In the early 50s of the last century, there were only two fighter design bureaus in the Soviet Union: A. I. Mikoyan and A. S. Yakovleva. It would seem that they should have become the main competitors in the creation of a new type of fighter. But, as described in the first part, Yakovlev was simply squeezed out of the competition. However, the competitive struggle still turned out, and quite intriguing. The main rival of A. I. Mikoyan, the disgraced P. O. Sukhoi, most recently appointed by order of the Ministry of Defense Industry No. 223 of May 14, 1953, Chief Designer of OKB-1 instead of V. V. Kondratyev. Earlier in 1949, Pavel Osipovich's design bureau was closed due to his conflict with the Minister of the Armed Forces of the USSR N. A. Bulganin. According to the official version, this design bureau was liquidated in connection with the disaster of the experienced Su-15 interceptor and the general "inefficiency" of the work: after all, during the existence of the design bureau, only one Su-2 machine was adopted.
Having accepted the material base on the territory of the Central Aerodrome, P. O. Sukhoi immediately set about recruiting people and solving organizational issues. And on July 5, 1953, the well-known Decree of the Council of Ministers of the USSR was issued, which ordered the "fighter" design bureau to start developing new types of aircraft; designed for high supersonic flight speed (at least 1750 km / h). From the level of the specified characteristics, it was clear that the aircraft being created was to become not just a new machine, but to provide a significant breakthrough in maximum speed. Recall that by 1953, there were no serial supersonic aircraft in the USSR at all. Despite the novelty and complexity of the assignment, the newly formed team, headed by P. O. Sukhim, actively began to develop the project. The base for it was the Su-17 (R) project, prepared back in 1948.
Su-17 (R) aircraft projections
The work went in two directions. The first is a front-line fighter (it was he who became the main competitor of the MiG-21), and the second is an air defense interceptor. Both aircraft were developed in two versions, differing in wings: one with a traditional swept wing, the other with a new triangular wing. A front-line fighter with a swept wing received the designation S-1 (Strelka), and with a triangular wing - T-1. The interceptors were named accordingly: C-3 and T-3. Sukhoi wanted to test both types of the wing in parallel and put the best option into service. After the redesign of the initial project "R" in accordance with the latest recommendations of TsAGI, C1 / C3 aircraft used a wing with a sweep of 60 ° along a 1/4 chord line of a symmetrical profile with a relative thickness of 7% and an all-turning horizontal tail. At the same time, they installed a high-pressure hydraulic system, an irreversible booster control system in all channels, an axisymmetric adjustable air intake with a retractable central body, and much more. The number of guns on board was limited to two - one in each wing plane. To achieve S-1 / S-3 higher flight speeds than the "R", Pavel Osipovich also decided to use a new turbojet engine (TRD) designed by A. M. Cradle AL-7F with a declared thrust on afterburner of 10,000 kgf. True, the engine was not yet ready, and as a temporary measure, the prototype could have been supplied with its unpowered version of the AL-7, which developed a third less thrust. Calculations showed that even with such a weak turbojet engine, aircraft "C" will reach supersonic speeds.
The design of the S-1 fighter went quite briskly, because its design largely repeated the previously built "R". Of course, for its time, the Su-17 was a revolutionary and advanced design, but 5 years have passed since its design, and this was sometimes ignored by the KB staff. This led to the fact that by the time the design was completed, the course of work was disrupted by the head of the brigade of general types E. G. Adler. He wrote about this in his memoirs as follows: “Pushed by the euphoria associated with the Su-17, which was ruined back in 1948, I passively watched as the young employees of the sketch design team Sizov, Ryumin, Ponomarev and Polyakov diligently repeated the main features of this ideal … But as the drawings from the preliminary design team moved to the main teams of the Design Bureau, a feeling of discontent gradually grew in me and a different constructive solution suggested itself. Signing the drawings with more and more disgust, I finally could not resist and went to Sukhoi with a guilty head …"
In his conversation with Sukhoi, Adler proposed to significantly revise the project. The democratic and calm Sukhoi approved of the "revolution." Adler presented his views on changing the project to the team a few days later. The main changes affected the location of the main landing gear - they were to be transferred from the fuselage to the wing, and the vacant space was to be taken with fuel tanks. The adjustable horizontal tail with elevators should be replaced with an all-turning stabilizer. It had to be moved from the keel to the tail of the fuselage, because the keel did not fit powerful boosters.
