| The XB-70 Valkyrie, Almost the Worlds First Nuclear Aircraft |
In the late 1940s, as the Cold War began to heat-up, the Soviet Union began research into the development of nuclear reactors as power sources to drive warships. The work was performed at first by an academic Russian engineer, I.V. Kurchatov, which added aviation as a possible recipient of the new nuclear power plants. On August 12th, 1955 the Council of Ministers of the USSR issued a Mandate which ordered certain groups within the aviation industry to join forces in this research. As a direct result of the Mandate, the design bureaus of Andrei Tupolev and Vladimir Myasishchev became the appointed chief design teams on a project to develop and produce several aircraft designs intended to be powered by nuclear propulsion while a bureau headed by N.D. Kuznetsov and A.M. Lyulka, were assigned to develop the engines for the aircraft.
They promptly decided on an energy transfer method: Direct Cycle. This method will enable the engines to use the energy supplied by the reactor, replacing the combustion chamber power supply that the jet engine utilizes. Several types of nuclear powered engines were tested: ramjet, turboprop and turbojet, with different transfer mechanisms for transmitting nuclear generated thermal energy across each one of them. After extensive experimentation with various engines and transfer systems, Soviet engineers concluded that the direct cycle turbojet engine offered the best alternative.
In the direct cycle power transfer configuration, the incoming air entered through the compressor mechanism of the turbojet engine, then, passed through a plenum that directed the air to the reactor core. Then the air, by this time acting as the reactor coolant additive, was constantly heated as it moved through the core. After exiting the core, the air went back to another plenum and from there was directed to the turbine section of the engines for thrust production. New coolant systems were also tested, as it was the protective shielding for the crew cabin. This and the size of the initial nuclear power plants were the main problem facing engineers working on the project. Shielding the crew and reducing the size and weight of the reactors in order to fit one on an airframe became the main technical hurdle in the project.
The Tupolev bureau, knowing the complexity of the task assigned to them, estimated that it would be two decades before the programme could produce a working prototype. They assumed that the first operational nuclear-assisted airplane could take to the air in the late 1970s or early 1980s. The programme was designed to operate in development phases. The first phase was designing and testing a small nuclear reactor, which properly began in late 1955. On March 1956, the Tupolev bureau was assigned by the Council of Ministers of the USSR the task of producing a flying test-bed plane as soon as possible. The Tupolev engineers decided to take an existing Tu-95M bomber and use it as a nuclear flying laboratory, the plane’s eventual designation was to be Tu-95LAL. By 1958, the ground phase of the programme, the rig used to install the nuclear reactor on the aircraft, was ready for testing. Some time during the summer of 1958, the nuclear power plant was turned on and testing commenced. Immediately, the required level of reactor power was achieved, thus opening the path for the flight test phase. Between May and August 1961, the Tu-95LAL completed 34 research flights.
Much of them made with the reactor shut down. The main purpose of the flight phase was examining the effectiveness of the radiation shielding which was one of the main concerns for the engineers. The massive amount of liquid sodium, beryllium oxide, cadmium, paraffin wax and steel plates; were the sole source of protection for the crew against the deadly radiation emerging from the core. The results were once again promising. Radiation levels were low in the crew cabin, paving the way for the bureau to design a new airframe. The next phase in the programme was to produce a test aircraft designed from the beginning to use nuclear power as its main propulsion force. This was to be the Aircraft 119. This aircraft was based on the Tu-95 design. The major distinction was that two of its four engines, inboard, were to be the new NK14a turboprops with heat exchangers. The NK14a operated in a very similar way to the direct cycle engines, the main difference being that the air, after passing through the compressor, did not go to the reactor, but directly to the heat exchange system. At the same time, the heat generated by the reactor, carried in the form of fluid; went to the heat exchange system. The combination of these two forces would enable the turbojet to produce the required amount of thrust. The other two outboard engines would remain NK12Ms.
