P-38 vs P-51

[FLYBOYJ]

The pilots who received the first Thunderbolts in England were dismayed at the lack of climb as compared to the SpitIX they had been flying. More than 1000fpm less than the Spit.

And they would have been more dismayed if given P-39s!

 

[tomo pauk]

"How about using one method so the playing field is fair? "

You coud not be serious with that proposal.
My, deadly serious proposal, is to use one volume of fuel for climb tests, and another, bigger volume of internal fuel + fuel in drop tanks that was not used historically for a fighter one favors. Say, P-39N. For fighters we should not be favoring at all, especially since it was very useful for hi-alt escort, we will use the least possible fuel volume to prove they were actually lousy despite what their users said, while not allowing for ADI, better prop and better fuel when talking about climb.
If this is not 100% fair, I don't know what is.
I've almost forgot it - we will also draw horsepower and consumption figures from a hat.

 

[CORSNING]

Are we seriously trying to compare a P-39 with a P-47?

...even if it is in an off way?

 

[Ivan1GFP]

2. Starting with late-production P-51Bs, a 322-liter (85 US gallon) tank that fit between the pilot's seat and the radio. The new tank gave the Mustang the necessary range, solving one problem, if at the expense of creating another. The new fuel tank was added without concern for its effect on the Mustang's center of gravity. With a full fuel load, getting the fighter off the runway was downright dangerous (a number of pilots lost control on takeoff, crashing on the runway or shortly after, when they tried to climb too steeply and the aircraft's tail dropped too low and it stalled at low altitude), and the aircraft was only marginally controllable for the first hour or so that it took to drain the tank. Ultimately, the USAAF was forced to limit the amount of fuel pumped into the fuselage tank to 246 liters (65 US gallons).

Hello GreenKnight12,
A simple description of this type is while true is not really the full story of how the 85 gallon fuselage fuel tank was used.
IF a pilot were to try to fly aerobatics of any kind with more than a minimal amount of fuel in the fuselage tank, the center of gravity would be too far aft and the tail plane would stall before the wing and the wing would collapse because of the sudden increase in angle of attack.
There was a member here whose father had seen it happen.
The solution was simply not to have such a situation during any part of the flight in which aerial combat might be expected.
The fuselage fuel tank was balanced by the drop tanks under the wings.
The fuel in the fuselage tank was burned FIRST (even before the drop tanks) so that over enemy territory, there never would be a situation where there was a significant amount of fuel in the fuselage tank.
In other words, if properly used, there wasn't a problem.

Hi Ivan,
I do not believe Robert was talking about fpm in altitude. I am pretty
sure he was talking about distance gained in ascending. If his P-47D
was capable of 440 mph. and loses 60 mph. in a 20 degree rise, and
the Spit9 is capable of 410 mph. and loses 50 mph. in a 20 degree rise,
which will gain height and distance the quickest?
All figures quoted for loss of speed are totally fictitious and are null and
void in a court of law. This is just a hypothetical example.

Hello Corsning,
I see you are also having trouble reconciling Johnson's claims with what you know about the aircraft involved.
The Court of Laws of Physics doesn't accept any fancy lawyers' arguments as we all know!
The problem here is that I also am hesitant to discount Johnson's accounts of testing against the Spitfires because he could fly the Thunderbolt so well.

I believe that the fuel falling out of suspension happened on P-38 versions with the core type intercooler. ie the P-38J and P-38L.

The leading edge intercoolers on earlier versions restricted the power available because they didn't cool the air sufficiently,so it is unlikely that these were the versions that had the fuel falling out of suspension.

Hello Wuzak,
I believe the issue was mostly with the early version of the intercoolers.
The problem is that without a core / heat exchanger, there wasn't a lot of efficiency but to make up for that lack of efficiency so there was a rather long run of ducting to the wing tips and back. The problem is that with low temperatures during cruise operation, the mixture isn't moving fast enough to keep the fuel in suspension.

- Ivan.

 

[Shortround6]

For those who have forgotten ( or misplaced the information/threads) the US figured the radius of action at 25,000ft as follows.

a, warm up and take-off equivalent to 5 minutes at normal rated power.
b, climb to 25,000ft at normal rated power (distance covered in climb not included in radius)
c, cruise out at 25,000ft and 210 I.A.S
d. drop external tanks/bombs before entering combat
e. combat 5 minutes at War Emergency power and 15 minutes at military power.
f, cruise back at 25,000ft and 210 I.A.S
g, no account is taken of reduced fuel consumption during decent
h. allowance is made for 30 minutes reserve at minimum cruise power
i. no allowance is made for formation flight or evasive action other than the 20 minutes combat.


