leaning below 5000

[Jose]

There was a discussion in my club about leaning the engine (of our
cherokees) below 5000 feet in cruise. This was prompted by the
observation in the manual that the engine should be leaned above 5000
feet at all times in cruise, and below 5000 feet at the pilot's
discrescion. So, how should the pilot discrede? The old timers seemed
to agree that:

1: at low power (say 65% or less) you can't hurt the engine by leaning
to peak EGT, but...

2: at high power (above that, including the 75% many like to fly at to
go fast) one should only lean if it's cold enough, and that the best
thing to do is run full rich if you're in doubt.

This runs counter to my understanding and practice. I lean (50 degrees
ROP) in cruise at all altitudes, including the ones where I can pick the
leaves off the trees, and I run 70-75% power. Running full rich is just
dumping a third of the fuel out the tailpipe.

Any opinions on Usenet about this?

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

[Peter Duniho]

"Jose" > wrote in message
. ..
> [...] The old timers seemed to agree that:
>
> 1: at low power (say 65% or less) you can't hurt the engine by leaning to
> peak EGT, but...
>
> 2: at high power (above that, including the 75% many like to fly at to go
> fast) one should only lean if it's cold enough, and that the best thing to
> do is run full rich if you're in doubt.
>
> This runs counter to my understanding and practice. I lean (50 degrees
> ROP) in cruise at all altitudes, including the ones where I can pick the
> leaves off the trees, and I run 70-75% power. Running full rich is just
> dumping a third of the fuel out the tailpipe.
>
> Any opinions on Usenet about this?

I lean at all altitudes. Yes, you need to ensure you don't lean at too high
a power setting, but I believe that even there, for the smaller,
lower-compression engines overleaning isn't going to cause any harm to the
engine, you just won't get smooth operation.

Of course, the airplane I'm flying most often -- my own -- has a TIT gauge
to allow for accurate leaning at any altitude. I'm of the opinion that with
a TIT or EGT gauge, leaning at any altitude with cruise power settings is
the correct operational standard. But if there's no TIT or EGT gauge, I
think one can still lean without harming the engine. If one is worried
about overleaning, then just err on the rich side. ANY leaning is going to
be much better than flying around at full rich all the time.

Of course, in all cases I restrict my comments to cruise power settings.
Unless the aircraft manual and/or engine manual says otherwise, I don't lean
during full-power operation (and I don't fly airplanes that have a "climb
power" setting, so I have no opinion on that :) ).

As far as your "old timers" #2, I don't understand the rationale behind the
"if it's cold enough" part. If anything, one would only lean in *warmer*
weather, as that translates to higher density altitudes. It sounds as
though the suggestion has to do with overheating the engine, but the primary
damage from improper leaning, as far as I know, is detonation. Cold weather
does nothing to prevent this.

Pete

[Mortimer Schnerd, RN]

Jose wrote:
> There was a discussion in my club about leaning the engine (of our
> cherokees) below 5000 feet in cruise. This was prompted by the
> observation in the manual that the engine should be leaned above 5000
> feet at all times in cruise, and below 5000 feet at the pilot's
> discrescion. So, how should the pilot discrede? The old timers seemed
> to agree that:


Generally speaking, I don't bother leaning if I'm staying at 2500 feet or lower.
At any altitude above, I will lean in cruise. The proof of inadequate leaning
is when you do your mag check during your runup... if it starts stumbling, it
wasn't leaned adequately. Since I'm reluctant to do mag checks at altitude,
this basically is a check of the aircraft's recent history rather than its
present condition.

For simple aircraft without reliable fuel management instrumentation, I
basically lean until the engine stumbles, then add gas to smooth it back out.
It seems to work.... nobody has ever complained that I was burning pistons or
exhaust valves. I'm pretty sure the neext guy to fly it doesn't have loaded
plugs from my flight.


