North American XB-70A Valkyrie

Last revised September 13, 2021

The North American XB-70A Valkyrie is, in my opinion, one of the sleekest, best-looking military aircraft ever built. Unfortunately, the aircraft appeared just at a time when military requirements were changing and the manned bomber was being de-emphasized in favor of intercontinental ballistic missiles. Consequently, only two examples were built.

The basic idea for the XB-70 can be said to begin back in January of 1954, when the Boeing Aircraft Corporation and the Rand Corporation began to consider what type of weapon system would be needed to deliver high-yield thermonuclear weapons against well-defended targets in the Soviet Union. Long range and high performance would be needed to deliver such weapons at long distances with a reasonable assurance of penetrating enemy defenses, and a high-speed, high altitude supersonic dash capability would be needed to ensure that the delivery system could escape the blast of its own weapon.

The idea of a nuclear-powered aircraft dated back almost to the time of the first atomic bomb in 1945, and since nuclear power offered the possibility of obtaining an almost unlimited range without requiring an aircraft of unreasonable size, it presented a tantalizing solution to the problem of delivering a thermonuclear weapon over intercontinental ranges. As a solution, Boeing proposed an aircraft that would be powered by chemically-augmented nuclear-powered engines. At the same time, both Lockheed and Convair offered similar solutions.

In the autumn of 1954, the Air Force endorsed two separate approaches, one for a nuclear powered bomber capable of short bursts of supersonic speed, and another for a subsonic conventional bomber powered by chemical fuels. In October of 1954, the Air Force issued General Operational Requirement No. 38, which was quite general and called simply for an intercontinental manned bomber which would replace the B-52 beginning in 1965. General Operational Requirement No. 81, issued in March of 1955, was more specific. It called for a nuclear-powered bomber with a combat radius of 11,00 nautical miles. The aircraft was to be capable of flying up to 1000 miles at a speed greater than Mach 2 at altitudes greater than 60,000 feet. It was to be capable of carrying up to 20,000 pounds of nuclear weapons.

GOR 38 was superseded by GOR 82 in March of 1955. GOR 82 called for a a piloted strategic bomber capable of carrying a 25,000 pound bombload of high-yield nuclear weapons. The Air Research and Development Command (ARDC) issued a study requirement, designated Number 22, which referred to the future bomber as "Weapon System 110A", and asked for a Mach 0.9 cruising speed, and "maximum possible" speed during a 1000-mile entrance and exit from the target. A revision in April removed the subsonic cruising speed requirement, and now asked for maximum possible "supersonic" performance within the combat zone. The target date for the first operational wing of these aircraft was July of 1964.

In early 1955, the Air Force issued GOR No. 96, which called for an intercontinental reconnaissance system with the same general requirements as WS-110A. The concept was referred to as WS-110L. The two requirements were combined soon afterwards, becoming Weapon System 110A/L.

The original WS-110 design from North American with floating wingtips was given the company designation NA-239, while the original Boeing design studies for the WS-110 requirement with floating wingtips were conceived under the Model 724 and Model 725 designations. The revised Boeing design for the WS-110 competition envisaged in 1957 carried the company designation Model 804, and the North American Aviation company designations NA-259, NA-264, and NA-267 were allocated to the Phase I, Phase II (Part 1), and Phase II developments of the XB-70.

In June of 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 6 contractors were contacted, only Boeing and North American Aviation chose to submit proposals. On November 8, 1955, the Air Force issued letter contracts to both Boeing and North American for Phase 1 development. The contracts called for models, design reports, wind tunnel tests, plus a mockup. The Boeing contract was AF33(600)-31802 , and the North American contract was AF33(600)-31801.

The USAF soon dropped the nuclear-powered requirement for reasons of cost, relying on a more conventional propulsion system. The Air Force specified that the WS-110A/L would have to be an all-weather system capable of having a minimum unrefuelled radius of 4000 miles. Minimum service ceiling was to be 60,000 feet, and the cruising speed had to be at least Mach 0.9 and supersonic dash capability was to be available over the combat zone. Since no existing aircraft designs could meet such requirements, new developments in high-energy fuels and new engines would be necessary.

