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Old 11-25-2010, 09:16 AM   #43
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Daniel I'm not sure about the 74's but my 73 some of the crossmembers were 1/2" smaller in height. This allowed for a 1/2" piece of plywood to sit between the frame and the floor. This was done at each seam of the floor sheets. The extra piece of plywood was used to add strength to the floor seams. I have seen 75's where A/S did away with this plan and all crossmembers are the same height. IIRC there are 12 xmembers and 6 were 4 1/2" in height and the angle iron over the fresh water tank was set lower for the seventh seam. So yes you could use the extra for crossmembers. Some x members are not as long as the others because the frame is boxed in at points.
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Old 11-25-2010, 10:24 AM   #44
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Thanks Chris.

Yes, there are shorter ones where the floor joins and was wondering about just eliminating that and make them all the same. I guess that would depend on the subfloor material and how it holds up around the edges then.
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Old 11-25-2010, 11:26 AM   #45
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Daniel you certainly can eliminate the shorter ones and make them all the same height. I would make xmembers with a wider top flange so as to have a wider attachment point and greater strength in the seam joint.
Here is a list of my xmembers. Yours may be different depending if your trailer is center or rear bath because of waste tank locations. I have listed them front to back.
1st 58"x4 1/2" solid w/ threaded holes for spare tire carrier.
2nd 58"x5" Slotted
3rd 61"x4 1/2" Slotted
4th 61"x5" Slotted
Angle Iron over fresh water tank
5th 61"x5" Slotted
6th 61"x4 1/2" Slotted
7th 61"x5" Slotted
8th 61"x4 1/2" Slotted
9th 61"x5" Slotted
10th 61"x4 1/2" Slotted
11th 61"x5" Slotted
12th 61"x5" Slotted
They are slotted to reduce weight and the slots are punched out leaving a flange around the slot to add strength. You could use solid xmembers but it will add a little weight. IMHO the extra weight is not worth worrying about.
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Old 11-25-2010, 06:58 PM   #46
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Dude, you are awesome..
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Old 11-27-2010, 06:46 PM   #47
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floor width?

This is a 1974 31' Excella center bath twin.

I got the chassis out from under the shell today. I measured the floor (plywood) and the attached drawing shows the lengths and widths of the existing flooring.

facts:
1) The floor is not original.
2) In no place was the floor all of the way in (seated) in the C channel.
3) Missing a piece of floor where the ? is.

problem/question:

The width of the floor at the rear of the chassis is 1 3/4" wider than the floor forward of the wheels (front of chassis). Is this correct?
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Old 11-27-2010, 07:24 PM   #48
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Hi Daniel, Excellent diagram very professional. I still have my old floor and just measured it for you. My floor is 91.5 inches wide for every sheet.I didn`t measure between the wheel wells,but can if you need that measurement. My front sheet is 35.5 inches and each sheet after that is a full 48 inches including rear sheet. so length measurements would be 35.5,83.5,131.5,179.5,227.5 and 275.5 total length of floor. you should have a uniform width to the floor or the shell will not fit straight from front to back.
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Old 11-27-2010, 07:44 PM   #49
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Thanks Chris. I think my measurement went long toward the back because the trailer has a hump in it.

You can see on the picture (left side is curbside-negative reverse photo) that the curbside had no outriggers aft of the wheels. I guess they guesstimated the floor width and were off.

I have a Mac and use Open Office. I found out today that it has a drawing program. Everything snaps in line.. really easy to use.

Another question.
I see that the outriggers have a hole drilled in the top 1/2" from the end. I'm gonna assume that this is for attaching the UC-channel? Should the outside of the UC channel be flush with the outside of the outrigger?

Thanks..
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Old 11-27-2010, 08:02 PM   #50
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Boy Daniel the PO really messed with that trailer. It`s no wonder the frame twisted and the shell sagged like it did. My old outriggers are gone so I cant tell you if the measurement for attaching to the channel. I did not measure my new one I just drilled down through channel and into outrigger. They were not predrilled. I had a bit of trouble getting the floor to match my new frame because it was built perfectly square and the old one was not. If I matched the floor using the original set up it was not square to the frame so I had to realign the floor a little bit. IIRC the outriggers ran right to the outside of the floor.
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Old 11-28-2010, 07:09 AM   #51
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Just a couple of FYI about buying steel:

Two dimensions are really important when buying steel : the depth and the thickness of the web. In your case the Channel is fixed at 5".
There are two standard US sizes of channels that are 5" : C 5X9 and C5X6.7.
the 5 refers to the depth the 9 refers to the number of pounds per foot.

