The "Aeroplane on treadmill" conundrum...
Why do it if it's not fun?
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Ok, I've decided not to follow my own advice, and I've not yet got my hat.
For those who don't get the idea that the prop moves the aircraft through the air, and not through the ground, here's an analagy:
Thing of the prop like a screw, and the air like a nut. Now you have an aeroplane with a screw on the front of it, with its wheels on a conveyor belt. The first two or three threads of the screw are already inserted into the nut.
As the screw turns, it will move forwards into the nut. This will cause the wheels to start turning, but the conveyor will move in the oposite direction, in an attempt to hold the aeroplane back. But no matter how fast the conveyor moves, the screw, if it continues turning, will continue to pull the aircraft forwards into the nut, and there's nothing the conveyor can do to stop it.
So yes, the aircraft will move.
FFF
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For those who don't get the idea that the prop moves the aircraft through the air, and not through the ground, here's an analagy:
Thing of the prop like a screw, and the air like a nut. Now you have an aeroplane with a screw on the front of it, with its wheels on a conveyor belt. The first two or three threads of the screw are already inserted into the nut.
As the screw turns, it will move forwards into the nut. This will cause the wheels to start turning, but the conveyor will move in the oposite direction, in an attempt to hold the aeroplane back. But no matter how fast the conveyor moves, the screw, if it continues turning, will continue to pull the aircraft forwards into the nut, and there's nothing the conveyor can do to stop it.
So yes, the aircraft will move.
FFF
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Long lie down over.
Tex, TKF and Distaff - thank you for saying that you too cannot see the emperor's new suit - I thought I was alone.
I'm never going to understand how the aircraft ever moves through the air if it can never move over the gound at all so I've made a decision.
DON'T CARE DON'T CARE DON'T CARE
Tex, TKF and Distaff - thank you for saying that you too cannot see the emperor's new suit - I thought I was alone.
I'm never going to understand how the aircraft ever moves through the air if it can never move over the gound at all so I've made a decision.
DON'T CARE DON'T CARE DON'T CARE
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Has anyone actually watched the video which proves that the plane will move forward?
Here it is again for any that missed it.
watch it carefully. The plane will fly.
http://videos.streetfire.net/player....D-D6BA1A43A06B
Here it is again for any that missed it.
watch it carefully. The plane will fly.
http://videos.streetfire.net/player....D-D6BA1A43A06B
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Join Date: Oct 2001
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Originally Posted by Yorks.ppl
Has anyone actually watched the video which proves that the plane will move forward?
Here it is again for any that missed it.
watch it carefully. The plane will fly.
Here it is again for any that missed it.
watch it carefully. The plane will fly.
It appears to show that the fan on wheels moves forward, due to the conveyor belt not moving as fast in the opposite direction.
Then AFTER it runs off the end of the conveyor, it continues to move forward.
So, it DOES show that something on non-driven wheels, propelled by a fan, will move forward. (Just like an SEP on its take-off roll, really).
It DOES NOT show that it will fly!
D-B
As puzzled as before, but now a fully paid up member of the "Emperer's New Clothes Society" and the "Flat Earth Society"
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"due to the conveyor belt not moving as fast in the opposite direction."
I rather thought it looked to me like the belt was moving faster in the opposite direction so the non flyers will think it should move backwards.
Of course, it doesn't matter a jot either way, you can pull the paper as fast as you like, the fan will still move forward .
I rather thought it looked to me like the belt was moving faster in the opposite direction so the non flyers will think it should move backwards.
Of course, it doesn't matter a jot either way, you can pull the paper as fast as you like, the fan will still move forward .
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Anyone got a treadmill and a small toy car at home?
Treadmill = our fancy conveyor belt runway.
Small toy car = pretend that's our aircraft.
Your Hand = pretend that's the result of the force between the aircrafts engines and the air.
Place the little car on your conveyor belt, hold it so it doesn't move relative to a fixed point off the treadmill, and turn the treadmill on. The wheels will spin, but the car shouldn't "move" because you're holding it in place. This is akin to the force of the aircrafts engines overcoming the relatively tiny amount of friction within the wheels that would cause it to be moved backwards by the treadmill runway.
Now try to push the car up the treadmill...lo' and behold, it IS possible
The force applied by your hand is similiar to the force caused by the aircraft engines. The air has no relation to the treadmill because they are not attached, just like your hand is not attached to the treadmill. If the aircraft engines cause a greater force to be applied via the air, than the conveyor belt can due to the tiny amount of friction in the wheels, the aircraft WILL move forward relative to the air, or any fixed point off the conveyor belt.
