THEORY OF OPERATION
a. Hydraulic Systems.
The hydraulic systems (fig. 76) (primary and utility) are used to store, pressurize,
and distribute hydraulic fluid used by hydraulic system components.
(1) The primary hydraulic system provides power assistance to onehalf of each flight control
servocylinder. The primary hydraulic system provides operational power for use by the stability augmentation
system (SAS) and BUCS.
(2) The utility hydraulic system provides power assist to the four pylon actuators, the area weapons
azimuth drive motor and elevation drive actuator, ammunition handling system carrier drive motor, APU starter, tail
wheel lock actuator, and the rotor brake actuator. The utility hydraulic system also provides power assist to the
other half of each flight control servocylinder and emergency pressure use of the flight controls.
(3) Each hydraulic system contains an identical constant displacement, variable delivery hydraulic pump
which provides 3000 psi pressure with a 6 gpm flow capability to the hydraulic system components. The hydraulic
pumps are driven by the main transmission accessory gear box.
(4) Each hydraulic system contains a hydraulic manifold to store system replenishment fluid. The hydraulic
manifolds filters and distributes fluid to using components. The primary hydraulic manifold stores approximately
one pint of fluid in its reservoir, while the entire system holds approximately three quarts of hydraulic fluid. The
utility hydraulic manifold stores approximately 5 quarts in its reservoir, while the entire system holds approximately
10 quarts of hydraulic fluid.
b. Primary Hydraulic System.
The purpose of the primary hydraulic system is to provide hydraulic pressure for electrical
or mechanical directional control of flight control servocylinders. The primary hydraulic system provides visual
indication of primary and utility system pressure.
(2) System Operation (fig. 77).
(a) The primary hydraulic pump draws low pressure fluid from the primary reservoir and provides
pressurized hydraulic fluid of 3000 psi to the primary hydraulic manifold. The fluid is then sent past a pressure
switch, filters and a pressure transducer before exiting the primary hydraulic manifold. The primary hydraulic
manifold provides high pressure hydraulic fluid to the longitudinal, collective, lateral, and directional
servocylinders. The fluid from the servocylinders is then returned to the primary hydraulic manifold reservoir. The
primary reservoir is serviced and bled through the primary GSE panel and ground power hydraulic unit, or through
the use of a hand pump and a container of hydraulic fluid.
(b) The primary hydraulic manifold (fig. 78) has two methods of operation, normal and GSE.