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Thread: Okay Krupski or other knowing people answer this please

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    Guns Network Lifetime Member #2

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    Okay Krupski or other knowing people answer this please

    I've been arguing with my cousin about this, I say it wouldn't fly, he says it will.

    Imagine a 747 sitting on a conveyor(treadmill) as long and wide as a runway. The conveyor is designed to move in the opposite direction at the exact speed of the wheels on the jet. Can the jet take off?


    I say no because the jet will not move relative to the ground if the treadmill moves exactly the opposite direction at the exact speed of the wheels, it will never develop airflow under and over the wings to create lift. It will stay in one place. Anyone?

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    Senior Member Viking350's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    I've been arguing with my cousin about this, I say it wouldn't fly, he says it will.

    Imagine a 747 sitting on a conveyor(treadmill) as long and wide as a runway. The conveyor is designed to move in the opposite direction at the exact speed of the wheels on the jet. Can the jet take off?


    I say no because the jet will not move relative to the ground if the treadmill moves exactly the opposite direction at the exact speed of the wheels, it will never develop airflow under and over the wings to create lift. It will stay in one place. Anyone?
    You are correct. If it were on a treadmill of sorts, there would be no airflow over the wings so no lift would be generated.

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    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by Viking350 View Post
    You are correct. If it were on a treadmill of sorts, there would be no airflow over the wings so no lift would be generated.
    Yup. The airfoil design of the wings uses air pressure to create lift. Ground speed, on a stationary plane, has nothing to do with making the plane fly. The only reason runways work is that the plane is able to travel fast enough for the air to create lift on the wings.

    All a treadmill will do is wear the tires out.....not create lift.
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    Administrator imanaknut's Avatar

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    Very interesting...

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    Team GunsNet Platinum 02/2015 davepool's Avatar

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    yep, air speed not ground speed makes you fly. in my hangliding days there were times when i had zero ground speed, but was flying at 20-25 mph air speed, it;s called static soaring

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    If the jet is not moving forward, then its wheels are not moving/turning. If the wheels are not turning, then the conveyor is not moving either.
    If the wheels can not turn because the conveyor counteracts their forward movement, thus the conveyor can not turn because it neutralized the force that caused it to turn.

    The solution is simple, set the brakes on the wheels, apply full power and slide down the conveyor without the wheels turning.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

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    Senior Member whiskeyman's Avatar

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    Wow.

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    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    I've been arguing with my cousin about this, I say it wouldn't fly, he says it will.

    Imagine a 747 sitting on a conveyor(treadmill) as long and wide as a runway. The conveyor is designed to move in the opposite direction at the exact speed of the wheels on the jet. Can the jet take off?


    I say no because the jet will not move relative to the ground if the treadmill moves exactly the opposite direction at the exact speed of the wheels, it will never develop airflow under and over the wings to create lift. It will stay in one place. Anyone?
    Did your cousin get this idea from Season 1; Episode 6 of The Republic of Doyle?

    The reason I'm asking is that I just saw this same debate in the first part of that episode and was curious about where this came from....

    If so, tell him the bartender was right....there is 0% chance of the jet taking off. Physics won't allow the plane to take off because the conveyor belt doesn't generate lift.
    "Valar morghulis; valar dohaeris."

    "Never say, "gun control" but instead say, "victim disarmament." - L Neil Smith

    Making good people helpless won't make bad people harmless.

    Freedom isn't free.

    "Attitude is the paintbrush that colors our world." TV Series, Haven.

    My Spirit Animal has rabies.

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    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by whiskeyman View Post
    Wow.
    I'm with you on this.....
    "Valar morghulis; valar dohaeris."

    "Never say, "gun control" but instead say, "victim disarmament." - L Neil Smith

    Making good people helpless won't make bad people harmless.

    Freedom isn't free.

    "Attitude is the paintbrush that colors our world." TV Series, Haven.

    My Spirit Animal has rabies.

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    Administrator imanaknut's Avatar

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    Quote Originally Posted by N/A View Post
    If the jet is not moving forward, then its wheels are not moving/turning. If the wheels are not turning, then the conveyor is not moving either.
    If the wheels can not turn because the conveyor counteracts their forward movement, thus the conveyor can not turn because it neutralized the force that caused it to turn.

