Will it take off?

[Splog]

Of course it does. It's because Splog won't accept the facts, so we have to keep repeating them until it sinks in.

Because no facts have been posted to back up your (and others) claims that the wheels will spin twice as fas as the belt ..

but surely for the plane to move along the conveyor when wheels must move faster than the conveyor which is a situation the original post says cannot happen as the conveyor belt control system will always match the speed of the wheels and therefore prevent the plane from moving along a horizontal plane?

As long as the wheels are turning, which they will then how can they stop the plane moving forward .. ?

The conveyor belt can go as fast as it likes. It does not matter.

In reality, as has been said, there is minimal resistance in wheel bearings, friction etc. but this only results in the plane taking maybe one or two seconds longer to reach take off speed.

The plane will still move forward as normal.

Pretty much spot on, in fact the wheels could even be going backward (in relation to the plane) and the plane will still move forward

The answer has to be a resounding 'NO' because ....

As the thrust of the engines moves the plane forward, to say 5mph, the conveyor belt will try and match the speed (ie 5 mph in the opposite direction). This means the wheels would see a speed of 10mph - but wait a minute, the conveyor belt will try and match this speed so it increases to 10mph. But now the wheels would see 15mph so the conveyor belt increases it's speed again, and again, and again, until the damn thing is going so fast it flies apart destroying the plane and killing everyone on board long before it gets airborne!

RIP

Andy

Please explain this as nobody seems to be able to Why if the wheels are in contact with the belt will they be spinning twice as fast? They will be at the same speed ... The maximum speed the wheels will achieve is that of the forward speed of the aircraft

It could be argued that in fact the wheels could be turning in the reverse direction to the aircraft's motion

I can't believe this is still going! lol

Because it's fun

 

[MisterE]

If this thread has shown anything, it has shown what a sorry state our education system has become. Not only here, but in the US with their seriously flawed Mythbusters videos. This stuff was basic Maths/Physics back in the 70s and earlier.

 

[AlexW]

It is fun.

Splog, in your version of this puzzle you say that the speed of the belt matches the speed of the wheels. Could i just ask, the speed of the wheels relative to what?

 

[Splog]

It is fun.

Splog, in your version of this puzzle you say that the speed of the belt matches the speed of the wheels. Could i just ask, the speed of the wheels relative to what?

not quite sure it's that relevant but ... the simple answer is: The conveyor 'always' matches the speed (but in the opposite direction) as measured at the wheels face i.e. the part of the wheel in contact with the belt.

HTH

 

[GrittyShaker]

Please explain this as nobody seems to be able to Why if the wheels are in contact with the belt will they be spinning twice as fast? They will be at the same speed ... The maximum speed the wheels will achieve is that of the forward speed of the aircraft

It's been explained loads of times, but you keep denying it. Just because you say something isn't true doesn't mean people are unable to explain something.

Can we clarify which argument we're dealing with here, as it keeps chopping and changing, which is getting us nowhere.

Either; we're dealing with the (original oldie) argument in which the wheels travel twice as fast as the belt, as the belt matches the plane's speed. They will. This has been explained before and can be again, if you require it.

Or we're dealing with the argument in which the belt (tries to) match the speed of the wheels' rotation.

Which is it?

If it's the latter, here is a selection of replies from the other forum:

I agree with you in the first point though, in that it appears he didn't understand his own post. The conveyor matching the speed of the wheels it is a totally different equation than the original much talked about concept (conveyor matching the speed of the plane).

As you've already stated Gritty the original question is phrased extremely poorly hence creating the discussion.

A **** poor set of criteria for a model/experiment as far as I'm concerned

Ergo, it's a really $hitty definition of a question

Again it comes back to shoddy phrasing of the original question

 

[Splog]

It's been explained loads of times, but you keep denying it. Just because you say something isn't true doesn't mean people are unable to explain something.

You seem to be avoiding these points that you quoted!

Why if the wheels are in contact with the belt will they be spinning twice as fast? - totally impossible

They will be at the same speed ... The maximum speed the wheels will achieve is that of the forward speed of the aircraft? - See above!

As for quoting others who seem to agree with you does not alter anything, neither does quoting some unproven theory by an unknown on an unrecognised website.

