THE 456th FIGHTER INTERCEPTOR SQUADRON

THE PROTECTORS OF  S. A. C.

 

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North American XB-70A "Valkyrie"

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NASA's Quicktime movies of the XB-70!
 

 

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The XB-70, one of the world's most exotic airplanes, was conceived for the Strategic Air Command in the 1950s as a high-altitude bomber that could fly three times the speed of sound (Mach 3). Because of fund limitations, only two were built, not as bombers, but as research aircraft for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic aircraft. The Valkyrie was built largely of stainless-steel honeycomb sandwich 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 supports part of the airplane's weight. For improved stability at supersonic speeds, the Valkyrie could droop its wingtips as much as 65 degrees.

The No. 1 XB-70 made its initial flight on September 21, 1964, and achieved Mach 3 flight on October 14, 1965. The No. 2 airplane first flew on July 17, 1965, but on June 8, 1966, it crashed following a mid-air collision. The No. 1 airplane continued in its research program until flown to the Museum on February 4, 1969.

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 The design and construction of the XB-70A had to account for the large variation in aircraft skin temperatures maximized by air friction during high speed flight. At Mach 3, skin temperatures ranged from about 400° F to more than 600° F. The interior framework surrounding the six YJ93 jet engines could reach temperatures of more than 900° F.

To solve the problems associated with aerodynamic heating at high speeds and radiant heating causes by the engines, the North American engineers designed the aircraft to be built largely of brazed stainless-steel honeycomb sandwich panels and titanium. Most of the fabrication, assembly and construction techniques associated with the steel honeycomb panels had to be 'invented' during the project. In fact, one of the most important legacies of the Valkyrie program is the knowledge gained in high strength, high temperature materials use for high speed aircraft.

Because the crew compartment and forward equipment bay had to be cooled to 'shirt sleeve' temperatures, the aircraft incorporated a sophisticated 'transpiration' system which used engine bleed air to drive two refrigeration pumps which provided both the cooling air and the cabin pressurization necessary because the crewmen didn't wear pressure suits. The air was evenly distributed throughout the crew compartment by a vast number of little holes in the compartment walls, this prevented the unacceptable temperature gradient which would have resulted if a conventional duct and vent system was used (the vent area would be too cold and the areas furthest away from the vents would be too hot).

Many very complicated engineering problems had to be overcome during the design and construction of the XB-70. Many of the techniques developed specifically for the Valkyrie program form the basis for processes still in use today for high performance jet aircraft.

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The XB-70, one of the world's most exotic airplanes, was conceived for the Strategic Air Command in the 1950s as a high-altitude bomber that could fly three times the speed of sound (Mach 3). Because of fund limitations, only two were built, not as bombers, but as research aircraft for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic aircraft. The Valkyrie was built largely of stainless-steel honeycomb sandwich 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 supports part of the airplane's weight. For improved stability at supersonic speeds, the Valkyrie could droop its wingtips as much as 65 degrees.

The No. 1 XB-70 made its initial flight on September 21, 1964, and achieved Mach 3 flight on October 14, 1965. The No. 2 airplane first flew on July 17, 1965, but on June 8, 1966, it crashed following a mid-air collision. The No. 1 airplane continued in its research program until flown to the Museum on February 4, 1969.

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 The initial XB-70A (S/N 62-1) was rolled out on May 11, 1964 and made its first flight on 21 September 1964. It flew a total of 83 times when, on 4 February 1969, it made its final flight to Wright-Patterson AFB, Dayton Ohio for delivery to the USAF Museum where the aircraft remains on public display. The aircraft flew supersonic (Mach 1.1) for the first time on its third flight, 12 October 1964. On 24 March 1965, the aircraft surpassed Mach 2 for the first time during its 15th flight. Mach 3 was achieved for the first time on 14 October 1965 during the 17th test flight.

On 25 April 1967, XB-70A-1 made its initial flight as a NASA test aircraft. Of the 83 flights of this aircraft, the USAF flew the first 60 and NASA conducted the last 23.

The delta wing of the XB-70 has a span of 52 feet 6 inches and is swept back 65.5°. The outboard sections of the wings (20 ft.) were capable of being drooped (lowered) in flight to increase high speed flight performance. The maximum drooped position was 65° down angle and was used during supersonic flight. A transitional position of 25° down angle was used as the XB-70 accelerated into supersonic flight. The variable geometry wingtips acted as vertical stabilizers when in one of the two drooped positions; however, their primary function was in the compression lift system. The lower fuselage was designed in a 'Vee', or wedge shape, specifically to slow the airflow around the lower fuselage by creating an air dam. At speeds around 2,000 mph (Mach 3), this 'air dam' slowed the air stream to about 1,600 mph which created the compression lift -- the aircraft essentially rode on top of the compressed air dam thus creating the lift. At 2,000 mph, with the wingtips drooped to the full down position, compression lift carried approximately 35 of the aircraft's weight. The drooped wingtips acted to confine the airflow and increased to efficiency of the compression lift phenomenon. With the wingtips in the full up position (0° droop) compression lift was lessened by about 10 percent.

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The XB-70 was equipped with two fully moveable vertical stabilizers, 12 elevons -- 6 on each wing trailing edge (an elevon is a combination elevator and aileron for pitch and roll control), and a canard surface mounted just behind the cockpit on the forward fuselage. The reason for having 12 small elevons rather than just two was to allow for greater control of the aircraft over the entire flight speed range. At landing speeds of less than 200 mph all twelve elevons were needed. At 2000 mph with the wingtips drooped, the three outboard elevons on each wing were locked to prevent over stressing the airframe if sudden violent control inputs were required. The canard surface was all flying but also had trailing edge flaps. The canard's primary purpose was to balance pitch forces (up and down movements) normally controlled by the horizontal stabilizer and elevator on a conventional airplane.

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The two XB-70A's completed were never intended to be anything other than very high speed test aircraft. Because of advances in enemy air defenses during the late 1950s and early 1960s in both interceptor and surface-to-air missile design, the high speed, high altitude penetration bomber mission was seen as too risky and left the aircraft and crew very vulnerable to attack. Bombers capable of low level penetration or standoff weapons delivery were judged more practical. The growing value of the Intercontinental Ballistic Missile (ICBM) for strategic deterrence also had a negative effect on the XB-70 and similar programs (e.g.. XF-108). ŠNews from North American Aviation, Inc.
Escape Capsule - The encapsulated ejection seat of the B-70 provides the crew members with secondary shirtsleeve environment in the event of a malfunction in the normal air vehicle system.

