Visit our Popular Forums

Bullit · 11-02-2015, 07:54 PM

I am going to have a new frame built and was considering replacing the 5 inch, 12 gauge C channel with something like an 8-10 inch, 10 gauge. This would give me more room for tanks and added strength. I know this has been talked about and someone had mentioned the taller frame. Not so concerned with stainless or aluminum.

Sent from my iPhone using Airstream Forums

Burnside Bob · 11-02-2015, 08:20 PM

I'm not sure that doubling the web of your frame from 5" to 10" is a good idea.

If you did go 10" and mounted the axle the same way, you will raise the floor of your trailer 5".

You can compensate for that rise by using a "drop" axle, but then the bottom of your frame will be 5" closer to the tarmac than your present frame, increasing the chances you will drag your belly pan when you go over irregular terrain, like your driveway's apron.

Why not use something like 2 x 6" .120 wall tubing? Your main frame will be significantly stronger than "C" channel and you will not significantly change the geometry of your trailer's under carriage/suspension.

millertimeUS · 11-02-2015, 08:29 PM

My concern would be the look of all of the lower wraps, it would definitely not look the same. Your banana wraps etc would all need to be custom made to fit the taller frame.

I had a new frame made using tube steel for my 76, it's a tank of a frame super strong just an idea and you won't have to reengineer everything.

It would be nice to have more room underneath for tanks though...

Sent from my iPhone using Airstream Forums

76 'Airstream Tradewind

Bullit · 11-03-2015, 05:14 AM

I would not be overly concerned with the look of the lower wraps. They would connect in the same area and the frame would just hang down the additional 3-5 inches. I have read people's posts about adding 3 inch supports to the frame for the axles and the slid plates are an additional 2 inches.
Thanks for the replies, I really appreciate the insight.
Bullit
71 Caravel

Sent from my iPhone using Airstream Forums

Belegedhel · 11-03-2015, 08:53 AM

My words of caution are around the monocoque system composed of your shell and your frame. The frame, in its original design, is quite flexible, and the shell actually supports the frame and gives it some added rigidity. The whole (original) design requires the frame to have a certain weight and rigidity that matches the shell's capacity for support.

If you essentially more than double the weight and rigidity of the frame one of two things might happen. Possibility 1 would be that the shell just sits on the newly rigidified frame like a house on a concrete slab, and you have no problem. Possibility 2 is that the added weight and rigidity of the frame results in sheared rivets every time you drive over a bump (remember, this new frame will still have some flex to it), or "oil-canning" of the shell when the trailer sits in the sun for a while (differing rates of thermal expansion, and a rock solid frame that doesn' move with the shell, etc.).

There was a thread that was active a while back where one of our members was having mystery dents appearing in the roof of his trailer when it sat in the sun. The thread ends without the mystery being solved, but the one thing that made the trailer different than it had been was a rebuilt, beefed up frame.

http://www.airforums.com/forums/f478...ng-105152.html

good luck

robwok · 11-03-2015, 08:57 AM

The only other question I would have is what if the new frame weight pulls on the shell? For example, think about this heavy steel flexing down after a big bump. However, this is a very short trailer, and it should only apply to the rear end, and considering it rarely happens on trailers even with a black tank, I personally think it's okay. A more rigid frame could prevent rivet pops instead of causing them. It's also really only going to apply to the long frame members. If you can still make open cross webs, I doubt that little extra steel will matter.

perryg114 · 11-03-2015, 09:49 AM

Taller frame won't hurt anything but wraps might be a little more challenging around the corners. The weakness with Airstreams are the poor connections between the frame and shell. If you made a perimeter frame that connected the outriggers together and then bolted the shell to that perimeter, you would have a much stronger trailer. Taller beams are much much stiffer than the 5 inch stuff that comes stock. There is also no reason the outriggers can't be narrow at the walls and the thickness of the beam at the root. This would probably solve your wrap issues. It might change the look of the trailer since the bottom won't be perfectly flat. If you paint the bottoms skins black, no one would notice. Get rid of that plate at the back of the trailer that funnels water into the floor.

