AIRCRAFT POWER PLANT ELECTRICAL
SYSTEMS
shaft through a generator. The turbine motor
A naval aircraft requires a mechanism to
section contains an axial flow turbine wheel and
propel it through the air. Aviation Machinist's
variable area nozzle that directs air and controls
Mates (ADs) maintain the power plant and its
turbine wheel speed. The planetary differential
associated controls. There are, however, several
transmission section is a variable gear assembly
electrical systems (such as starting, ignition, fire
with infinite gear ratios.
warning, fire extinguishing, anti-icing, fuel, and
In the start mode of operation, an external
indicating systems) that support the power plant.
air source drives the turbine wheel. The gear
AEs maintain these systems.
reduction in the transmission section converts the
high speed of the turbine to high torque. The
STARTING EQUIPMENT
to the engine input drive shaft.
After the engine gains a self-sustaining speed,
Learning Objective: Identify the types of
the ring brake releases and the system changes to
starting equipment used to start aircraft
the constant speed drive mode. In this mode,
engines.
electromechanical, pneumatic, and pneumatic-
hydraulic components act to vary the gear ratio
Jet engine starters provide high starting torque
of the planetary differential transmission. These
to initially overcome the engine rotor weight and
high speed to increase rotor RPM until the engine
components maintain an output of 8,000 RPM
is self-sustaining. The following paragraphs
from the engine input drive shaft.
describe the various starting systems used on
If it becomes necessary to shut down an
engine, airflow routes from the remaining operat-
turbojet, turboprop, and turbofan engines.
ing engine to the CSD/S. This places the system
in the air turbine motor-generator drive mode of
CONSTANT SPEED DRIVE/STARTER
operation. In this mode, power to drive the
generator comes entirely from the turbine drive
The starting system on the A-6 Intruder
wheel. A planetary differential transmission
aircraft is the constant speed drive/starter
section disconnects the generator and turbine from
( C S D / S ) . It has three separate modes of
the engine.
operation:
AIR TURBINE STARTER
1. Start mode.
2. Constant speed drive mode. This mode
The air turbine starter is a lightweight unit
maintains main generator frequency control
designed to start turbojet, turboprop, and
regardless of engine RPM or generator loads.
turbofan engines when supplied with compressed
3. Air turbine motor generator mode. This
air. The unit consists primarily of a scroll
mode is used for auxiliary and emergency
assembly, rotating assembly, reduction gear
operation of a main generator when the main
system, overrunning clutch assembly, and output
engine is shut down.
shaft. An overspeed switch mechanism limits
maximum rotational speed. Compressed air,
Air for starting or emergency/auxiliary
supplied to the scroll inlet, goes to the turbine
operation of the generator is received from the
wheel through the nozzle in the scroll assembly.
other engine or from an external source.
The reduction gear system transforms the high
The CSD/S unit (fig. 5-1) consists of two
speed and low torque of the turbine wheel to low
sections and connects to the engine input drive
5-1
