Soviet Mixed-Power Fighters

The 1-153 M-63 was the last Soviet biplane fighter to enter full scale production. Production Chaika fighters were constantly under test at the NIl WS during 1939-40, with both ski and wheeled undercarriages. It was very difficult to improve performance because, on the one hand, the design was practically at the limit of its development, and on the other it was clear that high speeds could not be achieved with the biplane configuration. To increase speed, two ramjets designed by I Merkulov were mounted on the fighter, and in September 1940 flight tests were undertaken to test the installation. During one of its last test flights the 1-153DM with DM-4 ramjets attained a maximum speed of 273mph (440km/h) at 6,500ft (2,000m) – the ramjets increased top speed by 31.6mph (51km/h). In spite of their high efficiency, the mixed powerplant was not considered suitable for the biplane fighters.

In 1935 young engineers Alexey Borovkov and Ilya Florov proposed an original biplane fighter, and this was produced in 1937 as the ‘Type 7211’. Later, in 1938-39, new biplane fighter based on this machine and designated 1-207 (I – istrebitel, fighter, or literally ‘destroyer’) was developed. By the spring of 1939 the two prototypes had been built, the first powered by a 900hp (671kW) Shvetsov M-62 and the second by an M-63 of the same power. The third prototype, powered by an ungeared M-63, was ready by the autumn. The first two had a fixed under- carriage, while the third had retractable gear. All three had open cockpits. In the spring of 1941 the fourth 1-207 prototype, powered by a geared M-63 and fitted with an enclosed cockpit with a sideward-hinged canopy was completed. All of these aircraft had four 7.62mm ShKAS machine guns, and two 551lb (250kg) bombs could be carried beneath the lower wings. When tested, they bettered the Polikarpov 18 1-15 biplane and 1-16 monoplane in climb rate and service ceiling, and were superior in manoeuvrability to the 1-15 but inferior to the 1-16. During flight tests in 1940 the third prototype reached a speed of 301mph (486km/h) at 17,400ft (5,300m), which for that period was inadequate. Moreover the configuration was also out of date, and for these reasons the type did not go into production.

The ‘D’ was designed as a mixed power fighter with a piston engine and Merkulin ramjet booster operating in the same duct. A 1,500 kW (2,000 hp) Shvetsov M-71 engine was intended to be the main powerplant but it is unclear how the thermodynamic cycles of the two engines were to be linked. Similar aircraft were built later in the German-Soviet War using the main engine to drive a propeller and a compressor to supply air to a ramjet/afterburner booster, both the Su-5 and MiG-13 were produced in limited numbers but the performance gains were limited and soon eclipsed by turbo-jet engines. The ‘D’ was to have been a gull- winged monoplane with high set wing, of stressed skin construction with exceptionally smooth skin stabilised by underlying corrugated structure. A heavy armament of two 37 mm (1.457 in) Nudelman-Suranov NS-37 cannon and two 20 mm (0.787 in) ShVAK cannon was included, but all work was abandoned with the German invasion of 1941.

In order to augment the fighter’s speed when necessary, the designers decided to equip it with one of Valentin Glushko’s liquid- propellant auxiliary rocket motors, including 0 the RD-l, RD-l KhZ, RD-2 and RD-3 with nitric acid and kerosene pump supply.

The unit considered most suitable for the Su-7 was the RD-l , delivering 661lb (300kg) of thrust. In addition, metal plate on the wooden section of fuselage was lengthened to protect the structure from flames emitted by the turbosupercharger. During the flight tests, which began in late 1944, 84 RD-l engine starts were performed on the ground and in flight. From 31st January to 15th February 1945 18 engine test starts were made on the ground using an ether/air starting system, and from 28th Au- gust to 19th December that year the investigations were continued using the RD-l KhZ rocket motor.

Frequent failures of the RD-l prolonged the tests, but finally, in late 1945, flights conducted by test pilot Komarov showed that when the rocket was started at 20,600ft (6,300m) it increased maximum speed by 56mph (91km/h). However, the RD-l was underdeveloped and often failed, and after five changes of the liquid-propellant booster the designers decided to abandon it altogether. Nevertheless, the development and testing of mixed-powerplant prototypes was an important stage in the development of high speed jet aircraft.

The Mikoyan-Gurevich I-250 (a.k.a. Samolet N) was a Soviet fighter aircraft developed as part of a crash program in 1944 to develop a high-performance fighter to counter German turbojet-powered aircraft such as the Messerschmitt Me-262. The Mikoyan-Gurevich design bureau decided to focus on a design that used something more mature than the jet engine, which was still at an experimental stage in the Soviet Union, and chose a mixed-power solution with the VRDK (Vozdushno-Reaktivny Dvigatel Kompressornyi – air reaction compressor jet) motorjet powered by the Klimov VK-107 V12 engine. While quite successful when it worked, with a maximum speed of 820 km/h (510 mph) being reached during trials, production problems with the VRDK fatally delayed the program and it was canceled in 1948 as obsolete.

