Monticello Flying Club Pilot Transition Manual: Mooney M20F
Page 26 of 42
C
RUISE
In making the transition from climb to cruise, lower the nose enough to maintain altitude,
close cowl flaps (if applicable, engine temperatures permitting and below 150MPH), accelerate to
cruise airspeed,
then
set cruise power using the cruise performance table.
Cruise should be kept
below 75% rated power.
To determine the MP and RPM’s you can consult the table in the POH
and determine what trade off you want between speed and fuel economy. The engine
performance charts in the original POH have been updated for the club’s Mooney after fuel
bladders were installed which reduced the fuel capacity by 9.2 total gallons, thus reducing range.
There is a full performance chart with additional information in the white aircraft folder. Keep in
mind that these tables are for true airspeed and were based on a brand new aircraft, with a new
paint job, and with much fewer antennae. Your indicated airspeed will be different depending on
altitude and your ground speed will be different depending on the winds aloft.
The engine allows for a wide range of MP and RPM settings, but in a few of our tables
there have been some settings that are eliminated for continuous ops. The original propellers had
trouble with harmonic oscillations that prevented continuous operations at low MP’s. This
aircraft has a new scimitar prop.
The only restriction on this propeller is that there shall be
No
continuous operations above 24
″
between 2350 and 2550 rpm.
This is placarded on the panel
and these settings are indicated on the table in the aircraft book.
The tachometer in N3275F has a
bottom red line on the tachometer, but this was applicable to the old prop. There is no bottom red
line value for this new prop.
There are however, other considerations, such as the higher pressures created within the
cylinders. Even though the Mooney POH's generally allow cruise at a lower RPM with higher
manifold pressure, Lycoming recommends using an RPM in the mid ranges (2350-2500),
provided that the engine runs smoothly at the selected RPM. Lycoming does not specifically
address the issue of RPM/MP selection, but it does leave it to the POH and the pilot.
There is a theory that at lower RPM and higher MP you will be "lugging" your engine.
Conversely, at a higher RPM and lower MP your engine will be turning more cycles, but they are
easier cycles with less internal pressure. The overriding consideration should be a smooth
running engine at whatever authorized combination of RPM/MP you select.
L
EANING THE
A
IRCRAFT
The club’s Mooney has an engine monitor that monitors both CHT and EGT on each
cylinder. Procedures for leaning are found in the checklist and the monitor’s quick guide. In
general, you should gradually and conservatively lean the aircraft during climb, and then upon
reaching cruise altitude, lean aggressively using the engine monitor. Lycoming recommends
leaning the engine to 150 degree rich of peak for max power cruise and at peak for economy
cruise (below 75% power).
At no point though should the EGT exceed 1600 degrees or should
the CHT exceed 400 degrees
. Keep in mind that engine temperatures change gradually, so lean
in increments while waiting several minutes between increments to allow the temperature to
stabilize.
Temperature changes should always be kept gradual to prevent engine damage.
Below
is a chart directly from the Lycoming Operating Manual that is very informative:
