1937-41: build your VVS

[Shortround6]

Wonder how much would it be good for VVS to have a force of long range bombers (even if those are not strictly 4-engined jobs) with escort fighters to support them?

Soviets have the same problem that everybody else did in 1940-41. The engines available will not support long range escort fighters. The Russians struggled with low powered engines as it was for the entire war. They sacrificed armament for performance in many cases. Trying to haul the needed fuel would have just made the problems worse. The DB-3/IL-4 actually had pretty decent range (IL-4 2,600 km (1,404 nmi; 1,616 mi) with 1,000 kg (2,200 lb) bombs)

Russians even resorted to such things as carrying I-16s under old TB-3 bombers as a way to extend the fighters range as as attack planes, figuring the TB-3 probably had zero chance of penetrating defended airspace.

 

[tomo pauk]

Soviets were trying to fulfill the need for escort fighter with two designs (at least?). The VI-100 (VI - 'visinsky istrebitel' - high-altitude fighter?), designed by Polikarpov's team while hi was imprisoned, was to have two turboed M-105 engines and crew of two. The MiG DIS ('Dalnij Istrebitel' Soprovozhdenya' - long range fighter for escort) was a dH Hornet-like aircraft, that was to use AM-37 engines. In the end of the day, the realities of the war intervened - VI-100 was modified into a dive bomber Pe-2 with turbo-less M-105 engines, since that was judged as better use of resources. The DIS was doomed by cancellation of the work on AM-37 engines, and, even after considerable modifications, it was considerably falling behind performance estimates.

With that said, we might note that Soviets were trying to make escort fighters later in the war, like Yak-9D and 9DD, that were still using less then stellar VK-105PF engines. Had they wanted it, they might design a fighter with AM-35A, 2 cannons and plenty of fuel, like it was the case for P-40, Re.2001 or Ki-61.

 

[tomo pauk]

The progenitor of the Tu-2 family of bombers, the 'aircraft 103'. Note the position of buried coolers. Powered with AM-37 engines, development production of those canceled shortly after Germans invaded.

Improved version, 'aircraft 103U', was a more battle-worthy prototype, OTOH the speed fell from 630 to 610 km/h at 7800 m (ie, down to 380 mph at 25600 ft). With that said, how would the Soviets fared with an unarmed bomber (ie. no defensive guns) with AM-35A or AM-38 in their service?

added: More about the 103 and 103U can be read here

 

[Shortround6]

The Russians have a problem in this time period. Not only is it a period of great advances in aviation technology in general ( 1937 sees the introduction of the I-16 with 4 mg instead of 2 and yet the I-16 is obsolete in another 2-3 years) but the political upheaval in the Soviet union takes a toll. Russian designers, both of aircraft and engines, have many good ideas that are as advanced as anybodies in the world. But the Russians cannot capitalize on them.
They do not have the manufacturing infrastructure to bring some of these ideas to a mass produced, service use level. Sounds strange I know. But consider that the Soviet Union was second only to the united states in the number of turbo-charged engines and prototypes built from the 1920s until 1941. The Soviets built aircraft diesel engines and also tried using an engine in the fuselage of a 4 engine bomber to provide supercharging for the wing engines. They were building prototype aircraft with pressure cabins in 1939-40. What they could not do was turn these prototypes into service aircraft or engines.

Work started on the M-106 in 1938, They gave up on in May of 1943 with about 150 built.
Work started on the M-107 in 1940, 2000 were supposed have been built by the end of 1941 but only 29 were ( how much due to relocation/invasion I don't know) but manufacture and service were spotty at best. Yes the 107A did get the Polikovskiy intake blades but only 41 were built in 1942 and it was only post war that the engine reached a 100 hour overhaul life and that required limiting the maximum rpm ( and power?) and an additional oil pump.

There were models of the M-100 (VK-105 predecessor) with twin turbos per engine but they never sorted out the the manufacture of the turbos, materiel/design/installation ???

They could and did manufacture all metal airplanes but they could not do it in the numbers required and had to use partial wooden construction. They could not manufacture instruments or radios in the required numbers. They could not manufacture Plexiglas (or an equivalent) with the desired transparency which caused many pilots to fly with the canopy open for better vision (and lower performance).

The Russians had a number of good designs but what was actually producible is rather unknown.

 

[tomo pauk]

Fine points. We might add there anothe rengine that have issues, the two-stage M-105PD, where 'D' should be for the supercharger's designer last name (Dolezhal). It featured the second stage driven via hydraulic coupling, in an arangement similar to the 2-stage V-1710. The intercooler was not installed. Tested in 1941 in an I-28 (variant of the I-26/Yak-1; not to be confused with Yartsev's I-28 with M-88 radial engine), it was prone to overheating. I-28 was about as good as MiG-1 in hi alt, and faster in low alt.

