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North American XB-70 Valkyrie

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764px-North American XB-70 above runway ECN-792

The XB-70A takes off.

The North American Aviation XB-70 Valkyrie was a prototype version of the proposed B-70 nuclear-armed deep penetration bomber for the United States Air Force's Strategic Air Command.

DescriptionEdit

Designed in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly at Mach 3 at an altitude of
3 1 (4)
70,000 feet (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.

Two XB-70 prototypes were built for U.S. Air Force. The aircraft program's high development costs, and changes in the technological environment with the introduction of effective 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 Force in Dayton, Ohio.

DevelopmentEdit

First attemptsEdit

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.[1] The new bomber was expected to enter service in 1963.[2] The March 1955 follow-on GOR.81 was more specific, calling for a nuclear-powered bomber with a combat radius of 11,000 nautical miles, capable of flying up to 1,000 miles at a speed greater than Mach 2 at altitudes greater than 60,000 ft with a 20,000 lb payload. The payload was revising upward to 25,000 lb in GOR.82 later that month.[3]

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 nautical mile entrance and exit from the target. The requirement also called for a 50,000 lb payload and a combat radius of 4,000 nmi.[2] The target date for the first operational wing of these bombers was July 1964, reduced a year in comparison to earlier GOR's date. The nuclear approach became "Weapon System 125A", while the ICBM work was organized under "Weapon System 107A".[4]

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.[5][6] The separate WS-110L reconnaissance requirement was combined with the WS-110A bomber requirement to become Weapon System 110A/L[6] in 1956, and the former WS-110L reconnaissance mission was canceled in February 1958 due to better alternatives (Samos satellite).[7] The nuclear-powered bomber work was dropped during the late 1950s, given the problems in that program's development.[3]

On 21 June 1955, the Deputy Chief of Staff directed WS-110A development to proceed.[8] Six contractors were selected to bid on WS-101A studies; Boeing and North American Aviation (NAA) submitted proposals.[9] On 8 November 1955, the Air Force issued letter contracts to both Boeing and North American for Phase 1 development.[10] The contracts called for models, design reports, wind tunnel tests, plus a mock-up.[5]

In mid-1956, initial designs were presented by the two companies.[11][12] Zip fuel was to be used in the afterburners to improve range by 10% to 15% over conventional fuel.[13] Both designs featured huge wingtip fuel tanks that could be jettisoned when their fuel was depleted before a supersonic dash on the target.[11] On both Boeing and North American designs, the entire outer portion of the wings was jettisoned with the fuel wing tanks.[11]

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 700,000 pounds (318,000 kg), making them too large and complicated for safe operation from existing runways and for fitting in existing hangers. General Curtis LeMay was not enthusiastic about the NAA design, claiming "Hell, this isn't an airplane, it's a three-ship formation."[4][14] NAA and Boeing's study contracts were extended to further develop their bomber designs.[1] In October 1956 the USAF directed WS-110A Phase 1 development be discontinued due to the 750,000 lb (340,000 kg) design weight and the wing design, and the two contractors were to continue development at a decreased level.[8][14]

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.[14]

Issues with sustained supersonic flight had to be addressed. One problem was the buildup of heat due to skin friction; 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 designsEdit

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 similar to those on the SR-71, but 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.[15] 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.[15] 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. Titanium, still an extremely expensive material, would be used only in high-temperature areas like the leading edge of the horizontal stabilizer, and the nose.[16] Fuel from the wing tanks was burned first.[17] For cooling, the XB-70 pumped fuel enroute to the engines through 10 heat exchangers.[17] The fuel tanks were made inert by filling with gaseous nitrogen as the fuel is pumped out.[18]

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 to 75,000 ft, a range of up to 10,500 miles, and a gross weight not to exceed 490,000 lb. 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.[19] In February 1958, the proposed bomber was assigned the number B-70,[19] 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.[20] The Air Force believed that "other systems" would be able to better meet the reconnaissance mission, and development of WS-110L was canceled in March 1958.[3][19] In December 1958, a Phase II contract was issued. The first operational wing of 30 aircraft was to be ready by late 1965. The mockup of the B-70 was reviewed by the Air Force in March 1959. Provisions for air-surface missiles and external fuel tanks were requested afterward.[21]

