Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (2 Viewers)

[pbehn]

I also think he is mixing and confusing information from the P-39N manual and the P-39Q manual. Both manuals show internal fuel capacity of 87 gallons in the weight and balance charts. I see no reference of 120 gallons.

He is correct about the IAS/ TAS conversion table only found in the P-39Q manual. With no instruction to convert in the earlier manuals, I think there was the source of some confusion (as you pointed out earlier).

Bottom line, I think with some of the numbers shown, the P-39 had a dismal high altitude intercept radius.

I think they removed fuel cells from the wings and supplied them as kits. Quote "500 of P-39Ns were built, with all but the first 160 featuring elimination of three internal fuel cells to reduce weight. The P-39N could of course carry an external tank to compensate for the smaller internal fuel load, and service units that wanted the full internal fuel load back could install a field upgrade kit to restore the deleted fuel cells. "
From The Bell P-39 Airacobra & P-63 Kingcobra.

 

[FLYBOYJ]

I think they removed fuel cells from the wings and supplied them as kits. Quote "500 of P-39Ns were built, with all but the first 160 featuring elimination of three internal fuel cells to reduce weight. The P-39N could of course carry an external tank to compensate for the smaller internal fuel load, and service units that wanted the full internal fuel load back could install a field upgrade kit to restore the deleted fuel cells. "
From The Bell P-39 Airacobra & P-63 Kingcobra.

Good info, but it seems our friend played with the example that was going to give the greatest range. The external tank installation is indicated clearly in the W&B report

 

[Thumpalumpacus]

Also -- this thread has longer legs than any -39 that ever flew.

 

[ThomasP]

I'm so confused!!

Which aircraft are we comparing now? The reason I ask is that the latest thread (now sub-thread) started with P-39 v P-40, then switched to the P-39 v F4U, then P-39 v ?, and now P-39 v P51.

Questions:

1. Is there really any question (in anyone's mind) that the P-39 (any variant) can be grossly outranged by the F4U-x, P-38x, P-51x? Except maybe on a Point Local intercept, where internal fuel and DTs would not be used for range (ie WUTO, ~max climb to intercept altitude (whatever is suitable for the aircraft), combat, return to Home base/nearby base and land on fumes if necessary)??

2. Is there any question that the main limitation to a P-39 long range mission is the internal fuel load (87 or 120 USgal)? Just as it is for any of the other aircraft (ie If the profile is internal for WUTO and initial climb, switch to DT for climb to operational altitude, DT for cruise outbound, drop DTs at/near point of contact, internal for combat, internal for cruise home, internal for some amount of reserve at/near home)??

3. Which variant of the P-39 are we using for the comparison? If I understand correctly, P-39 Expert is using a variant of the P-39N with either 87 or 120 USgal internal fuel (depending on mission profile), armed with 1x37mm or 20mm and 2x.50 cal, lightened and rebalanced through a change in armament, reduced armour, with a reposition/removal of some equipment. The idea being that the P-39 could have been significantly more capable in modified form. (I am leaving out the possibility of the engine change to the -93 model due to the current discussion being focused on the range and altitude issues of the standard variants.) It should not be difficult to specify the operational weights, and agree on ~speeds, ROC, fuel burn, etc.

Answers please.

 

[GregP]

I view this thread as a cognitive dissonance with regard to motivational committance.

It is similar to needing a good, long-range, high-altitude fighter, but only having a P-39 available.

What is the point, especially when you can't even take time to join up with your flight because the range is too short to go around the pattern more than a couple of times without drop tanks. The airplane is in a state of virtual fuel emergency when it is gassed up, oiled up, and ready to start the engine. Heck, with P-39's range, you don't even need a relief tube!

 

[Stig1207]

Lieutenant Colonel of the Guards Alexander I. Pokryshin, a Soviet ace with 59 kills to his credit, scored 48 of these in a P-39. He was awarded the Distinguished Flying Cross by President Roosevelt. There are eight other P-39 pilots with at least 20 kills. Among top Airacobra aces were Grigorii A Rechkalov (44 kills) , Nikolai D Gulayev (36 kills), Ivan I Babak, Aleksandr F Klubov, Andrei I Trud, and the brothers Boris B Glinka and Dmitrii B Glinka

Quoted from the link posted by PBehn to Joe Baugher's site.

