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Thread: Can this airplane take-off?

  1. #301  
    Forum Masters Degree bit4bit's Avatar
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    Quote Originally Posted by DrCWho
    Consider the laminar flow within the turbulent flow of an object moving at hypersonic velocities...


    They say it used to be a farm,
    Before the motor law.

    Rush- "Red Barjetta"

    Dr. CWho
    What do you mean by laminar flow within a turbulent flow? Laminar flow is a case of steady flow, which is actually the opposite of turbulent flow.
    Chance favours the prepared mind.
     

  2. #302  
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    Quote Originally Posted by Raymond K

    I thought no too, but what if the wheels just sort of slid across the runway and it took off anyways?
    Yeah, if the engine is strong enough to overcome the traction of the wheels and drag them skidding across the conveyor belt up to 70-80 mph, then yes, it could certainly take off.

    Quote Originally Posted by Pong
    Quote Originally Posted by kojax
    First you reach the take off speed, then you get lift, not the other way around.
    Never mind lift or takeoff speeds, just think about whether or not the airplane can move forward despite anything that happens to the wheels.

    Watch this dancer's feet. Imagine giving him a gentle, steady push throughout the performance... with a special effects fan perhaps. LOL.
    It's the same situation. If the wheels don't maintain their hold on the conveyor belt and start skidding, then it's sort of like taking off from a sled in the snow. No reason at all that wouldn't work.

    The question is how much traction the wheels have.


    Quote Originally Posted by DrCWho
    William is correct. Q is correct.

    Consider the conveyor to be an aircraft carrier due W. launching a Hornet due E. with no tail wind nor any catapult. ( A veeeery long carrier :wink: ) Without thrust the aircraft does nothing even though inertia of the westbound motion would tend to pull the "rug" of the carrier deck out from under it. This does not happen because of uniform acceleration of both plane and ship, from initial rest mass, in the westward direction. As soon as the engines provide thrust in the westward direction, the Hornet moves forward and accelerates eastward, sustentation is developed and the Hornet is airborne.

    In the conveyor situation, there is a time lag between the initiation of thrust and the movement of the conveyor. Although it will take longer to attain take-off speed, the plane will win.

    In my first year physics we performed a similar experiment with a train on a moving track. The wheels actually thrust the track in the oposite direction, but there is a time lag, once again, and the train slowly accelerates faster than the track. Friction is the transmitter of the energy, but (as another nameless member would remind us :wink: ) energy losses will be present during the transmission, so the train has the mechanical advantage.


    Dr. CWho
    If there's a delay between the wheels increasing speed and the conveyor being able to match them, that's the same as changing the initial assumptions to include the conveyor belt being slightly slower.

    Under these new assumptions, you would be right, because the wheels are able to move at a different, higher, speed than the conveyor belt. But, throwing that in kind of makes the whole question meaningless.
     

  3. #303  
    Time Lord
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    Maybe if we substitute the props for some other force:

    Set a conveyor belt on a steep incline. Run it up hill, fast. Now place a ball at the top, let go. What happens? Must the ball skid, to accelerate down the conveyor? Does the rotation speed of the ball matter?
     

  4. #304  
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    Kojax,
    There have been many modifications to the oversimplified question. You are correct regarding the skidding. Consider the Curtiss Golden Flyer of the early 1900's vintage, or Kitty Hawk. Much less powerful engines. Pusher models. They used skids before wheels and that had much to do with the absence of runways.

    The conveyor "runway" is absurd to begin with, but one must remember that aircraft wheels are not connected to a drive train. As I mentioned, like the aircraft carrier, say 176,000 lbs of thrust, as in a 747 with Rolls Royce 50,000 lb thrust engines... four of them..., assuming the jet is fully loaded to 175,000 lb capacity, that extra 1000 lbs of thrust will overcome the conveyor energy and move the jet forward. Even if it remains in equilibrium for a while, like the carrier catapult, it will actually lurch forward and require less runway length for takeoff.

    Another example is a dynamometer situation with a drive train providing the energy to drive the roller. If the car is not locked into psition, it will eventually jump off the roller.

    Bit,
    Hi! :-D



    Dr. CWho
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  5. #305  
    Forum Ph.D. Steve Miller's Avatar
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    That's also a little like an attitude to be overcome. Flatten them with still more power, I think. The subject was
    not about that. We can't get no further with simply applying more power.
     

  6. #306  
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    Quote Originally Posted by Pong
    Maybe if we substitute the props for some other force:

    Set a conveyor belt on a steep incline. Run it up hill, fast. Now place a ball at the top, let go. What happens? Must the ball skid, to accelerate down the conveyor? Does the rotation speed of the ball matter?
    In truth, it depends on how fast the conveyor belt is going, and how much angular inertia the ball has.

    Have you ever started a wheel spinning really fast, then thrown it out in front of you and had it roll back to you? The ground is trying to stop it from spinning, but the wheel has so much angular momentum that it rolls back to you anyway.