The Boeing design used a conventional swept wing design, whereas North American decided on a canard delta configuration similar to that of their SM-64 Navajo cruise missile. Both designs proposed to meet the range requirements by using a set of floating fuel-carrying wing panels which would carry fuel on the outgoing trip and be jettisoned when empty. The loaded weight was estimated to be about 700,000 pounds.

The Air Force was not happy with either design, since the gross weight was considered to be excessive and the floating wing panels would probably prove to be too cumbersome and unwieldy in practice. In September of 1956, the Air Force told both contractors that they would have to go back to the drawing board. A month later, quoting a shortage of money, the Air Force decided to discontinue the Phase 1 development program. However, both contractors were allowed to continue their studies, but solely on a research and development basis.

By March of 1957, the Air Force had significantly revised its future bomber requirements, and the project was now being envisaged as calling for an aircraft that would be able to cruise at supersonic speeds of up to Mach 3 for the entire mission as opposed to a subsonic cruise/supersonic dash aircraft, which really stretched the state of art at that time. The idea was that if the aircraft were really optimized for Mach 3 flight, then the range of the aircraft would automatically be improved to equal or even exceed that of a conventional subsonic aircraft. It was concluded that high-energy boron-based fuels would be needed to achieve this performance and that its use should be extended to the engine afterburner.

On August 30, 1957, the Air Force directed that enough data was available on the North American and Boeing designs that a competion could begin. On September 18, the Air Force issued requirements which called for a cruising speed of Mach 3.0 to 3.2, an over-target altitude of 70,000 to 75,000 feet, a range of up to 10,500 miles, and a gross weight not to exceed 490,000 pounds.

On December 23, 1957, the North American proposal was declared the winner of the competition, and on January 24, 1958, contract AF33(700)-36599 was issued for Phase 1 development. In December of 1958, a Phase II contract was issued. The first operational wing of 30 aircraft was to be ready by late 1965. In February of 1958, the aircraft was assigned the designation B-70. The Air Force believed that "other systems" would be able to better meet the reconnaissance mission than the Weapon System 110L part of the project, and development of WS 110L was cancelled at this time.

The Air Force was initially quite enthusiastic about getting the B-70 in service as quickly as possible. In the spring of 1958, a "Name-the-B-70" contest was held within the Strategic Air Command, and the name Valkyrie was chosen for the aircraft. The schedule was quite ambitious and the first flight of the aircraft was called for in December of 1961. The first operational wing of B-70s was to be ready in August of 1964.

However, in the autumn of 1958, funding limitiations surfaced which caused a delay in this ambitious schedule. In addition, the Eisenhower administration wanted to see if the basic idea would work before it committed a lot of money to the program. Furthermore, the Atlas and Titan long-range ballistic missiles were just starting to undergo testing at this time, and these might be a more cost-effective deterrent than a new fleet of bombers using as yet unproven technology.

The B-70 mockup was inspected at North American's Inglewood, California plant on March 30, 1959. Several changes were requested by the Air Force, but it was possible to get the work on these completed by the end of the year. In the meantime, on August 30 of that year the Department of Defense concluded that the high-energy boron fuel program was too expensive and too risky, and cancelled it outright. This did not have as much of a negative impact on the B-70 program as one might have expected, since greatly improved conventional jet fuels such as JP-6 were now available. Another blow to the B-70 came when the F-108 Rapier interceptor was cancelled on September 24, 1959. The F-108 was intended to act as a fighter escort for the B-70, and was essentially a scaled-down B-70 with a similar delta-winged configuration and powered by a pair of General Electric YJ93 engines. Systems which had been common to both aircraft would now have to be funded exclusively by B-70 funds.

In the last full year of his administration, President Dwight Eisenhower began to develop second thoughts about the B-70 program, concluding that the bomber made very little military sense, especially in view of the new intercontinental ballistic missiles which were at this time just beginning to enter service. The President pointed out that the B-70 would probably not be ready for active service for at least 8 to 10 years, and that by that time missiles rather than bombers would be the primary deterrent. In addition, the nation was at that time in the midst of an economic recession and the Administration was under pressure to cut costs. Consequently, the Air Force announced a major downsizing of the B-70 project on December 29, 1959. No longer would a large fleet of operational B-70s be acquired. Instead, the B-70 program would be reoriented to produce only a single experimental prototype, and most of the weapons subsystems planned for the aircraft were cancelled.