I read an article in Flypast the other day, by Chris Goss iirc. It states that 204 Me 109 pilots scored more than 5 kills during the BoB, so they were credited with at least 1020 victories, but obviously more, so what would the average be 7 or 8? That would make 1400 to 1600 kills by Me 109 aces.
RAF losses vary by source, but the highest figure I am aware of is 1500+ for Fighter Command, Bomber Command, and Coastal Command to all causes.

Aces scores are not a reliable yardstick for evaluating a particular fighter aircraft's combat performance. Perhaps the only thing that is overated with the P-39 is the Stalin Falcons' achievments with it.

 

[pbehn]

Good info, but it seems our friend played with the example that was going to give the greatest range. The external tank installation is indicated clearly in the W&B report

The internal tanks were removed to reduce weight, so the best combination of range and high altitude performance is chosen for the benefit of the discussion. Use the external tank then drop it to go through the 25,000ft speed trap.

 

[FLYBOYJ]

I'm so confused!!

Which aircraft are we comparing now? The reason I ask is that the latest thread (now sub-thread) started with P-39 v P-40, then switched to the P-39 v F4U, then P-39 v ?, and now P-39 v P51.

"Take off at S/L and climb immediately to 20,000 feet. For the climb chart I'm going to "interpolate" a climb to 20,000' (because the climb chart goes from 15K to 25K). I'll then plug in a 15 minute cruise at 20K followed by "combat" at max power for 10 minutes. After that I'll show at 20,000' what fuel is left and the maximum range that is left."

Questions:

1. Is there really any question (in anyone's mind) that the P-39 (any variant) can be grossly outranged by the F4U-x, P-38x, P-51x? Except maybe on a Point Local intercept, where internal fuel and DTs would not be used for range (ie WUTO, ~max climb to intercept altitude (whatever is suitable for the aircraft), combat, return to Home base/nearby base and land on fumes if necessary)??

No doubt in my mind but to convince "experts" sometimes you have to painfully jump through hoops!

2. Is there any question that the main limitation to a P-39 long range mission is the internal fuel load (87 or 120 USgal)? Just as it is for any of the other aircraft (ie If the profile is internal for WUTO and initial climb, switch to DT for climb to operational altitude, DT for cruise outbound, drop DTs at/near point of contact, internal for combat, internal for cruise home, internal for some amount of reserve at/near home)??

No question in my mind!

3. Which variant of the P-39 are we using for the comparison? If I understand correctly, P-39 Expert is using a variant of the P-39N with either 87 or 120 USgal internal fuel (depending on mission profile), armed with 1x37mm or 20mm and 2x.50 cal, lightened and rebalanced through a change in armament, reduced armour, with a reposition/removal of some equipment. The idea being that the P-39 could have been significantly more capable in modified form. (I am leaving out the possibility of the engine change to the -93 model due to the current discussion being focused on the range and altitude issues of the standard variants.) It should not be difficult to specify the operational weights, and agree on ~speeds, ROC, fuel burn, etc.

I used the example straight out of the posted P-39N flight manual with 87 gallons of fuel shown per the weight and balance report. It was pointed out that some aircraft had additional wing fuel tanks installed but those weren't used in my examples although our expert friend keep plugging in this and performance data from the P-39Q

Answers please.

Hope this helps, any additional information you can add would be appreciated but probably not convincing to some!

 

[P-39 Expert]

I'm so confused!!

Which aircraft are we comparing now? The reason I ask is that the latest thread (now sub-thread) started with P-39 v P-40, then switched to the P-39 v F4U, then P-39 v ?, and now P-39 v P51.

Questions:

1. Is there really any question (in anyone's mind) that the P-39 (any variant) can be grossly outranged by the F4U-x, P-38x, P-51x? Except maybe on a Point Local intercept, where internal fuel and DTs would not be used for range (ie WUTO, ~max climb to intercept altitude (whatever is suitable for the aircraft), combat, return to Home base/nearby base and land on fumes if necessary)?? About the same as F4U-1, see my previous post. Certainly not as good as P-38 and P-51, they held more fuel.

