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P39 What If - 7/12/2020 2:12:03 AM   
wga8888


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What if the P39 had a turbo-supercharger? (I think it was dropped as there was no room under the hood). If it had one, what is the guesstimation of its performance as a fighter/interceptor?

As it was, it was used in the Pacific as it was available in numbers. One fights the war with what you have.

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RE: P39 What If - 7/12/2020 2:36:11 AM   
Chickenboy


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quote:

ORIGINAL: wga8888

What if the P39 had a turbo-supercharger? (I think it was dropped as there was no room under the hood). If it had one, what is the guesstimation of its performance as a fighter/interceptor?

As it was, it was used in the Pacific as it was available in numbers. One fights the war with what you have.


Re-reading Bergurand's excellent "Fire in the Sky" now. He goes into quite a bit of detail with regards to airframes' strengths and limitations. His opinion was that the P-39 was a capable aircraft at <10,000 feet, but very difficult to work with above that altitude due to the lack of supercharger. In the 10,000-20,000 feet window (the A6M2 sweet spot), it performed poorly against the opposition as a result. A supercharger would have made performance at this altitude more reasonable, but it was unlikely to be a war-winning weapon against the heretofore unchallenged Zero.

Superchargers, at this stage of the war, were mechanically problematic as well. So (in game terms) the SR would have had to increase by at least 1 (go from 1 to 2 IIRC). Such operational limitations (fewer aircraft ready to fly in primitive SOPAC conditions) may have offset the gain in performance from a supercharger.

Net: net, a marginal increase in mid-altitude performance, offset by poorer reliability / fewer operational aircraft at the schwerpunkt.

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RE: P39 What If - 7/12/2020 2:53:00 AM   
Lowpe


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I found it interesting that the Russians liked the later version of the planes very much.


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RE: P39 What If - 7/12/2020 2:56:52 AM   
Chickenboy


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quote:

ORIGINAL: Lowpe

I found it interesting that the Russians liked the later version of the planes very much.


For what they were using it for-mostly low-level ground attack sort of stuff (think IL-2), it was great. Did they swap out the nose-mounted 37mm for a 20mm system?

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RE: P39 What If - 7/12/2020 3:12:39 AM   
Lowpe


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quote:

ORIGINAL: Chickenboy


quote:

ORIGINAL: Lowpe

I found it interesting that the Russians liked the later version of the planes very much.


For what they were using it for-mostly low-level ground attack sort of stuff (think IL-2), it was great. Did they swap out the nose-mounted 37mm for a 20mm system?


Didn't one of their best Aces fly the plane, even shooting down a misidentified American plane or two in dogfights?



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RE: P39 What If - 7/12/2020 3:44:40 AM   
RangerJoe


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I thought that the Russians used it as a low level fighter. The combats tended to be lower level on the Eastern Front.

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RE: P39 What If - 7/12/2020 3:59:13 AM   
Lowpe


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Quick search:

In fact, five of the Soviet Union’s top ten fighter aces primarily flew P-39s, including the number two scorer Alexander Pokryshin with fifty-nine kills (forty-eight on the P-39) and number four scorer, Grigory Rechkalov (fifty-six kills, all but six on the American fighter), though exact totals vary slightly across sources. These Soviet aces each individually scored more kills piloting P-39s than any other Allied pilot did flying any American fighter plane in World War II—quite an achievement for a designed deemed inadequate by the U.S. Army Air Corps!

Russians did mod the plane quite a bit, often removing the wing guns and even swapping out the engine and of course they were flying later versions than the early 42 ones AFBs complain about.


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RE: P39 What If - 7/12/2020 4:25:50 AM   
BBfanboy


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quote:

ORIGINAL: Lowpe

Quick search:

In fact, five of the Soviet Union’s top ten fighter aces primarily flew P-39s, including the number two scorer Alexander Pokryshin with fifty-nine kills (forty-eight on the P-39) and number four scorer, Grigory Rechkalov (fifty-six kills, all but six on the American fighter), though exact totals vary slightly across sources. These Soviet aces each individually scored more kills piloting P-39s than any other Allied pilot did flying any American fighter plane in World War II—quite an achievement for a designed deemed inadequate by the U.S. Army Air Corps!

Russians did mod the plane quite a bit, often removing the wing guns and even swapping out the engine and of course they were flying later versions than the early 42 ones AFBs complain about.


