6.5X12 aluminum trailer; HELP!!!

[jonnyo]

So, i m at the frame design phase. sorry, no fancy sketchup but on paper instead!

I want it light!
6.5X12 trailer frame
height inside will be around 58 inches
no water, electricity, heater....
all aluminum wall and roof structure of 1X1 X1/16
skin 0.40 aluminum
most likely 2200lbs dexter axel, i would like it low....not much above my Subaru forester roof line
shooting for 1000lbs total weight. Very basic kitchen at the back build light and simple. (wall .40alu, 1'' insulation'' 1/8 finish panel )

now, i m not sure what size aluminum tubes i should go with for the main frame (chassis)


option 1: box and first 2 cross member made of 6063 alu 4X2X 1/8 other cross members out of 2X3 X 1/8

tongue 2X3X 1/4 or 3/16

is this overbuild for a 1000lbs trailer?

option 2: box and all members made of 2x3 x 1/8
tongue 2X3 X 1/4 or 3/16

any comments? overbuild? underbuild? something wrong with the design? any comments are welcome. my only knowledge is from my actual tiny trailer that is a 5X8 all made of 2x3 x 1/8 with a single tongue of 3x3x 3/16. it s plenty stiff...nothing move in that trailer and rated for 2200lbs. never pass 750lbs in real life!

thank you
jonathan

[emiller]

Just remember alumiunm does not like to bend, it will crack. So for the tung and frame I would go heavy.

[jonnyo]

anyone?

[alaska teardrop]

Jonathan,

Pardon me if I repeat some things that you may already know. Anyway, when designing your tongue, the two points of concern are where the tongue rails meet the #1 front cross piece in your drawing. As you drive down the road the load at those points are constantly changing or "cycling". With steel we can design accurately using Andrew's tongue strength formula because steel has a given yield stress value.

The yield stress value for the various aluminum alloys would all be different from each other & of lower value than steel. When considering "cycling", aluminum becomes difficult to define. As emiller points out, it means using larger and/or thicker extrusions & hope that you did it right. To a certain extent the same considerations apply to your axle mounting points.

Speaking of your axle. Is your trailer going to weigh 1000 pounds empty or with all your stuff aboard? And are you aware that you can choose the load rating of a Dexter torsion axle according to load of your trailer? i.e. you don't have to install a #9-2200# axle on a 1000# trailer. For instance, the same #9 axle de-rated to more closely match the load will ride smoother, handle safer & probably reduce stress on the tongue.

As they say, 2 cts. worth.

Fred

[Bogo]

Just remember alumiunm does not like to bend, it will crack. So for the tung and frame I would go heavy.

In light of that, it is usually figured that a large cross section is better to use than one would normally use for steel construction. Years ago an engineer basically told me to figure that an aluminum section doing the same job would need to be at least 1.5X to as much as 2X as deep as a steel one would if any flexing was expected. That is to make it stiffer so it can better resist the flexing in the first place. So for vertical loading, use a 4" high x 2" wide beam instead of a 2" high by 2" wide one. You see this larger cross section in use in the large tubed aluminum bicycles. Wall thickness depends on the load needed to be supported. Look at the tensile strength of the aluminum versus the the tensile strength of steel used in steel frames. Due to the poor fatigue cracking abilities of aluminum, engineers also usually say to go a bit stronger, but I don't know the ratio.

Another issue with aluminum is welds. All of the high strength aluminum alloys loose allot of strength when welded. At this point my preference is to glue plus bolt or rivet aluminum structures together. Yes, welded aluminum can be re-heat treated, but do you have a heat treatment oven large enough for a trailer frame? All the better large tubed aluminum bicycles are heat treated after welding.

At this point, I'm not sure it is worth doing a full perimeter style frame for a TD unless you are gluing SIP panels to it. Looking at what companies have done for RV trailers, I see allot of them are using two central frame rails with cross ribs only. No frame member along the side of the RV, or if there is one, it is very light. Some even use the floor as a structural member and don't even have the cross ribs. Elddis has done this with their Solid Construction method. Making a SIP floor is an issue in it's self, but not outside the abilities of a home builder. It's is just that no corner can be shaved during the gluing and vacuum bagging process. They must be done properly as they are critical to the strength. It is also possible to buy pre made SIP panels, but then you generally need a perimeter frame to glue them into because you can't build in the attachment points.

[jonnyo]

i m thinking around 1000lbs empty.....but we never put more than 100-150lbs of luggage max so i expect it to be in the low 1000s.

i think my best bet at this point is to go to the trailer dealership, and look under some of those Aluma, mission, cargo pro all aluminum utility trailer and see what size and tickness tubes and design they used. no point in reinventing the wheel....

.

[alaska teardrop]

i m thinking around 1000lbs empty.....but we never put more than 100-150lbs of luggage max so i expect it to be in the low 1000s. In that case, you would probably want a #9 rated at about 1500#s. But here is a suggestion. Build your trailer, weigh it (empty & loaded with gear) & then order your axle accordingly.
i think my best bet at this point is to go to the trailer dealership, and look under some of those Aluma, mission, cargo pro all aluminum utility trailer and see what size and tickness tubes and design they used. no point in reinventing the wheel.... Please become our resident expert on building a small camping trailer with an aluminum chassis. Like, while you're checking out those trailers, ask about & get details to share. Are the tongues designed to a standard engineered formula? Alloys? Extruded shapes & sizes relative to the anticipated load ect. ? Close up pictures of where the tongue rails meet the front floor/cabin? And of course the welds. Thanks, Fred
.

It would be cool to see a sketch of your cabin plans - profile/floor plan/galley ect.

[jonnyo]

i m thinking around 1000lbs empty.....but we never put more than 100-150lbs of luggage max so i expect it to be in the low 1000s. In that case, you would probably want a #9 rated at about 1500#s. But here is a suggestion. Build your trailer, weigh it (empty & loaded with gear) & then order your axle accordingly.
i think my best bet at this point is to go to the trailer dealership, and look under some of those Aluma, mission, cargo pro all aluminum utility trailer and see what size and tickness tubes and design they used. no point in reinventing the wheel.... Please become our resident expert on building a small camping trailer with an aluminum chassis. Like, while you're checking out those trailers, ask about & get details to share. Are the tongues designed to a standard engineered formula? Alloys? Extruded shapes & sizes relative to the anticipated load ect. ? Close up pictures of where the tongue rails meet the front floor/cabin? And of course the welds. Thanks, Fred
.

It would be cool to see a sketch of your cabin plans - profile/floor plan/galley ect.

Well, the investigation as been a lot of fun so far. I come from the bicycle industrie and have work in the design of bicycle. We can make anything out of aluminum and Steel isnt competitive with well engineer aluminum design. it s not even a close match. So, it s interesting to see the way the company make those aluminum trailer.

my big realization. if it s a enclose trailer...they use much smaller tube for the chassis compare to the same weight/dimension rated utility/open deck trailer. For exemple, cargo pro all alumium enclosed trailer 6X12 beleive they can get away with light 2X3X1/8 chassis and 1X2X1/16 wall and roof.... but for the same exact model in utility trailer with no wall or roof, they have to go with a 4X2X1/8 and reinforcement. Aluma make huge double single tongue... there is a bit of everything! lots of very clever design......

i pass a good 20minutes under those trailer looking at all the details....the dealer though i was funny. That said, the dealer had very little good info to give on design...they dont know there product. that well. i might not have had the best sell person...

That said, i have found amazing knowledge in Bill at http://www.expresstrailer.com/ he is ''local'' to me, and he loves custom work. he was very generous of his time and sharing idea and recommendation on what to do and not do. I m considering having him build the main frame so i have peace of mind and can build the walls structure, roof etc but at least...main frame, tongue, axle done professionally.

they make amazing work and he is excited about any custom project.

For me, he recommend 2 option:

6.5X12 all aluminum lightweight axle, chassis similar to a utility trailer... (6.5 because you can put the adult bed sideway...) he said anything longer than 12 on a single axle make for a complex engineering problem with aluminum.....reliability become a issue.

or

a lightweight...but dual axle 6X14 with light rated axles(think a mini tandem)...and he said that would make it very easy to build with no flex of the aluminum and very good weight distribution...making aluminum design easier with 2 axle. this as advantage of not been as wide...hide better behind the car, very easy to tow etc. (anyone on here ever done a tandem teardrop??? good? bad? i m open minded so dont reject any ideas..)

i will draw the interior and exterior shape....and share. but really, there is no limits.....well, budget is 4-5k !

