Ultralight Design?

[Jiminsav]

Gee..i'm doing a moderistic, full size, with minimal frame for axles and tongue, 1/4 inch luan on the inside, framed and covered with cloth and paint..i wonder if it will be light?..

[mikeschn]

Hey Andrew,

I'm impressed... you gained me some extra space without extra weight... I like the way you think...

Okay, let's talk floorboards...

I'm thinking either a torsion box (aka a hollow core door) or a rigid panel covered only on the top with a couple layers of 1/4" luan... 1/2" baltic birch plywood would be a better choice, I'm sure...

But more importantly, each of the edges is a 2x? piece of oak so that I've got some material to bolt the axle to...

So if each side is a 2x3 piece of oak, with a piece of 1/2" plywood on top... then the bolt has to go thru 2" of wood (1 1/2" of oak and 1/2" of baltic birch). That should hold up, don't you think?

Now the tongue, that's another question indeed... at first thought, I'm thinking a straight tongue, that we can bolt a couple onto... This tongue can be 2x2 or 2x3... your choice... but what do we fasten it to? We could run a bolt thru the floor and thru the tongue, every foot or so. The floor would have to disintegrate for the tongue to come loose.

Your thoughts...

Mike...

[Jiminsav]

if you can find a piece of 4x4 live oak, that would make a groovy tongue..live oak was used to build clipper ships before steam came about, and clipper ships could take quite a beating..you could even drill a 2 inch hole 3 inches back from the front up from the bottom, and drill ¾ holes through the sides for dowl pins so the ball don't pop up..somebody draw that up and i'll see if it's what i imagine

[Jiminsav]

here's something i drew with Paint..I know..it sucks, but it conveys the idea

[toypusher]

Mike,

Steel tongue with a plate welded to the end that attaches to the bottom of the tear. Say about 18" wide by 24" or 36" long to distrubute the stress when you bolt it to the floor assembly. Or just make the tongue an 'A' frame type that connects at the axle stubs.

[Larry Messaros]

I'm thinking either a torsion box (aka a hollow core door) or a rigid panel covered only on the top with a couple layers of 1/4" luan... 1/2" baltic birch plywood would be a better choice, I'm sure...

But more importantly, each of the edges is a 2x? piece of oak so that I've got some material to bolt the axle to...

So if each side is a 2x3 piece of oak, with a piece of 1/2" plywood on top... then the bolt has to go thru 2" of wood (1 1/2" of oak and 1/2" of baltic birch). That should hold up, don't you think?
Mike...

Mike,

Here's a couple of thoughts, comments and questions:

Why use oak? How about spruce? Wooden airplanes were built with spruce so it should stand up quite well.

I would probably still use a metal frame, but you could probably get away with a basic perimeter and fill in with some 2x2 (spruce would work for this as well) with 1/2" plywood (spruce house sheathing) for the floor. Don't add flooring, paint would work or leave au natural.

If you use 1/8" ply + 3/4" spruce frame w/insulation it would be the same if not lighter than 1/4 " ply for walls.

Lights and electrical wire do not add a lot of weight so they shouldn't be an issue. If you leave your trailer plugged into the tow vehicle, you would still have lights but not the added weight of a battery. In my truck camper, that is all I ever used.

Propane piping is not overly heavy, If you are still going to carry a stove and propane, it will add the weight anyways, whether it is permanent or added in later.

If you still want to have storage and light weight, make the cabinets out of 1/8" plywood as well. Cabinet doors can be easily made with 1/8" plywood on each side of a spruce frame. Strong and light. The edges can be routed with an ogee bit and either painted or faux finished to match the plywood.

With my camper, 6' wide x 6' long x 5' high it was less than 250 lbs. Add a frame at about 200 lbs, and you could be less than 500 lbs.

One final thought, plywood is heavy so go easy if you have to add it. A friend of mine built the same size camper. He doubled his plywood for the floor and his other areas where I only used single ply. It added a lot of weight on, and I felt it wasn't nescessary.

[Randy G]

Ive been reading lots of great stuff here on this forum. When reading about the modernistic ultra light design, its just what I need and have been thinking about for sometime. I have a sports car with V6 and need light and cool looking. Im planning on starting with a very simple tear big enough to carry my bikes and gear and long enough to sleep in when the bikes are unloaded. Keep the great ideas coming, thanks guys. Randy

[dwgriff1]

I've been working on this for some time.

A torsion box is very strong. The defenition is a skin on both top and bottom with a grid in the middle. To bend something has got to stretch one side or compress the other.

The floor could be 1/8" top and bottom of the torsion box if the space in the grid is full of foam insulation. Same goes for the walls and the roof. Adding the insulation would increase the strength of the box. Use plenty of glue and narrow crown staples.

Reinforce the floor with some Oak to hold the bolts for the axle. Use a wood tongue, keep the extension short, and use an integral triangular tongue box to support the tongue, or use a trianglular vertical torsion box. Either way would easily support a 3 or 400 pound trailer.

Leave out the lighting, use a battery powered LED lamp inside. Use a fuel burner lantern for the gallery when necessary. Use a small 1 burner stove, a light weight cooler.

Cabinets made from 1/8 skinned torsion box would not be heavy or spendy. Keep everything simple.

Avoid any hardware item that is spendy. Stay with house hardware, avoid RV hardware.

Make windows (buy the glazing) etc. I camp where it is always cool to cold at night -- so for me large opening windows are not necessary.

I have spent a lot of time thinking and planning. I think it could be done both cheap and light.

That's my plan. Once I buy the #8 torsion axle, the rest would be made from a stack of 1/8 lauan with softwood for the webbing.

Cover the outside with tonneau fabric on top, or paint, or polyurethane. Don't let it set outside all winter in the snow, or all summer in the sun, cover it when not in use.

Build as much as possible from the inside out, with lots of srews, and captured nuts, glue and staples.

dave

[Roly Nelson]

Right on, Dave, that is what I call thinking out of the box. The more stuff you can leave out, the lighter it will be. Keep on planning and building, and soon tears will be in the 3 to 4 hundred pound range instead of the 12 to 14 hundred pound area. If smaller is better, then lighter must also be better, if it suits your needs....................Roly, Just a light weight builder.

[Roly Nelson]

Mike, construction of a truly ultra lite can be accomplished if a heavy trailer frame is eliminated, standard thick plywod sides are omitted and light weight structral construction is employed. My Stacker is simply built on an 1 3/8" hollow core door, for the floor, and 1/4 inch sides and 1/8" roof. No fancy plumbing, watertanks or cooler compartments. I know it is simply a basic, run-of-the-mill, lightweight teardrop trailer, but is suits my needs when camping alone, as long as I can pack my dutch oven in the trunk of the car and bring my paper plates and plastic cups along. So far, flipping it up up on end inside of the garage, works for me, and I am amazed that more tear owners aren't enjoying the same benefits. So far, it weighs in at much less then 300 pounds................Great!

Roly, just an off of the wall builder, thinking out of the box......:-)

[Guy]

Dear Mike,

There has been a long standing controversy regarding the use of Oak and Epoxy that now some companies are producing epoxies specially formulated for oak.

Here is one description from Glen-L boats

WHITE OAK: A slightly roughened surface (such as that resulting from bandsawing) may be preferable to planed, smoothed surfaces. Being a porous wood, care should be taken to prevent "glue-starved" joints. Using POXY-SHIELD®, apply a thin coat to mating surfaces and let cure without joining. lf obvious dry spots recur, apply another thin coat until the wood is sealed. Then glue in normal manner, avoiding excessive clamping pressure. lf joint is under bending stress, keep clamps in position until complete cure takes place.

The other factor I think should turn you off from oak is that it is a heavy wood, with long porous fibers and therefore it will expand and contract more than most woods. The level of coefficient of expansion of oak is also very different than that of plywood. Give the above difficulties with epoxy bonding compounded by the dissimilar expansion properties argues for a different combination.

Now let us look at another issue. Regardless of whether you choose douglas fir, spruce, ash, or oak, you should consider doing a little more work and have a layer of 1/4 " ply, a layer of 3/4" stock of choice, a layer of 1/8" plywood, another layer of 3/4" stock with the grain running opposite to the first layer, and another layer of 1/4" or 1/8" plywood. Only the layer under the floor should get a covering of double foil insulation with bubble or foam inside. The bubble insulation require a 3/4" air space from the exterior to be effective. Using sheet foam and gluing it to the ply will not give you any strength unless you clamp at 700 #/sq". The interior layer and the differing grain will give you a tremendous boost in strength for very little extra work

[mikeschn]

Thanks for all your input. There are some really good ideas here...

Seeing as how most of us agree that the torsion box is quite strong, I've started thinking about how one could be constructed.

I came up with something that I've never seen before, that should make this rather strong, and durable locally, where the axle is bolted to the torsion box.



Notice the pink colored square tubing that slips onto the side pieces of spruce! That gives you something solid to drill your holes into and bolt your axle to. The top and bottom skins of the torsion box can be notched out to clear the tubing.



The only other steel (besides the axle of course) is the tongue, shown in cyan. It can have a couple pieces of angle bolted to the axle... and a few bolts bolted to the 2x2 spruce running the length of the torsion box (not shown yet.)

Mike...



P.S. 2x2 spruce is dimensionally 1 1/2" x 1 1/2".

[toypusher]

Of course, I'm no 'Andrew', but it looks like a plan to me. When's the prototype going to be done???? How many test miles before putting the teardrop on top??? You can tow it over to my house and back to see how it works

[Loader]

That looks great Mike! Firm mount for the axle and draw bar, but still keeping the light weight goal in sight.

[angib]

OK, just to stir things up (it's not only Gage....) I'll say that I don't agree with more than half of what's been said.

Dave, beware of the phrase 'torsion boxes' as the 'torsion' bit doesn't really apply to any of this, except to stop the beams tripping over. What you are describing is many beams sandwiched between two skins and they still just behave, and carry load, like beams. Contrary to what 90% of people think, a 'grid' of beams (ie, at right angles) inside a sandwich structure is an inefficient way of carrying a load - unidirectional beams across the shorter dimension are more efficient (and a lot easier to build).

All this talk of oak makes me think you guys are trying to build a steel frame out of wood. Why? Design it to be made in wood (most probably plywood), using wood's natural strengths rather than working out how to make it look like a steel structure.

But, most of all, everyone stop thinking you're building a house with foundations, a floor and some walls. This is a monocoque trailer we're talking about and the walls are what holds everything else up. The floor is there because without it you would fall out of the trailer when you went to sleep. We need the wheels to hold up the sides of the trailer - holding up the floor is incidental.

If me being this dogmatic makes is sound like I know all the answers, I know that I don't - I'm really not sure whether 1/4" plywood is enough to make the tongue from or if it needs 3/8".....

I should manage to post some more design ideas later.

Andrew