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

Ahhh ...



OR your P-39.

fubar57 said:

View attachment 623621 VS View attachment 623622

WHO WOULD WIN?​

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That depends. Are we using real data, or self-made biased data that suits our narrative?

Note that the P-39 Groundhog still has nose armour attached here. You can tell because the tail is off the ground

P-39 Expert said:

Here's the Bell drawings showing that the rear engine compartment is exactly the same size on both the P-63 (which had the auxiliary stage supercharger) and the P-39 (which did not).

Regarding moving the radio from the tail cone to above the engine, there are numerous public photos to verify that.

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If you call those two engine compartments the same length, it puts in question your definition of exact.
Evidently you didn't look at it very close.

tyrodtom said:

If you call those two engine compartments the same length, it puts in question your definition of exact.
Evidently you didn't look at it very close.

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Exactly

P-39 Expert said:

Here's the Bell drawings showing that the rear engine compartment is exactly the same size on both the P-63 (which had the auxiliary stage supercharger) and the P-39 (which did not).

Regarding moving the radio from the tail cone to above the engine, there are numerous public photos to verify that.

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Lastly, after all these discussions, did you ever ask yourself or wonder WHY the radio was all the way in the tail???

FLYBOYJ said:

Lastly, after all these discussions, did you ever ask yourself or wonder WHY the radio was all the way in the tail???

View attachment 623632

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That's easy, the radio gets better reception when it is closer to your comrades in formation behind you

If it wasnt in the tail the pilot had to have a tin foil hat?

Clayton Magnet said:

That's easy, the radio gets better reception when it is closer to your comrades in formation behind you

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Точно мой друг!

FLYBOYJ said:

Errrr - no. that is not an engineering drawing that shows a radio installation, all you're showing is station locations and skin thickness. "Could have, would have. should have." Face it, there is NO Bell installation for the movement of the radio to another part of the aircraft that "could have" or was actually done to any P-39 operated by the AAF in a combat situation, once again you're trying to fabricate something that never existed to sustain your argument. We (those of us who have actually weighed aircraft) have showed you that in the factory configuration, you cannot remove the front armor on any model of the P-39 without moving the C/G beyond aft C/G limits when expelling all the cannon ammunition and allowing the fuel to go below 1/4 full. Go back and look at the W&B chart the Greg put together. Now please put it to rest!!!!

View attachment 623592

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A quick search resulted in five photos showing a radio installation under the rear canopy. The attached P-39N Flight Manual (page 6) shows a radio installed in the same location. Clearly a radio was mounted under the rear canopy on some models. Not all, but some.

Regarding the CG, we'll just have to disagree. Greg's chart does not have the radio in the tail cone to use as an adjustment. But deleting a 70-100lb slab of nose armor would more than be offset by moving (or removing) the IFF radio set in the tail cone, since it weighed 110-130lbs (AHT) and was farther away from the CG than the nose armor.

The five minute military climb limit was in effect until mid 1942, after then it was increased to 15 minutes. About the same time that Allison gave up on the backfire screens and began using the aluminum intake manifold instead of the old flammable magnesium manifold.

Hi thomas P,

I have flown in a P-40N and have spoken with people who operate P-40s of various sorts, including P-40E and M models. None of them have any trouble climbing at 2,500+ fpm at normal weights. Then again, none are being operated at very heavy weights, either. Most are operating just a small bit less than normal weight and none are at max weight, even with a belly tank. You should not be surprised by that since none have actual guns in them except for one very realistic P-40M restoration. And, none of them are limited to 1,000 HP. Most P-40s in combat in the Pacific didn't use only 43" - 43.5" of MAP. Most used 48" - 60" and the AVG used to use 70" - 75" if they needed to do so. Low MAP flight was the norm for training, not for front-line units. I'd think they would take off at normal power and cruise to battle at normal cruise power but, if it came to combat, my bet is they pushed the throttle forward and used what power it could make, without worrying overly much about MAP book maximums.

