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Old 04-30-2013, 12:23 PM   #1
1 Rivet Member
Vintage Kin Owner
Dallas , Texas
Join Date: Mar 2010
Posts: 15
Frame specifications question - c / u channel?


I am building an airstream-style trailer from the ground up, and I have most of it designed, but I have yet to finalize the frame material/size specifications.

Does anyone have a link to info regarding the type of frame material, the sizing, and any guides on it? I see that C Channel and U Channel are often times used, in varying sizes and thicknesses. What would be a good standard size that is very strong but not excessively heavy? Would like to get a really good starting point for the sides, sub floor and roof as well.

Unfortunately, I am a designer without a lot of experience in trailer frames, I'm really interested to learn as much about this as possible, so even pointing me in the right direction would be much appreciated Thanks!
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Old 04-30-2013, 01:19 PM   #2
Rivet Master
1981 31' Excella II
New Market , Alabama
Join Date: Sep 2011
Posts: 6,134
The two main frame rails are usually 5" tall Box beam or two C-channels welded together. There are rather thin cross members between the frame rails. On the outside of the frame rails are what we call outriggers that attach to the bottom of the wall C-channel. The floor is between the frame and the C-channel at the bottom of the walls. Airstreams are built with a rather weak connection between the frame and the shell. The main structural attachments are at the front and back of the trailer. The connections to the side walls are rather weak. The outriggers support the floor and keep the shell from changing shape.

If I were doing what you are doing, I would build a perimeter frame that would make a much stronger connection between the frame and the shell. This would mean running cross members from one side of the trailer to the other and putting them maybe 16inches apart. Then use some c-channel or angle iron and run that all the way around the trailer. This would match the shape of the shell. Now you have two c-channel one at the bottom of the wall and one on the frame at the bottom of the wall. You can now put bolts between these two every few inches. I would not put the floor between the wall and the frame but I would put some sort of insulator between them and paint the frame well. This would reduce corrosion from the two different metals. Now you have excellent structural contact between the shell and the frame which is going to make it strong. Here is a crude concept drawing.

Not putting the wood floor between the shell and frame make repair MUCH easier.


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Old 04-30-2013, 07:31 PM   #3
4 Rivet Member
1963 28' Ambassador
Vintage Kin Owner
Northern VT , Vermont
Join Date: Aug 2007
Posts: 360
A substantial project. Something to consider when going "Airstream style". They have a "flexable" frame. The bare frame on my 28 footer will flex 4 inches with the front anchored, a fulcrum where the axles go and my 200#s on the tail. The shell on an Airstream literally supports the frame. I forget the term, mono something or other built!. To accomplish this w/o cracking or distorting the aluminum body panels is going to take some serious R & D. A standard rigid frame will solve the problem but increase the weight substantially. Now the good news, Avion solved this problem way back when. I have one, a '64 T28. Heaven protect me form the arrows and stones. A better built trailer. Rigid 3 rail frame, dbl sandwich floor, morride walking beam suspension [with all replacement components still ava]. This trailer pulls, tracks and rides as well or better than my Airstreams. However they do not have the market value of an Airstream, yet. I urge you to research Avion and consider setting your body design on their platform. You can pick one up very reasonable.
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