Leaning / step climbing?

"Tom S." writes:

There may be planes where it's not OK to lean at 75%, but all of the
POH's I've looked at so far *require* leaning at 75% power to get the
performance numbers (fuel burn and range) that they list.

http://www.avweb.com/news/columns/182152-1.html (Article 57, but read 58 &
59 as well).

[As far as I understand, you're saying that people should run engines
full rich at 75% power. If that's not your point, apologies in
advance for the misunderstand.]

I'm a big fan of Deakin, and it's worth reading this article more
closely -- he's *not* recommending flying full rich at 75% power, but
rather, not leaning to 50 degF ROP. Here's the part that I'm guessing
you were looking at:

Take an engine set up at 50 ROP (rich of peak). Is it "too rich" or
"too lean"? We cannot say, without knowing what else is going on. At
any power setting above about 60 or 65%, 50 ROP is BOTH "too rich,"
and "too lean," in that it is the worst possible mixture setting for
the engine, and moving the mixture EITHER way will improve
things. On the other hand, at about 9,000 feet and above, with no
turbo, 50 to 80 ROP is an EXCELLENT mixture setting, for it will
produce just about the maximum possible power, and it won't overheat
anything at and above that altitude. You NEED 50 to 80 ROP up there!
But 50 to 80 ROP and full power at sea level will destroy your
engine.

To understand Deakin's point, you have to read this part as well:

The more accurate statement is, "Mixtures that are not rich enough,
or mixtures that are not lean enough may be harmful to your engine."
This is NOT a contradiction! The "harmful point" is a CENTER
POINT. Again, look back at the graph.

If you lean to best power or peak EGT at 75% (especially at lower
altitudes), you're going to be very close to that zone (on one side or
the other) -- in fact, some of your cylinders may be in it. That's
his point.

If you lean to 75% and enrich until you see a slight RPM drop (and
adjust throttle, etc. until you're back at 75%), you should be running
rich enough to be clear of the danger zone. If your engine runs rough
LOP, this is probably your best choice.

If you leave your throttle wide-open and lean until power settles at
75%, you should be running lean enough to be clear of the danger zone.
If your engine runs smoothly LOP, this is the absolute best choice.

If you leave the mixture full rich at 75%, you'll also be well clear
of the danger zone, but you'll burn lots of extra gas and are more
likely to have to deal with annoyances like fouled plugs and stuck
valves at some point down the road. More importantly, you're ensuring
that your engine is producing as much CO as it possibly can, so if
you're flying in the winter or at cold altitudes, you'll want to be
particularly careful that that heater shroud doesn't have any leaks.


All the best,


David

(Rick Durden) wrote in message om...
John,

Specifically, you should not be leaning if your engine in making 75%
power or better.

Not necessarily so. It is perfectly okay to lean at 75% power, the
manual for your airplane has a fuel burn for 75% with lean mixture.
In fact, if you don't lean when operating at 75% with that Lycoming,
you will significantly reduce your range and endurance and possibly
foul the plugs. www.gami.com has a good discussion of leaning and
what's going on during combustion. It may be perfectly okay to lean
at power settings above 75%.

(Rick Durden) wrote in message om...
John,

Specifically, you should not be leaning if your engine in making 75%
power or better.

Not necessarily so. It is perfectly okay to lean at 75% power, the
manual for your airplane has a fuel burn for 75% with lean mixture.
In fact, if you don't lean when operating at 75% with that Lycoming,
you will significantly reduce your range and endurance and possibly
foul the plugs. www.gami.com has a good discussion of leaning and
what's going on during combustion. It may be perfectly okay to lean
at power settings above 75%.


OK, perhaps I didn't include enough information. For the Lycoming
engines found in most common Cessnas & Pipers, Lycoming manuals
usually have caution against leaning above 75% power. Perhaps I
should have reworded my comment above to read "76%" or "75.5%".

I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

John Galban=====N4BQ (PA28-180)

"David Megginson" wrote in message
...
"Tom S." writes:

There may be planes where it's not OK to lean at 75%, but all of the
POH's I've looked at so far *require* leaning at 75% power to get the
performance numbers (fuel burn and range) that they list.

http://www.avweb.com/news/columns/182152-1.html (Article 57, but read 58
&
59 as well).

[As far as I understand, you're saying that people should run engines
full rich at 75% power. If that's not your point, apologies in
advance for the misunderstand.]

No...you snipped the part I was responding to (note the mark
indentations).


I'm a big fan of Deakin, and it's worth reading this article more
closely -- he's *not* recommending flying full rich at 75% power, but
rather, not leaning to 50 degF ROP. Here's the part that I'm guessing
you were looking at:

Take an engine set up at 50 ROP (rich of peak). Is it "too rich" or
"too lean"? We cannot say, without knowing what else is going on. At
any power setting above about 60 or 65%, 50 ROP is BOTH "too rich,"
and "too lean," in that it is the worst possible mixture setting for
the engine, and moving the mixture EITHER way will improve
things. On the other hand, at about 9,000 feet and above, with no
turbo, 50 to 80 ROP is an EXCELLENT mixture setting, for it will
produce just about the maximum possible power, and it won't overheat
anything at and above that altitude. You NEED 50 to 80 ROP up there!
But 50 to 80 ROP and full power at sea level will destroy your
engine.

To understand Deakin's point, you have to read this part as well:

The more accurate statement is, "Mixtures that are not rich enough,
or mixtures that are not lean enough may be harmful to your engine."
This is NOT a contradiction! The "harmful point" is a CENTER
POINT. Again, look back at the graph.

