The picture below is a JPEG made by copying the bottom of a Microsoft Word page from my current newsletter into my old Micrografx Picture Publisher. For some reason PP accepts these, but degrades the picture badly and sometime moves text boxes and "Word Art" expressions. Both happened here, and you can see that a couple numbers and a word box have been displaced upward. With a little effort though, you can still get the gist of what is shown.

Essentially, I built a horizontal tail, as in another thread, by creating a 3/16" thick, center trussed stabilizer core, cloth hinging that to a 3/16" elevator, and then laminating 1/16" sheet to the top and bottom of the stabilizer. I sandwiched fine CF veil between the stab laminations with West Systems epoxy resin. For each lamination, I left the assembly under a thick sheet of flat foam, under a board weighted down by a large collection of books and full bottles until the epoxy had cured. After contouring the assembly, I covered all - stab and elevator - with .56-oz fiberglass. The technique was to apply the resin and then squeegy it off, leaving a thin layer of resin onto which I applied the glass, rolling it through waxed paper to press it against the wood. When adhered, but still a bit tacky, I applied a second coat of resin and sanded smooth, pretty well down to (sometimes into, sometimes marginally over) the glass.

I weighed the parts before and after each step, giving me a rough idea of how much weight was gained in each process, as well as the resulting weight. Since my scale weighs only to the nearest .05 oz, I shouldn't really have shown zeros in the hundredth places. I think that each answer is good to + or - .025 oz. For instance the final weight is probably 1.80 +/- .025 oz.

So here's what happened.

1) I started with a hinged elevator and stab core assembly weighing .7 oz and two pieces of 1/16" sheet, roughly cut to match the stab, one weighing .25 oz and the other weighing .35 oz, due to mismatched wood. (These are all +/- .025 oz)

2) When I laminated the .35-oz piece to the .70-oz assembly (for a 1.05 oz total), with carbon veil and epoxy between and sanded off the excess 1/16" balsa edge and overflow, the resulting weight was 1.20 +/- .025 Oz. That places the CF/epoxy weight at about .15 oz.

3) Applying resin is touchy process because of needing to protect the hinge line, and even though I spread out the resin after mixing, it cured too fast during the second lamination, causing it to thicken too much and leave too much resin in the CF lamination. So starting with the 1.2-oz assembly and the remaining .25-oz piece of 1/16"sheet (1.45 oz total), the final assembly weighed 1.70 oz after trimming. So the second CF/epoxy weight was up to .25 oz, a 0.10 oz increase, or wasted weight.

4) Contouring the stabilizer, including rounding the tips (after the picture was taken) reduced the total weight by .30 oz to 1.40 +/- .025 oz.

5) Application of .56-oz fiberglass cloth and sanding, as described above to keep it from floating, including rolling it out under waxed paper, added .4 oz for a final overall weight of 1.80 +/- .025 oz.

This final weight is .1 oz less than a very similar horizontal tail (about 1/2" greater span out of about 21") I built with the same construction, but without the CF laminations. That stab had CF/epoxy and dope over the elevator and doped silkspan over the stabilizer, rather than the glass. This one is perhaps a hair stiffer than the other, but quite similar in stiffness, although I had to sand the balsa a bit thinner to fix mistakes.

Conclusions: FG/epoxy doesn't seem to cause any weight penalty over doped silkspan and may even be lighter. Since I used a total of about .4 oz of CF/epoxy to laminate the top and bottom stabilizer areas and the same weight of FG/epoxy to laminate the entire top and bottom tail surfaces (taking into account convexity plus elevator area too), the FG/epoxy was noticably lighter per square inch. Even if I had saved .1 oz on the second CF lamination, the ratio of weights would be 4:3, while the ratio of areas is 1.68. I calculated that the weight of CF/epoxy laminate more ideally would have been ,00257 oz/in², and that of FG/epoxy was .00203 oz/in² covered. So at best, the CF/epoxy would have weighed at least 25% more. The immeasurable compromise here is that the epoxy used to laminate CF was between and therefore absorbed by two surfaces.

The experiment to see how they really match is easy, of course, but I'm just showing that on this size surface, the two "cloths" are pretty comparable, and for contouring, FG is by far the most compliant. FWIW, I did once measure the weight of a double laminate of CF veil over pink 2.0 lb/in² foam. That came out to .0081 lb/in² covered area.

You might try putting on the glass and epoxy, then putting the carbon on the outside, cocured with the same batch of epoxy.  It makes a nice surface finish.  Vacuum bag it if you can.

The second post came out as a big blue quote, which I deleted inside the post. I just now amended the original to replace "+/1" with "+/-" three times. Maybe I'm developing a sort of 90^o dislexia? I also see on second examination that copying of that page bottom into Picture Publisher also kicked up two photos to obscure the last part of the caption and part of picture #3, which didn't lose anything of importance. The rest of the caption read, "West Systems Laminating Resin. Sanded."