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777 MLG Jacking.  
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Posted (8 years 2 months 1 week 3 days 22 hours ago) and read 4546 times:

Are there any weight restrictions when jacking the MLG of a 777? I presume that the 777 MLG trucks are similar to other Boeing MLG trucks in that there is a jacking point at either end   .

Assuming this is correct; due to the design of the 777 MLG, any jacking that was high enough would re-distribute the weight from a 6-point loading to a 3 point loading (two wheels and single jack point). This would place additional loads upon the two tyres and cause increased bending loads on the truck beam.

What happens if the plane is fully loaded at the terminal and the pilot does a last minute walk-around and decides he wants a MLG tire changed? Do passengers and cargo need to be off-loaded?

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[Edited 2006-10-21 04:40:34]


JetMech split the back of his pants. He can feel the wind in his hair.
17 replies: All unread, jump to last
 
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 1, posted (8 years 2 months 1 week 3 days 20 hours ago) and read 4523 times:

To change the fwd and aft wheels is the same as any other aircraft. You need an axle jack rated at 65tons, and can jack the aircraft up at MTOW. (But it is much easier if it is lighter!)
There is a pitfall on the rear wheels as there are two jacking pads, and only one is correct! Using the wrong one will make expensive noises (I always wondered why it is there.)
To change the centre wheels you MUST use two jacks, one at each end. If you jack up one end enough to change the centre wheels, the truck level actuator will bottom out and break. With two 65ton jacks you can change the centre wheels at MTOW.


User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 2, posted (8 years 2 months 1 week 3 days 15 hours ago) and read 4483 times:

Thanks for the answer TristarSteve  Smile. It seems as though the truck flexes enough such that you can get enough clearance to remove the fwd or aft wheels whilst there is still some weight on the centre wheels. I remember reading in the Boeing magazine that the truck beam is in-fact curved downward to help even out the loads amongst the three axles  Confused

Do you have any details about the connection between the centre axle, truck beam and the lower fork end of the inner MLG cylinder?

Is the centre axle secured to the truck, which then rotates in the fork, or is the centre axle attached to the fork, with the truck beam rotating about it? That junction seems as though it would be somewhat mechanically complex.



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 3, posted (8 years 2 months 1 week 3 days 14 hours ago) and read 4471 times:

Quoting JetMech (Reply 2):
Do you have any details about the connection between the centre axle, truck beam and the lower fork end of the inner MLG cylinder?

The Centre axle acts as the pivot for the truck.
To remove the truck, you have to remove the centre axle, then the truck can be lowered out of the shock strut fork.
So with everything removed the bottom of the shock strut is a y shape with two big holes in it. You jack up the truck assy, and then slide the centre axle through holes in the truck and the shock strut.
Rgds Steve


User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 4, posted (8 years 2 months 1 week 3 days 1 hour ago) and read 4396 times:

Thanks again TristarSteve  Smile. Just for a bit more clarification, is the centre axle motionless relative to the truck beam or the fork end of the MLG inner cylinder? Or is the centre axle fully floating in both? How exactly are the centre axle brake units mounted?


JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineCX flyboy From Hong Kong, joined Dec 1999, 6642 posts, RR: 55
Reply 5, posted (8 years 2 months 1 week 2 days 16 hours ago) and read 4344 times:

Had this the other day where our tyre number 8 needed replacing while we were sat at the terminal with passengers on board. Credit to the engineers, from when I told them about it to them finishing was about 25minutes.

User currently offlineTristarSteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 6, posted (8 years 2 months 1 week 2 days 13 hours ago) and read 4321 times:

Quoting JetMech (Reply 4):
Just for a bit more clarification, is the centre axle motionless relative to the truck beam or the fork end of the MLG inner cylinder? Or is the centre axle fully floating in both? How exactly are the centre axle brake units mounted?

Sorry, can't tell. There does not seem to be any ant-rotation bolts. I have never changed one so can't say.
At the bottom of the strut there are three holes each side. In the centre one is the centre brakes attach bolt. The fwd and aft have the brake torque rods attachment fro the fwd and aft brakes.
As far as I can tell the centre axle slides through the truck and the strut. Then the centre brakes are fitted and bolted to the bottom of the strut at each side (with one bolt each side). This holds the centre axle in place as the axle is stepped where the brakes sit. You need to wait for a hangar guy to read this who can tell you more, I work on the line, and in two years of B777 daily flights have never changed a wheel or a brake.


User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 7, posted (8 years 2 months 1 week 2 days 1 hour ago) and read 4259 times:

Quoting TristarSteve (Reply 6):
I work on the line, and in two years of B777 daily flights have never changed a wheel or a brake.

I'm guessing you work at an Outstation...?

Two years of working on the T7 and you've never changed a wheel or brake? How many flights a day do you see?



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 8, posted (8 years 2 months 1 week 1 day 15 hours ago) and read 4211 times:

Quoting Kaddyuk (Reply 7):
I'm guessing you work at an Outstation...?

Two years of working on the T7 and you've never changed a wheel or brake? How many flights a day do you see?

