Ignition System

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHAPTER THREE

WORKBOOK

CHANGE 2

shaft that drives the main oil pump. It removes oil from the compressor bearings and the bottom

of the accessory gearbox. The external scavenge pump draws oil from the reduction gearbox and

the power turbine shaft bearings.

After leaving the main oil pump, the oil is cleaned by a metal screen type oil filter located inside

the oil tank. A bypass valve allows the oil to be rerouted if the filter becomes clogged.

The oil breather is located inside the main oil tank and it vents air from the tank overboard. It

incorporates a two-way, gravity-operated valve to accommodate inverted flight.

Cooling of engine oil is accomplished by utilizing a radiator type heat exchanger located in the

accessory air intake duct. Air passing through the oil cooler removes heat from the oil and then

exits through a square opening on the lower left side of the engine cowling. There is a

temperature-sensitive bypass valve on the oil cooler that controls oil flow through the cooler.

A combination oil pressure and oil temperature indicator is located on the instrument panel in

both cockpits. The indicator uses DC power to display the pressure and temperature of the oil as

it leaves the main oil pump. It receives its signals from the oil pressure transmitter, located on

the right engine support frame and the temperature transmitter on the right side of the accessory

gearbox. The temperature portion of the gauge is graduated in 10 C increments, while pressure

is in 10 PSI increments.

NOTE

Gauge is rotated 90 for ease of reading.

OIL TEMPERATURE

LIMITATIONS

OIL PRESSURE

-40 C

Minimum

40 PSI @ idle (62-65% N1)

10 - 99 C

Normal

65 - 85 PSI (above 75% N1)

100 C

Maximum

100 PSI

(The NATOPS limit for minimum oil temperature is -40 C, but the gauge only reads to a

minimum of 0 C)

304.

IGNITION SYSTEM

The ignition system provides initial ignition (during engine start) for the fuel/air mixture in the

combustion chamber. There are two igniter plugs that protrude into the combustion chamber to

provide the spark. They receive power through two shielded ignition cables, from an exciter box

(also known as a spark igniter box). The exciter box is an electrical capacitor which changes the

aircraft nominal DC current to approximately 1400 volts pulsating DC current. It is located at

the 10 o'clock position on the engine support frame. When operating, the exciter box produces

stray voltage which will be seen on the fuel flow indicator as an increase in fuel flow, i.e., a false

reading.

PT6A-25 AIR/OIL/IGNITION SYSTEMS

3-5