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  1. #121
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    not a chance

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  3. #122
    imported_hookie
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    Re: Would the plane take off?

    [ QUOTE ]
    The guy who wrote that is incorrect.

    If you assume a jet turbo fan is connected to the engine:
    It will not fly, as an ideal system.
    Factoring in practical stuff, it will skid forwards across the belt such that the speeds of both
    the belt and the wheels remains equally opposite, caused by the lateral thrust of the engines
    overpowering the friction of the wheels to the belt. The wheels will not be moving twice as
    fast as normal as many external writeups claim. It could eventually reach enough airspeed
    to fly, but then assuming the tyres dont melt, blow up etc, throwing the thing offline and away
    from the belt, whereupon it will immeadiately accelerate straight into the terminal building.

    If you assume propellers are connected to the engines:
    It will lift vertically when the props chuck enough air across the wing span and immeadiatly
    begin to move forwards above the belt when the wheels loose contact with it.

    The statement just says engines though!

    [/ QUOTE ]

    as per the link, this quote says it all -

    February 9, 2006 | Posted by: Robin
    Good analysis. I think the real catch for most people -- it got me at first -- is that we think in terms of things that accelerate by pushing on the ground. Cars. Our feet. And, of course, if you put one of them on a treadmill like that, it doesn't go anywhere. Airplanes don't push on the ground to make 'em go, so that intuition is straight up your mom.

  4. #123
    audi5e's Avatar
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    Re: Would the plane take off?

    It's about relative position to the air around the aircraft. If the aircraft manages to accelerate and get the airflow over the wings up to a high enough speed then there will be a high pressure under the wing and a low pressure on top causing lift (air on top flowing at a higher speed than the air under the wing). To achieve this an aircraft must push itself along a surface until there is enough air flowing over the wings, ie until there is enough flow of air there will not be enough lift to overcome gravity, if the surface is moving backward then the aircraft first has to overcome the forces pushing it back. Say the aircraft did not run the engines, then it would simply go backward until the end of the conveyor belt (there would be gravity acting downward onto the conveyor and a rolling resistance inherant in the bearings and surfaces of ground and tyre). If the engines are then fired up and provided enough thrust to accelerate the aircraft forward enough to counter a backwards movement caused by the conveyor, but did not have enough power to completely overcome the movement backward, then the aircraft would simply stand still. However assuming that the engines had enough power to overcome those rearward forces, then the aircraft would be able to move forward against the direction of movement of the conveyor and ultimately into the air, in moving forward creating movement of air over the wing and eventually take off. So assuming that the wheel bearings of this aircraft could withstand very high revolutions and the engines had enough power, then the aircraft would be able to pull itself forward relative to the air and take off...

    Now, in the case mentioned above, the aircraft will never take off. This is because there is resistance on the tyres and bearings as well as the forces of gravity. The aircraft must achieve forward movement relative to the air not the ground. If it is unable to move forward on the ground (overcome the conveyor) then there will also be no movement of air across the wings and no lift hence no flight.
    If there was no rolling resistance and bearings could spin to any speed then it is irrelevant how fast the conveyor moves and the plane would simple have a much higher "ground" speed to achieve the same air speed.

  5. #124
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    Re: Would the plane take off?

    idiots [img]/ubbthreads/images/graemlins/smile.gif[/img]

  6. #125
    necroeire's Avatar
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    Re: Would the plane take off?

    WTF, this thread is still going.

    What do you call a boomerang that doesn't return?
    A stick.

    What do you call a plane that doesn't take off?
    A plane!

  7. #126
    bainsyboy
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    Re: Would the plane take off?

    Im looking at a 7 or a 14 if i start swearing again and you lot are pushing me over *****************

  8. #127
    imported_hookie
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    Re: Would the plane take off?

    [ QUOTE ]
    idiots [img]/ubbthreads/images/graemlins/smile.gif[/img]

    [/ QUOTE ]

    Indeed! They really can't grasp the concept at all can they!

    I'm gonna build me a conveyor belt and rent a plane for the weekend [img]/ubbthreads/images/graemlins/tongue.gif[/img]

  9. #128
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    Re: Would the plane take off?

    So let me get this straight, there is a plane on a conveyor belt, what happens if the plane is a harrier jump jet?

