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T-10 Su-27 FLANKER-A Prototype

Design work on a 4th-generation fighter, later known as the Su-27, began at the Design Bureau of P.O. Sukhoi on the designers' initiative under the supervision of O.S. Samoilovich at the end of 1969. The new plane was required to provide effective engagement of the F-15 fighter being developed in the USA under the FX program from 1966, the Soviet fighter being positioned, the same as its foreign rival, as an "air-superiority" aircraft. In contrast to the USSR's previous efforts to "catch up" with the Americans, Soviet aircraft designers decided this time to produce an aeroplane in no way inferior, and even superior, to "the adversary". To achieve this objective, the Design Bureau put quite a few challenging ideas into the configuration under development right from the start, such as placing the engines widely spaced in two nacelles under the fuselage body, and placing the vertical tail unit in between the wings and horizontal tail unit.

At the initial stage, the Design Bureau produced a great number of alternative configuration concepts, including the one based on a conventional solution, with an integral body, modelled on the F-15; but interestingly enough, it was ae new concept of airframe configuration that the subsequent design efforts were based upon. Another important feature of the new fighter was to be implementation of the concept of longitudinal static instability, with balancing achieved through use of an electronic distance control system (EDCS). Introduction of this innovation promised a substantial decrease in losses for balancing and a dramatic improvement in the plane's manoeuvrability in dogfighting.

In the period 1971-72, the aeroplane conceptual design was being developed on a tender basis by the Design Bureaus of A.I. Mikoyan, P.O. Sukhoi, and A.S. Yakovlev. The design of the Su-27 (factory code T-10) had been completed by September 1971 and was submitted for review to Air Forces in February 1972.

In 1972, after the aeroplane's PR for the conceptual design had been updated, it was decided to start parallel development of two fighter versions: a "light" one to be produced by Mikoyan Design Bureau and a "heavy" one, assigned to Sukhoi Design Bureau. Based on input from the military, the Su-27 was redesigned in 1972-73 to meet all the requirements, with the aircraft's wing area, engine design thrust and integral fuel tankage increased. This resulted in an exceptional range on internal fuel for a Soviet-made fighter. The high performance of the new AL-31F turbofans ("Article 99") developed by the Design Bureau of A.M. Lyulka, produced specially for the Su-27, were expected to provide the plane with a high thrust-to-weight ratio, and therefore superior characteristics of acceleration, rate of climb and manoeuvrability.

The problems caused by inadequacies of Soviet-produced avionics components, unavailable unless heavy and bulky, had to be dealt with by the Design Bureau through introduction of improved design and configuration solutions as well as use of new and promising technologies. In 1973-74, the Design Bureau continued its studies to identify and engineer the plane's optimal airframe and individual assembly configuration, and the composition of systems, equipment and weapons. The configuration options were tried out with large-scale models in wind tunnel installations at CAHI, SibNIA and MAI facilities. N.S. Chernyakov was appointed the Su-27's chief designer in 1973. The detailed design work on the aeroplane began in 1975.

The Su-27's 1975 production configuration featured standard aerodynamic design, with an integrated variable sweep ogive wing configuration, leading-edge root extensions, an all-movable horizontal tail unit mounted on the centre wing section continuation beams, and twin tail fins mounted on engine nacelles at the airframe stern-post. The adjustable engine air intakes with horizontal air brakes placed at the top were put on either side of the plane's roll axis, and suspended from the centre wing section. This inlet configuration ensured highly stable flow at high angles of attack, which is of vital importance for an aircraft designed for air-combat manoeuvring. The engine nacelles at the tail were an extension of the air intakes. The landing gear featured a standard tricycle type configuration. A major problem inherent in the configuration option chosen was finding a place for the main landing gear bays. Finally, a place for them was found in the "dead air" of the centre wing, under the intake ducts, the gear legs retracting with the wheels turned. The flaps were also used as speed brakes. The airframe was significantly lightened through compact configuration and optimization of the design structure, as well as large-scale use of titanium alloys in the design.

