XB-70 Valkyrie

XB-70 Valkyrie
XB-70 of Dryden Flight Research Center in 1968
Role	Strategic bomber Supersonic research aircraft
Manufacturer	North American Aviation
First flight	21 September 1964
Retired	4 February 1969
Status	Museum exhibit
Primary users	United States Air Force NASA
Number built	2 XB-70s
Program cost	US$1.5 billion[1]
Unit cost	$750 million each prototype[2]

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. Designed in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly at Mach 3 at an altitude of 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.

Development

Early studies

The genesis of the B-70 can be traced to a study by Boeing and Rand Corporation that started in January 1954. The study explored what sort of aircraft would be needed to deliver the very high-yield nuclear weapons then under construction. Long range and high payload were obvious requirements, but they also concluded that "a high-speed, high-altitude dash capability would be needed to … escape the nuclear blast of its own weapon."^[3]

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

In 1946, there was considerable interest in the use of nuclear powered aircraft, and particularly in the 1950s, in the bomber role. Nuclear engines used the heat generated by a nuclear reactor in place of jet fuel, giving an aircraft virtually unlimited cruising range. In addition to solving the range issue, these aircraft could be flown to holding areas away from the airbases and kept in the air for extended periods of time, making them immune to sneak attack. Accordingly, Boeing developed plans for a nuclear powered bomber that also included normal jet engines for takeoff and the high-speed "dash" portion of the flight, which were turned off during cruise. Lockheed and Convair also "offered similar solutions".^[3]

Another possibility was the use of boron-enriched "zip fuels", which improved the energy density of the fuel by about 40%.^[4] Various US government agencies had been experimenting with zip fuels for some time, and they believed that once the problems they were having were worked out, zip fuel would become almost universal for high-speed aircraft. Although the advantages of a zip fueled aircraft would not be as great as those of a nuclear powered one, it would offer a real performance increase and was a relatively straightforward development of existing engines and fuels.^[4]

NAA's original proposal for WS-110A. The "floating panels" are large fuel tanks containing conventional JP-4 fuel used during the long subsonic cruise, each the size of a B-47. Once ejected, the engines would burn "HEF", or zip fuel, during the high-speed dash phase.

First attempts

In October 1954 the Air Force issued General Operational Requirement No. 38 for a new bomber with the intercontinental range of the B-52 and the Mach 2 maximum speed of the B-58 Hustler^[5] -- the new bomber was expected to enter service in 1963.^[6]1 March 1955's 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.^[6] 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".^[7]

In early 1955, the Air Force issued GOR.96, which called for an intercontinental reconnaissance system with the same general requirements as WS-110A, called WS-110L.^[8] The two requirements were combined soon afterward, becoming Weapon System 110A/L.^[3] The nuclear-powered bomber work was dropped during this period, given the problems in that program's development, as well as optimism about the zip fuels.

In June 1955 the Air Staff directed that the details of WS-110A/L be released to the aviation industry and that a request for proposals be issued. Although six contractors were given the requirements, only Boeing and North American Aviation (NAA) submitted proposals.^[9] On 8 November 1955, the Air Force issued letter contracts to both Boeing ($19.9 million) and North American ($9.9 million) for Phase 1 development.^[10] The contracts called for models, design reports, wind tunnel tests, plus a mock-up.^[8]

In 1956, initial designs were presented by the two companies. Although zip fuels improved range, the overall effect was not very large, perhaps 10%, so both designs featured huge wingtip fuel tanks that could be jettisoned before a supersonic run on the target. In the case of the North American design, the entire outer portion of the wings was jettisoned as well, resulting in an aircraft that looked somewhat like a very large F-104 Starfighter after being "broken up".

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. Curtis LeMay was not enthusiastic about the NAA design, claiming "Hell, this isn't an airplane, it's a three-ship formation."^[7] NAA and Boeing's study contracts were extended to further develop their bomber designs.^[5] The next month the program was put on hold, although the companies were told to continue any low-level development they could.^[9]

The program was soon re-started in March 1957, after developments during that short period of time indicated that a significantly improved design could be built. The project was now for an aircraft that was intended to fly with afterburners at supersonic speeds of up to Mach 3 for the entire mission, as opposed to a subsonic/supersonic dash aircraft of the earlier work.^[9]

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 the slow the air as it travels towards the engine. This process creates drag significantly reduces performance; minimizing this drag is critical for cruise performance.

