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



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.


The Rotary Engine News Letter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
You Tube http://tinyurl.com/beqqxas
Copyright 1998-2014 All world wide rights reserved.