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timated, and the endurance and range shown in the charts
should be modified accordingly. Fuel allowances for takeoff
and climb are given in Section VI.
Normal cruising requires between 50% and 70% power.
The
manifold pressure and RPM settings required to obtain these
powers at various altitudes and outside air temperatures can
be determined with your power computer.
A maximum cruising
power of approximately 75% (24.5 inches Hg., and 2500 RPM)
may be used if desired.
Various percent powers can be ob-
tained with a number of combinations of manifold pressures,
engine speeds, •altitudes, and outside air temperatures.
However, at full throttle and constant engine speed, a speci-
fic power can be obtained at only one altitude for each given
air temperature.
For a given throttle setting, select the lowest engine
speed in the green arc range that will give smooth engine
operation without evidence of"'laboring.
The use of lower power settings and the selection of
cruise altitude on the basis of the most favorable wind
conditions are significant factors that should be considered
on every trip to reduce fuel consumption.
Additional range
can be achieved when operating at 55% power or less by lean-
ing to peak exhaust gas temperature (EGT) for Best Economy
mixture.
Refer to Economy Mixture Indicator in Section VII
if the optional EGT system is installed.
If the EGT system
is not installed, lean to a fuel flow of 6 pounds per hour
per engine less than the Recommended Lean fuel flow shown on
the power computer or the cruise performance charts shown in
Section VI.
This setting results in an airspeed loss of 4
KTAS and range increase of 8% compared to the Recommended
Lean mixture.
Do not lean to the extent that engine rough-
ness or excessive speed loss occurs.
CAUTION
Best economy mixture operation at 55% power
or less is not recommended until oil consump-
tion stabilizes or during the first 50 hours
of operation.
The purpose of this interval
of operation at higher power levels (65% to
75% power) is to insure proper seating of
the rings and is applicable to new engines,
and engines in service following cylinder
replacement or top overhaul of one or more
cylinders.
2-9
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