The crew members may encapsulate themselves within the escape capsule and continue to fly the air vehicle with limited capabilities. If a serious malfunction occurs that causes abandonment of the air vehicle, the crew members can eject themselves from the air vehicle. The escape capsule, with its clam shell doors closed and sealed, provides a safe environment for the crew members during ejection and descent to earth. Booms, which extend during the ejection process, provide aerodynamic stability, and a recovery parachute is automatically sequenced to open when a capsule descends to 15,000 feet. A pressurized bladder on the bottom of the capsule cushions the impact on touchdown.

The capsule (above) is seen during one of a series of several successful tests which consisted of rocket sled ejections and aerial drops from both subsonic and supersonic aircraft.

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On 8 June 1966, the second XB-70A (S/N 62-207) was scheduled to complete a flight test program and then participate in a photo session showing a formation of aircraft powered by General Electric engines. The XB-70A-2 took off from Edwards Air Force Base, California, shortly after 7 a.m. with pilot Al White and copilot Major Carl Cross. This was the 46th test flight of the No. 2 XB-70A and the first flight for Major Cross. After conducting approximately one hour of tests, the XB-70A-2 was ready to participate in the photo session.

Five aircraft were scheduled to participate in the session. The North American XB-70A with White and Cross at the controls, a Northrop T-38A flown by Captain Peter Hoag with Colonel Joseph Cotton flying in the back seat (Col. Cotton was an XB-70 test pilot also), a Northrop YF-5A flown by GE test pilot John Fritz (organizer of the photo session), a McDonnell F-4B flown by US Navy Commander Jerome Skyrud with E. Black in the rear seat, and a Lockheed F-104A (NASA chase plane) flown by NASA's chief test pilot Joseph Walker.

The photo session began about 8:30 a.m. and ended at 9:25 a.m. The aircraft were, at this time, flying in a V formation. The XB-70A-2 was in the lead, the F-4B was to its left with the T-38A to the left of the F-4B. Off the XB-70's right wing were the F-104 and the YF-5A. At 9:26 a.m., just after the end of the photo session the F-104 collided with the trailing edge of the of the XB-70A-2's right wing. The F-104 rolled up and left across the back of the XB-70, shearing off about 50% of the right vertical stabilizer and nearly 100% of the left vertical stabilizer. The F-104 continued to roll to the left in flames and was totally destroyed. The pilot of the F-104, Joseph Walker, was killed instantly in the midair collision.

It's probable that Walker flew his F-104 too close to the XB-70A and got caught in the right wingtip vortex (air corkscrewing off the outboard edge of the wing). The vortex generated by the XB-70A was powerful enough to violently flip the F-104 to the left.

In any case, the XB-70A-2 flew straight and level for about 15 seconds after the impact. The wingtips were in the 25° transitional drooped position and provided enough stability to prevent the aircraft from going instantly out of control. However, there wasn't enough vertical stabilizer remaining to hold the aircraft level for long and it rolled inverted, went nearly vertical (nose up), and entered a flat spin (nose low).

Initially, White and Cross were unaware that the XB-70 had been hit, even though there were urgent radio calls about the midair collision from the other aircraft which immediately broke formation and spaced themselves out to a safe distance. The XB-70A-2 was equipped with escape capsules rather than ejection seats, but only Al White was able to activate his. Major Cross never activated his capsule, possibly because he was knocked unconscious during the high g-forces caused by the out of control spin. Major Cross was killed when the XB-70A-2 impacted the desert near Barstow, California.

Al White was able to eject from the aircraft, but was severely injured when the escape capsule's air bag, designed to cushion the ground impact forces, failed to inflate.

The remaining XB-70 didn't fly again until 5 months later in November. The XB-70A-1 flew 33 more times between November 1966 and February 1969 when it was delivered to the USAF Museum for permanent display.

 

TYPE
XB-70A 		Number Built/Converted
2		 Remarks
Mach 3 bomber

SPECIFICATIONS
Span: 105 ft.
Length: 185 ft. 10 in. without boom; 192 ft. 2 in. with boom
Height: 30 ft. 9 in.
Tread (distance between main landing gear): 23 ft. 2 in. (strut to strut centerline)
Wheel base: 46 ft. 2 in. (strut to strut centerline)
Weight: 534,700 lbs. loaded
Armament: None (designed for up to 50,000 lbs. of nuclear or conventional bombs carried internally)
Engines: Six General Electric YJ93-GE-3 turbojets of 31,000 lbs. static sea level thrust each with afterburner.
Crew: 2 - Pilot & Copilot

PERFORMANCE
Maximum speed: 2,056 mph. (Mach 3.1) at 73,000 ft.
Cruising speed: 2,000 mph. (Mach 3.0) at 72,000 ft.
Range: 4,288 miles
Service Ceiling: 77,350 ft.

Courtesy of The Air Force Museum

 

The General Electric YJ93-G-3 Turbojet Engine

 

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YJ93-G-3 TURBOJET

General Electric designed the YJ93 engine to power a planned supersonic interceptor, the F-108, and a bomber, the North American XB-70, at speeds of 2,000 mph and at altitudes about 70,000 feet. The high-pressure variable-stator engine ran on special high-temperature JP-6 fuel and had a thrust-to-weight ratio above 5:1. The Air Force cancelled the F-108 program and only built two XB-70s. The engine was not used in any military or commercial aircraft other than the XB-70.
 

 

 

 

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XB-70 Cockpit Photos

   
 

Flight Deck

  
Pilot's Panel The Center Panel Co-Pilot's Panel
 

 
 

The Center Console

 

 

 

XB-70A "Valkyrie"

Greg Goebel / Public ddomain

 

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The North American XB-70 Valkyrie

After World War II, the US Air Force's (USAF) strategic bombers grew ever more capable, each reaching higher altitudes and greater speeds than its predecessor. By the late 1950s, the USAF was planning to develop a "super-bomber", the North American "B-70", that would be built in large numbers.

