Mikulin M-17

M-17
Type	Liquid-cooled V12 engine
National origin	Germany
Manufacturer	Factory No. 26
First run	1930
Major applications	Tupolev TB-3, Polikarpov R-5, Beriev MBR-2
Produced	1930–41
Number built	27,534
Developed from	BMW VI
Developed into	Mikulin AM-34

The Mikulin M-17 was a Soviet-licensed copy of the German BMW VI V-12 liquid-cooled aircraft piston engine, further developed by Alexander Mikulin and used by Soviet aircraft during World War II. Production began in 1930 and continued through 1942. More than 27,000 were produced, of which 19,000 were aircraft engines while the rest were used in Soviet tanks of the period.

The Soviets had bought examples of BMW's III and IV engines earlier in the 1920s and bought two examples of the VI engine in 1926 for evaluation. Following successful bench trials of the engine the Soviets decided to purchase a license for it. A deal was concluded in October 1927 after prolonged negotiations. The Soviets paid $50,000 and were to pay 7.5% of the price of each engine produced after the first fifty. In exchange, the German company was to inform the Soviets of all changes to the engine for a period of five years. Soviet engineers and technicians were to be trained in Germany and German technicians were to assist setting up production in the vacant factory at Rybinsk. The Soviets also hired a number of German skilled workers to work at Factory No. 26 in Rybinsk, mostly those with communist sympathies.

The need to refurbish the factory greatly delayed Soviet production, even though the more complex components, including all electrical equipment, were initially imported from Germany. Soviet changes to the design and production quality issues meant that the Soviet-built engines were some 31 kg (68 lb) heavier and produced less power than the original engine. The first M-17s, as the engines were designated by the Soviets, were not produced until spring of 1930, but were not accepted for service until an engine passed its service tests on 15 August 1930. The M-17 was the most powerful engine available to the Soviet aircraft industry and it was in high demand, so much that Factory No. 24 in Moscow also began to build the M-17. 165 engines were produced in 1930 at Rybinsk and Factory No. 24 had managed to build its first three engines by June 1930.

Unfortunately, the engines built by the Moscow factory were of very poor quality because the management there had made unauthorized changes to simplify production. These had a compression ratio of only 6.15:1 rather than the specified 6.3:1 and they could produce only 615–630 hp (459–470 kW) instead of the 680 hp (510 kW) of the Rybinsk engines. The Moscow engines, of which only thirty were made, were reclassified as training engines and bought for a reduced price. In the meantime production of the M-17 in Moscow had been cancelled in favor of the M-15. Production of engines at Rybinsk had been steadily increasing, 679 being built in 1931 and 5662 in 1934.

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