will it take off?

[daTeacha]

How about this analogy for the no fly crowd?

If we talk about a model plane for a bit, imagine that the plane is sitting on the MCB and a large rubber band is stretched forward from a hook on the plane to a distant point. When the plane is released and the rubberband starts to pull it forward, the belt speeds up. Will the plane move or will the belt spin so fast as to stop it from going forward?

There is no interaction between the belt and the rubberband, so it goes forward. When it reaches a sufficiently fast speed with respect to the air it will lift off.

Replace the rubber band with an engine, and the plane flys.

 

[SPYDERLK]

JK. There is an implication in the problem statement that the conveyor holds the plane stationary/cancels its motion. We are trying to explain the way in which it could do this. It is certainly true that if the problem statement were interpreted strictly as the conveyor moving backward at the same rate the plane moved forward, that the plane would take off almost as quickly as if on a normal runway. The reason for the small difference is most easily seen by recognizing that the plane leaving the conveyor has more energy. This is because, altho it has the same airspeed, its wheels are spinning faster. The plane engine is the only source of energy for the plane. It must work either harder or longer to store this larger take off energy. It cant work any harder than full throttle, so it has to work longer.
Larry

 

[Tig]

I can't resist any longer. The wind (air friction) caused by the conveyor trying to stop the plane would only assist the plane to take off sooner by causing a ground effect lift. The only way the plane does not take off is if the wheel bearings fail and the landing gear is destroyed causing the plane to crash. Ground speed is irrelevant.
Now, once the plane does take off it may promptly crash if the conveyor stops or the plane trys to leave the area of the conveyor air cushion. Most (all?) plane engines are not designed to provide enough lift on the wing surface to allow vertical take off. That's why we need airspeed over the entire wing surface.
Not convinced? Go see for yourself. The next time there is a strong west wind go to the airport. If you wait, you will see an airplane at the east end of the runway facing west into the wind. Since the earth is a giant conveyor spinning at about 465.11 m/s this plane is going backwards at an incredible speed. The plane will run the engines up and move along the conveyor we call earth. Note that as the plane speeds up it is actually trying to match earth's speed while you remain stationary on the earth's conveyor. Not only will it take off it will continue to fly and no one will be amazed or confused.
Therefore I would suggest that the experiment has been performed, the results are in, the discusion is complete.
Tig

 

[MossRoad]

I can't resist any longer. The wind (air friction) caused by the conveyor trying to stop the plane would only assist the plane to take off sooner by causing a ground effect lift. The only way the plane does not take off is if the wheel bearings fail and the landing gear is destroyed causing the plane to crash. Ground speed is irrelevant.
Now, once the plane does take off it may promptly crash if the conveyor stops or the plane trys to leave the area of the conveyor air cushion. Most (all?) plane engines are not designed to provide provide enough lift on the wing surface to allow vertical take off. That's why we need airspeed over the entire wing surface.
Not convinced? Go see for yourself. The next time there is a strong west wind go to the airport. If you wait, you will see an airplane at the east end of the runway facing west into the wind. Since the earth is a giant conveyor spinning at about 465.11 m/s this plane is going backwards at an incredible speed. The plane will run the engines up and move along the conveyor we call earth. Note that as the plane speeds up it is actually trying to match earth's speed while you remain stationary on the earth's conveyor. Not only will it take off it will continue to fly and no one will be amazed or confused.
Therefore I would suggest that the experiment has been performed, the results are in, the discusion is complete.
Tig

What?

 

[MossRoad]

Who wants to tackle time travel next?

 

[jk96]

Spyder wrote:

It is certainly true that if the problem statement were interpreted strictly as the conveyor moving backward at the same rate the plane moved forward, that the plane would take off almost as quickly as if on a normal runway.
Larry

My point exactly.

Patrick won't answer my question that I've posted several times. "How can you justify the conveyor moving faster than the plane if the original statement says it moves EXACTLY the same speed as the plane" Because he cannot say the plane will not fly without changing the parameters to fit his theory.

Now if the question was - Can a MCB moving backwards with no restrictions on speed or acceleration prevent a plane with wheels that wont explode or melt from taking off? I agree with Patrick, in theory it can. But that was not the question.

If you don't change the guidlines set by the question - EXACTLY the same speed as the plane, then the plane flies without a doubt.

The no flys are changing the statement to meet thier answer.

jk

 

[SPYDERLK]

Original problem statement: "a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction."

jk96 The two conceptual interpretations of the problem follow directly from its use of the term "match". One of its definitions is "to compete with successfully".

I think consideration of both interpretations is necessary in order to formulate an answer deserving of full credit. I see that we have done this in this thread.
Larry

 

[jk96]

I guess it depends on what the interpretation of the word "is" is.
"It depends on what the meaning of the word 'is' is. If the--if he--if 'is' means is and never has been, that is not--that is one thing. If it means there is none, that was a completely true statement....Now, if someone had asked me on that day, are you having any kind of sexual relations with Ms. Lewinsky, that is, asked me a question in the present tense, I would have said no. And it would have been completely true." - Bill Clinton - footnote 1,128 in Starr's report

Uncle, Uncle, Uncle....There I said it.

Good thread and very entertaining.

jk

 

[BillyP]

Original problem statement: "a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction."

jk96 The two conceptual interpretations of the problem follow directly from its use of the term "match". One of its definitions is "to compete with successfully".

I think consideration of both interpretations is necessary in order to formulate an answer deserving of full credit. I see that we have done this in this thread.
Larry

So the plane powers up and moves forward. The MCB powers up and moves backwards. At this point the plane isn't standing still, is it? The plane builds speed and the MCB speeds up in the opposite direction. So now the plane is moving forward at 100 MPH and takes off. It flies and flies and flies.

Now on landing. The MCB is free wheeling from spinning up for the plane's take off. The pilot doesn't realize this and tries to land the plane against the free wheeling MCB and takes a nose dive. He spills his coffee, ruins the front tire and has a crappy day

 

[Egon]

We need Burt Rutan in on this discussion!

He may be able to us a model and his cartop to iron out all discrepencies.