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Does The Main Gear On A 747 Turn?  
User currently offlineaxelesgg From Sweden, joined Jan 2010, 191 posts, RR: 0
Posted (3 years 6 months 2 weeks 3 days 10 hours ago) and read 9198 times:

Hello!
Was at my local airport today and i saw this...


Is the 747 made to do that? (It's a 744)

21 replies: All unread, jump to last
 
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 1, posted (3 years 6 months 2 weeks 3 days 10 hours ago) and read 9199 times:

Only the inboard main does.

On the 777 the rearmost axle on the mains is steerable (castering?) as well.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15842 posts, RR: 27
Reply 2, posted (3 years 6 months 2 weeks 3 days 9 hours ago) and read 9160 times:

Quoting Fly2HMO (Reply 1):
On the 777 the rearmost axle on the mains is steerable (castering?) as well.

I always thought it was active steering, but I could be wrong.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineTristarsteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 3, posted (3 years 6 months 2 weeks 3 days 9 hours ago) and read 9145 times:

Quoting BMI727 (Reply 2):
I always thought it was active steering, but I could be wrong.

It is. The amount is controlled by the amount the nose wheels move.
But on a B777 it is very hard to see. It doesn't move much.


User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 4, posted (3 years 6 months 2 weeks 3 days 8 hours ago) and read 9101 times:

Yep, it is a lovely (maybe not for maintenance) feature about the 747 and it is called 'body-gear steering'.

Speedbird741



Boa noite Faro, Air Portugal 257 climbing flight level 340
User currently offlineaxelesgg From Sweden, joined Jan 2010, 191 posts, RR: 0
Reply 5, posted (3 years 6 months 2 weeks 3 days 8 hours ago) and read 9088 times:

Oh! I've never noticed it before. Thank's for the answers!

User currently offlinelowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 6, posted (3 years 6 months 2 weeks 3 days 7 hours ago) and read 9042 times:

Quoting axelesgg (Thread starter):
Is the 747 made to do that? (It's a 744)

The classics have this feature as well. It greatly reduces the the stress on the main gear during sharp turns.



Proud OOTSK member
User currently offlineTranspac787 From United States of America, joined Jul 2007, 3217 posts, RR: 16
Reply 7, posted (3 years 6 months 2 weeks 3 days 6 hours ago) and read 8929 times:

Quoting lowrider (Reply 6):
The classics have this feature as well. It greatly reduces the the stress on the main gear during sharp turns.

I could be quite wrong but my understanding is that the body-gear-steering system on the 747 classics must be manually activated on the overhead panel in the cockpit, but on the 747-400 it is an automatic system and activates based on groundspeed and position of the nose-wheel tiller.


User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 8, posted (3 years 6 months 2 weeks 3 days 6 hours ago) and read 8925 times:

Quoting Transpac787 (Reply 7):
but on the 747-400 it is an automatic system and activates based on groundspeed and position of the nose-wheel tiller.

I believe it is so. If I recall correctly, it deactivates past 20 knots and arms at 15 knots. I also believe it must meet other criteria (i.e. nose gear angle) to arm. The good 747 pilots will hopefully pop in any time and clean up the issue for us.

Speedbird741



Boa noite Faro, Air Portugal 257 climbing flight level 340
User currently offlinelowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 9, posted (3 years 6 months 2 weeks 3 days 5 hours ago) and read 8901 times:

Quoting Transpac787 (Reply 7):
I could be quite wrong but my understanding is that the body-gear-steering system on the 747 classics must be manually activated on the overhead panel in the cockpit

True.

Quoting Speedbird741 (Reply 8):
If I recall correctly, it deactivates past 20 knots and arms at 15 knots. I also believe it must meet other criteria (i.e. nose gear angle) to arm.

I thought the speeds were disarm at 25 and arm at 20, but I wouldn't bet more than a cheap beer on those numbers. I also think the body gear steering actuation was based on tiller angle, not nose gear angle.



Proud OOTSK member
User currently offlinehorstroad From Germany, joined Apr 2010, 285 posts, RR: 0
Reply 10, posted (3 years 6 months 2 weeks 3 days 5 hours ago) and read 8888 times:

Quoting Fly2HMO (Reply 1):
On the 777 the rearmost axle on the mains is steerable (castering?) as well.

i think it's just castering, as well as the rearmost axle of the A380 body landing gear does... the 747 body landing gear is actively steering


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5947 posts, RR: 11
Reply 11, posted (3 years 6 months 2 weeks 3 days 3 hours ago) and read 8789 times:

Quoting Speedbird741 (Reply 4):
Yep, it is a lovely (maybe not for maintenance) feature about the 747 and it is called 'body-gear steering'.

Not bad from a MX perspective, UNTIL the hydraulic actuator explodes during power-up. In Anchorage. In February. In blowing snow.

THEN it's bad. Been there, done that.


User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 12, posted (3 years 6 months 2 weeks 3 days 1 hour ago) and read 8749 times:

Quoting axelesgg (Thread starter):
Is the 747 made to do that? (It's a 744)

Yes. Body gear steering assist nose steering during taxi and towing reducing stress and tire scrubbing.
When the system is armed, the body gear trucks are out of tilted position and the nose steering goes beyond 20 degrees hydraulic fluid is ported to the body gear steering actuators. (Closed loop system)
Full deflection, 13 degrees for the inboard truck and 11 degrees for the outboard (inboard/outboard of the turn) occurs when nose wheel is steered 70 degrees.
As lowrider mentioned the system is installed on the classics as well.
Arming switch on the classics is in the overhead panel. It's manually disarmed right after lining up for take off and armed during landing roll once the aeroplane reaches taxi speed. It's automatic on the -400.
Steering actuator position sensors will activate the take off configuration warning horn if thrust lever #3 is advanced with body gear steering actuators not locked & centered.

