Engine Shutdown Question...

HeyEng

NAHB Doesn't Give a Crap
So I can tell you ALL sorts of stuff about heavy jet systems, but I am still learning quite a bit about piston stuff.

I was reading a Lycoming reprint about engine RPMs/leaning/etc and came across this:

Prior to the 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.

I am curious about the 1800 for 15-20 seconds...what is the purpose of this? I have never heard about it and am not sure why?
 

HeyEng

NAHB Doesn't Give a Crap
Doesn't say, just a general "overview" of their engines. There was a separate section on the TC models.
 

scooter2525

Very well Member
It seems on some engines, if you leave them at 1000 rpm and shut down with the mixtures, some fuel will still burn and the engine will chug along for a bit, then shut down. I've found that pulling the mixtures then going full throttle will resolve this situation and the engine doesn't spool up either... maybe lycoming was thinking along those lines.
 

Lee D

Well-Known Member
Just speculation, but maybe they are trying to avoid fouled spark plugs and gunky cylinders from taxing at idle speeds. Have nearly 2000 hours of pistion, though it has been awhile I don't remember ever seeing a shut down like that in any thing I flew. Even turbocharged stuff just needed to cool down at idle. This for a particular engine or a blanket recomendaton?
 

B767Driver

New Member
So I can tell you ALL sorts of stuff about heavy jet systems, but I am still learning quite a bit about piston stuff.

I was reading a Lycoming reprint about engine RPMs/leaning/etc and came across this:

Prior to the 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.

I am curious about the 1800 for 15-20 seconds...what is the purpose of this? I have never heard about it and am not sure why?

Typically to minimize fouled spark plugs.
 

redrumracer

Well-Known Member
It says to do that in our check list for the warrior but we dont, it is supposed to prevent fouling of the spark plugs like b767driver said.
 

tgrayson

New Member
It says to do that in our check list for the warrior but we dont, it is supposed to prevent fouling of the spark plugs like b767driver said.
Bringing up the RPM to 1800 on the ramp is a poor idea. And it's completely unnecessary to prevent fouling the plugs. Just lean the engine during taxi.
 

tgrayson

New Member
I agree about not running at such a high RPM on the ramp. Here is the link for the article. It is on page 16, left column, sentence #4. I also assumed that leaning during taxi would suffice.

http://www.lycoming.textron.com/support/tips-advice/key-reprints/pdfs/Key General.pdf

The article appears to be mainly focusing its recommendations for the 80/87 engines, although at the very end it throws in that these are good for all engines. However, the recommendations don't appear in my O-360 Engine Operators Guide, so perhaps they didn't feel that strongly about it. ;)
 

matt152

Well-Known Member
Typically to minimize fouled spark plugs.
:yeahthat:

If you have been running at 1000 RPM for a few minutes, the temp may not be hot enough to burn off the deposits that form on the spark plugs. By increasing the temperature in the combustion chamber (i.e. running for a few seconds at a higher RPM) the higher temperature activates the lead scavenging agents in the 100LL. They get vaporized and blown out the exhaust, hopefully making the next start easier.

Plug fouling was a huge problem in the early Lycoming O-235 before they redesigned the combustion chamber and introduced some new spark plugs which are less susceptible to lead fouling.
 

matt152

Well-Known Member
Bringing up the RPM to 1800 on the ramp is a poor idea. And it's completely unnecessary to prevent fouling the plugs. Just lean the engine during taxi.
Yes, this is the best procedure. Prevents the problem rather than having to fix it later.
 

trafficinsight

Well-Known Member
I wish I knew who invented leaning for taxi so that I could go back in time and prevent it.

It's one of those things that's been perpetuated through endless strings of flight instructors and at best does nothing, at worst damages engines.

The best thing you can do to slow lead fouling is lean properly in flight, carbon fouling just happens whether you lean or not, and burns off just as easily. If you fly a 152, there's just nothing you can do about it ;)

Heresy, they cry.
 

trafficinsight

Well-Known Member
Source?

-mini
I have no source, idle mixture is set rich for cooling purposes though, and that "lean 1" for taxi" thing does little to nothing to the actual mixture below about 1400rpm. Next time you start up see how far you actually have to pull the mixture knob out to get an rpm drop ;)

The bottom line is that no engine or airframe manufacturer that I know of recommends the practice and yet somehow it made it onto everyone's checklists ;)

anyway I'm not trying to change anyone's mind about it, and I think the planets would probably have to align on a pretty hot day to do actual damage... I just don't believe that leaning for taxi does much of anything.
 

Hacker15e

Dunning–Kruger Observer
I've never even heard of touching the mixture during ground operations, except to shut the engine down.

That sure wasn't ever taught to me when I got my Private back in '95.
 

matt152

Well-Known Member
I wish I knew who invented leaning for taxi so that I could go back in time and prevent it.

It's one of those things that's been perpetuated through endless strings of flight instructors and at best does nothing, at worst damages engines.

The best thing you can do to slow lead fouling is lean properly in flight, carbon fouling just happens whether you lean or not, and burns off just as easily. If you fly a 152, there's just nothing you can do about it ;)

Heresy, they cry.
There is no way that leaning for taxi can damage an engine. If you forget to go full rich prior to takeoff, and you have properly leaned, the engine will stumble as you apply full power. On the other hand:

If you have done something like pull the mixture back an inch or two and then forget to go full rich for takeoff... well then yes bad things can happen.

If you are going to lean for taxi, really pull that knob back.

Lead fouling is generally not a problem in cruise flight since the engine is up at cruise power and leaned. It's those long, low power, full rich mixture descents that cause problems.
 
R

Roger, Roger

Guest
Leaning for a 20-50 RPM rise (at 1000 RPM) is pretty standard at my school. I tend to lean really aggressively, and when I've been running the mixture I've never experienced a fouled plug. I've had 2 or 3 foul when students forgot to lean.

There is no way that leaning for taxi can damage an engine. If you forget to go full rich prior to takeoff, and you have properly leaned, the engine will stumble as you apply full power.
:yeahthat:
Question for the other guy-how exactly does leaning in taxi damage an engine? You are not producing anywhere near enough power to damage the engine, no matter what the mixture setting is. Unless you habitually taxi at 85% power. Watch the CHTs-they will stay well cool of any danger zone no matter how you lean on taxi.
 

Orange Anchor

New Member
anyway I'm not trying to change anyone's mind about it, and I think the planets would probably have to align on a pretty hot day to do actual damage... I just don't believe that leaning for taxi does much of anything.
If I don't aggressively lean during taxi in my Swift (HIO-360 engine), I can guarantee I will see more than a 150rpm drop on a mag check. Without leaning the mixture, my fowl will be fouled. ;)
 
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