With that said, I've specified a more 'evolutive' engines, rather than 'revolutive ones. Guesss that a twin engined bomber with two AM-38s should be an elusive target for those pesky 109s?

added: the main effort in the development of the VK-107 was to increase the permissible RPM, up to 3000 (nominal) and 3200 (emergency). Even in 1945, the 107 was judged to be good for 25 hours of use, and pilots were reluctant to use emergency regime (shades of BMW-801?).

 

[wiking85]

Wonder how much would it be good for VVS to have a force of long range bombers (even if those are not strictly 4-engined jobs) with escort fighters to support them?

AFAIK the Soviets lacked the bombsights to make that a viable project, not to mention that they would only be using it to smash up their own country that they would have to rebuild with them until later in the war when they could hit Germany; by that point the Western Allies already had that job under control. It would make no sense to duplicate effort and instead it was better to just specialize and use tactical and operational bombers to accomplish the important things: taking down the German army itself. As it as I doubt the Soviets could have reached anything of value in Germany by late 1941 with four engine bombers. What they did have was lost trying to bomb Romania and even those bases were gone by 1942.

 

[tomo pauk]

Soviets did not make any significant use of drop tanks as well, without that no meaningful combat radius is to be expected by escort fighters.
Anyway, a 'Soviet Mosquito' is more appealing to me than 'Soviet B-17'. Added bonus is that it does nor require escort fighters to be designed produced.

 

[Shortround6]

The Russians have two problems trying to make a Russian "Mosquito" in 1940-41.

1. Lack of a really good engine. The M-105 offers 1050hp at 4000 meters or the same power as a Merlin III only 3000ft lower. The AM-35 may offer the power (or closer to it) but it is at least 180 Kg heavier (dry weight) per engine than the Merlin. You just sucked up about 40% of the bomb load of an early Mosquito (or about 110imp gallons of fuel).
2. Russian wood construction was not the same as DeHavilland wood construction. The Russians might find it a bit hard getting Balsa wood for the fuselage sandwich and the Russian glue/bonding/impregnation process was heavier (although perhaps more weather resistant?), meaning a higher structure weight.

Granted more combat was at low level on the Eastern Front and you could try to make a low level "Mosquito" using AM-38 engines ( every "Mosquito" costs two IL-2s) But the planes had better stay low as the power falls off so much at altitude and you still have the heavy engines. You also have the German fighters being able to dive from above to pick up speed for a pursuit.

You could use metal construction or mixed construction.

 

[tomo pauk]

The comparison between Mossie and B-17 were to point that I think that a fast bomber, using two Mikulins, will better serve Soviet military, than a bomber that uses 4 Mikulins and relies on it's machine gun firepower to fend off the enemy fighters. The materials for construction does not need to be strictly wood.
Soviets can use the AM-35A to power the fast bombers, akin to the 'aircraft 103U', that I've posted about in post #23 here. The AM-35A has 1350 HP* for take off, vs. 1450 of the AM-37. The M-105 engines, prior mid 1942, were pretty light (570 kg vs. 830 kg for the Mikulins), but the take off power was also 'light', only 1100 HP.

The Il-2 has mythic proportions in Soviet ww2 heritage, but was it that good? The surge to build more and more of them led to appalling quality problems (eg. the mass produced samples were some 50 km/h than prototype with AM-38 ), pilots were clamoring for a rear gunner, but that was not done until the AM-38F was available (winter of 1942/43), need for fighter escort, low payload (400 kg normal, 600 kg max; max 400 kg if 23mm cannons were installed; only 200 kg of bombs/rockets if 37mm cannons were installed, despite the increased power of the AM-38F), 37mm cannons were throwing out the pilot's aim due to slight mismatch of firing time (not an issue if two cannons are close to each other in fuselage), range was lousy 600 km (not radius; range!).
If Soviets build something along the lines of the '103U', each such aircraft can carry 3 times the payload, can have a rear gunner without eating much into the payload, will not rely much/any on fighter cover, the radius can be much greater (1900 km was for the '103U'), one can trade some fuel for additional armor, instead of 40 thousands pilots, one need to train 20000 etc, combat losses should be far smaller, the 45mm automatic cannon can be installed, one can offensively hit German A/C etc. Alternatively, they can build an aircraft sized like Pe-2 or MiG DIS, with Mikulins, high wing, with crew of just 2 and proper bomb bay, with even greater performance.

*actually, metric HP, ie. CV, or PS

 

[Shortround6]

trouble is the 103U used the AM-37 to get it's performance numbers. Without it things get a lot different. Top speed of the 103U was supposed to be 610kph at 7800 meters? 3rd airframe got early M-82 radials and speed dropped to 521kph at 3800 meters. Using the AM-35 means you are 100-200hp lower on power at altitudes or 4000 meters and above compared to the AM-37.

Essentially you are proposing building a TU-2 using either AM-35 or AM-38 engines. Granted you may gain a bit in drag but the engines are heavier (installed weight with radiators) and lower powered. TU-2 carried 1000kg internally normally with the rest of the bomb-load carried exteranlly and we know what that does to speed/range. I am sure there were a few odd ball combinations of bombs that would go over 1000kg internally but the use was not common ( B-17 could hold 12800lb inside the bomb-bay in theory eight 1600lb AP bombs which was a load never carried in service).