I bet a lot of those kills were Stukas. The Germans kept using their Stukas long after they should have been withdrawn. Fixing up the Stuka with a 37mm tank buster cannon probably didn't help it's agility either ...

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RE: P39 What If - 7/12/2020 4:28:45 AM   
RangerJoe


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I believe that it was the British that wanted the 20mm and other changes, hence the P-400.

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RE: P39 What If - 7/12/2020 4:58:28 AM   
Jorge_Stanbury


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a turbocharger was not possible with such a small plane. You need 2 engines (P-38) or a massive plane (P-47) to consider it.

But the P-63, with a supercharged engine, more or less answers that question; good, much better than the P-39 but not good enough to replace the already big fleets of P-38s, P-51s and P-47s

For the Russians: it was a plane that fits perfectly the conditions of their war; at lower altitudes the P-39 performance was equivalent to any 1st rate fighter
Plus they got a well made, reliable plane, with good reflector sights, good radios, good ergonomics. The Soviet designs were surprisingly good, at least on prototype, but they were crudely made due to war constraints, some even lacked sights

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RE: P39 What If - 7/12/2020 1:35:23 PM   
PaxMondo


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Russians did swap out the 37mm for the 20mm hispano almost unilaterally. The 20mm c/l hispano was very effective. The wing guns were often removed to improve the already very impressive roll rate which left it with only one gun albeit a very capable one that rarely ever jammed.
the high roll rate made the P39 an especially effective low level fighter, and yes, eastern front was fought at lower levels than the asia as the primary bombing missions were ground support, not strategic or base suppression.
The plane was designed for the super charged allison engine (same as the P40/P38), BUT while allison had the tooling in place to increase engine production, their induction vendor did NOT, hence the 9 month lag in production of the P40 and P38's and the P39 never getting it. super chargers don't take that much space, at least not compared to turbo or twin chargers, but in any case the P39 was designed and initially tested with it.
If you add the spercharger to the P39 just copy the P40 SR and adjust the altitude bands to mimic the changes that the P40 has. If you do, just remember that this is fantasy, those super chargers never existed and couldn't have. What you can do is replace P40 with P39, and THAT is a very good thing for the USAAF. The P39 was a far better plane, supercharged, then the P40 (it was also designed later), however the designer P*** off the army brass and it got no supercharger in the allocation process and hence was built in very small numbers until the russians took it up. Still not as good as the A6M, but a far more capable counter to the A6M than the P40.
The one unchangeable issue with the P39 was the cockpit: small. 5'8" was the max height that could comfortably fit, and 5'6" was the design. I was 5'10" when I tried to get into one (I hadn't finished growing) and I could just fold myself in and close the canopy, but I don't think there was any way I could have flown it. I was hunched over the stick with no way to see back or over my shoulders. You needed to be a small man, even by 40's standards, to fly a P39.

One of my most favorite "What-ifs" for the allies is to replace the P40 with supercharged P39's in the my ironman variants. It helps the allies a lot in the early war.

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RE: P39 What If - 7/12/2020 3:05:44 PM   
Jorge_Stanbury


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Removing the wing guns left 1 cannon (37mm or 20mm) + 2 50cal machine guns, and this is a lot of firepower from a Soviet point of view; no Soviet fighter, with the exception of the old I-16 had anything better; Soviet designs prioritized performance (rolling, maneuver) over firepower, if they needed a lot firepower they simple use numerical superiority

I haven't read about swaping the 37mm; the early versions were former RAF, and therefore they got Hispanos, but I haven't read anywhere they were fond of Hispano 20mms.

Check this interview, if they disliked the 37mms they could had swapped for their own ShVAKs, and they didn't

https://lend-lease.net/articles-en/conversations-with-n-golodnikov-part-three-p-39-airacobra-and-yaks/


A. S. Describe the machine guns, cannon, and sights.

N. G. The first Cobras that we received from Moscow had a 20mm Hispano-Suiza cannon and two heavy Browning machine guns, synchronized and mounted in the nose.
Later the Cobras arrived with the M-6 [should be M-4 – ed.] 37mm cannon and with four machine guns, two synchronized and two wing-mounted. We quickly removed the wing-mounted machine guns, leaving one cannon and two machine guns.
The Cobras had interesting charging and trigger mechanisms for the cannon—hydraulic. At first, in the English variant of the Cobra, we had a lot of trouble with them. The hydraulics froze up. It seems that the Cobras had been intended for North Africa, because the hydraulic fluid was thick and clogged up the passages in the hydraulic cylinders. Our technicians replaced the hydraulic fluid with Soviet fluid and enlarged the diameter of the passages. The charging mechanism began to work normally. By the way, on these Cobras all the hydraulics froze, not just the charging mechanism.
The machine guns were charged mechanically, by hand, with a special handle. The receiver portion of the machine guns extended back into the cockpit. The triggers for the machine guns were electric. The sight was American. A very simple sight—a reflector and crosshairs.

A. S. Nikolay Gerasimovich, if you compare the Hispano-Suiza 20mm cannon and the ShVAK, which was better in your opinion?

N. G. Ours, without a doubt. The ShVAK was twice as reliable. The Hispano simply required an unbelievable amount of maintenance. The smallest exposure to dust, congealed lubricant, or any other kind of little thing, and the gun would not fire. Very unreliable.
The ballistics of our cannon were better. Our cannon had a flatter trajectory, which is significant for applying lead. When you talk about the Yaks, then one didn’t even need a sight. The tracers were almost straight, take aim and fire, and where the nose is pointing is where the rounds struck.
Our ShVAK had a higher rate of fire. Regarding the target effect, these two cannons were about equal. In either case, there was no difference that I could see with the human eye.

A. S. Was a 37mm cannon necessary? Wasn’t this too large a caliber for a fighter? You had so few rounds of ammunition. And wasn’t its rate of fire slow?

N. G. One cannot say that the 37mm cannon was a disadvantage or an advantage. Look at it from this perspective. The M-6 cannon had its strong and weak points. One had to take advantage of the strong points and compensate, as much as possible, for its weaknesses.

These were the weaknesses: 1. Low rate of fire. 8 rounds/second [this is incorrect—the correct rate is slightly over 2 rounds/second (130 rounds/minute) – J.G.] This is indeed a low rate of fire.

2. The ballistics of the projectile were abysmal. The flight trajectory of the projectile was arching, which required large lead angles. But again this was at long ranges, especially when firing at ground targets. When firing at ground targets we had to apply two rings of the sight for lead.

3. Minimal ammunition supply. Thirty rounds.

All these deficiencies could be compensated for by proper selection of firing range. If one fired from 70—50 meters, there was sufficient rate of fire, the ballistics at this range were acceptable, and the lead required was minimal. Thus, all the weaknesses of the 37mm cannon listed above revealed themselves only at long ranges.

Now regarding the strengths: 1. The projectile was very powerful. Normally, one strike on an enemy fighter and he was finished! In addition, we fired this cannon at other types of targets. Bombers, vessels at sea. The 37mm cannon was very effective against these targets.

2. The M-6 cannon was very reliable. If it was properly maintained it worked very reliably. We could charge the cannon only one time from the cockpit, but this one re-charging was completely sufficient. If this cannon malfunctioned, it was due entirely to unqualified maintenance.


< Message edited by Jorge_Stanbury -- 7/12/2020 3:08:03 PM >


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RE: P39 What If - 7/12/2020 10:41:51 PM   
bomccarthy


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I think there has been some confusion in terminology - the P-39 did have a single-stage, single-speed mechanically driven supercharger, as did all combat aircraft in WWII, which maintained sea-level horsepower up to 12,000 feet. The XP-39 also had an exhaust-driven turbo-supercharger (as a second stage, blowing compressed air into the mechanically driven main stage supercharger), which maintained sea level horsepower up to 25,000 feet. However, the Army decided to have the turbo removed from the XP-39 in January 1940, so it was never fully tested with it. For background on this, see Francis H. Dean, America's Hundred-Thousand, Schiffer Publishing, 1997, pp. 188-94; and Graham White, Allied Aircraft Piston Engines of World War II, Society of Automotive Engineers, 1995, pp.263-305).

White cites problems with the GE turbo in the late '30s for the Army's decision to delete it from the P-39. However, the P-38 was undergoing testing at the same time with the turbosupercharged Allison and the Army contracted for the turbosupercharged P-47 in September 1940 (which itself was derived from the turbosupercharged P-43). With the P-40 as the only low-altitude fighter in its inventory, the Army may have felt that it needed another, since two other high-altitude fighters were already were already slated for operational service by the end of 1942.


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RE: P39 What If - 7/13/2020 2:28:30 AM   
Lowpe


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Great stories and insights into a fighter with great lines!

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