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AM-38

A. A. Mikulin

Of all the engines of the Mikulin Design Bureau, the AM-38 engine turned out to be the most demanded. The use of the AM-35 engine on the prototype of the future Il-2, the BSh-2 attack aircraft, showed that altitude is not needed for aircraft of this purpose. Therefore, on the basis of the AM-35, a special engine for the IL-2 was created with a design altitude lowered to 1650 m, which made it possible to increase the takeoff power to 1600 hp. and rated power on the ground up to 1500 liters, s. The motor received the designation AM-38.

The use of AM-38 on the IL-2 provided an increase in its speed, maneuverability and combat load. The attack aircraft was put into series, which required a significant increase in the production of motors, which was incredibly difficult to ensure due to the evacuation of some of the engine plants (including the plant that produced AM-35A, AM-37 and AM-38). Therefore, in order to provide the IL-2 with engines at the end of 1941, a difficult decision was made - to remove the AM-35A engines from production and concentrate all the efforts of the serial plant and the A.A. Design Bureau. Mikulin on AM-38 and its development.

Table 1

Basic data of AM-38 and AM-38F motors
Motor AM-38 AM-38F

Number of cylinders

12

Arrangement of cylinders

V-shaped at an angle 60°

Cylinder diameter, mm

160

Piston stroke, mm (left block)

190

Piston stroke, mm (right block)

196.77

Working volume of all cylinders, l

46.66

Compression ratio

6.8 6.0

Direction of rotation (viewed from the blower side) of the screw crankshaft


right
left

Reducer gear ratio

0.732

Supercharger gear ratio

11.05

Takeoff power, hp

1,600-2% 1,700-2%

The number of revolutions of the crankshaft at takeoff power per minute

2,150±2% 2,350±2%

Fuel consumption at takeoff power; g/e. h.p.h.

305-335

Suction (boost) pressure pa in mm Hg at takeoff power

1,285±25 1,510±25

Altitude rated power, h.p.

1,500-2% (Н=1650m) 1,500-2% (Н=750m)

Crankshaft revolutions per minute corresponding to rated power (in air)

2,050±2%

Rated suction (boost) pressure pa in mm Hg at takeoff power

1,180±25 1,320±25

Ground rated power (at n = 2150 rpm), h.p.

1,500-2%

Fuel consumption at terrestrial rated power; g/e. hp h.

285-305

operating power (equal to 0.9 of the earth's rated power), h.p.

1,350

Crankshaft revolutions per minute at operating power

2,050±2%

Suction (boost) pressure behind the carburetor pa in mm Hg at operating power

1,135±25 1,150±25

Fuel consumption at operating power; g / e. hp h.

270-285

Oil consumption at operating power; g / e. h.p.h.

12

The maximum permissible number of revolutions of the crankshaft per minute (no more than 30 seconds in dive modes)

2,250

Minimum crankshaft revolutions per minute

450

Fuel grade and octane

Бензин (бакинский) Б78+4см³ Р-9* на 1 кг. Октановое число не менее 95

Petrol pump

BNK-10 1pc. (rotary), with one pressure stage i=1.176

Carburettors

K-38, 4 pcs, located behind the blower

Compressor

AK-50, left-hand rotation, blowing air over the compressor at a speed of 20 m / s

Dry motor weight, kg

860 880

* - antiknock agent, tetraethyl lead.


Motor AM-38 differed from AM-35 and AM-35A in a reinforced crankcase due to increased loads; reduced compression ratio (6.8 instead of 7.0); the transmission to the impeller in the monitoring station has changed, 11.05 instead of 14.6 for the AM-35A; the oil system and the cooling system were improved to ensure reliable operation of the engine with some insufficiency of oil and water radiators located in the cramped armored compartments of the aircraft.

Due to the thermal stress of the motor, it was necessary to carry out a special event to equalize the temperature of the head. For this, the main flow of coolant was directed towards the exhaust side, which is much warmer than the intake side. The direction of flow to the heated points was carried out using five fins located only on the exhaust side and elongated plugs.

Motor AM-38. View of the meshed gears of the reducer

Gearbox of the motor consisted of a pair of chevron cylindrical gears. The gear ratio of the gearbox is i = 0.732.

