Shutting down engine Question

[Lisa]

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 Mixture: 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?

[Peter Duniho]

"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 Mixture: 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

[Don Tuite]

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 Mixture: 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

[Hilton]

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

[Peter Duniho]

"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

[Hilton]

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 Mixture: 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

[Roger Long]

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

[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

[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)
>
>

[Dennis O'Connor]

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?
>

[Steve Robertson]

Lisa, the reason for a relatively high RPM for a few minutes just before
shutdown is to help prevent lead fouling of the spark plugs. Lycoming engines
tend to run too cold at low RPMs to keep the lead salts from avgas burned off
the plugs.

Best regards,

Steve Robertson
N4732J 1967 Beechcraft Musketeer (Lycoming IO-360)

Roger Long wrote:

> 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)
> >
> >

[Tony Cox]

"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 Mixture: Idle Cut-Off at that
> RPM to shut down.
>
> The POH says throttle full aft, then mixture cut-off to shut
> down.

I run at 1100 RPM just before shutdown, set the throttle
lock, and then pull the mixture back. This way, when I
restart on a cold day, I know that the engine will fire and
idle nicely at 700 RPM without overrevving or conking out.
This minimizes engine wear on startup.

Not sure I agree with posts (from Lycoming recommendation)
which suggest high RPM. Too much risk of damage to the
prop.

[Nathan Young]

On Wed, 31 Mar 2004 06:31:51 -0600, "Dan Luke"
> wrote:

>
>"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."

Does the Lycoming service letter explain what running at 1800RPM
accomplishes?

[Dan Luke]

"Nathan Young" wrote:
> Does the Lycoming service letter explain what running
> at 1800RPM accomplishes?

It is part of a series of recommendations to prevent plug fouling.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[Dan Luke]

"Roger Long" wrote:
> 1800 is better (with the leaning mentioned above) but you won't
> make any friends in the tiedowns using those RPMs.

Yes. The procedure must be used with consideration for others.

Since I started following Lycoming's procedure, I no longer have any
fouling problems.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[Roger Long]

Yes, you will have more prop wear. However, if you have an O-320 H2AD, the
most vulnerable thing in the engine are the camshaft and lifters. Idling
below 1000 is hard on them because of reduced oil splash and higher metal
pressures. Better a $500 prop overhaul than the $8000 camshaft replacement
we just went through.

--
Roger Long

Tony Cox > wrote in message
ink.net...
> "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 Mixture: Idle Cut-Off at that
> > RPM to shut down.
> >
> > The POH says throttle full aft, then mixture cut-off to shut
> > down.
>
> I run at 1100 RPM just before shutdown, set the throttle
> lock, and then pull the mixture back. This way, when I
> restart on a cold day, I know that the engine will fire and
> idle nicely at 700 RPM without overrevving or conking out.
> This minimizes engine wear on startup.
>
> Not sure I agree with posts (from Lycoming recommendation)
> which suggest high RPM. Too much risk of damage to the
> prop.
>
>

[Peter Duniho]

"Hilton" > wrote in message
ink.net...
> [...]
> So the CFI wanted Lisa to shutdown "...at that RPM" and this does not
> "...clearly imply to reduce RPM".

It does to me. "A few moments before" could even be reasonably interpreted
as "run the engine at 1000 RPM for any period of time, but make sure there
are a few moments between reducing engine speed and shutdown".

> Hope that clarifies it.

I think you're pretty foolish to think that the original instruction was not
ambiguous. The fact that we're even having this discussion proves that it
is.

Pete

[John Galban]

Don Tuite > wrote in message >...
>
> 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,

Sounds like you have a fuel leak into the manifold. Pulling the
mixture to cutoff should, well, cut off the fuel flow. This could be
something in your carb, or might be a leak in your primer system.
Either way, it shouldn't continue to run after you've cut off the fuel
supply. That's an indication of a problem in the fuel system.

John Galban=====>N4BQ (PA28-180)

[Corky Scott]

On Wed, 31 Mar 2004 10:25:02 GMT, "Roger Long"
m> wrote:

>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.

