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Old 07-18-2010, 07:44 PM   #1
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Question Integrity (structural I mean)

OK, who wants to save me from myself?
Burning Man coming up in about 4-5 weeks and I want to bring my AS back for a second trip. However, I just came back from camping at Caples Lake and when I was unhitching the trailer, I noticed a gapping at the front end between the shell and the frame when I moved the frame/hitch up and down. I know that I hit a few spots in the road with unplanned dips so got some strong porpoising (sp?).

Inspection reveals:
1. Frame appears to be solid with only surface rust.
2. Hitch is intact
3. Removal of front band/bracket (u shaped channel at the base of the shell) shows that the rivets had been sheared along the front. Rivets to outside of frame are intact. Between the frame, either the shell is about a 1/2" up or the belly pan is 1/2' low.
4. Pulled the front bed/cabinet and found dry rot in the floor below the front window. I noticed some when I got the AS last summer but it appeared localized and nonstructural so I've been working on other stuff that couldn't wait. I pulled off a couple rows of tiles and found quite a bit especially where the frame runs on both sides.
5. Drilled out a few rivets and peeled back the inner wall and it looks like the front u-channel is broken and doesn't seem to have any bolts, screw or rivets between the u-Channel and the frame. Haven't taken off the whole panel(s) yet so visibility is poor.
6. Flat head bolts to the side frame brackets appear to be intact but I haven't cut back enough plywood or cut open the belly pan yet.
7. Belly pan at the frame in front (driver and passenger side) has some tearing in the pan (both sides along frame) which tells me the frame went down when the shell went up.

The obvious solution is to replace the entire floor or at least a large section of it. Also, to replace the front belly pan at the same time (I already replaced the back half). I know I don't have time to do this before Burning Man so I'm looking a temporary solution until I can do it right.

As a temporary fix can I:
1. Cut out the front of the plywood with dry rot to where the wood is solid and replace with new plywood (glued and screwed)?
2. Mount an angle iron brace inside and outside the shell, bolted through the u-channel, and then bolted to the frame as it runs to the back? (for strutural support)
3. Patch in a small area of the belly pan for the torn areas and to allow access?
4. Weather proof.

My goal would be to make the trailer structurally sound enough to travel to Burning Man, and not to make it really hard to fix the right way after I get back.

Your advice is appreciated,
Thanks,
Bob
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Old 08-11-2010, 12:44 AM   #2
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Just as a follow up. I ended up opening up all the interior panels and the lower c channel had in fact broken in a couple of places, the bolts were half rusted through and the front rivets had popped as shown in the photos.

Repair was to replace the c channel and added an angle iron support that was bolted to the frame and replaced the rivets. Sorry I didn't get any photos but will do so if I have to open the inner panels again. It's probably more solid now than when it was built.
Bob
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Old 08-11-2010, 03:26 AM   #3
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Is the angle iron in direct contact with the aluminum? Because that would be a big nono.
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Old 08-11-2010, 07:56 AM   #4
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Is the angle iron in direct contact with the aluminum? Because that would be a big nono.
Why? Galvanic reaction? There must be all kinds of contact between the frame and the belly pan.
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Old 08-11-2010, 09:17 AM   #5
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fixing it twice?

Hi Bob-my advice is along these lines: does fixing something twice bother you? I mean doing the work twice? If so, then you need to fix it right the first time. If not, do your tmpy repairs and go camping. If you decide to do it right, see if you cannot borrow/rent another camper and still go camping.
cheers
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Old 08-11-2010, 09:21 AM   #6
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...which is why so many bellypans have holes in them, are more patch than original.

Also remember that iron is more noble than aluminum so it will be sacrificed first. That is why the bottoms of the frames rot out first, being in closest wet contact with the belly pan.
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Old 08-11-2010, 09:38 AM   #7
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If your iron installed had a decent paint process coating on it then it is nearly as good as the factory work. If you want better than original a couple of extra steps are needed.

If it is mechanically secure now go enjoy yourself but make time later to check on it!
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Old 08-11-2010, 05:23 PM   #8
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Quote:
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Why? Galvanic reaction? There must be all kinds of contact between the frame and the belly pan.
Quote:
Originally Posted by Dave Park View Post
...which is why so many bellypans have holes in them, are more patch than original.

Also remember that iron is more noble than aluminum so it will be sacrificed first. That is why the bottoms of the frames rot out first, being in closest wet contact with the belly pan.

Aluminum and mild steel/iron are not all that dissimilar on Galvanic Order tables, and to label iron as more noble may be a stretch. Granted there are some exceptions, but these materials are commonly joined with little long term effect. This does not apply for galvanized steels which is a totally different scenario.

When design dictates the joining of dissimilar metals the galvanic compatibility, or Anodic Index needs to be considered.
The Anodic Index (AI) for aluminum typically is anywhere from 0.75V to 0.95V, while mild steel/iron is in the 0.85V range. In harsh environments it is desirable to keep the AI differential to 0.15V or less, so with steel positioned in between you’re normally pretty safe. Of course if you were to throw road salts, or sea waters into the mix...All bets are off.

Galvanic Corrosion (GC) is an electro-chemical process that causes the deterioration of one element in a coupled condition. The more dissimilar the metals, the greater the variation in electrical potential and the likelihood of a GC condition. This is an Anode/Cathode relationship where the Anode usually takes the brunt of the damage, hence the term “sacrificial anode”.

In the case of aluminum and mild steel they really aren’t that dissimilar and advanced frame corrosion caused by GC is not likely. Frame corrosion is usually attributed to continued exposure to wet insulating materials and prolonged shell leakage.

Regards,

Kevin
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Old 08-11-2010, 07:14 PM   #9
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I am coming at this from the "my Airstream is built not unlike an aircraft, and it's as important to me as an aircraft, so I'm going to follow aircraft rules when maintaining it" stance

And, although the difference is "not great" we already have much experience of what fifty years can do and that same experience has taught us how it can be easily avoided.

At the end of the day, we all own our own Airstreams and we decide for ourselves just how particular we want to be in our restorations or refurbishments. Too much info is better than too little, even if it does seem spurious at times!
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Old 08-11-2010, 08:55 PM   #10
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Won't speak to the similar/dis-similar aspects and corrosion but the Air force will not join steel and aluminum without specific treatment of both pieces and all fasteners to prevent corrosion.
I will say I am just finishing up replacing the bathroom sub floor on my 78 Excella.
There were several strips of steel bar added as support for bolts through the floor C channel and plywood subfloor. All the strips of bar stock and bolts, nuts and washers were severely rusted, almost to the point of being unrecognizable. The C channel was severly corroded through at each location. There was no preventive treatment to any of the pieces when installed.
Whatever the reason this is not a good repair tactic.
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Old 08-12-2010, 11:27 PM   #11
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Thanks all. I forgot to add that the bar was treated with POR first. You all are the one's that turned me on to the problem of disimilar metals when I had to do some belly pan work last summer.

Normally I like to do a job once and do it right. I tend to overbuild so I don't have to do it again. This is one of those times that I really want to take the Traveler with my son to Burning Man and just don't have time to do the full (whole new floor and channels etc) repair right. The front was the only really bad area but given a little dry rot here and there, I know that I have to do the entire floor but can't do it this summer and my wife and son can't live without the Twinkie.

Thanks again for your help.

Bob
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