leaning in climb

Hi everyone. I have a leaning question. The POH for my 152 says that the
mixture should be leaned to best power after passing 3000 feet in the climb.
However in other places in the POH (and the Lycoming site) they say not to
lean when at 75% power or higher in cruise. My question: Is the engine
developing less than 75% power during the climb; and is this why leaning in
the climb is OK? Does this guidance in the POH seem contradictory to anyone
except me?

Thanks for all your help.

Matt

Matt wrote:
: Hi everyone. I have a leaning question. The POH for my 152 says that the
: mixture should be leaned to best power after passing 3000 feet in the climb.
: However in other places in the POH (and the Lycoming site) they say not to
: lean when at 75% power or higher in cruise. My question: Is the engine
: developing less than 75% power during the climb; and is this why leaning in
: the climb is OK? Does this guidance in the POH seem contradictory to anyone
: except me?

: Thanks for all your help.

Few things have has much disinformation (DI) and old-wives-tales (OWT) as
aviation. Few things in aviation have as much DI and OWT as engine leaning. I
suggest you read through some of Deakin's articles on www.avweb.com to clarify.

My personal climb-leaning is to lean to a constant EGT. Hold whatever takeoff
EGT is until through 8000'. At that point it's impossible to go over 75% on a
normally aspirated plane.

Even though with the RPM low in a climb, it's probably not possible to exceed
75% power, it's the worst kind of "75% power"... low RPM max MP. Given the low speed
and high angle of attack in a climb, I wouldn't lean to best power until a bit higher
than 3000'. Of course, if it's in the POH is must be gospel.... always driven by the
goals of long engine life, low fuel burn, minimum maintenance, and least money
expended... never by marketing, performance numbers, or band-aid workaround covering
other problems. Nope... never. ;-)

-Cory



--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Of course, if it's in the POH is must be gospel.... always driven by the
goals of long engine life, low fuel burn, minimum maintenance, and least
money
expended... never by marketing, performance numbers, or band-aid
workaround covering
other problems. Nope... never. ;-)

One thing I've learned over a few years of aircraft ownership is that many
of these "rules" are made to fit the most common situation, and must take
into account the lowest common denominator pilot. Because of this, I think
most of the manufacturers are overly cautious about leaning, simply because
they don't want some ham-fisted pilot yanking the mixture back to an
over-lean condition at full power. Thus, the hard and fast "no leaning
below x000 feet rules."

Careful leaning is possible -- indeed desirable -- at any power setting and
altitude. For example, when it's hot (or high, or both), you want to lean
to best power for take-off, and that's at maximum power.

Just don't over-do it. (This is where, IMHO, an engine analyzer pays for
itself. When you have a graphic read-out of EGTs and CHTs for each
cylinder right in front of you, it's much easier not to over-lean.)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay,

to an
over-lean condition

Wazzat?

Thus, the hard and fast "no leaning
below x000 feet rules."


Actually, those rules aren't that hard and fast. I am not aware of any
manufacturer mentioning them for cruise power settings.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:
Jay,

to an
over-lean condition

Wazzat?

That would be if the engine is backfiring ;-)


Personally, I simply lean a fixed-pitch prop Lyc to find peak rpm and
have never had any performance or maintenance issues in nearly a decade
of flying. The engine always seems happy and I suspect that at peak
rpm, I'm probably still blowing a significant amount of unburned fuel
out the exhaust pipe. In those planes I've flown that were equipped
with cht guage, the temps never climbed high enough to be worrisome
either.

wrote:

Personally, I simply lean a fixed-pitch prop Lyc to find peak rpm and
have never had any performance or maintenance issues in nearly a decade
of flying. The engine always seems happy and I suspect that at peak
rpm, I'm probably still blowing a significant amount of unburned fuel
out the exhaust pipe. In those planes I've flown that were equipped
with cht guage, the temps never climbed high enough to be worrisome
either.

Here's a chart:

http://www.swaircraftappraisals.com/MeyersForum/Engine%20Info/Engine%20Operation/Pelican's%20Perch%20Mixture%20Magic_files/pp18d.jpg

The horizontal axis is leaning (left is leaner, right is richer). The
highest point of the BHP curve is peak power -- notice how close it is
horizontally to the highest point of the CHT curve, which represents
the hottest your engine gets.


All the best,


David

I suggest you read through some of Deakin's articles on www.avweb.com to
clarify.

Yes, I have been reading many great articles on avweb. Unfortunately, my
152 does not have EGT or CHT monitors, so I have to use the "listen, learn,
and pray" method of leaning. I find it mentally difficult to reach over and
start easing the mixture back with the throttle full forward.

Matt wrote:
: Yes, I have been reading many great articles on avweb. Unfortunately, my
: 152 does not have EGT or CHT monitors, so I have to use the "listen, learn,
: and pray" method of leaning. I find it mentally difficult to reach over and
: start easing the mixture back with the throttle full forward.

Yeah, I would be too. One thing you might be able to do to "calibrate your
discomfort" would be to climb to an altitude where you cannot get more than 75%...
like 8000' or so. Verify your power at 75% cruise and lean to best power. Note the
mixture position. Linearly interpolate the mixture/altitude from that...

If it's your plane, I'd consider adding a cheapie CHT and EGT from Westach.
They're not that expense and it lets you have more real information on engine health.
Not really useful for cruise leaning, but good for a climb leaning and to verify
non-roasted engine CHTs.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Maybe a cht would help. I think the egt on a carburetor engine isn't much
help. I had a Westach 4 probe EGT on my C150 and found that it didn't help
any except to verify that standard look and listen method was working just
as well. I removed it to put a clock back in the hole. For sale if you
want to try it. BTW I did the Holly Run one year to Tangier Island and many
of the small planes with carburetors had to make the flight with carb heat.
I leaned the engine while using full heat. The engine went to TBO without
any burned valves.

Roger C-150E @ MD43


wrote in message
...
Matt wrote:
: Yes, I have been reading many great articles on avweb. Unfortunately,
my
: 152 does not have EGT or CHT monitors, so I have to use the "listen,
learn,
: and pray" method of leaning. I find it mentally difficult to reach over
and
: start easing the mixture back with the throttle full forward.

Yeah, I would be too. One thing you might be able to do to "calibrate
your
discomfort" would be to climb to an altitude where you cannot get more
than 75%...
like 8000' or so. Verify your power at 75% cruise and lean to best power.
Note the
mixture position. Linearly interpolate the mixture/altitude from that...


If it's your plane, I'd consider adding a cheapie CHT and EGT from
Westach.
They're not that expense and it lets you have more real information on
engine health.
Not really useful for cruise leaning, but good for a climb leaning and to
verify
non-roasted engine CHTs.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Roger wrote:
: Maybe a cht would help. I think the egt on a carburetor engine isn't much
: help. I had a Westach 4 probe EGT on my C150 and found that it didn't help
: any except to verify that standard look and listen method was working just
: as well. I removed it to put a clock back in the hole. For sale if you
: want to try it. BTW I did the Holly Run one year to Tangier Island and many
: of the small planes with carburetors had to make the flight with carb heat.
: I leaned the engine while using full heat. The engine went to TBO without
: any burned valves.

For cruise leaning, I'll pretty much agree. I put a 4-probe EGT on my PA-28,
but like you say, it generally just will verify that the lean&listen approach works
(or doesn't). One way you may may make it more useful is to play with the carb heat
trick of getting a more even air/fuel distribution. With my analog gauges that's not
really possible, but for a digital readout it may be more useful.

For the lean in a climb, I still think it's *quite* useful... even on carb'd
engines.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************