Mr Spaceman
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Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 4:20 am

Hi guys. My question is... When an airliner "Takes Off" and the pilot retracts the landing gear, are the wheels still "Spinning" when they enter the wheel well bays?

When thinking back to the days when I worked on a ramp [a decade ago], all the aircraft that I worked with [mostly corporate], had "Spotless" wheel wells. I never thought to ask the pilots back then, so I'm wondering now if the pilots of retractables apply the brakes [once airborne] before raising the gear? Or does the aircraft's landing gear stop the tires automatically, if they stop at all?

I can only imagine that quite a mess could be made if an aircraft's tires are spinning at over 100 MPH inside their wheel wells, after they just lifted off a contaminated RWY covered in "Snow and Slush" or "Wet Mud and Gravel" etc!

Chris
"Just a minute while I re-invent myself"
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 4:41 am

On the 172 we apply brakes before we retract the gear, this stops the main wheels spinning while in the wheel bay, however the nose wheel had a pad that stopped it spinning as it entered the bay.
Hope this helps,
Iain
 
Western727
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 4:47 am

Most airliners have a "snubber" system, which applies the brakes to the wheels when the lever is thrown to retract the gear. So no, they don't spin in the wells.

Jack @ AUS
 
Mr Spaceman
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RE: Do

Tue Apr 10, 2001 5:12 am

Thanks! Western727 / Iainhol. I am only "Type Rated" on fixed gear aircraft, and have not been up flying since this question entered my mind. The only Pilots I have to ask this today were you guys. Once again , Thanks for confirming what I thought must be true. Hopefully some airline Pilots or Mechanics etc, can give me more detail on how their jets work in this area.

P.S. The next time I'm out at YYZ doing some spotting at the "Departure" end of an active, I'm going to look real close [with binoculars] at the landing gear on airliners as it retracts, to see if they are dead stopped or not.

Chris





"Just a minute while I re-invent myself"
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 6:10 am

On most larger aircraft, the main gear tires are automatically braked when the gear handle is raised. Gyroscopic forces would put tremendous loads on the landing gear if the tires remained "spinning" while being raised.

The nose gear is not subject to such gyroscopic forces while being raised and is normally braked by a snubber in the wheel well.
 
tygue
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 9:16 am

Once most aircraft rotate... the tires continue to spin until they are fully retracted. The nose gear is slowed by a large asbestos pad located in the wheel well. The main gear, however, continue to spin on their own until they come a stop. Unaided... no brakes... no pad... nothing.

This is speaking for large aircraft (Boeing/Airbus planes).


-Tygue
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 12:32 pm

Sorry Tygue,

But i disagree with you, the large Boeing aircraft which i am familiar with use residual brake pressure to slow and stop the spinning main wheels.

This is quite easily proven by the fact that with a brake deactivated or removed, the crew are required to leave the gear down for 2 minutes after takeoff in order for the wheels to stop spinning.

Heavyjet, I cant remember if the A300 is approved for gear down dispatch????
 
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HAWK21M
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Tue Apr 10, 2001 8:01 pm

The B737s use Hydraulics thru the metering valve to automatically brake the main gear during retraction & simultanously disable the Antiskid system to Facilate this braking.

The nose gear has snubber pads to mechanically stop the wheels.

Gyroscopic forces of a spinning wheel can cause
difficulty in controlling the aircraft If they were left spinning in addition to chances of FOD on retraction into the wheel well.

regds.
HAWK.
I may not win often, but I damn well never lose!!! ;)
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Wed Apr 11, 2001 12:28 am

Hawk21M,

Can you please explain what you mean by

Gyroscopic forces of a spinning wheel can cause
difficulty in controlling the aircraft If they were left spinning


How do spinning wheels interfere with aircraft control?
 
Panman
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Wed Apr 11, 2001 4:24 am

Go back to your basics on gyroscopes.

All gyroscopes have 2 properties.

Rigidity and precession.

Rigidity is the tendency for the gyro to remain pointed in one direction.

