747-400 AMM 飞机维护手册 起落架 LANDING GEAR 3(100)

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 D.  The outer cylinder has a trunnion on each side at the top. Trunnion pins inserted in the trunnions extend into nose gear support brackets which are mounted on each side of the wheel well. Upon retraction and extension the trunnion pins rotate in spherical bearings in the nose gear mounting brackets. The nose gear actuator attaches to an arm with double lugs. This arm extends above the shock strut right-hand trunnion arm.
 E.  The upper end of the nose gear shock strut is also supported by two side braces. These extend from the attach lugs at the center of outer cylinder to the outboard end of the trunnion arms. An upper tripod brace extends forward from the trunion arms to attach to the upper end of the lower tripod brace. The lower end of the lower tripod brace is attached to lugs on the forward side of the outer cylinder on the same level as the side braces. This forms tripod to support the drag strut assembly which is forward and above the top of the shock strut.
 F.  The lower centering cam is attached to the outer cylinder and will mate with the upper centering cam, attached to the top of the inner cylinder, on inner cylinder extension. This centering cam has an annular groove in which the rebound valve piston ring is located. An upper orifice support tube is connected to the outer cylinder. The fluid, which is compressed by the diminishing cavity between the upper and lower centering cams, is restricted to escape only through the small holes in a lip on the piston ring. A small portion of fluid will also escape through the piston rings working gap. The escaped fluid enters a cavity between the upper bearing spacer and the outer cylinder wall. The fluid is then forced through ports which are lengthwise in the upper bearing, into the cavity above the inner cylinder. This restricted flow of fluid acts as a snubber to slow the inner cylinder during extension.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 G.  Upper and lower orifice assemblies along with the metering pin assembly control the flow of fluid between the primary and secondary chambers of the shock strut during inner cylinder extension and compression. An upper orifice is in the upper orifice support tube which is attached to the outer cylinder and similarily a lower orifice is in the lower orifice support tube which is attached to the inner cylinder. The metering pin tapers from a relatively large diameter upper and lower ends to a minimum diameter approximately at its middle section.
 H.  Pressure for extending the shock strut is applied by charging it with compressed air or nitrogen through the valve at the top of the outer cylinder. As the inner cylinder moves outward, the primary chamber increases in volume and fluid is metered into it by the metering pin.
 I.  AIRPLANES WITH THE SHOCK STRUT PRESSURE GAGE; The pressure in the shock strut is measured by a pressure gage which is attached to the strut outer cylinder.
 J.  On all airplanes, the pressure in the shock strut is monitored by the green-band stabilizer system by a sensor assembly on top of the strut. A shutoff valve on this sensor assembly permits the removal of the pressure switch with pressure in the shock strut.
 K.  AIRPLANES WITH THE SHOCK STRUT PRESSURE GAGE;
 The air valve is on the pressure gage assembly.

 L.  AIRPLANES WITHOUT THE SHOCK STRUT PRESSURE GAGE; The air valve used to pressurize the shock strut is on the pressure sensor assembly (Fig. 4).
 7.  Nose Gear Operation
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 A.  Functional Description
 (1)  
Nose gear steering within approximately | 70 degrees limits is provided, controlled by tillers in the control cabin. Rudder pedal movement can control nose steering, to approximately | 10 degrees maximum limits. Gear design permits towing of the airplane at maximum gross weight up grades to 3 percent.

 (2)  
The normal landing gear control system is operated by moving a control handle projecting from the pilots' instrument panel. A cable system transmits the control handle movement to a selector valve located in the wheel well. When positioned by the control handle, the selector valve directs hydraulic pressure to a sequence valve and an actuator for nose gear retraction and extension. The control handle is provided with a lock, to prevent moving the handle into up position when conditions are not right for nose gear retraction. An override in the control handle may be used to bypass the lock in an emergency or a test.
　
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