In reality, improvements in Soviet air defenses and the development of the ICBM made the B-70 obsolete before it ever flew. The B-52, which was planned to have been an interim type leading to the B-70, still remains in first-line service in the 21st century. However, two XB-70s were completed as supersonic test aircraft, and were among the sleekest and most impressive aircraft that ever flew. This document outlines the history of the XB-70.

 

 

Organs

 

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The XB-70 began life in 1954, in design studies performed for a US Air Force (USAF) request that formally emerged in 1955 as "Weapons System 110 (WS-110)", which specified a high-altitude bomber that would carry a heavy war load and cruise at Mach 3 over long range at high altitude.

Boeing and North American submitted proposals, but the concepts weren't exactly what the USAF wanted. The aircraft would have had a loaded weight of over 450 tonnes (a million pounds); were too big to fit into existing B-52 hangars and other facilities; and could only achieve Mach 3 for a short dash over the target. The proposals were rejected. Both companies went back to the drawing board, and found that they could in fact build a bomber with a warload of 18.2 tonnes (20,000 pounds) that could cruise at Mach 3 at an altitude of over 21 kilometers (70,000 feet), and would be able to use existing facilities.

North American won the competition in December 1957. Their design, designated "B-70", was of canard configuration, featuring a long, sleek fuselage with small wings mounted near the cockpit, and a large delta wing in the rear that was fitted with twin vertical stabilizers. The bomber was to be powered by six General Electric J93 afterburning turbojets, each with an afterburning thrust in the range of over 127.5 kN (13,000 kgp / 30,000 lbf). The engines, bomb bay, and landing gear were all contained in a single wedge-shaped unit under the center of the delta wing. The tricycle landing gear featured twin-wheel nose gear and four-wheel main gear assemblies. The aircraft was to be constructed mostly of lightweight stainless-steel honeycomb, with titanium used in certain heat-critical sections.

The B-70 also incorporated an unusual feature: the outboard 6 meters (20 feet) of the wings could fold down. This scheme was derived from research that showed that trapping the shockwave generated from the nose of a supersonic aircraft wing could generate very high lift. The B-70 would take off with the wingtips straight. At subsonic cruise speed, they would be lowered to 25 degrees, and above about Mach 1.4, to 65 degrees. The folding wingtips not only improved lift, they also allowed smaller vertical stabilizers to be used, and compensated for the delta wing's backwards shift in its center of lift as speed increased.

* However, as the B-70 design solidified, the Air Force began to have second thoughts. Intercontinental ballistic missiles (ICBMs) were clearly the way of the future for strategic nuclear strike, and the B-70 began to seem like an expensive luxury. In December 1959, the entire program was cut back to a single prototype. This wasn't the last word on the matter, though, since big weapons procurement efforts acquire a momentum of their own, and by mid-1960 funding for the B-70 program had been restored to a level adequate for as many as a dozen of the bombers.

The logic working against the concept still held true, unfortunately, and had been aggravated on 1 May 1960, when an American Lockheed U-2 spy plane was shot down over the Soviet Union by an SA-2 surface-to-air missile (SAM). Not only was the B-70 redundant in the face of the emerging US ICBM force, but improved SAM defenses meant that its high speed, high altitude flight did not offer the same protection against SAMs that it would have against manned interceptors. On 1 March 1961, US President John F. Kennedy announced that the B-70 program was to be scaled back once more. Three aircraft would be completed, including two "XB-70" flight test prototypes and one "YB-70" operational prototype.

The two XB-70s were to be flight research aircraft only, most of the combat-related avionics, such as the bombing-navigation system, were deleted, and the bombardier and navigator positions were deleted as well, leaving provisions only for pilot and copilot. The US National Aeronautics & Space Administration (NASA) would collaborate with the USAF on the flight tests.

The YB-70 was to have full combat systems. The idea was that it would be useful as a hedge against changing conditions to retain the option of putting the B-70 into production after all. However, the expense and the continuously dwindling logic of fielding the B-70 meant that the YB-70A was never built.

 

 

The XB-70 In Flight

 

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The first XB-70 was rolled out at North American's Palmdale, California, facility on 11 May 1964. By this time the type had been named the "Valkyrie", and the initial prototype was designated "Air Vehicle 1 (AV/1)", with tail number 20001. AV/1 performed its first flight on 21 September 1964. After a number of teething problems, AV/1 punched through Mach 1 for the first time on 12 October 1964.

   NORTH AMERICAN XB-70 VALKYRIE:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                32 meters           105 feet
   wing area               586.2 sq_meters     6,298 sq_feet
   length (no test boom)   56.7 meters         185 feet 10 inches
   height                  9.38 meters         30 feet 9 inches

   empty weight            136,055 kilograms   300,000 pounds
   max takeoff weight      246,365 kilograms   542,000 pounds

   maximum speed           3,310 KPH           2,056 MPH / 1,787 KT
   service ceiling         23,580 meters       77,350 feet
   ferry range             6,925 kilometers    4,300 MI / 3,740 NMI
   _____________________   _________________   _______________________

Flight tests of AV/1 continued into 1965, with the aircraft demonstrating sustained supersonic flight at speeds of Mach 1.4 to above Mach 2. On its 12th flight, on 7 May 1965, while cruising at Mach 2.58, a piece of the wing broke away and shut down four of the engines. The aircraft managed to make it back to the runway, but all six engines had to be replaced.

By the summer of 1965, AV/2, with tail number 20207, had been rolled out and was ready to fly. There would be no AV/3, as the third XB-70 had been cancelled even before the initial flight of AV/1. AV/2 took to the air on 17 July 1965, and began its own series of supersonic flight tests. Tests continued with both XB-70s. On 14 October 1965, AV/1 made a short dash through Mach 3 at 21 kilometers altitude, but lost a small chunk of her outer wing. AV/1 was never flown faster than Mach 2.5 again. There were similar concerns that AV/2 might not be robust enough for Mach 3 flight, either. Flight tests were planned so that the aircraft would be run at Mach 2.8 or Mach 2.9 for an extended time to thermally condition the aircraft for dashes above Mach 3.

