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Will the airplane take off?


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#21 citationpilot

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Posted 29 November 2005 - 10:29 PM

Have you read one thing I have written!!! The airplane will be moving foward, the airplane will be moving foward, the airplane will be moving foward, do you get that yet!?! The conveyor belt will just make the tires spin twice as fast, the conveyor belt will just make the tires spin twice as fast, the conveyor belt will just make the tires spin twice as fast. The conveyor belt will not make the airplane stay stationary when compared to the air or other things not on the belt. It will only make the tires spin twice as fast.

#22 wnfaknd

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Posted 29 November 2005 - 10:31 PM

C172pilot, on Nov 29 2005, 12:00 PM, said:

So I had a false sense of lift as the wind acted as if I were flying through the air. It is SOMETHING VERY FUN!!!
C172, i don't fully understand what you are trying to say here.
You said the wind acted as if you were flying through the air.  Weren't you flying through the air though?
You also said "false sense of lift"... hmm... if you had no lift, you wouldn't be chatting with me right now...

#23 wnfaknd

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Posted 29 November 2005 - 10:33 PM

FL050, did you read my post about the 100 really strong man? :D
Didn't that make but a little bit of sense?  Close your eyes and picture it in your mind... what do you think now? :D

#24 wnfaknd

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Posted 29 November 2005 - 10:50 PM

Let's take this to the next level and hopefully you will understand.

Let's assume that the conveyor belt is moving forward at the same speed as the airplane.  Let's also assume, for the sake of argument, that there is absolutely no friction between the wheels and the conveyor belt.
Do you think that, since the conveyor belt is moving forward at the same speed as the plane, the airplane would take in half the distance it would take if there was no conveyor belt? Or it would take the same distance as if there was no conveyor belt?
If you think it would be the same distance, then you are right and you can probably understand the original question of this thread.
If you think the airplane would take off in half the distance, then you still have not grasped what is going on here.

This would be the instance where the airplane would take off without the wheels spinning at all, and if you were inside the airplane lookign down, you would not see the conveyor belt moving.

#25 IndependenceFAN

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Posted 29 November 2005 - 10:59 PM

wow this is a very interesting topic. i am kind of both sided on this one.  :D

#26 wnfaknd

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Posted 29 November 2005 - 11:11 PM

I don't see how one can be on both sides of this issue.
Here is yet another example and this one I copied from some other website talking about the same topic:

"Two different scenarios. Kind of like these two:

#1. Person standing on a treadmill. Person starts to walk forward, the treadmill moves backward to match his speed. Person goes "no where". Person runs faster, treadmill speeds up, person still "no movey". Reason? The person is propelling himself by pushing against the surface which is moving away just as fast as he is trying to propel himself forward. Exact same scenario as an automobile whose tires are *pushing* against the treadmill surface.

#2. Person wearing roller blades standing on a treadmill. Person grabs the hand rails of the treadmill and starts pulling himself forward. Treadmill starts moving backwards at the same speed. Net result? Person continues to move forward and wheels spin twice as "fast" as he is moving. Person continues to pull faster and faster on the handrails, continues to gain forward momentum while the treadmill futilely spins the opposite direction underneath him, unable to do anything other than make the wheels spin faster and faster! Reason? The person is now propelling himself by pushing against something that is independent of the treadmill, resulting in forward movement no matter what the treadmill is doing beneath him. The wheels allow him to do so by *almost* eliminating the drag that the treadmill can exert, in effect isolating him from the treadmill movement. The treadmill can run forward, it can run backward, it can sit completely still, and the person can still move himself forward by pulling on the handrails. Just like an airplane moves itself forward by *pulling* (or pushing if you prefer) on the air around it, no matter what the treadmill is trying to do underneath it. "

The #1 statement above is what some of you are thinking, but this is not what is happening, what is happening is example #2.  
The airplane is moving forward thanks to its engines and the conveyor belt is just making the wheels spin twice as fast.  Just like the guy on the roller blades is moving by pushing himself on the hand rails.

#27 Pavehawk

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Posted 29 November 2005 - 11:17 PM

The plane would indeed fly!  Check my drawing! :D
Posted Image

#28 KVNY

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Posted 29 November 2005 - 11:28 PM

wnfaknd, on Nov 29 2005, 09:11 PM, said:

I don't see how one can be on both sides of this issue.
Here is yet another example and this one I copied from some other website talking about the same topic:

"Two different scenarios. Kind of like these two:

#1. Person standing on a treadmill. Person starts to walk forward, the treadmill moves backward to match his speed. Person goes "no where". Person runs faster, treadmill speeds up, person still "no movey". Reason? The person is propelling himself by pushing against the surface which is moving away just as fast as he is trying to propel himself forward. Exact same scenario as an automobile whose tires are *pushing* against the treadmill surface.