With the engines off, the only thing which would cause the aircraft to move back on this conveyor belt runway, is friction within the wheel bearings. To move relative to the air on the conveyor belt runway, the aircraft must be able to overcome this frictional force - if it couldn't, how could any aircraft taxi on normal ground?
The misconception here is that the motive force and the "backwards" force by the conveyor belt are being applied through the same medium - the wheels. This is true in the case of a CAR, where the car engine may not be able to keep up with the conveyor belt. In an aircraft, where the motive force is applied via the air, the wheels can spin as fast as they like - the frictional force in the wheels will be so small that the force applied to the air by the engines will easily overcome it and the aircraft will move forwards. It will fly!
Treadmill = our fancy conveyor belt runway.
Small toy car = pretend that's our aircraft.
Your Hand = pretend that's the result of the force between the aircrafts engines and the air.
Place the little car on your conveyor belt, hold it so it doesn't move relative to a fixed point off the treadmill, and turn the treadmill on. The wheels will spin, but the car shouldn't "move" because you're holding it in place. This is akin to the force of the aircrafts engines overcoming the relatively tiny amount of friction within the wheels that would cause it to be moved backwards by the treadmill runway.
Now try to push the car up the treadmill...lo' and behold, it IS possible
The force applied by your hand is similiar to the force caused by the aircraft engines. The air has no relation to the treadmill because they are not attached, just like your hand is not attached to the treadmill. If the aircraft engines cause a greater force to be applied via the air, than the conveyor belt can due to the tiny amount of friction in the wheels, the aircraft WILL move forward relative to the air, or any fixed point off the conveyor belt.With the engines off, the only thing which would cause the aircraft to move back on this conveyor belt runway, is friction within the wheel bearings. To move relative to the air on the conveyor belt runway, the aircraft must be able to overcome this frictional force - if it couldn't, how could any aircraft taxi on normal ground?
The misconception here is that the motive force and the "backwards" force by the conveyor belt are being applied through the same medium - the wheels. This is true in the case of a CAR, where the car engine may not be able to keep up with the conveyor belt. In an aircraft, where the motive force is applied via the air, the wheels can spin as fast as they like - the frictional force in the wheels will be so small that the force applied to the air by the engines will easily overcome it and the aircraft will move forwards. It will fly!
But surely the original question stated that the conveyor belt tracked the aircraft's speed and adjusted the speed of the belt to match. Therefore the aircraft would never move forwards, therefore it would have no airspeed, therefore the emperor is naked.
Something like that, anyway.
Something like that, anyway.
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Why I am bothering I do not really know but for heaven's sake, read the question - quoted below:
"An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off?"
(a) Nowhere does it say the conveyor goes at the same speed as the plane. (b) It says the plane taxies - which most of us interpret to mean that it moves relative to the air it sits in and so also relative to the ground/earth upon which the conveyor's base and mechanism stand, because with low friction wheels that is just what it will do when acted upon by the force of its propellor pushing air backwards.
Chris N.
"An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off?"
(a) Nowhere does it say the conveyor goes at the same speed as the plane. (b) It says the plane taxies - which most of us interpret to mean that it moves relative to the air it sits in and so also relative to the ground/earth upon which the conveyor's base and mechanism stand, because with low friction wheels that is just what it will do when acted upon by the force of its propellor pushing air backwards.
Chris N.
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the conveyor belt tracked the aircraft's speed and adjusted the speed of the belt to match. Therefore the aircraft would never move forwards, therefore it would have no airspeed, therefore the emperor is naked.
It doesn't matter how fast the conveyor belt moves beneath the aircraft, as the only way the conveyor belt can move the aircraft backwards is due to the small amount of friction within the wheel axles. If the engines provide enough force in the opposite direction (remember the force is being applied via the air!! not the wheels) to overcome this tiny amount of friction (which they do so whilst beginning to taxi on normal ground every day!) then the plane can move relative to the air.
If you watch the video above, it is easy to see...the fan is applying the force via the air. It doesn't matter what speed the paper "conveyor belt" is moving at, as long as the force on the air by the fan is enough to overcome the friction within the wheels (it MUST be enough else aircraft would never be able to taxi!).
Try the thing with the toy car and the treadmill again. It doesn't matter how fast you set the treadmill - it is still possible to apply great enough force with your hand to move the car opposite to the direction of the treadmill belt. The net effect of this movement is simply that the wheels spin faster than they would if the car wasn't moving - the spinning becomes a component of the cars forward motion, and the belts rearward motion. This force from your hand is exactly the same as the force applied by the engines of a plane, in that it is a force on an object outwith the treadmill (the air or your hand).
