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Will this plane fly??

^my original argument is still in place (still awaiting it for it to be disproven as a matter of fact ;))

the treadmill analogy is not gonna convince me. if you really want to change my opinion, then lets get one thing straight:

are we speaking "theoretically" or "practically"?


MazDan said:
Please dont attack KB cos I know where he is at..........I was there not long ago.........just help him to work it through and be patient.
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LOL!

I actually think i took more offense at that.

Ive worked through the argument, and theres no way the plane can take off. When i first read the hypothetical, i thought it would, until i crunched the numbers and the scenario just couldnt add up.
 
theGreatUnknown said:
no movement, no flight.

simple.

anyone that doesnt understand this is stupid :P
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Of course, that's quite obvious, thanks for your contribution.
 
^^^^^^^^ I didnt mean it to sound that way mate.

And I am still toing and throwing.

My head is exploding..........I need something to clear it up
 
are we speaking "theoretically" or "practically"

Both.

I'm outta here. Good luck trying to win this one, THR. Mr. GreatUnkonwn called us stupid, I'm leaving!
 
-T{H}R- said:
...they merely allow the plane to move down the runway...
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This is where my confusion arises. In my vision of this problem, the plane doesn't move anywhere - the plane is thrust forward at the same speed that the conveyor belt moves in the reverse direction.

So, like a runner on a treadmill, it stays in the same spot. If I understand this correctly, what forces causes the plane to begin to rise from the ground?

A runner on a treadmill doesn't "move down the runway" neither does the plane. What am I missing?
 
^^ You're not missing anything. That's just it.

I'm with KB on this one.

The source of the thrust (wheels/jet/propeller) makes no difference because all it is doing is negating the backwards momentum of the conveyor.

I know it's slightly off what the question states, but picture it like this:
Assume the plane has nothing pushing it forward when the conveyor starts moving, so the plane starts moving backwards, lets say at 50km/h.

Apply thrust from any source you like, in equal amount to that coming from the conveyor. The thrust cancels out the backwards momentum.

Now the plane is moving forward at 50km/h in relation to the conveyor, which brings it back to stationary in relation to the rest of the world.

On a day with no wind movement, and a plane that is now stationary in relation to everything except the thing trying to move it backwards (the conveyor) there is no air movement over the wings, and therefore no lift.
 
^ Agreed.

Again, more simply put, given that there is no airflow across the wing could the "It will fly" lobby explain what force will cause this plane to rise from the ground?
 
I'm guessing no one read this article. Look at that... the plane took off! You guys are missing the point. The propeller only has to create enough veloicty to overcome the friction on the wheels. This is BASIC physics. The wheels will just spin.

Force of Propeller
<============
Plane
=============>
Friction

If the propeller generates more force than friction, it will move it forward. The converyer belt to increases the amount of friction backwards.... that's it.
 
I dont wanna sound like a geek, but the answer i thought was pretty logical, the one submitted by a proffesor or whoever?

the wheels are free to move forwards and backwards, if a motor propells via thrust / propella the plane will have no friction with the surface and will take off..
 
Pop Popavich said:
^^ You're not missing anything. That's just it.

I know it's slightly off what the question states, but picture it like this:
Assume the plane has nothing pushing it forward when the conveyor starts moving, so the plane starts moving backwards, lets say at 50km/h.

Apply thrust from any source you like, in equal amount to that coming from the conveyor. The thrust cancels out the backwards momentum.

Now the plane is moving forward at 50km/h in relation to the conveyor, which brings it back to stationary in relation to the rest of the world.
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50km/h is not a force. the force the conveyor belt is applying is ONLY FRICTION. how hard is that to understand? If I stand on a treadmill with rollerblades while its going 50mph, and grab the rails. I'm not thrusting myself forward at the rate of 50mph. What I am doing, is creating enough force in the opposite direction(by grabbing the rail) to counteract the friction going the opposite direction. This is the most basic of physics ~what makes an object move.
 
xXTOKERXx said:
I dont wanna sound like a geek, but the answer i thought was pretty logical, the one submitted by a proffesor or whoever?

the wheels are free to move forwards and backwards, if a motor propells via thrust / propella the plane will have no friction with the surface and will take off..
Click to expand...

well of course there's no such thing as "zero" friction, but more or less that is the idea.
 
Wow, it's like a 0.9r=1 thread I once had on another forum (1000 posts, 200 mine, with myself arguing against about 6 people who just didn't accept it does!).
bGIveNs33 said:
well of course there's no such thing as "zero" friction, but more or less that is the idea.
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Actually there are certain liquids, such as Helium 4 which will becomes "super fluidic" when you cool them enough. They lose all friction!

Crazy stuff, but very interesting. They used to do a lecture course on it at my uni, but they aren't doing it this year, and I don't like fluid mechanics.

