The great conveyor belt

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My new avatar maybe?
 
My physicist boss says it won't take off... but is being screwy with his answer saying "if it moves forward, sure, but I don't think it ever moves forward".

Heh.
 
wbarnhill said:
My physicist boss says it won't take off... but is being screwy with his answer saying "if it moves forward, sure, but I don't think it ever moves forward".

Heh.
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He is wrong. It will move forward. Take off of an airplane has nothing to do with pushing against the ground. It is all about pushing against the air. Now if there was a tailwind that would blow at the same rate of the speed of the plane then I agree it would never take off. But Newton's third law applies here and once you realize that wheel speed is not the factor to deal with the whole problem is easy. Of course I ignoring friction in the system too.
 
wbarnhill said:
My physicist boss says it won't take off... but is being screwy with his answer saying "if it moves forward, sure, but I don't think it ever moves forward".

Heh.
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The airplane GRABS onto the air and pulls itself forward. The prop could careless what it's wheels are doing. It will grab the air and it WILL move forward. The air is stationary no matter what the conveyor belt or wheels are doing. The prop will grab it and move like it always does.

Put a plane on ski's .. Does it have wheels? No. It still moves forward.

Now think about this--EVEN if you did consider friction into the equation. There is no possible way that the belt could move fast enough to cause enough friction to overcome the thrust from the prop. The bearings would fail and the wheels would start on fire long before this time.
 
...Like I've said a million times--It doesn't matter if there is friction. There simply will not be enough friction to overcome the thrust UNLESS you move the belt so fast the bearings fail and the tires fail.

What is that green thing in the above picture for??
 
Thats the pully. The illustration here is to connect the conveyer belt to the airplane so that the belt MUST move right at the exact speed that the plane moves left.

And yes, of course it will take off. But it will need one HELL of a clearance with that infinite conveyer belt trailing behind it.
 
its a pulley jesse. scotts drawing is a really easy way for the problem to work, without crazy controllers on the treadmill modulating the speed. The airplane pulls the treadmill out from under itself.

and yes, it flies. But the drag from pulling an infinitely long belt through the air would severely decrease cruise speed :D
 
Well if the belt is weightless, can't it be dragless too?
 
Upon consideration, however, this picture is not the same as the original problem described. For the airplane it works out the same, but consider for the car. The car would be pushing the belt with its wheels AND pulling it by the pully, while the airplane only pulls it by the pully.

However, its an excellent way to visualize WHY the problem is different for cars than for planes.
 
Greebo said:
For the airplane it works out the same, but consider for the car. The car would be pushing the belt with its wheels AND pulling it by the pully, while the airplane only pulls it by the pully.

However, its an excellent way to visualize WHY the problem is different for cars than for planes.
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LMAO, Chuck. Why muddy the waters any more than they already are? The car has nothing to do with this discussion.
 
Greg Bockelman said:
LMAO, Chuck. Why muddy the waters any more than they already are? The car has nothing to do with this discussion.
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Because the reason people get fuddled on this issue is they tend to think about the problem as if the plane were a car, where the forward motion is caused by the friction of the tires and the torque applied to them.

And because I rather enjoy this discussion, because its fun to explain. :)
 
Would you need to get a banner towing endorsement to try the problem out?

Jesse you need the pulley to be frictionless for the problem in the picture to work, along with the treadmill to be weightless and dragless. I do agree that the friction in the wheel bearing has little to do with the success of the problem.
 
Greg Bockelman on November 30th 2005:

Greg Bockelman said:
Let's not make this another marathon thread like the other two boards. Bottom line is what happens with the belt is irrelevent and the airplane will fly.
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:rofl:
 
jesse said:
The airplane GRABS onto the air and pulls itself forward. The prop could careless what it's wheels are doing. It will grab the air and it WILL move forward. The air is stationary no matter what the conveyor belt or wheels are doing. The prop will grab it and move like it always does.

