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F-84G Canopy Circle is ???


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Posting for a potential new member:

What is the purpose of the circle in the framed canopy of the F-84G on the right side, rear?

I tried looking it up and can't find anything.

Is there a wire or something attached to it (and where is the other end)?

I have one of the kits too and have wondered.

Thanks!

Rich

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I believe it was a pressure relief 'valve' to keep the canopy from blowing off. Don't quote me on that. It's been well over a decade since I looked in detail at the F-84.

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Now that it has been brought up I was wondering how it is suppose to be painted.

Like canopy framework? And how? I am getting ready to start the HB F-84E.

:cheers:

Jerry

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That's true - the F-84B/C had a clear bubble. They had trouble with them holding pressurization, so they put the fiberglass straps on them. Now that I think about it, I'm sure that's what the circle is. It's a blow-out plug.

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Posting for a potential new member:

What is the purpose of the circle in the framed canopy of the F-84G on the right side, rear?

I tried looking it up and can't find anything.

Is there a wire or something attached to it (and where is the other end)?

I have one of the kits too and have wondered.

Thanks!

Rich

It was purely for access to the area behind the pilot. It was not for pressure relief.

Steve

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What's your source for that? What would you need to access, and how could you possibly get your arm far enough in there to access anything? How would you do anything with one arm? It's a blow-out plug.

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That book is for the F-84F which has a completely different canopy.

The round cover on the F-84G reinforced canopy is for access only in my opinion. There are a lot of items not accessible on the canopy aft deck without the round cover. I've been searching for information or closer photos of the cover to be able to determine it's intended purpose but there isn't a lot out there.

Cheers,

John

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Okay, so what did they do when there was just a one-piece molded clear bubble as on the P-51 or P-47D? Hand access makes *no* sense whatever. It is a known fact that there were issues with the canopy cracking under pressurization. Common sense says it's a blow-out plug.

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If the circular panel was for access, it likely was connected to the radio compass gear as that's the only stuff that was ever back there as far as I'm aware.

There was a round instrument mounted on the decking directly behind that circular panel. I'm not sure if it was connected to the radio compass or something else entirely. Perhaps the panel was to access that.

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Access panel added during the F-84E production, according to D&S. I saw a photo, that I can't find now, that looked like there was a cable & plug that could be reached through the hole. I'll keep looking for the photo....

Ben

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I wouldn't rank D&S as a definitive source for reliable information. I'll need to see an excerpt from the F-84 tech manual before I'm convinced.

Edited by Jennings
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I couldn't find the pic I was looking for, but here's another one (From this site:

http://www.flevoaviationhobby.net/walkaround/aircraft/f84g_du24/f84g_du24.html)

0040.jpg

The other photo that I still can't find showed a bunch of screws holding the panel on. I didn't see anything that looked like any kind of release mechanism to cause it to blow off at X pressure, unless the round bit is thinner so it fails first. Could it be that they added the panel so the ground crew could put the cable back on the reel without pulling the entire canopy? I don't see anything else in there that could be reached or serviced with one hand, much less taken out through the hole. Somebody get Plankwing on the Bat Phone!

r-ADAM-WEST-BATMAN-large570.jpg

Ben :D/>/>

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Might be access to the pulley that opens the canopy. Instead of an explosive charge that you would have with a clamshell canopy emergency access, you would climb up and quickly penetrate the circle with some sort of tool and hand crank the sliding canopy to gain emergency access. Just a guess. But that would beg the question, what did they do with the sliding canopy on early models of the Sabre?

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Okay, so what did they do when there was just a one-piece molded clear bubble as on the P-51 or P-47D? Hand access makes *no* sense whatever. It is a known fact that there were issues with the canopy cracking under pressurization. Common sense says it's a blow-out plug.

Not the greatest analogy. Both the P-51 and P-47 bubble canopies didn't have a fixed deck with equipment on the canopy itself. Plus they were relatively easy to remove. Now you're talking ...common sense.... What's your source for that? And trust me, a lot of things are designed on aircraft that don't make sense at all.

Here is another photo showing the access panel on the canopy.

F-84 Canopy

The opening is quite large and one can access the ADF loop antenna, ADF sense antenna coupler, wiring cable reel, and canopy motor/transmission. In my nearly 3 decades as an aircraft maintenance engineer I would say common sense is that the panel is for access. On many occasions I've had to access components much larger with smaller openings with one hand tied behind my back.

The aircraft pressurization system would incorporate an outflow valve and an over-pressure relief valve. In most cases aircraft of this vintage incorporated a single combined outflow/over-pressure relief valve and in some cases a manually operated emergency pressure dump valve. Never heard of an aircraft pressurization system with a purpose designed blow-out plug. Most blow-out panels are placed on aircraft in areas where structural damage could occur if a bleed air duct ruptures.

Final points.... why would a blow out panel be placed on the canopy in line with the horizontal stab? There is no mechanism present to release the panel as it is screwed to the canopy doubler. You would want to design any blowout panel to not come in contact with the aircraft if it departs or have a means of containing it on the aircraft. All of my maintenance common sense and experience point to it being an access panel.

Cheers,

John

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I would have to say maintenance access as well. I can definatly say from experience, most aircraft, particularly military, have many panels you can only get one hand or arm in. Perfect example, drop tanks. Before anyone says it, I know a drop tank isn't a canopy, but since the F-84 had radio, the press. reg., and canopy actuating equipment......it makes sense.

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But why would you just make a circular access panel? The canopy has a birdcage frame, you can easily make a hatch with a piano hinge without it being in the air stream. If not that, then at least a bolt on section you can remove and replace that you can maintain a proper torque to keep it pressurized.

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But why would you just make a circular access panel? The canopy has a birdcage frame, you can easily make a hatch with a piano hinge without it being in the air stream. If not that, then at least a bolt on section you can remove and replace that you can maintain a proper torque to keep it pressurized.

Because a round hole is stronger than square one.

Steve

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But why would you just make a circular access panel? The canopy has a birdcage frame, you can easily make a hatch with a piano hinge without it being in the air stream. If not that, then at least a bolt on section you can remove and replace that you can maintain a proper torque to keep it pressurized.

Without getting too technical a circular access panel is perfect for a pressurized design. Square corners create fatigue points where stresses can cause failures after relatively few pressurization cycles. Google the DeHavilland Comet for some interesting reading regarding pressurization and proper design. This is why you won't find square access panels or windows on a pressurized fuselage. A radius is your friend.

The birdcage, as you call it, is actually not a bird cage. The F-84G has a single piece blown canopy with fibreglass reinforcing straps applied to the outer surface to prevent a blowout of the canopy. The round access panel is actually screwed to a round reinforcing plate bonded on to the inside the blown canopy.

Could be wrong, but this canopy does seem to have a nice little crack running down that one section all nicely covered up with tape...

You're wrong. What you're seeing is one of two ADF sense antennas bonded to the inner surface of the canopy. The second one is placed symmetrically opposite of the one you see and they are both connected to a small box, just to the aft right of the reel, called an ADF sense antenna coupler.

I've spent quite some time working on the CT-133, also known as the T-33, and there are quite a few similarities in the designs. The ADF sense antenna installation is one of them.

Cheers,

John

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