210 IAS at 25,000ft is 315 mph true. (may vary just a bit depending on calculator)

Now the P-39 has a bit of problem as while it is pretty zippy without a drop tank, when the drop tank is fitted a lot of the zip goes away.

Manual for a P-39Q (still with 87 gallons of internal fuel) says the plane can do 330mph at 25,000ft clean at 2600rpm and F.T. (yes it will go faster but 2600rpm is max continuous.
However with the 75 gallon drop tank the speed drops to 267mph true. Both conditions call for 63 gallons an hour.

Perhaps people will claim the P-39Q had those high drag gun pods. But lets face it, the P-39with drop tank isn't fast enough to do the escort mission.
Why is the P-39 buring 62 gallons an hour? because instead of making it's rated 1000hp at 25,000 it is making far less. Perhaps under 600hp
And to go this fast the engine is running in rich condition.
there is no WEP available at this altitude and military power (around 750hp?) might take 1.5 gallons a minute at that altitude rather than the 138 gallons an hour (2.3 gpm) at lower altitudes

Now our P-39 is in a rather perilous position. If it loses any altitude it's fuel consumption increase rather drastically. dropping from 25,000ft to 20,000ft at 2600rom and wide open throttle can increase fuel consumption by almost 33% for example. Military power (3000rpm) would show a similar increase.

 

[wuzak]

Hi Ivan,
I do not believe Robert was talking about fpm in altitude. I am pretty
sure he was talking about distance gained in ascending. If his P-47D
was capable of 440 mph. and loses 60 mph. in a 20 degree rise, and
the Spit9 is capable of 410 mph. and loses 50 mph. in a 20 degree rise,
which will gain height and distance the quickest?
All figures quoted for loss of speed are totally fictitious and are null and
void in a court of law. This is just a hypothetical example.

The Spitfire gains altitude faster.

A Spitfire LF.IX gets to 20,000ft faster than a D does to 15,000ft.

The P-47 probably gains more distance, though a IX could flatten out its climb to match the climb of the P-47 and gain more distance itself.

 

[CORSNING]

The P-47 probably gains more distance, though a IX could flatten out its climb to match the climb of the P-47 and gain more distance itself.[/QUOTE]

Robert Samuel Johnson did not believe it could once the P-47 got its new prop.

 

[Ivan1GFP]

The Spitfire gains altitude faster.

A Spitfire LF.IX gets to 20,000ft faster than a D does to 15,000ft.

The P-47 probably gains more distance, though a IX could flatten out its climb to match the climb of the P-47 and gain more distance itself.

Hello Wuzak,
I believe that if we are discussing sustained climbs or steady state climbs at War Emergency Power, the Spitfire IX in ANY version will climb faster. (It is pretty hard to match a climb rate over 4,000 feet per minute.)
The situation that Corsning was attributing to Johnson was a zoom climb from maximum level speed.
With a higher maximum level speed, there will be places at the high end of the speed range where the Thunderbolt will have excess power and the Spitfire won't.
Keep in mind that the late D model Thunderbolt (from D-25 onwards) was quite a different beast than the earlier models.

- Ivan.

 

[Dimlee]

Back to P-38

Whenever its performance in different theatres is compared this famous "temperature" argument is used. "Cold" Europe vs "warm" tropics. Unheated cockpit, impact on engine, etc.. But I wonder what is actual difference of air temperatures at (for example) 5000 m over France and over Southwest Pacific waters?
Attached graph is not precise, probably there are some tables to look at? Temperature - Altitude - Latitude.

 

[Shortround6]

I thank you for your attempt to bring some facts to the discussion.

However most major countries had temperature tables for altitudes.
Like standard day and hot day. Sometimes more than one hot day to cover the variations in latitudes shown by the chart you posted.
Air temp at 20,000ft on a 100 degree day in Michigan (rare) might be somewhat cooler than a 100 degree day in the tropics were it is 100 degrees on the ground for weeks on end.
For some reason several of winters during WW II were noted as being much colder than normal for the time.

 

[pbehn]

"How about using one method so the playing field is fair? "

You coud not be serious with that proposal.
My, deadly serious proposal, is to use one volume of fuel for climb tests, and another, bigger volume of internal fuel + fuel in drop tanks that was not used historically for a fighter one favors. Say, P-39N. For fighters we should not be favoring at all, especially since it was very useful for hi-alt escort, we will use the least possible fuel volume to prove they were actually lousy despite what their users said, while not allowing for ADI, better prop and better fuel when talking about climb.
If this is not 100% fair, I don't know what is.
I've almost forgot it - we will also draw horsepower and consumption figures from a hat.

