(2)
Include spacers between the spring and shoe at all six attach points.
3. Nose Gear Wheel Snubber Brake Shoe Inspection/Check
A. Replace brake shoe if worn to within 1/16 inch of shoe fastener head.
500 Nose Wheel Snubber
Feb 20/86 Figure 201 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 32-45-31 Page 201
Nose Wheel Snubber Installation 500
32-45-31Page 202 Figure 202 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Oct 20/84
NOSE WHEEL STEERING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. Nose wheel steering is provided for aircraft directional control during ground maneuvers and taxiing. Hydraulic power is used to turn the nose wheels from zero to 78 degrees to either side. Steering is controlled by a wheel on the left side of the control cabin, and by an interconnect mechanism from the rudder pedals and is spring-loaded to the center position. The airplane can be towed through turns up to 78 degrees without disconnecting the torsion links. Internal cams center the nose gear when the nose gear shock strut is fully extended, therefore turning the wheels or towing should not be attempted unless the inner cylinder is compressed more than two inches.
B. Normal steering is accomplished by using the steering wheel located on the left sidewall forward of the captain's position (Fig. 1). Movement of the steering wheel in either direction is transmitted by cables to a steering metering valve which directs 3000 psi hydraulic fluid to the nose wheel steering actuators for turning the steerable portion of the nose gear. A steering wheel movement of 95 degrees will give 78 degrees of nose wheel turning.
C. Rudder pedal steering is available during takeoff, landing, and taxiing where small directional changes are required. The rudder pedal linkage is connected to the steering cables. Full deflection of the rudder pedals produces about seven degrees of nose wheel turn. The rudder pedal steering mechanism is engaged for steering on the ground by the piston position system. The piston position system consists of linkage and cables connected to the upper torsion link on the nose gear. When the nose gear is compressed by airplane weight, the movement of the torsion link is transmitted by linkage and cables to reposition stops mounted on a clutch crank in the rudder pedal steering mechanism (Fig. 3). In this position any movement of the rudder pedals will be transmitted into ground directional control of the nose wheel through the action of the rudder pedal steering mechanism.
2. Steering Metering Valve
A. The steering metering valve is a piston and sleeve type valve located on the nose gear. Combined with the metering valve are a pair of swivel valves to direct hydraulic fluid for turns. The piston and sleeve assembly is ported to direct 3000-psi hydraulic fluid through the swivel valves to the steering actuators. Movement of the control cable positions the valve piston for the required turn. When the wheels reach the required turn angle, the piston is returned to neutral position by follow-up action of the control cable.
506
Feb 01/75 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 32-51-0 Page 1
B. During steering operation hydraulic fluid is directed by the metering valve to one side of the right actuator piston and to the opposite side of the left actuator piston producing a push-pull action on the steering collar (Fig. 2). This push-pull action continues as long as the valve piston is displaced or until approximately 33 degrees of steering. At this point the pulling actuator has reached the end of its stroke and the turning motion of the actuator has closed off the hydraulic pressure and return lines in the steering actuator swivel valve. Continued pushing by the other actuator moves the pulling actuator past the null point. Above 33 degrees of steering, hydraulic pressure for the steering cylinder that is overcenter has been closed off and both ports have been ported to return. Further turning from 33 degrees to the maximum of 78 degrees is provided by the pushing actuator only. The steering wheel must be turned 95 degrees to obtain the maximum turning angle of 78 degrees.
C. The steering metering valve incorporates a spring compensator to maintain a pressure of 70 to 130 psi against the actuator pistons to act as a shimmy damper. The valve structure includes two bypass check valves to allow flow of hydraulic fluid between each set of ports to prevent cavitation. A bypass valve protects the steering system from high pressures developed in the steering cylinders during towing. With the steering hydraulic system depressurized, residual pressure, coupled with small frictional forces within the valve, act to retain the bypass valve in the closed position (Fig. 2). When the nose gear is turned by the towing vehicle the steering actuator pistons act as pumps, forcing fluid out of the steering cylinders and creating a pressure differential across the bypass valve. The valve opens allowing equalizing pressure to act against the actuator pistons in opposition to the turning force supplied by the towing vehicle. The net result is that pressure is equalized on the opposing sides of the steering actuator pistons. The bypass valve is held in the closed position whenever the steering hydraulic system is pressurized.
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