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Old 04-17-2008, 01:48 PM   #127
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It's still going to flex, just not as much, which in my humble opinion is good. When it flexes to much, as in the 70's longer trailers, is when things start comming apart, and you get rear end sag and elephant ears as the shell just can't hold up the back end of the trailer. In my opinion there is benifical weight and then there's weight with no gain other then cosmetic. A better frame that prevents rear end sag is good weight.
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Old 04-17-2008, 02:47 PM   #128
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Compared to a C5x6.7, the 5x2x3/16 tube will give you about double the uniform load capacity and only weighs about 25% more. This substitution would only add about 90lbs to the frame. The problem will be that you will not be able to use the perforated cross members since they will be too long and not configured to be shortened that much. Substituting a 12ga bent plate will add quite a bit of weight to the frame.
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Old 04-17-2008, 02:56 PM   #129
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Quote:
Originally Posted by Aerowood
... prevents rear end sag is good ....
I agree.

I don't think AS designed in/out any flex. The construction method allows flexing. This method was created by the aircraft industry. It is just my opinion but I doubt AS did any studies as to how much flex a trailer had and what effect it had on the trailer. I would think too much flex puts adverse stresses on the trailer more than not enough. If what is preventing the flex is capable of handling the stress, I would think that this would
alleviate other flexing and stresses.

Weight is a balance (side to side, front to back) issue, a TV issue, and an axle/shock/tire issue. Weight not directly supported by the frame adds to this complexity.

I am not an engineer so all that I have said is only worth, well, not much.
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Old 04-17-2008, 03:00 PM   #130
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Hmmmm, well I AM an engineer, but of the electrical variety. I only took a couple of ME-type classes, and we sure didn't study complex monocoque design in my freshman Statics & Dynamics course, so what you're saying sounds good to me...
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Old 04-17-2008, 04:13 PM   #131
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weight issues

Quote:
Originally Posted by byamcaravanner
Compared to a C5x6.7, the 5x2x3/16 tube will give you about double the uniform load capacity and only weighs about 25% more. This substitution would only add about 90lbs to the frame. The problem will be that you will not be able to use the perforated cross members since they will be too long and not configured to be shortened that much. Substituting a 12ga bent plate will add quite a bit of weight to the frame.
Kip, and others, are suggesting replacing the cross-members and the outriggers with the 3/16 rectangular tube. I need to figure out how much extra material that will require? However, assuming I would need at least 40 extra feet that's another 326 lbs plus the extra 90 lbs bringing the total to roughly 416 lbs over the .190 channel. The grand total (main rails, cross-members and outriggers)would be 489 lbs plus 416 lbs or 905 lbs. So the question that seems to be developing here is: is an extra 416 lbs over the .190 channel (.190 is probably close to the original specs) worth doubling the uniform load capasity and avoiding the 1970's frame issues?

For the sake of argument, it's interesting to compare these numbers to the heavier 5" inch channel which is available with a 1.885 flange, and .325 web thickness. This material weighs 9.0 lbs per foot. Using this material, at 1,000 feet of channel (2-30 ft rails plus 40 ft of extra), the total weight here would be 900 lbs. So using the 3/16 tube versus the .325 channel materials would roughly come in at the same weight. Either way I'm looking at a 900 lbs frame. I wouldn't gain anything using the heavier channel versus the tubing.

We might as well take a closer look at the .190 channel weighing 6.7 lbs per foot:. Assuming the 5" channel, 1.750" flange, .190" web thickness is probably close to the factory specs 1000 feet of this material is 670 lbs Since the factory outriggers and factory cross-members are obviously constructed of lighter material it would seem that a factory frame would weigh somewhat less than 670 lbs Assuming an extra 40 feet of this material would be enough to construct cross-member and outriggers the weight of those components would be 268 lbs So, in other words factory outriggers and cross-members probably weigh less than 268 lbs (670 lbs less 402 lbs).

Whew! So if my thinking and calculations are correct the original frame should weigh less than 670 lbs (570 lbs?) and either a 3/16 tube replacement or a .325 channel replacement will weigh roughly 900 lbs or roughly 400 lbs heavier than a factory frame. I'm dizzy now and not sure what all this means! Give me a minute...I smell smoke!

Okay...what do you think about a 900 lbs frame versus a 570 lbs frame? What difference will an 400 extra lbs make? In terms of Axles? Tires? TV? Etc? Is this a huge difference? Or a small one?
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Old 04-17-2008, 05:03 PM   #132
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weight issues correction

Sorry I got a little wrapped around the axles in that last post. Please disregard. (To avoid spreading my confusion maybe one of the administrators will delete it. Please!)

I think I can simplify this. Assuming I use 60 feet of materials for the main rails and about 40 feet of materials for the outriggers and cross-members that's roughly 1000 feet of material.

