RampGuy From , joined Dec 1969, posts, RR: Posted (5 years 1 month 3 weeks 3 days 23 hours ago) and read 8276 times:
To all pilots.... Here is a question for you. Can any of you tell me when do the landing gears stop their spinning after lift off? I have been curious as to whether the pilot applies the breaks to stop the spinning or do you allow them to stop on their own even after they enter the wheel well and after the bay doors have closed? And if so, how long does it usually take? Thanks.
Cpd From Australia, joined Jun 2008, 4879 posts, RR: 44 Reply 1, posted (5 years 1 month 3 weeks 3 days 22 hours ago) and read 8261 times:
I think they have automated systems to stop it (which should be able to work once the plane no longer has weight on any of the wheels).
Concorde has brakes to do this as the gear is retracted. There are also systems to prevent the main brakes being applied until all wheels are moving at the same speed.
HAL From United States of America, joined Jan 2002, 2465 posts, RR: 53 Reply 2, posted (5 years 1 month 3 weeks 3 days 22 hours ago) and read 8239 times:
On most modern aircraft, moving the gear handle up not only starts the gear retraction, but also starts a gentle brake application on the mains. They should be pretty much stopped by the time they enter the wheel wells. Sometimes, especially with carbon brakes, this causes a small puff of brake dust to spew out:
As for the nose gear, I don't know about other aircraft, but the 767 has a pair of pads in the wheel well that the nose tires rub against when retracted. These help slow the wheels to a stop in about ten seconds or so. The sound is quite noticeable from the cockpit, since the nose gear well is right below us.
HAL
[Edited 2008-03-26 01:58:10]
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Goldenshield From United States of America, joined Jan 2001, 5417 posts, RR: 13 Reply 3, posted (5 years 1 month 3 weeks 3 days 22 hours ago) and read 8194 times:
Quoting HAL (Reply 2): As for the nose gear, I don't know about other aircraft, but the 767 has a pair of pads in the wheel well that the nose tires rub against when retracted. These help slow the wheels to a stop in about ten seconds or so.
I believe they are called "snubbers." As far as I know, all large (12,500+ lb.) transports have them, and they may be implemented in different ways depending on manufacture.
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ThirtyEcho From United States of America, joined Dec 2001, 1634 posts, RR: 1 Reply 4, posted (5 years 1 month 3 weeks 3 days 22 hours ago) and read 8161 times:
Well, if we start from the most simple example of a light twin or single, you don't want those wheels to be spinning when they go into the wells. On wet or snowy days, spinning wheels can throw water all over the gear assembly and the gear wells and doors; at altitude, this can freeze solid and make gear extension difficult at the end of the flight.
In addition, tires can pick up rocks and debris from the runway and hurl them into the airplane. All pilots are taught to tap the brakes after takeoff, prior to gear retraction.
In larger aircraft, this function is automated. In "big iron" there is the additional concern of gyroscopic forces if those big wheels remain spinning as they translate from a vertical plane to a horizontal plane of rotation.
JetMech From Australia, joined Mar 2006, 2586 posts, RR: 53 Reply 5, posted (5 years 1 month 3 weeks 3 days 22 hours ago) and read 8105 times:
Quoting HAL (Reply 2): They should be pretty much stopped by the time they enter the wheel wells.
G'day Hal,
I think the idea may actually be to have the wheels stopped before the retraction sequence begins. This is to prevent imposing the massive gyroscopic forces (developed by the wheels being moved out of their plane of rotation) upon the landing gear structure.
Quoting HAL (Reply 2): As for the nose gear, I don't know about other aircraft, but the 767 has a pair of pads in the wheel well that the nose tires rub against when retracted.
Same as the 747.
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
Crjfixer From United States of America, joined Mar 2008, 172 posts, RR: 0 Reply 6, posted (5 years 1 month 3 weeks 3 days 21 hours ago) and read 8026 times:
LOL anyone who had ever ridden in the cockpit of a CRJ knows the nose wheels dont stop for quite some time and if they arent balanced just right you can definately feel it when the gear goes up.