Mach 3 flight imposes a severe thermal burden on an aircraft. Heat buildup rises drastically with increases in speed at high Mach, and is far more a limiting factor to high-speed flight than engine power. The XB-70 was an extremely "clean" aircraft, which minimized heat buildup, but the nose and other leading parts of the aircraft did rise to 330 degrees Celsius (625 degrees Fahrenheit), while the rest of the aircraft remained at 232 degrees Celsius (450 degrees Fahrenheit).

Airframe cooling was provided by an ingenious, if somewhat hair-raising, arrangement of the fuel tanks that allowed the fuel to soak up the heat from the airframe. The hot fuel was bled off to the engines, conveniently preheated to improve engine performance. However, as the fuel was bled off, the space evacuated had to be replaced with inert nitrogen gas, since if any appreciable amount of oxygen leaked in the tanks would explode immediately.

In any case, tests continued, with AV/2 pushing the envelope up to and past the Mach 3 mark. It provided data relevant to the supersonic transport (SST) designs then being considered, in particular showing that the sonic booms caused by such an aircraft would be unacceptable over populated areas.

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 Since the two XB-70s were prototypes, and very big and complicated prototypes at that, the test flights often suffered from various system failures. On her 37th flight in March 1966, AV/1 almost came to grief when both hydraulic systems failed and the landing gear didn't deploy correctly. The aircraft managed to make a controlled landing at Edwards, though the landing roll was almost 4.8 kilometers (3 miles) and the aircraft went through a slow 110-degree turn on the ground.

AV/2 got into a similar jam on 30 April 1966, when various systems failed and the nose gear wouldn't go down. Trying two touch-and-go landings on the main gear to pop the nose gear down didn't work, and landing with the nose gear up would be certain disaster.

This left only the option of bailing out and let AV/2 crash, but the aircraft had plenty of fuel, and so the aircraft circled for a few hours at low speed while engineers on the ground tried to figure out what to do. Finally, the engineers suggested that bypassing a circuit breaker in a backup electrical system would do the job. Copilot Joe Cotton improvised a jumper with a paper clip, and the nose gear went down.

Despite the glitches, progress was good. On 19 May 1966, AV/2 flew at Mach 3 for a sustained 33 minutes. By this time, Phase 1 flight tests were nearing completion. Phase 2 would follow, with NASA becoming increasingly involved in the test flights.

Then, on 8 June 1966, AV/2 participated in a photo shoot, flying with four other aircraft powered by General Electric engines so GE photographers could take promotional pictures.

One of the aircraft was an F-104 Starfighter, flown by well-known test pilot Joe Walker. He was positioned off the XB-70's right wingtip when the photo shoot ended. He broke formation, and the turbulence off the big aircraft's wingtips spun the Starfighter around, causing it to collide with the XB-70. The Starfighter tore off both of the XB-70's vertical stabilizers and part of its left wing, then exploded in a fireball. Walker was killed immediately.

Pilot Al White and copilot Carl Cross heard the impact, but everything seemed to be OK for the moment. Then the aircraft went into two slow rolls and broke into a spin. White managed to eject, but Cross went down with the aircraft as it slammed into the ground a few kilometers north of Barstow, California.

Some modifications were made to the surviving AV/1 to eliminate a few of the problems discovered during her test flights, but since AV/1 was redlined to Mach 2.5, she was not a satisfactory replacement for supersonic tests, and the USAF dropped out of the test program after a few more flights. NASA conducted 33 more test flights until 4 February 1969, when AV/1 was flown to Wright Field near Dayton, Ohio and placed in the USAF Museum, where she resides today.

 

 

A Footnote: The F-108 Rapier

 

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The F-108

One of the interesting footnotes to the XB-70 program was that technology developed for the XB-70 was to also be applied to a huge long-range interceptor / escort fighter named the "F-108A Rapier". The F-108 had the sole distinction of being the last fighter project worked on by North American.

The Rapier project was initiated by the USAF in October 1955, originally under the designation of "Long Range Interceptor / Experimental (LIRX)", leading to the award of a contract to North American in June 1957 for two F-108A prototypes. The F-108A would have Mach 3 performance and range adequate to intercept Soviet bombers flying over the North Pole to attack North America, and was also considered as an escort for the B-70. The Air Force hoped to have the F-108A in service by 1963, and contemplated buying hundreds of them.

The F-108A was to be a two-seat aircraft, powered by twin J93 engines and armed with advanced Falcon missiles. It evolved through a number of configurations, converging on a design implemented in a mock-up unveiled in January 1959. The type received the name "Rapier" in May of that year.

As the F-108A was conceived at that time, it looked something like the fuselage of the North American "Vigilante" carrier-based bomber, then in flight test, mated to a high-mounted delta wing with drooping wingtip panels, featuring a single tall vertical tailplane on the end of the fuselage and a smaller vertical tailplane under the middle of each wing.

The crew were to set in tandem seats fitted with ejection capsules for high-speed escape. The Rapier was to be armed with three GAR-9 advanced Falcon long-range air-to-air missiles, directed by the aircraft's powerful AN/ASG-18 radar.

                NORTH AMERICAN F-108A RAPIER                 (ESTIMATED SPECIFICATIONS):
   _____________________   _________________   _______________________

 
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                17.5 meters         57 feet 5 inches
   wing area               173.4 sq_meters     1,865 sq_feet
   length                  27.2 meters         89 feet 2 inches
   height                  6.73 meters         22 feet 1 inch

   empty weight            23,000 kilograms    51,000 pounds
   max loaded weight       46,700 kilograms    103,000 pounds

   maximum speed           3,200 KPH          2,000 MPH / 1,740 KT
   service ceiling         23,000 meters       75,000 feet
   ferry range             4,000 kilometers    2,500 MI / 2,175 NMI

   _____________________   _________________   _______________________

Initial flight of the first prototype was scheduled for the spring of 1961, but the USAF was already having second thoughts. The Soviet nuclear force was moving towards ICBMs, and an expensive dedicated long-range interceptor didn't seem like it was worth the money any more.

