XP-39 and the Claims

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FLYBOYJ said:
YES!!! It was sent to the SWP and replaced the P-39s being flown by the 39th and 9th FS, V Fighter Command. So to be crystal clear, why was the P-39 replaced???? (In your opinion)
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My opinion, because it had a hard time intercepting Japanese bombers at 18000-22000ft and had a hard time cruising at over 18000ft, in both cases while carrying a 110gal drop tank. These P-39D/F/K/L models in 1942 weighed around 7800lbs clean and another 750lbs with the ever present drop tank for a total of around 8550lbs, all powered by an 1150hp engine. This was insanely heavy in comparison with other contemporary fighters with comparable engines.

These 1942 P-39s could have easily weighed 7160lbs clean and 7900lbs with drop tank. According to AHT the P-39D weighed 5525lbs empty, add a modified load of 1669lbs (pilot 160lbs, oil 70lbs, 120gal fuel 720lbs, 37mm cannon 300lbs, twox50calMG 275lbs and armor plate/glass of 130lbs without the nose armor, oxygen 10lbs, gunsight 4 lbs). 5525lbs empty + 1669lbs load = 7194lbs. Deduct 34lbs from "armament provisions" since without the 30cal wing guns their gun mounts, chargers, heaters and ammunition boxes aren't needed. Gross weight 7160lbs.

The P-39C weighed 7075lbs gross (only 85lbs difference) and had a top speed of 379mph and initial climb rate of 3720fpm as compared to 2720fpm for a P-39K. Performance increase would have enabled these lighter P-39s to handle Zeros/Oscars for the foreseeable future until Nov/Dec when the improved M/N/Q models were in production.

P-38s could have been sent to Europe to escort 8thAF bombers, if they had been available.
 

So it was ready for combat, but it wasn't ready...
 

"Could have, would have" Just face it, the P-39 in the SWP was just an inferior aircraft when compared to the P-38 and that will include the later model P-39s. Look at the performance of the 2 units I posted, what they accomplished with the P-39 and then their records with the P-38.
 
Look at the performance graphs for the contemporary P-38 and P-39. P-39N and P-38F/G.
 
For the P-39K, there was a 20 gallon allowance for takeoff not avilable in flight. It would burn 41 gallons getting fro S.L. to 25,000 feet.

So, we start off with 175 gal (195 - 20) and we burn 41 gals to get to 25,000 feet from sea level, leaving 134 gallons for the mission starting at climb airspeed and 25,000 feet. I'm assuming you want to be above the Betty bombers and going faster than climb speed.

If you cruise at max continuous, you have 1.3 hours before you are out of fuel. If you go to combat power, you have 1 hour before you run out of fuel, but you can't run cxombat pwoer for longer then eiher 5 minutes or 15 minutes, depending on who you believe. So, you have somehwere between 1 hour and 1.3 hours before you are out of fuel.

I'm assuming you really don't want to run out of fuel, so you start up, takeoff and get to maybe 21,000 feet and have something like 1hr 20 min to 1 hr 40 min to play with before you are out of fuel. Therefore, you limit your mission to something like 45 min to 1 hr and cruising at less the max continuous, and carefully plan our fuel burn. Basically, it flies a small bit longer than a Bf 109, which was the world standard for a short-range fighter. That means that in the Pacific, it was basically for local operations only and would not be considered for missions very far away.

So, while it wasn't uselsss, it also wan't going to ever be a plane selected for a 2.0 - 2.5-hour mission. If you cruise at 200 mph, that means you aren't ever going to get more than something like 100 miles from your home airfield. That doesn't offer much in the way of useful operations in the Pacific Ocean ... but, that's exactly where we sent quite a few of them. Makes me wonder a bit about the wisdom of our procurement policies.
 
For the P-39K, there was a 20 gallon allowance for takeoff not avilable in flight. It would burn 41 gallons getting fro S.L. to 25,000 feet.

