Why so few planes that fired thorugh the propeller hub?

[tomo pauk]

The Germans were selling technology to the Soviets even by the late 30's, so an Italian designed engine made available to the Soviets comes at no surprise.

Granted, even the Italians were selling blueprints to the Soveiet Navy yards, however the statements of M-34 being an Italian design are a surprise, since the only thing the M-34 and Italian V12s have had in common was the layout of valvetrain.
Curiously enough, we don't have any Italian or Soviet sources claiming that Fiat designed the M-34.

In regards to the M-17's similarities to the M-34: many engines in the aviation industry had parallels.
The V-1710 was a 60° V with four valves per cylinder driven by an overhead cam, just like the Merlin. They both had a 6" (152mm) stroke and a nearly identical bore: 5.4" (137mm) for the Merlin and 5.5" (140mm) for the Allison.
That however doesn't mean they shared any lineage as they were both developed independantly.

Nobody ever accused Merlin and V-1710 for sharing a lineage.

Also, from a visual standpoint, the M-17 doesn't bear much of a resemblance to the M-34.
However, the M-34 looks a great deal like Fiat's engines from the same time period, such as the AS.3 or the larger A.25 for example.

Visual inspection of a complete engine will not reveal bore, stroke, or what type of rods the engine uses. That M-34 shared with M-17, and didn't share with any Fiat V12 engine.
Also, unlike the M-34, looks like the A.25 and AS.3 have had separate cylinders..

 

[modelwiz]

It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.

The V2 might as well be a derivative of M-34 engine - it shared features found on the later, including DOHC, 4 valves per cylinder, articulated connecting rods.
FWIW, no Soviet source states the M-34 as foreign-designed engine.

Russian/ex-Soviet sources state that the M-17 was derived from the BMW VI. The M-34 was designed to replace the M-17, but was not based on it. It was an aero diesel; all 4 valves were exhaust valves. A significant feature of the Mikulin engines was perforated sleeves in the cylinders that supplied intake air from the manifold directly connected to the block. I doubt it was based on any other design other than in a very general way. In engineering, as in many other fields, one uses anything one knows, including information of foreign developments. The M-17 itself was installed in an unknown number of early T-34's, and they tended to burn or even explode when penetrated-crews were extremely critical.
The VD-2 (not BD-2) was the initial design of a scaled down AM-34, and like the V-2 also had perforated free sleeves as well as the features you list. Versions of the AM-34 were used in numerous aircraft, but also in a number of tanks and even small torpedo boats.
The Il-2M and Il-10 were designed around the M-71 and AM-42, respectively, but the Il-2M ended up being produced with th AM-42 anyway.

 

[GrauGeist]

Yes, the M-17 was based on the BMW IV, no the M-34 was NOT a diesel engine.

The Soviets had a diesel aircraft engine, which was the ACh-30, primarily used in the Pe-8 and Yer-2.

The Kharkiv V-2-34 was a diesel engine developed by the Kharkov Locomotive Factory and had nothing to do with any Mikulin engines.
The V-2-34 was used in the KV series, the BT-7, the T-34and IS series. The closest the V-2 series ever came to an aircraft, is the fitting of a supercharger from an AM-38, designated V-2SN and used on the larger KV tanks.

No M-34/AM-34 engine was ever used in a Soviet tank.

 

[modelwiz]

With apologies for my mistake, VD-2 was a very early designation of the V-2. The earliest version (450 HP) was used in the BT-7 tank.

 

[tomo pauk]

Russian/ex-Soviet sources state that the M-17 was derived from the BMW VI. The M-34 was designed to replace the M-17, but was not based on it.

Agree on #1. As for the #2 - you're probably right, the M-34 have had enough of new & modern features that we can consider it a new engine. We also cannot avoid the fact that M-17 and M-34 also shared several important design details, as mentioned before.

It was an aero diesel; all 4 valves were exhaust valves. A significant feature of the Mikulin engines was perforated sleeves in the cylinders that supplied intake air from the manifold directly connected to the block. I doubt it was based on any other design other than in a very general way. In engineering, as in many other fields, one uses anything one knows, including information of foreign developments. The M-17 itself was installed in an unknown number of early T-34's, and they tended to burn or even explode when penetrated-crews were extremely critical.

Please post the sources for the numerous claims here (M-34 being a diesel, all 4 valves used for exhaust only, M-17 installed on early T-34s).

The VD-2 (not BD-2) was the initial design of a scaled down AM-34, and like the V-2 also had perforated free sleeves as well as the features you list. Versions of the AM-34 were used in numerous aircraft, but also in a number of tanks and even small torpedo boats.

Yes, there was a version of the AM-34 that was used on 'surface' vehicles. As above, please post sources for V-2 having valves for exhausts only.

The Il-2M and Il-10 were designed around the M-71 and AM-42, respectively, but the Il-2M ended up being produced with th AM-42 anyway.

Soviet terminology does not know the designation 'Il-2M' (or the often quoted 'Il-2M3'). Please quote a source that proves any Il-2 being powered by AM-42, on anything that is more than prototype or test bed aircraft.

