Bill Freeman wrote:

Paul,

I would suggest good old wood for the prop core.  The
high damping of the wood core is very beneficial.  Perhaps
the syntactic epoxy core would also have good damping, but
wood is definitely good.  Also, relatively easy to carve.

If you carve the wood "core" to have the exterior contour
that you want in the final prop, then remove enough on the
lifting surface (uniformly) to apply your carbon, you'll
be very close to final shape.  Uniformly sand away the rear
surface, probably completely eliminating the wood in the outboard
3-4 inches or more.  The tips should be about 6% thickness
and pure carbon.  I recommend a ply schedule with alternating
plus and minus 30 deg from the long axis of the blades for
a good combination of torsional and bending stiffness.

Perry Mick wrote:

I didn't trust foam or "micro" as we Rutaners call it (micro-
ballons + epoxy) so I used a wood core on my carbon prop.  But
it's hardly a core at all because the blades are so thin, it really
just helped to form the forward surface camber.  But thought about
trying to use micro in this case since this is not supposed to be
a flying example - to prove out the concept.

The order of construction was: laid up the flat backside in a mold,
then glued thin strips of wood on top of that and shaped the forward
camber with templates, then put carbon over that to complete.

I've never tried to wrap carbon into a tight radius, so not sure
if you can even attempt to wrap the leading edges near the tip.
Avoiding a butt joint on the tip LE would be good if possible.

My prop is solid carbon at the tip.  I put one ply of fine-weave
BID glass around the leading edge, but I think two or more plies
would be better.


--
Perry J. Mick
Mick Duckt N7XR
http://www.mickaircraft.com/duckt.htm

 
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