 

[Splog]

Can we clarify which argument we're dealing with here, as it keeps chopping and changing, which is getting us nowhere.

I haven't changed anything! The original question remains as posted, perhaps you are confusing some of the clarifications or you can't answer the original question so would like a different one

 

[GrittyShaker]

Can we clarify which argument we're dealing with here, as it keeps chopping and changing, which is getting us nowhere.

Either; we're dealing with the (original oldie) argument in which the wheels travel twice as fast as the belt, as the belt matches the plane's speed. They will. This has been explained before and can be again, if you require it.

Or we're dealing with the argument in which the belt (tries to) match the speed of the wheels' rotation.

Which is it?

?????

If it's argument number one, the wheels will be spinning twice as fast as the belt, because the belt is moving backwards and the plane is moving forwards. Plane moves forwards, belt moves backwards, wheels have to spin twice as fast to compensate for this, due to the friction between them and the belt. Simple.

But your original argument doesn't state this, which is why responses from me and the folk on the other forum are all the same, that it's rubbish definition of a question.

So can we have an explanation as to which of the two quoted arguments we're discussing? That, at least, would get us onto the same page, and I can stop stating the bolded fact above, and start dealing with the original question posed.

In the original model, the wheels will rotate faster than the belt and plane's movement. In your flawed model you are telling us that the wheels' speed will be matched by the belt's speed, therefore this makes your first blue bit irrelevant (although your first blue bit is completely incorrect if we're discussing the original question, and not your flawed one).

 

[GrittyShaker]

I haven't changed anything! The original question remains as posted

You keep getting hung up on denying the fact that the wheels will rotate at x+y mph, whereby x is the plane's speed and y is the belt's speed. This is not relevant to your original question, so why do you keep asking it?

 

[Kev M]

Can't believe I missed the majority of this when it started. Work has some serious questions to answer.

yes BUT there is a constant thrust,

Not quite true. Thrust = Vo-Vi where Vo is the velocity of the gasses leaving the engine and Vi is the velocity of the gasses entering the engine. Vi is at its lowest when the engine is stationary so as the planes accelerates and moves forwards then the Vi increases and thrust reduces.


Now where di I leave that camera thingy?

 

[onomatopoeia]

Why if the wheels are in contact with the belt will they be spinning twice as fast? - totally impossible

Not impossible at all indeed absolutely necessary if the plane is to move relative to a fixed location.

Maybe the fact the plane is not wheel driven is distracting you but it is in fact an irrelevance due to how you posed the question. If the conveyor is moving backwards at 50mph and the plane's wheels are turning at 50 mph in the opposite direction the plane will be stationary relative to a fixed point. If for the plane to move forward relative to a fixed point at 10 mph on a conveyor travelling backwards at 50mph, how fast must the plane's wheels be turning? Here is a clue, the answer is not 50mph and it is not 10mph.

They will be at the same speed ... The maximum speed the wheels will achieve is that of the forward speed of the aircraft? - See above!

No. You are completely wrong.

If the aircraft is on a normal runway, the maximum speed the wheels will achieve is the forward speed of the aircraft. In the problem you posted, the plane is not on a normal runway.

 

[Splog]

You keep getting hung up on denying the fact that the wheels will rotate at x+y mph, whereby x is the plane's speed and y is the belt's speed. This is not relevant to your original question, so why do you keep asking it?

Because you keep asserting it as fact when it's rubbish and you are unable to back up your argument!

Here for you to read is the original question in the op, which quite clearly states the belt will match the speed of the wheels

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.

The wheels will not spin faster than the belt, quite simply because they do not need to :shrug: so the paradox theory you referred to is quite simply wrong!

What you appear to be doing is confusing distance travelled between two points and rotational speed

 

[Splog]

Why if the wheels are in contact with the belt will they be spinning twice as fast? - totally impossible

Not impossible at all indeed absolutely necessary if the plane is to move relative to a fixed location.

Maybe the fact the plane is not wheel driven is distracting you but it is in fact an irrelevance due to how you posed the question. If the conveyor is moving backwards at 50mph and the plane's wheels are turning at 50 mph in the opposite direction the plane will be stationary relative to a fixed point. If for the plane to move forward relative to a fixed point at 10 mph on a conveyor travelling backwards at 50mph, how fast must the plane's wheels be turning? Here is a clue, the answer is not 50mph and it is not 10mph.