Precession is the property whereby if a force is applied to a gyro it is felt 90 degrees perpendicular to the point of application.

You now have the main gear wheels spinning at very high RPMs and so acting like a gyro. Select retract and you now have a force acting on the axis of the gyro trying to move it along the lateral axis of the airplane, this force is felt at 90 degrees from the point of application so basically along the longitudinal axis of the aircraft. Now imagine you have a 747 with it's 16 wheel main gear. You have 16 forces all acting along the longitudinal axis of the aircraft, You now have an aircraft that is bucking like a rodeo horse. Not nice to control and with the different rotational speeds of each wheel (assuming that they all slow down at different speeds) it would be very hard to trim this aircraft.

Hope that helps.

PanmaN
 
galaxy5
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Wed Apr 11, 2001 5:44 am

the main tire on the plane i fly (C-5 galaxy ) use snubbed brake pressure through a anti-rotation valve and the spinning is sensed by spin-up detectors. once the brake handle is placed to up the brake pressure is applied and wheel rotation is stopped then the MLG retraction sequence is initiated if the anti-rotation vlv fails then the wheels must spin down by themselves ( takes approx 2 min ) before the gear retracts. the nose gear retracts regardless it doesnt require spin down because it retracts straight back and the gyroscopic forces are minimal. hope that helps.  Smile/happy/getting dizzy
"damn, I didnt know prince could Ball like that" - Charlie Murphy
 
L-188
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Wed Apr 11, 2001 6:05 pm

I remember reading about a crash of a C-109 (Tanker B-24) in India during the war when the gear was selected up when the aircraft was "flying" flying but the wheels where still on the ground. The brakes automaticly stop the wheels from spinning and it caused enough drag that it brought the aircraft back down. Since the airplane was full of aviation fuel it exploded on hitting. I think all of the crew save one was killed. And he was really badly burned.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
FBU 4EVER!
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Wed Apr 11, 2001 8:39 pm

Panman's explanation on gyroscopics is very good and to the point.
I believe it was in the late 40's or early 50's that experiments were performed with wheels that would spin up before landing so as to save wear upon touch-down.Needless to say,the gyroscopic forces put paid to that idea.Would have liked to hear the pilot's comments as they found out!!!
"Luck and superstition wins all the time"!
 
FDXmech
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Thu Apr 12, 2001 1:17 am

Amongst other reasons, theoretically, even if it were feasable to spin the wheels prior to touchdown. This would create many more problems than it would solve. Foremost in my mind is the fact that initial wheel spin up is a critical input to many systems such as antiskid, autospoilers, autoland systems and the like. A very important mode transition parameter indeed.
You're only as good as your last departure.
 
dc10hound
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RE: Do

Thu Apr 12, 2001 12:40 pm

1. The A300 automatically applies main gear brakes for three seconds at gear retract command.
2. "Gyroscopic Forces" have nothing to do with it. The wheels need to be stopped when they enter the wells, to avoid damage to the gear.
3. Spaceman, I don't know where you ever found a "spotless" wheel well. Most of the airliner wells I've seen are nasty with Skydrol, dirt, grease, and general crud...
"Eagles soar. But weasels never get sucked into jet intakes.."
 
VC-10
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Thu Apr 12, 2001 6:05 pm

The 747 brake sytem applies 400 psi to the brakes as the main gear is retracted.
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Fri Apr 13, 2001 1:00 am

DC10hound,

>>"Gyroscopic Forces" have nothing to do with it. The wheels need to be stopped when they enter the wells, to avoid damage to the gear.<<

Care to elaborate?
 
VC-10
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Fri Apr 13, 2001 1:15 am

I would have thought that was self explanitory. Imagine a spinning burst tyre with long bits of rubber hanging off the remains.
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Fri Apr 13, 2001 2:49 am

I meant the ("Gyroscopic Forces" have nothing to do with it) part of it.

I know all about bursting tires (tyres)in the wheelwells, especially close to hyd lines and reservoirs etc, etc.

