As the backbone of the American strategic forces from the mid-1970s until the late 1990s, the North American B-70 was produced in a bewildering number of variants over the twenty years the aircraft was in production. Indeed, since the B-103 and B-106 Auroras are only modified B-70s, it could be argued that the aircraft itself is still in production today, almost 40 years after North American delivered the first production aircraft.
The basic idea for the XB-70 began back in January of 1954, when the results of teh Red Sun exercises showed that the speed and service ceiling of interceptors was slowly but surely catching up with the bombers currently in Strategic Air Command service (the B-36 and B-60) or just entering operational status (the B-52). Boeing Aircraft Corporation and the Hudson Rover Institute began to consider what type of weapon system would be needed to deliver high-yield thermonuclear weapons against well-defended enemy targets. 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.
In October 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. GOR 38 was superseded by GOR 82 in March of 1955.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 Force specified that the aircraft 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. 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 Air Force was not happy with that concept since the floating wing panels would probably prove to be too cumbersome and unwieldy in practice. In September 1956, the Air Force told both contractors that they would have to go back to the drawing board.
By March 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. 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 a prototype development contract issued for three aircraft. This was followed in December 1958 with a further contract for 30 pre-production aircraft. The first operational wing of 25 aircraft was to be ready by late 1965 with a complete bomb group of 75 aircraft being in service by 1966. The 1958 contract also designated the aircraft as the B-70.
The Missile Massacre
In early 1957 a Snark intercontinental cruise missile was launched from Presque Island at a target in Greenland. The missile headed out to sea and vanished. Six months later, it's wreckage was found in Brazil. The missile had managed to hit the wrong continent, a fact that was gleefully reported by newspapers around the world. President LeMay was not completely satisfied with this situation and "found much cause for complaint" in the concept and management of the various strategic missile programs. This was the culminating point in a war that had been going on in U.S. Strategic circles between the advocates of manned bombers and strategic missiles. The advocates of missiles claimed that the weapons they favored were cheaper and less vulnerable to pre-emption than bombers and, unlike bombers, could not be intercepted or shot down. Bomber advocates pointed out that a manned bomber could be launched and recalled, retargeted in flight and could defend itself on the way to its target. They disputed the claimed invulnerability of the missile and suggested that a ballistic missile was actually a much easier target than a manned bomber due to the missile's inability to manoeuver. This issue was put to the test over Nevada in late 1957 when President LeMay ordered examples of the new missiles to be tested against American defenses. The missiles proved to be every bit as vulnerable to interception as their opponents had claimed and, in the famous 1957 Missile Massacre, President leMay personally cancelled every single U.S. strategic missile program.
Back To Bombers
With Strategic Air Command firmly committed to manned bombers, the Air Force was enthusiastic about getting the B-70 in service as quickly as possible. In early 1958, a "Name-the-B-70" contest was held within the Strategic Air Command, and the name Valkyrie was chosen for the aircraft despite reservations about its Germanic connotations. The stepped-up 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. 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.
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 not 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.
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. 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. 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. Due to production and material problems, two of the aircraft’s seven fuel tanks were sealed off and the aircraft was redlined at Mach 2.5. AV-1 was flown as part of the Valkyrie development program until mid-1969 when it was retired to the USAF museum. The XB-70 AV-2 was basically a product-improved version of the AV-1 with the leakage problems in its fuel tanks solved (thus allowing all seven tanks to be used) and improved construction materials allowed speeds of up to Mach 3.1. AV-2 was delivered in early 1965 but was lost in an accident during September 1966.
Specification of the North American XB-70 AV-1 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 radius 3,419 miles, maximum ferry range 8,900 miles. Dimensions: Wingspan 105 feet, Length 196 feet 6 inches, Height 30 feet 8 inches, wing area 6297.15 square feet. Weights: Empty weight 231,215 pounds, 521,056 pounds gross weight, 534,792 pounds maximum. Armament: The XB-70 AV-1 was strictly experimental and carried no weapons.
