The Mikulin AM-34 (M-34) was a Soviet mass-produced, liquid-cooled, aircraft engine of domestic design. Its initial development was troubled, but it eventually became one of the most successful Soviet aircraft engines of the 1930s. It was utilized on numerous aircraft, including the Beriev MBR-2, Tupolev TB-3, Tupolev TB-4, Tupolev ANT-20, Petlyakov Pe-8, Kalinin K-7, Polikarpov I-17, and Bolkhovitinov DB-A, as well as the G-5 and various prototype motor torpedo boats. A version of the maritime model was adapted for use in several prototype heavy tanks in 1939, although none was placed into production.
Design and development
Before World War II, the Soviet aeroengine industry was mainly engaged in producing foreign designs, notably Wright, Bristol, Hispano-Suiza, and Gnome-Rhône. Several engines of so-called original design were developed, although these were probably largely based on foreign models (e.g. Mikulin M-17, Shvetsov M-25, Klimov M-103 etc.) The M-34 was thought to have been originally designed in Italy by Fiat; it closely follows Italian inline aeroengine practice.[1][2][Notes 1]
The M-34 began development in 1928 as a replacement for the Mikulin M-17, a license-built copy of the BMW VI. It had similar dimensions and attachment points, but was otherwise an entirely new design. It was a direct-drive, block-type engine with the cylinder block connected by long internal studs with centrally coupled articulated connecting rods. The development of the engine process was prolonged, with the engineering drawings not completed until April 1931. The first engine was delivered to TsIAM (Tsentralniy Institut Aviatsionnogo Motorostroeniya, Russian: Центральный Институт Авиационного Моторостроения, Central Aviation Motors Institute) on 21 September 1931 for bench testing with imported carburetors and magnetos. It began state testing in November 1931, but failed. It was submitted again a year later with Soviet-designed K-34 carburetors, but was again rejected. It was resubmitted in January 1933, but again failed. It was flight-tested in a Tupolev TB-3 in October 1933.[3]
Despite these failures it began production in 1932 at Factory No. 24 in Moscow, and 64 engines had been delivered by the end of the year. 790 were built the following year, and it was exhibited in Paris as an achievement of the Soviet aviation industry. The M-34 was redesignated with Alexsander Mikulin's initials as the AM-34 on 9 August 1936 in honor of his achievement.[3]
The M-34 was used in an unusual system, first tried by Imperial Germany in 1918 with a Zeppelin-Staaken R.VI, that used a separate supercharger to supply pressurized air to the aircraft's M-34FRN engines. The first installation, designated ATsN-1 (Agregat tsentral'novo nadduva – central boosting unit), used an auxiliary M-34 fitted inside the fuselage to drive a central supercharger with ducts leading to the engines in the wings. This was flight-tested in a Tupolev TB-3 in 1935. It was adapted for use in a Petlyakov Pe-8 bomber prototype with a smaller Klimov M-100 engine substituted for the M-34 as the ATsN-2. It was flight-tested during 1938–39, but was not approved for production.[4] The same idea was revived in 1943 by Nazi Germany with the Henschel Hs 130E bomber prototype series, with the Höhen-Zentrale Anlage unit.
Like the BMW VI and the Mikulin M-17, the AM-34FRN and subsequent models used articulated connecting rods which caused a different stroke of 190 mm (7.5 in) and 199 mm (7.8 in) between right and left cylinder bank. The displacement was 46.9 L (2,863.7 in3). Combined with a number of other changes power significantly increased in most models to 1,200 horsepower (890 kW).[5]
Development of a version for motor torpedo boats began in 1932 as the GM-34, but it did not pass its state tests until December 1934, although it was put into production that same year. It was given a reversing gear, a free-wheel sleeve, and its cooling and exhaust systems were modified. Production continued through 1943 with the GM-34s adapting features from the aviation models. With the exception of the GAM-34BP and the original GM-34, all maritime engines used a benzene-alcohol fuel mixture.[6]
A version of the GM-34 was adapted for use in heavy tanks in 1939 as the GAM-34BT, although only small numbers were built. It was mounted in the prototypes of the T-100 and SMK heavy tanks and the SU-100y self-propelled gun, none of which was put into production. The cooling system was modified with an external fan, and it was given new gearing. An electric starter was used rather than the original pneumatic one. It was rated at 850 hp (630 kW).[7]
