Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (4 Viewers)

P-39 Expert said:

My whole point is that radios COULD be mounted behind the pilot, which they often were. This is just one way that CG could have been adjusted after removing the nose armor. I'm sure Bell had other ways of adjusting CG. The Soviets removed the IFF radios in the tail (and wing guns) as unnecessary and kept the nose armor and it didn't seem to affect their flying qualities.

Would be fun if Greg P could add the IFF radio in the tail cone to his P-39 CG chart.

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Have you ever done a proper Weight and Balance for all these changes you say could be done?

SaparotRob said:

Aside from my "humorous" answer, I believe those target 'Cobras were piloted by WASP pilots. Those guys were really under appreciated and certainly deserved more from Uncle Sam.

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WASPs were ladies, right? And they definitely weren't treated fairly by the AAF IMO.

Milosh said:

Have you ever done a proper Weight and Balance for all these changes you say could be done?

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We did one a few months ago, Greg came up with a W&B calculator on an Excel spread sheet. The data used in the chart was based on what was shown in the W&B charts within the flight manuals. Removing the wing guns helped the effort was well as some armor close to the C/G, but it was clearly shown removal of the armor in the nose would have the C/G go beyond C/G limits aft if all the cannon ammo (and I believe the nose guns IIRC) were expended and if fuel was allowed to go beyond 1/4 empty.

There was a restored TBF many years back which used Acetalene (sp) for the gunflashes. They ran afoul of the USN and the FAA when they made a dummy torpedo run on a docked USN ship.

Peter Gunn said:

I do recall last year in another thread where P-39 Expert pointed out (and I believed) that the engine compartment WAS large enough to hold the 2 stage supercharger. As SR6 points out, is the tail cone wide/tall enough to take it? Well, if it fit in the P-63 I don't think it's much of a stretch to say the P-39 could handle it, I'm sure Bell engineers (they did give us the supersonic X-1 after all) were capable of making it work.

Now if the 2 stage engine is installed, being longer and by extension then, more weight aft, how's the CG looking then? Making it fit is one thing, W & B issues would seem to me to be worse than ever but I'm no engineer.

I've always loved the P-39 for it's looks (it is literally my second favorite WWII a/c after the Mustang) and it is frustrating to think it could have been much better than it was but them's the breaks I guess.

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The auxiliary stage weighed about 175lbs (AHT) but remember it replaced the coolant tank which was moved up right behind the pilot basically on the CG. The coolant weighed 149lbs and the tank weighed 17lbs for a total of 166lbs. So basically the auxiliary stage supercharger replaced the coolant/tank for CG purposes. And a four blade propeller would be needed to absorb the extra power at high altitude which would add more weight to the nose.

P-39 Expert said:

WASPs were ladies, right? And they definitely weren't treated fairly by the AAF IMO.

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WASP - Women Air Force Service Pilot (USAAF)
WAVES - Women Accepted for Volunteer Emergency Service (USN)
And while the Marine Corps did not have women pilots, they did have a Women's Reserve (no acronym) - my Aunt Patricia was one.

special ed said:

There was a restored TBF many years back which used Acetalene (sp) for the gunflashes. They ran afoul of the USN and the FAA when they made a dummy torpedo run on a docked USN ship.

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Some people just can't take a joke.

What's the big deal? If it dropped a Mk. XIII the ship was perfectly safe anyway.

FLYBOYJ said:

You are correct about "a" radio mounted behind the pilot BUT the transmitter CANNOT be moved, so in the bigger picture you're still in the same boat by removing any nose armor. And again, I believe the later transmitter units had the IFF (SCR-535A) incorporated in the installation.

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The pilot's manuals for both the P-39K/L and N show two radios, the 522 voice and the 535 IFF radios. Appears the voice radio was mounted behind the pilot and the IFF radio was mounted in the tail. Why couldn't it be moved? It was deleted completely from Soviet P-39s.

FLYBOYJ said:

We did one a few months ago, Greg came up with a W&B calculator on an Excel spread sheet. The data used in the chart was based on what was shown in the W&B charts within the flight manuals. Removing the wing guns helped the effort was well as some armor close to the C/G, but it was clearly shown removal of the armor in the nose would have the C/G go beyond C/G limits aft if all the cannon ammo (and I believe the nose guns IIRC) were expended and if fuel was allowed to go beyond 1/4 empty.

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But, did Expert use it?

P-39 Expert said:

The pilot's manuals for both the P-39K/L and N show two radios, the 522 voice and the 535 IFF radios. Appears the voice radio was mounted behind the pilot and the IFF radio was mounted in the tail. Why couldn't it be moved? It was deleted completely from Soviet P-39s.

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Well after some research, I think I figured this out.

The SC-535 is the IFF radio. It was removed by the Soviets as you say. So we'll remove that from discussion for now...

The Radios in the P-39 - An SCR 274 or an SCR-522.

