# Second half of 1942: what fighter for VVS?



## tomo pauk (Mar 18, 2011)

Thinking about 3 contenders: La-5, Yak-1, MiG-3. Please vote/say what would you pick


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## Shortround6 (Mar 19, 2011)

You can pretty much scratch the MiG-3. It was done by the second half of 1942.


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## davebender (Mar 19, 2011)

I agree. The MiG-3 was a high altitude interceptor. Not much need for that on the Russian front.

Go with the YaK-1. Already in service by June 1941. More or less comparable in performance to the German Me-109. Plywood construction was a good thing as the WWII Soviet Union was critically short of aluminum. 

The Yak-1 had numerious manufacturing quality control defects but so did a lot of other Soviet equipment such as the T-34 tank. Leaky fuel tanks, plywood panels ripping off the wings, defective magnetos, engine oil leaks, unreliable radios and a jammed cockpit canopy did not receive the same attention in the VVS as they would receive in most other air forces.


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## Thorlifter (Mar 19, 2011)

IMO, this is an easy decision and that being the La-5. Beloved by the pilots and easy to maintain for the ground crew, it was an excellent dog fighter at low altitudes. Dave is right in that, what I would call low production standards, almost all the Soviet equipment had flaws of some type.


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## parsifal (Mar 19, 2011)

sorry guys, but just another germanic invincibility myth i am afraid. or if one want to be more accommodating, perhaps better described as a half truth. I have no information on production faults, but logically thats probably true, and therefore the coments on build quality i cannot refute. however, this is a vastly overblown effect. at the end of the day, on the eastern front, what counted most were serviceability rates, and this regard, the VVs compared extremely favourably to the germans. The best month for the germans, according to hayward (Stopped at stalingrad - the Luftwaffe and hitlers defeat in the east 1942-3 ), was in June, where richthofen was able to achieve a serviceability rate of just over 70%. thereafter it fell back rapidly, hovering between 40-55% for most of the summer, before plummeting to under 25% during the winter of 1942-3. Soviet serviceability rates are not as well documented, however according to von hardesty (Red Phoenix), they were generally and consistently above 50% in the summer, and fell to about 35% in the poor weather of the winter. The exception to this, was over sevastopol, where the VVS displayed a very poor serviceability rate, probably because the fortress had been cut off and under siege sincce 1941. 

one could argue that the soviets would list something as airworthy, though by western standards it was not fit to fly....still they managed to turn the battle around and win control of the skies, or at least challenge the luftwaffe, by the end of the year over stalingrad


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## fastmongrel (Mar 19, 2011)

The La-5 simply because it was armed with 2 x Shvak 20mm cannon, had a radial engine and on paper seemed to have had slightly better performance. 

Oh and it looks better


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## davebender (Mar 19, 2011)

The Soviet Degtyaryov light machinegun was designed for a quick barrel change. However I have read that Soviet LMG sections typically weren't issued a spare barrel. As if they didn't expect a LMG crew to live long enough to need one.


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## parsifal (Mar 19, 2011)

Once again, such statements have to be taken with a great deal of circumspection. I have no doubts the Soviets suffered their equipment and spares shortages, especially in the first half of the war, but then both armies suffered this sort of logistical problem. My opinion was during 1941-2, the german army suffered from shortages to a far greater extent than the russians. The russians were falling back onto their supply sources, whilst the germans were relying on ever increasing tenuous ones. An excellent example of the effects of this can be found in their issue of winter clothing in 1941. winter issue clothing was there 9within the OKH zone of operations)....apparently stuck enroute during the winter. There were also severe shortages of spare parts, everything from toothbrushes through to such things as tank engines, tank tracks, artillery shells, artillery recuperators, aero engines. This was due mostly to poor planning rather than the breakdown of the supply system. Germany had not planned for a long war, couldnt plan for a long war, because of her poor financial position at the beginning of the war. A disproportionate fraction of german production went into "the shopfront".....they tended to concentrate on whole units with only limited supply of spares. Most aero-engine production went into constructing whole planes for example, rather than spares, which affected their serviceability rates. Sanme thing for tank production. 

