Uber Ultra-light tear

[Trackstriper]

Always was fascinated with the facetmobile, near ultralight, for the aviation guys:

http://www.facetmobile.com/

Several thoughts. First, although it is a small detail, the weight difference between a 2" ball coupler and an 1-7/8" coupler is probably nil. If you had a 2" coupler you might be able to have a more universal ball size even though the smaller ball will handle the load just fine. If you tow other trailers with an 1-7/8" ball then disregard my guesswork.

I'd be in favor of the 4.80x12 load range B tires, probably for looks more than anything else. They can be had on galvanized wheels from Northern Tool for a look maybe a notch up from painted white wheels. I've run small trailers on both 8's and 12's and much prefer the 12" wheels. My 2 cents would suggest take the hit on the extra weight. Instead of a tongue jack you could make a pyramid shaped tongue support from composite material and make a custom composite ball to latch into the coupler. Maybe save ten pounds or more?

The crosstube of a full axle would probably be much heavier that what you you would need for a lightweight trailer. UCF apparently makes a set of adjustable half-axles rated at 550# load. Might be about right. You might be able to purchase directly from UCF and save some coin. Put smile here. Adjustable is nice.

http://www.ucfamerica.com/UCF%20WEBSITE%20LITERATURE/UCF%20flexiride%20half%20axle.pdf

How about an A-frame tongue arrangement of 16 gauge 2" square tube with the same tubing for the crosstube? Check the numbers with Andrew, but I think the weight would be similar to 2x1/8" angle but considerably stronger. You could weld the frame as a triangle and have the joints so that the interior of the tubing is totally closed and sealed for corrosion avoidance. Little tabs could be welded to the tube for attach points for your body. Better than drilling holes in angle, not simpler.

Bruce

[kennyrayandersen]

“by the time you've added the local reinforcement either side to bolt the half-axles to, you might as well have put in a metal cross-member. “
True dat

I was originally looking at the Dexter #8, but UCF, is just 30 miles from my house so I wrote them some questions and fired off an e-mail – I’ll see what they come up with. I’ll compare that against the Dexter #8. I ask about weights, and the 425 and 550 Lb cartridges. I think Andrew is right about just getting the full axle as I’m not going to have a steel frame anyway and the overturning moment from the wheels/spindles has to come out somewhere – better it comes out in the full axle than in my body. Although, if you use the minimum overhang, the moment would be reduced and you might be able to use a lighter gage cross axle (hmmm…).

With 8” wheels, I won’t have to worry about matching the tow vehicle wheel pattern, and to save weight I’ll just carry an emergency tire repair kit (plugs, can of air) which will be lighter than another tire and spare (and those I can carry in the tow vehicle anyway). I haven’t had a flat in years, and even then, I fixed it with a plug and had no problems after that. A slight risk, but I ain’t hauling it cross country or anything [so far], so that should be able to take care of 90% of the flats that you might see (running over the proverbial nail etc.).

I’ve also given the tongue some though and think despite the punch load in the floor, the single is probably way strong enough on such a light tear and saves me the trouble of having to angle in to meet the hitch. I think Andrew’s point is well taken and since it is a bit of a modernistic, I think I’ll go with a buried fir/pine frame in the front, on the sides for the axle loads, and in the back for the heavy cargo (water, ice chest). In order to save some more weight I’m thinking of fabricating my own wood/carbon/glass tongue. I have the luxury of being able to do a finite element model of the trailer and tongue (talk about overkill!), but it will at least tell me if I’m smoking crack on some of the ideas I’ve got. If I can’t save 30% of the weight or more on the tongue, I’ll have to hang up my stress-man spurs (I’ve been in TX too long!)

I did a preliminary layout. I wanted 80 inches of sleeping length, because I sleep with my arms above my head (not that anyone cares why!) – I got within a 1/10 of an inch of that. The other constraint was a 48-50 quart cooler, which after doing a survey of them, netted a required depth of 16 inches, a width of 28 inches and a height of 18 inches. With that you can put a cooler up to a 50 quart Coleman Extreme. To get the cooler and the extra sleeping length I had to do a 10 inch stretch on a standard 8 footer to give me a total of 106 inches. Because the foam is easily spliced, and I’m using glass, the cost increase is modest. Additionally, since the foam comes in 48 inch widths and I’m framing it in wood, I was able to stretch the height to 50.9 inches without too much fussing or cost. Since I need the fiberglass in a 60 inch width to cover the width of the tear, I’ll just get one roll to do everything with. The weight increase due to the extra length shouldn’t be too bad (I’ll calculate the actual increase later when I get the finite element model built. FYI, a 5 gallon potable water container is 10”X10”X14”H and weighs 44 Lbs filled. There are no front cabinets. The front is a constant radius to make manufacturing easier (a bit anyway).

