The Mikulin AM-34 (M-34) was a

Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the 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 The Beriev MBR-2 was a Soviet multi-purpose (including reconnaissance) flying boat which entered service with the Soviet Navy in 1935. Out of 1,365 built, nine were used by foreign countries (including Finland and North Korea). In the Soviet Unio ...

Tupolev TB-3 The Tupolev TB-3, OKB designation ANT-6, was a monoplane heavy bomber deployed by the Soviet Air Force in the 1930s and used during the early years of World War II. It was one of the world's first cantilever wing four-engine heavy bombers. Des ...

, Tupolev TB-4,

Tupolev ANT-20 The Tupolev ANT-20 ''Maxim Gorky'' (, sometimes romanized as ''Maksim Gorki'') was a Soviet eight-engine aircraft, the largest in the world during the 1930s. Its wingspan was similar to that of a modern Boeing 747, and was not exceeded until the ...

Petlyakov Pe-8 The Petlyakov Pe-8 () was a Soviet heavy bomber designed before World War II, and the only four-engine bomber the USSR built during the war. Produced in limited numbers, it was used to bomb Berlin in August 1941. It was also used for so-called " ...

Kalinin K-7 The Kalinin K-7 () was a heavy experimental aircraft designed and tested in the Soviet Union in the early 1930s. It was of unusual configuration, with twin booms and large underwing pods housing fixed landing gear and machine gun turrets. In th ...

Polikarpov I-17 The Polikarpov I-17 was a Soviet single-seat fighter prototype designed and built by a team headed by Nikolai Polikarpov at the Central Design Bureau (TsKB) in 1934. Development The I-17 was a lightweight single-seat low-wing cantilever monopla ...

, and Bolkhovitinov DB-A, as well as the 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 World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

, 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 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 and tanks during World War II. Production began in 1930 and continue ...

Shvetsov M-25 The Shvetsov M-25 was an aircraft radial engine produced in the Soviet Union (USSR) in the 1930s and 1940s, a licensed production variant of the Wright R-1820-F3. Design and development The first M-25s were produced from kits imported from the ...

Klimov M-103 The Klimov M-103 is a V12 liquid-cooled piston aircraft engine used by Soviet aircraft during World War II.Gunston 1989, p. 90. Design and development The M-103 was a further development of the Klimov M-100 engine that was itself a licensed co ...

, etc.). The M-34 was thought to have been originally designed in Italy by

Fiat Fiat Automobiles S.p.A., commonly known as simply Fiat ( , ; ), is an Italian automobile manufacturer. It became a part of Fiat Chrysler Automobiles in 2014 and, in 2021, became a subsidiary of Stellantis through its Italian division, Stellant ...

; it closely follows Italian inline aeroengine practice.''Armour in Profile'', Brereton 1967, p. 3. The M-34 began development in 1928 as a replacement for the

, a license-built copy of the

BMW VI The BMW VI was a water-cooled V-12 aircraft engine built in Germany in the 1920s. It was one of the most important German aero engines in the years leading up to World War II, with thousands built. It was further developed as the BMW VII and ...

. 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 () on 21 September 1931 for bench testing with imported

carburetor A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Ventu ...

s and

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

s. It began state testing in November 1931, but failed. It was submitted again a year later with

-designed K-34 carburetors, but was again rejected. It was resubmitted in January 1933, but again failed. It was flight-tested in a

in October 1933. Despite these failures it began production in 1932 at Factory No. 24 in

Moscow Moscow is the Capital city, capital and List of cities and towns in Russia by population, largest city of Russia, standing on the Moskva (river), Moskva River in Central Russia. It has a population estimated at over 13 million residents with ...