North American YB-70 Valkyrie
Sometimes called the XB-70A, the YB-70 was the first fully-equipped B-70 to be flown. The aircraft had all four crew members and was weapons-capable. Two YB-70s were built, the first being delivered in 1965 and the second in 1966. The second YB-70 (AV-4) had improved engines and skin fabrication that increased maximum speed to Mach 3.4.
Specification of the North American YB-70 Valkyrie
Engines: Six General Electric J93-GE-3 turbojets, 28,800 lb.s.t. with afterburning. Performance: Maximum speed 2,250 mph at 75,550 feet, 1,254 mph at 35,000 feet. Landing speed 184 mph. Service ceiling 79, 500 feet. Initial climb rate 28,450 feet per minute. Combat radius 4,750 miles, maximum ferry range 12,445 miles. Dimensions: Wingspan 105 feet, Length 196 feet 6 inches, Height 30 feet 8 inches, wing area 6297.15 square feet. Weights: Empty weight 251,635 pounds, 581,025 pounds gross weight, 600,131 pounds maximum. Armament: Up to 65,000 pounds of bombs, air-to-ground and air-to-air missiles.
North American B-70A Valkyrie
First full production version of the Valkyrie, the B-70A was essentially identical to the YB-70 and was the Cook-Craigie plan low-rate initial production aircraft. 50 aircraft were built between 1966 and 1969 entering service with the 100th Bomb Group. Severe problems with onboard systems delayed full operational capability until 1971.
North American B-70B Valkyrie
Full production version of the B-70 with faults found in the B-70A development corrected. 96 aircraft built in 1972 assigned to 100th and 35th Bomb Groups.
North American B-70C Valkyrie
Improved version of B-70B with four external hardpoints and the Defensive Anti-Missile System. 154 aircraft built in 1973 and 1974 with all B-70As and B-70Bs brought up to this B-70C standard. This allowed the formation of the first four B-70 groups (the 2nd, 19th, 35th and 100th Bomb Groups) that operated a mix of A, B and C version aircraft until well into 1976.
North American B-70D Valkyrie
Specialized version of the B-70C intended to carry Skybolt ballistic air-to-surface missiles. Originally it was planned that four of SAC’s 20 Heavy Bomb Groups would be equipped with Skybolt-capable aircraft, implying the production of 300 B-70Ds. This plan was changed to providing each of the 20 Bomb Groups with a detachment of 15 aircraft. This was then reduced to five (cutting planned B-70D production to 100 aircraft). Skybolt was never a particularly satisfactory weapon and eventually the B-70D production was curtailed at 48, the balance of the aircraft being completed as B-70Es. The B-70D entered service in 1972 alongside the B-70B.
North American B-70E Valkyrie
Main production version of the B-70 with 573 aircraft being delivered between 1975 and 1980. These, along with the B-70Ds, equipped eight Heavy Bomb Groups, bringing the total Valkyrie force up to twelve groups. The B-70E featured additional fuel capacity, uprated engines, a strengthened undercarriage to handle higher gross weight and an improved DAMS system.
Specification of the North American B-70E Valkyrie
Engines: Six General Electric J93-GE-10 turbojets, 31,200 lb.s.t. with afterburning. Performance: Maximum speed 2,310 mph at 75,550 feet, 1,325 mph at 35,000 feet. Landing speed 184 mph. Service ceiling 85,200 feet. Initial climb rate 28,650 feet per minute. Combat radius 4,950 miles, maximum ferry range 12,875 miles. Dimensions: Wingspan 105 feet, Length 196 feet 6 inches, Height 30 feet 8 inches, wing area 6297.15 square feet. Weights: Empty weight 252,685 pounds, 583,125 pounds gross weight, 602,131 pounds maximum. Armament: Up to 65,000 pounds of bombs, air-to-ground and air-to-air missiles.
