Mikulin AM-37 sees service

[Darthtabby]

While I was doing research on Soviet planes I noticed that quite a few aircraft projects seemed to be affected by the cancellation of the Mikulin AM-37 engine. Heavy fighter development seemed particularly affected since so many of the Soviet heavy fighter projects were designed for the engine. From this I had generally assumed the AM-37 was a fundamentally bad engine. But then I started reading google translated pages from a Russian Online Aviation Museum I was linked to. In the write up on the Yer-2 bomber, the AM-37 is described as a modification of the AM-35, to the point where an AM-35 could be converted to an AM-37 by swapping a few parts.

It is worth noting that the AM-37 engine and the AM-35A, which was serially built, were completely similar and interchangeable with each other in all nodes, with the exception of:

-AM-37 had an air-to-water radiator for cooling the air supplied to the carburetors after the supercharger, and the so-called spacer was installed on the AM-35A engine, i.e. section of the air duct;
-AM-37 had an additional pump for pumping water into the air-to-water radiator;
-the diameter of the impeller of the AM-37 motor supercharger was 285 mm instead of 275 mm for the AM-35A motor.

I'm no engineer. For all I know those changes might have been enough to turn a decent engine in a terrible one. But it does make me wonder if the issues with the AM-37 might have been solvable had Mikulin not been ordered to concentrate on production of the AM-35 and AM-38 (the latter being the engine used by the Il-2).

Does anyone who is more knowledgeable then I am about aero engines have any thoughts on how viable it might have been to fix the AM-37?

I'm also curious about how the AM-37 becoming a production engine might have affected Soviet aviation in WWII though of course the various fighter and bomber projects that were designed to use it give some indication of that.

 

[Андрей]

While I was doing research on Soviet planes I noticed that quite a few aircraft projects seemed to be affected by the cancellation of the Mikulin AM-37 engine. Heavy fighter development seemed particularly affected since so many of the Soviet heavy fighter projects were designed for the engine. From this I had generally assumed the AM-37 was a fundamentally bad engine. But then I started reading google translated pages from a Russian Online Aviation Museum I was linked to. In the write up on the Yer-2 bomber, the AM-37 is described as a modification of the AM-35, to the point where an AM-35 could be converted to an AM-37 by swapping a few parts.



I'm no engineer. For all I know those changes might have been enough to turn a decent engine in a terrible one. But it does make me wonder if the issues with the AM-37 might have been solvable had Mikulin not been ordered to concentrate on production of the AM-35 and AM-38 (the latter being the engine used by the Il-2).

Does anyone who is more knowledgeable then I am about aero engines have any thoughts on how viable it might have been to fix the AM-37?

I'm also curious about how the AM-37 becoming a production engine might have affected Soviet aviation in WWII though of course the various fighter and bomber projects that were designed to use it give some indication of that.

The reason for not working on the AM-37 is a combination of factors. I will start (as it seems to me) from the beginning. You understand perfectly well that the production of aircraft engines is a high-tech production. In Russia, and later in the Soviet Union, until the 1930s, there were no enterprises designing aircraft engines. The same goes for engineers. Plants started to be built, and people started to learn. The same applied to the production of fuel, engine oils, various gaskets, and of course metals (development and industrial production). We were never able to master these productions at the necessary high level. The technological lag was felt until the end of the war.
The beginning of the war had a negative impact. A huge number of enterprises were evacuated beyond the Urals. It was far from always possible to preserve the work collectives. Many skilled workers went to war, later they began to return to the enterprises, but not all remained alive.
Enterprises began to experience an acute shortage of raw materials. The quality of these raw materials was also not always at the proper level (for the same reasons). We had to save a lot of money.
To increase production of military equipment, research programs had to be reduced. It was forbidden to change technological processes if they could have a negative impact on the quantity of production.
All this was complemented by unskilled personnel, who were trained at short notice. Working conditions were very hard, working 10-14 hours, and at some point weekends were cancelled. There was an acute shortage of food. In the aviation industry, 18% of the workers were teenagers under the age of 16.
I have tried to name the main factors. You noted correctly that the production of AM-35 was curtailed for the sake of engines for IL-2. The AM-35 was installed on the MiG-3, Pe-8, but the IL-2 was needed.
In general, it is surprising that during the war, hungry, unskilled workers were able to provide their army with equipment.
Don't get me wrong, I am not trying to besmirch my country's history, I am saying that people made weapons out of their last effort, which made it possible to stop the enemy, and then to win.
At that time we could not afford to develop new engines, the work was in progress, but the funds were allocated on the residual principle. The VK-107 went into production with great difficulty. M-71, M-90 did not go into production.

 

[tomo pauk]

I'm also curious about how the AM-37 becoming a production engine might have affected Soviet aviation in WWII though of course the various fighter and bomber projects that were designed to use it give some indication of that.

With a working AM-37 in use, the Soviet aviation is all together one notch ahead vs. the historical state of things, performance-wise. To the best of my knowledge (that is pretty small on the AM-37), engine might've used the cooling system of greater capacity, but don't quote me on this.

 

[rinkol]

While I was doing research on Soviet planes I noticed that quite a few aircraft projects seemed to be affected by the cancellation of the Mikulin AM-37 engine. Heavy fighter development seemed particularly affected since so many of the Soviet heavy fighter projects were designed for the engine. From this I had generally assumed the AM-37 was a fundamentally bad engine. But then I started reading google translated pages from a Russian Online Aviation Museum I was linked to. In the write up on the Yer-2 bomber, the AM-37 is described as a modification of the AM-35, to the point where an AM-35 could be converted to an AM-37 by swapping a few parts.



I'm no engineer. For all I know those changes might have been enough to turn a decent engine in a terrible one. But it does make me wonder if the issues with the AM-37 might have been solvable had Mikulin not been ordered to concentrate on production of the AM-35 and AM-38 (the latter being the engine used by the Il-2).

Does anyone who is more knowledgeable then I am about aero engines have any thoughts on how viable it might have been to fix the AM-37?

I'm also curious about how the AM-37 becoming a production engine might have affected Soviet aviation in WWII though of course the various fighter and bomber projects that were designed to use it give some indication of that.

Considerable work and ingenuity was expended to increase power levels. However, high performance WW2 aircraft engines were operating on the edge of technology limitations and it didn't take much to degrade the reliability of an engine. For example, the DB 601N differed from the DB 601A, mainly in having an increased compression ratio and increased rpm. This was enough to significantly reduce reliability.

After the il-2 became a priority, even the AM-35 was dropped from production and the development of low altitude engines received the highest priority. Even if AM-37 engines were available, many of the planned applications would have disappeared because of the disruption caused by loss or relocation of industrial facilities and the importance of the il-2.

There is an interesting story behind the Mikulin engines if someone has access to the information and time to write it up.

 

[Shortround6]

The concept is simple, the execution may not be.

IF the Russians pushed a bit too hard the engine would go into detonation with the available fuel. The intercooler would help but if they were looking for several hundred HP more than the AM-35A they may have pushed a bit too hard. The total cooling load would go up (amount of heat produced in the cylinders) and while a larger radiator would help it might not cure passages that were too small in certain parts of the engine leading to local overheating. Just speculating here or pointing out potential problems.
Even if the intercooler keeps the intake charge within bounds the development of 150hp extra HP means a greater load is being put on the rod bearings and main crankshaft bearings.
Russians had a fair amount of trouble with bearings in general.
While the AM-35/A had passed a 100 hr, test in service the average life before overhaul was around 1/2 of of that or less. Boosting the engine power by 10% was going to lead to increased problems.