Vzlet From United States of America, joined Mar 2004, 820 posts, RR: 0 Reply 7, posted (5 years 1 month 3 weeks 3 days 21 hours ago) and read 8018 times:
This Mustang's wheels are still spinning as they enter the wells:
Birdwatching From United States of America, joined Sep 2003, 3573 posts, RR: 52 Reply 8, posted (5 years 1 month 3 weeks 3 days 13 hours ago) and read 7494 times:
On most gliders I fly, particularly the ASK21 two seater, the wheels spin for a couple of minutes after take off. You don't hear it while being towed, but when you're free you get the loud spinning sound, which is kind of annoying when you want to enjoy the quietness of the glider's flight. I could stop the wheel with the brakes, but they are connected to the speed brakes, so I would lose some amount of altitude even if I do it really fast. On some K8s, I have a bicycle-style mechanic brake independent from the speed brake. I could use it to stop the wheel from spinning, but as far as I remember the spinning on the K8 stops during towing. I guess it depends on how easy the wheel turns and how new the plane (or the part) is.
Soren
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RoseFlyer From United States of America, joined Feb 2004, 8737 posts, RR: 52 Reply 9, posted (5 years 1 month 3 weeks 3 days 12 hours ago) and read 7410 times:
Quoting HAL (Reply 2): As for the nose gear, I don't know about other aircraft, but the 767 has a pair of pads in the wheel well that the nose tires rub against when retracted. These help slow the wheels to a stop in about ten seconds or so. The sound is quite noticeable from the cockpit, since the nose gear well is right below us.
I think that is the same on all Boeing planes. Nose gear does not have brakes. I remember reading a flight squawk when that mechanism failed and the pilots complained about a noise under the flight deck for about 5 minutes after takeoff.
The main wheels will be stopped with brakes before entering the wheel well. Especially on the smaller jets, there are many many components inside the wheel well. A piece of tread coming off a tire spinning in the wheel well could do a lot of damage and take out a hydraulic system. There is a small prevention mechanism located as the tire enters the wheel well that is supposed to break off if there is a loose tread flying around and cause the gear to automatically extend. I have never heard of that little mechanism every being used though.
[Edited 2008-03-26 12:00:22]
If you have never designed an airplane part before, let the real designers do the work!
Buzz From United States of America, joined Nov 1999, 697 posts, RR: 24 Reply 11, posted (5 years 1 month 3 weeks 3 days 1 hour ago) and read 7195 times:
Hi Ramp Guy, Buzz here. I'm trying to recall which airplane... most likely a Boeing ... where I learned that the "spare" hydraulic pressure coming off the retract actuator is ported to the brakes to gently drag the MLG wheels to a stop. That's the pressure coming out of the retract actuator , not the pressure going in to shove the wheels into the wheel well. For some reason I recall a number of a couple hundred PSI.
Like some of the other guys have said, the NLG has brake pads that the nose tires rub up against. It's an item we used to check for wear on the B check.
RampGuy From , joined Dec 1969, posts, RR: Reply 12, posted (5 years 1 month 3 weeks 2 days 23 hours ago) and read 7157 times:
Thanks Buzz for the info. As you can tell, I am by no means a pilot, just a ramp rat. lol I think I'll just stick with loading the bags and let the rest of you take the controls in the driver's seat.
Kimberlyrj From United Kingdom, joined Mar 2008, 385 posts, RR: 1 Reply 13, posted (5 years 1 month 3 weeks 2 days 22 hours ago) and read 7157 times:
Hey
Just completed a long haul pond crossing, so bare with me on this one…
When an aircraft taxi’s the breaking system (pads etc) create heat which can sometimes build up, especially after landing or on an aborted take off.
