Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 8 Posted (14 years 7 months 3 weeks 1 day 9 hours ago) and read 4080 times:
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!
Iainhol From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 7 months 3 weeks 1 day 8 hours ago) and read 3912 times:
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,
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 8
Reply 3, posted (14 years 7 months 3 weeks 1 day 8 hours ago) and read 3863 times:
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.
HeavyJet From , joined Dec 1969, posts, RR:
Reply 4, posted (14 years 7 months 3 weeks 1 day 7 hours ago) and read 3859 times:
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 From Canada, joined Jul 1999, 222 posts, RR: 0
Reply 5, posted (14 years 7 months 3 weeks 1 day 4 hours ago) and read 3828 times:
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).
Panman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 9, posted (14 years 7 months 3 weeks 9 hours ago) and read 3737 times:
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.
Galaxy5 From United States of America, joined Mar 2000, 2034 posts, RR: 23
Reply 10, posted (14 years 7 months 3 weeks 7 hours ago) and read 3729 times:
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.
"damn, I didnt know prince could Ball like that" - Charlie Murphy
L-188 From United States of America, joined Jul 1999, 30206 posts, RR: 57
Reply 11, posted (14 years 7 months 2 weeks 6 days 19 hours ago) and read 3690 times:
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! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 12, posted (14 years 7 months 2 weeks 6 days 16 hours ago) and read 3682 times:
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!!!
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 31
Reply 13, posted (14 years 7 months 2 weeks 6 days 12 hours ago) and read 3671 times:
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.
Dc10hound From United States of America, joined Dec 2000, 463 posts, RR: 5
Reply 14, posted (14 years 7 months 2 weeks 6 days ago) and read 3634 times:
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.."
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 8
Reply 19, posted (14 years 7 months 2 weeks 5 days 10 hours ago) and read 3599 times:
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.
VC-10 From United Kingdom, joined Oct 1999, 3720 posts, RR: 32
Reply 24, posted (14 years 7 months 2 weeks 3 days 11 hours ago) and read 3537 times:
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.
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