Anybody have an input on the tongue weight? I was thinking 50 lb minimum (that’s 10%) with the ice chest, water and cook stove/propane on board. With any of those missing or the A/C omitted, the tongue just gets heavier. I REALLY don’t know that much about that aspect, so I’m all ears on that one.

Picture to follow

[kennyrayandersen]

here it is:

The thing I learned is it's not that easy to do even a simple layout!

[Trackstriper]

Just my experience with the spare tire issue. I had a small trailer with 8" tires that I towed my business equipment with...when I was younger. Probably put between 150K and 200K on that trailer. Had all sorts of failure modes. Tongue, springs, axle, bearings, tires. Yeah, it was a cheap trailer, but better than HF. Never had a "flat." Had about 4 or 5 total tire destructions though. If I picked up a foreign object (maybe?) the tire would deflate quickly enough (higher pressure needed to operate and much smaller volume than a larger tire), coupled with the lack of driving feel that will tell you if you have a low tire on your car, that the tire temperature would climb and that would be all she wrote. Never enough tire left to repair. Just my experience. That trailer loaded was probably 700-800#. Might have been a lack of keeping up with correct tire pressures, don't know. I finally built a custom beam axle using VW rabbit spindles and 13" tires and that solved my tire, bearing and axle issues. I think having automotive tires operating at 30psi was a big help.

If you could get some 8" tires of the same quality as you shoe your car with that would probably be great, like Michelin makes small guys? Like you, I haven't had a flat in my driver for years. If I had to tow my small cargo trailer a thousand miles out and back, I'd rather have the spare for it (two tires down on that baby too, both total failures - what am I not learning?) rather than the spare for my van. If you tow short distance you will probably be fine. It's just that if you shred a tire it might put you down for several hours getting a replacement at Walmart before you're on your way again, a cool high tech trailer waiting on the side of the road for you to return.

BTW What is a punch load? I don't have a clue.

Thanks for putting the drawing up. Nice profile!

[kennyrayandersen]

You bring up some very good points that I hadn't considered and I think that they are valid enough to rethink whether the 8 inchers are in fact the way to go. Let's say you are right and I have to carry (3) 8" wheels and tires. That would bring the weight up to 31.5 Lbs

Options:
8" - 4.80x8 tire at 5.8 lb, on 8x3.75 steel wheel at 4.7 lb; 21.0 lb total + 1 = 31.5
or
10" - 145/80R10 with a mini alloy or 10" narrow trailer wheel = 41 (or so)
12" - 4.80-12 tire at 9.7 lb, on 12x4 steel wheel at 10.0 lb total; 39.4 lb total
12" 145/80R12 car tire 11 Lbs + rim = 42

Lots of choices. Even packing 3 tires and rims, the 8" package is lighter, but if, for a minute, we consider the 8" must come in sets of 3, but the others in sets of 2, the weight difference does shrink quite a bit. Michelin used to make an actual 8" car tire, but I don't think you can get them any more. Also, there is a heavier duty 8" with a higher load rating -- think that would help?

I wonder if the car radial wouldn't be better as some have suggested -- it's almost the same weight as the trailer tire, but probably better built (and a bit more expensive). The problem there is I don't know if the mini rims are the same 4-bolt pattern (I got to go to bed tonight -- we're 14 hours out-of-sync with y'all over here) -- I'll have to check tomorrow. Still for the same weight as the 10" set-up you could run 12s in either a trailer tire or a road tire. I'm not sure what the implication is to running one verses the other.

Hmm.m...

[kennyrayandersen]

A/C

The little 5000 BTU window units are running from $99-$120 and all run about 40Lb a piece (the Frigidaire though appears to be a smaller package and can be bought with a remote).

Anybody know what a Petcool weighs? I'm pretty sure it's more expensive.

[Arne]

petcool is a bit over 40#.. no weight savings, but it gets the unit out of the tear when in use.

[Laurence M.]

Couldn't you include small Kevlar mesh sheets judiciously in your layup to avoid punch load problems in the floor from the tongue?

[kennyrayandersen]

Couldn't you include small Kevlar mesh sheets judiciously in your layup to avoid punch load problems in the floor from the tongue?

