Perry,
I choose steel for the prop hub sleeve for several reasons. The coeff
of thermal expansion is lower than aluminum and epoxy bonds to it
better than aluminum. It is also closer to carbon epoxy on
the atomic scale so galvanic corrosion should be less I think.
The area of the coupling in contact with the epoxy/carbon
fiber is about 19 square inches not counting the sign wave
surface. That is just a simple calculation based on the OD
and length of the sleeve. If the tensile load is 20,000 pounds
the shear load between the carbon fiber/epoxy and the steel
would be about 1000 psi which is in the range of epoxy adhesive.
The sine wave surface should help as it should act as a mechanical
lock not to mention the increased bond surface area.

I suggest putting a peel ply over the hub area when laying up
the first surface. Than place some plastic sheeting over that and
wrap large rubber bands around the hub sleeve to positively
keep the carbon/epoxy in contact with the sine wave surface 
of the coupling until the top cures. After the bottom is laid
up the same thing can be done. When the bottom is cured the
peel ply can be removed and a tensile wrap of continuos fibers
can be applied over the steel hub to lock everything together.

Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org