LOP operation

"Roger Long" om wrote in
message ...
Is anyone in this group interested in or experimenting with Lean of Peak
operation? I'm especially interested in the experience of anyone doing it
with a fixed pitch carb engine with single EGT and CHT probes.
--
Roger Long


While you are fiddling with that mixture control trying to set the elusive
25 degrees LOP you are spending considerable time at PEAK, which will cause
damage to cylinders and exhaust in a short time.

Just my thought on the matter.
Allen

Not at 60% power, at least with a simple engine that has wide detonation
margins like an O-320. The greatest stress on the engine will be at 50 ROP
which is where Lycoming says to run it. If they aren't turning into gliders
at that setting, a few minutes at peak aren't going to hurt them.

EGT doesn't exactly relate to the temperatures inside the cylinder. For
example, if you let the hot gas out sooner, EGT will go up while the gas
won't be in the cylinder as long to heat it up. CHT would go down in that
case.

I was fiddling to learn more about the engine and confirm where the sweet
spot related to peak. I think that's something you have to go through to
get to know your engine and to confirm that your FA ratios are balanced
enough to run this way, not all engines are. What takes some getting used
to is how small the adjustments are and doing them slowly. That doesn't
mean they are fussy. They are accompanied by engine sounds and changes that
you can learn.

Once you have confirmed that your engine can be operated in a regime where
enriching the mixture increases power, is running acceptably smooth (but
yes, it will never be as smooth sounding as ROP), and CHT is lower than the
corresponding ROP RPM or MP, try it this way:

1) Put on carb heat. Probably different amount for each engine. If there
is a point when you slowly pull the heat knob where the drop in RPM seems to
increase, try it about there.

2) Set RPM 100 above the 60% power setting for that altitude. This will be
nearly WOT for a carb 172 at 4000 - 6000 feet.

3) Lean until RPM goes way down.

4) Enrich until you and the engine are comfortable or to the 60% power RPM
(or MP). Forget the EGT gauge.

You should check your POH to be sure about the 60% power settings. Go
through the fiddling and peak finding steps first to get to know how your
engine reacts. If you can't get it to run as described above without
roughness that creates airframe vibration or is really annoying, your engine
will have to be run ROP.

I'm still experimenting with this so it isn't expert advice. I'd really
like to hear the results of others experiments as opposed to OWT repetition.
If it's a small bore engine, you aren't going to hurt it fiddling with
mixture at these power settings unless it's too rich in which case you'll
foul the plugs.

--
Roger Long


Allen wrote in message
m...

"Roger Long" om wrote
in
message ...
Is anyone in this group interested in or experimenting with Lean of Peak
operation? I'm especially interested in the experience of anyone doing
it
with a fixed pitch carb engine with single EGT and CHT probes.
--
Roger Long


While you are fiddling with that mixture control trying to set the elusive
25 degrees LOP you are spending considerable time at PEAK, which will
cause
damage to cylinders and exhaust in a short time.

Just my thought on the matter.
Allen

On Thu, 15 Apr 2004 13:34:30 GMT, "Roger Long"
om wrote:

The greatest stress on the engine will be at 50 ROP
which is where Lycoming says to run it.

I am asuming, since your email suggests that you are US based, that you are
talking degrees Farenheit. I agree that 50°F ROP is a bad place to run the
engine.

Which engine does Lycoming say to run 50°F ROP? Lycoming does NOT make
that recommendation for the O360 series of engines.

In my Lycoming O360 series engine manual, the recommendations for normally
aspirated engines a

1. Full Rich for take-off, climb and maximum cruise powers (above
75% power), with a caveat to lean just to a smooth running engine for
take-off from a high-elevation airport or during climb.