The NK Kuznetsov Design Bureau commenced work on the engines at the same time that the schematics of Aircraft 119 were drawn. As in the Tu-95LAL, the internal bomb bay would house the reactor. The connections leading from the reactor to the engines would run through the main fuselage, up to the wings and then directly to the heat exchangers attached to the two inboard engines. Tupolev estimated that the first 119s were to be available for runway trials by late 1965. After trials, the 119’s engines were to be replaced by a four NK14a engine configurations based on the Tu-114 commercial liner. However, the 119 never made it off the drawing board. Budgetary constraints and the development of new conventional aircraft designs were cited as the main reason for the cancellation of the programme in August 1966. The cancellation of Aircraft 119 did not mean that the Soviet Union terminated its research into a nuclear powered aircraft. Several attempts were made in designing a nuclear-powered, supersonic bomber. Around the same time that Tupolev began working on the 119, there was a parallel program code named Aircraft 120.
A vast amount of research was invested on this project. Mainly on the design of a new turbojet engine and the layout of a new nuclear reactor system that would have been able to offer more protection to the crew and the aircraft sensitive avionics systems. Aircraft 120 was to be fitted with two turbojet engines based on the development by Kuznetsov. The reactor was to be installed near the rear part of the plane, as far from the cabin as possible. The crew consisted of the pilot, co-pilot, and navigator; enclosed in a heavy lead radiation shielding cabin. The 120 would have a conventional aerodynamics configuration with a high mounted 45 degrees swept wing, a swept empennage and a tricycle landing gear. Tupolev’s goal of reaching the testing phase for the 120 in the late 1970s never materialized, as with the 119, the 120 existence was only on the drawing board. Termination of the programme was mainly for the same reasons as for the 119’s.
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| nuclear powered aircraft |
Next for Tupolev was the Aircraft 132. Another attempt by the Soviets to produce a serviceable nuclear powered bomber. The 132 was conceived as a low-level strike aircraft. The design 132 would have housed the reactor in the front two turbojet engines, the entire package would be accommodated in the rear of the airframe. The engines were to be designed to operate with nuclear power or with conventional kerosene. The kerosene would be only used for take-off and landing operations and the fuel would be housed in a tank installed in front of the reactor. As with the 120, the 132 would have had a conventional configuration, with the cabin, again, heavily shielded. The main difference was the wing configuration.
The 132 would have been a delta wing plane. The empennage was also to be swept and the horizontal stabilizer was to be located on top of the fin. As with the other projects, the 132 was cancelled in the mid 1960s for budgetary and, most importantly, technical difficulties. One last attempt was made by the Tupolev bureau to achieve a nuclear powered aircraft. This aircraft would have been supersonic, long ranged bomber designed to compete with Convair’s B-58 Hustler supersonic medium bomber. This time, the aircraft did not make it to the drawing board. In the late 1960s, the Soviet Union decided to abandon further research into the feasibility of a nuclear powered aircraft. The main reason given to the bureaux involved in the project was that with the introduction of more accurate and less expensive Inter-Continental Ballistic Missiles aboard nuclear powered Soviet submarines; the Soviet Union could achieve the same degree of nuclear capability at a fraction of the cost. Also, in consideration, but rarely mentioned by the Soviets, was the ecological impact of a crash during operations. Should one of these aircrafts were to crash in a populated area, the radiation fallout could have been disastrous.
Another nuclear powered aircraft program was started by the Myasishchev Design Bureau in the summer of 1955. On May 19th, 1955; a resolution passed by SovMin ordering Myasishchev to commence development of a supersonic nuclear bomber. The bureau first design was code name M-60. The first draft of the project was finished on July 1956. At the same time, Lyulka’s new engine design that would comprise a nuclear/turbojet engine with the heat the reactor generates transferred through air to the jet, a power plant configuration known as Open System; would had give the M-60 a thrust of 49,600lbs. The aircraft would take-off and land with a chemical mixture fuel as its propulsion. On reaching the desired operational altitude, the nuclear system would engage and provide the M-60 with its cruise speed. This engine configuration and thrust would have given the M-60 the ability to achieve Mach 2 speeds. Crew accommodations was to be housed in the centre of the fuselage, again, in an all enclosed, lead shielded cabin.
