Question: Will the plane fly? (warning: nerdy)
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Question: Will the plane fly? (warning: nerdy)
I was asked this by a friend and I thought it was an interesting question.
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
The question is:
Will the plane take off or not?
Lets see how smart SRIC really is
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
The question is:
Will the plane take off or not?
Lets see how smart SRIC really is
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i think it will fly. is it a jet or does it have a propeller?
edit, wait, i thought about it for a second. in order for it to lift off, the wings would need air to lift off. so no, i dont think it will fly. Thats my final answer.
edit, wait, i thought about it for a second. in order for it to lift off, the wings would need air to lift off. so no, i dont think it will fly. Thats my final answer.
Last edited by sytran666; Jan 21, 2006 at 10:06 PM.
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I'll probably be way off but...
I'd think it shouldn't matter. For take off, planes are driven by thrust generated by engines that do not drive the wheels so the fact that a conveyer is moving opposite the direction of the plane shouldn't make a difference. The plane should still be moving along the runway.
right?
I'd think it shouldn't matter. For take off, planes are driven by thrust generated by engines that do not drive the wheels so the fact that a conveyer is moving opposite the direction of the plane shouldn't make a difference. The plane should still be moving along the runway.
right?
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Oh god.
We went through this for like a week on SECCS. We got into all kinds of variants on whether it would be able to establish enough airspeed, based on how quickly the treadmill setup could accelerate to match the speed, etc.
Technically, if the treadmill always matches the speed, it can never move, becuase starting form zero, it could never even get motion to start moving. Therefore the treadmill could never really match the speed, becuase there's never any wheelspeed to match. If it's an actual mechanical system, and the treadmill is infinitely long, theoretically the plane could establish enough momentum and be moving slightly faster than the treadmill, gain forward velocity, and take off, witht he wheels effectively spinning twice as fast as the forward airspeed.
Too many variables if we allow them. Technically, because matching speed would imply that the plane would stay in a fixed postion relative to a reference point off the treadmill, and ignoring a 130mph headwind, you'd never get airspeed (wheelspeed is irrelevant except as a match for the treadmill and an approximation of how fast you have to be moving across the ground), you'd never get flow over the wings, no lift, so you couldn't take off.
The common logic would be that since there's no motive force being applied to the wheels, it can't be held back. The friction coefficient of the wheels to the treadmill ,and how reactive the system is, would determine whether the thrust from the engines could essentially push the plane forward, with the wheels at some point reaching an infinite velocity where the minute speed differential as a function of wheel speed relative to airspeed would allow takeoff velocity.
What's the maximum airspeed of an unladen African swallow?
We went through this for like a week on SECCS. We got into all kinds of variants on whether it would be able to establish enough airspeed, based on how quickly the treadmill setup could accelerate to match the speed, etc.
Technically, if the treadmill always matches the speed, it can never move, becuase starting form zero, it could never even get motion to start moving. Therefore the treadmill could never really match the speed, becuase there's never any wheelspeed to match. If it's an actual mechanical system, and the treadmill is infinitely long, theoretically the plane could establish enough momentum and be moving slightly faster than the treadmill, gain forward velocity, and take off, witht he wheels effectively spinning twice as fast as the forward airspeed.
Too many variables if we allow them. Technically, because matching speed would imply that the plane would stay in a fixed postion relative to a reference point off the treadmill, and ignoring a 130mph headwind, you'd never get airspeed (wheelspeed is irrelevant except as a match for the treadmill and an approximation of how fast you have to be moving across the ground), you'd never get flow over the wings, no lift, so you couldn't take off.
The common logic would be that since there's no motive force being applied to the wheels, it can't be held back. The friction coefficient of the wheels to the treadmill ,and how reactive the system is, would determine whether the thrust from the engines could essentially push the plane forward, with the wheels at some point reaching an infinite velocity where the minute speed differential as a function of wheel speed relative to airspeed would allow takeoff velocity.
What's the maximum airspeed of an unladen African swallow?
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The plane will indeed move and take off because its exerting a thrust force on the air rather than putting its power to the ground through the wheels. The wheels just spin freely and the only thing the conveyer is doing is spinning them twice as fast.
Edit:
Since the prop or turbine exerts force only on the air, the plane WILL move through the air. The wheels are free to spin at any rate they need to in order to keep up with the plane. The only difference in the case of the conveyer is that the wheels will have to spin at twice the rate they normally would on stationary ground. Now since the plane is in fact moving through the air, it generates lift just fine and takes off.