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.[22]

The "missile problem"Edit

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.[23] This helped the bomber evade enemy interceptor aircraft that were only effective anti-bomber weapon in the 1950s. The U-2 reconnaissance aircraft flying at very high-altitudes was unable to be reached by Soviet interceptors during the late 1950s.[24] The B-70 would fly at similar altitudes and much higher speeds. Anti-aircraft missiles by the late 1950s had developed to a point where they became effective weapons.[25] Missiles, such the as Soviet SA-2 'Guideline' could be fired as soon as a track was developed, and could reach high altitudes in a few minutes.

By the downing of the U-2 flown by Gary Powers in 1960, military doctrine shifted quickly 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.[26] 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. Low-altitude flight is taxing on both the aircraft and crews, however, requiring considerably more fuel to cover a given distance, and needs 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.[25] 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 without refueling, but flying over the target area "on-the-deck" at Mach 0.95 reduced range to 5,312 nmi even with in-flight refueling.[27]

Adding to the program's problems, the zip fuel program was canceled in 1959.[28] After burning the fuel turned into liquids and solids that caused wear on moving turbine engine components.[29] 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.[30] The program was also harmed in September 1959 by the cancellation of the F-108 and its support funding.[31]

Acceleration, downsizing, B-70 cancellationEdit

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 and formation of the first operational wing for August 1964.[19] 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.[32][7] In early 1959, 15 major B-70 subcontracts were awarded.[33]

In late 1959, President Dwight Eisenhower felt manned bombers were outdated in a "missile age" and would not support full funding for the B-70 program.[31] Then 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.[31]

Then interest increased due the politics of presidential campaign of 1960. 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.[31][34] In November 1960, the B-70 program received a $265 million appropriation from Congress for FY 1961.[35][36]

After the election, President-Elect Kennedy was briefed by the CIA and told that the missile gap was an illusion, and that the U.S. had a tremendous strategic advantage.[37] After taking office Kennedy re-evaluated the ongoing developments, and on 28 March 1961, he directed that the B-70 once again be reoriented strictly as a research and development project.[3]

The B-70 then became a political football within the U.S. Senate, and conservative senators tried on several occasions to rescue the program and asked that the B-70 be committed to production and service. Secretary of Defense Robert McNamara expressed his own dissatisfaction with the B-70 program, and the cutbacks remained.[3]

The design was also modified into the RS-70 (RS for "reconnaissance strike"), which was intended to fly in after the ICBMs, locate targets that had not been hit, and then attack those targets.[3] North American Aviation had offered to produce 62 RS-70s (RS for "reconnaissance strike") in February 1959.[38]


Experimental aircraftEdit

The B-70's prototype XB-70As were used for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic aircraft, in particular the American supersonic transport (SST) program. Initial plans were made to build three aircraft, each one incorporating modifications based on lessons learned from the previous aircraft's flight tests, but the program was cut down to two aircraft in July 1964. The first XB-70 structure was completed on 24 April 1964,[39] then displayed on 11 May 1964 in Palmdale, California to an "unbelieving crowd" that had not seen an aircraft of this size and shape before.[40][41]

The development of the Valkyrie, along with the U-2 and SR-71 reconnaissance aircraft led the Soviet Union to design and develop the MiG-25 "Foxbat" interceptor to counter these U.S. threats.[42] New, improved surface to air missiles (SAMs), were also developed. The flight test data and materials development of the XB-70 program also aided the later B-1 Lancer supersonic bomber program, as well as the commercial SST aircraft programs in the 1960s.[43]

DesignEdit

The Valkyrie was designed to be a large, high-altitude bomber with six engines to fly at Mach 3. It was configured as a canard-delta wing, and built largely of stainless steel, sandwich honeycomb panels, and titanium. It was designed to make use of a phenomenon called "compression lift", achieved when the shock wave generated by the airplane flying at supersonic speeds is trapped underneath the wings, supporting part of the aircraft's weight.

