Would It Take Off?
Discussion
galileo said:
Is this an 'ironic' repost or a genuine one 
This was a huge thread before - with links to a 300 page thread on another forum....
some of us are new to PH and quite happy to make fools of ourselves in front of you veterans (some bigger fools than others, looking at this thread)
I am not new to PH, come on everyday and I didnt see it previously either
but have seen it on other forums so it is a bit 
nowSounds to me like you're describing some sort of giant treadmill? If that's the case, then the plane will move relative to the 'treadmill' but not relative to the earth. As such, it would have no forward motion, have no air passing over it's wings and generate no lift.
Ergo ... it wouldn't go.
Ergo ... it wouldn't go.
Here it is
There are some links to a huge debate in there somewhere IIRC
Please don't confuse me with the REPOST POLICE - I couldn't give a toss if it is old or not....we all flit in and out of here and whatever is interesting gets read
However....I can save you a lot of time and trouble:
1) It is a horrible question
2) The plane does take off
3) It's to do with the fact that it WOULD still 'go along' the runway (moving belt or not)
4) It's a horrible question...
There is also a link somewhere to a video of an experiment based on this theoretical question
>> Edited by gorvid on Saturday 4th March 11:43
There are some links to a huge debate in there somewhere IIRC
Please don't confuse me with the REPOST POLICE - I couldn't give a toss if it is old or not....we all flit in and out of here and whatever is interesting gets read
However....I can save you a lot of time and trouble:
1) It is a horrible question
2) The plane does take off
3) It's to do with the fact that it WOULD still 'go along' the runway (moving belt or not)
4) It's a horrible question...
There is also a link somewhere to a video of an experiment based on this theoretical question
>> Edited by gorvid on Saturday 4th March 11:43
m.c said:
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
The question is:
Will the plane take off or not?
I think the reason that this question takes so long to [fail to] answer is that it is ambiguous, and one fairly obvious interpretation is describing a situation that is not logically possible. If you ignore the impossibility then the plane can't take off. Back in the real world, yes the plane will take off and the movement of the conveyor belt is irrelevant.
So, please resolve the ambiguity: When you say the control system tracks the plane's speed, exactly what is it tracking i.e. what are the two things that you are measuring speed between? Plane and conveyor belt? Plane and ground? Plane and air? Plane and something else (what)? I assume that you are defining the speed of the conveyor belt as the speed relative to the ground, but if not then please specify.
You would need air flow over the wings to create lift otherwise it would just sit there
it would work if it was a helicopter........
Read this it will help
http://en.wikipedia.org/wiki/Lift_%28
it would work if it was a helicopter........
Read this it will help
http://en.wikipedia.org/wiki/Lift_%28
gorvid said:
As I said...
The crux of the matter is:
It will still travel along the 'runway' as 'normal'
Because the free-spinning hubs on the wheels only match (and negate) the conveyor movement!
Gorvid is correct the conveyor contributes nothing.
It will only take off if the air is passing over the wings at the normal speed for take off.
I've just flicked into the previous thread and it seems that people took a tangent.
If the plane and conveyor counteract each others speed, then no airflow, no lift, no take off.
On the earlier thread, some posters started going on about ball bearings, resistance, friction, speed of wheels, speed of conveyor etc. not being able to prevent forward motion, but that is putting practical knowledge to a theoretical question, in order to prove that no conveyor could conteract the thrust... in other words, giving an answer to a completely different question.
Another thoery suggested that if the conveyor were to be going fast that there may be enough draught from the conveyor to cause lift.. sounds promising, until you consider what happens when it gets clear of the draught and is only travelling at few miles and hour relative to the surrounding air, at which point it crashes back to earth and blows up in flames.
So yes, it will take off if you answer a completely different question.. but no, it will not if you answer the one asked in the original post which from my understanding assumes that the conveyor can compensate for the thrust and the plane is stationary relative to the surroundings.
Right, I'm off to do something more useful with my day!
>> Edited by fozzi on Saturday 4th March 12:12
>> Edited by fozzi on Saturday 4th March 12:14
If the plane and conveyor counteract each others speed, then no airflow, no lift, no take off.
On the earlier thread, some posters started going on about ball bearings, resistance, friction, speed of wheels, speed of conveyor etc. not being able to prevent forward motion, but that is putting practical knowledge to a theoretical question, in order to prove that no conveyor could conteract the thrust... in other words, giving an answer to a completely different question.
Another thoery suggested that if the conveyor were to be going fast that there may be enough draught from the conveyor to cause lift.. sounds promising, until you consider what happens when it gets clear of the draught and is only travelling at few miles and hour relative to the surrounding air, at which point it crashes back to earth and blows up in flames.
So yes, it will take off if you answer a completely different question.. but no, it will not if you answer the one asked in the original post which from my understanding assumes that the conveyor can compensate for the thrust and the plane is stationary relative to the surroundings.
Right, I'm off to do something more useful with my day!
>> Edited by fozzi on Saturday 4th March 12:12
>> Edited by fozzi on Saturday 4th March 12:14
rich-uk said:
The plane isn't driven by the wheels so all a conveyor would do it make the wheels spin really quickly, the plane would accelerate and take of as normal.
Read the question again...
m.c said:
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
"tracks the plane speed and tunes the speed of the conveyer to be exactly the same"... e.g. the plane is not moving relative to the surroundings, hence no airflow, no lift, no take off!
gorvid said:
The thrust never reaches the conveyor belt... it pushes the plane forward - then the wheels spin faster to compensate.
Theory = take off
ah so the plane is using its engines, thrusting against the surrounding air, pushing the plane forward relative to said surrounding air. if the conveyor is going backwards relative to the direction of planes travel then all that will happen is the wheels will spin faster than normal. The conveyor will affect the wheels only and have no effect on the plane. Definately take-off if put like that. The question is ambigious at best and not a well laid-out scientific inquiry. This arguement is only to due to the ambuity of the question which should be layed out differently. no offence.
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