Using 5" channel, 1.750" flange, .190" web thickness at 6.7 lbs 1000 feet is 670 lbs. This material is probably close to the factory material. However the cross-members and outriggers are probably lighter. 40 feet of this material for outriggers and cross-member is 268 lbs. So the factory material is probably lighter than 268 lbs. The factory frame is probably between 402 and 670 lbs.

Using 5" inch channel with a 1.885 flange and .325 web thickness. 9.0 lbs per foot 1000 feet is 900 lbs.

Using 5x2 rectangular tubing in 3/16 gauge at 8.15 lbs per foot 1000 feet is 815 lbs.

Just for fun let's say the factory frame weighs 550 lbs. Compared to the .325 channel that's a 350 lbs difference. Compared to the 3/16 tubing that's a 265 lbs difference.

Assuming I use the 3/16 tubing what difference will 265 lbs (or even 350 lbs) make? In terms of axles, tv, etc? As Kip is suggesting it seems like worthwhile tradeoff.
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Old 04-17-2008, 06:15 PM   #133
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3/16 tube versus .325 channel

The above speculations seem to suggest that a factory frame made of .190 channel would weigh roughly 550 lbs. Using .325 channel a similiar frame would be roughly 350 heavier and using 3/16 tubing a frame would be roughly 265 lbs heavier.

I think most folks here would agree that a replacement frame should definitely be constructed out of heavier material. There is only an 85 lbs difference between the heavier channel and the tubing. To me this doesn't seem like much of a weight difference to fuss over? So which is better: tubing or channel?
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Old 04-17-2008, 07:30 PM   #134
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Quote:
Originally Posted by monocoque
Kip, and others, are suggesting replacing the cross-members and the outriggers with the 3/16 rectangular tube.
One problem to consider regarding using tube cross members is that you will not be able to bolt the floor to the tubes using elevator bolts.

The cross members I replaced to carry my tanks are made of 14ga bent plate.
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Old 04-17-2008, 10:40 PM   #135
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tube, channel or combination

Quote:
Originally Posted by byamcaravanner
One problem to consider regarding using tube cross members is that you will not be able to bolt the floor to the tubes using elevator bolts.

The cross members I replaced to carry my tanks are made of 14ga bent plate.
Steve, good point. That seems to be a mark in favor of using channel: ease of access to secure the floor and frame. Aside from the flooring how would the shell u-channel be secured to the frame without using bolts? If the outriggers were constructed out of tubing the outside ends would be open and accessible but the work space for wrenching bolts would be very narrow?

Just a thought but I suppose the possibility exists to use a combination of channel and tube. The main rails would be tube and the cross-members and outriggers would be channel?
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Old 04-18-2008, 04:35 AM   #136
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Quote:
Originally Posted by monocoque
The main rails would be tube and the cross-members and outriggers would be channel?
Good combination. If you like, tube could be used for the outriggers since they are either rounded or bevel cut on the outbound end, this would leave the top face exposed for bolting.
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Old 04-18-2008, 12:27 PM   #137
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outriggers and cross-members

Quote:
Originally Posted by byamcaravanner
Good combination. If you like, tube could be used for the outriggers since they are either rounded or bevel cut on the outbound end, this would leave the top face exposed for bolting.
Steve, if I use tube for the outriggers do you think there will be enough room to work inside the outbound-ends to tighten and loosen the u-channel bolts which secure the shell?

Also a number of the cross-members need to be somewhat shorter than the exact level of the frame to create space for the floor splices. So I need to consider the size and kind of material to use in those areas? Perhaps c-channel at something less than 5 inches.
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Old 04-18-2008, 02:57 PM   #138
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I would think that outriggers made of tube would be open along the bottom out near the ends because you would have to cut the sides to fit the necessary curve. That being the case you should be able to use an extension on your socket wrench to reach the nuts on the bottom of the bolts at the ends of the outriggers. Also I would think that you might be able to use an air powered socket wrench in the tight space at the end if you wanted to work just from the end. You would need to be carefull not to overtighten. I snapped off an elevator bolt with my air wrench so I decided to hand tighten them all.

If you can find a local sheet metal shop it might not be a bad idea to have them bend up some channel for the cross-members out of sheet metal of a suitable thickness - similar to the existing cross-members I would think. That way you could have them made up in two different heights as needed. You could probably also have them bend some channel for the outriggers. If they have a metal cutting band saw it would be nice to have them cut the curved bottom edge too.

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Old 04-18-2008, 03:03 PM   #139
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If you want more ideas on ways to build you frame out of tubing you should check out the following thread. I know that unit there is shorter than yours but the principles would apply never the less.

http://www.airforums.com/forums/f191...pod-37710.html

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Old 04-18-2008, 03:57 PM   #140
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Quote:
Originally Posted by malconium
If you want more ideas on ways to build you frame out of tubing you should check out the following thread. I know that unit there is shorter than yours but the principles would apply never the less.

http://www.airforums.com/forums/f191...pod-37710.html

Malcolm
Great thread and it gives me lots of ideas. Muchas Gracias Senor!
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