Classic Soviet fighters – The Mikoyan-Guryevich MiG-15 ‘Fagot’ (Part I)

Justifiably one of the most celebrated of all aircraft, the Mikoyan-Guryevich MiG-15 was a simple fighter whose debut in Soviet service came as a traumatic shock to the Western world when first encountered in combat over Korea in November 1950, and the type also marked the first occasion on which the speed of design and development for a Soviet warplane bettered that of any Western rival. The type was also built in greater numbers, the estimates for Soviet production being in the order of 12,000 or more aircraft, with another 6,000 built under licence in other countries.

The programme that led to the service debut of the MiG-15 was launched at a Kremlin meeting of March 1946. This meeting was attended by all the USSR’s major fighter design organisations, which were instructed to create a high-altitude day interceptor able to operate from rough airstrips, reach Mach 0.9, offer a high level of agility at altitudes of more than 36,090 ft (11000 m), and possess an endurance of at least 60 minutes. The use of a swept wing was assumed from the start, and the OKBs (experimental construction bureaux) were ordered to work closely with the TsAGI (Central Aerodynamics and Hydrodynamics Institute), where swept wings had been under investigation and consideration since at least 1935. The Mikoyan-Guryevich OKB looked at the possibility of a forward- rather than rearward-swept wing, as already test-flown by the Tsybin OKB, but finally opted to create its Samolyet S (Aeroplane S) on the basis of a mid-set and rearward-swept wing on shortest possible circular-section fuselage with a large T-tail. This was a layout that had been considered from a time late in 1945, mainly as a result of reports in German documents and research data captured in the closing stages of World War II in Europe, and was deemed to offer the best compromise between structural and aerodynamic requirements in an airframe light enough to attain high speeds on the limited power of the turbojet engines currently available or in prospect.

MiG-15bis at Monino Aircraft Museum

Engine design moves
The engine choice had to be made between two designs each rated at some 4,409 lb st (19.61 kN): one of these was a slim axial-flow unit derived from German (mainly BMW) work, and the other a larger-diameter centrifugal-flow unit based on the known external appearance of the Rolls-Royce Nene and designated as the VK-1PO from the engine design bureau headed by Major General V. Ya. Klimov. The latter was admittedly crude and generally outside current Soviet experience, which was based largely on captured German axial-flow manufacturing facilities, engine and data, but the Mikoyan-Guryevich OKB was authorised to proceed on the basis of the centrifugal-flow unit with a fuselage sized to the anticipated 4 ft 11 in (1.45 m) diameter of the VK-1 engine. The Soviets clearly foresaw that details and even drawings of the Nene would be provided by Soviet agents in the UK, and the design of the VK-1PO was already well advanced when, in September 1946, a trade agreement with the UK allowed the export of the Nene to the USSR. Ten British engines were immediately shipped to the USSR, with another 15 following in March 1947 and more engines later. The first British engine to reach the USSR was carefully stripped and Soviet drawings of components were issued from a time as early as 30 October 1946 at the GAZ-45 production facility in Moscow, headed by Klimov and boosted since 21 September by design personnel seconded from GAZ-117 in Leningrad, the home of Klimov’s main design office. Development of the VK-1PO was thereupon terminated and replaced by that of the RD-45, so designated after the factory at which it was being created.

The Mikoyan-Guryevich OKB received accurate installational drawings of the RD-45 engine in February 1947, and the project received the go-ahead in the same month under the leadership of deputy general constructor A. G. Brunov and chief engineer A. A. Andreyev: the OKB and NII (scientific test institute designations were Samolyet S (Strelovidnost, or swept) and I-310 respectively.

Early design choices
The new fighter began to take shape as a design of the well established stressed-skin type in light alloy with considerable emphasis placed on simplicity and a notably high load factor of 8 g. Characterised by a quarter-chord sweep angle of 35°, in structural terms the wing was based on a single main spar at quarter chord with a sheet web of D16-T (a Duralumin alloy that was the ruling material throughout the airframe). The rest of the wing comprised two rear spars, 21 stringers and 20 ribs under a flush-riveted skin. The wing was anhedralled at 2°, and its halves extended from the sides of the fuselage in panels that were only slightly tapered in thickness and chord to their rounded tips. There were two fences, each 3.94 in (10.0 cm) high, above each wing half from the leading edge to the trailing edge, and virtually the entire span of the trailing edges was occupied by outboard ailerons and inboard Fowler-type flaps hydraulically driven to angles of 20° for take-off and of 55° for landing.

