I'm trying for *reallllly* light.....

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I'm trying for *reallllly* light.....

Postby Thomcat316 » Fri Jan 14, 2011 9:28 am

I've done some browsing around here for a while, and finally became a member.

I saw the design links for the Superleggera (http://www.angib.pwp.blueyonder.co.uk/t ... tear32.htm) teardrop, which struck a loud chord in me, so i decided to do a bit of research and planning to see what I could come up with m'self.

Plans at the moment are to build a fiberglass and honeycomb monocoque box to be mounted on the axle and triangular frame of the SL design, using the stiffness of the floor panel (1-1/2" cored panel made of http://www.plascore.com/pdf/PP_Honeycomb.pdf and 15oz. fiberglass roving) to avoid relying on the frame for stiffness.

Sidewalls and top will be made of 1/2" honeycomb with the same roving for skin. I know I could go MUCH lighter with the skin, but I don't think it's necessary and I like the impact resistance of the heavier 'glass.

Floor-to-sidewall joints will be the usual right angles, with roof-to-sidewall being a rounded profile of about 3"-4" radius.

Overall footprint is about 5'x12' (yup, we're going for big *and* light here...) with a height above ground of 3" taller than my 1997 Subaru wagon.

What I'd like to know is if anyone's done a superlight cored trailer here before. I know my way around cored construction, so that's not a mystery, but I'd like some information about how to best design a molded hatch rim that won't leak, and suggestions for the same for doors. Ultralight kayaks don't have doors....

Thanks!
Whitney
Build Journal at viewtopic.php?t=44293

And then it went a' roamin'...
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Postby Miriam C. » Fri Jan 14, 2011 10:12 am

Image :thumbsup: Can't help with the molding but I sure hope you post lots of pictures. You can be sure lots of us are wanting to do something like this.
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Postby Mike-n-Britney » Fri Jan 14, 2011 10:14 am

Great idea! I can't say I've heard of anyone doing anything like this, but I'm pretty new here myself... I really like this idea, and am interested to see how the project progresses! So do you have the equipment/capabilities to mold/shape the pieces to get your radiused joints?

After considering this, it would be really nice to have all the pieces water-jet cut, then formed, then simply bond all the pieces together like a big model! With a proper design, this has tremendous mail-order kit potential!
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Postby DrCrash » Fri Jan 14, 2011 12:36 pm

Mike-n-Britney wrote:Great idea! I can't say I've heard of anyone doing anything like this, but I'm pretty new here myself... I really like this idea, and am interested to see how the project progresses! So do you have the equipment/capabilities to mold/shape the pieces to get your radiused joints?

After considering this, it would be really nice to have all the pieces water-jet cut, then formed, then simply bond all the pieces together like a big model! With a proper design, this has tremendous mail-order kit potential!


has been done.. Check out this guys camper..
http://thesupercamper.blogspot.com/2006/09/super-camper-construction-begins-nida.html
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Postby pete42 » Fri Jan 14, 2011 1:16 pm

Thomcat316
I built an all fiberglass airplane back many moons ago.
styrofoam core and bi-directional fiberglass and resin.
as you might already know the resin adds nothing to strength.
I would head on over to the airport and look for any of the fiberglass
airplanes and see how they made their doors.
There is a fiberglass and cardboard teardrop build here on this site
I'm old and I don't remember who he is but he was not in USA.
great light build someone will help me remember
good luck and like others have said pictures pictures pictures...

ol'pete
Last edited by pete42 on Sat Jan 15, 2011 1:16 am, edited 2 times in total.
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Re: I'm trying for *reallllly* light.....

Postby angib » Fri Jan 14, 2011 2:11 pm

Interesting. Is the build method to assemble the core and then laminate skins onto both sides, plus fair the outer skin?

Lightweight is good, but if you're building 5' x 12', it sounds like you want to fill up the inside which raises two issues:
- you need to build the interior cabinetry as light as the exterior;
- you have to not put anything in the interior cabinets.
Otherwise, it won't be ultralight anymore! No point going to a big effort to save 100lb and then adding 200lb to it.

I think the structural side needs to be looked at again. Just by gut feel, a 1-1/2" core in the floor seems total overkill - the unsupported areas of the floor are not that big even with a simple triangle chassis and this is not a house where you can walk on the floor. The floor does not support the body - it's the sidewalls that do that - the floor just stops the occupants falling out.

On the other hand, 1/2" core for the sides and roof sounds pretty thin. Core thickness neeeds to reflect panel width (that is, the lesser of length or width) and for the roof that's the 5 foot width. In contrast a kayak has 'panels' only 8" wide - giving bending moments only 1/50th as big. 15oz is generous as a skin weight but core thickess matters much more. 3/4" core feels more sensible to me.

I would be tempted to standardise all core thicknesses at 1".

For hatch rims and door frames, practicality says wood inserts are best. Wood (or an expensive alternative) will also be required at attachment points like where the body bolts to the chassis.

I don't think the hatch needs any rim - trailer hatches screw/bolt down to a flat surface so it just needs a wood frame instead of the core, to screw/bolt to/through. For the doors, the easiest thing might be to let a wide wood frame (maybe 1x4) into the core material, laminate both sides and then cut along the centre of the wood, leaving a laminated-in wood frame in both the sidewall and the door blanks.

The rounded profile on the roof-to-wall joint sounds like pie in the sky to me - this is maybe 100 times more difficult than the hatch and door question. I don't think it's even worth thinking about - just go for a regular square joint.

I haven't used this core material so I don't know how much in-plane stiffness it has. If one skin could be laminated to the core and then the result bent around the relatively large curves of a teardrop, the work saved would be enormous as the second skin could be restricted to the outside where it's so much easier to work. Presumably the floor and sidewalls could be fully finshed lying on a table before being assembled. Fairing and sanding the sidewalls horizontally would cut out loads of arm ache! Though with such a light body, I guess it would be no effort to turn it onto its side or roof and back repeatedly.
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Postby DrCrash » Fri Jan 14, 2011 2:35 pm

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Re: I'm trying for *reallllly* light.....

Postby Thomcat316 » Fri Jan 14, 2011 3:31 pm

angib wrote:Interesting. Is the build method to assemble the core and then laminate skins onto both sides, plus fair the outer skin?


Sort of a hybrid buildup - vacuum form and bond inner skin on the roundovers and sidewalls, inner skin on the floor panel, assemble the sidewalls to the floor panel, form, tab, and inner skin on top, locate and insert hard points for fasteners, then skin the entire exterior.

I don't have a better word for it than "top", but when I say that I refer to the panel that sweeps up from the floor in the front and ends up connecting to the floor in the back.

Lightweight is good, but if you're building 5' x 12', it sounds like you want to fill up the inside which raises two issues:
- you need to build the interior cabinetry as light as the exterior;
- you have to not put anything in the interior cabinets.


Fully agreed!! There will be minimal "stuff" inside for a number of reasons, most having to do with this trailer being a multipurpose hauler. I'll be using it to travel a Fall tradeshow circuit we do, haul long skinny telescopes and mounts to dark sites, and serve as a basecamp for kayaking trips.

The focus on an ultralight trailer is to allow payload while not stressing my Subie too much.

I think the structural side needs to be looked at again. Just by gut feel, a 1-1/2" core in the floor seems total overkill - the unsupported areas of the floor are not that big even with a simple triangle chassis and this is not a house where you can walk on the floor. The floor does not support the body - it's the sidewalls that do that - the floor just stops the occupants falling out.


I'm thinking of the floor as a torsion box panel. 1-1/2" is only a few dollars and three pounds more than 1" and adds a great deal of intrinsic strength and torsional stiffness all by itself.

On the other hand, 1/2" core for the sides and roof sounds pretty thin. Core thickness needs to reflect panel width (that is, the lesser of length or width) and for the roof that's the 5 foot width. In contrast a kayak has 'panels' only 8" wide - giving bending moments only 1/50th as big. 15oz is generous as a skin weight but core thickess matters much more. 3/4" core feels more sensible to me.


