will it take off?

[Paddy]

Patrick G,

All problems do have assuptions as you and I know from our sience/engineering back grounds. The entire difference between the fly and no-fly camp falls on the context of the convayer matching the speed of the plane. You summerize this in your statement;

""Now, with these assumption made, the only way for our plane to take off and remain flying is for it to travel, or move, from the start of the MCB toward the opposite end of the MCB, all the while gaining speed until it reaches 200 mph with relation to the ground. If it remains in one place on the MCB, I think we can assume it will not take off and continue to fly."

This where I think your assumptions begin to fail. Your statement;

"I am not reproducing the rest of your argument because it does not matter since it assumes the plane can move forward and it can't."

The problem clearly states, "as the plane moves''

Your next statement really starts to deviate from the problem;

"I will try to explain how the MCB can counter the thrust of those powerful Binford Belchfire 5000 Tim The Tool Man Taylor signature model engines!

I ask a simple question, where in the problem does it state or even imply the convayer can counter a plane's thrust? That is flat out re-wording the problem. As the plane moves..the conveyor has a system that tracks the speed of the plane and matches it exactly"" If you re-word the problem and make a new problem, sure it would take magic for this convayer but it could counter the small amount of friction. But than wasn't the in the problem.

You continue with this re-wrighting the problem;

"In your response you said something aboiut the friction not being too great. Well that depends on the speed of the MCB doesn't it? The faster you run the wheels the more force is transfered due to friction. Since there is no upper limit to the speed of the MCB, it runs as fast as is required to concel the thrust of the engines."

What do you mean there is no upper limit of the convayer?? The problem clearly states it is matched but in oposite direction. And again you move back to thrust but this time use the word concealed. Where do you get all these additional terms?

You state;
How did the plane suddenly get to be going 10MPH???
Wouldn't it have to go 9MPH first and 8MPH before that and 7,6,5,4,3,2,1,,,0.0000001MPH before that? The MCB is a very good device and doesn't wait for the A/C to get to 10MPH before it starts to work. The MCB starts countering the planes attempt to move

Of cource the plane doesn't instantly start at 10 mi/hr, it would begin gradually. So what the point? But you do it again in your statement the 'MCB starts countering the planes attemp to move' Theres two faults here 1) there's no attempt, problem states "as the plane moves", 2) the MCB doesn't counter the planes attempt to move it MATCHes the planes speed.


What tops it off is your statement implies the "Will fly" camp needs to use assumptions tt make the point.

Let me say it again. THE PROBLEM WAS WORDED TOO LOOSELY and it requires that unstated assumptions be made to support either camp.

What assumption do you think the Will-Fly camp is using that you think is out?
I think I know, we think the convayer matches the planes speed and the No-fly think it matches the wheel speed. In your camp it all comes down to convayer moving at high rates of speed and plane sitting still a top of spinning wheels. All the while using terms and arguments like matching thrust
or countering friction.

 

[jk96]

Paddy,

Thought this was kind of funny. Someone finally got tired of all the no flyers and videotaped a very simple experiment

YouTube - Airplane Conveyer Belt Experiment

jk

 

[RayH]

Lots of talk and long posts and I still think its a very simple problem.
The conveyor will only go as fast as the plane is capable of going (It matches the planes speed). A plane is limited by its thrust and drag. for instance, a Cessna 172 can only go about 200, a 727 can only go about 600, an F15 can only go about 1500. The conveyors speed can not go faster backwards than (insert plane type) can go forward.
This is so simple for me and I dont understand how it can be disputed.

The only arguement against this is that the question meant to state that the conveyor matches the wheels speed. If thats the case, guess what, it will always match wheel speed, it doesnt matter if the plane is moving or not. The way that I know the conveyor and wheels are ALWAYS matching each other is because the wheels are not skidding on the conveyor. If the wheels are not skidding, the conveyor and wheels are offsetting each other at the same speed. This also seems so simple to me I cant see how it can be disputed.

 

[patrick_g]

OK, OK, IT seems someone realy wants me to comment. OK, here is a comment.

If you go with the versioin where the speed of the conveyor matches the speed of the airplane then the plane will most assuredly take off. Lets say the plane needs 100KTS IAS and there is no wind except as caused by drag on the survface of the MCB and the propwash.

A speedometer attached to the landing gear will register 200KTS the IAS will be 100 and the A/C will rotate and climb out mormally if the tires don't explode from running 200 KTS. This is the obvious conclusion from the afore mentioned interpretatioin. It is quite mundane and pedestrian, not much fun and sure doesn't require a rocket scientist to understand.

The "other version" was just a heck of a lot more fun and would have been more fun yet if more folks could have followed the argument instead of insisting on all sorts of ridiculous assumptions fraught with inapplicability.

