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Old 11-17-2015, 04:28 PM   #29
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1975 31' Excella 500
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Replacement frame

An eight inch main rail is crazy overbuild in my opinion.

I see a six inch rail as overbuild, but more in the ballpark.

I would make the rails out of 5" x 2" rectangle tube if I was building from scratch.

Brevi tempore!
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Old 11-17-2015, 04:32 PM   #30
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Yes but they hold big tanks!
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Old 11-19-2015, 07:23 AM   #31
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Here are some thread links. Some of these you may have found already. The last one is Steve Bryant's rebuild with lots of frame mods.

http://www.airforums.com/forums/f36/...gn-100154.html

http://www.airforums.com/forums/f36/...ame-29294.html

http://www.airforums.com/forums/f36/...me-114946.html

http://www.airforums.com/forums/f36/...ted-85517.html


I did not find the guy with the perimeter frame but it is out there somewhere.

Perry
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Old 11-19-2015, 09:39 AM   #32
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Yes but they hold big tanks!

That is a fact. I do wish I had installed bigger tanks. There are ways to accomplish bigger tanks without running 8" the full length of the trailer.


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Old 11-19-2015, 09:49 AM   #33
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My center bath tanks hang way down below the frame. Make a tank pan.

Perry
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Old 11-21-2015, 04:31 PM   #34
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So I am leaning toward the following:

8 inch Structural C for the main rails, with 5 similar sized I beam cross members (poss a C in the front and rear?) Originally there were 6, but I would need to remove one to accommodate the new black and grey tanks on both sides of the axle. Fresh water tank will remain forward of that, same as original location.

More out riggers (every 6-12 inches???) 5 inches deep in order to maintain the original belly pan configuration (the deeper rails will be exposed 3 inches below the wraps).

Top perimeter plate 6 inches wide, 0125 thick (jimgolden, aerowood)

Similar original A frame with a spare tire mount under the front.

Extend the rear by 12 inches to accommodate a slightly larger trunk and a small separation between the back of the trailer and the trunk. This will help to address the problem of water accumulating or running down the back and leaking into the skin (I will also address the seam in that area by extending the rear panel to a belly wrap)

There has also been some thinking of adding a pneumatic or hydraulic leveling system. Pillars in each interior corner of the frame??? Who knows.

I am concerned about tongue weight, how heavy do the axle need to be (5000# dexters). Mostly tech stuff as I am no en-guh-neer or even Mechanically inclined.

All of this is speculative at best, though I will have to decide something soon.

Any thoughts.

Thanks again for all the suggestions.


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Old 11-21-2015, 04:45 PM   #35
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Well, I have a 45 foot flatbed trailer, the frame is made of 8" I-beam, it uses 4" crossmembers every two feet.

It weighs in excess of 7,500 pounds...

I expect a frame like you described will weigh between 4,500 and 5,500 pounds.

Are you going to haul rocks in that thing?

Imho, the frame you propose is ridiculously overbuilt.

You might consider how much that 10 to 15% tongue weight is going to be.


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Old 11-21-2015, 04:55 PM   #36
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There are pluses to a deep frame, if I wanted a deeper frame I might go eight inches, but it would be thinwall tube, not thickwall.


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Old 11-22-2015, 07:01 AM   #37
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Ya need to have more than a plate between the outriggers. This might be hard without hydraulic tubing benders etc. A plate with some gussets might be all you can fab on the corners but angle works fine for the straight sections. No having to put the floor under the walls has its advantages.

Perry
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Old 11-22-2015, 07:29 AM   #38
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What about having the 8" c channels formed out of 1/8" galvanized sheet metal? The original frame was about this thickness.
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Old 11-22-2015, 01:32 PM   #39
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Perry,

By a plate around the outriggers, I meant essentially a 1/8" thick (1/16" would probably suffice) plate that is 6" wide, cut to the outside contour of the trailer, going all the way around.