The gearbox shaft lay in three sliding steel continuous bearings, cast in babbitt and pressed into the gearbox nose housing (front and middle liners) and into the housing of the crankcase hood (rear liner). The inserts are locked with stoppers.

The axial force when operating on the pulling or pushing screws was taken up by two independent thrust ball bearings. One of the bearings was centered on the gear shaft, the other in a special diaphragm mounted on the toe.

Aggregates box. In the front of the motor, the drive housing of the units was attached to the end of the crankcase. On the body there was an R-7P motor speed controller, operating according to a direct scheme (in the case of a VISH-22T screw) and an R-6 reverse scheme (in the case of an AV-5 screw).

Motor AM-38. Accessory drive housing

Aggregate drive housing with installed aggregates

Compressor AK-50 (item 2) was located on the drive housing and was a two-stage air piston unit. The compressor could work only when its cylinder was blown with air at a speed of 20 m / s.

R-7P regulator was a unit designed to control a hydraulic screw of variable and pitch, and was installed on the unit box. The R-7P regulator worked in conjunction with a hydraulic or centrifugal-hydraulic propeller and maintained a given number of propeller revolutions within 1600-2700 rpm.

Altitude corrector. When the aircraft climbs to altitude, the working mixture prepared by the carburetor is enriched. An altitude corrector is used to regulate the composition of the mixture at altitude.

The action of the altitude corrector is based on a change in air pressure above the fuel level in the float chamber, and, consequently, on a change in the fuel outflow from the nozzles. So, for example, if the air pressure above the fuel level in the float chamber decreases, then the outflow of fuel from the nozzles also decreases and the mixture becomes leaner.

The AM-38 motor was adapted to work with two supercharges; one of them corresponded to the nominal mode, the other to the take-off mode of the engine operation. Maximum power at sea level - takeoff power - greater than rated power. With a variable pitch propeller, both modes can be obtained at the same speed. When operating in these two modes, the carburetor throttle valves opened the same amount (fully open), and only the valves that regulate the pressure in the supercharger, in this case, opened by a different amount. Fuel consumption at nominal boost and takeoff in K-38 carburetors and was regulated by the altitude corrector.

***

Motor AM-38F . The AM-35A engines launched into series and the AM-37 engines being mastered, as well as their modifications, were discontinued, and the aircraft were ordered to be altered for other engines or to cease their production. Nevertheless, the OKB continuously worked to improve not only the AM-38, but also other experimental engines, fine-tuning units and parts, as well as many prospecting work. However, work on engines for Il attack aircraft was the main one. For the two-seater version of the Il-2 at the beginning of 1942, the AM-38F (forced) engine was created, which, with less power than the AM-38, had an increase in power by 100 hp at altitudes. from. takeoff power and the ability to work for some time (10 minutes) in takeoff mode in the altitude range of 0-1.5 km ("combat mode"). In order not to increase the octane number of fuel (the supply of high-octane fuel at that time was a problem), the compression ratio was reduced (6.0 instead of 6.8), the number of revolutions was increased in takeoff mode (2350 instead of 2150) and the boost was slightly increased at a lower altitude. (See table 1). The impeller diameter of the monitoring station was reduced in comparison with the monitoring station of the AM-38 motor.

Table 2

Serial motors *
AM-38F AM-42 DB-603AM
Year of issue 1943 1944 1944
Country USSR Germany
Compression ratio 6,0 5,5 7,2
Motor weight, kg 880 996 970
Takeoff mode Power, h.p. 1,700 2,000 1,800
Rotation frequency, rpm 2,350 2,500 2,700
Boost pressure, mm Hg 1,360 1,565 1,090
Nominal ground mode Rotation frequency, rpm 2,050 2,350 2,500
Boost pressure, mm Hg 1,200 1,335 955
Power, h.p. 1500 1750 1600
Altitude mode Altitude, m 750 1,600 5,700
Power, h.p. 1,500 1,770 1,510
Nominal specific parameters Liter power, hp/l 32.15 37.5 35.95
Average effective pressure, kgf/cm² 14.11 14.36 12.94
Specific weight, kg / h.p. 0.59 0.57 0.61
Reduction rate 0.732 0.60 0.57

* - For all AM engines (cylinder diameter) • (piston stroke) = 60 • 190 (196.8) mm, working volume - 46.66 liters; for DB-603AM (cylinder diameter) • (piston stroke) = 162 • 180 mm, working volume - 44.5 liters.