Quoting lowrider (Reply 9):
I also think the body gear steering actuation was based on tiller angle, not nose gear angle.

Correct. Signals to the body gear steering are cable driven from the tiller.

Regards,
B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (3 years 6 months 2 weeks 2 days 21 hours ago) and read 8652 times:

Quoting horstroad (Reply 10):
i think it's just castering, as well as the rearmost axle of the A380 body landing gear does... the 747 body landing gear is actively steering

777 is powered too...you'll get a warning if you don't taxi straight ahead long enough on the runway for the steering actuator to lock before you start the takeoff roll.

Tom.


User currently offlineCCA From Hong Kong, joined Oct 2002, 846 posts, RR: 14
Reply 14, posted (3 years 6 months 2 weeks 2 days 21 hours ago) and read 8645 times:

Yes the -400 arms as said reducing through 15kts and disarms accelerating through 20kts.

It's the same as the classic and requires 20 degrees of nose wheel steering before the body gear starts moving.

The trucks on the 777 and A380 use a similar system however it's only the rear axle as said both are hydraulically actuated.

The 747 uses the big fat actuators as seen to steer the gear.


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Photo © Maxim Finchenko - Aviator project



The 777 uses a clever design of lever and pivot with a single actuator and fixed rod.


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Photo © Thomas Merkl



The A380 Uses a similar system and has a previous discussion here.

Body Gear Steering On A A380 (by Qslinger Oct 18 2007 in Tech Ops)


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Photo © Rhys Dudley




C152 G115 TB10 CAP10 SR-22 Be76 PA-34 NDN-1T C500 A330-300 A340-300 -600 B747-200F -200SF -400 -400F -400BCF -400ERF -8F
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17187 posts, RR: 66
Reply 15, posted (3 years 6 months 2 weeks 2 days 18 hours ago) and read 8556 times:

Quoting tdscanuck (Reply 13):

777 is powered too...you'll get a warning if you don't taxi straight ahead long enough on the runway for the steering actuator to lock before you start the takeoff roll.

So if you taxi straight along a taxiway does it lock as well? Do the pilots have to unlock it or is it unlocked by tiller position?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineqslinger From India, joined Apr 2006, 261 posts, RR: 0
Reply 16, posted (3 years 6 months 2 weeks 2 days 2 hours ago) and read 8266 times:

Is the body gear steering applicable for the push backs as well? is it why the the tug pushes the aircraft for some distance even after the aircraft is lined up with the taxi way lines..to get the body gear lined up as well?


Raj Koona
User currently offlinelowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 17, posted (3 years 6 months 2 weeks 2 days 1 hour ago) and read 8248 times:

Quoting qslinger (Reply 16):
Is the body gear steering applicable for the push backs as well?

Yes, provided you are pushing with the #1 hydraulic system pressurized (at least on the 747)

Quoting qslinger (Reply 16):
is it why the the tug pushes the aircraft for some distance even after the aircraft is lined up with the taxi way lines..to get the body gear lined up as well?

Possibly, but sometimes there are designated start positions as well, or the push may be long to clear another parking stand. Lots of reasons this could be.



Proud OOTSK member
User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 18, posted (3 years 6 months 2 weeks 1 day 17 hours ago) and read 8127 times:

Quoting lowrider (Reply 17):
Yes, provided you are pushing with the #1 hydraulic system pressurized (at least on the 747)

Ok, I am sorry but now I am a tad confused. If the body gear steering actuators are:

Quoting B747FE (Reply 12):
cable driven from the tiller

What is the system logic here since there are no (or so I assume) tiller inputs?

Speedbird741



Boa noite Faro, Air Portugal 257 climbing flight level 340
User currently onlineboeingfixer From Canada, joined Jul 2005, 534 posts, RR: 0
Reply 19, posted (3 years 6 months 2 weeks 1 day 13 hours ago) and read 8059 times:

Quoting Speedbird741 (Reply 18):
Quoting Speedbird741 (Reply 18):
What is the system logic here since there are no (or so I assume) tiller inputs?

The tiller is back driven through the nose wheel steering control valve and cables on the nose gear.

Cheers,

John



Cheers, John YYC
User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 20, posted (3 years 6 months 2 weeks 1 day 1 hour ago) and read 7870 times:

Quoting Speedbird741 (Reply 18):

Just to clarify: Body gear actuators are not cable driven from the tiller. A cam actuated switch that arms the system (when demand of nose steering goes beyond 20 degrees) is mechanically driven (by cables) from the tiller.
A series of transducers, servo & solenoid valves within the hydraulic module take care of the rest. All steering actuators are powered by the hydraulic system. (System #1)

Quoting Speedbird741 (Reply 18):
What is the system logic here since there are no (or so I assume) tiller inputs?

Not directly but as boeingfixer pointed out, the tiller is back driven.
There are placards right below the tillers advising not to hold or turn the tillers while pushing/towing the aeroplane. (Sorry no time right now to look for it in the database)

Regards,
B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 21, posted (3 years 6 months 2 weeks 18 hours ago) and read 7762 times:

Quoting boeingfixer (Reply 19):
Quoting B747FE (Reply 20):

Thank you for your explanations. It is now understood.

Quoting B747FE (Reply 20):
Sorry no time right now to look for it in the database

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Photo © Florian Kondziela



Speedbird741



Boa noite Faro, Air Portugal 257 climbing flight level 340
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