    The solution is simple, set the brakes on the wheels, apply full power and slide down the conveyor without the wheels turning.
    I believe we have a winner!

  11. #11
    Senior Member JTHunter's Avatar

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    1-Pat, if the conveyor is moving, then the wheels would be moving, as N/A pointed out. BUT, as Viking and Ali pointed out, wheel movement is immaterial. It is the speed of the air moving above and below the wings that control flight. If the conveyor neutralizes any forward motion, regardless of how fast, the plane won't fly.
    N/A - if the brakes are locked so the wheels don't turn, the plane won't fly. Even if the wheels don't scrub off so much rubber that they explode, their friction will prevent the plane from going fast enough to generate the lift necessary for flight.
    “I have little patience with people who take the Bill of Rights for granted. The Bill of Rights, contained in the first ten amendments to the Constitution, is every American’s guarantee of freedom.” - - President Harry S. Truman, “Years of Trial and Hope”

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    Administrator imanaknut's Avatar

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    Actually it says nothing about if the brakes are on, that the conveyor will lock to prevent forward movement. Figure the rollers allow forward movement of the aircraft with locked brakes, but not moving in relation to the wheels, the plane will be able to reach takeoff speed, but the conveyor relative to the wheels will not be moving.

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    Administrator Krupski's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    I've been arguing with my cousin about this, I say it wouldn't fly, he says it will.

    Imagine a 747 sitting on a conveyor(treadmill) as long and wide as a runway. The conveyor is designed to move in the opposite direction at the exact speed of the wheels on the jet. Can the jet take off?


    I say no because the jet will not move relative to the ground if the treadmill moves exactly the opposite direction at the exact speed of the wheels, it will never develop airflow under and over the wings to create lift. It will stay in one place. Anyone?

    The jet moves forward due to the thrust of the engines. The forward motion also causes the landing gear wheels to rotate. If the "treadmill" moved as fast as the jet, the effect would be that the wheels would be stationary, but the airplane would still take off and fly...

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    Administrator Krupski's Avatar

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    Quote Originally Posted by Viking350 View Post
    You are correct. If it were on a treadmill of sorts, there would be no airflow over the wings so no lift would be generated.
    Quote Originally Posted by alismith View Post
    Yup. The airfoil design of the wings uses air pressure to create lift. Ground speed, on a stationary plane, has nothing to do with making the plane fly. The only reason runways work is that the plane is able to travel fast enough for the air to create lift on the wings.

    All a treadmill will do is wear the tires out.....not create lift.
    You miss the point that the only thing that makes the wheels spin is the forward motion of the jet.

    Now, imagine a car with wings that has to drive fast enough to lift off. Driving on the treadmill would make the wheels spin, but the car would have zero motion relative to the air and would not fly. Of course, the car on a road would lose thrust from the wheels as soon as it lifted off and it would come back down to the road in a repeating liftoff - land - liftoff - land cycle.

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    Senior Member Viking350's Avatar

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    I may be overthinking it, but a conveyer belt has its own source of motion. If I walk or run on a treadmill, I feel no air movement on my sweaty face. If there is no relative air movement then no lift could be generated.

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    Team Guns Network Silver 04/2013 alismith's Avatar

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    Quote Originally Posted by Krupski View Post
    You miss the point that the only thing that makes the wheels spin is the forward motion of the jet.

    Now, imagine a car with wings that has to drive fast enough to lift off. Driving on the treadmill would make the wheels spin, but the car would have zero motion relative to the air and would not fly. Of course, the car on a road would lose thrust from the wheels as soon as it lifted off and it would come back down to the road in a repeating liftoff - land - liftoff - land cycle.
    What do spinning wheels on a stationary jet have to do with making it fly? If the jet remains stationary to the air around it, there is no lift created, no matter how fast the wheels are spinning. The jet must move, relative to the air around the wings in order for lift to be created.

    In the "thought game" of the OP, the jet remains stationary relative to the air; only the wheels and conveyor belt are moving opposite to each other. In this case the wheels have absolutely nothing to do with causing the air to move around the wings.

