Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-28-2005, 11:22 PM   #15
Rivet Master
 
1977 31' Sovereign
1963 26' Overlander
1989 34' Excella
Johnsburg , Illinois
Join Date: Jul 2005
Posts: 2,941
I am a mechanical engineer. The prior posting shows a very signifigant crack and it would be very unsafe to be on the road with anything like this. This crack could be a fatique crack from lots of miles of rough road or less likely from travelling with unbalanced tires. It also could have started from a single high overload from a big bump with the holding tanks full. Once the first crack starts on the top of the channel, the continuation of the crack can come at much lower loads because the stress concentration at the tip of the crack and the greatly reduced effective moment of inertial (an engineering term) caused by the loss of effect of the upper portion of the C channel. I have also seen frames that were merely bent between the wheels without cracks. These frames might be babyied along for a number of years with just the elephant ears fix without failing completely on the road.
__________________

__________________
dwightdi is offline   Reply With Quote
Old 11-29-2005, 05:13 AM   #16
Rivet Monster
 
wahoonc's Avatar

 
1975 31' Sovereign
1980 31' Excella II
Sprung Leak , North Carolina
Join Date: Jun 2003
Posts: 7,174
Images: 40
Quote:
Originally Posted by dwightdi
I am a mechanical engineer. The prior posting shows a very signifigant crack and it would be very unsafe to be on the road with anything like this. This crack could be a fatique crack from lots of miles of rough road or less likely from travelling with unbalanced tires. It also could have started from a single high overload from a big bump with the holding tanks full. Once the first crack starts on the top of the channel, the continuation of the crack can come at much lower loads because the stress concentration at the tip of the crack and the greatly reduced effective moment of inertial (an engineering term) caused by the loss of effect of the upper portion of the C channel. I have also seen frames that were merely bent between the wheels without cracks. These frames might be babyied along for a number of years with just the elephant ears fix without failing completely on the road.
dwighti,
The frame cracks were caused by a design flaw when the Airstream "engineers/designers" undersized the frames in an attempt to keep the weight down, or they did not think through the load calculations. I have seen trailers with bent frames and no rear end separation and I have seen trailers with the strengthening plates installed that had rear end separation as well as trailers that had been well cared for with neither issue. The frame stiffening plates pictured below were the factory fix for the weak frame issue. The elephant ear repair was a separate repair issue. Are the two related possibly but they are two different issues and have to be dealt with separately.

Aaron
__________________

__________________
....so many Airstreams....so little time...
WBCCI #XXXX AIR #2495
Why are we in this basket...and where are we going
wahoonc is offline   Reply With Quote
Old 11-29-2005, 05:59 AM   #17
Rivet Master
 
1977 31' Sovereign
1963 26' Overlander
1989 34' Excella
Johnsburg , Illinois
Join Date: Jul 2005
Posts: 2,941
The body separation from the frame is due to failure to hold these two subsystems together. They were designed to be held together by bolts between the lower aluminum channel (which is riveted to the skin) and the floor and frame assembly. The "elephant ears" fix increases the bolting strength and spreads the stress over a larger area of the channel. The forces that cause the separation are usually the bending of the main frame at the rear axle or between the axles or a fatique crack developing in the frame (as shown in a prevous posting). The installation of the elephant ears modification allows the body of the unit to become a better stress carring element in the design and lowers the stresses that need to be carried by the frame. The bolt-on frame strengther plate allows the frame to better resist the stresses and (in therory) reduce the stresses to the point that you never exceed the fatique strength of the material in the upper frame section and the fatique cracks will never occur. The fatique strength of steel is much lower than its yeild strength and that is why you do not see any yielding around the crack until the last minute when the last vestages of the frame fails and the unit collapses. (I used to design and test high performance boat motors and we had these kinds of problems more frequently than we desired.) Aircraft designers and aircraft maintenance personnel frequently have this problem. They replace whole areas on the planes to keep them in the air for 30 years. To them, it is a matter of economics because the planes are very expensive. For an old Airstream with fatique cracks,(in my opinion) it is most likely time to retire it to a permanent home as a summer cottage by the lake.
__________________
dwightdi is offline   Reply With Quote
Old 11-29-2005, 08:23 PM   #18
Got gandkids?
 
Jim & Susan's Avatar

 
1973 27' Overlander
'Possum Holler , Georgia
Join Date: Oct 2004
Posts: 5,406
Images: 39
So, to noodle this out, there are two basic problems with this era trailer. One problem is that the frames have a tendency to fail aft of the axles (for various reasons, including metal fatigue, rust and so on). The second problem is that the upper shell has a tendency to separate from the frame itself.

Problem number two can be corrected by reattaching the shell to the frame using additional bolts and steel plates between the U-channel that is riveted to the shell and the actual steel frame in the trunk area between the frame C-channel members.

