XP-39 II - The Groundhog Day Thread

FLYBOYJ said:

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Currently reading this P-39/P-400 Airacobra vs A6M2/3 Zero-sen: New Guinea 1942 and Wagner's report is an interesting assessment, based on his and his pilots perpective.

According to Claringbold one Zero was lost and the pilot FPO2c Hideo Izumi was killed.
Four P-39's were lost, with one pilot MIA, but not mentioned in the report?! The cause of loss given for the other 3 P-39's also differ from the report.
41-6930
41-7128
41-7186
41-6982

The combat the following day I have to re-check in the book but I think it is related differently; there is a Zero shot down, but I don't think a P-39 is lost?

The P-39 in the foreground is a P-39N-1, the Mustang is an A-36A, the P-40K-15-CU - the P-47 and P-38 I can't make out.

And Lo and Behold, that is a P-36A in the background, upper left!

That P-39 was used in USAAF evaluations, by the way.

Ivan1GFP said:

From the first combat report with P-39Ds, The Zeros encountered were reported as having larger cowls.
That factor is quite noteworthy.

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Given that the US pilots of the day often called every Japanese fighter a Zero that could also mean the previous Zeros those pilots encountered were Ki-43s

P-39 Expert said:

As we have discussed before, the engine compartment of the P-39 without the auxiliary stage supercharger was exactly the same size as the engine compartment of the later P-63 with the auxiliary stage supercharger. Exactly the same distance from the front of the engine section to the bulkhead at the rear. See the attached drawings. Now that is either an amazing coincidence or the P-39 was designed from the beginning to accommodate the auxiliary stage supercharger.

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Tomorrow I will demolish this claim. I was hoping to do it today but the material I need to do so is not at hand. The civil P-63 Pinball that I worked on in 72 had no ASB but the space where it fitted was very obvious and much of it was AFT of the split line. On the P-39 part of the oil tank intrudes forward of the split line. As such it is absolutely impossible to fit the ASB in a P-39. The rear fuselage extension on the P-39E would almost certainly have been the same concept as on the P-63 with the oil tank moved aft to make room for the ASB.

Elmas said:

It has to be said that in Italy, expecially in the South, until 1960, practically all the farming was done with carts like these.

I remember perfectly well, when I was a young lad, the clinging of the bells of the oxen going to work at sunrise, when I spent my summer holidays in a tiny village of the inner part of Sardinia, and also remember that in Sicily, same period, fishermen went to sea by oar and sail. (Not joking...)

For the average Italian, outside public transport, until early-mid 50s, when Piaggio started the production of the famous "Vespa" the only private transport available was the bicycle, and to have a car privately owned by practically every family we had to wait until early 60s, with the Fiat 600.

That, of course, does not mean that Italians could not master mechanics

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AND Italy had some very fast and technically advanced Schneider Trophy aircraft, winning four times. America only won twice.

PS I have fond memories of a (smaller) Fiat 500 Bambino with ejector doors just like the one in your photo. It was not as fast as a mini but it could go places that no mini could ever dream of getting to. Plus it had wind up windows and self adjusting brakes etc that the mini lacked. A truly fun vehicle.

MiTasol said:

Given that the US pilots of the day often called every Japanese fighter a Zero that could also mean the previous Zeros those pilots encountered were Ki-43s

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Hello MiTasol,

You could be correct, but there are a couple problems with this theory.
There are considerable shape differences between the Ki 43 and the A6M2 which were not noted.
The cowl size isn't particularly different between Ki 43 and A6M2.
There is no comment that they "new Zeros" now have cannon in their wings which probably would have been a pretty significant change.

I certainly wasn't there, so I am guessing as well.

- Ivan.

I guess the question then would be were there any Ki-43s based within the area where the combat took place that could have tangled with the Airacobras?

MiTasol said:

AND Italy had some very fast and technically advanced Schneider Trophy aircraft, winning four times. America only won twice.

PS I have fond memories of a (smaller) Fiat 500 Bambino with ejector doors just like the one in your photo. It was not as fast as a mini but it could go places that no mini could ever dream of getting to. Plus it had wind up windows and self adjusting brakes etc that the mini lacked. A truly fun vehicle.

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A Collegue, after his graduation, wento to work for Abarth.
Abarth used to modify Fiat cars for competitions
He told me that one time they installed on a Fiat 500 an overcompressed engine of 1500 cc and went to try she on the roads.
The most funny thing was the glimpse of other drivers when they were overtaken at more than 170 km/h, he told me....

I think we are letting national pride intrude on the discussion of how mechanically adept the Americans were.

It is not a question of how good a small group of engineers or designers were.

It is a question of how many troops (a percentage of total troops) had driven or worked on motor vehicles (or boats or industrial machinery).

What this means to an army (any army) is how much training is required to turn recruits into drivers or mechanics/fitters.
The army is going to put the troops selected for those jobs through some sort of training course and not just turn them loose.
How many hours or weeks should the course/s be given the average level of knowledge the troops bring from civilian life?
In case of casualties (or sickness) what does the 'reserve' of troops who did not go through the "school" look like.
This assumes the army is bright enough to steer people to the right jobs given their civilian experience. My father went to an civilian aviation school for 9 moths before WW II, he worked for Sikorsky on the VS-44 flying boat and then worked for Chance Vought building Corsairs. When He went into the Marines (only large scale user of the Corsair at the time) the Marines, in their infinite wisdom, sent him to school to be a signalman/radio operator.

My mothers father joined the army in WW I and wound up in Texas in the air corp as a machine gun instructor. Not on how to shoot them but on how to strip them and maintain them. I doubt he had ever seen a machine gun before. Between the wars he worked as a watch and clock repairman, gunsmith and machinist, during WW II he worked in a four man shop making parts for gyroscopes on old machinery driven by overhead belts. He was extremely mechanically adept. But his mechanical 'experience' training in 1917 was??????

Some people are naturally mechanically inclined. Even if from a primarily primitive agricultural area (and there some in the US) some people are going to catch on quicker. SOme people who have driven even a model T for years were never going to catch on (flat tire? call auto club.....or brother/cousin).

The American advantage was not that they were smarter or more mechanical adept 'naturally' but that they had much more experience driving/maintaining cars and machinery on average
per 1000 recruits. than other armies.
How good you were rebuilding a turret lathe in civilian life gives you some advantage in working on truck/tank but perhaps not as much as a guy who worked in a gas station and had seen any number of minor problems.

Peter Gunn said:

I guess the question then would be were there any Ki-43s based within the area where the combat took place that could have tangled with the Airacobras?

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Hello Peter Gunn,

The entire area of operations in New Guinea had both sides very close on a large land mass. The presence of Japanese Army units would have meant the presence of Ki 43 and other Army types.
These attacks were on the Japanese Navy airbase at Lae.
On the attached map linked, look toward the East at the Northern coast.
Look for the arrow marked Jun 1943.
It is amazing how little actual distance separated the two sides though a mountain range in between helped a bit.

- Ivan.

https://history.army.mil/books/AMH/Map23-43.jpg

windhund116 said:

No date on photo. Would be 1942-43, because of type of USAAF roundels?

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I was wondering because I think that is a P-36 at the top of the picture. I've never seen all those aircraft in the same picture.

SaparotRob said:

I was wondering because I think that is a P-36 at the top of the picture. I've never seen all those aircraft in the same picture.

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As I mentioned earlier, that is a P-36A and the other aircraft have either 41- or early production 42- serials plus the national insignia no longer has the "meatball" so this photo could be perhaps June of 1942.

Elmas said:

A Collegue, after his graduation, wento to work for Abarth.
Abarth used to modify Fiat cars for competitions
He told me that one time they installed on a Fiat 500 an overcompressed engine of 1500 cc and went to try she on the roads.
The most funny thing was the glimpse of other drivers when they were overtaken at more than 170 km/h, he told me....
View attachment 597278

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We need a "COOL" icon.

Ivan1GFP said:

Hello MiTasol,

You could be correct, but there are a couple problems with this theory.
There are considerable shape differences between the Ki 43 and the A6M2 which were not noted.
The cowl size isn't particularly different between Ki 43 and A6M2.
There is no comment that they "new Zeros" now have cannon in their wings which probably would have been a pretty significant change.

I certainly wasn't there, so I am guessing as well.

- Ivan.

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The Allies didn't recognize the Ki-43 as a distinct type until 1943. Prior to that point, all single-engine Japanese fighters with retractable undercarriage were Zeros, with the variation for the A6M3 identified when it entered service because of its clipped wingtips (and, of course, the Allied reporting names that were associated).

SaparotRob said:

I was wondering because I think that is a P-36 at the top of the picture. I've never seen all those aircraft in the same picture.

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Sorry, I have no history behind that photo.

Ivan1GFP said:

Hello Peter Gunn,

The entire area of operations in New Guinea had both sides very close on a large land mass. The presence of Japanese Army units would have meant the presence of Ki 43 and other Army types.
These attacks were on the Japanese Navy airbase at Lae.
On the attached map linked, look toward the East at the Northern coast.
Look for the arrow marked Jun 1943.
It is amazing how little actual distance separated the two sides though a mountain range in between helped a bit.

- Ivan.

https://history.army.mil/books/AMH/Map23-43.jpg

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Elements of the 26th Sentai flew Ki-43 out of New Guinea. Late 1942-43. The unit was decimated. So, they could have fought P-39s stationed at Port Moresby. From Fighters of Japanese Imperial Army. 1939-1945. Eduardo Cea. AF Editions. Pages 48-49.

