Hi Paul. I am revisiting the long drive shaft for a pusher design.
With the progress made on composite drive shaft, is the option of
long and light prop shaft becoming more of a reality now? I saw a
lot of automotive carbon shafts on the market now for very decent
prices. Could a simpler design with rubber couplings instead of
powerslip clutch be made to work without outlandish development cost
and headache? I would appreciate your thought. Luke F Wings.
How long?
I would use a minimum of 3.5 inch diameter aluminum tube. Cut the
wall thickness on a lathe to .062" to save weight. Then anodize it
so epoxy will stick . diagonally wrap carbon fiber to a total
thickness of .125 to .2 inch.
If not too long get a stock RX8 carbon drive shaft from a junk yard.
Yes rubber couplings are the way to go.
Paul Lamar
Will anodizing be as good as the process used on grumman GA? THANKS.
L F WINGS.
I don't know what they used on that airplane. You can buy a kit in
West Marine to treat aluminum for epoxy bonding.
How long is the prop shaft?
Paul Lamar
Isn't there a vibration issue with anodized parts. There was an award
winning Experimental helicopter where the builder had anodized a lot
of parts for a blingier look, including I think the drive shaft.
After about 60 hours the blingy part failed catastrophically causing
a complete wreck of the machine. IIRC the anodizing process
introduces microscopic stress risers. Feel free to correct me if
I've got this all buggered up.
John Gibbons
The aluminum tube is just a male mold for the carbon fiber.
BTW when you have a high modules of elasticity material (carbon)
sharing the load with a low modulus of elasticity material
(aluminum) the high modules material takes most of the load.
Paul Lamar
But when you attempt to adhesively bond two materials with widely
different Elastic Modulii you are asking for bond line failures -
Ask me how I know this Roland Friestad
I agree but not only that. When thermal expansion coefficients differ
you can also get bond line failures.
Again we are only using it as a male mold. The carbon will take all
the load. It is too hard to remove the plug so it can be left in
there. If the bond fails it will act like a torsional damper :)
Paul Lamar
It would be better to use a tube of the correct diameter and slice it
accurately longitudinally and use it as an OUTER mould. Use pre-preg
carbon and lay it up around a partially inflated tubular balloon.
Clamp the outer mould in place and inflate the balloon whilst warming
the outer mould with a heat gun. When cured remove outer mould and
balloon and you should have a perfect carbon tube. Chris in NZ.
Chris. Have you tried to cure pre-preg with a heat gun before? I
thought it needs very accurate temperature and time control. Am I
correct? Thanks. Luke Wings.
Hi Paul He can look at my aluminum plate damper set up to attach his
carbon fiber shaftting
JEAN PRUDHOMME
What the Gossemer Condor did was wrap an Al tube with carbon-fiber/resin,
cure it, then DISSOLVE out the Aluminum with NaOH.
Bill Schertz
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