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 the sample problem.
However, the power setting
selection for cruise must be deter-
mined based on several
considerations. These include the
cruise performance
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. For thze sample
problem, a cruise power of
approximately 65% will be used.
The cruise performance chart,
figure 5-7, is centered at 6000
feet altitude and 20°C above
standard temperature. These
values most nearly correspond
to the planned altitude and
expected temperature conditions.
The engine speed chosen is 2500
RPM, which results in the
following: •
Power
True airspeed
Cruise fuel flow
66%
112 knots
7.4 GPH
FUEL REQUIRED
The total fuel requirement for
the flight may be estimated using
the performance information in
figzres 5-6 and 5-7. For the
sample problem, figure 5-6 shows
that a climb from 2000 feet to
6000 feet requires 1.6 gallons of
fuel. The corresponding distance
during the climb is 10 nautical
miles. These values are for a
standard temperature and are
sufficiently accurate for most
flight planning purposes.
However, a further correction for
the effect of temperature may be
made as noted on the climb chart.
The approximate effect of a non-
standard temperature is to
increase the time, fuel, and
distance by 10% for each 10°C
above standard temperature, due
to the lower rate of climb. In this
case, assuming a temperature
16°C above standard, the
correction would be:
With this factor included, the fuel estimate would be calculated as follows:
16°C
10°C
10% = 16% Increase
Fuel to climb, standard temperature
Increase due to non-standard temperature
(1.6 16%)
Corrected fuel to climb
1.6
0.3
1.9 gal.
FLIGHT SIMULATION USE ONLY
PERFORMANCE
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