Airplane on a Conveyor Belt...

[sluggish]

Originally posted by eskimo2
To see this force watch these AVI's:


http://hallbuzz.com/movies/wheel_on_sander_250th.AVI



http://hallbuzz.com/movies/paper_treadmill.AVI

Argue all you want; here is proof that the force exists. [/B][/QUOTE] At this point eskimo, you're just preaching to the choir.  I went back and read the original thread last night and it was neat to see the light bulb go on in the heads of the few people that eventually got it (yourself included).  At this point the idea of converting any more people is futile. Those that refuse to see have decided that the problem is so ridiculously simple that any further thought on the subject would be a waste of time.

I wonder how many epiphanies we miss each day because the solution is so close and easy to see that we look right past it...

I do hereby concede to ignorance.

[AKIron]

Originally posted by sluggish
At this point the idea of converting any more people is futile.

Hope springs eternal, as does this subject.

[SaburoS]

Originally posted by SD67
This is getting out of hand.
An aircrafts' engine moves air, period. This air generates thrust and it is the thrust that moves the aircraft forward. If the belt is started only once the aircraft starts to move, the aircraft will continue to move forward regardless whether the belt is going faster or slower, speeding up or slowing down. The airflow will build until sufficient lift is generated and the aircraft will fly. The only thing that will be affected is the relative rolling resistance due to the speed of the belt.
Only if the belt is started before the aircraft starts to move, the aircraft will move backwards initially until the level of thrust reaches a level sufficient to overcome the backwards motion of the belt. In this case if the speed of the belt is increased (exponentially?) to prevent parity will the aircraft fail to build sufficient airflow to generate lift.

Bingo. But the 'aircraft will not take off' crowd just won't see that.

[SaburoS]

Originally posted by eskimo2
SaburoS,

Think about this: imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.

Do you see this?

Of course I see what you're saying and your line of thinking.
However, it is flawed.

I've already stated the reason(s) previously.

[SaburoS]

Originally posted by eskimo2
Why would the conveyor be satisfied with 100knts?  Why choose to have the conveyor fail at that particular speed?  

If you were asked to match the speed a hare and a turtle also happened to be running along as well, would you just all of a sudden decide to match the turtle's speed as soon as the hare got a tad ahead of you?  No, you would do you best to keep up with the hare.

Where in this question does it mention ground speed?
Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here.
You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.

Read on as I'll post a response to the appropriate post of yours.

[WWhiskey]

really wont take off you think? ok give the paramiters of the plane!
ill do it for you,
  fixed wing,
propeller drivin,
must have wheels,------------ i bet it will fly no matter what you do or what the belt does. come to amaillo texas and ill show just bring lots of money they dont fly those v-22's for nothing!
 o  and bring your belt, just make sure its big enough to go under the plane.(ever heard of vertical take off)
foul you say!
 you bring in a magical belt with infinite speed that does not exist,
i bring you a plane that does exist right now today that will fly with zero wheel speed or zero ground speed.     now who wins?
you try to tie the airplane to 20th century tech. but use future or non existince tech. for your belt. not fair, the plane was never even described in the original question only that the belt was going to be traveling 100knots!

[sluggish]

Originally posted by SaburoS
Where in this question does it mention ground speed?
Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here.
You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.

Read on as I'll post a response to the appropriate post of yours.

Last post.

Google a few things-

moment of inertia
rotational inertia

learn the difference between speed and acceleration

Also understand that the force is being applied at the edge of the wheel by the belt therefore creating directional force unlike if the force were applied at the hub Therefore creating rotational force effectively cancelling itself out (like chairboy thinks).

Your basic arguement SaburoS is that we don't understand the question.  We all agree that in it's simplest form (where the the belt goes the same speed as the plane but in the opposite direction), that the plane will fly.  We are discussing whether or not the plane will fly if the belt matches the WHEEL's speed. In this instance the plane, due to the forces of rotational inertia, WILL NOT FLY.


outy

[SaburoS]

Originally posted by eskimo2
To see this force watch these AVI's:


http://hallbuzz.com/movies/wheel_on_sander_250th.AVI



http://hallbuzz.com/movies/paper_treadmill.AVI

Argue all you want; here is proof that the force exists. [/B][/QUOTE]

Okay here we go:

Example #1.