Both the TU-2 and PE-2 used some rather low drag mounts/positions for some of the defensive guns, of course this also meant a rather restricted field of fire.

 

[Shortround6]

The VVS was a bit behind the curve even in 1941 as far as "service" engines went.

You have the M-25/M62/M63 series which is the licensed R-1820 that tops out at about 1000hp and due to Russian 95 octane gas is unlikely to go much further. Russians had turbo versions with twin trubo chargers and tried a higher rpm M-64 version but got nowhere.

You have the M-85/M-88 series which is the licensed Gnome-Rhone 14K upgraded to equal the 14N, also tops out at 1000-1100hp due to fuel and lack of center bearing on crankshaft.

You have the M-100/ M-105 series which is the licensed 12Y which was progressively upgraded. They were good for 1100hp in the M-105 versions that showed up in 1940 ( some what less before) and would not be rated at 1260hp until the spring of 1942 with some parts strengthened and a shorter service life.

You have the AM-34/AM-38 series which has a longer evolution and is the most home grown engine. It is also the equivalent of a DB-603 in size/weight with the power of a DB-605 or, if you prefer, the weight of a RR Griffon with the power of a later single stage Merlin.

Coming just a bit too late is the M-82 radial.

Because of the 95 octane fuel the Russian engines cannot use the same amount of supercharging as the western allied engines which limits their altitude performance. Part of the reason for the AM-35, use a whacking big engine to get power desired at altitude.

In 1941 the British are introducing Merlin XX series engines and Merlin 45 series engines and the Hercules is arriving in good numbers. The Americans have the Allison E F replacing the C series engines. Wright is delivering the 5th 1700hp R-2600 about the time the Germans invade Russia and P&W is delivering over 100 R-2800s a month (1850hp single stage versions). Germans are moving to DB 601N and E, later versions of the Jumo 211 and are introducing (sllooowwly) the BMW 801.

Russian aircraft cannot equal British, American, German types because of a lack of engine power so something else has to give if speed and climb are to stay competitive for fighters and speed/range in the usable area for bombers. Frontal fighters can also sacrifice some range. Russian aircraft often sacrifice armament but since the Russians did come up with a good 12.7 and 20mm gun fairly early this is not quite the problem it might first appear although the Russians always wanted more fire power. Russian bombers had to sacrifice defensive armament, bomb load and range. Defensive gun positions were often minimal and while some planes had a high "brochure" bomb load the practical bomb load over all but the shortest ranges was somewhat less. (But many other bombers are credited with a lot more range/radius for a given bomb load than they really possessed).

Perhaps the Russians could have made better choices but without different engines/fuel they were going to be behind the Western Nations.

 

[tomo pauk]

trouble is the 103U used the AM-37 to get it's performance numbers. Without it things get a lot different. Top speed of the 103U was supposed to be 610kph at 7800 meters? 3rd airframe got early M-82 radials and speed dropped to 521kph at 3800 meters. Using the AM-35 means you are 100-200hp lower on power at altitudes or 4000 meters and above compared to the AM-37.
Essentially you are proposing building a TU-2 using either AM-35 or AM-38 engines. Granted you may gain a bit in drag but the engines are heavier (installed weight with radiators) and lower powered.

We might also consider the 'aircraft 100' (same link as above), predecessor of the 100U. It was good for 635 km/h, the greater speed against the later 100U was largely due to having 3 crew members vs. 4, having one defensive MG less, and no provisions for rockets. Installing the AM-35A on that one will indeed mean some 15% less power in all altitudes - we are now down to 610-615 km/h at 7-8 km against 635 with AM-37? The speed at lower altitude would've probably be around what the heavier draggier 103U was capable for (470 km/h), or some 50 km/h faster than the Il-2 prototype, with AM-38, was capable for. Or 100 km/h faster than serial produced Il-2s.
Once the AM-38 is installed on the '100', the engine power is 50 HP short of the M-82 at low altitudes, but exhaust thrust cancels the difference. The drag is lower (both from engine and from armament), so it should beat the 530 km/h mark at low altitudes?

TU-2 carried 1000kg internally normally with the rest of the bomb-load carried exteranlly and we know what that does to speed/range. I am sure there were a few odd ball combinations of bombs that would go over 1000kg internally but the use was not common ( B-17 could hold 12800lb inside the bomb-bay in theory eight 1600lb AP bombs which was a load never carried in service).

Agreed all the way. In case the target is at some distance, only internal bomb load should be used. If the front line target is assigned, use also the external points for another 1000-1500 kg (depending whether the AM-35A or AM-38 is installed).

Both the TU-2 and PE-2 used some rather low drag mounts/positions for some of the defensive guns, of course this also meant a rather restricted field of fire.

It was probably so. It would be cool to find out how wide were the fire cones, not just for those two.

