New Teardrop - Basic approach, weigh analysis OK?

[angib]

My previous car (VW Golf) was rated to tow 1,000 pounds in the US, but the same car was rated to tow 2,800 pounds in Europe!

Yes, but that's European towing which is quite different from US towing - indeed there are some things that one continent does that other knows for sure is not just completely unsafe, but physically impossible! It's hard to believe gravity is the same in both continents....

Europeans tow:
- with low hitch weights (4-7% of trailer weight);
- at low speeds - trailer speed limits are 50 or 60mph;
- with a lot of attention (and an extra driving test in many countries);
- over fairly short distances and small hills;
- with cars that have higher-spec brakes and stiffer suspensions (Euro driving has many more stop/starts and turns).

Often the maximum hitch weight (in pounds/kilos) allowed by the manufacturer is the same on both continents - but that only allows for a much lighter trailer in the US, because they have to allow a higher hitch weight percentage. I sometimes wonder if it isn't hitch weight, not trailer weight, that manufacturers set the limit for.

Andrew

[kennyrayandersen]

My previous car (VW Golf) was rated to tow 1,000 pounds in the US, but the same car was rated to tow 2,800 pounds in Europe!

Yes, but that's European towing which is quite different from US towing - indeed there are some things that one continent does that other knows for sure is not just completely unsafe, but physically impossible! It's hard to believe gravity is the same in both continents....

Europeans tow:
- with low hitch weights (4-7% of trailer weight);
- at low speeds - trailer speed limits are 50 or 60mph;
- with a lot of attention (and an extra driving test in many countries);
- over fairly short distances and small hills;
- with cars that have higher-spec brakes and stiffer suspensions (Euro driving has many more stop/starts and turns).

Often the maximum hitch weight (in pounds/kilos) allowed by the manufacturer is the same on both continents - but that only allows for a much lighter trailer in the US, because they have to allow a higher hitch weight percentage. I sometimes wonder if it isn't hitch weight, not trailer weight, that manufacturers set the limit for.

Andrew

REALLY goo point! Kind of like biking in Holland, vs biking in Colorado! Of course there are places in Europe with mountains, but I can imagine towing 2800 lb with a Golf up Alpe D'Huez! Nothing can really replace a little common sense! What would be scarier still would be coming down with the same load!!!

[jmedclay]

[quote="McBrew"]John, since you're talking about keeping the towed weight down... I was just curious: What are you towing it with? A lot of people underestimate what their car can safely handle... especially since most foreign car manufacturers seriously lowball the towing capacity for the US market since we (Americans) tend to be lawsuit happy. For instance, my owners manual specifically says not to tow anything... but the European manual for the same car says I can tow up to 1,900 pounds... and that's with a slightly smaller engine! My previous car (VW Golf) was rated to tow 1,000 pounds in the US, but the same car was rated to tow 2,800 pounds in Europe![/quote]

Thanks for the feedback everybody. Right now I'm driving a 93 Volvo 240 but the next car will be smaller, lighter. If VW still made the 2006 style Jetta TDI wagon then that is what I'd be after, when I get tired of carrying spare ECUs, Power Stages and such for the 240.

Lighter is just nicer to deal with, all else the same.

Fiberglass/Foam panels? Is that sort of stock material available? I'll have to search but suddenly I wonder about a demi-frame, and FRP/Foam construction. Do you know of folks who have gone that route? It's starting to get into what Kenny has been talking about. Neat if you could pull it with a Cinqua Cento!
Ciao!
John

[chorizon]

Check out Kenny Ray's discussion on the ultralight construction method:

http://www.tnttt.com/viewtopic.php?t=28315

You'd probably be able to pull one with your Vespa, much less your Cinque-Cento!

[Forrest747]

Will you be checking your Tear or will that be your carry on. Carry on please, i know how rough baggage handlers were with my last Tear.

[kennyrayandersen]

I've analyzed this type of construction, though I haven't built yet as I'm out of the country [working in Korea] until Jan of next year (at least). However, There is one manufacturer building that way:

http://tadpoletrailers.com/index.html

If you want to check out the construction techniques, then you could search on foam wing home-built airplane etc. There are several home-built aircraft that utilize this method of construction. As it turns out though I posses the skills to analyze this type of structure, I wasn't clever enough to have come up with it on my own.

