TM 55-1510-222-10
EXAMPLE FUEL FLOW - LBS/HR
WEIGHT
POUNDS
ISA
ISA + 5°C
ISA + 10°C
16,000
645.0
---
680.0
15,000
615.5
662.5
629.5
14,000
586.0
---
579.0
Total Fuel flow = 622.5 Ibs/hr
Reserve Fuel = 45 minutes x 662.5 lbs/hr = 466.875 = 467 lbs
(8) Reserve Fuel. Reserve Fuel is the amount
of fuel required to fly at cruise altitude for 45 minutes at
Maximum Range Power. This example assumes the
average cruise weight while using Reserve Fuel to be
15,000 pounds. Enter the MAXIMUM RANGE POWER
AT 1500 RPM tables for ISA and for ISA + 10°C and
interpolate to find the total fuel flow for 25,000 feet at
16,000 pounds and 14,000 pounds. Interpolate between
these values for 15,000 pounds. Refer to the Example
FUEL FLOW table for an illustration of the reserve fuel
flow determination procedure.
(9) Total Fuel Requirements. Calculated Fuel
Usage + Reserve Fuel = Total Fuel Requirement.
(10)
Zero Fuel Weight Limitation. For this
example, the following conditions were assumed:
Ramp Weight................................................. 16,110 lbs
Weight of Usable Fuel Onboard........................ 3631 lbs
Zero Fuel Weight =(16,110 - 3631)................ 12,4791bs
Maximum Zero Fuel Weight (from LIMITATIONS
Section) ......................................................... 12,700 lbs
Maximum Zero Fuel Weight Limitation has not been
exceeded.
Anytime the Zero Fuel Weight exceeds the Maximum
Zero Fuel Weight Limit, the excess weight must be off-
loaded from PAYLOAD ONLY (i.e., not from fuel). If
desired, additional fuel may then be added. However,
the foregoing calculations will remain unchanged only if
the fuel added is equal in weight to the payload off-
loaded, since only then will the ramp weight and takeoff
weight remain the same as before.
n.
Range and Endurance. Estimates of the effect
of fuel load and power setting on aircraft range and
endurance can be determined from the RANGE and
ENDURANCE PROFILE graphs. The range of a
mission at normal cruise power can be determined by
entering the RANGE PROFILE - NORMAL CRUISE
POWER graph at 25,000 feet, reading right to the
anticipated fuel load and down to the resulting range.
This chart indicates that a fuel load as low as 1500
pounds would be sufficient for the planned 216 nautical
mile mission from Billings to Casper. The available
range with full main and aux. tanks (3631 pounds) for a
flight at 25,000-feet can be determined to be 990
nautical miles. If additional range is required, either a
higher altitude or a lower power setting could be
selected. To determine the range with a maximum fuel
load, enter the RANGE PROFILE - FULL MAIN AND
AUX TANKS graph at 25,000 feet, read right to the
desired power setting and down to the resulting range.
This chart shows that for a full-fuel mission, range can
be increased from 990 to 1078 nautical miles by
reducing power to Maximum Range power.
The aircraft endurance can be determined from the
various endurance profile graphs in a similar manner.
It should be noted that these graphs are all based on
standard day temperatures, and the range graphs are
also based on zero wind. If forecast temperatures differ
from standard values or if headwinds are expected, a
more rigorous mission analysis should be accomplished.
o.
Landing Example
NOTE
For this example, an expected fuel
usage of 834 pounds was assumed.
(1) Weight. The estimated Landing Weight is
determined by subtracting the fuel usage expected for
the trip from the Ramp Weight:
Ramp Weight................................................. 16,110 lbs
Fuel Usage Expected for Total Trip.................(-) 834 lbs
Landing Weight.............................................. 15,276 lbs
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