    No air movement means no pressure differences above and below the wings, therefore no lift. No lift means no flying. The jet will just stay on the treadmill with its wheels spinning.

    Without wings, a car can't fly. If it could, there would be a lot of airborne crashes at racetracks.
    "Valar morghulis; valar dohaeris."

    "Never say, "gun control" but instead say, "victim disarmament." - L Neil Smith

    Making good people helpless won't make bad people harmless.

    Freedom isn't free.

    "Attitude is the paintbrush that colors our world." TV Series, Haven.

    My Spirit Animal has rabies.

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    Team GunsNet Silver 12/2011 N/A's Avatar

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    Then the question comes up, "How do you get the 747 on the conveyor belt to start with?"
    If the taxi ways are normal, then the 747 pulls around to the end of the runway, lines up, and then proceeds to pull up on the conveyor belt. s soon as the nose wheels hit the conveyor belt it starts to turn. In this thought experiment, the minute the nose wheels are on the conveyor belt, the belt turns and the wheels can go no farther; but the main landing gear is still sitting on solid runway and can still move forward.
    Thus, you would seem to have a part of the plane that couldn't move forward and part that can still move forward. As Krupski said, it's the engine thrust that propells the plane forward, not the mechanical turning of the wheels like on a car. The planes tires just freewheel, like bearings.
    So, even tho the nose wheels are on the belt, they just freewheel as the 747 continues to taxi onto the conveyor belt. When it comes time to apply thrust for the take off roll, the wheels will just freewheel over the conveyor belt as thrust moves the plane forward. All the conveyor belt will do is match the "speed" of the wheels, but in the opposite direction.

    The only way this could affect the plane is if, like a car, the plane had to get it's forward momentum from mechanically turning the wheels. Otherwise, the wheels are just freewheeling rubber bearings that have no impact on the thrust pushing the plane forward.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

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    Quote Originally Posted by Krupski View Post
    The jet moves forward due to the thrust of the engines. The forward motion also causes the landing gear wheels to rotate. If the "treadmill" moved as fast as the jet, the effect would be that the wheels would be stationary, but the airplane would still take off and fly...
    ? I'm confused by your answer, the conveyor is moving at the exact speed in the opposite direction, that would counteract any forward movement no matter how much thrust was applied as in the OP the treadmill always keeps the same speed in reverse as the rolling wheels.

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    Quote Originally Posted by N/A View Post
    Then the question comes up, "How do you get the 747 on the conveyor belt to start with?"
    If the taxi ways are normal, then the 747 pulls around to the end of the runway, lines up, and then proceeds to pull up on the conveyor belt. s soon as the nose wheels hit the conveyor belt it starts to turn. In this thought experiment, the minute the nose wheels are on the conveyor belt, the belt turns and the wheels can go no farther; but the main landing gear is still sitting on solid runway and can still move forward.
    Thus, you would seem to have a part of the plane that couldn't move forward and part that can still move forward. As Krupski said, it's the engine thrust that propells the plane forward, not the mechanical turning of the wheels like on a car. The planes tires just freewheel, like bearings.
    So, even tho the nose wheels are on the belt, they just freewheel as the 747 continues to taxi onto the conveyor belt. When it comes time to apply thrust for the take off roll, the wheels will just freewheel over the conveyor belt as thrust moves the plane forward. All the conveyor belt will do is match the "speed" of the wheels, but in the opposite direction.

    The only way this could affect the plane is if, like a car, the plane had to get it's forward momentum from mechanically turning the wheels. Otherwise, the wheels are just freewheeling rubber bearings that have no impact on the thrust pushing the plane forward.
    Now we are adding nuances like my cousin. Th OP states the plane is already sitting on the treadmill, and the treadmill always is running in reverse as the speed of the wheels on the jet.

  20. #20
    Senior Member Full Otto's Avatar

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    So the initial thrust of the plane is what gets this whole thing moving?
    In that case wouldn't that thrust always be slightly ahead of the turning of the conveyor belt?
    Would that eventually be enough to get the lift?
    For peace of mind, resign as general manager of the universe

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