  10. #129
    Numptie of the highest order

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    Re: Would the plane take off?

    [ QUOTE ]
    So let me get this straight, there is a plane on a conveyor belt, what happens if the plane is a harrier jump jet?

    [/ QUOTE ]

    Look You - go away and sort your avatar out before you join in anymore conversations! [img]/ubbthreads/images/graemlins/tongue.gif[/img]

  11. #130
    bainsyboy
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    Re: Would the plane take off?

    I would just like to say what a splendid new avatar TDI has splendid splendid

  12. #131
    FactionOne's Avatar
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    Re: Would the plane take off?

    Which do we prefer?



    Or...



    ???

    [img]/ubbthreads/images/graemlins/wink.gif[/img]

    Rob.

  13. #132
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    [ QUOTE ]
    Say the aircraft did not run the engines, then it would simply go backward until the end of the conveyor belt (there would be gravity acting downward onto the conveyor and a rolling resistance inherant in the bearings and surfaces of ground and tyre). If the engines are then fired up and provided enough thrust to accelerate the aircraft forward enough to counter a backwards movement caused by the conveyor, but did not have enough power to completely overcome the movement backward, then the aircraft would simply stand still.

    [/ QUOTE ]

    Dude, please re-read and consider the original statement, the plane does not move backwards until the wheels start to move forwards. The belt speed is NOT constant, but adaptive to the wheel speed of the plane under thrust.

  14. #133
    bainsyboy
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    Re: Would the plane take off?

    factione seeming as i get carried away i best say the top one,

  15. #134
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    [ QUOTE ]
    Airplanes don't push on the ground to make 'em go, so that intuition is straight up your mom.

    [/ QUOTE ]

    Of course they do to start with. Everything with mass is attracted to each other by the force of gravity.

    The plane is attracted to the earth via the belt, of which contact is made by the planes wheels. Until of course sufficient lift is generated by the wings, usually from lateral movement created by thrust from the engines.

    So traditionally the plane must move forwards on the wheels before it can take off.

    If every forward movement of the wheels is equally opposed by a reverse movement of the surface they rotate on then the nett lateral displacement is zero. Hence no nett airspeed, no lift and no flight.

  16. #135
    imported_hookie
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    Re: Would the plane take off?

    no but the jet engines are psuhing against the atmosphere not the conveyor belt, the force at the wheel is relatively small comparitively.

    Can we put spinners on the airplane wheels to make this picture even more bizarre?

  17. #136
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    Re: Would the plane take off?

    [ QUOTE ]
    Which do we prefer?



    Or...



    ???

    [img]/ubbthreads/images/graemlins/wink.gif[/img]

    Rob.

    [/ QUOTE ]

    I prefer yours Rob at least it works mate [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  18. #137
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    Re: Would the plane take off?

    [ QUOTE ]
    [ QUOTE ]
    Airplanes don't push on the ground to make 'em go, so that intuition is straight up your mom.

    [/ QUOTE ]

    Of course they do to start with. Everything with mass is attracted to each other by the force of gravity.

    The plane is attracted to the earth via the belt, of which contact is made by the planes wheels. Until of course sufficient lift is generated by the wings, usually from lateral movement created by thrust from the engines.

    So traditionally the plane must move forwards on the wheels before it can take off.

    If every forward movement of the wheels is equally opposed by a reverse movement of the surface they rotate on then the nett lateral displacement is zero. Hence no nett airspeed, no lift and no flight.

    [/ QUOTE ]

    Your argument is flawed. Well, just plain wrong.
    The rotation of the wheels and the direction of the plane due to the thrust are seperate.

    If you want a proper mechanics diagram describing the forces and their directions, then the force acting on the plane from the wheels is that of the wheel bearing. This would be a very small arrow (vector) pointing backward. The thrust from the engines would be a very large vector pointing forwards.

    The opposite forces are not equal (at any point up to take off speed), and therefore the plane would move in the direction of the biggest arrow. Discussion closed (for the 23rd time).

  19. #138
    Charlies604's Avatar
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    Re: Would the plane take off?

    [ QUOTE ]
    So let me get this straight, there is a plane on a conveyor belt, what happens if the plane is a harrier jump jet?

    [/ QUOTE ]

    It would get very noisey, The belt would melt and the problem would be over! But from what i saw the other day, the harriers dont fly anymore... so that factors them out if they cant fly anyway!

