Ekranoplanes: Soaring above the waves

Translated from Russian by Boris Krotkov ©, special thanks to Caz Dalton




In a PURSUIT OF SPEED

The important quality of speed was, in all times, the object of the steadfast attention of ship-builders. But the increase of speed for ships was limited by quickly growing hydrodynamic resistance in the case of an insufficient capacity sail and oar movement.

This restriction was removed with the introduction on ships of mechanical engines in the middle or the end of the superstructure, but the situation did not change , even for ships at the beginning of the Nineteenth century. But speed could only go so far in any case, and even nuclear powered ships of the Twentieth century concede little to steamships. The trick in speed was connected to idea to lift the keel of a vessel from water to air, an environment 840 times less dense. The main obstacle, growth of resistance of water, disappeared.

The first vehicle in the world to use underwater wings (VOUW) was constructed in 1894 by French engineer Sharle D'Alambier. The boat was unsuccessful and steady movement to achieve it proved not possible. However, the idea was perceived with interest: in 1906 E.Forlanini constructed a winged-boat in America, developing a speed 40 knots. D'Alambier also constructed the first self-propelled sea-glider (1897), which tested at speed about 20 knots.

In 1935, under the direction of the professor of Moscow Air Institute V. I. Levkov , the first vessel to fly on an air pillow (VOAP) L-1 was created. The fact of its existence and subsequent airboats, including record L-5, were top secret and in the West irrespective of Levkov developed their own technique of account VOAP. In 1959 under a new management, Kokkeren in Great Britain constructed his "Hovercraft", the first one in which a wide public has seen.

The Sea-glider, VOUW, and VOAP were- just steps in the development of the idea of a high-speed vessel from water to air. The logic that led to the completion of this idea was Ekranoplanes (Screenplanes) flying above the water.

PRINCIPLE of MOVEMENT

To be brief about physical bases of the movement of this high-speed vessel at a surface of the screen (usually it is water, but it may be also be land and ice).

The screen effect, changing of carrying properties in water to a wing at small altitudes of flight - was opened by airmen. For the first time pilots met with it on take-off and landing modes of planes. As flying data of the plane, in particular its stability, were not designed for this effect, in some cases it caused disasters and accidents of planes on take-off and landing modes. Apparently, one of the first domestic works, devoted to the influence of ground on aerodynamic properties of a wing, was an experimental work of B.N. Yuriev (1923). During 1935 - 1937 a complex for the experimental and theoretical research in this direction was carried out by Y.M. Serebriyski and Sh.A. Biyachuev at TSAGI. At about the same period theoretical research was carried out by the outstanding foreign scientist: A. Betc, K.Wieselberg, S.Hagget, D.Bagleya, M.Finn. The results of his research allowed a qualitative estimation of the influence of the screen effect on the aerodynamic characteristics low-level-flying wing. In particular it was shown that as the elevating force of a wing grows more, i.e. the closer is the wing to ground; the resistance decreases longitudinal moment changes. It allowed developing the appropriate recommendations for controlling of aircraft, that has influence of the screen to the aerodynamic characteristics on take-off and landing modes. Nevertheless, for aircraft this effect continues to remain "harmful".

EKRANOPLANES in the AIR

Apparently, the first ekranoplane was created by Finnish engineer T.Kaario. In the winter of 1932 above a frozen surface of a lake he tested an ekranoplane, towed by aerosledges. Later, in 1935/1936 Kaario constructed an advanced ekranoplane, equipped with an engine with a propeller.

In 1939 the American engineer D.Warner, working with the speed boats, offered the project of a vessel with a system of carrying air wings.

By the order of military department of Sweden , extensive works were carried out in the 40's by I. Troeng. Two ekranoplanes were constructed, but the results did not satisfied the customer, and work was curtailed.