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

New designs

Both North American and Boeing returned new designs with very long fuselages and large delta wings. They differed primarily in engine layout; the NAA design arranged its six engines in a semi-circular duct under the rear fuselage, while the Boeing design used separate podded engines 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.^[11] 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.^[11] 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,^[12] the nose, and the air intakes. Fuel from the wing tanks was burned first. For cooling, the XB-70 pumped fuel enroute to the engines through 10 heat exchangers.^[12] The fuel tanks were made inert by filling with gaseous nitrogen as the fuel is pumped out.^[13]

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.^[14] In February 1958, the proposed bomber was assigned the number B-70,^[14] 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.^[15] 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][14] 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.^[16]

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.^[17]

The "missile problem"

The high-speed, high-altitude approach used by all U.S. bombers up to this point was intended to complicate the defense by giving them less time to deal with the aircraft as they flew over. Although it was possible to build interceptors with enough performance to catch even a Mach 3 target, the time needed to detect, track and guide the aircraft to its target was fixed by the operator workload, which was not improving at nearly the same rate. In the 1950s the Royal Canadian Air Force concluded that one interception per minute was the best that could be hoped for. Assuming the same was true in the USSR, the B-70 traveling at Mach 3 would be over land for only about ½ hour while approaching Moscow over the north pole, implying that even in perfect conditions most of the B-70s would fly right past the defending fighters. There was even some hope that the aircraft moved so fast that its radar return would be "smeared out" on the analog displays of the era due to an effect known as the "blip-to-scan ratio", rendering it partially invisible on long-range radars.

Anti-aircraft missiles in the middle-to-late 1950s developed to a point where they became useful weapons. This upset the equation completely. Missiles could be fired as soon as a track is developed, and reach high altitudes in a few minutes. Even at the speeds the B-70 would be traveling, the SA-2 Guideline missiles it would face, would be able to detect it over 100 miles away on their search radars, giving them as much as five minutes in which to plan and launch an attack. This was marginal, especially given that the SA-2's tracking radars had much shorter ranges, but as long as they were alerted in advance, an interception was possible. Newer generations of missiles already under development would offer much higher performance. There was a concern that the B-70 would be no more able to penetrate the USSR's airspace than the B-52 it was supposed to replace.

Following the downing of the U-2 flown by Gary Powers, 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, allowing them to fly right by most radar sites. 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, requires considerably more fuel to cover a given distance, and needs sophisticated obstacle-avoidance sensors and control equipment.

• High-high-high mission with in-flight refueling (dashed line at top): maximum range mission overflies the USSR at high altitude and lands at Diego Garcia.
• High-high-high mission without in-flight refueling (solid line below it): landing in Turkey.
• High-low-high mission (solid line at bottom): uses in-flight refueling and a high-speed cruise to the Baltic Sea, then descending to a short penetration at low altitude to deliver weapons before climbing for landing in Turkey.^[18]

Unsuited for low altitude penetration, the viability of the B-70 as a bomber was questioned. 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 range of 6,450 nmi without refueling but using a high-low-high profile this was reduced to 5,300 nmi with in-flight refueling, with a Mach 0.95 speed at low altitudes.^[18]

Adding to the program's problems the zip fuel program was canceled in 1959.^[4] After burning the fuel turned into liquids and solids that caused wear on turbine engine components.^[19] 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. This was a more serious concern as it limited the B-70's capability to carry the missiles needed to blast its way past defenses. The program was also harmed in September 1959 by the cancellation of the F-108 and its support funding.^[20]

Downgrade, rebirth, downgrade again

ARDC and Air Materiel Command 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.^[21] However, in the fall of 1958 Air Force Chief of Staff Thomas D. White announced that the acceleration program would not be funded,^[21] reflecting President Eisenhower's determination to reign in military spending on unproven designs.