>Roger Long

Roger, when you say "clear a mag" do you mean clearing plugs? Because
it isn't the mag that fouls, is it? Isn't it the plugs?

Thanks, Corky Scott

[Roger Long]

Yes, it is the plugs. Since you switch a mag off people often say clearing
a mag even though it's sort of like saying "digging a shovel".

Mags do foul for very different reasons but the only way to clear them is
with a wallet.

--
Roger Long
>
> Roger, when you say "clear a mag" do you mean clearing plugs? Because
> it isn't the mag that fouls, is it? Isn't it the plugs?
>
> Thanks, Corky Scott
>

[Frank]

John Galban wrote:

> Don Tuite > wrote in message
> >...
>>
>> 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,
>
> Sounds like you have a fuel leak into the manifold. Pulling the
> mixture to cutoff should, well, cut off the fuel flow. This could be
> something in your carb, or might be a leak in your primer system.
> Either way, it shouldn't continue to run after you've cut off the fuel
> supply. That's an indication of a problem in the fuel system.
>
> John Galban=====>N4BQ (PA28-180)

Concur. Our O-300 has never dieseled.

We do have a problem with fouled bottom plugs though. I never thought it was
related to shutdown procedure until this thread, but now I will consider
it. Always thought it was too much priming.


--
Frank....H

[Bob Martin]

"Dennis O'Connor" > wrote in message >...
> 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

We run an O-360 with an Ellison TBI... the plugs tend to foul very
quickly, even if the engine is leaned during taxi. Therefore, our
shutdown procedure is to run up to about 1300 rpm and pull the mixture
out to right about peak. We let it run like that for 20-30 seconds,
then throttle back to about 800. Mixture is chopped to cutoff, then
we push the throttle up. As soon as it starts to speed up, we cut the
ignition off.

This process results in a clean start for next time, and the least
amount of shaking we've managed to accomplish without the engine
deciding to spin backwards for a few revs.

[Robert M. Gary]

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 Mixture: 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?

The idle at 1,000 RPM sure helps in my IO-360 engine. My engine hot
starts great, and cold starts great, but is very hard to warm start.
Idling at 1,000 RPM (or 1,200 RPM) for a couple minutes seems to make
a huge difference.

-Robert

[Robert M. Gary]

"Dan Luke" > wrote in message >...
> "Roger Long" wrote:
> > 1800 is better (with the leaning mentioned above) but you won't
> > make any friends in the tiedowns using those RPMs.
>
> Yes. The procedure must be used with consideration for others.
>
> Since I started following Lycoming's procedure, I no longer have any
> fouling problems.

What made a HUGE difference for me was just leaning in taxi. If you
increase throttle and the RPM increases during taxi you have the
mixture set too rich. Before I realized this I had to have my IO-360's
plugs cleans twice in 6 months. Now I don't think about it until
annual.

-Robert

[John Galban]

Nathan Young > wrote in message >...
>
> Does the Lycoming service letter explain what running at 1800RPM
> accomplishes?

I'd be willing to guess that the purpose is to increase combustion
temperatures and burn off any lead deposits. At 1000 rpm my EGT will
barely move off the peg with max leaning. At 1800, it's good and hot.

John Galban=====>N4BQ (PA28-180)

[Dan Luke]

"Robert M. Gary" wrote:
> What made a HUGE difference for me was just leaning in taxi.

Ditto.

> If you increase throttle and the RPM increases during taxi you
> have the mixture set too rich.

Amen. (Two mechanics have told me I will "burn the valves" by doing
this!)

> Before I realized this I had to have my IO-360's plugs cleans
> twice in 6 months. Now I don't think about it until annual.

Yep.
--
Dan
C172RG at BFM
(remove pants to reply by email)

[Dan Thomas]

When we used to run Cessna 150s, we often found them hard to start.
Then we noticed that just after a flight, or lengthy runup before
inspection, that oil would dribble out of the bottom plug holes when
we pulled the plugs. These engines tend to foul the bottom plugs at
idle for some reason, and we instituted a 1700 RPM runup prior to
shutdown to clear them. No more hard starts or fouled plugs.
We have few fouling problems with the Lycs, other than with too
much circuit work.

Dan