    Same principle here, only it's the conveyor belt that's trying to make the ball start spinning and the ball's lack of angular momentum that is resisting the spin.
     

  7. #307  
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    Quote Originally Posted by DrCWho
    William is correct. Q is correct.

    Consider the conveyor to be an aircraft carrier due W. launching a Hornet due E. with no tail wind nor any catapult. ( A veeeery long carrier :wink: ) Without thrust the aircraft does nothing even though inertia of the westbound motion would tend to pull the "rug" of the carrier deck out from under it.
    No it wouldn't. Inertia would keep both plane and ship moving together. The rug pulling effect only happens with acceleration.
    This does not happen because of uniform acceleration of both plane and ship, from initial rest mass, in the westward direction.
    You mean uniform motion, not uniform acceleration.
    As soon as the engines provide thrust in the westward direction, the Hornet moves forward and accelerates eastward, sustentation is developed and the Hornet is airborne.

    In the conveyor situation, there is a time lag between the initiation of thrust and the movement of the conveyor. Although it will take longer to attain take-off speed, the plane will win.
    How do you know what the time lag would be? It wasn't specified. It was only stated that the runway matches the speed of the wheels in the other direction.

    In my first year physics we performed a similar experiment with a train on a moving track. The wheels actually thrust the track in the oposite direction, but there is a time lag, once again, and the train slowly accelerates faster than the track.
    Nonsense. There is no time lag in this situation. If the moving track is thrust back by the train, the train will move forward exactly at the same instant. It is called conservation of momentum. Surely you encountered the principle of conservation of momentum sometime during your doctoral studies. (snicker snicker)
    Friction is the transmitter of the energy, but (as another nameless member would remind us :wink: ) energy losses will be present during the transmission, so the train has the mechanical advantage.
    Friction has nothing to do with mechanical advantage.
    You are correct regarding the skidding. Consider the Curtiss Golden Flyer of the early 1900's vintage, or Kitty Hawk. Much less powerful engines. Pusher models. They used skids before wheels and that had much to do with the absence of runways.
    The Wright plane had a launching rail that was actually a kind of catapult. It wasn't taking off against the friction of skids on the sand. The Curtis Golden Flyer had wheels, or at least all the pictures I found on the internet did.
    The conveyor "runway" is absurd to begin with,
    At last, something I can agree with.
    assuming the jet is fully loaded to 175,000 lb capacity, that extra 1000 lbs of thrust will overcome the conveyor energy and move the jet forward.
    How do you know that?
     

  8. #308  
    Forum Masters Degree bit4bit's Avatar
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    ..Oh gosh, turnip farming here we come...
    Chance favours the prepared mind.
     

  9. #309  
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    I give up. So I believe the plane can take off, and get to think I'm smarter. Woo hoo.

    What this thread proves, is, the general lack of teaching ability. We all fail.
     

  10. #310  
    Forum Ph.D. Steve Miller's Avatar
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    I do think it's about the test site, which can not be set up as was asked for. That's the inherent problem to the whole issue.

    It's so dum cuz it's so clear. ---> How could a plane take off which does not move?
     

  11. #311  
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    No it wouldn't. Inertia would keep both plane and ship moving together. The rug pulling effect only happens with acceleration.
    I suppose you are discounting the difference in mass of the ship and the plane. The jest on a carrier aren't moored just for looks...

    You mean uniform motion, not uniform acceleration.
    I meant what I said. Study first year physics.

    {quote]How do you know what the time lag would be? It wasn't specified. It was only stated that the runway matches the speed of the wheels in the other direction. [/quote]

    I repeat. Study first year physics. Specifically friction. It can be deduced if you begin crunching numbers. In fact it would difficult to avoid it.

    Nonsense. There is no time lag in this situation. If the moving track is thrust back by the train, the train will move forward exactly at the same instant. It is called conservation of momentum. Surely you encountered the principle of conservation of momentum sometime during your doctoral studies. (snicker snicker)
    I repeat. STUDY first year physics. You may actually want to do the experiment, if you are so capable. (LOL@U) The train is retarded (RU?) for a moment then catches up, just like a real locomotive. The wheels on a real locomotive slip and slide on the track before forward inertia is developed. Maybe if you wake up [early enough] and cach a "Litle House" episode or two you'll see that in action...


    Friction has nothing to do with mechanical advantage.
    Harold, honey... we're back to a diatribe again. You may look at model railroad and airplane books and c&p from Wiki, but understanding what you see is simply not present in you. Like I said, in another thread, anyone, it seems, can become a forum "top gun" by making enough posts. It would be more venerable to see that happen by a display of understanding. Good luck with all that.

    BTW... I haven't looked at a pic of a Golden Flyer in probably 40 years or more. You may be right about that, but I believe there were more than one model of the same basic plane. Best of my recollection, the first of these had no wheels. Granted skids were early on, but the point is made the same. Go S&D somewhere else, but get your understanding in synch with your "knowledge" before coming at me.



    What this thread proves, is, the general lack of teaching ability. We all fail.
    Well, Pong... there's some truth in that, but what do you expect on a board that has built in difficulties for directly posting graphics. That's why I'm building my site in MSN. Hard to beat their graphics and they've tightened up control of the garbage over the years...

    Good luck.
    Darwin's Law
    Nature will tell us a lie if she can.

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    So will Darwinists

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  12. #312  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by Steve Miller
    It's so dum cuz it's so clear. ---> How could a plane take off which does not move?
    "It's so dumb because it's so clear." ---> How can the wheels (which were initially at rest, as was the conveyor) start to rotate if the plane doesn't move forward?!
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  13. #313  
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    Quote Originally Posted by DrCWho
    No it wouldn't. Inertia would keep both plane and ship moving together. The rug pulling effect only happens with acceleration.
    I suppose you are discounting the difference in mass of the ship and the plane. The jest on a carrier aren't moored just for looks...

    You mean uniform motion, not uniform acceleration.
    I meant what I said. Study first year physics.
    If you meant what you said, I gave you more credit than you deserved. Doc, you would do well to read the words of Galileo on uniform motion. Nobody's ever expained it better before or since.

    http://en.wikipedia.org/wiki/Galileo's_ship

    I repeat. Study first year physics.
    You need a new comeback, Doc. That one is wearing thin.
     

  14. #314  
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    Quote Originally Posted by william
    Quote Originally Posted by Steve Miller
    It's so dum cuz it's so clear. ---> How could a plane take off which does not move?
    "It's so dumb because it's so clear." ---> How can the wheels (which were initially at rest, as was the conveyor) start to rotate if the plane doesn't move forward?!
    Because the conveyor runs >>backwards>>!
     

  15. #315  
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    Good point, William. Do you suppose the question itself has insufficient criteria?


    Here's another example...

    At the equator, the Earth rotates at 1043.11 MPH due east. Let's say the wind is so nil the windsock hangs like Harold's proverbial C elegans while he's desperately searching for his Viagra supply. The aircraft has a static air takeoff velocity of 450MPH and it is due west. The "conveyor belt" terrain of the planet is traveling more than double the forward velocity of the plane. We know beyond a shadow of doubt the plane will take off.

    End of discussion.


    Dr. CWho
    Darwin's Law
    Nature will tell us a lie if she can.

    Bloch's extension to Darwin's Law:
    So will Darwinists

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  16. #316  
    Forum Ph.D. william's Avatar
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    I lost all concentration after this:


    Quote Originally Posted by DrCWho
    ... Let's say the wind is so nil the windsock hangs like Harold's proverbial C elegans while he's desperately searching for his Viagra supply. ...

    Sorry Harold, but that was kind of funny. (Although I don't want to offend you.)


    As a side thought, I'm sure someone will comment on the gale-force winds that would represent their willy....


    Cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  17. #317  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by Steve Miller
    Quote Originally Posted by william
    Quote Originally Posted by Steve Miller
    It's so dum cuz it's so clear. ---> How could a plane take off which does not move?
    "It's so dumb because it's so clear." ---> How can the wheels (which were initially at rest, as was the conveyor) start to rotate if the plane doesn't move forward?!
    Because the conveyor runs >>backwards>>!
    Not until it senses the wheels moving >>forward>>!
    (...didn't I say the conveyor is initially at rest...? )

    Steve, you fail to understand the subtlety of this conundrum....
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  18. #318  
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    Harold,

    I'll apologize ahead of the winds...

    I don't dislike you, but it seems as though you are an avid model builder that is taking on an aircraft designer. I suggest you get a book by Von Karman on aerodynamics called... well... "aerodynamics." It was required reading for me in 1973.

    I quit smoking over 23 years ago, so I have no problems with ED. From your avatar, I estimated you are about 68 or in your early 70's, so I hope you took no serious offense.

    You did mention you had some BPD symptoms and I'd hate to imagine you outdoors with a hooded guaust, entranced with evil utterances, issuing forth some winged bat of the night seeking out my very heartbeat.

    They're predicting some wild storms here for tomorrow...



    William,

    When you mentioned "unique method...et hoc genus omne," (In PM) do you think that would be relative to an x<SUB>1</SUB>, x<SUB>2</SUB> linear system where the solutions create

    l<SUB>1</SUB> and l<SUB>2</SUB> intersecting within +x<SUB>1</SUB>, +x<SUB>2</SUB> as both l<SUB>1</SUB> and l<SUB>2</SUB> progress positive to x<SUB>2</SUB>?

    Ya think?

    Dr. CWho
    Darwin's Law
    Nature will tell us a lie if she can.