They will be at the same speed ... The maximum speed the wheels will achieve is that of the forward speed of the aircraft? - See above!

No. You are completely wrong.

If the aircraft is on a normal runway, the maximum speed the wheels will achieve is the forward speed of the aircraft. In the problem you posted, the plane is not on a normal runway.

As I have said previously: The belt is totally irrelavent to the planes ability or not to take off!

You appear from what you say to have fallen into the whole reason for the op Are you saying that the plane cannot take off?

 

[bass_junkie83]

Every time this question comes up, i want to place a pencil up each nostril and head butt the desk.

:bang:

 

[onomatopoeia]

As I have said previously: The belt is totally irrelavent to the planes ability or not to take off!

You appear from what you say to have fallen into the whole reason for the op Are you saying that the plane cannot take off?

The belt should be irrelevant. However, the way you posed the question it isn't.

 

[boyfalldown]

no - the way you've posed th question the belt will act as a break - the aircraft will have no forward movement so will just sit there with no airflow over the wings to start generating lift. It would be like a plane sat at full power with the breaks full on

 

[bass_junkie83]

Well if it proves anything, it's that photographers would make terrible physicists.

 

[Splog]

no - the way you've posed th question the belt will act as a break - the aircraft will have no forward movement so will just sit there with no airflow over the wings to start generating lift. It would be like a plane sat at full power with the breaks full on

Possibly! or perhaps not

Well if it proves anything, it's that photographers would make terrible physicists.

Very true

 

[bass_junkie83]

Actually, i think it wont take off. The wings would foul the uprights of the treadmill.

 

[GrittyShaker]

Boyfalldown; that's not correct. The belt won't act as a brake as long as the bearings in the wheels are frictionless, or pretty much frictionless.

After explaining it a number of times, with lots of facts and linkies to back it up, whilst Mr. OP puts his fingers in his ears and goes "lalalala. I'm not listening. lalala", here is another link explaining the argument perfectly.

http://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/

"Interpretation 2" is absolutely correct if the OP stated that the belt moves at the same speed as the plane rather than the wheels. But it doesn't so that leads us onto...

"Interpretation 3", which onomatopoeia and me subscribe to, is the correct answer for the argument in the OP. Here's an excerpt which basically covers what we've been saying for a number of pages.:

(For those stubbornly clinging to vestiges of reality, in a system where the treadmill responds via a PID controller, the result would be the treadmill quickly spinning up to infinity.) So, in this system, the plane cannot have a nonzero speed. (We’ll call this the “JetBlue” scenario.)

But if we push with the engines, what happens? The terms of the problem tell us that the plane cannot have a nonzero speed, but there’s no physical mechanism that would plausibly make this happen. The treadmill could spin the wheels, but the acceleration would destroy them before it stopped the plane. The problem is basically asking “what happens if you take a plane that can’t move and move it?” It might intrigue literary critics, but it’s a poor physics question.

 

[Splog]

Boyfalldown; that's not correct. The belt won't act as a brake as long as the bearings in the wheels are frictionless, or pretty much frictionless.

After explaining it a number of times, with lots of facts and linkies to back it up, whilst Mr. OP puts his fingers in his ears and goes "lalalala. I'm not listening. lalala", here is another link explaining the argument perfectly.

http://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/

"Interpretation 2" is absolutely correct if the OP stated that the belt moves at the same speed as the plane rather than the wheels. But it doesn't so that leads us onto...

"Interpretation 3", which onomatopoeia and me subscribe to, is the correct answer for the argument in the OP. Here's an excerpt which basically covers what we've been saying for a number of pages.:

At least there is some reasoning in the link (The blag of the webcomic ) provided But again a simple issue arises that is not explained except by a 'straw man' argument. (example: don't like the question so lets change it to one I can answer)



The argument that the wheels will constantly double falls down for a couple of reasons.

