TM 55-1510-222-10
m. Flight
Planning
Example.
The
following
calculations provide information for flight planning.
Calculations for flight time, block speed, and fuel
requirements for the proposed flight are detailed below.
NOTE
For
example
purposes,
the
differences between MSL altitudes
and pressure altitudes have been
ignored in enroute calculations.
(1) ISA Conversion. Enter the graph at the
conditions indicated:
BIL
Pressure Altitude........................................3499 feet
FAT ..................................................................15°C
ISA Condition............................................ISA + 7°C
BIL - CZI
Pressure Altitude.....................................25,000 feet
FAT ................................................................ -40°C
ISA Condition..............................................ISA -6°C
CZI-CPR
Pressure Altitude.....................................25,000 feet
FAT ................................................................ -30°C
ISA Condition............................................ISA + 5°C
CPR
Pressure Altitude........................................5998 feet
FAT ..................................................................20°C
ISA Condition.......................................... ISA + 17°C
(2) Time, Fuel, and Distance to Cruise Climb.
Enter the graph at 15°C, to 3499 feet pressure altitude,
and to 16,000 pounds. Enter again at -40°C to 25,000
feet pressure altitude, and to 16,000 pounds. The
following results are obtained:
Time to Climb ................................ 18.3 - 1.4 = 16.9 min
Fuel to Climb ..................................... 310 - 30 = 280 lbs
Distance Traveled ........................... 52.5 - 4.3 = 48.2 nm
(3) Time, Fuel, and Distance to Descend. Enter
the graph at 25,000 feet, and enter again at 5998 feet,
and find
Time to Descend............................ 16.7 - 4.1 = 12.6 min
Fuel Used to Descend......................... 250 - 87 9163 lbs
Distance Traveled ..................................84 - 21 = 63 nm
(4) Cruise
Weight
(Estimated).
For
the
following cruise segment examples, the estimated
average cruise weight used was 15,600 pounds.
(5) Cruise Tables.. Enter the tables for
NORMAL CRUISE POWER. AT 1500 RPM for ISA -
10°C, ISA, and ISA + 10°C, and read the cruise speeds
for 24,000 feet and 26,000 feet at 16,000 pounds and
14,000 pounds. Interpolate between these speeds for
25,000-foot values. See Example Cruise True
Airspeeds table for the results.
Interpolate between the 25,000-foot speeds for ISA -
6°C and ISA + 5°C at 15,600 pounds.
Cruise True Airspeed (ISA -6°C) .......... 257 knots Cruise
True Airspeed (ISA+5°C)................................. 247 knots
Similar computations can be made to interpolate for
cruise torque setting and fuel flow.
Cruise Torque (ISA-6C) ......................................... 75%
Cruise Total Fuel Flow (ISA-6C) .................... 800 lbs/hr
Cruise Fuel Flow/Eng. (ISA-6°C) ..................... 400 lbs/hr
Cruise Torque (ISA + 5°C) ...................................... 68%
Cruise Total Fuel Flow (ISA + 5°C) ................. 740 lbs/hr
Cruise Fuel Flow/Eng. (ISA + 5C) .................. 370 lbs/hr
(6) Cruise Graphs. In addition to the cruise
performance
presented
in
tabular
form,
data
representing a cruise weight of 14,000 pounds is
presented in graphical form for quick reference.
NOTE
Use of these graphs for flight
conditions other than 14,000 pounds
gross weight may introduce errors.
a.
Cruise Speeds. Enter the NORMAL CRUISE
SPEEDS AT 1500 RPM graph at 25,000 feet, and read
the true airspeeds for ISA-6°C and ISA + 5°C:
Cruise True Air Speed (ISA-6C).................... 263 KTAS
Cruise True Air Speed (ISA +5C) .................. 255 KTAS
b.
Cruise Power Setting. Enter the NORMAL
CRUISE POWER AT 1500 RPM graph at 25,000 feet,
and read the recommended torque settings for ISA -6 "C
(-34 °C IFAT) and ISA + 5°C (-24°C IFAT):
ISA -6°C (-34°C IFAT) ................. 75% torque per engine
ISA + 5°C (-24°C IFAT) ............... 68% torque per engine
7-8
