ERichard

I'd like to get a bit of advice from you carbon experts out there about you process for your layups.
I have included a few photos of a recent project. I have an old F3A plane I designed and built from the late 90's and was eager to lighten it up a bit. The original version had a clear canopy with pilot and detailed inst. panels (see photo 1). The final weight was just at the 11 lb. limit. The wing I designed was thin (root at 10.5% and tip at 8%), so while it had great stap roll characteristics, it felt heavy during slow flight. The canopy assembly alone (photo 1) comes in at a whopping 14.6 oz. So, I knew that I could save some oz. by making a light glass version. I made a mold of the existing canopy assembly (two-piece with center parting line) and pulled a few parts to check weights. I made a real light version with 3.8 oz S-glass and West Sys. (105/206) single layer, vacuum bagged. The final, painted weight came in at 5.8 oz (see photo with alumin. painted canopy). A BIG savings and quite a difference in performance. The problem with going light on the glass is that it is not very stiff; after several years in the hot sun, a few deformaties are visible.
So last week I decided to make a carbon vesion. I used the 5.7 oz. 2x2 Twill weave and will probably leave the canopy portion unpainted to have that "cool" carbon look
The surrounding frame I'll paint like the others.
I did two tries before getting the one I was happy with. The first version involved the following procedure: first layer in the mold was the 5.7 carbon, this was then wet down with a coat of the 105/206 by roller, second layer was 2 oz. E glass , again rolled until all wet, then a bit more rolling just to make sure I got full saturation through all. Then a full layer of porus peel ply + breather and into the bag, then full vacuum (I'm in the Denver area so full psi is less than you guys at sea level) and placed into my home made heat box/oven to cure at 120 degrees for 24 hours. When I pulled it from the mold, I was disappointed to see that several areas of the outer surface of the carbon didn't get fully satuated and there was quite a few "pin-holes" everywhere[:@] Needless to say, not a pretty high gloss finish. I have done many glass parts over the years and always had good luck with the surface finish using this technique. I avoided a 0.75 oz first surface glass layer to avoid the issue of getting a "white flash" in areas. I also resisted the temptation of thinning the epoxy with isopropyl alc.
Take two: This time I did the same procedure except the first thing that I did was to coat the molds with a light coat of just West 105/206 BEFORE putting any cloth in. I let this cure until it was tacky to the touch and then layed in the carbon and glass as before. This had both an advantage and disadvantage for laying in the cloth, the advantage was that I could push the cloth into the corners and it would tend to "stick" and hold in place, the disadvantage was that the cloth would "stick" and I had to be REALLY careful not to distort the fibers.
After vacuum and curing, I pulled the part and was happier (see photos). Final weight was 6 oz. and it was nice and STIFF!
Any advice on an alternative procedure for getting the high gloss finish using the 5.7 oz. carbon?
Thanks!
-Erik
BTW, I've done several flat panels of the 5.7 oz. carbon on waxed Lexan and never had this problem.

ERichard

More photos...

Ed Smith

There is a much easier way to reproduce a glass canopy than going through the whole mold making process. Just wax the inside of the original and lay up the cloth inside the canopy. The result is a seamless, high gloss product.

See pictures.

Ed S

soarrich

My Feedback: (98)

First beautiful work.[sm=thumbup.gif]

I float on a coat of resin then lay the cloth in while it still wet, if you can use a wallpaper seam roller to flatten out the weave and push the epoxy through the cloth, then vacuum in the normal way.

Two things come to mind right away:
With the seam you'll have to sand the seam down, seems like a good time to shoot on a coat of clear coat with UV blocker in it.
I was reading a UK guy's site about Carbon "D" tubes, he was getting Russian CF cloth that was a little more than 2 oz, (but in metric measurements[:'(])

TeamSeacats

Interesting topic - I too have really struggled with pin holes in the carbon weave when vacuum bagging. I believe the problem is simply that the weave on 5.7oz carbon is too large to achieve a good finish when vacuum bagging. I also spray in a layer of epoxy and let it gel before laying up the fibers now - it takes some time and planning but it's the only way I know to achieve a good resulting finish (I still sometimes see small air pockets under the outer surface in the carbon weave).

Also note, however, that carbon is going to get much hotter in the sun (use a canopy cover). The epoxy can soften with heat leading to deformity. Heat curing the original part will help the epoxy be a little more heat resistant in the long run...so you're definitely on the right track.

ERichard

Ed, Soarrich & TeamSeacats,
Thanks for the replies. I know it won't sound very nice, but I'm glad to hear that I'm not alone in my struggles
I'm going to try another one this weekend. The seam was an issue and I will mold the whole part this time, rather than two-halves bagged and then joining them. For this I will join the mold and fill in the seam with wax and then lay a complete (full canopy) piece of 5.7 oz 2x2 (carefully[sm=spinnyeyes.gif]) into the mold. Before I do this I am going to first paint-in-the-mold my surrounding frame colors (Blue w/ yellow & white trim). Then I will give a good surface coat and wait until tacky before adding the final cloth.
The vac. bagging may be an adventure but I'll see how it goes and report back (maybe I'll even include the "meesy" pictures
I'll put a final PPG clearcoat on it.
-Erik

Darrinc

My Feedback: (5)

You would have better luck with 3oz carbon (T300) than the 5.7 oz carbon.

But with that said, the only problem I see is you are using a porous peel-ply. If you want that perfect finish, waxed paper would be a little better to keep from drying the layup out. Waxed paper is porous to a certain extent since it will pass the outgassing yet will not bleed the resin.

We do zero bleed layups for that great pinhole free layup. But then you will have to do test to see how much resin you can use without it getting heavy.

I have usually used a 50% resin to fabric ratio to layup for a nice finish and to be lite, but you can go down to 30% as long as you can make it zero bleed. 26% is the majic number, but you need a autoclave for that.

I have had great luck with spraying the waxed mold with Krylon paints and let it sit for a few hours, then do the layup.

Let me know how it turns out!

D

SCALECRAFT

My Feedback: (13)

We let the "cosmetic" coat of resin in the mold fully cure. It always comes out perfect. Added weight sure, but not enough to affect performance.

Also for additional stiffness, I have heard, haven't tried it yet, post cure at 140 degrees for 2 hours in mold to avoid distortion.

Also I would be interested to know the weight and finish quality between bagged and non bagged layup.

all west sys resin

Steve

TeamSeacats

That's some good information! Thanks.

ERichard

Thanks Darrin and Steve,
I hadn't thought of the peel ply bleed drying it out.....As you guys say there will be some compromise on finish quality weight.....or should I say some effort to get it just right[)]
I'm going to do a couple of test runs and see how it goes. I'll post my details and progress.
Thanks again guys.
-E