John wrote:
On Thu, 01 Apr 2010 18:24:44 -0700, Tim Wescott
wrote:

http://www.metalworking.com/dropbox/. Search on "cox_head".

Just finished running it -- ran through a whole tank of 10% nitro fuel.
I couldn't do that with the stock head; I think it just didn't have
enough compression. This head has stupid-high compression* -- it runs
better with a stack of three head gaskets than it does with none (I need
to try it with one or two).

_And_ it starts with a ni-starter -- Cox glow heads _demand_ a good dry
cell battery, and just sneer at you if you try to give them 1.2V from a
nicad.

* Note that it was built with more compression than the drawing
indicates, and wider fin spacing.


Congratulation. I don't know which model Cox you have, I used to fly
one of the tankless ones in 1/2A speed, back when they were the usual
class 1/2 A selection. Used to win a trophy with the little thing
every one in a while.
They were also commonly used in class 1/2A free flight in those days.

Oops -- I left that out.

Its a reed-valve engine, built from a bucket-o-engines with a Babe-bee
case and tank, but with a two-bypass cylinder as often came on the
'product' engines that went into the ready-to-fly airplanes.

There were two rotary-valve engines: the Medallion (sport) and the
Tee-Dee (competition) engine. The Medallion had a red plastic venturi,
while the Tee-Dee had an aluminum one. I never had the bucks for such
fancy things, so I have no personal experience with flying them. My
understanding is that the Tee-Dee was harder to handle, and needed
pressure feed (usually with a bladder tank), but would go like heck.

Unless you had a product engine (fuel nipple and needle valve on a big
plastic block in the back) you had either a Medallion or a Tee-Dee, you
lucky dog.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com