Why is LOP (lean of peak) controversial?

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 Thu, 28 Sep 2006 08:07:22 -0700, Mark Hansen wrote:

How's this for timing. Mike Busch at AVWeb just wrote a new "The Savvy
Aviator" column on this very topic. Have a look:

http://www.avweb.com/news/savvyaviator/193242-1.html

I'd just read it this morning. It doesn't actually address the aspect
that's leaving me puzzled: how someone can complain about "burning
cylinders" w/o seeing this ahead of time on an engine monitor.

But I think I saw one possible answer in this thread: if detonation is
occurring, EGTs (the metric used because it is quickly responsive to
mixture change) will drop but CHTs will - less quickly - go up. Someone
posted that detonation can ruin a cylinder very quickly (ie. a small
number of minutes, as I interpreted what I read).

So someone might not have evidence of detonation until it is too late.

Is this correct, or have I missed/misunderstood some aspect?

I still don't quite get why LOP would bring on detonation (even after
reading http://www.avweb.com/news/pelican/182132-1.html but I'm still
digesting parts of it).

- Andrew

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

: 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.

... *and* 400 degrees CHT.

: 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.

I haven't really noticed much different in mine whether running autogas or
100LL. One possible reason could be vapor pressure. I bought the vapor pressure
tester along with my autogas STC just so I could check for vapor-lock in the summer.
The 100LL has a slightly lower volatility than the autogas, at least here. If to
autogas vaporizes better and easier, it could do it sooner out of the carb jet and
make for a better distribution.

-Cory

--

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

Peter R. wrote:
Matt Barrow wrote:

"Peter R." wrote in message
...
Matt Barrow wrote:

What % of power are you using? I'm usually around 360-370, but I'm
running
70-75%.

I also cruise around 75% of the IO-520's 285 hp.

What altitude? FF?

In summer temperatures at 12,000-15,000 feet I get about 187-190 kts TAS at
about 15 gph. In the winter, I see 175-180 kts TAS and 16.5 gph or so.

--
Peter

Unless the LOP "formulas" have changed (which IS entirely possible,
been a few years since I had to think/worry about it) anything much
over 14.5 GPH would be considered higher than 75% power.

285 HP x .75 = 213.75 HP / 14.9 HP/G = approx 14.3 GPH @ 75% operating
LOP

If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...

TC

" wrote:

If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...

The cylinders are new Superior Millennium cylinders with about 250 hours on
them, if that has anything to do with the cooler temperatures.

And yes, my engine's CHTs are normally below or around 300 and have never
approached 400, routinely. If you would like some verification of this, I
would be happy to upload my engine monitor data (from several months ago, I
have yet to download a current set), which is in the latest JPI format, to
a free host site for anyone's perusal.

--
Peter

You more than likely have an CHT indication problem. There is no reason your
airplane should run much cooler than the fleet.

Karl


"Peter R." wrote in message
...
" wrote:

If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...

The cylinders are new Superior Millennium cylinders with about 250 hours
on
them, if that has anything to do with the cooler temperatures.

And yes, my engine's CHTs are normally below or around 300 and have never
approached 400, routinely. If you would like some verification of this, I
would be happy to upload my engine monitor data (from several months ago,
I
have yet to download a current set), which is in the latest JPI format, to
a free host site for anyone's perusal.

--
Peter

Peter R. wrote:
" wrote:


If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...


The cylinders are new Superior Millennium cylinders with about 250 hours on
them, if that has anything to do with the cooler temperatures.

And yes, my engine's CHTs are normally below or around 300 and have never
approached 400, routinely. If you would like some verification of this, I
would be happy to upload my engine monitor data (from several months ago, I
have yet to download a current set), which is in the latest JPI format, to
a free host site for anyone's perusal.


Is your JPI set up for the correct probe type? Your CHTs sound awful low

Peter R. wrote:
" wrote:

If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...

The cylinders are new Superior Millennium cylinders with about 250 hours on
them, if that has anything to do with the cooler temperatures.

And yes, my engine's CHTs are normally below or around 300 and have never
approached 400, routinely. If you would like some verification of this, I
would be happy to upload my engine monitor data (from several months ago, I
have yet to download a current set), which is in the latest JPI format, to
a free host site for anyone's perusal.

--
Peter

I'm not doubting your numbers-but am not sure if the LOP people are
still using 14.9 HP/G. Sounds to me like you've got an engine to hang
on to.

If you could spare the extra weight, I'd consider adding a pre-oiler
and flying that engine as long as I could...

Regards;

TC

One fly in the ointment for safe leaning is the likelihood of mechanical
tachs not telling the truth. When my mechanical tach says 2400 RPM, my
handheld optical tach tells me 2480. One of these days I'll replace that
old analog tach with an ignition based instrument.

--
Best Regards,
Mike

http://photoshow.comcast.net/mikenoel

"Peter R." wrote in message
...
" wrote:

If your CHT's are closer to 300 F than 400 F running those settings,
you've got one of the "cooler" installations that I've ever heard of...

The cylinders are new Superior Millennium cylinders with about 250 hours
on
them, if that has anything to do with the cooler temperatures.

And yes, my engine's CHTs are normally below or around 300 and have never
approached 400, routinely. If you would like some verification of this, I
would be happy to upload my engine monitor data (from several months ago,
I
have yet to download a current set), which is in the latest JPI format, to
a free host site for anyone's perusal.

--
Peter