In case anyone finds a photo the tail fin had "26" as stylized Kanji for "2" with Western "6" backwards and leaning.

Ivan1GFP said:

Hello P-39 Expert,



It depends on how you want to group things. Most books I have count the L through N models as the "Mid Production" series. There were about 240 M models produced and about 2000 N models produced.



This is still different from the 1.8:1 reduction gear originally used on the P-39C/D/F series. The propeller on the M was 11 feet 1 inch diameter. The N model changed the reduction gear ratio to 2.23:1 and used either a 11 feet 4 inch or 11 feet 7 inch propeller. The Q used a 11 feet 7 inch propeller.
The early series propellers on -35 and -63 engines were almost always 10 feet 4 1/2 inch regardless of whether they were Curtiss Electric or Aeroproducts manufacture.

You are correct on the reduction gear, but the 2:1 was also used on the D-2 with the -63 engine. I really can't be sure about the M propeller, some sources say the Curtiss prop was used, some say the Aeroproducts prop was used. I haven't read anywhere that either prop was larger then the 10'4" prop used on the earlier models.


This is a cool little bait and switch you are trying to pull here. There were plenty of P-39 models armed with the 37 mm cannon before the M model came along, notably the C, D, F, J, K and L.
To say the M had cannons weighing 140 pounds more is a pretty poor argument when the majority of US service models already carried the same gun as the M.

Guess I wasn't clear, didn't mean to imply that the 20mm was used in the M. The 20mm was used in the P-400 and the D-1. Point I was making was that the 140lb weight difference was compensated for by Bell to make prior and subsequent P-39 models balanced. Why would you say that I am trying to bait and switch?

- Ivan.

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Expand above.

MiTasol said:

Tomorrow I will demolish this claim. I was hoping to do it today but the material I need to do so is not at hand. The civil P-63 Pinball that I worked on in 72 had no ASB but the space where it fitted was very obvious and much of it was AFT of the split line. On the P-39 part of the oil tank intrudes forward of the split line. As such it is absolutely impossible to fit the ASB in a P-39. The rear fuselage extension on the P-39E would almost certainly have been the same concept as on the P-63 with the oil tank moved aft to make room for the ASB.

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I'm not sure what you mean by the term "split line?"

Look at the drawings of the P-39 and P-63 fuselages in my post #236. The distances are marked in inches. The engine compartments are exactly the same length. The bulkhead at the rear point of the triangle aft of the engine separates the engine compartment from the oil tank which was fully aft of that bulkhead.

The space for the aux. stage is exactly the same size on the P-63 as all P-39s including the E model that was the first to take the -47 engine with the aux. stage supercharger. Room for the aux. stage was created by moving the coolant tank from behind the engine to above the engine just behind the pilot. Coolant tank shape was changed to be flatter to fit in the new space. The aux. stage was then installed in the space formerly occupied by the coolant tank. The oil tank was aft of the aux. stage and aft of the bulkhead separating the engine compartment from the tail cone. Oil tank was in the same position on all P-39s and P-63s.

FLYBOYJ said:

Having worked on many aircraft (to include warbirds) I can somewhat agree with your field removal of some the equipment to save weight, 3 hours of maintenance is a bit skewed unless you're going to just hack the items mentioned out, not plug rivet holes and possibly leave wire bundles.

Your linear calculation does not address weight and balance of the items removed. If you're lucky enough to make the aircraft slightly tail heavy, it will fly faster but be more unstable, something already plaguing the P-39. You're comparing the C and D models and by your own post, no armor and no self sealing tanks. So you're making your point with performance numbers from an aircraft that was really not capable of entering combat????

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As I said before, for climb comparison purposes, the C and D as tested were identical. They had the same engine, propeller and aerodynamic shape. Only difference was weight. Didn't matter that the C model had no self sealing tanks or armor. What was proven was that a C model climbed 1000fpm faster than a D and was 836lbs lighter. This means that for every pound of weight saved the rate of climb increases by 1.2fpm. In other words, if you reduce the weight of a P-39 by 300lbs the rate of climb increases by 360fpm.

Yes the plane had to be in balance after the items were removed. Bell proved they could do that even with varying weights for propellers, nose cannons, aux. stage superchargers, rear armor plate and radio equipment in the tail. The plane was balanced on all those different forms.

GrauGeist said:

As I mentioned earlier, that is a P-36A and the other aircraft have either 41- or early production 42- serials plus the national insignia no longer has the "meatball" so this photo could be perhaps June of 1942.

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Correct. And the "Arnold Wings", those rectangles on either side of the roundel originated in June 1943. So the photo was sometime after the meatball was removed and the wings were added.