The development of the Su-27 was approved by a decree of the government on 19 January 1976 as "a single air-superiority fighter for Air Forces and ADF aviation". In February 1976, M.P. Simonov was appointed chief designer of the Su-27. By that time, the Design Bureau had already started building the first three T-10 prototypes (two for flight testing and one for structural testing), with brass-board marginal testing of all major systems of the future craft already in progress. Note that for trying out the Su-27 aerodynamics, powerplant, control system, attack and navigation equipment and weapons, the Design Bureau and FRI set up and tested a dozen various flying laboratories, conducting studies on an unprecedented scale in Sukhoi's practice of engineering systems for a new plane.

The engineering documentation produced was passed on to the Komsomolsk-on-Amur plant, which was appointed main contractor for production of the Su-27. In 1977, the facility started to gear up for full-scale manufacture. In October 1977, the Design Bureau's conceptual design of the Su-27 aeroplane successfully passed critical design review and was approved by an Air Forces committee chaired by 1st Deputy Commander-in-Chief of Air Forces, Air Marshal A.N. Yefimov. The first two flying prototypes of the Su-27 were fitted with AL-21FZAI engines.

Construction of the first prototype T10-1 was completed in April 1977. On 20 May 1977, the design bureau's chief pilot V.S. Ilyushin performed the first flight. In May 1978, the testing programme was expanded to cover a second prototype, T10-2, and the year after that, in 1979, it received the prototypes T10-3 and T10-4, fitted with operational engines AL-31F (Article 99, with low gearbox). To speed up the trials, it was decided to make available for testing the entire development batch of Su-27s made by the production plant in 1980-81. Later on, the planes were used by the Design Bureau and FRI for testing individual systems.

From the very beginning of designing, the Su-27 developed as a fighter-interceptor without any capability of operating against ground targets. The American F-15 Eagle fighter was taken as the starting point - a "rival." Its data were put into a computer and played through in competition with Sukhoi's initial design model, which obtained the ratio of 1.35:1. In accordance with the adopted concept, Sukhoi began building the T-10 aircraft. This was the first "unstable" fly-by-wire aircraft in the Soviet Union. In Western terminology, this is an aircraft with aerodynamics determined by the parameters of the control system, or an aircraft with electronic stability. The American F-16 was the first such aircraft. An ogival wing with a blunt strake and deformation of the middle surface were included in the integrated aerodynamic design developed jointly by the aerodynamics department of the Sukhoi OKB and the Central Aero-Hydrodynamics Institute.

In the summer of 1977, after Sukhoi's chief pilot, Hero of the Soviet Union Vladimir Sergeyevich Ilyushin, made the first flight in the T-10, and testing began. All went well, and 10 more aircraft were begun. But one day, having soberly weighed everything and having input theupdated data into the computer, Sukhoi obtained a reverse ratio - losing with a result of 1:1.35. Having fulfilled all points of the technical task, Sukhoi made a mediocre aircraft. It did not conform to the world level either in range or maneuverability. So, it was a typical scandal of the "times of stagnation" - the project conforms completely to the technical task, raised no doubts with the customer, and the ministry was ready to report on the next victory of Soviet scientific and technical thought. But the engineer suddenly "turns everything upside down and beats his chest", and states that everything must be started from the beginning.

Deputy Minister Ivan Stepanovich Silayev gave Sukhoi a lot of support. But there was a total lackof understanding on the part of Minister V. A. Kazakov. Sukhoi stood firmly, and by the time theissue was resolved they were armed with a new concept, returning to the starting positions of superiority overthe competitor. That is, Sukhoi's plan for a new aircraft was ready, although under the same name. Sukhoi also kept within the deadlines for putting it in service, although this required considerable efforts. Stanislav Kashafutdi, an aerodynamicist from the Siberian Scientific Research Institute of Aviation, made a large contribution to this.