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I am completely amazed how long this discussion goes on, in this forum and Jet blast and all of the other places. It amazes me even more that on a site for aviators that the idea of how an aeroplane works can confuse them. There have been some excellent explainations as to why the aircraft will fly and it WILL take off and fly. To debate it this far down the line beggars belief.
The conveyor belt acting on the wheels is a completely different system to the jet engines acting on the air. The conveyor belt will stop the aircraft moving forward as much as it will slow down a low flying aircraft that flies over it. Actually, why a low flying aircraft? just make it an aircraft.
It has essentially no effect on it.
Why the problem?
If you're flying at 60 knots into a 60 knot headwind what is your ground speed? ZERO. Why has the plane not crashed? Because ground speed has nothing to do with how an aircraft flies.
If an aircraft gained it's speed through driving it's wheels, as soon as it lifts off it would lose speed and land/crash. It pushes air not ground.
The conveyor belt acting on the wheels is a completely different system to the jet engines acting on the air. The conveyor belt will stop the aircraft moving forward as much as it will slow down a low flying aircraft that flies over it. Actually, why a low flying aircraft? just make it an aircraft.
It has essentially no effect on it.
Why the problem?
If you're flying at 60 knots into a 60 knot headwind what is your ground speed? ZERO. Why has the plane not crashed? Because ground speed has nothing to do with how an aircraft flies.
If an aircraft gained it's speed through driving it's wheels, as soon as it lifts off it would lose speed and land/crash. It pushes air not ground.
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If an aircraft gained it's speed through driving it's wheels, as soon as it lifts off it would lose speed and land/crash. It pushes air not ground.
It will fly (in my humblest of opinions...I am not a professional physicist or anything ).
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Is this for real?
Unless there is movement of air over and under the leading edges of the flying surfaces at a speed in excess of the aircrafts stall speed the aircraft will not fly.
The conveyor belt can be moving at 1000 kts and the aircrafts wheels can be turning at 1000 kts but, if there isn't sufficient airflow over and under the wings, the aircraft will not fly. (unless its a Harrier, JSF etc)
Try taking a small model a/c to LGW or similar and try it on a travelator! If the aeroplane has sufficient airflow over the relevant surfaces, in excess of its stall speed, it will fly, if it dosen't, it wont get off the ground (travelator).
Someone give it a go on the early shift!
Unless there is movement of air over and under the leading edges of the flying surfaces at a speed in excess of the aircrafts stall speed the aircraft will not fly.
The conveyor belt can be moving at 1000 kts and the aircrafts wheels can be turning at 1000 kts but, if there isn't sufficient airflow over and under the wings, the aircraft will not fly. (unless its a Harrier, JSF etc)
Try taking a small model a/c to LGW or similar and try it on a travelator! If the aeroplane has sufficient airflow over the relevant surfaces, in excess of its stall speed, it will fly, if it dosen't, it wont get off the ground (travelator).
Someone give it a go on the early shift!
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The conveyor belt can be moving at 1000 kts and the aircrafts wheels can be turning at 1000 kts but, if there isn't sufficient airflow over and under the wings, the aircraft will not fly. (unless its a Harrier, JSF etc)
What you say above is technically correct, because for the wheels to be spinning at the exact same speed as the conveyor belt, the aircraft must be stationary relative to the ground/air. You must realise that once the aircraft moves forwards relative to the ground/air, the wheels will spin FASTER than 1000kts, if the belt is going at 1000kts.
Try taking a small model a/c to LGW or similar and try it on a travelator! If the aeroplane has sufficient airflow over the relevant surfaces, in excess of its stall speed, it will fly, if it dosen't, it wont get off the ground (travelator).
1. The engine is left off/idling and the travelator builds up speed slowly enough that the friction within the wheels is not overcome. The model a/c moves backwards with the travelator.
2. The engine is powered up JUST ENOUGH that the frictional force within the wheels is overcome and the aircraft remains stationary relative to the air/any fixed point. This is exactly what would happen when the aircraft taxis on normal ground, except in this case, the wheels don't spin because of the aircraft going forwards - they spin because of the travelator belt going backwards underneath.
3. The engine is throttled up to full power, or any power setting beyond that used in outcome 2, above. The force applied between the propellor and the AIR is great enough to overcome the frictional force within the wheels, AND propel the aircraft itself forwards through the air. The wheels spin at the speed of the conveyor belt, PLUS the speed of the aircraft moving forwards. The aircraft easily takes off.
