5th wheel design

[skyking]

That third graph is what I was worried about Phil. It plots the height, not the angle and shows an increase as the height goes above a small value.
Opposite over Adjacent = 7/96 =.072916
angle is 4.17 degrees.
The ground clearance is 12", and yes it would have radiused corners.
If this long rising diffuser helps, I'd make a 4 sided boat tail instead of the simple two sides, two rounded corners, and top.

[aerohead]

Originally Posted by skyking

That third graph is what I was worried about Phil. It plots the height, not the angle and shows an increase as the height goes above a small value.
Opposite over Adjacent = 7/96 =.072916
angle is 4.17 degrees.
The ground clearance is 12", and yes it would have radiused corners.
If this long rising diffuser helps, I'd make a 4 sided boat tail instead of the simple two sides, two rounded corners, and top.

So many of the members have had to compromise on angles in order to 'survive' the real world of driving.
If you can do the passive,articulated diffuser,that'd be great,if not you're still probably at the cutting edge.
A 4-degree diffuser would have a 6.7" rise over 8-ft (bad night's sleep,hope that's right).
At 7" you'd be looking pretty good!

[skyking]

I got a quote for 2 lb and 3 lb EPS foam. 2" thick is $28 and $42 for a 4x8 sheet. I don't think the 2 lb will be strong enough for the roof, maybe OK for the fixed walls.
My plan is to build a "methods and materials" trailer this winter to prove out things. It will be beetle-sized. I want to have it built and out in the weather a few years before committing time and money to the big trailer. It would suck to get it all built and have delam or weathering problems. I have all but abandoned XPS hiload foam, due to the never ending outgassing and potential for delamination. Too bad, but now that I have found 3 lb EPS with nearly the same strength it is a no-brainer.
The 3 LB is 60 PSI compressive strength, 4 times the typical 1.5 lb foam.
It has 75 lbs flexural strength, more than double the 1.5 foam.
http://univfoam.com/wp-content/uploa...Data-Sheet.pdf

The weak part of EPS is shear performance. It is about half of a typical engineered structural foam.
http://achfoam.com/ACH/media/ACH/doc...ontrol1015.pdf
Since insulation value is a large part of my needs, I can work with that.
The weight of the roof is so low as to be insignificant, the big challenge is potential snow load. If I could always keep it under roof, that is great. Need to plan for other scenarios.
~196 sq. ft x 30 Lbs = 3 tons of distributed load!

[freebeard]

My plan is to build a "methods and materials" trailer this winter to prove out things. It will be beetle-sized.

So you're going to build a 5th wheel foamie to pull behind you '03 Beetle? That's awesome. I've seen Youtube videos of two custom 5th wheels that pivot in the center of an older Beetle (like the one from the 60s), but none on a New Beetle.

This 2" foam is going to be skinned with fiberglass isn't it? Maybe you could drill holes in the foam and put wood dowels or metal Z-straps in them to tie the two skins together.

[skyking]

Originally Posted by freebeard

So you're going to build a 5th wheel foamie to pull behind you '03 Beetle? That's awesome. I've seen Youtube videos of two custom 5th wheels that pivot in the center of an older Beetle (like the one from the 60s), but none on a New Beetle.

This 2" foam is going to be skinned with fiberglass isn't it? Maybe you could drill holes in the foam and put wood dowels or metal Z-straps in them to tie the two skins together.

Not a 5th wheel, a conventional trailer lower than the roof of the beetle. Looking for better mpg and multiple functions.
I had thoughts on tieing through with some twisted strips of saturated cloth, laying it flat on each side like a flower. It would be a 1/4" column of glass and epoxy through and then laid out in all directions. Labor intensive but strong.
The first thing is to build the foam bottom shell, cutting strips of foam and gluing together, fairing, shaping. Then I'd stop and make test pieces with various layers of cloth.
Test to destruction to see how much cloth can go on before it is a certain shear failure. See how strong that is and if it is enough, THEN order up the cloth and lay up the lower shell.
Stronger foams can support stronger layups. With a weaker shear modulus, there is no point in going past the limits except for making the floor surface more impact resistant. This yields a very light structure. My guess is no more than 6~10 oz cloth each side.
Ideal resin to cloth is 1:1 by weight, but real world is wetter at ~1.5:1
20 oz cloth plus 30 oz epoxy and fairing compounds plus 72 oz of EPS per square yard is close to 8 pounds.
The upper and lower shells of the small trailer are ~ 8 square yards each