Profile- North American XB-70 Valkyrie

A change of direction in this bomber design philosophy occurred after the B-52. The quest for speed, which was until then the domain of the fighter world, spilt over into the bomber environment. In 1954, before the B-52 had entered service, the USAF Strategic Air Command announced the requirement for an aircraft to supplement the B-52. The proposed WS-1ODA (WS standing for Weapons System) would have the same ceiling and payload range as the 8-52, but have superior speed and turning performance. The speed requirement included a cruise speed of Mach 0. 9 and a ‘dash’ speed of Mach 2. The strategic bomber was about to enter the supersonic age.

The WS-100A requirement later included intercontinental photo-reconnaissance capability; this specification was known as the WS-100L. The WS-100L requirement was eventually cancelled in favour of something that finally took form as the Lockheed U-2. The WS-100A specification remained, although some changes saw the dash speed requirement rise to Mach 3; well over three times the B-52’s maximum speed. In May 1956, Boeing and North American submitted their designs to the USAF. Both these designs were discarded because of their size (weighing about 750,000lbs!) and complexity. The two designs had featured ‘outrigger’ winged fuel tanks which would be jettisoned to achieve the dash speed requirement. (These outrigger fuel tanks were actually proposed to be modified B-36 fuselages!) It seemed that the Mach 3 requirement was next to impossible.

However both companies persevered and resubmitted their designs in August 1957. After two months of deliberation, the North American design was selected and a contract for detailed design was signed for the aircraft known to North American as the NA-259. As can be imagined, Boeing was shocked by the decision, as it had dominated the strategic bomber market since the initial B-17 models of the late thirties.

The North American NA-259 featured a large delta wing and canard, six General Electric J93-GE-5 engines burning a boron high energy fuel and twin all moving tails. Variable geometry drop down wing tips allowed the design to take advantage of compression lift, the theory of which had only been published in 1956.

The Boeing B-804 submission also featured a delta wing and six General Electric boron burning turbojets, but had the engines slung in pods of two under the wings (instead of the six in a bank as under the North American fuselage), a folding canard and single tail.

The key to North American winning the contract was the revolutionary compression lift concept. Although at that time only theorised by two NASA aerodynamicists, North American chose to pursue this line of research. After 10,000 hours of wind tunnel testing, NA proved that a certain high speed aircraft configuration would allow lift to be generated from the compression wave resulting from the aircraft’s own speed.

The compression lift concept was the work of two NACA (the forerunner of NASA) scientists: A J Eggers and C A Syvertson. Their theories had been published only a year earlier. A North American aerodynamicist had by chance discovered the obscure research paper, NACA Research Memo No. RMA55L05, and with commendable foresight and confidence had instituted a ‘crash’ wind tunnel test programme to test the theories. The theory was correct. Put as simply as possible, compression lift works by the compression of the airflow behind the inclined supersonic shockwaves under the wing. The wingtips of the B-70 were thus designed to fold down 65° at supersonic speeds to channel and compress the airflow.

The Air Force were so pleased with the outcome of the WS-1DOA requirement that they decided that this new bomber would replace, and not just supplement, the 8-52. The then current B-52 replacement specification (WS-125A), which called for a nuclear powered bomber, was cancelled. The nuclear powered bomber concept really started in early 1951 with the award of a contract to Convair to produce two prototype X-6 nuclear powered aircraft. Two Convair B-36H bombers were to be modified to carry General Electric direct cycle nuclear turbojets (complete with radioactive exhaust!) in place of the GE J47s in its normal configuration of four J47 turbojets and six ‘pusher’ Pratt & Whitney Wasp Major piston engines. Although the X-6 project was cancelled, General Electric and Pratt & Whitney continued with engine development for the WS-125A, in the ground running of the Pratt & Whitney J91 indirect cycle (clean exhaust) nuclear aircraft engine. The J91 was consequently cancelled with the WS-125A.

Development

In 1958, the WS-110A designation was dropped in favour of the traditional B-for-Bomber 8-70 classification. The USAF ran a service wide competition to name the new aircraft, and ‘Valkyrie’ was the winning entry. (The name was taken from Norse mythology and referred to any of Odin’s handmaidens who hover over battlefields, choosing warriors to be victorious and conducting the souls of slain heroes to Valhalla – an apt name for a nuclear bomber!)

