Soviet Luxuries

The Japanese experience would have been understandable to Soviet policy makers and designers. For most of World War II, the USSR regarded twin-engined fighters as a luxury it could not afford. Given the focus of the authorities on tactical air warfare, this might be considered a bit surprising. One could very well imagine a useful role for a heavily-armed twin-engined fighter-bomber over and behind the battefield, especially over a battle area that was as vast as the Eastern Front. And the USSR’s only twin-engined fighter in service, the Pe-3, actually found a lot of use in this type of mission, but only a few hundred of these aircraft were completed. A combination of small single-engined fighters and single-engined attack aircraft was preferred, with a modest investment in twin-engined light and medium bombers. And this regardless of a long-running effort to design heavy fighters, that achieved some excellent results.

Tupolev

Despite the isolation of their country in the late 1920s, Soviet policy makers appeared to have been as much influenced by the international fashion for twin-engined fighters as anyone else. In these years, the USSR was building a strategic, long-range air force, and it possessed a fleet of ANT-6 (military designation TB-1) heavy bombers that, by the standards of the time, was very impressive indeed. One of the roles envisaged for a twin-engined fighter was long-range bomber escort, but it was also expected to fly independent “cruiser fighter” missions deep into enemy territory, and to perform reconnaissance, bombing, and torpedo-bombing.

Andrei N. Tupolev suggested that the requirement could be met by a scaled-down version of the ANT-6. This made more sense than one would think, for in an age of biplane fighters with mixed structures, the huge monoplane ANT-6 had been a technological leap forward. His proposal was accepted, and in September 1929 the ANT-7, designated R-6 by the military, made its first flight. It had the familiar Tupolev trademarks: Thick monoplane wing and rectangular fuselage, corrugated metal skinning, fixed landing gear, and open cockpits. It was powered by liquid-cooled M-17 engines, a license-built version of the BMW VI. Production began in 1930 and ran for four years in a number of different versions, but at the end of that period the aircraft was already obsolete, overtaken by the rapid technological development of the 1930s. The KR-6 “cruiser recconaissance” version had a top speed of 226 km/h at sea level, needed no less than 13 minutes to climb to 2000 m, and had a range of 1480 km. The armament consisted of open nose and dorsal gunnery positions with two 7.62-mm DA guns each. Other versions (but not the KR-6) also had a retractable ‘dustbin’ below the fuselage with a single DA. This was nothing more than the standard bomber armament of the period.

In 1932 the prototype of a replacement for the ANT-7 had been ordered, the ANT-21. The ANT-21 initially re-used some parts of the ANT-7, including the engines and some structural components in the wing, but it featured a new semi-monocoque fuselage, smooth instead of corrugated metal skinning, and retractable landing gear. These refinements were amply rewarded, for the top speed at sea level rose to 351 km/h. An accident during flight testing resulted in the construction of a much-modified ANT-21bis, also known as the MI-3D, with M-34N engines. However, the type was not accepted for production.

	Tupolev KR-6	Tupolev MI-3D
Engines	M-17	M-34N
Rating	680 hp	820 hp
Wing Span (m)	23.20	20.76
Length (m)	15.06	11.57
Height (m)
Wing Area (m2)	80.0	59.2
Empty Weight (kg)	3,870	4,058
Loaded Weight (kg)	5,992	5,463
Max. Speed (km/h)	226 km/h at sea level	350 km/h at 5,000 m
Climb	2,000 m in 13 min
Ceiling (m)		8,300
Range (km)	1480
Fixed Guns		2 × 7.7 mm PV-1
Flexible Guns	2 × 7.7 mm DA in nose Tur-6 2 × 7.7 mm DA in dorsal Tur-5	1 × 20 mm ShVAK in nose mount 2 × 7.7 mm DA in dorsal mount

