Air Canada 767 Problems at Madrid
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How come the top of the wheel moves onwards faster than the axle? To put it other way round, does the bottom of the wheel move forwards slower than 100 knots?
I love it when we get arguments like this I use to bet my wallet on being correct but I lost everything over the years 
Yup the top of the tyre is going forward at the same speed that the bottom is going aft aft so it nets out as zero as long as it's attached to the aircraft,
But if a piece now leaves the aircraft it simply maintains the last vector that it was on when it was release (Forward, Aft or Up). That vector is made up of ground speed against the surface speed of the released fragment.
No bets until you work out the numbers. Of course one can always add in a moving runway like a conveyor belt or maybe an aircraft carrier to work your brain
Yup the top of the tyre is going forward at the same speed that the bottom is going aft aft so it nets out as zero as long as it's attached to the aircraft,
But if a piece now leaves the aircraft it simply maintains the last vector that it was on when it was release (Forward, Aft or Up). That vector is made up of ground speed against the surface speed of the released fragment.
No bets until you work out the numbers. Of course one can always add in a moving runway like a conveyor belt or maybe an aircraft carrier to work your brain
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Yes it does. It moves forward at precisely 0 knots. Otherwise it would be skidding. In fact my previous statement about the top NOT going 200kt is actually wrong. Assuming the wheel is perfectly circular, and the axle is dead center, then yes, we have a 1:1 lever so the top IS actually going forward at 200. My apologies.
yet at the same time you are saying that the top of the same tyre moves forward faster than the AC.
I really can't argue with that.
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Relative to the runway that's precisely what I'm saying. The very bottom of the tyre tread is moving at 0kt relative to the runway with which it is in contact. If not it would be skidding. The axle, x feet up from the runway is moving forward, relative to the runway, at 100kt (in this example.) The top of the wheel, 2x feet up from the runway, is moving forward, relative to the runway, at 200kt. The whole complete wheel, as a component piece, is obviously traveling forward at 100kt, however it is rotating, so the top has a forward velocity (speed in a given direction) greater than the axle or the bottom, and while the bottom is in contact with the runway, and is not skidding, it has the same forward velocity as the runway, which is obviously 0kt.
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take any car, a drag car for instance: the wheels are warmed up before run, and the rotational speed is significant, but the wheel isn't going nowhere.
on the other hand, an airplane, after take off, the wheels stop spinning, but the wheels are moving just as fast as the AC.
so, regarding the circumferential speed: it is constant at every location on every spot with identical distance from the center, neverminding the speed or direction of the wheel.
What I understood from the message above is that a vehicle moving at constant speed N would have a rotating tyre of which the top section is moving onwards with the rate of N*1,1 and bottom section with the rate of N*0.
What I am trying to explain is that the wheel it self is really moving onwards at the horizontal speed N, and the rotational speed is a different factor that really does not affect the actual horizontal speed of the wheel.
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there is a difference in horizontal speed and rotational speed.
take any car, a drag car for instance: the wheels are warmed up before run, and the rotational speed is significant, but the wheel isn't going nowhere.
on the other hand, an airplane, after take off, the wheels stop spinning, but the wheels are moving just as fast as the AC.
so, regarding the circumferential speed: it is constant at every location on every spot with identical distance from the center, neverminding the speed or direction of the wheel.
What I understood from the message above is that a vehicle moving at constant speed N would have a rotating tyre of which the top section is moving onwards with the rate of N*1,1 and bottom section with the rate of N*0.
What I am trying to explain is that the wheel it self is really moving onwards at the horizontal speed N, and the rotational speed is a different factor that really does not affect the actual horizontal speed of the wheel.
take any car, a drag car for instance: the wheels are warmed up before run, and the rotational speed is significant, but the wheel isn't going nowhere.
on the other hand, an airplane, after take off, the wheels stop spinning, but the wheels are moving just as fast as the AC.
so, regarding the circumferential speed: it is constant at every location on every spot with identical distance from the center, neverminding the speed or direction of the wheel.
What I understood from the message above is that a vehicle moving at constant speed N would have a rotating tyre of which the top section is moving onwards with the rate of N*1,1 and bottom section with the rate of N*0.
What I am trying to explain is that the wheel it self is really moving onwards at the horizontal speed N, and the rotational speed is a different factor that really does not affect the actual horizontal speed of the wheel.
I think you may be confusing angular velocity with linear velocity. You are absolutely right that every part of the wheel is ROTATING at the same angular velocity. The wheel as a component part of the aircraft is also moving forward, relative to the runway, at the same speed as the aircraft. However it is also rotating. The bottom of the wheel, in contact with the runway, and not moving relative to said runway, therefore has a LINEAR velocity of zero. Take another look at the image I posted above. It shows the linear velocity of a point element of the wheel as 0 when it's touching the runway and 160 km/h when it's at the top.
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https://scontent.fybz2-1.fna.fbcdn.n...7a&oe=5ED5DA9C
Looks like a pic taken from the F-18 surveying the damage.
Looks like a pic taken from the F-18 surveying the damage.
Last edited by ACA856; 5th Feb 2020 at 18:51. Reason: Pic detail
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Thanks for the link, good job as usual by VASAviation.
I'm wondering why Air Canada chose to retract the gear with the fighter observing? They had known tire damage and needed to burn off fuel.
They said the left side brake temps were 8's after landing, hopefully the junior ground engineer was able to place those fans in time to prevent the fuse plugs from blowing.
I thought all B-763's had brake temp indications. Tower Dog and others set me straight that this was an option that some carriers like American did not order.
Seems like Air Canada disabled all 767 fuel dump systems years ago to save maintenance costs.
I'm wondering why Air Canada chose to retract the gear with the fighter observing? They had known tire damage and needed to burn off fuel.
They said the left side brake temps were 8's after landing, hopefully the junior ground engineer was able to place those fans in time to prevent the fuse plugs from blowing.
I thought all B-763's had brake temp indications. Tower Dog and others set me straight that this was an option that some carriers like American did not order.
Seems like Air Canada disabled all 767 fuel dump systems years ago to save maintenance costs.
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Airbubba - Appears to be Flap 5, and not all AC 767's had the brake temp indication IIRC. I was not aware of the fuel dump disabling on the AC 767's but I am old and memory is the second thing to go.
Anyone still doubtful about wheels throwing debris forward should ride a bicycle through a mud puddle and then look at the back of their shirt. Fenders ruin the effect, of course.