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hydraulic line is damaged or cracked. If Combined/Utility system pressure is not
available, but brake system hydraulic lines are intact, the Auxiliary hydraulic system can
be used for brake operation. If no hydraulic pressure is available from aircraft systems,
accumulator pressure from the Parking/Emergency brake system will provide
approximately five to six brake applications without anti-skid protection.
Control of the brake system is either through a hydro-mechanical analog brake system
(HMAB) for aircraft S/Ns 1000 - 1213 with ASC 307 and S/Ns 1214 and subsequent, or
a brake-by-wire system for aircraft S/Ns 1000 - 1213 without ASC 307. In the analog
system, cockpit brake pedal application is mechanically linked to the system brake
metering valves that apply hydraulic pressure proportional to pedal depression. In the
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-32-00
Page 1
January 31/02
Revision 6
brake-by-wire system, cockpit brake pedals incorporate linear variable differential
transducers (LVDTs) that supply pedal deflection signals to a brake electronic control unit
(ECU) that opens the left and right brake control valves proportional to LVDT commands.
Brake feel is supplied by bungees that apply proportional resistance to pedal deflection.
Anti-skid circuitry is integrated into the brake-by-wire system. Analog braking uses a
separate anti-skid control box.
The Landing Gear System is composed of the following components.
• 2A-32-20: Landing Gear and Doors
• 2A-32-30: Extension and Retraction
• 2A-32-40: Wheels and Brakes
• 2A-32-50: Nose Wheel Steering
OPERATING MANUAL
2A-32-00 PRODUCTION AIRCRAFT SYSTEMS
Page 2
January 31/02
Revision 6
Simplified Landing Gear
Hydraulic System Diagram
Figure 1
OPERATING MANUAL
2A-32-00
Page 3 / 4
January 31/02
2A-32-20: Landing Gear and Doors System
1. General Description
The major components of each main landing gear assembly are: a landing gear
door, a shock strut, a sidebrace actuator/downlock mechanism and an uplock
mechanism. Each of the main landing gear assemblies has dual wheels with
integrated brakes mounted on an articulated trailing arm attached to the landing
gear structural post. The pneumatic/hydraulic shock strut is attached between the
wheel end of the articulated trailing arm and the top of the structural post. In flight
with the landing gear down, the shock strut extends and the articulated trailing
arm pivots downward, positioning the wheels for ground contact and compression
of the shock strut. The major components of the main landing gear are shown in
Figure 2 and Figure 3.
A side brace hydraulic actuator/downlock extends and retracts the main gear. In
the extended position, hydraulic pressure positions mechanical downlocks that
prevent gear retraction. The downlocks include mechanical springs loads that
maintain the locked position if hydraulic pressure is lost. In gear retraction,
hydraulic pressure compresses the springs, displaces the downlocks and allows
gear retraction inward into the wheel well in the wing root next to the fuselage
keel. An uplock roller mounted on the dual wheel axle assembly engages an
uplock hook in the wheel well and rotates to latch the main gear in the uplocked
position. The main landing gear door, hinged at the inboard side of the wheel well,
closes after the gear retracts and mates with the fairing door panel mounted on
the outside of the main gear assembly to seal the wheel well.
The nose gear assembly includes steerable dual wheels mounted on a shock strut
attached to a trunnion and a hinged two-piece truss brace. A drag brace between
the truss brace and the shock strut provides additional structural support and
limits the extension of the nose gear shock strut. The truss brace and trunnion
pivot axes allow the hydraulic actuator cylinder to retract the nose gear assembly
forward and up and extend the gear aft and down. See the illustration in Figure 4.
When the nose gear is fully extended, the forward and aft sections of the truss
brace move over center to lock the nose gear down. A downlock hydraulic cylinder
extends an actuating arm holding the truss brace in the over center position.
Springs are also incorporated in the over center downlock to maintain the over
center lock in the event of hydraulic failure. When the nose gear retracts, the
downlock actuator arm moves aft, allowing the forward and aft portions of the
truss brace to fold at the hinge point. As the nose gear reaches the fully retracted
position, a roller attached to the dual wheel axle assembly pushes aside a spring
latch and engages an uplock hook, with the spring latch then falling into place
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湾流4操作手册 Gulfstream IV Operating Manual 2(74)