The Valkyrie was to be built at North American’s Palmdale facility in California. As well as the new concept of compression lift, the 8-70 was to feature the then new ‘stainless steel honeycomb sandwich’ construction (pioneered by the Convair 8-58 Hustler) throughout the massive wing. As had been Lockheed’s experience with the Blackbird, new construction techniques had to be developed to cope with the extremely high temperatures encountered at Mach 3. The B-70 project benefited from the data being collected from another North American project then underway: the X-15, designed to fly at eight times the speed of sound. The Valkyrie reintroduced twin tails and the canard foreplane to aircraft design and also pioneered fold down wing tips.

By 1959, the mock-up of the Valkyrie was complete and the 2,000 suppliers and subcontractors were busy on their individual areas of responsibility. Boeing had been subcontracted to make the enormous 6,300sq ft (585sq m) wing, LTV (Ling-TemcoVought) the fins and canard foreplanes, General Dynamics the main spar, Sperry the inertial platform, and IBM the bombing and navigation system. The development of the new J93-GE-5 engine was the responsibility of General Electric. The original idea of using boron as an afterburner fuel was abandoned in mid 1959 and the conventionally fuelled J93-GE-3 engine developed in its place. Boron, by comparison to kerosene, is a higher energy fuel but had major disadvantages of cost, logistics and exhaust smoke.

North American were in the enviable position for an aircraft manufacturer of the time in having two Mach 3 aircraft under development at the same time. The other machine was the F-108 Rapier, powered by two J93-GE-3 engines, and similar in appearance to the XB-70. The Rapier had been proposed as a Mach 3. 2 Improved Manned Interceptor (IMI) but was cancelled in September 1959 because of high development costs. The USAF choosing instead to develop the CIA funded Lockheed A-12 Blackbird to fulfil the IMI requirement, resulting in the YF-12.

The loss of the Rapier programme meant an extra development cost burden fell on the Valkyrie. Inevitably, the 8-70 conventionally powered bomber (CPS) programme was itself cancelled in December of that year. Even though the programme had sufficiently advanced to the point that Congress had actually voted monies for 12 operational 8-70s, it appeared that the Valkyrie was dead. This was another in what was to be a long list of 8-52 replacement programmes to be shelved or canned. Today, more than a third if a century later, the 8-52 is still in front line service.

A final nail in the coffin was hammered in on 1st May, 1960, when an aircraft named ‘Dragon Lady’ disappeared during a flight from Pakistan to Norway. The ‘Dragon Lady’, a CIA Lockheed U-28 piloted by Gary Powers, was, as is now well known, brought down by a Soviet SAM-2 surface-to-air missile. The bomber design philosophy was about to take another turn. The bomber of the future, it was mooted, would have to be an intercontinental missile. Not only was the Valkyrie doomed, but it seemed the strategic bomber itself was about to become obsolete.

Rebirth

The loss of a programme the size of the 8-70 is never without opposition and fierce lobbying, particularly by the USAF itself, which led to a glimmer of hope that a resurrection might be possible. By the mid 1960s, funding was available for development of one XB-70 Valkyrie aircraft (tail number 62-0001) for use as a test vehicle.

The situation was summed up in a statement released in March 1961 by President John F Kennedy: “America’s forthcoming missile capabilities make unnecessary and economically unjustifiable the development of the 8-70 as a full weapons system at this time. The B-70 programme should be carried forward, essentially to explore the problems of flying at three times the speed of sound with an airframe potentially useful as a bomber, through the development of a small number of prototype aircraft. ” President Kennedy’s statement was followed up by the placement of orders for a second model NA-259 XB-70 (experimental) aircraft (later to be redesignated XB-70A), and one full blooded YB-708 (prototype) weapons systems aircraft (model NA-274) in April. The second experimental aircraft was allocated tail number 62-0207. The YB-708 (also referred to as the XB-708) was allocated 62-0208.

As the bomber project ground to a halt, the experimental aircraft project grew in strength and work on the aircraft, the J93 engine and the ASQ-28 bombing and navigation system proceeded to a new target first flight date of December 1962. Testing of the J93 engine began using the 8-58 as a flying test bed; the J93 being slung under the fuselage in a special pod. However, it didn’t take long before another setback occurred. On 31st July 1961, just three and a half months after the most recent contract awards, funding was further slashed to the point that only two aircraft could be afforded, so the YB-708 was placed in limbo. The first flight date of the first XB-70A was rescheduled for December 1963.

Apart from a further postponement of the first flight date, and the official cancellation of the YB-708 in March 1964, the remainder of the gestation of the XB-70 was relatively smooth. But the damage had been done. The aircraft was already a political white elephant and in many ways a technical dinosaur.