Perry

Silverflames · 11-03-2015, 12:41 PM

Quote:

Originally Posted by Belegedhel

My words of caution are around the monocoque system composed of your shell and your frame. The frame, in its original design, is quite flexible, and the shell actually supports the frame and gives it some added rigidity. The whole (original) design requires the frame to have a certain weight and rigidity that matches the shell's capacity for support.

If you essentially more than double the weight and rigidity of the frame one of two things might happen. Possibility 1 would be that the shell just sits on the newly rigidified frame like a house on a concrete slab, and you have no problem. Possibility 2 is that the added weight and rigidity of the frame results in sheared rivets every time you drive over a bump (remember, this new frame will still have some flex to it), or "oil-canning" of the shell when the trailer sits in the sun for a while (differing rates of thermal expansion, and a rock solid frame that doesn' move with the shell, etc.).

There was a thread that was active a while back where one of our members was having mystery dents appearing in the roof of his trailer when it sat in the sun. The thread ends without the mystery being solved, but the one thing that made the trailer different than it had been was a rebuilt, beefed up frame.

http://www.airforums.com/forums/f478...ng-105152.html

good luck

This last year I put the drain pan kit on my AC unit. I changed the way AC unit sets on the roof, and it seemed to help with the dents. This would be a great question to post to The VAP.

I have been considering the same idea of an aluminum frame with 10" main rails. It would need to be thicker than steel, but should last longer.

Aerowood · 11-03-2015, 01:43 PM

Quote:

Originally Posted by perryg114

Taller frame won't hurt anything but wraps might be a little more challenging around the corners. The weakness with Airstreams are the poor connections between the frame and shell. If you made a perimeter frame that connected the outriggers together and then bolted the shell to that perimeter, you would have a much stronger trailer. Taller beams are much much stiffer than the 5 inch stuff that comes stock. There is also no reason the outriggers can't be narrow at the walls and the thickness of the beam at the root. This would probably solve your wrap issues. It might change the look of the trailer since the bottom won't be perfectly flat. If you paint the bottoms skins black, no one would notice. Get rid of that plate at the back of the trailer that funnels water into the floor.

Perry

If I ever rebuild another, the frame would be very similar as stated by Perry, 2 X 6 tubing 12 ga with the shell setting on a 3/4" tall perimeter frame supported by the outriggers. The shell would not sit on the floor plywood. There are a large number of holding tanks available that would fit a 6" deep frame.

bwoodtx · 11-03-2015, 02:45 PM

Quote:

Originally Posted by Aerowood

If I ever rebuild another, the frame would be very similar as stated by Perry, 2 X 6 tubing 12 ga with the shell setting on a 3/4" tall perimeter frame supported by the outriggers. The shell would not sit on the floor plywood. There are a large number of holding tanks available that would fit a 6" deep frame.

This would be similar to the way Avion did it, correct?

Bullit · 11-03-2015, 02:50 PM

I would be doing a taller frame in order to extend my boondocking time. Extra strength would be a positive by product. As I said I am not worried about the esthetics. Function would be far better than form (for me). The perimeter frame is interesting. Would I shorten the outriggers? I can't imagine I would be able to replicate the shell perimeter with the frame rail. All this is just what I am looking for. I am thinking an 8 inch frame would work as well. Giving me room for tanks and insulation etc etc. Thanks

Sent from my iPhone using Airstream Forums

JimGolden · 11-03-2015, 04:20 PM

Bruce,

That is correct. On an Avion, the floor sets inside the skin.

I designed a new frame for my '77 Excella a few years back. I went 8" deep on it. Stiffness is a function of the cube of the depth; if you double the depth of the beam, all else being equal, it is eight times stiffer. So a little extra height gets you a lot more stiffness. When they went from 4" (like mine had) to 5", the sag and separation basically stopped.

I was using 8" I-beam sections, but a box section would be fine too.

But, I was building my house at the time and didn't have the time to do it, so I sold it. My trailer had both sag and separation.

I have a 34X Avion now (actually 36' long). It has a much stouter frame...three 6" channels with an 8" deep suspension frame under the center that the suspension hooks to. In the area of maximum flex, you get 14" of steel. It doesn't sag

Your trailer is so short that it's probably not an issue even with the old 4" frame. But what you want to do is certainly a good idea. If I were building a replacement frame, I'd certainly beef it up, change the way the shell attaches, and I'd consider getting the whole thing hot dip galvanized after it was welded up and before putting on the axles, shell, etc.

