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Thread: Okay Krupski or other knowing people answer this please

  1. #21
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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...
    How does a plane fly? It flies when the air movement is sufficient to provide lift. If the airplane is in the same spot relative to the ground it cannot provide lift. The treadmill is always canceling out any thrust/wheels turning except keeping up with the treadmill.

  2. #22
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    Quote Originally Posted by JTHunter View Post
    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.
    Yes but the latter nuance of NA's post is not material to the question. You are correct, brakes locked the plane would be able to overcome the friction, we're getting side tracked.

  3. #23
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    Quote Originally Posted by alismith View Post
    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.
    My cousin used this example https://www.youtube.com/watch?v=YORCk1BN7QY One. the plane isn't on a conveyor belt, you can clearly see the wheels are in contact with the ground. 2. This doesn't show the speed of their tarp in the reverse direction being the exact opposite of the wheels on the plane.

  4. #24
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    Quote Originally Posted by Full Otto View Post
    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?
    Nope in the hypothetical the treadmill ALWAYS moves at the same exact rate in reverse of the wheels.

  5. #25
    Senior Member Viking350's Avatar

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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.
    Yes!

  6. #26
    Team Guns Network Silver 04/2013 alismith's Avatar

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    This whole situation is screwed up.

    Follow along for a minute.

    Screw the treadmill; screw the plane wheels; screw the wings; screw the engines; screw the plane.

    If you screw it UP enough, the "UP" creates enough lift to make the plane fly.

    So, screw it all up! The plane flies.

    Problem solved.
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  7. #27
    Administrator Krupski's Avatar

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    Quote Originally Posted by Viking350 View Post
    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.

    OK, if the airplane were on a treadmill or conveyor and the airplane brakes were on and the treadmill moved the airplane forward above stall speed, the airplane would lift off the treadmill (and promptly land back down due to no longer having the "thrust" of the treadmill). As in post #14, the airplane would fly - land - fly - land......

  8. #28
    Administrator Krupski's Avatar

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    Quote Originally Posted by alismith View Post
    Without wings, a car can't fly. If it could, there would be a lot of airborne crashes at racetracks.
    I was talking about flying cars with wings.

    1964 homebuilt flying car


  9. #29
    Administrator Krupski's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    How does a plane fly? It flies when the air movement is sufficient to provide lift. If the airplane is in the same spot relative to the ground it cannot provide lift. The treadmill is always canceling out any thrust/wheels turning except keeping up with the treadmill.


    If you look at the shape of a typical aerofoil:





    You see that the top is curved more than the bottom. The air flows over the top and bottom of the wing. Since the TOP flow has further to go, it has to move faster to "keep up". Bernoulli's law says that if the flow is faster, it's pressure must be lower.

    To imagine this, think of a shoulder-to-shoulder crowd of people walking past an aerofoil shape (wing) standing on end. The people on the "top" side of the "wing" have further to walk, so they must speed up in order to keep up with the people on the "bottom" side of the "wing". Since they walk faster, they temporarily move further apart from each other (their density decreases).

    Going back to airflow, decreased density means lower pressure. Therefore, there is a LOW PRESSURE area at the top of the wing. The wings are not pushed up by the airflow, they are SUCKED UP by the low pressure above the wing!

    Ever take an air hose and blow the air straight up and suspend a ping-pong ball on the airstream? This works because the air flowing over the curve of the ball has to speed up as it flows around the ball, creating a low pressure area that pulls on the ball.

    If the ball, say, tries to fall off to the left, the right side is exposed to more airflow, the pressure on the right side gets lower and the ball is "sucked" back into the center. The ball does "dance around" in the stream, but that's just due to turbulence in the airflow. But the ball is always kept inside the "column" of moving air due to Bernoulli's principle.

  10. #30
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    Quote Originally Posted by Krupski View Post
    OK, if the airplane were on a treadmill or conveyor and the airplane brakes were on and the treadmill moved the airplane forward above stall speed, the airplane would lift off the treadmill (and promptly land back down due to no longer having the "thrust" of the treadmill). As in post #14, the airplane would fly - land - fly - land......
    The treadmill is moving the opposite direction of the planes facing.

  11. #31
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    Quote Originally Posted by Krupski View Post
    If you look at the shape of a typical aerofoil:





    You see that the top is curved more than the bottom. The air flows over the top and bottom of the wing. Since the TOP flow has further to go, it has to move faster to "keep up". Bernoulli's law says that if the flow is faster, it's pressure must be lower.

    To imagine this, think of a shoulder-to-shoulder crowd of people walking past an aerofoil shape (wing) standing on end. The people on the "top" side of the "wing" have further to walk, so they must speed up in order to keep up with the people on the "bottom" side of the "wing". Since they walk faster, they temporarily move further apart from each other (their density decreases).

