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  1. #81
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    Re: Would the plane take off?

    [ QUOTE ]
    lol, time to stop the brain from hurting and read from the experts:

    Ask A Scientist

    Aviation Web

    ...

    [/ QUOTE ]

    lol, yet a google gives the above results...

    g'wan somebody give this a go and end it all now [img]/ubbthreads/images/graemlins/smile.gif[/img]

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  3. #82
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    Re: Would the plane take off?

    So who's going to build a scale model to test this theory then - it's the only way to be sure in "the real world" - although I have reconsidered my original position to that of "you know what I really don't care either way"

    ps... I think after thinking further about the "wheel" part of the statement I agree it would make no difference and would take off as normal but with rodgered wheel bearings.

  4. #83
    NEiLS3LK51's Avatar
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    Re: Would the plane take off?

    Tremendous force, until the second order event of the tyres loosing friction with the surface of
    the belt, the plane begins to skid forward and eventually builds up airspeed to lift.
    Or the tyres catch fire,wear unevenly or blow out and the thing falls off line and crashes and
    burns whilst being dragged backwards by the residual momentum of the belt.

  5. #84
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    Re: Would the plane take off?

    [ QUOTE ]
    skid forward

    [/ QUOTE ]

    Why would it skid it has a bearing? [img]/ubbthreads/images/graemlins/confused.gif[/img]

  6. #85
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    Re: Would the plane take off?

    It's simply a matter of forces:

    Assuming the air is still (there is no wind) then as soon as the forces propelling the plane forwards exceed those propelling it backwards then the plane will have a net forward airspeed.
    When the airspeed is sufficient, the plane will take off.

    Groundspeed (relative to the conveyor) is irrelavent because the lift is produced by the airflow over the wings and has nothing to do with the ground.

    In order for the forward force to overcome backward force we have to understand what these forces are:

    Backwards - the plane initially moves backwards with the conveyor. This is caused by the friction of the wheels of the plane pulling it back.

    Forwards - the thrust from the engines drives the plane forward. This thrust is relative to the airspeed and has nothing to do with the groundspeed as the engines do not drive the wheels.

    Therefore, as soon as the force of the engine thrust overcomes the forces of friction from the wheels, the aircraft will stop moving backwards.

    As the thrust increases above what is required to counteract the friction, the aircraft will start to move forwards. As airspeed increases, the wings will start to generate lift and take some of the weight of the plane. This will reduce the friction of the wheels and allow the plane to easily reach rotation speed to take off.

  7. #86
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    Re: Would the plane take off?

    [ QUOTE ]
    Tremendous force, until the second order event of the tyres loosing friction with the surface of
    the belt, the plane begins to skid forward and eventually builds up airspeed to lift.
    Or the tyres catch fire,wear unevenly or blow out and the thing falls off line and crashes and
    burns whilst being dragged backwards by the residual momentum of the belt.

    [/ QUOTE ]

    When we're talking about a runway that is a conveyor belt, i don't think the wheels being able to take the strain is biggest logistical problem! [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  8. #87
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    Re: Would the plane take off?

    If the conveyor belt was moving in the same direction as the plane, would it lift off sooner?

  9. #88
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    Re: Would the plane take off?

    Bit wrong there too marc, the plane starts moving forward not back, as the conveyor is sensitive to the speed of the wheels, so the conveyor can't start moving before the plane had enough thrust to move forwards.

  10. #89
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    Re: Would the plane take off?

    [ QUOTE ]
    Bit wrong there too marc, the plane starts moving forward not back, as the conveyor is sensitive to the speed of the wheels, so the conveyor can't start moving before the plane had enough thrust to move forwards.

    [/ QUOTE ]

    Oops. Remind me to read the post properly. Still, the outcome is the same.

  11. #90
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    Re: Would the plane take off?

    Because the belt material is countering the lateral movement of the rubber of the tyres.
    Nothing to do with wheel bearings.

    Put it this way, image wheel rotatation speed = 0

    As wheel rotation speed = belt rotation speed in opposing directions, if the wheel speed is 0,
    than the belt speed is 0. The only way the wheel can move in a lateral direction along the belt
    is by skidding. Like pushing a mountain bike with the brakes on.

    If the pilot applied his brakes and they were beefy enough to overcome the friction of the tyres
    with the belt the plane would move forwards under thrust. The wheels are not rotating forwards
    so the belt is not moving backwards but it is skidding.

    You can apply any rotation speed and the case is the same, without the brakes mind,
    it must skid to move forwards and generate air speed.

    But its not going to skid at 100mph or whatever takeoff speed is without doing some serious
    damage to the tyres.

  12. #91
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    Re: Would the plane take off?

    [ QUOTE ]
    Still, the outcome is the same.

