SECTION 4
CESSNA
NORMAL PROCEDURES
MODEL 172RG
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.
The Cruise Performance Table, figure 4-3, illustrates the true airspeed
and nautical miles per gallon during cruise for various altitudes and
percent powers. This table should be used as a guide, along with the
available winds aloft information, to determine the most favorable alti-
tudes and power setting for a given trip. The selection of cruise altitude on
the basis of the most favorable wind conditions and the use of low power
settings are significant factors that should be considered on every trip to
reduce fuel consumption.
The tachometer is marked with a green arc from 2100 to 2700 RPM with
a step at 2500 RPM. The use of 2500 RPM will allow 75% power at altitudes
up to 7500 feet on a standard day. For hot day or high altitude conditions,
the cruise RPM may be increased to 2700 RPM. Cruise at 2700 RPM permits
the use of 75% power at altitudes up to 9000 feet on a standard day.
However, for reduced noise levels it is desirable to select the lowest RPM in
the green arc range for a given percent power that will provide smooth
engine operation.
The cowl flaps should be opened, if necessary, to maintain the cylinder
head temperature at approximately two-thirds of the normal operating
range (green arc).
Cruise performance data in this handbook and on the power computer
is based on a recommended lean mixture setting which may be established
as follows:
1. Lean the mixture until the engine becomes rough.
2. Enrichen the mixture to obtain smooth engine operation; then
further enrichen an equal amount.
75% POWER
65% POWER
55% POWER
ALTITUDE
KTAS
NMPG
KTAS
NMPG
KTAS
NMPG
3000
132
13.2
124
14.2
114
15.0
6000
136
13.6
127
14.6
116
15.3
9000
140
14.0
130
14.9
118
15.6
Standard Conditions
Zero Wind
Figure 4-3. Cruise Performance Table
4-18
1 July 1979
CESSNA
SECTION 4
MODEL 172RG
NORMAL PROCEDURES
For best fuel economy at 75% power or less, the engine may be operated
at the leanest mixture that results in smooth engine operation. This will
result in approximately 8% greater range than shown in this handbook
accompanied by approximately 3 knots decrease in speed.
Any change in altitude, power or carburetor heat will require a change
in the recommended lean mixture setting and a recheck of the EGT setting
(if installed).
Carburetor ice, as evidenced by an unexplained drop in manifold
pressure, can be removed by application of full carburetor heat. Upon
regaining the original manifold pressure indication (with heat off), use the
minimum amount of heat (by trial and error) to prevent ice from forming.
Since the heated air causes a richer mixture, readjust the mixture setting
when carburetor heat is to be used continuously in cruise flight.
LEANING
WITH
A CESSNA ECONOMY MIXTURE INDICATOR
(EGT)
Exhaust gas temperature (EGT) as shown on the optional Cessna
Economy Mixture Indicator may be used as an aid for mixture leaning in
cruising flight at 75% power or less. To adjust the mixture, using this
indicator, lean to establish the peak EGT as a reference point and
then
enrichen the mixture by a desired increment based on data in figure 4-4.
As noted in the table, operation at peak EGT provides best fuel
economy. This results in approximately 8% greater range than shown is
this handbook accompanied by approximately 3 knots decrease in speed.
When leaning the mixture under some conditions, engine roughness
may occur before peak EGT is reached. In this case, use the EGT corres-
ponding to the onset of roughness as the reference point instead of peak
EGT.
MIXTURE
DESCRIPTION
EXHAUST GAS
TEMPERATURE
RECOMMENDED LEAN
(Pilot's Operating Handbook
and Power Computer)
°
50F Rich of Peak EGT
BEST ECONOMY
Peak EGT
Figure 4-4. EGT Table
1 July 1979
4-1
