aero145
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Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 7:14 am

Hello fellas.

I hope this is a not-too dumb question, but I'm wondering why the front-wheel door doesn't close 100% while the gear is down on the McDonnel Douglas MD-11.

Here are some photos:


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Photo © Jurgen Radier
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Photo © Alex G.-Denicourt - Contrails Aviation Photography




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Photo © Tim de Groot - AirTeamImages



I've seen this many times before, so I decided to ask you clever guys about this. Ê


Regards and thanks,
David

PS: Sorry about the mistaken topic name, I couldn't add "100%" into the name.

[Edited 2006-04-21 00:15:36]

[Edited 2006-04-21 00:16:09]
 
LMP737
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 7:33 am

It's a little quirk with Douglas aircraft, MD-80's and MD-90's are the same way. Basically it's the way the doors are riggged to the nose gear. The doors won't fully "suck in" until the nose gear is fully retracted.
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DH106
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 7:37 am

I've seen this on other types as well - the Convair 880/990 for instance, see:

http://www.airliners.net/open.file/0747499/L/
and
http://www.airliners.net/open.file/0750484/L/

I think it's because the nose gear doors aren't operated directly by hydraulic sequencing of jacks as they are in more sophisticated aircraft, but by mechanical linkages linked directly to the gear strut - designed to close the doors when the strut is both fully retracted and fully extended, but open them while it's pivoting in between. Clearly for drag reasons it's important to have them fully closed when the gear's up for cruise, but less so in the landing config when a little extra drag is unimportant. So I think you're looking at rigging here.
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aero145
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 7:48 am

LMP737, DH106, thanks for you replies.

I have also seen this on other MD's, I guess that it's fully correct that you say.  Smile

Best regards,
David
 
SFOMB67
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 12:49 pm

Think DC-8's were like this, too. All done with rod working off the nose gear.
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VC-10
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 1:21 pm

Quoting DH106 (Reply 2):
I think it's because the nose gear doors aren't operated directly by hydraulic sequencing of jacks as they are in more sophisticated aircraft,

Why over complicate things? There is less to go wrong the DC way
 
474218
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 1:41 pm

Quoting Sfomb67 (Reply 4):
Think DC-8's were like this, too. All done with rod working off the nose gear.

Correct, when the gear is down the rods are not long enough to close the doors completely. However, when the gear is up and stowed the rods pull the doors completely closed.
 
Salukipilot
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 3:26 pm

The exact same thing happens on the 767 series!
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DH106
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Fri Apr 21, 2006 4:36 pm

Quoting Sfomb67 (Reply 4):
Think DC-8's were like this, too. All done with rod working off the nose gear

Wonder if that's why the front edges of a DC-8's nose gear doors are shaped to curve & bend inwards, - to reduce drag if they hang open a little.

Also, wonder if some main gears work like this as well - I've noticed (as discussed on another thread) that on DC-8's and DC-10's/MD-11's especially that when retraction starts the gear legs begin to pivot BEFORE the inner door fully opens. So maybe the initial action of the leg moving it's first couple of feet is linked to the door opening mechanically.

These pictures illustrate nicely what I mean - legs are moving before doors fully open:
http://www.airliners.net/open.file/0893404/L/

http://www.airliners.net/open.file/1010921/L/
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MD11Engineer
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Sat Apr 22, 2006 5:16 am

Quoting DH106 (Reply 8):
Also, wonder if some main gears work like this as well - I've noticed (as discussed on another thread) that on DC-8's and DC-10's/MD-11's especially that when retraction starts the gear legs begin to pivot BEFORE the inner door fully opens. So maybe the initial action of the leg moving it's first couple of feet is linked to the door opening mechanically.

No, the main gear doors on the MD-11 are actuated by a hydraulic actuator each through sequence valves.
The center gear door is operated like the nose gear dooe, but unlike the nose gear door it is rigged to be fully closed when the gear is out as well.

Jan
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aero145
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Sat Apr 22, 2006 5:40 am

Wow, thanks for all the replies, guys! Now I know how this works.  Smile


Best regards,

David
 
SFOMB67
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Sat Apr 22, 2006 8:46 am

Quoting DH106 (Reply 8):
when retraction starts the gear legs begin to pivot BEFORE the inner door fully opens.

I think that's more a result of hyd flow or hyd piping thru shuttle or priority valves. I've seen lots of aircraft do that during a gear retraction on jacks. If you slow down the flow, it's very pronounced, not so much under full pressure. The DC-8 main gear operating mech is nothing like the NG. I've never rigged it but I think it was a complicated system. Involved differential cables operating valves, but the gear and main door were hyd actuated.
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HAWK21M
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RE: Why Does The Front-wheel Door Not Close On MD-11?

Sun Apr 30, 2006 12:44 am

I believe it has got to do with the Mechanical Linkage used to Attach the door.In Retracted position the Door is flush.
regds
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