leaning in climb

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)

: 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 *
************************************************** ***********************

Thomas Borchert wrote:

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.

Density altitude cuts the other way as well. If you're flying in cold
weather on a clear day, 3,000 feet indicated altitude might not be that
far above sea level density altitude.

Some day, I'd like to get more information about how density altitude
and my engine interact. By the time the air hits my carb, it's likely
already been warmed up a fair bit, so air density at the carb is not
likely the same as the air density outside the plane.

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 John Deakin's advice as well, and it seems to work. The only
extra consideration is that you want to keep EGT where it would be at a
sea level (DA) takeoff, not necessarily where it was at *this* takeoff.
It might be worth finding a low airport on a day with close-to-ISA
conditions, and actually marking the glass with a blue marker to show
where the needle ends up, though I haven't gone that far yet.

Again, the winter can be a problem, since a sea-level takeoff on a cold
day can put you far below sea level density altitude, and your starting
EGT may be on the high side.


All the best,


David

Thomas Borchert wrote:


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.

You don't mean leaned here, you mean power-restricted.

For those of us who flew from 6000' airports, we leaned at engine
start and then set best power during the run up. We needed every
ounce of performance we could get to get 152's off the ground at
gross at 8000+ density altitudes.