caboclo
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What's This On The 777 Landing Gear?

Fri May 06, 2005 5:45 pm

What are those two lines extending from the strut to the rear wheels? Seems like they're very exposed, susceptible to FOD.


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Boeing Nut
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 12:19 am

I'd bet that it has something to do with the steering for the back two wheels.
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tinpusher007
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 1:25 am

My best guess would be some sort of hydraulic line.
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Lemurs
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 1:28 am

Considering this is the LR on a test flight, it almost certainly would be part of a test and measurement harness. Wiring for strain gauges, temperature gauges, etc. Boeing instruments their test planes out the wazoo, and I can't imagine this one would be any different.

Certainly I've never seen it on another 777, and you're right that it would be suseptible to damage where it's at in production. It doesn't make any sense for it to be part of a working model.
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citationjet
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 1:54 am

Quoting Lemurs (Reply 3):
it almost certainly would be part of a test and measurement harness

I agree. Instrumentation equipment and wiring is always orange in color.
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manzoori
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 2:48 am

If it's what you can see in these pictures (a non instrumented aircraft)

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Then it's the normal hydraulic services.

Rez
 

[Edited 2005-05-06 19:49:50]

[Edited 2005-05-06 20:02:54]
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Lemurs
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 4:22 am

Quoting Manzoori (Reply 5):
Then it's the normal hydraulic services.

So they are. I guess I just never took notice of them before. The orange screamed "TEST" to me in the first photo. Oops.
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EMBQA
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 4:32 am

The brake lines for the rear tires.
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HAWK21M
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 4:04 pm

Quoting TinPusher007 (Reply 2):
My best guess would be some sort of hydraulic line.

Very Unlikely considering its routing.Very likely to be suseptible to FOD.Cant risk a Hydraulic leak everytime.
Looks more like some Instrument wiring conduit.
regds
MEL
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tinpusher007
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 10:42 pm

Quoting HAWK21M (Reply 8):
Very Unlikely considering its routing.Very likely to be suseptible to FOD.Cant risk a Hydraulic leak everytime.
Looks more like some Instrument wiring conduit.
regds
MEL

If you look at the pics above that Manzoori posted, espcially the one on the bottom that shows the rear view of one of KLM's birds...I think its pretty obvious that they are hydraulic lines for the brakes.

I work on MD-88's all day long and they, too have hydraulic lines exposed right between the tires. I do see your point about them being exposed to FOD but I have never heard of anything happening because of it.
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muttley02
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RE: What's This On The 777 Landing Gear?

Sat May 07, 2005 10:47 pm

Just to add my 2c... Normally all test equipment wiring is orange or yellow.... When fitted to flight test aircraft...
 
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HAWK21M
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RE: What's This On The 777 Landing Gear?

Sun May 08, 2005 12:37 am


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Quoting TinPusher007 (Reply 9):
...I think its pretty obvious that they are hydraulic lines for the brakes.

You are correct.
But dont the lines look suseptable to FOD or the Strut protects them.
Also the No of lines in the pic looks different or is it just the angle.
regds
MEL
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Klaus
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RE: What's This On The 777 Landing Gear?

Sun May 08, 2005 1:09 am

TinPusher007: My best guess would be some sort of hydraulic line.

HAWK21M: Very Unlikely considering its routing.Very likely to be suseptible to FOD.Cant risk a Hydraulic leak everytime.

Since those lines are obviously regular components in all production models, the risk can´t be significant or they wouldn´t have routed anything that way. They´re not in line with the tires, so the risk is probably not that high.


HAWK21M: Looks more like some Instrument wiring conduit.

How exactly does the anti-skid mechanism work on the 777?

It looks like there are two main hydraulic lines (the thick black ones) and at least ten (four plus six) thinner blue lines which might be either hydraulic or electric.

So where does the anti-skid controller sit? Where are the control valves located? Are the control valves operated electrically or hydraulically?


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The different sensors (6 * wheel velocity, 6 * brake temperature, 6 * tire pressue, 1 * truck positioning angle, 1 * rear axle steering position plus possibly others) are probably multiplexed and would thus not require that many lines nor such thick ones.

My guess is that those ten thinner lines are:
• 6 lines for hydraulic brake control
• 2 lines for truck positioning actuator control
• 2 lines for rear axle steering control
The two thick lines would probably provide (redundant) hydraulic power for the servo-supported actuators (just the brakes? Or all actuators?).

The weak point of that theory would be that none of the images shows the additionally necessary bus lines for sensor signalling, even if they´d just need one or two of them. I´m also not aware whether there are brake cooling fans which would require power supply wiring. So maybe steering and/or the truck positioning actuator are controlled via electric servo valves and two or more of those thinner lines are used for signalling and electrical power.

Okay, so much for a wild theoryBig grin
Now does someone have actual information about those details?
 
KC135R
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 3:01 am

Quoting HAWK21M (Reply 8):
Very Unlikely considering its routing.Very likely to be suseptible to FOD.Cant risk a Hydraulic leak everytime.

