XP-39 II - The Groundhog Day Thread

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Hello P-39 Expert,

It seems like most of these points have already been addressed by other forum members but here goes anyway.

Don't know for sure until you try it.

Even with existing engines, the P-39 had a serious tendency to overheat on the ground. It also tended to exceed temperature limits in high power operation such as sustained climbs. Putting in a more powerful engine and running at higher altitude makes the problem worse. There is a reason why modern operators of P-39s tend to have spray bars installed to cool the radiators.

Stop trying to invent CG problems. P-39 didn't have any real CG problems. Not like a P-51 with a full fuselage tank.

The P-51 85 Gallon Fuselage tank certainly created a CoG problem for the aircraft that did not exist before.
To state that, "P-39 didn't have any real CG problems." means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation.

All that was needed was 30 extra gallons, 15 in each wing. The two outside tanks on the P-39 held over 8 gallons each. You couldn't fit the equivalent two more of those in each outer wing?

Let's say it is possible to add another 30 Gallons in fuel cells to the outer wing of the P-39 in place of the wing guns.
That would make a total of 150 Gallons.
Please note that the P-51 already had 184 Gallons of internal fuel BEFORE it was determined to be necessary to add a 85 Gallon fuselage tank that caused some CoG problems without drop tanks.
Note also that the P-51 could carry two drop tanks on the wings.
The P-39 could carry at most one drop tank on the centerline.
What makes you think this is sufficient fuel?

The plane had a 37mm cannon. It could not possibly be under armed.

The 37 mm cannon certainly is a big hammer, but it has a ridiculously low firing rate, low ammunition capacity and a low duration of fire and of course has a pretty loopy trajectory because of its low muzzle velocity.
This is not an ideal weapon to track maneuvering targets. 12 seconds of fire isn't much at all.
There are many better ideas for motor cannon and neither of the guns that were normally installed in the P-39 qualify as such.
The remaining two synchronized .50 cals even as you pointed out really do not deliver a great weight of fire.

- Ivan.
 
The P-51 85 Gallon Fuselage tank certainly created a CoG problem for the aircraft that did not exist before.
To state that, "P-39 didn't have any real CG problems." means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation

(Underlines mine.)
Have any of you folks read Eric Hoffer's The True Believer? It was required reading in the '60s when I went to school, and laid out the blueprint for ideology over factuality as a motivating force, fulfilling a human need formerly served by religion, except expressed at an even more fanatical level, and without any of the benevolent inluences. Primarily concerned with the mass movements of its era: Fascism, Naziism, and Communism, but discerns behavior patterns still with us today.
 
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If the 37mm cannon was all that great, they would have kept the M4 (T9) in the P-38, but they determined that the Hispano M2 and four .50 MGs were the better combination.

The P-39 may have been better served with the same M2, as it had a higher RoF and weighed less.
 
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Hello P-39 Expert,

*SNIP*

Another thing I have always wondered about is how effective the carb intake was on the P-39 for optimum ram effect. It looks like it would be sitting in a low pressure area. On the P-40, it is sitting at the nose in a high pressure area.

- Ivan.

Interesting point which got me reminiscing about my misspent youth. Had a '72 SS454 Chevelle which one of my dad's buddies (who was an engineer at GM) helped me 'retune' the engine to get a few more ponies out of it.

Most cars from the 60's - 70's just drew carb air from under the hood, it wasn't until the mid to late 70's that (GM at least) ran the carb intake to the high pressure area behind the headlights for better performance.

Long story short, the SS had Cowl Induction at the base of the windshield with a rear facing vacuum operated door that popped open under heavy throttle and closed at idle. I asked my engineer friend about changing that to get better airflow.

"Kid, we put that there for a reason and not just to look cool".

Two things:

1). I know, car =/= airplane

2). I was stupid for selling it.

This is really apropos of nothing and I just wanted to write about my old Chevelle that I NEVER should have sold.

BUT! Ivan brings up a point I had never considered regarding the location of the carb intake on the P-39 vs P-40.
 
This is really apropos of nothing and I just wanted to write about my old Chevelle that I NEVER should have sold.

