meister808
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A320 Nose Gear Retraction

Wed Apr 25, 2007 6:08 am

Ok folks, I guarantee this has been discussed before, but I can't find it - does the A320 family nosewheel turn 90° on retraction into the nose wheel well, or does it go straight forward? I can't seem to find anything that would suggest that it turns, but the topic came up in discussion and there's more than a few people I know that insist such a design was the reason for the well-publicized Jetblue incident at LAX last year.

Am I missing something?

-Meister

[Edited 2007-04-24 23:19:05]
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b78710
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 6:15 am

most nose gear have whats called a centering cam which ensures the nose gear is straight before retraction, if it isn't it will not retract! the gear probably wouldnt even fit into the bay if it was at 90 degree's.....but dont quite me on that!

wasn't the jet blue incident something to do with some kind of nose wheel steering failure causeing it to go full one way?
 
Tristarsteve
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 6:15 am

Well wrong twice.
It doesn't turn 90deg, and it goes straight forward, not back.

The only gear I know that turns 90deg is the HS Trident MLG. This MLG had 4 wheels on a single axle, and rotated 90 deg on retraction to fit into the wing.
 
meister808
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 6:20 am

Thanks - fixed the forward/back thing, brain fart on my part

Good to know I wasn't crazy.

-Meister
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Viscount724
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 11:35 am

Quoting TristarSteve (Reply 2):
The only gear I know that turns 90deg is the HS Trident MLG. This MLG had 4 wheels on a single axle, and rotated 90 deg on retraction to fit into the wing.

That wasn't the Trident's only unusual landing gear feature. It also had the strange off-center nosegear that retracted sideways. As I recall that was to facilitate the location of the Trident's then state-of-the-art autoland equipment.


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rwy04lga
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 12:19 pm

The USAF XB-70 MLG also rotated 90 degrees before retracting rearward.


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HAWK21M
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 4:28 pm

The centering cams will locate the NLG wheel in a Straight line along the Longitutional axis when the strut extends.
regds
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Tristarsteve
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RE: A320 Nose Gear Retraction

Wed Apr 25, 2007 5:10 pm

Quoting Viscount724 (Reply 4):
It also had the strange off-center nosegear that retracted sideways. As I recall that was to facilitate the location of the Trident's then state-of-the-art autoland equipment.

There was a myth around that the NLG retracted sideways so that the nose wheels did not hit the centre line landing lights when doing Cat 3 autoland.
 
PGNCS
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RE: A320 Nose Gear Retraction

Fri Apr 27, 2007 10:04 am

It centers. In my A-320 AOM under the topic of Brake and Steering Control Unit (BSCU) it says "An internal cam mechanism returns the nose wheel to the centered position after take-off."

Hope this helps!
 
Mir
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RE: A320 Nose Gear Retraction

Fri Apr 27, 2007 3:35 pm

Don't the main gear of the Tu-144 do some kind of funky retraction?

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HAWK21M
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RE: A320 Nose Gear Retraction

Fri Apr 27, 2007 3:56 pm

Quoting Mir (Reply 9):
Don't the main gear of the Tu-144 do some kind of funky retraction?



Watch the Bounce.

regds
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Tristarsteve
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RE: A320 Nose Gear Retraction

Fri Apr 27, 2007 6:05 pm

Quoting Viscount724 (Reply 4):
That wasn't the Trident's only unusual landing gear feature

Also the Trident mainwheels were single wheels with two tyres on each wheel. I remember the trouble we had getting them off. They seemed to be an interference fit over the brakes, and more than once we had to remove the whole wheel/brake assy because the wheel would not come off!

Also strange was the emergency lowering of the gear. This used a compressed air bottle which blew high pressure air into the normal retraction jacks. You then had to use a turner adaptor to let the pressure out on the ground.

There was a lot of engineering on the Trident.
 
memphis
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RE: A320 Nose Gear Retraction

Thu May 17, 2007 7:24 pm

hey, isn't that the airwolf soundtrack???
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Mir
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 1:25 am

Quoting Viscount724 (Reply 4):
It also had the strange off-center nosegear that retracted sideways. As I recall that was to facilitate the location of the Trident's then state-of-the-art autoland equipment.

I heard it was because the autoland system was too good, and was putting the nose gear down right on the runway lights, which created a lot of vibration, so they chose of offset it.

-Mir
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Starlionblue
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 2:45 am

Quoting Memphis (Reply 12):
hey, isn't that the airwolf soundtrack???

Hehe. Certainly is.

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baw2198
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 7:59 am

Quoting Meister808 (Thread starter):
does the A320 family nosewheel turn 90° on retraction into the nose wheel well,

some aircraft that do are

The Beechcraft Sierra the nose wheel turns 90 and then retracts backward and the Piper Malibu (the older ones without the gear doors) which retracts in the same manner as the Sierra.
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HAWK21M
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 3:12 pm

Quoting BAW2198 (Reply 15):
some aircraft that do are

I don't think the A320 Nose Wheel turns 90deg on before retraction.The centering cam ensures its Straight.
regds
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DH106
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 6:49 pm

Quoting HAWK21M (Reply 16):
I don't think the A320 Nose Wheel turns 90deg on before retraction.The centering cam ensures its Straight.

Exactly - what would be the point?
Twin wheels are pretty much as wide as long so no real space saving.
Usually when they turn on retraction it's so a single wheel can lie flat and save space.
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baw2198
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 10:24 pm

Quoting HAWK21M (Reply 16):
I don't think the A320 Nose Wheel turns 90deg on before retraction.The centering cam ensures its Straight.
regds

HAWK, I wasn't saying that the 320 did. Everybody above already answered that, I was just giving examples of planes that did use that retraction method.
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moo
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RE: A320 Nose Gear Retraction

Fri May 18, 2007 11:35 pm

Quoting Meister808 (Thread starter):
Ok folks, I guarantee this has been discussed before, but I can't find it - does the A320 family nosewheel turn 90° on retraction into the nose wheel well, or does it go straight forward? I can't seem to find anything that would suggest that it turns, but the topic came up in discussion and there's more than a few people I know that insist such a design was the reason for the well-publicized Jetblue incident at LAX last year.



