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Mike/ Randy,
I am building a Vision with composite core and although most cowls are thin fiberglass, they could be stiffer and lighter with a composite construction.
As the core foam is quite stiff, it will hold a shape, when heated, shaped then cooled, a thin section of core about 3/16 would be sufficient, with 2 layers of light glass (5 oz). Because the foam might distort when working on it in-situ, you could support it with some backing material - this would save making moulds. Once you have the outside glassed then take it off and glass the inside.
The Vision is make completely from this method.
This is how I will do my cowl.
Hope that helps.
George (down under)
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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