View source for North American XB-70 Valkyrie

{{short description|Prototype supersonic strategic bomber}}
{{Good article}}
{{Use dmy dates|date=March 2022}}
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{{Infobox aircraft
|name= XB-70 Valkyrie
|image= File:North American XB-70A Valkyrie in flight (cropped).jpg
|caption= XB-70 Valkyrie in flight
|alt=White delta-wing aircraft overflying mountains. The front of the fuselage features canard wings, and the wing tips are dropped.
|type= [[Strategic bomber]] <br />[[supersonic aircraft|Supersonic]] [[experimental aircraft|research aircraft]]
|national_origin=United States
|manufacturer= [[North American Aviation]] (NAA)
|first_flight= 21 September 1964
|introduction=
|retired= 4 February 1969
|status= Retired<!-- See "Aircraft on display" section for more. -->
|primary_user= [[United States Air Force]]
|more_users= [[NASA]]
|number_built= 2
|program cost= [[United States dollar|US$]]1.5&nbsp;billion<ref name=Knaack_p560-61/> (equivalent to ${{inflation|US|1.5|1969|r=1|fmt=c}} billion today)
|unit cost= US$750&nbsp;million (average cost)(equivalent to ${{inflation|US|.75|1969|r=1|fmt=c}} billion today)
|variants=
}}
The '''North American Aviation XB-70 Valkyrie''' is a retired [[prototype]] version of the planned '''{{nowrap|B-70}}''' [[thermonuclear weapon|nuclear]]-armed, deep-penetration [[Supersonic aircraft|supersonic]] [[strategic bomber]] for the [[United States Air Force]] [[Strategic Air Command]]. Designed in the late 1950s by [[North American Aviation]] (NAA) to replace the [[Boeing B-52 Stratofortress|B-52 Stratofortress]] and [[B-58 Hustler]],<ref name=":0">{{Citation |title=The World's Fastest Bomber: The XB-70 Valkyrie | date=31 March 2022 |url=https://www.youtube.com/watch?v=Yl32c352thE |access-date=2024-01-23 |language=en |archive-date=22 January 2024 |archive-url=https://web.archive.org/web/20240122033151/https://www.youtube.com/watch?v=Yl32c352thE |url-status=live }}</ref> the six-engine, [[Delta wing|delta-winged]] Valkyrie<ref>''Jane's all the World's Aircraft 1963-1964'', p. 254.</ref> could cruise for thousands of miles at [[Mach number|Mach]] 3+ while flying at {{convert|70000|ft|m}}.
At these speeds, it was expected that the B-70 would be practically immune to [[interceptor aircraft]], the only effective weapon against bomber aircraft at the time. The bomber would spend only a brief time over a particular [[radar]] station, flying out of its range before the [[Ground-controlled interception|controllers could position their fighters]] in a suitable location for an interception. Its high speed made the aircraft [[Blip-to-scan ratio|difficult to see]] on radar displays and its high-altitude and high-speed capabilities could not be matched by any contemporaneous Soviet interceptor or fighter aircraft.
The introduction of the first Soviet [[surface-to-air missile]]s in the late 1950s put the near-invulnerability of the B-70 in doubt. In response, the US Air Force (USAF) began flying its missions at low level, where the missile radar's [[line-of-sight propagation|line of sight]] was limited by terrain. In this low-level [[penetrator (aircraft)|penetration]] role, the B-70 offered little additional performance over the [[Boeing B-52 Stratofortress|B-52]] it was meant to replace, while being far more expensive with shorter range. Alternative missions were proposed, but these were of limited scope. With the advent of [[intercontinental ballistic missile]]s (ICBMs) during the late 1950s, crewed nuclear bombers were increasingly seen as obsolete.
The USAF eventually gave up fighting for its production and the B-70 program was cancelled in 1961. Development was then turned over to a research program to study the effects of long-duration high-speed flight. As a result, two prototype aircraft, designated XB-70A, were built; these aircraft were used for supersonic test-flights from 1964 to 1969. In 1966, one prototype crashed after colliding with a smaller aircraft while flying in close formation; the remaining Valkyrie bomber is in the [[National Museum of the United States Air Force]] near Dayton, Ohio.
==Development==
===Background===
In an offshoot of [[Boeing]]'s MX-2145 crewed [[boost-glide]] bomber project, Boeing hired [[RAND Corporation]] in January 1954 to explore what sort of bomber aircraft would be needed to deliver the various [[nuclear weapon]]s under development. At the time, nuclear weapons weighed several tons, and the need to carry enough fuel to fly that payload from the [[continental United States]] to the [[Soviet Union]] demanded large bombers. Boeing and RAND also concluded that the aircraft would need supersonic speed to escape the blast of its bombs.<ref>York 1978, p.&nbsp;70.</ref>
The aviation industry had been studying this problem for some time. From the mid-1940s, there was interest in using [[nuclear-powered aircraft]] as bombers.<ref name=Karman>von Kármán, Theodore. "Where We Stand: First Report to General of the Army H. H. Arnold on Long Range Research Problems of the Air Forces with a Review of German Plans and Developments". ''Atomic Energy for Jet Propulsion''. Washington, D.C.: Government Printing Office, 22 August 1945.</ref><ref>Bikowicz, Brian D. [http://www.atomicengines.com/ANP_politics.html "Atomic Powered Aircraft – Politics"] {{Webarchive|url=https://web.archive.org/web/20110807035251/http://www.atomicengines.com/ANP_politics.html |date=7 August 2011 }}. ''Atomicengines.com''. Retrieved: 24 May 2011.</ref>{{#tag:ref|Quote by Theodore von Kármán (1945): "The size and performance of the craft driven by atomic power would depend mainly on ... reducing the engine weight to the limiting value which makes flight at a certain speed possible."<ref name=Karman/>|group=N}} In a conventional jet engine, thrust is provided by heating air using [[jet fuel]] and accelerating it out a nozzle. In a nuclear engine, heat is supplied by a reactor, whose consumables last for months instead of hours. Most designs also carried a small amount of jet fuel for high-power portions of flight, such as takeoffs and high-speed dashes.<ref name=Karman/>
Another possibility being explored at the time was the use of [[boron]]-enriched "[[zip fuel]]s", which increase the [[energy density]] of jet fuel by about 40 percent,<ref name=Schubert/> and could be used in modified versions of existing jet engine designs.<ref name=Schubert>Schubert, Dave. [http://www.borax.com/pioneer54.html "From Missiles to Medicine: The development of boron hydrides"] {{webarchive|url=https://web.archive.org/web/20071023101907/http://borax.com/pioneer54.html |date=23 October 2007 }}. ''Pioneer Magazine'', March 2001.</ref> Zip fuels appeared to offer sufficient performance improvement to produce a strategic bomber with supersonic speed.
===WS-110A===
The Air Force followed these developments closely, and in 1955 issued General Operational Requirement No. 38 for a new bomber, combining the payload and intercontinental range of the [[Boeing B-52 Stratofortress|B-52]] with the Mach&nbsp;2 top speed of the [[Convair B-58 Hustler]].<ref name=Jenkins_B-1>Jenkins 1999, Ch. 1.</ref>{{#tag:ref|The [[Convair B-58 Hustler#Variants|NB-58 Hustler was used for XB-70 engine testing, and the TB-58]] was used for XB-70 chase and training. |group=N}} The new bomber was expected to enter service in 1963.<ref name=Jenk_Land_p9>Jenkins and Landis 2002, p. 9.</ref> Nuclear and conventional designs were considered. The nuclear-powered bomber was organized as "[[WS-125|Weapon System 125A]]" and pursued simultaneously with the jet-powered version, "Weapon System 110A".<ref name=Jenk_Land_p9-10>Jenkins and Landis 2002, pp.&nbsp;9–10.</ref>
[[File:WS-110 original proposal.gif|thumb|upright=1.3|NAA's original proposal for WS-110A. The "floating panels" are large fuel tanks the size of a [[Boeing B-47 Stratojet|B-47]].<ref name=Taube_II_p1>''B-70 Aircraft Study,'' Vol II. pp. II-2.</ref> Boeing's design was almost identical, differing largely in having a single vertical stabilizer and having two of its engines in pods at the outer edges of the inner wing section.]]