Put a plane on ski's .. Does it have wheels? No. It still moves forward.

Now think about this--EVEN if you did consider friction into the equation. There is no possible way that the belt could move fast enough to cause enough friction to overcome the thrust from the prop. The bearings would fail and the wheels would start on fire long before this time.
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Pretty much what I told him... He's still convinced that the wording of the problem makes it apparent that the plane will not move. I'll get it through his head somehow.
 
Greebo said:
Because the reason people get fuddled on this issue is they tend to think about the problem as if the plane were a car, where the forward motion is caused by the friction of the tires and the torque applied to them.

And because I rather enjoy this discussion, because its fun to explain. :)
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Just think how very short the takeoff roll could be for such an aircraft with powered main wheels.
 
Greebo said:
Because the reason people get fuddled on this issue is they tend to think about the problem as if the plane were a car, where the forward motion is caused by the friction of the tires and the torque applied to them.
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A good way (real world, no conveyor belts) way to illustrate how an airplane is different than a car is to think about a takeoff on a slick runway. Does the airplane fishtail and spin its wheels like a car? No, it accelerates straight ahead without any problem. Stopping is another matter.
 
:lightning:You guy are killing me. It still isn't going to take off,...unless I misunderstood the question.

If I am wearing a hanglider and run on a treadmill at 25 miles an hour will I suddenly start to levitate? HELL NO! The prop on the plane will serve to provide enough thrust to move the plane forward but no dang air is moving over and under the blasted wings if it is on a conveyor belt moving an equal speed in the opposite direction except the prop wash, which (at least on my plane) is not enough to get anything into the air but the tail section - and that is at full throttle.

Now I will have to come to gastons :lightning:
 
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alaskaflyer said:
You guy are killing me. It still isn't going to take off, unless the conveyor belt has found a way to move the airmass above it. Perhaps it has little fan paddles to stir the air? :no: The prop will serve to propel the plane along the belt to keep it even with a stationary observer, but it is the airfoils (wings) that make the darn thing fly. Now, if the belt stopped suddenly...
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Okay, you read my mind. I was predicting that the next thing Jesse would propose was hooking the pulley to a fan! :yes::rofl:
 
alaskaflyer said:
The prop on the plane will serve to provide enough thrust to move the plane forward but no dang air is moving over and under the blasted wings if it is on a conveyor belt moving an equal speed in the opposite direction except the prop wash, which (at least on my plane) is not enough to get anything into the air but the tail section - and that is at full throttle.
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Um.... If the plane is moving forward, how does is not have "dang" (or "dank", I don't care :)) air moving over and under the blasted wings? Unless, of course, you've set up that fan I was talking about! :yes::rofl:

alaskaflyer said:
Now I will have to come to gastons :lightning:
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Please do!
 
gprellwitz said:
Um.... If the plane is moving forward, how does is not have "dang" (or "dank", I don't care :)) air moving over and under the blasted wings? Unless, of course, you've set up that fan I was talking about! :yes::rofl:

Please do!
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I meant forward in relation to the moving conveyor belt (here we go with the wheels thing again!) not the real world :redface:
 
As a graduate (survivor?) of the US Navy Survival, Evasion, Resistance, and Escape (SERE) School at Warner Springs, CA, I am intimitely familiar with the construction and operation of the device known as the "water board" (needing only about six feet of 2x12, some rope, a washcloth, and a pitcher of water). If for no other reason, I may make the trip to Gaston's to introduce Jesse to it.
 
alaskaflyer said:
I meant forward in relation to the moving conveyor belt (here we go with the wheels thing again!) not the real world :redface:
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Why don't you think the airplane will move forward in relation to the air and outside world?

It will.

It doesn't give a **** less about what the conveyor belt is doing. The air that it's sitting in is not moving. The prop is going to grab onto this air. It will be moving forward like the belt wasn't even in existence.
 
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