Category Soviet x-plenes

Purpose: To test pressurized cockpits. Design Bureau: OSK (Department for Special Construction), Moscow, lead designerAleksei Y akovlevich Shcherbakov, and Central Construction Bureau (General Designer N N Polikarpov) where Shcherbakov also worked.

In 1935 Shcherbakov was sent to OSK to spe­cialize in the problems of high-altitude flight. He concentrated on the detailed engineering of pressurized cockpits, called GK (Ger – meticheskaya Kabina, hermetic cabin). By this time the BOK-1 had already been de­signed and was almost ready to fly, but Shcherbakov did not spend much time study­ing that group’s difficulties. His first GK was tested on S P Korolyov’s SK-9 sailplane, pre­decessor of the RP-318 described previously. The second was constructed in a previously built Polikarpov I-15 biplane fighter. Polikar-
pov’s biplane fighters were noted for their outstanding high-altitude capability, and from 1938 Shcherbakov spent most of his time as Polikarpov’s senior associate. The modified aircraft first flew in 1938. Later in the same year an I-15 was tested with a very much bet­ter GK. In 1939the definitive GKwas tested on an I-153, an improved fighter whose design was directed by Shcherbakov. The test-bed aircraft was designated I-153V (from Vysot – nyi, height). This cockpit formed the basis for those fitted to MiG high-altitude fighters, be­ginning with the 3A (MiG-7, I-222). Later Shcherbakov managed GK design for four other OKBs, and from 1943 created his own aircraft at his own OKB.

No details have been discovered of the first GK, for the SK-9, and not many of the second, fitted to an I-15 with spatted main landing gear. Like other aircraft of the 1930s, the I-15 fuselage was based on a truss of welded KhMA (chrome-molybdenum steel) tubing, with fabric stretched over light sec­ondary aluminium-alloy structure. Accord­ingly, Shcherbakov had to build a complete cockpit shell inside the fuselage, made ofthin light-alloy sheet. He had previously spent two years studying how to seal joints, and the holes through which passed wires to the con­trol surfaces and tubes to the pressure-fed in­struments. On top was a dome of duralumin,

Above right: I-153V.

Left. l – 153V cockpit.

hinged upwards at the rear. In this were set rubber rings sealing 12 discs ofPlexiglas, with bevelled edges so that internal pressure seat­ed them more tightly on their frames. Pilots said the view was unacceptably poor, as they had done with the original BOK-1. The instal­lation in the second aircraft, with normal un­spatted wheels, was a vast improvement. Overall pilot view was hardly worse than from an enclosed unpressurized cockpit (but of course it could not compare with the original open cockpit). The main design problem was the heavily framed windscreen, with an opti­cally flat circular window on the left and the SR optical sight sealed into the thick window in the centre. The main hood was entirely transparent and hinged upwards. Behind, the decking of the rear fuselage was also trans­parent. The I-153V had a different arrange­ment: the main hood could be unsealed and then rotated back about a pivot on each side to lie inside the fixed rear transparent deck.

Unknown in the outside world, by 1940 Shcherbakov was the world’s leading design­er of pressurized fighter cockpits.

Purpose: To modify a T-10 (Su-27) to set world records.

Design Bureau: P O Sukhoi, Moscow, General Constructor M P Simonov.

According to Simonov, The idea of entering a competition for world records for aircraft of this category was conceived during 1986. We realised that this aircraft was capable of doing many things. We were so confident that, for record setting, we decided not to build a ded­icated aircraft but took one of the pre-series ones which had already flown. This then had to be prepared in conformity with the strin­gent Federation Aeronautique Internationale rules. The aircraft was called the P-42 as a tribute to the turning point in the Stalingrad battle in November 1942, when Soviet avia­tion had played a large part in crushing the enemy’. The OKB organised a team of design engineers, test pilots and supporting ground staff under Chief Designer Rollan G Mar – tirosov (who later designed Ekranoplans). The modified aircraft was ready in October 1986. In two flights, on 27th October and 15th November 1986 Viktor Pugachev set eight climb-to-altitude records (four absolute and four for aircraft of up to 16 tonnes take-off weight): he reached 3km (9,843ft) in 15.573
seconds and 6km (19,685ft) in 37.05 seconds. On 10th March 1987 and 23rd March 1988 Nikolai Sadovnikov flew the P-42 to 9km (29,528ft) in 44.0 seconds, to 12km (39,370ft) in 55.20 seconds and to 15km (49,213ft) in 70.329 seconds. On 10th June 1987 Sadovni – kov set a world class record by sustaining an altitude of 19,335m (63,435ft) in level flight. Another record set by Pugachev was lifting a load of1 tonne (2,205 Ib) to 15km (49,213ft) in 81.71 seconds.