This was established in 1888 before powered flight. youtube where di you get that hat - Bing video

 

[michael rauls]

Back to P-38

Whenever its performance in different theatres is compared this famous "temperature" argument is used. "Cold" Europe vs "warm" tropics. Unheated cockpit, impact on engine, etc.. But I wonder what is actual difference of air temperatures at (for example) 5000 m over France and over Southwest Pacific waters?
Attached graph is not precise, probably there are some tables too look at? Temperature - Altitude - Latitude.

Also temperature extremes from I believe it was 30 to 70 degrees( been awhile since i looked it up but I believe thats verry close if not exact) result in about a 20 mph difference in the speed of sound at 25,000 feet. This would of course have a disproportionate impact on the p38 with a lower speed for the onset of compresability. Perhaps this is at least part of the reason compressabilty didn't seem to be much of an issue in warmer climbs even when oparating at higher altitudes but was so in those particulary cold European years. At least for the pre dive flap equipped earlier modles.

 

[XBe02Drvr]

Twin engine A/C = additional training vs. 1-engine type, not facilitated with complicated layout of handles and switches.

Sorry, but, as anyone who has worked on them will tell you, the P-38 is excessively complicated and it has nothing to do with having a second engine. It is so bad anyone would think it was British.

Switching hands? So what!! I fly a GA single engine aircraft with a simple 160 hp engine and I switch hands all the time, continually trimming the aircraft, working the radios, GPS and looking at charts.

Have to disagree with you here, Flyboy. How much experience do you have flying single pilot in high performance multi engine planes? When system complexity increases linearly, "brainload" rises exponentially. Increase aircraft speed, and brainload goes exponential again. With complex multis, there are many additional limitations, performance parameters, and system "gotchas" that have to be planned for and processed faster than single engine pilots are used to.
You're right, training is the answer, but let's take a look at that. Here's Dilbert, who's got 120 hours, and has managed to beat a T6 into submission enough to pass a checkride and he's all bright eyed and bushy tailed to fly the hot new Lightning. Now this bird is a new intrusion into the single engine pursuit community, and comes with a bunch of newfangled gewgaws and operational recommendations that look like heresy to the old hands in Training Command. Extended cruising with the engines in oversquare condition? "Good way to burn 'em out quick! Bunch o' ground pounder slipstick artists, never flown a plane in their life"! Keep it on the ground to 140 MPH? "They ain't no runway long enough, and hey, you'll burn out the tires!" VMC? "What's this crap? More slipstick stuff? Bullpucky"! On top of all this, you've got a plane with no two seat trainer version, no instructors with frontline experience in the type, and a budget to meet in both time and money.
Now, a couple months later, Dilbert has managed to wrassle the bird into submission in the allotted 25 hours and he's off to kick some Axis ass in this bird he's established a tentative truce with.
Now, yet another month and a half later, he's joined the mighty Eighth only to discover that they're actually USING the flight manual procedures his instructors labeled bogus and trained out of him. What's more, they're using three different block numbers of aircraft, none of which were what he trained on.
And finally, frozen to the core, with all the various switch twiddling, systems monitoring, and fuel management, how much brainpower does he have available for situational awareness, formation flying, and staying with his leader when the inevitable bounce occurs?
Cheers,
Wes

 

[GrauGeist]

We should perhaps keep in mind that the P-38 wasn't the only single-seat twin (single-seat meaning pilot only) fighter (or heavy/night fighter) in the war...there was the Whirlwind, KI-45, Bf110, Beaufighter, J1N, P-61, Me410, Mosquito, He219, KI-102, etc. and they all managed.

 

[XBe02Drvr]

We should perhaps keep in mind that the P-38 wasn't the only single-seat twin (single-seat meaning pilot only) fighter (or heavy/night fighter) in the war...there was the Whirlwind, KI-45, Bf110, Beaufighter, J1N, P-61, Me410, Mosquito, He219, KI-102, etc. and they all managed.

True enough, but were any of the experiences of those aircraft pertinent to early days of P38 training in the US? I doubt it.
Cheers,
Wes

 

[Dimlee]

Back to P-38

Whenever its performance in different theatres is compared this famous "temperature" argument is used. "Cold" Europe vs "warm" tropics. Unheated cockpit, impact on engine, etc.. But I wonder what is actual difference of air temperatures at (for example) 5000 m over France and over Southwest Pacific waters?
Attached graph is not precise, probably there are some tables to look at? Temperature - Altitude - Latitude.

I found such tables for Northern Hemisphere.
Atmospheric Temperature Profiles of the Northern Hemisphere

Just two examples.
(altitude vs temperature in Celsius, rounded)
Latitude 10 degrees winter:
2500 m +13C
5000 m -1C
7500 m -18C
Latitude 50 degrees winter:
2500 m -11C
5000 m -29C
7500 m -45C

Of course, standard tables do not take the weather and specific locations (ground/ocean) into account, but the difference is significant.