The Rapier program was cancelled in September 1959. The GAR-9 (later AIM-47A) missile and the AN/ASG-18 were later used with the Lockheed YF-12A, which was essentially an experimental interceptor version of the famed Lockheed "SR-71 Blackbird" reconnaissance aircraft. The YF-12A never got out of the prototype stage.

 

 

Comments

 

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 I have seen the surviving XB-70 at the USAF Museum at Wright-Patterson AFB. I recollect an old article that said this aircraft cost ten times its weight in gold. With variations in gold prices and the flexibility that can be applied to accounting schemes, this is not exactly a precise statement, but it does give some indication of exactly how much a billion or two dollars amounts to.

I didn't have access to the XB-70's cockpit, but it would likely be startling: a sleek, futuristic aircraft with a dashboard that looked like something out of a steam plant.

The original source for this document was a thorough web page titled "001 -- Flight Of The Valkyrie", by a fellow who calls himself "Thumper", AKA Steve Levin. This site included lots of fine pictures, and even general-layout bluelines. Details for the F-108A Rapier were mostly obtained from a nice web page by aviation enthusiast Joe Baugher.

The materials available on the XB-70 and the Rapier are rather sketchy and sometimes implausible. One of the particularly amusing things I found was that sources on the F-108A give weights and performance specifications from three to even five significant figures, which is a bit rich for a machine that was never actually built, let alone flew.

Formally speaking, it appears that the XB-70 was actually the "XB-70A", but as there never was an "XB-70B", I have stayed with the "XB-70" usage.

Greg Goebel / Public ddomain

 

Manufacturer's Model NA-278/ Weapon System 110A

Adapted and excerpted from Post-World War II Bombers by Marcelle S. Knaack, Office of Air Force History, 1988.   Reproduced with permission of the Office of Air Force History, all rights reserved.

 

Basic Development

 

 

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The XB-70A had its genesis in Boeing Aircraft Corporation's Project MX-2145, in which the contractor conducted studies relating to the type of weapon system required to deliver high-yield special weapons. The contractor, along with the Rand Corporation, considered various types of weapon system carriers. Among them were manned intercontinental bombers, delivering both gravity bombs and pilotless parasite bombers; manned bombers, air-refueled by tankers to extend their ranges and cover round-trip intercontinental distances; manned aircraft and drone bomber combinations; and unmanned bombers. During these studies Air Force Headquarters requested enlargement of the study program to include possible trade-off information; for example, the potential results of trading weight for speed, weight for range, or speed for range.

Boeing presented the requested information on 22 January 1954, pointing out the possibilities of a bomber aircraft powered by chemically augmented nuclear powerplants. For the first time, it appeared feasible to develop a weapon system of a reasonable size possessing the unlimited range characteristics of nuclear propulsion, plus a high-altitude, supersonic dash capability. In March 1954, Boeing presented promising data on a chemically augmented, nuclear-powered aircraft. At the same time, both the Convair Corporation and Lockheed Aircraft Corporation, under contracts with the Office of Aircraft Nuclear Propulsion, submitted similar data.

Developmental Changes

In the fall of 1954, the Air Force Council endorsed two independent but simultaneous development programs, one for a nuclear bomber capable of short bursts of supersonic speed; the other, for a subsonic, chemically powered, conventional bomber.

General Operational Requirement No. 81, issued in March 1955, specifically called for the development of a nuclear-powered weapon system that would be capable of performing a strategic mission of 11,000 nautical miles in radius, of which 1,000 miles were to be traveled at speeds in excess of mach 2, at an altitude of more than 60,000 feet.

The Air Force Council's announcement closely followed the October publication of General Operational Requirement No. 38. The document was brief. It simply called for an intercontinental bombardment weapon (a piloted bomber) that would replace the B-52 and stay in service during the decade beginning in 1965.

 

General Operational Requirements
The Air Force, on 22 March 1955, put out a second general operational requirement, No. 82, which superseded No. 38. Like its predecessor, the new general operational requirement was short. It called for a piloted strategic intercontinental bombardment weapon system that would be capable of carrying a 20,000-pound load of high-yield nuclear weapons, a requirement increased to 25,000 pounds by a September amendment. But the task of defining the Air Force's new project fell to the Air Research and Development Command. The command, therefore, had issued a study requirement, designated No. 22, which identified the Air Force's future new bomber as "Weapon System 110A" and established 1963 as the target date for the first wing of 30 operational vehicles.

Study Requirement 22's performance objectives were mach .9 for cruise speed and "maximum possible" speed during a 1,000-nautical mile penetration. Still, high speed was of less importance than the penetration altitude and radius. A revision of Study Requirement 22 on 15 April stipulated that the new weapon system's cruise speed should not be less than mach .9, unless a lower speed would result in a significant range increase. There were other important changes. Instead of the subsonic requirement covered by General Operational Requirement 38, maximum possible "supersonic" speed within the combat zone was desired. On 11 October, Air Research and Development Command amended the revised Study Requirement 22. The amendment set July 1964 as the target date for the first operational wing of B-70s--so designated in February 1958. The purpose of the delay was to avoid financial and overall weapon system risks, if at all possible.

In 1955, the Air Research and Development Command estimated the weapon system's costs through fiscal year 1962 at $2.5 billion. The estimate covered development, test aircraft, and 30 operational bombers, but assumed that a nuclear bomber would also be developed, that a new engine for the chemically powered bomber would be created, and that the price of certain subsystems, earmarked for the B-70, would be borne by the nuclear aircraft program.

 

Other Requirements
In early 1955, the Air Force released another general operational requirement (No. 96) for an intercontinental reconnaissance system having similar objectives as the previously established bombardment system, known as Weapon System 110A. In July, the Air Research and Development Command issued a study requirement of General Operational Requirement 96 that validated a reconnaissance version of the B-70. The reconnaissance system was identified as Weapon System 110L. The 2 systems were combined soon afterward, becoming in the process Weapon System 110A/L.

 

Program Implementation
In June 1955, the Air Staff directed that development of Weapon System 110A/L be initiated as soon as possible with a multiple, competitive "Phase 1" program. The use of "phase" contracts was not new, having been approved as early as 1944 by the Army Air Forces to facilitate the termination of contracts dealing with highly experimental and, therefore, very uncertain programs. Although six eligible contractors were contacted, only the Boeing Airplane Company and North American Aviation, Incorporated chose to submit proposals.

