Tu-95 - Design
An all-metal monoplane with a mid-swept wing and a single-fin tail, the aerodynamic layout ensures high aerodynamic quality at high flight speeds. Improvement in flight characteristics is also achieved due to the large aspect ratio of the wing, the corresponding choice of the angle of its sweep and a set of profiles along its span. The power plant of the Tu-95MS consists of four NK-12MP TVDs with coaxial four-bladed AV-60K propellers. Fuel on the aircraft is placed in eight sealed compartments in the wing box section (box-tanks) and in three soft tanks in the center section and rear of the fuselage. Fueling is centralized. There is a fuel receiver rod for the air refueling system.
The Tu-95 aircraft is made according to the normal aerodynamic configuration with a high-positioned cantilever three-spar wing. This aerodynamic layout ensures high aerodynamic quality at high flight speeds. Improvement in flight characteristics is also achieved due to the large aspect ratio of the wing, the corresponding choice of the angle of its sweep, and a set of profiles along its span. The power plant of the Tu-95MS consists of four NK-12M (MB) turboprops with a capacity of 4 x 15,000 hp. with coaxial four-blade screws AV-6ON. A feature of the new machine was the use of a swept wing and, most importantly, for the first time in the practice of world aircraft construction for aircraft of this class, the installation of turboprop engines. Unique turboprop engines NK-12 designed by N.D. Kuznetsov with coaxial multi-blade propellers K.I. Zhdanovs had no equal in power and efficiency in all flight modes.
The preliminary design of the 95 aircraft was ready in mid-December 1951. In it, the OKB promised to exceed the specified flight range requirements and guaranteed a cruising speed of 750-800 km / h at altitudes of 10,000-14,000 m, a practical flight range of 14,500-17,500 km. According to the technical project "95th" was intended for striking strategic targets, military bases, seaports, military-industrial facilities, political and administrative centers located deep behind enemy lines. In addition to a wide range of strategic tasks, the new machine was to be used in remote maritime theaters for laying mines, torpedo and bomb strikes on ships (the aircraft's combat arsenal was supposed to have mines and high-altitude torpedoes, up to four guided bombs on an external sling).
Since one of the most important purposes of the aircraft was to deliver strategic nuclear strikes using swap-falling nuclear bombs, its bomb bay was designed with thermal insulation and electrically heated. The temperature in the compartment had to be maintained within +5 - + 25¦. The maximum bomb load, according to the preliminary design, was guaranteed 15,000 kg, normal - 5,000 kg, maximum bomb caliber - 9,000 kg. At the same time, the OKB, together with TsAGI, with other enterprises and organizations, launched research work on the problems of the stability of aircraft structures to the effects of the damaging factors of nuclear weapons, as well as the problems of their impact on the crew and possible methods of protection.
According to the design bureau, the combination of high flight speed and high practical heights with powerful defensive weapons (a system of remote cannon fire with practically no dead zones, the proposed installation of passive and active REP systems on the aircraft) should have made an effective interception of the 95 aircraft by enemy interceptor fighters almost impossible.
It was envisaged to install the most modern domestic navigation and radio communication equipment on the aircraft at that time, which was supposed to ensure the performance of combat missions by the 95s both as part of formations of the same type of machines, and singly, day and night in difficult meteorological conditions. When designing and choosing navigation equipment, special attention was paid to ensuring autonomous navigation at high latitudes and over enemy territory.
With 2TV-2F engines, the aircraft was supposed to have a tactical radius of up to 6000 km with a bomb load of up to 9 tons, with TV-12 engines - up to 7500 km with the same bomb load. This made the 95 aircraft, when equipped with nuclear weapons, an effective weapon against targets located on other continents. In the future, the 95th was to become a global strike system. It was supposed to place on it a wing-based refueling system in the air (there were no other refueling options of the "Cone" type or with a rigid telescopic tube at that stage) from the same type of refueling aircraft. At the same time, the flight range was increased to 32,000 km (with two refuelings - when flying to the target and on the way back), which made it possible to reach any point in the world with a nuclear weapon on board, with the exception of a small part of South America and Antarctica, and guarantee a return to base. All these excellent parameters in terms of range, according to the draft design, were obtained with a very moderate maximum take-off weight of 156 tons and, accordingly, acceptable take-off characteristics.
The reality turned out to be not so rosy - the first production machine, with the condition of fulfilling the minimum requirements for practical flight range, had a maximum takeoff weight of 172 tons, and after modernization - 182 tons, with a significant deterioration in takeoff characteristics (according to the preliminary design 1120-1200 m, on the first production car - 2320 m). Well, the refueling system had to be set as a necessary condition for maintaining the intercontinental range after all the upgrades and modifications, and not as a condition for obtaining a global strike aviation system.
According to the project, both versions of the aircraft were structurally unified, one version differed from the other only in the type of engines, which made it possible to pass from the first version to the second rather painlessly. For the second version, OKB-276 promised to prepare the TV-12 engine with a maximum take-off power of 12,500 hp as soon as possible.
Since the future bomber had to make long flights, much attention was paid to providing the crew with the necessary living conditions: the crew accommodation is spacious enough, taking into account the provision of conditions for rest in flight in the workplace, in addition, special rooms for rest (folding bunks) were organized , eating, etc. Unfortunately, much of what was conceived in terms of ensuring normal living conditions for the crew disappeared in the process of finalizing the project and the real aircraft (the usual struggle of airplanes to reduce the mass of an empty aircraft, largely associated with the installation on board real blocks of aircraft systems and special equipment with their real dimensions and masses, sometimes very different.