At a secret meeting on 18 November 1959, General White admitted the Soviets would "be able to hit the B-70 with rockets" and advocated the B-70 be "a bare minimum research and development program" at $200 million for fiscal year 1960. President Eisenhower countered that the ICBM² is "a cheaper, more effective way of doing the same thing" as the B-70 and that he "saw no need for it". Eisenhower also identified that the "B-70 will not be in production before a date eight to ten years from now" and "said he thought we were talking about bows and arrows at a time of gunpowder when we spoke of bombers in the missile age."^[22]

On 29 December 1959 the Air Force announced a major downsizing of the B-70 project, reorienting the project to produce only a single prototype. Most of the weapons subsystems planned for the aircraft were cancelled.^[3][23] However, this downsizing did not last long.

Congressional studies during mid-1960 resulted in a letter contract for the single prototype of the XB-70 Development Program and an additional 11 YB-70 variants with "full weapon system development".^[24] After $60 million had been tacked onto the program's originally-planned $75 million in July, in November 1960 the Department of Defense announced the B-70 budget would total $265 million^[25] for fiscal year 1961.^[20] Many of the subcontracts for the weapons subsystems were reopened. 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] The "Budgetary and Planning Proposal" recommended 62 RS-70s be produced^[18] by 1969.

During the 1960 elections, Kennedy had run on a platform that centered on Eisenhower being weak on defense. In particular, he complained heavily about the "missile gap", the reported disparity in ICBM strength between the US and USSR. In early February 1961, Jerome Wiesner briefed President Kennedy "that the missile gap was a [sic] fiction", yet in the spring and summer of 1961, Kennedy continued with his promised defense increases^[26] — except for the B-70 program. On 28 March 1961 Kennedy directed the program once again be only a research and development project because the planned capabilities of the bomber "stood little chance of penetrating enemy defenses successfully."^[27] 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. On 10 April 1961, a contract for three aircraft was placed with North American, with the crew reduced to only the pilot and co-pilot; the navigator and bomb-aimer were not needed.^[3][5]

Experimental aircraft

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. Nearly complete in 1962, the first XB-70A was completed in mid-1963,^[7] then displayed on 11 May 1964 in Palmdale, California to an "unbelieving crowd".^[28]

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,^[29] along with new, improved surface to air missiles (SAMs), to counter these U.S. threats. The flight data and materials development of the XB-70 program also laid the foundation for the later B-1 Lancer supersonic bomber program, as well as the commercial supersonic transport (SST) aircraft programs.

Design

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, sandwiched 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.^[28] 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.^[30] With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings, rather than simply flowing out past the wingtips.

XB-70A Valkyrie on takeoff.

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 lbf class, but actually produced 28,000 lbf with afterburner and 19,000 lbf without afterburner.^[31]

Operational history

Flight testing

The first XB-70 made its maiden flight on 21 September 1964. 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.^[5] Construction of the honeycombed panels was much more difficult than anticipated by the designers. 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 October 12, 1964, and flew above Mach 1 for 40 minutes during the following flight on October 24.^[2] The wing tips were also lowered partially in this flight.

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). On 19 May 1966, aircraft number two flew at Mach 3 for 32 minutes,^[5] covering 2,400 miles (3,840 km) in 91 minutes of total flight.

The XB-70A also experienced unwanted altitude changes (porpoising) at high altitude and high speed (the SR-71 corrected similar +/-3000 ft changes with a specialized autopilot).^[32]

XB-70A #2 was selected for the National Sonic Boom Program (NSBP) to measure the response at the ground to sonic booms 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).^[5] The sonic boom reached the ground at higher levels than expected.^3[33]

XB-70 62-0207 following the midair collision on 8 June 1966.

Following the mid-air collision that destroyed XB-70A #2, XB-70A #1 made 33 more research flights and in March 1967 was transferred to NASA for their supersonic transport test program in March 1967.^[34] NASA ended the XB-70 flight test program on 13 January 1969.