The USAF Air Research and Development Command's (ARDC) requirement for WS-110A asked for a chemical-fuel bomber with Mach&nbsp;0.9 cruising speed and "maximum possible" speed during a {{convert|1000|nmi|mi km|adj=on}} entrance and exit from the target. The requirement also called for a {{convert|50000|lb|adj=on}} payload and a combat radius of {{convert|4000|nmi|mi km}}.<ref name=Knaack_p560-61>Knaack 1988, pp. 560–561.</ref> The Air Force formed similar requirements for a WS-110L intercontinental reconnaissance system in 1955, but this was later canceled in 1958 due to better options.<ref name=Knaack_p561>Knaack 1988, pp. 561, 566.</ref><ref name=Pace_p14/><ref name=Jenk_Land_p17>Jenkins and Landis 2002, p. 17.</ref> In July 1955, six contractors were selected to bid on WS-110A studies.<ref name=Jenk_Land_p9-10/> Boeing and North American Aviation submitted proposals, and on 8 November 1955 were awarded contracts for Phase 1 development.<ref name=Pace_p14>Pace 1988, p. 14.</ref>
In mid-1956, initial designs were presented by the two companies.<ref name=Jenk_Land_p13-4/><ref name=Knaack_p563>Knaack 1988, p. 563.</ref> Zip fuel was to be used in the [[afterburner]]s to improve range by 10 to 15 percent over conventional fuel.<ref name=Jenk_Land_p15-6>Jenkins and Landis 2002, pp. 15–16.</ref> Both designs had huge wing-tip fuel tanks that could be jettisoned when their fuel was depleted before a supersonic dash to the target. The tanks also included the outer portions of the wing, which would also be jettisoned to produce a smaller wing suitable for supersonic speeds.<ref name=Jenk_Land_p13-4>Jenkins and Landis 2002, pp. 13–14.</ref> Both became [[trapezoidal wing]]s after ejection, at that time the highest performance [[Planform (aeronautics)|planform]] known. They also featured flush [[cockpit]]s to maintain the highest [[fineness ratio]] possible in spite of its effects on visibility.<ref name=Jenk_Land_p14-5/>
The two designs had takeoff weights of about {{convert|750000|lb|kg}} with large fuel loads. The Air Force evaluated the designs, and in September 1956 deemed them too large and complicated for operations.<ref name=Jenk_Land_p14-5/> General [[Curtis LeMay]] was dismissive, declaiming, "This is not an airplane, it's a three-ship formation."<ref>Rees 1960, pp. 125–126.</ref> The USAF ended Phase 1 development in October 1956 and instructed the two contractors to continue design studies.<ref name=Knaack_p563/><ref name=Jenk_Land_p14-5/><ref name=Taube_I_p34>''B-70 Aircraft Study,'' Vol. I, pp. I-34–I-38.</ref>
===New designs===
While the original proposals were being studied, advances in supersonic flight were proceeding rapidly. The narrow delta was establishing itself as a preferred planform for supersonic flight, replacing earlier designs like the swept-wing and trapezoidal layouts seen on designs like the [[Lockheed F-104 Starfighter]] and the earlier WS-110 concepts. Engines able to cope with higher temperatures were also under development, allowing for sustained supersonic speeds.<ref name=Jenk_Land_p14-5/>
This work led to an interesting discovery: when an engine was optimized specifically for high speed, it burned perhaps twice as much fuel at that speed than when it was running at subsonic speeds. However, the aircraft would be flying as much as four times as fast. Thus its most economical cruise speed, in terms of fuel per mile, was its maximum speed. This was entirely unexpected and implied that there was no point in the dash concept; if the aircraft was able to reach Mach&nbsp;3, it may as well fly its entire mission at that speed. The question remained whether such a concept was technically feasible, but by March 1957, engine development and wind tunnel testing had progressed enough to suggest that it was.<ref name=Jenk_Land_p14-5/>
WS-110 was redesigned to fly at Mach&nbsp;3 for the entire mission. Zip fuel was retained for the engine's afterburner to increase range.<ref name=Jenk_Land_p14-5>Jenkins and Landis 2002, pp.&nbsp;14–15.</ref><ref>Conway 2005, p.&nbsp;33.</ref> 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,<ref name=Jenk_Land_p15-6/> like the Hustler.
[[File:North American XB-70 Valkyrie final proposal.gif|thumb|upright=1.3|NAA's final WS-110A proposal, built as the XB-70]]
North American scoured available literature to find any additional advantage. This led them to an obscure report by two [[NACA]] [[wind tunnel]] experts, who wrote a report in 1956 titled "Aircraft Configurations Developing High Lift-Drag Ratios at High Supersonic Speeds".<ref>Rees 1960, p. 126.</ref> Known today as [[compression lift]], the idea was to use the [[shock wave]] generated off the nose or other sharp points on the aircraft as a source of high-pressure air.<ref name=Pace_p16>Pace 1988, p. 16.</ref> 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. To take maximum advantage of this effect, they redesigned the 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 six individually-podded engines were repositioned, three in each of two separate ducts, under the fuselage.<ref>Winchester 2005, p.&nbsp;187.</ref>
North American improved on the basic concept by adding a set of drooping wing-tip panels that were lowered at high speed. This helped trap the shock wave under the wing between the downturned wing tips. It also added more vertical surface to the aircraft to maintain directional stability at high speeds.<ref name=Pace_p16/> NAA's solution had an additional advantage, as it decreased the surface area of the rear of the wing when the panels were moved into their high-speed position. This helped offset the natural rearward shift of the [[Center of pressure (fluid mechanics)|center of pressure]], or "average lift point", with increasing speeds. Under normal conditions this caused an increasing nose-down trim, which had to be offset by moving the control surfaces, increasing [[Aerodynamic drag|drag]]. When the wing tips were drooped, the lifting area of the wings was lessened, moving the lift forward and reducing [[trim drag]].<ref>Talay, Theodore A., ed. [http://www.centennialofflight.gov/essay/Theories_of_Flight/Stability_II/TH27.htm "Dynamic Longitudinal, Directional, and Lateral Stability"] {{webarchive|url=https://web.archive.org/web/20110820054436/http://centennialofflight.gov/essay/Theories_of_Flight/Stability_II/TH27.htm |date=20 August 2011 }}. ''Centennial of Flight Commission'', 2003. Retrieved: 24 May 2011.</ref>
The buildup of heat due to [[skin friction]] during sustained [[supersonic flight]] had to be addressed. During a Mach&nbsp;3 cruise, the aircraft would reach an average of {{convert|450|°F|°C|sigfig=2}}, with [[leading edge]]s reaching {{convert|630|°F|°C|sigfig=2}}, and up to {{convert|1000|°F|°C|sigfig=2}} in engine compartments. NAA proposed building their design out of [[sandwich panel]]s, with each panel consisting of two thin sheets of stainless steel brazed to opposite faces of a [[Honeycomb structure|honeycomb-shaped]] foil core. Expensive [[titanium]] would be used only in high-temperature areas like the leading edge of the horizontal stabilizer, and the nose.<ref name=Taube_III_p31>''B-70 Aircraft Study,'' Vol. III., pp.&nbsp;III-10, III-31, III-141, III-210.</ref> To cool the interior, the XB-70 pumped fuel en route to the engines through heat exchangers.<ref name=Taube_III_p496>''B-70 Aircraft Study,'' Vol. III., pp.&nbsp;III-496 to III-498.</ref>
On 30 August 1957, the Air Force decided that enough data were available on the NAA and Boeing designs that a competition could begin. On 18 September, the Air Force issued operational requirements that called for a cruising speed of Mach&nbsp;3.0 to 3.2, an over-target altitude of {{convert|70000|–|75,000|ft|m|abbr=on}}, a range of up to {{convert|10500|mi|km|}}, and a gross weight not to exceed {{convert|490000|lb|kg}}. The aircraft would have to use the hangars, runways and handling procedures used by 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.<ref name=Jenk_Land_p17/>
In February 1958, the proposed bomber was designated ''B-70'',<ref name=Jenk_Land_p17/> with the prototypes receiving the "X" [[United States Department of Defense aerospace vehicle designation|experimental prototype designation]]. The name "[[Valkyrie]]" was the winning submission in early 1958, selected from 20,000 entries in a USAF "Name the B-70" contest.<ref name=Pace_p17>Pace 1988, p.&nbsp;17.</ref> The Air Force approved an 18-month program acceleration in March 1958 that rescheduled the first flight to December 1961.<ref name=Jenk_Land_p17/> But in late 1958 the service announced that this acceleration would not be possible due to lack of funding.<ref name=Knaack_p566>Knaack 1988, p. 566.</ref> 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.<ref name=Jenk_Land_p24>Jenkins and Landis 2002, p. 24.</ref> At the same time, North American was developing the [[North American XF-108 Rapier|F-108]] supersonic interceptor. To reduce program costs, the F-108 would share two of the engines, the escape capsule, and some smaller systems with the B-70.<ref name=Jenk_Land_p18-26>Jenkins and Landis 2002, pp. 18, 26.</ref> In early 1960, North American and the USAF released the first drawing of the XB-70 to the public.<ref>[https://books.google.com/books?id=99sDAAAAMBAJ&dq=true&pg=PA86 "Here's A Peek At Tomorrow's Huge Planes"] {{Webarchive|url=https://web.archive.org/web/20230709011532/https://books.google.com/books?id=99sDAAAAMBAJ&dq=true&pg=PA86 |date=9 July 2023 }}. ''Popular Mechanics'', April 1960, p. 86.</ref>
===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 crewed bomber use.<ref name=Spick_1986_p4-5>Spick 1986, pp. 4–5.</ref> Through that same period, only two weapons proved effective against bombers: [[fighter aircraft]] and [[anti-aircraft artillery]] (AAA). Flying higher and faster made it more difficult for both; higher speeds allowed the bomber to fly out of range of the weapons more quickly, while higher altitudes increased the time needed for fighters to climb to the bombers, and greatly increased the size of the AAA weapons needed to reach those altitudes.<ref name=westerman>{{cite book |first=Edward |last=Westerman |title=Flak: German Anti-Aircraft Defenses, 1914–1945 |publisher= University Press of Kansas |year= 2001 |isbn=0700614206 |page=11}}</ref>
