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maximum gross weight for hover at a given wheel
height, pressure altitude, and temperature condition.
Enter at the known pressure altitude, move right to the
temperature, then draw a line down to the bottom of
the lower grid. Now enter upper left grid at maximum
torque available, move down to wheel height, and then
move right to intersect the previously drawn line and
read gross weight. This is maximum gross weight at
which the helicopter will hover.
7A.18. CONDITIONS.
The hover chart is based on calm wind, level surface,
100% rotor rpm and rotor BLADE de-ice switch off.
With rotor BLADE de-ice switch ON, torque required
will increase 1.4%.
7A-13
TM 1-1520-238-10
Figure 7A-6. Hover Chart
7A-14
TM 1-1520-238-10
7A.19.
Section V.
DESCRIPTION.
The cruise charts (figs 7A-7 thru 7A-17) present the
level-flight 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 °C 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.
7A.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.
7A.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
7A.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 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
may be used if it is available without exceeding the limitations
presented in Chapter 5. The limit torque line
shown on these charts as 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.
7A.20.3 Fuel FIow. Fuel flow scales are provided opposite
the torque scales. On any chart, torque may be
converted directly to fuel flow without regard to other
chart information. Sea level ground fuel flow at flat
pitch and 100% Np is approximately 555 pounds per
hour.
7A.20.4 Maximum Range. The maximum range lines
indicate the combinations of gross weight and airspeed
　
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