--
Mortimer Schnerd, RN

[Stubby]

Jose wrote:
> There was a discussion in my club about leaning the engine (of our
> cherokees) below 5000 feet in cruise. This was prompted by the
> observation in the manual that the engine should be leaned above 5000
> feet at all times in cruise, and below 5000 feet at the pilot's
> discrescion. So, how should the pilot discrede? The old timers seemed
> to agree that:
>
> 1: at low power (say 65% or less) you can't hurt the engine by leaning
> to peak EGT, but...
>
> 2: at high power (above that, including the 75% many like to fly at to
> go fast) one should only lean if it's cold enough, and that the best
> thing to do is run full rich if you're in doubt.
>
> This runs counter to my understanding and practice. I lean (50 degrees
> ROP) in cruise at all altitudes, including the ones where I can pick the
> leaves off the trees, and I run 70-75% power. Running full rich is just
> dumping a third of the fuel out the tailpipe.

Either the Warrior II POH or my instructor said to lean above 3000. But
I couldn't find it after a quick look at an ARROW POH. Nonetheless, I
would follow the manual and if it didn't mention a specific procedure, I
wouldn't do it.

[[email protected]]

Juse
Density altitude is what the engine responds to. When I was crop
dusting in Louisiana at near sea level with humid temps near 90, we
always leaned out to best power. Engines all went full TBO without
problems.
Here in Mobile, AL, we operate near sea level and as a general rule
will lean on the ground to avoid fouled plugs, and again when flying
above 1500'msl. If I'm doing high power operations I'll lean towards
the slightly rich side of lean for valve cooling. Otherwise I'll go for
best lean mixture. With fuel prices going where they are it makes good
sense to go as lean as you can safely but not to the detriment of the
engine.and overhaul costs. I've taken many high performance engines to
past the TBO with no excessive oil or fuel consumption by paying
attention to the temperatures and conditions.
Over 50 years of safe general aviation flying.
Ol Shy & Bashful

[[email protected]]

Why would you be reluctant to do a mag check at altitude? Nothing wrong
with it and especially if you suspect a problem? If you are flying a
helicopter it certainly isn't recommended lest you find yourself on the
way to the ground in autorotation mode!!
CFII/RAM

[Dan Luke]

"Jose" wrote:
>
> This runs counter to my understanding and practice. I lean (50
> degrees ROP) in cruise at all altitudes, including the ones where I
> can pick the leaves off the trees, and I run 70-75% power. Running
> full rich is just dumping a third of the fuel out the tailpipe.

Agree. Running full rich is wasteful, usually.

I lean for taxi and all flight regimes except low density altitude
takeoffs. However, my airplane has an engine analyzer that allows me to
monitor CHT's, which I never allow to exceed 380 deg. F.

--
Dan
C172RG at BFM

[Bob Gardner]

Key Reprints from the Lycoming Flyer, in discussing leaning of
non-turbocharged direct-drive engines, says "For 5000 feet density altitude
and above, or high ambient temperatures, roughness or reduction of power may
occur at full rich mixture. The mixture may be adjusted to obtain smooth
engine operation."

Bob Gardner

"Jose" > wrote in message
. ..
> There was a discussion in my club about leaning the engine (of our
> cherokees) below 5000 feet in cruise. This was prompted by the
> observation in the manual that the engine should be leaned above 5000 feet
> at all times in cruise, and below 5000 feet at the pilot's discrescion.
> So, how should the pilot discrede? The old timers seemed to agree that:
>
> 1: at low power (say 65% or less) you can't hurt the engine by leaning to
> peak EGT, but...
>
> 2: at high power (above that, including the 75% many like to fly at to go
> fast) one should only lean if it's cold enough, and that the best thing to
> do is run full rich if you're in doubt.
>
> This runs counter to my understanding and practice. I lean (50 degrees
> ROP) in cruise at all altitudes, including the ones where I can pick the
> leaves off the trees, and I run 70-75% power. Running full rich is just
> dumping a third of the fuel out the tailpipe.
>
> Any opinions on Usenet about this?
>
> Jose
> --
> Money: what you need when you run out of brains.
> for Email, make the obvious change in the address.