The B-70 became an issue in the 1960 presidential campaign, candidate John F. Kennedy repeatedly charging that the Eisenhower administration had allowed American defense capabilities to lag dangerously behind those of the Soviets. In August of 1960, the Air Force announced that the earlier downsizing of the XB-70 program would be reversed, and that the plane would now be scheduled for production and service. Twelve B-70 prototypes were now called for in the contract. Many of the subscontracts for the weapons subsystems had to be reopened. An RS-70 (RS for reconnaissance strike) was also offered, which would introduce a reconnaissance and recall capability not available for missiles. It was planned that 60 RS-70s would be available by 1969.

Once in office, President Kennedy found that the "missile gap" that he had been complaining about during the campaign did not actually exist and that Soviet capabilities had been grossly exaggerated during the heat of the campaign. In addition, he soon began to take a second look at the B-70 program. On March 28, 1961, he directed that the B-70 be once again be reoriented strictly to a research and development project, with no intention of production or operational service. The B-70 then became a political football within the US Senate, and conservative senators tried on several occasions to rescue the program and asked that the B-70 be committed to production and service. Undaunted, Secretary of Defense Robert S. McNamara expressed his own dissatisfaction with the B-70 program, and the reorientation stood. Only three aircraft would be built. On April 10, 1961, Air Force Contract AF-42058O was issued, which called for three XB-70A prototypes. The factory number assigned to the project was NA-278. The three planes would have no weapons provisions and would have only two crewmembers in the nose.

The North American design was a large, canard delta winged aircraft to be powered by six General Electric YJ93 afterburning turbojet engines, each offering a thrust of up to 30,000 pounds. The gross weight was to be about 500,000 pounds. The six engines were housed side-by side in the rear of a large underfuselage box. The box was fed at the front by a variable-inlet system consisting of a series of moveable ramps which optimized the airflow into the engines at varying Mach numbers.

The wing was a large delta configuration with a sweepback of 65.57 degrees, with an area of 6297 square feet. The aircraft was to achieve the required Mach 3 cruising speed by using "compression lift"--a technique in which an aircraft could use its own supersonic shock wave for lift and hence reduce the aerodynamic drag and increase the range. In order to incorporate compression lift, the outer wing panels folded downward as a unit to trap the shock wave, generating high-pressure air directly underneath the wing surface. The maximum downward anhedral angle achieved by the panels was 65 degrees. There were a series of elevons on the trailing edge of the delta wing. The outboard elevons extended into the outer wing panel, and were disengaged when the outer panels were folded downward. The trailing edges of the delta wing also had a pair of rudders and vertical stabilizers. Each one consisted of a fixed fin on the lower forward side, to which an all-flying rudder was attached.

The slim nose extended 84 feet ahead of the front of the inlets. It housed the crew compartment, inside of which the two crew members (pilot and copilot) sat side-by-side inside indivudal escape modules. The escape modules ejected individually through hatches in the upper cockpit, and would automatically close during an emergency and would protect the crew members against the violent windstream of a high-speed ejection. The windsheld in front of the cockpit could be changed in angle of incidence to the airflow to improve the high-speed aerodynamic performance--being set in the lowered position to provide better visibility at slower speeds and for landing and set in the raised position for high speeds. The cockpit was more than 20 feet above the ground and nearly 110 feet ahead of the landing gear. There were a pair of canard stabilizers fitted on the upper fuselage just behind the cockpit. Each of the canards was moveable as a unit to provide a variable trim, and in addition had a trailing edge flap which could be extended downwards.

The nose landing gear retracted backwards into a well underneath the center of the forward intake ramps. The main landing gear members were attached to strong points on the sides of the lower engine compartment and intake ramp, and retracted backwards, jacknifed, and turned 90 degrees to lie flat within wells. The landing gear doors were normally open only during the brief extension or retraction sequence.

In order to handle the high skin temperatures created by high-speed flight, a large fraction of the nose structure was manufactured out of titanium, a metal which provides good thermal resistance but which is brittle and difficult to machine. Stainless steel honeycomb structures were used for the aicraft's external skin to reduce cost and to improve the heat dissipation.

Since the XB-70A was no longer considered as an operational aircraft, it had no weapons bay and did not have any capability of delivering weapons. Only a minimal amount of avionics was fitted, just enought so that the aircraft could fly safely. The internal space that would ordinarily have been used for weapons storage and delivery was taken up by test flight instrumentation.

