 1958, selected from 20,000 entries in a USAF "Name the B-70" contest. In December 1958, a Phase II contract was issued. The mockup of the B-70 was reviewed by the Air Force in March 1959. Provisions for air-to-surface missiles and external fuel tanks were requested afterward.

At the same time North American was developing the proposed XF-108 Rapier supersonic interceptor. In order to save on overall program costs, the F-108 would use two of the same engines, the same escape capsule, and some smaller systems as the B-70.

[[File:B-70 mission profiles.png|thumb|right||upright=1.5|Reconnaissance/Strike to search/knock out rail-based ICBMs

June 23:

November 16:
November 18:
November 19: used refueling from tankers (at left) for two profiles.

•7,748 nmi: high altitude USSR overflight descends for Diego Garciamarker landing (spirals depicted at right)

•6,447 nmi: lands in Turkey after 1,200 nmi flight from target (mushroom clouds)

•5,312 nmi: 856 nmi (1½ hr) Mach 0.95 "on-the-deck" approach to target]]

The "missile problem"

The B-70 was planned to use a high-speed, high-altitude bombing approach that followed a trend of bombers flying progressively faster and higher since the start of manned bomber use. This helped the bomber evade enemy interceptor aircraft that was the only effective anti-bomber weapon in the 1950s. Soviet interceptors during the late 1950s could not intercept the U-2 reconnaissance aircraft that could operate at very high altitudes. The B-70 would fly at similar altitudes and much higher speeds.

The introduction of the first effective anti-aircraft missiles by the late 1950s had seriously upset this equation. Missiles like the Soviet SA-2 Guideline could be fired as soon as a track was developed, and could reach high altitudes in a few minutes. Although its performance against a target like the B-70 would be limited, missile performance was increasing much faster than aircraft performance, and the Soviets were already working on the 'SA-5 Gammon' to close this gap.

By the 1960 downing of the U-2 flown by Gary Powers, military doctrine had shifted away from high-altitude supersonic bombing toward low-altitude penetration. By flying close to the Earth and using natural terrain to hide behind, aircraft could dramatically shorten the detection distances. Those missile sites that could not be avoided, like those on the approach to Moscow, would instead be attacked at medium range using high-speed missiles launched by the bombers. Low-altitude flight is taxing on both the aircraft and crews, however, requiring considerably more fuel to cover a given distance and needing sophisticated obstacle-avoidance sensors and control equipment.

Designed for high-altitude flight, the B-70 lost this edge to improved Soviet high-altitude, anti-aircraft missiles. The aircraft would become increasingly vulnerable at high altitudes as newer missile systems were introduced, and at low altitudes it lost its supersonic performance and range. Using the original Mach 3 high altitude mission profile, the aircraft had a design range of 6,447 nmi (7,419 mi, 11,940 km) without refueling, but flying over the target area "on-the-deck" at Mach 0.95 reduced range to 5,312 nmi (6,113 mi, 9,838 km), even with in-flight refueling.B-70 Aircraft Report, Vol II., pp. II-2.

Nevertheless, Air Research and Development and Air Materiel Commands endorsed an 18-month acceleration that the Air Staff approved on 19 March 1958 that scheduled the first flight for December 1961. However, in the fall of 1958 Air Force Chief of Staff Thomas D. White announced that the acceleration of the program would not be possible due to lack of funding. In early 1959, 15 major B-70 subcontracts were awarded.

Adding to the program's problems, the zip fuel program was canceled in 1959. After burning the fuel turned into liquids and solids that caused wear on moving turbine engine components. This by itself was not a fatal problem, however, as newly developed high-energy fuels like JP-6 were available that made up some of the difference. By filling one of the two bomb bays with a fuel tank, range was reduced only slightly, although payload space suffered. Also, a portion of the preceding F-108 program's "150 million dollars expended" benefited the B-70 program, so the 23 September 1959 F-108 cancellation ended shared development (Hughes Aircraft would continue development of the advanced fire control system and the GAR-9 missile).

Downsizing, upswing, cancellation

At two secret meetings on 16 and 18 November 1959, General Twining recommended the Air Force's plan for the B-70 to reconnoiter and strike rail-mobile Soviet ICBMs, but General White admitted the Soviets would "be able to hit the B-70 with rockets" and requested the B-70 be downgraded to "a bare minimum research and development program" at $200 million for fiscal year 1960. President Eisenhower responded that the reconnaissance/strike mission was "crazy" since the nuclear mission was attacking known production and military complexes, and emphasized he saw no need for the B-70 since the ICBM is "a cheaper, more effective way of doing the same thing". Eisenhower also identified that the B-70 would "not be in production before a date eight to ten years from now" and "said he thought we were talking about bows and arrows at a time of gunpowder when we spoke of bombers in the missile age."

