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DEG indicator (fig 2-28), located in the upper right section
of the pilot and CPG instrument panels, provides a
visual indication of stabilator angle of incidence in either
manual or automatic modes of operation. It is calibrated
from 10 ° trailing edge up to 35 ° trailing edge
down to reflect the position of the stabilator trailing
edge. An OFF flag is displayed on the indicator face
when the instrument is not operating and dc electrical
power is applied to the indicator. With ac or dc power
loss, both the OFF flag and pointer are not displayed.
M01-311
Figure 2-28. Stabilator Position Indicator
e. Stabilator Placard. A placard installed to the
right of the position indicator in each crew station lists
stabilator incidence angles for given airspeeds. Refer to
Chapter 5 for limitations.
2-49
TM 1-1520-238-10
Section VI. HYDRAULIC AND PRESSURIZED AIR SYSTEMS
2.38 HYDRAULIC SYSTEMS.
Two independent hydraulic systems are installed so
that failure of one system will not affect operation of
the other. They are designated as the primary and utility
hydraulic systems. They are similar but not identical;
they have separate, as well as shared functions.
2.38.1 Primary Hydraulic System. The primary hydraulic
system (fig 2-29) provides hydraulic power to
the primary side of the lateral cyclic, longitudinal cyclic,
collective, and directional servoactuators. Only the
primary sides of these servoactuators (discussed in
more detail in Section V) have electrohydraulic valves
that allow the DASE and BUCS to affect the flight controls.
Consequently, failure of the primary hydraulic
system will result in the loss of DASE and BUCS. The
primary hydraulic equipment includes the hydraulic
pump, manifold, and servoactuators. The heat exchanger
may still be installed in the primary system on
some helicopters. The heat exchanger is obsolete and is
being removed through attrition.
a. Servoactuators. The servoactuators (fig 2-29)
can be commanded mechanically or electrically. Each
actuator contains two hydraulic pistons on a common
piston rod. One piston is driven by the primary hydraulic
system, the other by the utility hydraulic system.
The hydraulic provisions in the actuator are completely
independent of each other; there is no exchange of fluid
between systems.
HEach actuator is controlled by a common manual
tandem servo valve which ports hydraulic pressure to
each of the pistons. The servo valve spool is positioned
by the associated mechanical control system to provide
full authority control. Each actuator is also electrically
controlled through the electrohydraulic valve sleeve to
provide SAS or BUCS control. Each actuator is
equipped with a hydraulically powered plunger which
locks the manual servo valve spool at mid position
when the DASEC powers the BUCS solenoid valve for
BUCS engagement. Each actuator is also equipped
with a DASEC controlled SAS solenoid valve that ports
primary hydraulic pressure to the servo valve and the
BUCS solenoid. Position transducer LVDT’s measure
the position of the servo valve sleeve and the actuator
position. Each actuator incorporates a shear pin in the
feedback linkage to decouple the actuator motion from
2-50 Change 4
a jammed mechanical control and prevent damage to
the bellcrank attachments.
b. Primary Pump. The primary hydraulic pump is
mounted on the accessory drive case of the main transmission
(left side). The pump is of constant-pressure
variable-displacement design driven by the transmission
accessory gear train.
c. Primary Manifold. The primary manifold is
installed on the left forward quadrant of the transmission
deck. Its function is to store, filter, supply, and regulate
the flow of hydraulic fluid. The manifold reservoir
is pressurized on the return side by PAS air acting on
the manifold reservoir piston. This prevents pump inlet
cavitation. Servicing crews introduce fluid to the reservoir
through ground support equipment (GSE) connections
or the hand pump. Low pressure fluid entering
the fill port is filtered by a 45 micron screen filter (before
MWO 1-1520-238-50-52) or a 5 micron cartridge
filter (after MWO 1-1520-238-50-52). The primary hy
draulic system fluid capacity is six pints. The reservoir
stores about one pint. Section XV contains specifications,
capacities, and procedures for oil system servicing.
Other provisions within the primary manifold are
described below:
(1) Air-Bleed Valve. Used to deplete the pressurized
air on the manifold for system repair or service.
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