Hammer
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Registered: 11th Feb 04
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quote:
Originally posted by bradfincham
Question:
If an aeroplane is taking off but is on a conveyor belt that is moving at the same speed as the plane, would the plane take off?
Just so i get this straight in my head, and i can think again without assuming anything, which way is the conveyor belt moving in accordance with the original question.
Im starting to think this question was brought into fruition in order to descend the masses into chaos, maybe i'm wrong
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RichR
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it all relates to wether or not you believe that the level of friction between wheel and conveyor is enoguh to drive the conveyor at the same speed as the velocity of advance - negating any forward momentum
The way the question is worded, I believe that this is the case and for any increase in speed the conveyor will increase in speed at the same rate
if you look at it that the plane can overcome the friction component and mass acting; and the speed of the conveyor can be exceeded then it is possible
either way its a pointless argument because even if the conveyor was fitted with a limiter so that the thrust could exceed its drive, then the runway would have to be so long that it wouldnt make sense doing so
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Steve
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in the opposite direction to the intended direction of the plane
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Cosmo
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it all comes down to if the force exerted by the jet engines is greater than the friction caused by the weight of the plane and gravity. I dont think any of us know these?!
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gianluigi
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quote:
Originally posted by Steve
this is ike trying to educate pork 
when beef is doing the educating 
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RichR
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example to prove why it wouldnt take off
Using a non-electric treadmill, ie a leg powered treadmill
As you run the treadmill conveyor belt increases in speed as the runner increases in speed - however you never run off the end of it do you - you stay in the same static location, you just make the conveyor revolve faster
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3CorsaMeal
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quote:
Originally posted by Cosmo
quote:
Originally posted by 3CorsaMeal
if this chappy was going flat out, he would be still
and if you pushed the rear end, it would move off the rolling road.
the planes engine is forcing air back using the weight of plane to counteract its force, similar to a person stood on solid ground and pushing 
now your talking of a set size conveyor belt to be 'pushed off' it.
In your example, would the wheels move faster if you pushed the quad? Obviously faster, as would have to so it can get off the rolling road. So if the rolling road wasnt ending, and you pushed it, the wheels would move faster and therefore the conveyor speed up to counteract the movement.
but the energy given to the quad by the person pushing won't go to the wheels, the powered wheels are there to move the mass of the quad (pushing the road away if you like), you moving the mass of quad without the wheels, so you not pushing the road away
its a big debate, not gonna get settled by CS users
i'm happy if your happy
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SVM 286
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Registered: 13th Feb 05
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quote:
Originally posted by Steve
Ok, HERE ME NOW
the conveyor belt is rotating at say 50mph in the oposite direction.
if the plane was just sat with thrust idling it could quite happily sit then on the spot with its wheels rolling round and round underneath.
now think what would happen if you increased thrust the plane would start to move forwards.
so in this example the coneyor belt would start to rotate faster, so the wheels on the plane start to roll round and round faster, as the wheels are no way related to the jets on the plane this has no bearing on the thrust being applied forwards
In this case the principle would apply Steve.
The theory Brad started this thread with was that the belt would travel at the SAME speed as the craft.
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Jules S
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Registered: 24th Dec 03
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Cosmo, are you in some way trying to suggest that the conveyor belt will stop me extending my arm forwards?
It has no connection whatsoever to me. I (like the jets) am a third party force on the plane.
A jet engine uses turbiines to propel air out of the back of it thus producing thrust. The conveyor belt has no connection whatsoever to the engines. the jets will do their thing, push air out of the back of the jets....create thrust...
Again. the plane will move forward in the air as its designed to...the wheels are doing no pushing here...
