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 power/slip
   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


   The trickiest part are the end fittings for the couplings.
   Shall they be composite or aluminum?
   Gentleman, this is a good discussion.
   Luke Wings.

   Chrome molly is more fatigue resistant than aluminum.

   Paul Lamar



   Group, if you use carbon fiber on an aluminum shaft you will get
   galvanic corrosion. You MUST use a fiberglass layer first or you will
   get delamination later.
   Bill Jepson



It seems the OP was looking at fairly short sections of shaft.
Why not just go and buy carbon driveshafts at the breakers?
Or am I missing something?

Erik in Oz.



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