    Bloch's extension to Darwin's Law:
    So will Darwinists

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  19. #319  
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    Quote Originally Posted by DrCWho
    Harold,

    I'll apologize ahead of the winds...
    No need to apologize. I take no offense, but on the other hand I'm here for the science and have no interest in those other topics you want to discuss.
    I don't dislike you, but it seems as though you are an avid model builder that is taking on an aircraft designer. I suggest you get a book by Von Karman on aerodynamics called... well... "aerodynamics." It was required reading for me in 1973.
    No, no model builder. I just have an internet account and know how to do google searches. It's real easy to look stuff up nowadays, which makes it harder for a BS'er to blow smoke and get away with it.
    Anybody can log onto an internet forum and claim to be whatever they want. It don't mean a thing. People are going to figure out what they know or do not know.
     

  20. #320  
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    Quote Originally Posted by DrCWho
    Good point, William. Do you suppose the question itself has insufficient criteria?
    No, actually I think he didn't suppose, but I did.

    Quote Originally Posted by DrCWho
    At the equator, the Earth rotates at 1043.11 MPH due east. Let's say the wind is so nil the windsock hangs like Harold's proverbial C elegans while he's desperately searching for his Viagra supply. The aircraft has a static air takeoff velocity of 450MPH and it is due west. The "conveyor belt" terrain of the planet is traveling more than double the forward velocity of the plane. We know beyond a shadow of doubt the plane will take off.

    End of discussion.


    Dr. CWho
    Ah... and that's why helicopter and harrier take off? An airplane should not have to accelerate to take off
    if it was relevant for them too.

    Quote Originally Posted by william
    Steve, you fail to understand the subtlety of this conundrum....
    No I think I don't! I think there was more of it in even.
     

  21. #321  
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    Ah... and that's why helicopter and harrier take off? An airplane should not have to accelerate to take off
    if it was relevant for them too.
    You've obviously never flown either. I've never flown a Harrier. The principles, regarding force vectors, are similar, but the chopper (which doesn't fly on paper mind you... 'cept on mine :wink: There's that darn Omega factor again... Any concept of what Omega means in this situation?) uses the rotary wing to "beat the air into submission," as the standard accepted theory.

    The chopper has a cyclic. If you have ever watched one take off from a moving surface, i.e. the AC, it mimics the bumble bee in hovering backwards first, then tips it nose to scoot forward. I've never done the backwards hover. It's tough enough to feel the antitorque rotor to keep the tail from overspin on sustentation. If you can't handle rubbing your tummy, patting your head, jumping up and down, blowing a bubble with some Bazooka Joe and taking in your favorite TV show at the same time, you'll likely end up with centresis induced vertigo... :-D

    Harold,

    Web surfing has its good points and so do you. I appreciated you finding that so-called PM device in my intro thread. You were going after a "Seek & destroy" mission, but actually you helped my research. I'd been plugging in the wrong key words. Sometimes a monkey can do things that amaze a befuddled researcher.
    With all those posts, you must not have much else to do... As for me, I'm busy writing a treatise on gravity and temporal frames. It'll be months before I'm ready to put it online at my "Just Out of the Box" site in MSN, so be so advised that "Snickers" is my favorite candy bar... I devour them with Freudian enthusiasm... :wink:

    You might try that druid ghaust and the incantations sometime... it's amazing what can happen to an inexperienced magician... :wink: Some end up in mental wards... Hmmmm... is


    that why you have so much time on your hands? BPD... Well, take your meds...


    Dr CWho
    Darwin's Law
    Nature will tell us a lie if she can.

    Bloch's extension to Darwin's Law:
    So will Darwinists

    http://groups.msn.com/JUSTOUTOFTHEBOX
     

  22. #322  
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    Quote Originally Posted by Steve Miller
    Quote Originally Posted by DrCWho
    Good point, William. Do you suppose the question itself has insufficient criteria?
    No, actually I think he didn't suppose, but I did.
    Well, thank you Steve Miller for explaining what I did and didn't suppose.




    Quote Originally Posted by Steve Miller
    Quote Originally Posted by william
    Steve, you fail to understand the subtlety of this conundrum....
    No I think I don't! I think there was more of it in even.

    I'm sure you feel that you don't, but you indeed fail to see the conundrum. When I said the conveyor is initially at rest, you responded that it is moving backward. So, in your mind I suppose, conveyors can be motionless and move backward at the same instant.
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  23. #323  
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    Well, I want to point to the sample where one person was on the belt grabbing a rope and an other one
    would try to pull him off the belt.

    This was math. When the belt started running, in this sample, so did the wheels of the rollerblades he was
    wearing. The threads calling would have been answered.

    At the moment the person being off the belt starts pulling on the rope the number of rotations of the blades
    wheels will increase, whereas the number of rotations of the belt will remain the same. That means, when
    the friend has pulled his friend of the belt the number of rotations of the blades wheels, or even the velocity
    of the blades wheels, must have been greater as the number of rotations or the velocity of the belt.

