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ERichard -> Carbon Layup Advice (4/1/2008 6:25:56 AM)
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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 [:D]
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.
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