It's a mute point - the plane obviously goes backwards without making a sound.
Mythbusters plan to uncover plane on conveyor belt
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Last: 5 yr ago by toucan82
Okay, let me try this angle. If a plane's engines push on the air at 100 mph while on a conveyor belt that is moving 100 mph in the opposite direction, then the plane's motion relative to the ground is 0 mph. Yes?
So if air passing at high speed and downward movement of air speeding over the wings is crucial for a plane to LIFT off the ground, how is this achieved when a plane thrusting forward on a conveyor belt has no air speeding over and under its wings?
[This message has been edited by Kempster (edited 10/24/2007 9:53p).]
So if air passing at high speed and downward movement of air speeding over the wings is crucial for a plane to LIFT off the ground, how is this achieved when a plane thrusting forward on a conveyor belt has no air speeding over and under its wings?
[This message has been edited by Kempster (edited 10/24/2007 9:53p).]
Doesn't matter. My brain hurts.
Dreaded Double Post.
[This message has been edited by Kempster (edited 10/24/2007 9:52p).]
[This message has been edited by Kempster (edited 10/24/2007 9:52p).]
Dreaded Double Post.
[This message has been edited by Kempster (edited 10/24/2007 9:52p).]
[This message has been edited by Kempster (edited 10/24/2007 9:52p).]
Do we have an answer yet on MythBusters?
the mythbusters episode doesn't air until December.
Here is a video to help you guys out
http://www.youtube.com/watch?v=-EopVDgSPAk
Here is a video to help you guys out
http://www.youtube.com/watch?v=-EopVDgSPAk
No the FORCE is moot.
Kemp Elementary...
No, you are making bad assumptions...
you are assuming that the conveyor moving at -100 mph has any effect on the engines putting out enough thrust to push the plane at 100 mph...
this invalid assumption makes a connection between bodies that have no connection...(let the jokes begin). This is why you failed physics.
There is also no normal force while a plane is in flight...
Once again, I stand by my claim that it depends on how you interpret the problem...if the conveyor is reacting to the wheel speed of the plane, catastrophic failure will be the result. If the conveyor is simply reacting to the ground speed of the plane the wheels will simply be going twice their normal (non conveyor) speed.
quote:
Okay, let me try this angle. If a plane's engines push on the air at 100 mph while on a conveyor belt that is moving 100 mph in the opposite direction, then the plane's motion relative to the ground is 0 mph. Yes?
No, you are making bad assumptions...
you are assuming that the conveyor moving at -100 mph has any effect on the engines putting out enough thrust to push the plane at 100 mph...
this invalid assumption makes a connection between bodies that have no connection...(let the jokes begin). This is why you failed physics.
There is also no normal force while a plane is in flight...
Once again, I stand by my claim that it depends on how you interpret the problem...if the conveyor is reacting to the wheel speed of the plane, catastrophic failure will be the result. If the conveyor is simply reacting to the ground speed of the plane the wheels will simply be going twice their normal (non conveyor) speed.
Well I'll be a monkey's uncle! Simplified, you're right.
The penny finally dropped - the plane is driven by force applied to the air, not the ground. (D'oh!)
The penny finally dropped - the plane is driven by force applied to the air, not the ground. (D'oh!)
TexasRebel, you are right. I stand corrected.
simplified
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the conveyer is EVERYTHING
People who say the plane can take off aren't following the assumptions. If the plane is actually going to move forward then the conveyor is not moving the same speed as the plane.
Look at the skateboard example... you can hold yourself in place but then when you pull yourself forward you admit the wheels are spinning twice as fast... well then the conveyor should be spinning twice as fast too, keeping you in place (to meet the assumptions in the example)
I think the question is really asking if a plane can take off while remaining stationary... not can you make a plane go faster than a conveyor belt
Look at the skateboard example... you can hold yourself in place but then when you pull yourself forward you admit the wheels are spinning twice as fast... well then the conveyor should be spinning twice as fast too, keeping you in place (to meet the assumptions in the example)
I think the question is really asking if a plane can take off while remaining stationary... not can you make a plane go faster than a conveyor belt
What is it going to take to convice people that no matter how fast the wheels turn the plane takes OFF?!?!
The conveyor is MF'ing moot.
The conveyor is MF'ing moot.
Okay... To start with, I didn't read the whole thread, nor was i around when this originally came up. But, here are my thoughts:
Why does everyone assume that the treadmill will be at a constant speed? Is that stated somewhere? Airplanes have wheels to help them support the plane until there is enough lift on the wings (from thrust or whatever).
What if the treadmill were to speed up at the same speed and rate that the airplanes thrust increases? From the video link above, what if he increased the treadmill speed at the same speed that his son increased the speed of the plane.
In that case, no matter how much thrust the plane has, the wheels would still be supporting the plane because not enough lift is applied to the wings. The plane would still remain stationary if the increase in thrust was directly correlated to an increase in the speed of the treadmill.
I am not an engineer so I don't know if my terminology is correct.