I'm not trying to start an argument. I'm hoping to learn something new from someone who may know more than I.
 
Mr Spaceman
Topic Author
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RE: Dc10hound

Fri Apr 13, 2001 3:30 am

Well, like I originally posted, most of the aircraft [90%], that I worked with were "Corporate Jets/Turbo Props", so maybe they were just simply easier and quicker to clean up inside [because they were smaller]. Any time that I was hooking up a tow bar, or pulling a gear pin etc, I would be impressed on how clean the wheel wells were. Good maintanance personnel I guess. Either way, that's what made me wonder if the wheels were stopped?...The lack of [OK, "a lot"] of dirt.

Chris

"Just a minute while I re-invent myself"
 
dc10hound
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sat Apr 14, 2001 12:51 pm

Heavy Jet:
No, I don't care to elaborate. As VC-10 says, it is self explanatory. (Thanx VC!  Smile)
"Eagles soar. But weasels never get sucked into jet intakes.."
 
dc10hound
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sat Apr 14, 2001 1:00 pm

Mr Spaceman:
I know what you mean, I like clean jets, too!!
"Eagles soar. But weasels never get sucked into jet intakes.."
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sat Apr 14, 2001 8:08 pm

Dc10hound,

I think that you may find that Heavyjet was asking about this statement "Gyroscopic Forces" have nothing to do with it.

This certainly isn't self explanatory, why wont you elaborate?
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 1:42 am

>>No, I don't care to elaborate<<

Didn't think you knew what you were talking about!

If you can't explain yourself, why bother posting.
 
VC-10
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 2:22 am

I have to agree Dc10hound that gyroscopic effect would not be a consideration as you are retracting the gear along the rotational axis, unless it is a HS Trident.
Precession is only a factor if you twist the gyro around its axis.
 
EssentialPowr
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 8:43 am

Ever ride a bike? Most physics books call it angular momentum...

Hey Teygue...You're wrong (totally).
Mains are braked on Boeings, Lears, and Airbuses for the above reason. Please check your sources prior to responding...



 
tygue
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RE: Do

Sun Apr 15, 2001 12:00 pm

*pulls out the FCOM3 for the B757-200 and the A330-200*

I was wrong. My sincere appologies. And I quote: "During gear door opening, main gear wheels are automatically braked by the normal brake system. The nose gear wheels are braked by a brake band in the gear well".

Again, I'm sorry. Here I thought I knew this manual front to back  Big grin

Ambasaid: I was actually in a situation where the number six brake tachometer was unserviceable (therefore rendering the brake inoperative). ECAM message:

Brakes Released
Number 6 Brake Released

Neither FCOM nor ECAM calls for the gear to be left down for 2 minutes or any minutes for that matter.

The leaving out of landing gear has serious implications to performance. It is not recommended unless there is a wheel fire.

If the BSCU (Brake Steering Control Unit) detects residual braking of more than 15 bars (metric measurement of pressure), the Master Caution is triggered, and a single CRC chime is sounded. The wheel page is then displayed on the SD (lower ecam). This is a fault. No residual pressure is ever normally left in the brakes.

And by the way... the gyroscopic forces of 8 tires inside a 230,000kg aircraft are negligable.

-Tygue
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 12:21 pm

>>And by the way... the gyroscopic forces of 8 tires inside a 230,000kg aircraft are negligable.<<

Tucked away in the wheel wells is not the problem, no more than fully extended and spinning. It's the retraction process while the wheels are still spinning!

Take a bicycle tire and spin it real fast. Then move the tire perpenticular to it's spinning axis as if retracting into the wheel wells. You will feel the gyroscopic forces acting on the tire. Now think of 4 tires on each truck doing this multiple time a day and you'll realize the amount of stress on the gear.

If the engineers were so concerned about exploding tires then why are the nose tires still spinning (under my butt and the E/E compartment) as they come into the wells?
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 12:42 pm

Tygue,

Thanks for the explanation, I will try to find you a Boeing AFM or MEL page reference this morning, but note that I did say "This is quite easily proven by the fact that with a brake deactivated or removed, the crew are required to leave the gear down for 2 minutes after takeoff in order for the wheels to stop spinning."

