Extension shaft - Help! 7

[CC9]

I need to extend the shaft on a 25cc methanol engine a distance of 600 mm. The shaft has to be light and strong (chromolly tube??) about 20mm o.d. and joined at either end by some form of universal coupling capable of 8000 r.p.m (hellical joint??)and will be turning an 500 cm dia.propellor so the torque load will be fairly high. It is for use in the rear of a large model aircraft, so being light-weight is of great importance. Any suggestions on the best cost effective method of achieving this ?

 

[unclesyd]

There are two other approaches that one might take and that is thin wall Titanium Tube (6-4 Ti) or the type we used on very high speed drives.
We used a small diameter very high strength, at the time tool steel rod (T15), to drive high speed (60-70,000 rpm) pieces of equipment. If my recollection mechanism is working the devices were about .072" dia 14" long. I don't recall the power requirements, but were not insignificant.

There several people that make thin wall Ti tube especially for shafting. We looked at these for some of the high speed development work. I don't know the status of the project with straight Ti but they are using a Ti+CF composite shaft on one machine.

I'm trying to find my data on the Carbon Fiber Shafts that we used early on. MikeHalloran may be able to help as the same company made the shafts for Spanish Royal Yacht (big turbine driven speed boat with Z-Drives) given to the Crown Price by King of Saudi Arabia. The one property of the CF shafts was we took advantage of was being able to use longer shafts without the need for intermediate support.

 

[MikeHalloran]

CC9, I don't know if they're made commercially as small as what you need, but they're simple enough to make. For pictures, see:

http://www.lovejoy-inc.com/disccouplings.htm

http://www.couplingcorp.com/

http://www.imw.tu-clausthal.de/inhalte/forschung/publikationen/bereich_a/2000/pdf/2000_02.pdf

.. or try this search:

http://www.google.com/search?hl=en&lr=&q="flexible+disc"+"shaft+coupling"&btnG=Search

Lovejoy is the price and volume leader in a lot of coupling markets.

I do have pictures of some high-zoot boats, but mostly of exhaust pipes, not driveshafts. I'm not familiar with the Crown Prince's boat. Or maybe I am; we may have built parts for her. If I do my job right, I don't get to set foot on the boat, or meet the owner, or learn the boat's name.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA