Weight and Composite Panels

[Deryk the Pirate]

Hello Folks,

Well hopefully money situation will work out, this winter I want to build a Tiny Trailer to tow behind my PT Cruiser which has a max tow weight of 1000lbs.

The design I have in mind is just like Ptomaine's Boxcar
http://tnttt.com/viewtopic.php?t=40262

I really would love Steve's Little Gypsy cart
http://tnttt.com/viewtopic.php?t=26296
but obviously the weight for me wouldnt work, so the boxcar size is more likely an option. Now I was reading http://rumicaravan.fortunecity.com/ and he said it weighs in at 400lbs (Im guessing that is not counting the trailer?) Im not looking at building a galley into it, just a rectangular shape. Im about 230lbs and single so Im really looking for something that will hold a queen sized mattres. My intended use for the trailer is camping and SCA events http://www.eastkingdom.org/ So I intend on painting it to look "traditional"

So its got to be at least 5ft wide by 6.5ft long. I could add shelf storage to hold clothes and misc, or possibly raise the mattress just high enough to slide the short rubbermade tubs under the bed.

Now in the Rumi caravan is the first time I heard mention of building a composite panel with 1/4 inch ply with 1" dow foam insulation and luan for the inside useing the metal truss plates and lots of adhesive. I have a friend with a tablesaw so ripping 2x4's to make three 1.75"(ish) by 1" pieces 16" on center frameing. Its basically a rectangular cube with a rounded roof.

Im really familiar with CPES and RotDoctor, I live on a sailboat Im restoreing, so Im a little handy but have friends who are more handy lol. Im trying to get an idea of weight before I build something that my car cant tow lol. Im planning the entry door to be at the rear and 2 windows and an opening for an ac unit opposite the door.

Now from searches on google, a sheet of .25" plywood is about 25lbs, a 4x8 sheet of dow foam 1" is about 16lbs, and a sheet of 1/8th luan is about 15lbs. Im calculateing if I can get three 1.75" by 1" strips from a 2x4 that I will need for an 8ft long wall approximately two 2x4's that weigh about 10lbs each. So would it be safe to say a 4x8 composite wall would weigh about (25+15+16+10+10= 76 +10%overage) =84lbs

Does that sound about right?

thanks
deryk

[Tadlan]

I'm working on some ideas to keep the weight down as well. Under 750 lbs and I don't have to register in Utah, plus my tow limit is 1k as well. Whatever glue you use will add several pounds to your total. I dabble as an artist and have seen quite a few lightweight things accomplished with foam and epoxy. Even seen a desk made entirely out of foam insulation. I'm working on some fiberglass over foam and some ply composites. Hopefully it all turns out as well as it is in my head.

[Deryk the Pirate]

I did come across this...
http://tnttt.com/viewto ... 930#712930

"Sandwich
1/8 plywood weighs about 12 lb/sheet
The Home Depot foam is around 2 lb/cu ft.
To make a sandwich requires 2 sheets of the 1/8 inch
There are 32 square ft/sheet per sheet and we’ll assume the sheet is 1 inch thick
Weight of the core is 32/12*2 = 5.33 Lb+
Total weight for a 4X8 sheet of sandwich = 2*12+5.33 = 29.33 Lb
Weight per sq ft is 29.33/32 = .92 Lb/sq ft (not including adhesive between the skins and core) "

Now if I added a 1"x2" all the way around the sheet of plywood (well between the plywood pieces)with a few 1"x2"'s say 24" on center (per homedepot.com a 1x2 8 foot furring strip weighs 2lbs) say 10lbs, then throw in another 10lbs for epoxy and glue so that would bring it to about 50lbs a panel... that would do it weight wise for me. Should be able to get it built under 500lbs plus the trailer.

Seems reasonable to me, the Rumi Caravan weighed in at 415lbs...

[Tadlan]

We are probably going to have people start chiming in very soon about delamination and the horrors of foam core, but most of their examples will be from high speed boats. I have read about ultralight aircraft being constructed of foam core and a car. He has some great suggestions at the end.

http://www.home-built-cord.com/Page4.html

[Deryk the Pirate]

Well Im sure people have built trailers from half inch ply with wood frameing... so how much different is it?

[Shadow Catcher]

The construction of Forest River trailers and our Mega-Mini are Filon exterior 1'x1 1/2" .060 aluminum frame and 1/8 what ever the heck it is interior with foam in between. Forest River uses compisiteck flooring which was made originally by Kaiser for use in aircraft and currently used as truck beds. It is the panel that creates the strength.

[dmdc411]

I found your post a little(months) after you posted, yes aircraft panels have been built like this for years. I have worked on 747, DC10, and a little in the newer stuff, Airbus. Sandwich panels work very well, are very strong and lite in weight. The info is out there on the web. Its amazing how the newer aircraft are built, some use pop can thin alum skins with a honeycomb core, and they are amazingly strong. I would think the same could be done with the right foam core and thin plywood. Good luck.