, 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. 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 In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement (engine), displacement. It is a form of forced induction that is mechanically ...

to supply pressurized air to the aircraft's M-34FRN engines. The first installation, designated ATsN-1 (, '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 The Hispano-Suiza 12Y was an aircraft engine produced by Hispano-Suiza for the French Air Force before the Second World War. The 12Y became the primary French 1,000 hp (750 kW) class engine and was used in a number of famous aircraft, ...

engine substituted for the M-34 as the ATsN-2. It was flight-tested during 1938–1939, but was not approved for production. The same idea was revived in 1943 by Nazi Germany with the

Henschel Hs 130E The Henschel Hs 130 was a German high-altitude reconnaissance and bomber aircraft developed in World War II. It suffered from various mechanical faults and was never used operationally, only existing as prototype airframes. Development Develop ...

bomber prototype series, with the 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 and between right and left cylinder bank. The displacement was . Combined with a number of other changes power significantly increased in most models to . 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 Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

alcohol fuel Various alcohols are used as fuel for internal combustion engines. The first four aliphatic alcohols (methanol, ethanol, propanol, and butanol) are of interest as fuels because they can be synthesized chemically or biologically, and they have ...

mixture. 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 The SU-100Y, initially designated T-100Y,Pasholok was a Soviet prototype self-propelled gun, developed from the chassis of the prototype T-100 tank. It was developed during the Winter War with Finland to include a 130 mm gun to destroy conc ...

self-propelled gun Self-propelled artillery (also called locomotive artillery) is artillery equipped with its own propulsion system to move toward its firing position. Within the terminology are the self-propelled gun, self-propelled howitzer, self-propelled mo ...

, 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 .

Variants

; M-34: First production version. Direct drive. Early engines used imported

Zenith The zenith (, ) is the imaginary point on the celestial sphere directly "above" a particular location. "Above" means in the vertical direction (Vertical and horizontal, plumb line) opposite to the gravity direction at that location (nadir). The z ...

90R carburetors, although later ones used indigenous K-34 carburetors. In production until the end of 1939. Rated at with a weight of . ; Coupled M-34: Two engines driving one propeller, project for the

, no production. ; M-34F: Small batch built in 1933 with a rating at . ; M-34R: ''R'' for , 'reduction gear'. Rated at with a weight of . Passed its state trials in May 1933 and in production from the end of that year to the end of 1939. ; M-34RD: ''D'' for , 'long-range'. Ten engines built with special attention to quality, smaller tolerances, and K-34RD carburetors to equip the

Tupolev ANT-25 The Tupolev ANT-25 was a Soviet long-range experimental aircraft which was also tried as a bomber. First constructed in 1933, it was used by the Soviet Union for a number of record-breaking flights. Development The ANT-25 was designed as the r ...

record-breaking aircraft. RPMs were boosted to give a power of . Later fifty more were built to power

bombers converted to VIP transports. ; M-34N: ''N'' for , 'supercharged'. Development began in 1931 of this direct-drive model, but the first two-stage supercharger design proved to be quite unreliable. A single-speed replacement was developed at TsIAM and tested in November 1933 and production began in September 1934. The

centrifugal type supercharger A centrifugal supercharger is a specialized type of supercharger that makes use of centrifugal force in order to increase intake pressures and power. An increase in combustion intake air pressure allows the engine to burn more fuel, which results i ...

was designed as a removable module and could be installed on other versions of the M-34. Rated at . A PTK steam-powered supercharger was developed and tested from 1938 to 1940, but was not accepted for production. ; M-34RN: This geared model used the same geared centrifugal supercharger (GCS) as the M-34N and had the same rating. It failed state testing in September 1934 when the pistons burned through. ; M-34NA: A version of the M-34N with minor changes to some components to extend service life. It had the same power as the original model. ; M-34RA: A version of the M-34R with the same changes and power as the M-34NA. ; M-34RNA: A version of the M-34RN with all the changes introduced on the NA and RA models. Same power as before, but weighed . Flight-tested on a TB-3 in May 1935 and production began at the end of the year. ; M-34NB: The NA fitted with a strengthened

crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...

