Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)

tomo pauk · May 11, 2021

P-39 Expert said:
Removing unnecessary/redundant weight from an airplane will improve performance on the same engine power.

It was done other way around - up-engine the existing aircraft type (whether by introducing a brand new engine type, or the engine type better than what was previously used), while 'upgrading' the fuel tankage or/and firepower, so it can do things the previous version was incapable for. It was done with P-38, P-51 and, finally, with P-47 (not in the same time). It was done (if belatedly) with Spitfire and Tempest.
A P-39 that lost 500 lbs of stuff you deem redundant is still not an answer to what USAF needs in 1943 - a fighter that can do at least 400 mph and climb well at 25000 ft while having 500+ mile combat radius (preferably 650 miles) while cruising at 300+ mph TAS. Even the P-51A was incapable of that with wing racks on.

V-1710 had only 79% displacement of a DB605 and 82% of a DB601. Comparable? No replacement for displacement.

Yes, comparable in size and weight - just as I've wrote above.
Seems like nobody said to the people at RR that they are not supposed to beat the 33.5 L DB 601 and 35L DB 605 with the 27L Merlin. Either they were wrong, or you are wrong with the displacement idea.

Two stage -93 had a critical altitude of 21500', simply move the carb from the auxiliary stage to the engine stage (like P-38 and P-47) and increase critical altitude another 3000'. DB601 critical altitude was 18000'.

The DB-601 critical altitude was at 13-14 kft, at least for the 601A.
Critical altitude says nothing about the engine capabilities. Merlin XX, DB 605A and BMW 801D all have had critical altitude of 18700 ft, power delivered there was very different. At 22000 ft, the V-1710 E11 (P-63A fighter) was making the same power as the DB 605A.

P-39E was not all new. Just a P-39D fuselage with the coolant tank reshaped and moved up right behind the pilot and the auxiliary stage installed in it's place. Fuselage was longer because tail cone was lengthened, but engine compartment where the auxiliary stage was located was the same size/length. Posted P-39/P-63 drawings many times, engine compartments are the same size. P-63 had the auxiliary stage, P-39 did not.

I know that P-63 have had the auxiliary stage, P-39 did not. Once someone plops the 2-stage V-1710 on a P-39 and have it flying, I'll believe.

drgondog · May 11, 2021

SaparotRob said:
Not a problem. I learned a lot and perhaps someone might model Captain Stephens' P-51B. I believe he flew with the 355th.

355th FS/354th FG 9th AF

GregP · May 11, 2021

The P-39 was already at aft CG, removing anything forward of the CG just makes it worse. There isn't anything much aft of the CG that can be eliminated. The Aft cabin armor plate is only 18.2 pounds. That ain't gonna' do much in the real world.

And a 2-stage Allison would not fit into a P-39. I've looked at it up close in personal, like inside a fuselage of a real P-39 with a tape measure, a few years back. It is NOT going to fit. If you MAKE it fit, you won't have a P-39. Might was well use a P-63, which is altogether a larger airplane into which a 2-stage Allison DOES fit and was designed so that it would..

buffnut453 · May 11, 2021

How many effing threads do we need that discuss removing "unnecessary" weight from the P-39? For pity's sake, we've flogged this topic to death on at least 3 threads already. Can we please, PLEASE drop the dead donkey and/or quit flogging the dead horse?

Shortround6 · May 11, 2021

tomo pauk said:
Seems like nobody said to the people at RR that they are not supposed to beat the 33.5 L DB 601 and 35L DB 605 with the 27L Merlin. Either they were wrong, or you are wrong with the displacement idea.

Well, No replacement for displacement works rather well if.................................................................
Both engines are using the same fuel for roughly the same BMEP.
If both engines are using about the same RPM
If both engines are limited to a limited power transmission set up.