The VVS was a bit behind the curve even in 1941 as far as "service" engines went.

You have the M-25/M62/M63 series which is the licensed R-1820 that tops out at about 1000hp and due to Russian 95 octane gas is unlikely to go much further. Russians had turbo versions with twin trubo chargers and tried a higher rpm M-64 version but got nowhere.

I find Soviet turbo engines development interesting, unfortunately there is no much of available data around. Maybe buying Kotelnikov's book would be a good move, despite the controversial critique? The M-63 is about as good as most 9 cyl engines around, but I admit that does not mean a lot.

You have the M-85/M-88 series which is the licensed Gnome-Rhone 14K upgraded to equal the 14N, also tops out at 1000-1100hp due to fuel and lack of center bearing on crankshaft.

The M-88 was somewhere between single and 2-stage R-1830 in power. It is better than Taurus, or any Japanese or Italian 14-cylinder engine in 1941 (and in 1942?). Germans don't have anything in this class, the 801 is, as you say, slooowly introduced from mid 1941 on.

You have the M-100/ M-105 series which is the licensed 12Y which was progressively upgraded. They were good for 1100hp in the M-105 versions that showed up in 1940 ( some what less before) and would not be rated at 1260hp until the spring of 1942 with some parts strengthened and a shorter service life.

The M-105 is pretty much as good as early F/E Allison or DB-601A.

You have the AM-34/AM-38 series which has a longer evolution and is the most home grown engine. It is also the equivalent of a DB-603 in size/weight with the power of a DB-605 or, if you prefer, the weight of a RR Griffon with the power of a later single stage Merlin.

Coming just a bit too late is the M-82 radial.

Agreed.

Because of the 95 octane fuel the Russian engines cannot use the same amount of supercharging as the western allied engines which limits their altitude performance. Part of the reason for the AM-35, use a whacking big engine to get power desired at altitude.

It is not the fuel that limits the high altitude performance, not exclusively anyway. The 95 oct fuel was comparable with German C3 (started from 96 oct, lean rating?). It is the supercharger set up - the experiments with turbo went nowhere (somewhere?). The two stage M-105PD and inter-cooled AM-37 with slightly bigger supercharger were prone to overheating, and it's questionable how much resources the Soviets were willing or able to devote to those high alt engines in light of invasion and 'relocation' of air combat to mostly under 5 km.

In 1941 the British are introducing Merlin XX series engines and Merlin 45 series engines and the Hercules is arriving in good numbers. The Americans have the Allison E F replacing the C series engines. Wright is delivering the 5th 1700hp R-2600 about the time the Germans invade Russia and P&W is delivering over 100 R-2800s a month (1850hp single stage versions). Germans are moving to DB 601N and E, later versions of the Jumo 211 and are introducing (sllooowwly) the BMW 801.

Agreed. We might also note that low-drag V-1710 don't give substantial power for take off and at high altitudes, the more powerful R-2600 has plenty of drag, esp. vs. AM-38. The European V-12s are fine engines, as is the R-2800.

Russian aircraft cannot equal British, American, German types because of a lack of engine power so something else has to give if speed and climb are to stay competitive for fighters and speed/range in the usable area for bombers. Frontal fighters can also sacrifice some range. Russian aircraft often sacrifice armament but since the Russians did come up with a good 12.7 and 20mm gun fairly early this is not quite the problem it might first appear although the Russians always wanted more fire power. Russian bombers had to sacrifice defensive armament, bomb load and range. Defensive gun positions were often minimal and while some planes had a high "brochure" bomb load the practical bomb load over all but the shortest ranges was somewhat less. (But many other bombers are credited with a lot more range/radius for a given bomb load than they really possessed).

We can note that Soviet fighters were smaller lighter than US or British. Ie. no much of surplus airframe to lug around. So they were capable to give performance comparable to German, US or British fighters in time of importance for this thread.They were also better than Japanese or Italian fighters. Amount of fuel was comparable to other European fighters, but not to US or Japanese.
Bomber defensive armament was not on par with some US (B-25, -26) or British (Wellington, Whitley) bombers, but was comparable with most of the others, or better. Soviets rarely or never fielded a slow or short range bomber.

Perhaps the Russians could have made better choices but without different engines/fuel they were going to be behind the Western Nations.

Hence this thread

added: Mitsubishi Kinsei might be a contender vs. M-88 in 1941

 

[tomo pauk]

A table that covers most of the Tu-2 that mattered.
The 3rd column of weight 'group' (payloads) should represent the weight of fueled up aircraft, with crew, but no bombs. Or alternatively (under the line), with all of that, plus nominal bomb ammo load. Eg, for the Tu-2S, those values are 2886 kg, or 3886. The column with percentage symbol (%) is something called 'weight efficiency' - how much of total aircraft weight is used up for the fuel, crew, ammo, bombs. The bigger the number, the better. Again, for the Tu-2S, the respective numbers are 28 (when 'empty equipped') and 34 (equipped, with nominal bomb load). The figure for the range of the '100' is questionable to me; typo (2000 km?)?