  20. #139
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    Re: Would the plane take off?

    Idiots

  21. #140
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    Re: Would the plane take off?

    [ QUOTE ]
    Your argument is flawed. Well, just plain wrong.
    The rotation of the wheels and the direction of the plane due to the thrust are seperate.

    If you want a proper mechanics diagram describing the forces and their directions, then the force acting on the plane from the wheels is that of the wheel bearing. This would be a very small arrow (vector) pointing backward. The thrust from the engines would be a very large vector pointing forwards.

    The opposite forces are not equal (at any point up to take off speed), and therefore the plane would move in the direction of the biggest arrow. Discussion closed (for the 23rd time).

    [/ QUOTE ]

    But are you sure rob... [img]/ubbthreads/images/graemlins/cry.gif[/img]

  22. #141
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    Re: Would the plane take off?

    [ QUOTE ]
    [ QUOTE ]
    Your argument is flawed. Well, just plain wrong.
    The rotation of the wheels and the direction of the plane due to the thrust are seperate.

    If you want a proper mechanics diagram describing the forces and their directions, then the force acting on the plane from the wheels is that of the wheel bearing. This would be a very small arrow (vector) pointing backward. The thrust from the engines would be a very large vector pointing forwards.

    The opposite forces are not equal (at any point up to take off speed), and therefore the plane would move in the direction of the biggest arrow. Discussion closed (for the 23rd time).

    [/ QUOTE ]

    But are you sure rob... [img]/ubbthreads/images/graemlins/cry.gif[/img]

    [/ QUOTE ]

    Well, actually........












    ......yes!!! [img]/ubbthreads/images/graemlins/****_you.gif[/img]

  23. #142
    bainsyboy
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    Re: Would the plane take off?

    [ QUOTE ]
    Idiots

    [/ QUOTE ]


    LOL the one liners are the best ones

  24. #143
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    Re: Would the plane take off?

    Max from "Flight Of The Navigator" would NOT be impressed with your answers!

  25. #144
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    [ QUOTE ]
    The rotation of the wheels and the direction of the plane due to the thrust are seperate.

    [/ QUOTE ]

    Only separate when taxiing or flying.

    Every other forwards ground movement (wheel rotation), is controlled by thrust from the engines.

  26. #145
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    [ QUOTE ]

    If you want a proper mechanics diagram describing the forces and their directions, then the force acting on the plane from the wheels is that of the wheel bearing. This would be a very small arrow (vector) pointing backward. The thrust from the engines would be a very large vector pointing forwards.

    The opposite forces are not equal (at any point up to take off speed), and therefore the plane would move in the direction of the biggest arrow. Discussion closed (for the 23rd time).

    [/ QUOTE ]

    How many times must I type this?
    The belt moves backwards as the plane moves forwards at the same rate.
    There is no imbalance between the two vectors you describe.
    Even if the thrust vector from the engined is huge, the wheel bearing vector is equally huge
    the other way.

  27. #146
    necroeire's Avatar
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    Re: Would the plane take off?

    So lets sum it up. There is a plane on a runway that has jet enginers and...hang on....how long are the wings?

    What colour is it and where is the chicken? Left side or right side of the road?

  28. #147
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    Re: Would the plane take off?

    [ QUOTE ]
    [ QUOTE ]

    If you want a proper mechanics diagram describing the forces and their directions, then the force acting on the plane from the wheels is that of the wheel bearing. This would be a very small arrow (vector) pointing backward. The thrust from the engines would be a very large vector pointing forwards.

    The opposite forces are not equal (at any point up to take off speed), and therefore the plane would move in the direction of the biggest arrow. Discussion closed (for the 23rd time).

    [/ QUOTE ]

    How many times must I type this?
    The belt moves backwards as the plane moves forwards at the same rate.
    There is no imbalance between the two vectors you describe.
    Even if the thrust vector from the engined is huge, the wheel bearing vector is equally huge
    the other way.

    [/ QUOTE ]

    No matter how many times you type it, it won't make it right.

    The wheel bearing's will not and can not generate enough friction to stop the plane moving!!!!! Unless the brakes are on, the plane will move forward.

    Are you saying the plane won't move at all? and the conveyor belt won't move at all? Because that's what your statement implies. Meaning that the thrust from the engines will do nothing. (you say the forces are equal).

  29. #148
    imported_hookie
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    Re: Would the plane take off?

    I'll bring a definitive answer to this soon hopefully..... [img]/ubbthreads/images/graemlins/wink.gif[/img]

  30. #149
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    Rob in this system you have to assume that the wheels bearings are frictionless. It is not them,
    that is opposing the movement, it is the friction of the tyres with the belt. Tyres roll forward
    whilst belt rolls backwards at any speed. Tyres are coupled to the plane via the landing gear
    and are in a fixed position under the aircraft.

    From the start the plane's wheels and belt will begin to accelerate to finite speed
    governed by the thrust produced by the engines. Allthough the wheels will not be moving
    laterally they will be spinning very fast, but the plane will not take off, whilst friction remains between the tyres and the belt.

  31. #150
    TDI-line's Avatar
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    Re: Would the plane take off?

    Ok, so what happens if one of the wheels falls off or twists.


  32. #151
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    Re: Would the plane take off?

    Was it an Air France plane...


  33. #152
    imported_hookie
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    Re: Would the plane take off?

    <font color="black">Right we need some proper opinions on this, so I mass emailed all the Physics departments at the leading universities around the world.... [img]/ubbthreads/images/graemlins/smile.gif[/img]
    I have the first reply from the head of the Physics department at Bristol University, Professor Birkenshaw, which is as follows....

    [ QUOTE ]
    My opinion is that the plane would take off with no particular difficulty, unless the wheels are defective.

    The motion of the conveyor belt only causes the wheels to spin. The body of the plane is decoupled from the wheels by (notionally) frictionless bearings, and so moves forward relative to the air above the conveyor belt under the thrust of the propellors or jet engines. I don't attempt to analyse the effects of friction in the bearings, viscosity of the air, etc., etc. ...

    It would be a different matter if the plane were driven by motors in the wheels. Then the plane would never take off (and in the absence of a conveyor belt, such a plane would only "fly" in short hops as it gains enough speed to get some lift and rises, and then drag slows it down again and causes it to fall back to Earth).

    Mark Birkinshaw

    [/ QUOTE ]

    My thanks to Mark for answering this, I hope to get other points of view from others soon to support the fact I WAS RIGHT [img]/ubbthreads/images/graemlins/tongue.gif[/img] </font>

  34. #153
    imported_hookie
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    Re: Would the plane take off?

    whoops spelt Marks' name wrong as it is in fact 'Birkinshaw' but this stupid 30 minute edit rule stops me editing it!

  35. #154
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    Re: Would the plane take off?

    do you know what I'm gonna say yet?

  36. #155
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    Re: Would the plane take off?

    Yep.

  37. #156
    imported_hookie
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    Re: Would the plane take off?

    I think we don't need to say it, just gloat in our smugness [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  38. #157
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    Re: Would the plane take off?

    [ QUOTE ]
    I think we don't need to say it, just gloat in our smugness [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

    [/ QUOTE ]

    NSD=

  39. #158
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    Hookie, I shall endeavor to get my professor to give you an answer too.

  40. #159
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    Re: Would the plane take off?

    Have been reading this thread for the past few days and have PMSL, great to read a thought provoking thread mixed in with humour, very entertaining! Agree with NEiL though, even with the cat looking like its got the cream.

    As said before by NEiL, assuming the wheels/tyres can take the force of the thrust and don't melt etc any force that is produced by the engine is transmitted through the wheels, and through friction, the plane would normally gain velocity as the wheels turn against the stationary ground. With the belt instantly reacting to the speed of the wheels, the plane doesn't have any velocity as the belt, in a way, is moving the plane backwards as fast as the plane is trying to move forwards. The plane is in effect, stationary. No airflow, no lift etc etc Any extra thrust that is dialed in is just moving the wheels faster, which causes the belt to move faster. Nothing happens! No take off, just lots of noise.

    Now that I've just repeated what a couple of others have already said and got my 2p worth in, I will wait to be called an idiot...

  41. #160
    chazzy's Avatar
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    Re: Would the plane take off?

    Force and .... oh never mind. (PS it will) [img]/ubbthreads/images/graemlins/bang.gif[/img]
    Has this been put to a vote yet, i can't remember!

    Chas

 

 
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