Pat (an equal opportunity debater)

 

[jk96]

Pat,

Welcome to the "fly side" - lol

I retract my earlier statement. You do in fact "get it". Obviously much better than I do. Your ability to prove your theory on why it would not move was in fact very entertaining, and all admit, well above my knowledge base. Now I'm going to go watch some ice melt as well. Or at least have some fun trying to bust it up with my tractor - I almost forgot, tractors were the main topic on this website weren't they?

jk

 

[Egon]

JK; Pat has been waffling. He's also having a lot of fun!

Next week he has to clean out his fish ponds! and get ready for next years stock.

 

[patrick_g]

Turnkey, I'm curious, how is it that you declare the friction of the wheels can't equal the thrust? The force produced by the friction is propoertional to speed. With enough speed you can generate any finite force needed. Of course in the real world the bearings will melt and the wheels will fly apart but this isn't the real world.

Please note that all the force required to equal the thrust of the plane's engine is NOT produced by wheel friction. The rotating assembly also has inertia and stores energy when spun up. in order to get that energy into the rotating mass yoiu have to apply a force. That force is supplied by the friction between the tire and the MCB. Now if you claim the coefficient of friction is too small to transfer that force I have to agree that in the real world that is a consideration but in this world of MAGIC conveyor belts it should not be a problem (this particular magic conveyor belt has a very high traction coefficient.)

Now for JK and Tom K (Thanks again Tom for vote of confidence) Now as regards the relativistic issue. The speed of light is not approached in a linear fashion. The energy required to accelerate a mass (even something as light as a single electron) to the speed of light is infinite. The mass of the accelerated object increases such that it would be infinite at the speed of light. (See Einstein, A.)

This supports the contention that the MCB could accelerate as required to hold the plane back for a very long time even several refuelings (forever theoretically.) Of course the MCB will be running way faster than the motion of the planes inertial navigator is indicating. Requires the "OTHER" assumption.

There are two basic solutions to the problem:

1. It takes off with the wheels spining twice as fast as the plane is flying because the MCB was going the same speed as the plane.

2. It never takes off because the MCB can continue to accelerate at the rate required to generate through frictioin and inertia of the wheels a force equal to the plane's thrust.

2.1 Extra frills are things like the air pumped by contact with the whirling dervish of a MCB will allow the plane to generate lift and lift off. It would then accelerate and may or may not stall (we don't have enough information) when it got to the end of the MCB.)

2 and 2.1 are very much more interesting cases than 1 but both 1 and 2 are valid dep[ending on interpretation of the problem statement.

I'm not sure but I think I was insulted by some miscreant who may have compared me to Slick Willy. Just because very precise but small differences are teased out of a statement does not impart the sleaze factor of Slick Willy to the teaser. If guilt by associaton that tenuous is allowed then we are all breathing the same air as ****** and Sadam so where does that leave us?????

Tom K. Please consider any physics stuff I injected as a tax rebate. I was a physics major and math minor under the Viet Nam GI Bill. Thanks to all who paid federal taxes in the late 60's and early 70's. I later found true religion (COMPUTERS) and got a BS in Comp Sci and a MS in Software Engineering before getting into the engineering of training solutions (MS in Instructional Technology) Explains my professorial approach to problems like this. It does not explain my perverse sense of humor that frequently goes not only unappreciated but unnoticed.

Pat

 

[turnkey4099]

Turnkey, I'm curious, how is it that you declare the friction of the wheels can't equal the thrust? The force produced by the friction is propoertional to speed. With enough speed you can generate any finite force needed. Of course in the real world the bearings will melt and the wheels will fly apart but this isn't the real world.

Please note that all the force required to equal the thrust of the plane's engine is NOT produced by wheel friction. The rotating assembly also has inertia and stores energy when spun up. in order to get that energy into the rotating mass yoiu have to apply a force. That force is supplied by the friction between the tire and the MCB. Now if you claim the coefficient of friction is too small to transfer that force I have to agree that in the real world that is a consideration but in this world of MAGIC conveyor belts it should not be a problem (this particular magic conveyor belt has a very high traction coefficient.)

<snip>

Pat

I base the lack of enough friction on real world conditions. As the problem is stated, assuming a 100 kts TO speed, the weels would be going 200 kts. Not even close to developing anough friction, rolling resisstance or rotational intertia to soad up even a small engines thrust.

So far no-one has come up with a reason that the plane would not begin to move when the engine wound up. YOu might argue the 'magic' thing after it gets going (unusuccessfully IMO) but how do you get enough friction to keep it from going from say 0mph to 1 mph? The problem clearly states that the plane 'moves'.

