|April 2006 PLUS FLIGHT LOG|
|Since the cooling was pretty much where I wanted it in the test
flight of April 6, I decided that the cowl shape is good. I finished just in time to take
off for the annual flyin to Columbia (O22). Vilma couldn't go but Don went and a VE pilot
he knows named Stan. We had a great time flying formation (loose) up and back. There was
one incident during the trip. On landing at Columbia I found that I could not get full
right stick in the pattern. In fact only a little past center. However, with use of rudder
it was no problem landing. I quickly determined that the problem was aft of the firewall.
So the next day the cowls came off and I found that one of the nutplates I had drilled
off to put Cam Locks in had fallen behind the right wing root heat shield
and was intermittently lodging under the aileron bellcrank. While I was there I mentioned
to Stan that my cowl weighed 46 lbs. He was shocked and said he makes race car hoods and
that a cowl that sized should be 20 lbs made from carbon fiber. He offered to help me make
a mold and a carbon cowl. I figured that if I could save 26 lbs in the3 tail, then I could
also pull 13 lbs out of the nose for a total of 39 lbs. So his offer was one I could not
As soon as I got back we got started on the mold. We started with the bottom. The process starts with applying "flanging" material around the perimeter. This is a surface that allows the mold to extend past the edge of the part and makes a place in the mold for the vacuum bag to seal. Then you apply 3 coats of mold release wax. Then you put modeling clay on all the joints and cracks. This keeps the mold resin from leaking into the cracks and chipping when you remove the master part. All the holes have to be covered too.
On the bottom half we had to make a 2 piece section for the inlet lip and the also for each of the flanges that attach the top to the bottom. This is necessary so that the part does not get locked into the mold. Then the master part and the flanges are coated with PVA which is a water soluble parting agent. On top of that a gel coat type material called Surface Coat is applied. This is a creamy paste of about honey consistency made for epoxy and micro balloons. A thick coat of that is applied and dry flox is sprinkled on to it while it is wet. That has to dry a little so the next steps don't make any holes in it. Then, in our case, 3 layers of roving mat were applied. If the tool were to be used a lot then more layers would be added to make it more durable. Over the roving a layer of coarse weave "boat" cloth was laminated.
Then we added some ply wood legs to hold the mold in position. These were just bondo and then glassed into position. After it was cured the master part is removed by removing the 2 piece sections and then the master from the mold. It came out very nice. Then to make the part the mold was waxed 3 times and PVA sprayed on. A few minor flaws in the mold were repaired. Primer was then sprayed on the mold and allowed to dry. Now micro with black die was spread into all the sharp corners and edges. Then the carbon fiber. We used 3 layers over all and extra layers on the edges and corners. E-glass was used where screws would go because it adds toughness. Carbon is very strong but brittle. After all the carbon and glass are in place, then a perforated release film is applied and over that an absorbent bleeder cloth, almost like a cotton pad. Then the vacuum bag is put over the part and a special clay like tape is applied to all the edges with "ears" ever few inches to allow for extra bag in the center of the part to conform to the shape. We put 3 vacuum ports in the cowl film and applied vacuum. Then you start searching for leaks. Pressing the tape around the edges starts the sealing process. As the bag starts sealing, you start to hear where the leaks are. When it is sealed good the vacuum pump will cycle off and on. only one every few minutes. The first part (lower cowl) is done. It weighs only 7 lbs! I still need to add the inlet lip foam, and the airbox and attaching hardware but I estimate it will be about 10 lbs full up. That is even less than our target since the lower cowl is at least 40% bigger than the top. It's a little flexible but I think it will be fine when supported by it's attachments to the airplane.
I decided to take a break between the two halves and take a trip to see my sister. The trip report is at NW Territory Trip.