HEADQUARTERS OH-58A, Technical Manual

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TM 55-1520-228-10
Change 10 2-27
2-20. ENGINE AUTOMATIC RELIGHT SYS-
TEM (NOT USED).
An ENGINE RELIGHT ON/OFF switch and an ENGINE
RELIGHT light may be found on the instrument panel.
The automatic relight system has been deactivated and
is not functional. There is no approved functional system
for the OH-58A/C helicopter.
2-21. ENGINE INSTRUMENTS AND INDI-
CATORS.
The engine instruments and indicators are mounted in
the instrument panel or the caution panel in the lower
console. They are described in the following paragraphs
and shown in figure 2-13 and figure 2-14.
a. Engine Out Warning. An RPM sensor is con-
nected to the gas producer tachometer. Power is sup-
plied from the CAUTION PNL LTS circuit breaker and
connections are made to the ENGINE OUT warning
light (figure 2-13 and figure 2-14), and to a tone genera-
tor which produces a tone in the pilot headset. The warn-
ing system is activated when N1 is below 55
$
3% and
is deactivated above that N1 speed. The audio signal is
the same as the low rotor audio signal.
b. Engine Out Audio Warning. A switch con-
nected to the collective lever disables the engine out
audio warning when the collective lever is in the full
down position.
c. Torquemeter. The torquemeter (figure 2-13 and
figure 2-14), located in the instrument panel, displays
percent of torque produced by the engine. The torque-
meter is a direct reading, wetline indicator.
d.
A
Turbine Outlet Temperature Gage. A ther-
mocouple harness assembly with four integral probes is
used to sense the temperature of the gases on the outlet
side of the gas producer turbine rotor. A DC voltage
which is directly proportional to the gas temperature it
senses, is generated by each thermocouple. The ther-
mocouple and thermocouple harness provide an aver-
age of the four voltages representative of the turbine
outlet temperature (TOT) and this is the temperature
indication on the TOT gage on the instrument panel.
e.
C
Turbine Outlet Temperature Indicator. The
turbine outlet temperature (TOT) indicator (figure 2-14
)
,
located in the instrument panel, displays temperature in
degrees Celsius of the exhaust gases in the N1 turbine
outlet area. The indicator is powered by 28 Vdc and
protected by TURB OUTLET TEMP circuit breaker.
f. Gas Producer Tachometer. The gas producer
tachometer generator, located on the engine, generates
an AC voltage with a frequency that is a function of gas
producer turbine rotor N1 RPM. The output of the
tachometer generator is delivered to the gas producer
tachometer indicator which indicates the frequency in
terms of percent RPM of gas producer turbine speed.
The power for the gas producer tachometer is engine
generated
A
. The helicopter electrical system powers
the
C
model and is protected by a gas producer tach
circuit breaker.
g. Dual Tachometer. The dual tachometer (figure
2-13
A
, figure 2-14
C
) located in the instrument panel
displays percent RPM of the engine and rotor. The outer
scale is marked Engine and the inner scale is marked
Rotor. The OH-58A indicators are direct reading instru-
ments which are not dependent on the electrical system.
The OH-58C tach indicators are 28v DC-powered and
protected by the DUAL TACH and GAS PROD TACH
circuit breakers.
h.
A
Oil Pressure Gage. The oil pressure indica-
tor, located on the instrument panel, is a direct-reading,
wet-line system. Pressure from the pressure side of the
oil pump is indicated in psi. Refer to figure 2-13.
i.
A
Oil Temperature Gage. The engine oil tem-
perature gage, located on the instrument panel, is con-
nected to an electrical resistance type thermocouple
and indicates the temperature of the oil at the oil tank
outlet.
j.
C
Oil Pressure/Temperature Indicator. The
engine oil pressure/temperature indicator (figure 2-14),
located in the instrument panel, displays engine oil pres-
sure in psi and temperature in degrees Celsius. The
temperature circuit is powered by 28 Vdc and protected
by ENG OIL TEMP circuit breaker. The oil pressure
portion of the indicator is a direct reading wetline sys-
tem.