The fuselage was of circular section and nicely tapered fore and aft of the stainless steel attachments for the wing halves. The frontal area of the fuselage was 12.49 sq ft (1.16 m²) excluding the figure of 2.05 sq ft (0.19 m²) for the canopy, which was of the clear-view type with a rearward-sliding section providing access to the cockpit, which was pressurised and accommodated the pilot on an ejection seat. A plain nose inlet of circular section led to an inlet duct that was bifurcated past the cockpit and again above and below the unbroken wing centre section to a plenum chamber behind the wing. The fuselage was made in two parts, the rear section being quickly removable by the freeing of four bolts in line with the centre section’s rear spar, thereby providing all-round access to the engine. The broad-chord vertical tail surface was swept at 56° and at about three-fifths of its height carried the horizontal tail surface that was swept at 35°. The incidence of the tailplane could be adjusted on the ground, and all of the control surfaces on the tail unit were manually operated and fitted with trim tabs.

The airframe proper was completed by the landing gear, which was of the tricycle type with levered-suspension legs throughout. The nose unit retracted forward into a door-covered bay in the lower part of the duct bifurcation under the fuselage, and the main units retracted inward to lie entirely within door-covered bays in the underside of the wing between the spars: like that of the flaps and air brakes, the operation of the landing gear was hydraulically powered, although there was a compressed-air back-up system. The kerosene fuel for the engine was carried in a main protected flexible cell behind cockpit between the air ducts and in a second tank in the rear fuselage, totalling 338.3 Imp gal (406.3 US gal; 1538 litres).

The planned armament was that pioneered in the Samolyet FL (I-305) with one 37-mm Nudel’man N-37 cannon in centre of the nose and one 23-mm Nudel’man-Suranov NS-23 cannon at same level on each side. Engine flame-out problems suffered by the earlier MiG-9 then led to a major reconsideration of the armament arrangement. N. I. Volkov then designed an excellent gun pack that was winched up and down in its entirety on four cables: this pack accommodated one 37-mm N-37 cannon and its 40-round magazine on the starboard side and two 23-mm NS-23KM cannon and their 80-round magazines on the port side. The arrangement left the cannon muzzles just sufficiently far from the air inlet not to disrupt the airflow at normal flight speeds.

The Mikoyan-Guryevich OKB built two prototypes as the essentially similar Samolyet S-01 and Samolyet S-02. The Samolyet S-01 was rolled out 27 November 1947 and recorded its maiden flight on 30 December of the same year in the hands of Viktor Nikolayevich Yuganov. The initial flight trials indicated the need for some modifications, but the only major changes were an increase in tailplane sweep to 40°, slightl changes to the trailing edges and ailerons of the wing, the addition of a landing light above the splitter plate that bifurcated the air inlet, and the cutting back of the rear fuselage to shorten the jetpipe of the Nene RN.1 engine, rated at 4,920 lb st (21.885 kn) dry, by 1 ft 0.625 in (0.32 m).

The Samolyet S-02 was completed with the slightly more powerful Nene RN.2 engine, an S-13 camera gun above the nose, and a small rocket under each wing half to assist recovery from the spins to which the aeroplane had been revealed to be prone during stall tests. The Samolyet S-02 recorded its maiden flight on 27 May 1948 in the hands of Colonel Gregori Sedov.

During March 48 there appeared the quickly built Samolyet S-03 third prototype incorporating all the modifications that had been developed to date. The wing structure was considerably strengthened by use of a stronger alloy for the main spar web and booms and a thicker skinning of another stronger alloy. The flaps were increased in chord but reduced in span so that the ailerons could be enlarged from 10.33 to 12.59 sq ft (0.96 to 1.17 m²), each aileron being in two parts linked by a universal joint. Door-type air brakes, later increased in area from 5.17 to 5.60 sq ft (0.48 to 0.52 m²), were installed as hydraulically powered surfaces designed to swing out and slightly down on each side of a strengthened rear fuselage. The tailplane was moved rearward by 5.9 in (0.15 m) on a modified fin, and a bobweight was added to the elevator circuit. The fuel capacity was reduced slightly, but this was more than offset by provision for two detachable but not jettisonable 109.1 Imp gal (131 US gal; 496 litre) slipper tanks under the wing on hardpoints which could otherwise carry 220-lb (100-kg) FAB-100 free-fall bombs. Other changes facilitated the removal of the gunpack, added a new canopy locking system, incorporated an engine bay fire-detection and extinguishing system, and more instruments.

Maiden flight and revisions
The Samolyet S-03 recorded its maiden flight on 17 June 1948 in the hands of I. T. Ivashchyenko. Ivashchyenko and S. N. Anokhin completed the factory trials of the aeroplane, which was committed to its state trials at Saki in November of the same year as the I-310. The new Mikoyan-Guryevich fighter passed its state trials with flying colours, but nonetheless revealed that it was still prone to entering a spin in a tight turn, and possessed poor behaviour at high angles of attack. The tendency of the aeroplane to buzz and snake at high speed resulted in the decision to limit the maximum speed to Mach 0.92, and a later change ensured that the air brakes were triggered automatically at Mach 0.91.