#2. Person wearing roller blades standing on a treadmill. Person grabs the hand rails of the treadmill and starts pulling himself forward. Treadmill starts moving backwards at the same speed. Net result? Person continues to move forward and wheels spin twice as "fast" as he is moving. Person continues to pull faster and faster on the handrails, continues to gain forward momentum while the treadmill futilely spins the opposite direction underneath him, unable to do anything other than make the wheels spin faster and faster! Reason? The person is now propelling himself by pushing against something that is independent of the treadmill, resulting in forward movement no matter what the treadmill is doing beneath him. The wheels allow him to do so by *almost* eliminating the drag that the treadmill can exert, in effect isolating him from the treadmill movement. The treadmill can run forward, it can run backward, it can sit completely still, and the person can still move himself forward by pulling on the handrails. Just like an airplane moves itself forward by *pulling* (or pushing if you prefer) on the air around it, no matter what the treadmill is trying to do underneath it. "

The #1 statement above is what some of you are thinking, but this is not what is happening, what is happening is example #2. 
The airplane is moving forward thanks to its engines and the conveyor belt is just making the wheels spin twice as fast.  Just like the guy on the roller blades is moving by pushing himself on the hand rails.
exactly  :D  :D  :)  :lol:

The conveyor belt is NOT A FACTOR because the airplane propels itself using the AIR AROUND IT which is NOT AFFECTED BY THE CONVEYOR BELT. The wheels will spin twice as fast as normal, but the airplane will indeed move forward through the air at the normal rate of speed. It is exaclty like the person on rollerskates holding onto the railing in the post above.

Edited by KVNY, 29 November 2005 - 11:29 PM.


#29 Corsair1138

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Posted 30 November 2005 - 12:39 AM

Great replies guys!

Ok, since I started this post I'll let y'all in on the result.


Yes, the plane will fly...and the reason has been stated several times in this thread.


First, to undestand this, stop focusing on the ground and the conveyor belt. And stop thinking the airplane is a car or a person. You're aviation enthusiasts! Stop thinking like a race car enthusiast. :D

An airplane uses AIR to push  itself (normal aircraft, not from a carrier).  The engines PUSH against air to move forward. That's all it needs. It doesn't need anything else to move forward.

The airplane only uses the ground and its wheels to conteract gravity until it can create lift. The only force of consequence is acting on the wheels vertically. Not horizontally. Since the wheels turn FREELY, there's nothing a conveyor belt can do to keep an airplane from pushing against AIR to move forward.

Here's another example for proof. Attach an airplane to a hovercraft. The hovercraft in this case replaces the need for wheels. It provides the vertical force to conteract gravity for the airplane, just like wheels do.  What will happen when the plane accelerates?

Kinda obvious answer, huh? Yes, the plane will start to move forward. But why, what is the plane pushing against to move forward? Since its not touching the ground, then that means its not pushing against the ground to move forward. If that's the case, then how can the treadmill push against the plane to keep it stationary? Well, it doesn't.

As someone mentioned before, as the plane increases speed and the treadmill matches its speed in the opposit direction, the only thing the wheels are doing is moving at TWICE the speed of the plane/treadmill.

#30 beechboy

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Posted 30 November 2005 - 01:13 AM

As the Australian Talk show host Rove McManus likes to exclaim

WHAT THE???

:D



btw.- yeah i do understand it :D

Edited by beechboy, 30 November 2005 - 01:15 AM.


#31 Prancer

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Posted 30 November 2005 - 10:31 AM

Wouldn't the tires blow from the friction? If that be the case, then the answer would be no.

#32 Corsair1138

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Posted 30 November 2005 - 10:47 AM

Zarquen, on Nov 30 2005, 10:31 AM, said:

Wouldn't the tires blow from the friction? If that be the case, then the answer would be no.
Always has to be someone....:D

Tires are capable of going 200mph. This works for airplanes that only need 80 knots to lift off as well as 727's.

#33 [V1]-[VR]-[V2]

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Posted 30 November 2005 - 10:47 AM

no:

Pavehawk, on Nov 30 2005, 05:17 AM, said:

The plane would indeed fly!  Check my drawing! :D
Posted Image


Posted Image

its not about the wheel speed but about the wind speed going over and below the wing

Edited by [V1]-[VR]-[V2], 30 November 2005 - 10:54 AM.


