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Figure 18
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2A-32-00
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Brake-by-Wire BITE /
Fault Indications
Figure 19
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shown in Figure 20. With the nose wheel steering activated, moving the control
wheel turns a dual potentiometer located beneath the control wheel inside the
side console. Rudder pedal movement turns a similar potentiometer located under
the copilot floorboard. Electrical signals proportional to control wheel / rudder
displacement are routed from the potentiometers an Electronic Control Module
(ECM) installed in the left hand avionics rack. The ECM sums the control wheel
and rudder pedal inputs to obtain the desired steering command. The steering
command is compared to the present position of the nose wheel, and an electric
signal is transmitted to the Electro-Hydraulic Servo Valve (EHSV) in the nose
wheel well, porting hydraulic pressure to the steering actuator that turns the nose
wheel in the desired direction by moving the torque linkage connecting the
actuator and the nose wheel. The steering control wheel is returned to the neutral,
or straight ahead position by centering springs if it is released. The rudder pedals
are centered by the bungees that provide artificial feel for rudder inputs.
To ensure that the nose wheel remains centered prior to nose wheel retraction
into the nose wheel well, internal centering cams are incorporated in the shock
strut, and the steering system is restricted to ground operation only by several
safeguards. The landing gear lever handle must be in the down position to
complete the electrical circuits for steering. Hydraulic pressure for steering is
provided through the nose landing gear extend lines. The hydraulic pressure must
pass through two (2) shut-off valves (SOVs) before reaching the EHSV and
steering actuator. See the schematic in Figure 21. The first, SOV, #1, is powered
by 28V DC through circuit breaker STEER BY WIRE #1 (position C-12) on the
COP. For the SOV to open, the guarded PWR STEER switch next to the control
wheel must be on, and the nose gear down lock switch must be engaged. SOV #2
is powered by 28V DC through circuit breaker STEER BY WIRE #2 (position
D-12) on the COP, and requires that the nose gear nutcracker (squat) switch be
compressed in the ground (weight-on-wheels) position for the valve to admit
hydraulic pressure for the steering actuator. When the nose gear nutcracker
switch is compressed, the ECM initiates a one second delay before responding to
steering commands from the rudder pedals or the control wheel, maintaining the
nose wheel in the centered or straight ahead direction. The delay avoids abrupt
steering commands caused by large rudder pedal inputs during crosswind
landings.
The nose wheel steering linkage may be disconnected for aircraft towing by
removing the connecting pin on the torque link between the actuator and the nose
wheel. A tow bar is then connected to the nose wheel axle.
Several Aircraft Service Changes (ASCs) have modified the nose wheel steering
system from the original configuration.
• ASC 176: modifies aircraft S/Ns 1000-1242 (modification incorporated into
aircraft S/N 1243 and subsequent) to include additional circuits that monitor
operation of the system and prompt a STEER BY WIRE FAIL message on
the CAS if any of the following occur: nose wheel nutcracker switch stuck in
the ground (weight-on-wheels) position, causing the No. 2 SOV to remain
in the open position, loss of electrical power to the system, an improperly
installed ECU or ECU connectors, or the No. 2 SOV fails to open after
touchdown and nose wheel nutcracker switch compression.
• ASC 302A: available for installation on all aircraft, installs a separate switch
that shuts off rudder pedal nose wheel steering and restricts steering to the
hand control wheel only. The two (2) position switch is labelled NORMAL
and HANDWHEEL ONLY. When HANDWHEEL ONLY is selected, a blue
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PRODUCTION AIRCRAFT SYSTEMS 2A-32-00
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Revision 6
light adjacent to the switch is illuminated. For aircraft S/Ns 1000-1252
without SPZ 8400, a light installation, mounted above the pilot Primary
Flight Display (PFD) will illuminate with the legend RUD STRG OFF when
nose wheel steering is selected to HANDWHEEL ONLY. For aircraft S/Ns
1000-1252 with SPZ 8400 installed, and aircraft S/N 1253 and subsequent
an annunciation of RUDDER STRG OFF will appear on the CAS when the
steering switch is selected to HANDWEEL ONLY.
• ASC 302A AM2: installs an additional light above the copilot PFD, identical
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湾流4操作手册 Gulfstream IV Operating Manual 2(92)
