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Plane on a Conveyor - IT TOOK OFF!

Discussion in 'General' started by will., 13 Dec 2007.

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Will the plane fly

  1. Yay

    89 vote(s)
    72.4%
  2. Nay

    34 vote(s)
    27.6%
  1. MaximumShow

    MaximumShow Minimodder

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    Well Actually I was the 5th poster on the original topic (prior to wheels being changed to plane) HERE.

    I am not trying to say "I am smart, you are dumb". My intention is to demonstrate that the way a problem is presented, in the form of it's wording, is key to it's solution. The ORIGINAL problem is a paradox. A paradox cannot be tested for obvious reasons. When wheels is changed to plane, the answer is completely different and one in which we all AGREE on: The plane will fly.

    EDIT: I can see why this topic should die. I'm not trying to make anyone feel stupid, and if I came across that way I apologize. Thought experiments are extremely fun for me, and I love constructive debate. For peace of mind's sake, let's just agree to disagree.
     
    Last edited: 11 Mar 2008
  2. chrisb2e9

    chrisb2e9 Dont do that...

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    you know, if the coveyer belt matches the speed of the wheels, and the wheels and the belt keep speeding up, eventually the wheel bearings are going to overheat and seize. but that means that the wheels will stop turning, and the belt will stop if they do because its matching their speed. and since we are working in a world of fantasy lets say that the plane has enough thrust to still accelerate with the wheels locked up.
    So now it is accelerating and it still takes off even with the belt matching the speed of the wheels.

    problem solved.
     
  3. Lynx

    Lynx What's a Dremel?

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    On chrisb2e8's point. At some point if the wheel bearings are not frictionless then the couple retarding the wheels will overwhelm the contact friction between the wheels and the conveyer and so the wheels will start to skid and so the plane will take off.
     
  4. mvagusta

    mvagusta Did a skid that went for two weeks.

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    You seem to have the supposed original meaning of the myth confused - the conveyor is only meant to match the forward velocity of the plane, describing this velocity via wheel speed is just another way of measuring this speed - the fact the wheelspeed is doubled is just the result of the conveyor + forward motion of the plane - the conveyor does NOT have to try and match this resulting speed! That is not the meaning of the myth!

    The second scenario you are describing is not the myth - it is your own creation/play on words. They are two very similar things, but with a small change, things easily become very different, as illustrated by these two guys:
    [​IMG]
     
  5. Oclocker

    Oclocker What's a Dremel?

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    Ahh but what was the original myth seems like several exist - treadmill matches wheels, velocity? plane starts from rest to mythbusters version. Sometimes people say the opposite just to annoy people, I find the comments by certain people just so smug and condescending that it reflects the sunshine coming out there arse in a bad smell/light kinda way.. After all its a hypothetical question hardly justifies "piss off" does it. I'd rather be wrong about whether planes on treadmills fly so certain physics undergrads can be larfed at!
     
  6. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

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    The plane would take off in all scenarios. This is because the speed of the belt is irrelevant. Match to plane, match to wheels' rotation, it doesn't matter. It could hypothetically be going at the speed of light. It could be going at Ludicrous Speed. The plane's forward motion is totally detached from the motion of the belt by the fact that its wheels spin. It would move forward, it would fly. Mmmokay?
     
  7. Tomm

    Tomm I also ride trials :¬)

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    Argh. I've had this argument on other forums and it's like slamming your head against a brick wall. However, it's not often anyone gets to say this, so I'll continue. Nexxo - you're wrong about the scenario where the conveyor belt matches the speed of the wheels. If the speed of the belt (x) matches the speed of the wheels (y) exactly, the plane cannot move. At all. The only way it will go anywhere is if y > x .

    The problem would be that it's an impossible situation to be in - the conveyor could never match the speed of the wheels unless the plane was standing still.
     
  8. cjmUK

    cjmUK Old git.

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    You said it mate...

    No, I'm afraid you are wrong.

    And this is where you are wrong.

    The prop pulls the plane forward... the conveyor belt tries to resist... but no matter how fast the belt goes, the plane *always* goes forward. You see, the belt acts upon the wheels of the plane (which spin freely) but not on the plane itself. The faster the plane goes, the faster the belt will go, but this will only make the free-spinning wheels turn faster and faster - effectively at double the rate at which they would if the plane was on a runway. But that wont affect the plane.

    If it were a car on the conveyor belt, then clearly the car would remain stationary. The car moves through wheel traction with the road (or belt in this case), so if the belt moves against the car, it will impede the car.

    Again, this highlights your misunderstanding of the problem. It is difficult but not impossible to simulate this scenario. The difficulty is measuring the speed of the plane and making the conveyor belt match it (plus finding a belt that size that can go that fast).
     
  9. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

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    As I said, you are making a reasoning error. You are thinking that the forward motion of the plane is connected to the conveyor. It is not. Its wheels decouple the plane's movement from the movement of the conveyor belt.

    Think about it (ferchissakes). Put a stationary plane on the belt. Start Moving the belt backwards at speed S. What does the plane do?

    It stays in the same spot. The wheels spin. That's inertia for you.

    It is only after a while that the plane gradually starts to move backwards, as a little bit of the force of the belt movement manages to transfer through the tiny friction in the wheel bearings. But if we have really low-friction wheels, then you wait for a very long time for this to happen.

    It's a bit like pulling a sheet from under the plates on a table. Inertia keeps the plates in roughly the same place, as long as it can overcome the force of friction of the plate resting on the moving tablecloth. The faster you pull the cloth, the greater the inertia that has to be overcome, the more the plates stay put.

