Carbon Fiber/Aluminum build for a family of 5

[StrongFeather]

Carbon wall panels look amazing. What is your design plan for the roof?

Thank you for the compliment, OP.

As for the roof/ceiling design, think “the forest” of the cathedral at Notre Dame.

Okay, maybe not that complicated, but difficult to describe. It will pitched on both sides with a ~6” wide spine running front to back (the same width as the front of the tongue box). Inside, there will be an “attic” cavity that will disperse cold A/C air evenly along the cabin, hide some indirect lighting and be used to run a few wires. It will also have 2” of insulating vs 1” in the walls.

Stay tuned for pictures and more details.

Steve


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[aggie79]

Slight correction...

As for the roof/ceiling design, think of “the former forest” of the cathedral at Notre Dame.

[StrongFeather]

Sad but true.


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[StrongFeather]

It's been a long, busy summer and even though the posts don't show it, I have actually been working on the trailer. I feel like I could have built a house in less time than this is taking. Funny thing is I actually did build an in-ground swimming pool in less time - sadly, my family has been pointing that out a lot lately.

The two cabin door windows are in. <yawn>

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The roof spine was mocked up with the help of a broom stick and some 1.5" aluminum.

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This allowed me to make accurate measurements for the 4 large roof panels.

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More to follow...

[StrongFeather]

Unfortunately, two of the four roof panels had issues. I'm not sure what happened to one panel, but the last panel was by far the worst because my vacuum pump quit shortly after the infusion.

The result was not pretty and I was torn between infusing a new panel (cost of ordering more cloth, using more epoxy and consumables), or trying to fix the two messed up panels (time, time time...). In the end, I thought I'd try to fix the panels first - then re-make them if need be.

Here's a shot of the ugliest side of the ugliest panel (vacuum pump failure). Basically the carbon fiber wasn't pulled tight around the frame with some serious bridging where the "skin" meets the frame.

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So, I drilled a bunch of really small holes, clamped a straight edge along the outside and injected epoxy into the cavity between the wood frame and the carbon fiber.

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Once the outside edge and top were done, I drilled holes along the skin/frame transition and again used a syringe to inject epoxy into the cavity.

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Surprisingly, this worked great! These two panels are just as solid as all of the other panels. They look a little messy in certain spots, but no where that will be visible after their assembled.

One thing I forgot to mention, and take a picture of, was the clear coat for the panels above. Once the epoxy was injected and cured the edge was wavy, uneven and well - didn't have clear coat on it. So, I set the panel vertically on it's side and put blue tape around the top edge creating a sort of dam. I then used a syringe to lay down a layer of clear to make an even (as possible) edge. It sounds easy, but in reality, it took several layers of building up, filing down and filling in the low spots. But in the end, it looks good.

Oh, and if I didn't mention this earlier, the roof panels all have an extra layer of really heavy (18oz) fiberglass cloth to (hopefully) prevent hail damage and so on.

[StrongFeather]

So here are some pictures of the roof mock-up drawings. After taking these pictures, I decided to lower the roof spine by about 3/4", so the end result is a little different, but the concept is the same. I will do my best to explain how it's supposed to work, but the idea of three dimensional air flow on a two dimensional surface may be a little tricky.

This is a picture of a (nearly) full width view of the roof, which will be made up of a 6" spine and two ~33" wide panels. The entire roof will have 2" of pink XPS foam and there will be roof spars (1/2" plywood) every ~14" for support. The outer edges of the ceiling will follow the slope of the roof and will be skinned with 3mm baltic birch. The center of the ceiling will be suspended to allow for cool air and light to exit out of the gap between the two surfaces. The center section will be 1/8" hard board (for stability) laminated with 3mm baltic birch.

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This is where the explanation might get a little tricky. First, the two notches just off of the center line are for the side panels meeting the spine panel.

Although it's kind of hard to see, there are some light lines that depict the 2" foam insulation thickness. The gap that results from the area between the foam and the center section essentially creates a cold air duct that runs the length of the trailer from the tongue box to the rear wall.

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Originally, the spars had three "teeth" that dropped down 3/4". The two squares with X's in them are 3/4" supports that run the length of the ceiling, giving me a solid mount for the suspended ceiling, which will be rather flexible. The lines coming off those 3/4" mounts are LED strip lights that will also run the length of the ceiling and shine out the gap. In the final version, those 3/4" supports are 4" wide.
Notice there is a gap of a about 9/16" between the foam and the supports. This allows the air to flow over and out the gap.

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Some notes on the changes...
Because the ceiling height was dropped by 3/4", the angle on the spars was no longer correct. Unfortunately, I had already cut all of them. So, rather than buying another sheet of plywood, I decided to cut the existing ones in half and use them along with some sister braces to connect them in the center. This ended up having some advantages and allowed me to fix some things that I didn't particularly like, such as the spars every 14" blocking air flow. Now, although I don't have a picture of it, the air will have a much cleaner path front-to-back. It will also allow for a much easier assembly process. More on that later.

[StrongFeather]

Roof panels continued...

The four big roof panels, since they'll be angled towards the sides of the camper, needed to have slight angles cut on two sides. The angles are around 5°.
This is the cut along the spine. It was a little tricky because it had to be ran through with the open cavity down (the table saw blade tips away from fence), so I cut a piece of foam and basically used it as a sled. This cut also established the width for the panels, ensuring that they're all the same.

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This cut is the outer edge. It will sit on top of the side walls. Running a wobbly 33" tall panel along a 2.5" fence didn't exactly create a nice smooth cut. So, we plumbed-up and clamped some wood scraps from the roof rafters over the edge of the fence. It worked!