The ONLY thing allowing the conveyor belt to move the aircraft backwards is the friction within the aircrafts wheels and axles. As soon as this friction is overcome, the aircraft is able to move forwards just like any other taxying aircraft on normal, stationary ground! The only difference would be the wheels spinning at a greater speed -which DOES NOT MATTER because the motive force is applied via the air. The wheels only spin at this speed because they are free-spinning, and able to - NOT because an engine is making them (Not directly anyways...the increased speed is of course a component of the engine moving the rest of the aircraft forward).
The aircraft will fly!
UNBELIEVEABLE!
Yet strangely irresistable.
Friction on axles/bearings is a tiny percentage of the net force trying to prevent an aircraft accelerating. (Which is, mainly, mass)
True, on many light singles, you need a burst of power to start moving, then ground idle will usually suffice. This is due more to the tyres, which are slightly flat at the bottoms, and is called rolling resistance. Once they've started turning, rolling resistance rapidly decreases. A lot.
For the conveyer to respond to the aircraft movement (which of course, it will, at pretty much normal acceleration) it would have to rapidly spin up to close to infinity. Some conveyor! I suggest most structures wouldn't be up to the challenge. But, hypothetically (gee, you think?) if one could, tyre resistance might just be caused to increase sufficiently to prevent the engine thrust from accelerating the aircraft to takeoff speed. This would be accompanied by startling noises of tyres blowing out in overspeed, and chunks of rubber scattering like missiles. Best viewed from afar.
Yet strangely irresistable.
Friction on axles/bearings is a tiny percentage of the net force trying to prevent an aircraft accelerating. (Which is, mainly, mass)
True, on many light singles, you need a burst of power to start moving, then ground idle will usually suffice. This is due more to the tyres, which are slightly flat at the bottoms, and is called rolling resistance. Once they've started turning, rolling resistance rapidly decreases. A lot.
For the conveyer to respond to the aircraft movement (which of course, it will, at pretty much normal acceleration) it would have to rapidly spin up to close to infinity. Some conveyor! I suggest most structures wouldn't be up to the challenge. But, hypothetically (gee, you think?) if one could, tyre resistance might just be caused to increase sufficiently to prevent the engine thrust from accelerating the aircraft to takeoff speed. This would be accompanied by startling noises of tyres blowing out in overspeed, and chunks of rubber scattering like missiles. Best viewed from afar.
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Hi Folks
I am still not convinced either way on this one, so I have just looked at the video again.
It appears that the strip of paper being used as the 'conveyor belt' is being moved right to left, thus moving in the same direction as the skate-board wheels' rotation.
If so, wouldn't this help the skate-board 'aeroplane' move left to right, instead of opposing it?
D.B. - now terminally puzzled!
I am still not convinced either way on this one, so I have just looked at the video again.
It appears that the strip of paper being used as the 'conveyor belt' is being moved right to left, thus moving in the same direction as the skate-board wheels' rotation.
If so, wouldn't this help the skate-board 'aeroplane' move left to right, instead of opposing it?
D.B. - now terminally puzzled!
DB
I'm confused, too. To contradict my previous post it seems that, sadly, I do care.
Before anybody thinks they have to point it out I know that an aircraft pulls or pushes itself through the air, not along the ground. I know that the thing that makes aeroplanes fly is relative airflow over the wings but my, probably somewhat befuddled, thinking went thus:
1. Aircraft in contact with conveyor belt.
2. Aircraft pulls (or pushes) itself forwards through the air
3. Coveyor belt moves backwards therefore opposing this forward motion
4. Return to 2.
So, the aircraft never has any motion through the air because every time it moves forwards the belt moves it back. It never has enough airspeed to leave its contact with the belt, it never flies. I don't give a stuff about wheel friction or any other nebulous nonsense, it just doesn't move itself through the air because each time it tries it's moved backwards.
Probably a load of rubbish, though.
Can't understand any more than that - might just have to go rotary then I don't care what the bloody conveyor belt does.
I'm confused, too. To contradict my previous post it seems that, sadly, I do care.
Before anybody thinks they have to point it out I know that an aircraft pulls or pushes itself through the air, not along the ground. I know that the thing that makes aeroplanes fly is relative airflow over the wings but my, probably somewhat befuddled, thinking went thus:
1. Aircraft in contact with conveyor belt.
2. Aircraft pulls (or pushes) itself forwards through the air
3. Coveyor belt moves backwards therefore opposing this forward motion
4. Return to 2.
So, the aircraft never has any motion through the air because every time it moves forwards the belt moves it back. It never has enough airspeed to leave its contact with the belt, it never flies. I don't give a stuff about wheel friction or any other nebulous nonsense, it just doesn't move itself through the air because each time it tries it's moved backwards.
Probably a load of rubbish, though.
Can't understand any more than that - might just have to go rotary then I don't care what the bloody conveyor belt does.