500 Nose Gear Modular Package Schematic
Feb 01/76 Figure 5 32-33-0
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
7. Transfer Cylinder
A. The transfer cylinder momentarily equalizes hydraulic pressure on either side of the nose gear actuator piston at the start of each extension or retraction cycle to relieve the gear of the actuator force until the lock is released. The cylinder contains a piston, two springs and two spring retainers (Fig. 6). One end of the cylinder is connected to the DOWN line. The other end is connected to the UP line of the nose gear actuator. At the end of the gear retraction, or extension the cylinder spring retainer is bottomed on either side of the cylinder. When the control handle is moved to UP or DN for gear operation, pressure is directed to one side of the nose gear actuator. Pressure also enters the transfer cylinder and displaces the piston. Piston movement directs pressure from the opposite side of the cylinder to the actuator. Therefore, momentarily, system pressure exists on both sides of the actuator piston and actuator force is neutralized. During the neutral force period, the lock actuator unlocks the gear and starts the lock brace assembly folding. When the spring retainer bottoms, the counter pressure drops on the return side of the nose gear actuator and gear extension or retraction proceeds in the normal manner. After the spring retainer has bottomed and hydraulic pressure from A system is off the line, a further movement of the piston is available, acting against the spring tension. The extra piston movement is provided to damp out pressure surges generated in the system and so prevent pressure fluctuations from reaching the lock actuator and possibly unlocking the gear. The cylinder is symmetrical, with double springs, and may be installed either way in the system. The cylinder is mounted on the forward bulkhead in the wheel well.
Transfer Cylinder Schematic 500
32-33-0 Figure 6 May 15/68
Page 8
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
8. Nose Gear Door Linkage
A. The nose gear door linkage transfers motion from the nose gear to open and close the nose gear wheel well doors. (Fig. 7) Doors are open when gear is extended and close as the gear retracts. A link assembly connects a lug on the upper drag brace with the short arm of a bell crank. A pushrod between a long arm on the crank and a fitting on the door completes the linkage. The lugs on the drag brace and the arms on the crank are so positioned that they are passing over an overcenter position for 80 percent of the gear travel. Therefore, except for a very slight further opening, the doors barely move during gear retraction. When the gear is moving over the last few inches of retraction, the long arm on the crank is almost at right angles to the pushrod connected to door. The doors then rapidly close as gear fully retracts. On gear extension the initial extension movement opens the doors wide. At this point lugs and cranks reach overcenter position and the doors remain open for the rest of the extension cycle.
500 Nose Gear Door Linkage
Nov 15/66 Figure 7 32-33-0
Page 9
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
9. Operation
A. Retraction
(1) When the landing gear control lever is moved to UP postion for gear retraction, hydraulic pressure is directed through the selector valve and the nose gear modular package to the gear and the lock actuators. Flow to the gear actuator is controlled by a flow limiting valve. Flow leaving the lock actuator is controlled by a restrictor. (See figure 8.) The lock actuator starts retracting to apply a downward force to an extension on the lock link. The downward force pulls the lock link over center and starts both the lock strut and drag brace folding. As gear retraction proceeds, the lock link assembly swings through 90 degrees from horizontal to vertical position. In so doing the lock link extension passes across an over center position with respect to the lock actuator. From this point the lock actuator retracting force is opposed to lock link movement until the gear is almost retracted. During the opposition period the larger main gear actuator overpowers the lock actuator. The unlock force provided by the lock actuator when the gear is down, becomes the locking force when gear is up. The change over being caused by the lock link extension moving from the aft to the forward side of the lock link pivot. (See figure 9.)
B. Extension
(1) When the landing gear control lever is moved to DN position, hydraulic pressure is directed to the gear and lock actuators in the opposite direction to gear retraction, and a similar course of events would apply. However, with the gear up and locked the weight of the gear applies a high compression load on the lock strut. The gear load on the lock strut, plus the force applied by the pressurized nose gear actuator tends to make lock release noisy and stiff. Therefore, the transfer cylinder is used to direct down line pressure to the up side o f the nose gear actuator and so equalize pressure on both sides of the piston. The pressure impulse from the transfer cylinder is supported momentarily by the flow control valves in the modular package. By this means the main actuator extension force is reversed during the lock strut unlocking and the initial hinging of the drag brace. After unlocking, the extension cycle is opposite to retraction.
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