When an aircraft (heavy) has taken off, the gear is retracted and the wheels are ‘slowed down’ and then stopped. What’s happening to the heat? I know while the gear is retracting air will be passing at great speed but once fully retracted there will be no air movement.
I remember last summer on a very hot day I took off on a B744 heading for LAX. After a normal taxi and a normal (ish a little long) take off the pilots left the gear down for ages! It was three and a half minutes before the gear was retracted, I remember well as I timing it and thinking ‘Capt is about to tell me we have a problem’ just as the gear went up. Nothing happened after that stage, I mean not straight away, so there did not seem any clear reason for keeping the gear down, other then for calling them?
3MilesToWRO From Poland, joined Mar 2006, 266 posts, RR: 0 Reply 14, posted (5 years 1 month 3 weeks 2 days 22 hours ago) and read 7151 times:
Quoting Kimberlyrj (Reply 13): When an aircraft (heavy) has taken off, the gear is retracted and the wheels are ‘slowed down’ and then stopped. What’s happening to the heat? I know while the gear is retracting air will be passing at great speed but once fully retracted there will be no air movement
Not much air movement, but anyway there's some and additionaly the brakes will be warming all the rest of the plane - starting from gear parts and (theoretically) finishing at radome and top of fin
What's more, it's not the same braking as when you need to dissipate the kinetic energy of 100 Tons moving 100 km/h. It only needs to lose energy of 100 kg wheels rotating 10 times a second. For a brake system able to do the first, the second case is a piece of cake.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 15, posted (5 years 1 month 3 weeks 2 days 22 hours ago) and read 7147 times:
Most modern day Airliners use the Auto retract braking,that ports Hyd pr to the MLG Brakes just before it enters the MWW.For the NLG wheels there are Snubbers pads to stop the rotation by friction.
RoseFlyer From United States of America, joined Feb 2004, 8737 posts, RR: 52 Reply 16, posted (5 years 1 month 3 weeks 2 days 17 hours ago) and read 7075 times:
Quoting Kimberlyrj (Reply 13): When an aircraft (heavy) has taken off, the gear is retracted and the wheels are ‘slowed down’ and then stopped. What’s happening to the heat? I know while the gear is retracting air will be passing at great speed but once fully retracted there will be no air movement.
It eventually disappaits in the wheel well. One problem is that the heat from the brakes does heat the air in the tires which causes them to expand. It is actually quite impressive how much a tire can grow and shrink. Once the airplane is near cruise though, the wheel well gets quite cold. There isn't a problem with heat.
The problem with heat is after landings. The brakes do need some time to cool after landing before the plane is safe to take off again. This usually is brief enough not to matter, but short turn times and short flights can cause problems with brake heat.
If you have never designed an airplane part before, let the real designers do the work!
Bartonsayswhat From Canada, joined Oct 2007, 434 posts, RR: 0 Reply 17, posted (5 years 1 month 3 weeks 2 days 1 hour ago) and read 6917 times:
With regards to leaving the wheels down after take off to let the brakes cool, is this done on any 737 as the wheels are exposed letting air run over them?
3MilesToWRO From Poland, joined Mar 2006, 266 posts, RR: 0 Reply 18, posted (5 years 1 month 3 weeks 1 day 23 hours ago) and read 6894 times:
The outside of one wheel is. But not the brakes themselves. Additionaly the wheels are certainly made as "invisible" for airflow as possible. So it shouldn't be much difference compared to completly hidden gear.
A/c train From United Kingdom, joined Jun 2001, 501 posts, RR: 4 Reply 19, posted (5 years 1 month 3 weeks 1 day 22 hours ago) and read 6883 times:
Metered Hyd pressure is fed to the brakes from the retract circuit and the nose wheels have spin brakes. Some aircraft such as A320 are not allowed to takeoff with brake temps of 300 +, a way of cooling on others is to prolong gear retraction. Option on some aircraft are brake fans.