At this point in time, Soviet development of twin-engined fighter was influenced by a new armament option. In the early 1930s Leonid V. Kurchyevskii developed a family of recoilless guns, building on the earlier designs by the American Cleland Davis. The Davis and Kurchyevskii designs solved the recoil problem by firing two projectiles: A shell forward, and a counterweight to the rear. The recoil forces generated by the firing of the two projectiles compensated each other. The concept produced in a long gun, with muzzles at both ends and a complicated breech mechanism in the middle; all very inconvenient for a traditional fighter. However, the elimination of recoil made it possible to install 37-mm, 76-mm, and even 120-mm guns in a relatively small aircraft. A specially designed twin-engined fighter was thought to be the best candidate to carry such a weapon.

One of the possibilities was demonstrated by the ANT-23 fighter, a small twin-boom design with a tractor and a pusher engine in its short fuselage. The unique feature of the ANT-23 was that the tail booms were actually formed by the barrels of the 76.2-mm APK-4 cannon. Despite its unusual configuration the aircraft flew well, but it was overtaken by other developments.

The ANT-29, also known as DIP, appears to have been broadly based on the ANT-21bis, but had a short, deep and narrow fuselage designed to house two large APK-8 recoilless guns in its bottom, with the muzzle of the barrels protruding from the nose and a counterweight fired from the tail. In relation to the compactness of its fuselage the ANT-29 had a huge 56.8 square meter wing, and the engines were imported French Hispano-Suiza 12Ybrs V-12s of 760 hp. The ANT-29 flew late in 1935, but was not accepted for service. Nevertheless, the work on the ANT-29 was not entirely wasted: The aircraft was closely related to the ANT-40 or SB, which was the most important bomber of the late 1930s and represented a quantum leap forward in the design of combat aircraft when it entered service.

And fighter development in this family had not yet been abandoned. The development of the ANT-46 or DI-8 was allowed to continue in parallel with that of the ANT-49, and it was flown in 1936. The DI-8 was armed with a 37-mm APK-11 cannon buried in each wing outside the propeller arcs, plus four ShKAS machine guns in the nose. However, 1936 was also the year in which the great Stalinist purges began. And the victims of the purges were found not only among political and military leaders, but also included factory managers, scientists and engineers. Leonid Kurchyevskii disappeared. Andrei Tupolev and many of the members of his team were arrested. As a sign of the times, the accusations against him included the absurd claim that Tupolev had supplied the Germans with the plans for the Bf 110.

Petlyakov

One result of Stalin’s reign of terror was that many Soviet aircraft designers found themselves imprisoned in design and study offices controlled by the NKVD. Many Soviet combat aircraft were designed by what was in effect slave labour, engineering offices filled with a captive staff that in some cases had a suspended death sentence looming over them. Vladimir Petlyakov, formerly one of Tupolev’s closest associates, thus became the engineering lead of an imprisoned group of fifty people tasked with the development a twin-engined fighter. (The formal head of the design bureau was an NKVD officer.) They were ordered to design a highly ambitious high-altitude, long-range fighter, intended both as an interceptor and as an escort fighter for the new ANT-42 bomber. The specifications called for a top speed of 630 km/h at 10,000 m, with an operational ceiling of 12,500 m.

The VI-100, which made its first flight on 22 December 1939, certainly looked ready to meet this demanding specification. It had an elegantly streamlined fuselage, almost a monococque structure with its strength derived from a relatively thick skin attached to the fuselage frames, without supporting stringers. The wing carried the two M-105 engines in front of the leading edge, in neatly streamlined nacelles that also contained the TK-2 turbosuperchargers and the wells for the main landing gear. The superchargers also provided the compressed air for the crew of three in two pressure cabins, fore and aft. The fixed forward-firing armament consisted of two 20-mm ShVAK cannon (300 rpg) and two 7.62 mm ShKAS (900 rpg). The planned use of a pressure cabin made it hard to provide flexible guns for the defense of the rear, so the installation of a single fixed rearward-firing ShKAS was contemplated, although not proceeded with. The first prototype could also carry bombs under the wings, while the second prototype even possessed an internal bomb-bay.

