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Old 07-01-2013, 06:46 PM   #1
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.032 vs. .040

I am beginning to plan for replacing several exterior panels on our '54 Cloud. What does wisdom say concerning the best choice? It will be 2024 T3 in 4'x12' sheets. Is it best to go heavier, thicker or thinner easier to work with. These will be for replacing the bottom row of metal at the both ends plus one side panel. I will also have to rebuild the door skins as well. I am not interested in the price difference, I just want what will give the best results. Thanks all,
Barry
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Old 07-01-2013, 07:52 PM   #2
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I'm not sure what the orginial alloy was but I don't see why you would use 2024-T3 for something non-structural like a skin. Both 5052 and 6061 have better corrsion resistance and are more resistant to vibration cracking than 2024-T3. .040 2024-T3 is very stiff so don't use it if any curves are needed.
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Old 07-01-2013, 07:53 PM   #3
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I would stay with the thickness it came with. The frame design is the weak point on these things and the weak attachment points between the two.

Perry
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Old 07-01-2013, 08:03 PM   #4
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I'll relay what I've seen the experienced folks do....040 will lay flatter and not gain too much weight.

Like you noted, 2024 was the original alloy and the new panels will polish up to match the leftover originals.

post photos!!!
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Old 07-01-2013, 08:09 PM   #5
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I replaced all of the lower panels of my 58. I used .032 on all the front and rear curved sections. Used .040 for the flat front section and both long side panels. It gives a slightly smoother look to the side panels. i'd do it the same way again. Ed
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Old 07-01-2013, 08:17 PM   #6
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The front section is all one piece wrapping the whole front panel and a foot or so around the sides. Using the 2024 Alclad is to match the polished rest of the trailer. Hoping for those that have actually used the .040 for exterior work will weigh in to the advantages and disadvantages if there are any.
Thanks all for the answers offered up so far.
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Old 07-02-2013, 09:25 AM   #7
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I used .040 for all the side panel replacements on my GT. The weight gain is minimal but the results are a flatter smoother skin with less distortion around the rivets. I would highly recommend the .040 over the .032 and use the 2024-T3.
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Old 07-02-2013, 10:22 AM   #8
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Thanks Kip. I also need to replace the end panels both front and rear, do you think it will be hard to wrap .040 around the ends?
Then there is the whole 'door in a door' thing. I will need to re-skin both sides of both doors, and probably make some frame work. There is some actual brake work that will need to be done on them, so do you think it would be better to do this in .032? All-thanks for your input,
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Old 07-02-2013, 10:52 AM   #9
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Quote:
Originally Posted by crisen View Post
I'm not sure what the orginial alloy was but I don't see why you would use 2024-T3 for something non-structural like a skin. Both 5052 and 6061 have better corrsion resistance and are more resistant to vibration cracking than 2024-T3. .040 2024-T3 is very stiff so don't use it if any curves are needed.
The body of an Airstream IS structural, as the they are considered "semi monocoque". In a monocoque structure, like modern unibody cars, the floor, body, roof etc is all part of the structure, hence the name monocoque or "one shell". In a semi monocoque structure, there are several structural elements of differing materials that all contribute to the overall structural integrity. Alclad 2024 T3 was used by Airstream from 1936 through to around 1981, after that they moved to a softer & weaker alloy of 3003 & 3004. The shift from .032" alclad to .040" 3003 happend at the same time. Alclad is about double the ultimate shear strength & yield strength than the newer alloy, which I suspect is part of the reason why they added thickness with the change. Alclad 2024 also has great corrosion resistance, which is why it is used in the Aircraft Industry.
The frames on Airstream's are not strong enough to support the body etc on their own, in fact, they are not even strong enough to support themselves. Lift the body off one & shake one end of the chassis, it'll wobble all over, however add the floor & body & you'll have a very strong structure.
