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Post by iilforddave on Jul 13, 2009 19:52:51 GMT
[ If the plane was moving at the same speed as the treadmill it would be moving forward! only if the treadmill is on a truck ;D
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Post by neoisd1 on Jul 13, 2009 19:53:28 GMT
A planes engine is independent of its wheels, a plane on a treadmill is the same as you standing on a skateboard on a treadmill. The wheels just spin, but get a friend to push your back you will move forward, the same as a planes engine giving it forward motion. So if the treadmill is going backwards at 100mph and the plane accelerates to 100mph it will be moving forward thus the wind will pass over the wings causing lift and take off...... whooooosh.
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Post by iilforddave on Jul 13, 2009 19:55:30 GMT
A planes engine is independent of its wheels, a plane on a treadmill is the same as you standing on a skateboard on a treadmill. The wheels just spin, but get a friend to push your back you will move forward, the same as a planes engine giving it forward motion. So if the treadmill is going backwards at 100mph and the plane accelerates to 100mph it will be moving forward thus the wind will pass over the wings causing lift and take off...... whooooosh. No see you are actually missing the point of the original question
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Post by beagriestache on Jul 13, 2009 19:57:51 GMT
At the risk of spoiling this fun debate I think I may have worked this out.
There are two answers to this:
1. The wheels of the plane are free-spinning (ie there is no drive to them) so when the conveyor belt detects the increasing speed of the plane (let's not worry about how) and gets faster itself this has no impact on the speed of the plane relative to the treadmill since there is no drive to the wheels which will just spin beneath the plane. Assume that the wheel bearings are frictionless. The plane therefore creeps forward, gathers speed, air passes under the wings, lift is obtained and it takes off.
2. In a theoretical world where the speed of the treadmill can indeed keep pace with the aeroplane (let's not worry about how), the plane is stationary relative to the air beneath its wings, there is no lift and the plane remains grounded.
So you could argue for both and be right. Great question.
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Post by neoisd1 on Jul 13, 2009 20:00:12 GMT
A planes engine is independent of its wheels, a plane on a treadmill is the same as you standing on a skateboard on a treadmill. The wheels just spin, but get a friend to push your back you will move forward, the same as a planes engine giving it forward motion. So if the treadmill is going backwards at 100mph and the plane accelerates to 100mph it will be moving forward thus the wind will pass over the wings causing lift and take off...... whooooosh. No see you are actually missing the point of the original question Not at all! A plane is standing on a runway that is made of a large conveyor belt. The plane fires up its engines, but as it moves forward, the conveyor belt senses the speed of the plane's forward motion and instantaneously moves at exactly the same speed in the opposite direction. Can the plane take off? It doesn't matter how fast the conveyor belt moves! A planes engine provides thrust through the AIR, the wheels will just spin but the propeller will pull it forward through the air. Why is this so hard for people to understand?!!
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Post by beagriestache on Jul 13, 2009 20:00:23 GMT
But then again I may not have.
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Post by beagriestache on Jul 13, 2009 20:05:22 GMT
But how does a plane move forward on a treadmill when its wheels are spinning freely beneath it. When grounded planes move forward as a result of friction between the rubber of their tyres and the runway (as a result of thrust from the engine).
If there is no friction and the plane is not yet flying how does it move forward?
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Post by iilforddave on Jul 13, 2009 20:08:05 GMT
neoisd1: why not read the question again
A plane is standing on a runway that is made of a large conveyor belt. The plane fires up its engines, but as it moves forward, the conveyor belt senses the speed of the plane's forward motion and instantaneously moves at exactly the same speed in the opposite direction
Now think about it, its a hypothetical question, and in this hypocthetical question the plane is ALWAYS stationary to the air, as the treadmill reacts to any change in its speed relative to the treadmill
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Post by neoisd1 on Jul 13, 2009 20:12:31 GMT
But how does a plane move forward on a treadmill when its wheels are spinning freely beneath it. When grounded planes move forward as a result of friction between the rubber of their tyres and the runway (as a result of thrust from the engine). If there is no friction and the plane is not yet flying how does it move forward? I don't know if you're being serious anymore?!! it moves forward by thrust either from a jet engine or a propeller. Think of yourself in some top notch roller skates on a nice treadmill, strap a nice big jet engine to your back, lean forwards a light that baby up ;D which way do you think you will go?