On 4 February 1969, XB-70A #1 was flown to the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. This was the last flight of an XB-70.^[35][36]

Incidents

Landing gear fire

On 21 September 1964, after the landing gear failed to retract properly on XB-70A #1, the left-side rear wheels locked and a fire resulted.^[37]

Engine damage

On 7 May 1965, the divider separating the left and right halves of the engine inlet on XB-70A #1 broke off in flight and was ingested into the engines, damaging all six beyond repair.^[28]

Wing damage

On 14 October 1965, the first XB-70 reached a speed of Mach 3.02 at an altitude of 70,000 ft (21,300 m).^[5] The stress damaged the honeycomb panels, leaving two feet (0.6 m) of the leading edge of the left wing missing. These construction problems resulted in the imposition of a speed limit of Mach 2.5 on the first aircraft.^[38]

Mid-air accident

On 8 June 1966, XB-70A #2 was in close formation with four other aircraft (an F-4, F-5, T-38, and F-104) for a photoshoot at the behest of General Electric, manufacturer of the engines of all five aircraft. With the photoshoot complete, the F-104 drifted into contact with the XB-70's 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 spin and crashed into the ground.^[39] 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.^[40] 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. Lt. Colonel Joe Cotton, the USAF's Chief Test Pilot for the XB-70 who was flying the T-38 in the formation, likewise speculated Walker lost reference to his position relative to the XB-70 and simply closed up the formation until the T-tail of the F-104 struck the Valkyrie's wingtip.^[39] Chuck Yeager has also gone on record to echo the conclusion that Walker lost reference and closed up the formation.

Variants

• 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^[41][36]
  • Aircraft #2, NAA Model Number NA-278, USAF S/N 62-0207, 46 flights; total time: 92 hours, 22 minutes.^[39] 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.^[42]
• 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).^[24]
• B-70A - Planned bomber version of Valkyrie.^[5] A fleet of up to 65 operational bombers was planned.^[43]
• RS-70 - Proposed reconnaissance-strike version with a crew of four and in-flight refueling capability.^[18] A fleet of 62 was planned in 1959.^[44]

Aircraft on display

XB-70 at Wright-Patterson Air Force Base, 1988c. 1988

Valkyrie No. 1 (s/n 62-0001) is currently on display at the National Museum of the United States Air Force in Dayton, Ohio. The aircraft was flown to the Museum on 4 February, 1969, following the conclusion of the XB-70 testing program.^[45]

Specifications (XB-70A)

Data from USAF XB-70 Fact sheet^[46]

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^[31] (84.5 kN) each
  • Thrust with afterburner: 28,800 lbf^[31] (128 kN) each

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^[47]
• Thrust/weight: 0.314

See also

Related development

• XF-108 Rapier
• SM-64 Navaho⁴
  

Comparable aircraft

• Sukhoi T-4
• Avro 730
  

Related lists

• List of bomber aircraft
• List of military aircraft of the United States
  

References

Notes

Note 1: The NB-58 Hustler was used for XB-70 engine testing, and the TB-58 was used for XB-70 chase and training.^[37]

Note 2: Following the 1945 Army Air Force Scientific Advisory group Where We Stand forecast that identified ICBMs were "feasible",^[48] the Teapot committee urged the Air Force in February 1954 that an effective ICBM could be developed within six years or less, and on 1 June 1954, the project director was assigned.^[49]:133 On 22 January 1955, the Pentagon publicly announced ICBMs were being developed and on 27 July 1955, the Air Force assigned the ICBM program (SM-65 Atlas/Weapon System 107A) its highest priority (the follow-on LGM-25 Titan was approved in early 1957).^[50] The Atlas became operational in 1959 and the Titan in 1962.

Note 3: Following the 1963 formation of the National Supersonic Transport program, the 1964 Oklahoma City sonic boom tests and the 1966 XB-70A testing of the NSBP "influenced the 1971 cancellation of the Boeing 2707 supersonic transport and led to the United States' complete withdrawal from SST design."

Note 4: The XB-70 used high-speed technologies developed for the Mach 3 Navajo, as well as a modified form of the SM-64 Navaho's all-inertial guidance system.^[49]

Citations

Bibliography

External links

• Quest for Performance: The Evolution of Modern Aircraft, Chapter 12: Jet Bomber and Attack Aircraft, NASA SP-468
• XB-70 Flight Manual

External images
NASA photos NASA/DFRC videos Crash footage WPAFB images Wind tunnel model