In 1952, A.N. Tupolev Design Bureau began work on the creation of an intercontinental heavy supersonic carrier aircraft capable of reaching the United States or entering the launch zone of a manned outboard nuclear bomb carrier aircraft or unmanned projectile. In terms of these works, at the end of 1952, the design bureau team led by B.M. Kondorsky began studying the problems associated with the design and construction of a heavy supersonic aircraft with various types of wings (triangular, diamond-shaped and arrow-shaped). Foreign experience was studied, the preliminary design of such an aircraft was carried out according to various aerodynamic schemes - a normal scheme, a tailless scheme, etc. The options for power plants based on the AL-7, VD-5 turbojet engine with afterburner cameras and without them were considered, the number of engines varied from 3 to 12.
Each of the problems encountered by the creators of the "108" (Tu-108), in itself, was a very difficult task. Practically, it was a question of creating a multi-mode strategic supersonic airplane and an attack system based on technical and technological solutions that significantly exceeded the capabilities of the domestic industry of that period. In fact, this type of aircraft was realized only in the 70s and 80s with the advent of American and Soviet multi-mode attack aircraft carriers B-1 and Tu-160 with variable wing sweep.
Even before the start of the work on airborne strike composite systems, the Tupolev Design Bureau started work on creating an intercontinental heavy supersonic aircraft capable of reaching the US territory. At the end of 1952, they began to study the problems associated with the design and construction of a heavy supersonic aircraft with various types of wings: triangular, diamond-shaped and arrow-shaped.
By 1954, in general terms, determined the main parameters of the future carrier. July 30, 1954 the government issued a decree instructing the OKB to design and build a strategic aviation composite strike system. The compound long-range bomber "108" (Tu-108) was to consist of a carrier aircraft with six turbojet engines of the VD-5M type (take-off thrust of 15360 kg), and a suspended manned aircraft "100" (Tu-100).
The practical range of the system with an atomic bomb weighing 1250 kg was to be 14000 km, of which 5000-6000 km the system flew at a speed of 1400-1500 km / h with a suspension in the target area and with subsequent separate return of the hanging aircraft and carrier to the base.
In the variant of using the "108" aircraft as a strategic bomber, its range from 5000 kg of bombs at a speed of 950 - 1000 km / h and an altitude of 16000-17000 m was to be 12500-15000 km. At a supersonic speed of 1400-1500 km / h and at an altitude of 14,000 m, the bomber had to have a range of up to 4000 km. The ceiling above the target was specified 13000-14000 m. Bomb load: normal - 5000 kg, maximum - 12000 kg. The takeoff run length should not exceed 2300 - 2400 m. Defensive armament for the carrier aircraft should consist of one 30 mm twin aft remote installation. The crew was three or four people.
Three copies of the aircraft were to be built by 1957. After receiving the official assignment, intensive research and development work began. Heavy aircraft with triangular wings with sweep angles of 40-60° and with various types of engines (TRD and TRDF - AM-17, VD-5M, VD-7M and VK-9F, jet propeller engines P-8, powerful non-sparse TR-4 P-4). These studies allowed the team to optimize the main mass and dimensions parameters and choose the most suitable engines - four P-4s with a maximum take-off thrust of 25,000 kgf. In order to ensure the given characteristics, the aircraft should have a takeoff weight of 270-320 tons and a wing area of 370-400 m.
The creation of the P-4 turbojet engine proposed by the ND Kuznetsov Design Bureau for the "108" (Tu-108) project and having for its time exceptionally high absolute and specific parameters, taking into account the level of technology of the first half of the 1950s, was clearly unrealistic.
Therefore, OKB A, N. Tupolev soon revised the initial project under the TR-DDF NK-6 with significantly higher specific fuel costs. But, as in the case of the Tu-22, at the initial stage the further design was decided on the basis of the VD-7M TRDF, which was prepared for production.
In the summer of 1955 the task for "108" (Tu-108) was adjusted to six VD-7M or four NK-6. The team also worked out the option with a ramjet, while the flight speed increased to M = 2.85, but it was not taken as redundant for a given system and low-level for the level of technology of that time. The project for six VD-7M engines or for four NK-6 engines with afterburners that had significantly worse specific characteristics than engines of the P-4 and P-6 projects, but which were more real to them alternative, the achievement of the declared characteristics of which in the fifties was hardly possible. In addition to these projects under turbofan engines and turbojet engines, the design bureau was working on variants of the “108” aircraft with ramjet, in this version the carrier speed increased to a value corresponding to M = 2.85, but this direction of the project was not accepted as excessive for this specific tasks and very problematic in the limitations in the use of traditional structural materials for such an aircraft.
