777 gear swing question

[Check Airman]

Hello all,

Does anybody know why the retraction sequence here seems to be so slow? It almost seems to stall for a bit around 0:13

Gear Swing- 777-200 - YouTube

[EEngr]

Just a guess: The system is being supplied by an external hydraulic pump that has limited capacity.

Note the hoses just to the right of the gear bay in the video.

[westhawk]

See the two hoses going up to the open service panel just aft of the gear well? The forward hose is supplying hydraulic fluid at system pressure from a hydraulic mule to at least one of the aircraft hydraulic systems. When conducting a gear swing, it is common maintenance practice to swing the gear slowly to better inspect it's operation.

[Machinbird]

Not an aircraft I have worked with, but in addition to the swing rate being slowed by controlling the hydraulic supply, the left side side brace seems to have actuated first and the right side side brace didn't move until the left gear began to "climb the hill" into the wheel well thus increasing pressure enough to move the right side brace. Once the right side gear began to move, they both seem to have come up pretty evenly.

As previously stated by others, the gear is being actuated with much lower than normal flight hydraulic flow rates/ pressures to make it easy to visualize the sequencing of the retraction.

[EEngr]

I did get a laugh at the guy who walks right under the retracted gear (starting at 0:52) completely oblivious to the ongoing test.

Back in my days at Boeing, I probably would have gotten my kicked for wandering through a functional test like that.

[Tomescu]

@ EENG

There must be radio communication between flight deck and the ground techs.Every landing gear move has to be cleared first by the ground person to prevent any possible incident.

[flyryddyv]

Yeah, that looks way too slow than what it really does. I think the spec is within 16sec or something like that.

[laz219]

As a matter of curiosity- how do they support the aircraft while doing these tests?

[dixi188]

SKY HOOKS!!!!!!!!!!!!!!!!!





See the big yellow triangle things, they are jacks. One under each wing and one under the rear fuselage.

[Check Airman]

Thanks as usual for the informative answers.

[laz219]

Now that the jacks have been pointed out, I have no idea how I didn't see them.
Thanks.

[Terry McCassey]

My experience tells me there is nothing unusual with this clip. The retraction on both sides is symetrical and smooth as needs be, the times will depend on the pressure and flow rates of the ground source, plus of course any internal hydraulic leakage of the components. The gear operates only on the Centre hydraulic system and an idea of the timings using the aircraft pumps can be found in AMM 32-30-01 P 508 fig 502.

[Jetjock330]

The normal gear retracts faster in real life when supplied by on board hydraulics.

This is the gear of a 777-200 as it "flattens out" just before retraction.

777-300ER has another hydraulic strut forward of the gear, which locks the main landing gear "flat" during take-off rotation, thus the aircraft rotates off the aft axel, thus lower take-off speeds and provides better tail clearance at rotation.

[J.L.Seagull]

The correct term for it is "Semi Lever Gear"

[Takeoff53]

The chain of postings cleared some questions I had in mind regarding the B777 gear. However, in the test shown (apparently a 772) I did not see the mechnism which brings the wheelset into a horizontal position just before the swing starts?