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DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 8:58 am

On the DC-10 and MD-10/11 - when extending the gear, why do the main gear doors close very slowly?
On retraction they close pretty quickly - is there some reason (aerodynamic/hydraulic perhaps?) for them to be so slow on extension?

Gear extension in the air:-

Gear swing on the ground, showing rapid door closure on retraction, slow on extension:-
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Re: DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 9:22 am

I think it has to do with hydraulic pressure. On extension the system is still driving the gear down while it is closing the doors. On retraction the system has stopped applying force to the gear when the doors are moving. Also keep in mind when comparing hangar operation vs. regular, the hangar is using a cart which may not supply as much volume of fluid quickly.
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Re: DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 10:01 am

There may be restrictors in the gear down circuit to ensure the gear is deploying slower. With retraction you want the gear coming up quickly to reduce drag; extending that's not as important and your actuators may have a better mechanical advantage at full down. You don't want to slam the gear into the stops. And if the doors are plumbed on the same lines as the gear, they'll move slowly too.
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Re: DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 3:03 pm

Has to do with different areas on cylinder for retract and for extension on both sides.

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Re: DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 3:08 pm

I suspect the diffference is the extension is basically free falll with using hydraulic pressure to lock them in the down position, where as "gear up" is all the 3000 PSI working in sequence to unlock, and retract the gear. Not sure that the hydraulic mule really emulates the exact same conditions as an in flight cycle would. Just an educated guess...
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Re: DC-10/MD-11 Main Gear Extension

Thu Apr 12, 2018 6:15 pm

DH106 wrote:

Wow, that is a heckuva late extension of the gear on approach! Seems like they fully locked seconds before crossing the fence.

I thought that most SOPs dictate an approach be stabilized be stabilized (loc/GS established if necessary, Vref set (plus a few knots), flaps configured for landing, and gear down and locked.

Guess not for FedEx?
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