    There also was no difference if the belt would run faster at some point, thus, so would the blades wheels,
    plus the rotations from pulling the rope.

    Therefore I referred to the sum. The sum of the actions of the wheels of the blades must have been greater
    than that of the belt. Otherwise the person on the belt can not get closer to his friend assuming he still was
    being on the blades.

    The thread but asks for the number of rotations/speed/velocity of the wheels of the plane and the belt to
    equal! not the sum of either one side to be greater.

    What do you mean by saying the belt was at rest first. The belt and the wheels of the plane do match
    speeds.

    Perhaps you've got something wrong?
     

  24. #324  
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    Quote Originally Posted by Steve Miller
    What do you mean by saying the belt was at rest first. The belt and the wheels of the plane do match
    speeds.

    Perhaps you've got something wrong?

    Well, at the beginning of the experiment, the airplane engines are off (or idling, but with the brakes on), and the plane is sitting motionless on the conveyor. (You can interpret this as the experiment having not begun yet.) If the plane is motionless, then so are its wheels. Since the wheels are motionless, as you have stated - the conveyor matches the wheels - then the conveyor is also motionless.


    Cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  25. #325  
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    hi william,

    well, that's being correct.
     

  26. #326  
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    Quote Originally Posted by Steve Miller
    Well, I want to point to the sample where one person was on the belt grabbing a rope and an other one
    would try to pull him off the belt.

    This was math. When the belt started running, in this sample, so did the wheels of the rollerblades he was
    wearing. The threads calling would have been answered.

    At the moment the person being off the belt starts pulling on the rope the number of rotations of the blades
    wheels will increase, whereas the number of rotations of the belt will remain the same. That means, when
    the friend has pulled his friend of the belt the number of rotations of the blades wheels, or even the velocity
    of the blades wheels, must have been greater as the number of rotations or the velocity of the belt.

    There also was no difference if the belt would run faster at some point, thus, so would the blades wheels,
    plus the rotations from pulling the rope.

    Therefore I referred to the sum. The sum of the actions of the wheels of the blades must have been greater
    than that of the belt. Otherwise the person on the belt can not get closer to his friend assuming he still was
    being on the blades.

    The thread but asks for the number of rotations/speed/velocity of the wheels of the plane and the belt to
    equal! not the sum of either one side to be greater.
    Steve, it has taken 22 pages but The Science Forum has finally come up with the perfect answer to the question. I don't see how anybody could argue with your logic. If anybody else posts on this topic, I think I will tell them to go see Steve Miller's post on page 22. This should end all debate. But it won't because people will just keep on posting, without reading the correct answer on page 22.
     

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    hmm...

    i'm no expert on the subject of aviation, but i do think that although the engines provide thrust pushing the plane forward, the conveyor belt would match the rotation of the tires moving forward. the engines are not what pushes the plane upward (that is, if we are thinking of a conventional airplane, like a boeing 757 for example)

    relative to something not on the conveyor belt (such as the air around the plane's wings) the plane is not moving at all.

    since moving air is required to push up underneath the air planes wings to give it lift so it can fly, this plane would not fly, because relative to the air, the plane is not moving.

    therefore, the plane will not take off.

    ----------------

    that's my answer. the purpose of science is to discuss, debate, and disprove. so long as there is something left that falls within these categories, the post will continue.

    steve miller pointed out that there may be something wrong or incomplete with the actual question, and there very well may be.

    in any case, i just wanted to join in and give my two pennies
     

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    Quote Originally Posted by platinum
    that's my answer. the purpose of science is to discuss, debate, and disprove. so long as there is something left that falls within these categories, the post will continue.
    There is nothing left.
     

  29. #329  
    Forum Ph.D. Steve Miller's Avatar
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    Thank you Harold!

    I am pleased you enjoyed reading the post, although, I wasn't expecting your cheering reaction.

    Steve
     

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    Quote Originally Posted by Steve Miller
    Thank you Harold!

    I am pleased you enjoyed reading the post, although, I wasn't expecting your cheering reaction.

    Steve
    Steve, here is why your post made me so happy. It is so simple and obvious, yet I could not think of saying it that way.

    I kept thinking about some super conveyor that could turn at infinite speed and destroy the wheels. That is so unnecessary. Just build a regular conveyor, perhaps big enough for Piper Cub. Let the plane go ahead and take off. Did the plane win? No, it broke the rules of the thread. Just count the revolutions of the wheels!
     

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    Quote Originally Posted by william
    Quote Originally Posted by Steve Miller
    What do you mean by saying the belt was at rest first. The belt and the wheels of the plane do match
    speeds.

    Perhaps you've got something wrong?

    Well, at the beginning of the experiment, the airplane engines are off (or idling, but with the brakes on), and the plane is sitting motionless on the conveyor. (You can interpret this as the experiment having not begun yet.) If the plane is motionless, then so are its wheels. Since the wheels are motionless, as you have stated - the conveyor matches the wheels - then the conveyor is also motionless.


