Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
DFW17L
Topic Author
Posts: 264
Joined: Fri Nov 20, 2015 2:53 am

Wheel retraction question

Fri Feb 07, 2020 9:41 pm

When the wheel's are retracted, and prior to storage, are the brakes applied automatically to stop rotation? Or are the wheels spinning after storage until their momentum ceases?
 
Dalmd88
Posts: 3157
Joined: Fri Jul 28, 2000 3:19 am

Re: Wheel retraction question

Fri Feb 07, 2020 9:45 pm

Yes, the wheel is slowed to a stop by either an automatic hydraulic brake command using the gear retract sequence or by a wear surface in the gear well for nose gear.
 
User avatar
Starlionblue
Posts: 20180
Joined: Fri Feb 27, 2004 9:54 pm

Re: Wheel retraction question

Fri Feb 07, 2020 10:26 pm

Adding to this, you have to stop rotation on the mains or the gyroscopic effects can damage the gear mechanism. This is why if brakes are inop on an axle you have to delay gear retraction until the wheels have spun down.

For the nose gear, it doesn't matter, and it has no brakes anyway, so there's a snubber that stops the wheels as it comes in. You can often hear this as a little screech sound in the cockpit.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
bradyj23
Posts: 96
Joined: Thu Apr 19, 2007 9:24 am

Re: Wheel retraction question

Sat Feb 08, 2020 3:00 pm

Starlionblue wrote:
For the nose gear, it doesn't matter, and it has no brakes anyway, so there's a snubber that stops the wheels as it comes in. You can often hear this as a little screech sound in the cockpit.


The CRJ 200 didn’t have snubbers. You could hear the nose wheel spinning away for quite awhile after retraction. Snubbers were added on the 700/900.
 
gregorygoodwin
Posts: 70
Joined: Wed Jun 11, 2014 10:01 pm

Re: Wheel retraction question

Mon Feb 10, 2020 6:20 pm

Quite a bit of sequencing goes on with gear retraction and deployment. Although not related to the authors brake question, if the main gear has multiple axles on the bogie beam, such as a 757, 767, etc, the bogie must be centered upon gear retraction to go up into the gear well. This is done by a actuator on the bogie beam.We had one fail on one of our MD10s a few years back. The gear still retracted into the gear well and along the way tore up a lot of structure. Took about two days of around the clock work to get everything repaired and do a gear swing.

Gregory
 
User avatar
CALTECH
Posts: 3428
Joined: Thu May 17, 2007 4:21 am

Re: Wheel retraction question

Thu Feb 13, 2020 5:15 pm

Stopping the mains and all that energy inside the wheel well is a good thing. Gets rid of vibrations too.
You are here.
 
DH106
Posts: 636
Joined: Wed Jun 15, 2005 5:32 pm

Re: Wheel retraction question

Thu Feb 13, 2020 11:18 pm

gregorygoodwin wrote:
.... if the main gear has multiple axles on the bogie beam, such as a 757, 767, etc, the bogie must be centered upon gear retraction to go up into the gear well. This is done by a actuator on the bogie beam.


Not necessarily actively 'centered', the 767 I believe for example has no active bogie positioning other than a passive jack that returns the bogie to it's 'default' nose-down postion when in the air. This came up in a thread a few years ago concerning the 767 retraction dynamics and the necessary 'little door' on the wing top surface that opens & closes during the retraction sequence. Apparently, on the 767 there is no active bogie positioning - the forward sweep of the retraction axis allows alignment of the nose-down bogie into the wheel well.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
User avatar
fr8mech
Posts: 8083
Joined: Mon Sep 26, 2005 9:00 am

Re: Wheel retraction question

Fri Feb 14, 2020 12:08 am

DH106 wrote:

Not necessarily actively 'centered', the 767 I believe for example has no active bogie positioning other than a passive jack that returns the bogie to it's 'default' nose-down postion when in the air. This came up in a thread a few years ago concerning the 767 retraction dynamics and the necessary 'little door' on the wing top surface that opens & closes during the retraction sequence. Apparently, on the 767 there is no active bogie positioning - the forward sweep of the retraction axis allows alignment of the nose-down bogie into the wheel well.


The B767, along with the B747 and the B757, has a gear positioning actuator on each gear. The bogie is not “centered”, it positioned so that it can enter the wheel well without interference. These cylinders are hydraulically actuated.

The little door on above the gear, on the wing, is the result of Boeing having to widen the footprint of the gear, without having to do a major wing and/or redesign. The B767-100 had too high a runway loading for some airports, LGA & SFO, come to mind. By widening the distance between the mains, the runway loading was spread out.
When seconds count, the police are minutes away, or may not come at all.
It’s hard to win an argument with a smart person, but it’s damn near impossible to win an argument with a stupid person. ~B. Murray
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
DH106
Posts: 636
Joined: Wed Jun 15, 2005 5:32 pm

Re: Wheel retraction question

Fri Feb 14, 2020 8:14 am

Okay - I stand corrected, the 767 bogie is actively positioned during retraction?
In the previous thread I mentioned one poster stated that the gear retracts with the bogie in it's default nose-down position, with no active positioning for retraction.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
User avatar
fr8mech
Posts: 8083
Joined: Mon Sep 26, 2005 9:00 am

Re: Wheel retraction question

Fri Feb 14, 2020 12:10 pm

DH106 wrote:
Okay - I stand corrected, the 767 bogie is actively positioned during retraction?
In the previous thread I mentioned one poster stated that the gear retracts with the bogie in it's default nose-down position, with no active positioning for retraction.


I guess it depends what “active positioning” means. Once the gear is off the ground, the bogie is automatically positioned at the correct angle to enter the wheel well. If the bogie is not in the proper position, the gear handle will not move from the down position.
When seconds count, the police are minutes away, or may not come at all.
It’s hard to win an argument with a smart person, but it’s damn near impossible to win an argument with a stupid person. ~B. Murray
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
DH106
Posts: 636
Joined: Wed Jun 15, 2005 5:32 pm

Re: Wheel retraction question

Fri Feb 14, 2020 2:34 pm

fr8mech wrote:
I guess it depends what “active positioning” means. Once the gear is off the ground, the bogie is automatically positioned at the correct angle to enter the wheel well. If the bogie is not in the proper position, the gear handle will not move from the down position.


I think we mean the same thing here - the bogie is retracted in it's normal 'in the air' position - there is no repositioning specifically for retraction as in some aircraft. The strut used to position the bogie is 'passive' in that it's not sequenced and active part of the retraction process.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
kalvado
Posts: 2931
Joined: Wed Mar 01, 2006 4:29 am

Re: Wheel retraction question

Sun Feb 16, 2020 1:27 pm

If I remember correctly, A-380-800 doesn't have a full set of brakes on mains. How they handle the free axle?
 
DH106
Posts: 636
Joined: Wed Jun 15, 2005 5:32 pm

Re: Wheel retraction question

Sun Feb 16, 2020 10:42 pm

kalvado wrote:
If I remember correctly, A-380-800 doesn't have a full set of brakes on mains. How they handle the free axle?


The brakeless wheel axles are on the body gears which don't change orientation/direction on retraction, so those gyroscopic forces don't come into play.
...I watched c-beams glitter in the dark by the Tanhauser Gate....

Who is online

Users browsing this forum: 817Dreamliiner, Jalop, thepinkmachine and 27 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