HEADQUARTERS OH-58A, Technical Manual

Page: 214 / 292

TM 55-1520-228-10
(7-61 blank)/7-62 Change 11
SECTION XIII. CRUISE
7-47. DESCRIPTION.
The cruise charts (figure 7-15, sheets 1 through 13)
show the torque pressure and engine rpm required for
level flight at various pressure altitudes, airspeeds,
gross weights, and fuel flows.
NOTE
The cruise charts are basically arranged
by FAT groupings. Figure 7-15, sheets 1
through 13, are based upon operation
with clean configuration.
7-48. USE OF CHARTS.
The primary use of the charts is illustrated by the exam-
ples provided in figure 7-15. The first step for chart use
is to select the proper chart, based upon the planned
drag configuration, pressure altitude, and anticipated
free air temperature; refer to chapter 7 index (paragraph
7-2). Normally, sufficient accuracy can be obtained by
selecting the chart nearest to the planned cruising alti-
tude and FAT, or the next higher altitude and FAT (chart
Example A, Method 2). If greater accuracy is required,
interpolation between altitudes and/or temperatures will
be required (chart Example A, Method 1). You may enter
the charts on any side: TAS, IAS, torque pressure, or
fuel flow, and then move vertically or horizontally to the
gross weight, then to the other three parameters. Maxi-
mum performance conditions are determined by enter-
ing the chart where the maximum range or maximum
endurance and rate of climb lines intersect the appropri-
ate gross weight; then read airspeed, fuel flow, and per-
cent torque. For conservatism, use the gross weight at
the beginning of cruise flight. For greater accuracy on
long flights it is preferable to determine cruise informa-
tion for several flight segments in order to allow for de-
creasing fuel weights (reduced gross weight). The
following parameters contained in each chart are further
explained as follows:
a. Airspeed. True and indicated airspeeds are pre-
sented at opposite sides of each chart. On any chart,
indicated airspeed can be directly converted to true air-
speed (or vice versa) by reading directly across the
chart without regard for other chart information. Maxi-
mum permissible airspeed (V
NE
) limits appear as red
lines on some charts. If no red line appears, V
NE
is
above the limits of the chart.
b. Torque (%Q). Since pressure altitude and tem-
perature are fixed for each chart, torque varies accord-
ing to gross weight and airspeed.
c. Fuel Flow. Fuel flow scales are provided oppo-
site the torque scales. On any chart, torque may be
converted directly to fuel flow without regard for other
chart information. All fuel flow information is presented
with engine deice and heater off. Fuel flow increases 5%
with reverse flow inlets installed, 4% with anti-ice on,
and 4% with bleed air heater on.
d. Maximum Range. The maximum range lines in-
dicate the combinations of weight and airspeed that will
produce the greatest flight range per gallon of fuel under
zero wind conditions. When a maximum range condition
does not appear on a chart it is because the maximum
range speed is beyond the maximum permissible speed
(V
NE
); in such cases, use V
NE
cruising speed to obtain
maximum range.
e. Maximum Endurance and Maximum Rate of
Climb. The maximum endurance and maximum rate of
climb lines indicate the airspeed for minimum torque
required to maintain level flight for each gross weight,
FAT, and pressure altitude. Since minimum torque will
provide minimum fuel flow, maximum flight endurance
will be obtained at the airspeeds indicated.
7-49. CONDITIONS.
The cruise charts are based upon operation at 100%
rpm, engine deice and heater off.