North American B-70F Valkyrie
Skybolt being something of a failure, the capability to carry the weapon was removed from the B-70Ds and the aircraft were rebuilt as B-70Fs. Later, the surviving B-70Cs were also upgraded to B-70F configuration. There was little difference between a B-70E and a B-70F although the F-models were rated at Mach 3.4 as opposed to Mach 3.5 of the Es
North American B-70G Valkyrie
Follow-on from B-70E differing only in having additional fuel capacity. 672 aircraft delivered between 1981 and 1988 completing the phase-out of the B-52 fleet.
North American RB-70H Valkyrie
Proposed strategic reconnaissance version of the B-70E, not proceeded with due to pressing need for bomber aircraft to replace the B-52.
North American B-70J Valkyrie
Major modernization applied to B-70E and B-70G aircraft. Aircraft reskinned, electronics stripped and replaced by new-generation equipment. New engines installed offering longer life and improved reliability.
North American B-70K Valkyrie
300 B-70K aircraft built between 1989 and 1995. Replaced the old B-70Fs. Minor improvements over B-70J including revised workstations.
North American B-70L Valkyrie
Proposed export version of the B-70K. Greatly simplified and dumbed-down electronics and defense systems, used older skin materials that restricted speed to Mach 3.3
North American B-70M Valkyrie
Actual export version of the B-70K intended specifically for the Triple Alliance, less drastically simplified than the B-70L and speed remained redlined at Mach 3.5. Sold to Thailand (48 ), India (64) and Australia (48 ).
North American RB-70N Valkyrie
Strategic reconnaissance version of the B-70 Valkyrie intended to replace aging RB-58 Hustlers. 360 built between 1989 and 1996 equipping 5 strategic recon groups.
North American B-70P Valkyrie
Major rework of B-70J and B-70K aircraft with new glass cockpits, complete replacement of all on-board computers and instrumentation.
North American RB-70Q Valkyrie
Major rework of RB-70N aircraft along lines of B-70P. 360 additional aircraft built 1994-1997 replacing remaining RB-58s. These aircraft ended B-70 production.
North American B-70R Valkyrie
Proposed version of the B-70P to be powered by SJ-58 scramjets. Estimated maximum altitude, 125,000 feet, maximum speed Mach 4.62. Not proceeded with due to development of SJ-93 that offered much superior performance and a simpler installation,
North American XB-70S Valkyrie
Eight-engined derivative of the B-70 with extreme lightening of airframe intended to act as manned launch platform for orbital and sub-orbital craft. No weapons capability. Redesignated YB-100. 24 built.
North American B-70T Valkyrie
Derivative of the B-70P powered by six SJ-93 scramjets. Originally known as the Super-Valkyrie. One prototype built, was redesignated XB-103 Valkyrie prior to completion. First prototype flew in 1995.
North American B-70U Valkyrie
Designation applied to 100 surplus B-70P aircraft (replaced by B-103) and modified for sale to the United Kingdom. Sometimes called the B-70UK
North American YB-103A Valkyrie
Pre-production aircraft used for flight trials. Six built 1996-1997.
North American B-103A Valkyrie
Cook-Craigie low initial production rate version of the B-103 Valkyrie. 50 built between 1997 and 2001 delivered to the 35th Bomb Group.
North American B-103B Valkyrie
Full production version of B-103A. 250 built between 2003 and 2005. Production of B-103 terminated due to development of B-106
North American B-103C Valkyrie
Experimental version of B-103A with turboscramrockets. First flown 2001. Redesignated B-106 Aurora.
North American XB-106 Aurora
Redesignation applied to single B-103C
North American YB-106 Aurora
Modified version of XB-106. Aircraft significantly enlarged to provide additional fuel capacity and fitted with six rather than four hardpoints. Eight built, first flew in 2003.
North American B-106A Aurora
B-106A Cook-Craigie pre-production version of the YB-106. 50 built in 2005-6 and delivered to the 100th Bomb Group
North American B-106B Aurora
Full production version of B-106. Multi-year procurement order placed in 2007 for the delivery of 750 B-106 aircraft by 2014.