You can tell which one the original was by the thickness of the web (the top and bottom portion of the channel. It would be 5/16” for the C 5X9 and 3/16” for the C 5X6.7.

In terms of strength the C5X9 is 19% stronger in bending strength, 34% greater in shear, 15% in deflection.

This is for A36 steel the most commonly available steel, also relatively common is A441 which is +/-16% stronger then A36.

Much of the original design of the early Airstreams was based on making them as light as possible to permit hauling them with the vehicles commonly available at the time, ton and ton pickups. Today many vehicles today are capable are hauling great weights (towing capacity),
So many thing that were not even considered before are becoming standard, corian countertops, large water tanks etc.

Where I am going with this is consider what your final product is going to be weight wise, and select steel members according. If your original trailer was say 2.5 tons and you figure modified is 3.5 tons , you need 40% greater strength in your steel frame.
This is a bit simplified since it does matter greatly where the weight is located. Something located at the tail end of the trailer will amplify the stresses on the beam greatly (versus a load over the axles). So do not do this without some professional advise/design).

I will be retrofitting my sons 31’ Airstream later this year. Instead of sand blasting and removing the corrosion I plan to simply put in a new frame and axles (3500 lbs). Given the cost of steel is not all that great and he needs a beefed up frame (he will have things like a big bookshelves, 50 gallons tanks and larger kitchen) it makes sense to me.

I will post stuff when I start to work on it this spring.

Hope this helps, I don't post much so if I missed some protocal please enlighten me (nicely).

Claude
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Old 11-28-2010, 04:51 PM   #52
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I was pondering this today as I was stripping the trailer frame down. Previous owners had bolted a total of 30' of thicker 5" C Channel to the existing rails for support. The good news is that I already have 30' now of the thicker 5" C Channel (no rust on it).

12x~60" = 60' for cross channels
2x~28' = 56' for main rails
60+56 =116' of 5" C channel
Lets round it up to an even 120'
120' @ 6.7 lpf= 804 lbs
120' @ 9 lpf= 1080 lbs
close to 3 hundred lbs difference, more or less, for a 31' trailer.

Lets say I wanted to make outriggers out of this same stuff..
Lets say 12 outriggers @ ~15"=15'
But the outriggers are 1/2 of a square (close enough for quick figuring) so the weight per foot would be ~ 1/2
So lets say 7.5 foot/pounds for outriggers
7.5x6.7= 50.25 lbs
7.5x9=71 lbs
~20 pound difference
so using the heavier steel for main rails, cross members and outriggers:
6.7 pounds per foot =~855 pounds
9 pounds per foot = ~1151 pounds
~ 300 pound difference.
It is more than 300 lbs compared to the original, because the cross members and outriggers are slotted. But still..
I'll take it.

Thanks for the info Claude. Very helpful.
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Old 11-28-2010, 05:07 PM   #53
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Quote:
Originally Posted by wasagachris View Post
My old outriggers are gone so I cant tell you if the measurement for attaching to the channel. I did not measure my new one I just drilled down through channel and into outrigger.
Thanks Chris. I measured today. All of the outriggers except for the front two and the two holding the steps are 14 3/4".
The front 2 are 11" and the step ones are 15".

So 14 3/4" X 2= 29 1/2" for the outriggers (trailer width-wise)
and 61.5" outside to outside on the main rails
= 91" width for the floor if it goes out flush to the end of the outriggers.

You said that your floor was 91.5 wide. I gotta figure out what is up with that 1/2 inch.
Yours is a 73, mine is a 74. I wonder if that is it or what I am missing..
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Old 11-28-2010, 05:30 PM   #54
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Daniel if you split the difference then a quarter inch on each side between egde of outrigger and edge of floor. I think you can live with that. Plus that way the side wraps do not contact the edge of the outrigger.
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Old 11-28-2010, 05:54 PM   #55
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Awesome.
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Old 11-29-2010, 06:13 PM   #56
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I called the steel place again today.. armed with a little more knowledge .

They sell C5x6.7 and C5x9 in 20 and 40 foot lengths.
The guy said that if I get the 40s they'd cut them down so that I'd have 2 the right length for the main rails and whatever is left (easy to transport on my existing trailer frame).

C5x6.7 x 40' @$157.05 USD
C5x9 x 40' @ $186.10 USD

Crawford Allied Steel, North Charleston, SC

The original steel on the frame is so thin.. I'm betting that it is < 6.7 lbs per foot. the 6.7 might be a significant enough upgrade to go with that.

Welding (cost) is the next big issue. We have a saying in the software development field..
1) Fast
2) Good
3) Cheap
Pick 2. I want 2) and 3)
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