In the late nineties and early 2000s, the highlight of the program of Russian air shows was the new C-37 Berkut aircraft, which later received the new Su-47 index. The unusual appearance of the aircraft, associated with the use of a forward-swept wing (CBS), attracted the attention of all people associated with aviation or simply interested in it. The excitement around the S-37 project, often called the main reliable domestic combat aviation, was in no way inferior to later disputes and discussions of the current PAK FA program. Aviation experts and amateurs predicted a great future for the development of Sukhoi and tried to predict how effective it would be in the army. However, more than 15 years have passed since the first flight of the Su-47 aircraft, and the Russian Air Force has not received serial fighters based on this project. It was only after several years of heated discussions in the mass consciousness that the understanding of the fact that the C-37 was purely experimental and from the very beginning was not considered as the basis for combat equipment for the near future was established. Nevertheless, a number of nuances of the Berkut project remain secret to this day, which sometimes leads to renewed disputes.
Secrecy mode
The first prototype of the C-37 aircraft took off on September 25, 1997. However, the existence of a secret project became known earlier. Back in 1994-95, the foreign aviation press wrote about the development of some promising Russian fighter. Western journalists cited the alleged name of the development - C-32. In addition, some publications have suggested an interesting technical feature of the project. According to the information provided, the new C-32 was supposed to have a forward swept wing.
As it turned out, foreign aviation journalists were partially right. Confirmation of their assumptions appeared already in early 1996. Then the publication "Bulletin of the Air Fleet" published a photo from the meeting of the Air Force Military Council. In addition to representatives of the aviation industry and the air force, it was attended by two small aircraft models. In one of them, the already well-known Su-27M fighter was quickly identified, and the second raised a lot of questions. The black mock-up with white numbers "32" on board had a forward horizontal tail and, most importantly, a characteristic forward swept wing. A few months after this publication, diagrams and drawings based on the existing photograph appeared in the foreign press.
At the same time, one cannot fail to note the official reaction of the Sukhoi company. The representatives of the design bureau answered all questions about the project of the fighter with KOS in the same way: no work is being done in this direction. As it turned out later, such answers, more like excuses, were due to the secrecy regime. As for the classified works themselves, they started back in the early eighties.
On the way to "Berkut"
In the late seventies and early eighties, the leadership of the Air Force, together with the State Committee for Aviation Technology under the USSR Council of Ministers (GKAT), reflected on the state of the aircraft fleet in the next decades. In 1981, the I-90 program was launched, the purpose of which was to define the appearance and develop the "Fighter of the nineties". The head enterprise in the I-90 project was the design bureau named after V. I. Mikoyan. The Sukhoi Design Bureau managed to convince the industry leadership that the existing Su-27 aircraft has great modernization prospects and therefore the organization can engage in other projects.
The new general designer of the design bureau im. Sukhoi M. P. Simonov, appointed in the early eighties, nevertheless suggested starting a new fighter project, but leading it on an initiative basis. The last nuance of the project was probably due to the desire of the designers to tackle a promising, but controversial topic, which could not give any practically applicable results. In the aircraft with the symbol C-22, it was proposed to use a forward-swept wing. Compared to traditional designs, it had several significant advantages:
- greater aerodynamic quality when maneuvering. This is especially pronounced at low speeds;
- high lift in comparison with a straight swept wing of the same area;
- better working conditions for mechanization, which leads to improved take-off and landing characteristics and controllability;
- lower stall speed in comparison with a straight swept wing and better anti-spin characteristics;
- the displacement of the structural elements of the wing closer to the tail of the fuselage, which makes it possible to free up the volumes for the cargo compartments near the center of gravity of the aircraft.