 

[Shortround6]

Uh, if all four valves are exhaust valves and the intakes are through ports in the cylinder walls that
A, makes the engine a two stroke?
B means the engine needs a supercharger to run to blow the air in through the cylinder ports?

Unless there is a seperate sleeve valve the ports would be uncovered when the pistons are near the bottom of their stroke and making little suction to suck fresh air in.

 

[fliger747]

To reduce the question originally asked to the basics? Almost foremost in a fighter's performance is the engine. Most improvements model to model showing real performance involved engine development. Firing through the hub is going to cause compromises in engine design, a luxury perhaps not eventually compensated for by any purported advantage by such an armament configuration. Smaller fighters with smaller wings did have issues with finding room for guns and ammo. For larger planes (ie. USA) the wings were larger and not having such issues as where to store wheels, guns and whatnot.

 

[GrauGeist]

When the hub weapon idea really took hold, was in the days when most aircraft had cowl and/or wingroot weapons, which had to fire through the propeller arc, thus slowing their rate of fire through synchronization.
This problem had plagued fighter aircraft since WWI and several remedies were tried, like the Foster mount used in WWI, which saw the MG mounted to the upper wing above the propeller arc and the Hispano mounted a Lewis in the "valley" of a SPAD's HS-36 engine, firing through the hub - making it the first hub weapon.

As monoplanes matured, so did their engines and with the V-engine came the idea that a weapon can be mounted in the "valley" of the Vee and fired through the hub.
Several advantages to this: first, no synchronization and secondly, there is no convergence as the weapon is firing from the aircraft's centerline.

 

[Shortround6]

In part the gun through the hub was to allow the mounting of guns of such size and power than mounting them in multiples would affect aircraft performance severely. Or allowed the pilot access to the gun while flying.

French setup close to that used in the SPAD XII. manually loaded 37mm cannon.
On WW I and early 20s aircraft mounting heavy recoiling guns was a bit of challenge.

I would also note that once a country started down a certain path it was hard to get off of it.

Some of the 1930s V-12 Hispano engines used the same bore spacing (or very close) which allowed some of the same machinery used to make the old V-8s to be used on the V-12s. The V-12s seeing a much larger increase in stroke.

 

[modelwiz]

Uh, if all four valves are exhaust valves and the intakes are through ports in the cylinder walls that
A, makes the engine a two stroke?
B means the engine needs a supercharger to run to blow the air in through the cylinder ports?

Unless there is a seperate sleeve valve the ports would be uncovered when the pistons are near the bottom of their stroke and making little suction to suck fresh air in.

Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated. Postwar versions added a turbocharger, different pumps, an electric starter even. There may not have been any original part of the engine that has not been replaced, redesigned or improved in these last 80 years of development and production. The original had an air distributor through which compressed air was supplied for starting.

 

[modelwiz]

Agree on #1. As for the #2 - you're probably right, the M-34 have had enough of new & modern features that we can consider it a new engine. We also cannot avoid the fact that M-17 and M-34 also shared several important design details, as mentioned before.



Please post the sources for the numerous claims here (M-34 being a diesel, all 4 valves used for exhaust only, M-17 installed on early T-34s).



Yes, there was a version of the AM-34 that was used on 'surface' vehicles. As above, please post sources for V-2 having valves for exhausts only.



Soviet terminology does not know the designation 'Il-2M' (or the often quoted 'Il-2M3'). Please quote a source that proves any Il-2 being powered by AM-42, on anything that is more than prototype or test bed aircraft.

АМ-34 — Википедия
В-2 — Википедия
М-17 (двигатель) — Википедия
For starters
I also based myself on a set of 1942 manufacturing drawings and several wartime and postwar user, maintenance and repair manuals, particularly for the V-2; I would not have attempted a virtual engineering model without.

 

[tomo pauk]

АМ-34 — Википедия
В-2 — Википедия
М-17 (двигатель) — Википедия
For starters
I also based myself on a set of 1942 manufacturing drawings and several wartime and postwar user, maintenance and repair manuals, particularly for the V-2; I would not have attempted a virtual engineering model without.

You might want to be a bit more specific. For example, this is what the Russian-language Wikipedia entry says about the fuel distribution system and fuel used on the AM-34:

Топливная система
карбюраторная

Тип топлива
этилированный бензин 2Б-70, 3Б-78(93), 4Б-74, Б-95

Meaning:

Fuel system
Carburetor

Fuel Type
Leaded Gasoline 2B-70, 3B-78 (93), 4B-74, B-95

So, as before - please post specifics that prove your points.

 

[Shortround6]

Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated.

Ok, what closes off the perforations as the piston goes back up?
Something has to or the air in the cylinder will be blown right back out as the piston rises, let alone what happens the charge burns with piston going down.

Not say you can't build an engine with both sleeve valves and popper valves but it does seem to be a huge compilation. (sorry complication is what I meant)

 

[tyrodtom]

When I look at the pictures of the m-34 I see a exhaust manifold on the outside of the V, and a intake manifold on the inside of the V at the same height as the exhaust.
The cutaway pictures show no holes in the upper cylinder, nor any way of feeding air to them if they were there, or any way of shutting off that air so the engine could build compression.