[alaska teardrop]

Well, the investigation as been a lot of fun so far. I come from the bicycle industrie and have work in the design of bicycle. We can make anything out of aluminum and Steel isnt competitive with well engineer aluminum design. it s not even a close match. So, it s interesting to see the way the company make those aluminum trailer.

my big realization. if it s a enclose trailer...they use much smaller tube for the chassis compare to the same weight/dimension rated utility/open deck trailer. For exemple, cargo pro all alumium enclosed trailer 6X12 beleive they can get away with light 2X3X1/8 chassis and 1X2X1/16 wall and roof.... but for the same exact model in utility trailer with no wall or roof, they have to go with a 4X2X1/8 and reinforcement. Aluma make huge double single tongue... there is a bit of everything! lots of very clever design...... I imagine the difference is that they are depending on the walls of the enclosed trailer to help support the outer chassis framing. They are still designing the floor for heavy & possibly uneven loads. A small camping trailer doesn't need that consideration. By designing with your aluminum sheet walls securely fastened to the thin wall tubing you're accomplishing the same strength without the added weight of all the heavy perimeter rails & cross members.
i pass a good 20minutes under those trailer looking at all the details....the dealer though i was funny. That said, the dealer had very little good info to give on design...they dont know there product. that well. i might not have had the best sell person...

That said, i have found amazing knowledge in Bill at http://www.expresstrailer.com/ he is ''local'' to me, and he loves custom work. he was very generous of his time and sharing idea and recommendation on what to do and not do. I m considering having him build the main frame so i have peace of mind and can build the walls structure, roof etc but at least...main frame, tongue, axle done professionally.

they make amazing work and he is excited about any custom project. Sounds like a good guy to know. Building a 1000# trailer of the size that you are planning will be a challenge! For me, he recommend 2 option:

6.5X12 all aluminum lightweight axle, chassis similar to a utility trailer... (6.5 because you can put the adult bed sideway...) he said anything longer than 12 on a single axle make for a complex engineering problem with aluminum.....reliability become a issue. See above.

or

a lightweight...but dual axle 6X14 with light rated axles(think a mini tandem)...and he said that would make it very easy to build with no flex of the aluminum and very good weight distribution...making aluminum design easier with 2 axle. this as advantage of not been as wide...hide better behind the car, very easy to tow etc. (anyone on here ever done a tandem teardrop??? good? bad? i m open minded so dont reject any ideas..) IMO a second axle is totally unnecessary for a lightweight trailer as long as you design so that the backend doesn't drag on inclines. It would also take up 80-100# of your total. I will draw the interior and exterior shape....and share. but really, there is no limits.....well, budget is 4-5k ! Well?

Fred

[angib]

Copying an existing aluminium trailer is a great idea, since then you get a tested design - the only problem is that you won't know which aluminium was used, which is a pretty important piece of information.

The great difficulty with aluminium is deciding what strength to use in the design process - it's tempting to use something like the 0.1% proof stress, but then that's often not quoted. And even then you are left with the question what are you going to do about the fatigue strength.

If you assume any aluminium is a third the strength of steel, you will be safe - but it won't save any weight over a steel structure.

Incidentally, the tongue members take the biggest load and (except in flatbed/utility trailers) it is unlikely that failure will occur anywhere else, so I see no need to make the main frame any deeper or thicker than the A-frame members. 2x3x1/8 for everything except the tongue sounds OK to me. For the tongue I would use my tongue strength spreadsheet but with one third the stress of steel - there's no harm in over-building just those two members.

Bicycle experience is likely to lead you astray - something where you make thousands of examples and get to extensively test prototypes isn't quite the same as building and using a one-off with no prototype.

[jonnyo]

after looking at so many All alumium trailer on the market...utility and enclosed, i decided that i m jumping in! i m follow the general way company like snopro and Aluma build there trailer. I m just making it a little lighter as it will never exceed 1500lbs...i hope...

13 feet long plus 1 feet overhanging at the front, and 77inch wide. At the front, a queen bed, the on the side, bunk bed for kids and kitchen Galley at the back and it s gonna be a almost standy at around 65 inches of inside height. It will be low to the ground and on a small double axle.....

Purchased a welder...and today was day one....





going with 2X3 1/8 for most of the frame....and everything will be reinforce as i will build the front bench/bed and bunk bed directly welder on the side members and cross members.... so there is gonna be a lot of support and link between all the members....


PS: one cross member missing...and the 2 diagonal members of the tongue

After talking with so many fabricatior in my area, i have seen that most of them all have big restrain in building aluminum trailers. Most done like this material for this kind of application. But i also think many builder lost track of what a teardrop/tiny travel trailer is compare to a utility trailer that see lots of abuse. time will tell if i m making the right choice or not.....