flexo
Posts: 344
Joined: Thu Mar 29, 2007 6:55 pm

A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 8:50 am

As many of you will of course already know, the A380 uses a quite unique system to retract the rear main landing gear. Instead of folding inwards it gets retracted upwards into the bay.

View Large View Medium
Click here for bigger photo!

Photo © Vasco Garcia (VDG-Images)


Now, in the past there have been a couple of incidents where the landing gear was retracted while the aircraft was on the ground. Due to the design of the inward folding main gear the aircraft's weight prevented retraction there so that it was always only the front gear that retracted then, limiting the damage.

View Large View Medium
Click here for bigger photo!

Photo © Weimeng


So what would happen to the A380 if the gear was retracted on the ground? It seems that the upward moving main gear could be retracted even on the ground. What safety measures are in place to prevent that?
 
GST
Posts: 811
Joined: Wed Jun 11, 2008 10:27 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 10:15 am

Only the inboard gear legs retract vertically, the outer gear does infact have a conventional inwards folding mechanism. The A380 is certified to land normally & safely with only half of the main gear legs (presumably one on each side  Wow! ) deployed. Therefore if the main gear were to be retracted on the ground, the upwards retracted gear would raise up, but the outer gear would not be able to, and is still capable of taking the aircraft's weight.
 
flexo
Posts: 344
Joined: Thu Mar 29, 2007 6:55 pm

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 10:20 am



Quoting GST (Reply 1):
The A380 is certified to land normally & safely with only half of the main gear legs

Wow, I didn't know that!
Is it normal to add this amount of redundancy to civil aircraft? It seems like a huge weight penalty to carry an extra set of main gears just "to have some extra in case one fails".
 
GST
Posts: 811
Joined: Wed Jun 11, 2008 10:27 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 10:23 am

Dont think of it as a weight penalty. Though the aircraft can land on two main gear legs a number of times, I'll bet it isnt designed to do that too frequently and so eventually it would lead to damage to the gear legs and the fuselage structure around them.
 
kalvado
Posts: 487
Joined: Wed Mar 01, 2006 4:29 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 12:53 pm



Quoting Flexo (Thread starter):
ue to the design of the inward folding main gear the aircraft's weight prevented retraction there so that it was always only the front gear that retracted then, limiting the damage.

from purely mechanical perspective, it's not inward folding what ensures inability to fold while on the ground (especially for a single wheel design) - it's how that folding is implemented.
And one can easily envision something similar for vertical retraction as well - e.g. something like those retractable ballpoint pens. Part has to move out (down) before being able to retract, and that can provide adequate protection
 
flexo
Posts: 344
Joined: Thu Mar 29, 2007 6:55 pm

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 1:08 pm



Quoting Kalvado (Reply 4):
And one can easily envision something similar for vertical retraction as well - e.g. something like those retractable ballpoint pens. Part has to move out (down) before being able to retract, and that can provide adequate protection

I see where you are going with that, is that part of the actual gear design of the A380 or merely a hint of what it could look like?
 
kalvado
Posts: 487
Joined: Wed Mar 01, 2006 4:29 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 1:23 pm



Quoting Flexo (Reply 5):
, is that part of the actual gear design of the A380 or merely a hint of what it could look like?

I'm not privileged enough to see any drawings from A or B.. It's more like engineering common sense, IMHO.
 
EMBQA
Posts: 7798
Joined: Sat Oct 25, 2003 3:52 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 3:08 pm

Actually there is / was a safety issue with the landing gear during the free fall tests. The main gear would get stuck on the doors as they tried to open deploy. Even after the modifications they still got stuck. Speaking of that.....what happened to the multi part PBS special that was being done on the A380. I only saw the first 2 and no more, nor did I see anymore adverts. Did Airbus pull the plug when all the delays started..?

[Edited 2008-06-28 08:11:49]
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
GST
Posts: 811
Joined: Wed Jun 11, 2008 10:27 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 3:38 pm



Quoting EMBQA (Reply 7):
The main gear would get stuck on the doors as they tried to open deploy.

I believe that was only the conventionally inward folding outer gear. And besides, they established that when the aircraft is in flight the airflow around the gear will stop it jamming when opening for some reason. Regardless, I do believe there was some fix Incorporated into the design of the undercarriage for this for the production aircraft.
 
474218
Posts: 4510
Joined: Mon Oct 10, 2005 12:27 pm

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 3:55 pm



Quoting Kalvado (Reply 4):
from purely mechanical perspective, it's not inward folding what ensures inability to fold while on the ground (especially for a single wheel design) - it's how that folding is implemented.

Friction is the reason that the inward folding gear can not be retracted on the ground. The retract actuator can not over come the friction between the ground and the tires.
 
smeg
Posts: 51
Joined: Thu Feb 21, 2008 10:43 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 6:10 pm



Quoting GST (Reply 8):
I believe that was only the conventionally inward folding outer gear. And besides, they established that when the aircraft is in flight the airflow around the gear will stop it jamming when opening for some reason. Regardless, I do believe there was some fix Incorporated into the design of the undercarriage for this for the production aircraft.

