and how strong is it?
Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)
- Thread starter greybeard
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Thumpalumpacus
Major
I'm no pilot, but as a guitarist who uses tube amps to amplify his instrument, I can say that they can be sensitive to heat, even the heat the amp itself generates. I would imagine that putting such a tube amp (and that's what a transmitter was, in that era) atop another heat-source will shorten tube life and increase unreliability.
How much in this case, I've got no idea. I'd want to know the temperature of the mounting deck, the ventilation designed to accommodate it, and the insulation involved.
Additionally, the capacitors will be prone to leakage when exposed to excess heat.
Neither of these issues are instakill issues in most cases, especially not with the maintenance those P-39 radios presumably received. But it can be an issue, and tube failure due to heat can happen very quickly when it does happen. I lost a power-tube on an amp a couple of years ago, the voltage bounced back to the output transformer, and killed the amp then-and-there.
My amps use tubes designed in that era and commonly used in radios of that era (6L6 and 12--7s). The amps I use are actually based off of radio designs from the 30s, with design mods to make a guitar sound smokin' loud.
Tube-amplifier designs must, repeat must, take heat-generation and heat dissipation into account.
FLYBOYJ
"THE GREAT GAZOO"
I'm no pilot, but as a guitarist who uses tube amps to amplify his instrument, I can say that they can be sensitive to heat, even the heat the amp itself generates. I would imagine that putting such a tube amp (and that's what a transmitter was, in that era) atop another heat-source will shorten tube life and increase unreliability.
How much in this case, I've got no idea. I'd want to know the temperature of the mounting deck, the ventilation designed to accommodate it, and the insulation involved.
Additionally, the capacitors will be prone to leakage when exposed to excess heat.
Neither of these issues are instakill issues in most cases, especially not with the maintenance those P-39 radios presumably received. But it can be an issue, and tube failure due to heat can happen very quickly when it does happen. I lost a power-tube on an amp a couple of years ago, the voltage bounced back to the output transformer, and killed the amp then-and-there.
My amps use tubes designed in that era and commonly used in radios of that era (6L6 and 12--7s). The amps I use are actually based off of radio designs from the 30s, with design mods to make a guitar sound smokin' loud.
Tube-amplifier designs must, repeat must, take heat-generation and heat dissipation into account.
This why I'm thinking you didn't see anything mounted here in earlier models, and even though the flight manual indicates as a "radio" goes there, I believe this area was possibly strengthened in time or there was some other equipment mounted there (camera?). In either case I think it's not a place for ice cubes.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
If I'm not mistaken, the transmitter and receiver were mounted in it's own compartment in the rear of the fuselage, just ahead of the horizontal stabilizer.
somewhere it was nice and cool, away from vibration...
FLYBOYJ
"THE GREAT GAZOO"
Exactly, or one was mounted behind the pilot (in later models) and another in the empennage along with that pesky IFF.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
And it is, I just checked and the transmitter and receiver are at the rear of the fuselage, side by side in the compartment just before the tail-plane.
Also double-checked and there was not an "IFF transponder" in the tail - the equipment in the tail is the actual two-way communication system.
I also wonder if development of better vibration isolators allowed them to move radios forward. There are so many issues that people don't fully understand. It's not as simple as removing the radio and bolting it somewhere else.
FLYBOYJ
"THE GREAT GAZOO"
Correct, mentioned a few post back.
This is what is looked like, mind you this is a later unit;
FLYBOYJ
"THE GREAT GAZOO"
According to the flight manuals, you would of had 2 models of radios
SCR-274 Command Radio
Or the SCR-522
I think in many of the cutaways you're looking at the Transmitter/ Receiver in one case and the transponder unit sitting next to it.
SCR-274 Command Radio
Or the SCR-522
I think in many of the cutaways you're looking at the Transmitter/ Receiver in one case and the transponder unit sitting next to it.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
In detailed cutaways, the radio compartment is just aft of the oil reservoir and ahead of the tail-plane, the access door being on the port side and the full width of the fuselage.
While not being all that large, it was packed full of equipment. Also, the antenna lead to the aerial ran through an access port just above the compartment door.
While not being all that large, it was packed full of equipment. Also, the antenna lead to the aerial ran through an access port just above the compartment door.
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SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Are P-39's owned by collectors twiddled with so that they're easier to fly? There were issues that mil spec P-39's had. With military equipment removed, did the Groundhog become pleasant to fly or do these "sport" planes need tinkering?
GregP
Major
I'll ask one of the pilots soon, but an Allison V-1710 gets as hot as any engine, and the shelf would be very warm.
If aluminum were any good as an insulator, they wouldn't make cookware out of it. I'd assume (before asking, that is) that the shelf will get plenty warm. However, it is possible it has asbestos insulation on the bottom and is, in fact, fairly cool. Again, I'll ask.
I would not think there would be a lot of engine vibration on the shelf itself. When breaking in freshly-overhauled Allisons, I have put my hand on the engine when it was running to warm up after startup, and it is pretty smooth. The vibration SHOULD come mostly from the propeller and driveshaft, and THAT vibration is felt throughout the entire aircraft, moreso in the nose than elsewhere. Just thinking out loud.
When I get a chance, I'll ask.
If aluminum were any good as an insulator, they wouldn't make cookware out of it. I'd assume (before asking, that is) that the shelf will get plenty warm. However, it is possible it has asbestos insulation on the bottom and is, in fact, fairly cool. Again, I'll ask.
I would not think there would be a lot of engine vibration on the shelf itself. When breaking in freshly-overhauled Allisons, I have put my hand on the engine when it was running to warm up after startup, and it is pretty smooth. The vibration SHOULD come mostly from the propeller and driveshaft, and THAT vibration is felt throughout the entire aircraft, moreso in the nose than elsewhere. Just thinking out loud.
When I get a chance, I'll ask.
FLYBOYJ
"THE GREAT GAZOO"
Yes, but at the same time I wouldn't trust those to be exact. As shown configuration of radio equipment will vary.
wuzak
Captain
Did the USN have radar in 1942? Was it equipped with IFF?
Did the USN operate anywhere near where P-39 bases were in 1942?
I think it should be enough for the P-39 that it was in some ways innovative and it served honorably with the Soviets. The work of the designers and the builders was realized by verifiable results.
Now. Let's do something useful like talk about the Australian Boomerang or post war 109's with Merlin engines.
Now. Let's do something useful like talk about the Australian Boomerang or post war 109's with Merlin engines.
FLYBOYJ
"THE GREAT GAZOO"
Start a thread!
fubar57
General
.....or Boomerangs with Merlin engines
Greg Boeser
1st Sergeant
Why did it fail? I mean on paper it's a world beater. Faster than a P-40, better climb than a P-51, able to go toe to toe with the FW-190A-6. And yet, the USAAF chose to go a different way. The British discovered a host of problems with theirs and dumped them on the Russians, or gave them back to the US. Only one US pilot made ace in them and that was in the Pacific. Two P-39 equipped fighter groups sent to Europe were re-equipped with Spitfire Vs before deploying to North Africa. the P-39 Groups that did go to NA were badly mauled and had to be relegated to coastal and convoy patrol. P-39 units flying ground attack missions needed air cover provided by P-40s. The Russians loved them, but if you had the choice between an I-16 or a Guaranteed Lacquered Coffin and a P-39 what would you choose?
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Here's a good diagram showing the compartment area.
Over time, the equipment combinations would change, of course - the compartment, however, would remain the same.