Contractual Arrangements
On 8 November 1955, the Air Force awarded letter contracts to both Boeing and North American for the Phase I development of Weapon System 110A/L. Boeing's letter contract amounted to $2.6 million; that of North American, to $1.8 million. Each contractor had to furnish a design for the required weapon system; provide models, drawings, specifications, reports, and other data; conduct studies and wind tunnel tests, and construct a mockup. The mockup was to be completed and ready for Air Force inspection within 2 years of the date on which the contractor accepted the contract. Contractor fees could not exceed $450,000.

The two letter contracts became definitive in 1956. The Boeing contract, AF33(600)-31802, signed on 15 March, specified a total estimated cost of $19.9 million; the North American contract, AF33(600)-31801, signed on 16 April, $9.9 million, subject to renegotiation. The Air Force, in its definitive contracts, allotted originally $4.5 million to Boeing and $1.8 million to North American.

 

Military Characteristics
Concurrent with the letter contracts of 1955, the Air Force established specific requirements that were included in the final documents signed in 1956. To begin with, each contract emphasized that the purpose of the entire program was to develop, test, and produce for wing strength by 1963 (much sooner than decided in October 1955) a chemically powered weapon system which, in conjunction with the nuclear-powered bomber, would replace the B/RB-52 as a "first line operational weapon."

With regard to operational characteristics, the new weapon system was to rely primarily on nuclear weapons to accomplish its mission, and the origin and termination of its operations were to be within the limits of the North American continent. The Air Force specified that weapon system 110A/L would have to be capable of performing during the day, at night, and in any kind of weather. A minimum unrefueled radius of 4,000 nautical miles, and a desirable extended radius of 5,500 nautical miles were required, with aerial refueling allowed in the latter case. Finally, the minimum target altitude was to be 60,000 feet, and the contracts reiterated that cruise speed could not be less than mach .9, with maximum supersonic dash speed in the combat zone.

These were exacting characteristics. Studies of conventional aircraft had shown that no such performance could be obtained with proven design techniques. The Air Force acknowledged that the ability to satisfy its demands, particularly the radius-of-action and speed requirements, would depend on the use of high-energy fuels, new engines, new design techniques, and some other break-through in the state-of-the-art by the operational date of 1963. The Air Force also made sure that the contractors knew that while range and speed trade-offs would be acceptable in order to assure maximum supersonic dash at a "practical" gross weight, every reduction would have to be minimal. Finally, the new weapon system's configuration would have to allow for the easy addition of state-of-the-art improved subsystems and components, not initially incorporated.

 

Design Proposals
Naturally enough, the preliminary design proposals submitted in mid-1956 by Boeing and North American were quite different. Boeing utilized a conventional swept-wing configuration; North American, a canard-type, resembling a scaled-up Navaho missile. The North American SM-64A Navaho (System 104A) was a vertically launched, air-breathing, intercontinental surface-to-surface, delta-wing missile, with a length of 87 feet and a diameter of 6.5 feet. Production was canceled in July 1957 because of budgetary and technical problems. The Navaho development cost over $600 million, but the work expended on the canceled program was not a loss and benefited other projects significantly.

Still, in order to attempt meeting the payload requirements and ranges stipulated in the spring of the year, the contractors had incorporated similar features in their respective designs. The aircraft envisioned by both would weigh some 750,000 pounds and require the use of cumbersome floating wing panels. These panels would carry fuel for the outgoing trip and be jettisoned when empty. Maximum speed might then exceed mach 2 by a significant margin.

The Boeing and North American preliminary designs had another common factor: both were unsatisfactory. The gross weights were excessive. The proposed fuel devices, whether fuel panels or straight floating wing tips, while promising to extend the aircraft's subsonic range, seemed impractical. To begin with, the enormous expendable panels (or non-folding floating wing tips) would create logistical problems and runway difficulties because of the total width of any airplane so equipped. In September, a disappointed Air Staff recommended that both contractors "return to the drawing board." And money being short, a more drastic decision followed that nearly spelled the program's cancellation. On 18 October, the Air Force discontinued the weapon system's Phase I development. Boeing and North American were allowed to resume their studies, but solely on a reduced research and development basis.

Concerned that the contractors might construe their contract's reorientation as resulting from lack of funds--an interpretation not far from the truth--and would merely mark time while refining their current designs, the Air Force promptly minimized the impact of its October decision. First, new work statements were issued, underscoring the necessity of achieving acceptable, but less exacting, performance characteristics. Then on 20 December, the Air Force sent identical letters to the presidents of Boeing and North American asking that every possible means be explored to improve the aircraft's range "through complete redesign if necessary"

 

Selecting A Contractor

After the delay induced by the rejected proposals, events moved swiftly. By March 1957, it seemed almost certain that the new weapon system could be an all-supersonic cruise air vehicle as opposed to a "split-mission" (subsonic cruise-supersonic dash) aircraft. Theoretical research on the "supersonic wedge principle" conducted by the National Advisory Committee for Aeronautics in 1956, actually had much to do with the graduation to an all-supersonic flight pattern. In other words, aircraft designers had discovered that, if the entire design (especially engines, air induction system, and airframe) was geared for a single flight condition such as mach 3, the range of the supersonic system would compare favorably with that of a subsonic vehicle. Both contractors had also concluded independently that, as suggested by the Air Force, high-energy fuel would be needed and that its use should be extended to the engine afterburner.

In mid-1957, believing their re-oriented contractual commitments had been fulfilled, Boeing and North American asked for an early competitive selection of one contractor over the other. Dual contracting and dual funding made extra work and was costly. Moreover, the Air Research and Development Command was convinced that state-of-the-art advances had been fully exploited by both contractors. Further study of the project would mean more delay and be self-defeating. Hence, the tempo of activities quickened. On 30 August, the Air Force directed a 45-day competitive design period, ending with the onsite inspection of each contractor's facilities. On 18 September, the Air Force gave Boeing and North American the new system characteristics established for the competition. These characteristics called for a speed of mach 3 to mach 3.2, a target altitude of 70,000 to 75,000 feet, a range of 6,100 to 10,500 miles, and a gross weight between 475,000 and 490,000 pounds. Meanwhile, a source selection evaluation group had been organized. It comprised three teams: representatives from the Air Research and Development Command, the Air Materiel Command, and, for the first time, a using command--the Strategic Air Command, in this case. The evaluation group, numbering about 60 members, reviewed the North American proposal during the last week of October; that of Boeing, during the first week of November.49 The 3-team evaluations were presented to the Air Force Council on 15 December. The North American proposal was found unanimously to be substantially superior to that of Boeing. The Air Force formally announced North American's selection on 23 December.