Best of luck,

Aerowood · 11-03-2015, 04:42 PM

Quote:

Originally Posted by Bullit

Would I shorten the outriggers?

Sent from my iPhone using Airstream Forums

No, the frame would go on top of the outriggers

Bullit · 11-03-2015, 06:11 PM

Purple stuff just flew out the top of my head. So, the perimeter frame would sit on top of the out riggers? More information will be required. I have read about more out riggers in order to bolster the floor and shell connection. The perimeter frame would sit on top of them? How thick? Where would the floor connect, C channel, shell etc? I am interested?

Sent from my iPhone using Airstream Forums

JimGolden · 11-03-2015, 06:57 PM

I think by perimeter frame, they actually mean a "sub frame" in addition to the main frame. If not, then I'm not sure how that would work...

I suggest you build the main frame conventionally with two deeper main rails running the length of it, minus the A-frame up front. They should be about 4' apart. Say 6" deep box section or 8" deep I-beam section.

Weld the outriggers to these main rails, along with cross pieces every so often up the middle between the two main rails.

Across the tops of the outriggers, you don't need a frame so much as you'd want like a 6" wide plate, 0.125" would be fine, that would go all the way around the outer perimeter of the coach. The plate lays flat. The outside edge would just match the outside line of the trailer all around. The inside would extend inwards about 6".

To this 6" wide plate, along the outer edge, you would bolt down a channel. The channel would provide the stiffness that the flexibility of the plate might not give....but the plate doesn't have to be super heavy...the channel is strong in that direction.

The shell would bolt to this channel.

The floor would then sit inside the shell, on top of the 4-5" or so of plate that is remaining inside the shell. It's like an edge carrying platform all the way around. The center is carried by the outriggers and the cross pieces between the two main rails. Your tanks and stuff go in that space in the middle.

With the two main rails, your axles can mount conventionally.

If you dispense with the two main rails and try to just do a heavy frame around the outside, how would you attach the axles?

Personally, I'd ditch the rubber axles as well and go back to leaf springs. Unless you're going through the jungles of Africa or South America, leafs work great and they don't wear out.

On the axles, get heavy duty ones with big brakes (or even go disks with an electric over hydraulic unit...but not really necessary....just get the big drums) and heavy bearings but springs adjusted for the weight of your coach. Also put real shock absorbers on it.

Run 16" or better yet 17" wheels with E rated truck tires, and never look back.

Aerowood · 11-09-2015, 04:43 PM

The perimeter frame would be a upside down "U" channel with 3/4" legs. Where ever it crosses a outrigger, a plate would need to be welded to the bottom. A flange then could be welded to the inside vertical leg for the plywood floor would rest on. The regular "C" channel would be bolted to this framework with a barrier in between the two dissimilar metals.

Bullit · 11-11-2015, 07:47 AM

Just read perryg114's thread from 2013. There was talk of using angle iron as a perimeter frame. Also saw tubular material bolted to the out riggers in an unrelated blog about frames. How difficult would it be to duplicate the end C channels in heavier steel u channel? Thanks again

Sent from my iPhone using Airstream Forums

Bullit · 11-11-2015, 07:51 AM

Perry, what was the end verdict and result of your frame discussion?

Sent from my iPhone using Airstream Forums

Aerowood · 11-11-2015, 03:43 PM

Quote:

Originally Posted by Bullit

Just read perryg114's thread from 2013. There was talk of using angle iron as a perimeter frame. Also saw tubular material bolted to the out riggers in an unrelated blog about frames. How difficult would it be to duplicate the end C channels in heavier steel u channel? Thanks again

Sent from my iPhone using Airstream Forums

It would be labor intensive. Most likely have to take out Pie shaped wedges and weld.

Bullit · 11-12-2015, 05:14 AM

Would it be possible to cut a plate that would match the circumference of the trailer (matching the C channel) and weld that to the top of the out riggers? How thick would it have to be in order to accomplish a similar effect? The floor could sit inside the plate and the C channel. I like the idea of more outriggers and top plate, perimeter framing.

Sent from my iPhone using Airstream Forums