The soviets with their command economy structure were much better organized than the germans in this regard. There were always plenty of spares produced, well at least after the initial shock of invasion wore off in the second half of '42. Where the Soviets failed repeatedly was in their logistic arrangements, getting the spare parts from the point of production, to where they were needed they were needed. but even here, thanks in no small part to the allies, things improved as the war progressed. The US supplied MT greatly assisted in this regard, as did also the provision of trains, both rolling stock and prime movers. Soviet logistic support from the second half of 1943 was vastly improved, and was one of the major reasons they were able to sieze and hold the strategic inititiative.


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## tomo pauk (Mar 19, 2011)

La-5 is my candidate too, for decent performance, good maneuverability, firepower radial engine being less susceptible to battle damage.


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## davebender (Mar 19, 2011)

That's true only for some equipment. For instance the YaK1 which was produced at Saratov. For other equipment such as T-34 tanks the opposite holds true. One of the most important T-34 manufacturing complexes was captured by Germany at Kharkov. Another T-34 plant was located at Stalingrad. I believe the KV-1 tank was manufactured in Leningrad, a city that was economically isolated by the fall of 1941.

So a realistic answer to this poll requires an examination as to where the various Soviet aircraft and their major components were produced. It's pointless to order an increase in production if Germany has just captured the pre-war factory complex.


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## parsifal (Mar 20, 2011)

no, you are wrong. soviet re-equipment passed through its training centres, which invariably were concentrated around their major cities in particiular moscow. so even though major factories were located in the west of the country, these seldom provided re-equipment directly to the front. this has to do with soviet policy on rest replacement and retraining. usual policy was to allow air and ground formations divisional sized and smaller 9including air formations) to be run down to typically about 10% of its strength, then this hardened cadre, would be withdrawn to a rear area, some hundreds of kilometres behind the front for rebuilding. typically this rebuilding occurred around their population nodes....the so-called mlitary district training centres, where they would receive their new equipment, and an infusement of fresh manpower. The new manpower was considered expendable, the trained cadres were not. Soviets would go to extraordinary lengths to save those seasoned cadres.

Because the retraining and resting occurred in the home military districts, it was irrelevant where the production centres were. what was important was where the retraining and re-equipment took placce, invariably, as i indicated above, this occurred around places like Leningrad, moscow, Stalingrad, Kirov, Tblisi (in the far south).

So the important determinant was the proximity of the production centres to the retraining centres, not the proximity to the front. In the initial 6 months there was an enormous strain on the soviet rail system as fully 35% of its industrial complex was picked and moved often more than 1000km east. This had largely been completed by the end of 1941, so that from the beginning of 1942, there was a massive amount of spare rail capacity (although some was of dubious condition, and was replaced and expanded by massive amounts of lend lease rolling stock). point is, that Soviet re-equipment and strategic movement of its reserves was largely covered by the second half of 1942 .

Germany didnt capture a lot of the strategic factories from the soviets, though its capture of manpower centres was a serious impact on soviet industrial output. Allied lend lease largely overcame this by providing huge quantities of foodstuffs, thereby releasing huge numbers of men (and women) for work in the factories and for the military.

So, by the second half of 1942, far from having a negative effect on Soviet production, by dint of huge sacrifices by the soviet population, and good planning by its central comittee, soviet production was actually powering ahead of that of its german rivals, there was no shortage that I know of of most weapons, including aircraft, by the latter part of 1942. Soviets were beginning to feel the manpower pinch, so were spending more time training their formations to higher levels of proficiency. The divisions used to destroy the germans at stalingrad were already in existence at the beginning of 1942, but the long summer of that year was spent getting these formations properly equipped and trained, whilst the germans were kept busy with whatever was at the front at that time. It was a strategy for ultimate victory, and the russians played it to a tee


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## danjama (Mar 20, 2011)

La-5 for me.