The cabin configuration would have curtailed visual observation. Consistent with other Soviet nuclear configurations, the reactor would be housed in the rear of the aircraft to offer further protection. . The initial fuselage configuration called for a long, slim airplane with trapezoid wings and a trapezoid T-shaped tail. The nuclear/jet engines were to be placed side-by-side in the fuselage. The length of the M-60 was proposed at 169ft, 3.5in; with a wing span of 86ft, 11in. Sub sequential design modifications of the M-60 had the aircraft fitted with four engines mounted up in pairs at the rear of the airframe. As with the other nuclear programs, a tricycle undercarriage was selected for the M-60. Later, a swept wing design was incorporated on the aircraft. Another variant for the M-60 was introduced in December 1957; it called for the M-60 to be a delta winged design with both engines placed on under wing pylons and in tip nacelles which resemble the configuration of the M-50 Bounder. After an extensive research phase, the Myasishchev bureau determined that with the correct nuclear power plants, a strategic bomber with a 1,989 mph speed, an operational range of 15,500 miles, and a service ceiling of 65,600ft was achievable. The M-60 also did not make it out of the planning stage.
After the cancellation of the M-60 program in 1959, the Myasishchev bureau put much of its research assets on the M-30 program, which started back in 1953; but by this time SovMin interest on a nuclear powered aircraft was winding. Several other attempts were made to design an operational nuclear aircraft, chiefly the M-30, but also the M-62 program, ran similar along the lines of the M-60 The final blow to the nuclear powered aircraft programme came in early 1961, when the Soviet leadership called for the abandonment of all related programmes, ending one of the their most expensive and technically challenging programmes ever. The end of the M-60 and the M-30 was also the end of Myasishchev’s affiliation with the design and production of heavy bombers.
At the time of the cancellation of the program, the overall state of available technology, atomic science and aerodynamic designs, had progressed to the point that if the program had run its service course, it is very plausible that the Soviet Union would had reach its goal of deploying a nuclear powered bomber platform by the late 1970s. Instead, the flow of new aerodynamic information and designs, the vast amount of economic resources needed in the program, not only to develop a nuclear powered bomber, but to maintain it were cited as the reason for the cancellation. Also the emergence of a new Soviet doctrine that would rely heavily on the new submarine launched ICBM; with improve targeting mechanism, coupled with the sheer number of Land Based ICBM that the Soviet were rapidly deploying, doomed the Soviet nuclear power bomber program. At around the same time the Soviets commenced its nuclear powered aircraft program, the other Cold War warrior, the United States, was already working at a fast pace to field its own nuclear bomber.
At the same time that the Soviet effort was taking hold. In the United States fascination about a potential nuclear power that might offer limitless energy led the US Air Forces commenced in 1944 an experimental programme designed to produce an operational nuclear powered bomber. The idea of nuclear propulsion energy to power an aircraft dates back to 1942, when Enrico Fermi, one of the fathers of the atomic bomb discussed the idea with members of the Manhattan Project. For the first two years, engineers were immersed on the issue of how radiation would affect the performance of a flying platform, its avionics, materials, and more importantly, its crew. The programme seemed lost in endless detailed fights and controversies, when in 1947, it received new life. The newly formed U.S. Air Forces decided to invest the necessary resources to make the program feasible. Allocation for ten million dollars was promptly made available to the program.
From early 1948 to 1951, extensive research was made in reactor technologies and engine transfer systems; the backbone of the nuclear powered aircraft. Many configurations were proposed, Dual reactor, combination (chemical and nuclear) and single systems were tested. Eventually it was decided that a single reactor would provide the aircraft with the necessary flight reliability. Next came the debate about what type of transfer mechanism would be implemented. Transferring nuclear power to a conventional engine had long been seen by engineers as the main obstacle in the development of the program.
In 1949, the programme ran a series of tests, known as the Heat Transfer Reactor Experiment (HTRE), involving three types of reactors, with the purpose of determining the most efficient method of transferring energy from the reactor. After an extensive trial series, the HTRE-3 emerged as the selected transfer system. The HTRE-3 was a Direct-Cycle Configuration. In a direct cycle system, the air entered the engine through the compressor of the turbojet, it then moved to a plenum intake that directs the air to the core of the reactor. At this point the air, serving as the reactor coolant, is super-heated as it travels through the core. After that stage, it goes to another plenum intake; from there the air is directed to the turbine section of the engine and eventually to the tailpipe.