As early as 1942, German flak commanders had already concluded that AAA would be essentially useless against jet aircraft, and began development of guided missiles to fill this role.<ref name=westerman/> Most forces reached the same conclusion soon afterwards, with both the US and UK starting missile development programs before the war ended.<ref>{{cite book |first=Mary |last=Cagle |url=http://ed-thelen.org/mono-1-2.html#table |title=Nike Ajax Historical Monograph |publisher=U.S. Army Ordnance Missile Command |date=30 June 1959 |page=I |access-date=12 November 2015 |archive-date=9 July 2013 |archive-url=https://web.archive.org/web/20130709165221/http://ed-thelen.org/mono-1-2.html#table |url-status=live }}</ref> The UK's [[Green Mace]] was one of the last attempts to develop a useful high-altitude AAA weapon, but its development ended in 1957.<ref>{{Cite book |last=Robert |first=Gardiner |title=Conway's All the World's Fighting Ships 1947 – 1982 – Part I: The Western Powers |publisher=Conway Maritime Press |year=1983 |isbn=978-0851772257 |page=130}}</ref>
[[Interceptor aircraft]] with ever-improving performance remained the only effective anti-bomber weapons by the early 1950s, and even these were having problems keeping up with the latest designs; Soviet interceptors during the late 1950s could not intercept the high-altitude [[Lockheed U-2|U-2]] reconnaissance aircraft,<ref>Ben Rich and Leo Janos. ''Skunk Works''. Boston: Little, Brown & Company, 1994. {{ISBN|0-316-74300-3}}.</ref> despite its relatively low speeds. It was later discovered that flying faster also made radar detection much more difficult due to an effect known as the [[blip-to-scan ratio]], and any reduction in tracking efficiency would further interfere with the operation and guidance of fighters.<ref>Pedlow and Welzenbach 1992, p. 9.</ref>
The introduction of the first effective anti-aircraft missiles by the late 1950s changed this picture dramatically.<ref name=Jenkins_1999_p21>Jenkins 1999, p. 21.</ref> Missiles could stand ready for immediate launch, eliminating operational delays like the time needed to get the pilot into the cockpit of a fighter. Guidance did not require wide-area tracking or calculation of an intercept course: a simple comparison of the time needed to fly to the altitude of the target returned the required [[Deflection (ballistics)|deflection]]. Missiles also had greater altitude capability than any aircraft and improving this to adapt to new aircraft was a low-cost development path. The US was aware of Soviet work in the field, and had reduced the expected operational lifetime of the U-2, knowing that it would become vulnerable to these missiles as they were improved. In 1960, a U-2 flown by [[Gary Powers]] was [[U-2 Crisis of 1960|shot down]] by one of the earliest Soviet guided air-defence missiles, the [[S-75 Dvina]], known in the west as the SA-2 Guideline.<ref name=PnW2>Pedlow and Welzenbach 1992, p. 2.</ref>
Faced with this problem, military doctrine had already started shifting away from high-altitude supersonic bombing toward low-altitude ''penetration''. Radar is line-of-sight, so aircraft could dramatically shorten detection distances by flying close to the Earth and hiding behind terrain.<ref name=Spick_1986_p6-7>Spick 1986, pp. 6–7.</ref> Missile sites spaced to overlap in range when attacking bombers at high altitudes would leave large gaps between their coverage for bombers flying at lower levels. With an appropriate map of the missile sites, the bombers could fly between and around the defenses. Additionally, early missiles generally flew unguided for a period of time before the radar systems were able to track the missile and start sending it guidance signals. With the SA-2 missile, this minimum altitude was roughly {{convert|2000|ft|m|-2}}.<ref>Hannah 2002, p. 68.</ref>
Flying at low level provided protection against fighters as well. Radars of the era did not have the ability to look down (see [[look-down/shoot-down]]); if a higher altitude aircraft's radar was aimed down to detect targets at a lower altitude, the reflection of the ground would overwhelm the signal returned from a target. An interceptor flying at normal altitudes would be effectively blind to bombers far below it. The interceptor could descend to lower altitudes to increase the amount of visible sky, but doing so would limit its radar range in the same way as the missile sites, as well as greatly increasing fuel use and thus reducing mission time. The Soviet Union would not introduce an interceptor with look-down capability until 1972 with the High Lark radar in the [[Mikoyan-Gurevich MiG-23#23m|MiG-23M]], and even this model had very limited capability.<ref>Koenig and Scofield 1983, p. 132.</ref>
Strategic Air Command found itself in an uncomfortable position; bombers had been tuned for efficiency at high speeds and altitudes, performance that had been purchased at great cost in both engineering and financial terms. Before the B-70 was to replace the B-52 in the long-range role, SAC had introduced the [[B-58 Hustler]] to replace the [[Boeing B-47 Stratojet]] in the medium-range role. The Hustler was expensive to develop and purchase, and required enormous amounts of fuel and maintenance in comparison to the B-47. It was estimated that it cost three times as much to operate as the much larger and longer-ranged B-52.<ref>Miller 1985, p. 69.</ref>
The B-70, designed for even higher speeds, altitudes and range than the B-58, suffered even more in relative terms. At high altitudes, the B-70 was as much as four times as fast as the B-52, but at low altitudes it was limited to only Mach&nbsp;0.95, only modestly faster than the B-52 at the same altitudes. It also had a smaller bomb load and shorter range.<ref name=Taube_II_p1/> Its only major advantage would be its ability to use high speed in areas without missile cover, especially on the long journey from the US to USSR. The value was limited; the USAF's doctrine stressed that the primary reason for maintaining the bomber force in an era of ICBMs was that the bombers could remain in the air at long ranges from their bases and were thus immune to sneak attack.<ref>Barry, John. [http://www.thedailybeast.com/newsweek/2009/12/11/bye-bye-bomber.html "Bye-Bye Bomber?"] {{Webarchive|url=https://web.archive.org/web/20120114130242/http://www.thedailybeast.com/newsweek/2009/12/11/bye-bye-bomber.html |date=14 January 2012 }}. ''Newsweek'', 11 December 2009.</ref> In this case, the higher speed would be used for only a short period of time between the staging areas and the Soviet coastline.
Adding to the problems, the zip fuel program was canceled in 1959.<ref name=Schubert/> After burning, the fuel turned into caustic and abrasive liquids and solids that increased wear on moving turbine engine components and were toxic, making servicing difficult.{{#tag:ref|Quote: "deleterious to metallic components".<ref name=Jenk_Land_p98>Jenkins and Landis 2002, p. 98.</ref>|group=N}} Although the B-70 was intended to use zip only in the afterburners, and thus avoid this problem, the enormous cost of the zip program for such limited gains led to its cancellation. This by itself was not a fatal problem as newly developed high-energy fuels like [[JP-6]] were available to make up some of the difference. Most of the range lost in the change from zip fuel was restored by filling one of the two bomb bays with a fuel tank.<ref name=Jenk_Land_p25>Jenkins and Landis 2002, pp. 25–26.</ref> Another problem arose when the [[North American XF-108 Rapier|XF-108]] program was canceled in September 1959, which ended the shared development that benefited the B-70 program.<ref name=Jenk_Land_p18-26/>
===Downsizing, upswing, cancellation===
At two secret meetings on 16 and 18 November 1959, the [[Chairman of the Joint Chiefs of Staff]], Air Force [[Nathan Farragut Twining|General Nathan Twining]], recommended the Air Force's plan for the B-70 to reconnoiter and strike rail-mobile Soviet ICBMs, but the [[Chief of Staff of the United States Air Force|Chief of Staff of the Air Force]], [[Thomas D. White|General Thomas 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 (equivalent to ${{inflation|US|.200|1960|r=1|fmt=c}} billion today). President Eisenhower responded that the reconnaissance and strike mission was "crazy" since the nuclear mission was to attack known production and military complexes, and emphasized that 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 manufacturing until "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".<ref>{{cite report |url=https://www.eisenhower.archives.gov/Research/Subject_Guides/Subject_Guides.html |title=WHITE HOUSE OFFICE, Office of the Staff Secretary: Records, 1952–61 – Subject Series, Department of Defense Subseries |last=Goodpaster |first=Andrew J. |date= |location=Dwight D. [[Eisenhower Presidential Library]] |author-link=Andrew Goodpaster |archive-url=https://web.archive.org/web/20110816203047/http://eisenhower.archives.gov/Research/Subject_Guides/Subject_Guides.html |archive-date=16 August 2011 |url-status=dead}}
: {{cite report |title=Memorandum of Conference with the President: June 23, 1959 – 11:40&nbsp;am |last=Goodpaster |date=24 June 1959 |quote="DECLASSIFIED ... 4/10/79" |work=Box 1: Joint Chiefs of Staff (6)}}
: {{cite report |title=Memorandum of Conference with the President: November 16, 1959 |last=Goodpaster |date=December 1959 |others=The memo for the 18 November meeting took two months to write, e.g., due to the transcription time |work=[probably box 3]}}
: {{cite report |title=Memorandum of Conference with the President: November 18, 1959 – Augusta |last=Goodpaster |date=20 January 1960 |quote="DECLASSIFIED ... 18 January 1981" |work=Box 4: Joint Chiefs of Staff (8)}}<br />''Note'': 18 November 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.</ref> 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.<ref name=Jenk_Land_p26>Jenkins and Landis 2002, p. 26.</ref>
