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having ASC 342. These actuators are designed to alleviate frozen or
stiff trim tab actuators possible in extreme cold temperatures. The
system receives power from Phase C of the Left Main AC bus.
Operation of the system is automatic and transparent to the flight
crew.
F. Angle-of-Attack / Stall Barrier System:
(See Figure 4, Figure 10 and Figure 11.)
While in flight, the Angle-of-Attack (AOA) system monitors aircraft AOA to
provide warnings of an approaching stall. If AOA continues to increase
toward aerodynamic stall, the system applies a nose down control input
through the stall barrier system.
The AOA / stall barrier system consists of the following units and
components:
OPERATING MANUAL
2A-27-00 PRODUCTION AIRCRAFT SYSTEMS
Page 10
October 11/02
Revision 8
• AOA probes
• AOA display and approach indexer
• Stall warning computers
• Pilot and copilot control column shaker motors
• Stall barrier system
AOA becomes fully functional as the aircraft becomes airborne, i.e., when
the nutcracker shifts to the AIR mode. The control column shaker, however,
is disabled for the first five seconds following rotation to eliminate nuisance
activity. Pulling the SHAKER #1 and / or SHAKER #2 circuit breakers, as
appropriate, is the only way to disable a control column shaker in flight;
however, such action completely disables the associated stall warning
computer(s). System design is such that either stall warning computer is
capable of operating the control column shaker and control column pusher
should the other computer become disabled.
(1) AOA Probes:
An AOA probe / transducer assembly is installed on the left and right
forward fuselage. The cone-shaped probes freely rotate in the
airstream to provide AOA reference data for the stall warning / stall
barrier systems and AOA display data for the flight crew. The left
AOA probe provides data the No. 1 stall warning computer while the
right AOA probe provides data the No. 2 stall warning computer.
Heating elements prevent ice accumulation on the probe and
condensation within the transducer case.
(2) AOA Display and Approach Indexer:
AOA display data supplied by the probes includes the normalized
AOA display and the approach indexer. Normalized AOA display is
shown on the lower left portion of the Primary Flight Display (PFD)
and consists of a vertical scale marked from 0.2 to 1.1 in 0.1
increments. At the bottom of the scale is a three-digit display
surrounded by a pointer that provides AOA indication within a 0.01
resolution. As AOA changes, the display / pointer moves up and
down to correspond with the indication on the scale.
An AOA approach indexer on either side of the windshield center
post indicates the optimum AOA for approach and landing. The No.
1 AOA system drives the pilot’s indexer while the No. 2 AOA system
drives the copilot’s indexer. During approach and landing, the AOA
system illuminates each indexer’s red chevron if AOA is too high, a
green circle if AOA is correct or an amber chevron if AOA is too low.
(3) Stall Warning Computers:
The No. 1 and No. 2 stall warning computers receive the following
inputs and then provide outputs to the control column shaker motors
and stall barrier system:
• AOA reference data from the associated probes
• Altitude data from the DADCs
• Nutcracker mode from the nutcracker relays
• Flaps position from the 39° flap relay
(4) Control Column Shaker Motors:
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-27-00
Page 11
October 11/02
Revision 8
A control column shaker motor is attached to the pilot and copilot
control columns. When activated by a stall warning computer, the
motor drives an off-center weight that vibrates the control column.
Activation of one motor affects both control columns due to their
mechanical interconnection.
(5) Stall Barrier System:
A stall barrier system (control column pusher) is incorporated in the
pitch flight control system to prevent a stall by forcing the control
columns forward when the flight crew fails to respond to either visual
indications or to the control column vibrations that warn of
impending stall. The system consists of two normally closed stall
barrier valves and an actuating cylinder that is mechanically linked
to the elevator actuator input sector. One valve receives signals
from the No. 1 stall warning computer while the other valve receives
signals from the No. 2 stall warning computer. If one system fails,
the remaining system is capable of operating the system.
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湾流4操作手册 Gulfstream IV Operating Manual 2(10)