To this flat plate, you would attach your U channel. With the U rigidly attached to the plate, you now have a big L with a ton of Moment of Inertia. Very stiff. You can attach the shell to the U, and let the outer edge of the floor bear upon the remaining width inside the U.

In fact, I'd change the floor as well. I'd do it like Avion does, with three layers: 1/2" plywood bottom, 1.5" spacer (with a cross piece every 4' and insulation filling the gaps otherwise), 1/2" plywood top. You'll lose a little bit of headroom, but the result is a very stiff floor that is insulated. It works well for the Silver Sister, so would do well here....as long as you're not 6'6" tall

As for the curved portions, I'd recommend grinding the flat plate to a width of 5 15/16" wide, taking the 1/16" off the outer edge on the rounded areas. Then, get a strip of 1.5" tall by 1/16" thick steel and weld it to the outside edge, making an L in the corners. So, use the U channel on the straights, have the outer edge 1/16" steel piece welded to the corners match the outer portion of the U, and you have a continuous vertical web 360 degrees all the way around the outside.

It would be a little harder to form a 1/16" inner portion to match the U channel out of plate, but it could be done with spacer blocks without too much trouble.

On the outer plate, I'd weld it solid on a short section of straight. Then, for every 3", I'd bend it into place and weld, then bend the next 3" into place and weld, and keep going all the way around the circumference.

Anyway, I think you, AeroWood, and I are all saying essentially the same thing. Put a stiffened "perimeter frame" atop the outriggers, have something with it to carry the floor, and bolt the shell to this perimeter frame and let the floor bear within. This in addition to a proper main frame and it'll be goodness.

If he does this, he will be Gold
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Old 11-22-2015, 04:14 PM   #40
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FYI , your banana wraps will no longer work with an 8 inch tall frame. IMHO an 8 inch tall frame would be grossly overbuilt for a Caravel. You could carry a skid loader inside you trailer.
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Old 11-22-2015, 04:46 PM   #41
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Quote:
Originally Posted by Bullit View Post
So I am leaning toward the following:

8 inch Structural C for the main rails, with 5 similar sized I beam cross members (poss a C in the front and rear?) Originally there were 6, but I would need to remove one to accommodate the new black and grey tanks on both sides of the axle. Fresh water tank will remain forward of that, same as original location.

More out riggers (every 6-12 inches???) 5 inches deep in order to maintain the original belly pan configuration (the deeper rails will be exposed 3 inches below the wraps).

Top perimeter plate 6 inches wide, 0125 thick (jimgolden, aerowood)

Similar original A frame with a spare tire mount under the front.

Extend the rear by 12 inches to accommodate a slightly larger trunk and a small separation between the back of the trailer and the trunk. This will help to address the problem of water accumulating or running down the back and leaking into the skin (I will also address the seam in that area by extending the rear panel to a belly wrap)

There has also been some thinking of adding a pneumatic or hydraulic leveling system. Pillars in each interior corner of the frame??? Who knows.

I am concerned about tongue weight, how heavy do the axle need to be (5000# dexters). Mostly tech stuff as I am no en-guh-neer or even Mechanically inclined.

All of this is speculative at best, though I will have to decide something soon.

Any thoughts.

Thanks again for all the suggestions.


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You will still be beyond reality with an 8 inch frame.

You must remember that the Airstream is semi-monocoque construction.

Why semi ? Because the underbelly is not really a part of the monocoque.

However, you MUST KEEP IN MIND, OR ELSE, that the frame must flex with the shell. If it does not, then since the shell will still flex, it will suffer extensive damages in a very short period of time.

Then you can start all over again.

5 inches is the maximum size frame, with the current designed shell, also using heavier gauge metal sheet metal than your older Airstream.

You will indeed waste a ton of money and time, if you insist on pursuing your mechanical and structural Airstream dreams.

Andy
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Old 11-22-2015, 05:18 PM   #42
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They can, if a lip to catch them is welded in the proper location on the frame.


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