 

[P-39 Expert]

These fuel consumption values - what is the source?

P-39Q Pilots Manual.

 

[P-39 Expert]

Standard cruise for US escort fighters was figured at about 205 or 215 IAS not the max cruise that you claim.
Reason the P-39 fuel burn at 25,000ft looks so good is that the engine didn't have much more power to give. It was running at max continuous (2600 rpm and full throttle) to do 330mph true for a Q.
How about we slow the P-47 down to 330mph and figure the Fuel burn?
I believe we have explained before the different allowances used to figure the operational radius of the escort fighters. How about using one method so the playing field is fair?

The fuel burn at 25000' at normal power was good, and increasing the throttle to military power 3000rpm would climb a clean P-39N at almost 2000fpm at that altitude which was still better than a contemporary P-47B/C or P-38F/G. Plenty of power at 25000', the engine HP chart says 660HP at 2600rpm and 770HP at 3000rpm. Sounds rediculously low, I know.

I'm trying to use the same rules for everybody, just the information in the flight manuals and the tests in wwiiaircraft.

 

[P-39 Expert]

For those who have forgotten ( or misplaced the information/threads) the US figured the radius of action at 25,000ft as follows.

a, warm up and take-off equivalent to 5 minutes at normal rated power.
b, climb to 25,000ft at normal rated power (distance covered in climb not included in radius)
c, cruise out at 25,000ft and 210 I.A.S
d. drop external tanks/bombs before entering combat
e. combat 5 minutes at War Emergency power and 15 minutes at military power.
f, cruise back at 25,000ft and 210 I.A.S
g, no account is taken of reduced fuel consumption during decent
h. allowance is made for 30 minutes reserve at minimum cruise power
i. no allowance is made for formation flight or evasive action other than the 20 minutes combat.


210 IAS at 25,000ft is 315 mph true. (may vary just a bit depending on calculator)

Now the P-39 has a bit of problem as while it is pretty zippy without a drop tank, when the drop tank is fitted a lot of the zip goes away.

Manual for a P-39Q (still with 87 gallons of internal fuel) says the plane can do 330mph at 25,000ft clean at 2600rpm and F.T. (yes it will go faster but 2600rpm is max continuous.
However with the 75 gallon drop tank the speed drops to 267mph true. Both conditions call for 63 gallons an hour.

Perhaps people will claim the P-39Q had those high drag gun pods. But lets face it, the P-39with drop tank isn't fast enough to do the escort mission.
Why is the P-39 buring 62 gallons an hour? because instead of making it's rated 1000hp at 25,000 it is making far less. Perhaps under 600hp
And to go this fast the engine is running in rich condition.
there is no WEP available at this altitude and military power (around 750hp?) might take 1.5 gallons a minute at that altitude rather than the 138 gallons an hour (2.3 gpm) at lower altitudes

Now our P-39 is in a rather perilous position. If it loses any altitude it's fuel consumption increase rather drastically. dropping from 25,000ft to 20,000ft at 2600rom and wide open throttle can increase fuel consumption by almost 33% for example. Military power (3000rpm) would show a similar increase.

Let's do the math on the combat radius.

P-39N P-47
a. 9 gal. 17 gal
b. 42 135
d. 24 92
h. 20 30
Total 95 274 This is what each plane used just getting up and down with reserves.
Cruise 25 31 This is available for cruise
GPH 62 150 P-39 at normal power, P-47 at column II power
Hours .4 .2 Time available for cruising
MPH 280 315 TAS
Miles 112 63 Cruising miles flown on internal gas
Radius 56 32 Half the cruising miles
Each plane has a 110gal external tank:
Cruise 135 141 Gas available for cruise plus 110gal
GPH 62 150
Hours 2.2 .9
MPH 280 315 TAS
Miles 616 296 Cruising miles with 110gal external tank
Radius 308 148 Radius is half the cruising miles. Does not allow for dropping the external tank. Appears that the P-39N has about twice the combat radius as a P-47.

That's a half hour I won't ever get back.

Add about 14mph to the Q if you are comparing it to the N.

Climbing was not a perilous position for a P-39N, it was it's absolute strong suit. At 25000' it could easily climb higher and burn even less fuel.

 

[GrauGeist]

True enough, but were any of the experiences of those aircraft pertinent to early days of P38 training in the US? I doubt it.
Cheers,
Wes

Not likely, but their pilots had to start out somewhere and I imgine they had the same (or similar) challenges that the P-38 pilots experienced.
In the case of the Hs129 (not a fighter, but a small twin airframe), they pilot not only had to deal with an overly cramped cockpit, but the majority of his gauges were placed outside, on either nacell just aft of the engine cowling.