The fact that the series-produced Su-27's differ from the T-10 prototype on permanent display at the Moninskiy Air Force Museum is readily apparent to the aviation enthusiast. First of all, there was a decrease in the mid-section by 20 percent. Anyone who is familiar even with the rudiments of designing will know what this means. It turned out that the ejection seat designed by Gay Severin and the wheels of the side landing gear struts remained from the previous aircraft. Everything else was done over. Next came the wing. It was totally different on the series-produced Su-27. The wingroot strake had a sharp edge. The leading edge of the wing is straight and has an adaptive slat its entire span which operates in conjunction with the fiaperons. The electric-command system commands all this equipment, as if its channels are spread out to ensure combat survivability of the aircraft. If the readings of the channels differ, the system obtains a "quorum," and the "inaccurate" channel is disconnected. That is why the reliability is so high.

The position of the nose gear was changed. On the prototypes, worried about high loads on it, Sukhoi positioned it closer to the nose. Taking radical steps, the designers reinforced the strut and moved it more to the rear. As a result, maneuverability on the ground was increased. The aircraft turns around practically in place. The new position of the strut was favorable for reducing the likelihood of foreign objects from the runway getting into the engine air intakes. Grids installed in the air intake ducts also served to protect the compressor blades. They retract atcruising flight.

One of the visible differences between the prototype and the series-produced aircraft is the configuration of the tail fins. The aerodynamics of the Su-27 are, to a considerable extent, vortical. The vortices generated by the leading-edge wingroot extensions serve to increase the efficiency of the control and stabilizing surfaces andto prevent boundary-layer separation at large angles of attack. The wingroot extensions on the T-10 and the Su-27 are fundamentally different. And the positioning of the tail fins was chosen accordingly. It cannow be said that the tail fins are positioned where they should be. But it should be noted that vortical aerodynamics are very complex. During the process of testing and development, Sukhoi figuratively speaking, "pulled" the tail fins all over the aircraft.

The collective of the OKB imeni Arkhip Mikhaylovich Lyulka, and during the development of the AL-31F engine simply its design bureau, was Sukhoi's colleague and thought like Sukhoi in spirit and in the approach to designing the aircraft. They had designers working there who were willing to take a risk using the most modern technologies. The AL-31 was the first bypass engine of this class in the Soviet Union. It is at the highest level of world achievements for specific parameters, as all developments of this design bureau were at one time.

The test pilots of the design bureau were people for whom risk, courage, and a willingness to devote their lives to learning the unknown were categories deprived of any literal sense. Initially, Sukhoi did not know how the frequency responses of control match the human capabilities. Test pilot Yevgeniy Solovyev ended up in a resonant mode and was killed, and the aircraft was destroyed. The "black box" remained intact and accurately recorded the tragedy. This helped sukhoi to correct everything immediately. Then another aircraft was lost. Aleksandr Komarov perished. Sukhoi searched for a long time for the cause of this accident.

Everything finally became clear after a unique flight by Nikolay Sadovnikov, in which a large part of a wing panel flew off at extreme operating conditions. It turned out that Sukhoi under-estimated by several fold the design hinge moments introduced when designing the adaptive slat. During wind tunnel tests, there are errors that are usually corrected by introducing correction factors. In this case, the model effect gave a compound error. It also resulted in Komarov's death.

Located in the cockpit of an aircraft with part of the wing torn off, Sadovnikov already had his hands on the ejection seat levers. Suddenly, by some feeling characteristic only of such extraordinary pilots, he understood that the plane was settling down. He left the ejection detonator alone and brought the aircraft to altitude. There he understood that he could control it and even land. The Su-27, obeying the will of the master, actually landed with one wing. When information about a similar incident with an F-15 Eagle appeared in Western journals, Sukhoi designers were not surprised. But the main result of Sadovnikov's courageous act, bringing the damaged aircraft to the airfield, was that the causes of Komarov's accident became completely clear. One of the versions given by the accident board was confirmed. Since then, there was not a single accident due to technical reasons in a series-produced aircraft.




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