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Post by neoisd1 on Jul 13, 2009 20:16:51 GMT
Dave a plane only requires the ground to pick up enough speed to take of, it doesn't matter if that ground is going backwards as the plane is being propelled through the AIR!! It doesn't matter how much the "conveyor belt senses the forward motion and responds" as the plane is moving through the air!
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Post by beagriestache on Jul 13, 2009 20:21:32 GMT
But the plane isn't in the air and if it's on the ground and there's no friction between it and the ground how does it go forward?
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Post by neoisd1 on Jul 13, 2009 20:25:54 GMT
But the plane isn't in the air and if it's on the ground and there's no friction between it and the ground how does it go forward? The plane isn't in the air no, but it's engine is ;D The engine is pulling the plane forward through the air, the wheels are just spinning!
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Post by Olgrligm on Jul 13, 2009 20:26:25 GMT
Just to create a bit of clarity here,
are we to assume that rather than moving backwards at the same speed as the plane, the treadmill is to exert a horizontal resistive force on the plane via the wheels that will be equal to the forward force enacted by the engine/propeller/thruster/warp engine?
If that is the case, then surely it's a simple case of the horizontal forces being balanced there being no forward motion, resulting in the plane not taking off.
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Post by mermaidsal on Jul 13, 2009 20:30:24 GMT
I don't think I've ever seen a thread show so little early promise then come good, just shows how wrong you can be ;D
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Post by beagriestache on Jul 13, 2009 20:31:11 GMT
Yes, that's been the basis for my argument which I accept is probably hypothetical now if we allow aeroplane wheels to spin frictionlessly.
I see where Neoisd1 is coming from I think.
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Post by Northy on Jul 13, 2009 20:32:24 GMT
transfer this theory to a ships gas propulsion system where the thrust acting on a power turbine acts against a current and water friction, Airspeed is the only thing that matters to an airplane, the speed of the wheels has nothing to do with anything as they will rotate (as you look at them) in a clockwise direction as the thrust of the plane acts from left to right, and the belt right to left. The only influence the runway has on the airplanes normal forward acceleration is that it roughly doubles the amount of rolling friction that the wheels need to overcome. Rolling friction is a small, even negligible, force hardly worth mentioning in comparison to the other forces that aircraft normally overcome to achieve flight. You will need air flowing very quickly over the wings and tail to generate the lift required. The only time an airplane can take off from a slow ground speed is if it was facing into a very very strong headwind.
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Post by neoisd1 on Jul 13, 2009 20:34:42 GMT
Just to create a bit of clarity here, are we to assume that rather than moving backwards at the same speed as the plane, the treadmill is to exert a horizontal resistive force on the plane via the wheels that will be equal to the forward force enacted by the engine/propeller/thruster/warp engine? If that is the case, then surely it's a simple case of the horizontal forces being balanced there being no forward motion, resulting in the plane not taking off. A planes wheels just spin, if it was a car then you would be right, the car would have to keep accelerating to keep up with the conveyor belt but a plane is powered by thrust through air and is in no way affected by how fast it's wheels are going in the opposite direction, as they are just "free spinning".
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Post by Northy on Jul 13, 2009 20:36:49 GMT
I use to work on Rolls Royce Olympus & Tyne gas turbine engines, had a brief spell with Trent and also was offered a job to manage Heathrow's standby power station driven by gas turbines, I didn't take the job and moved back up North
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Post by Beardy200 on Jul 13, 2009 20:44:17 GMT
If EVER we needed Paul Bearer to come and sort something out once and for all it's now ;D C'mon fella, what's the crack?
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Post by mermaidsal on Jul 13, 2009 20:44:52 GMT
How do seaplanes get up enough speed to take off with the extra resistance of water??