The VI-100 had important teething troubles, and was slightly slower than has been hoped, but nevertheless the design was regarded a success. However, its intended purpose was to be changed abruptly. In 1940, it became apparent that the potential enemies of the USSR would not be putting into service high-altitude bombers at any time soon. In that context, the production of the complex and expensive VI-100 was not justified. However, the VVS urgently needed a new tactical low-altitude bomber to replace the obsolescent SB. Hence it was decided to use the VI-100 as the basis for the development of a twin-engined dive-bomber, the PB-100.

The VI-100 was not cancelled outright, but the relatively low priority accorded to it inevitably resulted in its neglect. For the changes required to create the bomber version were very substantial, and only by great exertion was it possible to fly the first PB-100 on 15 December 1940. It entered service as the Petlyakov Pe-2, which soon proved itself an excellent light bomber. A total of 10,574 were delivered to the VVS during the war.

This left the USSR without a twin-engined fighter, and soon after the opening of the war with Germany a need was felt for just such an aircraft, mostly as a nighfighter. As the Pe-2 was the most suitable of all available aircraft, the conversion of one to a fighter prototype was ordered — and reportedly only seven days passed between the formulation proposal and the completion of its state flight tests. The new fighter was known as the Pe-3.

Of course, development in such a short time was only possible because very limited modifications were allowed. The fuel tankage was increased, the crew reduced to two, and the armament slightly increased: The production Pe-3 initially had two fixed UBK 12.7-mm machine guns with 250 rounds each, a ShKAS in the turret at the rear of the cockpit, and (because the ventral gunner had been omitted) a fixed ShKAS on a ventral mount to deter attackers. This was clearly too light, and fixed armament was soon increased by installing a 20-mm ShVAK cannon, while the flexible ShKAS was replaced by a 12.7-mm UBT. With some other changes, this resulted in the updated Pe-3bis. A later change relocated the machine guns from the nose to the former bomb bay. As could be expected for a hastily improvised fighter, the armament installation of the Pe-3 was never entirely satisfactory. In the summer of 1941 a more through fighter modification, the Pe-2I, was ready for testing, but despite better performance and a better armament installation, it was not accepted.

Because the Pe-2 had possessed excellent performance, the Pe-3 could match a Bf 110C in speed, though not in manoeuverability, and it was lightly armed for a heavy fighter. It also lacked basic equipment for the nightfighter mission; the initial production runs had poor radio and not even a radio compass. Only 360 Pe-3s were completed, and they were more useful as long-range reconnaissance aircraft and ground attack aircraft than as fighters.

Yakovlev I-29

There was another light bomber that held, at least on paper, some potential as a twin-engined fighter. Yakovlev’s BB-22, later called the Yak-2, was a fast light bomber. The prototype made its first flight in early 1939, and the BB-22 short-range, fast bomber version entered production in 1940. A highly streamlined design, it was greeted as something of a miracle by the Soviet leadership, but it turned out to be a very disappointing combat aircraft. The high speed of the prototype, 567 km/h at 9,900 m, had been achieved by sacrificing operational equipment and armament. Adding these reduced speed by over 50 km/h, and the handling characteristics left something to be desired, too. Worse, the production aircraft was barely able to carry 400 kg of bombs.

From the start, the aircraft had also been intended as a fighter, but characteristic for the initial concept was that the proposed fixed armament was just a single 20-mm ShVAK, replacing the fixed 7.62-mm ShKAS of the bomber version. This was later revised to a more realistic pair of ShVAK, a single ShKAS in the lower nose, and two ShKAS more installed between the cylinder banks of the engines, firing through the propeller hubs. The compensate for the weight increase, the crew of the fighter version was reduced to one.