Why does everyone assume that the treadmill will be at a constant speed? Is that stated somewhere? Airplanes have wheels to help them support the plane until there is enough lift on the wings (from thrust or whatever).
What if the treadmill were to speed up at the same speed and rate that the airplanes thrust increases? From the video link above, what if he increased the treadmill speed at the same speed that his son increased the speed of the plane.
In that case, no matter how much thrust the plane has, the wheels would still be supporting the plane because not enough lift is applied to the wings. The plane would still remain stationary if the increase in thrust was directly correlated to an increase in the speed of the treadmill.
I am not an engineer so I don't know if my terminology is correct.
How is the conveyor moot... you need lift for the plane to leave the ground... lift requires air moving over the wings, if the plane is staying the same place, now is air moving over the wings?
As long as the conveyor belt is matching the "ground speed" of an airplane, it will not take off.
If the conveyor belt is moving, the plane will move backwards unless a force is applied to move it forward. If the belt is moving at 20mph, you have to apply enough force that would push the plane at 20mph to keep the plane stationary.
So if the take-off speed of an airplane is 50mph and the conveyor belt is also moving at 50mph, then you would have to apply a force that would make the wheel speed be 100mph.
If the conveyor belt is moving, the plane will move backwards unless a force is applied to move it forward. If the belt is moving at 20mph, you have to apply enough force that would push the plane at 20mph to keep the plane stationary.
So if the take-off speed of an airplane is 50mph and the conveyor belt is also moving at 50mph, then you would have to apply a force that would make the wheel speed be 100mph.
mph != force...
somebody please retitile this thread:
"if you aren't willing to read this entire thread and use your grey matter, please don't click here"
or
"if you don't know the origin of 'the conveyor is moot' please ignore this thread"
or
"there are 2 types of people in this world, those who sleep on airplanes, and those who never take off"
somebody please retitile this thread:
"if you aren't willing to read this entire thread and use your grey matter, please don't click here"
or
"if you don't know the origin of 'the conveyor is moot' please ignore this thread"
or
"there are 2 types of people in this world, those who sleep on airplanes, and those who never take off"
I never said MPH = force. I said enough force to move the plane at a certain speed. I'm not an engineer nor do I want to figure out all the math to determine how much force is needed to move the plane forward.
But if you apply so much thrust to a plane, it will move forward at a certain speed.
If the conveyor belt is moving at the takeoff speed, you have to apply the amount of thrust needed to take off just to keep the plane stationary.
So whatever amount of thrust is needed to make a plane take-off, it would have to be doubled to make the plane take off from a conveyor belt moving at take-off speed.
But if you apply so much thrust to a plane, it will move forward at a certain speed.
If the conveyor belt is moving at the takeoff speed, you have to apply the amount of thrust needed to take off just to keep the plane stationary.
So whatever amount of thrust is needed to make a plane take-off, it would have to be doubled to make the plane take off from a conveyor belt moving at take-off speed.
aero ag 2010, great post too. Thanks for the explanation.
I guess it all depends on how you view the friction of the wheels on the runway... if you say there is no friction then there's no way the plane stays on the conveyor
dammit KWarner04 I wanted your username!
I also got the gmail account too!
The conveyor is moot.
But I was thinking...
Taking the non-takeoffers viewpoint for a moment that the conveyor can indeed pull the plane back and keep it stationary due to the friction in the wheels.
If the conveyor is going fast enough to keep the plane stationary (really damn fast), it might be pulling enough air back with it to provide motion of air over the wings to create lift.
If you're going to count the negligible friction in the wheels, you might as well count the friction of the air on the conveyor, and the conveyor will be throwing some air back with it.
But I was thinking...
Taking the non-takeoffers viewpoint for a moment that the conveyor can indeed pull the plane back and keep it stationary due to the friction in the wheels.
If the conveyor is going fast enough to keep the plane stationary (really damn fast), it might be pulling enough air back with it to provide motion of air over the wings to create lift.
If you're going to count the negligible friction in the wheels, you might as well count the friction of the air on the conveyor, and the conveyor will be throwing some air back with it.
the velocity profile of the air's motion due to friction of the conveyor would not allow enough of air at the wings of the plane...
if it did...once the plane begins to lift, the friction will be reduced and the plane will once again begin forward motion causing the conveyor to move faster causing more lift...until eventually...
the conveyor fails catastrophically and takes the plane down with it.
and the plane arrives at it's final destination:
"TWA Flight 800 now arriving at the scene of the crash"
if it did...once the plane begins to lift, the friction will be reduced and the plane will once again begin forward motion causing the conveyor to move faster causing more lift...until eventually...
the conveyor fails catastrophically and takes the plane down with it.
and the plane arrives at it's final destination:
"TWA Flight 800 now arriving at the scene of the crash"
no problem kempster.
Incidentally, the mythbusters episode is going to fail miserably... because the airplane will just shoot right off the end of it unless it is the length of a runway.
Incidentally, the mythbusters episode is going to fail miserably... because the airplane will just shoot right off the end of it unless it is the length of a runway.
wait... are there still ppl who think the plane WON'T take off?