The punch-load is a function of the geometry. The front of the tongue pushes up due to the load from the car (same as tongue load), the front of the trailer body pushes down on the tongue due to the weight of the trailer, and there is a balancing load that pulls down on the bottom of the trailer. These loads exist independent of anything else. Kevlar, does do pretty good in tension, but is quite weak in compression. You could put it on the bottom facesheet, which would be in tension in and around the area around where this local down [punch-type] load is applied; but, the Kevlar is kind of expensive so there are two other ways to solve it a little less ‘exotically’.

Method one is to bury a plug of plywood inside the composite panel to react the local high shear load. The load then spreads out and is carried by the floor panel.
Method two is to bury a cross-member that is capable of ‘bridging’ the load from the center to the side walls which are stiff and can react the loads.
Either method is acceptable – it just needs to be sized appropriately (coming up in the next few days).

Arne,
I'm thinking of mounting the A/C (standard window unit) on sliders. Pull up, pullout, fire up.

[aggie79]

I'm thinking of mounting the A/C (standard window unit) on sliders. Pull up, pullout, fire up.

This probably brings up the one door versus two door issue, but some have made an alternate second door that is fitted for the window unit. Of course, the more holes you punch in the sidewall the less they will be able to contribute to the structure.

Somewhere on here, I've even seen a window unit that sits outside of the tear with supply and return air ducts. Several do their Petcools this way. (Mine will be permanently installed in the tongue box.)

[kennyrayandersen]

This probably brings up the one door versus two door issue, but some have made an alternate second door that is fitted for the window unit. Of course, the more holes you punch in the sidewall the less they will be able to contribute to the structure.

Somewhere on here, I've even seen a window unit that sits outside of the tear with supply and return air ducts. Several do their Petcools this way. (Mine will be permanently installed in the tongue box.)

I was planning on a single beam tongue, which would make mounting a box a little more challenging, though certainly possible, but I wanted to keep the front clean (for now anyway). I was planning on just one door.

[Laurence M.]

kennyrayandersen, thanks for the geometry/stress load lesson . . . just thinking outloud.


Laurence

[brian_bp]

Always was fascinated with the facetmobile, near ultralight, for the aviation guys:

http://www.facetmobile.com/...

Excellent reference... I had forgotten about the Facetmobile. It is not only made of flat facets, it's even a lifting body (no distinct wings), and it still flies!

[brian_bp]

...although it is a small detail, the weight difference between a 2" ball coupler and an 1-7/8" coupler is probably nil. If you had a 2" coupler you might be able to have a more universal ball size even though the smaller ball will handle the load just fine. If you tow other trailers with an 1-7/8" ball then disregard my guesswork...

I bought a coupler for a utility trailer a while ago, and noticed that the weight difference was a significant fraction of the total coupler weight. I don't think it's the socket size difference; instead, it is the thicker steel used for higher load capacity in the 2" unit, since a 2" coupler is normally rated for at least the Class 2 limit of 3500 lb (the one on my travel trailer is good to 5000 lb), and 1-7/8" couplers are routinely rated for only the Class 1 limit of 2000 lb (but some are much higher).

The compatibilty thing makes sense; however, trailers routinely end up at different coupler heights, and with the low cost of both fixed-drop ball mounts and the balls themselves I keep a dedicated mount and ball for each trailer. Whether any two have the same size ball doesn't matter. On the other hand my lawn tractor has only a fixed ball mounting hole, so it would be nice if everything I tow with it (a lawn-and-garden cart, utility trailer, whatever) had the same size ball so I'm trying to standardize on 2" just for the tractor's sake.

For the Uber Ultra-Light, I would definitely go 1-7/8".

[brian_bp]

...The crosstube of a full axle would probably be much heavier that what you you would need for a lightweight trailer. UCF apparently makes a set of adjustable half-axles rated at 550# load. Might be about right. You might be able to purchase directly from UCF and save some coin. Put smile here. Adjustable is nice.

http://www.ucfamerica.com/UCF%20WEBSITE%20LITERATURE/UCF%20flexiride%20half%20axle.pdf

It's too bad UCF does not offer full axles down in the little sizes, and uses a non-square rubber cartridge so even their dealers can't build up a full axle with a suitably light crosstube.

I've been thinking of designs, and the closest thing to a full axle using the lightest Flexiride bits I've come up with is two of the lightest half-axle, bolted up to the body, with the A-frame tongue members sharing a couple of the forward bolts on each of the six-bolt axe mounting brackets, and a simple light rectangular tube sharing two of the rear bolts on each of those brackets... perhaps with no matching plate on the body at all.