insights on frame

[swessling]

Hello Everyone and thank you for sharing your insights and knowledge. My wife and I are currently looking for an Airstream to purchase and rebuild. I have seen a lot of concerns with frame sag and understand the issue with carbon steel touching aluminum and causing corrosion. I have not seen anyone who has just replaced the steel frame with an aluminum frame and i am wondering if i am missing something. I have heard rumors that if the frame is replaced it could cause issues with the title. Does anyone know if this is true? If not, why don't people just replace the frame with an aluminum frame and eliminate the issues of corrosion all together?

Thanks in advance,
Stephen

[TheGreatleys]

An aluminum frame is possible, but would be prohibitively expensive. Galvanic corrosion does occur, but isn't a big enough issue for most people to justify the expense. Steel is strong and cheap.

I don't see any reason you'd have title issues with a replaced frame. The VIN is affixed to the shell, not the frame.

[SpletKay06]

The frame would have to be reengineered to ensure its strong enough. It could be done but it would be cheaper and easier to powder coat a new steel frame.

[swessling]

Thank you for the feedback. I thought the corrosion was a bigger issue and something that would be inevitable in time. Hoped an aluminum frame system would be justified as a resale aspect

[Kemblkr]

Originally Posted by TheGreatleys

An aluminum frame is possible, but would be prohibitively expensive. Galvanic corrosion does occur, but isn't a big enough issue for most people to justify the expense. Steel is strong and cheap.

I don't see any reason you'd have title issues with a replaced frame. The VIN is affixed to the shell, not the frame.

The VIN on my 03 is on the tongue. However, the vin could easily be
restamped onto the new frame. However, I agree an aluminum frame would be more trouble than it's worth

Aluminum doesn't have the raw strength of steel and it takes a master TiG welder to put something together like that. Could be done but guessing $20-30k for design and build.

Galvanic corrosive is more of an issue with raw metals and fasteners. Painted steel frames and aluminum are fine together. You can always zinc chromate aluminum as well. A properly protected steel frame will last 50 years.

Having been a pilot for 25 years corrosion in aluminum happens and fatigue is also an issue.


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[cwf]

Right.. Don't go aluminum.

Why?

Steel of same dimensions as aluminum can handle and the shocking of road use ... Otherwise OTR businesses would be driving fewer steel frame vehicles. Cost factor and efficiency are very important when building...

Using the proper alloys of aluminum (or al-u-min-e-um depending your dialect... We have great fun with our British Pastor over his attempts to correct our pronunciations of the "English" language... And offhand phrases... )

Ahem, pardon my diversion...
Using proper alloys of aluminum, proper design and welding can give you the result you are asking about. But, why nearly double or more the cost for the frame when the frame and shell will "fatigue" at different rates during use?

Steel can be made more resilient to corrosion... Sure... However, many of the "separation" events have other causes and contributing factors... Unaddressed leaks, stiff suspension due to bad axles, improperly balanced running gear, improper loading, rough roadways... All that hammers on your Airstream..

With that in mind, steel will weigh more for same size aluminum, giving the frame more mass to absorb roadway shocks. It is sorta cool that our Airstreams survive the punishment so well... Even if they had a lousy construction... But we know THAT never happens.

So, perhaps Airstream is right... Have you seen the comparison between steel and aluminum truck beds?? Your call.

[HiJoeSilver]

It would likely be cheaper to have a steel frame built and then hot dip galvanized than build aluminum, depending on if you lived near a galvanizing plant.

Engineers rule of thumb, Aluminum is 1/3 as strong as steel, therefore you'd need 3x as much to compensate for the same size frame. Aluminum weighs about 1/3 but again you'd need more. Kind of washes out. Aluminum is more expensive because it is very energy intensive to refine. Welding aluminum is very time intensive, therefore expensive.
It's possible to design a steel frame to have an infinite fatigue life. This is not possible with aluminum.
Most of the corrosion on AS's is not galvanic, but simply from steel components being wet for long periods due to unaddressed leaks. Especially hold down bolts where they pass through the wood floor.
Rear end separation/sag is caused by exactly that, AS notoriously leaking in the rear keeping the wood wet and rusting away the bolts between the frame and she'll in the rear. Then there is no solid connection between the shell and frame in the rear causing them to move independently vertically. This can be handled by fixing the leaks and using better bolts. Which AS still struggles with.

[dwightdi]

Young's modulus for Aluminum is 10 million. Steel is 30 million. That means that an aluminum part of the same size will deflect 3 times more that the equivalent steel part. Since most of the deflection in the trailer is flexual, that means the cross sectional moment of inertia of the aluminum part must be triple that of the steel part to yield the same stiffness (resistance to bending). This can be quite easily be done by increasing the height of the frame. As pointed out in previous postings, the cost of the material and fabrication of an aluminum frame will not be cost effective. The new aluminum skinned Ford pickups still use a steel frame. Newer airplanes use lots of aluminum, fancy metals, and plastics resulting in an increased cost of manufacture.

[RandyNH]

While there seem to be a lot of naysayers here who are quick to talk you out of anything different, think people who say "don't start that business, it'll never work", I have often wondered the same as you. Especially whereas my trailer has a completely aluminum frame and it performs perfectly.
To help you on your research here is a link to a company that is in my area, the only build custom trailers and sell direct (they are very reasonably priced), I would think that working with them on timeframe that are during their slow point they would be able to assemble you a complete frame based on your specs. It's worth looking into.

http://www.nhtrailers.com/whyproline.htm

Good luck, let us know.

[AtomicNo13]

Didnt someone on the forums fab a complete aluminum frame a few years ago?

[cwf]

We hope it woks out!!!

Originally Posted by RandyNH

While there seem to be a lot of naysayers here who are quick to talk you out of anything different, think people who say "don't start that business, it'll never work", I have often wondered the same as you. Especially whereas my trailer has a completely aluminum frame and it performs perfectly.
To help you on your research here is a link to a company that is in my area, the only build custom trailers and sell direct (they are very reasonably priced), I would think that working with them on timeframe that are during their slow point they would be able to assemble you a complete frame based on your specs. It's worth looking into.

http://www.nhtrailers.com/whyproline.htm

Good luck, let us know.

[SSquared]

There is a company called Vinstream in Golden, Co., that restores vintage trailers. One of their specialties is replacing damaged frames with custom aluminum frames.

Their ideas on aluminum frames are laid out at http://www.vinstream.com/ALUMINUM-CHASSIS.html.

[HiJoeSilver]

Originally Posted by AtomicNo13

Didnt someone on the forums fab a complete aluminum frame a few years ago?

Yes, there is even a company that makes them. Unfortunately I can't find their web site.
Found it,

http://www.vinstream.com/ALUMINUM-CHASSIS.html

If you have enough money anything is possible!

Increasing frame height is a good way to compensate for most of the difference in strength. Personally I think AS should add 2" to their frame height. Would significantly improve trailer strength. Plus allow bigger tanks. Not adding to much weight in the process.

Dwightdi I tried not getting to technical. I love moments, especially of inertia.