I am working on the design of the carbon fiber six inch diameter tube spar.

The spar is the heaviest part of the aircraft structure so it pays
to make it out of expensive carbon. The skins of course can be glass
or carbon depending how much money you want to spend.


Paul Lamar

Paul,
I am sure you are aware of the method that Paul McCready used to make the
carbon fiber spars for the Gossemer Albatross:

He used Aluminum irrigation tubing (~3-4" D) and laid the carbon fiber
up on
the tubing, then dissolved the Aluminum out with KOH.
Bill Schertz

I was called in as an aerodynamic consultant on the one that eventually
won the
Kremer prize by Jack Lambie round about 1976 or 1977. My girl friend
Rhonda and I drove up
to the valley to have a look. I was surprise to see a propeller about 4
or 5 feet in diameter
made from two model airplane wings and wire braced. I suggested a larger
diameter prop
not wire braced and further geared down. They did that and went on to
win the $50,000 prize :-)

I was not aware he built the spar that way. I was thinking of using a
metal or plastic
tube covered with several layers of garbage bag or other thin plastic
material cut in long strips.
After the epoxy is cured the spar can be slipped off the tube. I have
done that
many times on shorter composite tubes. Sometimes the strips can just be
pulled
out from between the surfaces. That gives enough clearance to remove the
spar from the tube.

How's the Kiss Cruiser doing? Do you like living up  there in the US
bush? :-)

Paul Lamar

Paul.
If you're going to lay up a tube spar over an aluminum mandrel, why make it
round?  Just  bend two C channels out of aluminum and put them together to
make a box spar that is much more efficient, structurally.  I like to cover
things like this with Teflon tape.  Another thing that you can do insert a
tube in the hollow mandrel made of bagging film then vacuum bag to the ends
of the tube; this way, the spar is vacuum bagged without distorting the
aluminum mandrel which can be fairly thin gauge.  This technique also makes
it easy to make a tapered spar.

Steve Brazil

That would be a good plan for a tapered wing. It would also allow removing
the aluminum male mold  from inside the carbon spar.

Paul Lamar

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