Fiberglass Frame ?

[Wobbly Wheels]

Hey all,

I've been kicking around an idea for a while now and after reading TrailerEd's "Wooden Frame" thread, I figured I'd post it up for critique & opinions....

Even though my current build isn't finished yet, I'm thinking about the next one. I'm thinking about an ultralight build with a fiberglass A frame for the trailer - partly because I want to build the frame myself (and I'm no welder) and partly in an attempt to reduce weight.

The idea is to make a male mold for each side and lay it up in alternating layers ('units') of mat and roving. The profile would likely be either C channel or hat section with the flanges glassed to the underside of the floor. The long straight section of the mold would also be used to lay up the cross members as needed. There would need to be solid blocking at the spring mounts and likely a heavier layup there as well to spread out the loading. It will have to be a substantially thicker section than steel to achieve the same strength....but with a lightweight build overall the usual dynamic forces will also be reduced.

There will be bugs to be worked out but I think it should be doable. I've built a few structural members for boats (albeit with epoxy and unidirectional cloth) and have been impressed with the strength-to-weight. The corrosion resistance is another plus, as is the rigidity once the frame is tied into the shell.

Alternatively, one could shape the frame members from foam and glass them, increasing the stiffness and/or allowing a lighter laminate schedule.

I know that most folks aren't as familiar with glass as with other materials, but I'd love to hear any thoughts on the idea.

[H.A.]

.....

[martymcfly]

I like people thinking outside of the box, however fiberglass has it's limits. I had a rear leaf spring break on my Corvette a few years ago. It was not pretty and left other damage to suspension parts and the floor behind the passenger seat. When I ordered a new spring, it did only weigh 8 lbs. though. It looked like fiberglass but may have been some other composite.

[KCStudly]

I had a surf casting fishing pole in carbon fiber. It got a tiny nick in it just above the reel seat, I thought just a chip in the paint layer. The next time a hooked into a big blue fish and went to set the hook it blew up in my face and I was left holding the hilt with the reel on it. Had to pull the line in hand over hand, a good 175 yrds of it just to unhook the very energetic fish. I was happy that I was wearing a casting glove that day.

Point being, composites can be very strong and flexible, but fragile at the same time. In the time that it takes to build the mold, and for less money than the materials it would take, you could learn to be a decent welder and build the ultralight chassis from steel. Just saying.

I think it would be an interesting project to follow, but I couldn't justify doing it that way just because it sounds like a challenge and would be cool if (big if) it ends up being durable enough.

[Wobbly Wheels]

Thanks for the input folks. It would definitely be an experiment (just a thought experiment at this point).

I come into glassing from a boatbuilding background and I've seen it used successfully across a wide range of structural applications. All of the criticisms are noted, and the failures noted share the common trait of being the result of loading a structure in a way that the layup wasn't built to withstand. Leaf springs and fishing rods are built to do very different jobs from what we're talking about here and that's both a strength and a weakness of composite materials and methods.
The trick (one of the 'bugs to work out' that I mentioned above) are to anticipate the loading and overbuilding it to a reasonable design factor. To wit: the main spar of what is arguably the finest aerobatic aircraft in the world is a carbon-heavy composite.

It wouldn't be built as a 'body-on-frame' the way we normally build these little gems - the structure and frame would act as a structural unit (unibody). It would require a wet layup between the frame members and belly in order to get a primary bond (chemical rather than mechanical bond).

Thinking out loud (ok, with fingers...), the way to lay it up would be:
1) Lay out the foam core for the flat floor on the table (Divinycell, Klegecell, etc).
2) Bond the frame member coring onto that. The table would need to be long enough to support the A-frame's coring right up to where the coupler bolts on. The frame's profile would change from a hat section to a rounded rectangular tube section where it came out from under the floor. Hard points would replace foam where structural attachments were to be made.
3) The layup would run from one outside edge across to the other. The layup would need to be much heavier and incorporate more unidirectional cloth in the forward part of the frame members where they aren't tied into the floor. Compression tubes would be located for the coupler bolts to pass through.
4) When cured, the whole works would be flipped and the cabin construction could continue, with the outer layers wrapping under the trailer and the inner bonded to the upper side of the foam floor coring.

Thanks for the input all: I'm not quite ready to shelve this idea just yet but I most definitely appreciate a skeptical eye.
BTW, it's not about the ease of doing it, nor even the cost...which would be substantially higher than traditional construction. It's about seeing if it can be done reliably and safely and about creating something unique. It would definitely require some destructive testing of the frame tube sections before taking the 'real thing' out on the highway.

Who knows, it might even serve to inspire someone to see one of the ubiquitous "floating trailer" ideas to fruition.

[rowerwet]

Fiberglass is medium that does not take flexing over and over well. A fishing rod only has so many bends before it fails. The issue has more to do with the resin holding the fibers together. Unlike Gods composite, wood which is made of stretchy cells held together with a stretchy bond. The glass strands don't stretch compress, putting the load on the resin, it heats up and fails.
Same thing with boats, the hull can only take so much flexing, then you cut it up. Masts for sails also last in wood and metal, not fiberglass.
If it could be done you would see aircraft with fiberglass spars, instead you see fiberglass skins reinforced with foam wood or metal.
You could build a foam trailer with fiberglass skin and no frame. Look at the rutan foam and fiberglass skin aircraft. Make the "tounge" a wedge snapped nose that flows out and up to become the sides and roof. Extra layers of fiberglass kevlar etc. Will be the skin in tension, making the whole tear the frame. You will still want steel or wood internal structure to attach the coupler and axle.
Alternatively, it would be possible to build a fiberglass frame, however you would want it so stiff it could not flex, this would be hard on the tear, and heavy.

[jhhayesii]

I think it is a cool idea. Yes fiberglass and carbon fiber do tend to fracture when stressed, but things are made from them because of other advantages. There are several bicycles made from fiber glass and carbon fiber. They are some of the lightest in the world.

In archery applications, fiber glass is the industry standard for making recurve bows, compound bows, recurve cross bows and compound cross bows - and these are nothing but huge springs. So yes, it can be flexible!

I'm working on a teardrop camper for my motorcycle. I said I was going to be quick about it but the project is still mostly in the design stage. I have bought all the accessories, and had the A frame trailer welded (from steel). That thing weighs about 140 pounds. I realize this is about 120 pounds lighter than a harbor freight utility trailer BUT I'd be ecstatic if it only weighed 80 pounds!

I estimate my finished trailer without mattress and appointments to weigh about 300 pounds. It will be 52 inches wide and 80 inches long with a half galley something like the mobey1 c2 but made from 2" thick foamular insulation so will be 48" wide on the interior. I'm borrowing aksnowrider's idea!

If you designed your trailer with reinforced replaceable parts for those places most likely to break you may have something rock solid.

aksnowrider used epoxy resin and 2" thick foamular for the floor. He laminated a layer of 24 oz FG cloth to the top of the floor and 2 layers of 6 oz FG cloth to both the top and bottom of the floor. He said due to an accident 300 pounds of weight accidentally fell on the finished floor and only produced some minor scratches.

I think you could take a floor like that, build up some mounting lugs on the bottom and install a couple of torsional half axels witth great success. I think you coulld similarly fabricate some fiber glass tongue yolks that you could bolt to some additional built up FG lugs on the front of the floor bottom to finish the entire floor idea! Then build the camper on top of this! aksnowrider's camper looked pretty solid! He built it in 2012 and he's still happy with it!

[aggie79]

I'm away from my computer now but someone on this forum built a lightweight teardrop with a pultruded fiberglass frame. The floor, walls and roof were made from Plascore composite panels. Maybe tomorrow I can find a link to the build journal.

[aggie79]

Okay, I found the project. Here's the link to the part where the pultruded fiberglass is being bonded to the composite floor:

http://www.tnttt.com/viewtopic.php?p=840910#p840910

[Dale M.]

Key word here might be "monocoque" design..

monocoque
[mon-uh-kohk, -kok]

noun
1.
a type of boat, aircraft, or rocket construction in which the shell carries most of the stresses.
2.
Automotive. a type of vehicular construction in which the body is combined with the chassis as a single unit.

Dale