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

[P-39 Expert]

Interestingly, that chart shows the 120USG internal fuel is divided into 104USG normal and 16USG overload.

The fuel capacity was 120 gallons including the 16 gallon reserve. Wasn't actually additional fuel, the inside left fuel tank had two lines to the carburetor, one emptied the tank and the other was shorter forcing the pilot to switch to the "reserve" which was the 16 gallons left over in that tank. Kind of like the "standpipe" reserve the navy used. A standpipe in the bottom of the tank held fuel after the tank was emptied, forcing the pilot to switch tanks to the reserve in the standpipe. In addition to the fuel gauges this arrangement ran the main tank dry and forced the pilot to switch to reserve as a last measure to remind him that fuel was almost gone. Awful description by me, I'll try and find a drawing that explains it better.

 

[Shortround6]

The "Weight and Balance Chart" for the P-39K that I posted earlier was one page before the chart for the P-39L, shows a difference of 50# from the K so I would guess that was the difference in the two props. The only real differences in any of the P-39 models were propellers, (different versions of the same) engines (incl. reduction gears), radios and wing guns.

The front "balloon tire" was on all the P-39s (D,F and K) until the L (and M,N and Q) switched to the slimmer tire.

EW of P-39L....5733lbs
EW of P-39K....5658lbs
difference...........75lbs

Due to prop, front wheel, pixie dust???

The N and Q had the bigger diameter props. Weight unknown?

 

[Shortround6]

The fuel capacity was 120 gallons including the 16 gallon reserve. Wasn't actually additional fuel, the inside left fuel tank had two lines to the carburetor, one emptied the tank and the other was shorter forcing the pilot to switch to the "reserve" which was the 16 gallons left over in that tank. Kind of like the "standpipe" reserve the navy used. A standpipe in the bottom of the tank held fuel after the tank was emptied, forcing the pilot to switch tanks to the reserve in the standpipe. In addition to the fuel gauges this arrangement ran the main tank dry and forced the pilot to switch to reserve as a last measure to remind him that fuel was almost gone. Awful description by me, I'll try and find a drawing that explains it better.

This is actually quite familiar to anybody who has ridden motorcycles.

two pipes stick up into tank, you draw fuel from the taller leaving the difference between the taller pipe and the shorter one as the reserve.

 

[P-39 Expert]

The thing with the P-39 is that you were yanking 2 guns out of each wing
View attachment 487713
This is a dummied up installation for a Museum on a P-39Q.
and you had two chartridge slots in the bottom of the wing.
And replacing them with the podded .50 cal.
Both the 109 and Mig 3 had nothing coming out or any holes covered over.
The under wing pods could very well have had more drag than the .30 cal installation. But we have no figures on how much drag was saved by pulling and covering the .30s and we have no real figures on a P-39Q with and without pods.

Edit, better picture.
View attachment 487714

Those .30s in the wing weighed almost 400# total with the original 1000 rounds per gun. Later in the K,L,M and N they reduced the ammo to 300rpg and cut the weight in half to 200# for all 4 guns. Total firing time was about 15 seconds with 300rpg. Then with the Q they switched to the underwing .50cal MGs which weighed 330# including ammo, so the shift to the .50s weighed 130# more. The Q with the underwing .50s was slower than the N by 14mph (399 vs 385). I wish they had discarded the wing armament all together (like the Russians), saved the weight and had the 37mm cannon and the two .50s in the nose.

 

[DarrenW]

I added a P-39N to the chart already provided by Milosh (I know that you really like these ). You can plainly see that, while it could match the early P-47 in range, it's not really a fair contest because the P-39N requires a 75 gallon drop tank to achieve the same results. The P-47 is flying clean from T/O. By the way, before you ask where I got my statistics to chart this, I actually used the information you provided us earlier in this thread......

87 US Gallons internal fuel
75 US Gallon drop tank (only tank available for the Airacobra)
162 US Gallons total fuel
62 gal/hour rate of fuel use equaling roughly 2 hours 40 minutes of flight time
20 minute fuel burned during take-off/climb to altitude/ forming up
20 minute reserve
Actual flight time available for mission = 2 hours
cruise speed = 230 mph
Radius of action (to/from) = 230 miles

 

[pbehn]

After reading a lot I now no longer believe what I am reading. Early test results were never reproduced and by a masterly piece of denial, plausible denial, omission and evasion Bell managed to get a plane that was unsuitable in every way into production and service. Bell's claims about performance and handling were never reproduced in the field, its speed and climb were never satisfactory and the last official test rejected it as a fighter for the US military at all.

 

[P-39 Expert]

EW of P-39L....5733lbs
EW of P-39K....5658lbs
difference...........75lbs

Due to prop, front wheel, pixie dust???