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
Edit:
Since the prop or turbine exerts force only on the air, the plane WILL move through the air. The wheels are free to spin at any rate they need to in order to keep up with the plane. The only difference in the case of the conveyer is that the wheels will have to spin at twice the rate they normally would on stationary ground. Now since the plane is in fact moving through the air, it generates lift just fine and takes off.
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
Last edited by MethodBuilt; Jan 21, 2006 at 11:14 PM.
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Originally Posted by EQ Tuning
The plane will indeed move and take off because its exerting a thrust force on the air rather than putting its power to the ground through the wheels. The wheels just spin freely and the only thing the conveyer is doing is spinning them twice as fast.
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
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Originally Posted by EQ Tuning
The plane will indeed move and take off because its exerting a thrust force on the air rather than putting its power to the ground through the wheels. The wheels just spin freely and the only thing the conveyer is doing is spinning them twice as fast.
Edit:
Since the prop or turbine exerts force only on the air, the plane WILL move through the air. The wheels are free to spin at any rate they need to in order to keep up with the plane. The only difference in the case of the conveyer is that the wheels will have to spin at twice the rate they normally would on stationary ground. Now since the plane is in fact moving through the air, it generates lift just fine and takes off.
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
Edit:
Since the prop or turbine exerts force only on the air, the plane WILL move through the air. The wheels are free to spin at any rate they need to in order to keep up with the plane. The only difference in the case of the conveyer is that the wheels will have to spin at twice the rate they normally would on stationary ground. Now since the plane is in fact moving through the air, it generates lift just fine and takes off.
Anyway... mods please feel free to delete this since it seems its an old topic.
Thanks
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Wasn't trying to say it should be closed, just nothing that it's been gone through and ended in stalemate other places, too
The problem with the 2x hypothesis, is that, while the thrust is acting on the air, not through the wheels, if the treadmill perfectly matches wheelspeed, that implies the wheels can't go any faster than the treadmill. Simple physics means that if the wheels are spinning 130 mph, and the treadmill is moving 130mph at the same time in the opposite direction, there's no net accelerative force, and so the object does not move through space.
In other words, even though the wheels aren't a motive force, if their speed is relative to a treadmill, the whole plane is kept from moving because it's essentially being moved backwards on the treadmill at the same rate it's moving forward, at 0 mph indicated airspeed, which is what we care about.
Then there's other variables. Is this a powered treadmill, or is its movement triggered solely by an opposite force by the object on it? The 0 mph indicated airspeed hypothesis applies if it's powered and actively matching speed. If it's non-powered, and simply reactive, the treadmill will never even move as the plane moves forward, thrusting against the air, because there's no motive force on the wheels that would cause it to move in the opposite direction, meaning the wheelspeed would be the same as airspeed.....so the plane takes off.
The question is worded poorly in the first place (I know you didn't create it) which leaves it open to these alternate hypotheses....
The problem with the 2x hypothesis, is that, while the thrust is acting on the air, not through the wheels, if the treadmill perfectly matches wheelspeed, that implies the wheels can't go any faster than the treadmill. Simple physics means that if the wheels are spinning 130 mph, and the treadmill is moving 130mph at the same time in the opposite direction, there's no net accelerative force, and so the object does not move through space.
In other words, even though the wheels aren't a motive force, if their speed is relative to a treadmill, the whole plane is kept from moving because it's essentially being moved backwards on the treadmill at the same rate it's moving forward, at 0 mph indicated airspeed, which is what we care about.
Then there's other variables. Is this a powered treadmill, or is its movement triggered solely by an opposite force by the object on it? The 0 mph indicated airspeed hypothesis applies if it's powered and actively matching speed. If it's non-powered, and simply reactive, the treadmill will never even move as the plane moves forward, thrusting against the air, because there's no motive force on the wheels that would cause it to move in the opposite direction, meaning the wheelspeed would be the same as airspeed.....so the plane takes off.
The question is worded poorly in the first place (I know you didn't create it) which leaves it open to these alternate hypotheses....
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if the prop/turbine can create enough airflow over the wings to generate enough lift to let the plane take off why do i have to dive my plane to recover from a stall? why are there not just big rollers similar to a car dyno, except free spinning, at the takeoff end of a runway?
if this theory was true why don't aircraft carriers make use of it? why would they waste that much space making a runway? why would they spend so much energy, time, and expense on steam powered catapults? not to mention the danger
if this theory is true the wheels on the airplane WOULD NOT SPIN, the wheels on an airplane ARE NOT POWERED. there is NO CONNECTION between the airplane's engines and it's wheels except for hydralics or other power steering components
if any of you doubt this then go to a local airport and pay $20 for a intro flight, besides it's fun
btw ... are any of you pilots?