So, we start off with 175 gal (195 - 30) and burn 41 gals to get to 25,000 feet, leaving 134 gallons for the mission starting at climb speed at 25,000 feet. I'm assuming you want to be above tbe Betty bombers and going faster than climb speed. Max continuous burns 103 gph and combat power burns 132 gph. So, if we need to go fast to catch Betty bombers, our mission is somewhere between 1.0 and 1.3 hours untl we're out of fuel. Since we don't really want to BE out of fuel, I'd say we're looking at about a 45-minute mission and ecomony cruise back home. That doesn't allow for the P-39 to be selected for many mnissions other than extremely local, say 100 miles away more or less.

No wonder it got replaced in the Pacific Ocean areas ... there just seemingly weren't that many missions it could be assigned to perform, even if we just look at range. Nevermind hauling some bombs. You could apparently haul up to 500 pounds of bombs, but then you wouldn't have the belly tank and you lose 75 gallons of fuel. So, the target better be CLOSE, slightly more than the end of the runway, but not too much farther than beyond visual distance from the runway overrun or ocean, which ever was closer.
 
So a P-39K/L with 120 gallons internal and a 75 gallon drop tank has "a bit" more endurance than a 109 with 88 gallons?

You're double counting the fuel used for climb. Either use the 20gal takeoff reserve that gets you to 5000' or use the 41gal to 25000', but not both.

And fuel burn at 25000ft at max continuous power (2600rpm) is only 54gph, not 103gph so combat at 25000' would burn about 62gph.

Using 41gal to climb to 25000ft, deduct reserves of 21gal for 20min combat at 25000ft and 10gal for 20min landing reserve leaves you 123gal using 54gph at 25000ft for a patrol endurance of 2.3hrs or 2hrs 18min.

Using the 20gal reserve for takeoff and climb to 5000ft, deduct the 21gal combat reserve and the 10gal landing reserve leaving 144gal using 54gph for a patrol endurance of 2.7hrs or 2hrs 42min. Deduct the additional 15 min to climb from 5000ft to 25000ft and you have 2hrs 27min.

Take your pick, 2hrs 18min or 2hrs 27min. Nine minutes difference.

Now after September/October 1942 there was radar at Port Moresby. Not ineffective Australian radar hundreds of miles away, but local radar at PM. In theory patrol with a drop tank was no longer necessary, planes could be ready and waiting for interception. Upon detection of incoming bombers clean P-39s could be launched with 120gal internal fuel. Deduct the 20gal reserve for takeoff, the 21gal combat reserve and the 10gal reserve for landing and 69gal were available for cruise at 25000ft at 54gph gave 1.3hrs or 1hr 18min, plenty of time to intercept incoming bombers.

Normal medium bomber/transport escort missions lasted a little over 3hrs at around 15000'.
 
Peter Gunn said:
Actually, with a little forethought, the USAAF could have been operating Allison Mustangs by January 1942. I mean, it's no more of a stretch than the magical climb/speed the P-39 could attain if several criteria were met... theoretically.
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Shortly (end December 1941) after war was declared by Germany on USA there were circa 150 Mustang Mk Is in UK, using the trade definition of "free on board" that is somewhere between the hold of a vessel in Liverpool and an airfield in England. Mustang MkIs were operational in squadron service by April 1942 so it isn't a giant leap to suggest the USA could have had them operational 3 months earlier. With all these things there is a question of what things mean, receiving 150 aircraft doesn't mean you can fly them the next day against the enemy, pilots and ground crew need to be trained, in fact with the Mustang MkI the first thing was to decide what to do with it, but then you need to find out what it can do.
 
P-39 Expert said:
Look at the performance graphs for the contemporary P-38 and P-39. P-39N and P-38F/G.
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I have - and at the end of the day the P-38 was still the better fighter and outperformed the P-39 in combat, THAT'S HISTORY! But since you like to slant information and want to talk charts, look at the performance graphs for the P-38L and the P-39N. Case closed.
 
XBe02Drvr said:
And even if their performances were identical, the P38 was the better machine because of its range. P39 just wasn't suitable for anything beyond interception and local air superiority.
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Agree, but when discussing the P-39 in the SWP, I have a problem using "air superiority" in the same sentence.
 
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