2. Is there any question that the main limitation to a P-39 long range mission is the internal fuel load (87 or 120 USgal)? Just as it is for any of the other aircraft (ie If the profile is internal for WUTO and initial climb, switch to DT for climb to operational altitude, DT for cruise outbound, drop DTs at/near point of contact, internal for combat, internal for cruise home, internal for some amount of reserve at/near home)??

3. Which variant of the P-39 are we using for the comparison? If I understand correctly, P-39 Expert is using a variant of the P-39N with either 87 or 120 USgal internal fuel (depending on mission profile), armed with 1x37mm or 20mm and 2x.50 cal, lightened and rebalanced through a change in armament, reduced armour, with a reposition/removal of some equipment. The idea being that the P-39 could have been significantly more capable in modified form. (I am leaving out the possibility of the engine change to the -93 model due to the current discussion being focused on the range and altitude issues of the standard variants.) It should not be difficult to specify the operational weights, and agree on ~speeds, ROC, fuel burn, etc. There were really only two P-39s, despite the variations that ran all the way up to Q. Main difference was their engines. 1942 P-39D/F/K/L had the -35 or -63 engines with critical altitude of 12000ft. They were limited to low and medium altitude (under 20000ft) because they were too heavy for their engine power. Unnecessary/redundant items (30cal wing guns, one piece or armor plate, IFF radio) could have been removed at front line bases to greatly improve climb/ceiling.

1943 P-39N/Q had uprated -85 engines with higher S/C gear ratio and critical altitude of 15000ft. The N model had a 38,500ft ceiling and an excellent rate of climb at all altitudes at stated weight, nothing needed to be removed. Only real difference in the N and Q was wing guns. Remove the underwing podded 50calMGs from the Q and they were about the same as an N.

Answers please.

Please expand above.

 

[P-39 Expert]

Shortround post #1564: Yes IAS was mislabeled in column I from P-39Q range chart. Correct that to TAS for cruising speeds at max. continuous. 330mph at 25000ft etc.
Shortround post #1590: Your combat reserve of 33gals vs mine of 24gals results in about a 50 mile difference. Not really significant. I'll stick with mine.
Flyboy post #1567: Regarding fuel capacity, every production P-39 was built for 120gal internal fuel. AAF reduced fuel in some N and Q models, probably at the request of their primary user the Soviets. Kits were available to restore the full 120gal in the field. Any range discussion should use the normal 120gal. Also if the wing guns are removed there is room for more fuel, at least 30gal which would bring internal fuel up to 150gal, same as P-38F/G.
Flyboy post #1584: Again, 1942 P-39s were way too heavy (could have been lightened easily). Gen. Kenney had made up his mind about the P-39 and welcomed the P-38s. They came in about the time the vastly improved P-39N was available, end of 1942. And the AAF had already decided that (based on the 1942 P-39s) the war would be fought primarily with the P-38 and P-47 and the P-39 would be sent to Russia or used for training. Compared to the P-38F/G the P-39N climbed better and was faster under 20000ft. The Russians greatly benefitted from the lend lease P-39N/Q.

 

[wuzak]

P-39 was built for 120gal internal fuel. AAF reduced fuel in some N and Q models, probably at the request of their primary user the Soviets. Kits were available to restore the full 120gal in the field. Any range discussion should use the normal 120gal. Also if the wing guns are removed there is room for more fuel, at least 30gal which would bring internal fuel up to 150gal, same as P-38F/G.

The reduction from 120 USG to 87 USG was to reduce weight, like you've been banging on about for years now.

The N and Q were produced with 87 USG from the factory. Kits could be applied in the field to bring them up to 120USG, but how many were fitted and where?

Did the wings have the facilities for extra fuel tanks where the guns were mounted?

 

[Peter Gunn]

So much to parse out, well...

Shortround post #1564: Yes IAS was mislabeled in column I from P-39Q range chart. Correct that to TAS for cruising speeds at max. continuous. 330mph at 25000ft etc.

So, you're guessing at the TAS?

Shortround post #1590: Your combat reserve of 33gals vs mine of 24gals results in about a 50 mile difference. Not really significant. I'll stick with mine.

Because it fits your narrative better?

