Will it take off?

Splog said:
Do you mean the above statement? If so, care to suggest what aircraft uses 'driven' wheels for take off :thinking:

The speed of the wheels and belt are exactly the same. To clarify The tread of the wheels will travel exactly 10 miles in one hour if the planes speed was 10mph. :D
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No, because the plane would remain stationary. The wheels would be spinning at 10mph, and the belt would be spinning at 10mph, but the plane is unmoving. It is most definitely not travelling at 10mph.

For the plane to travel at 10mph, it would have to have forward thrust from the engines, and the wheels would spin at 20mph to compensate for the backward motion of the conveyor belt.

If the plane's engines are generating forward thrust, the wheels' speed and the conveyor belt speed will never be the same.
 
Splog said:
Do you mean the above statement? If so, care to suggest what aircraft uses 'driven' wheels for take off :thinking:
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They don't. I was using the falsehood to illustrate the point that if planes were driven by the wheels, your argument would work. But they're not, so physics steps in and makes your argument impossible. :D
 
GrittyShaker said:
No, because the plane would remain stationary. The wheels would be spinning at 10mph, and the belt would be spinning at 10mph, but the plane is unmoving. It is most definitely not travelling at 10mph.

For the plane to travel at 10mph, it would have to have forward thrust from the engines, and the wheels would spin at 20mph to compensate for the backward motion of the conveyor belt.

If the plane's engines are generating forward thrust, the wheels' speed and the conveyor belt speed will never be the same.
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GrittyShaker said:
They don't. I was using the falsehood to illustrate the point that if planes were driven by the wheels, your argument would work. But they're not, so physics steps in and makes your argument impossible. :D
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I think you are completely missing the point ... The belt does not affect the wheels

I don't have an argument I am just ponting out that wheel speed is not changed by the belt speed :) ... totally irrelavent!

The discussion is:
So will the plane be able to take off or not? .. and why?
 
Splog, you're right that the plane will take off, but wrong about wheel speed. wheels will be 'spinning' at twice their normal take off speed.

When the runway is stationary they would spin at a certain take off speed. But now the runway is also travelling backwards at the same speed as the plane is moving forwards, doubling their normal speed.

Already explained rather elegantly by someone with math further up.

This is why bearing resistance would come into play, but not enough to stop the plane taking off.
 
The problem is that the original "plane on a conveyor belt" question has a conveyor belt that moves at the same speed as the plane, and not the same speed as the wheels on the plane.

To that the answer is easy; the plane will take off. Physically it is an absolute given that it will take off. And assuming a conveyor belt large enough can be built, it could very easily be demonstrated. And apparently has been, according to earlier posts.

In answer to your argument; no, the plane can't possibly take off, because to meet your brief the wheels and conveyor belt have to remain completely stationary. That's the only time the speed of the wheels and the speed of the belt will be the same.
 
There is no problem ...
On Ice the wheels need not rotate at all...
take off lift depends on airspeed.. not wheel rotation.
The wheels cold rotate with the belt the wrong way for all it would matter.
There is no connection between wheel rotation speed and take off.
 
Unfortunately, as is so often the case with problems of this nature, they have to be stated very carefully and accurately. It should be conveyor matches the 'aeroplane' speed in the opposite direction, not the wheel speed. That would be impossible. For one thing different parts of the wheel move at different speeds.
 
Terrywoodenpic said:
There is no problem ...
On Ice the wheels need not rotate at all...
take off lift depends on airspeed.. not wheel rotation.
The wheels cold rotate with the belt the wrong way for all it would matter.
There is no connection between wheel rotation speed and take off.
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Good point. So the answer is to leave the brakes on the wheels. The wheels don't spin, the conveyor doesn't move, but you get a shedload of tyresmoke, and the plane eventually takes off. :D
 
The OP is correctly worded for wheel speed i.e.

Splog said:
An oldie but could be fun to discuss :D


Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?
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The wheel speed cannot double because of the belt, if it did the belt would speed up ... Consider another way to think about this ... If you imagine two rollers one above the other with a slight gap between them and both rollers are rotating at exactly the same speed but in opposite directions, then you bring the two rollers gently together! .. Do either of the roller speeds change? no, of course not .. :)
 
Think of it this way: Imagine standing on a treadmill (that is turned on at say walking speed). You are wearing roller-skates. You are holding a rope which is attached to the wall in front of you. It this situation the wheels on the roller skates would be spinning at a given speed. what then happens to the speed of the wheels if you start pulling yourself towards to wall using the rope?

