DVINNY
2-time 10K winner
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Excuse me if I am missing the sarcasm, but are you guys really serious?? A wing produces lift from motion relative to the air, not movement relative to the ground or relative to a treadmill. An airplane on a treadmill will not take off by virtue of the belt rolling under it's wheels.
I am going to assume you are all joking and too much studying has killed my sense of humour. Is this like that guy on the radio who pretends to espouse ridiculous beliefs just so listeners will call up in an outraged tizzy, so as to derive a laugh at the people who were taking it all so seriously?
I am going to assume you are all joking and too much studying has killed my sense of humour. Is this like that guy on the radio who pretends to espouse ridiculous beliefs just so listeners will call up in an outraged tizzy, so as to derive a laugh at the people who were taking it all so seriously?
DVINNY
2-time 10K winner
Okay,
I'm really suspecting everyone is PM'ing each other and saying "get on there and tell DVINNY that the plane won't fly, it'll be funny"
^^^ gotta be something like that. You can't be serious that it won't move. Not at this point.
I'm really suspecting everyone is PM'ing each other and saying "get on there and tell DVINNY that the plane won't fly, it'll be funny"
^^^ gotta be something like that. You can't be serious that it won't move. Not at this point.
Oh, ok I see now that I did not understand the question. No, the treadmill should not prevent the airplane from gaining wind speed and taking off. I first thought the question was whether the airplane could take off with no motion relative to the ground simply because it was rolling on the treadmill. lol
DVINNY
2-time 10K winner
Correct ^^^ and an airplane (jet or prop) produces thrust through the air not through the ground via its wheels. It's wheels just roll along freely.
Nope, see above.
Desert Engineer
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I'm with you DV,
The plane will f-ing fly. You could never spin a treadmill fast enough to make the wheels provide enough resistance to overcome the thrust of the prop. Are you guys assuming the treadmill speed goes to infinity or something?
Think about it how little force would it take to make the plane remain stationary on the moving treadmill. I havent done the calculations, but i know it is not that much. The plane is on round wheels not blocks. I know for sure that the thrust of the props is well enough to overcome the resistance of the wheels moving at a higher speed.
The plane will f-ing fly. You could never spin a treadmill fast enough to make the wheels provide enough resistance to overcome the thrust of the prop. Are you guys assuming the treadmill speed goes to infinity or something?
Think about it how little force would it take to make the plane remain stationary on the moving treadmill. I havent done the calculations, but i know it is not that much. The plane is on round wheels not blocks. I know for sure that the thrust of the props is well enough to overcome the resistance of the wheels moving at a higher speed.
cement
gray haired dude
your assertion that the plane will fly only works if you change the rules and state that the conveyor can not keep up.
this discussion is predicated on the fact that the conveyor will match the thrust and prevent the airplane from moving forward.
the plane does not move forward, then no flow over the wings.
it does not take off.
this discussion is predicated on the fact that the conveyor will match the thrust and prevent the airplane from moving forward.
the plane does not move forward, then no flow over the wings.
it does not take off.
Desert Engineer
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Ok, I agree with you that if you could (some how, maybe by removing the wheels completely) make the plane stand still via the conveyor belt, then it wouldn't take off due to lack of air movement by the wings. But, I don’t think that is possible. The rolling/bearing friction will always be negligible compared to the thrust of the motor.
ktulu
Well-known member
WGASA
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cement
gray haired dude
Sschell
Dude?
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DVINNY
2-time 10K winner
The rules are, the conveyor keeps up. No problem.
Conveyor matches the "SPEED" of the airplane, not the thrust. It would have to go MANY MANY times faster than the plane to have the wheel friction match the thrust of the plane. This is where you are missing it. Thrust and Speed are quite different. If the THRUST was matched then Sapper's free body diagram would have equal forces in the horizontal direction, causing the plane to sit still. If the SPEED is matched by the conveyor, then the wheels just spin twice as fast.
cement
gray haired dude
this may be a disagreement between the theoretical and the practical.
when you run on a treadmill, it keeps up with you (or you adjust your speed to stay on)
regardless, there is no forward motion, no apparent wind created by running, so you sweat.
there is a finite amount of thrust provided by the engines, the treadmill is set to match it, and the airplane goes nowhere.
no sweat!
when you run on a treadmill, it keeps up with you (or you adjust your speed to stay on)
regardless, there is no forward motion, no apparent wind created by running, so you sweat.
there is a finite amount of thrust provided by the engines, the treadmill is set to match it, and the airplane goes nowhere.
no sweat!
Ok, I haven't weighed in on this. So let me try (yet) another approach at explaining this in the off chance that DV is not correct in his conspiracy theory.
Let's say we have the plane sitting motionless on the conveyor. Let's say it's a small plane; small enough for a couple of people to easily push around. Now say a couple people off to the side of the conveyor (feet on solid ground) approach the plane, one on either side, and push forward equally on each wing with enough force to overcome friction. Does the plane move relative to the ground?
If you think it does not, please explain what the conveyor is doing to prevent the plane from moving when an external force is applied to it. In order to keep the plane from moving, an opposite force of equal magnitude must be applied. As far as I can see, there is no way for the conveyor to apply this force--if the conveyor moves forward, the plane moves forward with it. If the conveyor does not move, the plane rolls forward. If the conveyor moves backward (as the riddle states), the plane rolls forward with its wheels spinning faster.
If you think the plane does move relative to the ground, then (assuming no wind) it must be moving relative to the air around it as well, which I think we all agree causes lift. If you replace the force applied by the people with the thrust provided by an engine (propeller, turbine or whatever), it will still move--force is force, whether it is applied against the ground or against a fluid. And I think we all agree that if the plane can move forward it can continue to accelerate to takeoff velocity.
Please feel free to voice disagreement with anything above.
Let's say we have the plane sitting motionless on the conveyor. Let's say it's a small plane; small enough for a couple of people to easily push around. Now say a couple people off to the side of the conveyor (feet on solid ground) approach the plane, one on either side, and push forward equally on each wing with enough force to overcome friction. Does the plane move relative to the ground?
If you think it does not, please explain what the conveyor is doing to prevent the plane from moving when an external force is applied to it. In order to keep the plane from moving, an opposite force of equal magnitude must be applied. As far as I can see, there is no way for the conveyor to apply this force--if the conveyor moves forward, the plane moves forward with it. If the conveyor does not move, the plane rolls forward. If the conveyor moves backward (as the riddle states), the plane rolls forward with its wheels spinning faster.
If you think the plane does move relative to the ground, then (assuming no wind) it must be moving relative to the air around it as well, which I think we all agree causes lift. If you replace the force applied by the people with the thrust provided by an engine (propeller, turbine or whatever), it will still move--force is force, whether it is applied against the ground or against a fluid. And I think we all agree that if the plane can move forward it can continue to accelerate to takeoff velocity.
Please feel free to voice disagreement with anything above.
Similar to what I'm trying to illustrate in my post above, the key point is the application of an external force. When you are running on a treadmill, you are applying force against the treadmill itself and you are moving relative to the treadmill but not relative to the surrounding air. The thrust from the plane's engines is not applied to the conveyor, it's applied to the air around the conveyor and thus it moves forward relative to the air.
cement
gray haired dude
^^ My eyes unfurled!
you win.
you win.
Desert Engineer
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^^^ Now that we've come to a consensus... Lets all watch the show, when the plane fails to take off! LOL
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Dark Knight
Silent Guardian
I cannot wait to see the end of this conflict!!!!!!!!!!!!
DVINNY
2-time 10K winner
good explanations mudpuppy. Nicely done.
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