    Going back to airflow, decreased density means lower pressure. Therefore, there is a LOW PRESSURE area at the top of the wing. The wings are not pushed up by the airflow, they are SUCKED UP by the low pressure above the wing!

    Ever take an air hose and blow the air straight up and suspend a ping-pong ball on the airstream? This works because the air flowing over the curve of the ball has to speed up as it flows around the ball, creating a low pressure area that pulls on the ball.

    If the ball, say, tries to fall off to the left, the right side is exposed to more airflow, the pressure on the right side gets lower and the ball is "sucked" back into the center. The ball does "dance around" in the stream, but that's just due to turbulence in the airflow. But the ball is always kept inside the "column" of moving air due to Bernoulli's principle.
    There would no no airstream to provide lift, whatever speed the wheels are moving forward, the treadmill is running backward at the exact speed. The plane would never move, and there would be no airflow in the question I pondered. How does it fly when it essentially never moves from one spot? I'm aware of how lift works, flew a plane as a student pilot, with a student pilot certificate. I'm thinking a couple people including you missed the part that the treadmill is always running the opposite direction as the plane's wheels.
    Last edited by 1 Patriot-of-many; 08-27-2019 at 09:21 AM.

  12. #32
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    [QUOTE=1 Patriot-of-many;486954]There would no no airstream to provide lift, whatever speed the wheels are moving forward, the treadmill is running backward at the exact speed. The plane would never move, and there would be no airflow in the question I pondered. How does it fly when it essentially never moves from one spot? I'm aware of how lift works, flew a plane as a student pilot, with a student pilot certificate. I'm thinking a couple people including you missed the part that the treadmill is always running the opposite direction as the plane's wheels.[/QU

    It really doesn't matter about the treadmill and the wheels. As I pointed out the wheels are free wheeling, like bearings in a machine. They are not mechanically linked to the frame to impart any forward motion. Even sitting on a solid surface, those wheels will not move until thrust is applied. Then all the wheels do is act like bearings between the plane and the runway.
    The same with the conveyor belt, it doesn't matter how fast the conveyor turns in the opposite direction, the wheels are still free wheeling bearings that have nothing to do with imparting movement to the plane. Thrust from the engines propels the plane forward completely independent of what the conveyor does.
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  13. #33
    Team GunsNet Silver 12/2011 N/A's Avatar

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    [QUOTE=1 Patriot-of-many;486954]There would no no airstream to provide lift, whatever speed the wheels are moving forward, the treadmill is running backward at the exact speed. The plane would never move, and there would be no airflow in the question I pondered. How does it fly when it essentially never moves from one spot? I'm aware of how lift works, flew a plane as a student pilot, with a student pilot certificate. I'm thinking a couple people including you missed the part that the treadmill is always running the opposite direction as the plane's wheels.[/QU

    It really doesn't matter about the treadmill and the wheels. As I pointed out the wheels are free wheeling, like bearings in a machine. They are not mechanically linked to the frame to impart any forward motion. Even sitting on a solid surface, those wheels will not move until thrust is applied. Then all the wheels do is act like bearings between the plane and the runway.
    The same with the conveyor belt, it doesn't matter how fast the conveyor turns in the opposite direction, the wheels are still free wheeling bearings that have nothing to do with imparting movement to the plane. Thrust from the engines propels the plane forward completely independent of what the conveyor does.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  14. #34
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    [QUOTE=N/A;486956]
    Quote Originally Posted by 1 Patriot-of-many View Post
    There would no no airstream to provide lift, whatever speed the wheels are moving forward, the treadmill is running backward at the exact speed. The plane would never move, and there would be no airflow in the question I pondered. How does it fly when it essentially never moves from one spot? I'm aware of how lift works, flew a plane as a student pilot, with a student pilot certificate. I'm thinking a couple people including you missed the part that the treadmill is always running the opposite direction as the plane's wheels.[/QU

    It really doesn't matter about the treadmill and the wheels. As I pointed out the wheels are free wheeling, like bearings in a machine. They are not mechanically linked to the frame to impart any forward motion. Even sitting on a solid surface, those wheels will not move until thrust is applied. Then all the wheels do is act like bearings between the plane and the runway.
    The same with the conveyor belt, it doesn't matter how fast the conveyor turns in the opposite direction, the wheels are still free wheeling bearings that have nothing to do with imparting movement to the plane. Thrust from the engines propels the plane forward completely independent of what the conveyor does.
    So if that's the case, why don't we use treadmills instead of catapults or runways to take off? I have yet to see an actual treadmill being used with a plane to prove this theory that it would take off. The wheels are still connected to the ground. Airflow over the and under the wing is what matters. Still not comprehending, Half of people agree it won't fly, another section says it will fly. where does the extra energy come from. As you increase thrust in a plane the wheels move faster, but the treadmill moves in the opposite direction just as fast. The plane never moves relative the ground position.
    Last edited by 1 Patriot-of-many; 08-27-2019 at 10:50 AM.

