F2C Project, Page 2
  The finished, carved wing weighs in at 45.3 gm, now I'm going to add the carbon TE. I use window film as my release layer, it's .003" thick and when waxed, comes off quite easly. I cut  out two pieces about 2" wide and the same shape of the TE and tape one to the wing with Scotch tape. I prepare two strains of 3000K tow by wetting out away from the wing and then position it on afterwards. The photo shows a couple of blocks to weigh down the TE so the carbon doesn't creep under the wing and when satisfied, tape on the other piece of film and insert in the press, use a couple of pieces of light film to protect the foam incase the lamination decides to bleed. Close the press down about 1 1/4". The press is design to squease out the excess resin but, more importantly, keep the wing flat while curing.My press is made of two pieces of 3" high density foam and 3/4" particale board with laminated fomica and 8" long 3/8" bolts.
  I use Formula 2000 resin from Fiber Gast Corp with the 1 hour gel hardner, leave in the press for 24 hours. The next day remove and pull the film off, trim the excess carbon to shape,  leave on about 1/8", this process adds on 2.6 gm, so now the wing weighs in at 47.9 gm.
  A little sanding on the carbon, just to take the shine off and now a coat of unthinned nitrite dope to seal the pores of the wood to help keep the resin from wicking into the when it's vacuumed bagged, I let the dope gas off for a couple of hours and then insert into the press with some light film for 24 hours to keep it from warping, the dope tacked on an additional 2.1 gm so I'm at 51 gm even.
   Now is the last step, bagging. I tried the French method of glueing on a cured skin and didn't like it much, the reason being if you don't get the skin smooth and blimish free it just doesn't lay down smooth enough to prevent air pockets and if you do manage to get those pockets filled with resin, it adds more weight. I only waited 8 hours for the skin to cure and the sanding was quite difficult still in a rubber state and if you wait any longer, the skin doesn't want to form over the tips very well. Plus, I just can't see using 20 cc of resin per side ( 10cc for the cured skin and 10 for the attachment ) when I can probably get away with only 10 for wetting out and attachment. I tried this out on a F2CN wing and the TE excess miced out at .006", the glass, two pieces of .75 oz mics at .003" so I have .003 buildup of resin and I figured out the weight of the cloth used at 6.18 gm, the wing accually gained 19 gm after wet sanding it out, 24 gm before sanding. Not the best ratio mix, I think I can use 1.4 oz cloth, get a stronger matrix at the same weight. This method may work well for the French but, it didn't for me.
  I searched for Mylar as my release film and just didn't found any at .003", in a quanity I wanted and at a decent price so, I though of window tinting film as an alternative. I picked up a 25" X 100' roll for $20, it's .003" thick and is the two ply variety, the water adesive tinting with a backing, I use the backing toward the glass laminate and once waxed, releases with no problems.
  The first step is to cut the release film and mark the wing outline on both pieces so you can position the glass for wetting out and for when you close the bag, they won't be misaligned. Photo shows the glass layed out on the release-waxed film, the first strip of white outside the glass is the breather strip about 2" wide fixed on with some double-stick Scotch tape, the next is the bag sealer strip with the lease tape still on, note how it overlaps in the corners, just lift the lease paper and put the other over and lay it back down. Do not remove the lease paper on the sealer tape til you put the wetted sides together because once it touches, it's impossible to reposition.
  I made a couple of manifoils for each tip of the wing, it's 3 pieces of 1/8" tubing on each side connected to a larger piece. This helps to keep the thickness down and the bag from krinkleing badly, in the tip area, when the bag is closed. This is layed over the seal strip and another seal tape piece is put on top, some extra  breather is added.
  Wet out each side with about 8 cc of resin ( for this batch of cloth, they do vary ) and when your happy lay the two together and position it properly then, pull off the lease paper off the seal strip and press together to seal up the bag.
  The two photos above show the 1" oversized, cut 1.4 oz cloth, cut on a 45 degree biased and, when wetted out, you can easily see the marker reference outline.
  Try to force the larger bubbles out before you hit the vaccum. After you turn on your vacuum pump make sure you check for leaks, then take a playing card and using the edge, start working out the air pockets. Don't press too hard otherwise you'll end up with a dry lamination. The large bubbles are not a problem but the little ones, it's easier to gather them together and make a big bubble and then pull that one out. I tried heating up the area with a heat gun but, it seems that just made more air pockets. Once your happy, take it to the press and close it up, take it down to about 4" thick ( remember it's two pieces of 3" foam ) or about half it's thickness. Once the press is closed, you can pinch off the vaccum line and turn the pump off. The purpose of the press is to get the wing flat by creating equal pressure on both sides cause the vacuum bagging proccess can cause it to warp.
  Now you've got to wait, I usually pull it out after about 18-24 hour to check it out, I know it's too late to do anything about problems but, I just can't resist. I'll trim off the excess, about 1" off the wing outline ( leave the film on the wing ) and re-insert into the press for a full 3 day cure.
  After the required press time, I removed the wing and trimed off the excess. The glass/resin matrix added on 27 gm compared to the French method which added 24 gm but, the big difference was, I used 1.4 oz cloth compared to .75 oz for the French method I had tried on another wing. The glass weight to resin ratio is much more to my liking with the method presented here, .427 to 1 vs. the French method at .257 to 1. Pictued is the pressed wing at a weight of 76.5 gm, after wet sanding with 400 grit it dropped 1.5 gms to the final finished weight of 75 gm, without controls or, tip weight.
  Shown is the carbon bellcrank with my method of line attachment via bottons screwed on with a 0-80 screw ( single shear strenght of 320 lbs. min.)