[Thomas Borchert]

Jose,

> Any opinions on Usenet about this?
>

Uhm, in what cave have you been hiding? ;-)

You are right. Except for running at 50 ROP, which is a bad spot. Read
Deakin's columns on engine management at www.avweb.com. And learn to
use Google to search Usenet.

--
Thomas Borchert (EDDH)

[Scott Skylane]

Stubby wrote:

/snip/ Nonetheless, I
> would follow the manual and *if it didn't mention a specific procedure, I
> wouldn't do it*.

Stubby,

That is a ridiculous statement. No where in your manual does it state
how to make a right turn in the air, or how to close the baggage door.
There are acceptable techniques for everything, some that work better
than others. I can assure you that leaning an O-320, to some degree, at
any cruise power setting, at any density altitude, will not be harmful.
At lower density altitudes, and higher power settings, you don't want
to lean *a lot*, but say 100-150 degrees ROP would not hurt a thing.

Happy Flying!
Scott Skylane

[Gilbert Smith]

Thomas Borchert > wrote:

>Jose,
>
>> Any opinions on Usenet about this?
>>
>
>Uhm, in what cave have you been hiding? ;-)
>
>You are right. Except for running at 50 ROP, which is a bad spot. Read
>Deakin's columns on engine management at www.avweb.com. And learn to
>use Google to search Usenet.

When I did a biennial at Bishop, CA, the pre take-off procedure in the
club 152 was to lean the mixture for max revs at max throttle. The
difference to full rich was so marked that I am confident we would
never have got airborne, even off their long runway, at full rich.

My experience with a syndicate Robin 140 here in UK was that a climb
at full power started to go lumpy like a car on full choke above 4000
feet.

[[email protected]]

Jose,

If you read the POH and look at the power setting charts, it says
something along the lines of "with lean mixture".

Lean anytime you are in level flight, otherwise you cannot get the fuel
burn numbers in the POH. That includes if you are 500 feet MSL or
15,000 feet MSL.

At power settings above 65% lean to about 75 to 100 degrees F rich of
peak (50 degrees ROP is about the worst possible mixture setting - see
John Deakin's engine operation articles on AVweb www.avweb.com). At
65% power or less, you can lean any way you want, you cannot generate
enough heat or pressure to damage the engine through detonation. You
are not running a fuel injected engine, so you may or may not be able
to operate lean of peak without it running rough, although you can try
it without hurting anything. Sometimes running carb heat will stir
things up enough that you can run smoothly LOP.

The stuff in the POH about leaning below 5,000 or 3,000 or whatever,
has to do with leaning in the climb. It has lead to the aviation
falsehood that one should not lean in cruise below some magic altitude.


With avgas at $5 a gallon, it's utterly foolish not to lean in cruise
flight.

All the best,
Rick


Jose wrote:
> There was a discussion in my club about leaning the engine (of our
> cherokees) below 5000 feet in cruise. This was prompted by the
> observation in the manual that the engine should be leaned above 5000
> feet at all times in cruise, and below 5000 feet at the pilot's
> discrescion. So, how should the pilot discrede? The old timers seemed
> to agree that:
>
> 1: at low power (say 65% or less) you can't hurt the engine by leaning
> to peak EGT, but...
>
> 2: at high power (above that, including the 75% many like to fly at to
> go fast) one should only lean if it's cold enough, and that the best
> thing to do is run full rich if you're in doubt.
>
> This runs counter to my understanding and practice. I lean (50 degrees
> ROP) in cruise at all altitudes, including the ones where I can pick the
> leaves off the trees, and I run 70-75% power. Running full rich is just
> dumping a third of the fuel out the tailpipe.
>
> Any opinions on Usenet about this?
>
> Jose
> --
> Money: what you need when you run out of brains.
> for Email, make the obvious change in the address.