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7. Body Gear Downlock Bungee
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A. The spring type body gear downlock bungee is installed between the lower drag strut and the lower jury strut (Fig. 1). This bungee aids the downlock actuator in locking the gear down. It also provides a holding force to keep the gear in the locked position. In the alternate extension condition where the gear drops of its own weight, the bungee pushes the jury strut overcenter to lock the gear down.
8. Body Gear Door Actuator (Fig. 7)
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A. The body gear door actuator provides the force required to open and close the wheel well doors. The actuator is a hydraulic piston type with an internal mechanical lock to hold the piston in the fully extended position (doors closed). Hydraulic pressure applied to open the doors normally unlocks the actuator. A manual release for the lock is provided for the alternate gear extension condition and when using the ground door release handle to open the doors on the ground (Fig. 7). A snubbing action slows down the movement as the actuator piston approaches either end of its stroke. The cylinder end of the actuator end is attached to the structure outboard of the wheel well, while the rod end is attached to the door actuator beam. The end of the beam is attached to the outboard half of the doors.
9. Body Gear Door Safety Valve
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A. The body gear door safety valve (modular assembly) is located on the outboard bulkhead of the body gear wheel well. It is connected in the hydraulic actuator closed line from the body gear door actuator to the gear uplock-operated sequence valve. The safety valve bypasses pressure from the door actuator during emergency gear operation or ground door release. This allows doors to open by gravity. The valve is identical to that used in the wing system.
10. Operation
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A. Functional Description (Fig. 8 and 9)
(1)
The body landing gear operating sequence is shown in figure 8. Hydraulic schematics of the body landing gear system in various conditions are shown in figure 9.
(2)
When the gear is up and the gear doors are closed, the door-operated sequence valve blocks fluid from unlocking the uplock and from lowering the gear. When the gear is selected DN and the doors are opening, the sequence valve is positioned so that fluid is directed to the unlock side of the uplock actuator which unlocks the body gear. As the doors continue to open, the sequence valve is positioned so that fluid is directed to the down side of the gear actuator and the gear extends.
(3)
After the gear is down and locked, the doors close, repositioning the sequence valve to shut off fluid to the door actuator and the uplock actuator. When UP is selected, fluid is blocked by the selector valve until the doors begin to open. When the doors are fully open, fluid is directed to the unlock side of the downlock actuator and to the up side of the gear actuator. When the gear is up and locked, the doors again close repositioning the sequence valve so that fluid is blocked from the actuators.
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Body Gear Door Actuator Release Mechanism
Figure 7
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本文链接地址：747-400 AMM 飞机维护手册 起落架 LANDING GEAR 4(112)