  15. #35
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    We're not talking about the plane flying; basically the question is how would a treadmill interact with the wheels.

    Take this example. Get a small Timken bearing about the size of a quarter with a 3/16 hole in the center. Put a 6 inch long dowel thru the hole, so you have a "wheel" on an "axle", so to speak. Now walk over to your bench grinder and turn it on. Hold the bearing up to the grinding wheel such that the outer race of the bearing runs on edge of the grinding wheel. The outer race will turn, the inner race will remain stationary. Now move the bearing up and down against the grinding wheel. No matter what you do, the outer race continues to turn while the inner race remains stationary even tho it changes location on the wheel.

    Why? Because the ball bearings between the races isolates the grinding wheel from the inner race.

    The same with the plane. The conveyor belt is the grinding wheel, the landing gear wheels are the bearings with the tires being the outer race. The bearings in the hub mounted to the gear be axle are the bearings and inner race. Thus, the plane is isolated from the conveyor belt much like the small bearing on a stick isolates the stick from the grinding. No matter how fast the grinding wheel turns, you can still push on the stick and move the bearing up or down against the grinding wheel.

    The same is true of the plane. No matter how fast the conveyor belt or wheels turn, the inner race of the wheels isolates the plane from the conveyor and you are free to apply force(thrust) to it and move it "up or down" the conveyor belt.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  16. #36
    Administrator imanaknut's Avatar

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    Yes, forward thrust of the engines is countered by the treadmill running against forward motion. The plane will never fly because no airflow is generated over the wings.

    Like a person running on a treadmill, you never move forward because the treadmill speed, which in this case you control, is moving in the opposite direction keeping you stationary.

    Since the 747 treadmill is directly proportional to wheel speed, the split second the aircraft starts moving forward, the wheels turn causing the treadmill to match that speed in an equal and opposite direction. Like a runner on a treadmill, except in this illustration the treadmill is computer controlled to match tire speed, the faster the wheels turn, the faster the treadmill matches that keeping the aircraft at it's starting point. Assuming a treadmill that can only move in one direction, locking the brakes has no affect as the aircraft won't move, and the neither does the treadmill.

    Given these limitations, a lot of fuel will be used going nowhere.

  17. #37
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    Put some roller skates on, get on a treadmill and see what happens.
    No enemy of America would have ever been killed if they didn't show up to be killed. HDR

  18. #38
    Senior Member NAPOTS's Avatar

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    Are the engines driving it? If so it will just drive right off of the treadmill (and then take off). The thrust doesn't come from the wheels driving it. If not it would need to chained down so it didn't fall off forward or backward off the treadmill (like a car on a dyno). In that case, no lift, no takeoff.

  19. #39
    Administrator Krupski's Avatar

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    Quote Originally Posted by 1 Patriot-of-many View Post
    The treadmill is moving the opposite direction of the planes facing.


    Does not matter.

    If the airplane has takeoff thrust, and it's sitting on a treadmill that matches the wheel speed so that they don't turn, all you're doing is removing the minuscule drag of the wheel bearings and the airplane takes off even easier.

    Remember, the wheels have ABSOLUTELY NOTHING to do with how the airplane flies. It's all airflow over the wings, caused by the engine thrust pushing the airplane forward into the air.

  20. #40
    Administrator Krupski's Avatar

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    Quote Originally Posted by N/A View Post
    Take this example. Get a small Timken bearing about the size of a quarter with a 3/16 hole in the center. Put a 6 inch long dowel thru the hole, so you have a "wheel" on an "axle", so to speak. Now walk over to your bench grinder and turn it on. Hold the bearing up to the grinding wheel such that the outer race of the bearing runs on edge of the grinding wheel...
    My dad was a master tool & die maker and in his younger foolish days, he put a ball bearing in his left index finger and, using a 350 psig air hose, revved it up somewhere past warp factor 9.

    Well, the bearing seized and all that stored energy went into his finger and created the coolest looking spiral fracture ever!

    Worse yet, the bearing got hot before it seized and my dad was torn between ripping the hot bearing off his mangled finger or letting it burn.

    He ripped off the bearing and got dizzy from the pain, but he didn't pass out (so he told me).

    He never went to the doctor, so when his finger healed, it was slightly twisted and slightly crooked.

    You had to see it to believe it... one fingernail about 15 degrees off parallel with the others!

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