Yes the aircraft transits through us with a 1hr 20min stop. 6 days a week.
I think the Radial tyres on the B777 are great. Very rare to even see a cut to look at.
There are similar radial tyres on the A320. I have 4 A320 a day, and they have been coming here since June 1988, and I have never changed a mainwheel on that either.
I think it all hinges on the fact that both aircraft are looked after at their (different) main bases. They do not release aircraft with worn out tyres. But my stock of mainwheels for the A320 is regularly borrowed (they are in IATA pool) by another European carrier here who must change them here every six months.


User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 9, posted (8 years 2 months 1 week 1 day 12 hours ago) and read 4198 times:

Quoting TristarSteve (Reply 8):
There are similar radial tyres on the A320. I have 4 A320 a day, and they have been coming here since June 1988, and I have never changed a mainwheel on that either.

Lucky...



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 10, posted (8 years 2 months 1 week 1 day 12 hours ago) and read 4194 times:

G'day TristarSteve / Kaddyuk  Smile . I have been working at a line station on and off for the last six years, and I can only remember personally being involved with one NLG and one MLG wheel change in that time, but never a brake. This is at a station that is responsible for more than 5 flights a day on average.

Previously when I was working at a major maintenance base, I changed wheels far more often than that, but curiously, the number of brake changes still remained quite low.



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 11, posted (8 years 2 months 1 week 1 day 11 hours ago) and read 4183 times:

Quoting TristarSteve (Reply 8):
think the Radial tyres on the B777 are great. Very rare to even see a cut to look at.

It also determined on the condition of the Runway surface & Taxipath.
regds
MEL



Think of the brighter side!
User currently offlineVenus6971 From United States of America, joined Dec 2004, 1445 posts, RR: 0
Reply 12, posted (8 years 2 months 1 week 1 day 8 hours ago) and read 4156 times:

Quoting JetMech (Reply 10):
Previously when I was working at a major maintenance base, I changed wheels far more often than that, but curiously, the number of brake changes still remained quite low.

Is it possible that the 777 has carbon fiber brakes installed. The 747-4 has them and last much longer than the metal ones.



I would help you but it is not in the contract
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 13, posted (8 years 2 months 1 week 20 hours ago) and read 4088 times:

Quoting Venus6971 (Reply 12):
Is it possible that the 777 has carbon fiber brakes installed. The 747-4 has them and last much longer than the metal ones.

G'day Venus6971  Smile,

When I was at the major maintenance base,I worked on a mix of B74SP / B742 / B743 with steel brakes, and B744 / B762 / B763 with carbon brakes.

I don't really recall changing too many of either. I probably changed more of the carbon brake units but then again, there was a greater number of aircraft with these types of brakes in the fleet.



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineBuyantUkhaa From Mongolia, joined May 2004, 2915 posts, RR: 3
Reply 14, posted (8 years 2 months 1 week 14 hours ago) and read 4060 times:

How is this done on the Tu154? Does anybody know?

Obviously a Tu154 is lighter than a 777, do they just lift the entire gear (like on single-bogey gear e.g. 737/320?)



I scratch my head, therefore I am.
User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 15, posted (8 years 2 months 1 week 8 hours ago) and read 4023 times:

Quoting TristarSteve (Reply 8):
I think the Radial tyres on the B777 are great. Very rare to even see a cut to look at.

you wanna take a look at a kuwait airways one  Wink

i had a lecturer at my old college who used to work for BA at LGW when they first got their 777's apparently they didnt have to do a brake change for the 1st 4 years they had them, and when one did come up the whole of BA engineering went to watch so they could write it up in their log book!


User currently offlineVenus6971 From United States of America, joined Dec 2004, 1445 posts, RR: 0
Reply 16, posted (8 years 2 months 1 week 5 hours ago) and read 4005 times:

Quoting JetMech (Reply 13):
When I was at the major maintenance base,I worked on a mix of B74SP / B742 / B743 with steel brakes, and B744 / B762 / B763 with carbon brakes.

When I was in the USAF working KC-135A's they had 4 rotor steel brakes and 1 U.S. dime 10cents piece would work good as a no go gauge for checking for brake wear, now they are modding the KC-135R's with carbon fiber brakes and hearing from troops in the field they are changing a whole lot less brakes, with the old four rotor steel ones it seemed every swing shift I was changing about 2 a night.
I was working a brand new Atlas Air 747-400 freighter about a year ago and got into conservation with the pilot about its carbon fiber brakes, he said he could abort a MTOW takeoff and taxi back to the gate and let them cool for an hour with out any mx actions. Any 744 mechs out their that can confirm that.



I would help you but it is not in the contract
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 17, posted (8 years 2 months 1 week 4 hours ago) and read 3991 times:

Quoting Venus6971 (Reply 16):
KC-135R's with carbon fiber brakes and hearing from troops in the field they are changing a whole lot less brakes

Not to mention that carbon brakes are more resistant to fade at high temperatures and also a whole lot lighter as well!



JetMech split the back of his pants. He can feel the wind in his hair.
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