Aluminum tube skeleton?

[C3Cole]

Hello all:

I posted a "Hello" in the Intro forum with a question similar to this, but I have several questions regarding my plan and appreciate the vast knowledge available here. I have been lurking (occasionally) for several years. Thank you in advance.

I am slowly working towards building a teardrop styled as a plagiarized hybrid of the generic Benroy and a Grumman 2. I plan to build a 1" square 1/8 wall aluminum skeleton, cover with .040 aluminum, insulate with foam to 1.5" wall thickness, and cover the foam interior with (probably cloth), similar to the headliner in a car.

Here is a sketchup pic of the idea (special thanks to Danlott71 for his youtube sketchup guide).


The main side tubes of the frame (I already have a trailer to modify) are 2x4 by .125 (and they might actually be .187 thick). My shell/camper will not provide much if any stiffness to the system, so my frame will be heavier than most (and I already have it). I will weld the aluminum skeleton.

1 inch sq .125 wall aluminum tube skeleton covered by .040 aluminum be okay?

(I will ask some other frame and tongue and roof rack and.... questions later)

I hope everyone is having a great day,

Cole

[starleen2]

Hello all:
I am slowly working towards building a teardrop styled as a plagiarized hybrid of the generic Benroy and a Grumman 2. I plan to build a 1" square 1/8 wall aluminum skeleton, cover with .040 aluminum, insulate with foam to 1.5" wall thickness, and cover the foam interior with (probably cloth), similar to the headliner in a car.

Cole

I would advise using hull liner (lightweight carpet) instead of foam backed headliner. While it would work, the problem with foam backed headliner comes with the aluminum frame and condensation formed by the all aluminum shell and frame transmitting the coldness to the interior. The water vapor will collect on the aluminum and the foam on the headliner fabric will adsorb it and start to saturate and deteriorate over time. if you could insulate the aluminum spars (perhaps a 1/4 inch layer of rigid foam panels) then it would not be as much a problem. That's why autos have a shell of cardboard or fiberglass for the headliner to be glued to instead of the steel underside of the roof panels.

[danlott]

I am glad the SketchUp tutorial helped.

As for your build I am not real familiar with metal work, so do not really have much to add.

Dan

[Shadow Catcher]

Compass Rose has 1X1.5X.060 aluminum which stood up surprisingly well in the accident.
Bones exposed.

The interior is the whatever it is on very thin luan used in most RV's and we have never noted a condensation problem. I would however not want a fabric inside for a number of reasons i.e. smell, mold...

[Lgboro]

If you sandwich your walls, ceiling and floor you will most likely have a much stronger skeleton than you think you will have. I keep reading post on how weak cedar is and how bad it splits etc. but I just built using fencing cedar from sLowes (had to pick through a gazillion board feet to find boards clear enough to work with). I sandwiched two layers of blue insulation glued to sub 1/8 inch cedar strips with floated aluminum and 3/4 framing built into a T with opposing grains. It is so strong I could have planed the framing members to 1/2 inch and been plenty strong. At least I overbuilt as lightly as possible.

[C3Cole]

Dan: yes, thank you for the SketchUp tutorial. I had to watch and replay it multiple times trying to catch exactly which tool/button you selected, but I couldn't have done the design/drawing without your tutorial. Interesting, I have a multi-thousand dollar, most popular CAD program that I don't yet know how to use, and your tutorial led me into using Sketchup- so thank you very much.

Starleen2: Thank you for the thoughts about the boat carpet. I did not provide enough of my plans to be clear. I plan to insulate between the skeleton tubing with3/4"-1" extruded polystyrene (the blue/pink sheets that are largely waterproof) and/or perhaps a 1/4" piece of the foil-backed closed cell polyethylene (to reach the full 1" thickness of the skeleton tubing), and then place a 1/2" sheet of the extruded polystyrene layer as a thermal break on the inside of the above. The total wall thickness is planned at 1.5" plus the outside aluminum skin and the inside (something) covering/liner. According to my current plan, the only place where the metal skeleton is open to the humans/breath/condensation is around the door jam, and if I get an idea about how to fix that, I will. I would probably leave the interior as plain blue/pink extruded polystyrene because it is (mostly) waterproof and I don't care that much about how it looks (it will be light years better than a tent wall).