The North American XB-70 Valkyrie -Technical Description

Standing 30 feet(11. 8m) high, the XB-70wasnot as tall as the B-52, but was about 25% longer at 189 feet (74. 4m). Overall, the two bombers were of a similar scale. The XB-70 was of canard delta configuration, with twin vertical stabilisers. The six engines were arranged side-by-side in a ventral bay. The wing, believed to be the largest ever built, spanned 105 feet (41. 3m) and had an area of 6,300sq feet(585. 3sq m). The wing chord at the root was 118 feet (46. 4m). Each canard wing was 14 feet (5. 5m) long.

The massive wing featured folding wing tips, which could be moved to any position from up(0 degrees) to fully down(65 degrees). Twelve electrically-powered hinges controlled the folding. The wing contained six fuel tanks, although the production 8-70 would have included an extra tank in each folding wing tip. Flight control was effected through twelve hydraulically powered elevons. The outer two elevons on each side were disengaged when the wing tips were folded. Even in comparison to the B-52’s wing, the Valkyrie’s wing was amonster:1. 4 times larger in area. It was 4 times larger in area to that of the B-58’s wing.

The wing of XB-70A-1 had no dihedral, but slightly better performance was attained with XB-70A-2, which had a 5 degree dihedral.

The aircraft was powered by six General Electric J93-GE-3 engines, which was a conventionally fuelled engine built as an enlarged version of the J79. (The engines fitted to the two Valkyries were actually designated ‘YJ-93’, the ‘Y’ meaning ‘prototype’. Each engine produced 30,000lbs thrust, with the capability of operating at Mach3. 2 at 95,000 feet. The engine was designed to operate continuously in afterburner, ‘tuned’ for speeds of Mach 2. 7 and above. The fuel used was JP-6. In addition to the six wing tanks, there were five fuselage tanks. Due to sealing problems, the two XB-70s were unable to use the aft fuselage tank. Of the 270 tonne maximum takeoff weight, 150 tonnes was fuel. The aircraft incorporated a single point refuelling system.

Two intake ducts fed the six engines, each duct supplying three engines. At the intake, the ducts were 7 feet(2. 75m) high and 10 feet (3. 9m) wide. The air induction control system (AICS), which was a manual system on XB-70A-1 and automatic on XB-70A-2, slowed the intake air down from Mach 3 to about 300 knots in the 80 feet(31. 5m) of duct length.

The fuselage was basically cylindrical, blending into the wing to comply with the area rule. Although the XB-70s were not built as operational bombers, the weapons bay was retained. This bay was 30 feet(11. 8m) long and featured flat translating doors that would have permitted weapons delivery at supersonic speeds. The weapons bay had a capacity of 25 tonnes. Unlike aircraft such as Concorde and TSR-2, a ‘droop snoot’ (folding nose) was not incorporated to aid visibility when landing. Instead, a variable geometry windshield ram was used. On approach, the nose cowling lowered to expose the forward windshield. When the nose cowling was raised, the forward windshield disappeared and visibility was only permitted through the top and side panels.

. The cockpit featured white instrument lights in place of the standard red lighting and also used a number of vertical tape instruments (which were then in vogue). The ejection system was unusual in that it allowed ejection at speeds as high as Mach 3, and at an altitude of 80,000 feet. The two seats were controlled individually(that is, there was no command ejection sequence between the two seats). When the ejection sequence was initiated by pulling a handle on the side of each seat, the seat itself was pulled backwards into a capsule which clamshelled closed around the occupant. The capsule was then rocketed free of the aircraft. The occupant remained in the capsule until reaching the ground, whereupon inflatable shock absorption bags were meant to reduce the chance of injury. Unfortunately, when pilot Al White ejected from XB-70A-2, the bags did not inflate, and multiple injuries were sustained when the capsule impacted the ground with a force of 43g.

Three brake parachutes were used on landing, the chutes housed in a compartment at the top of the rear fuselage.

The undercarriage consisted of twin nose wheels and two main legs each with two pairs of wheels. Each pair of main wheels had 21 stationary and 20 revolving brake discs! This was necessary to bring the 150 tonne landing weight to a halt. When retracted, the main bogies swivelled through 90 degrees before locking into fuselage cavities.