Then interest increased due to the politics of [[1960 United States presidential election|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, "I endorse wholeheartedly the B-70 manned aircraft."<ref name=Zuckert>Zuckert, Eugene M. [https://archive.today/20130414183247/http://www.foreignaffairs.org/19660401faessay44308/eugene-m-zuckert/the-service-secretary-has-he-a-useful-role.html "The Service Secretary: Has He a Useful Role?"]. ''Foreign Affairs'', April 1966. Retrieved: 8 December 2008.</ref> Kennedy also made similar campaign claims regarding other aircraft: near the Seattle Boeing plant he affirmed the need for B-52s and in Fort Worth he praised the B-58.<ref name=JFK_Seattle>Kennedy, John F. [http://www.presidency.ucsb.edu/ws/index.php?pid=25654#axzz1NnZVQQ6F "Speech of Senator John F. Kennedy, Civic Auditorium, Seattle, WA"] {{Webarchive|url=https://web.archive.org/web/20121002135800/http://www.presidency.ucsb.edu/ws/index.php?pid=25654#axzz1NnZVQQ6F |date=2 October 2012 }}. ''The American Presidency Project at [[University of California, Santa Barbara|ucsb.edu]]''. Retrieved: 30 May 2011.</ref>
[[File:North American XB-70 on ramp ECN-1814.jpg|thumb|left|XB-70A parked at Edwards Air Force Base in 1967]]
The Air Force changed the program to full weapon development and awarded a contract for an XB-70 prototype and 11 YB-70s in August 1960.<ref name=Jenk_Land_p26/><ref name=Taube_YB-70>Taube, Vol I, pp. I-29, I-31, I-37, I-38, I-47.</ref> In November 1960, the B-70 program received a $265&nbsp;million (equivalent to ${{inflation|US|.265|1960|r=1|fmt=c}} billion today) appropriation from Congress for FY 1961.<ref name=Jenk_Land_p26-27>Jenkins and Landis 2002, pp. 26–27.</ref><ref name=York_p26-27>York 1978, p. 56.</ref> Nixon, trailing in his home state of California, also publicly endorsed the B-70, and on 30 October Eisenhower helped the Republican campaign with a pledge of an additional $155&nbsp;million (${{inflation|US|.155|1961|r=1|fmt=c}} billion today) for the B-70 development program.<ref name=Kennedy/>
On taking office in January 1961, Kennedy was informed that the [[missile gap]] was an illusion.<ref name=Preble>Preble, Christopher A. "Who Ever Believed in the 'Missile Gap'?: John F. Kennedy and the Politics of National Security". ''Presidential Studies Quarterly'', December 2003, pp. 816, 819.</ref>{{#tag:ref|Wiesner ... a member of Eisenhower's permanent Science Advisory Committee, explained that the missile gap was a fiction. The new president greeted the news with a single expletive "delivered more in anger than in relief".... Herken 1961, p. 140. This quote taken from Herken's interview with Wiesner conducted 9 February 1982.|group=N}} On 28 March 1961,<ref name=Knaack_p569>Knaack 1988, p. 569.</ref> after $800&nbsp;million (equivalent to ${{inflation|US|.8|1961|r=1|fmt=c}} billion today) had been spent on the B-70 program, Kennedy canceled the project as "unnecessary and economically unjustifiable"<ref name=Kennedy>Kennedy, John F. [http://www.presidency.ucsb.edu/ws/index.php?pid=25935&st=&st1= "Remarks of Senator John F. Kennedy, Horton Plaza, San Diego, CA, 2 November 1960"] {{Webarchive|url=https://web.archive.org/web/20120914185529/http://www.presidency.ucsb.edu/ws/index.php?pid=25935&st=&st1= |date=14 September 2012 }}. ''The American Presidency Project at [[University of California, Santa Barbara|ucsb.edu]]''. Retrieved: 6 April 2009.<br />[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950002358_1995102358.pdf "1961 Budget Message"] {{Webarchive|url=https://web.archive.org/web/20200919222316/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950002358_1995102358.pdf |date=19 September 2020 }}. ''Kennedy Archives'', 28 March 1961, pp.&nbsp;I-38.</ref> because it "stood little chance of penetrating enemy defenses successfully."<ref name=Greenwood>Greenwood 1995, p. 289.</ref> 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."<ref name=Kennedy/> After Congress approved $290&nbsp;million (${{inflation|US|.29|1961|r=1|fmt=c}} billion today) of B-70 "add-on" funds to the President's 12 May 1960 modified FY 1961 budget, the Administration decided on a "Planned Usage" of only $100 million (${{inflation|US|100|1961|r=-1|fmt=c}} million today) of these funds. The Department of Defense subsequently presented data to Congress that the B-70 would add little performance for the high cost.<ref name=Enthoven>Builder, Carl H. [https://books.google.com/books?id=kL0QE2I4FXAC&pg=PA183 "Presentation to Congress by Alain Enthoven"] {{Webarchive|url=https://web.archive.org/web/20230915103003/https://books.google.com/books?id=kL0QE2I4FXAC&pg=PA183 |date=15 September 2023 }}. ''The Icarus Syndrome: The Role of Air Power Theory in the Evolution and Fate of the U.S. Air Force.'' Cream Ridge, NJ: Transaction Publishers, 2002. {{ISBN|978-0-7658-0993-3}}. Retrieved: 31 May 2011.</ref>
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 resurrect bomber development. After Secretary of Defense [[Robert McNamara]] 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 HASC, 21 of whose members had B-70 work in their districts, had written an appropriations bill to "direct"—by law—the Executive Branch to use all of the nearly $500&nbsp;million (equivalent to ${{inflation|US|.5|1962|r=1|fmt=c}} billion today) appropriated for the RS-70 (see [[#Variants|Variants]]). McNamara was unsuccessful with an address to the HASC on 14 March, but a 19 March 1962 [[wiktionary:eleventh hour|11th hour]] [[White House Rose Garden]] agreement between Kennedy and HASC chairman [[Carl Vinson]] retracted the bill's language<ref name=NewYorkTimes>"House Unit 'Directs' Production of B-70." ''[[The New York Times]]'', 1 March 1962.</ref> and the bomber remained canceled.<ref name=Pace_p20-1>Pace 1988, pp. 20–21.</ref>
===Experimental aircraft===
[[File:North American XB-70A Valkyrie on the taxiway with a cherry picker. Photo taken Sept 21 1964, the day of the first flight 061122-F-1234P-017.jpg|thumb|left|XB-70A on the taxiway on 21{{nbsp}}September 1964, the day of the first flight]]
The XB-70s were intended to be used for the advanced study of [[aerodynamics]], [[Air propulsion|propulsion]], and other subjects related to large supersonic transports. The crew was reduced to only the two pilots, as a [[navigator]] and a [[bombardier (air force)|bombardier]] were not needed for this research role.<ref name=Jenk_Land_p28_73>Jenkins and Landis 2002, pp. 28, 73.</ref> The production order was reduced to three prototypes in March 1961<ref name=Taube_I_p39>''B-70 Aircraft Study,'' Vol. I, p. I-39.</ref> with the third aircraft to incorporate improvements from the previous prototype.<ref name=Jenk_Land_p27-28>Jenkins and Landis 2002, pp. 27–28.</ref> The order was later reduced to two experimental XB-70As, named Air Vehicle 1 and 2 (AV-1 and AV-2). XB-70 No. 1 was completed on 7{{nbsp}}May 1964,<ref name=Taube_I_p39-44>''B-70 Aircraft Study,'' Vol. I, pp. I-39–I-44.</ref> and rolled out on 11{{nbsp}}May 1964 at [[Palmdale, California]].<ref name=Taube_I_p41_88>''B-70 Aircraft Study,'' Vol. I. pp. I-41, I-88.</ref><ref name=brsappl>{{cite news |url=https://news.google.com/newspapers?id=2fxVAAAAIBAJ&sjid=dOMDAAAAIBAJ&pg=5851%2C2489587 |work=Eugene Register-Guard |location=(Oregon) |agency=Associated Press |title=XB70A triggers burst of applause |date=11 May 1964 |page=5A |access-date=31 December 2020 |archive-date=31 January 2023 |archive-url=https://web.archive.org/web/20230131214127/https://news.google.com/newspapers?id=2fxVAAAAIBAJ&sjid=dOMDAAAAIBAJ&pg=5851%2C2489587 |url-status=live }}</ref><ref name=flanpln>{{cite news |url=https://news.google.com/newspapers?id=44MzAAAAIBAJ&sjid=e_cDAAAAIBAJ&pg=5885%2C2113499 |work=Spokane Daily Chronicle |location=(Washington) |agency=AP photo |title=First look at new plane |date=11 May 1964 |page=2 |access-date=31 December 2020 |archive-date=15 September 2023 |archive-url=https://web.archive.org/web/20230915103003/https://news.google.com/newspapers?id=44MzAAAAIBAJ&sjid=e_cDAAAAIBAJ&pg=5885,2113499 |url-status=live }}</ref> One report stated "nothing like it existed anywhere".<ref name=Boyne>[[Walter J. Boyne|Boyne, Walter J.]] [http://www.airforcemag.com/MagazineArchive/Pages/2006/June%202006/0606valkyrie.aspx "The Ride of the Valkyrie"] {{Webarchive|url=https://web.archive.org/web/20160304192119/http://www.airforcemag.com/MagazineArchive/Pages/2006/June%202006/0606valkyrie.aspx |date=4 March 2016 }}. ''Air Force Magazine'', June 2006. Retrieved: 29 October 2008.</ref><ref name=Jenk_Land_p39>Jenkins and Landis 2002, p. 39.</ref> AV-2 was completed on 15 October 1964. The manufacture of the third prototype (AV-3) was canceled in July 1964 before completion.<ref name=Jenk_Land_p39/> The first XB-70 carried out its maiden flight in September 1964 and many more test flights followed.<ref name=Jenk_Land_p39-44>Jenkins and Landis 2002, pp. 39–44.</ref>
The data from the XB-70 test flights and aerospace materials development were used in the later [[Rockwell B-1 Lancer|B-1 bomber program]], the American [[supersonic transport]] (SST) program, and via espionage, the [[Soviet Union]]'s [[Tupolev Tu-144]] SST program.<ref>Moon 1989, p. 92.</ref>{{#tag:ref|In response to the British/French treaty in 1962 that lead to the [[Concorde]] SST, President [[John F. Kennedy]] began the American SST project in June 1963.<ref name=Greenwood/> North American entered a design with some elements from the B-70, but it was eliminated from the competition in June 1964.<ref name=Greenwood/>|group=N}}{{#tag:ref|Following the 1963 formation of the National [[Supersonic transport|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."|group=N}} The development of the [[Lockheed U-2]] and the [[Lockheed SR-71 Blackbird|SR-71 Blackbird]] [[reconnaissance aircraft]], as well as the XB-70, prompted Soviet [[aerospace engineers]] to design and develop their high-altitude and high-speed [[Mikoyan-Gurevich MiG-25|MiG-25]] [[interceptor aircraft|interceptor]].<ref>Pace, Steve. ''F-22 Raptor: America's Next Lethal War Machine''. New York: McGraw-Hill, 1999. {{ISBN|0-07-134271-0}}.</ref><ref>Eden, Paul, ed. ''Encyclopedia of Modern Military Aircraft''. New York: Amber Books, 2004. {{ISBN|1-904687-84-9}}.</ref>
== Design ==
The Valkyrie was designed to be a high-altitude Mach&nbsp;3 bomber with six engines. [[Harrison Storms]] shaped the aircraft<ref name=Heppenheimer>Heppenheimer 2006, pp. 96, 112, 116.</ref> with a [[Canard (aeronautics)|canard surface]]<!--NASA TM X-2215--> and a [[delta wing]], which was built largely of [[stainless steel]], [[Sandwich structured composite|sandwiched honeycomb]] panels, and [[titanium]]. The XB-70 was designed to use supersonic technologies developed for the Mach&nbsp;3 [[SM-64 Navaho]], as well as a modified form of the Navaho's [[inertial guidance]] system.<ref name=von_Braun_p122>von Braun 1975, p. 122.</ref>