 

New Planning

As winner of the 1957 competition, North American on 24 January 1958 signed contract AF33(600)-36599. Strictly speaking, this document again covered only the new weapon system's Phase I development. Just the same, availability of the first operational wing (30 planes and 15 test vehicles) was already planned for late 1965. In February 1958, believing that by late 1965 or thereabouts, when the RB-70 would become operational, other systems could better satisfy the reconnaissance requirements, the Air Force canceled the development of Weapon System 110L (part of WS 110A since 1956).

While the reconnaissance requirement was being deleted, an 18-month acceleration of the B-70 program was planned. This change, endorsed by the Air Research and Development Command and Air Materiel Command, scheduled the aircraft's first flight for December 1961 and formation of the first operational wing for August 1964. No performance decrease would result, and the increase in costs would not exceed $165 million. The Air Staff approved the accelerated plan in principle on 19 March 1958. In the same month, a revised general operational requirement was issued, updating such matters as the speed specification. In April, a preliminary operational concept was published.

In the fall of 1958, the Air Force's apparent optimism had a severe jolt. Gen. Thomas D. White, Air Force Chief of Staff since August 1957, announced that the B-70 program's planned acceleration was no longer viable because of funding limitations. A first flight, therefore, should not be expected before January 1962; an operational wing, in August 1965, at the earliest. This reversal damaged the program, particularly the weapon system's components. General White wanted more judicious use of currently available equipment and flight test inventory. He further wished to reduce the overall complexity of the bombing-navigation and missile guidance subsystems. Of greater import, and a harbinger that worse might yet come, General White also told his staff that the Eisenhower Administration believed that no large sums of money should be committed to the program before the B-70 prototype had proven itself. General White's words reflected the Administration's determination to hold military expenditures for radically new or unproven weapon systems to a minimum, while taking advantage of technological advances. Deployment of the free world's first long-range ballistic missiles, and accelerating the operational readiness of additional weapons systems of this type, which appeared more cost-effective and less speculative, fell under the purview of such a philosophy.

Mockup Inspection
A development engineering inspection and mockup review were conducted at North American's Inglewood plant on 2 and 30 March 1959, respectively. The mockup review differed from the inspection in that it was styled to present the operational characteristics and suitability of the weapon system's configuration, rather than to introduce detailed system analysis and theory. On both occasions, the Air Force requested a great many changes, some of which were considered of primary importance. Nevertheless, almost 95 percent of the work generated by the requested alterations was accomplished before the end of the year.

New Setbacks

Decisions made in the second half of 1959 hampered Air Force aircraft development efforts, placing additional pressure on the B-70 program. The nuclear-powered bomber, after overshadowing the chemically powered aircraft for years, began to suffer from financial malnutrition in 1956. By mid-1959, decisions at the highest executive level had put the program into almost total eclipse. The project's downfall was bound to impede the B-70 program since the cost of several B-70 subsystems were to be borne by the nuclear-powered bomber -- officially canceled by the Kennedy Administration in March 1961.

On 11 August, the Department of Defense canceled the high-energy fuel program. The use of this fuel had been counted on to extend the B-70's range substantially over its required radius. As it turned out, the high-energy fuel program cancellation had a lesser impact than anticipated because other jet fuels, JP-6 especially, were greatly improved. Just the same, as planning stood in mid-1959, elimination of the high-energy fuel program required additional configuration changes and, more specifically, a new engine for the B-70.

Termination on 24 September of the North American F-108 Rapier, a never-flown long-range interceptor under letter contract since 1957, was another blow. The B-70 program was directly affected. It would now be compelled to finance, at least partially, such development items as engines, escape capsules, and fuel systems that had been common to both aircraft systems and previously covered by F-108 funds. The loss was expected to boost B-70 program costs by at least $180 million.

Near Cancellation
General White's words of caution notwithstanding, more than 15 major subcontracts were let during the early part of 1959. In the ensuing months, after the high-energy fuel program and F-108 project were given up, money became increasingly scarce, and most B-70 activities were slowed down. But the program's new predicament was only a beginning.

In November 1959, during a meeting concerning the military programs of the coming year; President Eisenhower told the Air Force Chief of Staff that the "B-70 left him cold in terms of making military sense." General White conceded there were important questions involved and that the aircraft was very different from anything previously developed. He said the B-70 must overcome the terrific heat generated by high speed and high altitude and that the shape of the aircraft's wings and fuselage must be studied. However, to eliminate such unconventional aircraft would be going too fast and too far. Hardly impressed with the many pro-B-70 arguments put forth, the President stressed that the B-70, if allowed to reach production, would not be available for 8 or 10 years, when the major strategic retaliatory weapon would be the missile. The President finally agreed to take another look at the B-70 proposition, but in the same breath pointed out that speaking of bombers in the missile age was like talking about bows and arrows in the era of gunpowder.

The Air Force announced on 29 December that the B-70 program was reoriented to produce a prototype vehicle only and that the development of most sub-systems was canceled. The program's near demise was generally attributed to the Administration's budget.

Program Re-endorsement
The politics of the 1960 presidential campaign kindled the interest of both parties in the B-70. Thus, with the approval of the Defense Department, the Air Force in August 1960 directed that the XB-70 prototype program once again be changed to a development and test program. Twelve B-70 prototypes were added, and the program was designed to demonstrate the bomber's combat capability. This directive, coupled with a congressional appropriation of $265 million for fiscal year 1961, restored the B-70 to the status of a weapon system headed for production.