At first, the innovations of E. G. Adler was not rejected, and the brigades began to work out a new task. But the rearrangement of the landing gear required a change in the power set of the wing and the kinematic scheme of the chassis itself. There were some nuances in the control system, etc. The work slowed down. Adler himself spent a lot of time not only on solving the problems that had arisen, but also on convincing employees that they were right, which, in fact, made himself a lot of ill-wishers. The conflict was growing, and E. G. Adler was forced to leave Sukhoi in the Yakovlev Design Bureau. As a result of this story, Adler wrote: “From a comparative calculation of the weights of the two design variants of the Su-7 at the same time, it was found that the total weight saving in the new version was 665 kg … I will not hide that it is pleasant it was heard when one day Sukhoi, who was stingy with praise, nevertheless threw at one of the meetings the phrase: "According to Adler's schemes, structures are easier to obtain."
The completed S-1 project had an unpretentious cylindrical fuselage with a large aspect ratio, a frontal air intake with a central cone, a mid-swept wing and a single-fin tail unit. All these design solutions were aimed at reducing aerodynamic drag and achieving high speeds, especially since such a scheme was studied as much as possible by TsAGI. And if the S-1 glider was familiar and even classic for domestic aircraft, then the power plant was unique at that time. While developing his new AL-7 turbojet engine, Arkhip Mikhailovich Lyulka decided to achieve an increase in thrust by increasing the air compression ratio in the compressor. This problem could be solved by simply adding stages, but at the same time the weight and dimensions of the engine grew. And it was possible to use the so-called supersonic compressor. In it, thanks to the special profile of the blades, the air flow between them moves faster than the speed of sound. It has fewer steps, but the air pressure is greater. Accordingly, less weight and more traction.
However, it is very difficult to achieve stable performance from a supersonic compressor. In addition, the blades are subjected to heavy loads, and even small nicks on the surface can lead to their destruction. In view of these shortcomings, usually not all stages are made supersonic, but only a few, then it is easier to make them work. Cradle decided to make only the first stage supersonic. In terms of its effectiveness, it replaced 3-4 subsonic ones.
To increase the pressure head, the diameter of the wheel of the new stage was increased, but the diameter of the old stages remained the same, because of this, a characteristic hump was formed in the air path. During the tests, the engine started working and showed the calculated characteristics, but its hump did not give rest to the design team. But all their attempts to correct the "ugliness" have not been crowned with success. Smooth compressor stubbornly did not want to work. In the end, he was left alone, and the unusual shape of the flow path of the AL-7 compressor became his hallmark.
Cradle even joked about this. One day his OKB was visited by an American delegation from General Electric. The leading specialist of the company, seeing the compressor of the "seven", asked Lyulka in surprise: "Why does your engine have a humped compressor?" To which he jokingly replied: "He is like that from birth!"
The supersonic stage raised the compression ratio of the AL-7 compressor to 9, 1. While on the previous AL-5 with a conventional compressor, it was only 4, 5. The maximum thrust increased by 1340 kgf compared to the "five".
The competitor engine AM-11 (RIF-300), developed for Mikoyan's aircraft at the Mikulin Design Bureau, had a completely supersonic six-stage compressor. But General Electric for its engine intended for the American front-line fighter F-104 (which was considered the main enemy in the design of Soviet machines) went by a simple way of increasing the number of stages. The designers have piled up 17 of them in J79 (It should be recalled that the cost of one jet engine blade is several tens of dollars, and the cost of the engine grows in proportion to the number of stages. In addition, the dimensions and weight of the engine grow.)
The designers took completely different paths both in ensuring the stability of the engine operation and in the fight against surging. The cradle used air bypass from the flow path. "Excess" air was removed from the fourth and fifth stages, and was thrown into the atmosphere through holes in the engine casing, which were aligned with two cutouts in the upper part of the aircraft fuselage. In the normal state, the holes on the engine were covered with steel bands. The bypass was the simplest and at the same time the most uneconomical system. At the moment of opening the holes in the housing of the turbojet engine, the thrust decreased and the fuel consumption increased.
At General Electric, for the stability of the engine, rotary compressor vanes were used. This system had practically no side effects, but it is an order of magnitude more complicated and more expensive than a bypass. On the Mikulin engine, a two-stage compressor was used, which did not require anything at all, all the regulation ensured the rotation of the low and high pressure rotors at different speeds.
When comparing engines, you need to know that the most advanced turbojet engine is one that achieves the thrust specified by the customer with minimum weight, dimensions and fuel consumption. Moreover, each extra kilogram of engine mass causes an increase in the mass of the aircraft by about three kilograms.
The design level of perfection of an engine can be determined by its specific gravity - the ratio of mass to maximum thrust. The smaller it is, the better: the more rationally its constructive scheme is chosen.
As can be seen from the analysis of the table, the AM-11 (R11F-300) A. A. engine can rightfully be called the best of the three turbojet engines. Mikulin. Lyulkov's AL-7 engines were not the best of the best in their class, but their thrust was unmatched, and Sukhoi relied on it. However, it was possible to place a very large engine, its systems and fuel only in a sufficiently voluminous fuselage. As a result, the S-1 looked very impressive against the background of domestic and foreign competitors.
