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View Full Version : Landing gear uplock?



Freiwillige
07-31-2009, 11:34 PM
On a discussion over at AAA there was talk of video footage where an aircraft gets shot up and the gear drops partially. I was under the idea that most aircraft have a hydraulic uplock and when the hydraulic lines are hit pressure is released letting the uplock fall free and gravity does the rest pulling the gear down with only remaining hydraulic pressure holding it partially up?

Does anybody know how this works in reality?

KG26_Alpha
08-01-2009, 10:07 AM
Originally posted by Freiwillige:
On a discussion over at AAA there was talk of video footage where an aircraft gets shot up and the gear drops partially. I was under the idea that most aircraft have a hydraulic uplock and when the hydraulic lines are hit pressure is released letting the uplock fall free and gravity does the rest pulling the gear down with only remaining hydraulic pressure holding it partially up?

Does anybody know how this works in reality?

This would make no sense.

The gear locks are there to prevent the gear from inadvertently dropping if there any damage to the hydraulic gear system.
The pilot usually has a release lever to drop the gear manually (mechanical lock release) and if need be give it a shake to get it to lock down, but not the way you suggest where it falls down if the hydraulics are hit.

There's probably guncam footage showing partial gear release due to damage but this is more likely to be damage to the release mechanism (locks) its self and the hydraulics are holding up the gear.

Of course a combination of both and the undercarriage would fall free from their housings.

Freiwillige
08-01-2009, 07:00 PM
Well that doesnt make sense to me either since I believe that the gear deploy\retract feature is usually one switch.

Also why would it make any less sense for the uplock to be hydraulic? To me it would make more sense.

I believe there is a manual release in case of hydraulic failure but only if hydraulic failure occurs.

joejoemonkey
08-01-2009, 09:45 PM
Im not sure if this is applicable to any other type of aircraft but the kind i work on use positive pressure to keep the gear up, there is nothing mechanical. The pump will work to retract the gear and a valve will close trapping pressure in the lines. Once or twice we have had gear systems with pinhole leaks that would cause the pressure to drop slightly triggering the pump to "top off" the pressure. it sounds like someone using an air ratchet for 3 seconds every 10 minutes.

Another type of aircraft we have uses a more complicated gear extension/retraction method that incorporate hydraulically operated gear doors where the landing gear had to extend to a certain point before actuating a valve to continue articulating the whole thing. I think it would be possible if that were the case, that loss of pressure would allow the gear to sag and by the lack of pressure, not allow the rest of the gear system to allow full extension, ie. getting hung up on the gear doors. Manually bypassing for emergency extension automatically disables locks and allows the gear to be brought down with either accumulator pressure or wind/gravity.

also, the gear extension/retraction handle is actually a bar that operates 4 or so lever switches and some relays. this is mostly for warnings or inhibition under certain parameters like being on the ground while retracting, extending with power levers at idle while in the air, stuff like that. i think that would be similar to ww11 type systems because there are no IC's or any computer components, other than switches and relays.