SHOULD the P39 have been able to handle the Zero? Was it training or performance?

P-39 Expert · Mar 27, 2018

Shortround6 said:
May I say balderdash!

As to any extra performance due to deleting wing guns from the P-39Q and going back to the four .30 cal guns.

P-39Q at sea level with drop tank.....259mph...2600rpm.......39in map.......96 gallons an hour
P-39K at sea level with drop tank.....256mph....2600rpm......37.5in map.....96 gallons an hour

Not seeing any big reduction in drag here. certainly not 10-15mph worth.

You want the performance of the 87 gallon plane but you want the endurance of the 120 gallon tank plane. Sorry, reality doesn't work that way.
you also are planning on using a 110 gallon drop tank which seems to be only slightly more common than unicorns. No mention of them in P-39 manuals. I am sure they existed somewhere but then adding another 210lbs of fuel just makes the initial climb out worse.
There is no need to guess at the fuel needed to get to 25,000ft, it is in the tables in the manuals.
for a P-39Q with a take off weight of about 8100lbs Which is close enough to our P-39X with four wing guns, 87 gallons of internal fuel and a 76 gallon drop tank (within 50lbs?) it needs 39 gallons using a combat climb and 42 gallons using a ferry climb.
ALl of these planes took of using one of the main tanks and switched to the drop tanks (subject to restrictions of CG) as soon as possible. However most of the planes arranged for any venting, overflow form the carb to go back to the main tank used for take-off so they partially filled in flight.

True test/criteria of combat radius is not how far you can get in but how far you can get back from, extra large drop tanks are no help.
after you drop the tanks you need 20 minutes at max power for the P-39, other planes were rated at 5 minutes WEP and 15 minutes at military power at altitude. P-39 can't make military power at these altitudes so take what you can get. It will suck up 82 gallons an hour at 20,000ft at nax continuous so perhaps the 71 gallons hour is an underestimate for full power at 25,000ft?
If we use the pounds of fuel per hour for military power at 15,500ft (1125hp for 138 gallons=0.736) and use it for 772hp at 25,000ft we get a consumption of 94.7 gallons an hour. Round it down to 90 or 1.5 gallons per minute.
Combat allowance is 30 gallons, leaves 57 gallons in our 87 gallon plane assuming that the return fuel fully filled the wing tank. Now you have to get the heck out of Dodge. You can fly at 224IAS (313 true) at 20,000ft using 77 gallons an hour. You do want 16 gallons or so (the reserve?) to find your own airfield and land so you have about 40-41 gallons for the withdrawal. chart says 40 gallons is good for 150 miles but you can slow down some over the Channel.
Basically you can escort a bit past Amsterdam and Antwerp. Paris might be out of reach.

cutting things too close leads to incidents Like No 133 Squadron in their Spitfires being blown off course by high winds and 11 planes out of twelve being lost.

Your 96 gph figure is at sea level. P-39Q burned 62gph at 25000' at max continuous 2600rpm from the pilots manual. Developed less power at 25000' so burned less gas.

The gondola wing guns on the Q cause the speed reduction and you are comparing two planes with different (versions of the same) engines that developed different power.

110 gal tank was nearly ubiquitous in the 8th AF in England for Thunderbolts, they also had a paper version of the tank. 110 gal tank was also used extensively in New Guinea.

The fuel to climb to 25000' IS in the manual, but that is assuming that you climb to 25000' over your own base and then start your cruise. Deduct the 20 gallon reserve to get to 5000' then climb the rest of the way to 25000' on your target heading as part of cruise.

Regarding weight, I'm figuring closer to 8400# at takeoff (7650# with 120gal internal plus 750# for the 110 gal including tank). There is no way that the N/Q could burn MORE than 62gph at 25000' That was max continuous at 2600rpm. Only higher power setting was 3000rpm combat military where it burned about 71gph. No WEP at this height. The higher the altitude the less power hence less fuel burned above critical altitude. Go a little higher than 25000' and burn even less fuel.

