Steel to Aluminum frame

[Andy Moreau]

Aside from the initial cost of building a new frame out of AL, what would be the negatives? Is structural integrity going to be a problem? Has anyone done this yet?

Thank you!
Andy

[55AS]

Will not be as stiff unless you upsize the members, which you could do given the weight savings.

[Silverflames]

They discussed this on the VAP a couple of weeks ago. Collin Hyde stated that when they do things like this in the car mod world, they increase the thickness of the metal by 50% for added strength. It think it's a great idea overall.


I saw a post here on the forums where some one made a frame out of SS. Talk about a frame that will out live you!

http://www.airforums.com/forums/showpost.php?p=322122

[sgschwend]

I do like the idea of the frame never touching the wood floor, since you asked for issue here are the ones I know.

Aluminum has the same issues with water as steel does. It is also more sacrificial next to zinc on the galvanic scale. There are stories of construction wire being left inside of aluminum boats, those boats develop leaks.

For strength aluminum needs to be thicker which tends to eliminate the weight savings.

From what I can see, AS construction issues are based on fresh water intrusion control (from all sides).

[kdickinson]

What about carbon fiber? Will that bond or attach properly - could get strength and weight benefit

[biyak269]

The reasons for increased thickness of aluminum structures compared to steel are basically twofold: strength and stiffness. The yield strength of 6061-T6 aluminum (your most logical choice) is only slightly lower than the steel of the trailer, which I assume to be low carbon steel. However, aluminum is about 3x as "springy" as steel of the same thickness. Bottom line is that your trailer's body and other parts might bend excessively on an aluminum frame the same thickness of your steel one due to increased operational deflections. Likewise, your interior walls, floor, and other parts could also suffer from the increased movement. Therefore, you would likely increase aluminum frame thickness by a factor of 1.5-2, resulting in a potential weight saving of around 20-25% for the frame. I have to raise a question: why in the world would you want an aluminum frame?

[55AS]

Originally Posted by biyak269

The reasons for increased thickness of aluminum structures compared to steel are basically twofold: strength and stiffness. The yield strength of 6061-T6 aluminum (your most logical choice) is only slightly lower than the steel of the trailer, which I assume to be low carbon steel. However, aluminum is about 3x as "springy" as steel of the same thickness. Bottom line is that your trailer's body and other parts might bend excessively on an aluminum frame the same thickness of your steel one due to increased operational deflections. Likewise, your interior walls, floor, and other parts could also suffer from the increased movement. Therefore, you would likely increase aluminum frame thickness by a factor of 1.5-2, resulting in a potential weight saving of around 20-25% for the frame. I have to raise a question: why in the world would you want an aluminum frame?

Stiffness, not strength, is the issue when replacing steel structures with aluminum. Steel modulus is 29E6 compared to 10E6 for aluminum.

[Silverflames]

I always thought the reason for an aluminum frame was avoiding rusting. I have assumed that aluminum corrodes at a much slower rate than steel rusts. Is this correct?

[J. Morgan]

That is true, but if steel lasts thirty years in the worst of cases....


Brevi tempore!

[Ganaraska]

They make transport truck frames of aluminum so it is possible. Reason not to do it, mostly cost.

There is a trailer manufacturer near here that sends out all their chassis to be galvanized. You see galvanized trailers all over the place now, Home Depot sells them. You could probably get a new heavy duty chassis made by a trailer manufacturer and galvanized, it would last indefinitely.

[Andy Moreau]

Thanks everyone. I am doing a frame off resto. It was just a thought about the AL frame. I have a buddy who owns an AL fabricating shop. That's why I asked. I spoke with him the other day and he said he just opened a steel shop also and moved to a bigger location for full fabrication/restorations. I am currently gutting the AS and pulling all the belly pans off. I work 10 hour days minimum so not much time in the evenings for more work. I'm trying to do the easy stuff and then when it comes to the shell, I'll leave it to him and his team. seeing as he will be making my new frame.

Thanks again for the info guys.
Andy Moreau

[Ganaraska]

Ist question - How long did the original frame last? How long do you want the new one to last?

A stock type steel frame, protected with the best rust proof paint, or the type of paint used on seagoing ships, will last twice as long as a stock one.

Have it galvanized and the life will be indefinite. Possibly 50 - 100 years.

[Andy Moreau]

I will bring this to my welders attention when he arrives. May as well do it right the first time!

[Silverflames]

Build it out of steel, once it is done and one Soild piece have the whole frame hot dipped galvanized. After that, acid wash it, and paint it with poor 15. That should last a little while!

[Andy Moreau]

Hmm that sounds expensive.... I mean, there is a point of me rerun as far as money goes.

[Andy Moreau]

I don't want to spend as much as a coach or even a new airstream would cost. I don't mind walking from this with 16-20k into it total, because I believe I can get that out of it so long as I do the major things right and take care of it for the time that I have it. Would you all agree?

[Silverflames]

It's all up to you! I still like the idea of an aluminum frame. I would expect it to last much longer. Have your friend run a cost comparison steel VS aluminum.

[Bob662]

Originally Posted by Andy Moreau

I will bring this to my welders attention when he arrives. May as well do it right the first time!

Andy, often rust starts at the weld site. Have your welder spray all weldments, while they are still hot, with a good primer paint. This will help prevent the weld from pulling in moist air as it cools.

[J. Morgan]

It will also cause a small flash fire.....

If I were making a new frame I would use 2" X 5" rectangular tube for the rails and for some of the cross members, the balance in 2" X 4" channel.

It would be steel, and barring a bad accident it would last many decades.


Brevi tempore!