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Old 01-30-2016, 07:22 PM   #1
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Re-Engineering Skin/Belly/Frame/Floor Connection

how can the connection between the shell-skin, the belly-skin, the floor, and the frame be redesigned so these are all de-coupled?

ideally a re-engineered solution would allow:
  1. removal/replacement/repair of dented belly-skins and banana peels without having to remove the interior skin and all the buck rivets around the waste-line.
  2. removal/replacement/repair of sub-floor without wedging it into the gap between the c-channel and the frame
  3. removal/replacement/repair of external shell skins without affecting the belly skin
  4. anything else?

i have some ideas, which i will share, but for now i just wanted to get this thread started and start the conversation.


btw, i've heard rumors of this topic being addressed on the forum but haven't been able to find a dedicated thread yet. apologies if i'm duplicating information! (links to existing posts would be much appreciated)
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Old 01-30-2016, 10:23 PM   #2
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Look at headroom epiphany- darkspeeds thread. Good stuff.
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Old 01-31-2016, 12:14 PM   #3
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Thanks for the tip. Can you clarify how you guys attached the belly skin w/out trapping it under the exterior skin?
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Old 01-31-2016, 03:58 PM   #4
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Most belly pans overlap on the shell right at the floor connection (no wonder they rot). I jacked mine up 3 inches and plan to underlap and rivet them in. The center pan will be screwed into the main frame rails. The part that is riveted to the skin is 2 ft wide and will wrap to the main rail. Click image for larger version

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Here is a pic of how I reengineered the floor and shell connection. It's 1.5 square stock welded to the edge of the outriggers. The floor can be removed/replaced without lifting shell again. Hope this helps
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Old 01-31-2016, 07:30 PM   #5
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Awesome thanks for the pics. So you're not trying to decouple the exterior and belly skin? (My ideal arrangement would allow the belly pan to be removed without messing w buck rivets not exterior skin)
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Old 02-01-2016, 10:20 AM   #6
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You could always modify the belly skin connection the way it is done in the 70's vintage trailers, in which the shell is bucked to the C-channels, which are bolted to the floor/frame, and then the edges of the bellypan are brought up to overlap the shell by about 3/4" and pop riveted in place. There is then a piece of beltline trim that is installed over the juncture in order to hide all the ugly.

The obvious shortcoming of this setup is that every pop rivet you put in there is another opportunity for a leak, and with the bellypan overlapping and looking up, it will likely funnel water into the bellypan. Judicious amount of vulkem might help get things sealed up.

On a more radical line of reasoning, why not eliminate the undereath part of the bellypan so that only the banana wraps and other visible curved side parts are there. That would give you complete access to the frame and tanks underneath, and if a wrap gets damaged, it is just some pop rivets to correct it. I'm sure someone will opine that the belly skin is a structural component, but as long as you are re-engineering, don't let existing paradigms slow you down!

There was also another thread that discussed pretty much this same topic. I think the conclusion that one came to was that by building a metal frame around (and on top of) the perimeter of the existing frame, and then bolting the shell on top of that, you could eliminate the plywood trapped under the walls. The floor would then be installed completely on the interior. I don't know how to tell you to even search for that thread, though.

Having done a shell-off, and completely replaced my bellypan once, I have no interest in doing it a second time (ever)--even if I had devised an easier means of doing it. Therefore I focused more on keeping water out and rendering my floor rot-resistant than trying to make up for the shortcomings in the original design.

good luck!
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Old 02-01-2016, 11:01 AM   #7
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ok so here are some rough sketches of what i have gathered so far...

first pic- Airstream's original connection

second pic- darkspeed/rugjenkins solution (as i understand it):
weld a 1.5" steel tube to the frame all along the perimeter. this decouples the floor from the the other connections but the banana and exterior skin are still buck riveted together.

third pic- my proposed solution v1.0
as you'll see this relies on the creation of a custom connection profile. the end result allows the floor, belly pan, and exterior skin to each be removed without affecting the other components.

fourth pic- how i imagine assembling my proposed solution.


i'd love to hear any thoughts you guys might have.
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Old 02-01-2016, 12:24 PM   #8
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Awesome drawings but I'm not sure how it will work in the corners.. You could just make the perimeter belly pan from light gauge steel and weld it all the way around it might be easier.
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Old 02-01-2016, 01:59 PM   #9
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I like your design for the custom extrusion that will act as the "C" channel and support the floor at the edges--It would be hard to execute in the curves of the corners, but there are solutions.

Similarly, getting your banana wraps (on the corners) to wrap and to extend up under the wall like on the straight sections would be a challenge.

As I look at your design, it looks like there are blind rivets in a vertical position connecting the "C" channel of the wall to the frame. So the only thing holding your shell to your frame will be some (a bunch) of blind rivets in axial tension? Are there any bolts involved?
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Old 02-01-2016, 07:40 PM   #10
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Yes the curves at the corners need to looked at more closely. In terms of connection to the frame I propose bolting the new profile to the outriggers (see step 2 in the last image)
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Old 02-02-2016, 08:52 AM   #11
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So, in step 2, I see that you are bolting the extrusion to the ends of the outriggers, which I would expect will close up the space. How do you insert the belly-wrap then in step 3?
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Old 02-02-2016, 09:41 AM   #12
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Quote:
Originally Posted by Belegedhel View Post
So, in step 2, I see that you are bolting the extrusion to the ends of the outriggers, which I would expect will close up the space. How do you insert the belly-wrap then in step 3?
good question! that's the key point of the design...

not sure i can illustrate it better, but the new banana skin will only be riveted to the bottom of the new profile between the outriggers. the banana skin pieces will be notched around the outrigger connections so they can slip in between the outriggers after the new profile has been bolted down. does that make sense?

i'll see if i can draw something up to make this clearer...
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Old 02-02-2016, 10:15 AM   #13
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Ok, I see what you have in mind.
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Old 02-02-2016, 10:38 AM   #14
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btw, i don't mean to get off-topic, but while we're talking about structure... around the ceiling curve there seem to be several ribs running fore-aft that are not riveted to the exterior skin (pictured below). do you know what those are for? seems like the interior skin makes them redundant. can they be removed and discarded?
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