Problem number one, what I believe to be at the base of the issue here (my novice opinion) is more dicey. The basic “fix” here is to beef up the frame aft of the axles. There is a lot of unnecessary movement back there which I believe leads to shaking, wiggling, and up and down movement which in turn causes bolts to loosen, rivets to pop, steel frames to twist and bend, etc. In addition, the weight back there tends to push the very back of the trailer toward the ground. Everything begins to pull apart. So, the $64,000 question is how to strengthen the frame here?

One option is to purchase the axle plate mentioned by Zommzoom, above. This, apparently, bolts to the frame C-channel on the outside of the channel aft of the axles. Another option would be to weld a vertical plate between the upper and lower “flange” on the C-channel inboard on each rail.

Ok, y’all, tell me where my thinking is wrong.

Jim
__________________
www.nesa.org

Air No. 6427
Jim & Susan is offline   Reply With Quote
Old 11-30-2005, 07:26 AM   #19
Rivet Master
 
1977 31' Sovereign
1963 26' Overlander
1989 34' Excella
Johnsburg , Illinois
Join Date: Jul 2005
Posts: 2,941
The factory fix for the problem (installing a stiffener plate bolted to the exterior of the frame) is a cost effective solution that does not intail taking the whole thing apart. Welding a plate in the inside of the C frame to make it into a complete box frame can only be accomplished by removing the belly pan and means welding on the frame which anneals the existing metal and usually reduces the strength of the material. I believe the original frame is made from a cold rolled material (which increases its strength). If it were a hot rolled product it would not be as bad but still, the quality of the fix would dramatically depend on the quality of the weld and welder. Having welded on a few frames myself, this is not an easy talent to learn. Airstream would be placed in a poor position of defending the quality of dealer installed welds. It is not a good idea. The bolts in the back, allowing the shell to better take part of the load, is also a good low tech field partial fix.

Whether you think the problem is: Airstream's fault for undersizing the frame or the users' fault for abusing the product too much, or unrealistic user expectations of having a trailer that is usable for 50 years, is a matter of viewpoint. I am a frequent user. Sometimes you can not control the quality of the roads which you get into (such as road construction). The Airstream image of doing these round the world caravans has likely lead to unrealistic view of what these trailer can take. If you look closely at the pictures you will see the tow vehicles and trailers are frequently not exactly stock units. If you read the actual chronicals you will see not all units completed the treck.

If I knew I was expecting to use my trailer to do a large amount of rough road travel, I would buy a smaller unit with less overhang and a 5 inch frame and four wheels built after 1984.
__________________
dwightdi is offline   Reply With Quote
Old 12-05-2005, 11:56 AM   #20
Rivet Master
 
JimGolden's Avatar
 
Vintage Kin Owner
1977 31' Excella 500
Berkeley Springs , West Virginia
Join Date: Sep 2005
Posts: 1,619
Images: 7
On the welding issue...

I used to work for a major crane company and we made the booms out of 100ksi yield strength steel, sometimes even stronger material. We welded everything together and always took the plate strength as 100ksi (or whatever it was). We never reduced it due to welding messing up the plate strength. Never had a failure.

I can't imagine the frame of an Airstream being made out of anything exotic. It's probably just plain old 36ksi steel like they make car frames out of. As such, I wouldn't think welding to it would hurt it at all. Granted, the doublers contribution to enhanced structural rigidity would be dependent upon the quality of the welding to make the load path, but you'll have that with anything that you change.

But you make a good point: it would be much easier to just sell the trailer and buy a newer one. I'm torn with what to do. I really like this model. All these mods are just a patch. The real way to "fix" it is to make a new frame and just transfer the shell over. That's a lot more work than I was planning on.

I am trying to talk my wife into a new mig welder for Christmas though
__________________
JimGolden is offline   Reply With Quote
Old 12-13-2010, 09:23 PM   #21
1 Rivet Member
 
1975 31' Sovereign
newburgh , Maine
Join Date: Dec 2009
Posts: 9
Images: 1
There are some really good posts on here.
I'm not sure if the failures are due to fatigue or bending failure.
It sounds more like fatigue. I do think the frames are probably A36
steel, most cost economical to manufacturer.

The solution regardless of the cause is to beef up the frame. I think the patch
from airstream is minimal and at a cost of $250 for $35 worth of steel. I thought Toyota was bad.
__________________

__________________
claudebo is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Oval Window Frame Replacement MikeMikeMI Windows & Screens 8 12-30-2007 11:49 AM
year frame size reduced yukonsilver Airstream History 1 04-19-2004 01:53 PM
Cushion Dimensions, Front Sofa Alan and Julie General Interior Topics 2 08-05-2002 03:14 PM
Window Frame Removal 64GT Windows & Screens 4 04-09-2002 01:40 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 07:09 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.