On March 3, 1964, the Air Force cancelled the third prototype, citing budgetary considerations. It was agreed that lessons learned during the flight testing of the first XB-70A would be applied to the construction of the second example.

The first XB-70A (serial number 62-0001) was rolled out at Air Force Plane 42 in Palmdale, California on May 11, 1964.

The first flight of the XB-70A took place on September 21, 1964, with North American test pilot Alvin S. White and Col Joseph F. Cotton at the controls. The flight was nearly four years later that initially planned back in 1958. The plane flew for about an hour, then landed at Edwards AFB. Aside from problems with the landing gear, the flight went smoothly.

Supersonic flight was achieved for the first time on the third test flight. On March 4, the XB-70A achieved a speed of Mach 1.8, sustaining supersonic speed for over an hour. A flight time of 50 minutes at speeds of over Mach 2 was achieved on the eighth test flight.

The second prototype (serial number 62-0207) took off on its flrst flight on July 17, 1965. It differed from the first example by having 5 degrees of wing dihedral. In addition, it had improved hydraulics, better fuel tanks, and an automatic control system for the air intake ramps which replaced the manual system installed on the first prototype.

62-0001 achieved Mach 3 performance at 70,000 feet for the first time on October 14, 1965. On May 19, 1966, the second prototype maintained a speed of Mach 3 for 33 minutes, covering a distance between Utah and Califorinia in only 18 minutes.

On June 8, 1966, the second XB-70A was scheduled to make a low-performance instrument calibration flight, followed by participation in an airborne publicity photo to be taken of aircraft powered by General Electric jet engines. On that day, the XB-70A was being piloted by Alvin White and Major Carl Cross. The photographic sequence was almost complete when another plane in the formation, an F-104N piloted by experienced test pilot Joseph A. Walker, collided with the wing of the XB-70A at an altitude of 25,000 feet near Barstow, California. The F-104N immediately burst into flames, killing Walker instantly. The collision threw the XB-70A into an uncontrollable spin. White ejected successfully but was seriously injured when his escape capsule landed. Cotton was probably incapacited by the g-forces of the spin and was unable to eject, and was killed when the XB-70A hit the ground. The films taken of the incident seemed to show that Walker's F-104N had gotten too close to the XB-70A's wing during the formation and the vortex generated by the wingtip had pulled the smaller aircraft upward and into the wing of the larger one, shearing off the starboard rudder of the XB-70A in the process.

The test program continued with the remaining XB-70A. In March of 1967, the plane was transferred to the National Aeronautics and Space Administration, where it participated in an expanded test flight program designed to verify data for a projected supersonic transport.

The XB-70A made its last flight on February 4, 1969, when it was flown to Wright Patterson AFB in Dayton, Ohio and handed over to the USAF Museum. It is now on display there.

The canceled third B-70 prototype (AV-3) was assigned the serial number 62-0208 and would have had the full B-70 weapons delivery system and four man crew planned for the production B-70. It was the first of eleven YB-70 aircraft assigned the company designation NA-274 by North American) that the US Air Force procured in the August 1960 contract for the B-70, which was later reduced to just one aircraft, and it was also planned to have 62-0208 serve as the prototype for the RS-70 reconnaissance/strike aircraft. The RS-70 was conceived in 1961, and besides the original plan to deliver 60 RS-70s by 1969, the USAF also planned to deliver another 150 RS-70s by 1971.

Specification of the North American XB-70A Valkyrie

Engines: Six General Electric YJ93-GE-3 turbojets, 28,000 lb.s.t. with afterburning.
Performance: Maximum speed 1982 mph at 75,550 feet, 1254 mph at 35,000 feet. Landing speed 184 mph. Service ceiling 75, 500 feet. Initial climb rate 27,450 feet per minute. Combat range 3419 miles, maximum range 4290 miles.
Dimensions: Wingspan 105 feet, Length 196 feet 6 inches, Height 30 feet 8 inches, wing area 6297.15 square feet.
Weights: Wmpty weight 231,215 pounds, 521,056 pounds gross weight, 534,792 pounds maximum.
Armament: The XB-70A was strictly experimental and carried no weapons.


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  7. E-mail from Vahe Demirjian