If someone wants to use this method, I would be happy to give some assistance such as areas that will need to reinforced locally due to load introduction ( like axle and tongue attach locations). I had hoped to get some more construction details on the ultra uber thread, but have been on a constant diet of 60-70 hours a week, though lately it's been merely 60 hours a week. If you were to combine the techniques from that thread with Rolly's little trailer and not include AC, and a kitchen etc. you could conceivably get the weight near 300 Lb which could easily be towed by a smart car.

[jmedclay]

Thanks Kenny!

I was hoping to find that some manufactured FRP/Foam/FRP panels might be easily available but on second thought, that would introduce construction methods that I'm not sure I want to tackle. Maybe, but probably not....which gets me back to wood.

1/8 luan IS inexpensive, and easily available here, from real lumberyards. B-Birch isn't. I think I've read that it's not so happy being bent, though if using transverse orientation should be OK? One layer is what I would prefer for the roof.

Any structural concerns if using 1/8 luan for wall construction? My approach would be to use it in a fully bonded skin/foam/skin stringered construction. I'd like to be able to use the same adhesive for the wood to wood joints as well as the wood to foam. I'd also plan fiberglass (cloth+resin) reinforcement of all perimeter panel junctions.

Still thinking out loud.
Thanks,
John

[jmedclay]

As of lunchtime: For better or worse I've decided on 1/8" stick construction in/out, top and sides, with adhesive-affixed, voidless-fitted foam insulation. Unsure of the floor. I will seal with fiberglass cloth and resin all of the exterior edges, then paint the entire thing with a marine epoxy or similar. It won't be ultra light, but reasonably light I hope. 5x9 box dims.

*** The one question I have about Luan: Will the glues used in manufacture be a problem, i. e. do I need to be sure to get a particular type of glue or rating in the luan sheet goods?

*** The one other question I have is adhesive: Is there one adhesive that is suitable for gluing wood as well as typical residential sheet insulation, and easy to use. If there isn't, which adhesives are recommended for each use (wood/wood, foam/wood)? Pourable polyurethanes might be a possibility too.

Profile and general approach to kitchen and shelving will be based on this:

http://www.davisengineering.net/52tear/52tear.html

Stoked!
John

[kennyrayandersen]

As of lunchtime: For better or worse I've decided on 1/8" stick construction in/out, top and sides, with adhesive-affixed, voidless-fitted foam insulation. Unsure of the floor. I will seal with fiberglass cloth and resin all of the exterior edges, then paint the entire thing with a marine epoxy or similar. It won't be ultra light, but reasonably light I hope. 5x9 box dims.

*** The one question I have about Luan: Will the glues used in manufacture be a problem, i. e. do I need to be sure to get a particular type of glue or rating in the luan sheet goods?

*** The one other question I have is adhesive: Is there one adhesive that is suitable for gluing wood as well as typical residential sheet insulation, and easy to use. If there isn't, which adhesives are recommended for each use (wood/wood, foam/wood)? Pourable polyurethanes might be a possibility too.

Profile and general approach to kitchen and shelving will be based on this:

http://www.davisengineering.net/52tear/52tear.html

Stoked!
John

I’ve thought about that as well and I think it would work fine. I would still frame out the foam on all exterior and interior edges with pine or fir (fir is a little stronger – nearly as strong as spruce per unit weight and it’s a lot cheaper). Then you can use the frame for attaching panels together (biscuits or dowels etc.), or for installing hinges etc. The trick is going to be the curves. Your choices are to put some slices in the foam so that it will ‘bend’ or using thicker foam and then hot wiring the curve into it. Since I was thinking about using 1 ply of glass for most of it, I thought I would need to fill in the slits which will open up as the panel is wrapped around; so, I’ve thought I will probably use a combination where I adhere the inside panel to the thick foam while it is flat, cut glue it up like barrel staves, tape and glue the segments on the inside, and using the side panels as a template hot-wiring the outside.