2. Maximum Power cruise (75% power): 150°F on the rich side of
peak EGT.

3. Best Economy cruise (below 75% power): operate at peak EGT

For turbocharged engines:

1. Best Economy Cruise: Lean to peak TIT or 1650°F, whichever
occurs first.

2. Maximum Power Cruise: 125°F on the rich side of the temperature
determined in step 1 (peak TIT vs 1650°F).

Certain "airframe" manufacturers may have different recommendations in
their POH's, and those take precedence. But, even though Lycoming states
that a manufacturer's POH takes precedence, that's a far cry from stating
that "Lycoming" says to run the engine at 50°F ROP.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Quite right. However our 172 N did not come with EGT as standard equipment.
The "lean to rough, enrich till smooth" I was taught in primary training
(and used for the first couple of years when our EGT didn't work) ends up
about 50 ROP on our engine if you do it quickly and without carb heat. It
was sloppy of me to call it a Lycoming recommendation.

--
Roger Long
Ron Rosenfeld wrote in message
...
On Thu, 15 Apr 2004 13:34:30 GMT, "Roger Long"
om wrote:

The greatest stress on the engine will be at 50 ROP
which is where Lycoming says to run it.

I am asuming, since your email suggests that you are US based, that you
are
talking degrees Farenheit. I agree that 50°F ROP is a bad place to run
the
engine.

Which engine does Lycoming say to run 50°F ROP? Lycoming does NOT make
that recommendation for the O360 series of engines.

In my Lycoming O360 series engine manual, the recommendations for normally
aspirated engines a

1. Full Rich for take-off, climb and maximum cruise powers (above
75% power), with a caveat to lean just to a smooth running engine for
take-off from a high-elevation airport or during climb.

2. Maximum Power cruise (75% power): 150°F on the rich side of
peak EGT.

3. Best Economy cruise (below 75% power): operate at peak EGT

For turbocharged engines:

1. Best Economy Cruise: Lean to peak TIT or 1650°F, whichever
occurs first.

2. Maximum Power Cruise: 125°F on the rich side of the temperature
determined in step 1 (peak TIT vs 1650°F).

Certain "airframe" manufacturers may have different recommendations in
their POH's, and those take precedence. But, even though Lycoming states
that a manufacturer's POH takes precedence, that's a far cry from stating
that "Lycoming" says to run the engine at 50°F ROP.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Thu, 15 Apr 2004 14:56:57 GMT, "Roger Long"
om wrote:

Quite right. However our 172 N did not come with EGT as standard equipment.
The "lean to rough, enrich till smooth" I was taught in primary training
(and used for the first couple of years when our EGT didn't work) ends up
about 50 ROP on our engine if you do it quickly and without carb heat. It
was sloppy of me to call it a Lycoming recommendation.

I don't think I really learned how to lean until I had an EGT indicator.
and discovered how slowly the engine parameters change with changes in the
mixture control. At least in my fuel injected IO360.

And the lean to rough, enrich to smooth IS Lycoming's recommendation for
carbureted engines without EGT indicators or flowmeters. But they do say
to lean *slowly* and they also state it is for Economy cruise at 75% power
or less).

If you lean slowly in your 172N to rough, then slowly enrich until just
smooth -- where do you wind up with regard to EGT?




Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

If you lean slowly in your 172N to rough, then slowly enrich until just
smooth -- where do you wind up with regard to EGT?



I'm going to try and trace my thought processes back here because I think a
lot of 4 banger, fixed pitch pilots are still flying the way I have at
various times.

I started out without an EGT knowing only that leaner was hotter, too lean
made the engine rough, and too hot would burn the valves. I also didn't
really believe that the engine would restart if I leaned so much that it
quit. A CFI would have done me a big favor by showing me that you could
lean it until it was producing almost no power and then bring it back again.

So, I would carefully turn the mixture listening intently for the slightest
change in engine sound (Is that rough?) I was afraid to ever lean it enough
to learn what rough actually sounded like. Carefully doesn't mean slowly.
New pilots tend to do everything like this quickly because they look up to
find themselves 200 feet off altitude if they don't. The care was in
jumping like a rabbit back to richer from the slightest burble in the
exhaust sound. I know from later flying with the EGT that this method was
putting me about 50 - 75 ROP.