Looks like just any other 4 valve engine, two valves for exhaust, and two for intake.

 

[elbmc1969]

Some of the 1930s V-12 Hispano engines used the same bore spacing (or very close) which allowed some of the same machinery used to make the old V-8s to be used on the V-12s. The V-12s seeing a much larger increase in stroke.

All of the 12X and 12Y engines used the exact same bore spacing as the older V-12s and the V-8s, per Manuel Lage, Hispano Suiza in Aeronautics. This was one of the reasons that the engines hit a power plateau: the bore couldn't be increased to increase displacement. Changing the bore spacing was a problem because Marc Birkigt customed-designed all of the critical machine tools for manufacturing his engines (Birkigt was Hispano Suiza's chief engineer, the designer of the original Hispano Suiza V-8, the credited chief designer of the HS-404 20mm cannon which because the chief US and UK aircraft cannon of WWII, and much more). Changing the bore spacing would have required retooling at a basic level. It's hard to believe, I know.

 

[GrauGeist]

Suction is generated by the down stroke of the piston. Air is drawn from the perforations towards the top of the cylinder. The original V-2 was normally aspirated. Postwar versions added a turbocharger, different pumps, an electric starter even. There may not have been any original part of the engine that has not been replaced, redesigned or improved in these last 80 years of development and production. The original had an air distributor through which compressed air was supplied for starting.

I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
A engine's valve set is designed to allow the intake of fuel and the removal of exhaust.
Two, four or twenty valves mean nothing unless they have a specific purpose.

On a four stroke engine, you have a "cycle", and that is Intake, Compression, Ignition and Exhaust. During that cycle, the Intake valves open and allow the air-fuel mixture into the cylinder as the piston starts it's downward stroke (the vacuum created by the plunging piston creates the draw for the air-fuel mixture), then the intake valve closes and the piston starts it's upward climb, compressing the air-fuel mixture in the cylinder to a considerable degree.
Then the spark plug ignites the compressed volatile mixture, violently forcing the piston downward (turning the crankshaft as it goes) and once the piston reaches the end of it's travel, the exhaust valve opens and the upward travel of the piston drives out the exhaust gases in the cylinder.

Many engines have a single intake and exhaust valve per cylinder, high-performance engines will have two per set (two intake, two exhaust) to increase performance.

And all of the Soviet engines were either crank-started (by hand) or used an electric starter (late war).
Pneumatic starters are typically used on diesel engines in commercial trucks (again, the Soviets only had ONE diesel aircraft engine in service during the war - the ACh-30)

 

[modelwiz]

I'm going out on a limb here, based on observation, and think that you're not all that familiar with how an internal combustion engine works.
A engine's valve set is designed to allow the intake of fuel and the removal of exhaust.
Two, four or twenty valves mean nothing unless they have a specific purpose.

On a four stroke engine, you have a "cycle", and that is Intake, Compression, Ignition and Exhaust. During that cycle, the Intake valves open and allow the air-fuel mixture into the cylinder as the piston starts it's downward stroke (the vacuum created by the plunging piston creates the draw for the air-fuel mixture), then the intake valve closes and the piston starts it's upward climb, compressing the air-fuel mixture in the cylinder to a considerable degree.
Then the spark plug ignites the compressed volatile mixture, violently forcing the piston downward (turning the crankshaft as it goes) and once the piston reaches the end of it's travel, the exhaust valve opens and the upward travel of the piston drives out the exhaust gases in the cylinder.

Many engines have a single intake and exhaust valve per cylinder, high-performance engines will have two per set (two intake, two exhaust) to increase performance.

And all of the Soviet engines were either crank-started (by hand) or used an electric starter (late war).
Pneumatic starters are typically used on diesel engines in commercial trucks (again, the Soviets only had ONE diesel aircraft engine in service during the war - the ACh-30)

But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.

 

[Milosh]

The 2 stroke diesel engine, How Diesel Two-Stroke Engines Work

 

[modelwiz]

And BTW, when the exhaust valves open the pressure differential between the burnt fuel air mixture and outside air also create what you would call a vacuum as the piston moves upward in the exhaust stroke. In all kinds of internal combustion engines.

 

[GrauGeist]

But this is not how a DIESEL operates. And I was referring to the V-2, which was a diesel with four exhaust valves per cylinder operated by two separate camshafts. But of course you knew that. You know everything. You know me so very well. Thank you for the lecture and condescension.

My apologies if you seemed to think my post was condescending, however, you seem to fail to grasp the basics of either gasoline or diesel engine function. I have no idea where this "four exhaust valves" thing is coming from, but it's not even close to accurate.

The V-2-34, which was the actual production engine, the V-2 was the early prototype of the series, had a regular configuration. This means it had two Intake valves and two Exhaust valves per cylinder driven by overhead camshafts.

In this diagram of the V-2-34, please note the Intake valve(s) facing inboard and the Exhaust valve(s) facing outboard.