    Cheers
    Quote Originally Posted by Harold14370
    There is nothing left.
    Before we call this thread dead, someone needs to explain how the wheels can start to rotate without the plane moving forward.


    Cheers,
    william
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  32. #332  
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    Harold,

    thank you again. Yes I think that's the right answer.

    william,

    as for my perception, the wheels start to rotate when the planes jets are providing sufficient thrust. The conveyor
    senses the rotation of the planes wheels, matches the speed to the opposite direction, and thus, negates any forward
    motion of the plane. I think that's what's gonna happen as all was working as was asked for.

    Steve
     

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    Quote Originally Posted by Steve Miller
    william,

    as for my perception, the wheels start to rotate when the planes jets are providing sufficient thrust. The conveyor
    senses the rotation of the planes wheels, matches the speed to the opposite direction, and thus, negates any forward
    motion of the plane. I think that's what's gonna happen as all was working as was asked for.

    Steve
    Steve, here is where we disagree. When the conveyor starts going in the opposite direction, it does not negate the forward speed of the plane. It just makes the wheels spin faster and faster while the plane continues ahead. So now we have to start thinking again about a super infinite speed conveyor that destroys the wheels. That's where I didn't want to have to go. Rather, I think we have a stalemate. When the plane starts to move, already we are outside the conditions specified in the thread, because the conveyor cannot ever catch up.
     

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    Quote Originally Posted by william
    ...at the beginning of the experiment, the airplane engines are off (or idling, but with the brakes on), and the plane is sitting motionless on the conveyor. (You can interpret this as the experiment having not begun yet.) If the plane is motionless, then so are its wheels. Since the wheels are motionless, [and] the conveyor matches the wheels - then the conveyor is also motionless.

    Quote Originally Posted by william
    Before we call this thread dead, someone needs to explain how the wheels can start to rotate without the plane moving forward.

    Quote Originally Posted by Harold14370
    When the conveyor starts going in the opposite direction, it does not negate the forward speed of the plane. It just makes the wheels spin faster and faster while the plane continues ahead. So now we have to start thinking again about a super infinite speed conveyor that destroys the wheels. That's where I didn't want to have to go. Rather, I think we have a stalemate. When the plane starts to move, already we are outside the conditions specified in the thread, because the conveyor cannot ever catch up.

    Yes! This is exactly what I was getting at.

    The conveyor can never catch up.
    Harold said it best;
    When the plane starts to move, already we are outside the conditions specified in the thread, because the conveyor cannot ever catch up.
    The problem, as posed, is unphysical. The conveyor can't match the wheels' rotation.

    In an ideal case (no friction, etc.) the plane takes off. From a real world standpoint, it depends on friction, engine thrust, etc.


    Thank you Harold.

    Now...
    I think we can finally lay this problem to rest.


    Cheers,
    william


    P.S. Look at the "N.B." of my first post on page 1.
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

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    I'm sorry william, I still want to add some thoughts to the thread.

    Harold,

    the conveyor will not further accelerate the planes wheels! This only will happen as it runs faster than
    the wheels. The result was the belt moving the plane backwards.

    Therefore the belt senses the speed of the wheels, the plane will stay where it was.

    It depends on where the energy came from, and if the situation will change if it was reckoned. I think if
    the belt accelerates the wheels further, the plane will move backwards.

    When the jets will accelerate the plane and thus the wheels, the plane will move forward. It's being
    due to the wheels are not directly connected to neither the energy of either of one side (the belt or
    the jets ), but do spin freely. It's being al little odd but it's true, actually.

    The sole difficulty was to reach an actual equilibrium of the planes wheels and the belt.

    Steve
     

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    Quote Originally Posted by Steve Miller
    I'm sorry william, I still want to add some thoughts to the thread.

    Harold,

    the conveyor will not further accelerate the planes wheels! This only will happen as it runs faster than
    the wheels. The result was the belt moving the plane backwards.
    I don't follow you here, Steve. As you said yourself, the roller skater holding onto the rope does not go backwards, and can go forward as his friend pulls him along. The wheels spin faster as the belt turns faster. You said it yourself.
     

  37. #337  
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    Yes Harold, and I still think that was true, although I don't see how was the thread answered therewith.

    Sure, pulling on the rope was like the jets providing energy to further accelerate the wheels of the blades
    or the airplane respectively. Same in both situations was, the additional energy was not added by the belt.

    Additionally, the whole issue has become rather static since a fixed link to a fixed spot off the belt was
    established. I mean the belt could run as fast as was wanted (as long as it was not being destroyed ), the
    energy provided by pulling the rope simply was added to the rotation of the blades wheels even if caused
    by the belt. This was to be differed between in both samples.

    Further, in this sample (the rope sample ) it wasn't asked for sensing the speed of the wheels or the belt,
    thus, they will never match, and even if it's not relevant since the goal was to pull your friend off of the belt,
    not to let him stick to where he was.

