Planes that are simultaneously both the most over rated and the most under rated.

P-39 Expert · Aug 27, 2019

AlfaKiloSierra said:
What about a 56" P-47 instead of that 70" one I used
http://www.wwiiaircraftperformance.org/p-47/p47d-44-1-climb.jpg
Slightly over 2000ft/min at 25000ft.

Again, the P-39 significantly out-climbs the P-47 at low altitude, but stop saying it outclimbs P-47 at an altitude the P-39 is suffering from its single-stage supercharger.

Again, you are citing

Shortround6 said:
We are back to the magic P-39N that could outclimb (by hundreds of feet per minute) any other P-39 of any model.

Of course it did this (in part) by flying hundreds of pounds lighter than any other P-39 model.

You can't have it both ways, you either have the good climb of a light P-39 and not enough fuel to get home or you have enough fuel and the less than steller climb.

A P-39Q-5 using the same engine as the P-39N was climbing at 1570fpm at 25,000ft. The early P-47s with tooth pick props and no water injection could climb around 1800fpm.

a late war P-47D using an experimental fuel not even available yet. P-39N outclimbs any contemporary production P-47 at all altitudes.
Now they have about the same ceiling, so the difference in climb is greater at lower altitudes and narrows as you go higher, but at 25000' the N outclimbs any contemporary production P-47. Compare models that were available at about the same time, or we're debating whether a SPAD is better than an F-22. The P-39N had already completed it's production run of 2000 planes before the P-47 got into combat in May '43. Thunderbolts were good planes but they did not want to climb much at all.

P-39 Expert · Aug 27, 2019

Shortround6 said:
We are back to the magic P-39N that could outclimb (by hundreds of feet per minute) any other P-39 of any model.

Of course it did this (in part) by flying hundreds of pounds lighter than any other P-39 model.

You can't have it both ways, you either have the good climb of a light P-39 and not enough fuel to get home or you have enough fuel and the less than steller climb.

A P-39Q-5 using the same engine as the P-39N was climbing at 1570fpm at 25,000ft. The early P-47s with tooth pick props and no water injection could climb around 1800fpm.

That test was not hundreds of pounds lighter. That P-39N weighed 7274#, the following WEP climb test article weighed 7301#, the M model tested weighed 7430#. Gross weight for those models was about 7650# so the N tests were about 360# lighter which represented half the fuel load (average weight for the test flight) or the 95% adjustment the British used for their tests.
ALL of those official performance tests at wwiiaircraftperformance.org were lighter than normal gross weights.
The P-51A test plane weighed 8000# which was 600# lighter than normal gross. That's the test where that P-51A made 415mph and climbed at 2000fpm at 20000'. Those are the numbers most commonly used for P-51A performance.
The P-38G test plane weighed 13900# which was a FULL TON less than a normal P-38G. Put that into perspective for a single engine plane and it was 1000# lighter than normal. The climb numbers were fantastic but way overstated when compared to the other information and performance graphs for the P-38F/G.
P-47B/C tests were all around 12500# when the gross weight in the manual was listed at 13300#. That's 800# light. Sure they used 6 guns instead of 8 but that only accounts for about 400#.
They were all tested lighter than their normal gross weights. The tests were reflecting some weight adjustment to simulate less than full fuel to give an average weight during the test flight. A P-39N weighed 7650# at take off with full fuel and 7000# when landing since most of the fuel had been burned. So how much did that P-39N weigh for test purposes? The average weight during the flight would be about 7300# just like the tests say. The British listed their test weights as a "corrected" (their term) weight of 95% of gross to simulate the average weight of the plane during a flight. That's just how those planes were tested.
If anybody knows different please say so.

Shortround6 · Aug 27, 2019

"You can't have it both ways, you either have the good climb of a light P-39 and not enough fuel to get home or you have enough fuel and the less than steller climb.

A P-39Q-5 using the same engine as the P-39N was climbing at 1570fpm at 25,000ft. The early P-47s with tooth pick props and no water injection could climb around 1800fpm. "

P-39 Expert said:
a late war P-47D using an experimental fuel not even available yet. P-39N outclimbs any contemporary production P-47 at all altitudes.
Now they have about the same ceiling, so the difference in climb is greater at lower altitudes and narrows as you go higher, but at 25000' the N outclimbs any contemporary production P-47. Compare models that were available at about the same time, or we're debating whether a SPAD is better than an F-22. The P-39N had already completed it's production run of 2000 planes before the P-47 got into combat in May '43. Thunderbolts were good planes but they did not want to climb much at all.