Or another way: You are walking along one of those long airport corridors at 4 mph. The wheels of your case are at a set speed. You approach one of those travellator things moving in the opposite direction to you. You walk 'along side' it pulling your case down the wrong way travellator What has happed to the wheel speed?
 
I think the explanation in Joe's link is a good one.

However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way.
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Bolded the bit we've been saying for the last page or so. :D
 
My two cents..

The plane will take off because once it has got past the friction from the wheels it only needs to get to its takeoff speed relative to the ground before it has the lift to take off.

I think that when a plane takes off its not the 80mph wind that lifts it off but more the thrust from the engines angled towards the ground by the wing.

Therefore it would take off

I am probably wrong...
 
AlexW said:
Think of it this way: Imagine standing on a treadmill (that is turned on at say walking speed). You are wearing roller-skates. You are holding a rope which is attached to the wall in front of you. It this situation the wheels on the roller skates would be spinning at a given speed. what then happens to the speed of the wheels if you start pulling yourself towards to wall using the rope?

Or another way: You are walking along one of those long airport corridors at 4 mph. The wheels of your case are at a set speed. You approach one of those travellator things moving in the opposite direction to you. You walk 'along side' it pulling your case down the wrong way travellator What has happed to the wheel speed?
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GrittyShaker said:
I think the explanation in Joe's link is a good one.



Bolded the bit we've been saying for the last page or so. :D
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Thanks for the link :) but that's wrong too :LOL:

Okay, I did say this would be fun :D Now will someone kindly explain what they believe is driving the wheels to double their speed :thinking:
 
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A combination of the friction from the backward moving conveyor belt and the forward motion of the plane as it's propelled along at its normal pace by the engines. It's not a matter of what we "believe". It's just fact. The link is absolutely correct. Really, it is. :D
 
GrittyShaker said:
A combination of the friction from the backward moving conveyor belt and the forward motion of the plane as it's propelled along at its normal pace by the engines. It's not a matter of what we "believe". It's just fact. The link is absolutely correct. Really, it is. :D
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Almost there now.. :) What now needs to be considered are a couple of points.

1: The friction from the wheels to their axles is very low, yet the friction from the contact of the wheels to the belt is very high!

2: If you agree with 1 above? What happens when the plane starts to roll forward (if you think it does?) to the wheels of the plane? simple, the belt starts moving due to the wheels turning :cool:

Now all I need is for someone to explain how the low friction overcomes the high friction? :cool:
 
Yes it will, the best way i can describe this is:

imagine if you were standing on a treadmill wearing roller blades.
The treadmill is traveling at 10km/h but your gym buddy is standing behind you pushing you.
You will move forward right? right....still with me?

Thats the basic idea of the plane. the wheels are only there to stop the plane scraping along the floor. they do not propel the plane in anyway.

The forward motion is provided by the engines which push against the air.

The lifts off due to the pressure differential across the wing profile. the air traveling over the top has to travel faster due to the wing shape, faster moving air has lower pressure and as such the pressure below the wing is greater than that above the wing effectively pushing the plane upwards



Edit: just noticed AlexW hs posted a very similar analogy
 
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alastairb said:
yes BUT there is a constant thurst, which always makes plane accelerate which in turn makes the wheels try to move faster than the belt, thus the belt travelling at the same speed as the wheels is impossible
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Yes, there is a constant thrust and yes it will 'try' to make the wheels turn faster, but 'try' does not mean 'will' the belt is actually driving the wheels ..
 
griffo said:
Yes it will, the best way i can describe this is:

imagine if you were standing on a treadmill wearing roller blades.
The treadmill is traveling at 10km/h but your gym buddy is standing behind you pushing you.
You will move forward right? right....still with me?

Thats the basic idea of the plane. the wheels are only there to stop the plane scraping along the floor. they do not propel the plane in anyway.

The forward motion is provided by the engines which push against the air.

The lifts off due to the pressure differential across the wing profile. the air traveling over the top has to travel faster due to the wing shape, faster moving air has lower pressure and as such the pressure below the wing is greater than that above the wing effectively pushing the plane upwards



Edit: just noticed AlexW hs posted a very similar analogy
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But this analogy is flawed :) simply because the treadmill is running at a set speed! .. The conveyor is running at whatever speed the aircraft wheels turn .
 