With engines AM-38 and AM-38F, the famous "flying tanks" IL-2 - unique aircraft of the Second World War, inscribed many glorious pages in its chronicle - flew throughout the war. To a large extent, this was facilitated by the AM motors.

Photo Description
AM-38 motor from the side of the gearbox shaft

View of the AM-38 motor from the side of the gearbox shaft

AM-38 motor from the supercharger side

View of the AM-38 motor from the supercharger side

View of the throttle control levers of the AM-38 engine

View of the throttle control levers of the AM-38 engine

AM-38F motor (front view)

AM-38F motor (front view)

Motor AM-38F (rear view)

Motor AM-38F (rear view)

AM-38F motor (side view)

AM-38F motor (side view)

In 1943 A.A. Mikulin became the general designer of the OKB, which had its own experimental plant. In 1942-1946, the OKB created many experimental engines, including the AM-39 and several of its modifications. In 1944 - 1945 this engine was installed on experimental modifications of the Tu-2 aircraft, experimental fighters A.I. Mikoyan I-231 and I-220, N.N. Polikarpova and some others. See table 2.

Altitude characteristics of  A. A. Mikulin motors

By 1944. Design Bureau S.V. Ilyushin designed the Il-10 attack aircraft, for which the AM-42 engine with a takeoff power of 2000 hp was created. from. and nominal 1770 liters. from. at an altitude of 1600 m (its chief designer was M.R.Flisky). To achieve these indicators, the design of the motor has been significantly changed:

reduced compression ratio to 5.5;

boost is increased (suction pressure in takeoff mode is 1565 mm Hg, i.e., twice the atmospheric pressure);

the crankshaft, connecting rods, pistons and some other components are reinforced;

revised oil system - introduced oil deflectors and check valves in the oil pan to ensure better pumping of oil and reduce its temperature;

a crankshaft with counterweights is used to unload the main bearings and a gearbox without an elastic gear.

This was the last serial motor of the OKB. At the end of the war and after it, several more experimental engines were created, in particular, the AM-43, AM-44 and AM-47; a turbocharger for the AM-44TK engine was developed, which was installed on the Tu-2D ("65") prototype aircraft. On some engines, the installation of direct injection equipment was worked out, one of such engines was the AM-39FNV. However, these motors were not put into serial production, as it was already clear that the era of piston motors had come to an end. The OKB began to deal with turbojet engines.

The number of motors developed at the A.A. Mikulin and mass-produced, is quite large. According to A.I. Shakhurin and A.S. Yakovlev, the supply of engines to ensure the production of aircraft was: before the war - about 8000, during and after the war - more than 41000. This means that the total number of manufactured engines was even greater.

A.A. piston motors Mikulin were the world's largest gasoline engines in terms of cylinder sizes, and although such cylinder sizes in themselves created objective difficulties in fine-tuning and forcing, the power of serial engines increased in 10-12 years: takeoff - from 850 for the M-34 to 2000 hp. from. from AM-42; nominal on the ground - from 670 liters. from. for the M-34 up to 1750 hp. from. from AM-42; at an altitude of 6 km - from 420 liters. from. for the M-34 up to 1200 liters. from. - at the AM-35A.

There were no engines with such large cylinder sizes abroad. Only at the end of the war in Germany was the Daimler-Benz DB-603 engine with cylinder dimensions 162x180 mm and a take-off power of 1800 hp created. from. Table 1 shows the data of A.A. Mikulin's serial motors during the Great Patriotic War, and in Fig. 5 - their altitude characteristics (dashed lines for the AM-38F and AM-42 and the German engine indicate an emergency or combat mode for a short-term boost of the engine in flight).

Bibliography

  • Aircraft construction in the USSR 1917-1945 / TsAGI /
  • Aviation engine AM-38 and AM-38F / NKAP USSR Moscow 1944 /