Under the center of the wing, the Valkyrie featured a prominent wedge at the center of the engine inlets, designed to produce a strong shock wave. By acting upwards upon the wings, this shock wave would allow the aircraft to recover energy from its own wake. At high speeds, compression lift increased the lift of the wings by thirty percent, with no increase in drag.[40] 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.[44] 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 JP6 jet fuel. The engine was stated to be in the "30,000-pound class", but actually produced 28,000 lbf with afterburner and 19,900 lbf without afterburner.[45][46] The Valkyrie used fuel for cooling; It was pumped through heat exchangers before reaching the engines.[47] The fuel tanks, which had a total capacity of 43,646 US gal (165,213 litres),[48] were made inert by filling with gaseous nitrogen as the fuel is pumped out.[18][47]

Operational historyEdit

Flight testingEdit

The XB-70 Flight Test program was conducted from the maiden flight on 21 September 1964 through 6 August 1966.[N 1] 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.[1] The first aircraft was also continually troubled by hydraulic leaks, fuel leaks, and problems with the aircraft's complicated landing gear.

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.[49] 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).[50]

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.[51] On 19 May 1966, XB-70 #2 reached Mach 3.06 and flew at Mach 3 for 32 minutes, covering 2,400 miles (3,840 km) in 91 minutes of total flight.[52]

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).[53] Sonic boom testing was planned to achieve a range of overpressures on the ground similar but higher than the proposed American SST.[54]

Mid-air accidentEdit

On 8 June 1966, XB-70A #2 was in close formation with four other aircraft (an F-4 Phantom II, Northrop F-5, T-38 Talon, and F-104 Starfighter) for a photo shoot at the behest of General Electric, manufacturer of the engines of all five aircraft.[N 2] With the photo shoot complete, the F-104 drifted into contact with the XB-70's wing, flipped over, rolling 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 flat spin, [56] hitting the ground in an almost level attitude about four miles north of the city of Barstow.[55] 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) successfully ejected.

The U.S. Air Force conducted the accident investigation and released an accident summary report.[57] The report 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 to the side of, and 10 feet below, the fuselage of the XB-70. In addition, the report found that from that position, there would be no suitable alignment points to maintain a precise position relative to the Valkyrie. The report concluded that due to the unavailability of 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.[58][59] The incident led to PR exercises and aerial photography involving the US armed forces being prohibited for many years.[N 3]

AftermathEdit

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),[60] 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,[61] the subsequent subsonic flight on 4 February 1969 ferried XB-70A #1 to Wright-Patterson Air Force Base for museum display (now the National Museum of the United States Air Force).[62]

VariantsEdit

  • 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[63][64]
    • Aircraft #2, NAA Model Number NA-278, USAF S/N 62-0207, 46 flights; total time: 92 hours, 22 minutes.[56] Crashed on 8 June 1966 north of Barstow, CA.
  • 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 in March 1964 while under construction.[65]
  • YB-70 - Before a September 1960 letter contract for a "full weapon system development" program (11 YB-70s plus 1 XB-70 prototype) could be "definitized", the YB-70 Program Plan was reduced to 3 XB-70 prototypes on March 31, 1961 (in December 1961, funding for the prior YB-70 expenditure was definitized).[34]
  • B-70A - Planned bomber version of Valkyrie.[1] A fleet of up to 65 operational bombers was planned.[66]
  • RS-70 - Proposed reconnaissance-strike version with a crew of four and in-flight refueling capability.[27] In 1959 a fleet of 62 was planned.

Aircraft on displayEdit

XB-70A #1 has been on display at the National Museum of the United States Air Force since being ferried there on 4 February, 1969, after the Flight Research Programs.

