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Randy,
You are setting yourself up for a ton of work. I built a custom cowl for my RV-4 out of carbon fiber (got a really good deal on the fabric). When I built it it was lighter than the then current RV-4 cowl and stiffer too. It has now been hacked/patched so many times to accomodate changes to cooling systems, exhaust, etc.... that it has gained weight. It weighs about the same as the fiberglass RV-6A cowling from the airplane I'm flying.
I built a plug from foam directly on the airplane. Carved to shape, covered with fiberglass cloth and then body worked and painted to get it smooth. Once I was happy with it I waxed the crap out of it and shot a couple of coats of PVA (mold release) on it. I laid the carbon up directly on this. I used 4 layers of 8 ounce standard weave cloth. Once cured I split it lengthwise and removed it from the plug. I then removed the plug from the fuselage.
Obviously this leaves a smooth interior surface (good for cleaning) and a rough exterior (lots of filler and sanding). Once its all smoothed up then fitment to the airplane was standard Vans (combination of piano hinge and screws/nutplates for attachment).
No idea how much time this tookbut it was definitely multiple 100s of hours. And this is not the lightest/best way. If you really wanted the best method, build the plug as described and then lay up a female mold on the plug. Make your cowl pieces in the female mold. This saves the time/effort/weight of the filling and sanding. It also provides a means to use composite sandwich core construction where there is some sort of core material installed between inner and outer layers of glass. This makes the cowl MUCH stiffer and allows you to use fewer layers of cloth. But the additional work of making a female mold was too much for me. Glad in the end that I didnt go this route as I would have been pissed if I'd gone to all the effort and then had to hack the finished cowl as I did.
The guys building composite planes will probably have other ideas on how to do this but this is what worked for me. Good Luck.
Mike Wills
RV-4 N144MW
----- Original Message ----- From: "randy echtinaw" <rjechtinaw@toast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, August 31, 2008 7:37 AM
Subject: [FlyRotary] Composite instruction
I am eventually going to have to build a custom composite radiator/oil cooler pod ala P-51 and possibly a cowling if I cannot get aluminum to work around my RX-8 engine. I am looking for some good reference books on how to do this especially concerning making male molds - release agents - cloth to use - number of layers required - etc.??
My plane is wood/tube/fabric - thought I might as well use a little fiberglass too :))
My biggest concern is making them as light as possible but still having the needed strength and stiffness.
Thanks
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