Airstream Aluminum Frame

[Kawabonga]

Hi. I'm new to the forum. I'm currently looking at buying a 1976 31' Airstream. This will be a project restoration. The trailer has been gutted to bare exterior shell. The shell has been lifted off the frame and a new frame and sub-floor have been installed and the shell reattached.

My concern is that the new frame is aluminum. On the face of it, this seems like a good idea with regard to corrosion and weight savings. The downside is I am not sure of what size aluminum members would be needed to achieve the same strength, torsion and flexibility to match the original steel design. I am trying to contact the welder who made the frame to find out exactly what was used as I have not been able to inspect the trailer in person yet. Apparently, the original design was copied, but in aluminum. My understanding is that up-sized members were used, but I'm not sure.

New running gear has been installed which is steel. I'm not sure if this has been isolated from the aluminum frame to avoid galvanic corrosion. Does anyone have knowledge on how this installation could be done correctly? Some kind of spacer, I assume?

The sub-floor that has been installed is painted 3/4" plywood - not marine grade or equivalent that I am aware of. Any comments about this?

I have looked at some of the other forums that discuss aluminum frames but would like to know if anyone has first hand knowledge of what an aluminum frame spec would be. I am aware that the aluminum design must be beefier than a steel design.

Thanks in advance for any helpful information.

[KK4YZ]

Plywood floors (not marine grade) have been standard on Airstreams. I hear they might move to composite in 2022?.

The plywood flooring used is WPB which supposedly can withstand a boiling water test without coming apart. BUT it will still rot, which is the major concern.
The standard flooring does have an “anti wicking” coating on the edges.

My guess is that if the new floor is painted completely it’s probably as good or better than what new AS have now.

DISCLAIMER on the following: I’m an Electrical Engineer, not Mechanical, but I’ve worked closely with ME’s that are responsible for structural design....and have had to understand and explain the results.

To be certain of the adequacy of the aluminum frame, you’d probably have to have an ME model both frames and do an analysis. Not cheap.
Hopefully someone with direct knowledge/experience in this area might know rules of thumb that could be applied to the situation.

[Bubba L]

You may consider leaving your question on the VAP Podcast. Colin Hyde has either built an aluminum chassis or researched the possibility. I would also imagine there would be some forum members who have engineering knowledge for this. Good luck and be safe.

[jaybauman]

Originally Posted by KK4YZ

I hear they might move to composite in 2022?.

Airstream began the transition for 2020 model year. All 2021 trailers (excepting Base Camp and Nest) have composite flooring.

[KK4YZ]

Originally Posted by jaybauman

Airstream began the transition for 2020 model year. All 2021 trailers (excepting Base Camp and Nest) have composite flooring.

So maybe my 2020 FC might have a composite floor? It was built in summer of 2019 so I’m feeling doubtful....

[jaybauman]

Originally Posted by KK4YZ

So maybe my 2020 FC might have a composite floor? It was built in summer of 2019 so I’m feeling doubtful....

Airstream marketing has suggested that the flooring transition coincided with inception of production at the new manufacturing facility, which opened earlier this year. I admit my facts are a bit dodgy, but it would seem unlikely that you have the single-piece composite subfloor.

[Flostream66]

Originally Posted by Kawabonga

I have looked at some of the other forums that discuss aluminum frames but would like to know if anyone has first hand knowledge of what an aluminum frame spec would be. I am aware that the aluminum design must be beefier than a steel design. Thanks in advance for any helpful information.

Hi Kawabonga. There is a thread for a 49 Trailwind - the owner, "DiscoStu" is doing a shell off resto, and just took everyone through the process he used to design the aluminum cross members (including CAD drawings). He is very responsive and I would suggest that you reach out to him - or at least check out his resto: https://www.airforums.com/forums/f48...to-214550.html - you will see just how excellent his workmanship is. Down[under]-side is that he is in Australia!

Best of luck with your restoration.