    Got the picture? Good. Now put wheels under the plate, and you have very little friction, so you find it is easier to pull the cloth from under it now, without disturbing its position.

    Now strap a jet turbine to the plate. See the plate move forwards, regardless if how hard you pull the table cloth. Because a jet turbine connected rigidly to the plate transfers force very efficiently compared to a conveyor belt having to act through wheel bearings.

    Add wings. See the plate take off.


    Christ. Education these days really is going down the can...
     
  10. MaximumShow

    MaximumShow Minimodder

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    Let's do the math then :)

    EDIT: JK... luff you all.
     
    Last edited: 12 Mar 2008
  11. mvagusta

    mvagusta Did a skid that went for two weeks.

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    Someone mentioned this earlier:

    Just imagine the wheels lock/fail/seize due to excessive bearing heat/age/wear/whatever - as long as the motor has enough thrust, the plane will skid along the conveyor belt, like a long handbrake/ebrake/straight drift, and the plane will still take off - need for speed tokyo drift style, so if there are a few neons under the plane, a couple of oversized blow off valves on the motor, and your passengers are petite asain chicks in mini skirts, the plane will take off even faster!
     
  12. chrisb2e9

    chrisb2e9 Dont do that...

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    thats one of the better dumbed down explinations that I have read so far.
     
  13. Mord

    Mord What's a Dremel?

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    Let me try and get my head around this.

    For the plane to take off, it needs air to pass under its wings to generate lift and pull the plane up overcoming gravity.

    When the place is on the Conveyer, the planes propeller pulls it left => and the conveyer reacts by moving right <= or vice versa.

    If the Conveyer matches the planes forward momentum from the propellor (say 2x =>) against ( 2x <=) then there net result equals no forward or rear motion hence no lift, no take off... right?

    But what people are saying is if the propeller eventually increases more then the conveyer is pulling against it, (say 3x =>) against (2x <=) the result will be 1x => and eventual take off.

    Thats the only way I can see any lift being generated from air passing under the wings of the plane. If the conveyer and the propellor are evenly matched, the plan isnt going anywhere let alone up... surely?

    :wallbash::confused:
     
  14. will.

    will. A motorbike of jealousy!

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    Read the damn thread. Several of us have explained this in more than enough detail.

    Here, I did it for you: An explanation for the simpletons

     
  15. mvagusta

    mvagusta Did a skid that went for two weeks.

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    Well i think it's more than clear that the question: "will a plane on a conveyor belt take off?" should be on every IQ test from hereonin :wallbash:

    The plane will go forward mord, just like a seaplane on water - no wheels required, it slides along the water, so who cares what the wheels do on the conveyor!

    edit: I like your original explanation will :thumb:
     
  16. Stickeh

    Stickeh Help me , Help you.

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    Mord, you are correct if you were thinking about a car, as these are what drive a car forward.

    The wheels of a plane just disconnect it from the ground, so as the plane moves forward the wheels just rotate twice as fast as a usual take off, the only thing that would potentially pull it backwards is the friction in the wheels bearings.

    Theres a video on youtube of a guy with his remote control plane on a treadmill, he boosts the treadmills speed up and up and up, and yet he need not increase the power to the propellers of the plane to keep the plane in the same position on the treadmill, so the propellers are doing 1x and yet hes increased the treadmills speed to three or four times the planes take off speed, and all that has happened? The wheels span faster and the plane sat still on the treadmill.

    When he finally did up the throttle the plane had no problem counter-acting the treadmill and flying off the end of it, as it still had the rest of the throttle range to play with.

    See here:http://youtube.com/watch?v=4owlyCOzDiE
     
  17. Nexxo

    Nexxo * Prefab Sprout – The King of Rock 'n' Roll

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    The mistake you guys keep making is to think in vectors. A vector is direction * speed. So you think: plane moves forward at speed v; conveyor belt moves backwards (or in negative direction) at speed v; so the equation is v - v = 0. Plane can't take off.

    But you are WRONG. Because the speed (and hence vector) of the plane is, in the end, a result of the forces acting on it. The engines produce a force F. The conveyor belt produces an equal force in the opposite direction, -F. However (and pay attention now, this is the crucial bit), the engines can transfer their force to the plane very efficiently, by being rigidly physically connected to it. The conveyor belt has to act through its spinning wheels, which is a very inefficient way of transfering its force (as it relies on the tiny bit of friction in the wheel bearings). So the equation is not F - F = 0, but F - tiny F = still a whole lot of F.
     
  18. Oclocker

    Oclocker What's a Dremel?

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    but this only applies to the mythbusters barstardisation - the original scenario i've read/worked on is the treadmill matches wheel speed ! its in effect a paradox - all the headslappers basically are trying to say they can explain it with science - which in the hypothetical original scenario don't work to sciece rules. they say planes thrust will spin wheels twice as fast - but in the scenario the treadmill matches the increased speed of wheels. Is this gonna be possible ? dunno & tbh irrelevant as its probably impossible to prove hence its a conundrum. Just shows science isn't infallible.. or like religion open to miinterpretation.
     
  19. mvagusta

    mvagusta Did a skid that went for two weeks.

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    This explains everything, perfectly:
    [​IMG]
     
  20. chrisb2e9

    chrisb2e9 Dont do that...

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    I somewhat agree and I think the biggest problem here is that people simply misunderstood the question.
    That and anyone who thinks that the thrust that is being produced by the engine is directly causing the wheels to rotate )like in a car), doesn't understand how an airplane works.
     

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