For the plane "108" (Tu-108), a large volume of theoretical and experimental studies of the design and strength of triangular wings. The influence of the chosen structural scheme on the strength and mass of the wing and the distribution of loads in triangular wings were studied in detail, mass-dimensions parameters were evaluated and practical wings for heavy aircraft were developed. The accumulated experience was used in the design of the 125 and 135 aircraft, and then in the design of the wings for unmanned supersonic aircraft 121 and 123, and for the creation of the supersonic passenger TU-144.
In February 1956, the OKB summed up the first results of the work on the project "108" (Tu-108), noting the overall technical complexity faced by the developers, and outlining further ways of carrying out the work. Analysis of possible routes for air strikes against the United States showed that the guaranteed achievement of the main objectives in the territory of the United States from the territory of the USSR, subject to the return of the carrier back to the base, is possible only with double refueling in flight.
At the same time, it was necessary to provide aerodynamic quality of "108" (Tu-108) at subsonic level - 13-15, for supersonic - 5.5-6.5 and to bring fuel weight return to 72-75%. The project "109" with four P-4 turbojet engines satisfied most of all these general design requirements. The transition to more real NK-6 or VD-7M only complicated the problem with ensuring the required range of flight. The use of several in-flight refuellings required the improvement of existing equipment, taking into account the need for highly responsible refueling at large distances from the basing sites. For the attack ["shock"] system, it was also necessary to create effective navigation and communication systems.
In spite of all these problems, measures were proposed to overcome the crisis in the creation of the aircraft. To improve the aerodynamic quality during cruising and to increase the lift during takeoff and landing, new wing profiles were introduced, in the aerodynamic configuration, the "area rule" was applied, the use of a suction and blowoff system for the boundary layer was envisaged. In addition, measures were proposed to further improve the overall aerodynamic scheme, PS projects appeared for the canard ["duck"] scheme with a floating front horizontal empenage, etc.
Based on the studies carried out to improve the basic project, the OKB was able to prove the feasibility of continuing work on this topic. In February 1956, some results of the work on the 108 aircraft were summed up. The technical difficulties that the design encountered and the further development paths of the project taking into account the real level of development of aviation equipment and technologies in the USSR were noted. The most important of them are the following: An analysis of the possible routes for delivering strategic air strikes across the North American continent showed that the guaranteed achievement of important goals from the USSR, provided that the carrier is returned back to the base, possibly with double refueling in flight. When creating a carrier aircraft, it is necessary to achieve an aerodynamic quality value for a cruise flight at a subsonic of the order of 13-15 and supersonic - 5.5-6.5,
On March 28, 1956, a new government decree issued, prescribing to continue work on the aircraft "108" 4NK-6. The time for the commencement of the tests was shifted to 1959. Gradually, the design of the aircraft was completely transferred to the department of technical projects of SM Eger.
The original project "108" (Tu-108) had significantly changed: the airplane layout became more traditional - the low-wing of the traditional scheme with a wing of a moderate sweep of 45 "and tail fins, nacelles placed in pairs in the fuselage above the central part of the wing. Most of the fuselage and wings were occupied by fuel tanks. In the bow were placed the airtight cockpit of the pilot and navigator, in the rear part in a separate hermachine cabin the arrow-radio operator was placed, who operated a strelkovaya-cannon installation. In the cargo compartment in the central part of the fuselage, a manned attack aircraft or an unmanned airplane was suspended on a retractable beam holder.
By 1957, the Soviet aviation industry was to ensure the construction of the first three "108 " aircraft , and according to the draft fifth five-year plan for 1956-1960, in 1959 the aviation industry was to produce 10 aircraft of this type, and in 1960 - another 30. OKB-23 the design of an experienced composite supersonic bomber was asked, with the deadline for the start of factory tests in the third quarter of 1957 and its submission to state tests in the third quarter of 1958.
Project works on the system "108" (Tu-108) continued for another two years. In the end, the project shared the fate of the M-50 and M-52 aircraft constructed in the OKB by VM Myasishchev, according to the characteristics close to "108": the missile era came and the Soviet military and political leadership made a bid to create and deploy intercontinental ballistic missiles. July 31, 1958 a government decree was issued, according to which all work on the project "108" ceased.
The time of such an aircraft came only after 20-25 years, when on the basis of the latest achievements in the field of aerodynamics, aircraft design, engine construction and avionics, it was possible to build and then transfer to the strategic intercontinental multi-mode Tu-160 airplane with variable sweep wing.
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