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

To save time, money and possible death or injury, buy a drive shaft from a
company that has worked out the problems for you.
http://www.acpt.com/Products/Composite-Driveshafts.aspx  is one to check.

Murry Rozansky



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.