The highest priority was given to the bomber version, and then to the R-12 reconnaissance model; so an actual fighter prototype was not flown until December 1940. This I-29 was powered by M-105 engines and was armed with two ShVAK cannon in the lower fuselage. However, with the evacuation of the aviation industry to the East, beyond the reach of the German forces, work on the I-29 was halted.

Polikarpov

In 1935, the Nikolai Polikarpov started work on the development of a twin-engined multi-role aircraft. After what appears to have been considerable debate on the intended role of such an aircraft, with a related series of designation changes, a prototype finally emerged in 1937 as the VIT-1, a designation indicating that it was a Vozdushny Istrebitel Tankov, or anti-tank fighter. It was a three-seater powered by two 960 hp M-103 engines, and its most striking features were the two long barrels of the powerful ShK-37 cannon installed in the wing roots. A 20-mm ShVAK in the nose, with a limited range of movement, and a 7.62-mm ShKAS in the rear cockpit completed the gun armament. An internal bomb bay and external bomb racks were the other part of it, for the VIT-1 was also expected to act as a dive bomber.

The VIT-1 was a good basis for further development, but more powerful engines were required to improve the top speed (450 km/h) and take-off and landing characteristics. Hence the development of the VIT-2, powered by 1050 hp M-105 engines and distinguished most easily by its twin tail fins, but in fact extensively redesigned and provided with heavier armament. The aircraft was ready in the spring of 1938 and with M-105 engines installed, the VIT-2 prototype reached a speed of 513 km/h at 4500 m. However, the type still suffered from unreliable engines and numerous aerodynamic problems, and needed considerable modifications to rectify the worst of them. It was early 1939 before the VIT-2 finally passed its state testing and was recommended for production. But it was not to be. Limited industrial resources, political disagreements, and a preference for the SPB dive-bomber version of the same airframe, all led to the abandonment of the project.

Of course, even if the projected VIT-2S production version had been built, it would have been a ground attack aircraft with perhaps a limited air combat capability. Before the type fell by the wayside, Polikarpov was asked to design a proper twin-engined fighter, intended as a heavy escort fighter, the TIS. Work on the VIT and SPB delayed progress on the TIS, and the first flight of the TIS(A) prototype was made in September 1941. It was smaller than the VIT, but nevertheless considerably heavier, despite the use of all-metal instead of mixed construction. This was a characteristic of several Soviet twin-engined fighter designs, and the result of building them to very high stress factors, up to loads of 12 g. Of course, the additional weight hampered performance, and especially take-off and landing from rough fields.

But the TIS(A) had very clean, elegant lines, with closely cowled 1400 hp Mikulin AM-37 in-line engines and twin tailfins. The wing had a broad chord at the root and tapered sharply towards the tips, with most of the taper on the trailing edge. Top speed achieved during tests was 555 km/h at 5800 m, but clearly the AM-37 engines were far from ready for service use. The German attack, the evacuation of the design offices to the East and the urgency of other work caused work on the TIS to be temporarily set aside, until the second half of 1943. In June 1944 flight testing began of an improved TIS(MA), intended to have AM-39 engines, but in fact equipped with much more readily available AM-38F power plants. With these low-altitude rated engines it was capable of 535 km/h at 1650 m. As impressive the aircraft could have been in 1941, by late 1944 there was little future and no operational need for the type; and after the death of Polikarpov in July 1944 his design bureau was closed down.

The original TIS(A) had been armed with four fixed 7.62-mm ShKAS machineguns in the upper nose, two ShVAK cannon in the wing roots, and two more ShKAS guns on a dorsal TSS-1 and a ventral mount. The latter two were both controlled by the observer, for the TIS was a two-seat aircraft. The ventral gun was rather impractical, for its use required the observer not only to leave his seat, but to squeeze his way to under the armour plate that protected his station. It was abandoned on the TIS(MA); the dorsal mount was replaced by a more powerful VUB-1 with a 12.7-mm UBT but the biggest change was made to the nose armament. Two 12.7-mm UBS were installed in the nose instead of the four rifle-calibre machine guns, and two Sh-37 37-mm cannon were placed in the wing roots. A ventral pack could accomodate a NS-45.