This configuration allowed the aircraft engine to start on chemical power and then switch to nuclear heat as soon as the core reached optimized operational temperatures, thus providing the proposed aircraft the ability to take-off and land on conventional power. Another system considered was the Indirect-Cycle Configuration. In this configuration, the air did not go through the reactor core, air instead passed through a heat exchanger. The heat generated by the reactor is carried by liquid metal or highly pressurized water, to the heat exchanger where the air is, thus heating the air in its way to the turbine. Engineers preferred the direct-cycle approach due to the fact that was simpler to produce; programme managers preferred the idea because its development time was relatively short compared to the indirect system.
After establishing the parameters for the power plant and the transfer mechanism, engineers commenced work on the shielding for the crew and aircraft avionic systems. Initial plans called for the shielding of the reactor by massive layers of cadmium, paraffin wax, beryllium oxide, and steel. The idea behind this setting was that the more protection the reactor have, the less shielding the crew cabin would require. Technically, this was a sound approach, but in a rapidly functioning environment such as an aircraft setting, this shielding proved to be ineffective. For this reason it was decided to implement what is known as Shadow Shielding Concept. In shadow shielding, the layers of protection would be equally divided between the reactor and the crew cabin. Shadow Shielding would also provide a more robust protection for the aircraft’s avionics systems. An added plus from the implementation of this system was the reduction in the weight of the aircraft due to the distribution of the shield.
Having tackled the reactor, transfer mechanism, and shielding problems, the programme moved it to the aircraft design stage. By late 1951, the program was heavily involved in the acquisition of a test-bed type aircraft for the initial trials of the configuration. The only proven airframe large enough to carry the massive reactor and Heat Transfer system was the Convair’s B-36 Peacekeeper Bomber. The Peacemaker started to enter front line service with the U.S. Air Force in late 1948 and at the time of the nuclear powered programme, was the Strategic Air Command (SAC) main nuclear deterrent platform.
The B-36 was indeed massive. The dimensions are impressive even today. A wingspan of 230ft, a length of 162ft 1in, high of 46ft 8in, and a wind area of 4,772sq ft. This bomber maximum take-off weight was an amazing 410,000lbs; which is why the program managers selected the B-36. A service ceiling of 39,900ft and a climb rate of 2,220ft per minute were also pluses in the selection process. Once the testing aircraft had been identified, the next phase would commence at once; the conversion of the B-36 into an experimental aircraft. The main modification made to the original B-36 airframe was on the nose cone section. The original crew and avionics cabin was replaced by a massive 11tons structure lined with lead, and rubber. Water tanks were also placed in the aft section of the frame to absorb any escaping radiation.
The other section of the plane that underwent significant modifications was the rear-internal bomb bay. Internal cross sections were removed as well as many of the bomb carrying rafts in order to make space for the nuclear reactor power plant. These alterations made it possible for the aircraft to receive a new designation. It is from this moment on that this sole B-36 Peacemaker, numbered 51-5712, would be called Nuclear Test Aircraft-36. A further designation change was made when the nuclear powered plant was installed on the aircraft. Thus the NB-36 “Crusader” was born. Identifying the aircraft was the radioactivity symbol painted on the tailfin. The R-1, one standing for the energy it would generate, a megawatt; reactor installed on the aircraft was a liquid-sodium cooled power plant winched up into the plane’s bomb bay at a dedicated pit on Convair’s Fort Worth plant every time the NB-36 was scheduled to take to the air. When the NB-36 landed, the R-1 was removed for research purposes. The original B-36 was powered by six Pratt & Whitney 3600hp, R4360-53 radial piston engines, supplemented by four General Electric 54000lb thrust J47-19 turbojets.
After conversion, the engines were removed and a new configuration was incorporated. The NB-36 now had four GE J47 nuclear converted piston engines generating 3,800hp augmented by four 23.13Kn turbojets generating 5,200lb of thrust. Each of the engines utilized the Direct-Cycle Configuration for power conversion. The NB-36 was designed from the beginning, to be propelled into the air with a conventional chemical mixture, and then the crew would switch on the reactor after achieving the necessary heat requirements on its core. On landing approaches, the aircraft would switch back to chemical mixture. This procedure was implemented in order to minimize the possibility of a major radiation leak in case of a crash landing.
