THEORY OF OPERATION -- CONTINUED
Cable Cables used on the main winch, auxiliary winch, hoist winch and stayline cables consist of strands (1) which
are made up of wires twisted together to form the cable. The core (2), a foundation of wire, supports the strands (1)
holding them in position during use. Multiple strands (1) around the core (2) increase the strength of the cable.
The length of one strand (1) of cable around the core (2) is called a lay.
LAY (LAY LENGTH)
AUXILIARY POWER UNIT (APU)
The auxiliary power unit (APU) (1) consists of an overhead valve, two--cylinder, four--cycle, air--cooled, diesel en-
gine connected directly to a 300--ampere, 28--volt, shunt--wound, direct--current generator (which is also used as a
starter) (2), and auxiliary hydraulic system pump. The auxiliary power unit (1) provides hydraulic power to raise and
lower the spade, stow and raise the boom and retrieve the main and hoist winch cables under no--load conditions.
The 300--ampere, 28--volt generator (2) is used as a starter motor for the APU (1). This is accomplished by first
feeding 24 V dc to the field coil of the generator (2) from the preheat relay when the preheat switch is activated and
then applying 24 V dc to the generator armature through a starting relay when the starter switch is activated. This
motorizes the generator (2), which is directly coupled to the APU (1) by a drive chain (3). When the APU (1) starts,
the current in the generator armature reverses direction and the system automatically changes from a motorizing
mode to a generating mode. After the APU starts, the start and preheat switches must be released to prevent load-
ing down the engine since the voltage regulator is bypassed during the start cycle and full voltage is being applied
to the field. After the auxiliary power unit (1) has started, the preheat and start switches are released and the gen-
erator output is controlled by a solid--state voltage regulator, located inside the vehicles engine compartment.