Textron Cessna 172R, Pilot Operating Handbook

Page: 139 / 500

CESSNA
MODEL 172R SECTION 4
NORMAL PROCEDURES
ALTITUDE
80%
POWER
70%
POWER
60% POWER
KTAS NMPG KTAS NMPG KTAS NMPG
Sea
Level
113 12.3 108 13.4 100 14.5
4000 feet 117 12.8
111
13.9
103 14.9
8000
feet
122 13.3 115 14.3 105 15.3
Figure 4-3. Cruise Performance Table
LEANING USING THE EGT INDICATOR
At
or below
80%
power in level cruise flight, the exhaust
gas
temperature (EGT) indicator is used
to
lean the fuel-air mixture for
best
performance
or
economy. The Cruise Performance charts
in
Section 5 are based on the EGT
to
adjust the
mixture
to
Recommended Lean per Figure 4-4.
MIXTURE DESCRIPTION
EXHAUST GAS
TEMPERATURE
RECOMMENDED
LEAN
(Pilot’s Operating Handbook
)
50°
Rich of Peak EGT
BEST ECONOMY Peak EGT
Figure 4-4. EGT
Table
Use the mixture
control vernier adjustment (rotate the knob CCW
to
lean the mixture)
to
slowly lean, from full rich or maximum RPM
mixture,
while
monitoring the EGT indicator. As the EGT indication
begins to increase, continue
to
slowly
lean the mixture until an EGT
indication decrease is just detectable.
Reverse the adjustment
slowly in the rich direction until an EGT indication
decrease is
again just
detectable,
then
set
the EGT index pointer
to match the
peak indication. The mixture may
be leaned slightly to return to
peak EGT
or
may be
further
richened
to
Recommended Lean
mixture as
desired. Continuous operation at mixture settings
lean of peak EGT is prohibited.
Any change in altitude or throttle
position will require that peak EGT be redetermined
and the desired
mixture be
reset.
Under some conditions, engine roughness may
occur
at
peak EGT. In this case,
operate at
Recommended Lean
mixture.
As noted in Figure 4-4,
operation at peak EGT provides
the best
fuel economy.
Operatoion at peak EGT results in approximately
4%
greater
range and approximately a
3 knot decrease in airspeed from
the figures shown in the Performance section of this
handbook.
Recommended
Lean mixture provides best level cruise
performance
(generally close
to "best power"
or
maximum RPM).
Revision
7
4-27
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