You might actually have a small advantage in that you could use 1/8 luan on the inside, the 1 inch foam which would be slit across the trailer, and then just bent around the curve (you may have to use a curved ‘nail strip’ on the inside of the trailer to bend it around). Then you could curve the 1/8 inch and glue to the outside which would easily bridge the gap and remain very strong. In fact I like this idea so well that I may combine it with the vintage boat carrier on the Nick’s garage site: http://www.nicksgarage.com/petersen05cg.htm?load_img=8 The curved front of that trailer could be made easily using the method I just described.
Now, having said that, I don’t like the idea of using just the luan merely painted. Almost every boat forum that I read was replete with examples of the luan delaminating/going to crap at the slightest moisture issue and additionally it seems to be prone to cracking which make moisture a double threat; so, if I were to use the luan on the outside, which I may, I think I will use a thin fiberglass ply at least on the top and front where there is more exposure to moisture (especially going down the road at a highway rate of speed). They make a very thin cloth that won’t add much weight and is reasonably priced and since it’s thin it also uses much less epoxy to wet out.

As far as glue, I would stick to the epoxy. It’s structural and it properties are well known with lots of experienced users here on the forum. I plan on doing a few test specimens where I will investigate surface preparation methods for the home Depot foam. One ‘should’ be able to remove any plastic (or buy the foam without it) from the surface and rough up with 40 grit before gluing to the 1/8 inch plywood. Anyway, since we are not going to load the adhesive in tension it should be fine (we are just looking for shear between the plywood and foam).

[jmedclay]

[quote="kennyrayandersen"]

I’ve thought about that as well and I think it would work fine. I would still frame out the foam on all exterior and interior edges with pine or fir (fir is a little stronger – nearly as strong as spruce per unit weight and it’s a lot cheaper). Then you can use the frame for attaching panels together (biscuits or dowels etc.), or for installing hinges etc. The trick is going to be the curves. Your choices are to put some slices in the foam so that it will ‘bend’ or using thicker foam and then hot wiring the curve into it. Since I was thinking about using 1 ply of glass for most of it, I thought I would need to fill in the slits which will open up as the panel is wrapped around; so, I’ve thought I will probably use a combination where I adhere the inside panel to the thick foam while it is flat, cut glue it up like barrel staves, tape and glue the segments on the inside, and using the side panels as a template hot-wiring the outside.

You might actually have a small advantage in that you could use 1/8 luan on the inside, the 1 inch foam which would be slit across the trailer, and then just bent around the curve (you may have to use a curved ‘nail strip’ on the inside of the trailer to bend it around). Then you could curve the 1/8 inch and glue to the outside which would easily bridge the gap and remain very strong. In fact I like this idea so well that I may combine it with the vintage boat carrier on the Nick’s garage site: http://www.nicksgarage.com/petersen05cg.htm?load_img=8 The curved front of that trailer could be made easily using the method I just described.
Now, having said that, I don’t like the idea of using just the luan merely painted. Almost every boat forum that I read was replete with examples of the luan delaminating/going to crap at the slightest moisture issue and additionally it seems to be prone to cracking which make moisture a double threat; so, if I were to use the luan on the outside, which I may, I think I will use a thin fiberglass ply at least on the top and front where there is more exposure to moisture (especially going down the road at a highway rate of speed). They make a very thin cloth that won’t add much weight and is reasonably priced and since it’s thin it also uses much less epoxy to wet out.

As far as glue, I would stick to the epoxy. It’s structural and it properties are well known with lots of experienced users here on the forum. I plan on doing a few test specimens where I will investigate surface preparation methods for the home Depot foam. One ‘should’ be able to remove any plastic (or buy the foam without it) from the surface and rough up with 40 grit before gluing to the 1/8 inch plywood. Anyway, since we are not going to load the adhesive in tension it should be fine (we are just looking for shear between the plywood and foam).[/quote]

Thank you Kenny!

I've been planning on framing the perimeter and figured I'd use up some leftover fir rips from other projects. It's easily available here too.

I too was wondering if the marine finish would be adequate, and whether or not a layer of the lightest glass cloth over the entire exterior would be hassle well spent. I'll look into that some more. Glassing the edges is a heck of a lot less work than doing the entire surface!

