Is an aluminium chassis a smart choice?

[iconicflux]

I think aluminum is not as light as some people think. Once you account for the larger tubing needed for the same strength its maybe 30% lighter so maybe 150 lbs on some large frames. Couple that with it being harder to find a welder for aluminum and i just dont think it makes much sense but thats just my opinion.

Hi Everyone,

Long time lurker and first time poster! I am in the process of designing and building my first teardrop trailer and I am pretty torn on going with aluminium or steel for the chassis. A lot of weight savings comes with the aluminium, but I am a little concerned with stress fractures originating at the welds over time. Having a bunch of stuff bolted together just seems like to many points of failure for me. I don't think flexion in the frame will be a problem as the cabin bolted to the frame provides a lot of resistance to bending.

I do have access to skilled welders who would build the aluminium or steel chassis for me, but they are not designers and do not have experience with lower weight vehicles. Anyone with an aluminium trailer chassis care to comment on how it has performed? and more interestingly, how it is built? My trailer design sits 146" tongue to tail. The camper itself is 107" long and 62.5" wide.

The other big perk of going with aluminium is not having to do any surface finishing of the frame. With mild steel I would need to get it powder coated. For this reason to me there both come in at roughly the same cost.

Any documents that I could reference would be greatly appreciated in designing this. I really seem to be stuck at this point as all resources I have found are for much heavier duty trailers.

Thanks!

[Happy Fun Ball]

I know I am a bit late to the thread, but only by about a year...

I work in aerospace with some very smart mechanical engineers, including one who grew up in the Colorado mountains with parents who had a rafting company and is an expert (NASA certified!) welder. He had built several trailers over the years that saw very hard usage and he was very adamant that aluminum should not be used for the trailer. He said it would not last and would fail catastrophically at some point. I said that I was very interested in the weight savings, and he said that didn't make much sense as I could use much thinner steel and would not save much weight with an aluminum frame.

I just joined and was planning on starting a build this year, so I have no personal experience but I must say may friend is an expert and was very convincing.

[Lile]

I'm agonizing about steel vs. aluminum for a trailer frame right now. Aluminum is tempting. Folks that state "Aluminum bicycles are the same weight as steel bicycles" haven't actually weighed one. They are most definitely lighter and I'll go out and weigh a frame for you if someone wants me to. However the previous post here about an actual aluminum trailer failing soon is the one that most has me worried.

Previously I've built teardroptrailers on a purchased commercial trailer. WAY heavier than it needed to be for what I'm putting on it.

On this build I'm aiming for building the lightest teardrop I can get away with, as I'm towing it with a little car. I have a torison axle coming on order pretty soon and the frame will be next.

I would be competent to weld a steel trailer frame myself, if I made an aluminum frame it would be done at a welding shop. This thread seems to be indicating that aluminum frames will eventually fail. Are there any counterexamples of success stories with aluminum trailers?

There are a number of older threads on this forum to calculators for things like tongue size or trailer balance, but so far all of the links I have tried are dead. Are there any fresh links to any of the design calculations for building a steel trailer that still work?

[John61CT]

1. Aluminum in itself is 100% better against corrosion long term,

so long as galvanic issues are prevented where there (inevitably) is steel present as well.

The specific alloy selected is key, especially if salts are involved.


2. To get the advantage of optimizing adequate strength for **that** load at minimum weight requires design work by a knowledgeable and experienced mechanical engineer

3. In order for welding to not be the "weak link" factor, it needs to be done by skilled expert with very specialized equipment, and likely re-tempering treatments performed afterwards.

Rather than welding, best to use "lock bolts" e.g. Huck bolts for the structural joins.


So yes it is "possible" to get a far superior result to steel

just as aircon "can" be powered from battery stored energy.

But the expense involved compared to alternatives makes it difficult to justify as a practical project for a lay person DIYer.


However, if you think this

https://www.clcboats.com/shop/products/ ... 0-clc.html

would meet your needs, then it's just a matter of being willing to pay the price.

[western traveler]

I think Tony’s plans are nice. I am incorporating them in my build. Just picked it up from a ranchers shop two days ago. The welder had nearly zero questions.
I would call this more Ranch Tough than light though.

[friz]

I know I am a bit late to the thread, but only by about a year...

I work in aerospace with some very smart mechanical engineers, including one who grew up in the Colorado mountains with parents who had a rafting company and is an expert (NASA certified!) welder. He had built several trailers over the years that saw very hard usage and he was very adamant that aluminum should not be used for the trailer. He said it would not last and would fail catastrophically at some point. I said that I was very interested in the weight savings, and he said that didn't make much sense as I could use much thinner steel and would not save much weight with an aluminum frame.

I just joined and was planning on starting a build this year, so I have no personal experience but I must say may friend is an expert and was very convincing.

Your engineering friend was referring to the fact that aluminum has a limited fatigue life. The closer that stress on an aluminum structure gets to "yield", the fewer the cycles the structure can endure before failure. So a very lightly loaded a structure can live though many cycles. Heavy loaded structures can handle far fewer cycles. This is not linear with aluminum. The fatigue life is reduced exponentially with increased load. Aircraft play this game because every ounce counts when making something fly and carry a pay load. Steel has an almost unlimited fatigue life. Think about your springs. Many cycles, never think about them breaking. I chose aluminum because I knew the weight of my camper was so far under the design weight of the trailer that fatigue life was a non issue.

