XB-70 VALKYRIE gallery 1

It all began in October 1954, when General Curtis E. Lemay, a former bomber pilot during WWII, and commander in chief of the USAF Strategic Air Command (SAC) since 1948, requested that a new jet-powered bomber be developed that was in service during the period 1965-75. The General hoped that the new bomber would replace the B-52 Stratofortress and B-58 Hustler…..which were not even in service yet!. General Lemay hoped that the new bomber could carry 25 tons of weapons 11,000 km away at the highest possible speed. For this, a type of mission was specified in which the plane would fly at a cruise speed of Mach 0.9 up to about 1,000 nautical miles from its target, and then perform a “dash” at maximum altitude and speed, (21,000 meters and Mach 2 plus ) to return to its base later at the cruising speed of Mach 0.9. Everything could be summed up in the phrase “subsonic cruise – supersonic dash”.
In February 1955 the USAF submitted its WS-110A/WS-125A requirements to manufacturers, hoping that the new bomber would be ready by 1963. The WS-110A proposal was for an aircraft equipped with conventional jet engines, while The WS-125A was for an aircraft equipped with nuclear reactors as engines. In mid-July 1955, Boeing, Convair, Douglas, Lockheed, Martin and North American were awarded contracts to study a bomber and an intercontinental photographic reconnaissance aircraft under the designation WS-110A/L. For the WS-125A project, only Convair and Lockheed were designated as developers. In November 1955 there were only two competitors left for the WS-110A/L project, Boeing and North American Aviation, which in December 1955 began work to carry out their proposals, which were to end with the manufacture of a full-size model. Likewise, the race to develop the engines for the new bomber began among the main manufacturers, such as Pratt & Whitney, General Electric and Rolls Royce among others.
(XB-70A-1 image). In October 1956 Boeing and North American presented their two initial proposals for a new bomber, since the photo reconnaissance aircraft was canceled after the arrival of the Lockheed U-2 aircraft. In January 1957, a key event occurred in the development of the WS-110A/L project, and it was the chance discovery of an article in a scientific journal. A North American engineer found a publication by two NASA engineers explaining a phenomenon called “Compression Lift” that occurred during flight at supersonic speeds at high altitude. In the paper, NASA engineers explained how the shock waves generated by an aircraft in supersonic flight could be used to produce additional lift. This discovery occurred in 1954 while one of them was mowing the lawn, and it would turn out to be correct. In March 1957 Lemay returned the two proposals and urged both companies to carry out new designs. Apparently, the proposals were very far from what the General had in mind.
(XB-70A-1 image). The second proposal from both companies contemplated the use of six jet engines that used a fuel called “boron” that improved speed and range. These bombers were known as chemically-powered bombers or CPBs, and North American applied the “Compression Lift” concept to its design. These new proposals were well received by the USAF and had innovative technological advances. The Boeing aircraft (Model 804) had retractable canard foreplanes, a delta-winged design and six underwing GE X279E turbo-ramjet engines. North American’s proposal (WS-110A CPB) was also delta-winged, but these wings were equipped with variable geometry tips that remained lowered during subsonic flight and were raised during supersonic flight to improve stability and lift. This novelty was the practical application of the “Compression Lift” concept. In addition, the aircraft carried six GE J-93-GE-5 jet engines located side by side in a rectangular space placed under the fuselage and between the wings.
(XB-70A mock up image). In August 1957, both proposals were evaluated by the USAF and on December 23 of this same year, the winner was announced, which turned out to be the North American Aviation proposal. On January 2, 1958, it was agreed that North American must manufacture a full-scale mock-up of its proposed “Model NA-259” and was declared the main contractor for the entire WS-110A program except for the engines, which were ordered exclusively to General Electric. Likewise, the “WS-125A nuclear-powered bomber” project was canceled. Following these decisions, the USAF advanced the entire WS-110A program so that the first flight would take place during December 1961, the delivery of the first aircraft would be in December 1963 and the first 12 bombers would be ready for combat in August 1964.
(XB-70A-1 image). On February 6, 1958, the new bomber was officially born under the official designation “XB-70“. In April 1958 some design changes were made to increase the overall weight and payload. In May 1958 North American subcontracted the manufacturing of various systems and elements. The AiResearch company would be in charge of the air data computing system, Autonetics of the navigation system, IBM of the stellar-inertial bombing-navigation system, General Electric of the “unjammable” radar…and so on until reaching the figure of 2,000 sub-contractors! In addition, the Strategic Air Command organized a contest to give the new bomber an official name, and after more than 20,000 proposals, “Valkyrie” was chosen. From July 3, 1958 the new aircraft would be officially known as “XB-70 Valkyrie“.
(XB-70A-1 image). During the summer of 1958 GE was testing its YJ-93-GE-5 boron burner engine installed under the fuselage of a Convair B-58A Hustler bomber. During the tests, speeds exceeding Mach 2 were achieved. In March 1959, more than 200 USAF engineers inspected the XB-70 model in detail and in April more than 750 design changes were suggested. In August 1959, the installation of the very expensive GE boron-fed engines was canceled and it was decided to use, in their place, a version of the same engines powered by JP-6 called YJ-93-GE-3. These engines shortened the range of the XB-70 by 10%, but this deficiency was resolved by performing a single in-flight refueling.
(XB-70A-1 image). Work continued at a good pace, but at the end of December 1959 the Eisenhower Administration decided to reduce costs and canceled the B-70 (XB-70) program based on the preeminence and effectiveness of ICBM missiles. A huge debate then arose about whether or not it would be useful to pay for an expensive fleet of manned bombers when missiles could do a similar job for a fraction of the cost. Defenders of manned aircraft argued that once the missiles were launched, there was no turning back, however the bombers could always abort their mission if an agreement was reached, thus avoiding starting a nuclear war. Finally, in July 1960, Congress approved a new spending item for 1961 and allowed two prototypes of the B-70 bomber to be completed (62-0001 and 62-0207) and up to 12 aircraft to be purchased. Until this moment, 1.2 billion dollars had been invested in the program.
(XB-70A-2 image). In July 1961 the expenditure item for the XB-70 was reduced by 80% and despite attempts to raise more funds through different alternatives, such as expanding the range of missions to save the program, the XB-70 seemed hurt of death at this time. General Electric continued to develop the engine and by July 1963 had achieved excellent results, conducting thousands of hours of bench tests, more than 500 of them at Mach 2. In addition, the afterburning thrust was 33,000 pounds (14,950 kg), only 3% less than that achieved with the boron-powered engine. In March 1964, the B-70 program was reduced to the manufacture of only 2 prototypes, and it seemed that both were only going to serve as test beds for the “American SST (super sonic transport) program”.
Finally, on May 11, 1964, the XB-70A-1 Valkyrie (on the image) was seen for the first time under the light of the Californian sun. The vision was truly spectacular and amazed everyone present. There was no doubt that the aircraft was extraordinarily beautiful and its design was light years away from any previously manufactured aircraft. Even today, 60 years after its manufacture, the Valkyrie continues to look futuristic and its lines continue to be at the forefront of aviation design and dazzle any aviation enthusiast. It is probably the most beautiful aircraft ever designed. The second prototype, XB-70A-2, rolled out on May 29, 1965 and benefited from some technical improvements as well as the absence of minor problems discovered during testing of the first prototype.
(XB-70A-2 image). The XB-70 Valkyrie represented an enormous technical and technological challenge from the beginning. It was necessary to mix in the same aircraft the speed of a fighter, the capacity of a tanker and the range of a bomber, which was not an easy task at all. North American Aviation engineers had to deploy all their knowledge and skills to achieve the requirements established by the USAF, because due to the intended performances and the materials used, there was no applicable previous data and everything had to be done practically from scratch. For example, they included canard foreplanes to counteract trim at supersonic speed and to reduce landing speed. They also installed folding wingtips that were used during flight and lowered to about 65º to increase lift by 5% thanks to the shock waves caused by them at supersonic speeds. But it wasn’t just these innovations, there were many many more.
The windshield was retracted during subsonic flight to improve the pilot’s visibility and extended during supersonic flight to improve aerodynamics and avoid high-drag shock waves produced at those high speeds. The incorporation of an intake splitter duct under the wings and fuselage was what allowed the aircraft to create the compression lift effect. Thanks to this intake, the free flow air stream was slowed from Mach 3 to Mach 2.3, which created an area of static pressure in front of the shock wave. In this way, the airflow over the wings continued at Mach 3 and the aircraft was boosted up. This effect was achieved by North American engineers after more than 10,000 hours of wind tunnel testing with scale models at speeds up to Mach 3.5.