These and other advantages of KOS made it possible to create a new fighter, the characteristics of which would be noticeably higher than those of the machines of the traditional scheme. But, as always happens, the advantages were accompanied by serious disadvantages and problems that had to be solved in the near future. The forward-swept wing posed the following questions to the designers:
- elastic wing divergence. The WWTP begins to twist at certain speeds, which can lead to its destruction. The solution to the problem was seen to increase the rigidity of the wing;
- weight of the structure. A fairly rigid wing, made from the materials available at that time, turned out to be too heavy;
- frontal resistance. With a further increase in speed, the rather rigid negative sweep wing faces new problems. The specific nature of the flow around the wing leads to a noticeable increase in drag in comparison with the characteristics of a straight swept wing;
- shift of the aerodynamic focus. At high speeds, an aircraft with a KOS is forced to actively carry out longitudinal balancing.
Only the solution of all these problems, directly related to the reverse sweep of the wing, could have a positive effect in the form of the advantages described above. Designers under the leadership of M. P. Simonov started looking for solutions.
Already in the early stages of the C-22 project, the main technological solutions were determined, which were later applied to the C-37. A wing of sufficient rigidity was proposed to be made with extensive use of carbon fiber reinforced plastics. The number of metal parts has been reduced to a minimum. In addition, the wing was equipped with advanced mechanization with deflectable toes, designed to optimize the flow at high angles of attack. The appearance of the S-22 aircraft was determined by the mid-eighties. It was a single-engine fighter with a canard aerodynamic configuration. Perhaps by the end of the decade, the S-22 could have made its first flight, but there was no suitable engine in the Soviet Union. All available aircraft engines did not provide the required thrust-to-weight ratio.
Studies were carried out for a possible change in the project for a new engine from among the existing ones. This work ended without much success: the plane was still too heavy for the available engines. In this regard, on the basis of the C-22, they began to design a new C-32 aircraft. The aerodynamic features of the C-32 were almost completely consistent with the previous project, but a new power plant was used. Two TRDDF RD-79M with a thrust of 18,500 kgf each could provide a heavier machine with sufficient thrust-to-weight ratio. Moreover, calculations showed that these engines were capable of providing the S-32 aircraft with a long flight at supersonic speeds without using afterburner.
In 1988, due to the deteriorating economic situation in the country, the S-32 project was almost closed, but the command of the navy stood up for it. The admirals got acquainted with the design characteristics of the promising aircraft and demanded to create a carrier-based fighter on its basis. For several months KB im. Sukhoi created the Su-27KM project. In fact, it was a significantly modified S-32 airframe, equipped with Su-33 equipment and weapons. According to the project, the vehicle had a maximum take-off weight of 40 tons, which, when using RD-79M engines, did not allow aircraft-carrying cruisers to take off from a springboard as the Su-33 did. To solve this problem, the so-called. ballistic takeoff. The essence of this technique was that the insufficient speed when taking off from the springboard was compensated by the height and characteristics of the forward sweep wing. Thanks to KOS, losing several meters of height, the plane could pick up the required speed and go into level flight. Airplanes with straight swept wings could not use ballistic take-off, since insufficient lift and horizontal speed would have been guaranteed to lead to a fall into the water.
Multipurpose carrier-based fighter Su-27KM (later S-32), designed at the OKB im. P. O. Sukhoi for equipping Soviet aircraft carriers of projects 1143.5 (Kuznetsov), 1143.6 (Varyag) and nuclear 1143.7 (head - Ulyanovsk). After the collapse of the USSR, the Su-27KM project in the form of a combat fighter was discontinued due to the curtailment of the construction of aircraft carriers and the financial problems that arose, and the topic was transformed into a research work on the study of the "forward swept wing" (KOS), during which a copy for static strength tests was completed to the experimental aircraft C.37 "Berkut", now known as the Su-47 (photo
Project S-37
The deteriorating economic situation in the country did not allow the Navy to obtain a promising carrier-based fighter. In the plans of KB them. Sukhoi included the construction of several prototypes of the Su-27KM aircraft, but the cessation of funding did not allow this to be done. In the early nineties, aircraft manufacturers decided to continue research on the reverse swept wing, using existing developments. The next project was intended to combine all the achievements and technical solutions, adjusted for financial problems and the state of the aviation industry. The project was named S-37.