I worked on Allisons for about three years with Joe Yancey and ALL of them had no trouble getting to 48"+ MAP very briefly during break-in. Not exactly SURE of the HP they were making, but it was lifting the front wheels of a Ford F-350 dualie truck we were using as a test stand with a 6-blade club prop set for break-in loading. We never pulled 57" because it would pull the truck over. All we really needed to do was to run it sufficiently and with the correct fluids and break-in techniques to seat the rings. Once they seated, we didn't run it anymore. It was usually then time to crate it and ship it. Mostly, we could seat the rings in 7 - 9 hours of run time on the truck, usually for 25 - 30 minutes at a time, with careful throttle management. What you don't do is move the throttle quickly in either direction, open or closed.

Here's an Allison V-1710 backfire screen that I have:


It fits right into the intake manifold where it connects to the cylinder heads, assuming you have the right manifolds. You can see that it would restrict the intake flow and that is why they were not needed except in training. Once you know how to start an Allison, no screens are required. But, if you make a mistake on startup, you can blow gaskets. Same is true for ANY big WWII aero engine, including radials.

The worst was if a pilot pulled the power off too quickly when landing. That usually blew a gasket and dropped oil everywhere. Fires were one result of this mishandling.

P-39 Expert said:

A quick search resulted in five photos showing a radio installation under the rear canopy. The attached P-39N Flight Manual (page 6) shows a radio installed in the same location. Clearly a radio was mounted under the rear canopy on some models. Not all, but some.

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Ok - I'll give you that, "not all but some." Radio" - are we talking the actual communication radio or IFF?

P-39 Expert said:

Regarding the CG, we'll just have to disagree. Greg's chart does not have the radio in the tail cone to use as an adjustment. But deleting a 70-100lb slab of nose armor would more than be offset by moving (or removing) the IFF radio set in the tail cone, since it weighed 110-130lbs (AHT) and was farther away from the CG than the nose armor.

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The only way you'll know for sure is by doing the math with exact weights of the components.

BTW - he can adjust the chart just for that

P-39 Expert said:

A quick search resulted in five photos showing a radio installation under the rear canopy. The attached P-39N Flight Manual (page 6) shows a radio installed in the same location. Clearly a radio was mounted under the rear canopy on some models. Not all, but some.

Regarding the CG, we'll just have to disagree. Greg's chart does not have the radio in the tail cone to use as an adjustment. But deleting a 70-100lb slab of nose armor would more than be offset by moving (or removing) the IFF radio set in the tail cone, since it weighed 110-130lbs (AHT) and was farther away from the CG than the nose armor.

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Went back and looked at this - there is a RADIO behind the pilot on some models. There is ALSO one in the tail on ALL models!!!! Receiver/ Transmitter. This is not an optional installation, two units, two locations, "on some models."

From the manual you posted!




I can tell you flat out, the transmitter was not moved behind the pilot nor can it be!!!!

Same set up on the P-63.

So, the transmitter was left in the tail - I wonder why???

Hey guys,

At the risk of fanning flames, P-39 Expert is correct as to the length of the engine compartment being the same in both the P-400/P-39 and the P-63.

_________________P-400_______ P-63
Aft Station_______228.50"_____ 231.50"
Fwd Station____ -138.25"_____-141.25"
Length___________90.25"__=___ 90.25"

Hey GregP,

Any reasonable chance you could find out the actual TARE and TOGW for any of the Warbirds?

I seem to remember, reading, and probably seeing film footage somewhere, that the P-39, ( and / or the later "Kingcobra" ), was very successful when its weight was increased - when it was flown ( by a real pilot, not by R/C ) as a target aircraft, when fighters attacked it, and fired at it, using frangible rounds !!!
So maybe it did have a use, after all !!!

fubar57 said:

Note that the P-39 Groundhog still has nose armour attached here. You can tell because the tail is off the ground

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But did it have its IFF removed?