The experience of the Second World War showed the efficiency of high-speed ships, especially for sudden attacks on the enemy . After the war , the NAVY order for a small (weight up to 5 tons) experimental ekranoplanes to be constructed in the different country of the world. However, the large apparatus (military and civil) had not left the drawing stage. Designing the flying apparatus, intended for a high-speed movement near the border of two environments (air and sea water), presents a set of problems, that are not met in the other areas of engineering. Among them was maintenance of the stability in the movement of the apparatus at very small (0.5 to 2 m) heights of flight; durability and simultaneously small weight of a design, considered on impact with a crest of a wave at high (200 to 400 km/h) speeds; a choice a material that would not be destroyed in sea water (ship-building materials are too heavy, and air materials are quickly corroded); the creation of powerful and easy engines for work in sea conditions (which are not affected by water splashes and salt) and set of other no less difficult problems. The decision to these problems required a lot of theoretical work and experimental research, design and experimental-design work, and tests. Probably, for this reason western firms hesitated to develop ekranoplanes completely because of the fear and risk and stopped work, as soon as the government refused to invest in the research. Such fate overtook the missile ship of Grumman, the anti-sub ekranoplane RAM1, its descendant RAM2 and many other projects. Successful experimental apparatus were used sometimes as prototypes for the small civil ekranoplanes (for example, there was a series of ekranoplanes by G.Yorg, Switzerland-Germany).

If one trusts the writing of the press in the 1960 to the 1980s, in the USSR, work on an ekranoplanes was at the same stage as abroad; also on a half-legal basis enthusiasts created easy experimental machines by handicraft methods, but further development failed. However, at this particular time at least in two design offices (G.M.Beriev's air design bureau in Taganrog and ship-building R.E.Alekseyev's Central design bureau (CKB) in Gorky) were developed, where they built and tested prototypes (instead of an easy experimental machines!) of the Soviet battle ekranoplanes.

The increase of an elevating force can reach 50 % growth of an aerodynamic quality in relation of the elevating force to the force of resistance in 1.5 to 2.5 and more times. The influence of the screen to a wing , a very complex physical phenomenon, had to be completely clear in the understanding of the mechanism of this influence. For example, there are such modes of a movement of a wing above the screen, when at reduction of the height of flight the elevating force is not increased, but on the contrary, decreased.

TREE of EKRANOPLANES


The British aviation magazine "Flight International" recently published the genealogical tree of the Soviet ekranoplanes. The scheme, which is reproduced here completely, is indicative in two relations. First, until now there was no open information on the results of work in Taganrog (the apparatus designated by "Bartini", the author and chief of work was R.L.Bartini), there are marks of a question. Errors in designations and schemes of the Alekseyev's CKB (top family on the scheme) have been also made: a missile ship has a firm designation "Lun", instead of "Utka"; the second copy of "Lun" (on the scheme "Lun") has 8 engines, instead of 6. Secondly, the lines of development of three families (top - Alekseyev's CKB, middle - Bartini, bottom - light machines) are crossed nowhere. This scheme indirectly shows a degree of the secrecy of the work with a battle ekranoplanes in the USSR, as it not only did not show the plans to experts in the West, even the developers were not informed about businesses of the colleagues.


The apparatus created in Taganrog was not an ekranoplane. The collective of R.L.Bartini ( born in Italy, founded Italian Communist Party in 1921, and emigrated to the USSR in 1923, deserves a separate conversation), placed after moving from the Moscow area on the territory of Beriev's KB, offered to use screen effect for the improvement of the take-off and landing characteristics of a planes. In the words of N.A. Pogorelov's, who was the first assistant of R.L.Bartini in that time, one of the basic directions of work was the realization of the idea of a so-called contactless take-off and landing: the plane rises off ground or from water vertically on a small height, and then starts "leaning on the screen ". The realization of such a way in the rise and landing would result the creation of the plane that could be based without airfields, but on sea , which had the considerably best characteristics, than at the usual vertically flying plane.


In this concept, two anti-sub planes ?14s were built (reduction from the complete name "Vertically Take-off Amphibian"). For the account non-contact take-off and landing improvement reached the sea quality, there was the opportunity to fly up and to land in any heavy sea. Due to this, the time of patroling and efficiency of the application of the plane grew much. The vertical rise was provided through a gas pillow, which was formed under the centerplane through special blow-under engines. In 1976 one of these apparatus was transformed into an ekranoplane. It has received a designation 14M1P. On a nose, for blowing-under under a wings, there are two starting engines D-30M installed, plus the inflatable pontoons were replaced by rigid floats.


Through some time after the death of R.L.Bartini in 1974, the work on these flying apparatus was stopped from working on the flying boats A-40 and A-50 by TANTK (Beriev's KB). One of the apparatus, VVA-14 ?10687, harmed by a fire and without the tail, engines and wings, is on display in the Monino air museum today.

Alekseyev's KB (complete modern name is "Research-and-production association-Central design bureau on ships with underwater wings" of a name R.E.Alekseyev, the General Director V.V.Sokolov) descended from that organized in 1943 at the factory "Red Sormovo Hydrolaboratory". It formed under the initiative of the talented engineer Rostislav Alekseyev (1916 - 1980), who headed it. The theme of work - ships on underwater wings - was secret, and it was almost forty years to the moment of the successful test of a Forlanini's boat. Probably, this veil of secrecy prevented forty years after, the inclusion in the encyclopedia a few lines about the Main designer, winner State and Lenin's premiums, Deserved Inventor of the RSFSR, Doctor of the technical sciences R.E. Alekseyev, whose results of the work on VOUW are widely known and are used not only in Russia, but also in the West. Now the CKB is known by civil production - VOUW "Raketa", "Meteor", "Cometa", "Kolkhida", "Burevestnik", "Sputnik", "Voskhod". But little is known about the 50th in the CKB, that was development on the creation of a battle ekranoplanes. The conditions, which was so in those years in the USSR, when for the defensive projects money and the resources were allocated practically without restrictions, have allowed us to realize the fact, that seemed impossible for the Western economy with its strict and sober account: to overcome huge financial and technical risk and to create quiet battle machines, moreover - to build them serially.


The CKB worked in the several basic directions: creation of the attack ship, anti-sub ekranoplane, and cargo-descent vessel.

As result of work by the NAVY's order on the CKB's factory "Volga" in 1963 was constructed the huge (length 348-ft, span 131-ft, weight Loaded - 1091,000-lb) ekranoplane KM ("Korabl-Maket" (ship - model"), received the NATO nickname "Kaspian Monster". It was the largest and heavy flying apparatus in the world. The tests, proceeding for a several years, have shown the correctness of the basic engineering decisions. The first copy suffered from accident in 1969, when the pilot lost the visual horizon and had water impact at high speed, because of the strong fog. The second copy also suffered an accident in 1980 by pilot error and sank in the Caspian Sea, but all the crew were rescued.


"Kaspian Monster" became an ancestor of the several ekranoplanes. In 1987 the "Lun" was launched on water, the first ship of a series battle missile ekranoplanes (length: 242-ft, span: 144-ft 4-in, weight 882,000-lb). The main designer was V.Kirillovykh. The ship was armed by three pairs of cruise missile 3M80 or 80M "Mosquito" (NATO's designation SS-N-22 Sunburn). The second "Lun" was also pawned as missile boat, but the beginning of conversion has brought the corrective amendments, and it was built as a rescue boat.


In 1972 after a number of experiments and tests of the manned self-propelled models, the cargo-descent ekranoplane "Orlyonok" was constructed ( length: 190-ft 3 1/2-in, span: 103-ft 4-in, weight: loaded; 308,640-lb). The design of this machine has been successful and reliable and the survivability has exceeded all expectations.

EKRANOPLANE "ORLYONOK" A-90


The creation of this unique-properties flying apparatus, from the origin of an idea up to its realization and then cessation of work on this perspective direction is very interesting, but is not a well known page of engineering history.

Working on the further increase of speed for vessels on underwater wings, R.E.Alekseyev met a physical restriction on growth of speed VOUW: by strong growth of resistance and cavitation (low-temperature boiling) of water on underwater wings and propeller. A natural resolve was to rise completely from water in air, so Rostislav Alekseyev decided to go by use of screen effect.

At first, as well as with the VOUW, towed models were tested. The VOUW "Volga" was used as the tow. To the point, the first models of the VOUW Alekseyev tested on a tow for sailboat - the case if not unique, in any case, untypical in the world's shipbuilding. But we shall return to the ekranoplanes. The models were tested in an aerodynamic pipe at the Chkalovsky branch of the CKB (Gorky area) and were tested on a track: they were dispersed by the special launcher and flied on inertia along a long equal path. A heavy sheet of plywood was used for researching the stability of movement: the airwave from its fall forced model to be rocked. Further movement was the subject of more researches. Once, to be honest, this test bed was too strong and the force of the air caused the model to break loose from the track, climb up in the air, and punch the roof. But as a whole the tests gave encouraging results: the movement was steady.


Since 1961 the CKB has begun the construction and tests of self-propelled manned models: SM-1, SM-2 and so on. The apparatus SM-6 has become an actual prototype of the "Orlyonok". On these machines the basic constructive decisions were fulfilled, amphibian characteristics were tested for coming onto dry land, and tests were performed on its controlablety. Tests were carried out in Gorky's water pool, far from curious eyes.

In autumn 1972 the first work copy of the "Orlyonok" was taken out for a test. Telyachy island down from the Nizhny Novgorod (Gorky) on the river Volga was used, as it was separated from the coast by the non-navigable, yet had a lenght of around 8 km on its left shore.There the first tests of the "Orlyonok" were performed. It was already impossible to hide such "huge thing", and keep it a secret from the local, that it is the plane of lost failure, and now it is trying to pass it on airfield. The tests passed successfully, and in the spring the ekranoplane in the disassembled condition was transported down on the Volga to the Caspian Sea, there reassembled, and the tests proceeded under sea conditions again.

The ekranoplane was projected and built as a cargo-descent vessel for carrying machines and also armed forces into regions of battle action and landings descent. And for the uninitiated has invented the legend: "the floating stand for improvement of new engines of high-speed boats".


On tests under sea conditions the ekranoplane showed good results. The high speed, "amphibability", take-off from water ata small speed (for the account blowing under a wings by jets of forward engines) made this apparatus unique by its opportunities.

In 1975 during the tests the ekranoplane was sat on stones. Then the pilot switched the blowing-under on, and the machine left on water, flew up, and without any undue incident has reached base. But landing on stones did not pass without consequences. One case of the pre-series "Orlyonok" was made of an alloy K482T1, which is very rigid and strong, but fragile. Probably, the impacts with stones damaged the case, in the tail there were cracks, which were not noticed in the external survey. The next tests were spent at the heavy sea. During a rise from water, from impact of the damaged case about crest of a wave, the tail together with tailwings and mid-flight engine simply fell off. The pilot dumped gas of the start engines. R.E.Alekseyev, who sat in the pilot's cabin too (Main designer personally attended practically all tests), did not become puzzled, took control himself. He set the start engines on the cruiser mode, which kept the ekranoplane from plunging into water (in this case ship would sink, which would be unavoidable, as the tail was not present). This set the "Orlyonok" on the gliding mode and it landed on the coast. The people sitting in the ship got rid by a fright, but for Rostislav Alekseyev, this failure had much heavier consequences. Everyone expected, that Alekseyev would receive the rank of a Hero of the Socialist Labor for creation of ekranoplanes. But instead of the Minister of a ship-building industry B.E.Butoma, already "having a grudge" against Alekseyev for the independence of his character has used failure as the pretext and removed Alekseyev from his post of the Main designer and the CKB chief, by lowering him down to the chief of a department, and then to the chief of perspective sector.

But the militarians and Alekseyev looked at this failure a little otherwise: the "Orlyonok" had shown surprising survivability (tear off a tail of the plane or usual vessel - what would happen?). Analysing the reason of this failure, the Main designer replaced the material of the case to an aluminum-magnesium alloy AMG61. After this was launched, another three ekranoplanes were made for the Soviet NAVY. All of them were under construction in a factory "Volga" at the CKB. There were a total of five "Orlyonok's" on chronology:

"Dubl" - a copy for static tests; was sent to demolition;
S-23 - first "Orlyonok" that has committed the flight (made of K482T1 alloy); after crash was sent for demolition;
S-21 - was handed to NAVY in 1978; now in service;
S-25 - was handed to NAVY in 1979; now in service;
S-26 - was handed to NAVY in 1980; now in service.

The series of ekranoplanes S-21 and S-25 and S-26 was a pre-series: by the plans of development the USSR NAVY was provided construction 120 "Orlyonok's. The military seamen were attracted with efficiency of an ekranoplane as a descent vessel. The high speed provided a speed for army transferring, unattainable for usual descent ships, and sudden impact. Usual anti-descent obstacles and mine fields for "Orlyonok" were not a handicap (it would simply fly through them), and for capture of a "fortress" on a well-protected coast of the opponent, an ekranoplane would be simply irreplaceable.

But the plans did not come true; in 1985 the Defense Minister Marshal of the Soviet Union D.F.Ustinov, support for the idea of the construction of a fleet-descent ekranoplanes died. The new Defence Minister Marshal of the Soviet Union S.L.Sokolov by the strong-willed decision closed the program, and money intended for it, to spend on construction of nuclear submarines.