[Kawabonga]

Thanks for the responses everyone. So, a little further information. I spoke with the frame fabricator. He copied the original Airstream design with 5" channels but 1/4" thick aluminum which he said is about twice as thick as the original steel frame. All the outriggers were stamped and dimpled for rigidity. Also, the frame has been powder coated for durability and to help against galvanic corrosion between hitch plate and where running gear attaches. All in all it sounds like he knows what he is doing.

He did tell me that from what he recalls, the shell leaks - so that will be another issue to resolve. His suggestion was to re-punch all rivets and seal the inside with an undercoating prior to installing interior shell.

Thoughts ... ??

[57Vintage]

I would not consider 'punching' all the rivets. Water test for leaks and replace/rebuck rivets as needed. You may find some leaks are failed weather strip around doors/windows.

I do agree to reseal all the seams and rivets, but at least remove any original sealant that has failed. (Some will say remove all old sealant.)

[Flostream66]

Originally Posted by 57Vintage

I do agree to reseal all the seams and rivets, but at least remove any original sealant that has failed. (Some will say remove all old sealant.)

Harold, I have bought Parbond from Burnstines to use as a seam sealant, based on the recommendation of Melody Ranch. It arrived yesterday. I wondered if you have used a method you thought was successful for removing old sealant. Thanks. Hollie

[57Vintage]

I just removed any loose sealant. I used a plastic scraper from Harbor Freight that I had for another project.

https://www.harborfreight.com/4-piec...QaAuigEALw_wcB

I recall reading some people used some type of solvent to soften up the sealant and scrape off (WD40, PB Blaster, something like that).

I covered all the seams and rivets with new sealant. I used Eastwood's automotive seam sealer. It can be brushed on. I used some cheap brushes from a box store and cut the bristles shorter so they were stiff enough to force sealant into hard to reach areas.

https://www.homedepot.com/p/Better-2...0200/202197878

[kidjedi]

It sounds like you are really going to be "going for it" if you take on this project. The floors are likely adequate, but since you're this far, you might consider swapping in coosa (not cheap, but water proof and lighter). With an aluminum frame and coosa subfloors, you'd have the lightest Airstream possible. It also *sounds* like the fabricator knew what he was doing, but it's still a bit of a gamble, especially on a 31' (as opposed to something shorter). I wouldn't go drilling out rivets to try and fix an unknown leak (which is likely at a window or other opening anyway). Best to seal the seams and existing rivets, and then if you have the option, insulate with spray foam, as it will also act like a sealant and add additional rigidity to the exterior skin. Downside is if you get a dent, it makes things difficult to repair. Also, if you go this route, you need to use a cold-method application, as the heated application can warp your skins. A realistic aluminum frame is a bit of a "unicorn" on these forums, so take that into consideration when weighing this purchase. Incidently, if you get the opportunity, PLEASE post pics, as just about EVERYONE wants to see an aluminum frame in real life (not just in terms of the theoretical).

[GPurcell]

Following along with this. Very shortly thought about doing an aluminum frame but decided against it. Would love to see one done.

[mikextr]

Your welder was correct using aluminum that is twice as thick as steel to get the same strength. For better or worse, it will be stiffer than the old steel frame.

[Kawabonga]

Here are a couple of pictures

[mikextr]

You're doing great work. Going to be real jewel.

[GPurcell]

This is very cool. I would love to know the weight difference between the steel and aluminum.

[crispyboy]

What a perfect time to search for leaks when the interior skins are out. I would reseal the interior seams with Sikaflex or Vulkem and spend some time inspecting during the rain event. Painted plywood should work fine but at this point I would highly consider a composite type floor.

[GPurcell]

I would consider the composite floor as well. Happy I went with it on mine.

[Kawabonga]

Does anyone have any suggestions with regard to axles? I'm considering upgrading to 5200lb axles with 6 bolt rims. Does this make sense or would these be too stiff? What about tires, any suggestions there?