The XB-70 used [[compression lift]], which resulted from a [[shock wave]] generated by the leading edge of the engine intake [[Splitter plate (aeronautics)|splitter]] below the apex of the wing.<ref>Jenkins & Landis 2002, p. 49</ref> <!--III-233--> At Mach 3 cruising speed, the shock wave is bent back about 65 degrees and the wing is superimposed on the shock system which has a pressure {{convert|40|psf|kPa}} higher under the aircraft than in front of the shock. The compression lift provided five percent of the total lift.<ref name=Jenk_Land_p76>Jenkins and Landis 2002, p. 76.</ref> [[Camber (aerodynamics)|Camber]] was added to the wing leading edge inboard of the folding tips to improve subsonic handling and reduce supersonic drag. The outer portions of the wings were hinged to pivot downward by 65 degrees, acting as a type of variable-geometry [[wingtip device]]. This increased the aircraft's [[directional stability]] at supersonic speeds, shifted the [[center of pressure (fluid mechanics)|center of pressure]] to a more favorable position at high speeds, and caused the shock originating at the intake splitter to reflect from the vertical tip surface giving additional compression lift.<ref name=Taube_III_p162>''B-70 Aircraft Study'', Vol. III. p. III–162.</ref>
Like a number of other delta-wing aircraft designed for supersonic speeds (Concorde, Tu-144, FD2), the Valkyrie needed a feature to improve the pilot's view during nose-high low-speed flight and on the ground. An outer windshield and ramp, which could be lowered, was provided enabling viewing through the fixed cockpit windshield. With the ramp raised into its high-speed position, the forebody was more streamlined. Rain removal and windshield anti-ice was accomplished by utilizing {{cvt|600|F|-1}} [[bleed air]] from the engines.<ref name=Jenk_Land_p7576>Jenkins and Landis 2002, pp. 75–76.</ref> The lower forward section included a [[radar]] bay, and production machines were to be equipped with a refueling receptacle on the upper surface of the forward fuselage.<ref name=Jenk_Land_p81>Jenkins and Landis 2002, p. 81.</ref>
The XB-70 was equipped with six [[General Electric YJ93]]-GE-3 [[turbojet]] engines, which used [[JP-6]] jet fuel, specially formulated for the mission requirements. The engine was stated to be in the "30,000-pound class", but actually produced {{convert|28000|lbf|kN|abbr=on}} with afterburner and {{convert|19900|lbf|kN|abbr=on}} without afterburner.<ref name=Taube_III_p476>''B-70 Aircraft Study'', Vol. III. pp. III–476, III–479.</ref><ref name=Jenk_Land_p83>Jenkins and Landis 2002, pp. 83–84.</ref> The Valkyrie used fuel for cooling; it was pumped through [[heat exchanger]]s before reaching the engines.<ref name=Taube_III_p496/> To reduce the likelihood of [[autoignition]], nitrogen was injected into the JP-6 during refueling,<!--III-497--> and the "fuel pressurization and [[inerting system]]" vaporized a {{convert|700|lb|kg|adj=on}} supply of [[liquid nitrogen]] to fill the fuel tank vent space and maintain tank pressure.<ref name=flightmanual>[http://www.avialogs.com/en/aircraft/usa/northamericanaviation/xb-70/to-1b-70xa-1-interim-flight-manual-xb-70a.html "XB-70 Interim Flight Manual"] {{Webarchive|url=https://web.archive.org/web/20150702074458/http://www.avialogs.com/en/aircraft/usa/northamericanaviation/xb-70/to-1b-70xa-1-interim-flight-manual-xb-70a.html |date=2 July 2015 }}. ''[[USAF]]'', Series 25 June 65 (original publication: 31 August 1964), pp. 1-40B, 1–49.</ref>
==Operational history==
[[File:North American XB-70 above runway ECN-792.jpg|thumb|left|XB-70A Valkyrie taking off in August 1965|alt=White delta-wing aircraft taking off with landing gears retracting. At the front of aircraft are canards.]]
The XB-70's maiden flight was on 21 September 1964.<ref name=fpbflt>{{cite news |url=https://news.google.com/newspapers?id=O49YAAAAIBAJ&sjid=mPcDAAAAIBAJ&pg=6240%2C4973602 |newspaper=Spokesman-Review |location=(Spokane, Washington) |agency=Associated Press |title=Troubles plague bomber's flight |date=21 September 1964 |page=2 |access-date=1 January 2017 |archive-date=20 September 2022 |archive-url=https://web.archive.org/web/20220920233422/https://news.google.com/newspapers?id=O49YAAAAIBAJ&sjid=mPcDAAAAIBAJ&pg=6240%2C4973602 |url-status=live }}</ref><!--I-43--> In the first flight test, between Palmdale and Edwards AFB, one engine had to be shut down shortly after take-off, and an undercarriage malfunction warning meant that the flight was flown with the undercarriage down as a precaution, limiting speed to {{cvt|390|mph|km/h}} – about half that planned.<ref>[http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%202576.html "The B-70 Flies"] {{Webarchive|url=https://web.archive.org/web/20121023093558/http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%202576.html |date=23 October 2012 }}. ''Flight International'', 1 October 1964, p. 577.</ref> During landing, the rear wheels of the port side main gear locked, the tires ruptured, and a fire started.<ref>Pace 1990, pp. 56–57, 59.</ref><ref>{{cite web|url=https://theaviationist.com/2015/12/09/xb-70-rare-emergency-video/|title=Impressive video of an XB-70 Valkyrie Mach 3 bomber's emergency landing|date=9 December 2015|access-date=5 June 2017|archive-date=8 July 2017|archive-url=https://web.archive.org/web/20170708170715/https://theaviationist.com/2015/12/09/xb-70-rare-emergency-video/|url-status=live}}</ref>
The Valkyrie first became supersonic (Mach 1.1) on the third test flight on 12 October 1964, and flew above Mach&nbsp;1 for 40 minutes during the following flight on 24 October. The wing tips were also lowered partially in this flight. XB-70 No. 1 surpassed Mach&nbsp;3 on 14 October 1965 by reaching Mach 3.02 at {{convert|70000|ft|m|abbr=on}}.<ref name=Jenk_Land_p50>Jenkins and Landis 2002, p. 50.</ref> 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.<ref name=Jenkins_B-1/> On two occasions, honeycomb panels failed and were torn off during supersonic flight, necessitating a Mach 2.5 limit being placed on the aircraft.<ref name=Jenk_Land_p50-51>Jenkins and Landis 2002, pp. 50–51.</ref>
The deficiencies discovered on AV-1 were almost completely solved on the second XB-70, which first flew on 17 July 1965. On 3 January 1966, XB-70 No. 2 attained a speed of Mach&nbsp;3.05 while flying at {{convert|72000|ft|m|abbr=on}}. AV-2 reached a top speed of Mach&nbsp;3.08 and maintained it for 20 minutes on 12 April 1966.<ref name=Jenk_Land_p54>Jenkins and Landis 2002, p. 54.</ref> On 19 May 1966, AV-2 reached Mach&nbsp;3.06 and flew at Mach&nbsp;3 for 32 minutes, covering {{convert|2400|mi|km|abbr=on}} in 91 minutes of total flight.<ref name=Jenk_Land_p56>Jenkins and Landis 2002, p. 56.</ref>
{| class="wikitable floatright"
|+ XB-70 performance records<ref>Pace 1990, pp. 76–82.</ref>
|Longest flight || 3:40 hours || 6 January 1966
|-
|Fastest speed || {{convert|2020|mph|km/h|abbr=on}} || 12 January 1966
|-
|Highest altitude || {{convert|74000|ft|m|abbr=on}} || 19 March 1966
|-
|Highest [[Mach number]] || Mach 3.08 || 12 April 1966
|-
|Sustained Mach 3 || 32 minutes || 19 May 1966
|-
|Mach 3 total || 108 minutes/10 flights || – <!-- The objective was 180 Mach 3 flight hours for which 327 more 33 minute Mach 3 A/V No. 2 flights would have been needed -->
|}
A joint NASA/USAF research program was conducted from 3 November 1966 to 31 January 1967 for measuring the intensity and signature of sonic booms for the National Sonic Boom Program. Testing was planned to cover a range of sonic boom overpressures on the ground similar to but higher than those anticipated from the proposed American [[Supersonic Transport|SST]].<ref name=Jenk_Land_p63>Jenkins and Landis 2002, pp. 62–63.</ref> <!--for "combining the theoretical sonic boom intensity due to lift and due to volume". I-32, I-43, II-5--> In 1966, AV-2 was selected for the program and was outfitted with test sensors. It flew the first sonic boom test on 6 June 1966, attaining a speed of Mach&nbsp;3.05 at {{convert|72000|ft|m|abbr=on}}.<ref name=Jenk_Land_p61-2>Jenkins and Landis 2002, pp. 61–62.</ref> Two days later, AV-2 crashed following a mid-air collision with an F-104 while flying in a multi-aircraft formation.<ref>Pace 1990, pp. 62–68.</ref> Sonic boom and later testing continued with XB-70A #1.<ref name=Pace_p62-9>Pace 1988, pp. 62–69.</ref>
The second flight research program (NASA NAS4-1174) investigated "control of structural dynamics" from 25 April 1967 through the XB-70's last flight in 1969.<ref name=Taube_I_p32_43>B-70 Aircraft Study, Vol. I. pp. I–32, I-43.</ref><ref name=Taube_II_p5-6>''B-70 Aircraft Study,'' Vol. II. pp. II–5 to II-6.</ref> At high altitude and high speed, the XB-70A experienced unwanted changes in altitude.<ref>Jenkins 1997, p. 45.</ref> NASA testing from June 1968 included two small vanes on the nose of AV-1 for measuring the response of the aircraft's stability augmentation system.<ref name=Taube_II_p5-6/><ref name=Jenk_Land_p60>Jenkins and Landis 2002, p. 60.</ref> AV-1 flew a total of 83 flights.<ref name=NASA>[http://www.nasa.gov/centers/dryden/news/FactSheets/FS-084-DFRC.html "XB-70A Valkyrie"] {{Webarchive|url=https://web.archive.org/web/20080604094150/http://www.nasa.gov/centers/dryden/news/FactSheets/FS-084-DFRC.html |date=4 June 2008 }}. ''Fact Sheets: Dryden Flight Research Center''. Retrieved: 6 April 2009.</ref>
The XB-70's last supersonic flight took place on 17 December 1968. On 4 February 1969, AV-1 took its final flight to [[Wright-Patterson Air Force Base]] for museum display (now the [[National Museum of the United States Air Force]]).<ref name=B-70_report_pi30>''B-70 Aircraft Study,'' p. I-30.</ref> Flight data was collected on this subsonic trip.<ref>Pace 1990, p. 71.</ref> North American Rockwell completed a four-volume report on the B-70 that was published by NASA in April 1972.<ref name=B-70_report_front>B-70 Aircraft Study, preface.</ref>
==Variants==
[[File:XB-70 AV-2 Palmdale 1966.jpg|thumb|XB-70A AV-2 at the Palmdale Air Show in May 1966]]
;XB-70A
:Prototype of B-70. Two were built.