The SCR 274 was a 5 unit system, 3 receivers and 2 transmitters. It would be obvious you need to keep the transmitter away from RF interference, so most of the time you would have a transmitters mounted as far away as possible, so that's why it was initially shoved in the empennage with the control head in the cockpit. This system was sometimes contained in one metal box (US Installations) or had separate unit installations (RAF).

This is what the installation looked like in the P-51B. Although there is more equipment in this aircraft, the basic units are shown.



Now it seems the British and Australians used the same system but those units were not contained in one box and they seemed to fit in the area behind the pilot.



Why did the Aussies install their system this way? To move the C/G forward? It would seem you would have heat issues. I seen photos and cut-aways of the P-39 D with nothing in the deck above the engine but the "boxed" SCR-274 unit was firmly in the empennage.



Here's early P-39s with the RAF - no radio behind the pilot.



And a P-39N



Unless you use the same set-up was the Aussies and "unbox" the system, I don't think it was going to fit behind the cockpit.


The SCR 522 was also a 2 system unit but was eventually combined into one box. It replaced the SCR 274. It also came with a separate "dynamotor" or power supply. The SCR 522 was 16 x 12 x 10 and weighed 49 pounds. The dynamotor was 12 x 8 x 6 and weighed 37 pounds. The control head was about 2 pounds and was in the cockpit.



Now it seems on some P-39Qs part or all of this installation was squeezed into the deck behind the pilot.


This P-39Q was from the 4th Reconnaissance Squadron.






P-39Q of the 82d Reconnaissance Squadron (Fighter), 71st Reconnaissance Group, New Guinea 28 May 1944, they seemed to have this installation but was it all radios or photo equipment?

Now with along with this installation, was the IFF removed from US aircraft? I would say not if they were in theater.

So at the end of the day - are you going to be able to move the radios? If you have the "boxed" SCR 274 US set up - no.

If you use the RAAF SCR 274 set up - yes.

If you use the SCR-522? It looks like it was factory or field installed but were all the components installed on the deck or within the radio compartment in the empennage?

So I'll somewhat stand to be corrected.

Milosh said:

But, did Expert use it?

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He did to a point.

P-39 Expert said:

The coolant weighed 149lbs and the tank weighed 17lbs for a total of 166lbs

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Another yes, no and maybe.

The coolant may well have weighed 149lbs but it was not all (or even most of it) in the "tank".
The tank is an overflow tank to hold the expanded fluid as the engine heats up.
Most of the coolant is in the engine block and the radiator with a bit in the lines connecting them.

Much like many cars have a small plastic tank near the radiator with a hose connecting the tank and the radiator at the pressure cap. As the coolant gets hot and expand the over flow goes through the tube and into the "expansion tank" and once the coolant cools it is syphoned back into the cooling system.

At any rate, there is no 149 lbs to move, Modern Prestone coolant weighs about 10lbs per gallon. I think that Allison may have been running a 70-30 mix?

Tank is only going to hold a few gallons even when full.

GrauGeist said:

WASP - Women Air Force Service Pilot (USAAF)
WAVES - Women Accepted for Volunteer Emergency Service (USN)
And while the Marine Corps did not have women pilots, they did have a Women's Reserve (no acronym) - my Aunt Patricia was one.

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I ran across a long series of photos of these lady pilots, quite an impressive bunch, made me wonder what happened to them after the war.

Apparently they were not who were flying the P-63 target planes though, the article I linked has a few quotes from pilots who flew them, a combination of young officers right out of flight school and combat veterans with 80+ missions. The job wasn't to just fly around and get shot at by ground based AA though, instead they made fake attack runs at B-17s while the gunners shot at them, which some of them seem to have enjoyed. It sounded quite hazardous though and there were many accidents.

Clayton Magnet said:

Does anyone know if those are actual M2's? I may be wrong, but I suspect those are some sort of pyrotechnics in the wings, simulating gunfire. Even with blank firing adaptors, they probably aren't allowed to fire them off that close to crowds.

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I believe they are real, but blanks. Anyway they have put real ones back into P-40s and P-51s that I've seen (on video, not in person yet)

This is one of those ones shown flying in the New Zealand air show

Pretty neat.

Yeah that first one inside the hanger was particularly intense. I think we may be seeing two different types of M2 here, the fast firing one and the older slower firing one. You can see quite a difference.

Blanks are not going to cycle a gun like live ammo. In fact you may need a restrictor in the bore to get full automatic functioning?

On recoil operated gun having no bullet certainly affects the recoil. They can play games with the powder and other things.

I mean...

1) Watch the videos. Clearly they are shooting bullets, you can see the casings and the links piling out. You can see the flames and smoke coming out of the gun barrels. I don't think they are shooting live ammo inside of a hangar. And I don't think that's some kind of pyrotechnic trick, with the links and shell casings pouring out. If so that would be very well coordinated.
2) I don't know what you are talking about re: blanks. When I was in the service, we did exercises with blanks loaded into all of our guns, including the machine guns, which worked along with the Miles gear (laser tag, essentially). It worked, more or less. We did have caps on the end of the weapons but I think that was for safety (to ensure nobody shot a live round out of one).