Is an aluminium chassis a smart choice?

[Adam-is-Teardropping]

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!

 

[John61CT-TNT]

I've only got close to the boat trailer designs, and the huge advantage, there besides the ratio of trailer weight to load carried

is the lack of corrosion.

Decades later the steel ones are dead, unless basically restored & repainted / re-galved

while the aluminum is whole without needing that maintenance.

The connection points with steel need care, high tech sealants like Tefgel, plastic washers and sheet barriers, or galvanic corrosion emerges quickly in the wet.

But these are big expensive jobs produced well by only a few places at ten grand and up, custom would be more.

Little units like under 5000lb capacity people don't seem as willing to spend so shorter lived galv steel dominates there.

US engineers would be liability shy of a non-commercial project, maybe a Chinese / Indian shop could be found online. . .

 

[TimC-TNT]

---

 

[Socal Tom]

Aluminum still corrodes, and anywhere that vibrates will eventually work harden which makes it brittle. Unless the frame and trailer are well designed and tested the risk of failure is higher. If you were buying something mass produced and the design had been on the market for years, I'd say go for it, but for a home built, I'd be concerned.
Tom

 

[Tony Latham]

I think any (proffesional) fabricator can create a fine steel trailer that will last longer than any of us. But I can't say that about designing and crafting one out of aluminum. Someone would have to have his ducks in a straight line. Unless you can find a craftsman that has specialized in fabricating aluminum trailers, stay away.

That's my two-bits.

Tony

 

[PhilipE-SKO]

I used to work in a Fab/welding shop. The rule with alumin. Its not if its going to crack. Its when is it going to. Light alumin and road vibrations. Its going to crack sooner or later. When it happens it will take a very good welder to repair it. With many miles of road debris hitting it. It will be thinner from age and all the debris blasting it sees. There is no such thing as a one pass weld on it. Its almost impossible to get it clean enough to weld. You have to make a pass to burn the debris out of the crack. Then if your lucky the second pass takes.

I would recommend a steel frame. Remember in your travels with the trailer. You can find many people that can glue a steel frame back together. You might not find a local that can repair a alumin frame.

 

[gudmund-TNT]

I 'second' what was just said...... Note, aluminum, 'pound for pound' is more rigid than steel which would make for a stiffer frame = but very little is saved in weight (example = aluminum vehicle wheels, very stiff and yes they help in handling being they flex less - but are they that much lighter in weight?? = NO.) Also, it would take more mass of aluminum in the producing of frame material so as not to end up with as much cracking but, cracks will still happen in due time. Case in point = bicycle frames made of aluminum have mass/thickness used in their tube material and end up weighing as much as a steel frame, so what is the gain in using it over steel? = stiffness less flex .. along with the "wise" suggestion of keeping a close watch for cracking over time..... Aircraft, yes aluminum is very common in it's build-up, but the welding of it?? = just about never!! rivets/riveting are used always (and now with the advent of carbon fiber = it's the cooking, gluing and screwing them all together - Boeing 787 - and bicycles frames) .............

 

[friz-TNT]

Steel has an almost unlimited fatigue life. Aluminum has a short fatigue life. Aluminum has to be engineered or over built to avoid stress risers and reduce fatigue.

Sent from my SM-G965U using Tapatalk

 

[kfh227]

Funny fact. Rust on steel is just oxidization. Aluminum oxidizes too.

The difference? When steel oxidizes it's size changes. That's why it flakes off into nothing. When aluminum oxidizes it doesn't change size so it never flakes apart.

Hope I got this right. I went to an engineering school a long time ago and a mechanical engineer told me.

 

[Ed Harris]

There are also Aluminum trailers sitting there waiting for you to build on.

Just a quick search should find used well made trailers ripe for the picking for reasonable cost have you looked at all for these?


Sent from my iPhone using Tapatalk

 

[MickinOz]

Hope I got this right. I went to an engineering school a long time ago and a mechanical engineer told me.

Close enough to correct for me.
The difference is rust is hydrated iron oxide. The approximate formula is Fe2O3.32H2O, the number of oxygen molecules being some what variable.
Anyway, the result is a huge increase in mass and volume from all those extra atoms attaching to the iron.
So it flakes, and the surface of the iron remains vulnerable to further attack from water and oxygen.
Aluminium on the other hand, unless exposed to lots of water, oxidises to Al2O3 almost immediately it when exposed to the air.
That oxide layer stays put, passivating the metal. It will only continue to oxidise to any significant degree is something damages/removes the layer.

 

[Shadow Catcher]

Compass Rose is now 12 years old, the frame is all aluminum, unfortunately they did not use heavy enough aluminum for the tongue. The first one they built (and we owned) failed at the point where it goes under the body fortunately the second owner was going slowly and had it repaired. I had ours reinforced but was still concerned with too much flexing. During rebuild we moved the axel forward and again reinforced the tongue and no more flex.

 

[John61CT-TNT]

Wow.

Those A-frame legs must be undisturbed continuous right back through to the point where they join the main outer rails.

Just tacked onto the leading edge like that, is I'm sorry just pitiful engineering design.

 

[Shadow Catcher]

As I said it was reinforced. The original welds were rather poor MIG, my working career involved a lot of weld inspection, and I had them TIG welded. The gauge of the tongue aluminum is too lite but the rest has not had a problem.

 

[John61CT-TNT]

Not talking about the poor quality welding, nor the strength of the materials

but the actual design, intention on paper or screen before anything physical.

Fatally flawed design can (sometimes) be compensated for in the buildout

but FFR for others, saving a couple inches of vertical space that way is IMO not worth it.

Or, if that factor **is** considered critical, then as I said, keep the integrity of the A-frame all the way back to where it attaches to the main beams

and do the outer crossmembers forward of that point as smaller segments welded at their joining faces

since they do not have as heavy nor "as critical" load bearing roles.

But two separate "layers" is really the way to go for good strength at that transition point.

http://imgur.com/4WfVzyw

.

 

[iconicflux-TNT]

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-TNT]

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-TNT]

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.