So back to my original formula per the pilot's manual. 120gal + 110gal drop = 230gal less 20 gallon reserve for T/O and climb to 5000'. Turn to your heading and climb the remaining 20000' flying toward your target. I don't care how you figure it, the remaining 210 gals after deducting reserve for T/O is burned at 62gph which will take you 3.4 hours. Deduct 15 minutes for combat at 3000rpm and 20 minutes landing reserve and you have 2.8 hours of actual escort time. You fly faster than the B-17/24 but you weave to stay with them so you are going their speed which is about 230mph x 2.8 hrs = 644mi. Half of that is your combat radius 322 miles at max continuous 2600rpm after all reserves. That's not even factoring in that you may come home at a lower power setting and lighter weight. That's how the pilot's manual says to do it. Of course this is theoretical and the pilot had to monitor both his fuel gauge and the clock. Pretty simple really, when your 110gal drop tank ran dry it was time to head home with your internal fuel and reserves.

varsity07840 · Mar 27, 2018

P-39 Expert said:
You're exaggerating a little, all I'm saying is that the P-39 wasn't as bad as you thought. Was competitive with most planes (especially in 1943) except for the Spitfire IX and the Merlin P-51 (Dec '43) and they had two stage engines. Got it's bad reputation in '42 because it was overloaded by the AAF (British with the P-400 contract actually) and didn't have oxygen at Guadalcanal. AAF gave up on it just as the P-38 was about to enter combat (late '42). Problem was the P-39N was starting production and with the 9.6 geared engine was a MUCH better plane. They shuttled them off to training command and the Russians who loved them and demanded more. And the early Lightnings (F/G) and Thunderbolts (B/C) were not as great as advertised until vastly improved models came basically after the Luftwaffe was done. That's what I think anyway.

So, you have a VERY short range aircraft with armament that includes useless .30 cal and 37mm gun(s), an altitude performance that in no way comes close to the P-47 and P-38, not to mention the P-51. It can't land on or take off from aircraft carriers. What's the upside of the P-39N?

Shortround6 · Mar 27, 2018

I would note that short ranged as the P-47C was it had roughly double the range of an 87 gallon Aircobra at similar low speeds.
In fact an 87 gallon Aircobra was roughly equal in range to the P-47C when using a 75 gallon drop tank.
Trouble is the drop tank knocked about 30mph indicated off the airspeed.

pbehn · Mar 27, 2018

P-39 Expert said:
You're exaggerating a little, all I'm saying is that the P-39 wasn't as bad as you thought.

Although this post was directed at DarrenW it could be directed at almost everyone on this forum, you assume what our opinion is and evangelise to change that opinion. This is an international forum and we all have our point of view and even our favourites. Mine is the Hurricane, not on any metric of performance, but just for being there, when nothing else was and being of a design that was simple enough to build and fly that it turned the issue over to number of pilots available not aircraft. Despite all the fabulous aircraft produced in WW2 my opinion doesn't and won't change, even though I enjoy such discussion.

pbehn · Mar 27, 2018

Shortround6 said:
I would note that short ranged as the P-47C was it had roughly double the range of an 87 gallon Aircobra at similar low speeds.
In fact an 87 gallon Aircobra was roughly equal in range to the P-47C when using a 75 gallon drop tank.
Trouble is the drop tank knocked about 30mph indicated off the airspeed.

As I understand it, the P47s range was as long as it was asked to be. When asked for a long range P47 Republic came up with the "N" version, which was about equal/on par with the P 51.

DarrenW · Mar 27, 2018

I was trying to help out your cause Mr. P-39 but it would seem that I have been over-ruled!

Milosh · Mar 27, 2018

Still waiting for the FOIC for the P-39N to be posted.

Shortround6 · Mar 27, 2018

pbehn said:
As I understand it, the P47s range was as long as it was asked to be. When asked for a long range P47 Republic came up with the "N" version, which was about equal/on par with the P 51.

The P-47 edit>N<end edit also required a new engine, new propeller knowledge, a new turbo and water injection. It couldn't have been built in 1942, at least not successfully.

I would note that the short ranged P-47 could fly at 200IAS (300mph true?) at 25,000ft without drop tank using 95 US gallons an hour. So even if it reached 25,000ft with only 200 gallons left in the tanks it could fly 215 miles further than a P-39Q carrying a 75 gallon drop tank and while going 30mph faster.

Now figure how good an escort the P-39 would have been.

pbehn · Mar 27, 2018

Shortround6 said:
The P-47 also required a new engine, new propeller knowledge, a new turbo and water injection. It couldn't have been built in 1942, at least not successfully.