	Polikarpov VIT-2	Polikarpov TIS(A)
Engines	Klimov M-105	Mikulin AM-37
Rating	2 x 1050 hp at 4000 m	2 x 1400 hp
Wing Span (m)	16.50	15.5
Length (m)	12.25	11.7
Height (m)
Wing Area (m2)	40.76	34.8
Empty Weight (kg)	4332	5800
Loaded Weight (kg)	6302	7840
Max. Speed (km/h)	513 km/h at 4500 m	535 km/h at 7000 m
Climb	5000 m in 7.2 min	5000 m in 7.3 min
Ceiling (m)	8200	10250
Range (km)	2900	1720
Fixed Guns	2 × 37-mm ShK-37 and 2 × 20-mm ShVAK in wing roots	2 × 20-mm ShVAK in wing roots and 4 × 7.62-mm ShKAS in nose
Flexible Guns	1 × 20-mm ShVAK in nose, 1 × 20-mm ShVAK dorsal, 2 × 7.62-mm ShKAS ventral.	1 × 7.62-mm ShKAS dorsal, 1 × 7.62-mm ShKAS ventral

Mikoyan-Gurevich

Of the several Soviet twin-engined fighters that got close to production, one of the most interesting ones was the DIS-200, designed by the new OKB or design bureau constituted by Artyom Mikoyan and Mikhail Gurevich. (Both, incidentally, managed to stay out of Stalin’s jails.) Their initial concept included the use of the new powerful diesel engines then being developed by Charomskyi. Diesel engines may sound like an unlikely choice for a fighter, but the advantage of such power plants was that they were fuel-efficient, and on paper allowed the aircraft to have a long range. However, the intended engines never matured sufficiently, and the first prototype had conventional liquid-cooled Mikulin AM-37 V-12 engines, while the second switched to M-82F radials.

The DIS-200 was a compact single-seat fighter, with a wing span and length close to that of the Fw 187. It was considerably heavier, however, and wing loading was high. The wing had a very deep chord at the wing root, and tapered sharply towards the tips. To reduce take-off and landing speeds the aircraft was given generous flaps on the trailing edge, as well as ailerons that could be lowered together with the flaps. The engine nacelles were slung below the wing, which in turn was attached to the bottom of the slender, short-nosed fuselage. The pointed engine cowlings were reminiscent of that of the MiG-3, with prominent oil coolers installed at each side. The radiators for the engine coolant were narrow slots, also on each side of the engine cowling, with an exhaust at the rear of the cowling near the wing trailing edge.

The bubble cockpit and inverted gull shape of the wing gave the pilot a good view forward and in the upper hemisphere, but he could look downwards only through glass panels in the bottom of the nose. The wing roots carried a fixed armament of two 12.7-mm UBS and four 7.62-mm ShKAS guns. Options for armament fitted under the fuselage included a pack with a powerful 23-mm VYa-23 cannon for the fighter role, a torpedo for anti-shipping missions, or a bomb. (The second prototype, with more powerful engines, could reportedly carry a pack with two cannon.)

In weight and performance, the DIS-200 was close to the Mosquito. It was, incidentally, also built largely of wood, to save on scarce light alloys. High performance and multi-role versatility could have given it a formidable potential. However, the first prototype had the misfortune to fly at the end of May 1941; the German attack in the next month upset all planning, and the notion of producing the aircraft in series as the MiG-5 had to be abandoned. As in the case of the TIS, the type was also handicapped by its underdeveloped and unreliable AM-37 engines.

