Cessna Skyhawk 172N Pilot Operating Handbook page 75

CESSNA
SECTION 5
MODEL 172N
PERFORMANCE
CRUISE
The cruising altitude should be selected based on a consideration of
trip length, winds aloft, and the airplane's performance. A typical cruising
altitude and the expected wind enroute have been given for this sample
problem. However, the power setting selection for cruise must be deter ­
mined based on several considerations. These include the cruise perfor ­
mance characteristics presented in figure 5-7, the range profile chart
presented in figure 5-8, and the endurance profile chart presented in figure
5-9.
The relationship between power and range is illustrated by the range
profile chart. Considerable fuel savings and longer range result when
lower power settings are used.
The range profile chart indicates that use of 65% power at 5500 feet
yields a predicted range of 523 nautical miles with no wind. The endurance
profile chart, figure 5-9, shows a corresponding 4.7 hours.
The range figure of 523 nautical miles is corrected to account for the
expected 10 knot headwind at 5500 feet.
Range, zero wind 523
Decrease in range due to wind
(4.7 hours
x
10 knot headwind) 47
Corrected range 476 Nautical Miles
This indicates that the trip can be made without a fuel stop using
approximately 65% power.
The cruise performance chart, figure 5-7, is entered at 6000 feet altitude
and 20°C above standard temperature. These values most nearly corres ­
pond to the planned altitude and expected temperature conditions. The
engine speed chosen is 2500 RPM, which results in the following:
Power
64%
True airspeed
114 Knots
Cruise fuel flow 7.1 GPH
The power computer may be used to determine power and fuel consump ­
tion more accurately during the flight.
FUEL REQUIRED
The total fuel requirement for the flight may be estimated using the
performance information in figures 5-6 and 5-7. For this sample problem,
figure 5-6 shows that a climb from 2000 feet to 6000 feet requires 1.3 gallons
1 July 1978 5-5