Please open the pic separately.

Now, what about fighters

 

[Shortround6]

I'll trying covering the "100/TU-2" in another post.

I find Soviet turbo engines development interesting, unfortunately there is no much of available data around. Maybe buying Kotelnikov's book would be a good move, despite the controversial critique? The M-63 is about as good as most 9 cyl engines around, but I admit that does not mean a lot.

I have Kotelnikov's book and while it has a lot of interesting stuff in it (just about every Russian aircraft piston engine ever built including 7hp training school shop projects) what is does NOT have is very often rpm to go with the power figures OR boost pressures, OR altitudes. The translation is not the best and in the text altitudes are sometimes given as "ceilings" when they should (by my guess) be FTH or critical altitudes leaving one confused or wondering. WHile it helps to fill in a lot of gaps it is certainly NOT a "stand alone" book.

The trouble with the M-25/M-63 series is that it trailed some of the other 9 cylinder radials. Sometimes not by much. First fully Russian built engine (not using any imported parts) was in 1936. The 1935 M-25 was good for 635/700hp (direct drive) followed by the M-25A (715/730hp) which is followed by the M-25V which passes tests in 1936 and goes into production in 1937 (750/775hp) and a later version in 1941, no change in model number but using some M-62 parts was good for 750-790 hp.
The M-62 had a number of modifications ( 2 speed supercharger, increased fin area on cylinder head, strengthened pistons, new master rod, modified crankcase and more) mass production starts in March of 1939 but the first version is good for 800/1000hp and weighs 520kg for a direct drive engine and is far from trouble free, engines built before Nov 1939 use imported bearings and production is stopped twice in 1939 while defects are sorted out. Early geared versions (M-62R and early M-62IR) used imported gears. The M-62IR was turned into the ASh-62IR used in the post-war AN-2 Biplane but had further modifications. The M-63 used higher rpm and more supercharging(?) to shift it's FTH higher than the M-66. NONE of these engines was rated for more than 1000 hp until after WW II according to Kotelnikov but other sources disagree. The M-62 is also rated at 800hp at 4200 meters. The M-62 basically matched the Cyclone used in the first Brewster Buffaloes.

The M-88 was somewhere between single and 2-stage R-1830 in power. It is better than Taurus, or any Japanese or Italian 14-cylinder engine in 1941 (and in 1942?). Germans don't have anything in this class, the 801 is, as you say, slooowly introduced from mid 1941 on.

Perhaps you are right. But it's margin over some of the better 9 cylinder radials is slight. It uses the same size cylinders as the Bristol Mercury and Hercules. It weighs 1500lbs ( several hundred more than it's French equivalent) So it's power to weight isn't that much better. The M-88B goes into production in the fall of 1940. If the Russian charts/figures are correct it tends to show the limit of the engine, 1100hp/2300rpm for take-off, 1100hp/2375rpm at 4000 meters and 1000hp/2375rpm at 6000 meters? The Taurus was nowhere near as good at height (in fact the engine should have been trashed in the development stage and never put into production) but did over the same take-off power for around 200lbs less and even the old Pegasus was good for a bit over 1000hp for take-off at 370-400lbs less weight.
The engine is a bit odd as it offers decent performance at altitude but lousy take-off performance for a bomber engine.

The M-105 is pretty much as good as early F/E Allison or DB-601A.

The M-105, the M-105P or the M-105PA? all pretty much rated the same but weight crept up as "improvements" ( strengthened crankcase, stiffened con rods) were made. It offers 100hp less than a -39 Allison 1400ft higher. No better take-off and, unfortunately, little scope for improvement. The PF gains a slight amount of weight and offers 1260hp at 890 meters vs 1100hp at 2000 meters and 1180hp at 2700 meters instead of 1000hp at 4000meters and trades engine life to do it.

It is not the fuel that limits the high altitude performance, not exclusively anyway. The 95 oct fuel was comparable with German C3 (started from 96 oct, lean rating?). It is the supercharger set up - the experiments with turbo went nowhere (somewhere?). The two stage M-105PD and inter-cooled AM-37 with slightly bigger supercharger were prone to overheating, and it's questionable how much resources the Soviets were willing or able to devote to those high alt engines in light of invasion and 'relocation' of air combat to mostly under 5 km.