    [/ QUOTE ]

    Yep... agree with you on that one! [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  13. #92
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    Re: Would the plane take off?

    [ QUOTE ]
    As wheel rotation speed = belt rotation speed in opposing directions

    [/ QUOTE ]

    How did you come to this conclusion? There is nothing stopping wheel rotation speed > belt rotation speed.

  14. #93
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    Re: Would the plane take off?

    It says in the original statement that the conveyor belt senses the speed of the plane's wheels
    and moves at exactly the same speed in the opposite direction.

    And rob I am very worried about these tyres!

  15. #94
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    Re: Would the plane take off?

    [ QUOTE ]
    It says in the original statement that the conveyor belt senses the speed of the plane's wheels
    and moves at exactly the same speed in the opposite direction.

    And rob I am very worried about these tyres!

    [/ QUOTE ]

    I am starting to see where you are coming from on this one.

  16. #95
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    Re: Would the plane take off?

    Just been speaking to some chaps about this at work, one of whom used to work for NASA Jet
    Propulsion Labs and has given university courses on space craft design.

    He says this,

    It says engines so you must first assume if it is a propeller or a jet turbine.

    If the plane is powered by propeller/s it could eventually blow enough air across the wings
    to produce lift without moving forwards at all.
    So a vertical take off is possible depending on the design.
    This is why all short take off planes (non catapult assisted) are propelled from the front of the
    wing rather than jet engined. They provide extra lift during takeoff when the thrust pushing it
    forwards is also forced over the wings.

    With a jet no chance of take off.

    The discussion was soon hijacked by talk of quantum mechanics and the probability of it
    dissapearing at 88.8mph!

  17. #96
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    Re: Would the plane take off?

    [ QUOTE ]
    Neil said stuff

    [/ QUOTE ]

    Hi Neil,

    I think you should send him the exact wording and see if he still feels the same way.

    I think even if a 747 had the wheel brakes on (worst case of the conveyor) It would still move forward on full power. I may be wrong but who knows and as I said above I am curious but I won't be loosing sleep over it. There was a thread with exactely this question over on pistonheads with lots of clever people posting and a link to a physics forum (who were all discussing) - I'm guessing if anyone is actually that interested they would be a good read!

  18. #97
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    Re: Would the plane take off?

    The original post simply states that the conveyor moves at the same rate as the plane (but in the opposite direction). It does not mention the wheels.

    The relationship should be:

    Plane's airspeed = groundspeed relative to conveyor surface / 2

    Seeing as there is no limit to the speed at which the wheels can turn, I dont' see why the plane cannot take off.

    IF HOWEVER, the plane had a tailwind that always matched the plane's forward speed then it would never take off as it's airspeed would always be zero, even if it's groundspeed was not.

  19. #98
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    Re: Would the plane take off?

    [ QUOTE ]
    Marc said more stuff

    [/ QUOTE ]

    again nearly there Marc but and I quote... [img]/ubbthreads/images/graemlins/grin.gif[/img]

    [ QUOTE ]
    ... wheels and moves at exactly the same speed in the opposite direction...

    [/ QUOTE ]

    It's the wheels the convyor is acting against, but you're still correct about the bloody thing taking off the way I see it [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  20. #99
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    Re: Would the plane take off?

    Problem is there seem to be a few different versions of this floating around the internet. ARG!

    This site http://www.kottke.org/06/02/plane-conveyor-belt states:

    "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 the opposite direction). Can the plane take off?"

  21. #100
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    Re: Would the plane take off?

    i think we're missing some vital information here, like:

    has the plane been remapped?
    does it have furry dice?

    but perhaps more importantly, does it have DSG?

    i suspect that if the plane has DSG, then the launch control lag will be so bad, it will bounce off the rev limiter, change up to 4th, and end up off the back of the conveyor belt.....

  22. #101
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    Re: Would the plane take off?

    at first i didn't get what you were on about Neil, but yeah it kinda make sense if the wheels are in constant contact with the conveyer though relatively at any one the wheels at they would have exactly the same but opposite speed, but relative to a static position on the conveyer belt, say the start of the belt where the plane starts from,, the wheels would have to be running faster than that point to move along the conveyer belt with out skidding , not sure if that is possible , so maybe the wheel bearing speed would keep increasing, in reality the wheels would burn to bits at the bearing, most logical explaination is they skid with a runway constantly matching the speed, that is if i haven't had a stroke thinking about this lol

    this topic can get as deep as the ocean

  23. #102
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    Re: Would the plane take off?

    What a classic thread, lots of interesting answers here, I was 99% sure it would fly, based on RichA3turbo's assumptions, which was the same as I was thinking, but now i'm not sure....
    Time for a beer methinks lol

  24. #103
    imported_Nigma
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    Re: Would the plane take off?

    Has anyone been to tescos yet to try the toy car at the checkout?

