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Old 06-26-2010, 07:10 PM   #1
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rib failure - ouch.

Well for those of you who have never observed crumple failure of an alum rib, here is a nice example. I have yet to find the exact cause, except to say that I did have the trailer very well loaded, and the frame seems to have failed. I was planning on doing a shell off, thinking that it would be mostly a paint job, as the previous owner told me he had removed all of the bad frame...well at least 1 weld failed and I am days away from finding all the causes.

One of the things I do in my job is look at how buildings fail, and figuring out why....so I guess this stuff facinates me....
now the money shot...
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Old 06-26-2010, 07:14 PM   #2
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Well for those of you who have never observed crumple failure of an alum rib, here is a nice example. I have yet to find the exact cause, except to say that I did have the trailer very well loaded, and the frame seems to have failed. I was planning on doing a shell off, thinking that it would be mostly a paint job, as the previous owner told me he had removed all of the bad frame...well at least 1 weld failed and I am days away from finding all the causes.

One of the things I do in my job is look at how buildings fail, and figuring out why....so I guess this stuff facinates me....
now the money shot...
Can you post a photo?

A rib failure could only happen from corrosion or vibration.

Andy
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Old 06-26-2010, 08:20 PM   #3
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photo - trouble uploading...

here it is I think...
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Old 06-26-2010, 08:39 PM   #4
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@ Andy,
not to disagree with experiance, but the shell is a mondified monoque, in this case no interior skin was present when this happened (gutted when I got it)
conceptually speaking a monoque's members can fail through crumpling if the load on the tail was significant, I think that is what happened here, it looks like a series of frame members failed, dropping the back, basicly loading the skin like a large truss, because the frame failure was asymetrical (curb side) the rib under the most strain failed, I did get buckling in the outer skin, but thank goodness I am pretty sure it will be fine when I reset the shell on the repaired frame. Now, my big question is, replace rib, sister to the rib, or some other option?

More images - I have another rib issue at the AC unit but that is for another day...
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Old 06-26-2010, 11:27 PM   #5
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I'd be tempted to cut that busted rib above the damage, and either make a replacement with a good splice plate and plenty of rivets, or take the damaged area to a sheet metal shop with the tools I didn't have and let them make it. Maybe the 70's was different, but trying to help Wally change bows here I've yet to see 2 bows that have the same curve, almost like they eyeballed to a certain extent.

Looks to me that it could have bounced real hard. Our 22' had a lot of crunch damage in the rear due to bad frame/shell connection.
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Old 06-27-2010, 12:52 AM   #6
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Hi, what does the outside of the trailer look like? Are there any items added on or welded to the rear frame/bumper area? Bike racks, spare tire, generator, or gas/water cans etc.
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Old 06-27-2010, 03:57 AM   #7
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Originally Posted by mbattin View Post
I have yet to find the exact cause, except to say that I did have the trailer very well loaded, and the frame seems to have failed...
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... the shell is a mondified monoque, in this case no interior skin was present when this happened...
Not saying that the frame isn't a contributing factor in your case but the interior skin contributes significantly to the shell structure. If the skin wasn't installed and the trailer was heavily loaded then a rib/frame failure could easily occur.

Good luck and let us know what you discover.

Kevin
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Old 06-27-2010, 08:35 PM   #8
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So Bob, there was a gear basket back there, that was on a hitch, that is something I added, but didn't put much weight there as I had some sag already. From the sound of it, the PO pulled out the steel plate during a repair ( not there now but told it should be) and makes sense based on my observations taking it apart watching it break as well as trying to repair it on the road.

When I got the wheel wells off I had quite a surprise. The frame is bent (crumpled) btwn the axles.

I am going to follow up in the area devoted to frames, but this might be a game ender for me.
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Old 06-27-2010, 08:39 PM   #9
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Oh and Kevin, thanks for your thoughts. I know the skin works, but my total bs guess is it's doing less than 25% of the work, and maybe more like 5 to 10%. I am basing this on the fastener count, and factors of safety. Perhaps it's more, but if it is, I want to know how.
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Old 06-27-2010, 08:42 PM   #10
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So Bob, there was a gear basket back there, that was on a hitch, that is something I added, but didn't put much weight there as I had some sag already. From the sound of it, the PO pulled out the steel plate during a repair ( not there now but told it should be) and makes sense based on my observations taking it apart watching it break as well as trying to repair it on the road.

When I got the wheel wells off I had quite a surprise. The frame is bent (crumpled) btwn the axles.

I am going to follow up in the area devoted to frames, but this might be a game ender for me.
Breaks in the frame between the axles are a known weakness of the 70's vintage long trailers, AS actually made a repair/stiffening plate to take care of this issue. Mine had the plate installed prior to my owning it.

Aaron
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Old 06-27-2010, 08:54 PM   #11
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Breaks in the frame between the axles are a known weakness of the 70's vintage long trailers, AS actually made a repair/stiffening plate to take care of this issue. Mine had the plate installed prior to my owning it.

Aaron
That frame failure, is due to many miles with unbalanced running gear.

We have gone thru this many dozens of times.

Andy
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Old 06-27-2010, 09:36 PM   #12
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That frame failure, is due to many miles with unbalanced running gear.

We have gone thru this many dozens of times.

Andy
Yes we have, but surprisingly the factory DOES NOT balance running gear, only SOME dealers. I agree that running gear balance does play into the issue, but the fact the frames were downsized to save weight certainly plays into the equation, as does the length and poor layout of the tanks. AND if running gear balance was the end all you would have hundreds if not thousands of trailers with frame failure and I have yet to see that on any other Airstream other than the longest of the 1970's models. The earlier ones and the later ones don't seem to have this issue.

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Old 06-27-2010, 09:36 PM   #13
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Breaks in the frame between the axles are a known weakness of the 70's vintage long trailers, AS actually made a repair/stiffening plate to take care of this issue. Mine had the plate installed prior to my owning it.

Aaron
There is a Airstream factory service bulletin on that. See below.
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Old 06-27-2010, 11:16 PM   #14
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There is a Airstream factory service bulletin on that. See below.
Lee.

That bulletin as been around many years.

It addresses a fix, not the cause.

Andy
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