We use .032" alclad 2024 for all of the panel replacements on the pre 81 trailers & lesser alloys on the bellypan, as it is not a major structural element.
Thanks,
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Old 07-02-2013, 11:51 AM   #10
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Thanks Colin..!
I am not a pro and in fact a very rank novice. That said I have replaced several skins on our past 66 Safari and used the .032 . There are a few places where there are 'indents' from over tightening the rivets. On this trailer we will have the ability to buck everything and the thought was to help prevent these 'witness marks' by using thicker .040 skins, that plus never having 'bucked' before there will be a learning curve. I have seen some sides that used this extra thickness and it does appear to give a smoother, less wavy, skin. With that in mind , I have posed these questions.
Again, I am not under a cost restraint, or have a budget to meet, but rather looking for a nicer finish. I can see .040 on the sides but am wondering about the ends and doors. BTW we are about ready to put the body back on, thanks for the axle and your kind patience and help,
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Old 07-02-2013, 01:04 PM   #11
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Quote:
Originally Posted by goshawks00 View Post
Thanks Colin..!
I am not a pro and in fact a very rank novice. That said I have replaced several skins on our past 66 Safari and used the .032 . There are a few places where there are 'indents' from over tightening the rivets. On this trailer we will have the ability to buck everything and the thought was to help prevent these 'witness marks' by using thicker .040 skins, that plus never having 'bucked' before there will be a learning curve. I have seen some sides that used this extra thickness and it does appear to give a smoother, less wavy, skin. With that in mind , I have posed these questions.
Again, I am not under a cost restraint, or have a budget to meet, but rather looking for a nicer finish. I can see .040 on the sides but am wondering about the ends and doors. BTW we are about ready to put the body back on, thanks for the axle and your kind patience and help,
In order to prevent "witness marks", turn your impact gun pressure down a bit, or don't pull the trigger so far. Also make sure the person operating the bucking bar starts to push a bit, once you start bucking. It takes some practice, so don't feel bad. New Airstream's have these marks, if you have a close look at them.
If you're planning on fabricating a hatch or any section that needs a bend over 90 degrees, get Alclad 2024 T0. This temper allows you to fold it over on itself without cracking.
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Old 07-03-2013, 12:04 PM   #12
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Quote:
Originally Posted by Colin H View Post
The body of an Airstream IS structural, as the they are considered "semi monocoque". In a monocoque structure, like modern unibody cars, the floor, body, roof etc is all part of the structure, hence the name monocoque or "one shell". In a semi monocoque structure, there are several structural elements of differing materials that all contribute to the overall structural integrity. Alclad 2024 T3 was used by Airstream from 1936 through to around 1981, after that they moved to a softer & weaker alloy of 3003 & 3004. The shift from .032" alclad to .040" 3003 happend at the same time. Alclad is about double the ultimate shear strength & yield strength than the newer alloy, which I suspect is part of the reason why they added thickness with the change. Alclad 2024 also has great corrosion resistance, which is why it is used in the Aircraft Industry.
The frames on Airstream's are not strong enough to support the body etc on their own, in fact, they are not even strong enough to support themselves. Lift the body off one & shake one end of the chassis, it'll wobble all over, however add the floor & body & you'll have a very strong structure.
We use .032" alclad 2024 for all of the panel replacements on the pre 81 trailers & lesser alloys on the bellypan, as it is not a major structural element.
Thanks,
Colin

Obviously you are in the business and have lots of experience with Airstreams however there are too many errors in your statement to let it stand. By the way my experience is over 25 years in automotive component design and manufacturing including building race cars and at least 20 years working on aircraft, so I understand the structural issues.

When I said structural I ment from the above prespective the use of 2024 is not justified. A good example is that the rivet strength used in airstreams and the rivet spacing will not support as high of loads as will the basic 2024 sheet so the rivets are the weak points not the sheet material. See AC 43.13 for reference.

Maybe what I should have said is the use of 2024-T3 is not justified by the structural considerations. Design wise a lower strength material with better corrosion properties can be used.

