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  #451  
Old 11-23-2005, 11:31 PM
mostsmooth mostsmooth is offline
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Default Re: think about this...

for the people who say the plane isnt moving:
the conveyor increases speed to match the wheel speed, if the plane isnt moving, neither would the belt.everybody arguing against the plane talking off has acknowledged in some way the belt moving. the only way the belt moves is if the plane is moving. if the plane is moving, lift will occur.

im no rocket scientist, so i hope pat comes in and splains it better [img]/images/graemlins/cool.gif[/img]
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  #452  
Old 11-23-2005, 11:32 PM
man man is offline
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Default Re: think about this...

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why are the more than one posts?

if there is no wind with respect to the airplane, it will not take off. if there is no wind with respect to the runway, it will take off. lift cannot be generated without wind with respect to the plane. (wind in the negative direction of the plane's orientation.)

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As far as I can tell, the system is impossible. The question seems to state that the plane is not moving wrt to the runnway, but this is not possible given the setup since the jets/props provide thrust and there is no way for the runway to exert an opposite force via the free rolling wheels.

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yeah, but it's an ideal system, so plausibility isn't what we're concerned with. I think the question means to state that the plane does not move with respect to the air, though:
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The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels. There is no wind.

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this of course doesn't make any sense in a strict way of speaking, because the wheels have angular velocity, not retcilinear velocity, but you get the idea. the engines of the plane have nothing to do with the system, though. they exist only as a means of propulsion so that "wind" will be generated with respect to the plane.
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  #453  
Old 11-24-2005, 12:05 AM
fnord_too fnord_too is offline
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Default Re: think about this...

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
why are the more than one posts?

if there is no wind with respect to the airplane, it will not take off. if there is no wind with respect to the runway, it will take off. lift cannot be generated without wind with respect to the plane. (wind in the negative direction of the plane's orientation.)

[/ QUOTE ]

As far as I can tell, the system is impossible. The question seems to state that the plane is not moving wrt to the runnway, but this is not possible given the setup since the jets/props provide thrust and there is no way for the runway to exert an opposite force via the free rolling wheels.

[/ QUOTE ]
yeah, but it's an ideal system, so plausibility isn't what we're concerned with. I think the question means to state that the plane does not move with respect to the air, though:
[ QUOTE ]
The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels. There is no wind.

[/ QUOTE ]
this of course doesn't make any sense in a strict way of speaking, because the wheels have angular velocity, not retcilinear velocity, but you get the idea. the engines of the plane have nothing to do with the system, though. they exist only as a means of propulsion so that "wind" will be generated with respect to the plane.

[/ QUOTE ]

I'm not talking about plausibility, I'm talking about possibility. If the engines are providing thrust, you cannot, as far as I can figure, have the plane not moving in relation to the conveyor belt frame (and thus the wind).

The thing about the wheels having angular velocity only is the real reason for this contradiction if I am thinking about this correctly. There is no way for the conveyor to counter the thrust of the engines so the plane will move forward. If the question said something like "the plane's wheels rest on a conveyor belt that turns with no friction" then the answer is clear, but Ray specificly says:

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The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels

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I don't think there is a reasonable interpretation of that other than the wheels are not moving with respect to the conveyor frame (not considering the angular velocity) and thus the whole plan is stationary with respect to the air. I suppose the plane could be really long and the wheel axels free to move along the length of the plane, but that is quite a stretch.
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  #454  
Old 11-24-2005, 12:14 AM
TBag TBag is offline
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Default Re: Physics graduate from Daryn\'s alma mater\'s answer

[ QUOTE ]
There is a plane (Boeing 777, prop plane, whatever) on a moving, conveyor-type runway. The runway moves in the opposite direction of the plane at the exact same speed as the plane's wheels. There is no wind. Can the plane take off?

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No.

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thats the whole point of a treadmill, so you can run WITHOUT MOVING.

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Now throw rollerskates on and use the handles to pull yourself forward.

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I'm going to expand on this a little. Imagine you're on the treadmill, on roller skates with perfect bearings. Someone is controlling the speed of the treadmill for you, and they keep turning it up. Since you're on frictionless wheels, the speed of the treadmill doesn't affect you, right? Okay, grab hold of the handles now. Imagine that the dude keeps cranking up the speed on the treadmill. Is there any speed he could possibly turn it up to that could stop you from simply pulling yourself forward with the handles if you wanted to?

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people are going to say

"but when you pull yourself forward, the wheels will be going faster than the treadmill" which is partially true

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They'd be wrong. The wheel center is moving at a different speed, but the surface in contact with the treadmill is not, assuming non-slip conditions (which we are). Do I have to draw a picture of this too, when I unleash my fury?

[/ QUOTE ]
You're retarded.
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  #455  
Old 11-24-2005, 02:01 AM
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Default Re: Physics graduate from Daryn\'s alma mater\'s answer

[ QUOTE ]

You're retarded.

[/ QUOTE ]

The plane will fly. End of story.
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  #456  
Old 11-24-2005, 02:05 AM
Slow Play Ray Slow Play Ray is offline
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Default Re: think about this...

final clarification, FBD style:

wheel velocity = conveyor velocity = lim(x) as x -> infinity. this is defined by the OP and the fact that the continual (feedback) acceleration of both is inevitable.

thrust velocity + wheel velocity - conveyor velocity = net velocity

since wheel velocity = conveyor velocity, then net velocity MUST equal thrust velocity

therefore, the plane can take off, as long as thrust velocity is great enough to create lift.
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  #457  
Old 11-24-2005, 02:10 AM
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Default Re: think about this...

ding ding ding, let's move on with our lives. Nice 46 page thread though
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  #458  
Old 11-24-2005, 02:24 AM
fluxrad fluxrad is offline
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Default Re: think about this...

The government should totally use this thread to thin the herd.
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  #459  
Old 11-24-2005, 02:28 AM
milliondollaz milliondollaz is offline
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Default Re: think about this...

SOLVED!!!11

the plane will take off if the conveyor belt gets fast enough. saying that there is no air flow over the wings is retarded. the conveyor belt causes viscous drag on the air above it, and forces the air over the wings corresponding to a velocity profile that is in chapter one of any fluid dynamics book.

it's the same reason your canoe slows down after you row it. if the conveyor belt is acutally going 3000 mph relative to the plane, the air speed right at the edge of the belt is also 3000 mph relative to the plane. (that is a fact, don't debate it.) this speed drops off drastically, but it might be 100 mph by the wing. which would create lift, and the plane would take off and instantly be carried backwards unless it was producing trust of its own.
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  #460  
Old 11-24-2005, 02:59 AM
d10 d10 is offline
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Default Re: think about this...

[ QUOTE ]
final clarification, FBD style:

wheel velocity = conveyor velocity = lim(x) as x -> infinity. this is defined by the OP and the fact that the continual (feedback) acceleration of both is inevitable.

thrust velocity + wheel velocity - conveyor velocity = net velocity

since wheel velocity = conveyor velocity, then net velocity MUST equal thrust velocity

therefore, the plane can take off, as long as thrust velocity is great enough to create lift.

[/ QUOTE ]

I thought we agreed that everyone agreed on the problem and the problems causing the problem? The only thing we're doing now is starting up an argument about whether infinity=infinity+X, where X>0.
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