Gulfstream G550 Operating Manual Download

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right essential DC control

Control inputs to drive the actuator come from two (2) sources:

(1) The Flap / Horizontal Stabilizer Control Unit (FCU) to compensate

for flap extension.

(2) Pilot or Copilot yoke trim switches in the Emergency Stabilizer mode

to provide aircraft pitch control if the elevators malfunction or jam.

All control inputs to move the horizontal stabilizer are routed through the
Flap Control Unit (FCU) that coordinates stabilizer position with aircraft
configuration. The FCU prioritizes control inputs to the stabilizer AC motors
so that:

•

The stabilizer position schedule is matched to flap position

•

Arming the Emergency Stabilizer cancels all other stabilizer
operating modes

Other control and coordination functions of the FCU are discussed in the
following wing flap section - the position of the stabilizer is scheduled by
wing flap extension settings to allow the greatest range of elevator
effectiveness for takeoffs and landings.

If the elevators become jammed or otherwise malfunction, selecting the
EMERG STAB pushbutton switch (shown in Figure 14) to ARM (the
pushbutton legend will illuminate amber) enables the trim switches on the
pilot and copilot yokes to control the position of the stabilizer. As soon as
the yoke trim switch is moved in either direction, the FCU isolates the
stabilizer from all other command inputs. The yoke trim switches can then
be used for a reduced amount of pitch control during flight and landing.

The emergency stabilizer mode is communicated from the FCU to the
Flight Management System (FMS) Actuator Input / Output Processor
(AIOP) modules in MAU #1 and #2 and the MWS processors in MAU #1,
#2 and #3. The MWS initiates the display of a CAS message indicating
emergency stabilizer operation and provides the stabilizer position display
on the Flight Controls 2/3 synoptic page and HSI on the PFD.

B. Flap Control Unit (FCU) and Horizontal Stabilizer Operation:

The Flap and Stabilizer Controller, most often termed the Flap Control Unit
(FCU) is located in the Baggage Compartment Electronic Equipment Rack.
The FCU is a processor that receives external position commands for the
flaps and horizontal stabilizer and also internally computes position
commands for the horizontal stabilizer to coordinate stabilizer position with
flap position. External commands for the flaps are initiated by the flap lever
in the cockpit, and external stabilizer commands are sourced from the
electric trim switches when the emergency stabilizer mode is selected. The
FCU responds to position commands for the flaps and stabilizer by
providing dual channel DC control signals to position the flaps and dual
channel DC control and AC actuator power to move the stabilizer to
commanded positions. A block diagram of the Flap / Stabilizer Controller
(or FCU) is shown in Figure 13.

Flap position commands are obtained from two RVDTs on the cockpit flap
control lever. The FCU compares the commanded position with the existing
flap position derived from RVDTs on each wing flap. If there is a difference
in the two positions, the FCU signals operation of the Power Drive Unit
(PDU) that hydraulically actuates the flaps to the commanded position.

OPERATING MANUAL

PRODUCTION AIRCRAFT SYSTEMS

2A-27-00

Page 48
August 14/03

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