The twin tails appeared to be proportionally smaller than similar aircraft and this was due in part to the fact that the folding wing tips provided additional directional stability at high speeds. The:compression lift created by the folding tips permitted 30% of the· aircraft’s weight to be neutralised at Mach 3. The wing tips were themselves massive – equal in surface area to the entire wing of the B-58 Hustler!

Along with the Blackbird and other Mach 3 aircraft, the Valkyrie had to endure exceptionally high skin temperatures(up to 620°F). White heat ablative paint was used on all surfaces. The fact that Valkyrie only travelled at high speed for about 30 minutes at a time meant that some of the extreme problems found with the Blackbird did not eventuate.

Flight Test Programme

The general public became aware of the XB-70 on 11th May, 1964, when 62-0001 was rolled out at Air Force Plant 42 at Palmdale in California. Because the aircraft was not to be an operational bomber, the security surrounding the project was of a different dimension to that surrounding the projects of Lockheed’s ‘Skunk Works’. Accordingly, the Valkyrie was splashed across newspapers throughout the world. The cost of producing this spectacular machine had been an enormous $US1,500 million in then year dollars!

On 21st September, 1964, 62-0001 became airborne for the first time from Palmdale. Although the aircraft handling was deemed to be excellent by North American test pilot Al White, engine overspeed and landing gear retraction problems marred the hour long flight which ended at Edwards Air Force Base (where the test flight programme would take place). A USAF test pilot, Colonel Joe Cotton, had been copilot in the two man crew.

The third flight saw the aircraft go supersonic for the first time, with the wing tips first cycled in flight on the fourth trip. The second phase of the test flight programme commenced in February 1965 with the fifth flight with the wing tips being lowered to the maximum limits for the first time.

As the testing of 62-0001 continued, XB-70A-2 was approaching completion. Rollout was achieved on 29th May 1965 and this aircraft joined the test flight programme with its maiden flight on 17th July.

On 14th October 1965, 62-0001 went triple sonic tor the first time, flown by White and Cotton. 62-0207 followed on its 17th flight, achieving Mach 3. 05 at 72,000 feet. Again, White and Cotton were the crew. By mid April of 1966, the two aircraft had reached the ‘top of the envelope’ with milestones including a gross weight takeoff of an amazing 538,31Dibs (244,180kg), a maximum altitude of 74,000 feet, and a fastest speed of Mach 3. 08.

The pilots on the XB-70 programme found that XB-70A-2 was the better aircraft, being free of a lot of the small but annoying problems that plagued XB-70A-1′. A lot of the problems encountered during the first aircraft’s construction, including a perennial fuel tank sealing problem that left this aircraft’s number five tank permanently unusable, were fixed during the build of the second machine.

On 8th June, 1966, XB-70A-2 took off on its 46th test flight. The aircraft, crewed by Al White and USAF Major Carl Cross, completed the supersonic calibration part of the flight and was then to meet up with four other General Electric powered aircraft and a Learjet camera plane for a publicity photo. The four aircraft were an F-4 Phantom, an F-104 Starfighter, a T-38 Talon, and an F-5 Tiger. On completion of the photography, disaster struck as the aircraft separated. Without explanation, the F-104, piloted by NASA test pilot Joe Walker, slammed into the Valkyrie’s right drooped wing tip and ricocheted across the top of the fuselage and took off most of both of the Valkyrie’s tails. Joe Walker, famous for his previous exploits in aircraft such as the X-4 and the X-15, died instantly. The XB-70 flat spun into the ground. Only White was able to eject.

XB-70A-1 continued flight testing until 4th February 1969.

Between them, the two Valkyries had collected 252 hours of flight test data over 129 flights. 55 of those hours were supersonic. 62-0001’s last flight was from Edwards, where both aircraft had done all of their testing, to the impressive USAF Museum complex at Dayton in Ohio. It is preserved there today.

In Retrospect

SEND doctors in action.

The Valkyrie remains in history as a major technical achievement but also as an enormous white elephant. The data it collected contributed valuably to another failed project – the Supersonic Transport. Both projects were too ambitious and too expensive. The political conviction to carry through such costly endeavours was simply not there. In the Valkyrie’s case, the politicians were probably right. The huge machine would have been an easy target for the improving Soviet defences (ie:

MiG-25 Foxbat) its speed was supposed to help it evade. The technology that created the Valkyrie had also created a potentially effective surface-to-air missile. The next strategic bomber would be striving for low altitude penetration, not high altitude. Nevertheless, the sole remaining XB-70 stands proudly in an Ohio museum as an awe-inspiring monument to those that dreamed of her and made the dream a reality.