    But, this was my interpretation of the threads calling. The set up of the construction was thought to let
    the plane stick to where it was, although, energy was provided by the engines to be started.

    The belt and the plane are being at rest firstly. The jets are started --> the wheels, initially trying to roll, are
    sensed (they have to roll a little, otherwise, how to sense anything ). The belt running backwards (afterwards )
    will not prevent the wheels from rolling, but the plane from moving forward since the belts motor will only
    provide energy in an according amount.

    I do understand the test site as if it was thought to not let the plane roll to gain the speed which was
    necessary for it to take off.

    So the goal for the plane was not to get off the belt, but to stay on the same position. Additional energy in
    form of rotation also was not provided to move the plane backwards, which would accelerate the wheels
    further, but an compensative energy was added by the belt.

    Interestingly now II wonder if the planes wheels are slowed down by the belt actually or do they need to run
    faster. We should not, by mistake, do blend the possible speed of the plane, of the wheels or of the belt.

    To apply mathematical terms here, would be, perhaps, conclusive.
     

  38. #338  
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    Oh please, would someone do an experiment on this just to put this to rest. I can't believe this has taken up 23 pages already. No wonder nothing gets done in the western world.
    Life is 10% what happens to you and 90% how you react to it.
     

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    Prove it in practical application. Otherwise to find the BS you only have to look at your own work.

    I suggest you find a good RC model builder who can build both plane and runway, then take some undoctored videos and post them. Till then, you are throwing your monkey feces at us...
    Darwin's Law
    Nature will tell us a lie if she can.

    Bloch's extension to Darwin's Law:
    So will Darwinists

    http://groups.msn.com/JUSTOUTOFTHEBOX
     

  40. #340  
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    Quote Originally Posted by GrowlingDog
    Oh please, would someone do an experiment on this just to put this to rest. I can't believe this has taken up 23 pages already. No wonder nothing gets done in the western world.
    Quote Originally Posted by DrCWho
    Prove it in practical application. Otherwise to find the BS you only have to look at your own work.

    I suggest you find a good RC model builder who can build both plane and runway, then take some undoctored videos and post them. Till then, you are throwing your monkey feces at us...
    Somewhere way back in this thread, a few people have posted links to the mythbusters video. Here it is again:


    Part 1:
    http://www.youtube.com/watch?v=MuXK1nr9_jg

    Part 2:
    http://www.youtube.com/watch?v=U9STo3fjfGg
    Chance favours the prepared mind.
     

  41. #341  
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    Well, the whole episode in above links seem to have been removed for copyright, but heres the important bits:

    http://www.youtube.com/watch?v=S377HwOthjo

    http://www.youtube.com/watch?v=0ul_5DtMLhc

    The theory agrees, the experiment agrees....it takes off.
    Chance favours the prepared mind.
     

  42. #342  
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    Quote Originally Posted by DrCWho
    Prove it in practical application. Otherwise to find the BS you only have to look at your own work.

    I suggest you find a good RC model builder who can build both plane and runway, then take some undoctored videos and post them. Till then, you are throwing your monkey feces at us...
    I don't fully understand what you are saying, but in case you address me, I think it's clear. The plane
    won't take off. What else do you regard as an scientific approach other than to shine a light at all aspects
    of the issue one could think of? To shut down the thread, the forum, the internet and all platforms providing
    this spaces of freedom to the community, at best?

    Research yields results by trial and error, and that's what I was trying to do.
     

  43. #343  
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    Well, as stated before, a test is only a test if it models the stated contiditons accurately. The mythbusters modeled one interpretation of the condition, but not the one we are talking about now. What we are discussing is when the conveyor moves in a direction with respect to earth equal and opposite to the speed of the plane with respect to the conveyor.

    Steve, suppose the belt is driven by rollers of the same diameter as the wheels. Now if the plane (or roller skater) is held in a fixed position, the wheels are going the same speed as the conveyor belt rollers. This is true no matter the speed of the conveyor. Any movement of the plane forward and this condition, which is the condition stated at the beginning of the thread, is no longer true. The game is over.
     

  44. #344  
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    Quote Originally Posted by Harold14370
    Any movement of the plane forward and this condition [that the conveyor matches the wheels], which is the condition stated at the beginning of the thread, is no longer true. The game is over.

    And in order for the conveyor to start to move, the plane must move forward.

    Hence, the problem as posed in unphysical. The conveyor can't match the wheels.

    As Harold said, the game is over.


    Cheers,
    william
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
     

  45. #345  
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    Harold,

    a very nice metaphor, but you object with your own statement. When the plane or else are held at the same
    position and the belt and so the wheels? are not being at rest, conditions asked for are true. That's how I do
    understand the threads claim.

    Steve
     

  46. #346  
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    [spam deleted]
     

  47. #347  
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    That's bad. I get so promising mails I do delete normally. Should I forward them to you instead?
    Still better was, if you got to know the sender could you swap my email address for yours? Only
    if they (the emails ) did help you.

