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"

Matt,

My question: Is the engine
developing less than 75% power during the climb; and is this why leaning in
the climb is OK?

Yup. That's where the 3000 feet come from. Because of the lower air density up
there, your airplane will develop less than 75 percent rated power up there.
Two big caveats:

1. We're talking density altitude here. So you might well be leaned during the
roll down the runway at 100 ft MSL elevation, if the temperature is high
enough. Not rare at all.

2. It might make sense to lean even earlier when you want to maintain max
power. One advice given is: Keep the EGT where it was when it stabilized after
took off at full power. If you don't lean, EGT will decrease slowly with
altitude.



--
Thomas Borchert (EDDH)

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)

: My question: Is the engine
: developing less than 75% power during the climb; and is this why leaning in
: the climb is OK?

: Yup. That's where the 3000 feet come from. Because of the lower air density up
: there, your airplane will develop less than 75 percent rated power up there.
: Two big caveats:

Actually, 3000' isn't high enough to limit power to 75%. It's only 3" less
than full MP... that'd be 26". If climb RPM is only 2100-2200 or so, THEN it may be
limited to 75%. Cruise power at 3000' DA can easily exceed 75%.

: 1. We're talking density altitude here. So you might well be leaned during the
: roll down the runway at 100 ft MSL elevation, if the temperature is high
: enough. Not rare at all.

Quite normal to have in excess of 2000' increase in DA during the summer.

: 2. It might make sense to lean even earlier when you want to maintain max
: power. One advice given is: Keep the EGT where it was when it stabilized after
: took off at full power. If you don't lean, EGT will decrease slowly with
: altitude.

That's what my post suggested. Very quick, easy, accurate, and safe way to do
things. It does require and EGT, however. It should also be noted that keeping CHTs
below "too high" takes precidence over leaning to a specific EGT. In a long climb you
may have to either nose over for better cooling, or bite the extra fuel burn, fouled
plugs, and decreased power of running WAY rich for best engine long-term health.

Also note that cheaper thermocouple EGT gauges are subject to "cold junction"
errors. They don't read the absolute temperature, but rather the difference between
the probe (hot junction) and connection to the meter (cold junction). Between winter
and summer where that may fluctuate 100 degrees, the indication on the meters will
fluctuate by the same. Colder cold junction (winter) = hotter reading on gauge.

I suspect the more advanced engine monitors compensate for this internally,
but my dumb analog meters do not.

-Cory



: --
: Thomas Borchert (EDDH)


--

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

My practice has always been to lean for highest rpm when I start the take
off roll. Then richen it up a couple hundred feet up when clearing something
is no longer a factor.



"Matt" wrote in message
.. .
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

Can your 152 produce 75% power at 3000 feet?

"Robert M. Gary" wrote:
Can your 152 produce 75% power at 3000 feet?

I don't have real-world numbers to back this up, but doing some
interpolation from the cruise numbers in the POH: 75% power is possible at
2425 RPM at 3000 feet with a TAS of 102. In a climb I would be at around 70
knots, so the engine should not be able to reach the cruise RPM of 2425. So
I suppose in a climb at 3000 feet, the engine would not be producing 75%,
and it would be OK to lean.

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.