I would note that the short ranged P-47 could fly at 200IAS (300mph true?) at 25,000ft without drop tank using 95 US gallons an hour. So even if it reached 25,000ft with only 200 gallons left in the tanks it could fly 215 miles further than a P-39Q carrying a 75 gallon drop tank and being going 30mph faster.

Now figure how good an escort the P-39 would have been.

Are you telling me that between the late 1930s and early 1940s people in the aviation industry learned a lot very quickly? Excuse me, I must take a seat and take time to absorb this.

DarrenW · Mar 27, 2018

Glider said:
Pilots flying for you would have Voodoo dolls with your effigy on them.

Shortround6 · Mar 27, 2018

pbehn said:
Are you telling me that between the late 1930s and early 1940s people in the aviation industry learned a lot very quickly? Excuse me, I must take a seat and take time to absorb this.

Sorry, I type too fast and leave things out, I meant the P-47N couldn't have been built in 1942. The early P-47s obviously were.

But yes, knowledge was being gained very quickly. Maybe even faster than cell phones advance now

pbehn · Mar 27, 2018

Shortround6 said:
Sorry, I type too fast and leave things out, I meant the P-47N couldn't have been built in 1942. The early P-47s obviously were.

But yes, knowledge was being gained very quickly. Maybe even faster than cell phones advance now

Of course it was there was a war on, everything goes quicker in war time. Now tell me a time between 1939 and 45 when the Spitfire didn't need a better engine, a better field of view, better wings, better armament and better cooling. Of the thousands produced I doubt the maximum of any type that was completely identical apart from paintwork (squadron markings) was only a few hundred.

Milosh · Mar 27, 2018

I think someone forgot to look at the other charts in the P-39Q manual.

So,
warm up, take-off, climb to 25k - 40gal
cruise to target - 62gal (minimum for 1 hour, 2 hour 124gal)
combat - 40gal (max)

Gee, that leaves 88gal left out of the 230gal the a/c started with for 1 hour of cruise time. That is not factoring in lost fuel if the drop tank had to be dropped before empty.

AAF heavy bombers cruised at 180mph or less.

edit: As been pointed and made a correction.

Still, 180-200mi barely gets the bombers over Holland.

DarrenW · Mar 27, 2018

pbehn said:
This is an international forum and we all have our point of view and even our favourites. Mine is the Hurricane, not on any metric of performance, but just for being there, when nothing else was and being of a design that was simple enough to build and fly that it turned the issue over to number of pilots available not aircraft. Despite all the fabulous aircraft produced in WW2 my opinion doesn't and won't change, even though I enjoy such discussion.

I'm in complete agreement with pbehn. For whatever reason we all gravitate toward one aircraft or another, mine happens to be the Grumman Hellcat (big surprise, right?), yours the Airacobra. But I learned early on that the people on this forum know A LOT more than you might initially give them credit for. There are some seriously well-read aviation enthusiasts here, along with bonafide pilots, engineers, designers, artists, and practically everything else that has something to do with the passion of flight. Just being a fan of a particular airplane and spewing your opinion everywhere just isn't enough if you want to persuade people to your way of thinking.

It was extremely humbling to realize that my opinion about a particular WWII aircraft wasn't the only one in the universe, and I'm a better person for it. People like Tomo and pbehn in particular set me straight early on and I'm glad I decided to ease off a little and not let my ego get in the way of learning something new or having an open mind to vewing things a little bit differently going forward.

I for one am not saying that the points you've made thus far have zero merit. My main problem was your approach. I was hoping that you could make a powerful argument for the Airacobra, and in particular the P-39N, because it is often neglected by historians. It was when you began to denigrate the abilities of truly remarkable aircraft to somehow lift the Airacobra up a notch or two that you lost some credibility with me.

I just hope we can put this discussion back where it was about 4,000 posts ago and start over with a fresh look at the facts. Do you think that's even possible?

Shortround6 · Mar 27, 2018

Milosh said:
I think someone forgot to look at the other charts in the P-39Q manual.

Climb to 25,00ft took 39 > 42 gal.

So,
warm up - 20gal
take-off - 14 gal
climb to 25k - 40gal
cruise to target - 62gal (minimum for 1 hour, 2 hour 124gal)
combat - 40gal (max)

Gee, that leaves 54gal left out of the 230gal the a/c started with. That is not factoring in lost fuel if the drop tank had to be dropped before empty.