The N and Q had the bigger diameter props. Weight unknown?

Yes, I agree and the gross weights are different by 75# also, everything else is the same. My 50# figure is from the original hydromatic prop on the F versus the Curtiss electric on the D. These were 10' props and the extra 25# may have been because of the larger propeller. The hydro prop replaced the Curtiss electric prop from the F model on except for the L (250 mfgd.).

 

[Shortround6]

cruise speed = 230 mph

Which makes you a target for Luftwaffe fighters, not an escort.
This is why the escorts "cruised" at 300mph or above and "S" over the bombers. If you are cruising down around 230mph it take around two minutes to accelerate to top speed at which either you are toast or the attackers have come and gone. You are also using up 2 minutes of your 5 min combat power "allowance" just to get up to combat speed.

 

[P-39 Expert]

I added a P-39N to the chart already provided by Milosh (I know that you really like these ). You can plainly see that, while it could match the early P-47 in range, it's not really a fair contest because the P-39N requires a 75 gallon drop tank to achieve the same results. The P-47 is flying clean from T/O. By the way, before you ask where I got my statistics to chart this, I actually used the information you provided us earlier in this thread......

87 US Gallons internal fuel
75 US Gallon drop tank (only tank available for the Airacobra)
162 US Gallons total fuel
62 gal/hour rate of fuel use equaling roughly 2 hours 40 minutes of flight time
20 minute fuel burned during take-off/climb to altitude/ forming up
20 minute reserve
Actual flight time available for mission = 2 hours
cruise speed = 230 mph
Radius of action (to/from) = 230 miles
View attachment 487807

Can we agree that at least some of the Ns had 120 gals internal and carried a 110gal drop tank? This is absolutely true.

You have figured out how to figure range/endurance from the pilots manual. 120 gal + 110 gal drop = 230gal less 20 gal reserve = 210 gal divided by 62gph = 3.4 hrs less 15 min combat and 20 min reserve for landing = 2.8 hr x 230mph = 644mi divided by 2 = 322mi radius after reserves. The 230mph is the bomber speed TAS and you are weaving to stay at their speed. Drop tank of up to 175 gal was available for the P-39.

 

[P-39 Expert]

Which makes you a target for Luftwaffe fighters, not an escort.
This is why the escorts "cruised" at 300mph or above and "S" over the bombers. If you are cruising down around 230mph it take around two minutes to accelerate to top speed at which either you are toast or the attackers have come and gone. You are also using up 2 minutes of your 5 min combat power "allowance" just to get up to combat speed.

Please read my calculations again. I explained that the N with the tank cruised at 281 TAS but since it had to weave to stay with the bombers who were going 230mph TAS that forward progress was at bomber speed. Slow, I know, but that is why you could drop the tank for performance.

 

[Milosh]

That 322 mi is not a straight line but a zig zag line.

 

[Milosh]

So there was no fuel burn during the climb to 25k?

 

[Shortround6]

Can we please not use ferry tanks or tanks that were not in existence for large parts of 1943 to figure out useful the the P-39 would have been as an escort in early 1943?
The P-47 first used 200 gallon paper tanks only part filled on July 28th 1943, They couldn't pull the fuel out of them at higher altitudes but they at least got the Planes up to 20-22,000ft. and thus extended the range somewhat.
Locally made (in the UK) 108 gallon tanks don't show up until Sept, 1943, in the mean time they figured out how to mount 75/85 gallon tanks (and how to pressurize the tank) and by the end of Aug 43 over ten thousand tanks are enroute.
This is all waaaaaay to late to make any decisions about using the P-39 as an escort in late 1942/very early 1943.

Allowable take-off weights from hard runways in good conditions for ferrying are often not the same as from grass/unpaved fields in combat areas. overloaded aircraft can lead to broken landing gear and failing to clear the fence.
going from 7600lb to 8100lbs increased take-off run on a sod runway from 1400ft to 1700ft and adjusting form 32 degrees F to 72 degrees F kicks that up 20%. Take off at 8600lbs would be?????
Yes the P-47 needed a lot of runway.

 

[pbehn]

I added a P-39N to the chart already provided by Milosh (I know that you really like these ). You can plainly see that, while it could match the early P-47 in range, it's not really a fair contest because the P-39N requires a 75 gallon drop tank to achieve the same results. The P-47 is flying clean from T/O. By the way, before you ask where I got my statistics to chart this, I actually used the information you provided us earlier in this thread......

