TM 55-1520-240-23-6
7-1
FLIGHT CONTROL HYDRAULIC SYSTEM
(Continued)
7-1
Power Transfer Unit
A power transfer unit (PTU) in each hydraulic system
allows boost to be applied to the flight controls when the
drive system is shut down. Each PTU consists of a pump
driven by a hydraulic motor. The motor is hydraulically
powered by the auxiliary power unit motor pump, utility
hydraulic pump or ground support equipment. It drives
the pump through splined coupling to supply hydraulic
pressure of 3,000 psi at 3.5 gpm to the controls.
NO BREAK - WORK HARDER
The No. 1 PTU is in the forward transmission fairing, aft
and right of the forward transmission. The No. 2 PTU is
in the aft pylon, on the left side.
Servocylinders
A pivoting and a swiveling servocylinder are installed
at each rotor head. At the forward head, lower (fixed)
part of each servocylinder is mounted on the forward
transmission and the upper (movable) part is attached to
the forward swashplate stationary ring. At the aft head,
the lower part is mounted to aft pylon structure. The
upper part is attached to the aft swashplate stationary
ring. Each servocylinder receives 3,000 psi boost
pressure from each flight control system. The pressure
lifts dual pistons, raising the swashplate on the rotor
shaft. Each servocylinder has individual manifolds and
cylinders for each of the hydraulic systems.
7-5
