Shutting down engine Question

Perhaps this doesn't matter much for a non-turbocharged engine,
but an instructor says that it is best to idle the engine at
1,000 RPM for a few moments before Mixtu Idle Cut-Off at that
RPM to shut down.

The POH says throttle full aft, then mixture cut-off to shut
down.

Which is best?

"Lisa" wrote in message ...
Perhaps this doesn't matter much for a non-turbocharged engine,
but an instructor says that it is best to idle the engine at
1,000 RPM for a few moments before Mixtu Idle Cut-Off at that
RPM to shut down.

I doubt 1000 RPM is an idle setting for most piston aircraft engines.
Probably best to avoid confusing the issue by not using the word "idle" when
you don't really mean having the throttle set to idle.

With that out of the way, I don't see any compelling reason to run a
non-turbo engine prior to shutdown. I suppose that if you also lean the
mixture, you might get rid of some plug fouling, but if you're having
trouble with plug fouling, you can better address the issue operationally by
making sure the engine is leaned during taxi.

Obviously, with a turbocharger, allowing the engine to run prior to shutdown
is a good way to help circulate engine oil through the turbo and allow it to
cool down more gradually, and without cooking the oil. AFAIK, whether you
do this at 1000 RPM or at idle is less important than whether you do it at
all.

But with a non-turbo engine, I don't see why idling or running the engine at
1000 RPM would be beneficial, as a general rule of thumb (allowing for the
possibility of some particular instance where it might be useful).

What reason does this instructor to which you refer give for running the
engine at 1000 RPM prior to shutdown? Also, what does "a few moments" mean?
To me, that's less than five seconds, which I can't imagine would make a
difference in any case.

Pete

On Tue, 30 Mar 2004 21:38:31 -0500, Lisa wrote:

Perhaps this doesn't matter much for a non-turbocharged engine,
but an instructor says that it is best to idle the engine at
1,000 RPM for a few moments before Mixtu Idle Cut-Off at that
RPM to shut down.

The POH says throttle full aft, then mixture cut-off to shut
down.

Which is best?

On hot days, the O-300 in the 'Hawk tends to diesel on after you pull
the mixture. Opening the throttle a little makes it stop.

Don

Peter Duniho wrote:

What reason does this instructor to which you refer give for running the
engine at 1000 RPM prior to shutdown? Also, what does "a few moments"
mean?
To me, that's less than five seconds, which I can't imagine would make a
difference in any case.

Some engines seem to shake a whole lot less on shutdown when set to 1000
RPM.

Hilton

"Hilton" wrote in message
ink.net...
Some engines seem to shake a whole lot less on shutdown when set to 1000
RPM.

Then the instruction should be to *set* engine power 1000 RPM before
shutting down.

Telling a pilot to run the engine at 1000 RPM before shutting down is
ambiguous and could (probably will) lead to the pilot simply reducing RPM
before pulling the mixture, after running the engine at 1000 RPM.
Especially if the instruction is to run the engine at 1000 RPM "for a few
moments" (which would clearly imply to reduce RPM again before actually
shutting the engine down).

Pete

Peter Duniho wrote:
Hilton wrote:
Some engines seem to shake a whole lot less on shutdown when set to 1000
RPM.

Then the instruction should be to *set* engine power 1000 RPM before
shutting down.

Telling a pilot to run the engine at 1000 RPM before shutting down is
ambiguous and could (probably will) lead to the pilot simply reducing RPM
before pulling the mixture, after running the engine at 1000 RPM.
Especially if the instruction is to run the engine at 1000 RPM "for a few
moments" (which would clearly imply to reduce RPM again before actually
shutting the engine down).

Quoting the full sentence: "...an instructor says that it is best to idle
the engine at
1,000 RPM for a few moments before Mixtu Idle Cut-Off at that
RPM to shut down."

So the CFI wanted Lisa to shutdown "...at that RPM" and this does not
"...clearly imply to reduce RPM".

Hope that clarifies it.

Hilton


Hilton

This is the procedure we use on our O-320 and have had noticeably smoother
and quicker starts since we started it:

RPM - 1200
Lean for maximum RPM rise. (Don't worry, no amount of leaning will hurt the
engine at this low power)
Run 20 seconds
Throttle - Quickly to Idle
Mixture - Idle Cut Off
Switches - OFF

Leaning for all ground operations is vital to keep the mags clear on this
engine. On startup and after exiting the active runway, set RPM to 1000 and
lean slowly for maximum RPM rise. This will often be about 100. Lean
slightly past until RPM just starts to fall. If the engine runs a hair
rough, that's OK. It will be lean enough that it will start to stumble and
quit if you try to run it faster than about 1300. This means you can't
accidentally take off with it leaned.

Since we started doing this, I have only had to clear a mag a couple of
times in two years.

Speaking of idle. Lubrication is poor on startup and especially critical in
this engine. The parts most susceptible to damage are the camshaft and
lifters. It is counter intuitive but, due to the valve train dynamics, the
stresses become less the faster the engine turns. Running at minimum idle
while it "warms up" actually is harder on the parts most likely to wear.
As soon as the oil pressure gets into the green, set the RPM to 1000 and
lean.

Keep the RPM at 1100 on the ground whenever this will not require rolling
use of the brakes. RPM over 1000 also gets combustion temperature high
enough to scavenge lead deposits and reduce plug fouling.

--
Roger Long

Take a look at our club operations manual for more on how we operate our
plane:

http://baldeagleflyingclub.org/Manual.htm

There is a section on running it lean of peak. Not all engines will do
this, even within the same make and model. Ours won't do it in all weather
conditions. When it works, its great though.

--
Roger Long

1800 is better (with the leaning mentioned above) but you won't make any
friends in the tiedowns using those RPMs. We've found the 1200 to be
sufficient.

--
Roger Long

Dan Luke wrote in message
...

"Lisa" wrote:
The POH says throttle full aft, then mixture cut-off to shut
down.

Which is best?


According to Lycoming Service Letter L192:

"Prior to engine shut-down the engine speed should be maintained between
1000 and 1200 RPM until the operating temperatures have stabilized. At
this time the engine speed should be increased to approximately 1800 RPM
for 15 to 20 seconds, then reduced to 1000 to 1200 RPM and shut-down
immediately using the mixture control."
--
Dan
C172RG at BFM
(remove pants to reply by email)

Lotsa "depends"... One of the benefits of owning a plane, or flying the
same one most of the time, is that you get to know the idiosyncrasies... On
mine, from experience I know the proper rpm for mixture cutoff that gives
the smoothest shutdown, and 99 times out of a 100 results in both props
stopping at the same angle... Just a game I play for my own satisfaction...
There is also the method of going to 1800-2000 rpm, pulling the mixture as
lean as it will go without shutting down, wait 10-15 seconds, then gently
close the throttle to idle, wait until the engine slows, then fully cut the
mixture... This helps to clear lead fouling off the plugs...
denny

"Lisa" wrote in message Which is best?