To achieve the range established by the USAF, the aerodynamics had to be carefully studied and the engineers had to improve the lift to drag relationship of the aircraft until it was double that obtained for any other aircraft for flights at supersonic speeds. Furthermore, this had to be done taking into account the angle of attack at all times. During flight at supersonic speed, 30% of the weight was compensated by the compression lift effect, which greatly improved its consumption. It can be said that thanks to its careful design, the Valkyrie “surfed” on the crest of the shock wave generated at supersonic speed.
In addition to aerodynamics, in the construction of the XB-70 all the metallurgical techniques of the time were improved and new ones had to be created. Due to the very high temperatures produced during flights at Mach 3, a multitude of alloys and new materials had to be used in the manufacture of the fuselage, as well as welding and sealing techniques had to be improved. Three different types of titanium alloys were used which made up about 10% of the weight of the aircraft. Many parts of the aircraft were made of titanium alloy that was covered with a steel skin capable of resisting temperatures ranging from 205 to 540º C.
(XB-70A-2 image). The maximum speed for which the XB-70 was designed was Mach 3 (3,675 km/h), although the materials could have withstood flights up to Mach 4 (4,900 km/h). To achieve this objective, the XB-70 was manufactured with brazed stainless steel honeycomb sandwich panels in many areas of its structure. About 2,024 m2 of these panels were installed, which represented 10 tons of the total weight of the aircraft. Although these panels were insulating, strong and lightweight, they were prone to becoming loose the external steel skin during supersonic flights. In the first prototype (XB-70A-1) it was too common for the plane to return to base with tears and losses of these panels that sometimes caused serious damage to the engines.
(XB-70A-1 image). The problem with the brazed stainless steel honeycomb sandwich panels occurred mainly due to the thermal expansion produced by high temperatures. This caused the steel skin to crack and the high air flow ended up tearing off the panel. Careless assembly of these panels aggravated the problem, so in the second prototype (XB-70A-2) the quality control during its manufacturing was much stricter and almost completely avoided this damage. The use of a heat-resistant silicone paste called “red thunder”, used to smooth some surfaces of the aircraft, also helped solve the problem.
(XB-70A-1 image). North American Aviation created a multitude of machines and methods to weld the thousands of parts that made up the Valkyrie and that would greatly facilitate future production. But there were big problems to solve, for example with fuel tanks. The JP-6 fuel had to be mixed with nitrogen inside the fuel tank to avoid auto-ignition at high temperatures, so the fuel tanks had to be gas-tight. The problem was that the nitrogen leaked out through the sealing joints of the tubes and cables that passed through the fuel tanks, which forced the delay of the first flight of the first XB-70. After a year and a half of fuel tank leaks, it was discovered that a substance called “Viton B” could be the solution. Sometimes it was necessary to apply up to 10 layers of this substance in the leak areas and each layer had to be heated for 6 hours applying 180º heat. In this way the problem was finally solved.
(XB-70A-1 image). The Valkyrie has a delta-type wing with folding tips, a long slender forward fuselage with two canard foreplanes, a central fuselage arranged between the wings and a rear body that houses the engines and the twin vertical tails. The main alloys and materials used in the manufacture of the Valkyrie are steels type AM-355, H-11, PH15-7M and 17-4PH steels, titanium alloys type 4A1-3Mo-1V and 6A1-4V, polyester fiber glass (vibran) for the nose radome and shell-type titanium for the movable windshield ramp. Of course, these materials make up different pieces and parts distributed throughout the aircraft and often some parts were made up of various pieces made of different materials combined.
(XB-70A-1 image). The XB-70 aircraft was cooled using a method invented by North American called “transpiration wall” that cooled the crew cabin walls through a water circulation system. In addition, it had an environmental control system that was responsible for pressurizing and maintaining a temperature in the cockpit and electronics bay of between 21 and 26ºC, thus preventing the crew from having to carry heavy and cumbersome oxygen systems. This system consisted of two subsystems that used Freon gas and operated in parallel with the transpiration wall, maintaining a continuous air loop. In case of sudden decompression, the system had an emergency system that injected air from outside into the internal circuit to repressurize the cabin.