My donor trailer is built as a 2000 pound utility trailer, closed box, 4x8 rectangle 2' deep with lift up lid. As such, it is very strongly built = heavy, and I am trying to save weight on my camper shell. Therefore, my plan for the aluminum tubing skeleton and minimal weight everything else. And aluminum tube skeleton with aluminum skin with expanded polystyrene insulation will not rust, rot, or de-laminate.

Shadow Catcher: Thank you for your guidance. Compass Rose has a similar, if not the same, construction method. Your thoughts about cloth mildew/smell are right on target to guide me away from a mistake. We are semi-planning to cover the floor with linoleum, and have discussed covering the walls and ceiling with the same. I have also thought about using plastic cabinet laminate for the wall covering (and maybe the ceiling) as it is waterproof and light weight.

I have to get my wheels next week so I can finalize the frame width and axle (cut and extend) work.

Great day wishes to all,

Cole

[C3Cole]

Hello aagain:

I am getting ready to start cutting off the utility box (see earlier post pic above) and make my frame mods.

Here is a sketchup pic of my plan.


My plans call for an a-frame style tongue with a 24" single tube stinger as shown in the above pic. The tongue overall length is 72" from the frame (I intend to carry a 19' kayak on top and need a long camper). From the tongue strength site, http://www.angib.pwp.blueyonder.co.uk/t ... tear84.htm, the calculated strength requirement for a 1500 pound camper is 54,000 - using 2"x3" rectangular 1/8" tubing, the vertical strength of the "A" portion of my planned tongue is 56,000. Does anyone think that the horizontal strength of the "A" portion will be realistically understrength at 44,600 (82% of the requirement)? The angle between the "A" frame tubes is ~39 degrees.

Thanks for your thoughts.

I hope everyone is having a great day,

Cole

[angib]

With a composite tongue/A-frame like you show, there is no transverse strength requirement for the triangular A-frame part as the triangle shape is soooo strong.

The only place where you need to check the horizontal strength is at the back end of the single tongue section, as that can bend sideways. A single 2x3x1/8 has a transverse capacity of 22,300 so for a 1,500 lb trailer that allows you to make the single tongue section up to 30" long (22300 * 2 / 1500).

You need to do two checks on vertical strength:

- one at the back end of the single 2x3x1/8 tongue allows a single tongue length up to 37" (28000 * 2 / 1500)

- the other at the back end of the 2x3x1/8 A-frame allows a total tongue/A-frame length of 75" (28000 * 2 * 2 / 1500)

Those are all to the very strict Australian trailer rules which are good for off-road use. If you will only normally drive on-road, you can be less strict.

[C3Cole]

With a composite tongue/A-frame like you show, there is no transverse strength requirement for the triangular A-frame part as the triangle shape is soooo strong.

The only place where you need to check the horizontal strength is at the back end of the single tongue section, as that can bend sideways. A single 2x3x1/8 has a transverse capacity of 22,300 so for a 1,500 lb trailer that allows you to make the single tongue section up to 30" long (22300 * 2 / 1500).

You need to do two checks on vertical strength:

- one at the back end of the single 2x3x1/8 tongue allows a single tongue length up to 37" (28000 * 2 / 1500)

- the other at the back end of the 2x3x1/8 A-frame allows a total tongue/A-frame length of 75" (28000 * 2 * 2 / 1500)

Those are all to the very strict Australian trailer rules which are good for off-road use. If you will only normally drive on-road, you can be less strict.

Thank you Angib. You are awesome, as always.

Have a great day,

Cole

[MeelisV]

i have aluminium tube skeleton

thread is here - viewtopic.php?f=50&t=44096

[C3Cole]

i have aluminium tube skeleton

thread is here - viewtopic.php?f=50&t=44096

That is wonderful. I have looked at your build thread. Thank you for sharing. It is at very much like my plan. I hope I can do almost as well as you.

Have a great day,

Cole