NOTE: November 18 meeting quotations in this article are Goodpaster's paraphrasing of White & Eisenhower (e.g., "said he [Eisenhower] thought we [White, Goodpaster, et al]") -- possibly from an audio recording if one was made at Augusta. In December 1959 the Air Force announced the B-70 project would be cut to a single prototype, and most of the planned B-70 subsystems would no longer be developed.

Then interest increased due the politics of presidential campaign of 1960. A central plank of John F. Kennedy's campaign was that Eisenhower and the Republicans were weak on defense, and pointed to the B-70 as an example. He told a San Diego audience near NAA facilities that "I endorse wholeheartedly the B-70 manned aircraft." Kennedy also made similar campaign claims regarding other aircraft: near the Seattle Boeing plant he called for more B-52s and in Fort Worth he praised the B-58.

The Air Force changed the program to full weapon development and awarded a contract for a XB-70 prototype and 11 YB-70s in August 1960.Taube, Vol I, pp. I-29, I-31, I-37, I-38, I-47. In November 1960, the B-70 program received a $265 million appropriation from Congress for FY 1961. Nixon, trailing in his home state of California, also publicly endorsed the B-70, and on October 30 Eisenhower helped the Republican campaign with a pledge of an additional $155 million for the B-70 development program: "... why do you think they did it this week? I wonder." (Kennedy)

On taking office in January 1961, Kennedy was informed that the missile gap was an illusion. On 28 March 1961 after $800 million had been spent on the B-70 program, Kennedy canceled the B-70 Mach 3 manned bomber as "unnecessary and economically unjustifiable"Kennedy, John F. "Remarks of Senator John F. Kennedy, Horton Plaza, San Diego, CA , November 2, 1960." The American Presidency Project at ucsb.edumarker. Retrieved: 6 April 2009.

"1961 Budget Message." Kennedy Archives, 28 March 1961, pp. I-38. because it "stood little chance of penetrating enemy defenses successfully." Instead, Kennedy recommended "the B-70 program be carried forward essentially to explore the problem of flying at three times the speed of sound with an airframe potentially useful as a bomber."

After Congress approved $290 million of B-70 "add-on" funds to the President's 12 May 1960 modified FY 1961 budget, the Administration decided on a "Planned Utilization" of only $100 million of the add-ons. The Department of Defense subsequently presented data to Congress that the B-70 would add little performance for the great cost. However, after becoming the new Air Force Chief of Staff in July 1961, Curtis LeMay increased his B-70 advocacy, including interviews for August Reader's Digest and November Aviation Week articles, and allowing a 25 February General Electric tour at which the press was provided artist conceptions of, and other info about, the B-70. Congress had also continued B-70 appropriations to (unsuccessfully) resurrect development of the bomber. After the Secretary of Defense explained again to the House Armed Services Committee (HASC) on 24 January 1962 that the B-70 was unjustifiable, LeMay subsequently argued for the B-70 to both the House and Senate committees—and was chastised by McNamara on 1 March. By 7 March 1962, the House Armed Services Committee (HASC)—with 21 members having B-70 work in their districts—had written an appropriations bill to "direct"—by law—the Executive Branch to use "the full amount" of the nearly $500 million appropriated for the RS-70. McNamara was unsuccessful with an address to the HASC on 14 March, but a 19 March 1962 11th hour White House Rose Gardenmarker agreement between Kennedy and HASC chairman Carl Vinson retracted the bill's language and, notwithstanding their earlier campaign and budget advocacy, Presidents Kennedy and Johnson subsequently left the bomber canceled.

Experimental aircraft

The experimental XB-70As were used for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic transports. The production order was reduced to three prototypes in March 1961B-70 Aircraft Report, Vol. I. p. I-39. with the third aircraft to incorporate improvements from the previous prototype. The crew was reduced to only the pilot and co-pilot for the XB-70; the navigator and bomb-aimer were not needed. The first XB-70 was completed on 7 May 1964 (the second on 15 October 1964),B-70 Aircraft Report, Vol. I. pp. I-39–I-44. and XB-70A #1 was displayed on 11 May 1964 in Palmdale, Californiamarker.B-70 Aircraft Report, Vol. I. pp. I-41, I-88. One report claimed "nothing like it existed anywhere". The planned third prototype was canceled in July 1964 while being built. The first XB-70 had its maiden flight in September 1964 and flight testing followed.