Specifications (XB-70A) Edit

General characteristics
  • Crew: 2
  • Length: 185 ft 10 in (56.6 m)
  • Wingspan: 105 ft 0 in (32 m)
  • Height: 30 ft 9 in (9.4 m)
  • Wing area: 6,296 ft² (585 m²)
  • Airfoil: Hexagonal; 0.30 Hex modified root, 0.70 Hex modified tip
  • Empty weight: 210,000 lb (93,000 kg)
  • Loaded weight: 534,700 lb (242,500 kg)
  • Max takeoff weight: 550,000 lb (250,000 kg)
  • Powerplant: 6× General Electric YJ93-GE-3 afterburning turbojet
    • Dry thrust: 19,000 lbf (84.5 kN) each[45]
    • Thrust with afterburner: 28,800 lbf (128 kN) each[46]
Performance
  • Maximum speed: Mach 3.1 (2,056 mph, 3,309 km/h)
  • Cruise speed: Mach 3.0 (2,000 mph, 3,219 km/h)
  • Range: 3,725 nmi (4,288 mi, 6,900 km) combat
  • Service ceiling 77,350 ft (23,600 m)
  • Wing loading: 84.93 lb/ft² (414.7 kg/m²)
  • lift-to-drag: about 6 at Mach 2
  • Thrust/weight: 0.314

Note: Data from USAF XB-70 Fact sheet[67]

BibliographyEdit

  • von Braun, Wernher (Estate of), Frederick I. Ordway III and Dooling, David Jr. Space Travel: A History. Harper & Row, 1985. ISBN 0-06-181898-4.
  • Jenkins, Dennis R. B-1 Lancer, The Most Complicated Warplane Ever Developed. New York: McGraw-Hill, 1999. ISBN 0-07-134694-5.
  • Jenkins, Dennis R. and Tony R. Landis. North American XB-70A Valkyrie WarbirdTech Volume 34. North Branch, Minnesota: Specialty Press, 2002. ISBN 580070566.
  • Jenkins, Dennis R. and Tony R. Landis. Valkyrie: North American's Mach 3 Superbomber. North Branch, Minnesota: Specialty Press, 2005. ISBN 1-58007-072-8.
  • Machat, Mike. "XB-70 Valkyrie: Rollout and First Flights, May 1964-June 1966." Wings Volume 35, No. 8, August 2005.
  • Pace, Steve. North American XB-70 Valkyrie, second edition. Blue Ridge Summit, PA: TAB Books, 1990. ISBN 0-8306-8620-7.
  • Pace, Steve. "Triplesonic Twosome." Wings Volume 18, No. 1, February 1988.
  • North American Rockwell. B-70 Aircraft Study Final Report, Vol. I, Vol. II, Vol. III, Vol. IV, NASA, April 1972.
  • Winchester, Jim. "North American XB-70 Valkyrie". X-Planes and Prototypes. London: Amber Books Ltd., 2005. ISBN 1-904687-40-7.
  • York, Herbert Jr. Race to Oblivion: A Participant's View of the Arms Race. New York: Simon and Schuster, 1978. ISBN 0-06-181898-4.

External links Edit


Text originally from: http://en.wikipedia.org/wiki/XB-70_Valkyrie

ReferencesEdit

NotesEdit

  1. The research flights often saw the XB-70 escorted by a TB-58A chase aircraft.[48]
  2. The photographs were taken from a Learjet powered by GE engines, whose crew were in control of the formation.[55]
  3. Although the prohibition was eventually lifted, it is still more difficult to organise air-to-air photo shoots involving USAF aircraft than it was before the Valkyrie incident.[55]