The data for the Samolyet S-03 included a fuel weight of 2,668 lb (1210 kg), span of 33 ft 1.5 in (10.085 m) with area of 221.74 sq ft (20.60 m²), length of 33 ft 1.75 in (10.102 m), empty weight of 6,515 lb (2955 kg), maximum take-off weight of 10,595 lb (4806 kg), maximum speed of 556.5 kt (640.5 mph; 1031 km/h) at 9,845 ft (3000 m) declining to 488.5 kt (562.5 mph; 905 km/h) at sea level, climb to 16,405 ft (5000 m) in 2 minutes 18 seconds and to 32,810 ft (10000 m) in 7 minutes 6 seconds, service ceiling of 49,870 ft (15200 m), and range of 825.5 nm (951 miles; 1530 km) with two slipper tanks.

The performance of the Mikoyan-Guryevich OKB in designing, building and testing the three Samolyet S prototypes far outstripped those of its rivals, and in August 1948 the Samolyet S was accepted for mass-production as the MiG-15, with authorisation for a dual-control trainer version issued at the same time. The MiG-15 was known to the design bureau as the Samolyet SV (aeroplane, swept, air force) and introduced the powerplant of one RD-45 turbojet engine rated at 4,850 lb st (21.57 kN) dry. The production model introduced many changes from the prototype standard represented by the Samolyet S-03. The airframe was completely reassessed to ensure structural integrity while operating at higher weights and at 8 g, and within this concept special attention was given to the wing spar booms and upper skin, the rear-fuselage frames and the air brakes, the last being enlarged to 9.47 sq ft (0.88 m²) with its geometry revised to eliminate nose-up pitch. In a move that was new for the design bureau, the ailerons were fitted with a hydraulic boost system, and a trim tab was added to the port aileron. The outer ends of the leading edges were also fitted internally with 66 lb (30 kg) anti-flutter masses. The overall effect was a reduction in stick forces at high speed in both the longitudinal and lateral planes.

A revision of the fuel system added pressurisation of the tanks using air tapped from the engine’s compressor, and the underwing hardpoints were upgraded so that they could carry, as an alternative to the slipper tanks, 551-lb (25- kg) FAB-250 free-fall bombs. The gunpack was also much improved to speed the process of rearming the aeroplane. The N-37 cannon was replaced by an N-37D weapon of the same calibre but with new anti-vibration mounts, and the NS-23 cannon were replaced by 23-mm Nudel’man-Rikhter NR-23 weapons with new mounts, raised hydraulic shock absorbers, and all three guns fitted with larger link chutes (characterised by external blisters) to avoid blockages. The cockpit was also improved with a rear-view periscope, a one-piece blown canopy with hot-air demisting, a new ejection seat with a trigger on each side to jettison the canopy and then initiate seat ejection, more effective armour protection, the ASP-3N gun sight, a remote gyro compass with its sensing unit near the starboard wing tip, the improved SRO-1 IFF system, and other items.

Production begins
The MiG-15 entered production at GAZ-1 in Moscow, and aircraft were delivered from here to service units (including those of the naval and air-defence air forces) from 8 October 1948 to a standard that differed from that of the Samolyet S in details such as an internal fuel weight of 2,701 lb (1225 kg), length of 32 ft 11.25 in (10.04 m), empty weight of 7,456 lb (3382 kg), maximum take-off weight of 10,595 lb (4806 kg), maximum speed of 567 kt (652 mph; 1050 km/h) at sea level declining to 556 kt (640 mph; 1030 km/h) at 9,845 ft (3000 m), climb to 16,405 ft (5000 m) in 2 minutes 18 seconds and to 32,810 ft (10000 m) in 7 minutes 6 seconds, service ceiling of 49,870 ft (15200 m), maximum range of 1,036 nm (1,193 miles; 1920 km) with slipper tanks, and typical range of 766 nm (882 miles; 1420 km) with standard fuel.

Even as the MiG-15 was being manufactured in a programme that gathered pace rapidly, the fighter was being further improved by features that soon included a special tank to maintain the delivery of fuel to the engine under negative-g conditions, and provision for 66 Imp gal (79.25 US gal; 300 litre) drop tanks under the wing. The wing was further strengthened for improved resistance to torsional loads, and many of the pipes in the fuel and hydraulic systems were replaced by steel pipes with welded joints. Other changes included a more powerful landing light, improved VHF radio, and an uprated engine in the form of the RD-45F engine rated at 5,004 lb st (22.26 kN) dry.

