LANDING GEAR - DESCRIPTION AND OPERATION
1. General
A. The landing gear system consists of the gear which support the airplane while on the ground; a gear extension and retraction system; an alternate gear extension system; wheels and brakes for each main gear; means for steering the airplane; gear and door indicating and warning system; and
control and operation of the gear for landing, takeoff and ground movement.
2. Main Gear and Doors
A. Main Gear
(1) The main landing gear consists of four main gear; two body gear and two wing gear. Each gear is comprised of a four-wheel truck. The body gear is located at station 1463.5 in the fuselage. The wing gear is located aft of the rear wing spar inboard of the engine nacelles at station 1342.5.
(2) Landing impact is absorbed by five air-oil shock struts, functioning primarily as air springs. Rolling vibrations and variances in runway are absorbed by the hydraulic forces within the shock strut.
(3) Body gear trucks are steerable, providing directional control in conjunction with the nose gear in sharp turns during low speed taxiing and towing. This capability also reduces tire scrubbing in sharp turns.
B. Main Gear Doors
(1) The landing gear doors consist of body gear doors and wing gear doors. The body and wing gear doors each have wheel well doors and shock strut doors. The wheel well doors are hydraulically actuated and can be closed with the gear extended or retracted. The shock strut doors are mechanically attached by linkage rods to the gear shock strut and move only when the gear is moved. All doors are of frame construction with skin paneling on the inner and outer sides.
The doors close over all gear openings and fair with the fuselage contour to provide aerodynamic smoothness.
3. Nose Gear and Doors
A. Nose Gear
(1) The nose landing gear is a steerable wheel assembly which supports the forward end of the
airplane and provides directional control while on the ground. The gear is hydraulically actuated
and retracts forward in the wheel well. Landing loads are absorbed by an air-oil shock strut.
Steering is provided by hydraulically actuated cylinders. The airplane can be towed forward or
aft from the nose gear.
B. Nose Gear Door
(1) The nose gear doors are clamshell type and consist of four doors that fair with the fuselage
contour when closed. All doors are of alclad rib and skin construction.
4. Landing Gear Extension and Retraction
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 (PAGEBLOCK 32-35-00/001). Gear and doors then extend by
mavity.
(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
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 Figure 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
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.
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.
7. Landing Gear Indication System
A. The landing gear position indication system monitors the position of the landing gear and landing
gear doors. The position data is supplied to the flight crew through the EICAS display units.
B. The landing gear position is monitored by proximity switch sensors. The sensors are located on all
landing gear and landing gear doors. The sensor signals supply the position data to EICAS display
units and other airplane systems.
Thats the general description of the landing gear system out of the 747-400 AMM. Not sure how much detail you want as its a big subject.