After I took over as maintenance officer, I had the EGT probe tested and it
was working. The gauge had never been adjusted so it was off scale most of
the time. I leaned and looked at the gauge and it didn't seem to react so I
just ignored it for another couple of years.

Then I learned two new things. You can't hurt the engine at 75% power with
any mixture setting and these engines, which were not designed to burn
100LL, need to be really leaned to avoid plug and valve stem fouling. This
prompted me to dig out and read through the stuff that came with the Alcor
EGT gauge. I'd heard about LOP by this time but thought it was only for
GAMI customers. I also went out and calibrated the EGT according to the POH
supplement which, along with some patience, suddenly made it a usable
instrument. I was still focused on plug fouling so I leaned to peak and
then back 50 degrees to cover the spread in FA ratios and make sure none of
the uninstrumented cylinders were in the "dangerous" LOP zone. So, I was
still flying the same way but with an EGT gauge.

The information that carb heat helps to even out mixture distribution was
coming to light just about the time our plane went down for a three month
refit so it was a frustrating winter. Here's what I know now.

If you keep leaning our engine with carb heat off, it does not get steadily
rougher from the first change in engine sound that used to spook me into
giving the mixture knob a couple turns back. You can keep going to peak and
a little beyond with little change. Jumping back from the first flaw in
smoothness was the mistake I'd been making for years. It's noticeably rough
by peak though. Lean it really smooth again and you'll wind up about 50
ROP.

Now put on the carb heat and forget about roughness, lean it until it really
sags and slowly turn the mixture in. With WOT or close to it, the engine
will settle down to about the same power output and roughness as it had at
25 - 50 ROP without carb heat but CHT will be 15 - 25 degrees lower. With
the ROP operation, the throttle would be pulled back farther to keep the
power in the 60 - 75% range but RPM, not throttle position is the measure of
power output. (For fixed pitch, anyway).

This is clearly only going to work in the lower half of our 172's service
ceiling but that's where a lot of our flying is done. There are also a lot
of subtle factors that effect mixture distribution. It would not surprise
me a bit if another O-320 H2AD in a 172N didn't have good enough mixture
distribution to make this work.

I also don't think you can do it cookbook style. I suspect you have to go
through the fiddling stage, trying different amounts of carb heat and
learning the way the engine sounds and reacts at different points. After
that, it should be easier.

I'm still learning about it which is why I'm curious what kind of experience
other simple engine fliers have if they try it (as opposed to just
pontificating about it).


--
Roger Long

On Thu, 15 Apr 2004 22:34:24 GMT, "Roger Long"
om wrote:

If you lean slowly in your 172N to rough, then slowly enrich until just
smooth -- where do you wind up with regard to EGT?



I'm going to try and trace my thought processes back here because I think a
lot of 4 banger, fixed pitch pilots are still flying the way I have at
various times.


I also don't think you can do it cookbook style. I suspect you have to go
through the fiddling stage, trying different amounts of carb heat and
learning the way the engine sounds and reacts at different points. After
that, it should be easier.

I'm still learning about it which is why I'm curious what kind of experience
other simple engine fliers have if they try it (as opposed to just
pontificating about it).

Interesting and educational story. It is clear that, in your engine,
following Lycoming's recommendations does result in running 50°F ROP. That
may not be what L intended, but that surely seems to be the result.

I, too, was never taught to properly lean. And I probably didn't really
learn to do it correctly until I'd owned my own airplane for five or ten
years (or maybe longer). There were a number of Mooniacs who were
recommending leaning to 50° rich for best power. In retrospect, although I
probably was aiming for that, I was likely a lot richer due to making the
adjustments too quickly.

But my "mature" Mooney would never show cruise CHT's much above 325°; and
my engine problems necessitating early O/H have not been related to
leaning.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)