When I build kayaks, the panel thicknesses are 3MM (plus 4 or 6oz. skins). I talked this over with some folks I work with in the marine industry, and most of them suggested 1/4" would provide adequate rigidity - they were wondering why I was building so heavy...

For hatch rims and door frames, practicality says wood inserts are best. Wood (or an expensive alternative) will also be required at attachment points like where the body bolts to the chassis.


Default "hard point" will be either a high density urethane foam plug in place of core material or a section of cells cut out and replaced with epoxy putty. I was thinking it would be nice to mold a "S" form into the door and sidewall to make a more water-resistant seal, but if it's not necessary I'll skip it.

I don't think the hatch needs any rim - trailer hatches screw/bolt down to a flat surface so it just needs a wood frame instead of the core, to screw/bolt to/through. For the doors, the easiest thing might be to let a wide wood frame (maybe 1x4) into the core material, laminate both sides and then cut along the centre of the wood, leaving a laminated-in wood frame in both the sidewall and the door blanks.


Nice and elegant solution for the door! Thank you! Sometimes I'm resistant to seeing the forest *or* the trees...

As for the "hatch", I was thinking more of the galley hatch, so the question of keeping water out still stands...or maybe just let some water in but use no wood inside the galley area and let it drain out again?

The rounded profile on the roof-to-wall joint sounds like pie in the sky to me - this is maybe 100 times more difficult than the hatch and door question. I don't think it's even worth thinking about - just go for a regular square joint.


Nope - going to do it the hard way.... I've done fun stuff of this particular genre before - all I need is a good female mould and a source of vacuum to pull the core down with. Throw a bit of heat on it, let it cool, then bag a skin onto it and it won't even spring back when unmoulded. I also want the form rigidity of the curved sections for supporting roof racks...

I haven't used this core material so I don't know how much in-plane stiffness it has. If one skin could be laminated to the core and then the result bent around the relatively large curves of a teardrop, the work saved would be enormous as the second skin could be restricted to the outside where it's so much easier to work.


Almost exactly the plan, actually! I'll have to test how it does without kerfs, but the panels can be successfully kerfed for tight radius curves.
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Postby Mark72 » Fri Jan 14, 2011 8:57 pm

Best I recall after reading their whole blog is that they found out that method was heavier than they thought. Fiberglass is actually a heavy material.

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Postby goldcoop » Fri Jan 14, 2011 9:04 pm

Heat Shrink Dacron?

http://www.gaboats.com/

Cheers,

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Postby unimogdave » Fri Jan 14, 2011 10:01 pm

Note that Nidacore also has insulating properties so the 1 1/2 floor will not require additional insulation. One of the Later "Turtle Expedition" campers was made of Nidacore and it was an extreme offroad expedition camper.
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Re: I'm trying for *reallllly* light.....

Postby angib » Sat Jan 15, 2011 7:23 am

Thomcat316 wrote:....all I need is a good female mould and a source of vacuum to pull the core down with. Throw a bit of heat on it, let it cool, then bag a skin onto it and it won't even spring back when unmoulded.

Fine - if that's "all" you need, then that's my 100 times more work explained!

If I were going this far, I would be tempted to use a complete male plug for the top and sidewalls, building from the inside outwards so access and vacuuming was easy, and then take the bottom-less body off the plug and join it to a completed floor. OK, you have to fair the outer surface but you have to do that sometime anyway even if it's making a male plug to take a female mould from.

The idea of fairing the rounded side-top joint on the inside of a one-use female mould is making me feel tired and I'm gonna go and have a lie-down.....
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Postby pete42 » Sat Jan 15, 2011 8:32 am

The sides of my fiberglass airplane and I'm talking about a two place real airplane not a toy model were only about 1/2 inch thick.
the foam is for shape only the strength is in the fiberglass cloth when covered with resin. the cardboard teardrop was even thinner and was strong strong strong.
But I have read many post where someone starts out wanting to build light which is subject to what is light?
when you start adding cabinets, shelves ect light isn't as light as it once was.
good luck remember pictures.