2024 is used in aircraft for its strength not for corrosion, alclad was an inovation to improve corrosion resistance. When aircraft structures need corrosion resistance, such as a Cessna with a float kit, liberal use of zinc chromate is involved.

Alclad and 2024 are not the same, i.e. 2024 is available plain and coated in the alclad form. Plain 2024 is not good for corrosion resistance period. The use of Alclad which is a thin coat of essentially pure aluminum on 2024 sheet improves the corrosion resistance dramaticly. See quotes below.

Using 2024 Alclad to match the appearance makes perfect sense but I don't think that the OP mentioned Alclad, just 2024.

Also it should be noted that the way pure aluminum gets it's corrosion resistance is forming a thin alumimun oxide layer. By continually polishing this oxide off the corrosion resistance is reduced and you are now relying on the polish used. Since this layer is very thin, about .0015 on .032 material it is very easy to scratch thru the layer and get into the base 2024 below.

Alloys such as 5052 and 6061 get their corrsion resistance by the basic alloying elements used and maintain the same corrosion properties all of the way thru the material.

Quoted from Alcoa who make Alclad-
"ALCLAD 2024
Two side cladding. Nominal cladding thickness is 5% on gauges under 0.062 in."
"All alloys of the 2XXX series are susceptible to
atmospheric corrosion, especially in industrial
or seacoast atmospheres. These alloys should
be protected, at least on faying surfaces, when
exposed to these conditions. Alcladding these
alloys provides high resistance to atmospheric
corrosion."

Summary from Keystone Metals -

"2xxx wrought alloys and 2xxx casting alloys, in which copper is the mayor alloying element, are less resistant to corrosion than alloys of other series, which contain much lower amounts of copper.
Alloys of this type were the first heat-treatable high-strength aluminum base materials and have been used for more than 75 years in structural applications, particularly in aircraft and aerospace applications

5xxx Wrought Alloys and 5xx.x Casting Alloys. Wrought Alloys of the 5xxx series (aluminum-magnesium-manganese, aluminum-magnesium-chromium, and aluminum-magnesium-manganese-chromium) and casting alloys of the 5xx.x series (aluminum-magnesium) have high resistance to corrosion, and this accounts in part for their use in a wide variety of building products and chemical-processing and food-handling eguipment, as well as applications involving exposure to seawater

6xxx Wrought Alloys. Moderately high strength and very good resistance to corrosion make the heat-treatable wrought alloys of the 6xxx series (aluminum-magnesium-silicon) highly suitable in various structural, building, marine machinery, and process-equipment applications."
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Old 07-03-2013, 12:46 PM   #13
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Thanks Rick for your support to this thread. I believe it was assumed by the other posters being that my Flying Cloud was a 1954 that I would be replacing the 2024 with matching skin , ie, Alclad. And yes it will be polished which I did mention. Also in post #6 I said it would be Alclad. The rest of your post was helpful, though my interest is in the ability to use .040 T3 for the front and rear skins. According to you I should not use it there as .008 makes the skin to hard to curve around the lower panel. Thanks again for your support.
Barry
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Old 07-03-2013, 01:07 PM   #14
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Bending the 2024 around the corners is where the problem is as you mention. I don't really know what the radius is but say on a wing leading edge the skin might be .020 and you need to use ratchet straps to pull it tight to the ribs. You might try this trick on the AS if you can find a place to anchor the straps without doing damage to the anchor points. If the skin isn't tight you will dimple the skin and potentially damage the rib when you rivet it. I would think that some of the damage folks see with using .032 is due to having a gap between the skin and the rib. So getting this fit tight is critcal. Also as mentioned turn down the pressure to the rivet gun and try a heavier bucking bar.

I know the .008 doesn't seem like a lot but that is a full 25% thicker so it makes a significant difference. If you can visit a aircraft repair shop where they have some alum sheet you could potentially get some scraps to play with and see. You may have trouble finding 2024 this thick at a hanger since most is thinner than .040 in airplanes. Another source might a sheet metal shop that might have some waste.
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