LOOK TO THE FUTURE

Now three ekranoplanes are at the NAVY base in Kaspiysk. The conditions in the world have sharply changed, and now they have become a military burden - not the ships, not the planes, and it is unclear what to do with them. The situation is complicated by that close Caucasus with its numerous centers of intensity and open wars.

Nevertheless, "Orlyonok" is not going to hand over positions. On its base the passenger version, known on the West as A.90.150, was developed. It can work on a regular lines, transporting up to a 150 people, or be used as a cargo-passenger high-speed vessel, transporting loads and replaceable crews for the floating sea installations, fishing boats, and polar stations (it can land on a drifting ice). Further development of the ideas, incorporated to "Orlyonok" and "Lun", could become a large passenger ekranoplane for up to a 250 persons. The research version of "Orlyonok" MAGE (sea arctic geological ekranoplane) is actively under development. Besides a changes of designs, usual for converting from the military to the civil version (arms and descent equipment are removed), in the tail a small water propeller with a drive from a diesel engine was installed. Also in the tail, large open doors are made and special equipment is placed for the ekranoplane to take tests of the bottom ground, seismic messages, magnetic, and gravity investigation. Together with the Ukrainian ANTK "Antonov" the very interesting project of a unique air - sea rescue system is developed. There is the rescue version of the "Orlyonok" installed "on the back" to the giant plane An-225.This increases range of a mission and equipment for all people necessary for rendering assistance in the sea (ambulance station, folded beds, and so on). The plane - carrier delivers an ekranoplane to a hospital with the speed 700 km/h. Further on the "Orlyonok" starts the engines, releases from An-225, and sits on water, turning into a seaworthy rescue vessel. Due to large durability of a design, the ekranoplane can sit on a strong harsh sea, perilous for hydroplanes, and has the value of a course, that will allow it to work practically in any point of global ocean (you see, fuel is spent only for a return way up to the nearest port). This system will work also in a polar regions - the ekranoplane sits on the ice. Such a system can deliver a polar station crew with urgent supplies (not only in the Arctic, but in the Antarctic too). And all these projects are financed by interested customers, so, despite difficulty, which the whole industry of the SNG now experiences, there is the basis to look in the future with optimistism.

INSTEAD OF a CONCLUSION

To win strong positions, a steamship was required almost a century, vessels on underwater wings - a half-century, sea-gliders - more quarter of a century. Recently an ekranoplane celebrated 60 years - a solid age. The researches on transport economics, spent by a number of organizations, in Russia and in the West, have revealed an original niche, which could be filled with the flying ships. It is a means of sea transportation of passengers and urgent loads (and for an ekranoplane, flight above sea is much more safe, than for an airplane), and also ekranoplanes could be used as a transport line between islands in archipelagoes and between continent and islands: for an ekranoplane mooring is unnecessary , as for a vessel; nor an airfield, as for a plane, and building a seaport or airport is economically unprofitable. And, knowing about the results of R.E.Alekseyev's and other CKB designers works, about the scope of both intensive modern researches and experiments, it is possible to hope, that for final recognition the ekranoplane should not wait for a century anniversary.

THE EKRANOPLANE "Orlyonok" is designed on an airplane scheme. It is a three-implement low-plane with large engine housing tail and the case-boat.

THE CREW consists of a commander, co-pilot, mechanic, navigator, radio operator and gunner. For transportation of a descent in structure of crew two mechanics are joined in addition.

THE HULL is made of the alloy AMG61. In separate units steel is applied. Radio-transparent aerials are made from composite materials. Electrochemical protectors provide the protection of the case from corrosion. The underwater part is painted with a special paint, preventing growth of sea animicules.

The hull is intended for accommodation in it useful loads, crew, arms, starting engines, and ship systems. Useful loads are placed in a cargo cabin of length: 92-ft, width: 11-ft, height: 15-ft. The load and unload occur through the hatch, formed at turn to the left around of hinges nose part of the case. The cabin of crew, engines and machine-gun installation are placed in a rotary part. System cross and longitudinal reads form the bottom. In the nose part of the case to the bottom fastens hydroski (nose one). Basic (main) hydroski fastens in region of center of weights. Both they can shake in vertical. An input and output of crew comes through doors, located on boards of the case above a wing. Emergency escape - through the hatch on a roof of the pilot's cabin.

THE WING has aerodynamic configuration, optimized for a movement near to the screen. On the ends of a wing are placed floats, playing the role of aerodynamic and gliding disks. Along the back edge are located five-section flaps-ailerons. Along the forward edge on the bottom surface of a wing (closer to the ends) are special starting plates. An axis of rotation of the plate passes on their forward edges. Corners of a deviation: flaps-ailerons - from -10 up to + 42 degrees, starting plates - 70 degrees. The mechanization of a wing is used at the start for the creation of a gas pillow, lifting an ekranoplane from the water. On start the back edge of a wing is in the water. For climb, special nose starting engines are switched on, jet exhaust from which are directed under a wing. The pilot lower flaps and plates, so that no gases comes through under back and forward edges. The raised pressure of gases under a wing lifts an ekranoplane from water. Structurally the wing consists from centerplane and two consoles that have Kesson design.

THE TAIL On the "Orlyonok" there are engine-tail wings with the purpose of reducing the influence of the screen by the characteristics of stability and controlability of the ekranoplane. The relative large sizes of the stabilizer are explained by necessity of maintenance of steady flight at various heights from the screen. Rudders used for height are of four-sections, those of the rudder used for direst are of two-sections. The vertical tail represents one whole with the fuselage. On top of the tail the mid-flight engine, navigating antenna, and radio aerials are installed.

THE CHASSIS includes two-wheel nose and ten-wheel basic gear. Wheels - non-breakable, nose gear - rotary, gear independent. Retracting it into the case produces the retracting of the nose wheels, and the basic wheels with the help of hydrocylinders are filled up for main water ski. Bay doors of a retracted station are absent, the hydroski in a retracted situation partially cover depressions in the chassis. The chassis together with ski-amortization device (nose and basic hydroski) and blowing-under provide passable practicality on any ground, snow and ice.

THE POWER INSTALLATION consists of two starting turbojet engines NK-8-4K and mid-flight turbo-propeller NK-12MK. All engines represent itself sea version of the same air engines. Starting engines (the static maximum draft in standard conditions 10.5t each) are installed on boards in rotary part of the fuselage. Air intakes are placed before the canopy of a cabin of the pilots for prevention of hit splashes and dust at a movement above the sea or land. Rotary jet exhausts of engines allow to direct a jet exhaust under a wing (mode blow-under) or above a wing (if increase of draft in cruise flight is necessary). The mid-flight engine results in rotation two one-axis propellers by a diameter 6m (static maximum draft in standard conditions 15.5t). Onboard auxiliary power installation TL-6L is also available. The fuel tanks are located in root parts of a wing.

THE SYSTEMS of an ekranoplane represent a combination of a traditional ship and aircraft equipment. A ship navigating complex "Ekran" with survey RLS is onboard available. A control system - hydraulic. Analogue of the auto pilot is system of automatic control by a movement. With its help piloting is possible as in hand-operated, and in automatic modes. In the nose end of the case is installed the aerial of navigating radar-tracking station of the warning of collisions - "Ekran-4" with high resolution. The aerial survey RLS is placed on the top part of the case beside the machine-gun. The hydrosystem provides functioning steering surfaces, mechanization of a wing, retracting of the chassis and water skis, turn nose part of the case on hinges. The electrosystem provides with a current the piloting-navigating, radiocoherent, electrotechnical equipment, and also control system. The ekranoplane is equipped by the complete set of ship navigating fires. In the rotary part of the case in forpik is located drogue-tow device. The anchor is retracted in kluse. There are inflatable saving rafts and motor inflatable boats onboard of an ekranoplane.

THE ARMAMENT consists of defense machine-gun installation "Utyos" and shooting weapon of crew.

COLORING: a surface part of the case, including tail wings is gray; a underwater part of the case - dark-green; of RLS aerials - light-gray; a waterline, tactical numbers - white; blades of the propeller, trunks of machine guns, visires, jet exhausts of engines, niche of jet exhausts of the nose engines - black; ends of disks - red; the ends of blades - yellow. From both boards on vertical tail the image of a Russian NAVY flag is put.

References

1. S.Kravchuk A.Maskalik A.Privalov. Flying above waves. Aerohobby. i2. Kiev. 1992
2. A.Belyaev. Magic flight. Aviko Press. Moscow. 1993
3. The Osprey Encyclopedia of Russian Aircraft. Osprey Aerospace, England, 1995.

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