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## claidemore (Mar 21, 2011)

Yak1 for 1942. 
In 1942 the La5 still had considerable teething problems. 
Yak 1 had already been in combat for over a year, faults and flaws had been corrected and they were just starting to use the M105PF engines. Yak 7's had been in service almost as long, Yak 9's coming into service about same time as La5's, but the Yaks were already a combat proven design. La5 had a slightly faster top speed, but Yak 1's had a lower wing loading and better power loading (PF engine late 42). Yak was most produced Soviet fighter. 

That being said, both types were needed. Different engines provide diversity for production. Eventually tactics were devised using La5 variants for fighter sweeps and Yaks for close escort, which worked perfectly for the Soviet Unions tactical doctrine.


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## davebender (Mar 21, 2011)

I agree that both types are needed but my reasoning is a bit different.

Fighter aircraft are cutting edge technology. Without the benefit of hindsight you don't know which airframes and engines have the best development potential. During peacetime you can build a single fighter type and hope the design ages gracefully. During wartime you cannot take that chance. So you need at least two different fighter airframes and at least two different fighter engines.


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## essexalan (Mar 22, 2011)

La-5 for me especially the La-5FN which I believe entered service late 1942. Yak-1 was not really competitive until the Yak-1M, VK-105PF engine, was produced followed by the Yak-3 which was a superb aircraft. Both aircraft were produced in large quantities but of course the VVS were somewhat lacking in skilled pilots by this time due to attrition. Mig 3 was not in contention this late in the war. Not sure how much armour any of these aircraft carried but their armament was sufficient for their roles ie they did not have heavy bombers to shoot down.


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## tomo pauk (Mar 22, 2011)

La-5FN was from late 1943, so not very much for this thread. As for Yak-1M with better engine, again too late for this. What period of war 'this late in the war' phrase cover?
About the armament, Soviet 20mm was firing one of the lightest shell, and the wide usage of 37mm in small fighters signals us that it was needed.


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## essexalan (Mar 22, 2011)

Book I have states service production for LA-5FN was from late 1942. Yak-1M first flight Spring 1942 service delivery I do not know, Yak-3 first flight Spring 1943, service delivery approx July 1943. I really meant the first part of the conflict with the VVS fighting with inferior aircraft was coming to an end and soon they would be flying aircraft with at least equal performance to the Luftwaffe. Certainly too late for a lot of VVS fighter pilots. You do not need many hits from a 12.7mm machine gun to put down any fighter let alone hits from a 20mm cannon. I would have thought a high rate of fire was preferable. I did read somewhere that the VVS liked the P-39 for its 37mm cannon for ground attack purposes. Don't know of any Russian built fighter aircraft with 37mm cannon so I do not know where the wide usage in small fighters comes from. In fact I would think that the rate of fire and the number of rounds carried would make a 37mm cannon totally unsuitable for air combat. I believe the RAF replaced the 37mm with its 15 rounds (later 30 rounds) in their P-39s with a 20mm Hispano plus extra Brownings


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## parsifal (Mar 22, 2011)

Im not any sort of ballistics expert, but the amount of hitting power for any projectile is the amount of energy it possesses, is it not. The formula for calculating Kinetic energy is E= 0.5 x mv2, whereE= Energy M= mass of the projectile and V= velocity of the projectile. A heavier mass travelling at slower speed, will have less kinetic energy and therefore a lot less hitting power. I would have thought that the 20mm shvak round would travel at a slighter higher velocity than say a Hispano Suiza round. If so, it is going to have relatively more hitting power.

Whether a small projectile travelling at high speed does as much damage, is a different matter


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## davebender (Mar 22, 2011)

That's how armor penetration works. For soft targets (including aluminum aircraft skin) the amount of HE filler delivered on target is more important. German 3cm autocannon are an obvious example.

3cm Mk103 cannon. Muzzle velocity = 2,822 feet per second. 380 rpm.
3cm Mk108 cannon. Muzzle velocity = 1,770 feet per second. 650 rpm.

Both cannon fire the same 3cm Minengeschoß ausf C projectile which contains 72g of PETN filler. When shooting at soft targets from a WWII fighter aircraft at a distance of 100 meters the Mk103 velocity advantage is more then outweighed by the Mk108 cannon having a higher rate of fire. Being lighter in weight and having less recoil is icing on the cake for the Mk108 cannon.