The thrust will make the wheels turn as the plane moves forwards. Fact.
The backward motion of the belt will make the wheels turn faster. Fact.
There are only so many ways it can be explained, and only so many analogies we can use, and so many links to other resources backing this information up.

Can you explain why you believe your argument, because the above facts have been posted hundreds of times already, but we have no information from you as to what makes you think we are wrong. :D
 
Splog said:
But this analogy is flawed :) simply because the treadmill is running at a set speed! .. The conveyor is running at whatever speed the aircraft wheels turn .
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You need to explain if the conveyor has its own source of drive or it is soley moving due to the friction between its surface and the plane wheels.

This potentially changes the entire experiment, there is no point in trying to provide any further answers to your question without this information. I (and I think others) have been working on the basis that the conveyor is powered.
 
GrittyShaker said:
The thrust will make the wheels turn as the plane moves forwards. Fact.
The backward motion of the belt will make the wheels turn faster. Fact.
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I don't believe that, if the conveyer belt is moving at 100mph the wheels will be moving at 100mph just in a different direction. Fact.
 
GrittyShaker said:
The thrust will make the wheels turn as the plane moves forwards. Fact.
Not if they're being held back by the greater friction from the belt

The backward motion of the belt will make the wheels turn faster. Fact.

But if the wheels are being held back, why would the belt be moving?

There are only so many ways it can be explained, and only so many analogies we can use, and so many links to other resources backing this information up.

You've explained nothing to explain why the wheels will be turned by the aircraft moving against a greater friction than that of the wheel bearings / axle.

Can you explain why you believe your argument, because the above facts have been posted hundreds of times already, but we have no information from you as to what makes you think we are wrong. :D
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I see no facts :shrug:
 
onomatopoeia said:
You need to explain if the conveyor has its own source of drive or it is soley moving due to the friction between its surface and the plane wheels.

This potentially changes the entire experiment, there is no point in trying to provide any further answers to your question without this information. I (and I think others) have been working on the basis that the conveyor is powered.
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The conveyor is powered and has nothing do do with the plane wheels other than that it is the speed of the wheels that dictate the speed of the belt.

SarahLee said:
I'm past caring whether this plane will take off or not.
Had enough of waiting for the damn thing and I'm getting the train instead :p ;)
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:LOL: I don't blame you :D I did say that it could be a fun discussion and I think were nearly there now ;)
 
Liam said:
I don't believe that, if the conveyer belt is moving at 100mph the wheels will be moving at 100mph just in a different direction. Fact.
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Only if the plane was stationary (fixed somehow) and the conveyor moving backwards at 100mph. If the plane is moving forwards under the thrust of its engines, the wheels will be moving faster than the belt.
 
GrittyShaker said:
If the plane is moving forwards under the thrust of its engines, the wheels will be moving faster than the belt.
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But: The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
 
GrittyShaker said:
Only if the plane was stationary (fixed somehow) and the conveyor moving backwards at 100mph. If the plane is moving forwards under the thrust of its engines, the wheels will be moving faster than the belt.
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If the wheels are moving faster than the belt the plane wouldn't be stationary..
 
GrittyShaker said:
Only if the plane was stationary (fixed somehow) and the conveyor moving backwards at 100mph. If the plane is moving forwards under the thrust of its engines, the wheels will be moving faster than the belt.
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The reason people assume the wheels will turn should carefully consider what force actually turns the wheels!
 
I no longer care and am getting the train with Sarah... or maybe I'll walk.

Either would be quicker than the damn plane.
 
Liam said:
If the wheels are moving faster than the belt the plane wouldn't be stationary..
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I know that. That's why I said it. :shrug: You said the wheels and belt would be turning at the same speed, so I said that would only be the case if the plane was stationary. If it was moving forwards under the thrust of its engines, the wheels would be moving faster.

But that's not relevant if we're discussing the OP, because the belt apparently moves at the same speed as the wheels' rotation.
 
GrittyShaker said:
I know that. That's why I said it. :shrug: You said the wheels and belt would be turning at the same speed, so I said that would only be the case if the plane was stationary. If it was moving forwards under the thrust of its engines, the wheels would be moving faster.

But that's not relevant if we're discussing the OP, because the belt apparently moves at the same speed as the wheels' rotation.
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It does! I will try to move this on a bit further :D

Consider this ... If the wheels were actually turning in the opposite direction i.e. running backwards! Would that prevent the plane from moving forward or even restrict it in anyway :thinking: assuming for this discussion that the wheel bearings / axle etc are working perfectly!
 
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