TM 1-1520-238-T-5
8–26
8–7.
SYSTEM DESCRIPTION (cont)
8–7
(f) The CPG RAI (fig. 8–19) receives pitch and roll synchro inputs from heading attitude reference
system (HARS). The CPG RAI operates on 115 VAC, single phase 400 Hz. The input is applied to the RAI pitch
trim knob and an internal stepdown transformer. The internal stepdown transformer converts VAC to excitation
voltages for pitch and roll servos. The pitch trim control knob adjusts the pitch of the gyrosphere horizon to the
fixed aircraft symbol. HARS pitch data is applied as pitch synchro signals are sent to the RAI pitch servo stator.
The pitch servo rotates the gyrosphere to a new up or down position. HARS roll data is applied as roll synchro
signals are sent to the RAI roll servo stator. The roll servo rotates the gyrosphere to a new degree–of–roll position.
The word CLIMB appears on the gyrosphere when the helicopter upward pitch reaches 35. The word DIVE
appears on the gyrosphere when the helicopter downward pitch reaches –35. An OFF flag is displayed if the
HARS fails.
HARS
115 VAC BUS
CPG INTR
LT PANEL
ROLL SERVO
STATOR
ROTOR
PITCH SERVO
STATOR
ROTOR
FLAG
RELAY
OFF
FLAG
PITCH
TRIM
T1
ROLL SYNCHRO
PITCH SYNCHRO
WARNING (28 VDC)
115 VAC, 400 HZ POWER
0 - 5 VDC EDGE - LIGHTING
M68-128
PITCH TRIM
POTENTIOMETER
CPG RAI
Figure 8–19.
CPG RAI Functional Block Diagram
(g) The pilot magnetic compass (fig. 8–20) is liquid filled to keep vibrations from affecting operation. The
offsetting magnets adjust the compass pointer to true magnetic North. Magnets correct compass errors caused by
magnetic forces of the helicopter structure (deviation). A compass correction card is provided to note errors that
remain after magnetic correction. The compass card rotates on the pivot point inside the sealed liquid–filled bowl.
The compass card lines up with the earth’s magnetic field.