When cars were limited to 4-5 speed transmissions it was harder to keep the small high revving engine on it's power peak.
With airplanes the constant speed prop keeps the engine turning within a few hundred rpm, broad band power not really needed (or think infinitely variable transmission between two limits) Power is changed by the throttle controlling the amount of air the supercharger is forcing into the engine.
Limit on the air going into the engine was the capacity of the supercharger, the ability of the fuel in use to avoid detonation. The ability of the cooling system to keep the temperature in limits. and finally the strength of the engine, nothing bends or breaks after several minutes at high power.

wlewisiii · May 12, 2021

If they had axed the P-39 and ordered the XP-51 right away, could Bell have also built more P-40's for Curtis? Not that it didn't have it's own quirks and flaws, but it was still a far better aircraft than the P-39 especially when flown with significant overboost.

Ovod · May 12, 2021

drgondog said:
Excellent relative to ? A6M, Bf 109F/G, Fw 190A, P-40, P-51, Spitfire V, VIII, IX or I-16 and Buffalo? As noted earlier the XP-39 was AWFUL and program nearly cancelled until NACA made bout a dozen critical cooling and aerodynamic changes to bring it to 'functional'.

How does the P-39 compare to the successful P-40? I always thought the P-39 was the more aerodynamically refined aircraft, a faster aircraft to the Curtiss in a straight line - what about climb and dive rate? I believe the P-40 had a better range and bomb load though?

Exactly one US pilot scored 5 victory credits in the P-39 in a target rich environment in SWP.

And yet on the Eastern Front the Soviets had numerous aces who flew on the Airacobra.

Ovod · May 12, 2021

SaparotRob said:
The Soviets operated their P-39's close to the front and mostly for ground support.

I don't think that was true. Soviets appreciated the P-39's air-to-air qualities and mainly used it for air defence and escort duties.

Marcel · May 12, 2021

Oh god, not another groundhog thread

drgondog · May 12, 2021

Ovod said:
How does the P-39 compare to the successful P-40? I always thought the P-39 was the more aerodynamically refined aircraft, a faster aircraft to the Curtiss in a straight line - what about climb and dive rate? I believe the P-40 had a better range and bomb load though?

I would not say that the P-39 was 'excellent when compared to the P-40'. The P-39 in its variations was slightly faster and climbed slightly faster and dived slightly slower - in other words marginal in performance advantage but not 'excellent' in comparison. Range was very different for full internal combat loading with significant advantage as well as external load advantage going to P-40. There was no theatre that US contested in which Range was not a key performance attribute.

And yet on the Eastern Front the Soviets had numerous aces who flew on the Airacobra.

The USSR liked the aircraft very much - primarily because it was a better fighter in quantity versus LW than existing operational Soviet fighters. As a weapons system it was far superior. That said the Yak 3 and LaaG 7 quickly replaced them as better front line fighters.

Additionally it should be noted that USSR air fighting doctrine for low to middle altitudes, and the fact that the P-39 was not required to contest the LW at high altitudes put the P-39 in its most favorable envelope. The early P-51 was 'excellent' in comparison to both the P-40 and P-39

P-39 Expert · May 12, 2021

Ovod said:
How does the P-39 compare to the successful P-40? I always thought the P-39 was the more aerodynamically refined aircraft, a faster aircraft to the Curtiss in a straight line - what about climb and dive rate? I believe the P-40 had a better range and bomb load though?

And yet on the Eastern Front the Soviets had numerous aces who flew on the Airacobra.

P-39 was faster than every contemporary P-40 and was far superior in climb/ceiling. Range/endurance was about the same. P-40's extra 30 gallons of fuel was eaten up by a higher takeoff/climb allowance and lower cruising speed at the same power settings.

P-39 Expert · May 12, 2021

drgondog said:
The USSR liked the aircraft very much - primarily because it was a better fighter in quantity versus LW than existing operational Soviet fighters. As a weapons system it was far superior. That said the Yak 3 and LaaG 7 quickly replaced them as better front line fighters. Lend-lease P-39N/Q began arriving in Russia in spring '43. Yak-3 didn't get into combat until summer '44 and Lagg-7 until fall '44. Their performance figures were no better than the P-39.

