signal polarity. The follow-up rod is attached to
control systems located in the engine room.
the forward end of the piston and extends through
The system has two basic parts or groups
the OD box end cover. It moves with the valve
of components. One part of the system is the
rod assembly and positions a pointer on the OD
CRP electronics enclosure mounted on vertical
box pitch indicator. The follow-up rod also
stanchions near the free-standing electronics
positions the sliding contacts on the two OD box
enclosure (FSEE) in each engine room. The other
potentiometers. The shaped potentiometer pro-
basic group is the components mounted on the
vides the signal source for electronic display of
OD box. This group consists of the control oil
the actual blade pitch. The linear potentiometer
servo valve and two slide-type potentiometers.
provides the feedback signal that cancels the pitch
Figure 8-27 shows the relationship between the
command signal. It also provides the feedback
two basic parts of the system. Although the
signal that allows the control oil servo valve to
systems for each shaft are identical, they are also
close when the pitch ordered by the pitch com-
independent. The propeller pitch on the starboard
mand signal has been reached. The CRP electronics enclosure provides
shaft can be set to the same value or to a different
the supply voltage for both potentiometers.
value than the port shaft pitch. The setting
Besides providing control and potentiometer
depends on what is ordered through the consoles.
voltages, the CRP electronics enclosure receives the potentiometer
feedback and position signals. It also supports a
Electronic pitch control begins with the pitch
local five-point pitch level display and a local
command signal generated by the console. The
digital output monitor display intended primarily
command signal is sent to the CRP electronics
to aid in testing and calibrating the electronic
enclosure. It then causes a servo valve position
signal to be sent to the control oil servo valve on
the OD box. The servo valve is driven off center
Control Oil Servo Valve
and allows control oil to enter the OD box piston
chamber, thus moving the control piston and
The control oil servo valve located on the OD
valve rod assembly. The direction in which the
box is an electrohydraulic valve. It uses an
servo valve opens is determined by the command
Figure 8-27.--Electrical and hydraulic signal flow between CRP system components.
8-42
