SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[Shortround6]

Sounds good, I would even by the 6mph just stop the argument

There has been some discussion about how different in performance were the P-39Q and N. They did differ in armament, the two .30 cal. machine guns in each wing being replaced by a .50 cal. mounted in lower-wing gun pods. I checked wind tunnel testing concerning the extra drag of these gun pods in NACA report L5A30 to verify. NACA concluded that the CD of the airplane (in this case, a P-63) was increased by 0.0010, which amounted to a -6 mph change in level speed. So if we add 6 mph to the speed of a P-39Q we will pretty much have the speed of an average P-39N. But then again, those four missing .30 cal. machine guns had to reduce drag slightly as well. So the addition of 4-5 mph is a reasonable amount to add, but never more IMHO.

Sounds good, I would even go with -6mph to avoid the argument.
I would say that the increased weight will affect climb more than the drag will affect speed.

 

[DarrenW]

.
Altitude SpeedMPH RPM b.h.p. Man.Pr.Hg. Oil Cooler ShutterPosition Prestone Shutter Position

*16,100 389.5 3000 1125 46.7 Flush 6 turns from W.O.
**9,700 398.5 3000 1420 59.8 Flush 6 turns from W.O.
2,700 358.0 3000 1330 57.0 Flush 6 turns from W.O.
30,100 353.0 3000 655 26.7 Flush 6 turns from W.O.


Airplane does not meet Air Corps cooling requirements at any of these powers.


On the test of the P-39N the report says the oil cooler shutters "flush" and Prestone sutter 6 turns from W.O. (as above) followed by "

Airplane does not meet Air Corps cooling requirements at any of these powers. " How is this allowed was a valid test?

​

I see your point and it is well taken. I plan to create a speed chart of the N model using the P-39Q test results instead. There is no mention of cooling problems so the results are probably more reliable. I will add 6 mph to the speed at the various heights in order to recreate the actual speeds that a typical P-39N would have attained. Hopefully we will have a better picture of the P-39N's capabilities after that.

 

[pbehn]

I see your point and it is well taken. I plan to create a speed chart of the N model using the P-39Q test results instead. There is no mention of cooling problems so the results are probably more reliable. I will add 6 mph to the speed at the various heights in order to recreate the actual speeds that a typical P-39N would have attained. Hopefully we will have a better picture of the P-39N's capabilities after that.

It was a general question, it seems to me that cooling drag was reduced by not cooling the engine. Overheating on tests and in service seems to be a feature on the P-39.

 

[Shortround6]

On the test of the P-39N the report says the oil cooler shutters "flush" and Prestone shutter 6 turns from W.O. (as above) followed by "

Airplane does not meet Air Corps cooling requirements at any of these powers. " How is this allowed was a valid test?
​

The test may have been valid (unless done on a highly polished, specially prepared aircraft).

It is the conclusions that may not be valid.

You don't know what is going to work and what won't until you test.
The P-39 seems to have had chronic cooling problems, get it sorted out for one level of power and the Allison (or the Army) upped the power rating/s the problems came back at the higher power levels.
A number of other planes went through the same thing. Spitfires got ever larger radiators/oil coolers.​

 

[DarrenW]

Sounds good, I would even by the 6mph just stop the argument



Sounds good, I would even go with -6mph to avoid the argument.
I would say that the increased weight will affect climb more than the drag will affect speed.

Good point. So 6 mph it is....

 

[Shortround6]

I see your point and it is well taken. I plan to create a speed chart of the N model using the P-39Q test results instead. There is no mention of cooling problems so the results are probably more reliable. I will add 6 mph to the speed at the various heights in order to recreate the actual speeds that a typical P-39N would have attained. Hopefully we will have a better picture of the P-39N's capabilities after that.

Climb chart may be harder but just as valuable.

 

[pbehn]

The test may have been valid (unless done on a highly polished, specially prepared aircraft).

It is the conclusions that may not be valid.

You don't know what is going to work and what won't until you test.
The P-39 seems to have had chronic cooling problems, get it sorted out for one level of power and the Allison (or the Army) upped the power rating/s the problems came back at the higher power levels.
A number of other planes went through the same thing. Spitfires got ever larger radiators/oil coolers.​

Shutters were open in climb and closed in level flight, as a layman I would have thought the engine overheating is as invalid as using uncertified boost or revs on the test.