SourcesEdit

  1. 1.0 1.1 1.2 1.3 Jenkins 1999, Ch. 1.
  2. 2.0 2.1 Jenkins and Landis 2002, p. 9.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Baugher, Joe. North American XB-70A Valkyrie, American Bombers, 10 June 2001.
  4. 4.0 4.1 Lost Classics - North American XB-70 Valkyrie. Unreal Aircraft
  5. 5.0 5.1 Pace 1988, p. 14.
  6. 6.0 6.1 Knaack 1988, p. 561.
  7. 7.0 7.1 Knaack 1988, p. 566.
  8. 8.0 8.1 B-70 Aircraft Report, Vol. I., pp. I-34–I-38.
  9. Jenkins and Landis 2002, p. 10.
  10. B-70 Valkyrie, B-70 Valkyrie Construction, B-70 Valkyrie Cancellation. GlobalSecurity.org
  11. 11.0 11.1 11.2 Jenkins and Landis 2002, pp. 13–14.
  12. Knaack 1988, p. 563.
  13. Jenkins and Landis 2002, pp. 15–16.
  14. 14.0 14.1 14.2 Jenkins and Landis 2002, pp. 14–15.
  15. 15.0 15.1 Pace 1988, p. 16.
  16. B-70 Aircraft Report, Vol. III. pp. II-31, III-141, III-210.
  17. 17.0 17.1 B-70 Aircraft Report, Vol. III. pp. III-495 to III-503.
  18. 18.0 18.1 Jenkins and Landis 2002, p. 81.
  19. 19.0 19.1 19.2 19.3 Jenkins and Landis 2002, p. 17.
  20. Pace 1988, p. 17.
  21. Jenkins and Landis 2002, p. 24.
  22. Jenkins and Landis 2002, pp. 18, 26.
  23. Spick 1986, pp. 4-5.
  24. Rich, Ben and Leo Janos. Skunk Works. Boston: Little, Brown & Company, 1994. ISBN 0-316-74300-3.
  25. 25.0 25.1 Jenkins 1999, p. 21.
  26. Spick 1986, pp. 6-7.
  27. 27.0 27.1 B-70 Aircraft Report, Vol II., pp. II-2.
  28. "From Missiles to Medicine: The development of boron hydrides"
  29. Jenkins and Landis 2002, p. 98.
  30. Jenkins and Landis 2002, pp. 25–26.
  31. 31.0 31.1 31.2 31.3 Jenkins and Landis 2002, p. 26.
  32. Jenkins and Landis 2002, p. 19.
  33. Knaack 1988, p. 568.
  34. 34.0 34.1 Taube, Vol I, pp. I-29, I-31, I-37, I-38, I-47.
  35. Jenkins and Landis 2002, pp. 26-27.
  36. York1978, p. 56.
  37. Preble, Christopher A., "Who ever believed in the 'missile gap'?: John F. Kennedy and the politics of national security". Presidential Studies Quarterly, 1 December 2003
  38. Taube 1972, p. I-307.
  39. B-70 Aircraft Report, Vol. I. pp. I-39 to I-44.
  40. 40.0 40.1 Boyne, Walter J. "The Ride of the Valkyrie". Air Force Magazine, June 2006. Accessed on 29 October 2008.
  41. Jenkins and Landis 2002, p. 39.
  42. Pace, Steve. F-22 Raptor, America's next lethal war machine. New York: McGraw-Hill, 1999. ISBN 0-07-134271-0.
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  44. B-70 Aircraft Study, Vol. III. p. III–162.
  45. 45.0 45.1 B-70 Aircraft Study, Vol. III. pp. III–476, III–479.
  46. 46.0 46.1 Jenkins and Landis 2002, pp. 83-84.
  47. 47.0 47.1 B-70 Aircraft Report, Vol. III., pp. III-496 to III-498.
  48. 48.0 48.1 World Aircraft Information Files Aviation Partwork. Midsummer Books Ltd. File 879 Sheet 6 (Aviation technology:N Search for Speed - XB-70 Valkyrie briefing)
  49. Mach 3 Legend: The North American XB-70 Valkyrie. Flight Line, Issue 7, Fall-Winter 1995.
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  51. Jenkins and Landis 2002, p. 54.
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  53. Jenkins and Landis 2002, p. 62.
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  55. 55.0 55.1 55.2 WAIF File 809 Sheet 5 (Air Accidents:Military Accidents - Last ride of the Valkyrie)
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  65. Jenkins and Landis 2002, p. 73.
  66. B-70 Aircraft Study, Vol I, p. I–29.
  67. XB-70 Fact sheet. United States Air Force.

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