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[KCStudly]

The fact that aluminum weighs about 1/3 of the equivalent volume of steel is offset by the fact that it is only about 1/3 the strength.

Another problem is that, say you use T3 temper for the added strength, when you weld on it you are annealing it back to zero in the heat affected zone, losing even more strength.

[friz]

The fact that aluminum weighs about 1/3 of the equivalent volume of steel is offset by the fact that it is only about 1/3 the strength.

Another problem is that, say you use T3 temper for the added strength, when you weld on it you are annealing it back to zero in the heat affected zone, losing even more strength.

A good point about loosing heat treat in the welds. I have been involved in some bicycle manufacturing. We used 7005 (pretty sure, been a while) tubing in a "soft" state, welded the frames, then "aged" the frames in an oven to make them "hard". At the time, this was the common method. Thing evolve rapidly with bicycle construction, so it may be different now.

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[Zedok]

Hi,
As a newby, I was really aiming towards building an aluminium chassis. The replies to this post were the most useful read I have had in a long time. Aluminium is not on the agenda anymore. Cheers.

[Philip]

I would call this more Ranch Tough than light though.

Nice welding. But I would weld the front of any connections that face into the direction of travel. The Y that ties into the tonque. Where it meets the cabin frame needs welded to the Y. He did side weld's but that does not keep wheel thrown trash packing that unwelded connection full of debris and rusting the tubes out.

[John61CT]

rust?

[friz]

rust?

Iron oxide, no. Aluminum oxide, yes.

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[MickinOz]

To be Frank, although my real name is Michael, I was once quite interested, but after a bit of thinking and research I wouldn't touch a DIY aluminium chassis with a ten foot pole.
For all the reasons stated so far. Aluminium does have a higher strength to weight ratio than steel but, given the density difference, the members have to be a lot bigger.
As someone has stated here, by the time you match strength, the actual weight difference isn't as much as you might think.
Welds at home can be a problem. Need to get everything spot on if you don't want cracks down the road.
I checked out a commercial aluminium boat trailer the other day. All connections were made with galvanised steel brackets and stainless steel (I think) bolts.
That's how Quintrex, one of the country's biggest aluminium boat builders makes its factory trailers.
To do that at home requires real engineering, not "if it looks right, it probably is right".

Nice welding. But I would weld the front of any connections that face into the direction of travel. The Y that ties into the tonque. Where it meets the cabin frame needs welded to the Y. He did side weld's but that does not keep wheel thrown trash packing that unwelded connection full of debris and rusting the tubes out.

Welding across the drawbar tubing runs the risk of warping the tubing. Better to run some seam sealer in there before painting.

[MickinOz]

Hi,
As a newby, I was really aiming towards building an aluminium chassis. The replies to this post were the most useful read I have had in a long time. Aluminium is not on the agenda anymore. Cheers.

Good decision.

Its not absolutely a no-no, of course.
If you look at Friz' CLC, he's got a commercial chassis supporting a cabin that started out weighing 250 lbs. He's never going to have a problem. The chassis is very lightly loaded and will probably outlast him.
But for people building more traditionally, more thought is required.

There is another thing about steel, especially if you live where I do.
Most people who read this will probably laugh, and say I'm making it up.
BUT, years ago there was a TV show here called Bush Mechanics. It was about Aboriginals living in truly remote areas and their ingenious tricks for keeping cars running.
That was where I saw a bloke put two car batteries in series and weld an exhaust pipe back together with fencing wire.
I doubt that sort of running repair would work on aluminium.

[Mbettman]

I've built two trailers on Northern tool 5X8 frames. The first one was with the steel frame (Ironton), the second was with an aluminum frame (Ultra Tow). Both have served adequately, although the steel frame is starting to show corrosion. I've build both primarily for on-road use, but they have seen their fair amount of logging roads, washboard roads, bumps, dips, potholes etc, etc. I will always use the aluminum trailer frame if available - In fact if I were to do this professionally, I would consider a bolted together aluminum frame over a welded one (accounting for galvanic corrosion from the fasteners). I've done quite a bit of searching and have yet to find any information about a teardrop frame that has broken due to fatigue (though there are plenty of examples of badly corroded frames on vintage teardrops). For reference the NT steel frame weighs in at 274 lbs and the aluminum frame weighs in at 186 lbs - a 40%ish difference. Both support the same payload (1715lbs) when used as a flat bed - This is with a variable weight distribution and no additional support. For a teardrop, especially one that is built well, the box construction serves as a stiffening member. Additionally the overall weight can be controlled as well as the distribution of said weight. So I see a lot of advantages in going with aluminum, but like others I can't get over the uncertainty of the welds. Even if they look good on the outside, they might be problematic internally. Even if the welds are perfect the aforementioned fatigue problem persists, especially if you use a lighter gauge to take advantage of the weight savings. So why not bolt it together like the NT frame? All the advantages of aluminum with none of the drawbacks of the welds. You can crawl under there once a year to tighten things up and squirt some waterproofing over the bolts to prevent galvanic corrosion. Field repairs can be handled with a wrench and a drill. One of the primary advantages of a teardrop is that it's much much lighter than larger RV's - and therefore requires a lot less structure.