Here you have a belt sander starting off at full speed almost instantaneously.

a) Why is the belt sander dictating the wheel speed?
b) Isn't it supposed to react to the wheel and not the other way around?
c) The conveyor belt in this example is the sole source of power here.
d) Remember the conveyor's belt speed is to match the wheel's speed, not the other way around.
e) Now try your experiment in a real world fashion in that the wheel is being pushed forward at a realistic acceleration rate (starts off at zero and gradually  increases in speed from there (to match the wheel's speed).
f) Then try this one. Pull the wheel back against the spring tension. Bring the sander to full speed and let the wheel and belt match their respective speeds. Let go of the wheel. What happens?
g) The moment you allow the conveyor to dictate the wheel rpm speed, you go outside of the intention of the original question.
h) Remember that unless the aircraft actually starts rolling forward, the wheel speed is zero, hence the conveyor's speed is zero. The conveyor is always going to have to react to match, not create a greater force to bring the plane back to its starting position. It's a losing battle for the conveyor as the wheel speed is going to increase by virtue of the plane's ground speed increasing. Remember that the wheels are powered by the forward movement of the aircraft, not by engine torque.

Example #2

Again you load up the test to prove a point that will not be valid for the question.
The glass ball, tube with rubber bands, and the rubber ball(?) is starting at rest. The paper starts out at full force. Notice that non of the objects have an external force acting on them to accelerate?
You are confusing the question of 'matching the wheel's speed' to that of 'neutralizing the forward movement of the plane.'

Again, in the original question the aircraft's forward movement dictates wheel speed which will then dictate conveyor runway speed, not the other way around.

Go you get this principal?

[eskimo2]

Originally posted by SaburoS
Where in this question does it mention ground speed?
Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here.
You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.

Read on as I'll post a response to the appropriate post of yours.

Here is the original question from the original thread:

Originally posted by rabbidrabbit
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.

The question is:

Will the plane take off or not?

Pay attention to the sentence: "This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."

If it is supposed to “track and tune the plane's wheel speed to the speed of the conveyor”, why would it do anything else?  Why would it try to match the plane’s speed?  That’s not what it is supposed to do…

If you are at a light in a hot rod, and there is lesser hot rod to your right and he wants to race, and there also is a moped to your left, and your buddy tells you that he’ll give you $1,000 if you can tie the other hot rod, why in the world would you try to tie the moped?

[john9001]

but the hot rod will not move, when the driver starts to go the rotational inertia of the drive wheels will use up all the engine power and the hot rod will not move.

[SaburoS]

Originally posted by sluggish
Argue all you want; here is proof that the force exists.

At this point eskimo, you're just preaching to the choir.  I went back and read the original thread last night and it was neat to see the light bulb go on in the heads of the few people that eventually got it (yourself included).  At this point the idea of converting any more people is futile. Those that refuse to see have decided that the problem is so ridiculously simple that any further thought on the subject would be a waste of time.

I wonder how many epiphanies we miss each day because the solution is so close and easy to see that we look right past it...

I do hereby concede to ignorance. [/B][/QUOTE]

My it's so nice of you to grace us with your superior intellect. I'm glad you're not charging a monthly fee for this enlightenment.

Originally posted by sluggish

Last post.

Google a few things-

moment of inertia
rotational inertia

learn the difference between speed and acceleration

Also understand that the force is being applied at the edge of the wheel by the belt therefore creating directional force unlike if the force were applied at the hub Therefore creating rotational force effectively cancelling itself out (like chairboy thinks).

Your basic arguement SaburoS is that we don't understand the question. We all agree that in it's simplest form (where the the belt goes the same speed as the plane but in the opposite direction), that the plane will fly. We are discussing whether or not the plane will fly if the belt matches the WHEEL's speed. In this instance the plane, due to the forces of rotational inertia, WILL NOT FLY.

I know very well the difference between acceleration and speed.
Inertia? Acceleration? Action/reaction? Yup, those too.
Rotational acceleration and rotational inertia? Yup.
Friction? Yup.