The XB-70 flight test data and materials development aided the later B-1 Lancer supersonic bomber program, the US Supersonic Transport program and, through intelligence, the Soviet Tupolev Tu-144. The development of the US U-2 and SR-71 reconnaissance aircraft along with the B-70 bomber led the Soviet Unionmarker to design and develop the MiG-25 interceptor.


Compression lift design of the XB-70 Valkyrie
The XB-70 was designed to be a high-altitude bomber-sized Mach 3 experimental aircraft with six engines. Harrison Storms shaped the XB-70 with a canard surface and a delta wing, which was built largely of stainless steel, sandwiched honeycomb panels, and titanium. The XB-70 was designed to use supersonic technologies developed for the Mach 3 Navaho, as well as a modified form of the SM-64 Navaho's all-inertial guidance system.von Braun 1975, p. 122.

The XB-70 used compression lift, which was generated from a prominent wedge at the center of the engine inlets that created a shock wave below the aircraft. The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave (the airflow at the XB-70 wing's leading edge was subsonic). The compression lift increased the lift by five percent. Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees. This increased the aircraft's directional stability at supersonic speeds, shifted the center of lift to a more favorable position at high speeds, and strengthened the compression lift effect. With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings.

The XB-70 was equipped with six General Electric YJ93-GE-3 turbojet engines, designed to use JP-6 jet fuel. The engine was stated to be in the "30,000-pound class", but actually produced 28,000 lbf (124.6 kN) with afterburner and 19,900 lbf (88 kN) without afterburner. The Valkyrie used fuel for cooling; it was pumped through heat exchangers before reaching the engines. To reduce the likelihood of auto ignition, nitrogen was injected into the JP-6 during refueling, and the "fuel pressurization and inerting system" vaporized a 700 lb (320 kg) supply of liquid nitrogen to a gas to fill the fuel tank vent space and maintain tank pressure.

Operational history

XB-70A Valkyrie on takeoff

Flight Test program

The XB-70 Flight Test Program was conducted from the maiden flight on 21 September 1964 through 6 August 1966. The first aircraft was found to suffer from weaknesses in the honeycomb panels, primarily due to inexperience with fabrication and quality control of this new material.

XB-70 Performance
Longest Flight: 3:40 hrs (on 1-6-66)

Fastest Speed: (on 1-12-66)

Highest Altitude: (on 3-19-66)

Highest Mach number: Mach 3.08 (on 4-12-66)

Sustained Mach 3: 32 minutes (on 5-19-66)

Mach 3 total: 108 minutes/10 flights

The Valkyrie first became supersonic (Mach 1.1) on the third test flight on 12 October 1964,and flew above Mach 1 for 40 minutes during the following flight on 24 October. The wing tips were also lowered partially in this flight. XB-70 #1 surpassed Mach  3 on 14 October 1965 by reaching Mach 3.02 at 70,000 ft (21,300 m).

Honeycomb panel deficiencies discovered on XB-70 #1 were almost completely solved on XB-70 #2, which first flew on 17 July 1965. On 3 January 1966, the second XB-70 attained a speed of Mach 3.05 while flying at 72,000 ft (21,900 m). XB-70 #2 reached a top speed of Mach 3.08 and maintained it 20 minutes on 12 April 1966. On 19 May 1966, XB-70 #2 reached Mach 3.06 and flew at Mach 3 for 32 minutes, covering 2,400 mi (3,840 km) in 91 minutes of total flight.

Flight Research Programs

After completion of the Flight Test Program on 6 August 1966, two flight research programs were conducted using the XB-70 and NAA support. The first was a joint NASA/USAF research program conducted from 3 November 1966 to 31 January 1967 for "combining the theoretical sonic boom intensity due to lift and due to volume". Prior to the first program for "Sonic Boom Measurements", XB-70A #2 was selected for the National Sonic Boom Program (NSBP) and flew the first sonic boom test on 6 June 1966, obtaining a speed of Mach 3.05 at 72,000 ft (21,900 m). Sonic boom testing was planned to cover a range of overpressures on the ground similar but higher than the proposed American SST.

The second flight research program (NASA NAS4-1174) investigated "control of structural dynamics" from 25 April 1967 through the last supersonic XB-70 flight on 17 December 1968. At high altitude and high speed, the XB-70A experienced unwanted altitude changes (porpoising), and the second program added two small vanes to the XB-70 #1 nose for flight control.

