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torque required and total fuel flow at various
conditions of airspeed, pressure altitude, free air temperature,
and gross weight. Cruise charts are provided
for pressure altitudes from sea level to 16,000 feet in
2000-foot increments. Free air temperatures range
from -50° to +60° in 10 °C increments. In addition to
basic cruise information, the charts show speed for
maximum range, maximum endurance, and maximum
rate of climb. Change in torque with change in frontal
area information is presented in the upper left corner of
each chart.
7.20 USE OF CHARTS.
The primary uses of the charts are illustrated by the examples.
To use the charts, it is usually necessary to
know the planned pressure altitude, estimated free air
temperature, planned cruise speed, IAS, and gross
weight. First, select the proper chart on the basis of
pressure altitude and FAT. Enter the chart at the cruise
airspeed, IAS, move right and read TAS, move left to
the gross weight, move down and read torque required,
and then move up and read associated fuel flow. Maximum
performance conditions are determined by entering
the chart where the maximum range line or the
maximum endurance and rate-of-climb line intersects
the gross weight line; then read airspeed, fuel flow, and
torque required. Normally, sufficient accuracy can be
obtained by selecting the chart nearest the planned
cruising altitude and FAT or, more conservatively, by
selecting the chart with the next higher altitude and
FAT. If greater accuracy is required, interpolation between
altitudes and/or temperatures is permissible. To
be conservative, use the gross weight at the beginning
of the cruise flight. For greater accuracy on long flights,
however, it is preferable to determine cruise information
for several flight segments to allow for the decreasing
gross weight.
7.20.1 Airspeed. True and indicated airspeeds are
presented at opposite sides of each chart. On any
chart, indicated airspeed can be directly converted to
true airspeed (or vice versa) by reading directly across
the chart without regard for the other chart information.
The applicable MACH No. or gross weight maximum
permissible airspeed limits (VNE) determined
from figure 5-2 appear on the appropriate charts.
CRUISE
7.20.2 Torque. Since pressure altitude and temperature
are fixed for each chart, torque required varies according
to gross weight and airspeed. The torque required
and the torque limits shown on these charts are
for dual engine operation. The torque available shown
on these charts are maximum continuous torque available
and maximum torque available, 30 minute limit,
where less than the maximum torque-two-engine
transmission limit. These torque lines are the minimum
torque available for ATF = 1 at the engine limits
specified in Chapter 5. Higher torque than that represented
by these lines maybe used if it is available without
exceeding the limitations presented in Chapter 5.
The limit torque line shown on these charts is for dual
engine transmission limit and is defined as 100%
torque. An increase or decrease in torque required because
of drag area change is calculated by adding or
subtracting the change in torque from the torque
change (D Q) curve on the chart, and then reading the
new total fuel flow.
7.20.3 Fuel FIow. Fuel flow scales are provided opposite
the torque scales. On any chart, torque maybe converted
directly to fuel flow without regard to other
chart information. Sea level ground fuel flow at flat
pitch and 100% Np is approximately 550 pounds per
hour.
7.20.4 Maximum Range. The maximum range lines
indicate the combinations of gross weight and airspeed
that will produce the greatest flight range per pound of
fuel under zero wind conditions.
7.20.5 Maximum Endurance and Rate of Climb. The
maximum endurance and rate of climb lines indicate
the combinations of gross weight and airspeed that will
produce the maximum endurance and the maximum
rate of climb. The torque required for level flight at this
condition is a minimum, providing a minimum fuel flow
(maximum endurance) and a maximum torque change
available for climb (maximum rate of climb).
7.20.6 Change In Frontal Area. Since the cruise information
is given for the primary mission configuration,
adjustments to torque should be made when operating
with alternative wing-stores configurations. To
determine the change in torque, first obtain the appropriate
multiplying factor from the drag chart (fig
7-18), then enter the cruise chart at the planned cruise
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