In September, North American was instructed to proceed with the design, development, fabrication, and testing of a number of YB-70s. Also, development of the major systems for an operational mach 3 bomber had to be ensured, which meant that many of the recently canceled subcontracts (let by the prime contractors early in 1959) had to be reopened. This exercise might be time-consuming as well as difficult, since some of the subcontractors might now be involved in other work. Even so, by mid-October the defensive subsystem contract with Westinghouse Electric Corporation had been reinstated. In November, North American reactivated the contract with Motorola, Incorporated for the mission and traffic control system of the B-70. In the same month, development of the B-70's bombing and navigation system, under the auspices of the International Business Machines Corporation and significantly reduced since the summer of 1959, regained the impetus normally afforded a system intended for production. Still, the B-70 programs recaptured importance was to be short-lived.

Definite Cancellation

Once in office, it did not take long for President John F. Kennedy to take a critical look at the B-70 program. Like his predecessor, President Kennedy obviously doubted the aircraft's reason for being from the standpoint of future operations. On 28 March 1961, he recommended that the program be continued in order to explore the problems of flying at three times the speed of sound in an aircraft "potentially" useful as a bomber.

President Kennedy's recommendations were part of his special message on the Defense budget, as submitted to Congress on 28 March. The President emphasized the importance of accelerating long-range missile programs and of increasing the armed forces' capability to handle limited wars.

This, President Kennedy underscored, should require only the development of a small number of YB-70s and bombing and navigation systems. No more than $220 millions should be needed in fiscal year 1963, and the program's total cost should not exceed $1.3 billion.

President Kennedy's words gave the Air Force no choice but to redirect the B-70 program from full weapon systems status to that of a mere prototype aircraft development. Since the aircraft's eventual production appeared now most unlikely, the Air Force immediately began to consider various alternatives to the defunct B-70. In May 1961, there was talk of an improved B-58, armed with both bombs and air-launched missiles; of a specially designer, long-endurance, missile-launching aircraft; of transport planes modified to launch ballistic missiles; of the nuclear-powered aircraft, and again of a reconnaissance B-70, which would also be capable of striking the enemy.

The Air Force's persistent search for a new manned bomber seemed unrealistic. On 25 May 1961, in an address to a joint session of the Congress, the President proposed to reinforce further the military establishment's capabilities in limited warfare and to expand substantially the Defense programs related to the newly accelerated national space effort. These specific goals clearly indicated that production of a costly new aircraft was excluded from President Kennedy's foreseeable planning.

In August, the U.S. Senate attempted once more to rescue the B-70 and asked that a production program be outlined for the purpose of introducing the aircraft into the operational inventory at the earliest possible date. Undaunted, Secretary of Defense Robert S. McNamara expressed his thorough dissatisfaction with North American Aviation's handling of the B-70 development.

The year 1962 did not resolve the B-70 predicament. The President insisted that only $171 million of FY 63 funds ($49 million less than proposed in 1961) be spent on the prototype program, instead of the $491 million requested by the Air Force and previously approved by Congress. In March, Congress indicated that the Air Force should use the $491 million for planning and procurement of a reconnaissance and strike B-70 (RSB-70), but later in the month reduced the amount to $362.6 million. In April, a group headed by Gen. Bernard A. Schriever, Commander of the Air Force Systems Command, developed several approaches to the proposed RSB-70 system. The development plan preferred by the group would cost $1.6 billion and it programmed the RSB-70's first flight within little more than two years. In June, this plan and others were disapproved by the Department of Defense. Nevertheless, on 23 November the President authorized the addition of $50 million to the currently approved $1.3 billion B-70 development program. The extra money was intended for the development of highly experimental sensor components, a requirement if the RSB-70 (as unlikely as it was), or any similar new weapons system should be considered later.

 

Technical Problems
As explained to members of the Congress in January 1960 by Thomas S. Gates, Secretary of Defense during the last two years of the Eisenhower Administration, the B-70 program was hampered from the start by technical problems stemming from the "use of metal and components . . . still in the research stage." By 1962, although much progress had been made, severe problems remained. North American was still working on an automatic air induction control system for regulating the flow of air to the J93-3 jet engines, originally designed to power the canceled F-108 and, following the end of the high-energy fuel program, immediately earmarked for the B-70.

The secondary power generating subsystem, due to provide current to the pump that maintained hydraulic pressure, also was unsatisfactory. Excessive vibration caused failures in the generator gear boxes, and the hydraulic pumps frequently broke down. Braces were added to steady the gear boxes, but the pumps had to be rebuilt with metals capable of withstanding the intense heat of supersonic operations as well as the extreme pressure generated within the hydraulic lines.

At the close of 1962, other serious problems still prevented completion of the first air vehicle, accounting for North American's continual revision of the XB-70's delivery schedule. Defective stainless steel honeycomb panels necessitated an unanticipated number of repairs. The panels of the air ducting system bay and the fuel tank areas had numerous examples of such defects. A nickel-plating process was sufficient to eliminate most imperfections, but repairs on the fuel tank areas had to be airtight to prevent the escape of nitrogen gas. In December, North American was considering giving up the use of polyimide varnish in favor of vitron sealant. Another significant problem was that the wings did not fit properly to the wing stubs. Special adapters had been developed and were being manufactured, but again this took time and money.

 

Other Difficulties
In 1963 and 1964 frustrations with the B-70 increased. Almost 40 of the $50 million approved for the development of sensor components was diverted to the experimental bomber to allow continuation of the three-plane program. In June 1963, the Air Force converted the XB-70 contract from the cost-plus-fixed-fee to the cost-plus-incentive-fee type. But no spectacular progress ensued. In September, North American suggested further delivery revisions. The first aircraft, North American said, would be completed in April 1964--four months past the latest deadline assigned by the Air Force. In October, continued technical problems and rising expenses prompted the Air Force to request that the cost of a two-vehicle program be defined. On 7 January 1964, Gen. Curtis E. LeMay, Air Force Chief of Staff since 30 June 1961, although a strong supporter of the B-70, endorsed the Air Force Council's recommendation favoring the one-vehicle reduction. The decision was dictated by the compelling need to avoid exceeding the program's approved total cost of $1.5 billion. The decision also practically closed the case of the two-XB-70 program and definitely prevented the start of RSB-70 development.

 

 

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