 

[Shortround6]

The open during climb and closed for speed was normal, just about all planes did that, what varied was by how much they were open during climb or if they needed to open in level (high speed) flight.
If you are climbing and doing 180mph true you are getting 1/2 the air than if you are doing 360mph in level flight. Some sort of adjustment is needed. And with air being roughly 1/2 the density at 20,000ft that it is at sea level (even though colder) they have to make allowances for that.

I can easily tests that pushed boundaries or limits and even exceeded them just to find out where they were. Using such results as indicators of operational ability is the problem.

There are some tests where the climb had to be broken into stages to allow the engine to cool off. That test might tell you what the plane could do for a few minutes in combat. It sure didn't tell you what the plane needed for time to get from sea level to 25-30,000ft for an intercept. Except perhaps it wasn't going to make it.

 

[Schweik]

In my opinion (from reading about 601 Squadron during those dark Airacobra days), what killed the aircraft for the RAF was chronic unserviceability, and they were unwilling to put in the mountain of effort that was required to fix it - while the Soviet NII and VVS made a special case out of the P-39 and went all-out to turn it into a real fighter. No small feat - but they sure did it.

A great read here:
Early Cobra's in Soviet Aviation

That Lend Lease aircraft site is a fantastic resource, and that article in particular is indeed a good read and it helped me understand how the Soviets did so well with the P-39. The Soviets got their P-39's in December and January of 1941/42, and spent the next 4 moths preparing them, training pilots and doing their workup. Some quotes from the article mentioned:

The first party of 20 aircraft (all series AH, from 599 to 677) arrived in 22d ZAP in the period between late December 1941 and early January 1942. Their arrival was taken very seriously. The Scientific Research Institute (NII) of the VVS sent a group of specialists to the regiment, from which was formed a separate team (22d ZAP order no. 7 of 2 January 1942).
*
The assembly of the first party of aircraft was begun in mid-January. This author does not know the specific site of the assembly and test flight of the first Airacobra. The literature only makes reference to a large airfield on the outskirts of the town. Drawing from the basing of 22 ZAP, the site was one of three airfields: Kineshma, Ivanovo-South, or Ivanovo-North.
*
Typical deficiencies for foreign aircraft surfaced from the first days of its use: reduced outflow of oil from the lubrication system, the remnants of which quickly froze in the cold weather. The technicians quickly had to rework the lubrication system by means of installing additional oil taps [as in "faucets"] and also to create a special collector for the simultaneous induction of hot air into the crankcase, reduction box, radiator, and other areas that required warming before starting the engine. This collector successfully withstood testing and was recommended for implementation in the employment of the airplane.
*
After completion of testing, approximately in April 1942, the Airacobra I fighter began to be issued to combat units. The procedure for re-equipping a unit with new aircraft was standard. A fighter air regiment that had suffered losses at the front turned over its remaining serviceable aircraft to neighboring units. The personnel of this regiment were sent to the 22d ZAP. Here over the course of 1-2 months the regiment was re-trained, reconstituted in personnel up to TOE [table of organization and equipment] level, issued new equipment, and then returned to the front. Losses in aircraft of the new type were also made up by deliveries from the same 22d ZAP.

This is one of the key aspects of solving the mystery of why the Soviets got so much mileage out of this aircraft when nobody else could. They liked it initially and recognized it's potential, they had already had experience with Anglo-American fighters and had recognized certain problems they wanted to avoid with the P-39. So they collected all the ones they were sent in some airfield in Siberia, had test pilots fly them, did a complete workup on systematic adjustments, some already widely known like removing the wing-guns to save weight, but others were less widely understood like winterizing and working out maintenance systems in advance. For example they had to modify all Anglo-American fighters so that all fluids could be drained out every night (not just during overhauls) during the Winter, which meant adding plugs and drains on some systems not designed for it - and do it in such a way that would not damage hydraulics, coolant or oil. They did this much more carefully with the P-39's thanks to the work-up, by comparison with the P-40's and Hurricanes this was done in the field, haphazardly, often with damaging results. Another major issue was the "oil culture" and fuel requirements. Finally they trained their pilots to use the new aircraft and worked out tactics (exploiting the radios, among other things) for their optimal use.