I found the cardboard and fiberglass trailer post:
bgordon's 5 week cardboard & fiberglass build
you will have to do a search but nice strong light build.
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Re: I'm trying for *reallllly* light.....

Postby Larry C » Sat Jan 15, 2011 8:55 am

Thomcat316 wrote:I've done some browsing around here for a while, and finally became a member.

I saw the design links for the Superleggera (http://www.angib.pwp.blueyonder.co.uk/t ... tear32.htm) teardrop, which struck a loud chord in me, so i decided to do a bit of research and planning to see what I could come up with m'self.

Plans at the moment are to build a fiberglass and honeycomb monocoque box to be mounted on the axle and triangular frame of the SL design, using the stiffness of the floor panel (1-1/2" cored panel made of http://www.plascore.com/pdf/PP_Honeycomb.pdf and 15oz. fiberglass roving) to avoid relying on the frame for stiffness.

Sidewalls and top will be made of 1/2" honeycomb with the same roving for skin. I know I could go MUCH lighter with the skin, but I don't think it's necessary and I like the impact resistance of the heavier 'glass.

Floor-to-sidewall joints will be the usual right angles, with roof-to-sidewall being a rounded profile of about 3"-4" radius.

Overall footprint is about 5'x12' (yup, we're going for big *and* light here...) with a height above ground of 3" taller than my 1997 Subaru wagon.

What I'd like to know is if anyone's done a superlight cored trailer here before. I know my way around cored construction, so that's not a mystery, but I'd like some information about how to best design a molded hatch rim that won't leak, and suggestions for the same for doors. Ultralight kayaks don't have doors....

Thanks!
Whitney


Hi Whitney,
I applaud your desire for light weight. I too have similar desires. I don't know your ultimate weight goal, but mine is 5-600# total loaded trailer. I think this is doable and should not tax even a small car.
Here's my build journal if your interested:

http://www.tnttt.com/viewtopic.php?t=35852&postdays=0&postorder=asc&start=0

I am wondering if your choice of materials will actually be as light as a lightly framed wood/foam core with 1/8" plywood skins. Your choice of 15oz. roving will require a lot of heavy epoxy to fill and fair. Also, my experience with honeycomb foam is it soaks a lot of epoxy, adding even more weight.

If I were you, I would assemble a small test panel of your proposed materials and alternate methods, then weigh each to see if the time /expense is justified.

I do agree using light weight materials is worth the effort, especially if gas prices keep climbing. I have built several wood strip kayaks and each one has been lighter.
On my last one I used 1/8" cedar wood strips and 3.25 oz glass. It's plenty strong and super light. I will use the same materials on my teardrop.
Anyway.... Good luck with your build. I will be following your project with great interest. :applause:
"If its worth doing it's worth doing Light"

http://www.tnttt.com/viewtopic.php?f=50&t=35852
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Re: I'm trying for *reallllly* light.....

Postby Thomcat316 » Mon Jan 17, 2011 8:49 am

angib wrote:
Thomcat316 wrote:....all I need is a good female mould and a source of vacuum to pull the core down with. Throw a bit of heat on it, let it cool, then bag a skin onto it and it won't even spring back when unmoulded.

Fine - if that's "all" you need, then that's my 100 times more work explained!


We're thinking the same thing from different angles - I'm planning on using a female mould to form the material, but not to finish. I will be laminating the inner skin first on all panels but the floor.

If I were going this far, I would be tempted to use a complete male plug for the top and sidewalls, building from the inside outwards so access and vacuuming was easy, and then take the bottom-less body off the plug and join it to a completed floor. OK, you have to fair the outer surface but you have to do that sometime anyway even if it's making a male plug to take a female mould from.


Hadn't thought of it that way, but it makes a lot of sense. I'll do a small-scale mockup of both and see how it turns out. Thanks!
Build Journal at viewtopic.php?t=44293

And then it went a' roamin'...
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