If you lean to best power or peak EGT at 75% (especially at lower
altitudes), you're going to be very close to that zone (on one side or
the other) -- in fact, some of your cylinders may be in it. That's
his point.

If you lean to 75% and enrich until you see a slight RPM drop (and
adjust throttle, etc. until you're back at 75%), you should be running
rich enough to be clear of the danger zone. If your engine runs rough
LOP, this is probably your best choice.

If you leave your throttle wide-open and lean until power settles at
75%, you should be running lean enough to be clear of the danger zone.
If your engine runs smoothly LOP, this is the absolute best choice.

If you leave the mixture full rich at 75%, you'll also be well clear
of the danger zone, but you'll burn lots of extra gas and are more
likely to have to deal with annoyances like fouled plugs and stuck
valves at some point down the road. More importantly, you're ensuring
that your engine is producing as much CO as it possibly can, so if
you're flying in the winter or at cold altitudes, you'll want to be
particularly careful that that heater shroud doesn't have any leaks.

David, what he's doing is reiterating, then dispelling, the conventional
wisdom.

Read the article in there where he does a 1100nm CC with the mixture set 250
degrees LOP.

"John Galban" wrote in message
om...
(Rick Durden) wrote in message
om...
John,

Specifically, you should not be leaning if your engine in making 75%
power or better.

Not necessarily so. It is perfectly okay to lean at 75% power, the
manual for your airplane has a fuel burn for 75% with lean mixture.
In fact, if you don't lean when operating at 75% with that Lycoming,
you will significantly reduce your range and endurance and possibly
foul the plugs. www.gami.com has a good discussion of leaning and
what's going on during combustion. It may be perfectly okay to lean
at power settings above 75%.


OK, perhaps I didn't include enough information. For the Lycoming
engines found in most common Cessnas & Pipers, Lycoming manuals
usually have caution against leaning above 75% power. Perhaps I
should have reworded my comment above to read "76%" or "75.5%".

http://www.avweb.com/news/columns/186015-1.html

November 9, 2003
Pelican's Perch #75:
Those Dreadful POHs (Part 1)

Everything your POH says is correct, and anything it doesn't say you can do,
you can't, right? Did you really think John Deakin -- AVweb's favorite
contrarian -- could let that kind of gross generality continue unquestioned?
I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

http://www.avweb.com/news/columns/183094-1.html
March 2, 2003
Pelican's Perch #66
Where Should I Run My Engine?
(Part 4 -- Descent)

After a short discussion about whether running engines the factory way or
the skydiving way will hurt or help engines, AVweb's John Deakin settles in
for the descent. And, yes, there are more old wives tales to be debunked,
and better control settings to use.
-----------------------------------------
http://www.avweb.com/news/columns/182583-1.html
February 2, 2003
Pelican's Perch #65
Where Should I Run My Engine?
(Part 3 -- Cruise)

Cruise -- Time to sit back and enjoy the flight. But wait ... did you leave
the mixture set where it was during the climb? Or do you just set it where
it
------------------------------------------------

Picture, charts, loads of data... Deakin makes some very strong points that
much of what has been presented in POH's over the last several (read: 30 or
more) years has been downright BOGUS.

Tom
--
"What's our vector, Victor?"

"David Megginson" wrote in message
...
"Tom S." writes:

There may be planes where it's not OK to lean at 75%, but all of the
POH's I've looked at so far *require* leaning at 75% power to get the
performance numbers (fuel burn and range) that they list.

http://www.avweb.com/news/columns/182152-1.html (Article 57, but read 58
&
59 as well).

[As far as I understand, you're saying that people should run engines
full rich at 75% power. If that's not your point, apologies in
advance for the misunderstand.]

I'm a big fan of Deakin, and it's worth reading this article more
closely -- he's *not* recommending flying full rich at 75% power, but
rather, not leaning to 50 degF ROP. Here's the part that I'm guessing
you were looking at:

Nope, he's recommending 40 LOP or even more lean than that. After peak,
CHT's AND EGT drop.

Read the article again (closely, as you mentioned) and read the four part
series. Hell, read his entire series of engine management articles (in the
sidebar).

(John Galban) writes:

I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

Was it heat damage? I'd imagine that they'd be even worse if they
were leaned to just above peak.


All the best,


David

"Tom S." writes:

Read the article in there where he does a 1100nm CC with the mixture
set 250 degrees LOP.

It sounds like we're in very noisy agreement here, after all.


All the best,


David

"Tom S." writes:

Nope, he's recommending 40 LOP or even more lean than that. After peak,
CHT's AND EGT drop.

Read the article again (closely, as you mentioned) and read the four part
series. Hell, read his entire series of engine management articles (in the
sidebar).

I've read them all several times -- they're great. When I wrote "he
recommends not leaning to 50 degF ROP", I meant that he recommends
leaning more, not less. I think that the thread became confused, and
that you and I each ended up thinking that the other was arguing
against LOP operations rather than of in favour of them.


All the best,


David

David Megginson wrote in message ...
(John Galban) writes:

I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

Was it heat damage? I'd imagine that they'd be even worse if they
were leaned to just above peak.


Yes, it was heat damage. The plane in routinely ran leaned at about
85% power for about 150 hrs. Two of the 4 exhaust valves were
toasted.

On a well instrumented engine you could probably get away with
leaning at higher power settings. I think the reason Lyc. puts the
limit at 75% is that the average spam can does not have enough
instrumentation to keep all cylinders in the green during all types of
operation.

John Galban=====N4BQ (PA28-180)