AAF heavy bombers cruised at 180mph or less.

you have to read the fine print, lower right of middle chart, "Fuel includes warm up and take-off allowance."

I will note that on some other planes the warm up and take-off allowance on the engine chart doesn't seem to match up with the fuel needed to climb to altitude

The P-39 cannot fight with the tank attached.

I would also note that climb to altitude chart is for a plane weighing 8100lbs. MR P-39 Expert wants to put another 68 gallons in/under the plane (408lbs) a bigger drop tank (10-15lbs?) and replace the 4 outer fuel cells, 70-80lbs? over 500lbs more?

DarrenW · Mar 27, 2018

Well it looks like the climb rate of the P-39Q loaded to 7,200lbs can be equaled or even bested by the F6F-3 under similar WEP conditions. But seeing that it's not the N model, does this even count?

F6F-3:

P-39Q:

wuzak · Mar 27, 2018

P-39 Expert said:
Regarding weight, I'm figuring closer to 8400# at takeoff (7650# with 120gal internal plus 750# for the 110 gal including tank). There is no way that the N/Q could burn MORE than 62gph at 25000' That was max continuous at 2600rpm. Only higher power setting was 3000rpm combat military where it burned about 71gph. No WEP at this height. The higher the altitude the less power hence less fuel burned above critical altitude. Go a little higher than 25000' and burn even less fuel.

No WEP at the altitude at which you want to fight?

Wouldn't that mean you are pretty muck fucked?

wuzak · Mar 27, 2018

DarrenW said:
The actual documents may have been mostly unavailable to the general public, but the data from them could most certainly be found in period books of the time. For instance, here is the performance figures for the P-39N that I gleaned from Combat Aircraft of the World (W.R. Taylor) which was published way back in 1969. See any similarities with your oft-quoted document?

The documents have, probably, been publicly available for decades. I'm sure that authors of books have researched them, as did Mike Williams at wwiiperformance.org, publishing his results in 2012.

Getting the documents in question likely required a trip down to the national archives of the US (or whatever they are called).

wuzak · Mar 27, 2018

P-39 Expert said:
Why did the AAF pull them so quickly to be replaced by the P-38, P-47 and P-51? Please remember I'm comparing the P-39N which was produced between Dec '42 and April '43. During that period the P-38F/G had just begun combat in Dec '42 and the P-47 would not see combat until May '43 after the N was out of production. These were the AAFs turbocharged super planes that were in production but not yet in combat. They had a vested interest in playing down the P-39 accomplishments and overstating their new planes. How would it play to have the AAF saying "We're giving the Russians a great little plane here, but our Lightnings and Thunderbolts are not quite ready yet". The AAF's motto was "Better planes coming", but the better planes were not that much better if at all in their earlier models. The Lightning couldn't dive and the Thunderbolt couldn't climb, and neither were very maneuverable at all. The Thunderbolt had a very short Spitfire-like range before they got drop tanks in August '43, and then still couldn't get much into Germany proper. But the biggest problem was cost. Now there are various cost figures for these planes that all got lower as production ramped up, but the Lightning was about 2.5 times the cost of a P-39 ($50k) and the Thunderbolt was about 1.7 times. American won WWII because we could pay the cost, but if a LIghtning cost 2.5 times as much then it should have been 2.5 times as capable. Put another way, you got almost a group of P-39s for every squadron of LIghtnings, or instead of the 9500 lightnings produced you could have had almost 24000 P-39s. Nobody really looks at it this way, but that's the way it was.

Did they have a vested interest in paying down the achievements of the P-39 in order to acquire more P-40s? From an earlier post of drgondog's, it seems that is what happened prior to P-38s, P-47s and P-51s being available in quantity.

Shortround6 · Mar 27, 2018

wuzak said:
No WEP at the altitude at which you want to fight?

Wouldn't that mean you are pretty muck fucked?

Not really, plenty of planes fought at altitudes well above WEP or it's equivalent. Think Spitfire Is and 12lbs boost in the BoB,
However the later P-39s were over 7000lb airplanes with around 770-780hp at 25,000ft (including RAM). And in 1943 that puts you behind the curve.

SHOULD the P39 have been able to handle the Zero? Was it training or performance?

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