WHEEL NO.
Wheel Numbering Diagram
Figure 2
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747-400
MAINTENANCE MANUAL
4. Landing Gear Extension and Retraction_____________________________________(Ref 32-30-00/001)
A. Extension and retraction of the wing, body and nose gear and their wheel well doors is by hydraulic power. An electrically powered alternate extension system is provided to unlock the gear and doors when hydraulic power is not available (Ref 32-35-00/001). Gear and doors then extend by gravity.
(1)
The gear is controlled from a single handle mounted on the pilots' P2-3 panel. Cables from a quadrant actuated by the handle transfer motion to selector valves which apply hydraulic pressure for gear actuation. A safety lock prevents inadvertent operation of the control handle to the gear up position when conditions are not right for gear retraction.
B.
When the control handle is placed in the DN position, the gear doors open the gear unlocks and extends and the gear doors close. When the control handle is placed in the UP position, the gear doors open, the gear retracts and locks and the gear doors close. Sequence valves control gear and door operation.
5. Wheels and Brakes_________________(Ref 32-40-00/001)
A. The airplane is supported during landing, takeoff, and ground operations on 18 wheel and tubeless tire assemblies. Eight are on the wing gear, eight on the body gear and two are on the nose gear. Main gear wheels are numbered as shown in Fig. 2. Each main gear wheel (wing and body) is provided with a brake unit installed on the axle on the side nearest the shock strut. The brakes are a multidisk type with stationary elements fitted with replaceable linings and segmented rotor brake disks. The brakes are fitted with combination return springs and automatic adjusters. The adjusters compensate for brake wear.
B. When the airplane brakes are applied, the antiskid system automatically compensates for wheel skid by control of the brake pressure through the antiskid valves. A brake temperature monitoring system is included to enable monitoring of brake temperatures and to alert the flight crew of a brake overheat condition.
6. Steering________(Ref 32-50-00/001)
A. Two steering tillers, each with steering control authority of approximately | 70 degrees at the nose gear, are provided. One tiller is to the left of the captain, the other to the right of the first officer. The rudder pedals are also coupled to the steering control system by an interconnect mechanism. Full rudder pedal deflection provides approximately | 7 degrees of nose wheel steering. Towing angle can range between approximately | 65 degrees without disconnecting torsion links. Disconnecting the torsion links enables towing at any angle. Hydraulic system 1 powers both nose gear steering cylinders. Steering power is available only when the gear selector lever is DOWN.
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MAINTENANCE MANUAL
B. Body gear steering supplements nose gear steering for directional control during towing and taxiing of the aircraft. Body gear steering also reduces tire scrubbing when maneuvering on the ground. A switch, actuated by a cam that is mechanically driven from the nose gear steering tiller, arms the body gear steering system. The system is controlled by a closed loop servo system which modulates hydraulic pressure (system No. 1) to a pair of steering actuators on each body gear. As the nose gear turns in one direction, the body gear turns smaller proportional angles in the other direction. The body gear steering arming circuit is deactivated whenever the gear is in tilted position, or when wheel speed is greater than 20 knots. Back lash within the system creates a difference in nose wheel position for the arm and disarm functions. When the angle of nose wheel steering increases, the system is armed at 21 degrees. When the angle of nose wheel steering decreases, the system is disarmed at 20 degrees. 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：747-400 AMM 飛機維護手冊 起落架 LANDING GEAR 1(11)