The DIS was not abandoned. In late 1941 the design team was reinforced with Petr Grushin, whose own Gr-1 twin-engined fighter had been destroyed by German ttack before its first flight. (Very little is known about the Gr-1, but sketches show an aircraft remarkably similar to the Bf 110.) The second DIS-200 prototype, completed after the OKB had been evacuated to the East, flew in January 1942, with better developed 1,700 hp M-82F radials, in close-cowled nacelles and driving four-bladed propellers. This was well ahead of the TIS(MA), but nevertheless too late; the VVS had already settled on a policy of tactical air support and no longer needed a long-range fighter.

The Unfortunate

The Polikarpov and Mikoyan-Gurevich bureaus found a competitor in the OKO team, lead by Vsevolod Tairov. His OKO-6 design was ambitious and radical. Of mixed construction, with a relatively generous use of duralumin and magnesium alloy, the OKO-6 was very compact, with a wing span of 12.65 m and only 25.4 square meter wing area. It had a deep but narrow and short fuselage, ending in a single tail fin; the rather plump engine nacelles housed M-88 radials, cooled through narrow slots behind large spinners. The propellers rotated in opposite directions. Armament consisted of four ShVAK cannon in the fuselage bottom and two ShKAS in the upper nose decking.

The OKO-6 looked like a recipe for aerodynamic problems, and indeed tests, following the first flight on the last day of 1939, revealed a need for substantial changes. A year passed before a modified OKO-6bis flew, also known as Ta-1 in honor of its designer, with a longer fuselage ending in twin tail fins, besides a series of other improvements. But an engine failure resulted in a crash, and again several months were lost before the first prototype had been rebuilt. This was brought to OKO-6bis configuration but with M-89 engines, and renamed Ta-3. In this form, the aircraft was said to posses better handling than the MiG-3. This was very faint praise indeed, but the type’s high performance and heavy armament still resulted in a recommendation for production. However, a requirement for a considerable range increase triggered yet more delays, and it was May 1942 before the Ta-3bis (with fuel tanks in the magnesium alloy outer wing panels) entered official tests.

By August 1942, two and a half years had passed since the first flight of the OKO-6, but aerodynamic problems persisted and the M-89 was still too unreliable for production. Designer Tairov himself had been killed in an air accident in December 1941, and the interest in twin-engined fighters had waned. The aircraft was abandoned and forgotten.

Loss

And so the Soviet effort to develop twin-engined fighters turned out to be a waste of time. Despite a surprisingly large number of prototypes: The VI-100, I-29, VIT-2S, TIS, DIS-200, Gr-1 and Ta-3, the only twin-engined fighter to see service was the improvised and rather unsatisfactory Pe-3. This was operated on a limited scale and mostly in a light bomber role. After the war some nightfighter developments of the Tu-2 bomber appeared.

Some technical reasons can be pointed out. In the story of the aircraft above, engine troubles are a constant. A good twin-engined fighter needed the most powerful available engines, but Soviet engine development during the war years largely failed to make new designs sufficiently reliable. The M-105 was too small for a heavy fighter, and the M-82 reached a sufficient state of development in late 1942, when it was already too late. The AM-38 was a good engine, but heavy and rated only for low altitudes. Without a good turn of speed, a twin-engined fighter flying at low level was very vulnerable to being bounced.

Other factors helped to eliminate the operational need. As Soviet night-fighter radars were not developed until after the war, there was evidently no need for an aircraft able to carry one and its operator. Operations over sea were mostly limited to areas where the enemy had no fighter bases, so there was no requirement for a long-range fighter for a naval role either.

In the end, however, it was a doctrinal choice. The VVS chose not to deploy such aircraft, and as long as it did not want to operate deep over enemy territory, in did not need to. There was always the possibility of constructing airfields close to the front. One can speculate that tactical air operations over the vast area of the Eastern Front would be an excellent environment for a fast, long-range fighter and fighter-bomber, striking at gathering areas and transport infrastructure behind the enemy front lines. However, for most of the war the USSR could rely on partizan forces to make the hinterland unsafe for the enemy.

Next: Chapter IX