Re: More 1/48 Stuff in brief - MS-L

John P. Roll (
Sat, 16 Sep 95 19:46:09 -0500

In message <> writes:
<<Stuff Deleted>>

> One question for the lists engine experts. Are those copper pipes (flat
> brass, as noted in Marks review) curving into the cylinder heads REALLY
> exhausts. I thought they were intake manifolds, (fuel air mix into
> cylinder) and that the cutout, or cutaway section beneath the engine on
> many rotary powered a/c was to allow the exhaust free flow direct from
> exhaust ports on each head. I AM NOT an expert on this, I just want a
> laymans explanation.

Hi All!

I don't believe that those copper pipes are exhausts. In fact for a Gnome, I
don't believe that there should be any induction or exhaust piping. For a Le
Rhone, they are probably induction pipes. However, I haven't seen the kit or
the pipes and can't comment directly.

The Gnome used a rather um, interesting, method of getting the mixture to the
combustion chamber. Like most rotaries, the Gnome had a carburetor attached to
the end of the fixed hollow crankshaft. The fuel and air moved from the
crankshaft and into the whirling crankcase along with the castor oil. The very
rich mixture was then introduced to the combustion chamber through an intake
valve in the piston crown. This valve was opened by centripetal (centrifugal)
force. The exhaust valve was held open long enough to admit some additional air
which brought the mixture more or less to the appropriate ratio. The
head-mounted exhaust valve was opened in a relatively standard fashion. A
pushrod was actuated from a front-mounted cam ring which opened the exhaust
valve directly to the atmosphere. Hence, on the Gnome, there was no intake or
exhaust piping visible externally.

An interesting variation - which would be pretty-much externally
indistinguishable except to a very careful observer - was the monosoupape or
mono-valve. This engine dispensed with the piston-mounted intake valve and
replaced it with a series of internal intake ports around the base of the
cylinder - not unlike many two-stroke engines. When uncovered at the bottom of
the stroke, these ports opened the cylinder to the crankcase. This improved the
greatest weakness of the basic Gnome design and resulted in a much simpler
engine. And, if all went well, the low exhaust pressure in the cylinder (the
exhaust valve opened very early) by the time the piston uncovered the intake
ports prevented the hot exhaust gases from contaminating the fresh mixture in
the crankcase - and just perhaps igniting it and blowing the crankcase apart!

The Le Rhone was a bit more 'conventional' to our eyes. In the Le Rhone, the
mixture entered a spinning chamber atached to the back of the crankcase and then
to a set of "attractive polished copper pipes" (which are, I believe the parts
in the kit) which led to an intake port and valve in the cylinder head. There
were two poppet valves in the head - exhaust and intake. Both were, however,
operated by the same pushrod (actually it was a push/pull rod) and rocker arm.
When the rocker arm was pulled-down by the rod, it actuated the intake valve.
When the rocker arm was pushed-up by the rod, it actuated the exhaust valve.
the exhaust was vented directly from the valve to the atmosphere. There was no
manifold or pipe of any kind.

This is probably much more than you ever wanted to know - but it explains why I
believe those parts are very probably intended only for the Le Rhone and that
they are not exhaust pipes, but rather induction piping.

Most of the information here came from a very interesting book called "The
history of Aircraft Piston Engines" by Herschel Smith.

Happy Modeling!
John Roll