Flyboy post #1567: Regarding fuel capacity, every production P-39 was built for 120gal internal fuel. AAF reduced fuel in some N and Q models, probably at the request of their primary user the Soviets. Kits were available to restore the full 120gal in the field. Any range discussion should use the normal 120gal. Also if the wing guns are removed there is room for more fuel, at least 30gal which would bring internal fuel up to 150gal, same as P-38F/G.

Why should the range discussion be based on non-factual data? The plane did not have 120 gallons of internal fuel, it also had wing guns instead of any extra fuel in that space and therefore it weighed what it weighed, there's no getting around those two FACTS.

Flyboy post #1584: Again, 1942 P-39s were way too heavy (could have been lightened easily). Gen. Kenney had made up his mind about the P-39 and welcomed the P-38s.

Why do you suppose that was? You don't think a general in command of a numbered air force with responsibilities for the entire theater was unaware of any changes in hardware coming down the pipeline? I'd wage General Kenney was eminently aware of what aircraft with attending upgrades were in the works or on the horizon. Bottom line, the short ranged low altitude P-39 was not a viable asset for his command. Hell, he even had reservations about getting the P-47 because of range issues with the Thunderbolt. So when it came to the P-39 he correctly said Nyet.

They came in about the time the vastly improved P-39N was available, end of 1942. And the AAF had already decided that (based on the 1942 P-39s) the war would be fought primarily with the P-38 and P-47 and the P-39 would be sent to Russia or used for training. Compared to the P-38F/G the P-39N climbed better and was faster under 20000ft. The Russians greatly benefitted from the lend lease P-39N/Q.

Why do you think the AAF ditched the Airacobra for the P-38 and the Thunderbolt? Perhaps AAF leadership was cognizant of realities you are not, like ETO ops required high altitude long range, and more importantly, high performance fighters, something the P-39 was incapable of achieving. You're saying your smarter than all the AAF gentlemen (and RAF) that tested, flew, examined etc. this plane and universally reached the conclusion that it was not suited for any combat EXCEPT short range low altitude ops? Also, the VVS fought a different war than did the AAF or the RAF, or are we forgetting this?

 

[wuzak]

There were really only two P-39s, despite the variations that ran all the way up to Q. Main difference was their engines. 1942 P-39D/F/K/L had the -35 or -63 engines with critical altitude of 12000ft. They were limited to low and medium altitude (under 20000ft) because they were too heavy for their engine power. Unnecessary/redundant items (30cal wing guns, one piece or armor plate, IFF radio) could have been removed at front line bases to greatly improve climb/ceiling.

Again, where are you planning to use this aircraft?

You are claiming that the P-39N compares to aircraft in the ETO. Do you want to use the P-39 in the ETO, then you need to keep the IFF.

1943 P-39N/Q had uprated -85 engines with higher S/C gear ratio and critical altitude of 15000ft. The N model had a 38,500ft ceiling and an excellent rate of climb at all altitudes at stated weight, nothing needed to be removed. Only real difference in the N and Q was wing guns. Remove the underwing podded 50calMGs from the Q and they were about the same as an N.

The Spitfire V of 1941 had a critical altitude of 20,000ft (with ram). So a 15,000ft critical altitude in 1943 isn't very impressive.

 

[Glider]

And we still have the questions
a) How much weight is involved adding the extra fuel plus its tanks and plumbing
b) If the N was so good why was it replaced with the Q which had less performance
c) You don't just rip out guns and add fuel
d) what is the performance of the N with the extra weight. My guess is that it will be very similar to the P39Q which was a very similar aircraft, which in turn knocks great holes in your claim for the P39N being such a wonder weapon

 

[FLYBOYJ]

Flyboy post #1567: Regarding fuel capacity, every production P-39 was built for 120gal internal fuel. AAF reduced fuel in some N and Q models, probably at the request of their primary user the Soviets. Kits were available to restore the full 120gal in the field. Any range discussion should use the normal 120gal. Also if the wing guns are removed there is room for more fuel, at least 30gal which would bring internal fuel up to 150gal, same as P-38F/G.