The fuel octane limit does help govern the amount of boost that can be used (low in the case of the some of some of the Russian engines due to the strength of the engines) and also places a limit on the pressure ratio of the supercharger. How high a temperature you can tolerate in the supercharger before it causes problems in the engine. This may (or may not) be part of the problem with a number of the 2 stage or highly supercharged experimental engines that were noted as "over heating" without any more details. IF you increase the temperature of the intake charge by 100 degrees due to supercharging (or even atmospheric conditions-dessert vs winter) that 100 degree difference shows up ALL through the engine, 100 degree higher peak gas temperature in the cylinders and 100 degree hotter exhaust gas temperature this can cause problems with the cooling system and things like exhaust valves which will run hotter. Higher octane fuel will NOT solve the cooling problem BUT will be less likely to detonate in the hotter conditions. Changing the gear ratio on a supercharger to provide more boost higher up means that the supercharger needs more power ( power goes up with the square of the tip speed) and since few superchargers were much more than 70% efficient (70% of power goes to compressing the air (and the resulting heat of compression) while 30% of the power simply heats the intake charge to no purpose. A M-105 engine used over 60% more power in high gear to run the supercharger than in low gear. 30% of the extra 60% is just causing more heat to the charge. adding a second stage or different supercharger to compress the air more also heats up the air more. See Allisons in P-63 without inter-coolers and try to figure out power with 95-100 octane fuel instead of 100/130.

Getting 10% more power for the same weight and/or drag of engine can make a difference.

We can note that Soviet fighters were smaller lighter than US or British. Ie. no much of surplus airframe to lug around. So they were capable to give performance comparable to German, US or British fighters in time of importance for this thread.They were also better than Japanese or Italian fighters. Amount of fuel was comparable to other European fighters, but not to US or Japanese.

Again, they knew they had to get what performance they could from low powered engines. The M-103 went into production in 1938 and while it offered 1000hp for take-off it was giving 850hp at altitude. Compare to Merlin II. The M-105P was flight tested in Jan 1940 in the I-26 (Yak-1 Prototype) and "officially" put in production May 23,1940. Merlin XX goes into production in just a couple of months as does the Merlin XII and within 7 months the Merlin 45 is going into production. The Lagg, Mig and Yak design teams KNEW that there was no major increase in power coming. Me 109, Spitfire, P-40, had all been flying for months if not years before the Russian planes and the designers knew that they could not build big planes with limited power and match them. They were helped by the Russian light weight guns.

Bomber defensive armament was not on par with some US (B-25, -26) or British (Wellington, Whitley) bombers, but was comparable with most of the others, or better. Soviets rarely or never fielded a slow or short range bomber.

damning with faint praise. Bomber armament was actually pretty poor. A few hand held (aimed), although in a few cases the gunner was actually expected to hold the gun in his arms 7.62mm machine guns. usually replaced by 12.7mm guns on mounts of varying effectiveness.

Most common Russian "bomber" was the DB-3/IL-4 series. Pretty much started and stayed with 3 7.62 machine guns until the IL-4 replaced the dorsal gun with a 12.7mm. Also please note that ranges given for the DB-3/IL-4 are often for a bomb load of 1000kg or less and sometimes for 'cruising' speeds of 340 down to 250kph.
These aircraft sucked up the vast majority of M-88 engine production.

 

[tomo pauk]

The M-88 and weaker could be called 'decent engines' at best, the Soviet war fortunes were more dependent upon better stuff.

Changing the gear ratio on a supercharger to provide more boost higher up means that the supercharger needs more power ( power goes up with the square of the tip speed) and since few superchargers were much more than 70% efficient (70% of power goes to compressing the air (and the resulting heat of compression) while 30% of the power simply heats the intake charge to no purpose.

(*)The two stage supercharger will suck less power while providing better pressure ratio. Ie. for pressure ratio of 5:1, the 2-stage s.charger will use about same power as a good 1-stage supercharger that provides the pressure ratio of nly 3:1.

See Allisons in P-63 without inter-coolers and try to figure out power with 95-100 octane fuel instead of 100/130.

We know that Soviet 'better' fuel was of 95 oct - that would be for lean mixture? How high was the PN with engine running on rich mixture? BTW, looking at the charts of Merlin, we can note that, above certain height, the supercharger can provide only, say, +18 pci boost, the engine needs to be at lower alt in order for supercharger to provide greater boost.
Even the worst 2-stage V-1710s (no intercooling, no ADI, carburetor prior aux stage) were providing circa 8000 ft of altitude gain for same rated power against the best 1-stagers (1125 HP military power both).

The Lagg, Mig and Yak design teams KNEW that there was no major increase in power coming.

We cannot be sure of that. Soviets were testing the AM-37 in at least 2 aircraft, we cannot dismiss that MiG designers were looking how to incorporate it on their MiG-1/3. Klimov was promising the VK-106, while testing the 2-stage M-105PD. The turbo experiments were conducted years before Germans invaded.

Me 109, Spitfire, P-40, had all been flying for months if not years before the Russian planes and the designers knew that they could not build big planes with limited power and match them.

The Soviets were also flying the I-16, a small fighter by any standards. The abortive I-17 was also small, and so was the I-180 (another Polikarpov's fighter, with M-88 aboard). Their math was clear - the Soviet constructors were competing 1st against each other (and then vs. foreigners), and there was no point in extra lbs of airframe to lug it around. The purchased Bf-109E and He-100 only assured them that their philosophy was sound.

damning with faint praise. Bomber armament was actually pretty poor. A few hand held (aimed), although in a few cases the gunner was actually expected to hold the gun in his arms 7.62mm machine guns. usually replaced by 12.7mm guns on mounts of varying effectiveness.