An early P-47 with toothpick prop was not using an experimental fuel. The P-47 was being produced at the same time as the P-39N.

In fact the first P-47C was produced in Farmingdale in Sept 1942, Evansville Indiana completed their first P-47 in late Sept 1942, and Oct 1942 also sees the improved P-47C-1 produced in Farmingdale and 3 are sent to Eglin Field for comparative tests. the P-47G by Curtiss was first produced in Dec 1942. Farmingdale has switched to the P-47D-1 by Feb 1943

Bell started delivering P-39Ms (yes M, not N) in Nov 1942. While they started working on P-39Qs in March. They delivered 511 P-39Ns in April of 1943.

It is a little deceptive to compare when planes were produced and when they were used in combat as it often took the US several months to get a plane from the factory apron to a combat theater.

So I am not comparing a Spad to an F-22. I am comparing planes that were coming through the factory doors at the same time or within a few weeks of each other.

.

Shortround6 · Aug 27, 2019

P-39 Expert said:
That test was not hundreds of pounds lighter. That P-39N weighed 7274#, the following WEP climb test article weighed 7301#, the M model tested weighed 7430#. Gross weight for those models was about 7650# so the N tests were about 360# lighter which represented half the fuel load (average weight for the test flight) or the 95% adjustment the British used for their tests.
ALL of those official performance tests at wwiiaircraftperformance.org were lighter than normal gross weights.

If anybody knows different please say so.

Ok, let's accept your hypothesis, great climb numbers for P-39N were done with half fuel (half of 90 is 45 rounding up) so your superduper P-39 escort fighter is engaging the German fighters with 45 gallons of fuel on board? shades of the 109 over London, except the P-39 has a lot further to fly to get home.

For the P-47 you are right, they were tested at lower than gross weight, however a P-47 with 205 gallons in the main tank and 6 guns went about 12,500lbs, the aux tank held 600lbs of fuel and the extra two guns and their ammo went about 300lbs. So adjust the weight as you see fit, the P-47 at 12,500lbs or so (eight guns and ammo means 155 gallons of fuel) will fly a bit further than a P-39 with 45 gallons

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
Again, you are citing

a late war P-47D using an experimental fuel not even available yet. P-39N outclimbs any contemporary production P-47 at all altitudes.
Now they have about the same ceiling, so the difference in climb is greater at lower altitudes and narrows as you go higher, but at 25000' the N outclimbs any contemporary production P-47. Compare models that were available at about the same time, or we're debating whether a SPAD is better than an F-22. The P-39N had already completed it's production run of 2000 planes before the P-47 got into combat in May '43. Thunderbolts were good planes but they did not want to climb much at all.

You may be talking about a P-47 with some Curtiss Electric propellers. I'm talking about the ones with Hamilton Standard. Anyways, I'd like to see your source.

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
Again, you are citing

a late war P-47D using an experimental fuel not even available yet. P-39N outclimbs any contemporary production P-47 at all altitudes.
Now they have about the same ceiling, so the difference in climb is greater at lower altitudes and narrows as you go higher, but at 25000' the N outclimbs any contemporary production P-47. Compare models that were available at about the same time, or we're debating whether a SPAD is better than an F-22. The P-39N had already completed it's production run of 2000 planes before the P-47 got into combat in May '43. Thunderbolts were good planes but they did not want to climb much at all.

No P-39 ever has the same ceiling as any P-47, assuming same load conditions.

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
Again, you are citing

a late war P-47D using an experimental fuel not even available yet. P-39N outclimbs any contemporary production P-47 at all altitudes.
Now they have about the same ceiling, so the difference in climb is greater at lower altitudes and narrows as you go higher, but at 25000' the N outclimbs any contemporary production P-47. Compare models that were available at about the same time, or we're debating whether a SPAD is better than an F-22. The P-39N had already completed it's production run of 2000 planes before the P-47 got into combat in May '43. Thunderbolts were good planes but they did not want to climb much at all.

First, performance is unrelated to fuel unless the given power setting is unobtainable with the existing fuel. A 56" P-47 burning 87 octane fuel and a 56" P-47 burning 150 octane fuel have the exact same performance, but a 70" P-47 cannot burn 87 octane fuel.

Second, comparing a P-39 to a contemporary P-47 means you can take the first variant of P-47 and the best variant of P-39, rendering the comparison moot. I can claim that because the 76" P-47M is faster than the prototype Hawker Tempest V, and therefore the P-47 is faster than the Hawker Tempest?

Third, why is citing a bad thing? You've provided nothing that I can see for myself. If you have a different source, please put it here.

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
You are comparing a P-39N from late '42 to a P-47D from July '44 (after air superiority had been won) using an experimental fuel that was not even in service yet. The P-39N outclimbed all production P-47s at all altitudes in '43 and early '44. Pretty good for a little single stage Allison.

In late 1943 the P-47 is running 56", making my comparison true.

P-39 Expert · Aug 27, 2019

I'm using the same source as you are, wwiiaircraftperformance.org.

Look at the climb figures for the P-39N. Compare them to the P-47B/C/D climb figures before 1944.
The P-39N was produced 11/'42 through 4/'43. Unfair to compare a much later (mid '44) plane using an experimental fuel not available until June '44. Also don't use any comparison using a Hamilton Standard propeller. That HS prop was never used in production P-47s. Use the standard models produced in '43 for a true comparison. A P-47 could not touch a P-39N in climb.

P-39 Expert · Aug 27, 2019

Shortround6 said:
Ok, let's accept your hypothesis, great climb numbers for P-39N were done with half fuel (half of 90 is 45 rounding up) so your superduper P-39 escort fighter is engaging the German fighters with 45 gallons of fuel on board? shades of the 109 over London, except the P-39 has a lot further to fly to get home.

For the P-47 you are right, they were tested at lower than gross weight, however a P-47 with 205 gallons in the main tank and 6 guns went about 12,500lbs, the aux tank held 600lbs of fuel and the extra two guns and their ammo went about 300lbs. So adjust the weight as you see fit, the P-47 at 12,500lbs or so (eight guns and ammo means 155 gallons of fuel) will fly a bit further than a P-39 with 45 gallons

That's not my hypothesis. I believe that the tested weights were averages of weights at the beginning (takeoff) and the end (landing). How much does any plane weigh during flight? It weighs less every minute of flight because fuel is being burned. So they list an average weight for that particular flight. Seems to me the variance has to be fuel since each test normally lists the loading condition of the flight for the other variable weights (guns and ammunition, oil etc) so fuel is the only other variable.
But the main point I'm making is all the planes were tested at weights lighter than their listed gross weight. So they are all somewhat comparable, and the P-39N test was just more of the same.
In other words, why discount the P-39N tests when all the other fighters were light for their tests? I believe the planes were tested at their normal takeoff weights (unless that test lists normal items not included) and the weight listed for that flight was some average weight for the flight. Or the takeoff weight was the actual lighter weight to simulate the average weight of the flight.
Just my opinion, I can't believe nobody on this forum knows the correct answer.

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
I'm using the same source as you are, wwiiaircraftperformance.org.

Look at the climb figures for the P-39N. Compare them to the P-47B/C/D climb figures before 1944.
The P-39N was produced 11/'42 through 4/'43. Unfair to compare a much later (mid '44) plane using an experimental fuel not available until June '44. Also don't use any comparison using a Hamilton Standard propeller. That HS prop was never used in production P-47s. Use the standard models produced in '43 for a true comparison. A P-47 could not touch a P-39N in climb.

First, the so called experimental fuel is the 150 octane fuel, which is only necessary if you want to run 65" or 70" with water injection on the R-2800-63 or -59, both of which belong to newer P-47Ds. The P-47 could run 56" without water injection with 87"fuel.

Second, there were testings as early as December 1942 with Hamilton Standard propeller fitted to P-47s, and P-47s produced earlier can be easily modified in the field to carry the Hamilton Standard propeller. Farmingdale produced 850 P-47D-22-RE, 385 P-47D-25-RE, 615 P-47D-27-RE, and Evansville produced 250 P-47D-26-RA, all fitted with the Hamilton Standard propeller in the factory. Therefore, the Hamilton Standard propeller was not "never used in production P-47s".

Third, the only P-47 that is contemporary to the P-39N is the P-47B, which is the worst variant of P-47. In comparing the best variant of the P-39 with the worst variant of P-47, no useful conclusion can be drawn.

Fourth, even in the useless comparison between P-39N and 52" P-47B, your statement that the P-39 out-climbs a P-47 at all altitude is false. With the Curtiss Electric 13ft propeller, the P-47B attained a climb rate of 700ft/min at 35000ft. At that altitude, a P-39N has a climb rate of 580ft/min. At 30000ft, the P-39N has a climb rate of 1260ft/min, whereas a P-47B at that altitude out-climbed the P-39 with all tested propellers except for the Curtiss 12'2" 714-1C2-12. At the same altitude, the second worst propeller, which is the Curtiss 12'2" 101350-12, gave a rate of climb of 1300ft/min. The P-39N out-climbs the P-47B (and in most cases, significantly) at most altitudes, but not all altitudes. Please think twice before saying something so absolute.

P-39 Expert · Aug 27, 2019

When I use "contemporary" I mean models that were produced around the same time. Your examples are all late war models benefiting from later engine and fuel improvements. More comparable to the P-39N would be the C and earlier D models.
And yes, you had to go all the way up to 35000' before a turbocharged P-47 could outclimb a P-39N. And them by a whole 120fpm. Congratulations, all your research paid off. But wait, that was another one-off test comparing a prototype larger propeller to the standard 12'2" propeller. The larger 13' Curtiss propeller wouldn't be in production until your -23 model in mid'44. You are comparing various prototype propellers being tested instead of the production propellers used on real airplanes.
No Thunderbolt with a standard 12'2" Curtiss propeller would outclimb a P-39N. Period.
You going to nitpick everything I say?

AlfaKiloSierra · Aug 27, 2019

P-39 Expert said:
When I use "contemporary" I mean models that were produced around the same time. Your examples are all late war models benefiting from later engine and fuel improvements. More comparable to the P-39N would be the C and earlier D models.
And yes, you had to go all the way up to 35000' before a turbocharged P-47 could outclimb a P-39N. And them by a whole 120fpm. Congratulations, all your research paid off. But wait, that was another one-off test comparing a prototype larger propeller to the standard 12'2" propeller. The larger 13' Curtiss propeller wouldn't be in production until your -23 model in mid'44. You are comparing various prototype propellers being tested instead of the production propellers used on real airplanes.
No Thunderbolt with a standard 12'2" Curtiss propeller would outclimb a P-39N. Period.
You going to nitpick everything I say?

No Thunderbolt with a 12'2" Curtiss propeller would out-climb a P-39N at any altitude indeed. It's just that there are two P-47Bs with the Curtiss 12'2" that out-climbed the P-39N at 30000ft. What you previously said did include "at all altitudes", I just checked that again. If you'd like to stay true, abstain from using the word "all". It seems you are hardly ever right when saying something absolute. Furthermore, all my examples are indeed all late war models, including the P-47B I just used in comparison above. Is that what you want to say?

Edit: Is nitpicking everything something you have not done?

pinehilljoe · Aug 27, 2019

this is an interesting thread. If the P-39 was that much better than the P-47, why did the US send half (4719) the 39 production to the Soviets and only 203 out of 15,000 P-47s?

wuzak · Aug 27, 2019

AlfaKiloSierra said:
The P-47 could run 56" without water injection with 87"fuel.

I doubt that. And, besides, P-47s didn't use 87 octane fuel during the war. Mostly ran on 100/130.

AlfaKiloSierra · Aug 27, 2019

wuzak said:
I doubt that. And, besides, P-47s didn't use 87 octane fuel during the war. Mostly ran on 100/130.

Sorry, it should've been 100 octane fuel, my mistake.

michael rauls · Aug 27, 2019

AlfaKiloSierra said:
Sorry, it should've been 100 octane fuel, my mistake.

Ya, when you said 87 I thought maybe they were stopping to fill up at the chevron station down at the corner.

Shortround6 · Aug 27, 2019

I don't like the P-39N test because the P-39Q tests differ so much. The two P-39Q tests seem to be the airplane several months apart. In these tests the plane was ballasted to the equivalent of 120 gals of fuel (gross weight 7821lbs).