Anyways, I'd call this a debate not an arguement. I only get frustrated at myself for not being able to explain it better 
[Edited on 24-05-2006 by Jules S]
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RichR
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if all four wheels of the quad were in rollers; you could push the quad side to side, easily but you couldnt push it backwards or forwards, the quad would be suspended in its static equilibrium - as you pushed the velocity of advance would increase and the rollers would increase to counteract the increase in speed - the quad would go nowhere but the wheels would simply rotate faster, as would the rollers
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J da Silva
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quote:
Originally posted by LiVe LeE
example to prove why it wouldnt take off
Using a non-electric treadmill, ie a leg powered treadmill
As you run the treadmill conveyor belt increases in speed as the runner increases in speed - however you never run off the end of it do you - you stay in the same static location, you just make the conveyor revolve faster
I still don't think the plane can take off, if anyone could prove that it will, feel free, but until you can, zip it up, your all boring me.
My reason is I think applied movement cannot create naturally given inertia and the physics (weighted zones and flexibility in the planes body) of the whole thing aren't right.
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Steve
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Registered: 30th Mar 02
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quote:
Originally posted by LiVe LeE
example to prove why it wouldnt take off
Using a non-electric treadmill, ie a leg powered treadmill
As you run the treadmill conveyor belt increases in speed as the runner increases in speed - however you never run off the end of it do you - you stay in the same static location, you just make the conveyor revolve faster
yes again your going on the fact that the wheels are doing the propulsion, the legs are the wheels, if the wheels are powered then yes the plane will not move, however lets stay with your example, say your running on a treadmill going nowhere obviously, say your holding onto a rope that your mate standing in front of the treadmill is holding, he pulls you forwards, so you run faster, the treadmill goes round faster, but he will still be able to pull you off the end of the treadmill.
If you cant understand that then this really is hopeless
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Cosmo
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quote:
Originally posted by 3CorsaMeal
but the energy given to the quad by the person pushing won't go to the wheels, the powered wheels are there to move the mass of the quad (pushing the road away if you like), you moving the mass of quad without the wheels, so you not pushing the road away
its a big debate, not gonna get settled by CS users
i'm happy if your happy
but the weight of the quad and the planets gravity pushes the wheels onto the rolling road, so any forward mvoement would (even if it wasnt the intention) move the wheels and if they are already moving fast would cause them to move faster (i.e. faster than the conveyor)
CS Mass debate...think we need more scientist members. 
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RichR
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Jules when on the ground the forward momentum of the plane which is provided by the movement of air through the jets is transmitted through the plane, to the wheels which in turn translate the forces acting into forward propulsion
so although the wheels are not driven by an engine in the smae way as a car wheels are driven - they are the connection between the plane and ground and this is where forward propulsion is translated
if your argumnet was true a plane wouldnt need wheels at all - it would simply need posts to hold it in situ before take off at which point the plane would just take off; it wouldnt need wheels at all
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Steve
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ORRR put it another way, there is a toy car on the treadmill with a piece of string attached to it you are standing off the treadmill holding the other end of the string.
The car will be sat there with its wheels spinning on the spot yes?
you pull the string the car moves forwards and the treadmill goes faster, and will go faster the faster the car goes are you telling me that you wouldnt be able to pull the car off the end of the treadmill in this scenario?
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Cosmo
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quote:
Originally posted by Jules S
Cosmo, are you in some way trying to suggest that the conveyor belt will stop me extending my arm forwards?
It has no connection whatsoever to me. I (like the jets) am a third party force on the plane.
A jet engine uses turbiines to propel air out of the back of it thus producing thrust. The conveyor belt has no connection whatsoever to the engines. the jets will do their thing, push air out of the back of the jets....create thrust...
Again. the plane will move forward in the air as its designed to...the wheels are doing no pushing here...
Anyways, I'd call this a debate not an arguement. I only get frustrated at myself for not being able to explain it better
[Edited on 24-05-2006 by Jules S]
No....if I had been trying to suggest it had a connection I would of said it!
What Im saying is that the weight and gravity would cause the jet engines and wheels to be linked whilst the plane is on the ground. Due to this weight and gravity if the plane wanted to move forward the friction would cause the wheels to move faster...conveyor to move faster...jet engines to push harder...wheels to more faster...conveyor to move faster.