, a lightened

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

with a modified nose and a refined supercharger. The power remained the same, but the weight dropped to . A TK-1

turbocharger In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into th ...

was tested with the prototype on a

Polikarpov R-Z The Polikarpov R-Z was a Soviet reconnaissance bomber aircraft of the 1930s. It was a revised version of the Polikarpov R-5 which was built in large numbers between 1935 and 1937. It was used in combat during the Spanish Civil War as well as th ...

in 1936. ; M-34RNB: A geared equivalent of the NB model with a lightened reduction gear. The power remained the same, but the weight dropped to . In production from October 1935 until the end of 1939. ; M-34P: ''P'' for , 'cannon'. A version of the M-34RN adapted to mount an

autocannon An autocannon, automatic cannon or machine cannon is a automatic firearm, fully automatic gun that is capable of rapid-firing large-caliber ( or more) armour-piercing, explosive or incendiary ammunition, incendiary shell (projectile), shells, ...

in the V between the cylinder banks that fired through a hollow gear shaft. The specification was issued in August 1934, but no further information is known. ; M-34NV: ''NV'' for , 'fuel-injected'. It passed its bench tests in 1935 and was flight-tested in 1937, but was not accepted for production. Rated at . ; M-34RNV: Geared version similar to the NV. ; AM-34RNV-TK: Prototype built in 1938, similar to the RNV with the addition of a TK-1 turbocharger. Rated at and an estimated weight of . ; AM-34RS: Prototype built in 1938 with mixed cooling; air-cooled sleeves, and

ethylene glycol Ethylene glycol ( IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes: as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...

-cooled

cylinder head In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...

s. Rated at . ; AM-34NF: Prototype with a geared centrifugal supercharger and a TK-1 supercharger. Flight-tested in a TB-3. Compression ratio of 6.6:1 and rated at . ; M-34N2B: A prototype with a supercharger, two turbochargers, and four K-4 carburetors. Rated at . ; AM-34FRN: ''F'' for , 'boosted'. Development began in 1934, but development was not completed until 1938. The crankshaft, crank case, gearing, and the side joints of the connecting rods were reinforced. The lubrication system was modified, the supercharger improved, and a new gas-distribution system was fitted. The carburetors were moved to behind the supercharger. Rated at and the weight dropped to . It was exhibited in the 1937

Paris Air Show The Paris Air Show (, ''Salon du Bourget'') is a trade fair and air show held in odd years at Paris–Le Bourget Airport in France. Organized by the French aerospace industry's primary representative body, the ''Groupement des industries frança ...

. ; AM-34FRNA: First main production version of the FRN model. Equipped with four carburetors. ; AM-34FRNB: Next production model of the FRN. Equipped with six carburetors. A small batch was adapted for the ATsN-2 system with pressurized air provided by an external supercharger and flight-tested in a Pe-8 in 1938–1939. ; AM-34FRNV: The last main production variant of the AM-34. Built during 1938–1939. The crankcase was modified and bronze bushings were used for the main supports. It had a longer crankshaft nose, four K-4 carburetors, and a modified lubrication system. The valve castings were made of magnesium alloy. The power remained the same, but the weight increased to . Variants with fuel injection and two TK-1 turbochargers were tested, but not put into production. ; AM-34RB: Superchargers were removed from AM-34RNB engines during 1938–1939 to create this model.

Maritime variants

; GM-34: Intended for motor torpedo boats. Rated at with a weight of . ; GAM-34F: A boosted version of the GM-34 it had bronze main bushings and used the

, block, heads, and some other components of the AM-34FRNV aircraft engine. Rated at with a weight of with a

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

of 7.3:1. ; GAM-34FN: A version of the GAM-34F with a FN-25 geared centrifugal supercharger and one K-4 carburetor. It used the oil system of the GAM-34BS and was in production from August 1939. ; GAM-34BP: Intended for armored river boats. ; GAM-34BS: An improved version of the GAM-34BP. Rated at with a weight of .