Why is LOP (lean of peak) controversial?

"Andrew Gideon" wrote:


One of those two people tells a story of someone that bought gami
injectors, ran LOP, and then cooked four of six cylinders.


Another example of how a little knowledge is a dangerous thing.

*Improper* LOP operating technique can harm cylinders, even cause
catastrophic failure by detonation.

--
Dan
C172RG at BFM

On Wed, 27 Sep 2006 09:20:12 -0500, Dan Luke wrote:

*Improper* LOP operating technique can harm cylinders, even cause
catastrophic failure by detonation.

Hmm. Detonation, if I follow all this correctly, yields lower EGTs. So
someone leaning by EGT could be fooled into thinking that all is well,
even while cylinders are being damaged. This is exactly the type of idea
I was missing; now I think I see.

But CHT goes up, right? Would it go up enough (ie. beyond 400) to raise a
pilot's concern?

- Andrew

"Andrew Gideon" wrote in message
news
On Wed, 27 Sep 2006 09:20:12 -0500, Dan Luke wrote:

*Improper* LOP operating technique can harm cylinders, even cause
catastrophic failure by detonation.

Hmm. Detonation, if I follow all this correctly, yields lower EGTs. So
someone leaning by EGT could be fooled into thinking that all is well,
even while cylinders are being damaged. This is exactly the type of idea
I was missing; now I think I see.

But CHT goes up, right? Would it go up enough (ie. beyond 400) to raise a
pilot's concern?


http://www.avweb.com/news/pelican/182132-1.html

Pelican's Perch #43:
Detonation Myths

We've all been taught about detonation in piston aircraft engines. It's what
occurs when combustion pressure and temperature get so high that the
fuel/air mixture to explodes violently instead of burning smoothly, and it
can destroy an engine in a matter of seconds. Right? Well, not exactly.
AVweb's John Deakin reviews the latest research, and demonstrates that
detonation occurs in various degrees - much like icing and turbulence - with
the milder forms not being particularly harmful. Heavy detonation is
definitely destructive, and the Pelican offers some concrete data on how to
avoid it.
---------------------

"Dan Luke" wrote in message
...

"Andrew Gideon" wrote:


One of those two people tells a story of someone that bought gami
injectors, ran LOP, and then cooked four of six cylinders.


Another example of how a little knowledge is a dangerous thing.

*Improper* LOP operating technique can harm cylinders, even cause
catastrophic failure by detonation.

As can *proper* ROP operating techniques...particularly the 50ROP as
recommended by some POH's.

The biggest problem is getting LOP, then enriching "just to be on the safe
side", usually right into the worst possible operating range.

I ussed to be timid on the "red knob" easing it out until I hit peak EGT
and then kept going until I would get 20 degrees or more LOP and then
stay there. That technique though probably OK, kept me in the red box a
little longer than I preferred.

My current technique is to get to cruising altitude and then do "the big
pull" on the mixuture until a definite power loss is noticed. I know
know I am way on the LOP side so I come in a tad to smooth it out and
note the EGT and CYL head temps. Both are nice and cool ( CYL 400 &
EGT 1400). I'm usually cruising at 150 + KIAS nad 9 GPH. Gotta love
those Mooney's.

Jon Kraus
'79 Mooney 201
4443H @ UMP

Dan Luke wrote:
"Andrew Gideon" wrote:


One of those two people tells a story of someone that bought gami
injectors, ran LOP, and then cooked four of six cylinders.



Another example of how a little knowledge is a dangerous thing.

*Improper* LOP operating technique can harm cylinders, even cause
catastrophic failure by detonation.

Andrew,

So...what am I missing?


The inertia of the pilot population, myths, misinformation, engine
manufacturer's law departments - all factors. "Show me the numbers" is
the old trick to silence the LOP opponents. They can't.

I take it you are familiar with John Deakin's columns on the topic and
engine management in general at avweb.com?

--
Thomas Borchert (EDDH)

: I take it you are familiar with John Deakin's columns on the topic and
: engine management in general at avweb.com?

These articles basically say:

- LOP done improperly *WILL* damage engines. Only at 75% or less can it be done
safely.
- Absolute EGT doesn't matter... CHT primarily controls detonation margin, top end
longevity, and exhaust valve temperatures. (Lycoming and Cont have too high of
redlines... 400 CHT is as high as should be periodically seen... 375 max continuous)
- ANY leaks in ANY valves are unacceptable and will cause damage, LOP or not.
- ROP provides the most power for a single "power setting" (i.e. MP+RPM setting...
*actual* power setting also includes the mixture). Thus marketing likes ROP since it
makes the plane go faster on paper.

