John wrote:
On Sun, 04 Apr 2010 11:43:33 -0700, Tim Wescott
wrote:
John wrote:
On Sat, 03 Apr 2010 15:30:07 -0700, Tim Wescott
wrote:
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.
I don't really remember, it was a LONG time ago. But from what I think
I remember all the Cox of that time were reed valve engines. All the
competition engines were two bypass, I think. I seem to remember that
some had a integral fuel tank and some were flat backs. I don't
remember how the timer worked but seem to remember that the freeflight
engines could be tanked engines and the speed guys had to run around
and locate a flat back version.There were also some baby Cox, or some
such name, that had a plastic tank, I seem to remember that weren't
very popular. To be frank I only flew 1/2A speed because if you could
build anything that flew even reasonably quick it was almost a free
trophy.
A and B speed were my specialties and I flew 1/2 A and C more because
that is what the other guys did, rather then because I really liked
it. A full bore 0.60 cu.in. engine in even a mediocre design is sort
of scary :-)
I see you talking about batteries. In those days everyone had two
lantern batteries, wired in parallel, sat in the end of the flight
box. worked with everything. I seem to remember that the Cox could
burn out the '"glowplug" if you had a brand new set of batteries. Kind
of irksome as heads cost more then glow plugs.
Cheers,
John D.
(jdslocombatgmail)
Unless it was a Really Long Time Ago (before 1961) the "flat back"
engines were front rotary valve. Of course you don't have to believe it
-- there's a web page on Cox engines:
http://en.wikipedia.org/wiki/Cox_engine. Search down to "Tee Dee" or
"Medallion".
Well, it would have been about '55 - '59 during my first tour in
Japan. From looking at the Wiki you reference the engines must have
been a Thermal Hopper as there is nothing further down the page that
looks anything like what we used.
The front induction engines came along later and as I remember weren't
particularly highly rated.
My understanding of the Tee Dee is that it was a very strong engine for
its day, but because it was an all-out performance engine it was a bear
to handle. I remember when I was a kid, _every_ competition 1/2A design
that appeared in the magazines had a Cox Tee Dee, without exception.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com