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The panels will be held together with biscuits and epoxy. Here's a shot of one of the spines dry-fit onto one of the big roof panels.

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More to follow...

[StrongFeather]

Front roof panels mocked-up in place. I'm pretty sure it's sitting a little higher than the finished height in this picture, but I'm really happy with the look.

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And a look from the inside. You can see the opening in the front bulkhead where the cool AC air will enter the ceiling duct/cavity.

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And here's a shot of the roof spars and the first inch of insulation being dry fit.

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Still more...

[StrongFeather]

I created a gauge block that is the same width of the camper's side walls to locate the end of the spars. This is critical because the outer 20" of the ceiling panels will be skinned on the bench. If the spars are too close, the outside edge of the roof won't be flush with the outside of the walls; too far away and there will be a gap between the walls and ceiling inside the camper.

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Still dry-fitting here, but I wanted to show the sister pieces that will connect the spars from each side. There's only one sister in the picture, but they'll be doubled-up, one on each side of each spar, when all is said and done. There will also be a cut-out in the center to decrease the air flow resistance. Sorry, the cut-out is not in the picture. The 3/4" x 4" supports will be secured to these sister pieces and run the length of the ceiling so that the center, suspended part of the ceiling will be nice and flat (hopefully).

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And here's a shot of one of the panels pretty much ready to be put on the camper - it just needs to be skinned. The insulation and spars are epoxied in place and I used a surfform plane to level everything so that there are (hopefully) no waves in the skin. I only put the 2nd inch of insulation on the outer 20" (where the skin follows the ceiling) because I need to be able to epoxy and clamp the sister pieces in place when the roof is sitting on the camper. I might reconsider that decision and add the other inch while it's on the bench so that I don't have to figure out a way to hold the insulation in place while upside down - but that'll mean I'll probably have to use screws instead of clamps to clamp the sisters in place while the epoxy cures.

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I apologize if this isn't completely clear right now, but I promise it will be once the roof is actually installed.


Steve

[StrongFeather]

Hello strangers! Sorry it's been so long. Quite a bit of progress has been made since the last post, so here's a catch-up.

This picture just shows how I laminated the inside of the 4 main roof panels. A little epoxy and a little weight to hold all of them down. After they were cured, I followed up with a flush-trim router bit to clean up the edges. Wipe-on clear poly was used to seal them later, just like the walls.

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This picture is looking rear-to-front on the drivers side. Still dry-fitting, but you can see that the outer 20" of the ceiling will follow the slope of the roof.

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And here it is with the passenger side dry-fit. The center section (where the clamps are) is where the false ceiling will be. It'll be horizontal and sit a little lower and will create the attic duct that will carry the cool air from the air conditioner into the cabin. It will also be used for running a few wires and contain some cabin lights.

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Steve

[StrongFeather]

Roof assembly was quite tricky. The 4 large panels (~3'x5' each) and 2 spine panels (~6" x 5' each) were epoxied together first to make the 6'x10' roof. The hard part was maneuvering and fitting the individual sections together, with wet epoxy and biscuits on the edges. The two big passenger side panels were epoxied together and the drivers side panels were epoxied together and allowed to cure first. Then they were put in place on the walls and all 6 pieces were epoxied and clamped together and cured. After a few days, I raised the entire roof by a few inches and epoxied it down to the walls. The pictures that follow detail the process.

The gap between the front and rear panels didn't look great because of how the flush cutting bit followed the splines. The baltic birch skins didn't meet and the gaps were uneven.

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So, I filled the gap with some scrap birch...

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...and ran a 1/4" bit down the middle, creating a nice little detail that looks like it was meant to be there. Later, I shot some black spray paint in the gap and it turned out looking pretty nice.

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Steve

[StrongFeather]

After the 6 main roof panels were assembled, there was still the v-nose roof and this area above the rear wall that had to be dealt with.

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I cut some foam pieces to roughly cover the opening, and...

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...used some epoxy and fiberglass to encapsulate them. I used the plate glass and some of the aluminum tubing from making the carbon fiber panels to keep the sides smooth and reduce the amount of "body work" to achieve a flat, smooth finish. It worked great!

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Steve

[StrongFeather]

The process for the v-nose roof was essentially the same, just with a lot more angles and a lot more test fitting.
Cut and shape the foam to roughly the correct size.

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Encapsulate the foam with epoxy and fiberglass.

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Do a bunch of test fitting and tweaking until they fit perfectly.

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All of these pieces will be assembled with biscuits and epoxy.


Steve

[StrongFeather]

To skin these smaller roof panels, I laid some carbon fiber cloth on the glass, wetted it with epoxy...

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...buttered the parts and laid them on the cloth with some weight to hold them down.

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Here they are before the skins were flush trimmed using a router and/or a file.

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I also used the extra carbon fiber that was wetted on the glass and cut strips out of it to trim-out the edges of the panels.

Steve

[StrongFeather]

Once the entire roof structure (6 main panels, rear cap and v-nose roof) was completely assembled, epoxied, trimmed and cured, the whole assembly was set on the walls with spacers. Biscuits were place and the entire roof/wall interface was slathered with thickened epoxy.

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In the first two pictures, you can see how the roof sits on top of the walls and the ceiling extends down onto the top 1" of the walls inside the cabin. This is what made assembly so tricky because of the interference between the roof, walls and biscuits. In the end it just took some creative thinking planning and it all worked out great.

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After the epoxy was slathered and the spacers were removed, the roof was set in place (for good) and clamped down with some straps.

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That was a big milestone day!

Steve