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

pbehn · Mar 15, 2019

Glider said:
Just when the Spit IX entered service, a comparison which the P39 is guaranteed to lose.

Same time as the Mustang MK I appeared too.

Glider · Mar 15, 2019

good point

Shortround6 · Mar 15, 2019

P-39 Expert said:
The five minute rating was increased to 15 minutes mid 1942.

I think you missed the point. The Airacobras on your chart are running at 3000rpm for the first 5 minutes of their climb. The Spitfire is running at 2850 rpm instead of 3000rpm like it would do in combat. Granted the Allison didn't have a 30 min rating. It's next lower rating to military power was at 2600rpm so that wouldn't be fair either.

pbehn · Mar 15, 2019

Glider said:
good point

The Mustang Mk I blows most of the arguments out of the water, it was built and supplied to the British as a purchase and lend lease and much loved by the pilots that flew it, the engine was OK within the altitude limits known by all, the problem with the P-39 was the P-39 airframe.

fubar57 · Mar 15, 2019

Ka-freakin'-boom!

tomo pauk · Mar 15, 2019

pbehn said:
The Mustang Mk I blows most of the arguments out of the water, it was built and supplied to the British as a purchase and lend lease and much loved by the pilots that flew it, the engine was OK within the altitude limits known by all, the problem with the P-39 was the P-39 airframe.

Airframe was a small part of the problem, it was less draggy than Spitfire, P-40, Re.2005 or G.55.
Engine was the biggest part of the problem, and then we also have a problem of sticking 900 lbs worth of guns and ammo on a nominal 1150 HP engine.

pbehn · Mar 15, 2019

fubar57 said:
Ka-freakin'-boom!

I cannot possibly be the only person here that doesn't remember all these points being done to death in the past.

fubar57 · Mar 15, 2019

pbehn · Mar 15, 2019

tomo pauk said:
Airframe was a small part of the problem, it was less draggy than Spitfire, P-40, Re.2005 or G.55.
Engine was the biggest part of the problem, and then we also have a problem of sticking 900 lbs worth of guns and ammo on a nominal 1150 HP engine.

The British had a use for the Mustang Mk I and would have taken more right up to end of 1944, they had no use for the P-39. Basically the P-51 could cross the channel and get back the P-39 couldn't.

tomo pauk · Mar 15, 2019

pbehn said:
The British had a use for the Mustang Mk I and would have taken more right up to end of 1944, they had no use for the P-39.

I've never said they had use for P-39. P-39 was unsuitable for major use for ETO.

Basically the P-51 could cross the channel and get back the P-39 couldn't.

It certainly could.

P-39 Expert · Mar 16, 2019

The P-51A (MkI) and the P-39N had the same engine.

P-51A was a little cleaner so it was 10-15mph faster.

P-51A weighed about 800-1000# more so the P-39N climbed better and had a higher ceiling.

P-51A had 50% more fuel so range was a good bit farther.

P-39 probably a little more maneuverable. Easier ground handling.

Armament? Who knows. P-51A had four wing mounted .50 MGs. P-39 had center fire cannon and two synchronized .50 MGs.

One is a better interceptor, one is a better escort.

Replace the .30cal wing guns and substitute 50gal fuel in the P-39 and you have about the same plane as the P-51A.

Shortround6 · Mar 16, 2019

P-39 Expert said:
Replace the .30cal wing guns and substitute 50gal fuel in the P-39 and you have about the same plane as the P-51A.

Except you don't.

Four .30 cal guns = 99lbs
1200 rounds of 30 cal ammo= 72lbs

50 gallons of fuel weighs 300lbs
Weight of the self sealing tanks to put the fuel in???????

Wonder what the Mustang could do if you magicly took out 180lbs and added 400lbs of "stuff" with no penalty?

tomo pauk · Mar 16, 2019

P-39 Expert said:
The P-51A (MkI) and the P-39N had the same engine.