BUT! Ivan brings up a point I had never considered regarding the location of the carb intake on the P-39 vs P-40.
MODS: We need a rating icon for KOOWUL!! to fit in somewhere between LIKE and WINNER, especially for mildly off-topic sorties like this one.
ROCKERS: You're welcome too, as long as you play nice.
YOUNG 'UNS: Scratching your heads? Ask your elders. (or any Brit on this forum)
 
Ice is for mint juleps.
In February?? Funny you should mention them. There was a specialty tire retreader back in the day who used to do ice racing tires with walnut shell fragments embedded in the tread, a super soft compound, green sidewalls, and trademarked "Mint Juleps". Affordable, and tough to beat on the ice!
 
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Hey Peter Gunn

Maybe we could fix the P-39 with some Chevrolet "SS" letters along the lower nose in front of the door? And might as well install a Hurst "pistol-Grip" shifter handle on the control stick, too, along with a push-button radio.

I had a Burgundy 1970 Chevelle SS 454 LS-7 with rock crusher 4-speed and have been weeping about it for 50 years. I've heard people say they had an LS-7, but they always miss when I ask them about the axle ratio. It only came with ONE axle ratio in 1970, and that was a 4.11 . My ex-wife wrapped it around a Police car when she ran a stop sign. Nobody was killed, but the car was a total loss.

At least my 2019 Ford Mustang GT PP1 6-Speed with more horsepower than the Chevelle (not as much torque, though) helps a bit.


Mustang_GT1.jpg


It's actually quicker than the old Chevelle and very definitely handles better, but I loved that old Chevelle and the cowl induction. The Mustang is unrelated to the P-39, but likely has a better drag coefficient at sea level!

Reminds me of my favorite kitplane. Take a garden-variety Vans RV-4 kitplane as below:

maxresdefault.jpg


Remove the 4-cylinder 160 hp and add a six-cylinder 285 hp Lycoming and chop off one wing bay from each side to get a fire-breathing Harmon Rocket:

3fcc4c3faee1a967d7ac6c3ab78d57bf.jpg


Outclimbs a stock P-51 handily, at least in the lower altitudes. Just shy of 4,000 fpm (3,950)!

Cheers!
 
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Hey Peter Gunn

Maybe we could fix the P-39 with some Chevrolet "SS" letters along the lower nose in front of the door? And might as well install a Hurst "pistol-Grip" shifter handle on the control stick, too, along with a push-button radio.

I had a Burgundy 1970 Chevelle SS 454 LS-7 with rock crusher 4-speed and have been weeping about it for 50 years. I've heard people say they had an LS-7, but they always miss when I ask them about the axle ratio. It only came with ONE axle ratio in 1970, and that was a .411 . My ex-wife wrapped it around a Police car when she ran a stop sign. Nobody was killed, but the car was a total loss.

At least my 2019 Ford Mustang GT PP1 6-Speed with more horsepower than the Chevelle (not as much torque, though) helps a bit.


View attachment 597984

It's actually quicker than the old Chevelle and very definitely handles better, but I loved that old Chevelle and the cowl induction. The Mustang is unrelated to the P-39, but likely has a better drag coefficient at sea level!

Cheers!
Betcha it ain't tail heavy, neither!
 
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If the 37mm cannon was all that great, they would have kept the M4 (T9) in the P-38, but they determined that the Hispano M2 and four .50 MGs were the better combination.

The P-39 may have been better served with the same M4, as it had a higher RoF and weighed less.
You may be right. 37mm was still very effective though.
 
ARMY AIR FORCES
MATERIEL COMMAND
Wright Field, Dayton, Ohio
28 July 1944
MEMORANDUM REPORT ON
P-39Q Airplane, AAF No. 44-3455


Subject: Report of Spin Tests
Section: Flight
Serial No: ENG-47-1779-A

Conclusions
1. The P-39 should not be spun intentionally under any circumstances.
2. The P-39 should not be snap rolled as the roll usually ends in a spin.
3. The best spin recovery is to simultaneously apply opposite rudder and neutralize the stick.
4. Power should be cut immediately if a power on spin is entered.
5. Care must be excercised during the recovery to prevent an accelerated stall and re-enty into the spin.
6. The wing tip spin chute does not aid recovery of the P-39Q from a flat spin.


P-39 Performance Tests

Any aircraft that naturally sits at the most aft end of it's CG envelope will inherently have potential spin issues despite being "within balance" or not!
That was the P-39Q with the underwing .50calMG pods, made the plane a little more unstable.

As you know, spins were prohibited in the pilot's manual on all AAF and USN fighters.
 
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