WRONG... this only happens because this isn't a perfect world, so there isn't zero friction in the wheel bearings. Ideally, though, the rolling wheels keep it from moving... this isn't a skidded helicopter, for christ sake.
CLARIFICATION FOR THE NON-TECHNICAL PEOPLE WHO STILL THINK THEY KNOW SOMETHING WE DON'T:
The feking plane is not propelled allong the ground by a force transmitted through the tires, like a car. ALL of the force pushing the plane is from the engines, through the air... you don't have planes with driven wheels, becuase that would be retarded. The wheels do nothing but support the plane and allow it a near-frictionless surface on which to translate (just like aero said). The conveyor. is MOOT!
quote:
If the conveyor belt is moving, the plane will move backwards unless a force is applied to move it forward.
WRONG... this only happens because this isn't a perfect world, so there isn't zero friction in the wheel bearings. Ideally, though, the rolling wheels keep it from moving... this isn't a skidded helicopter, for christ sake.
CLARIFICATION FOR THE NON-TECHNICAL PEOPLE WHO STILL THINK THEY KNOW SOMETHING WE DON'T:
The feking plane is not propelled allong the ground by a force transmitted through the tires, like a car. ALL of the force pushing the plane is from the engines, through the air... you don't have planes with driven wheels, becuase that would be retarded. The wheels do nothing but support the plane and allow it a near-frictionless surface on which to translate (just like aero said). The conveyor. is MOOT!
If the plane's forward motion was powered through the wheels, and the wheels turning moved it down the runway and it was the wheels that gave the plane forward motion, only then would the conveyor belt matter.
For instance, if you had a car on the belt, and had wings attached so that it could fly, but the car had to use the tires for forward motion, then the belt would keep the car in one place.
However, the tires on the plane will spin faster than the conveyor belt, and there is nothing that can be done to stop it. The plane is powered by engines that use the expansion of gas as its propulsion mechanism. The wheels will turn at a speed of the conveyor belt, say x and will add the speed of the plane as it moves, say y. The turning of the wheels will be x+y always. If you speed up the belt, the wheels will speed up too, but the speed of the wheels will still be x+y.
Imagine that there were no wheels, but skis instead. The belt could spin as fast as it wanted to, but the plane would still go forward. This does assume that the planes power can overcome the added friction caused by the ground turning.
^
|
(damn, too late.)
[This message has been edited by whoop91 (edited 10/24/2007 11:40p).]
For instance, if you had a car on the belt, and had wings attached so that it could fly, but the car had to use the tires for forward motion, then the belt would keep the car in one place.
However, the tires on the plane will spin faster than the conveyor belt, and there is nothing that can be done to stop it. The plane is powered by engines that use the expansion of gas as its propulsion mechanism. The wheels will turn at a speed of the conveyor belt, say x and will add the speed of the plane as it moves, say y. The turning of the wheels will be x+y always. If you speed up the belt, the wheels will speed up too, but the speed of the wheels will still be x+y.
Imagine that there were no wheels, but skis instead. The belt could spin as fast as it wanted to, but the plane would still go forward. This does assume that the planes power can overcome the added friction caused by the ground turning.
^
|
(damn, too late.)
[This message has been edited by whoop91 (edited 10/24/2007 11:40p).]
very nice explanation... but i just said that.
maybe now ppl will finally stfu about it.
maybe now ppl will finally stfu about it.
I would just like to go on the record as saying that the plane will take off with the conveyor moving at any reasonable velocity (such as the velocity of the plane at takeoff). There is a theoretical velocity where the plane would not be able to lift off, but the conveyor and wheels would fail well before that speed could be reached.
This thread is special...
[This message has been edited by AggieOgre09 (edited 10/25/2007 2:36a).]
You are special...
How would the conveyor belt keep the plane from moving?
As soon as the engines started putting out more thrust than the rolling resistance of the wheels, the plane moves forward. The conveyor belt could not "match the speed of the plane" because the speed of the plane isn't related to the speed of the wheels. The wheels spin freely (with some friction obviously) so the thrust that comes out of the engines will serve to make the jet move ***relative to the earth***.
If what you say is true, planes could only take off three directions. They wouldn't be able to move when they tried to move against the rotation of the earth. Newsflash, the earth is rotating, making it the biggest conveyor belt in the world... planes take off in all directions. You are wrong.
Read the thread, it has been explained.
How would the conveyor belt keep the plane from moving?
As soon as the engines started putting out more thrust than the rolling resistance of the wheels, the plane moves forward. The conveyor belt could not "match the speed of the plane" because the speed of the plane isn't related to the speed of the wheels. The wheels spin freely (with some friction obviously) so the thrust that comes out of the engines will serve to make the jet move ***relative to the earth***.
If what you say is true, planes could only take off three directions. They wouldn't be able to move when they tried to move against the rotation of the earth. Newsflash, the earth is rotating, making it the biggest conveyor belt in the world... planes take off in all directions. You are wrong.
Read the thread, it has been explained.
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