One of the big differences between the P-39's and the P-40's and Hurricanes they had gotten earlier was that the P-39's came with spare engines and at least some spare parts. The other parts and supplies were figured out by Soviet engineers, copied as needed added to the Soviet logistics systems. Thus when P-39 engines burned out, as they quickly did in field conditions partly due to using them at high power settings, they could be replaced with new engines. This was much more of a problem with P-40's for example which initially came without any spare engines.

Once all of this was all worked out, and only then, the Soviets committed the P-39 in some numbers, and it caused something of a shock to the Germans.

Why they liked it so much

• It was the most similar to Soviet fighters. The P-39 was the only Anglo-American single-engined fighter with a cannon in the spinner plus nose guns. Their aerial gunnery training was mostly oriented toward nose guns and most (except I-16 pilots or those checked out on P-40's or Hurricanes) were not used to wing-guns. The P-39 was streamlined like a Soviet fighter. It was agile and climbed well. These characteristics endeared it to the Russians and marked it for the careful work-up it got.
• It was fast. Properly stripped down, the P-39 was faster than a Bf 109E at low altitude and arguably, maybe even Bf 109F. No Soviet planes could match this down low (the MiG 3 could at high altitude only but that really didn't matter in combat along the Russian Front).
  
• They got some new ones. Most of the P-40's and Hurricanes they had gotten to that point were already worn out battle veterans with weakened engines. But the British didn't use their P-39's very much at all before sending them on, and the Americans sent new ones.
  
• It had good radios. The Soviets had been unable to get enough radios into production and the ones they had suffered from very short range and ineffective transmitters, due to ineffective grounding and other problems. All the Anglo-American planes, the American in particular, had good reliable radios for both transmitting and receiving. This was a huge help for the Soviets!
  
• It was all -metal. Soviet planes were mostly made with substantial wooden parts, using new types of plywood which had not in all cases been fully developed and sometimes failed in flight. The P-39 had none of these problems.
  
• Superior build quality. All of the newer Soviet fighters - MiG-3 / La GG-3 / Yak 1 / Yak 7 etc., suffered from severe problems with build quality. Many parts which would be interchangeable on a Western fighter were unique one-off's on Soviet planes. Variations in production quality, which in many cases was being done in factories that had just been moved across the Urals and didn't even have roofs, could mean that an aircraft with an official speed of 350 mph was in reality limited to 280 or 290 mph. The early P-39 didn't have the world's best build quality (some serious defects were revealed by British testing such as landing gear doors opening up at speed etc.) but it was better than all of the newer era Soviet planes up until probably 1943.
• The altitude ceiling didn't matter - almost all of the bombing in the Russian Front zone was tactical and there was often a cloud ceiling at ~4-5,000 feet especially during the long winter. So not only did most of the fighting take place at low altitude the Germans couldn't use their superior climb and ceiling to attack from above all the time like they did so much in North Africa.
  
• They liked the heavy armament and heavy construction. The Soviet pilots actually liked the Oldsmobile 37mm as it allowed them 'authority' in a head-on pass with German fighters (who would veer off to avoid what they described as an "anti-aircraft caliber weapon") and the Soviets seemed to be able to get it working, although in some cases it was replaced by 20mm guns. They also felt the P-39 could survive belly landings which would destroy most other aircraft.
• Dive speed and high-G turns. One effect of the heavy construction was that the P-39 could out-dive most other Soviet planes, which had fairly low speed limits due to their partly wooden construction and typically uneven-build quality. The P-39 could dive very fast and could evade Bf 109's this way. This was key to the survival of Soviet P-39 pilots, the ability to disengage. This also meant that the P-39 could pull higher-G turns (so long as the pilot could keep it out of a Spin) than some other Soviet types.

Most of this of course is well known. So we can see why the Soviets liked the P-39. The question remaining is why they did so well with it compared to say, the British, the Americans, the Free French, the Italian Co-beligerant forces who suffered from it so badly, and whoever else got stuck with it (I think Australians maybe?). This is the biggest question to me.

Why the Soviets did so well with it compared to others

• The main reason is I think the big workup described in that article.on Leand Lease P-39's. In general with early war Anglo-American aircraft, success seemed to hinge on modifying the aircraft appropriately for actual use (as opposed to however they arrived from the factory) usually involving both weight saving and maintenance issues, and training on the particular fighter type. Flying a P-39 in combat right out of flight school was a recipe for death. The Soviets solved both of these problems with their extended workup of the P-39.
  
