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The cruising altitude should be selected based on a consideration of trip length, winds aloft, and the airplane's performance. A 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. For this sample problem, a cruise power of approximately 65% will be used.
The cruise performance chart for
8000 feet pressure altitude is entered using 20 C above standard temperature.
These values most nearly corres pond to the planned altitude and expected
temperature conditions. The power setting chosen is 2300 RPM and 22 inches of
manifold pressure, which results in the following:
Power 65%
True airspeed 132 Knots
Cruise fuel flow 8.8
GPH
The power computer may be used
to determine power and fuel consump tion more accurately during the
flight.
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 normal climb from 2000 feet to 8000 feet requires 2.4 gallons of fuel. The corresponding distance during the climb is 20 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. dueto the lower rate of climb. In this case, assuming a temperature 16 C above standard, the correction would be:
16 C x 10% = 16% Increase
10 C
With this factor included, the
fuel estimate would be calculated as follows:
Fuel to climb, standard
temperature
2.4
Increase due
to non-standard temperature
(2.4 X
16%)
0.4
Corrected fuel to
climb
2.8 Gallons
Using a similar procedure for the distance during climb results in 23 nautical miles.
The resultant cruise distance
is:
Total
distance
425
Climb
distance
-23
Cruise
distance
402 Nautical Miles
With an expected 10 knot headwind, the ground speed for cruise is predicted to be:
3.3 hours x 8.8 gallons/hour = 29.0 Gallons
A 45-minute reserve requires:
45 X 8.8 gallons per hour = 6.6 Gallons
60
The total estimated fuel
required is as follows:
Engine start, taxi, and
takeoff
1.4
Climb
2.8
Cruise
29.0
Reserve
6.6
Total
fuel
required
39.8 Gallons
Once the flight is underway,
ground speed checks will provide a more accurate basis for estimating the time
enroute and the corresponding fuel required to complete the trip with ample
reserve.
A procedure similar to takeoff
should be used for estimating the landing distance at the destination airport.
Figure 5-10 presents landing distance information for the short field technique.
The distances corresponding to 2000 feet pressure altitude and a temperature of
30 C are as follows:
Ground
roll
705 Feet
Total
distance to clear a 50-foot
obstacle 1465
Feet
A correction for the effect of
wind may be made based on Note 2 of the landing chart using the same procedure
as outlined for takeoff.
DEMONSTRATED OPERATING TEMPERATURE
Satisfactory engine cooling has been demonstrated for this airplane with an outside air temperature 23 C above standard. This is not to be considered as an operating limitation. Reference should be made to Section 2 for engine operating limitations.
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