First of all, it should be noted that the reduction in funding and the return of the initiative status to the project affected the number of planned prototypes. It was decided to build only one prototype. According to some sources, the constructed glider was first sent for static tests, where, using the most modern techniques, its actual strength was assessed. In this case, no destructive loads were applied, and all impacts corresponded to the calculated operational ones. This made it possible to significantly reduce the cost of the project due to the construction of additional gliders. After static tests, the first glider was retrofitted to the state of a full-fledged aircraft.
The finished experimental aircraft C-37 "Berkut" is interesting both for specialists and for the general public. The first attracts the attention of the applied technologies, the second - the unusual appearance and the declared possibilities. From an aerodynamic point of view, the C-37 is an integral longitudinal triplane with a high swept back wing. The front and tail horizontal empennage is made all-turning and has a relatively small area. According to some reports, the aerodynamic characteristics of the C-37 allow it to reach angles of attack up to 120 ° and perform the so-called. dynamic braking ("Pugacheva's cobra"), however, on tests and during demonstration performances, this opportunity was almost never used due to restrictions on flight modes.
One of the main achievements of KB them. Sukhoi, Irkutsk Aviation Plant and related enterprises can be considered the creation of a technology for the production of long composite parts. During production, large flat parts are formed, which can then be given complex configurations. The finished parts fit together with the highest precision. The outer surface of the airframe of the C-37 aircraft consists of a large number of such composite panels, the largest of which are about 8 meters long. This minimizes the number of joints and various protruding parts, including fasteners. Ultimately, the use of large composite panels has a beneficial effect both on the rigidity of the wing structure and on the aerodynamics of the entire aircraft.
The empty weight of the S-37 aircraft was 19,500 kg, with about 13% of parts made of composite materials. Due to the experimental nature of the project, not only elements specially created using new technologies were used in the design of the aircraft, but also those already mastered in production and borrowed from other aircraft. For example, the landing gear, canopy and some onboard systems were taken almost unchanged from the Su-27 aircraft.
The forward-swept wing of the C-37 aircraft has consoles with sweep along the leading edge of -20 ° and -37 ° along the rear. In the root part, the leading edge forms an influx of straight sweep. The conjugation of the inflow and the cantilever with forward and reverse sweeps made it possible to improve the flow around this part of the airframe. The leading edge of the wing is equipped with a deflectable nose, the rear edge is equipped with a single-section flap and aileron. Mechanization almost completely occupies the wing edges. Due to the stiffness requirements, the wing structure is 90% composed of composite parts. The remaining elements are made of metal and are used in the power set.
Close to the central part of the fuselage, on the sides of the air intakes, the Su-37 has an all-moving forward horizontal tail of a trapezoidal shape. The horizontal tail is also made all-turning and has a characteristic elongated shape with a large sweep of the leading edge. The vertical tail is similar to the keels of the Su-27 fighter, but has a smaller area. Due to some design nuances, it was possible to significantly increase the efficiency of its work, which made it possible to reduce the area.
The fuselage of the S-37 aircraft has smooth contours, and its section is generally close to oval. The design of the nose is close to the design of the corresponding units of the airframe of the Su-27 aircraft. On the sides of the rear of the cockpit there are unregulated air intakes. Their shape is formed by a sector of a circle, truncated by the surfaces of the fuselage on the side and the root inflow of the center section from above. On the upper surface of the middle fuselage, near the wing root, there are additional air intakes used for takeoff and landing or during intensive maneuvering. As can be seen from the shape of the fuselage, the air intake channels are bent on the way to the engines, which, among other things, covers the compressor blades and thereby reduces the visibility of the aircraft in the frontal projection. On the sides of the engine nozzles on the C-37 aircraft, there are relatively small fairings, inside which the necessary radio-electronic equipment of the appropriate size can be placed.