"Could have, would have, should have" once again you're cherry picking. I think you know as well as I the AAF units in the SWP (80th FG, 35th FS for example) that were using P-39Ds and P-400s did not operate with 120 gallon fuel tanks. Even with the extra fuel the P-38 F/G, let alone the J easily outranged the P-39. So please, stop trying to throw "what ifs" into what actually happened.

Flyboy post #1584: Again, 1942 P-39s were way too heavy (could have been lightened easily).

Could have, would have, should have."

Gen. Kenney had made up his mind about the P-39 and welcomed the P-38s. They came in about the time the vastly improved P-39N was available, end of 1942. And the AAF had already decided that (based on the 1942 P-39s) the war would be fought primarily with the P-38 and P-47 and the P-39 would be sent to Russia or used for training. Compared to the P-38F/G the P-39N climbed better and was faster under 20000ft. The Russians greatly benefitted from the lend lease P-39N/Q.

The P-38 F/Gs that were replacing the P-39 in front line units were already in theater at the end of 1942 and General Kenney made up his mind because the P-39s performance in that theater was not suitable for what was actually needed and the P-38 was a flat out better aircraft for the mission required. He really didn't want the P-47 either but had to take them because P-38s were being diverted to North Africa and England (That's another story).

If you're going to make comparisons, why don't you compare what was being used at the time?!?!? P-39D or P-400!! The little bit of cherry picked advantage you're trying to show for the P-39N did not make up for the deficiencies in range and high altitude performance when compared to the P-38. For that matter let's compare the P-39M, N or Q to the P-38 J or L!

Now I will give credit were credit is due. The 39th an 9th FS while flying the P-39 really didn't do to badly and their experience carried over when they transitioned to the P-38. Tom Lynch and Curran Jones were two standouts with multiple credits. Pilot skill was probably the main factor of this success as Lynch became one of the top fighter pilots in the SWP and possibly could have scored higher than Richard Bong if he wasn't killed. Bottom Line V Fighter Command aerial victories soared after the P-38 entered combat.

Total agreement with the Soviets and the P-39, it was perfect for them and their operations and their combat record confirmed that despite leaving the gear box armor installed!

 

[Shortround6]

A short, incomplete and confusing "history" of the P-400 weight growth.

From Page 120 of "Cobra!" by Birch Mathews.

These are attributed to Bell model specifications. weight in pounds.

date.............................Empty...................useful load...................Gross...........................notes
Feb 1940....................4,524.......................1,325...........................5,849............................1 cannon, two machine guns
March 1940..............4,715.......................1,285............................6,000............................2machine guns added in each wing
May 1940.................5,149........................1,841............................7,000............................wing gun caliber increased
July 1940...................5,383.......................1,974.............................7,350...........................Armour and self-sealing tanks added
Jan 1941....................5,406.......................2,006.............................7,466...........................Minor empty and useful load increases
June 1941.................5,548........................2,087.............................7,635.........................Engine and fixed equipment weight increases
July 1941...................5,550.......................2,087..............................7,637..........................actual weight of Serial number AH 621

Now a few remarks about the 1325lb useful load in the first line. this starts my conclusions
20mm cannon...................................131lb
37mm ammo.....................................32.4lb
2 .50 cal machine guns.................161lbs
.50 cal ammo....................................129lbs
Pilot.......................................................160lbs
oil..............................................................75lbs.
sub total ............................................688lbs

weight left for fuel..........................637lbs=106 US gallons.
Spaces in the wings would hold 170 gallons, the "tanks" were integral (seal up spaces in the wing, no separate tank/s)

The first 165 P-400s were ordered by the French in April of 1940, the French were supposed to supply the guns. 20mm, 13.2mm and 7.5mm.
The British don't get involved until May-June of 1940 when the design has to be redone (converted back to imperial measurements from Metric), use British/American guns and other accessories (radios, etc)
I don't know if the French asked for the four wing machine guns or if Bell offered to make the plane look better?

The 3rd line is rather suspect. The increase in wing gun caliber is from 7.5mm to 7.7mm
The French MAC 34 gun weighed 10.7kg. the Browning weighed about the same. Empty weight does not include the guns although it includes mounts and ammunition bins/tracks/boxes. Increase in useful load and gross weight cannot be blamed on change of guns or change in ammo supply except for around 230lbs.