Clearly this "problem" the thread is about is a thought experiment because as soon as you start saying things like "Friction in the tires will cause the plane to slow down" you are being inconsistent, because you've already been assuming the conveyor belt can instantly and perfectly adjust it's speed to that of the plane, which is not going to happen in reality.

Given various idealised assumptions (no friction in the wheels, the belt can instantly and perfectly respond to the plane etc) then the plane will take off. The wheels are free to rotate as fast as they like.

I don't know if any of you have been to an airport which has a moving walkway (ie a conveyor belt). I think Atlanta has one, but it's been about 10 years since I was there. Heathrow certainly does. Imagine sitting on a shopping trolley on one of them, facing the wrong way, and holding a rope with your friend at the end of the belt is also holding.

You turn on the conveyor belt, and it pulls you away from your friend, the rope running through your hands. If you and your friend then gripe the rope, you stop moving, though the wheels of the trolley start turning as the conveyor belt moves underneath you.

If you and your friend then start pulling on the rope, you begin to move against the flow of the conveyor belt, and get closer and closer. Since you are applying additional force to the rope, you can move against the flow of the conveyor belt. A similar principle works with this situation with the plane.
 
.999r most definately doesn't = 1 ;) ;)(there's still a little piece missing, it can't be one, i hate that response)

i'll have to look into helium 4, it's been a year or so since I was a regular at the saturday morning physics/lectures on campus.
 
I have an answer that i would like given some consideration.

I have read and re-read the article from AVweb and there are some things that still dont add up.

In providing my answer i have tried to ensure that at all times, the complete questions rules have been met.

My answer.

It will depend on the plane.

Yep, allow me to explain.

If the plane is built for a snow or ice take off or for water then YES it will take off.

Reason........both of these planes would use skids, NOT wheels. The skids and the conveyor belt would have NO relationship with each other and the skids can simply slide over the conveyor and yes the plane will take off and satisfy all the requirements of the question.


If the plane has wheels then the answer is NO. (Actually to be more precise the question cannot have an answer.......its a bit like the chicken and the egg)

Reason. There IS a relationship between the wheels of the plane and the conveyor belt. Anytime the plane moves forward (lets say one rotation of the wheels) the conveyor belt must move backwards by an identical ammount.

In order for the plane to take off, the wheels would need at some point to slide across the conveyor, however this isnt possible unless we add in considerations that were not included in the question such as bearings locking up etc.

It is also important to remember that the belt is only moving as fast as the actual plane...........NOT the speed of the wheels turning.

It is possible for the wheels to be spinning a zillion rotations a second and the belt moving at the same speed with the plane standing still however the fact is that the question did NOT state this.

It stated that the belt was moving at the same speed as the plane.

That being the case as the belt can "magically" move at the same speed as the plane and at an identical point in time as the plane is "moving", the fact is that the plane will not move and by the questions definition..........neither will the belt.


I hope that makes sense and await your thoughts.

Cheers.
 
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yes it takes off. Why?:

(edit, I had a lengthy response, but this seems to be the simplest way to explain it)

Two systems at play here. One of the relationship between the plane and the ground (the wheels). One of the relationship between the plane and the air around it. The key is to keep them separate.

Because the conveyor moves in the exact opposite direction of the wheels, at the same speed, it essentially creates a frictionless relationship between the plane and the ground. Normally, its the wheels that allow the plane to move forward because the friction between the fuselouge (sp?) and the ground would be too great to get up to the appropriate speed.

Now add in the the thrust the engine creates. It pushes one way, the plane must go the other (law of conservation of energy?). The plane must move through the air, it eventually takes off. The wheels are, in fact, irrelevant. No different than if the plane had no wheels and were sitting on a sheet of ice. Turn on the engines, and its goin to move forward.
 
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the question states that the plane does not move forward becase the belt moves back at the same speed .i fail to see where the lift will come from to get the plane off the grond unless it is a vertical takeoff jet there is no way a fixxed wing plane will fly it needs air flowing over its wing to provide lift
 
The question does not state the plane does not move forward. The question states that the plane moves in one direction, the conveyor belt the other.
 
^ ...at exactly the same speed. That's rather an important omission.

I now understand where my own confusion arises. If the plane does not move forward (because of the equal speed but opposite motion of the plane and the belt) the plane cannot possibly take off.

If the plane is able to move forward at a fast enough speed to allow the wing to create lift, it can surely take off.

In all my visions of the problem so far, the plane has not moved forward. Now i see this problem as analogous to the runner on the treadmill. If the runner runs faster (the plane speeds up) the treadmill runs faster in the opposite direction to keep the runner in the same position (say, relative to somebody standing next to the treadmill).

Replace the runner with the plane and there is no movement forward. No movement forward means no airflow over the wing. The plane can not take off.
 
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