KELPkid From United States of America, joined Nov 2005, 5929 posts, RR: 4 Reply 20, posted (5 years 1 month 3 weeks 1 day 20 hours ago) and read 6866 times:
Quoting Vzlet (Reply 7): This Mustang's wheels are still spinning as they enter the wells:
In fact, if you tap the brakes in the P-51 after leaving the runway, your next landing will result in a noseover if you land with the wheels down (I forget the exact technical reason for that, but it's definitely on the "don't do this" list!).
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Sprout5199 From United States of America, joined Feb 2005, 1779 posts, RR: 2 Reply 21, posted (5 years 1 month 3 weeks 1 day 19 hours ago) and read 6845 times:
Quoting KELPkid (Reply 20): In fact, if you tap the brakes in the P-51 after leaving the runway, your next landing will result in a noseover if you land with the wheels down (I forget the exact technical reason for that, but it's definitely on the "don't do this" list!).
I bet its because the pads don't release from the rotor(there is no return spring like on a drum brake---did the P-51 use disc brakes?). So when the tire hit the pavement, the brakes wouldn't release right away, and you get a nose over.
I had a caliper stick on a Jeep Grand Wagoneer once, the pad dragged enough to make the rotors glow orange. thank god I had to pi$$ to cool it down before it melted all the grease in the bearings, but smelled real bad.
Then again I could be wrong(not that has ever happened, I thought I was wrong once, turns out I was incorrect about that.
Askr From Poland, joined Mar 2008, 45 posts, RR: 0 Reply 22, posted (5 years 1 month 3 weeks 1 day 18 hours ago) and read 6834 times:
Quoting RoseFlyer (Reply 16): It eventually disappaits in the wheel well. One problem is that the heat from the brakes does heat the air in the tires which causes them to expand. It is actually quite impressive how much a tire can grow and shrink. Once the airplane is near cruise though, the wheel well gets quite cold. There isn't a problem with heat.
Aren't aircraft wheels filled with nitrogen?
AFIK nitrogen has very little thermal expansion, so the tires won't grow so much compared to an identical wheel filled with just plain air.
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FlyASAGuy2005 From United States of America, joined Sep 2007, 6506 posts, RR: 11 Reply 23, posted (5 years 1 month 3 weeks 1 day 18 hours ago) and read 6826 times:
I remember reading this in a book but on the CR2, on wheels up, fluid is sent to the breaking system and that's how they are stopped. Is that right?
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Rwessel From United States of America, joined Jan 2007, 1984 posts, RR: 2 Reply 24, posted (5 years 1 month 3 weeks 1 day 12 hours ago) and read 6734 times:
Quoting Askr (Reply 22): Aren't aircraft wheels filled with nitrogen?
AFIK nitrogen has very little thermal expansion, so the tires won't grow so much compared to an identical wheel filled with just plain air.
Very often they are filled with nitrogen and I believe it's required for airliners. But the expansion of essentially all gases for a particular temperature change is basically identical in this sort of application. And even if there were a meaningful difference between the gasses present, air is already 78% nitrogen, so that would dampen any such effect. OTOH, there isn't any such effect, as the other two major gasses in air (oxygen 21%, and argon 1%), don't have major differences from nitrogen in the temperature and pressure ranges we're talking about.
The main advantages for nitrogen in tires are the displacement of oxygen and water vapor (and the other trace gasses), which can degrade the materials in the tire. Worse, water vapor can freeze, causing mechanical damage to the tire and rim (which would actually reduce the pressure in the tire a bit more than expected, but the total amount of water vapor is quite small).
Pure nitrogen gas is also a bit lighter than air (about 3.3%), which, according to a quick back of the envelope calculation, works out to something like 10lbs total for all 18 wheels on a 747.
25 474218: I have been watching this item for days and no one has had the right answer yet: The landing gear never spins so it doesn't have to stop. Only the wh
26 Viscount724: The noise of the nose gear retracting is also very noticeable if you're sitting in the forward cabin of a 747 where the gear retracts almost under yo
27 Tdscanuck: It also avoids the exploding wheel problem. I'm not sure if this occurs with today's rubber formulations, but older rubbers would offgas when they go
28 Motopolitico: So why not use pure Helium? Helium, being a noble gas, is even less reactive, and would be even lighter than nitrogen. Imagine the weight savings!