Due to the lack of other suitable engines ready for production, the D-30F11 turbojet engine was chosen for installation on the C-37 aircraft. These engines represent a further development of the D-30F6 used on the MiG-31 interceptors. It was assumed that in the future the S-37 will be able to get new, more advanced engines with higher thrust, lower fuel consumption and a thrust vector control system. Turbojet engines with afterburner thrust of 15600 kgf gave an aircraft with a normal take-off weight of about 25.6 tons rather high performance. The declared maximum flight speed is 2200 km / h at high altitude and 1400 km / h at the ground. The practical ceiling was determined at the level of 18,000 meters, the practical range was 3,300 kilometers.
Until now, not much is known about the composition of the onboard equipment of the S-37 aircraft. According to reports, the aircraft is equipped with a fly-by-wire control system based on the EDSU of the Su-27 aircraft. There is also an inertial navigation system with the ability to use the signal of navigation satellites, as well as modern communication systems. To facilitate the work of the pilot, an ejection seat K-36DM was installed on the C-37 aircraft, which differs from the serial products of this model. The back of the chair on the "Berkut" is located at an angle of 30 ° to the horizontal. This helps the pilot to more easily endure the overload arising from intensive maneuvering. According to some sources, the C-37 used controls unusual for domestic combat aircraft: instead of the standard central control stick of the aircraft, a small knob was used, located on the right dashboard. The engine control sticks and pedals remained the same, similar to those used on the Su-27.
As an experimental aircraft, the C-37 prototype did not carry any weapons. Nevertheless, in the left wing influx, a place was provided for the GSh-301 automatic cannon with ammunition (according to some reports, the prototype aircraft still received a cannon), and in the middle of the fuselage there was a cargo compartment for weapons. As far as is known, during the first tests, the S-37 did not carry any weapons, since the purpose of the flights was to test the flying qualities of the machine.
Challenges and notoriety
The first flight of the C-37 aircraft (the first prototype, taking into account the possible construction of several machines, was called the C-37-1) took place on September 25, 1997. Under the control of test pilot I. Votintsev, the new aircraft spent about half an hour in the air and did not cause any serious complaints. The first series of test flights lasted until the spring of 1998, after which a break was made. For some time, the designers of the Sukhoi company analyzed the information collected, made the necessary adjustments to the project, refined the car and made a program for the next stage of testing.
For the first time to the general public, the C-37 "Berkut" aircraft was shown only in 1999 at the MAKS international aerospace show. The demonstration could have taken place earlier, at the MAKS-1997 exhibition. In the summer of 97, the prototype was already in Zhukovsky and was preparing for testing. There were proposals to show an experimental aircraft in a static parking lot, but the Air Force command did not approve of them. It is worth noting that two years later the Berkut also did not make it to the static parking lot. The level of secrecy of the project was such that the only plane taxied to the runway of the airfield just before its demonstration flight. After landing, he was towed to one of the hangars, away from the viewer's eyes.
Despite an almost two-year delay in showing the plane to the public, the first information about it appeared in the media just a few days after the first flight. The official confirmation of the existence of a new Russian aircraft with KOS produced the expected result - all over the world disputes about the features and prospects of the S-37 erupted. An interesting feature of the media coverage of the project was the fact that the Berkut was almost immediately declared a promising fifth-generation fighter, which will go into series production in the very near future and begin to enter the army. The statements of the Sukhoi firm about the experimental nature of the project barely made their way through the other information noise.
Against the background of a mass of discussions and heated debates, employees of the Sukhoi company, LII and related enterprises were testing the new aircraft, collecting a lot of important data. The C-37-1 prototype helped to establish the correctness of some technical solutions and to show the fallacy of others. At the beginning of the 2000s, talks were resumed again about the creation of a combat aircraft on the basis of the C-37. It was proposed to equip it with a modern complex of on-board electronic equipment, including a forward-looking radar with a phased antenna array and an additional radar for monitoring the rear hemisphere. It was proposed to include guided and unguided missiles and bombs in the armament of a promising fighter, which it could carry on the internal and external sling.
Naturally, all attempts to create a combat aircraft based on the experimental "Berkut" did not lead to any result. Sukhoi continued to use the only prototype for purely research purposes, showing it at exhibitions from time to time. So, for example, at the MAKS-2001 salon the S-37-1 aircraft was first shown under a new name - Su-47. The reasons for this change were dictated, first of all, by drawing attention to the project. In the practice of the Sukhoi firm, the letter "C" was always assigned to prototypes, and the finished aircraft received the index "Su". The name change did not affect the test program in any way.
Tests of the S-37-1 or Su-47 aircraft continued for several years. The aircraft was tested at different speeds and flight modes. According to some reports, an active test of the Berkut's capabilities led to some problems with various structural units. For this reason, at the end of the first stages of testing, restrictions were introduced on the maximum flight speed, angle of attack, etc.
The S-37 / Su-47 Berkut project allowed Russian aircraft manufacturers to test several important ideas and collect a wealth of information about forward-swept wing aircraft. The information obtained about the nature of the flow and the behavior of an aircraft with a KOS in different flight modes allowed the domestic aviation science to close several blind spots in theories. By the middle of the last decade, the only prototype of the Berkut completed all the planned flight programs and parked.
It should be noted that after the end of the main test program, the Su-47 had a chance to take part in one more research work. Since this was the only domestic aircraft with the dimensions of a fighter, but at the same time equipped with an internal cargo compartment, it was chosen as a platform for testing some elements of the future T-50 fighter (PAK FA program). In 2006-2007, Berkut received a new cargo compartment, created according to the T-50 project. The purpose of this revision was to test the doors and internal equipment of the compartment for operability in real flight conditions. Su-47 with such a cargo compartment made about 70 flights with open doors. Interestingly, the doors of the first test compartment were opened and fixed while still on the ground. In 2008-2009, the Su-47 received an updated payload volume with flap opening mechanisms. In 2009, 25 flights were performed with the opening of the flaps.
As far as we know, the Su-47 was used as a stand not only for the doors of the cargo compartment. During new tests under the PAK FA program, he carried weight simulators of promising guided missiles. The information obtained during the new test flights of the Su-47 aircraft was actively used at the final stages of creating the cargo compartments of the promising T-50 fighter.
An unambiguous result
The first prototype of the C-37-1 aircraft began to be built two decades ago, took off in 1997 and was actively tested until the first half of the 2000s. The forward-swept wing project was closed several years ago. The experimental aircraft showed everything it was capable of and made it possible to collect the maximum of necessary information. Moreover, the Su-47, which was only mistakenly considered a fifth generation fighter, has become a flying laboratory for testing new technologies related to the armament of promising aircraft.
The aircraft's participation in important experiments and tests has had a partly negative effect on possible displays to the general public. The Su-47 regularly took part in air shows in Zhukovsky until the middle of the last decade, but never got into a static parking lot. All demonstrations consisted of demonstration flights. Experts and the interested public were not able to closely inspect the interesting, but almost no practical prospects for the aircraft.
Despite the long-term completion of the project, disputes about the pros and cons or prospects of both the Su-47 aircraft and the entire class of aviation technology with a forward-swept wing still do not stop. The pros and cons of KOS, aircraft projects with it, etc. are discussed over and over again. There is still no consensus on the prospects for aircraft like the Su-47. As for the "Berkut" project itself, it should be recognized as successful. Although the Su-47 did not become the basis for promising fighters that surpass all modern technology in their characteristics, it did everything it was intended for. The S-37 / Su-47 was created as an experimental aircraft for testing new technologies. He coped with this task brilliantly, and the role of the latest combat aircraft with unique characteristics should be taken over by other developments.
