Gulfstream G550, Operating Manual

Page: 9 / 94

If a malfunction or failure in any portion of the loop between a cockpit yoke and the
corresponding elevator prevents control surface movement, the mechanical
torque tube connection between the two control yokes can be separated to allow
control of the aircraft with the free (unjammed) elevator. The autopilot may be
used in single elevator operation.
2. Description of Subsystems, Units and Components:
A. Elevator Hard Over Prevention System (HOPS):
Movements of the elevators contrary to the commanded position are
limited by a Hard Over Prevention System (HOPS), illustrated in Figure 3.
The system incorporates eight switches for each elevator to monitor
mechanical and hydraulic elevator operation. Four external mechanical
switches are integrated into the elevator control linkage to provide a
comparison reference for four switches mounted internally within the
hydraulic actuator. Of the four external switches, two are for left hydraulic
system reference and two are for right hydraulic system reference. Of the
two switches for each hydraulic system, one provides a up elevator
command reference and the other provides a down elevator command
reference. The switches are plunger-type contact switches, and are
installed on each side of a bracket attached to the command input side of
the elevator actuator. On one side of the bracket are the up elevator
command input switches for the left and right hydraulic systems. On the
other side of the bracket are the down elevator command input switches for
the left and right hydraulic systems. Inserted between the switches in the
bracket is a cam-type arm mated to the elevator hydraulic actuator output
linkage. The cam arm is positioned with a defined amount of clearance
between the plunger-type switches. Under normal conditions, the bracket
holding the switches moves with elevator command input and the cam arm
moves with the elevator hydraulic actuator output, so the clearance
between the switches and the arm is maintained.
If a malfunction occurs and the elevator moves opposite to or further from
the commanded direction, the cam arm that is attached to the output
linkage of the elevator actuator will move to close the clearance gap
between the cam arm and the plunger-type switches, making contact with
the switches on the side of the bracket. When the plungers of the switches
are depressed, a relay closes and an electrical signal is sent to a
corresponding set of switches mounted internally within the hydraulic
actuator.
Four pressure switches monitor left and right hydraulic system pressures
within the pistons of the elevator actuator. In normal conditions, all four
switches sense stabilized pressures since hydraulic outputs positioning the
elevator are balanced by air load pressures on the elevator surface acting
against actuator pressures. When a malfunction occurs and the elevator
moves contrary to the commanded direction, the hydraulic actuator shaft
moves in the contrary direction, causing an increase in hydraulic pressure
on the opposite sides of the pistons within the actuator. The left and right
system opposite side pressure switches close, completing the circuit
initiated by closure of the bracket plunger switches, and an electrical signal
is sent to a timing relay. If the contrary elevator movement persists for
longer than one tenth (1/10) of a second, hydraulic pressure from both left
an right systems is shut off to the elevator actuator.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS
2A-27-00
Page 9
August 14/03
Title Page Prev Page Next Page TOC