[kennyrayandersen]

Thank you Kenny!

I've been planning on framing the perimeter and figured I'd use up some leftover fir rips from other projects. It's easily available here too.

I too was wondering if the marine finish would be adequate, and whether or not a layer of the lightest glass cloth over the entire exterior would be hassle well spent. I'll look into that some more. Glassing the edges is a heck of a lot less work than doing the entire surface!

Of course repairing it after it’s gone to crap doesn’t sound particularly fun either! Let’s say when you are making the sides, you put down a layer of the really light-weight cloth first, then your 1/8 plywood, the framed-out foam, and the final 1/8 plywood. You’d get a smooth sealed exterior that wouldn’t take much refinishing and then do the top like I suggested. You’ll probably have to give the top an extra coat or two, but the whole thing would be nice and smooth. Then hit it with a UV paint and you’d have years of trouble-free maintenance. I fear that if you don’t put the glass on that, depending on where you’re at in the country, it might not last nearly as well.

[Roly Nelson]

I built my 8 ft woody with 1/4" sides and 2 layers of 1/8"on the roof. No problem. However, I made my 6 footer out of 1/4" sides and only 1 layer of 1/8" on the roof. All told, the entire wood structure before I bolted it to the frame was only 95 lbs. The frame, springs, axle, wheels, tires, and tongue weighs 150 lbs for a total of 245 lbs.

My 1/8" roof has some serious bends in the plywood, which makes it stronger, but if gentle bends are in the design, I would discourage using it. I guess I could slam my fist through the roof, if I had a mind to. Bottom line, make it as light as you can, but I feel that one layer of 1/8" spells trouble later on.
Roly

[kennyrayandersen]

Roly,
In this case it would be 1/8 in ply inside and out with a ‘structural’ foam core in-between, so I guess it would be more like your 8 footer in that respect (and probably overkill). If your double 1/8 is enough – this would be (I haven’t run the numbers) 4 times as strong. That’s why ideally, you could use just 1 ply of fiberglass on the inside and outside with the foam core – the core puts the structural material further from the middle which makes it much stronger.

[jmedclay]

[quote="kennyrayandersen"]

Of course repairing it after it’s gone to crap doesn’t sound particularly fun either! Let’s say when you are making the sides, you put down a layer of the really light-weight cloth first, then your 1/8 plywood, the framed-out foam, and the final 1/8 plywood. You’d get a smooth sealed exterior that wouldn’t take much refinishing and then do the top like I suggested. You’ll probably have to give the top an extra coat or two, but the whole thing would be nice and smooth. Then hit it with a UV paint and you’d have years of trouble-free maintenance. I fear that if you don’t put the glass on that, depending on where you’re at in the country, it might not last nearly as well.[/quote]

Thinking.

4.5'x8, 5x8, very spartin/simple interior & galley - gaining traction

Lightweight FRP covering - gaining traction.

Demi chassis - neutral: floor in bending @ bumps and when occupied. Who carries the loads? Floor when in sudden pitch moment and people sleeping, no? What is strong enough? Make box floor with transverse framing & foam, but what outer fiber to outer fiber distance would be adequate (1/8" or 1/4" ply faces)? Fir stringer sizes? Whole thing has to be lighter than the (KISS - reliable) 50 pounds of steel I'm trying to loose. Not sure if it works out to great benefit over simple steel frame (and with adequate Factor of Safety for good sleep!).

I can see the minimalistic 1/8 in/out skin + FRP finished box being pretty light, but the minimum demi chassis weight I'm comfortable with is around 150-175. Full chassis looks to be 225 or so. Still wrestling with that.Thinking.

Weight really is the enemy. I'll drive the Volvo 245 until the wheels come off, but next car gets better than 35mpg highway.

[jmedclay]

A local lumberyard can get non-marine grade Meranti in 1/8. I'll have to visit the yard in order to get on the phone with the supplier to find out what grade/glue it is, but have any of you run into this and have an idea of what it might be (in terms of quality, cores, glue, suitability)? It's about $12.70 per 4x8 sheet. I like the price but I'd hate to order a dozen sheets only to discover that it's not so hot for this use.

Thanks,
John