I didn’t know my audience, so I really didn’t want to expand into the differences between deactivating brakes by capping the lines and removing them, or by deactivating the system using a "deactivation" tool.

Using the deactivation tool allows you to do a normal takeoff with some performance adjustments as it uses residual pressure to stop the wheels. Capping/removing leaves the brakes with no residual pressure; therefore you have a 2-minute spin down time, hence the requirement to calculate a gear down departure.

I have NO A330 knowledge, so I will check out if this procedure applies to the 757, it most certainly does on the 747.

=========

As for the gyroscopic forces, I have browsed through the Boeing Jet Transport Performance Methods manual and can find no reference to these forces during takeoff or climb. Panman, could you please point me towards a technical reference, which states that, they are a factor. Thanks, Smile
 
tygue
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RE: Do

Sun Apr 15, 2001 1:06 pm

Judging by your profile, it sounds like you have a good number of hours in your books  Big grin I'm not too sure what you're talking about... (possibly because I'm overly tired at the moment)... but I'll ask you this:

When you call gear up after takeoff... I'm SURE you've experienced the effects of a worn pad or an out of balance wheel. This results in a fairly strong shake/vibration when the nose wheel is being snubbed on the pad. There is no nosewheel brake system, as I'm sure you're aware... so there's nothing else to stop it other than that pad.

The main gears on an aircraft are designed to withstand the gyroscopic force of the gear being retracted. As I stated, I was incorrect... I wasn't aware there was a automatic braking system on the main trucks. There would be a minor gyro. force... but not as much as there would have been if there was no after takeoff brake function.

I had originally read the statement as "the spinning wheels would have a tremendous affect on the aircraft" instead of "the main gear"... hence my 8 tires vs. 230,000kg comment.

Boy, am I on a roll tonight *lol* I'm off to get some sleep. Thanks to you guys for teaching me something new today  Smile

Take care,
-Tygue
 
EssentialPowr
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RE: Do

Sun Apr 15, 2001 1:35 pm

Why no one has offerred the the calculation of the Moment of Inertia of, say, a tandem 757 whel assembly at 140 kts perpendicular to the axis of rotation, compared to Moment of Inertia of the same tandem at "0" kts?

The diff b/t those numbers (on any transport cat a/c) would have provided a succint and satisfactory resolution to this thread...days ago.
 
EssentialPowr
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 2:02 pm

Nose GEar snubbers - if installed, aren't Asbestos...typically they're rubber; then smooth metal after the rubber's gone (EMB135/45).

And yes, out of balance tire/wheel assemblys WILL vibrate the flight deck and everything they're attached to until they stop rotating. The angular momentum (M.O.I.) is way different between wheel positions...
 
Guest

RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 4:32 pm

Tygue,

This is taken from the B757 Dispatch Deviations Guide.

MEL 32-41-1 Wheel Brakes.

A: One brake may be deactivated with a deactivation tool provided performance complies with AFM for One Brake Deactivated.

B: One brake may be deactivated by capping off the brake line provided:
1: Takeoff performance is in accordance with the AFM for Gear Down Dispatch.
2: Takeoff and Landing Performance complies with the AFM for 1 brake deactivated.
3: After takeoff the gear must remain down for two minutes.
4: Anti-skid operates normally.

This goes on to say that when the line is capped, after takeoff the landing gear must remain extended for a minimum of two minutes to allow the wheel to spin down prior to retraction. Second segment takeoff performance will be limited by the requirement to keep the gear extended.

The MEL also applies to both the 747 and 777.
 
VC-10
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RE: Do "Gear" Tires Keep "Spinning" Inside Bay?

Sun Apr 15, 2001 5:48 pm

Just a thought........If gyroscopic forces are such a problem when retracting the gear why are there no controlability problems with the 2 or 3 hugely larger gyroscopes out on the wings, and thay are spinning a lot faster than the wheels ?

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