The aircraft selected was T10-15. It was simplified and its weight reduced until it was able to take off at a weight of 14,100kg (31,08515). With AL-31F engines uprated to 13,600kg (29,982 Ib) this gave a thrust/weight ratio of 1.93, believed to be the highest of any aircraft ever built. Modification to the equip­ment included removal of the radar and mili­tary equipment (including the GSh-301 gun and its ammunition container, wingtip mis­sile launchers and weapon hardpoints) and removal of avionics other than the flight, nav­igation and communications needed for safe flight. Modifications to the airframe included replacement of the nose radome by a metal fairing, simplification of the wings by in­stalling a fixed leading edge and a fixed struc­ture in place of the flaperons, removal of the
ventral fins and the tops of the fins, replace­ment of the airbrake by a fairing and simplifi­cation of the airbrake supporting structure, removal of the parabrake container, simplifi­cation of the variable engine inlets which were locked in their optimum positions, and removal of the mudguard from the nose – wheel. The aircraft was left unpainted.

The P-42 set a total of 27 world records.

Purpose: To improve a German design for a jet bomber.

Design Bureau: OKB-1, formed of German engineers led by Dipl-Ing Brunolf Baade, at Podberez’ye.

From late 1944 the Red Army overran many sites where German aircraft engineers had been working on jet aircraft and engines. The largest group had been in the employ of the vast Junkers Flugzeug und Motorenwerke in the Dessau area and at Brandis near Leipzig. At Brandis the principal project had been the Ju 287 jet bomber. Having flown the Ju 287 VI (a primitive proof-of-concept vehicle incor­porating parts of other aircraft) on 16th Au­gust 1944, work had gone ahead rapidly on the definitive Ju 287 V2, to be powered by two triple engine pods, but the Soviet forces over­ran Brandis airfield before this could fly. This work was clearly of intense interest, and with the aid of a large team of ex-Junkers engi­neers, who were prisoners, the programme was continued with all possible speed. The Ju 287 V2 stage was skipped, and parts of this aircraft were used to speed the construction of the next-generation EF 131 (Entwicklungs Flugzeug, meaning research aircraft). This was built at Dessau, dismantled, and, to­gether with many of the German engineers and test pilots, taken by train to Moscow. As explained in the next entry, they formed OKB-1. Final assembly took place at the test airfield then called Stakhanovo (today at LII Zhukovskii) where on or about 23rd May 1947 it was briefly flight tested by Flugkapitan Paul Julge. According to legend, he was never al­lowed enough fuel to reach ‘the West’. By this time more advanced aircraft and engines were being developed in the Soviet Union, and the EF 131 spent long periods on the ground. MAP Directive 207ss of 15th April 1947 had demanded that ‘two prototype EF – 131 with six RD-10 engines to take part in the August Tushino display…’ but this was im­possible to achieve. Eventually the first air­craft was again made airworthy and flown to Moscow’s other experimental airfield, Tyopliy Stan. On 21st June 1948 the order was given to stop EF 131 work. This was because it had been overtaken by the much better Type 140.

The EF 131 was an impressive-looking jet bomber, characterised by its swept-forward wing. To postpone the rapid increase in drag as Mach number exceeds about 0.75 German aerodynamicists had from 1935 studied wings swept either backwards or forwards. The FSW (forward-swept wing) appeared to offer important aeroelastic advantages, but because such wings diverge under increasing aerodynamic load they are structurally very difficult. The Ju 287 VI avoided this problem by being a slow-speed aircraft, but the prob­lem was met head-on by the 131 and 140, and also by the Tsybin LL-3 (which see). The first structurally satisfactory FSW was that of the Grumman X-29, almost 40 years later, and a more advanced FSW is seen in today’s Sukhoi S-37 (which see). Thus, the FSW of the EF 131 can be seen to have been an enor­mous challenge. Aerodynamically it was di­rectly derived from that ofthe wartime Ju 287, with considerable dihedral and a leading edge swept forward at 19° 50′. It was fitted with slats at the wing roots, slotted flaps and outboard ailerons. It was also fitted with mul­tiple spoiler/airbrakes (items 18 in the de­tailed drawing overleaf) and a total of eight shallow fences (in the drawing marked QV). Because of the limited (900kg, l,9841b) thrust of the Junkers Jumo 004B engines these were arranged in groups of three on each under­wing pylon. By late 1947 this engine was in limited production at Kazan as the RD-10, and because they were considered superior to the German originals the engines actually in­stalled were RD-lOs. The crew numbered three, and to save weight armour was omit­ted. A neat tricycle landing gear was fitted, the main tanks occupied the top of the fuselage, a braking parachute occupied a box under the tail, and at the end of the fuselage was a remotely sighted FA15 barbette with super­imposed MG 131 guns as fitted to some wartime aircraft such as the Ju 388.

The FSW and primitive engines made this an unattractive aircraft.

EF131

Centre: Page from EF 131 maintenance manual, Fig. 10 ‘covers and flaps’.

Bottom: EF 131 (the only known photograph, enlarged from distant background).

Purpose: To investigate the maximum load that could be carried by an aeroplane powered by a single M-l 1 engine.

Rivals included the Grokhovskii G-31 and KhAI-3, both described later.

Design Bureau: Oleg K Antonov, Kiev.

The idea was that of L E Malinovskii, Director of the Civil Aviation Scientific-Technical Insti­tute (hence the designation). AviAvnito and Osoaviakhim (the Society of Friends of Avia­tion and the Chemical Industry) provided funds in 1936, enabling the Kiev (Ukraine) constructor to create his first powered air­craft. The single example built was given the OKB designation of OKA-33, because it was their 33rd design. The flight-test programme was opened by test pilot N I Ferosyev on 20th April 1937. Results were satisfactory.

The LEM-2 was predictably almost a flying wing, based on the aerodynamics of Prof V N Belyayev, with a PZ-2 aerofoil modified from the common CAHI (TsAGI) R-ll. The M-l 1 five-cylinder radial, rated at l00hp, was mounted on the front in a long-chord cowl­
ing, driving a two-blade carved-wood pro­peller of the type mass-produced for the U-2 (later called Po-2). Construction was almost entirely wood, with ply skins of varying thick­ness. The wing comprised a centre section and two outer panels with long-span but nar­row ailerons. The inboard part of the wing had a chord of 6.7m (22ft) and so was deep enough (1.47m, 4ft 1 0in) to house the payload of 1,280kg (2,822 Ib). The payload compart­ment between the spars measured 2.4 x 1.5 x 1.2m (7’101 /2"x4’ll"x3’ll"). In the LEM-2 built the pilot was the only occupant, though it was the intention that a production aircraft should have provision for 11 passenger seats. Access to the main payload space was to be via large doors in the leading edge ahead of the front spar, but these were absent from the LEM-2 built. There was also a door in the upper surface behind the cockpit. The twin – finned tail was carried on two upswept booms attached at the extremities of the wing centre section. Landing gears comprised two main wheels (the intended spats were never fitted) attached to the centre-section end ribs,

and a skid under the trailing edge.

Development of aircraft in this class was soon discontinued, it being decided they were of limited practical use. In fact, espe­cially with slightly more power, they could have been used in the USSR in large numbers in huge regions devoid of roads and railways.

Purpose: To investigate the tailless delta configuration.

Design Bureau: B I Cheranovskii.

With the advent of the jet age Cheranovskii recognized that he should think in terms of much lower aspect ratio. He followed his 1944 project by the graceful BICh-24 jet fight­er, which he hoped to demonstrate in the Tushino ‘parade’ of 1949. To prove its flying qualities he first tunnel-tested the model depicted.

Few details have been found, but the model picture reproduced here shows the configuration. Curiously, the documents on the BICh-24 call it the Che-24. No air intake is visible on the tunnel model, and it is not known whether the 24 would have been a turbojet or rocket aircraft.

It is not known if the full-scale aircraft was built.

No data.

BICh-26, (Che-26)

Purpose: Jet fighter.

Design Bureau: B I Cheranovskii.

After the War Cheranovskii had an enhanced reputation, and he was able to build up a small team of designers to assist him with projects far more ambitious than those with which he made his name. In June 1948 the BICh-24 was followed by the BICh-25, a pro­ject for a jet fighter with variable-sweep wings with outboard pivots, uncannily like the American TFX projects of more than ten years
later. With the BICh-26 he returned to the BICh-24 formula with a fixed planform of al­most delta, or gothic-delta, outline. Though Cheranovskii lived to the end of 1960 this pro­ject remained on the drawing board.

The BICh-26 was designed to have a single Mikulin (later Tumanskii) AM-5 turbojet rated at 2,000kg (4,409 Ib) thrust, fed by flush inlets in the underside of the flattened forward fuse­lage. The latter could equally be described as the centre section of the wing, to which the conventional outer wings were attached. On
the trailing edge were inboard elevators and outboard ailerons, and though one report states that these surfaces were fully powered they all had deeply inset hinges for aerody­namic balance. There were also upper and lower rudders, again with inset hinges. No other details have appeared.

Like its various jet predecessors, the BICh – 26 appears to have been an outstanding de­sign with many features ahead of its time.

Purpose: To create a more manoeuvrable fighter.

Design Bureau: Brigade led by Mikhail Ivanovich Gudkov, Moscow.

Gudkov was one of the three partners who created the LaGG design bureau, later led by Lavochkin only. In early 1940 Gudkov be­came convinced that the Bell P-39 Airacobra, with the engine behind the cockpit, had a su­perior configuration. It gave the pilot a better view, and by placing the heavy engine in the centre of the aircraft greatly reduced the long­
itudinal moment of inertia, and thus should improve manoeuvrability. As well as working on supposed improved derivatives of the LaGG, Gudkov managed to obtain funding for a mid-engined fighter in early 1942, as well as a contract with the A A Mikulin bureau for the supply of an engine. The resulting Gu-1, also called the Gu-37, was completed in the early summer of 1943. After prolonged taxi trials test pilot A I Nikashin said ‘It seems glued to the ground’. On 12th June 1943 Nikashin at­tempted the first flight. The Gu-1 reached about 200m (650ft) but then appeared to sideslip into the ground, Nikashin being killed. Gudkov’s brigade was disbanded.

The configuration followed the Airacobra exactly, with the major difference that the Gu-1 was constructed largely of wood, with bakelite-ply skin. Metal parts included the fuselage back to the firewall between the cockpit and engine (aligned with the front spar), which was based on a steel-tube truss with skin of removable Dl panels, Dl wing spars and Dl control surfaces. The wing was of 1V-10 Type V-2 aerofoil profile, and was fit­ted with automatic leading-edge slats and hy­draulically driven split flaps. The engine was an AM-37 rated at l,380hp (the designer’s notes on the preliminary drawing show that he wanted an AM-41). Carburettor inlets were in the wing roots, and long inlets further out­board served the radiators inside the wing ahead of the inwards-retracting main landing gears. The drive was taken through a steel tube of 120mm (4%in) diameter to the reduc­tion gear in the nose. The long nose gear re­tracted back into a bay in the lower part of the nose. Armament comprised a massive Taubin 37mm cannon firing through the pro­peller hub, fed by an 81 – round magazine (sur­prisingly large for this calibre) and six ShKAS machine guns in the fuselage and wing roots.

Few documents on the Gu-1 have been found. One is led to conclude that either the wing or vertical tail was too small, or possibly both.

Purpose: T o investigate light flying-wing aircraft.

Design Bureau: Moscow Aviation Institute.

In 1958 the academic faculty of the Institute decided to carry out a major investigation into LK (Letayushcheye Krylo, flying wing) air­craft. The programme began with the LK-MAI glider and the MAI-59 ultralight, but these re­mained on the drawing board. Extensive tun­nel testing of models led to a configuration with a broad diamond or lozenge-shaped centre section and swept outer panels which at their tips turned back (sweepback 90°) to terminate in surfaces doubling as airbrakes and as elevens. The MAI-62 was designed and built in 196I-62, but it was not flown until in 1965 AI Pietsukh attempted a take-off. Dur­
ing the long run the engine seriously over­heated and ran intermittently, and the take­off was abandoned. The MAI-63 glider followed in 1963, first flown in 1964 by AI Pietsukh. In 1965 an engine was fitted, to produce the MAI-63M, but again the engine proved ‘unsteady’ and the aircraft never flew in this form.

Both the MAI-62 and MAI-63 were made al­most entirely of wood, with birch ply veneer covering. Both had a single-seat cockpit with a sideways-hinged canopy, cable-operated wingtip elevons which could split into upper and lower halves to act as airbrakes, and fixed nosewheel landing gear. The MAI-62 was powered by a Khirt air-cooled engine of 80hp driving a two-blade pusher propeller. The years 1962-65 were spent tinkering with
the details of the wings, which had a leading – edge sweep of 45° (shown in drawings as 50°), adding or subtracting various fences, inboard flaps, trim tabs and servo tabs. Re­leased photographs carefully avoided show­ing these surfaces. The MAI-63 had a much greater span, with leading-edge sweep re­duced to 25°, and two different forms of split tip airbrakes supplemented by constant – chord hinged trailing edges to the main wing. The engine of the MAI-63M was a VP-760, rated at 23hp.

One is left wondering whether the failure of these aircraft to fly was really due to the en­gine or to doubts about their controllability.

Purpose: To evaluate a STOL fighter larger than the MiG-21.

Design Bureau: OKB-155 of A I Mikoyan.

By the 1960s, though the MiG-21 was going from strength to strength, the family of so – called heavy interceptors were being over­taken by the Ye-155 project (which became the MiG-25), and, by now facing severe com­petition from Sukhoi, there was an urgent need for a new tactical family more capable than the MiG-21. The new engine KB of K Khachaturov had produced an outstanding new engine, the R-27-300 (as before, the suf­fix -300 signified Factory No 300), an after­burning turbojet with maximum thrust of 7,800kg (17,196 Ib). This was intermediate be­tween MiG-21 engines and those ofthe big in­terceptors. Mikoyan began studying future prospects for this engine in 1960. In 1964 he obtained an order for the 23-01 with a delta wing and a lift-engine bay, and in 1965 he was ordered to build the competing 23-11 with no
lift engines but a variable-geometry ‘swing wing’. Even though the 23-01 was managed by V A Mikoyan, second son of the General Constructor’s brother Anastas, President of the Supreme Soviet, it was considered in the OKB (correctly, as it turned out) to be a waste of time. This was because of the American fixation on the V G wing for the F-l 11. Despite this, the 23-01 was the subject of meticulous effort. The wing was like a scaled-up version ofthe blown-flap MiG-21, almost as large as a Ye-152, but with different main landing gear geometry. The tailplanes were of a new de­sign, with sharp taper (almost becoming delta shape) and tips cropped at the Mach angle. The fuselage was totally new, with a nose designed to accommodate a powerful radar fire-control system (not fitted), lateral inlets with sliding centrebodies for the main engine, and a lift-engine bay between the main-engine ducts almost identical to that of the 23-31. The two RD-36-35 lift turbojets had a combined thrust of only 4,700kg (10,362 Ib),
and as this was a mere 29.5 per cent of the gross weight the 23-01 was never flown slow­er than 150km/h (93mph). Thus, it was not fit­ted with reaction-control jets. The landing gears were new, the large KT-133 main- wheels being housed upright in the sides of the fuselage and the nose unit having twin wheels, power steering and retracting not for­wards but backwards. The KN-type seat was installed in a cockpit similar to that of con­temporary MiG-21 s. Ostapenko began the brief factory test programme on 3rd April 1967. He was soon joined by Fedotov, but long before the 23-01 was completed Mikoy­an had ceased to be interested in lift jets. With one eye on disinformation the number 23 was painted on the fuselage, an inoperative GSh-23L gun was fitted, and dummy Vympel R-23R and R-23T missiles were hung under the wings. The 23-01 was then briefly demon­strated at the big airshow at Moscow Do – modyedovo on 9th July 1967.

Performance

Take-off run (light) 1 80-200 m 59I-656 ft

Landing run (with parabrake) 250m 820ft

Two views of 23-01, with dummy R-23

guided missiles.

Purpose: To test ramjet engines and investigate performance of aircraft thus boosted.

Design Bureau: Joint effort by A Ya Shcherbakov (aircraft) and Igor A Merkulov (ramjet engines).