The NB-36 made 47 recorded flights between the summer of 1955 and the fall of 1957. All these tests were made operating the NB-36 with conventional chemical power. The R-1 reactor was turned-on on many of these flights, not to actually power the aircraft, but to test and collect data on the feasibility of a sustained nuclear reaction on a moving platform. All the data collected by these tests showed the program managers that the possibility of using a nuclear power plant to provide an aircraft with unlimited operational range was indeed at their disposal at this time. Impressive as the taxi and flight testing were for the NB-36, the complete concept of a nuclear powered aircraft was made irrelevant by advances in conventional aircraft and engine design and the public concern about the dangers of flying a nuclear reactor over their homeland. In the end, after expending no less than $469,350,000 on the nuclear powered programme and having a concept aircraft flying, the U.S. Air Force shelved the programme in the late 1960s, thus ending any major attempt by the United States to utilize nuclear propulsion to power an aircraft in combat.
Why the United States and the Soviet Union, clearly on a path to develop and produce a serviceable nuclear powered air platform; decided to terminate their respective programs? If the technology was there, what was missing? As with any programme involving a military project, there political and social forces driving it in reverse directions. These same forces that drove the U.S. and U.S.S.R. into investing so many resources were the same ones that drove their programmes to a halt. The nuclear power aircraft program of both the U.S. and the U.S.S.R. started an a time when atomic energy was view as a “do it all” energy source. But here is where the similarities ended. From the late 1940s to the early 1960s, atomic power was viewed very favourably by the general population in the United States. Atomic energy was being used to supply electricity to cities and small towns across the country. The U.S. military rapidly responded to this new found energy source with its own research and development programmes. Beside the ordinance harness of the atom, such as in bombs or missiles; nuclear propulsion was an intriguing subject among military leaders.
The U.S. Navy began to experiment with nuclear reactors aboard vessels, specially, aircraft carriers; with the purpose of generating an unlimited source of steam to drive them. Submarine use of nuclear propulsion was also researched and vigorously tested during this period. Seen their main competitor for funds implementing nuclear propulsion programs, the newly formed United States Air Force decided to join the fray. Immediately, the Air Force recognized the strategic bomber as the platform that would argument its operational profile if it were nuclear powered. Aircraft do not have the capacity to carry enough fuel to achieve maximum operational capability. For long distance flights or combat patrols, bombers usually needed to make more than one re-fuelling stop. Subtracting time from the mission profile.
A nuclear powered aircraft could solve this problem. As previously stated, studies had demonstrated that the U.S. possessed the technical ability to produce a workable nuclear powered bomber. Here is where the political aspect of the equation enters. Through its history, the nuclear powered aircraft programme was plagued by a lack of short term vision and political interfering. The Air Force, who was tasked to oversee the programme by the Department of Defence, almost immediately failed to set short-term, achievable goals for the programme. Major shifts in the programme’s objectives were made with relative frequency. Causing the programme managers to shift resources from one aspect of the programme to another. This lead directly to wasting of valuable time and financial resources. One example was the construction of massive test facilities for the programme at great expenses, only to be closed after they were never used.
In March of 1953, the programme was placed on termination phase by then Secretary of Defence Charles Wilson due to a lack of progress. However, the Soviet’s successful lunch of Sputnik changed all of this. Sputnik did more than start the space race; it brought back to centre stage the nuclear technological race between the superpowers. Congressmen were flowing letters to the Eisenhower Administration to re-invest in the nuclear powered bomber program at once. Vigorous lobbying on behalf of the Air Force created an increase in available funds for the programme. Adding to the public sentiment of fear; reports began to surface about an experimental Soviet nuclear powered bombers flying test runs near the Polish border. The net effect on the programme was an influx of funds and human resources. A new life, albeit, a short one.