:*AV-1, NAA Model Number NA-278, USAF S/N ''62-0001'', completed 83 flights spanning 160 hours and 16 minutes.<ref name=Jenk_Land_p64>Jenkins and Landis 2002, p. 64.</ref><ref name=nationalmuseum>[http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=592 "XB-70 Fact sheet"] {{webarchive|url=https://web.archive.org/web/20070311031636/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=592 |date=11 March 2007 }}. ''National Museum of the United States Air Force'', 26 August 2009. Retrieved: 31 May 2011.</ref>
:*AV-2, NAA Model Number NA-278, USAF S/N ''62-0207'', flew 46 times over 92 hours and 22 minutes, before it crashed in June 1966.<ref name=Jenk_Land_p58_93>Jenkins and Landis 2002, pp. 58, 93.</ref>
;XB-70B
:AV-3, NAA Model Number NA-274, USAF S/N ''62-0208'', was originally to be the first YB-70A in March 1961. This advanced prototype was canceled during early manufacture.<ref name=Jenk_Land_p39/><ref name="Taube_I_p40-1">''B-70 Aircraft Study,'' Vol. I. pp. I-40 to I-41.</ref>
;YB-70
:Planned preproduction version with improvements based on XB-70s.<ref name=Jenk_Land_p26/><ref name=Taube_YB-70/>
;B-70A
:Planned bomber production version of Valkyrie.<ref name=Jenkins_B-1/> A fleet of up to 65 operational bombers was planned.<ref name=Taube_I-29>''B-70 Aircraft Study,'' Vol I, p. I–29.</ref>
;RS-70
:Proposed reconnaissance-strike version, the overall B-70 program intended to go into service with [[Strategic Air Command]] as a [[Wing (military unit)|wing]] of RS-70s, in mid-1964.<ref>''B-70 Aircraft Study,'' Vol II. pp. II-1.</ref>
==Incidents and accidents==
===Incidents===
On 7 May 1965, a {{convert|3|ft|m|0|adj=on}} piece of the apex of the wing broke off in flight and caused extensive damage to five of the six engines. They were sent to GE and repaired. The sixth engine was inspected and re-installed in the aircraft.<ref>''Valkyrie North American's Mach 3 Superbomber'', Jenkins & Landis, {{ISBN|1 58007 072 8}}, p. 139.</ref>
On 14 October 1965, AV-1 surpassed Mach&nbsp;3, but heat and stress damaged the honeycomb panels, leaving {{convert|2|ft|cm|-1|abbr=on}} of the leading edge of the left wing missing. The first aircraft was limited to Mach&nbsp;2.5 afterwards.<ref name=Jenk_Land_p50-51/>
===Mid-air collision===
{{multiple image
| image1            = North American XB-70A Valkyrie in formation 061122-F-1234P-035.jpg
| caption1          = The aircraft formation before the collision on 8 June 1966; the F-104, with a red tail, is the second plane from the right.
| image2            = North American XB-70A Valkyrie just after collision 061122-F-1234P-037.jpg
| caption2          = Immediately after the collision: the F-104 has exploded, and XB-70A AV-2 has lost one of, and a portion of its second, vertical stabilizers. The F-4, F-5 and T-38 have yet to break formation.
}}
On 8 June 1966, XB-70A No. 2 was in close formation with four other aircraft (an [[McDonnell Douglas F-4 Phantom II|F-4 Phantom]], an [[Northrop F-5|F-5]], a [[Northrop T-38 Talon|T-38 Talon]], and an [[Lockheed F-104 Starfighter|F-104 Starfighter]]) for a photoshoot at the behest of General Electric, manufacturer of the engines of all five aircraft. A sixth aircraft, a [[Learjet 23]], had been contracted by General Electric to photograph the formation.<ref name=":0" /><ref name="clpoxb">[https://news.google.com/newspapers?id=G24dAAAAIBAJ&sjid=G5sEAAAAIBAJ&pg=4172%2C2392386 "Colonel loses post over XB-70 crash."] {{Webarchive|url=https://web.archive.org/web/20231102091947/https://news.google.com/newspapers?id=G24dAAAAIBAJ&sjid=G5sEAAAAIBAJ&pg=4172,2392386 |date=2 November 2023 }} ''Tuscaloosa News'', August 16, 1966, p. 1.</ref>
After the photoshoot, the F-104 drifted into the XB-70's right wingtip, flipped and rolled inverted over the top of the Valkyrie, before striking the bomber's vertical stabilizers and left wing. The F-104 then exploded, destroying the Valkyrie's vertical stabilizers and damaging its left wing. Despite the loss of both vertical stabilizers and damage to the wings, the Valkyrie flew straight for 16 seconds before it entered an uncontrollable spin and crashed north of [[Barstow, California]]. NASA Chief Test Pilot [[Joseph A. Walker|Joe Walker]] (F-104 pilot) and Carl Cross (XB-70 co-pilot) were killed. [[Alvin S. White|Al White]] (XB-70 pilot) ejected, sustaining serious injuries, including the crushing of his arm by the closing clamshell-like [[escape crew capsule]] moments prior to ejection.<ref>Winchester 2005, p. 186.</ref><ref name="Jenk_Land_pp58-9">Jenkins and Landis 2002, pp. 58–59.</ref>
The USAF summary report of the accident investigation stated that, given the position of the F-104 relative to the XB-70, Walker, 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 said that it was likely that Walker maintained his position by looking at the fuselage of the XB-70, forward of his position. The F-104 was estimated to be {{convert|70|ft|m|abbr=on}} to the side of the fuselage of the XB-70 and {{convert|10|ft|m|abbr=on}} below. 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 the XB-70's wing.<ref name="Jenk_Land_p60" /><ref name="accident_report">''Summary Report: XB-70 Accident Investigation''. USAF, 1966.</ref> The accident investigation also pointed to the wake vortex from the XB-70's right wingtip as the reason for the F-104's sudden roll over and into the bomber.<ref name="accident_report" />
The General Electric photoshoot had not been authorized by the Air Force. After the catastrophe, Col. Albert W. Cate was dismissed from his position, and Col. Joe Cotton, Col. James G. Smith and John S. McCollom were reprimanded.<ref name="cffstr">[https://news.google.com/newspapers?id=RhdZAAAAIBAJ&sjid=TOEDAAAAIBAJ&pg=6826%2C3497703 "Colonel fired for stunt role."] {{Webarchive|url=https://web.archive.org/web/20231102091948/https://news.google.com/newspapers?id=RhdZAAAAIBAJ&sjid=TOEDAAAAIBAJ&pg=6826,3497703 |date=2 November 2023 }} ''Eugene Register-Guard'', August 6, 1966. p. 4A.</ref><ref name="clpoxb" /><ref>[http://www.check-six.com/Crash_Sites/XB-70_crash_site.htm "The Crash of the XB-70."] {{Webarchive|url=https://web.archive.org/web/20041207154714/http://www.check-six.com/Crash_Sites/XB-70_crash_site.htm |date=7 December 2004 }} ''Check-Six.com.'' Retrieved: September 8, 2010.</ref>
==Aircraft on display==
[[File:North American XB-70 Valkyrie at Wright-Patterson USAF Museum - June 2016.jpg|upright=1.7|thumb|North American XB-70 Valkyrie at Wright-Patterson USAF Museum{{dash}}June 2016]]