After 33 research flights following the mid-air collision, the subsequent subsonic flight on 4 February 1969 ferried XB-70A #1 to Wright-Patterson Air Force Basemarker for museum display (now the National Museum of the United States Air Forcemarker). The program concluded in April 1972, when North American Rockwell issued a four-volume B-70 Aircraft Study final report.

Incidents and accidents

Landing gear fire

On 21 September 1964, after the landing gear failed to retract properly on XB-70A #1, the left-side rear wheels locked and a fire resulted.

Engine damage

On 7 May 1965, the divider separating the left and right halves of the engine inlet on XB-70A #1 broke off in flight and was ingested into the engines, damaging all six beyond repair.

Wing damage

On 14 October 1965, the first XB-70 surpassed Mach 3, but heat and stress damaged the honeycomb panels, leaving 2 ft (0.6 m) of the leading edge of the left wing missing. These construction problems resulted in the imposition of a speed limit of Mach 2.5 on the first aircraft.

Mid-air collision

The formation of aircraft shortly after the collision on 8 June 1966
On 8 June 1966, XB-70A #2 was in close formation with four other aircraft (an F-4, F-5, T-38, and F-104) for a photoshoot at the behest of General Electric, manufacturer of the engines of all five aircraft. With the photoshoot complete, the F-104 drifted into contact with the XB-70's right wing, flipped over, and rolling inverted, passed over the top of the Valkyrie, struck the vertical stabilizers and left wing and 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, CA. NASA Chief Test Pilot Joe Walker (F-104 pilot) and Carl Cross (XB-70's co-pilot) were killed, while Al White (XB-70's pilot) ejected, sustaining serious injuries, including one arm being crushed as it was caught in the clamshell-like escape capsule as it closed around him just before ejection from the aircraft.

The USAF summary report of the accident investigation stated that, given the position of the F-104 relative to the XB-70, the F-104 pilot would not have been able to see the XB-70's wing, except by uncomfortably looking back over his left shoulder. The report concluded that Walker, piloting the F-104, likely maintained his position by looking at the fuselage of the XB-70, forward of his position. The report estimated that the F-104 was 70 ft (21 m) to the side of, and 10 ft (3 m) below, the fuselage of the XB-70. The report concluded that from that position, without appropriate sight cues, 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 wingtips as the reason for the F-104's sudden roll over and into the bomber.


  • XB-70A - prototype of B-70. Two were built.
    • Aircraft #1, NAA Model Number NA-278, USAF S/N 62-0001, 83 flights; total time: 160 hours, 16 minutes
    • Aircraft #2, NAA Model Number NA-278, USAF S/N 62-0207, 46 flights; total time: 92 hours, 22 minutes. It was lost in a crash on 8 June 1966.
  • XB-70B - Aircraft #3, NAA Model Number NA-274, USAF S/N 62-0208, Originally to be first YB-70A in March 1961, this advanced prototype was canceled while in manufacturing.
  • YB-70 - Preproduction version with improvements based on XB-70s.
  • B-70A - Planned bomber production version of Valkyrie. A fleet of up to 65 operational bombers was planned.B-70 Aircraft Study, Vol I, p. I–29.
  • RS-70 - Proposed reconnaissance-strike version with a crew of four and in-flight refueling capability.

Aircraft on display

Valkyrie No. 1 (AF Ser. No. 62-0001) is currently on display at the National Museum of the United States Air Forcemarker at Wright-Patterson AFBmarker in Dayton, Ohiomarker. The aircraft was flown to the Museum on 4 February 1969, following the conclusion of the XB-70 testing program. Over the years the Valkyrie became the Museum's signature aircraft, appearing on Museum letterhead, and even appearing as the chief design feature for the Museum's restaurant, the Valkyrie Cafe. As of 2009 the XB-70 is in the Museum's Research & Development Hangar where it is displayed alongside other experimental aircraft in the Museum's collection.

Specifications (XB-70A)

See also



The NB-58 Hustler was used for XB-70 engine testing, and the TB-58 was used for XB-70 chase and training.

In response to the British/French treaty of 29 November 1962 which would produce the supersonic Concorde airliner, US President Kennedy started the national SST project in June 1963. North American entered a design with some elements from the B-70, but it was eliminated from the SST airframe competition in June 1964.

Following the 1963 formation of the National Supersonic Transport program, the 1964 Oklahoma City sonic boom tests "influenced the 1971 cancellation of the Boeing 2707 supersonic transport and led to the United States' complete withdrawal from SST design."


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