87 US Gallons internal fuel
75 US Gallon drop tank (only tank available for the Airacobra)
162 US Gallons total fuel
62 gal/hour rate of fuel use equaling roughly 2 hours 40 minutes of flight time
20 minute fuel burned during take-off/climb to altitude/ forming up
20 minute reserve
Actual flight time available for mission = 2 hours
cruise speed = 230 mph
Radius of action (to/from) = 230 miles
View attachment 487807

Informative map but misleading, the P 38 could reach Berlin but could not escort a bomber formation to Berlin, this because of the fuel burned on forming up and weaving which wastes fuel. Also with respect to the map the "THE" on "The Rhein" is where P-51s reached when involved on a raid by the RAF on the Dortmund Ems Canal in October 1942.

 

[Peter Gunn]

Can we agree that at least some of the Ns had 120 gals internal and carried a 110gal drop tank? This is absolutely true.

You have figured out how to figure range/endurance from the pilots manual. 120 gal + 110 gal drop = 230gal less 20 gal reserve = 210 gal divided by 62gph = 3.4 hrs less 15 min combat and 20 min reserve for landing = 2.8 hr x 230mph = 644mi divided by 2 = 322mi radius after reserves. The 230mph is the bomber speed TAS and you are weaving to stay at their speed. Drop tank of up to 175 gal was available for the P-39.

No.

Maybe because drgondog post #736...

The 110 gallon tank was used initially in late 1943 on P-47C/D C/L but AFAIK never on the P-39. First used on P-51B in May 1944.

I'm unaware that Bell added a tank pressurization capability such as slaving off exhaust or instrument vacuum pump. Did Bell modify the P-39 so that they could carry ANY tank above 20K? Do you have any source documentation of either a mission flown with 110 gallon tank or any mission flown above 20K w/75 gallon combat tank?

Please point to your sources.

I may have missed it but I do not see a response to this, if so, please point it out for me.

 

[P-39 Expert]

That 322 mi is not a straight line but a zig zag line.

View attachment 487820

I'm not doing a good job of explaining this, my bad. The bombers are going 230mph TAS. Escort is going faster. But escort has to stay with the slower bombers. Bombers fly straight, escort weaves (zig zag) above them. The whole parade is making forward progress at 230mph.

So you can't use the escort speed to figure range, you have to use the slower bomber speed.

If the mission was not escort, but say patrol or ferry then the TAS of your plane would be used to figure range.

 

[Elmas]

The problem with P-39 was not about a few gallons fuel more or a few gallons less: it was how all the weights of the aeroplane, on the whole, were distributed.
When, for obvious reasons, jets had to install the engine amidship, and to adopt, for aerodynamic reasons, swept back wings, all the problems the P-39 had, not yet fully (if any) understood in the late '30s, were exacerbated. That, added with insufficient thrust of the engines, made some aeroplane really dangerous.


View: https://youtu.be/Q2qqKwndFW0

 

[pbehn]

I'm not doing a good job of explaining this, my bad. The bombers are going 230mph TAS. Escort is going faster. But escort has to stay with the slower bombers. Bombers fly straight, escort weaves (zig zag) above them. The whole parade is making forward progress at 230mph.

So you can't use the escort speed to figure range, you have to use the slower bomber speed.

If the mission was not escort, but say patrol or ferry then the TAS of your plane would be used to figure range.

P39, your flat refusal to read posts and be informed from them is frustrating to say the least. A plane has to take off and form up with its own squadron, then with other squadrons, then rendezvous with the bombers. The airspeed of the bombers was more like 180MPH from what I have read but with headwinds could be down much lower, as low as 120MPH ground speed, which had a big effect when in a flak belt. The Spitfire MkIX could reach the Swiss border with maximum fuel, but this didn't make it any more or less useful than the P-47 which wasn't the answer. It was used to help with bomber withdrawal, now what would you like to be in?

 

[Elmas]

P39, your flat refusal to read posts and be informed from them is frustrating to say the least.
*snip*

"Whenever a theory seems to you to be the only one possible, take it as a sign that you have not understood either the theory or the problem that you intended to solve. »
(Karl Popper, Objective Knowledge: an evolutionary point of view.)

This is a typical way of acting of self-taught people: they always look for something that can corroborate their theories, and reject, or even ignore, anything that can challenge them.
The reading of the works of the philosopher Karl Popper (Wien 28 July 1902– London 17 September 1994) would probably be useful, but it seems to me a hopeless thing.

 

[DarrenW]

Can we agree that at least some of the Ns had 120 gals internal and carried a 110gal drop tank? QUOTE]

I will agree to your unsubstantiated claim concerning the drop tank when you also agree that "at least some" carrier-based Hellcats were equipped with the ADI jets used during the combat power testing we discussed a few days back. And in reality only the first 166 P-39Ns had the larger internal fuel capacity. ALL P-39N-1s (which is what the test aircraft was) had 33 less gallons available. There's really no wiggle room there. Sorry.