Absolutely correct!

From what I remember, the initial static test failed on the "folding" gear. The weight of the gear was supposed to force the doors open, but there was a point where the tyres got hung up and stuck on the door. The initial fix for the static test was to simply place a shedload of grease on the inside of the landing bay door so that the tyre would still be able to force the door open!  Wow! (I kid you not, and it worked like a charm)

Then once it was established that that it was only a very minor change that was needed, from what I remember, they "tweaked" the inside of the door.

As GST stated, they were confident however that once airborne, the airflow would ensure that the landing gear would drop under gravity even without the "tweaks"

Also I think that the "upward" moving gear (rather than the folding gear) have to move down first before they can move up, thus preventing them from being retracted on the ground.
 
kalvado
Posts: 487
Joined: Wed Mar 01, 2006 4:29 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 6:16 pm



Quoting 474218 (Reply 9):
Friction is the reason that the inward folding gear can not be retracted on the ground.

well, it's a design feature of making friction work for you, not the idea of inward folding itself. Just think of aircraft standing on half-folded gear. Friction probably wouldn't prevent further folding. It's still same friction, though.

My point is that it's not retraction direction that keeps it safe, but engineering implementation properly using forces in a system (e.g. friction and/or aircraft weight).
 
User avatar
jetmech
Posts: 2316
Joined: Wed Mar 29, 2006 2:14 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 9:39 pm



Quoting GST (Reply 1):
The A380 is certified to land normally & safely with only half of the main gear legs (presumably one on each side ) deployed.

I'm quite certain that the 747 is certified as such as well. I definitely remember seeing a video of a United 747 (744/) - in the old orange colour scheme - performing an emergency landing with the wing gears extended only. I seem to remember it may have been at SFO. Does anyone else know of this, or is it a figment of my imagination? I have Googled without success to find the video.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
fr8mech
Posts: 6714
Joined: Mon Sep 26, 2005 9:00 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 9:40 pm



Quoting Flexo (Thread starter):
quite unique system to retract the rear main landing gear. Instead of folding inwards it gets retracted upwards into the bay.

Not unique. B747 body gear retracts forward.

Not sure about the A380, but the B747 body will retract on the ground...and given the correct weight distribution, the aircraft will promptly sit on its tail, if the nose doesn't retract.

Does the A380 body gear sit forward of aft of the wing gears? If the body gear sits aft, then its possible that the A380 would also sit on its butt.
When seconds count...the police are minutes away.
 
GST
Posts: 811
Joined: Wed Jun 11, 2008 10:27 am

RE: A380 Gear Retraction - Potential Danger?

Sat Jun 28, 2008 10:10 pm



Quoting Fr8mech (Reply 13):
Does the A380 body gear sit forward of aft of the wing gears? If the body gear sits aft, then its possible that the A380 would also sit on its butt.

It also sits aft of the wing gear on the A380.
 
User avatar
HAWK21M
Posts: 29917
Joined: Fri Jan 05, 2001 10:05 pm

RE: A380 Gear Retraction - Potential Danger?

Sun Jun 29, 2008 6:45 am

What would be the pitch of the A380 while on Ground.would 1deg nose down pitch be accurate.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
User avatar
moo
Posts: 4171
Joined: Sun May 13, 2007 2:27 am

RE: A380 Gear Retraction - Potential Danger?

Sun Jun 29, 2008 9:42 am



Quoting EMBQA (Reply 7):
The main gear would get stuck on the doors as they tried to open deploy. Even after the modifications they still got stuck.

The modifications were only temporary - they did fix the problem later on, before the aircraft went into service.

Quoting EMBQA (Reply 7):
Speaking of that.....what happened to the multi part PBS special that was being done on the A380. I only saw the first 2 and no more, nor did I see anymore adverts. Did Airbus pull the plug when all the delays started..?

I guess not, since the first airing of it was after the first delay. Its still shown periodically here on the Discovery Channel.
 
Ceph
Posts: 104
Joined: Tue Jun 12, 2007 1:29 pm

RE: A380 Gear Retraction - Potential Danger?

Sun Jun 29, 2008 12:27 pm



Quoting GST (Reply 8):
I believe that was only the conventionally inward folding outer gear. And besides, they established that when the aircraft is in flight the airflow around the gear will stop it jamming when opening for some reason. Regardless, I do believe there was some fix Incorporated into the design of the undercarriage for this for the production aircraft.

I believe that it was a Teflon coating on a ramp inside the gear door that solved the problem.
 
Filton
Posts: 41
Joined: Wed May 24, 2006 4:54 pm

RE: A380 Gear Retraction - Potential Danger?

