Besides the props, what are the diferences between the P-39 and P-63?

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grampi

Senior Airman
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63
Aug 22, 2013
I would think the P-63 is probably the later of the two models, but there doesn't seem to be a whole lot of differences between the two. I'm curious as to why they felt the need to designate two different models when it seems like they could've just designated the P-63 as a later model of the P-39...
 

Totally different airframe. 4' longer span and longer fuselage to accommodate the 2 stage Allison engine. Much improved cooling system and much easier to service than the P-39. I think the only thing that was interchangeable was the cockpit doors.
 
warbird51 said:
Totally different airframe. 4' longer span and longer fuselage to accommodate the 2 stage Allison engine. Much improved cooling system and much easier to service than the P-39. I think the only thing that was interchangeable was the cockpit doors.
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Any particular reason they went with an Allison power plant instead of a Merlin?
 

New fuselage, not just in order to accomodate the 2-stage V-1710 easier, but also with shorter length between prop and back of pilot's seat (a try to remedy the tricky handling?). A whole new wing, of laminar-flow 'flavor' offering lower drag despite being thick; it also enabled to carry ADI fluid + fuel + ammo for the wing guns. New engine and tail.

grampi said:
Any particular reason they went with an Allison power plant instead of a Merlin?
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As-is, the V-1710 was available for 'remote installations', much due to it's reduction gear not being intergral with crankcase. Merlin needed a redesign of the crankcase, so the reduction gear can be separated. The resulting engine, Packard Merlin V-1650-5, was running late vs. 2-stage V-1710. One also needs to provide for intercooler and it's radiator vs. V-1710.

P-63 have had it's shortcomings (initially the weak fuselage, not enough fuel to provide LR escort), engine choice is/was well down the list.
 
Weak fuselage? On the P-63? Never read that. There was some speculation on the P-39 having a weak aft fuselage
 
I never read that, either. But, I was also not looking for it. Tomo is usually pretty accurate when he gets specific. So, while I haven't read about it, I also have no argument. I know they "strengthened" the "pinball" P-63s, but was not aware that not playing flying target might reveal a weak fuselage.
 
I also understand the P-63 had a pretty impressive climb rate. Was the P-39 like that too?
 

When P-39, Race 75 "Cobra I" crashed just before the 1946 Cleveland air races, there was concern that the aft fuselage had failed. So, they added a .25" external strap on both sides of the aft fuselage as a precaution. None of the P-63's that raced at Cleveland received that modification as I recall.
 
warbird51 said:
Weak fuselage? On the P-63? Never read that. There was some speculation on the P-39 having a weak aft fuselage
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At pg.412 of the 'America's hundred thousands' book, the remark dated April 45 states: 'The Russians express dissatisfaction with the P-63, saying the plane is weak. The aft fuselage is beefed up in a field modification'.

grampi said:
I also understand the P-63 had a pretty impressive climb rate. Was the P-39 like that too?
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Both P-39 and P-63 were, at least when compared with other US aircraft, very light. With plenty of power available from late 1942 and late 1943 respectively (up to 1450 and up to 1850 HP, respectively), we are bound to see good climb figures.
 
Of course some P-39's had four blade props, too..

One big difference from the P-39 was that the P-63 had a laminar flow airfoil section, but that was only one aspect of the completely new airframe.

The engine was still a V-1710, which in the P-39 was supposed to have a turbosupercharger but that did not work out; the airframe was too small for the turbo to be mounted in a manner that did not cause excessive drag. The V-1710 in the P-63A was equipped with a mechanically linked auxillary supercharger, hooked via the starter connection, rather than a turbo. The P-63B was supposed to use the V-1650-5 Merlin but they never built it. Given that Merlins were needed for P-51's, it is not surprising that they stuck with the V-1710.

The P-63 also used a lot of Magnesium in the structure. I think the ailerons were all MG.


 
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Another important systems that were changed were cooling systems, both for engine coolant and oil. The 2-stage V-1710 especially needed an enlarged oil cooling system (not just due to increased engine power, but also to cater for hydraulic drive for auxiliary S/C), the one installed on P-39 will not cut it.
 
P-63 was irrelevant in my opinion. Bell and the AAF could have installed the two stage Allison in a P-39 easily enough and had them from May '43 (when the engine was in production) instead of waiting until basically the end of '43 for the P-63 to get into production.
 
Take a look at the pictures of the single stage and two stage V-1710. You'd have never got that 2 stage engine into the P-39; the greater length would have prevented it. Aside from that, even in the P-63 and F-82 they did not have room to install an intercooler, which that installation sorely needed.
 
Actually the size of the engine compartment was exactly the same on both the P-39 and P-63. Same amount of room for the second stage in either plane.
 

The lack of an intercooler had nothing to do with a lack of space. The P-63 lacked one because the original design sucked and there just wasn't enough production capacity to meet all the demand. For the most part you only need a intercooler for high power operation. If you plan on using ADI there is no loss in power or a greater risk of detonation. At lower power settings the higher charge temperature will lead to a small loss in power.

The F-82 lacked one because the development wasn't complete and the AAF didn't want to spend the money. Tlack of an intercooler had nothing to do with The problems of the V-1710-143/145. The major problems were oil frothing and and spark plug fowling. The latter was caused by the spark plugs running to cold.
 
The auxiliary supercharger added 175 lb and that was waaaaaayyyy in the back, in an airplane with legendary CG problems. Aside from that I don't know where they would have put the radios. In the P-63 modified with a second seat for the Bell X-1 test flights they had to take the auxiliary supercharger out. They clearly put the radios up front where the guns had been, as is evidenced by the AN-104 antenna on the nose.

And I did not say that they lacked the space for the intercooler. In fact, Allison designed and tested a liquid cooled intercooler (not aftercooler) for ther two stage engines, so there was no need to affect Merlin production, not there was any reason it would have. I think that originally neither the P-39 nor the P-63 could accomodate an air to air intercooler, which was the way everyone did it before Stanley Hooker came up with the idea of a liquid cooler afterccoler for the special high altitude Merlin. In the F-82 they had a large water injection tank near the engine and I think an liquid cooled intercooler would have fit in that space. NAA tried to fix the V-1710 in the F-82 by installing antibackfire screens but when word got back to Allison it appears they had their friends at GM call SECAF Symington because NAA was told to stop fooling with things they did not understand. Allison had its hands full with the J-33 and had no further interest in the V-1710, especially after crash of the XB-42 due to engine failure.

 
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My apologies I misread what you said. I largely agree with you. I believe the claim that NAA installed backfire screens originated with Schmued. He wasn't actually involved with the F-82 project at that time. He claimed Forrestal intervened on GM's behalf. Regardless of the details backfire screens will only prevent backfires from damaging the intake. They will not prevent the actual backfires or othe mechanical problems they can cause.. The simple and cheap interim solution was to limit the G6 to power levels (60in @ 3200rpm) that the intake manifold could safely tolerate backfiring and research why the F-82 specifically. It's important to point out that this backfire problem was exclusive to the F-82. No other aircraft fitted with a two-stage Allison experienced this problem. This includes the Allison's XP-51J test mules that were refitted with G6 prototypes. It took about two years to sort out and remedy the problem. The truth is that the F-82 was largely obsolescent the moment it entered production and the USAF did not want to spend more than the minimum necessary.
 
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