29 Tdscanuck: Imagine the cost increase and how much more often you'd have to fill the tires due to greatly increased diffusion rates. Tom.
30 Rwessel: You'd, in fact, save about 250lbs (total, all 18 wheels), but a single fill of the tires will cost you about $1200. And it would leak like crazy with
31 RoseFlyer: That idea does keep getting thrown out there, but the diffusion rate just does not make it work. Helium would leak very quickly out of the tires. Air
32 Panserbjorne: Another important reason for filing up the tires with nitrogen....to reduce the risk of fire...there were few incidents regarding this,that is why th
33 Panserbjorne: Haha....Good one there....I guess nobody noticed it,we were so into explaining the facts about the tires and wheels,that we didn't realise what does
34 HAWK21M: Tires are mounted on the hubs which form a wheel when combined so the "Wheel" spins.Wheel is part of the LG.....so that explains. But on the topic Th
35 Panserbjorne: Well I hope you know the difference between car spinning,and it's wheels spinning,so I guess u may apply the same to landing gear spinning,and the wh
36 Kimberlyrj: Hello Don’t I know it, while back we had to wait 40 minutes on a hot dry summers day after aborting a fully loaded B744 at LHR for the breaks to coo
38 Baron95: When I was learning to fly light retractable gear aircraft, only one instructor insisted that I tapped the breaks just prior to moving the gear handle
39 Kay: Perhaps in normal situations, the heat of the brakes are not an issue after the wheels have been retracted. But there has been a plane crash because
40 BAe146QT: I believe that a front brake set was optional on the 727. Other than that, I believe you're right.
41 3MilesToWRO: And what you describe (yes, I think I remember reading about it) is exactly dissipating the energy of 100T @ 100 knots (random numbers, of course, or
42 Kay: Agree (therefore, the procedure mentioned above whereby after an aborted take off, one must wait, and cannot take off immediately and raise the gear,
43 474218: There is another reason the main landing gear wheels are stop before they are stowed in the wheel wells: The gyro effect the mass of the spinning whee
44 Panserbjorne: I dont really remember the accident,but i do know that there is a procedure to leave the gears down right after the lift off,the purpose is to cool t
45 QANTAS747-438: I work for WN, and as explained to me by a MX guy, on our 737s there is a ring around the wheel well that has layered rubber squares. They extend abou
46 Kay: Everytime I look inside a landing gear well I get fascinated and scared at the same time. Kay[Edited 2010-05-01 13:55:20 by srbmod]
47 Rwessel: I dunno, these look too light to really do much to stop the wheel, the look more like spray shields to me...[Edited 2010-05-01 13:56:05 by srbmod]
48 Tdscanuck: Those are aerodynamic seals to improve airflow over the wheelwell. The gear is already stopped by the brakes before it makes contact with the seals.
49 HAWK21M: on my 1st day at work during a major check I remember looking insde a B737 MWW & wondering.Today it seems so simple. regds MEL
50 Liedetectors: In response to Kay's inquiry (reply #39) some of the details are as follows: Date: September 4, 1963 Aircraft: Swissair SE-210 Caravelle III HB-ICV "S
51 Kay: Thanks for the recollection of the accident and the details! Based on the flight number, I found links of it in airdisaster and another couple of web
52 DocLightning: AFAIK, all gases are governed by the Ideal Gas law (with minor variations). PV=nRT. That is that the for a given number of molecules of gas, n, the p
53 SashA: As a kid noticed a wheel on an An-24B spinning while being shoved into the wheel bay of the turboprop engine.We took of from my hometown, whose airpor
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(I forget the exact technical reason for that, but it's definitely on the "don't do this" list!).
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