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## Shortround6 (Mar 22, 2011)

parsifal said:


> I would have thought that the 20mm shvak round would travel at a slighter higher velocity than say a Hispano Suiza round. If so, it is going to have relatively more hitting power.


 Except it doesn't travel at a higher speed. It travels either 20m/s slower or 10m/s faster depending on the barrel length of the Hispano. Actually that is close enough to call it the same depending on the barrel wear of the individual weapon and a few other variables, we are talking around a 2% difference after all. The projectile weight at 97 grams to 128-130 is much larger though and those heavier shells will tend to retain velocity better. 

The Shvak gun, with it's higher rate of fire and lighter weight than the Hispano was an effective weapon but each round was not as powerful no matter how it was measured.


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## parsifal (Mar 23, 2011)

Thanks guys, and you are both right.

A quick comparison with the Hs 404 cannon reveals the following

SHVak

Explosive weight 2.5 gms min (APIHC round, optimised for armour penetration)
6.7 gms max (HE-frag, optimised for max explosive effect)

Practical ROF 650-850 RPM
M/V 750-790 M/S

the russians also developed mixed he/incendiary rounds and the ap round was essentially discarding sabot round

Hs 404 cannon

Explosive weight 6 gms min 
11 gms max 

Practical ROF 600-700 RPM
M/V 840-880 M/S


These figures mean that a Shvak cannon can deliver 1625-5695 gms of HE per min. The HS 404 delivers 3600-7700 explosive per min. 

In terms of kinetic energy each Shvak cannon delivers 2-008-2.175 x 10(10) units of energy (gm/metres???whatever that is) permin. The HS 404 delivers 2.75-4.55 x 10(10) units of energy per min (same units as the Shvak, so the numbers are comparable)


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## tomo pauk (Mar 23, 2011)

essexalan said:


> Book I have states service production for LA-5FN was from late 1942.



Though I don't know what is 'service production', the book by Gordon Khazanov 'Soviet combat aircraft' states that 1st prototype of La-5 FN was completed in March 1943.



> Yak-1M first flight Spring 1942 service delivery I do not know,



Same book states 1943 as production year.



> Yak-3 first flight Spring 1943, service delivery approx July 1943.



Same source: 1st production Yak-3 rolled out on 1st March 1944.



> I really meant the first part of the conflict with the VVS fighting with inferior aircraft was coming to an end and soon they would be flying aircraft with at least equal performance to the Luftwaffe. Certainly too late for a lot of VVS fighter pilots.



Indeed, Luftwaffe possessed performance edge over 5km/15kft, thinning down under that alt.



> You do not need many hits from a 12.7mm machine gun to put down any fighter let alone hits from a 20mm cannon.


Many of targets were not fighters, but sturdy Junkers' planes. Even Ju-87Ds were well armored, so heavy punch was needed.



> I would have thought a high rate of fire was preferable. I did read somewhere that the VVS liked the P-39 for its 37mm cannon for ground attack purposes.



P-39 was used in fighter units, for fighter duties. Attack vs. ground units were occurrences, not something regular. 



> Don't know of any Russian built fighter aircraft with 37mm cannon so I do not know where the wide usage in small fighters comes from. In fact I would think that the rate of fire and the number of rounds carried would make a 37mm cannon totally unsuitable for air combat. I believe the RAF replaced the 37mm with its 15 rounds (later 30 rounds) in their P-39s with a 20mm Hispano plus extra Brownings



Yak-9T (T for Tezheko-kaliberny - 'of heavy calibre'), featuring NS-37, produced in 2700+ copies. Guess Russians were able to use the US 37mm too


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## davebender (Mar 23, 2011)

A good point. 

Practically every book mentions how heavily armored the Hs-129 was. Not many mention that the more numerous Ju-87D and Fw-190F CAS aircraft also had significant armor protection. You don't want to be exposed to fire from a Ju-87D tail gunner longer then necessary. Heavy firepower (on target) = a quick kill.


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## Shortround6 (Mar 23, 2011)

parsifal said:


> the russians also developed mixed he/incendiary rounds and the ap round was essentially discarding sabot round.


 
More properly it could be described as an APCR (armor piercing composite rigid) round, since nothing is discarded (falls off) on the way to the target. 

For a quick reference to guns you may want to book mark this page. WORLD WAR 2 FIGHTER GUN EFFECTIVENESS


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## parsifal (Mar 23, 2011)

Your right again, it wasnt a discarding sabot, however it had a mild steel jacket formed around an explosive sheath, inside of which was a hardened steel core. thats looks to me that on impact it was designed to explode, thereby shedding the outer casing, and allowing the hardened core to continue to penetrate what was now probably a weakened armoured surface, because of the detonation. if thats how it was designed to operate, it looks to me to be using the same principal as a discarding sabot round


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## essexalan (Mar 23, 2011)

Book I was reading is "Combat Aircraft" by Bill Gunston so I guess he must be wrong about service production. "Kursk" by Christer Bergstrom states that the LA-5FN was introduced prior to and in operation during Zitadelle although I cannot find any VVS unit which were equipped with this aircraft, perhaps the unit lists do not differentiate between LA-5 and LA-5FN. Agree about the Yak-3 although the original Yak-3 was cancelled back in 1941 due to lack of alloys and the invasion. I think most ground attack aircraft would have been amoured against flak not against fighter attack from the rear. Exception to this would appear to be the Ii-2 which seems to have been amoured all over except for the tailfin! P-39 was indeed used in fighter units and seems a number of VVS aces did like this aircraft. Still do not see the need for a 37mm cannon on a pure interceptor. Yak-9T, some sources say designed for ground attack, some say it was equipped with the 37mm to correct the lack of firepower in the Yak-9s and was used primarily for air combat. I will throw Gunstons book in the bin!


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## Shortround6 (Mar 23, 2011)

It is not really using the same principal. 
The Idea behind APCR or arrow head or what ever an army called it was to use a very dense penetrator to concentrate the weight of the projectile in a small area. The collar/shell body/outer jacket/what ever was designed to be as light as possible so that the projectile weighed less than a standard AP projectile and could be given higher velocity, usually much higher. The dense core at the higher speed offered more energy per unit of frontal area and thus higher penetration (tungsten carbide cores also allowed for higher impact speeds without shattering than steel). A problem for long range fire, not really applicable to aircraft, was that the light projectile lost velocity much quicker than the standard round and performance, while impressive at the muzzle soon dropped below standard AP rounds. 
The APDS projectile offered no better penetration near the muzzle than the APCR but since the only thing flying to the target was the dense core which had an even better ballistic co-efficient than the standard projectile it's performance fell off the least with range. 
The Russian round sounds strange. Sort of a dual purpose round, I an't imagine it goes through much more armor than a standard 20mm AP shot, if even as much. The HE surround may give a flash on impact or help ignite fuel tanks if hit? I doubt a few grams of explosive detonated along the sides of the core are going to weaken the target much.


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## tomo pauk (Mar 23, 2011)

essexalan said:


> Book I was reading is "Combat Aircraft" by Bill Gunston so I guess he must be wrong about service production. "Kursk" by Christer Bergstrom states that the LA-5FN was introduced prior to and in operation during Zitadelle although I cannot find any VVS unit which were equipped with this aircraft, perhaps the unit lists do not differentiate between LA-5 and LA-5FN. Agree about the Yak-3 although the original Yak-3 was cancelled back in 1941 due to lack of alloys and the invasion. I think most ground attack aircraft would have been amoured against flak not against fighter attack from the rear. Exception to this would appear to be the Ii-2 which seems to have been amoured all over except for the tailfin! P-39 was indeed used in fighter units and seems a number of VVS aces did like this aircraft. Still do not see the need for a 37mm cannon on a pure interceptor. Yak-9T, some sources say designed for ground attack, some say it was equipped with the 37mm to correct the lack of firepower in the Yak-9s and was used primarily for air combat. I will throw Gunstons book in the bin!



If you intent to throw it, better idea is to send it to me - I'll pay to FedEx 

An interim variant of La-5 existed - La-5F, that was indeed used from beginning of 1943, so that might caused issues in the 'Kursk' book you own.

The 37mm was the US idea, exactly for interceptors. The lack of firepower ( most of the Soviet fighters did have about 1/2 of firepower of Spitfire of 1941, if even so), and their wings of modest size were ill suited for straping a pair of cannons there. Add that Yaks were having 1100-1200 HP for better part of war, installation of heavier centreline-mounted gun was the only way. IMO they've perfected the French/US(P-39) principle to the very usable degree.


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## parsifal (Mar 23, 2011)

The explosive component was only 0.8 gms, so no thats not going to produce much effect. maybe the explosive sheath/cone (I dont know which) was there simply to push the mild steel jacket away from the point of impact. In any event, even their AP rounds were not that impressive. Functional, yes, but not outstanding. The AP round was the fastest, at 790 M/S, and the lightest, at 91 gms, but even the HS 404 HE round was still faster (at 840 M/S) and heavier (168 gms, I think).


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## claidemore (Mar 24, 2011)

Hi essexallan, 
Just to clear up a misconception. The Yak 1M was actually the prototype for the Yak 3 (only two built). The 'improved' Yak 1 that flew from 1942 on is usually referred to as the Yak 1B. Officially it would have been referred to as a Yak 1, or Yak 1 improved, or Yak 1 M105PF. This was the model initially used by the Normandie Nieman regiment.
There was a Yak 7M which never entered series production, and a Yak 9M, over 4200 built starting early in 1944.


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## CORSNING (Apr 17, 2011)

Hi all,
I have been a WW2 aviation enthusiast since 1968 and have focused my studies on the USSR since 2003.
The topic of this thread is very intriguing for me. I checked through my books and files and this is what I came up with concerning July-December 1942:

LaG-5: 7,385 lbs. M-82A/1,510 WE hp. 332mph/S.L. 365mph/16,400ft. 2x20mmShVAK. LaGG-3 airfames converted to accomodate M-82 radial engine. Suffered from internal balance units for the control surfaces resulting in poor control and considerable workload for the pilot. Engine suffered from overheating problems. Early models had no leading edge wing slats. Performance disapointing that it was not much better than LaGG-3 at the time. 3,350 fpm initial climb. 16,400'/5.7min.

Yak-1: 6.128 lbs. M-105PF/1,260 WE hp. 327mph/S.L. 368mph/12,500ft. 1x20mmShVAK 2x12.7 ShkAS.
Superior roll rate to Bf.109F and other VVS fighters. Lower stall speed. Lower wing load. Vastly superior sustained turn rate. Control harmony excellent and light. Easily flown by average pilots to its limits.
3,715 fpm initial climb. 16,400'/4.7min.

That's what I've come up with to date. At the very end of 1942 the VVS start receiving the P-39M(?).
P-39M 7,500 lbs. V-1710-83/1,420 WE hp (~1,700 hp at 66" boost) 386mph/13,800ft. 4,000fpm initial climb. 15,000'/4.4min. 1x37mm. 2x12.7mm. and 4x7.62mm (often removed to improve turn, roll and climb.)
Considered dynamic and resposive at low and medium levels by several VVS pilots.


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## tomo pauk (Apr 17, 2011)

Are you sure Yak-1 was mounting 2 x 12,7mm? 
IIRC P-39s were better climbers to 5-6 km than Spitfire Vs VSS received, according to Soviet tests.


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## CORSNING (Apr 17, 2011)

Nice catch tomo. The ShKAS was 7.62mm. Muzzle speed 825 m/s. 1,800rpm. The 1942 LaG-5 had two of these MGs and one ShVAK 20mm.