(XB-70A-2 image). The Valkyrie also had a capsule type ejection seat system for emergency escape. These capsules were spherical in shape and surrounded the seat, having clamshell-type upper and lower doors, so that they closed when the ejection system was activated. Once closed, they were automatically pressurized with an atmospheric pressure similar to that at 2,700 meters of altitude. These capsules were ejected from the cabin using a rocket system and could be used between 0 and 26,000 meters altitude. In case of sudden decompression, they could be activated until pressurization was restored. The capsules had controls that allowed the pilot to operate the aircraft to a lower altitude. Once restored, the capsule doors retracted so the pilot could take full control again. These capsules floated, they carried warm clothing, water and food for several days and an inflatable raft along with some survival utensils.
The cabin of the XB-70 was quite spacious and full of panels and navigation and control elements. A color code was introduced in the displays and instruments to make the crew’s work as easy as possible. In addition, the lighting of the instrument panels was changed from the usual red light to white light, which greatly improved visibility. The flight control system was operated by a complex hydraulic fluid system. This system had to be specially studied, since the usual fluids could not be used due to the extreme temperatures reached during the flight. The system featured 12 engine-driven variable output hydraulic pumps, 44 hydraulic motors, 50 mechanical valves and 400 electrically operated solenoid valves. The system contained 830 liters of fluid at room temperature, which became 980 liters when operated at maximum temperature.
The XB-70 was powered by 6 General Electric YJ93-GE-3 (on the image) afterburning turbojet engines with 14,950 kg of thrust each. They measured 6.02 meters long by 1.06 meters wide (air inlet) by 1.33 meters high (deep) and burned JP-6 fuel. These engines produced around 200,000 hp at Mach 3, although they were prepared for speeds of Mach 4. They were very reliable, as was demonstrated on May 19, 1966, when the second prototype (XB-70A-2) made a flight of 32 minutes at Mach 3. The engines were interchangeable with each other and could be easily assembled and disassembled in about 25 minutes thanks to a plug-in system. This engine had two-stage turbines and the blades were cooled by an air system that allowed them to operate at temperatures several hundred degrees higher than conventional ones.
(XB-70A-1 image). This aircraft was equipped with a variable geometry Air Induction Control System (AICS) that reduced the speed of the air reaching the engines. This system slowed the air that reached the inlet at a speed of Mach 3 up to Mach 0.5. The reduction was carried out through several mobile panels installed in the inlet duct. These were moved by hydraulic actuators that provided a correct air flow to the engines. The system consisted of 3 positions that were selected by the pilot. Initially the XB-70A-1 had a manually operated AICS, while the XB-70A-2 had a computerized one, but the XB-70A-1 received a computerized one before beginning test flights.
(XB-70A-1 image). The XB-70 carried about 178,000 liters of JP-6 fuel that weighed about 136 tons, which represented 60% of the maximum takeoff weight. The XB-70A-1 had 11 fuel tanks, of which only 10 were used due to sealing problems in the one installed in the rear part of the fuselage. The XB-70A-2 also had 11 tanks, which it could use without problems thanks to the technical improvements applied during its manufacturing. There were 5 tanks installed in the fuselage and 3 in each wing that had two transfer pumps each. The engines were fed from tank number 3, which was above the center of gravity of the aircraft. This tank was used as a kind of distributor, in such a way that fuel from other tanks was automatically transferred to tank 3. In this way, the weight of the aircraft was always well leveled and stability problems during flight were avoided.
The Valkyrie was a pretty thirsty bird and consumed about 355 kg of fuel per minute at cruising speed. Regarding fuel, it is said that it took around an hour and a half to fill its tanks due to the complexity of the operation. JP-6 fuel was pumped from one tanker truck to another empty tanker while it was pressurized with dry nitrogen. In this way, while the fuel entered this second tanker, the oxygen contained in the JP-6 was expelled by the nitrogen gases. In this way, an attempt was made to make the fuel as inert as possible, and the absence of oxygen prevented a possible explosion caused by the degradation of the fuel and the increase in its temperature inside the fuel tanks as the amount of JP-6 decreased. In addition, the aircraft could be refueled in flight through a receptacle installed in front of the windshield ramp.

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