First: The conveyor is designed to match the speed of the wheels, which it does. As the plane accelerates the wheels speed up as does the conveyor (it is not the other way around)

Second: So where is this fictitious force that increases the speed of the wheels beyond the speed of the plane? Put it another way The wheels will reach a point and settle down and the plane will be moving forward as long as there is no resistance from the belt. It would be like the aircraft was sliding on a very slippery surface. The belt and the wheels speed will match perfectly.

 

[AlexW]

not quite sure it's that relevant but ... the simple answer is: The conveyor 'always' matches the speed (but in the opposite direction) as measured at the wheels face i.e. the part of the wheel in contact with the belt.

HTH

Haven't had time to read everything else that followed but you still haven't answered the question. You say at the wheel face. So the speed of the wheel is measured relative to it's own wheel face? Maybe you didn't understand the question.

All speeds are measured relative to something else. Otherwise they are meaningless.

As an example, a glider measures its speed relative to the ground, but also relative to the air (airspeed). It could be possible to have an airspeed of 100mph but ground speed of 0mph.

Its all to do with frame of reference something that is critical to any physical calculation such as this.

Just for clarity, I think:

- the plane will take off
- the wheels of the plane will be spinning considerably faster than they would on a normal takeoff

 

[Splog]

Haven't had time to read everything else that followed but you still haven't answered the question. You say at the wheel face. So the speed of the wheel is measured relative to it's own wheel face? Maybe you didn't understand the question.

All speeds are measured relative to something else. Otherwise they are meaningless.

As an example, a glider measures its speed relative to the ground, but also relative to the air (airspeed). It could be possible to have an airspeed of 100mph but ground speed of 0mph.

Its all to do with frame of reference something that is critical to any physical calculation such as this.

Just for clarity, I think:

- the plane will take off
- the wheels of the plane will be spinning considerably faster than they would on a normal takeoff

OK Alex, I'll play

Of course the glider can have a ground speed different to it's airspeed and yes it could have ground speed of 0 mph (Probably a bit too windy for gliding though )

For clarity and argument:

Lets say that the rotational wheel speed is measured in reference to it's 'axle' and calculated for the radius of the wheel, but I think you knew that anyway.

 

[onomatopoeia]

Second: So where is this fictitious force that increases the speed of the wheels beyond the speed of the plane? Put it another way The wheels will reach a point and settle down and the plane will be moving forward as long as there is no resistance from the belt. It would be like the aircraft was sliding on a very slippery surface. The belt and the wheels speed will match perfectly.

The additional force comes from the conveyor, which you have stated is driven.

At various times throughout this topic you have stated two contradictory things:

1. The plane moves relative to a fixed point
2. The wheels and conveyor move at the same speed but in opposite directions at their mating faces and don't slip relative to each other.

If you can't see how these things contradict each other despite it being explained multiple times then really there isn't any point. You posed the question incorrectly and persist in trying to argue for what would have been the correct answer if you had posed the question correctly.

 

[AlexW]

Hi Steve, hope you don't think I'm being patronising, just making sure we actually disagree about something and its not just confusion about terms etc..

The problem is that fora plane taking off on a conveyor as you describe wheel speed = conveyor speed + plane speed, but you say also that conveyor speed = wheel speed. If we drop that definition of conveyor speed in we see that wheel speed = wheel speed + plane speed which is of course impossible.

Which part of this discription do you dispute. The fact that the forward movment of the plane would have any effect on wheel speed?

 

[GrittyShaker]

Save for translating it into another language, I'm not sure the point can be put across any differently to how it has been explained already, many, many times over.

We could try upside down?

˙ǝlqıssodɯı ǝsɹnoɔ ɟo sı ɥɔıɥʍ pǝǝds ǝuɐld + pǝǝds lǝǝɥʍ = pǝǝds lǝǝɥʍ ʇɐɥʇ ǝǝs ǝʍ uı pǝǝds ɹoʎǝʌuoɔ ɟo uoıʇıuıɟǝp ʇɐɥʇ doɹp ǝʍ ɟı ˙pǝǝds lǝǝɥʍ = pǝǝds ɹoʎǝʌuoɔ ʇɐɥʇ oslɐ ʎɐs noʎ ʇnq 'pǝǝds ǝuɐld + pǝǝds ɹoʎǝʌuoɔ = pǝǝds lǝǝɥʍ ǝqıɹɔsǝp noʎ sɐ ɹoʎǝʌuoɔ ɐ uo ɟɟo ƃuıʞɐʇ ǝuɐld ɐ ɹoɟ ʇɐɥʇ sı ɯǝlqoɹd ǝɥʇ

 

[Splog]

There appears to be confusion and quite a lot of deviation.