I use these articles (and Lycomings recommendations) to operate my 180 hp
Lycoming O-360. It's carb'd so LOP doesn't quite get there. Below 75%, I can do
anything I want with the mixture so long as CHT stays cool enough. I typically
consider 65% power and 350 CHT my maximums. At those settings, I can lean to
where there is a noticable power loss, but before it's rough, and 8-8.5 gph.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

One thing no one has mentioned is LOP may not be possible with
carbureted engines. The flows to each cylinder just aren't consistent
enough to make it work. Also you really need CHT and EGT guage on each
cylinder to do it right. The problem with LOP, isn't running LOP, its
that you are running peak and THINKING you are running LOP. The same
could be said of running rich of peak too. Running AT peak is really
only a problem at higher power settings. So most of this LOP stuff is
really for turbocharged fuel injected engines. I said MOST. Some people
with just fuel injection use LOP and a FEW at least claim to use it
with carburetion.

LOP works, but I think you have to really know what you are doing and
have the right equipment. But if you are running at 65% power or below,
it doesn't hurt to try it, no matter what sort of equipment you have
(unless of course you dont even have a mixture knob :-))

Thomas Borchert wrote:
Andrew,

So...what am I missing?


The inertia of the pilot population, myths, misinformation, engine
manufacturer's law departments - all factors. "Show me the numbers" is
the old trick to silence the LOP opponents. They can't.

I take it you are familiar with John Deakin's columns on the topic and
engine management in general at avweb.com?

--
Thomas Borchert (EDDH)

Doug wrote:
: One thing no one has mentioned is LOP may not be possible with
: carbureted engines. The flows to each cylinder just aren't consistent
: enough to make it work. Also you really need CHT and EGT guage on each
: cylinder to do it right. The problem with LOP, isn't running LOP, its
: that you are running peak and THINKING you are running LOP. The same
: could be said of running rich of peak too. Running AT peak is really
: only a problem at higher power settings. So most of this LOP stuff is
: really for turbocharged fuel injected engines. I said MOST. Some people
: with just fuel injection use LOP and a FEW at least claim to use it
: with carburetion.

: LOP works, but I think you have to really know what you are doing and
: have the right equipment. But if you are running at 65% power or below,
: it doesn't hurt to try it, no matter what sort of equipment you have
: (unless of course you dont even have a mixture knob :-))

I guess that's what I was trying to say. I'm assuming that most people
reading the thread know that carb'd engines (particularly 6's) generally have too poor
fuel/air distribution between the cylinders to run LOP.

I do know that I am running about half of my cylinders slightly LOP and about
half AT peak. Although the EGT is higher than LOP, the CHT is *lower*, and thus
should have cooler exhaust valves (or at least about the same). That's also why I
tend to limit myself to 65-70% at most. A little safety margin. Besides for my bird
(PA-28), the airframe doesn't buy much speed increase from 65-75% on a 180hp engine.
It's not worth the extra fuel burn for the additional 5 mph or so.

Again, the *at peak* operating condition is mentioned in one of the Lycoming
publications as the "best economy cruise" setting and is considered acceptable.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On 28 Sep 2006 07:58:18 -0700, "Doug"
wrote:

One thing no one has mentioned is LOP may not be possible with
carbureted engines. The flows to each cylinder just aren't consistent
enough to make it work.

This may not be a problem if you're flying with autogas. I've noticed
in my Warrior that leaning too much causes roughness and missing when
flying with 100LL. I'm sure that everyone else has noticed the same
thing. When running on autogas, you can lean aggressively and the
engine continues to run smoothly. I've wondered what causes the
difference, and how much I can take advantage of it without proper
instrumentation. I've read that generally you can lean as aggressively
you want as long as you're below 75% power.

I've wondered if the smoothness might be due to cleaner plugs, but
100LL causes lean roughness even with new plugs. I've also wondered if
those ads that the oil companies used to run about their gasolines
making your car's engine run smoother due to better fuel distribution
suggest an explanation of the difference. I've suspected that this
might explain it. If true, it might be another reason to get the
autogas STC--better fuel economy.

RK Henry