    Thank you.

    (edited )
     

  48. #348  
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    Quote Originally Posted by Steve Miller
    I'm sorry william, I still want to add some thoughts to the thread.

    Harold,

    the conveyor will not further accelerate the planes wheels! This only will happen as it runs faster than
    the wheels. The result was the belt moving the plane backwards.

    Therefore the belt senses the speed of the wheels, the plane will stay where it was.

    It depends on where the energy came from, and if the situation will change if it was reckoned. I think if
    the belt accelerates the wheels further, the plane will move backwards.

    When the jets will accelerate the plane and thus the wheels, the plane will move forward. It's being
    due to the wheels are not directly connected to neither the energy of either of one side (the belt or
    the jets ), but do spin freely. It's being al little odd but it's true, actually.

    The sole difficulty was to reach an actual equilibrium of the planes wheels and the belt.

    Steve
    It would merely be the weight of the wheels, and the conveyer belts ability to move fast enough, to use the weight of the wheels to keep the plane from moving. If the plane was under its own power. But it would only be the weight of the wheels holding the plane back. The conveyor would have to keep increasing in speed. Till the wheels blew apart.


    If the conveyer was moving air along with the belt. The plane would still take off.
    Like the earth moves air along with its surface. Even though the surface is going something like 1500+ feet a second. If you stopped a plane, on the earths surface while the plane was facing east. It would instantly take off providing the elevator, flaps were up.

    Sincerely,


    William McCormick
     

  49. #349  
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    However, sticking to the ip's scope there can't be conditions of which the plane would fly.
     

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    Paradox!
     

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    To help everyone conceptualize this experiment visually, imagine a Macro-Treadmill. This treadmill would be 100s of kilometers long and 100s of kilometers wide.
    We place a conventional Boeing 747 directly at the center of the treadmill's belt.
    To make things even easier, lets also assume this treadmill is not powered by a motor but rather spins in result to the forward motion.

    Sorry, this is the best picture I could find -

    Take that treadmill for instance, and super-size it. This way, there is no confusion about when or how the treadmill (conveyor belt) neutralizes the forward motion because in this way, the forward motion itself induces the backwards motion.

    So will that plane take off if it was placed on a giant version of that treadmill?

    My hypothesis: Not in the 'real' world. The tires would burn to rubble (friction) and the plane would slowly melt down to ashes and the thrusters might just fly away for a second (if they somehow fall off the plane) because they are pushing against air and the down force of gravity will be overcome the few seconds they are falling ...... only to crash into something.

    However, here is where the 'realistic' hypothesis begins to collapse on itself. Lets replace the conveyor belt with a man-made river of water. We can control the direction and speed of the water's flow. Put a Water-Plane on that river with skis as landing gear instead of tire. By doing that we have the exact same situation without friction. Will the plane take off in this experiment? Definitely.
     

  52. #352  
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    no, your replacement experiment adds considerably MORE friction. Water is much more powerful at preventing movement than the friction of the wheels.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

     

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    Err, how about we turn that water to ice and landing gear to blades. I know you understand the point I'm trying to 'convey'. haha
     

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    I do, but either way, the point stands that With friction, at a high enough amount, the plane won't take off. if the friction is low, it will take off. The only question is; how much friction will the wheels have?
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

     

  55. #355  
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    They'll have as much friction as there was thrust and opposite motion of the belt.
     

  56. #356  
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    After 24 pages, is there anything new to say? No, but I will repeat. It depends on how you interpret the problem statement.

    Is the runway measuring the speed of the plane with respect to earth, and matching that speed by moving the same speed, relative to earth, in the opposite direction? If so, the plane reaches takeoff speed with the runway moving at the same speed in the other direction, so the wheels spin twice as fast as normal. No problem, except the plane may blow a tire.

    Or is the runway measuring the speed of the wheels relative to the runway itself? Then if the plane speeds up to say 1 mph, the runway has to go 1 mph in the other direction. This means the plane gains another 1 mph relative to the runway, without gaining any more air speed. Repeat. It's a positive feedback loop, and a runaway condition occurs. Something is going to break, real fast.
     

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    not necessarily, maybe the wheels will achieve a speed at which the friction will be great enough in the bearings that the speed can not increase further, and that the plane can move forward, despite the friction.

    True, the 24 pages are redundant, I've read about 4 of um and figured it would be the same throughout. But still, gotta love the results of the poll.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

     

  58. #358  
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    Quote Originally Posted by Steve Miller
    They'll have as much friction as there was thrust and opposite motion of the belt.
    That's just flat out not true.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

     

  59. #359  
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    As Harold14370 has said, it is entirely up to the what the conditions of the original question really are. That being said, all possible conditions have been covered and the is nothing new to be said about this. Since there is no sense in flogging a dead horse, I am locking the thread.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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