In July 1939 Merkulov proposed that simple subsonic ramjets (PVRD) should be hung under the wings of fighters to boost their per­formance. Given the go-ahead by Narko – mavprom, he collaborated with Shcherbakov in thus boosting Polikarpov biplane fighters. Bench testing the small DM-1 (Dvigatel’ Merkulov) engine began in August 1939, and the larger DM-2 (or DM-02) began bench test­ing a month later. In December 1939 two DM-2 engines were attached under the lower wings of I-152 (I-156/s) No 5942, then ski – equipped, at the M V Frunze Moscow Central Aerodrome. Towards the end of the month pilot Piotr Loginov began flight testing without operating the ramjets. In late December Logi­nov tested the fuel and ignition systems, and on 27th January 1941 official NIl-WS trials
began with the ramjets firing. This was the first flight in the world of any ramjet-equipped mannedaircraft. The DM-2 testing involved 54 fiights by late June 1940, 34 by Loginov, 18 by A V Davydov and two by N A Sopotsko. By this time Merkulov had extensively tested the considerably larger DM-4. On 3rd September 1940 Loginov first flew an I-153 (No 6034) fit­ted with two DM-2 ramjets, and on 3rd Octo­ber he made the first flight of this aircraft with two DM-4s. The DM-4 was also flown under the I-152. Use of the two biplanes as DM test­beds was abandoned in December 1940 after 20 flights with DM-4s.

The Merkulov ramjets were simple profiled propulsive ducts burning the same petrol (gasoline) fuel as the aircraft main engine. This was fed by an engine-driven auxiliary pump around the double-skinned jetpipe throat and nozzle to cool the inner wall. Still liquid, the fuel was then sprayed into the in­terior duct where to initiate combustion it was ignited electrically. The static-tested DM-1 had a diameter of 240mm (91/2in). The DM-2, flown on the I-152, had a diameter of
400mm (1ft 3%in), length of 1.5m (4ft llin) and weight of 19kg (41.91b). The fabric cov­ering over the I-152 rear fuselage and tail was replaced by thin aluminium, flush-riveted. This proved to be a wise precaution, because with the ramjets operating the flame extend­ed beyond the tail of the aircraft. The DM-4 had a diameter of500mm (1 ft 7%in), length of 1.98m (78in) and weight of 30kg (66 Ib).

The ramjets were never fired in the air for as long as a minute, though on bench test five hours was once demonstrated. Most tests were in bursts of about ten seconds, and Loginov recorded the simplicity of control and smoothness of ramjet operation. The two DM-2 ramjets boosted the maximum speed of the I-152 by a maximum of20km/h (12.4mph), but at the cost of much poorer performance and manoeuvrability with the ramjets inoper­ative. The DM-4 ramjets boosted the speed of the I-153 by a maximum of51 km/h (31.7mph), from 389 to 440km/h (241.7 to 273.4mph) but again with severe penalties and with exces­sive fuel consumption.

Purpose: To evaluate Su-27 foreplanes. Design Bureau: P O Sukhoi, Moscow, General Designer M P Simonov.

In 1977 Simonov authorised studies into the possibility of adding foreplanes (canard sur­faces) to the Su-27. Such surfaces appeared to offer improved controllability, especially in extreme manoeuvres at high AOA (angle of attack), when flight testing had shown that the tailerons were in the wake of the wing. Following tunnel testing of models work con­tinued in 1979 in collaboration with CAHI
(TsAGI). This research revealed that in some flight conditions there were longitudinal-con­trol problems. A canard system free from these problems was devised in 1982, and in May 1985 flight testing of the T10-24 began.

The Tl 0-24 was fitted with the PGO (Pered – neye Gorizontal’noye Opereniye, front hori­zontal tail). After prolonged research this was fitted not on the forward fuselage, as in most other canard aircraft, but to the leading edges of the modified centroplan (centre wing). The two surfaces had a cropped-delta plan shape, with a thickness/chord ratio of 3 per
cent, and they were mounted horizontally and pivoted at about 60 per cent root chord. They were driven by power units linked to the FBW flight-control system. Depending upon the flight regime they increased stability in pitch and roll and also instability in pitch. They significantly reduced trim drag, and they increased the maximum attainable lift coeffi­cient (at an AOA of 30°) from 1.75 to 2.1.

Testing the T10-24 substantiated the pre­dicted advantages and supported develop­ment of later fighters, beginning with the navalSu-27K.