ignition windings, through the ignition exciter,
initiating engine combustion during aircraft
to the igniter plugs. Current flows from the
armament firing, during starting, and for
alternator, through the control amplifier, to the
automatic reignition in case of engine flameout.
ignition exciter. At the ignition exciter, current
The ac ignition system consists of an ignition
increases and discharges as a high-voltage output,
exciter, a control amplifier, leads and ignition
which is conducted through the igniter cables to
plugs, and an alternator stator.
the igniters. Current crossing the gaps in the
igniters produces a continuous high-intensity
ENGINE IGNITION EXCITER.-- The exciter
spark to ignite the fuel mixture in the combus-
is a dual-circuit and dual-output unit that supplies
tion chamber. When engine speed reaches 8,500
a high-voltage, high-energy electrical current for
rpm Ng and interturbine temperature (ITT)
ignition. The exciter consists of a radio frequency
reaches operating range, a T5 signal is generated.
interference filter. The exciter also contains
This signal goes from the T5 temperature
power, rectifier, storage, and output elements.
detectors through the T5 circuit, and to the control
The exciter is on the forward part of the com-
amplifier ignition logic circuit. The control
pressor section of the engine.
amplifier ignition relay opens and ignition stops.
Combustion then continues as a self-sustaining
ENGINE CONTROL AMPLIFIER.-- The
process.
amplifier is the electronic control center of the
Ignition is automatically reactivated when
engine. It controls the function of the ignition
either a flameout occurs or when aircraft arma-
system as well as other engine functions. The
ment is fired. When T5 temperature drops in
amplifier is on the compressor section aft of the
excess of 800F (427C) from T5 selected by PLA,
engine front frame.
a signal transmitted from the T5 detectors causes
the control amplifier T5 flameout logic to close
ENGINE IGNITION LEADS AND IGNITER
the amplifier ignition relay. This activates igni-
PLUGS.-- The ignition leads are high-tension
tion system operation. Ignition continues until
cables that "transmit electrical current from the
engine operating temperature is again attained and
the 800 "F temperature error signal is canceled.
located in the combustion chamber housing.
This action causes the control amplifier to end
ignition operation.
ENGINE ALTERNATOR STATOR.-- The
A n armament-firing protection circuit
alternator is an engine-driven, single-phase, ac
prevents flameout from armament gas ingested
electrical-output unit on the engine accessory gear-
by the engine. When the aircraft armament is
box. It supplies the engine with electrical power
fired, the armament-firing logic circuit is activated
independent of the aircraft electrical system. It
by a signal from the armament trigger switch. The
contains three sets of windings. Two windings
amplifier logic then causes ignition operation to
supply electrical power to the ignition exciter, and
be activated. Ignition operation ends after a
the third winding supplies electrical power to the
1-second time delay in the amplifier logic follow-
control amplifier.
ing release of the armament firing trigger.
Ignition Operation
Ignition System Maintenance
The operation of an ignition system is
The only maintenance performed at the
explained in the following paragraphs. Refer to
organizational level is cleaning and replacement
figure 6-7.
of ignition parts. Ignition parts are sealed units
Starting procedures call for the ignition switch
and must be replaced as complete assemblies.
ON, the engine cranking for starting, and the
Degrease spark igniters and clean the outer
throttle advanced to the 10-degree power lever
shell with a wire brush. If deposits exist on
angle (PLA) position. At that time, current flows
the ceramic tip and on the center and ground
from the alternator stator to power the control
electrodes, remove them by light abrasive blasting.
amplifier. Simultaneously, the PLA ignition
However, this abrasive blast should not be used
switch in the fuel control closes. The gas generator
on the ceramic barrel surface. Clean the ceramic
speed (Ng) logic circuit will close the ignition relay
barrel of the igniter with a soft swab and a suitable
to provide ignition whenever the Ng is within the
solvent. Dry the igniter with compressed air.
10 to 48 percent Ng range. With the relay closed,
Visually inspect the barrel and shell threads. If
a circuit is completed from the alternator stator
6-10