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Post by Northy on Jul 13, 2009 20:51:47 GMT
How do seaplanes get up enough speed to take off with the extra resistance of water?? they gain lift and skim across the water
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Post by neoisd1 on Jul 13, 2009 20:51:58 GMT
How do seaplanes get up enough speed to take off with the extra resistance of water?? Great point ;D Like I've said it has nothing to do with the wheels and surface, a plane and it's engine are in the air, the wheels just provide balance (and something to land on ;D ) until the plane picks up enough AIR speed. If the surface it's on is moving backwards it will have no effect on the planes ability to move forward and take off.
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Post by iilforddave on Jul 13, 2009 20:54:44 GMT
How do seaplanes get up enough speed to take off with the extra resistance of water?? through the trust off the engine, same as any other plane. But its already been explained that the plane stays staionary, and its a hypothetical question.... which also explains why the "myth busters" plane took off, as they tried it in reality. But as the original question was for a hypothetical scenario, you have to work within the parameters of that scenario ... and if the plane doesn't move through the air, it doesn't take off
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Post by neoisd1 on Jul 13, 2009 20:56:02 GMT
How do seaplanes get up enough speed to take off with the extra resistance of water?? through the trust off the engine, same as any other plane. But its already been explained that the plane stays staionary, and its a hypothetical question.... which also explains why the "myth busters" plane took off, as they tried it in reality. But as the original question was for a hypothetical scenario, you have to work within the parameters of that scenario ... and if the plane doesn't move through the air, it doesn't take off The plane will move through the air though as it will be moving forward!
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Post by SegaMegaDave on Jul 13, 2009 20:56:32 GMT
NO
Planes are fucking massive.
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Post by neoisd1 on Jul 13, 2009 21:03:28 GMT
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Post by iilforddave on Jul 13, 2009 21:03:46 GMT
The plane will move through the air though as it will be moving forward! OK I will say this ONE MORE TIME ONLY. The original question is a hypothetical scenraio in which there is no way that the plane moves forward relative to the treadmill. WE ALL KNOW IT COULDN'T HAPPEN IN REAL LIFE, all you keep doing is answering a question NOT SET IN A HYPOTHETCIAL SCENARIO. (see funky's myth buster video) How ever neither YOUR answer or the myth buster video are answering the original hypothetical scenario. of course if you tried it in real life the plane would move, but that isn't the question being asked is it.
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Post by neoisd1 on Jul 13, 2009 21:11:28 GMT
The plane will move through the air though as it will be moving forward! OK I will say this ONE MORE TIME ONLY. The original question is a hypothetical scenraio in which there is no way that the plane moves forward relative to the treadmill. WE ALL KNOW IT COULDN'T HAPPEN IN REAL LIFE, all you keep doing is answering a question NOT SET IN A HYPOTHETCIAL SCENARIO. (see funky's myth buster video) How ever neither YOUR answer or the myth buster video are answering the original hypothetical scenario. of course if you tried it in real life the plane would move, but that isn't the question being asked is it. "WE ALL KNOW IT COULDN'T HAPPEN IN REAL LIFE" "of course if you tried it in real life the plane would move" This kids is why you should say no to drugs.
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Post by iilforddave on Jul 13, 2009 21:37:31 GMT
probably used less than you, your the one who's ignoring the hypothetical original question, and deciding your going to answer a question which wasn't asked.
Would the thrust of the planes engines cause it to move faster than this hypothetical plane sized conveyor belt no matter what spead the conveyor belt did ?
well of course it fucking would, but thats not what has been asked ...............
The plane fires up its engines, but as it moves forward, the conveyor belt senses the speed of the plane's forward motion and instantaneously moves at exactly the same speed in the opposite direction. Can the plane take off?
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Post by jonesinamillion on Jul 13, 2009 21:53:33 GMT
The surface of the treadmill is not the substrate that force is being aplied to though? The thrust of the jet is being applied to the air immediatley behind the plane, it would move forward no matter how fast the coveyor was going. The only force being applied to the conveyor is downwards (gravity) from the weight of the plane. The conveyor remains irrelavent to the mass / volume of the earths atmosphere, to which the thrust is being applied to.
So yes it can!
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