To obtain the required performance characteristics for the 95 aircraft, an aerodynamic configuration was chosen that would ensure high aerodynamic quality at high flight speeds. This was achieved by an appropriate choice of the wing sweep angle, a set of profiles along its span and a large wing elongation (it should be noted that the creation of a swept wing of high aspect ratio in itself was a rather complex strength and design problem, successfully solved on the 95 and M-4 aircraft ). When assembling the aircraft, much attention was paid to reducing harmful drag by reducing the midsection of the fuselage and engine nacelles. It should be noted that the choice of a power plant based on 4 theaters, sharply limited the possibilities of linkers to choose the most rational aerodynamic design. For giant engine nacelles with theaters, there was only one place left - on the wing or on the pylons under the wing. All airframe assemblies and their interfaces were shaped to provide the least harmful interference when flowing around the air stream. The relative fuselage midsection of the 95 aircraft was reduced to 2.33%, the main landing gear nacelles were made in conjunction with the internal engine nacelles and had a shape, the combination of which with the wing had the midship of the bodies of least resistance (compliance with the area rule). As a result of the large research and design work, it was possible to obtain a high aerodynamic quality - in the cruise flight mode (M = 0.7) the quality of the aircraft "
In the fuselage layout, the approved solutions of the "85" aircraft were mainly chosen. The main difference was that the introduction of a swept wing on the 95th made it possible to move to a single large bomb bay with combat loads located practically in the center of mass. A feature of the 95 aircraft project was the absence of ejection seats for the crew, which distinguished this aircraft from other long-range jet bombers of that period (M-4, B-52, Tu-16, British aircraft of the "V" family). Eight crew members in an emergency left the aircraft through the hatches and through the front landing gear compartment. This technical solution was justified primarily by the relatively low cruising flight speeds.
From the very beginning of the development of the 95 aircraft, great responsibility fell on the strength department of the Design Bureau headed by A.M. Cheremukhin. He and his staff participated in the analysis of a possible power scheme of the aircraft structure, taking into account the optimal placement of the engines. The responsibility of the decisions made was extremely high, since simultaneously with the R&D work began on the deployment of the series at plant No.18, where the equipment was already being manufactured and assembly lines were being prepared. Such a solution significantly complicated the work of the strength specialists, because the changes in the design required for reasons of strength led to a change in the finished equipment and the refinement of the aircraft on assembly lines or, even worse, in operation.
New for structuralists in the design of the aircraft "95" there was a need to introduce changes in the Norms of strength and in the methods for determining the design loads, since the previously accepted overestimated safety margins in the design of the 95th and M-4 led to a significant increase in the masses of empty aircraft. For this group of aircraft with a flexible swept wing of large aspect ratio, A.M. Cheremukhin proposed to calculate the external loads on the wing taking into account its deformation in flight for static loading cases. Research carried out jointly with TsAGI and OKB-23 made it possible to obtain a significant gain in the weight of the wing structure for the 95 and M-4 aircraft. and M-4s resulted in a significant increase in empty aircraft masses.
For this group of aircraft with a flexible swept wing of large aspect ratio, A.M. Cheremukhin proposed to calculate the external loads on the wing taking into account its deformation in flight for static loading cases. Research carried out jointly with TsAGI and OKB-23 made it possible to obtain a significant gain in the weight of the wing structure for the 95 and M-4 aircraft. and M-4s resulted in a significant increase in empty aircraft masses. For this group of aircraft with a flexible swept wing of large aspect ratio, A.M. Cheremukhin proposed to calculate the external loads on the wing taking into account its deformation in flight for static loading cases. Research carried out jointly with TsAGI and OKB-23 made it possible to obtain a significant gain in the weight of the wing structure for the 95 and M-4 aircraft.
A serious problem in the design of the 95 aircraft was the creation of an effective control system. If on the M-4 OKB-23 boldly went to the introduction of irreversible hydraulic boosters into the control system, then the Tupolev "managers" were clearly guided by the general instruction of Andrey Nikolaevich, expressed in his catchphrase: "The best machine gun is the one that is not on the plane." Therefore, both the Tu-16 and, which is absolutely on the verge of a possible, "95th" received control systems with direct mechanical connection. The aerodynamics, managers, designers of the OKB and TsAGI (which was for the introduction of a system with irreversible hydraulic boosters) were tasked with achieving normal efforts on the pilot's controls while maintaining their direct mechanical connection with the rudders. To reduce the hinge moments of the controls on the "95" aircraft, axial compensation was applied on the elevator and rudder, and internal compensation on the ailerons.
Numerous theoretical studies and tests of models were carried out in a full-scale TsAGI wind tunnel, before the nose shape and the corresponding compensation degrees were finally chosen: aerodynamic elevators and rudders - 30%, and internal ailerons - 34%. In addition to aerodynamic compensation, servo compensation was used to reduce the hinge moment on the rudder and ailerons, functionally combined with the trim tabs. And yet, for all Andrei Nikolayevich's dislike for unreliable boosters, they still had to be put on board. Application of aerodynamic, internal compensation and servo compensation on the rudder and ailerons did not allow reducing the efforts on the controls to normal values. To normalize these efforts, reversible hydraulic boosters were nevertheless introduced into the control channels with reversibility coefficients for the rudder 1/3, and for the ailerons - 1/2. As a result, it was possible to obtain a sufficiently reliable control system with acceptable efforts on the pilots' control bodies for such a large and heavy aircraft as the "95" was.
Interesting innovations in the systems of the "95" aircraft include: the use of lighter aluminum wires in the power supply system, electrothermal heating of planes and propeller blades, as well as the development of an automatic control system and launch of powerful HPTs. The design of the 95 aircraft was supposed to make maximum use of materials, semi-finished products and components of previous developments of the OKB, in particular the 85 aircraft, which made it possible to speed up the process of creating the aircraft.
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