edit: i'm dumb and made a stupid assumption:
I was wrong because I was thinking about the situation wrong.
when i first read the question i assumed that the aircraft would be stationary, that the wheels would move and the plane wouldn't. this is the car on a dyno comparrison, that was a wrong assumption.
the aircraft would still move down the runway and thus create the required airspeed and lift.
the aircraft's tires would simply be rolling twice as fast as the aircraft was moving.
this is because the aircraft is generating the force that moves it forward from the prop/turbine, not the tires just as EQ said
this is similar to a seaplane taking off while headed upstream, the water is flowing backwards (according to the plane)
sorry for bein so adamant, it's been a long day here
thanks to sybir for phrasing it so i caught my mistake before having to flame myself.
if this theory was true why don't aircraft carriers make use of it? why would they waste that much space making a runway? why would they spend so much energy, time, and expense on steam powered catapults? not to mention the danger
if this theory is true the wheels on the airplane WOULD NOT SPIN, the wheels on an airplane ARE NOT POWERED. there is NO CONNECTION between the airplane's engines and it's wheels except for hydralics or other power steering components
if any of you doubt this then go to a local airport and pay $20 for a intro flight, besides it's fun
btw ... are any of you pilots?
edit: i'm dumb and made a stupid assumption:
I was wrong because I was thinking about the situation wrong.
when i first read the question i assumed that the aircraft would be stationary, that the wheels would move and the plane wouldn't. this is the car on a dyno comparrison, that was a wrong assumption.
the aircraft would still move down the runway and thus create the required airspeed and lift.
the aircraft's tires would simply be rolling twice as fast as the aircraft was moving.
this is because the aircraft is generating the force that moves it forward from the prop/turbine, not the tires just as EQ said
this is similar to a seaplane taking off while headed upstream, the water is flowing backwards (according to the plane)
sorry for bein so adamant, it's been a long day here
thanks to sybir for phrasing it so i caught my mistake before having to flame myself.
Last edited by knight1833; Jan 21, 2006 at 11:52 PM.
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Originally Posted by sybir
Wasn't trying to say it should be closed, just nothing that it's been gone through and ended in stalemate other places, too
The problem with the 2x hypothesis, is that, while the thrust is acting on the air, not through the wheels, if the treadmill perfectly matches wheelspeed, that implies the wheels can't go any faster than the treadmill. Simple physics means that if the wheels are spinning 130 mph, and the treadmill is moving 130mph at the same time in the opposite direction, there's no net accelerative force, and so the object does not move through space.
In other words, even though the wheels aren't a motive force, if their speed is relative to a treadmill, the whole plane is kept from moving because it's essentially being moved backwards on the treadmill at the same rate it's moving forward, at 0 mph indicated airspeed, which is what we care about.
Then there's other variables. Is this a powered treadmill, or is its movement triggered solely by an opposite force by the object on it? The 0 mph indicated airspeed hypothesis applies if it's powered and actively matching speed. If it's non-powered, and simply reactive, the treadmill will never even move as the plane moves forward, thrusting against the air, because there's no motive force on the wheels that would cause it to move in the opposite direction, meaning the wheelspeed would be the same as airspeed.....so the plane takes off.
The question is worded poorly in the first place (I know you didn't create it) which leaves it open to these alternate hypotheses....
The problem with the 2x hypothesis, is that, while the thrust is acting on the air, not through the wheels, if the treadmill perfectly matches wheelspeed, that implies the wheels can't go any faster than the treadmill. Simple physics means that if the wheels are spinning 130 mph, and the treadmill is moving 130mph at the same time in the opposite direction, there's no net accelerative force, and so the object does not move through space.
In other words, even though the wheels aren't a motive force, if their speed is relative to a treadmill, the whole plane is kept from moving because it's essentially being moved backwards on the treadmill at the same rate it's moving forward, at 0 mph indicated airspeed, which is what we care about.
Then there's other variables. Is this a powered treadmill, or is its movement triggered solely by an opposite force by the object on it? The 0 mph indicated airspeed hypothesis applies if it's powered and actively matching speed. If it's non-powered, and simply reactive, the treadmill will never even move as the plane moves forward, thrusting against the air, because there's no motive force on the wheels that would cause it to move in the opposite direction, meaning the wheelspeed would be the same as airspeed.....so the plane takes off.
The question is worded poorly in the first place (I know you didn't create it) which leaves it open to these alternate hypotheses....
BTW, when I read the question, I assumed the treadmill was matching the speed of the speed of the plane, not the tires directly. Maybe it could have been worded better in that respect, but in the end it really wouldn't matter.
Last edited by MethodBuilt; Jan 22, 2006 at 12:18 AM.