HEADQUARTERS OH-58A, Technical Manual

Page: 199 / 292

TM 55-1520-228-10
SECTION X. TORQUE AVAILABLE
7-37. DESCRIPTION.
The torque available charts show the effects of altitude
and temperature on engine torque.
7-38. CHART DIFFERENCES.
Both pressure altitude and FAT affect engine power
production. Figures 7-11 and 7-12 show power available
data at 30 minute power and maximum continuous
power ratings in terms of the allowable torque as
recorded by the torquemeter (%Q).
Note that the power output capability of the T63-A-720
engine can exceed the transmission structural limit (100
%Q) under certain conditions.
a. Figure 7-11 (sheet 1) is applicable for
maximum power, engine deice and heater off, 30 minute
operation at 100% N2 rpm.
b. Figure 7-11 (sheet 2) is applicable for
maximum power, engine deice and heater on, 30 minute
operation at 100% N2 rpm.
c. Figure 7-11 (sheet 3) is applicable for
maximum power, engine deice and heater off and
reverse flow inlet installed, 30 minute operation at 100%
N2 rpm.
d. Figure 7-11 (sheet 4) is applicable for
maximum power, engine deice and heater on and
reserve flow inlet installed, 30 minute operation at 100%
N2 rpm.
e. Figure 7-12 (sheets 1 through 4) is
applicable for maximum continuous power for the above
mentioned conditions.
f. Prolonged IGE hover may increase engine
inlet temperature as much as 1 0ºC , therefore, a higher
FAT must be used to correct for the increase under this
condition.
7-39. USE OF CHARTS.
The primary use of the charts is illustrated by the
examples. In general, to determine the maximum power
available, it is necessary to know the pressure altitude
and temperature. By entering the upper left side of the
chart at the known pressure altitude, moving right to the
known temperature, then straight down to the bottom of
the lower grid, available torque is obtained. If the CONT
XMSN LIM line is intersected prior to reaching the
temperature line, TORQUE AVAILABLE is 85%.
Operations in the yellow area of the chart (between 85
and 100%) are limited to 5 minutes duration.
7-40. CONDITIONS.
Chart (figure 7-11) is based upon speeds @ 100%
rotor/engine rpm with grade JP-4 fuel. The use of
aviation gasoline will not influence engine power. Fuel
grade of JP-5 will yield the same nautical miles per
pound of fuel and being 6.8 pounds per gallon will only
result in increased fuel weight per gallon. Because JP-4
and JP-5 have the same energy value per pound, then
JP-5 fuel will increase range by almost 5 percent per
gallon of fuel. The 30 minutes operation limit is based on
TOT indication.
7-47