Harry K

 

[patrick_g]

OK already, just give me the address of where to send the pound of flesh and the pint of blood...

I say again I can work the problem either way depending on interpretation of the problem. If anyone can't stand the thought of anyone having a way to formulate a different understanding than they have then the problem is an emotional one but not at this end.

Lets see, here is a simple restatement of some of the lines of comentary... if you don't believe what I/we believe the way I/we believe it then we will have to kill you. Get over it. I do not insist that either fly or don't fly is correct. Either is depending on assumptions.

Now as regards friction and inertial effects of the rotating mass... Why involve yourself with a problem that has magic involved if you insist on only real world values for everything? If the no fly assumtions are made then lots of interesting things happen. If you allow the MCB to run faster than the plane's airspeed lots of interesting things are at play and the plane can be made to stand still with respect to the inertial frame of reference of the ground around the MCB. This is done throiugh friction and the inertial effects of the rotating mass of the wheels.

If you want to go with the interpretation that the MCB is not very M and runs in the direction opposite to the plane at the same speed the planes CG moves forward then as I said before the plane takes off pretty normally except for the wheels spining twice as fast and maybe tearing the tires apart.

Now since I am willing to agree to either set of conditions and the obvious results of those conditions the only bone left for anyone to pick wilth me is that I don't believe what they believe the way they believe it so they are going to have to kill me. I have offered to send in a pound of flesh and a pint of blood. What else does anyone need?

I still want to know if you have a bird in a box and know the weight of the bird and box separately whether or not you can tell with a pair of scales whether the bird is perching or flying.

I still wanna know why anyone cares so much whether or not they are agreed with. If you know you are right, why get excited if someone disagrees? This must be close to the reason all those middle eastern fanatics want to kill each other. After all if they don't believe what you believe the way you believe it you should kill them.

Pat

 

[Tom_Veatch]

...
So far no-one has come up with a reason that the plane would not begin to move when the engine wound up. YOu might argue the 'magic' thing after it gets going (unusuccessfully IMO) but how do you get enough friction to keep it from going from say 0mph to 1 mph? The problem clearly states that the plane 'moves'.

Harry K

But, it doesn't say what it moves in relation to. A person sitting under a tree beside the conveyor sees the plane move at a speed relative to the ground. Someone sitting on the conveyor sees the plane move at a speed relative to the conveyor. The problem doesn't explicitly define which of those relative speeds is matched by the conveyor.

In fact, the answer to the problem is entirely contained in that definition of speed. If the tree sitter sees movement, the conveyor is matching the plane's speed relative to the ground and the plane flies. If only the conveyor sitter sees movement, the conveyor is running at a speed relative to the ground that's the same as the plane's speed relative to the conveyor.

Since the problem statement doesn't define which aircraft speed is matched, either one can be assumed. And, depending on which assumption is made, either answer can be theoretically justified using the theories of Newtonian physics. To apply those theories to physical objects, you have to move from the scientific/theoretical realm into the engineering realm. Now, you have a whole mess of new assumptions that have to be made (and stated).

I believe a successful defense of the "no-fly" case ultimately depends on the nature of time. Is time truly a continuous function or does it have a quantum nature. We know Newtonian physics is a special case only valid at speeds that are slow relative to the speed of light. Is it also a special case which is invalid over extremely small units (quanta) of time?

...
The force produced by the friction is propoertional to speed.
...

Pat, I believe you are thinking of viscous forces which are proportional to speed. Friction force is proportional to the normal or perpendicular force between surfaces and, other than different values for static and dynamic coefficients of friction, are not generally dependent on the relative velocities of the surfaces. Of course, you may be assuming a fluid layer of lubrication, e.g. grease, oil, molten metal, with no solid surface contact between the bearing races. In that case you are correct. The bearing force will be viscous in nature. But, you also need to account for viscosity changes in the lubrication as the bearing assembly gets hotter.

In any case, I believe the bearing force can be neglected as small compared to the force necessary to accelerate the tire/wheel rotation. I've been tempted to calculate the conveyor acceleration necessary to hold an airplane static relative to the tree sitter. But, so far, have successfully resisted that temptation.

...
I still want to know if you have a bird in a box and know the weight of the bird and box separately whether or not you can tell with a pair of scales whether the bird is perching or flying.

At equilibrium in each state, the box containing the flying bird and the box containing the perched bird will weigh the same on a set of scales external to the box. The Laws of Thermodynamics admit no other solution. A more interesting question is what happens to the scales at the instant the bird lands or takes off, and a comparison of those two events. I'm having a hard time not seeing a violation of the 2nd Law of Thermodynamics in those two events.