Additionally it should be noted that USSR air fighting doctrine for low to middle altitudes, and the fact that the P-39 was not required to contest the LW at high altitudes put the P-39 in its most favorable envelope. The early P-51 was 'excellent' in comparison to both the P-40 and P-39. The P-39 had to fight the LW at whatever altitude they chose. P-39 had comparable performance to contemporary LW fighters at all altitudes. Early P-51 meaning Allison P-51? Slightly faster (10-20mph) but not as good climb or ceiling. Allison P-51 grossed 8600lbs, P-39N/Q grossed about 7150lbs after the Russians deleted the wing guns and IFF radio. Kept the voice radio.

swampyankee · May 12, 2021

Denniss said:
P-39 is somewhat strange, most western allied nations disliked them but the soviets loved them.

Oddly, the USAAF managed to specify and Bell to design an aircraft that didn't suit any missions the US had for it, but it was perfect for the Soviets. I don't know quite how they managed this.

P-39 Expert · May 12, 2021

tomo pauk said:
It was done other way around - up-engine the existing aircraft type (whether by introducing a brand new engine type, or the engine type better than what was previously used), while 'upgrading' the fuel tankage or/and firepower, so it can do things the previous version was incapable for. It was done with P-38, P-51 and, finally, with P-47 (not in the same time). It was done (if belatedly) with Spitfire and Tempest. The 1942 P-39 (D/F/K/L) was way too heavy when compared with contemporary fighters power/weight ratio. Delete the unnecessary/redundant wing guns, nose armor plate and IFF radio and those P-39s weigh 7150lbs.
A P-39 that lost 500 lbs of stuff you deem redundant is still not an answer to what USAF needs in 1943 - a fighter that can do at least 400 mph and climb well at 25000 ft while having 500+ mile combat radius (preferably 650 miles) while cruising at 300+ mph TAS. Even the P-51A was incapable of that with wing racks on. No plane will meet these specs until the Merlin P-51 in 1944. A 1943 P-39N was very competitive with any other 1943 fighter. Except the early two stage Spitfire MkIX.

Yes, comparable in size and weight - just as I've wrote above.
Seems like nobody said to the people at RR that they are not supposed to beat the 33.5 L DB 601 and 35L DB 605 with the 27L Merlin. Either they were wrong, or you are wrong with the displacement idea. I'm wrong that a 20% larger engine should make more power?

The DB-601 critical altitude was at 13-14 kft, at least for the 601A.
Critical altitude says nothing about the engine capabilities. Merlin XX, DB 605A and BMW 801D all have had critical altitude of 18700 ft, power delivered there was very different. At 22000 ft, the V-1710 E11 (P-63A fighter) was making the same power as the DB 605A. Yes, with 20% less displacement.

I know that P-63 have had the auxiliary stage, P-39 did not. Once someone plops the 2-stage V-1710 on a P-39 and have it flying, I'll believe. Never said any P-39 had the two stage engine (except the P-39E), just said it would fit with minor modifications. The engine was in production in April '43 but the first P-63 airframe wasn't ready until October '43. Put the engine in the P-39 until the P-63 was ready.

buffnut453 · May 12, 2021

pbehn · May 12, 2021

buffnut453 said:
View attachment 622970

On doctors advice, I am no longer allowed to install or remove fuel tanks, armour or weapons, at any time.

DerAdlerIstGelandet · May 12, 2021

Marcel said:
Oh god, not another groundhog thread

Excuse me while I go bang my head against the wall.

buffnut453 · May 12, 2021

wuzak · May 12, 2021

P-39 Expert said:
A 1943 P-39N was very competitive with any other 1943 fighter. Except the early two stage Spitfire MkIX.

The "early 2 stage Spitfire MkIX" was a 1942 aircraft.

By 1943 the engines had improved.

Do you think the P-39N is actually a match for the P-51A? The P-51A being faster and longer ranged.

What about the Spitfire XII? Sure only 100 made, but top speed about the same as the P-39N, best performance in a similar altitude band, but better climb rate than the P-39N.

Typhoon Ib? Faster, with more firepower. And range.

Fw190A (not sure which subvariant was best by 1943)? By your own reckoning, the P-39N was no match for the Spitfire IX, the Fw190A was, or was close. Surely that would mean the Fw 190A outmatched the P-39N?

GrauGeist · May 13, 2021

Well, here we are once again...

(image source: Fubar57's gallery of nessecary and practical illustrations)

Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)

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