Valkyrie AV-1 (AF Ser. No. 62-0001) is on display at the [[National Museum of the United States Air Force]] at [[Wright-Patterson AFB]] near [[Dayton, Ohio]]. The aircraft was flown to the museum on 4 February 1969, following the conclusion of the XB-70 testing program.<ref>''United States Air Force Museum Guidebook'' 1975, p. 87.</ref> 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''.<ref>[https://archive.today/20110707092714/http://www.afmuseum.com/pls/apex/f?p=145.:6:3685402257790914.::NO::P0_NODEID:995.:: "Valkyrie Cafe page"]. ''Air Force Museum Foundation''. Retrieved: 23 December 2009.</ref> In 2011, the XB-70 was on display in the museum's Research & Development Hangar alongside other experimental aircraft.<ref>[http://www.nationalmuseum.af.mil/exhibits/r&d/index.asp "Research & Development Gallery"] {{webarchive|url=https://web.archive.org/web/20110628163241/http://www.nationalmuseum.af.mil/exhibits/r%26d/index.asp |date=28 June 2011 }}. ''National Museum of the United States Air Force''. Retrieved: 23 December 2009.</ref> After completion of the fourth hangar at the museum's main campus, the XB-70 was moved there in late October 2015.<ref>[http://www.nationalmuseum.af.mil/Upcoming/PressRoom/News/ArticleDisplay/tabid/466/Article/626004/xb-70-valkyrie-moved-into-museums-new-fourth-building.aspx "XB-70 Valkyrie moved into museum's new fourth building"] {{Webarchive|url=https://web.archive.org/web/20151126173305/http://www.nationalmuseum.af.mil/Upcoming/PressRoom/News/ArticleDisplay/tabid/466/Article/626004/xb-70-valkyrie-moved-into-museums-new-fourth-building.aspx |date=26 November 2015 }}. ''National Museum of the United States Air Force'', 27 October 2015. Retrieved: 2 November 2015.</ref>
{{clear left}}
==Specifications (XB-70A)==
[[File:North American XB-70A Valkyrie 3-view line drawing.png|thumb|upright=1.7|3-view line drawing of the North American XB-70A Valkyrie]]
{{Aircraft specs
|ref= Pace,<ref>Pace 1990, p. 75.</ref> USAF XB-70 Fact sheet,<ref name=nationalmuseum/> B-70 Aircraft Study,<ref>''B-70 Aircraft Study'', Vol I. pp. I-312 to I-316.</ref> and others<ref name=NTRS>Walker, Harold J. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790021968_1979021968.pdf "Performance Evaluation Method for Dissimilar Aircraft Designs"] {{Webarchive|url=https://web.archive.org/web/20100514071625/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790021968_1979021968.pdf |date=14 May 2010 }}. ''NASA'', RP 1042, September 1979.</ref><ref name=Jenk_Land_p83/>
|prime units?=kts
<!--
General characteristics
-->
|crew=2
|length m=
|length ft=185
|length in=0
|length note=
|span m=
|span ft=105
|span in=0
|span note=
|height m=
|height ft=30
|height in=0
|height note=
|wing area sqm=
|wing area sqft=6297
|wing area note=
|aspect ratio=<!-- sailplanes -->
|airfoil=Hexagonal; 0.30 Hex modified root, 0.70 Hex modified tip
|empty weight kg=
|empty weight lb=253600
|empty weight note=
|gross weight kg=
|gross weight lb=534700
|gross weight note=
|max takeoff weight kg=
|max takeoff weight lb=542000
|max takeoff weight note=
|fuel capacity= {{convert|300000|lb|kg}} / {{cvt|46745|USgal|impgal l}}
|more general=
<!--
Powerplant
-->
|eng1 number=6
|eng1 name=[[General Electric YJ93]]
|eng1 type=afterburning [[turbojet]]
|eng1 kw=<!-- prop engines -->
|eng1 hp=<!-- prop engines -->
|eng1 shp=<!-- prop engines -->
|eng1 kn=<!-- jet/rocket engines -->
|eng1 lbf=19900
|eng1 note=
|power original=
|thrust original=
|eng1 kn-ab=<!-- afterburners -->
|eng1 lbf-ab=28000
<!--
Performance
-->
|perfhide=
|max speed kmh=
|max speed mph=
|max speed kts=1787
|max speed note=
|max speed mach=3.1
|cruise speed kmh=
|cruise speed mph=
|cruise speed kts=1738
|cruise speed note=
|stall speed kmh=
|stall speed mph=
|stall speed kts=
|stall speed note=
|never exceed speed kmh=
|never exceed speed mph=
|never exceed speed kts=
|never exceed speed note=
|minimum control speed kmh=
|minimum control speed mph=
|minimum control speed kts=
|minimum control speed note=
|range km=
|range miles=
|range nmi=
|range note=
|combat range km=
|combat range miles=
|combat range nmi= 3725
|combat range note=
|ferry range km=
|ferry range miles=
|ferry range nmi=
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling m=
|ceiling ft=77350
|ceiling note=
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|lift to drag= about 6 at Mach 2
|climb rate ms=
|climb rate ftmin=
|climb rate note=
|time to altitude=
|wing loading kg/m2=
|wing loading lb/sqft=84.93
|wing loading note=
|fuel consumption kg/km=
|fuel consumption lb/mi=
|power/mass=
|thrust/weight=0.314
|more performance=
<!--
Armament
-->
|armament=<!-- add bulletted list here or if you want to use the following
specific parameters, remove this parameter-->
|guns=
|bombs=
|rockets=
|missiles=
|hardpoints=
|hardpoint capacity=
|hardpoint rockets=
|hardpoint missiles=
|hardpoint bombs=
|hardpoint other=
|avionics=
}}
==See also==
{{Portal|Aviation}}
{{aircontent
|see also=<!-- other related articles that have not already linked: -->
* [[Pye Wacket]], a program to develop a defensive missile to be carried by the B-70
* [[ArmaLite AR-5]] survival rifle (originally developed for XB-70 aircrew survival kits)
|related=<!-- designs which were developed into or from this aircraft: -->
* [[North American XF-108 Rapier]]
<!-- * [[SM-64 Navaho]] no diret connection found, yet -->
|similar aircraft=<!-- aircraft that are of Similar Role, Era, and Capability as this design: (note similar Era part) -->
* [[Avro 730]]
* [[English Electric P.10]]
* [[Sukhoi T-4]]
* [[Tupolev Tu-125]]
|lists=<!-- relevant lists that this aircraft appears in: -->
* [[List of bomber aircraft]]
* [[List of military aircraft of the United States]]
<!-- See [[WP:Air/PC]] for more explanation of these fields. -->
}}
==Notes==
{{reflist|group=N}}
==References==
===Citations===
{{reflist}}
===Bibliography===
{{refbegin|40em}}
* Conway, Erik M. [https://books.google.com/books?id=2ppC_VU6WrUC&pg=PA33 ''High-speed Dreams: NASA and the Technopolitics of Supersonic Transportation, 1945–1999''.] {{Webarchive|url=https://web.archive.org/web/20230915103002/https://books.google.com/books?id=2ppC_VU6WrUC&pg=PA33 |date=15 September 2023 }} Baltimore: Johns Hopkins University Press, 2005. {{ISBN|0-8018-8067-X}}.
* "Fundamentals of Aerospace Weapon Systems". ''Air University'', [[Maxwell AFB]], May 1961.
* Greenwood, John T. (ed). ''Milestones of Aviation: [[National Air and Space Museum]]''. Westport, Connecticut: Hugh Lauter Levin Associates, Inc., 1995 (first published: 1989). {{ISBN|0-88363-661-1}}.
* Hannah, Craig. [https://books.google.com/books?id=CEb1sFobGgcC&pg=PA68 ''Striving for Air Superiority: The Tactical Air Command in Vietnam.''] College Station, Texas: Texas A&M University Press, 2002, First edition 2001. {{ISBN|978-1-58544-146-4}}
* Heppenheimer, T. A. [https://history.nasa.gov/sp4232-part1.pdf ''Facing the Heat Barrier: A History of Hypersonics, part 1''] {{Webarchive|url=https://web.archive.org/web/20160521113002/http://history.nasa.gov/sp4232-part1.pdf |date=21 May 2016 }}, [https://history.nasa.gov/sp4232-part2.pdf "part 2"] {{Webarchive|url=https://web.archive.org/web/20130702213656/http://history.nasa.gov/sp4232-part2.pdf |date=2 July 2013 }}. ''NASA,'' NASA History Series, 2006. Retrieved: 6 April 2009.
* 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. [https://books.google.com/books?id=lEpWE748QUsC ''Lockheed SR-71/YF-12 Blackbirds'' (WarbirdTech Series, Volume 10).] {{Webarchive|url=https://web.archive.org/web/20240227171955/https://books.google.com/books?id=lEpWE748QUsC |date=27 February 2024 }} North Branch, Minnesota: Specialty Press, 1997. {{ISBN|0-933424-85-X}}. {{asin|0933424752}}
* Jenkins, Dennis R. and Tony R. Landis. ''North American XB-70A Valkyrie'' WarbirdTech Volume 34. North Branch, Minnesota: Specialty Press, 2002. {{ISBN|1-580-07056-6}}.
* 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}}.
