Nose gear lifting and parking brake.

[izatrue]

Dear all,

Prior to push back from stand, ground crew asks to set the parking brakes in order to lift the nose gear.

Doesn't it put a sensible amount of torque stress on the main wheel gears with brakes on?

As a lift of around 2-3 feet, an arm length of 40-50 feet ( middle sized aircraft) will induce a couple of degrees of torque: could we assume that this stress is absorbed in tire flexibility?

Which method would you recommend?

[catchup]

For my opinion neglicable compared to forces at normal braking.

regards

[dusk2dawn]

Provided your tires are round :) the a/c will rotate around the tire/tarmac contact point = no problem whatsoever.

[SeldomFixit]

Not to mention those pesky bogie beam pivots :)

[izatrue]

well the truth is, i was deferently asked by a ground mechanics why some operators insist on lifting the plane with brakes released: i told him i didn't really have a precise answer, all i could think of immediately against the idea was about having a backup in case the pushback truck skidded on a possibly greasy tarmack, slopy stand... :confused:

so, catchup, you have a point here :ok:

dusk2dawn Provided your tires are round the a/c will rotate around the tire/tarmac contact point = no problem whatsoever.

remember: with parking brake on, no rotation whatsoever is to be allowed, even on round tires:}

[Flap Sup]

Iza,

towbarless only lift the ac approx 2 inches => practially no torque stress...

/fs

[batty]

There is no movement with the parking brake set, no movement of the aircraft relative to the wheel. There is however the wheel rotating on the ground as the nose wheel is lifted....thus no force. Remember the wheel is braked relative to the a/c and not the ground, in effect even with the brake set when the nose is lifted the main wheel rotates fractionaly with respect to the ground, only a few mm but enough.

I would have to agree with DawntoDusk

[mono]

You guys have all missed Seldom fixit's subtle comment.

There are lots of a/c out there with double, triple or more axle bogies. If the wheel rotated about it's contact patch then a/c with multiple axle bogies would have a problem.As usual the answer is a bit more complicated.

On single axle bogies yes, the wheel will rotate slightly relative to the ground not the a/c.

On multiple axle bogies, the bogie simply tilts slightly.

However, as the a/c is lifted vertically in effect it is pulled slightly forward. The forces acting on the wheel/tyre are minimal when compared to the same forces while braking.

I would always keep the brake on just in case. :ok:

Edited for clarification.

[allthatglitters]

perhaps a relook at the towing manual for the procedures maybe required, to see if it's brakes on or off for lifting.

[blackmail]

hello everyone,

i think technically there is no real problem with lifting the nose gear with or without parkbrakes on.

it is more of a safety concern for the groundstaff around the aircraft to have the parkbrake on, same procedure as when connecting/disconnecting a classic towbar.

i had one airline where they insisted on parkb. on before lifting & another one where no guidelines where given, with some ground engineers asking for pb on before lifting & others asking the contrary. a bit confusing i admit. the real problem is not being pushed with the parkingbrakes still on, especially when english is not the first langage of the groundcrew.

[Ziggy]

I would have to disagree with Dusk2Dawn and Batty, since the aircraft will have to be lifted along the arc prescribed by the nosegear with the centrepoint at (actually very near to but not at) the contact point of the main gear wheel with the surface.
Since the aircraft is lifted verically there will be a force at the nosegear and/or main gear.

The smaller the arm between nose and main gear gets, the bigger this effect will be. Just try lifting the nose gear of a Warrior 3 feet vertically and see what happens.

I would say this force is negligable on longer aircraft but if not, this could possibly be fixed by releasing the parking brake on the tow truck. The truck will be pulled forward slightly while lifting the nosegear.

Is this possibly a procedure in use.....

Ziggy

[dusk2dawn]

Just where does this magical
centrepoint at (actually very near to but not at) the contact point of the main gear wheel with the surface come from ?

If you lift a Warrior 3 feet vertically, you will turn it around its tail skid ;)

Anyway, got boogie - they can lift us as they please - aint movin nowhere before I release the brakes.

[catchup]

The biggest problem when lifting the nlg are the air/grd sensors. They turn completely mad and the aircraft does'nt know what's going on. The computers get confused about offblock-time, the pressurisation pumps the cabin up, the ins(irs) sense a too high altitude, and so on.
So, its one of the reasons we earn so much money, cause we make it all work after such a mess.

regards

[keel beam]

In my experience - Brakes on , towbarless tractor positions (but does not lift) when brakes are indicated off then the tractor lifts. As for sensors etc - the nose leg oleo stays compressed so the sensors etc do no move so the as far as the aircraft is concerned it is still on the ground. Catchup - if you are getting the warnings you describe then your aircraft has a problem!

[catchup]

;) .;) .;) .;) .;) .;) .;) .;) .;) .;) .

[SeldomFixit]

I hope CATCHUP is flying a chopper !!!! Big problems if he isn't :p :ooh:

[Charles Darwin]

I do not really think we have a problem. Anybody want to calculate the movement of the pivots in the main gear. Let´s say we have 20 meters between nose and main gear, and the nose is raised 5 cm off the ground with park brake set. If these forces were too much to handle for the jet, I wouldn´t want to sit in it during flight, let alone landing!:=

[supercarb]

Actually there is no problem at all. Bogie landing gears are usually designed so that the leg can rotate relative to the bogie, even when the brakes are applied. The brake units are attached to brake rods which transmit the brake torque into the leg. If the nose of the aircraft is raised causing the MLG leg to tilt backwards, the brake units will rotate on the axle by the same amount, while the bogie remains parallel to the ground.

[PAXboy]

Warning! Thread Hijack in progress!! Using the towbar-less tug method - does it really save a lot on manpower? Is the saving in another direction??

--------------------
"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.

[Blacksheep]

It saves a small fortune in tow bars... :hmm:

[tomcat69]

All towbar-less tugs I've worked with need to pull/roll the aircraft onto a lifting plate which then lifts off the ground lifting the aircraft with it. So how is the nose supposed to be rolled onto this lifting plate if the aircraft cannot be rolled with the parking brake set??? Perhaps you havn't noticed the roll because it is subtle but it's there, unless there are new towbarless tugs out there that somehow levitate the nose tires off the ground without the need to roll the aircraft that I haven't seen before, which is quite possible.

[dusk2dawn]

Perhaps we havn't noticed the roll because the tugs are not braked during lift-up and thus the tugs can move freely under the nosegear (as long as the a/c is braked).

[tomcat69]

hmmmmmm, imagine trying to squeeze a metal plate under your car's tire without moving the car, a damn near impossibility. And one other thing I forgot to mention, the "cradling" procedure as it's called calls for leaving the aft chocks in place during the process so the aircraft won't roll back in case someting goes wrong.

[Flap Sup]

tomcat et al,

the towbarless (tbl) wraps itself around the wheels, it can be done when the ac is parked and it dosn't lift the ac before push.

Paxboy,

yes it saves money. Many stations are allowed to do a one man tbl operation. Furthermore, there is one less link to turn so it is easier for the driver than with a towbar, resulting in less aircraft damages - the most usual being nosewheel limit not kept.

I really wish I knew a lot less about ground handling....

/fs