• The lower altitude ceiling - the tactical flight ceiling of the Russian Front battlefield really made a difference. It was a low-altitude battlefield, and due to the frequent cloud ceiling, German fighters often could not attack from above. Almost all of the bombing on both sides was dive bombing or close-support (Sturmovik) low altitude attacks. This was one of the main weaknesses of the P-39 for other Theaters but it just didn't matter nearly as much on the Russian Front.
  
• Range didn't matter as much on the Russian Front- I think range is the main reason the P-39s did so poorly in general in the Pacific. Altitude ceiling of course was more important there too, since the Japanese were using level-bombers that were coming in at 20-25,000 feet. But short range exacerbated that problem because short range meant less time to get up to altitude. But the Russians were already operating from forward airfields close to the front and combat was at low altitude, so range wasn't as important.
• The Russians were used to twitchy planes. I think this is one of the other main factors. Western allied pilots were afraid of the P-39, they didn't trust it, because it was somewhat unstable aircraft which could go into an unforgiving spin (the 'flat spin' and tumble are debated issues, but lets agree a spin in a P-39 could be dangerous). The Soviets had a head start on this due to the 4 month training and evaluation period they did, but they also had a lot of pilots already used to 'twitch' fighters and able to fly well in them and get kills in spite of their touchy handling. The I-16, the LaGG-3, the MiG 3, and the early Yak 1 were all known to be 'twitchy' fighters. Many Soviet pilots assigned to P-39 fighters came directly from flying these somewhat 'difficult" planes. This I suspect is one of the other crucial missing ingredients.
• The Soviets had some input into the aircraft development. Later model P-39's were adjusted according to feedback from their only happy customer, the Soviets, and the P-63 was basically built to Soviet specifications and under direct Soviet supervision.

I think ceiling and range were the two biggest performance issues preventing the P-39 from doing well in the Pacific. i suspect the 'twitchyness' and training were the major issues in the Med.

Anyway, that's my $.02

S

 

[buffnut453]

Great post Schweik. The info about the work-up time taken by the Soviets is particularly enlightening. I think your assessments of why the Soviets succeeded when others failed also bang on the money.

 

[Shortround6]

I would agree with everything except

It was fast. Properly stripped down, the P-39 was faster than a Bf 109E at low altitude and arguably, maybe even Bf 109F. No Soviet planes could match this down low (the MiG 3 could at high altitude only but that really didn't matter in combat along the Russian Front).

By late spring or early summer of 1942 the Bf109E was fading fast from front line inventory (if it was there at all) and the 109G was starting to be introduced during the summer.
I would also note that the Mig-3 was pretty much out of production in Jan of 1942 with only small numbers trickling out built of spare parts. An overhaul/repair facility did help keep some in operation but one book says only 134 in service (and not all combat capable) in May of 1942. The Mif stayed in service in ever decreasing number until 1943 but there was never any question of it coming back or equipping any new units.
This makes it's performance vs the P-39 almost irrelevant except for academic purposes.

 

[Elmas]

*snip*
I think ceiling and range were the two biggest performance issues preventing the P-39 from doing well in the Pacific. i suspect the 'twitchyness' and training were the major issues in the Med.
*snip*
S

I generally do agree with you but I suspect that the 'twitchyness' affected quite a bit P-39 as a gun platform. That, in pair with the lousy armament, put P-39 clearly at a disadvange in a fighter to fighter combat, unavoidable in ETO and PTO, while in RTO, in which the Luftwaffe lost the vast majority of his transport force, Ju 52 and He 111, flying relatively low and with small escorts, could have been easy game. Luftwaffe had to keep a difficult balance between fighters defending German towns in ETO and fighters escorting transports in RTO. End 1942, with P-39 in numbers, Stalingrad.

 

[DarrenW]

I would say that the increased weight will affect climb more than the drag will affect speed.

So in your opinion how much extra weight would the P-39N have then? It gained two .50s but lost four .30s. Did one .50 cal machine gun weigh more than twice that of a .30 cal? You know a lot more about this than I do so just curious. Maybe it was the fairings that added the extra weight???

 

[Shortround6]

You can find the weights on the P-39Q and P-39K/L weight charts.
Basically it was 99lbs for four .30 cal guns and 150lb for two .50s.
Weight of ammo was 262lbs for the K/L (300rpg for the .30s) and 370lbs for the Q.

 

[DarrenW]

You can find the weights on the P-39Q and P-39K/L weight charts.
Basically it was 99lbs for four .30 cal guns and 150lb for two .50s.
Weight of ammo was 262lbs for the K/L (300rpg for the .30s) and 370lbs for the Q.

Excellent!

 

[Shortround6]

Excuse me, that weight is the total weight of ammo for all guns.

 

[XBe02Drvr]

I suspect that the 'twitchyness' affected quite a bit P-39 as a gun platform. That, in pair with the lousy armament, put P-39 clearly at a disadvange in a fighter to fighter combat, unavoidable in ETO and PTO, while in RTO, in which the Luftwaffe lost the vast majority of his transport force, Ju 52 and He 111, flying relatively low and with small escorts, could have been easy game.

I beg to differ on the twitchiness angle. Twitchiness is usually a low speed/high AOA phenomenon, unless workmanship or shoddy materials has weakened flight controls. The Soviets praised the high speed controllability of the 'Cobra and used tactics that took advantage of it. The twitchiness comes into play when you are foolish enough to get into a high G, energy draining knife fight with a Zero at tropical air densities and altitudes where your aircraft is running out of steam. This also is where dealing with the three separate trajectories of your gun package is at its most vexing.
Now let's go to the forested plains of NW Russia. (NOT Siberia, BTW). Bitterly cold, air so dense you can cut it with a knife, one less trajectory to deal with, and all your remaining firepower boresighted line of sight. Combat is high speed, down low, and against fighters optimized for altitude, while yours has been carefully adapted and optimized for this environment, and flown by pilots used to living and fighting rough. What more could a poor, maligned venomous snake ask for?
BTW, the victory tallies in the Lend Lease article don't seem to show high kill numbers against LW bombers and transports. Looks like mostly fighters. Also, not many kills against JU-87s. I thought they were pretty numerous on the Eastern Front. Were they depleted by this time, or was it due to their agility and their tail gunner?
Cheers,
Wes

 

[Shortround6]

We may be getting into arguments about semantics. One man's "twitchy" is another man's "highly responsive"

I have a brother-in law who owned a Mudry Cap 10 for a number of years

NOT his.
He would fly it when giving rides to other people with his forearm resting on his thigh to avoid over controlling the plane.
One time some old college buddies wanted to rent a Cessna 172 and have him fly it. He went up for a check ride with an instructor first as it had been years since he flew a 172. After a 1/2 hour he landed and called it off, he had been under controlling the 172 the whole time.

 

[CORSNING]

Could you explain further what you mean by "operational"? Both the P-47D and F4U-1A were operational by this time. What am I missing here? Also, you did asked people to "help you out".

Operational: A fully combat ready aircraft in a fully combat ready unit positioned in an
area capable of putting a hurt on the enemy immediately. And, proven themselves
so by putting their aircraft in hostile air.

Thank you Darren, you are right I did ask for help of which P-47D variant was in fully combat
operational service by 25 December 1943. That was the limiting date that pbehn put on his
post. So I used that limitation. Wuzak is partly right about the P-39N's luck against the P-38J-5.
While I believe the Spitfire 14 would do just fine against the Airacobra at tree top levels, I
believe the J-5 lightning would more than have its hands full in a maneuvering contest.

 

[Dimlee]

I generally do agree with you but I suspect that the 'twitchyness' affected quite a bit P-39 as a gun platform. That, in pair with the lousy armament, put P-39 clearly at a disadvange in a fighter to fighter combat, unavoidable in ETO and PTO, while in RTO, in which the Luftwaffe lost the vast majority of his transport force, Ju 52 and He 111, flying relatively low and with small escorts, could have been easy game. Luftwaffe had to keep a difficult balance between fighters defending German towns in ETO and fighters escorting transports in RTO. End 1942, with P-39 in numbers, Stalingrad.

RTO - Eastern Front, I assume.
P-39 did hunt Ju 52 of course as well as any other fighter. Those were rare operations. Probably the most famous (for P-39): free hunting of 16 GIAP over Black Sea in 1944.
As for "twitchyness" as of a gun platform - this is one of those questions about Soviet P-39 which were (and probably still are) subject of endless discussions in Russian language community. Same as many other: M4 cannon qualities, flat spin risks, engine overheating, agility, etc. etc.