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## CORSNING (Apr 17, 2011)

WOOPS, I'm sorry tomo. My mistake again. The Yak-1 had 2x7.62mm and 1x20mm. The LaG-5 of 1942 had two 20mm ShVAKs


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## CORSNING (Apr 17, 2011)

With my limited time I have come up with Spitfire V (Nov.25, 1941) initial climb: 3,710 fpm. The pilots in the VVS pushed their Allisons like the pilots in the middle east and Austrailia: 66" boost = ~1,745 hp. and
70" boost =~1,780 hp. at 60 degrees F. I really wish I had some test figures showing how that translates into speed and climb for the P-39M. The N and Q had V-1710-85 and could not be push to that high of boost. It had something to do with gearing I think. I'd have to look it up.


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## tomo pauk (Apr 17, 2011)

Any good info about Russian pilots pushing their Allisons, both for P-40 P-39?


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## CORSNING (Apr 17, 2011)

Conversations with N.Golodnikov
It is an interview titled: Conversations with N. Golodnikov. Part 3 he admits to pushing the P-39 boost. He talks about the P-40 in Part 2. The entire article is very informative. It tells how they used the P-39 as escorts and how it performed against the Bf.109 and Fw-190. He talks of several other aircraft that he flew in combat also.


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## parsifal (Apr 18, 2011)

i cannot answer the direct question as to whether VVs pilots would push their boost over limit. however, as a general observation, a criticism that regulalry comes up about inexperienced pilots is that they dont fly their mounts to the limit. Becuse these pilots are unsure of when they have reached the performance limits of their plane, and are unsure of what to do if they exceed those limits, there is a universal tendency for these rookie pilots not to push their aircraft to and beyond the safe working limits of that aircraft, even in situations where their lives depended on it. So my bet is that the relatively inexperienced VVS pilots would tend not to push hard on their machines


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## Shortround6 (Apr 18, 2011)

Corsning is right. many Allisons were boosted beyond official recommendations. However this only worked a low altitudes, in some case very low altitudes. The engines with the 8.80 gears for the supercharger were rated at 1325hp for take -off at 51in. Official WER was 1590hp (or so) at 2500ft at 61 in. the lower down than 2500ft you go the more boost there was. the higher you go the less there was until at at about 12,000ft they were down to 42in of boost and 1150hp. That was all the supercharger would supply. getting the engine to 70in of boost might require over revving the engine beyond 3000rpm. 
The later engines with the 9.60 supercharger gears took more power to drive the supercharger and heated the intake charge more. They were operating closer to the detonation limits to begin with. Allison was quite worried that units that were used to getting away with overboosting the 8.80 gear engines would wind up with a lot of wrecked engines and lost aircraft if they tried running the 9.60 gear engines at the same limits. The 9.60 gear engines offered the same 1150-1125hp another 3,500 higher than the 8.80 gear engines.


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## CORSNING (Apr 18, 2011)

Hi parsifal,
You should also read Conversations with Golodnikov. There are some other interviews and other information on that sight as well. Several USSR pilots had fought in China in the late 1930, so they were not all inexperienced. Golodnikov admits that they pushed their P-39 in such a way that the Allisons lasted about 50 hrs. for the early models and 100 hrs for the later Allisons.

On December 12, 1942 the Allison Division sent out a letter to the Commanding General of the Army Air Forces, Materiel Center in Washington, D.C. stating that they have received reports from the Middle East and Australia indicating the use for considerable periods of time of very high manifold pressures on the V-1710-39 and -73 engines. The Quote from Australia reads:

"Some pilots admit operating for prolonged periods at around 70" Hg.
( 20 lbs. / sq. in.) of boost"

The letter continues: "and from the Middle East our Representative who just returned advises that they are resetting boost controls to 66" Hg. (18 lbs./sq.in.)."
The confidential letter continues saying: " This company has agreed to the war emergency operation at 60" Hg. (15 lbs./sq.in) which is approximately 1,570 hp. at
3,000 rpm.

66" Hg. is approximately 1,745 hp. at S.L. or 1,770 hp. at 2,000 ft.

70" Hg. is approximately 1,780 hp. at 60 degrees F.

Wow. I wonder what the performance figures of the P-39D (-35) would be pushed to those limits?


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## CORSNING (Apr 18, 2011)

Thanks Shortround6, I haven't checked my files yet, but that info looks dead-right-on-the-head to me.


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