I am and have been discussing three issues that I don't agree on:

1, That the question is wrong or worded incorrectly!

My answer to that is quite simple ..... No it isn't! The question is the question and to argue over the answers based on a different question is a classic case of the 'straw man argument' ... The detail is in the op.

2, That the conveyor would spin up to an infinite speed (the case for the disagreement as in 1).

My answer to this is again quite simple .... No it wouldn't!

3, That the wheels will always be spinning twice as fast as the belt as long as the plane is moving forwards therefore the wheels will cause the belt to speed up? ( (the case for the disagreement as in 1 & 2)

My answer (in part) to this is:

A number of people appear to have made some simple errors or assumptions regarding the question and it's answer! (see below)

A:
The plane will be able to take off and that for it to do so it must be travelling along the belt .. So why is this wrong? It's probably not, but it assumes the plane will be able to move! ...

B:
The real problem with this is that it assumes that if the plane moves along the belt the wheel speed will increase and create the paradox mentioned elsewhere, this is not true! It is quite possible for the plane to move forward without increasing the wheel speed.

C:
That it would be impossible to design or engineer such a belt conveyor!
Of course such a conveyor could be built, but it would be dammed expensive

Please humour me here and play nicely and we will attempt to clear up issue B
So if the plane can move without increasing the wheel speed? Would it be plausible that the wheel speed and belt speed would equalize?

Please note I say IF in the question so bear that in mind in your response and I will try to clear up issue B

 

[Cobra]

Just get one of the VTOL Jobbies,
"job" done

 

[onomatopoeia]

It is quite possible for the plane to move forward without increasing the wheel speed.

How? State the following:

Wheel speed
Plane speed relative to a fixed point
Conveyor speed (which should be the same as the wheel speed but in the opposite direction, according to your OP)

 

[Splog]

How? State the following:

Wheel speed
Plane speed relative to a fixed point
Conveyor speed (which should be the same as the wheel speed but in the opposite direction, according to your OP)

Try reading the whole post :shake: What about this bit:

Please humour me here and play nicely and we will attempt to clear up issue B
So if the plane can move without increasing the wheel speed? Would it be plausible that the wheel speed and belt speed would equalize?

Please note I say IF in the question so bear that in mind in your response and I will try to clear up issue B

and your answer is ... ?

 

[onomatopoeia]

My answer is that given your experimental conditions the plane can't move irrespective of the wheel speed and matching conveyor speed. That is why I asked "how?" and asked for numbers to make it plain.

 

[Kev M]

If the pilot left the brakes on the free wheeling of the conveyor belt would allow the plane to move forward under its own thrust and take off.

No:shrug:

 

[onomatopoeia]

If the pilot left the brakes on the free wheeling of the conveyor belt would allow the plane to move forward under its own thrust and take off.

No:shrug:

There's not supposed to be any friction other than at the interface between the tyre and the belt though - brakes would introduce friction elsewhere, unless I (and others) have interpreted the experimental conditions incorrectly.

 

[Kev M]

Well, the opening post doesn't state if the brakes are on or off and only states that the conveyor will match the wheel speed but doesn't say if that wheel speed is rotational speed or speed relative to a stationary object. If the brakes are on then the contact point between the wheel and the conveyor will have exactly the same velocity (also the same velocity as the aircraft).

 

[Gary]

blimey, is this still going?

 

[onomatopoeia]

blimey, is this still going?

Yes, as its unresolved.

 

[whatdoesthisbutt]

Does it have a BA crew on board?

 

[Jimmy_Lemon]

why? (that isn't to the last post, just to the whole thread in question).

 

[Splog]

why? (that isn't to the last post, just to the whole thread in question).

Because it causes debate and just a touch of creative thinking

 

[david1701]

Because it causes debate and just a touch of creative thinking

and makes me want to cut those (lovely) legs off