Tue Jul 15, 2008 7:02 am

The A380, like all Airbus aircraft, has a solenoid that locks the gear handle in the down position while on the ground to prevent inadvertent retraction. It only unlocks after several inputs indicate that the aircraft is flying.
 
A10WARTHOG
Posts: 200
Joined: Mon Jul 12, 2004 7:32 am

RE: A380 Gear Retraction - Potential Danger?

Tue Jul 15, 2008 5:00 pm



Quoting Filton (Reply 18):
The A380, like all Airbus aircraft, has a solenoid that locks the gear handle in the down position while on the ground to prevent inadvertent retraction. It only unlocks after several inputs indicate that the aircraft is flying.

ERJ have the same thing, but you can overide the feature. Is that the same on Airbus?
 
GST
Posts: 811
Joined: Wed Jun 11, 2008 10:27 am

RE: A380 Gear Retraction - Potential Danger?

Tue Jul 15, 2008 5:40 pm



Quoting A10WARTHOG (Reply 19):

It would have to be as aircraft are required to undergo periodic gear retraction tests on jacks. You can bet the sensors wont classify that as flight!
 
Filton
Posts: 41
Joined: Wed May 24, 2006 4:54 pm

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 6:54 am



Quoting A10WARTHOG (Reply 19):
you can overide the feature. Is that the same on Airbus?

There is a procedure going through the MCDU to test the gear lever, but the gear will still stay down. When it's on jacks there is another procedure to raise the gear but it is fairly straight forward as the sensors indicate wieght off wheels.
 
User avatar
jetmech
Posts: 2316
Joined: Wed Mar 29, 2006 2:14 am

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 7:00 am



Quoting GST (Reply 20):
It would have to be as aircraft are required to undergo periodic gear retraction tests on jacks. You can bet the sensors wont classify that as flight!

This reminds me of a gear retraction test we once did on a 767. The plane was all jacked up ready to go with power on. Gradually, we noticed a burning smell, and shortly thereafter, smoke emanating from the drain mast.

Apparently, the amount of power required by the heating element to prevent the mast freezing includes the cooling effect of the slip stream, which is not present in the hangar!


View Large View Medium
Click here for bigger photo!

Photo © Piotr Marek (EPGD Spotters)



Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
User avatar
HAWK21M
Posts: 29917
Joined: Fri Jan 05, 2001 10:05 pm

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 7:34 am



Quoting JetMech (Reply 22):
This reminds me of a gear retraction test we once did on a 767. The plane was all jacked up ready to go with power on. Gradually, we noticed a burning smell, and shortly thereafter, smoke emanating from the drain mast.

Apparently, the amount of power required by the heating element to prevent the mast freezing includes the cooling effect of the slip stream, which is not present in the hangar!

Shouldn't there be an Electrical switching from 115vAc to 28vDc when jacked up by the Air-Gnd sense to avoid excessive current flow to the Heating elements to avoid overheat & personell injury...aka B737.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
anthob
Posts: 11
Joined: Tue Jul 19, 2005 4:54 am

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 9:30 am

The drag brace which is the mechanical linkage going forward (may be rearwards on the A380) from the main leg is hinged in the middle. This hinge is over centre with the gear locked down so with the weight on the wheels you would have to overcome the weight to break the over centre lock. Purely a mechanical safeguard. Also if you are on the ground doing anything with the gear you should have the downlock pins in.
 
A10WARTHOG
Posts: 200
Joined: Mon Jul 12, 2004 7:32 am

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 1:35 pm



Quoting GST (Reply 20):
It would have to be as aircraft are required to undergo periodic gear retraction tests on jacks. You can bet the sensors wont classify that as flight!

It might not count it has a flight, but the gear will retract normally, since the weight on wheel would have an air signal.

ERJ you could pin the gear, disconnect a cannon plug and I believe you looked for voltage when the gear handle was moved up. It was an op's check that could be done, instead of jacking the plane and doing a gear swing.
 
User avatar
jetmech
Posts: 2316
Joined: Wed Mar 29, 2006 2:14 am

RE: A380 Gear Retraction - Potential Danger?

Wed Jul 16, 2008 1:59 pm

Quoting HAWK21M (Reply 23):
Shouldn't there be an Electrical switching from 115vAc to 28vDc when jacked up by the Air-Gnd sense to avoid excessive current flow to the Heating elements to avoid overheat & personell injury...aka B737.

G'day Mel,

I'm really not too sure on this one, as I never really had the inclination to learn about any of the electrical distribution systems. All I remember is everyone looking about the hangar as they could smell something burning, followed by the observation of smoke from the drain mast.

I suspect it would be relatively easy to use certain sensor inputs to differentiate between a genuine flight condition, and a weight off wheels only condition (airspeed perhaps), but I'm really not sure if the 767 would have any such feature.

Regards, JetMech

[Edited 2008-07-16 07:23:21]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .

Who is online

Users browsing this forum: packcheer and 12 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos