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Old 10-08-2013, 11:33 AM   #1
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Aluminum frame?

Has anyone replaced a steel frame with an aluminum frame? Other than the obvious cost difference of aluminum over steel what cons would be encountered? I would think the dissimilar metals corrosion problems would "almost" be eliminated. A steel hitch and possibly axle connection plating would be needed.
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Old 10-09-2013, 12:24 AM   #2
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Using your best Google-FU (add site:airforums.com and include exact search terms in quotes) one can find there is more than a few write-ups on AL frames. Yes they've been done by folks who had cheap access to HD aluminum & technology to weld it up w/o reinventing the wheel.

Once you heavied up the box beams and cross pieces to eliminate chances of fatigue failures from flexing the weight savings would be minimal - and looking at the long term picture of forty years abuse damaging steel and iron there could be similar spot problems with aluminum.

Many older Airstreams are just fine, the ones that negligent owners let plumbing acids/salts loose beneath the floor and long term acid rain exposure eat the iron are just seen & heard about more often.

The 'deal' with using iron is proper preparation - our 70's trailers got a cheap tar-based undercoating on the frames that is difficult to remove completely to use a modern step-process that will effortlessly protect for 15-25 years.
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Old 10-09-2013, 07:45 AM   #3
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Aluminum has 1/3 the young's modulus of steel. Therefore, the height of the frame needs to be higher for equivalent stiffness. A structural or mechanical engineer could figure out what beam sized will be required. The fabrication techniques would need to be changed, if you intend to use high strength, heat treated, aluminum. Welding will ruin the heat treatment.
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Old 10-09-2013, 09:13 AM   #4
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Originally Posted by Ringoo7 View Post
Has anyone replaced a steel frame with an aluminum frame? Other than the obvious cost difference of aluminum over steel what cons would be encountered? I would think the dissimilar metals corrosion problems would "almost" be eliminated. A steel hitch and possibly axle connection plating would be needed.
An Airstream aluminum frame was tested in the mid 60's by Southwest Research in San Antonio.

It was an absolute failure.

Andy
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Old 10-10-2013, 09:25 PM   #5
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Thanks Andy. I can see your not an "outside the box" kind of guy.
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Old 10-13-2013, 12:40 AM   #6
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The first question that comes to my mind is Why?

Steel is good stuff, it is easier to work with and in this use, I think that in general steel would have a longer fatigue life.

Overall, compared to what I am used to, airstream trailers are relatively light even with a steel frame.

If electrolysis is a concern there are other things that could be done in the limited areas where steel ant aluminum come together like poly shims, etc.

Sometimes reinventing the wheel is good, sometimes not so good.

IMHO in replacing the frame with aluminum, a cost/benefit evaluation would render the reason for doing this to a curiosity.
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Old 10-15-2013, 10:40 PM   #7
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There are large semi truck trailers that have aluminum framed trailers. They work fine, but they are very expensive. As stated above, you have to allow for the strength difference. For the minimum weight savings it isn't worth it. Besides, Airstream could probably use a stronger frame, not a weaker one. You would still need steel axles and steel couplers so the hassle of making the transition is also an issue. Rectangular steel tubing or structural steel channel is hard to beat. Airstream uses "C" channel on most of the trailer frames that I have seen. I have seen Bambi trailers rated at 4,500# GVW with 3" structural channel for the frame.
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Old 10-15-2013, 11:28 PM   #8
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Aluminum is used for structural applications when weight is paramount, or corrosion resistance is critical.

If I were building a better frame for an older Airstream, I'd focus on adequate room for tanks & spare tire, a deeper, stiffer frame to reduce shell flex, and the use of air suspension (for a better ride, fore-aft equalization, adjustable ground clearance & easier leveling on-site) and ABS disc brakes... oh yes, and raceways for wiring, better step supports, a perimeter steel member to support C channel, epoxy coatings to prevent rust, etc.

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Old 10-16-2013, 05:06 AM   #9
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... The fabrication techniques would need to be changed, if you intend to use high strength, heat treated, aluminum. Welding will ruin the heat treatment.
You're absolutely right. We worked with large scale 6061 T-6 molds and it took a lot of time and money to get the fabrication process right.

I can see how a frame could fail miserably if not properly post-weld heat treated. You'd have stiff frame members with really soft metal around the welds. Bouncing down the road would tear it apart.

This link gives a good pictorial overview of the process involved. Doing this on a large scale with multiple sizes of frames would be VERY expensive, especially with all the waste involved in learning how to manufacture them without warpage.
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Old 10-16-2013, 07:57 AM   #10
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Thanks for the responses. Like I originally posted. I know the cost difference would be the major factor in an AL frame construction. The semi trailers and AL car haulers are what inspired my thought process.
I've started my frame rebuild with steel because of the cost factors of AL. Stiffness, ride height, and tank space are the main factors I'm incorporating in the design. Luckily, I'm near large scale trailer manufactures and one has agreed to power coat the frame once I build it.
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Old 11-03-2013, 09:07 PM   #11
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Thanks for the responses. Like I originally posted. I know the cost difference would be the major factor in an AL frame construction. The semi trailers and AL car haulers are what inspired my thought process.
I've started my frame rebuild with steel because of the cost factors of AL. Stiffness, ride height, and tank space are the main factors I'm incorporating in the design. Luckily, I'm near large scale trailer manufactures and one has agreed to power coat the frame once I build it.
Be careful with Powder Coating a frame with rubber torsion axles. Powder Coating requires heat, and the rubber in the torsion axles don't like heat.
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Old 11-04-2013, 09:08 AM   #12
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Be careful with Powder Coating a frame with rubber torsion axles. Powder Coating requires heat, and the rubber in the torsion axles don't like heat.
I would think that powder coating the frame itself would be the process BEFORE installing the torsion axles. One of my hot rods has the entire frame, running gear and suspension components powder coated and it still looks like new 16 years later. I recently bought an aluminum 20' tilt bed car trailer and even with the additional weight of the hydraulic system, I've gained about 500 - 600 pounds in payload over the old steel trailer with ramps.

BTW, that's the 2013 Grand Cherokee I use to tow my 25' AS.
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Old 11-06-2013, 06:53 AM   #13
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Check out this link - Aero Flite did an aluminum frame back in the 40's. Very cool restoration has been done on the trailer.

http://www.aeroflitetrailers.com/construction.html


But....for a little more current info, check out Vinstream.com - Todd is building an AS-inspired trailer and it has an aluminum chassis. His website is really cool - click on the "Aluminum Chassis" tab for lots of pictures of his process.

Also - Featherlite and Exiss trailers both have aluminum and aluminum/steel chassis combinations - they make horse/stock trailers, toy-haulers, etc...

Kathy
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Old 11-09-2013, 09:18 AM   #14
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I knew I wasn't the only person with what some people think are crazy ideas. Everywhere you look there are semi trailers, car haulers, and boat trailers are utilizing AL. I believe innovation takes a back seat to the "that's the way it's always been done" mentality. As stated before, cost and lack of redily available material has forced me to rebuild my frame in steel. I really was surprised by the multitude of failures in the original frame, buckled axle plate, cracked main rail, twisted cross braces. I can promise these wont be problems I'll have to worry about with the new frame.
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