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By the end of the Second World War the USA and Great Britain had developed practical jet fighters, even if they came a bit too late to take part in the action. Germany achieved even greater success, using jet fighters operationally in the closing stages of the war. The Soviet Union had fallen behind in this area, which is due to the Soviet government's scant attention to jet aircraft development and the lack of indigenous jet engines. True, as early as 1939 the design bureau led by Nikolay N. Polikarpov (OKB-51) had begun working on mixed-power fighters; the lead was quickly followed by other design bureaux headed by Aleksandr S. Yakovlev (OKB-115), Semyon A. Lavochkin (OKB-301), Artyom I. Mikoyan (OKB-155), Pavel O. Sukhoi (OKB-134) and Semyon M. Alekseyev (OKB-21). (OKB = opytno-konstrooktorskoye byuro - experi- mental design bureau; the number is a code allocated for security reasons.) These fighters employed ramjets or liquid-fuel rocket motors to give them a performance boost as required, but for various reasons none of them achieved production and service.

Several rocket-powered fighters were brought out as well, including the BI developed by A. Ya. Bereznyak and A. M. Isayev, the '302' designed by A. G. Kostikov and the Mikoyan 1-270 (aka izdeliye Zh). (Izdeliye (product) such and such was a common way of coding Soviet military hardware). However, the dangers associated with the rocket motor running on corrosive and/or toxic fuels and oxidisers, coupled with the motor's limited operation time, meant this was not a viable powerplant for a high-speed aircraft. Early research and development work on turbojet engines in the USSR dates back to the late 1930s. In 1938 Arkhip M. Lyul'ka and a group of engineers who shared his ideas came up with the project of the RTD-1 turbo- jet rated at 400 kgp (881 Ib st). Approving the project, the People's Commissariat of Aircraft Industry (NKAP - Narodnyy komissariaht aviatsionnoy promyshlennosti) allocated funds for manufacturing a prototype engine; mean- while, Luyl'ka was transferred to Leningrad to continue his work on jet engines at SKB-1 (Special Design Bureau - spetsiahl'noye konstrooktorskoye byuro). The RTD-1 evolved into the RD-1 (reaktivnyy dVigatel' - jet engine) delivering 500 kgp (1,102 Ib st) In early 1942 the Council of People's Commissars, one of the Soviet Union's highest government bodies, considered several jet fighter projects, including Mikhail I. Goodkov's proposal to re-engine the LaGG-3 fighter with an RD-1 turbojet. Concurrently the jet engine development programme was dusted off in accordance with Iosif V. Stalin's personal orders. In reality, however, the work really got underway in 1944 when Lyul'ka was put in charge of the gas turbine engine R&D section at a newly-established institute specialising in propulsion research.

Jet aircraft and jet engine development became a priority task for the Soviet aircraft industry after the war. Huge resources were committed to this task; still, all the money in the world can't buy you time, and the research and development effort was certainly going to be a lengthy one, which meant the service entry of the first Soviet jets would occur rather later than desired. Therefore, to speed up the work the Soviet government chose to make use of Germany's experience in this field.


In order to augment the fighter's speed when necessary, the designers decided to equip it with one of Valentin Glushko's liquid- propellant auxiliary rocket motors, including 0 the RD-l, RD-l KhZ, RD-2 and RD-3 with nitric acid and kerosene pump supply.

The unit considered most suitable for the Su-7 was the RD-l , delivering 661lb (300kg) of thrust. In addition, metal plate on the wooden section of fuselage was lengthened to protect the structure from flames emitted by the turbosupercharger. During the flight tests, which began in late 1944, 84 RD-l engine starts were performed on the ground and in flight. From 31st January to 15th February 1945 18 engine test starts were made on the ground using an ether/air starting system, and from 28th Au- gust to 19th December that year the investigations were continued using the RD-l KhZ rocket motor.

Frequent failures of the RD-l prolonged the tests, but finally, in late 1945, flights conducted by test pilot Komarov showed that when the rocket was started at 20,600ft (6,300m) it increased maximum speed by 56mph (91km/h). However, the RD-l was underdeveloped and often failed, and after five changes of the liquid-propellant booster the designers decided to abandon it altogether. Nevertheless, the development and testing of mixed-powerplant prototypes was an important stage in the development of high speed jet aircraft.