Well, SB-2 was expected to be able to outrun enemy fighters, so it's light gun armament can be excused. It was about as good as anybody else's when introduced. Here is the armament of the early B-25 (from Wiki, FWIW):
Up to 3,600 lb (1,600 kg) bombs and defensive armament of three .30 machine guns in nose, waist and ventral positions, with one .50 machine gun in the tail.
B-26:
The armament consisted of two .30 caliber and two .50 caliber machine guns.
..improved with B-26A:
Incorporated changes made on the production line to the B-26, including upgrading the two .30 caliber machine guns in the nose and tail to .50 caliber.

So not even the newest US medium bombers were that well armed. They improved, so did the Soviets, with 2 cannons and 4-5 LMG for their perspective bomber.

These aircraft sucked up the vast majority of M-88 engine production.

Not here! The M-88s are going to the Pe-2s as we speak

* Please, don't quote me on that. That passage is not correct.

 

[tomo pauk]

The power chart for V-1710-39 (F3 in USAAF parlance) on military power + take off power, red line; M-105, 'nominal power', whatever that means (black line); DB-601A, with 'new' supercharger as most/all of those were furnished by the time tyrants clashed, 5 min rating, plus 1 min rating for take off (dashed), blue line. Of course, the majority of 109s by mid 1941 were with DB-601N, and the DB-601E is to be introduced. The M-105 retained these power values by spring/summer of 1942, when the M-105PF (or VK-105PF) was introduced. The V-1710 has 1166 CV (1150 HP) for take off and at 12000 ft.

 

[Shortround6]

The two stage supercharger will suck less power while providing better pressure ratio. Ie. for pressure ratio of 5:1, the 2-stage s.charger will use about same power as a good 1-stage supercharger that provides the pressure ratio of nly 3:1.

Do you have a source for that?

2 superchargers each at 2.26 pressure ratio operating in series need less total power than a single 3.0 pressure ratio supercharger? That is a LOT of efficiency

Even the worst 2-stage V-1710s (no intercooling, no ADI, carburetor prior aux stage) were providing circa 8000 ft of altitude gain for same rated power against the best 1-stagers (1125 HP military power both).

That is same rated or crankshaft power. Engine was actually making around 200-225hp more to drive the auxiliary supercharger. Trading a bit of power from the engine supercharger by dropping from 9:60 gears to 8:10 gears. Without 100/130 or water injection it was dead in the water.

We cannot be sure of that. Soviets were testing the AM-37 in at least 2 aircraft, we cannot dismiss that MiG designers were looking how to incorporate it on their MiG-1/3. Klimov was promising the VK-106, while testing the 2-stage M-105PD. The turbo experiments were conducted years before Germans invaded.

OK Mig team got a more powerful engine, it also weighed 180-230 kg more dry than the N-105P did. So for a given landing speed or field length you need more wing or less weight somewhere else. Like guns or fuel.
The Turbo experiments were going on allover the place. Soviet designers had to walk a fine line between picking an engine that was reliable but low powered ( = failed design)and one that was unreliable but high powered. Please remember if the engine doesn't make it into production the airplane may not either and at least one designer would up in prison (or arrest) due to prototype/s crashing due to engine failure.

Well, SB-2 was expected to be able to outrun enemy fighters, so it's light gun armament can be excused. It was about as good as anybody else's when introduced. Here is the armament of the early B-25 (from Wiki, FWIW):
Up to 3,600 lb (1,600 kg) bombs and defensive armament of three .30 machine guns in nose, waist and ventral positions, with one .50 machine gun in the tail.
B-26:
The armament consisted of two .30 caliber and two .50 caliber machine guns.
..improved with B-26A:
Incorporated changes made on the production line to the B-26, including upgrading the two .30 caliber machine guns in the nose and tail to .50 caliber.

So not even the newest US medium bombers were that well armed. They improved, so did the Soviets, with 2 cannons and 4-5 LMG for their perspective bomber.

The American aircraft had the extra power to improve although they may have gone a bit overboard. The TU-2 with a pair of "fixed" 20mm guns doesn't really come into the same class just as the "cheek" .50 cal guns on the B-25 and B-26 don't count as 'defensive' armament. TU-2 with 1850 hp engines doesn't show up until late in the war.

Unfortunately the SB-2 was the Russian equivalent of the Bristol Blenheim. Pretty much a match for bomb load, speed, range, and defensive gun. What edge one has in one area gets canceled out in another

Now a more modern "bomber" using M-105 engines could very well use a smaller/thinner wing with some sort of low tech flap in stead of the SB-2 "no-tech" flap

610 sq ft of wing is an awful lot for an under 2000hp 17,000lb bomber.

Pe-2 was 436sq ft for 18.700lbs. much shorter ranged though.

