(Ref. Fig. 017)
A. Main Landing Gear
(1) Retraction
When you set the L/G control lever to UP, the hydraulic pressure goes to each MLG actuator and lock-stay actuator. Because the lock-stay actuator is more lightly loaded, it retracts first to release the overcenter lock of the lock stay. The lock stay folds against the tension of the lock springs. The retraction actuator then extends, to retract the MLG. The cardan joints of the lock stay and the side-stay let these units retract in different planes from that of the MLG.
The retraction cycle is:
-
the MLG doors open
-
the MLG retracts
-
the MLG doors close.
(2) Extension
When you set the L/G control lever to DOWN, the hydraulic pressure goes to:
-
the uplock actuator
-
the annular side of the retraction actuator
-
the full area side of the lock-stay actuator.
The uplock actuator opens quickly (to keep a minimum load-time on the uplock hook). The tension in the lock springs and its own weight help to extend the MLG.
At the same time, the movement of the MLG causes the side-stay and the lock stay to open, until they go to their overcenter position. These movements help the hydraulic pressure in the lock-stay actuator to mechanically extend it. The lock-stay actuator then makes sure that the lock stay is overcenter. Also, it helps the lock springs keep the MLG in the locked down position, when the MLG doors close.
The extension cycle is:
-
the MLG doors open
-
the MLG extends
-
the MLG doors close.
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MLG - Extension and Retraction Positions
Figure 017
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A ground-lock sleeve can be installed on the rod of the lock-stay actuator, when it is in the overcenter position.
B. Shock Absorber
(Ref. Fig. 008, 011)
(1) Compression
During the compression, the sliding tube goes into the barrel of the main fitting. The capacity of the shock absorber reduces, which compresses the gas. The fluid goes through the damping head and lifts the compression-orifice plate off its seat, to let the fluid flow fully.
Initially, the fluid also flows from the compression chamber to the 1st stage gas chamber, through the first-stage orifices of the damping tube. While the shock absorber compresses, the damping tube and the first-stage orifices go through the damping head. The flow through the first-stage orifices stops, and the flow limits to that through the compression-orifice plate. This produces a two-stage damping effect. The gas compression in the 2nd stage chamber, pushes on the floating piston to help the damping. It also helps to make the damping effect and the compression effect of the oleo smooth.
At the same time, the fluid goes from the 1st stage gas chamber into the recoil chamber, through the openings in the upper bearing. This flow of fluid moves the recoil-orifice plate against the flange of a retaining ring, to let the fluid flow fully. The gas compression and the fluid transfer absorb the shock-loads from the MLG.
(2) Recoil
The energy in the gas, which is in the 1st stage and the 2nd stage gas chambers, starts the recoil travel. The fluid goes through the recoil-orifice and the compression-orifice plates. The flow of fluid moves these plates to their almost closed position, so that the fluid movement is slow. This decreases the speed of the recoil travel.
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