The Su-7 also looked impressive against the background of the previous generation fighters.
The draft design of a front-line fighter with a swept wing (variant "S-1") was defended in November 1953, and in February 1954 a mock-up commission passed. By order of MAP No. 135 of October 26, 1953, OKB-1 was transferred as a production base to a branch of plant No. 51 MAP.
On June 1, 1955, a flight test station (LIS) of plant No. 51 was opened at the LII in Zhukovsky - only a couple of weeks remained until the completion of the construction of S-1. After testing the units and systems, the aircraft was transported from Moscow to the LIS under covers in compliance with all regime regulations and was transported by a police escort on motorcycles on the night of July 15-16, 1955. The test team was headed by the leading engineer V. P. Baluev. Since OKB-51 did not yet have its own test pilots, A. Kochetkov from the State Red Banner Scientific Testing Institute of the Air Force (GK NII VVS), who had previously tested the first jet aircraft P. O. Sukhoi Su-9. July 27 A. G. Kochetkov performed the first taxiing in C-1. This was followed by new runs with the nose wheel coming off, but, despite the absence of comments on the car, the date of the first flight was postponed. September 6 P. O. Sukhoi sent an application to the MAP for the first C-1 flight, but the events of the next day made their own adjustments. On September 7, another taxiing and a small approach were planned, but as soon as the car broke away from the strip, it suddenly soared 15 meters. The length of the landing strip in front was clearly not enough. The pilot had no choice but to help the very "flying" machine. Having increased the thrust of the turbojet engine to maximum speed, A. G. Kochetkov continued his flight. Having made a flight in a circle, C-1 made a landing. For the salvation of the prototype, the pilot was commended and given a bonus in the amount of a monthly salary. The Chief's mood was not even spoiled by the fact that the competitors managed to get ahead of him - their cars took to the wing in 1954. Mikoyan was the first to distinguish himself - his E-2 under the control of E. K. Mosolov took off on February 14, and two and a half weeks later, Johnson's XF-104A fighter took off from the factory runway.
The first stage of factory tests of the S-1, equipped with an afterburner turbojet engine AL-7, was completed on January 23, 1956. By this time, the car had completed 11 flights and flew four hours and five minutes. At the same time, it was possible to cross the sound barrier in level flight and to determine the main characteristics of the stability and controllability of the aircraft. In the meantime, the engine builders prepared a flight copy of the AL-7F engine with an afterburner and an adjustable two-position nozzle. Engine thrust at maximum was 6850 kg, and afterburner was 8800 kg. After minor modifications, it was installed on the C-1, and in March 1956, the second stage of testing the machine began. Already in the first flights after switching on the afterburner, the plane easily accelerated to a speed of M = 1, 3-1, 4. One more step, and the barrier at M = 1, 7 was taken. Now the testers swung at two speeds of sound!
In each new flight, to reduce the risk of losing the only prototype, the speed was increased by Mach 0.1. On June 9, the aircraft reached a speed of 2070 km / h (M = 1, 96), but suddenly the air intake surge began, accompanied by a shaking of the fuselage nose, pops and "bubbling" in the air intake channel, as well as periodic changes in engine thrust. Makhalin, turning off the afterburner, slowed down. The surge has stopped. The next flight ended the same. It became clear that flights to achieve maximum speed would have to be stopped until the reasons for the surging were clarified and the means to overcome it were developed. But even then the achieved speed exceeded the required TTT of the Air Force, which aroused the enthusiasm of the customer and the MAP leadership, since it promised a sharp increase in maximum speed compared to the fastest Soviet MiG-19 fighter at that time … The reason for the negative phenomena in the air path was the uneven air flow at the entrance into the engine and stall phenomena on the blades of the supersonic stage. Then the designers changed the shape of the nose cone, which allowed Makhalin to accelerate to 2.03M (2170 km / h) and finally take the "second sound".
Aircraft S-1 during testing at maximum speed
References:
Adler E. G. Earth and sky. Aircraft designer's notes.
Markovsky V. Yu., Prikhodchenko I. V. The first supersonic fighter-bomber Su-7B. "Get out of the shadows!"
Aviation and time // 2011. №5. "The plane of the era of jet classicism."
AviO. Anthology of Su-7.
Wings of the Motherland // Adler E. G. How the Su-7 was born.
Tsikhosh E. Supersonic aircraft.
Wings of the Motherland // Ageev V. On the threshold of the "second sound".
Astakhov R. Front-line fighter Su-7.
The history of aircraft designs in the USSR 1951-1965