That's why many (probably most, but I don't know for sure) airplanes have fuses installed in the brake lines which will set after a predetermined amount of fluid passes through them. This prevents losing an entire hydraulic system in the event of a blown line. Though 10 years as a hydraulic maintainer in the USAF, I have yet to see a brake line blow.
 
SWISSER
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 6:57 am

Quoting KC135R (Reply 13):
That's why many (probably most, but I don't know for sure) airplanes have fuses installed in the brake lines which will set after a predetermined amount of fluid passes through them. This prevents losing an entire hydraulic system in the event of a blown line. Though 10 years as a hydraulic maintainer in the USAF, I have yet to see a brake line blow.

Indeed!
It works and no problems either since 1994,and a quick inspection of them
is enough to see something is wrong!It is a great landing gear!
I'am currently producing a model kit of it and resembling all those lines will
take time,ouch  Wink

Thanks to the authors for the great pictures!
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777wt
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 11:37 am

Wasn't these hyd fuses designed and installed in a/c after the JAL 123 fatal flight?
 
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HAWK21M
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 2:06 pm

Quoting KC135R (Reply 13):
Though 10 years as a hydraulic maintainer in the USAF, I have yet to see a brake line blow.

What about FOD to a brake line.Experienced any.
regds
MEL
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KC135R
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 3:23 pm

Quoting HAWK21M (Reply 16):
What about FOD to a brake line.Experienced any.

I have not personally seen any, which is not to say it does not happen of course - the worst we normally see on brake lines is the occasional dent or ding - nothing major.
 
air2gxs
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RE: What's This On The 777 Landing Gear?

Mon May 09, 2005 9:46 pm

Quoting 777WT (Reply 15):
Wasn't these hyd fuses designed and installed in a/c after the JAL 123 fatal flight?

Hydraulic fuses have been installed in aircraft for many years, usually in the brake system. Fuses were introduced into main systems after JAL and the lesson was reinforced in Sioux City several years later with a UAL DC-10.
 
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HAWK21M
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RE: What's This On The 777 Landing Gear?

Tue May 10, 2005 5:48 pm

Quoting Air2gxs (Reply 18):
Fuses were introduced into main systems after JAL and the lesson was reinforced in Sioux City several years later with a UAL DC-10.

Tell me about this.
regds
MEL
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Staffan
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RE: What's This On The 777 Landing Gear?

Tue May 10, 2005 6:06 pm

Quoting HAWK21M (Reply 16):
What about FOD to a brake line.Experienced any.

Hyd leaks always occur in places less accessible than brake lines close to the wheels  Wink

Staffan
 
air2gxs
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RE: What's This On The 777 Landing Gear?

Tue May 10, 2005 10:12 pm

Quoting HAWK21M (Reply 19):
Quoting Air2gxs (Reply 18):
Fuses were introduced into main systems after JAL and the lesson was reinforced in Sioux City several years later with a UAL DC-10.

Tell me about this.
regds
MEL

In brief, the JAL incident involved a failed repair on the aft pressure bulkhead of a B747. When the bulkhead ruptured, the mass of debris and air blew into the stabilizer compartment and shredded the hydraulic lines. As all 4 systems run in that compartment, all 4 systems were rapidly depleted. Without hydraulics the B747 flight controls are useless. The aircraft eventually flew into a mountain.

Sioux City involved a DC10 where the #2 engine fan cam apart and tore up the hydraulics in the tail. Though uncontrollabe with flight controls, the flight crew, with help from a jumpseating captain, was able to bring the aircraft to the airport and bring it down inside the fence line. That crew is creditied for saving the lives of a sizable percentage of the passengers.

I'm sure some folks can come up with the official links to these accidents.
 
AA173HEAVY
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RE: What's This On The 777 Landing Gear?

Tue May 10, 2005 10:24 pm

Insert some famous meaningful quote here
 
Klaus
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RE: What's This On The 777 Landing Gear?

Wed May 11, 2005 12:19 am

Does anybody know the actual functionality of the individual control and / or sensor lines on the 777 MLG (reply 12)?

I´d really like to know...
 
aeropiggot
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RE: What's This On The 777 Landing Gear?

Fri May 13, 2005 5:57 am

Most of the original question has be answered in some form by our members. But I would just like to add the following. These are indeed hydraulic lines for the steerable two rear wheels on the 6 wheel truck. If fact they have been upgraded since the original 777-200 flight test program in 1995/1996. Due to a part of the landing gear bay doors becoming dislodge, and stroked the hydraulic lines you see in the picture. Pilot was concern about landing gear collapse on landing. Boeing fix was to cover them in a steel sheet coating, I believe.
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UAL Bagsmasher
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RE: What's This On The 777 Landing Gear?

Fri May 13, 2005 12:43 pm

Even the little CRJ-200 has fuses in the brake system. You have to override them to bleed the brakes.

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