#34 Corsair1138

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Posted 30 November 2005 - 10:50 AM

[V1]-[VR]-[V2], on Nov 30 2005, 10:47 AM, said:

no:

Posted Image
Wow, you need to go back to physics class :D

#35 [V1]-[VR]-[V2]

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Posted 30 November 2005 - 10:51 AM

why? is it wrong?

Edited by [V1]-[VR]-[V2], 30 November 2005 - 11:04 AM.


#36 Corsair1138

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Posted 30 November 2005 - 11:19 AM

[V1]-[VR]-[V2], on Nov 30 2005, 10:51 AM, said:

why? is it wrong?
Yes, it is wrong. You are under the assumption that the forces are dependent on each other.

But the forces of the plane pushing itself forward and the forces of the treadmill turning the wheels are independent of each other.

For example, take this simplified real world scenario:


Take a walking treadmill, like the ones in the airport (long, flat, treadmill).

Put on rollerblades.

Now, if you stand on the treadmill and the treadmill starts moving, it will push you backwards. This is because there are no forces acting on you to propel yourself forward. The wheels of the rollerblades are not moving.

Now take a rope and tie it to the far end of this treadmill and hold onto the rope. As the treadmill starts moving at 1mph backwards, what happens? You stand still in relation to the ground around the treadmill. In relation to the treadmill you are moving at 1mph and the wheels are spinning!! The difference here is that now you have a force pulling on you, that is the force of you holding the rope.

Now what would happen if you started to PULL yourself forward with the rope? Would you move?

Yes, you would start moving forward. Pretty obvious huh? Lets say the treadmill is moving backwards at 1mph and you pulling yourself forward at 1mph in relation to the ground around the treadmill. Well, in relation to the treadmill you will be going 2mph, hence why the wheels would turn at 2mph.

Now you can see why these two forces are independent. You are using the rope to move forward, NOT the treadmill.

The plane uses the AIR to move forward, not the treadmill. The plane pushing against AIR is no different than you pulling against the rope to move forward.

#37 sweetfracture3

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Posted 30 November 2005 - 11:20 AM

Well. in a frictionless world the plane would takeoff in the same distance, but there has got to be some friction between the plane and the wheels somewhere in there.

#38 Corsair1138

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Posted 30 November 2005 - 11:27 AM

sweetfracture3, on Nov 30 2005, 11:20 AM, said:

Well. in a frictionless world the plane would takeoff in the same distance, but there has got to be some friction between the plane and the wheels somewhere in there.
Oh, of course. THere will be added friction, since the wheels will be spinning faster than normal. It would add some minimal amount of distance to the required length of the runway, but it still wouldn't keep it from taking off.

Good observation  :D

#39 [V1]-[VR]-[V2]

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Posted 30 November 2005 - 11:33 AM

well i might have done things wrong but

the plane won't move so there won't be any wind speed so there will be no lift

#40 Pavehawk

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Posted 30 November 2005 - 11:37 AM

[V1 said:

-[VR]-[V2],Nov 30 2005, 10:47 AM] no:

Pavehawk, on Nov 30 2005, 05:17 AM, said:

The plane would indeed fly!  Check my drawing! :D
Posted Image


Posted Image

its not about the wheel speed but about the wind speed going over and below the wing
Of course its about the airspeed over the wing...  :D

In both of my cases the plane is moving forward with an airspeed of 55 knots.....

I noted the wheel speed to show you what exactly happens with the WHEELS in both cases...

The wheels on a plane spin freely, there is no transmission connected to it.  If the plane was stationary at idle power sitting on a treadmill going backwards then it will obviously move backwards....

But when the plane is moving there is no signifcent force on the plane from the conveyor belt...  so your representation of a negative force if false.  There will be some negative force but it will never be equal to the forward force.

Like said before imagine yourself on a treadmill with roller blades.  

A planes powerplant has nothing do to with its wheels.  If somehow you connected the AIR to the conveyor belt and it moved backwards at the same speed well, thats a different storey.  The plane would actually takeoff almost instantly when power is applied to overcome the headwind.

The GROUND is moving away, not the AIR.  Therefore, the item the plane is "pushing" on is not moving.   So to your drawing: NO.

Edited by Pavehawk, 30 November 2005 - 11:39 AM.