will it take off?

[JimParker]

Now, the original parameters state – “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”

I copied this just to frame the reference...

As thrust is applied by the engines, they begin to push the plane forward along the MCB.

The "no fly" crowd assumes that the "and matches it exactly in the opposite direction" statement means that the MCB can run at whatever speed it takes to counteract the thrust. From their viewpoint, the plane never moves, because the infinitely accelerating MCB can create enough drag (even with the low-friction bearings) to counteract the thrust generated by the engine/propeller or jet blast.

The "will fly" crowd assumes that the MCB instead can only turn at a speed (reactive to the plane's speed) that equals the plane's speed. In other words, if the plane is moving at 10 MPH, the MCB can only move at 10 MPH in the opposite direction. They view the problem from the opposite perspective - that the MCB can only respond after there is movement. Once movement occurs, the MCB accelerates to match that speed. However, the plane is already moving, and has more thrust than drag, and therefore will continue to accelerate. If it is moving, and accelerating, it will continue to accelerate to the point where it can fly.

I may be the only one in the entire world who can see this problem from both points of view. I don't know which is correct. If I look at the problem from each perspective, I can see clear evidence to support both theories (assuming the "magic" part to be true). Of course, in the real world, with real conveyor belts, the plane would unquestionably fly, because the large surplus of available thrust when compared to the drag produced by the wheels and bearings.

As a software engineer, if I were assigned to solve this problem, I would categorically state say that the problem definition is too ambiguous to allow for a definitive solution.

Kind of reminds me of an argument I witnessed in a calculus class in college: Professor challenged a brilliant student (not me!) to mathematically prove that parallel lines were possible. Student took the bait, and used the definition of parallel lines as his proof. From his perspective - case closed. The Professor, on the other hand, countered with calculus proof starting with two lines at 90 degree angle to each other. He measured off a point about 4 inches below from the intersection, and pivoted the vertical line clockwise around that new point. As he did so, he used calculus to measure the acceleration of the point of intersection as it moved to the right. He went on to show the detailed calculus proof that this point of intersection would accelerate to infinity, but that the lines would never uncross. As long as you measured from one point in time to the next point in time, there was an increment where the point continued to accelerate at even faster speeds... but you could never show a time interval where the lines magically uncrossed.

It was an exersize in exquisite mathmatics to the two of them, and an exercise in frustration for the rest of us, who just really wanted to know how to solve the nearly impossible homework problem that started the discussion! That was the day I decided I would never again take a class where the professor was a Jesuit monk...!

 

[jk96]

"Of course, in the real world, with real conveyor belts, the plane would unquestionably fly, because the large surplus of available thrust when compared to the drag produced by the wheels and bearings"

Jim, thanks. This is the problem I'm having. I'm operating in the real world, and the no flys keep adding "magic" to the original statement/question. It states the conveyor matches the speed of the plane. It will no doubt fly if applied in a real world application.

jk

 

[SPYDERLK]

Rback,

Yeah I know, the artwork could use a little work. Hopefully the illustration makes up for my stupidity on post #442 though.

One other note on this subject. One person I talked to had a good point. There have been several people converted from the "no fly" to the "fly side", but no one I know of has been converted from the "fly side" to the "no fly" side.

jk

That is because no one has been able to grasp the way in which the conveyor can apply counterthrust to the plane even tho its only connection to it is thru free spinning wheels.
Larry

 

[jk96]

Spyder,

I understand what they are trying to say. However, the plane will reach take off speed well before the speed needed from the conveyor to create this type of friction to counteract thrust. Again, the coveyor matches the speed of the plane. Are you trying to say that at 200 mph, the conveyor belt will produce enough counterforce to slow and stop the airplane.

jk

 

[RayH]

That is because no one has been able to grasp the way in which the conveyor can apply counterthrust to the plane even tho its only connection to it is thru free spinning wheels.
Larry

SPYDERLK, Do you think the plane will move forward?

 

[TomKioti]

Your on an icee lake and your trying to push your brother in a sled. Hard to do even by a strong fellow. Now move the ice in equal opposition to your push. Even harder.You will probably move backwards if you enter the yet un-applied downward effect of weight (mass) into the equation. Totally leaving flight out of the equation. I submit that you wold be hard pressed to have forward movement not to mention lift from the required V.

 

[RayH]

Your on an icee lake and your trying to push your brother in a sled. Hard to do even by a strong fellow. Now move the ice in equal opposition to your push. Even harder.You will probably move backwards if you enter the yet un-applied downward effect of weight (mass) into the equation. Totally leaving flight out of the equation. I submit that you wold be hard pressed to have forward movement not to mention lift from the required V.

Has nothing to do with it.
Does the plane move?
Your answer=NO.
If the plane doesnt move, the conveyor doesnt move, right?

I gotta go to bed.
Here it is in a nutshell (again).

If no plane movement = no conveyor movement (as per the question)
No conveyor movement = plain old normal runway
plain old normal runway + plane with engine running and brakes released = no forward movement.

It doesnt add up.

 

[TomKioti]

In the original crux the convyer keyed off the wheels of the plane. If I was wrong about my interpretation that I apolgize and the world is definately flat and NASA filmed the moon walk in Hollywood. Kidding. Other than that
I would submit... Why doesn't the Navy apply conveyers instead of catapults to invoke quick flight?
C'Mon Ray just one more!

 

[SPYDERLK]

SPYDERLK, Do you think the plane will move forward?

It depends on:
1) How much thrust it has, and
2) How much weight is left on the wheels at full engine thrust, and
3) How much power the conveyor has - 10x engine HP would do.

If there is too little weight on the wheels the conveyor will slip against them. Thus an effective counterthrust could not be developed and the plane would move forward.

With appropriate weight and thereby traction of the wheels against the conveyor surface, The plane could be forced to stand still or even move backwards until the wheels exploded.

 

[MossRoad]

Will-flys....

Read this article.
The Straight Dope: "A plane is standing on a runway. . ." No, it's not. Here's why.

IF you can build a conveyor that moves EXACTLY at the same speed as the airplane, but in the opposite direction, it WILL keep accellerating at the same speed as the airplane, but in the opposite direction. To quote the article:
"The only mathematics needed to demonstrate this is the well-known physics axiom F = ma--that is, force equals mass times acceleration. Given that the conveyor exerts some backward force F on the plane, we simply crank up the acceleration as much as necessary to equal any forward force F generated by its engines. Result: The plane stands still and doesn't take off. Welcome to BR #2."

Now I could say "what you fail to understand is..." but I won't. But I will say, open your mind to the possibility that if you could make a conveyor that would move EXACTLY at the same speed as the airplane, but in the opposite direction, it will keep accellerating to counter the planes accelleration in the opposite direction, preventing the plane from moving.

Read the article, please. Thanks.

Nice weather in the mid west for flying tonight, no? (rain, ice snow, wind, YIKES!!!)