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of flap position, as the stabilizer is mechanically driven from the flap central
gearbox. If a malfunction occurs rendering the stabilizer immovable, a safe
landing can be made using normal pitch trim.
Horizontal stabilizer position is displayed on the FLAP / STAB position indicator
located on the copilot’s skirt panel.
The horizontal stabilizer system is composed of the following subsystems, units
and components:
• Stabilizer drive system
• Torque limiter
• Dwell box
• Stabilizer actuator
• Stabilizer position and warning system
2. Description of Subsystems, Units and Components:
(See Figure 16 and Figure 17.)
A. Stabilizer Drive System:
The stabilizer drive system consists of torque shafts installed beginning
from the aft side of the flap central gearbox, rearward through the tail
compartment via a dwell box, then upward through the vertical stabilizer to
the stabilizer actuator. Bearing housings and pillow blocks installed at
defined intervals support the torque shafts, preventing whiplash as they
rotate.
B. Torque Limiter:
A torque limiter is installed at the input side of the central gearbox. If the
gearbox, dwell box or stabilizer actuator should jam or fail, the torque
limiter spring jams to lock the torque shafts. This stalls the central gearbox
hydraulic motor, stopping further flap and horizontal stabilizer movement.
If a torque shaft fails, the flaps are still operable throughout their full range.
The stabilizer, however, remains at its last position prior to shaft failure. The
flight crew would then use pitch trim as necessary to compensate for the
immovable stabilizer.
C. Dwell Box:
A dwell box, located in the tail compartment, is incorporated in the stabilizer
drivetrain to control stabilizer movement during flap extension and
retraction. It contains an input side and an output side.
During flap extension, the shaft connected to the input side of the dwell box
rotates but the output side does not rotate until the flaps reach a specified
position. At the final stages of central gearbox rotation, the shaft connected
to the output side of the dwell box rotates to drive the stabilizer actuator.
During flap retraction, the shaft connected to the output side of the dwell
box immediately begins rotation to drive the stabilizer actuator. When the
flaps reach a specified position, output shaft rotation ceases, although
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-27-00
Page 49
October 11/02
Revision 8
input shaft rotation continues during flap retraction.
D. Stabilizer Actuator:
The irreversible stabilizer actuator consists of a double Acme™ screw with
a reduction gear. One end of the actuator connects to the leading edge of
the horizontal stabilizer and the other end connects to the vertical stabilizer
structure. The reduction gear reduces the input torque shaft speed of 730
RPM to an actuator screw speed of 33 RPM to remain commensurate with
the speed of flap movement. Should a malfunction, jam or failure occur, the
actuator remains in its last commanded position.
E. Stabilizer Position and Warning System:
A transmitter at the aft upper end of the stabilizer surface supplies stabilizer
position information to the FLAP / STAB position indicator on the copilot’s
skirt panel. Although power for the system is normally supplied by the
Essential 28 VDC bus, position indication remains functional down to, and
including, emergency battery operation. Horizontal stabilizer angle of
incidence and FLAP / STAB indicator position relative to flap position is
outlined in the following table:
FLAP POSITION FLAP / STAB INDICATOR STABILIZER ANGLE OF INCIDENCE
0° (UP) UP 1° leading edge down
10° T/O 2.2° leading edge down
20° (T/O APPR) APP 3.2° leading edge down
39° (DOWN) LDG 4.6° leading edge down
A limit switch below the stabilizer position transmitter provides a warning if
the stabilizer fails to move to the proper position with flap retraction. If the
stabilizer fails to reach the 1° leading edge down position with the flaps
retracted, the limit switch causes an amber FLAP/STAB FAIL caution
message to be displayed on the Crew Alerting System (CAS).
3. Controls and Indications:
(See Figure 16 and Figure 17.)
A. Circuit Breakers (CBs):
Circuit Breaker Name: CB Panel: Location: Power Source:
FLAP/STAB POS CP E-5 Emergency DC Bus
FLAP/STAB WARN P D-3 Essential DC Bus
B. Caution (Amber) Messages and Annunciations:
CAS Message: Cause or Meaning:
STAB-FLAP FAIL Flaps UP (0°) and stabilizer not UP.
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湾流4操作手册 Gulfstream IV Operating Manual 2(20)