Quoting B78710 (Reply 1):
wasn't the jet blue incident something to do with some kind of nose wheel steering failure causeing it to go full one way?

There was a very good reason for the Jet Blue incident last year, and infact the actions of the nose gear on that occasion was by design.

When the A320 series leaves the ground, a mechanical cam system centres the gear (as Hawk21M said). If this mechanism fails, the gear system does not infact know where the wheel is pointing with any certainty.

In order to provide for a safe landing in this case, the gear is rotated until it locks at the 90 degree point - its safer to land in this way and destroy the front gear and strut than it is to land with the gear facing an unknown direction with the potential for an uncontrolled forward motion off the central axis at speed.

Thats the reason for the 90 degree rotation.
 
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HAWK21M
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RE: A320 Nose Gear Retraction

Sun May 20, 2007 12:06 am

Quoting BAW2198 (Reply 18):
I was just giving examples of planes that did use that retraction method.

My Apoligies.Guess I read the sentence Differently.

regds
MEL
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320tech
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RE: A320 Nose Gear Retraction

Sun May 20, 2007 6:29 am

Quoting Moo (Reply 19):
There was a very good reason for the Jet Blue incident last year, and infact the actions of the nose gear on that occasion was by design.

When the A320 series leaves the ground, a mechanical cam system centres the gear (as Hawk21M said). If this mechanism fails, the gear system does not infact know where the wheel is pointing with any certainty.

In order to provide for a safe landing in this case, the gear is rotated until it locks at the 90 degree point - its safer to land in this way and destroy the front gear and strut than it is to land with the gear facing an unknown direction with the potential for an uncontrolled forward motion off the central axis at speed.

Thats the reason for the 90 degree rotation.

As far as I can tell, this isn't true. This incident had nothing to do with a failure in the centring cam, and there's hardly anything in there to fail, anyway.

It was actually a failure in the nosewheel steering system. An oring failed, causing hydraulic pressure to turn the wheels over to the mechanical stop, which is at the (approx, I forget) 86 degree position. This has happened several times.

You can read the article on Jet Blue flight 292. http://en.wikipedia.org/wiki/JetBlue_Airways_Flight_292
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Starlionblue
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RE: A320 Nose Gear Retraction

Sun May 20, 2007 10:05 am

Quoting 320tech (Reply 21):

As far as I can tell, this isn't true. This incident had nothing to do with a failure in the centring cam, and there's hardly anything in there to fail, anyway.

It was actually a failure in the nosewheel steering system. An oring failed, causing hydraulic pressure to turn the wheels over to the mechanical stop, which is at the (approx, I forget) 86 degree position. This has happened several times.

If we ignore for a second the cause, didn't the gear go to the mechanical stop at about 90 degrees? That would seem to be the objective right?
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320tech
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RE: A320 Nose Gear Retraction

Sun May 20, 2007 12:57 pm

Quoting Starlionblue (Reply 22):
If we ignore for a second the cause, didn't the gear go to the mechanical stop at about 90 degrees? That would seem to be the objective right?

Well, my point is that having the gear rotate isn't a design feature, it's just the way it happens in that particular failure. I think the A320 is a well-designed airplane, but let's not give Airbus more credit than they deserve.  Smile
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HAWK21M
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RE: A320 Nose Gear Retraction

Sun May 20, 2007 6:04 pm

Quoting 320tech (Reply 21):
It was actually a failure in the nosewheel steering system. An oring failed, causing hydraulic pressure to turn the wheels over to the mechanical stop, which is at the (approx, I forget) 86 degree position. This has happened several times

What was the ADs Instructions like.
regds
MEL
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troubleshooter
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RE: A320 Nose Gear Retraction

Wed May 23, 2007 1:23 am

Quoting HAWK21M (Reply 24):
What was the ADs Instructions like.

FAA AD 99-23-09
This is the only one I could find in a minute...
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Starlionblue
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RE: A320 Nose Gear Retraction

Wed May 23, 2007 2:41 am

Quoting 320tech (Reply 23):

Well, my point is that having the gear rotate isn't a design feature, it's just the way it happens in that particular failure. I think the A320 is a well-designed airplane, but let's not give Airbus more credit than they deserve.

From what I have heard it is in fact a design feature. I may be wrong of course.
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320tech
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RE: A320 Nose Gear Retraction

Wed May 23, 2007 5:05 am

Quoting Starlionblue (Reply 26):
I may be wrong of course.

I may be wrong, too. I'll see what I can find next time I'm at work.
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HAWK21M
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RE: A320 Nose Gear Retraction

Wed May 23, 2007 6:34 pm

Quoting Troubleshooter (Reply 25):

requires modification of the electro-distributor for the nose wheel steering servo-control
Thanks.
regds
MEL
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David L
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RE: A320 Nose Gear Retraction

Thu May 24, 2007 4:44 am

Quoting 320tech (Reply 23):
Well, my point is that having the gear rotate isn't a design feature, it's just the way it happens in that particular failure



Quoting Starlionblue (Reply 26):
From what I have heard it is in fact a design feature. I may be wrong of course.

I seem to recall from previous discussions that it was considered safer to land with the nose gear stuck 90o off-centre, producing no tendency to veer to either side, than with it stuck at, say, 15o off-centre, which may result in a severe tendency to steer off-centre at landing speeds.

But I may be even wronger.

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