For some reason the engine was a bit down on power in the 2nd test. but trying to use that explanation for the entire performance change seems a bit much. Like at 25,000ft having the power drop from 740hp to 720hp causes the rate of climb to drop from 1570fpm to 1365fpm?

While in the 2nd test the plane was ballasted for the external .50 cal guns they were not present and so there was less drag than in the first test. Small as that difference may have been.

The P-39M is a real puzzle, at 7430lbs (just 156lbs more than the N but almost 400lbs lighter than the Q) and at 25,000ft it supposedly had 725hp but it's climb rate was only 1400fpm.
The power section was the same in the P-39M as the P-39N and Q. the latter two used a different reduction gear to the propeller.

The N for some reason is a real outlier when compared to the planes just before it and just after it.

P-39 Expert · Aug 28, 2019

pinehilljoe said:
this is an interesting thread. If the P-39 was that much better than the P-47, why did the US send half (4719) the 39 production to the Soviets and only 203 out of 15,000 P-47s?

P-47 was a good plane, a good deal faster than the P-39N but the P-39N climbed a good deal better. Endurance was about the same. Maneuverability favored the P-39N, roll and dive favored the P-47. P-39N was not better but certainly in the same class as the P-47.

Regarding the Soviets, the P-39 fitted their needs like a glove and they begged for more. They likely viewed the P-47 as more complicated and more difficult to maintain and being turbocharged was likely that the AAF didn't want to share that tech with the Soviets. The P-39N was available from late '42 and the P-47 didn't get into combat until mid-'43.

In any event, turbocharger development was long and expensive. It was the AAF's baby (nobody else used it) and the P-47 (and P-38) were long awaited and were going to be used as soon as they were available. This decision was very logical and probably made prior to the results of the P-39N tests.

The early P-39s (D/F/K/L) suffered from excessive weight (although easily corrected) that caused slow climbs and low ceilings. An early P-39D/F/K/L with a drop tank could only climb to about 20000' before the climb rate fell below 1000fpm (combat ceiling). The Japanese G4M Betty bombers operated between 18000' and 22000' and the Zeros/Oscars escorted them a couple thousand feet higher. So the early P-39s normally had the initial altitude disadvantage in any engagement with the Japanese. Giving your opponents the first punch is not the way to a long life. The AAF was really ready for the P-47 and P-38 to become operational.

Then in late '42 everything came together for the P-39N (new more powerful engine, 2.23 reduction gear to handle the larger prop) but the decision had already been made.
The later P-39N/Q were split pretty evenly between the Soviets (who loved them) and training command. Virtually every AAF fighter pilot trained on the P-39.

P-39 Expert · Aug 28, 2019

Shortround6 said:
I don't like the P-39N test because the P-39Q tests differ so much. The two P-39Q tests seem to be the airplane several months apart. In these tests the plane was ballasted to the equivalent of 120 gals of fuel (gross weight 7821lbs).

For some reason the engine was a bit down on power in the 2nd test. but trying to use that explanation for the entire performance change seems a bit much. Like at 25,000ft having the power drop from 740hp to 720hp causes the rate of climb to drop from 1570fpm to 1365fpm?

While in the 2nd test the plane was ballasted for the external .50 cal guns they were not present and so there was less drag than in the first test. Small as that difference may have been.

The P-39M is a real puzzle, at 7430lbs (just 156lbs more than the N but almost 400lbs lighter than the Q) and at 25,000ft it supposedly had 725hp but it's climb rate was only 1400fpm.
The power section was the same in the P-39M as the P-39N and Q. the latter two used a different reduction gear to the propeller.

The N for some reason is a real outlier when compared to the planes just before it and just after it.

The M, N and Q all used the new (from late '42) higher rated engine with the 9.6 supercharger gears. The differences in performance were the smaller prop with 2:1 reduction gear for the M and the underwing gondola guns and gradually increasing weight for the Q. Remove the wing guns and the N and Q are the same plane if weight is kept the same.
A big difference in the tests were the M was tested with drop tank sway braces and the N was not. These sway braces were horribly inefficient and likely were the reason for the speed difference (and some climb) between the M and N.

Planes that are simultaneously both the most over rated and the most under rated.

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