Orders for the MiG-15 were now so great that on 20 May 1949 the Soviet authorities decided that the factories currently manufacturing the Lavochkin La-15, Lisunov Li-2 and Yakovlev Yak-17 and Yak-23 would switch to production of the MiG-15. The manufacture of the type was also licensed to Czechoslovakia (853 examples of the S-102 built in 1953/55) and Poland (54 examples of the LiM-1). Including licence-made aircraft, some 12,000 examples of the MiG-15 were made in 17 versions by 1956, about half of them as trainers. The original NATO reporting name for the MiG-15 was ‘Falcon’, but this was soon replaced by the less complimentary ‘Fagot’.

The desirability of a trainer version of the imminent single-seat fighter derived from the Samolyet S had been appreciated by 1947. It was 13 April 1949 before work on such a programme was authorised, however, and by this time the Mikoyan-Guryevich OKB had completed the design of what it termed the Samolyet ST. The airframe of the trainer was basically identical to that of the MiG-15 single-seater except over its forward portion. Here there was an arrangement of tandem cockpits each with identical instrumentation, controls and ejection seats with armoured headrests, of which the rear seat fired before the front seat. The windscreen was the same as that on the I-301T and therefore taller than that of the single-seat fighter, and while the front canopy over the pupil hinged to the right, the rear canopy for the instructor was designed to slide to the rear. The installation of the rear cockpit reduced the capacity of the main fuel tank, trimming the total tankage to 246.4 Imp gal (295.9 US gal; 1120 litres), but provision was made for 61.6 or 88 Imp gal (74 or 105.7 US gal; 280 or 400 litre) drop tanks under the wing. Armament was not always fitted, but on the first series of aircraft comprised a dismountable tray carrying one NR-23 cannon with 80 rounds and one 0.5 in (12.7 mm) Beresin UBK-Ye machine gun with 150 rounds on the starboard and port sides respectively; there was also provision for two 110- or 220-lb (50- or 100-kg) FAB-50 or FAB-100 free-fall bombs carried under the wing. The front cockpit was equipped with an ASP-1N sight, and other equipment included an S-13 camera gun above the nose. Additional armour was fitted behind the cockpit and gun magazines.

The Samolyet ST prototype, which was later subjected to state trials as the I-312, was manufactured by the Mikoyan-Guryevich OKB using components from the MiG-15 production line Kuibyshyev, and recorded its maiden flight on 23 May 1949. The aeroplane was subjected to extended tests right through to May 1950, mainly by a MiG-15 regiment based at Kubinka. The satisfactory outcome of these trials is affirmed by the very large numbers of MiG-15UTI aircraft that then came off the production lines. The total of about 6,500 Soviet-made aircraft was complemented by large numbers of equivalent aircraft made under licence in Czechoslovakia (2,012 examples of the CS-102), Poland (more than 1,200 examples of the LiM-3) and China (the JJ-2).

Third series
The third series of MiG-15UTI trainers introduced the RSIU-3 radio (in place of the original RSI-6) and the SRO-1 IFF system, the fourth series eliminated the NR-23 cannon and replaced the original ASP-1N sight with the ASP-3N unit, and the sixth series replaced the NR-23 cannon on the starboard side of the weapons tray with the OPS-48 ILS receiver, a change that also necessitated another small reduction in the capacity of the forward tank.

From 1952 it was standard for every fighter regiment to have four examples of the MiG-15UTI on its establishment, and so successful was the type that it was retained for the conversion and continuation training of pilots for the later MiG-17 and MiG-19 fighters. More than 1,960 examples of the MiG-15UTI, which received the NATO reporting name ‘Midget’, were exported. Like the MiG-15 single-seat fighter but to a somewhat greater scale, the MiG-15UTI two-seat trainer is still in service with a number of less advanced nations.

Powered by the RD-45FA engine supplied with 1,984 lb (900 kg) of fuel, the MiG-15UTI had the same dimensions as the MiG-15 but otherwise differed in details such as its empty weight of 8,210 lb (3724 kg), normal take-off weight of 10,692 lb (4850 kg), maximum take-off weight of 11,905 lb (540 kg) with two 66 Imp gal (79.25 US gal; 300 litre) drop tanks, maximum speed of 548 kt (631 mph; 1015 km/h) at 9,845 ft (3000 m) declining to 486 kt (559 mph; 900 km/h) at sea level, climb to 9,845 ft (3000 m) in 1 minute 36 seconds, to 16,405 ft (5000 m) in 3 minutes 12 seconds and to 32,810 ft (10000 m) in 7 minutes 48 seconds, service ceiling of 47,980 ft (14625 m), maximum range of 809.5 nm (932 miles; 1500 km) with external tanks, and typical range of 512.5 nm (590 miles; 950 km) with standard fuel.

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