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Old 10-11-2010, 11:16 AM   #43
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On the topic of Aluminum frames. I work and weld aluminum every day ( i own a fabrication business in Canada) and an aluminum frame is absolutely doable. Unfortunately by the time your done it would probably weigh more than a steel frame and would cost 5 times the price due to the time it takes to properly TIG weld the frame. Aluminum is great to work with and has a coolness factor but as a trailer frame i would walk away.
And these words of "experience" comes from a well qualified person, who has nothing to gain or lose. Just trying to be helpful.

Thanks for the info.

Andy
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Old 10-11-2010, 12:53 PM   #44
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On the topic of Aluminum frames... cost 5 times the price ... and has a coolness factor
Sounds just like an Airstream product to me.

BTW, doesn't Wally's Bubble have a Magnesium frame?
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Old 10-11-2010, 02:45 PM   #45
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If i were to build a frame it would be mild steel as the original but would get it zinc coated then powdercoated. It would last longer than your will to continue owning the trailer.
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Old 10-11-2010, 05:28 PM   #46
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There is a utility trailer manufacturer near Colborne Ontario, about 20 miles from me. All their trailers seem to be galvanized. Sometimes when I go by I see several bare steel frames on a trailer, going to be galvanized.

So, if you want a galvanized trailer frame they should be able to build it for you.
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Old 11-28-2010, 08:52 AM   #47
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I would never consider an aluminum frame for the following reasons:

The fatigue characteristics of aluminum versus steel (steel is much better)

The connections required of aluminum frames versus steel.
Steel can be welded quite well, aluminum looses considerable strength when welded, bolted connection are therefore better but bring up a number of other issues I won’t go into. Yes, a aluminum channel can have the same strength as a steel channel, but the connection details: its always the details!!!

Cost of materials, big difference.

The weight saving are not that big an issue. What are we talking about 500 lbs? Traveling with empty water tanks will more then equal that.

Finally steel can be protected with a number of very good coating that will prolong the live frame many years, no not forever, but long enough so your grandkids won’t to have to worry about it when they are taking their first cross country trip : ).

What is the goal here to go camping or get into and adhoc study of: strength of materials, dynamic loading, connection detailing, fatigue engineering. Either one is a noble goal just as long as you are clear as to what you want.
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Old 11-28-2010, 08:41 PM   #48
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OK, my inner dweeb is showing through here, but this has been bugging me, so I ran some numbers. Here we go.

Dwight is 100% correct on the issue of having to pump up the moment of inertia to balance out the lower elastic modulus. It is indeed a direct relationship. While not necessary to match for strength, it's necessary to match for deflections. I'm not sure how much the shell can deflect, but let's assume that we're going for about the same as factory.

E = Elastic Modulus (=29E6 for steel, = 10E6 for aluminum)
I = Moment of Inertia (=5.3in^4 for a 4" by 2" by .25" wall square tube)

I assumed a load of 400lbs at 10 feet out from the back axles. This is a simplification for mathematical purposes, but probably isn't too far off. This gives us a moment of 4000 ft-lbs.

OK, so we do the deflection equation:

Y=-PL^3/3EI

The term EI is the elastic modulus times the moment of inertia, and its commonly referred to as "flexural stiffness". It's not directly related to overal strength, but how much the beam will spring back and forth under load.

OK, so we do the math and we find that the "stock" frame I've listed above will deflect 1.50" under the imposed load (actually 1.499 but we'll round it.)

OK, let's look at the 6" channel I recommended. Do the math and get I=14.18 in^4. Not quite triple the box beam, but close to it. Do the deflection calc and for the same load, we get a deflection of 1.61". So we've deflected the frame about 1/8" more with this frame. I think that should be fine.

How about strength? Stress = M*Y/I = 4000(12)*2/5.3 = 18,113psi for steel, = 10,155psi for the aluminum frame. So the aluminum frame, if made of a comparable stress grade (about 36ksi) to the steel, is actually stronger. It will just deflect a hair more because aluminum is more springy.

How about the weight? Stocker weighs about 560lbs for 60' of it, new one weighs about 221lbs for the same length. Weight savings = 339lbs, or about 60%, for roughly equal stiffness.

You could go to a 7" deep section and be both stiffer and way stronger, as well as probably 50% lighter.

Anyway, sorry to bore. I'm obsessive/compulsive like that

And that, ladies and gents, concludes tonight's show.
Not that I even came close to catching all of what you so eloquently expressed but I will give you a AAA for knowing all of that information. I'm impressed!!
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Old 02-26-2011, 08:23 PM   #49
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Not to keep digging into this thread, but I keep thinking about the frames. I have to rebuild my frame on my Overlander. I think it would be cool to use another material if it made sense. I could stretch my wallet a bit and invest in something else if it seemed like a good idea. I have a bunch of airplane guys around me who are very interested in the Airstream. So we get to talking about things and I'm excited about possibilities. I also work in the marine trade, rebuilding classic boats. One customer recently ordered this amazing aluminum frame for a hardtop for his boat. I have not seen such work before- quite beautiful, but it's all round stock and it is welded- I think it's TIG welded- the joints have little disk-like rings that are neatly folded on top of each other around the joint. I'm impressed. BUT- there again, it isn't going to be under quite the same type of stresses as it will be even on rough jarring seas. A friend also just had a custom made bolted aluminum frame for his 8000 pound boat. Quite beautiful with 8" -I beams. Galvanized is interesting. Stainless might be the most expensive, and lately I have been witnessing a lot of rusting stainless. Anyway, the thoughts haven't stopped. I keep mulling this over. Maybe I'll ask around for some quotes for fun and see if that immediately turns me belly-up.
Rae
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Old 02-26-2011, 10:03 PM   #50
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AL Frames ...

I see them every time I go to the lake and every time I go to the boat dealer. So perhaps many things (other than the physical properties of the material !) have changed.
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Old 02-27-2011, 12:38 PM   #51
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it would be cool to use another material if it made sense... I have a bunch of airplane guys around me who are very interested in the Airstream.

You could always build a Bowlus style frame... these were the predecessors to Airstream trailers.

Very light

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Old 02-27-2011, 02:50 PM   #52
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You could always build a Bowlus style frame... these were the predecessors to Airstream trailers.

Very light
Wow, is that ultra cool! I think if it was a smaller trailer that would work great!
Was having a discussion with my hubby this morning and he seems to like the galvanized idea at the moment...
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Old 02-27-2011, 09:11 PM   #53
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The only drawback will be the cost.

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Old 02-27-2011, 10:07 PM   #54
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I'm willing to invest a little to get something more trustworthy. The frame I have now is in pretty tough shape. Granted it's been around for a while, but I could also be around for a while myself (I hope) and would like my airstream to live a nice 2nd life with me. If I can make a good decision now that might save me in the long run, then it's okay by me.
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