Swapping M-88s for M-105s in a PE-2 gets you more power higher up but not much at low level. Doesn't save much weight. The 150-200lb heavier radials suck up some of the radiator weight. And then you have the radial drag problem. Even on the DB-3/IL-4 they had some troubles with not enough airflow and overheating the engines at times.

 

[Shortround6]

The power chart for V-1710-39 (F3 in USAAF parlance) on military power + take off power, red line; M-105, 'nominal power', whatever that means (black line); DB-601A, with 'new' supercharger as most/all of those were furnished by the time tyrants clashed, 5 min rating, plus 1 min rating for take off (dashed), blue line. Of course, the majority of 109s by mid 1941 were with DB-601N, and the DB-601E is to be introduced. The M-105 retained these power values by spring/summer of 1942, when the M-105PF (or VK-105PF) was introduced. The V-1710 has 1166 CV (1150 HP) for take off and at 12000 ft.

Thank you for the chart. It took the Russians 3 tries to get the M-105 to that power level and survive. They started with the M-105S in 1937 and it took two years to get it into production but early examples were less than reliable and teh 105 was quickly replaced by the 105P which was replaced by the 105PA in 1941 at same power rating but heavier weight.

We also know the Allison would tolerate overboosting better even if it was not official. Americans just loaded the planes with too many guns and too much ammunition.

 

[tomo pauk]

The chart lacks the lines fo contemporary Merlins (XX, 45), those were giving considerably more power at all altitudes than those 3 depicted. Agreed about Americans overloading their fighters - 7 guns for P-39!

Do you have a source for that?
2 superchargers each at 2.26 pressure ratio operating in series need less total power than a single 3.0 pressure ratio supercharger? That is a LOT of efficiency

No, I don't have source, apparently I've calculated 2+2 and arrived at 5. Will edit the previous post.
My line of thinking was that, once the supercharger system is really pushed to the limits, the 2-stage system provide greater pressure ratio, than a single stage will, due to it's greater efficiency.

That is same rated or crankshaft power. Engine was actually making around 200-225hp more to drive the auxiliary supercharger. Trading a bit of power from the engine supercharger by dropping from 9:60 gears to 8:10 gears. Without 100/130 or water injection it was dead in the water.

Agreed.
I'd still love to see the PN rating for Soviet 95 oct fuel, when engine is operating in rich mixture.

OK Mig team got a more powerful engine, it also weighed 180-230 kg more dry than the N-105P did. So for a given landing speed or field length you need more wing or less weight somewhere else. Like guns or fuel.
The Turbo experiments were going on allover the place. Soviet designers had to walk a fine line between picking an engine that was reliable but low powered ( = failed design)and one that was unreliable but high powered. Please remember if the engine doesn't make it into production the airplane may not either and at least one designer would up in prison (or arrest) due to prototype/s crashing due to engine failure.

The saga of Soviet designers, the prisons, pressures etc is a material for a book
I was not refering to the MiG receiving the AM-35, but that Soviet designers knew that engines with supposed greater power were in pipeline. Both people in MiG and at Yakovlev's bureau were flying the new engines in 1941.

The American aircraft had the extra power to improve although they may have gone a bit overboard. The TU-2 with a pair of "fixed" 20mm guns doesn't really come into the same class just as the "cheek" .50 cal guns on the B-25 and B-26 don't count as 'defensive' armament. TU-2 with 1850 hp engines doesn't show up until late in the war.

The 100U was carrying the 2 x 20mm and 5 LMGs with 1450 HP engines, that were heavier (when cooling system is accounted for) than M-82 radials.

Unfortunately the SB-2 was the Russian equivalent of the Bristol Blenheim. Pretty much a match for bomb load, speed, range, and defensive gun. What edge one has in one area gets canceled out in another

Now a more modern "bomber" using M-105 engines could very well use a smaller/thinner wing with some sort of low tech flap in stead of the SB-2 "no-tech" flap

610 sq ft of wing is an awful lot for an under 2000hp 17,000lb bomber.

Pe-2 was 436sq ft for 18.700lbs. much shorter ranged though.

Agreed all the way. Pe-2 was sort of A-20 with slightly longer legs (until later A-20s doubled the fuel carried), but with lower payload.

Swapping M-88s for M-105s in a PE-2 gets you more power higher up but not much at low level. Doesn't save much weight. The 150-200lb heavier radials suck up some of the radiator weight. And then you have the radial drag problem. Even on the DB-3/IL-4 they had some troubles with not enough airflow and overheating the engines at times.

Seems to me that designers were too smart with adjustable louvers? Anyway, the radial Pe-2 should fly faster than Db-4 = more air through the finning

 

[Shortround6]

The PE-2 was sort of a Bf-110 equivalent.
The DB-3/IL-4 was sort of a HE 111 equivalent.

With less than a few squadrons of anything bigger, not counting the TB-3

They really need both.

Unfortunately the SB-2 wasn't even a Do-17 equivalent and they built too many in 1938-40 trying to build up numbers ( a common failing of may pre war air forces, building too many semi-obsolete aircraft).