Line 4 with the added armor and self sealing tanks might well be attributed to the British. US followed in Sept. This also cut the theoretical fuel capacity with full (instead of part filled ) tanks from 170 gallons to 120 galls (US gallons). Not to pick on the P-39. The P-36/Hawk and P-40s were NOT measured for performance with the tank behind the pilot filled at this point in time.

The plane also gained weight due to increases in the engine weight and some of the other parts over which neither Bell or the British had any control over. The book the above list is from claims the weight of the Allison engine and accessories (which were government furnished equipment ) increase 380lbs from the start of design for the P-400 (well before French order) to the production versions.

So I ask again what were the items/equipment that the British asked for in order to reduce the performance of the Aircobra I so they could get out of the contract.

every plane escalated in weight.

 

[Shortround6]

And we still have the questions
a) How much weight is involved adding the extra fuel plus its tanks and plumbing
b) If the N was so good why was it replaced with the Q which had less performance
c) You don't just rip out guns and add fuel
d) what is the performance of the N with the extra weight. My guess is that it will be very similar to the P39Q which was a very similar aircraft, which in turn knocks great holes in your claim for the P39N being such a wonder weapon

Somewhere I had post with the listed performance of not only the P-39N but the P-39M (same plane with different reduction gear and propeller) the P-39Q, (same plane with different wing guns), the P-40 using the Allison with 9.6 supercharger gears and the P-51A using the Allison with 9.60 gears.

The P-39N was way, way better in many categories, suspiciously so. like double digit percentage changes in climb.

Maybe the test aircraft did perform that well, sometimes you get a plane where everything just "clicks" but what happens when you don't?

If somebody made a graph with all the P-39 models in speed and climb from the D through Q all of the planes except the N would be somewhat closely gathered together in a bunch, with the lines for P-39N way out by themselves. There doesn't seem to be enough difference for the N to justify that change in performance.

 

[buffnut453]

Somewhere I had post with the listed performance of not only the P-39N but the P-39M (same plane with different reduction gear and propeller) the P-39Q, (same plane with different wing guns), the P-40 using the Allison with 9.6 supercharger gears and the P-51A using the Allison with 9.60 gears.

The P-39N was way, way better in many categories, suspiciously so. like double digit percentage changes in climb.

Maybe the test aircraft did perform that well, sometimes you get a plane where everything just "clicks" but what happens when you don't?

If somebody made a graph with all the P-39 models in speed and climb from the D through Q all of the planes except the N would be somewhat closely gathered together in a bunch, with the lines for P-39N way out by themselves. There doesn't seem to be enough difference for the N to justify that change in performance.

But it's in the charts so it must be true!

 

[Glider]

Somewhere I had post with the listed performance of not only the P-39N but the P-39M (same plane with different reduction gear and propeller) the P-39Q, (same plane with different wing guns), the P-40 using the Allison with 9.6 supercharger gears and the P-51A using the Allison with 9.60 gears.

The P-39N was way, way better in many categories, suspiciously so. like double digit percentage changes in climb.

Maybe the test aircraft did perform that well, sometimes you get a plane where everything just "clicks" but what happens when you don't?

If somebody made a graph with all the P-39 models in speed and climb from the D through Q all of the planes except the N would be somewhat closely gathered together in a bunch, with the lines for P-39N way out by themselves. There doesn't seem to be enough difference for the N to justify that change in performance.

I totally agree that two aircraft the P39N and the P39Q were in many ways very similar and yet the performance was so different, to me it doesn't feel right.

However it seems to be the official performance so it isn't up to me to blame P39 for jumping on the P39N bandwagon. He needs something to support his belief.

What I can ask him is why the P39Q which was in many ways inferior in performance brought into service in the first place. Plus all the other questions that people have raised without response. The silence is deafening and yet speaks volumes

 

[buffnut453]

What I can ask him is why the P39Q which was in many ways inferior in performance brought into service in the first place. Plus all the other questions that people have raised without response. The silence is deafening and yet speaks volumes

The deafening silence is replaced with constant repetition of his beliefs...the wing 30 cals were useless and should have been removed, same for the gearbox armour, no need for IFF, perfidious Albion unnecessarily increased the weight to get out of the contract etc, etc, etc.