  25. #104
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    Re: Would the plane take off?

    [ QUOTE ]
    Has anyone been to tescos yet to try the toy car at the checkout?

    [/ QUOTE ]Yeh but got told to leave even though i told them thats i'm conducting a very important experiment for audi-sport.net also tried a small toy plane with a firework straped to it never to be seen again but did acheive vertical lift off though, oh and i also think the plane wont take off.

  26. #105
    bainsyboy
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    Re: Would the plane take off?

    Has this plane taken off yet ? how much compansation did the passgengers get, id be well fuming if i was stuck on it. " switch the f--king belt of mate ive already missed 3 days of me holiday, due to you boffins dicking about " is what i would have said before raiding the drinks trolley and nicking a packet of the 3 salted nuts in a bag to get my thirst up.

  27. #106
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    Re: Would the plane take off?

    5 *****.

    Should keep this thread running for another week.

  28. #107
    imported_fingermouse
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    Re: Would the plane take off?


    NO

  29. #108
    bainsyboy
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    Re: Would the plane take off?

    [ QUOTE ]

    NO

    [/ QUOTE ]

    Ill second that, although im going to try the tescos experiment

  30. #109
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    Re: Would the plane take off?

    I don't think it will. The thrust of the engines is purely to create a forward motion. As atated before, the forward motion and the speed of the air over the wings causes a differential pressure, thus generating lift. If the plane does not move forward, no airflow and no lift. This is the reason we need such long runways to build up enough speed to cause an airflow. A stationary plane is going to generate nothing but static air and a sh*t load of screaming people as the conveyor belt gets sucked down the intake LOL

  31. #110
    bainsyboy
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    Re: Would the plane take off?

    This thread beats buying nytol from boots the chemists, mods can you make it a sticky as just reading a couple of these posts puts me in a nice relaxed state to sleep. Thanks in advance bainsboy chairman of insominacs of great brittain

  32. #111
    imported_hookie
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    Re: Would the plane take off?

    I didn't even bother reading this thread apart from the first few posts, clearly the plane will take off as the force is between the jet engines and the atmosphere, the bearings in the wheels cancel out the effects of the forces below in the conveyor belt, force applied is to the atmosphere not below due to basic mechanics.
    A plane slows down when it lands because it applies brakes and powers down mainly....

    It's not rocket science! :P

  33. #112
    imported_hookie
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    Re: Would the plane take off?

    [ QUOTE ]
    The original post simply states that the conveyor moves at the same rate as the plane (but in the opposite direction). It does not mention the wheels.

    The relationship should be:

    Plane's airspeed = groundspeed relative to conveyor surface / 2

    Seeing as there is no limit to the speed at which the wheels can turn, I dont' see why the plane cannot take off.

    IF HOWEVER, the plane had a tailwind that always matched the plane's forward speed then it would never take off as it's airspeed would always be zero, even if it's groundspeed was not.

    [/ QUOTE ]

    Or would it's forward speed just be double......

    Tailwind would add pressure to which to apply force

  34. #113
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    Re: Would the plane take off?


  35. #114
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    Re: Would the plane take off?

    Well that's killed the thread NSD. [img]/ubbthreads/images/graemlins/lol.gif[/img]

  36. #115
    bainsyboy
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    Re: Would the plane take off?

    Neversaydie i owe you a thousand pints, Thankyou Thankyou Thankyou Thankyou, now be gone Would the plane take off? thread page to page 170 of general chat, you are deceased you live no more, now please go
    [img]/ubbthreads/images/graemlins/MexWave.gif[/img]

  37. #116
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    Re: Would the plane take off?

    What's to say the guy that wrote that is correct? [img]/ubbthreads/images/graemlins/smile_smoking.gif[/img]

  38. #117
    imported_Nigma
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    Re: Would the plane take off?

    Although he is correct... its just his opinion.

    [ QUOTE ]
    don't think it will. The thrust of the engines is purely to create a forward motion. As atated before, the forward motion and the speed of the air over the wings causes a differential pressure, thus generating lift. If the plane does not move forward, no airflow and no lift. This is the reason we need such long runways to build up enough speed to cause an airflow. A stationary plane is going to generate nothing but static air and a sh*t load of screaming people as the conveyor belt gets sucked down the intake LOL


    [/ QUOTE ]
    If you read back through the thread..... the plane IS moving forward and IS NOT stationary. The forward movement is what causes it to lift.

  39. #118
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    Re: Would the plane take off?

    lol, great comments.

    [ QUOTE ]
    so that intuition is straight up your mom.

    [/ QUOTE ]

  40. #119
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    Re: Would the plane take off?

    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!

  41. #120
    bainsyboy
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    Re: Would the plane take off?

    OH NO it lives, be gone you dammed thread

 

 
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