Problem being that P-51A was Mustang Mk.II, that entered service by September 1943 in MTO and CBI.
Mustang I was roughly XP-51 that is combat capable, RAF's Mustang I was in service by Spring 1942.
Mustang Ia was P-51.

pbehn · Mar 16, 2019

The RAF were disappointed with the P-39 speed and pleased with the Mustang Mk1 but the difference was 10-15MPH on top speed? Where does the Spitfire figure in this?

tomo pauk · Mar 16, 2019

pbehn said:
The RAF were disappointed with the P-39 speed and pleased with the Mustang Mk1 but the difference was 10-15MPH on top speed? Where does the Spitfire figure in this?

Spitfire V was faster above ~15000 ft than P-39D, and climbed better at all altitudes. It will also out-climb the Mustang I, and probably be faster above 20000 ft.

Ivan1GFP · Mar 16, 2019

drgondog said:
Ivan the airfoil for the wing for X73 through P-51K was NAA/NACA 45-100. Only the root chord and inboard leading edge of the wing changed for the D/K.The 50 caliber guns could have been mounted vertically in A-36, P-51A/B/C but probably were angled to preserve option to install 20mm (angled) from P-51-NA to A-36. Discussions between Material Command and NAA regarding adding 20mm to P-51B and D were finally killed in November 1943 and the gun mount to 50 caliber was changed to vertical for the P-51D and Subsequent. At that time there were still on-going discussions about P-51F (interceptor- production) with Oldsmobile 20mm guns that would have imposed significant change to LE spar and aft spar for the evolving NACA 66 series wing on the future P-51F, and cancelled.

Hello Drgondog et al,
I was basing my statement on comments from a pilot who had flown both the P-51B and P-51D and noted that the handling between the two machines was noticeably different. He attributed the difference to modifications required by the gun arrangement. There certainly were some other changes after the death of Col. Hitchcock in a high speed dive but perhaps they had no real aerodynamic effect.

- Ivan.

Greyman · Mar 16, 2019

From what I gather the RAF's problem with the P-39 was that it didn't work, and not how the performance shook out a few mph/fpm in whatever direction. Reading 601 Squadron's trials and tribulations with the aircraft, they went from a very experienced unit excited for their new aircraft -- to a demoralized shell of what they were.

Engine troubles and forced-landings were so constant that 'getting a four-ship section airborne became cause for celebration'. Though they gave it everything in their power, 601 Squadron wasn't able to overcome the difficulties, which were beyond what they were capable at the squadron level and what the Air Ministry were prepared to devote to the aircraft.

Conversely -- 'It is not an exaggeration to say that Soviet pilots and engineers, front-line troops and researchers, gave their maximum effort to turn the Airacobra into a fully capable combat aircraft. And in doing so they saved the Bell firm from great unpleasantness associated with the production of a series of "unfinished" aircraft.'

(from Airacobras Enter Combat by Valeriy Romanenko ... a lot of relevent bits online at Early Cobra's in Soviet Aviation)

Kevin J · Mar 16, 2019

The Brits would certainly know from May 10th 1941 that the Germans were about to attack the USSR as that is when they picked up Rudolf Hess. They probably had a good idea perhaps 6 months before that the Germans were about to attack the USSR as they had Spitfire spy planes overflying Germany and would have detected all the troop movements which pointed away from an invasion of the UK. I can't remember when we actually warned them of an impending attack. The P-400's were heavier because they had more armour and what did they do with them, they shot up some invasion barges. Maybe that's what we needed them for in the first place, but no invasion, no P-400's required.

wuzak · Mar 16, 2019

P-39 Expert said:
Armament? Who knows. P-51A had four wing mounted .50 MGs. P-39 had center fire cannon and two synchronized .50 MGs.

Except for the P-400, the centre fire cannon was rather poor as an air-to-air weapon. And the cowl .50" hmgs fired much slower than the same gun on the P-51. Maybe half the rate?

Clayton Magnet · Mar 16, 2019

The Browning action did not synchronize well, I think they were in the 400-500 RPM territory

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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