You are confusing wheel speed (RPM) and ground speed.

You care to show the question because I'm not even sure at this point that we're answering the same question?

Answer this.
From where and how does the wheel get its rpm speed from the aircraft?

[SaburoS]

Originally posted by eskimo2
Here is the original question from the original thread:

 

Pay attention to the sentence: "This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."

If it is supposed to “track and tune the plane's wheel speed to the speed of the conveyor”, why would it do anything else?  Why would it try to match the plane’s speed?  That’s not what it is supposed to do…

If you are at a light in a hot rod, and there is lesser hot rod to your right and he wants to race, and there also is a moped to your left, and your buddy tells you that he’ll give you $1,000 if you can tie the other hot rod, why in the world would you try to tie the moped?

What gets the aircraft's wheel going to even start the wheel rpm?
The forward movement of the aircraft or the conveyor belt?

You're stuck on the conveyor belt's powering the wheel speed and ignoring the aircraft's forward movement dictating the wheel speed.

[SaburoS]

Plane flies.

[AKIron]

There are several aspects to this question. Sometimes it's difficult to understand exactly where the disagreement lies. Breaking down a problem oftens helps to solve it. From my perspective there are two fundamental questions:

1. Does the belt match the plane or wheel speed?
2. If the latter, will the belt cause the wheel to spin increasingly faster at a rate limited only by the mechanical ability of the belt? and the power of the plane

I don't think there's any point arguing until both of these questions are answered and agreed upon.

[eskimo2]

Originally posted by SaburoS
Argue all you want; here is proof that the force exists.

Okay here we go:

Example #1.

Here you have a belt sander starting off at full speed almost instantaneously.

a) Why is the belt sander dictating the wheel speed?
b) Isn't it supposed to react to the wheel and not the other way around?
c) The conveyor belt in this example is the sole source of power here.
d) Remember the conveyor's belt speed is to match the wheel's speed, not the other way around.
e) Now try your experiment in a real world fashion in that the wheel is being pushed forward at a realistic acceleration rate (starts off at zero and gradually  increases in speed from there (to match the wheel's speed).
f) Then try this one. Pull the wheel back against the spring tension. Bring the sander to full speed and let the wheel and belt match their respective speeds. Let go of the wheel. What happens?
g) The moment you allow the conveyor to dictate the wheel rpm speed, you go outside of the intention of the original question.
h) Remember that unless the aircraft actually starts rolling forward, the wheel speed is zero, hence the conveyor's speed is zero. The conveyor is always going to have to react to match, not create a greater force to bring the plane back to its starting position. It's a losing battle for the conveyor as the wheel speed is going to increase by virtue of the plane's ground speed increasing. Remember that the wheels are powered by the forward movement of the aircraft, not by engine torque.

Example #2

Again you load up the test to prove a point that will not be valid for the question.
The glass ball, tube with rubber bands, and the rubber ball(?) is starting at rest. The paper starts out at full force. Notice that non of the objects have an external force acting on them to accelerate?
You are confusing the question of 'matching the wheel's speed' to that of 'neutralizing the forward movement of the plane.'

Again, in the original question the aircraft's forward movement dictates wheel speed which will then dictate conveyor runway speed, not the other way around.

Go you get this principal? [/B][/QUOTE]

I used the sander and paper treadmill because they were easy to build with household items and they illustrate the forces involved that most people could not see.  The sander must start at rest, because the only time the force described can be shown is while it accelerates; a constant speed does not show the effect.  Looking at the clip frame by frame shows that the acceleration phase may be about ½ a second (around 15 frames out of 30 fps).  Also note that the wheel is being pulled to the left by a rubber band that is stretched during acceleration.  The rubber bands represent the force of the plane’s motor.  Of course all forces are greatly skewed, but that doesn’t matter.  The force exists and can be increased in acceleration rate and duration.

If the original question had a twist that stated that the conveyor had a governor that limited its speed to max-out at 100,000 mph, the system would hold the plane in place until the conveyor reached 100,000 mph, at that point it would hold steady at 100,000 mph and the plane would then take off normally!