So yes their is no direct connection between the conveyor and jet engines but the frictions would cause and indirect connection between the two.
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Cybermonkey
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TTT
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Steve
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quote:
Originally posted by Steve
ORRR put it another way, there is a toy car on the treadmill with a piece of string attached to it you are standing off the treadmill holding the other end of the string.
The car will be sat there with its wheels spinning on the spot yes?
you pull the string the car moves forwards and the treadmill goes faster, and will go faster the faster the car goes are you telling me that you wouldnt be able to pull the car off the end of the treadmill in this scenario?
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Cosmo
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quote:
Originally posted by Steve
ORRR put it another way, there is a toy car on the treadmill with a piece of string attached to it you are standing off the treadmill holding the other end of the string.
The car will be sat there with its wheels spinning on the spot yes?
you pull the string the car moves forwards and the treadmill goes faster, and will go faster the faster the car goes are you telling me that you wouldnt be able to pull the car off the end of the treadmill in this scenario?
not if the treadmill went fast enough to match your ability to pull the string (and the wheels didnt give out at that speed!!)
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Steve
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AHHH I HAVE YOU NOW, THIS IS WHERE I CAN PROVE YOU WRONG so what would happen to the string then? the string is not unlimited length, it is fixed, you would be pulling the string hence shortening the string length between you and the car each time, the car would HAVE to move towards you
[Edited on 24-05-2006 by Steve]
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Cybermonkey
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how long is a piece of string?
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RichR
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quote:
Originally posted by Steve
ORRR put it another way, there is a toy car on the treadmill with a piece of string attached to it you are standing off the treadmill holding the other end of the string.
The car will be sat there with its wheels spinning on the spot yes?
you pull the string the car moves forwards and the treadmill goes faster, and will go faster the faster the car goes are you telling me that you wouldnt be able to pull the car off the end of the treadmill in this scenario?
the treadmill your talking about would have a constant speed - so yes any extra energy exerted would cause the toy car to accelerate
however for this question we are to assume that the conveyor is travelling at the exact same speed and opposite direction to the velocity of advance - and as the plane speeds up, so to does the conveyor so any extra energy exerted will cause the conveyor to speed up at the same rate
you'd never overtake the conveyor!
furthermore the mass of the plane is multiplied by the action of gravity (9.81 m/s) to give Newtonian units of weight - a 100T plane would weigh 981 kN
a 15 g car would weigh 0.000147 kN
the two have a copmpletely different reaction on the groundplane
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J da Silva
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quote:
Originally posted by Cybermonkey
how long is a piece of string?
Depends where you cut.
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Steve
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I need everyone to concentrate on this, then surely you must get it.
You are holding a 2 meter piece of string, the car is rolling on the spot on the treadmill, everytime you pull the string the car moves towards you by say for arguments sake 2 foot, even if the treadmill sped up to match the acceleration of the car, the string is fixed to the car and is shortenening in length each time, the car would have to move towards you, else you would be pulling on a piece of string that never ended
as for going on weight LIVELEE the theory is the same, if you were strong enough to pull a normal size car on a big conveyor belt using a piece of string the same would happen
[Edited on 24-05-2006 by Steve]
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Cosmo
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quote:
Originally posted by Steve
AHHH I HAVE YOU NOW, THIS IS WHERE I CAN PROVE YOU WRONG so what would happen to the string then? the string is not unlimited length, it is fixed, you would be pulling the string hence shortening the string length between you and the car each time, the car would HAVE to move towards you
[Edited on 24-05-2006 by Steve]
you would either beable to pull it wouldnt beable to pull it, or it would go pete tong. But to be honest we are talking push here (jet engines) not pull (string).
the big question is.....
If this was a plane, the engines would either run out of power and not be strong enough to overcome the friction between the wheels and conveyor so not move anywhere...or if they are strong enough they would push the plane forward but if thats at a speed to take off I dont know.
I dont know the maths, or the figues for the engines, weight of plane, lift, etc. to work that out and wouldnt want to guess!
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