* Lang, Walt N. United States Military Almanac. New York: Random House, 1989. {{ISBN|0-517-16092-7}}.
* Knaack, Marcelle Size. [https://web.archive.org/web/20071025174047/http://www.airforcehistory.hq.af.mil/Publications/fulltext/encyclopedia_postww2_bombers.pdf ''Post-World War II bombers, 1945–1973.''] Washington, D.C.: Office of Air Force History, 1988. {{ISBN|0-16-002260-6}}.
* Koenig, William and Peter Scofield. [https://books.google.com/books?id=1V_fAAAAMAAJ ''Soviet Military Power.''] London: Arms and Armour Press, 1983. {{ISBN|978-0-85368-592-0}}.
* Machat, Mike. "XB-70 Valkyrie: Rollout and First Flights, May 1964 – June 1966." ''Wings'' Volume 35, No. 8, August 2005.
* Miller, Jay. ''Convair B-58 Hustler'' (Aerograph 4). Tulsa, Oklahoma: Aerofax, 1985. {{ISBN|978-0-942548-26-6}}.
* Moon, Howard. ''Soviet SST: The Techno-Politics of the Tupolev-144''. Westminster, Maryland: Orion Books, 1989. {{ISBN|978-0-517-56601-5}}.
* Pedlow, Gregory W. and Donald E. Welzenbach. [http://www.foia.cia.gov/docs/DOC_0000645397/DOC_0000645397.pdf "Chapter 6: The U-2's Intended Successor: Project Oxcart, 1956–1968"]{{dead link|date=July 2022|bot=medic}}{{cbignore|bot=medic}}. ''The Central Intelligence Agency and Overhead Reconnaissance: The U-2 and OXCART Programs, 1954–1974.'' Washington, D.C.: Central Intelligence Agency, 1992. No ISBN.
* Pace, Steve. ''North American XB-70 Valkyrie'', second edition. Blue Ridge Summit, Pennsylvania: TAB Books, 1990. {{ISBN|0-8306-8620-7}}.
* Pace, Steve. "Triplesonic Twosome". ''Wings'' Volume 18, No. 1, February 1988.
* Rees, Ed. [https://books.google.com/books?id=v0QEAAAAMBAJ&pg=PA124 "The Furor Over Fantastic Plane"]. ''Life'', 17 October 1960, pp.&nbsp;125–126.
* Spick, Mike. ''Modern Fighting Aircraft: B-1B''. New York: Prentice Hall, 1986. {{ISBN|0-13-055237-2}}.
* Taube, L.J., Study Manager. [https://ntrs.nasa.gov/api/citations/19950002358/downloads/19950002358.pdf "SD 72-SH-0003, B-70 Aircraft Study Final Report, Vol. I"] {{Webarchive|url=https://web.archive.org/web/20210412130342/https://ntrs.nasa.gov/api/citations/19950002358/downloads/19950002358.pdf |date=12 April 2021 }}. [[North American Rockwell]] via [[NASA]], April 1972: [https://ntrs.nasa.gov/api/citations/19950002359/downloads/19950002359.pdf Vol. II] {{Webarchive|url=https://web.archive.org/web/20210421000949/https://ntrs.nasa.gov/api/citations/19950002359/downloads/19950002359.pdf |date=21 April 2021 }}: [https://ntrs.nasa.gov/api/citations/19950002360/downloads/19950002360.pdf Vol. III]{{dead link|date=July 2022|bot=medic}}{{cbignore|bot=medic}}: [https://ntrs.nasa.gov/api/citations/19950002361/downloads/19950002361.pdf Vol. IV] {{Webarchive|url=https://web.archive.org/web/20210421000947/https://ntrs.nasa.gov/api/citations/19950002361/downloads/19950002361.pdf |date=21 April 2021 }}.
* von Braun Wernher (Estate of), [[Frederick I. Ordway III]] and David Jr. Dooling. ''Space Travel: A History''. New York: Harper & Row, 1985, first edition, 1975. {{ISBN|0-06-181898-4}}.
* Winchester, Jim. "North American XB-70 Valkyrie". ''Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft''. Kent, UK: Grange Books plc., 2005. {{ISBN|978-1-84013-809-2}}.
* York, Herbert Jr. [http://www.learnworld.com/ZNW/LWText.York.RaceToOblivion.html ''Race to Oblivion: A Participant's View of the Arms Race''.] {{Webarchive|url=https://web.archive.org/web/20151031012138/http://www.learnworld.com/ZNW/LWText.York.RaceToOblivion.html |date=31 October 2015 }} New York: Simon & Schuster, 1978. {{ISBN|0-06-181898-4}}.
{{refend}}
==Further reading==
{{refbegin}}
*{{cite tech report |last=Goodpaster |first=Brig. General Andrew J. |author-link=Andrew Goodpaster |title=White House Office, Records of ... Andrew J. Goodpaster ... 1952–1961 |location=Dwight D. [[Eisenhower Presidential Library]]}}
*{{cite tech report |last= Goodpaster |date= 24 June 1959 |title= Memorandum of Conference with the President: June 23, 1959 – 11:40&nbsp;am |location=Subject Series, Dept. of Defense Subseries, Box 1: Joint Chiefs of Staff (6) |quote="DECLASSIFIED ... 4/10/79"}}
* {{cite tech report |last= Goodpaster |date= 2 December 1959 |title= Memorandum of Conference with the President: Monday, 16 November 1959, Augusta, Georgia, 8:30&nbsp;am |url=https://books.google.com/books?id=xxeuSvsmfscC&pg=PA495 |location=Papers as President of the United States, 1953–1961 [Ann Whitman File]; DDE Diary Series Box No 46; Staff Notes—Nov 1959 (3) |pages=6–7 (B–70) |quote="DECLASSIFIED ... 23 August 1979"<!--The 16 Nov memo is NOT in the Dept. of Defense Subseries, Box 4: Joint Chiefs of Staff (8) [September 1959 – May 1960]-->}}
* {{cite tech report |last= Goodpaster |date= 20 January 1960 |title=Memorandum of Conference with the President: November 18, 1959 – Augusta |location=Subject Series, Dept. of Defense Subseries, Box 4; Joint Chiefs of Staff (8) [September 1959 – May 1960] & Papers as President of the United States, 1953–1961 [Ann Whitman File]; DDE Diary Series Box No 46 |pages=6–8 (B–70) |quote="DECLASSIFIED ... 18 January 1981"}}
* {{cite tech report |last= Goodpaster |date= 21 November 1960 |title=Memorandum for the Record: Meeting ... Augusta, November 19, 1959 – from 8:30&nbsp;am to approximately 10:20&nbsp;am |location=Papers as President of the United States, 1953–1961 [Ann Whitman File]; DDE Diary Series Box No 45; Staff Notes—Nov. 1959 (6) |quote="DECLASSIFIED ... 1/6/78"}}
{{refend}}
==External links==
{{Commons category|North American XB-70}}
<!-- Neither of the links in the External box work
{{External media|align=right|images=
[http://www.history.com/media.do?action=clip&id=mf657_xb70_44 History.com XB-70 crash footage]<br />[http://www.airliners.net/search/photo.search?aircraft_genericsearch=&airlinesearch=&countrysearch=&specialsearch=&daterange=&keywords=XB+70+valkyrie&range=&sort_order=&page_limit=15&thumbnails=&calccount=1240021&truecount=false&engine_version=6.0 USAF WPAFB images]}}
-->
* {{cite journal |journal=Flight International |title=B-70 The State of the Art Improver Part 1 |last=Pike |first=Iain |url=http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%201912.html|archive-url=https://web.archive.org/web/20140301104531/http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%201912.html|url-status=dead|archive-date=1 March 2014|date=25 June 1964 |pages=1055–1062}}
* {{cite journal |journal=Flight International |title=B-70 The State of the Art Improver Part 2 |last=Pike |first=Iain |url=http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%201993.html |archive-url=https://web.archive.org/web/20140301114000/http://www.flightglobal.com/pdfarchive/view/1964/1964%20-%201993.html |url-status=dead |archive-date=1 March 2014 |date=2 July 1964 |pages=18–24}}
* {{Internet Archive |NASA_NTRS_Archive_19660018723 |Summary of preliminary data derived from the XB-70 airplanes}}
* {{YouTube|KMbOl6Hn0yQ|"XB-70 Valkyrie Supersonic Bomber Flight Test Program Restored Color – 1966"}}
* {{cite book |url=https://media.defense.gov/2020/Nov/23/2002540204/-1/-1/1/B-70%20VARIANTS.PDF |title=A Look Back... NAA B-70 Valkyrie Variants, A Future That Never Was... |editor=Landis, Tony R. |publisher=Air Force Materiel Command (AFMC) History & Heritage Program |date=23 November 2020|archive-url=https://web.archive.org/web/20210103183639/https://media.defense.gov/2020/Nov/23/2002540204/-1/-1/1/B-70%20VARIANTS.PDF|archive-date=3 January 2021|url-status=live}}
{{North American Aviation aircraft}}
{{USAF bomber aircraft}}
{{US reconnaissance aircraft}}
{{USAF system codes}}
{{Authority control}}
{{DEFAULTSORT:North American Xb-70 Valkyrie}}
[[Category:Cancelled military aircraft projects of the United States]]
[[Category:Canard aircraft]]
[[Category:Delta-wing aircraft]]
[[Category:North American Aviation aircraft|B-70]]
[[Category:1960s United States bomber aircraft]]
[[Category:Six-engined jet aircraft]]
[[Category:NASA aircraft]]
[[Category:Aircraft first flown in 1964]]
[[Category:Variable-geometry-wing aircraft]]
[[Category:Aircraft with retractable tricycle landing gear]]