As the political situation worsened. Desk officials were overriding field managers on key aspect of the programme. Datelines were frequently missed. Goals were half-met, if met at all. The programme was also plagued by a lack of a central, unified voice. A voice that could command respect and inspire the personnel working on the project. In the end, this was the undoing of the whole programme. Critics had pointed to the development of more accurate Inter Continental Ballistic Missiles or a serviceable mid-air refuelling system, or even the ecological effects of a crash landing by one of these “special” bombers; as the main reasons behind the cancellation of the programme. These facts played an important role in the programme’s demise, but the factor that ultimate undid the programme was mismanagement. The atmosphere surrounding the programme’s operational management team never fully complemented the team on the ground. Waste after waste of scarce financial resources as well major time delays, gave the access the politician coveted to take a measure of control over the programme; and in the end, destroying any hope a achieving a successful conclusion.
The Soviet approach to their programme was, from the very start, quite different than that of the U.S. Their main goal in achieving a nuclear powered bomber was to enhance their ability to strike deep into Continental America. At the time, the leaders at the Kremlin were alarmed at the U.S. installation of offensive medium-range ballistic missiles in Europe and Turkey. These developments were added to the fact that the Soviet Union had failed in its attempts at develop a truly intercontinental and technological advanced heavy bomber platform. After the first reports of an interest in the part of the U.S. to commence research into the possibility of an atomic plane, the U.S.S.R., partially motivated by pride and the reality that one superpower was getting technological superior to them, started a crash programme to look into the possibility of producing an atomic plane. The nature of the Soviet political system did not allow for much political squandering.
After the Kremlin made its decision to start or back a development programme, especially one of this scale, full resources were allocated for the project without political interference. That is how the Soviet effort began. As with the American programme, extensive research was performed and valuable data collected. Also, as it was the case of the American programme, technology pointed to the possibility of producing a workable nuclear powered bomber in relative short time. Then why the Soviets, so close to realizing the programme’s main objective, decided also to abandon it? Managerial practices were not to play a role on the programme’s demise. The Kremlin gave orders to start or terminate any programme, but in those days, they did not micromanage. So, what was the reason? Politics. Geo, and military politics. In the mid 1950s, the U.S.S.R. made a political decision in regards to their strategic offensive nuclear force.
They calculated that with advances made in tracking radar systems and the development of accurate surface-to-air missiles batteries, a nuclear powered bomber would be hard pressed to penetrate the U.S. airspace; missiles on the other hand, possessed a greater survival capability over the enemy’s airspace. The other aspect of the political decision was maintenance. The Soviets calculated that with the financial resources needed to maintain an airworthy atomic bomber force, it could field a vast array of Inter Continental Ballistic Missile systems. Soviet leaders, watching the development of their space programme, a programme that was centred on the launching of massive rockets, felt in love with the ICBM. Missiles are relatively inexpensive to produce and maintain compared to atomic planes. And enough deployable missiles would allow the Soviet Union to implement their long standing military doctrine of brute force. They calculated that the possession of an overwhelming number of missiles and the ability of these missiles to shower the United States, they would be able to deter the U.S. from taking any offensive action against the Soviet Union or its interests around the world.
Another key development was the introduction of nuclear propulsion into the Soviet Union’s submarine force. This, coupled with the introduction of the Sea Launched Ballistic Missile, gave the Soviet another potent brute force type of platform from which to deter the U.S. The Soviets decided to invest vast amounts of resources in the development of a nuclear submarine force. A feat they were able to achieve with impressive results. When the Cold War ended, the Soviet Union possessed the largest nuclear missile carrying force in the world. Those factors combined to make the nuclear powered bomber programme obsolete accordingly to the new Soviet doctrine that relied on the ability of the missile to get through a dense air defence network.
In both cases, politics, not technology, was the primary factor in abandoning their respective nuclear powered aircraft programme. One can only imagine what would have happened if these atomic planes were built to an operational status. Although today there is still interest in the concept, major advances in unmanned air platforms had rendered the concept almost obsolete. But almost did not mean, completely. One example being Custer’s Channel Wing Concept of the early 1950s. As of today, the concept is being revised for possible application to today’s airframes. Can this sort of renew interest happen with the atomic air platform?
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