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#338289 - 08/21/07 07:46 PM The case of the plane and conveyor belt  
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LanierBoater Offline
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"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

Lots of "experts" on both side of the fence. What say you?


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#338293 - 08/21/07 07:52 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Jack T Offline
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Unless the propeller creates enough air movement to give the wings lift, the plane will not take off--assuming your standard fixed wing aircraft.


Have a great day of boating
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#338294 - 08/21/07 07:54 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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markas Offline
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Nope. Plane needs airspeed relative to the atmosphere. The conveyor will cause the plane to stay in the same place relative to the surrounding air, therefore the windspeed over the wings will be zero, therefore no lift.


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#338295 - 08/21/07 07:59 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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the plane won't lift off

if all it took was for the plane's wheels to be moving fast, then since the earth rotates at 700,000 mph all planes should immediatly be able to just instantaneously fly,
it also takes a difference in the earth's speed and the plane's speed .. some air flowing neath the wings


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#338296 - 08/21/07 08:01 PM Re: The case of the plane and conveyor belt [Re: markas]  
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+3 no, there is no air passing over the wing to create lift.


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#338302 - 08/21/07 08:14 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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deepv Offline
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No. Didn't we have this discussion last year about the kite tube thing?


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#338305 - 08/21/07 08:23 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Hockey Family Offline
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No Take Off!

Likewise, if there is enough wind speed coming from the back of the plane, No Take Off!

That's why our local airport reverses direction of the take offs when the winds are-a-blow'n off shore.


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#338307 - 08/21/07 08:32 PM Re: The case of the plane and conveyor belt [Re: Hockey Family]  
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From "Straightdope.com" :

"First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.

A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.

As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off."


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#338310 - 08/21/07 08:38 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Also see:

http://www.newton.dep.anl.gov/askasci/phy05/phy05023.htm

I told you there were different opinions.....


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#338328 - 08/21/07 09:30 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Al Offline
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This is a joke, right?

Lift is generated across a wing by air flowing across it. The upper part of the wing is curved in respect to the lower part.

This means the airflow must be going faster across the upper part if it is going to meet up with the air going across the lower part. Since the air is going faster across the upper part, the air pressure is lower, and the wing is sucked upwards.

So the ability for a wing to create lift is airflow across the wing, and it really doesn't matter how that air flow is created, as long as it is sufficient to create enough lift.

You could fly an aircraft in a hurricane coming at you if you could maintain control.

But generally engines are not powerful enough themselves to generate enough lift, or generate enough air movement across the entire wing area, so it is a requirement for the aircraft to have forward movement in respect to the immediate air surrounding it to create sufficient lift.

Sure, there are exceptions such as an F-15 where the engines have more thrust than the aircraft weight (but you would have to launch it rocket-style if you didn't want to use the wings for lift).

This is especially true of engines mounted below the wings, such as a 747 or Cessna 172. There is little or no airflow from the engines above the wing, only below the wing. Therefore, the engines actually create negative lift. The job of the engines is to get the aircraft moving in respect to the surrounding air, and its the surrounding air that creates lift, not the engines.

If the "reverse conveyor" logic were true, then if the conveyor was not running at all, but stationary, it seems the system would be even more efficient, so the pilot should be able to put the brakes on, fire up the engine, generate sufficient lift from just the engines, then vertically lift off the ground.

As well, if the conveyor theory were true, you should be able to throttle the engines so they are in equilibrium with the amount of lift needed to fly the airplane without causing forward movement, and park the aircraft in the sky.

And how could you even land the aircraft unless you turned the engines off?

But I could be wrong.

But I'll caveat that you could probably get a RC model aircraft to lift off from a dead stop, but this is because the engine is much more powerful than in real life, and the engine itself is pulling the aircraft into the air.

------------------------------------------------------------------

Uh oh, this reminds me of a story.

When I was a dumb teenager, me and a buddy of mine were really into gas powered model airplanes. It was in the old days, before computers or video games, we used to have fun with gas airplanes.

We would build several of them, then on fly day, fly them all day long. Eventually, we would usually bust them up, but that did not mean the end of fly day.

If any of you are familiar with Cox 049 engines, some had a gas tank mounted in the back of the engine. We actually would grasp on the gas tanks with the palm of our hand, and actually START THE ENGINE, then vertically throw them up into the sky!

They would go up maybe 100ft, but the engine would be unbalanced, and at some point, the engine would quit and fall to the ground.

As long as it didn't land on something hard, we simply cleaned the dirt off the engines with a bit of gas, fire them up, and repeat.

We had larger engines as well, but would not dare try anything like that on a .40 engine.

(You cannot make this stuff up)





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#338332 - 08/21/07 09:39 PM Re: The case of the plane and conveyor belt [Re: Al]  
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If I see someone from the aerospace engineering dept tomorrow, I will ask. \:\)


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#338335 - 08/21/07 09:54 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Jack T Offline
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"Unless the propeller creates enough air movement to give the wings lift, the plane will not take off--assuming your standard fixed wing aircraft."

Isn't what Al said what I said? \:b
And everyone around here says I use too many words.


Have a great day of boating
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#338339 - 08/21/07 10:04 PM Re: The case of the plane and conveyor belt [Re: Jack T]  
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Al Offline
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Yep, but we just said the same thing differently.

Besides, I probably took a couple of hours to say what I said, and maybe you snook in ahead of me....

(but I thought of the negative lift thing with a below-wing engine)


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#338347 - 08/21/07 10:31 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Jack T Offline
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\:b Al once again.


Have a great day of boating
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#338350 - 08/21/07 10:59 PM Re: The case of the plane and conveyor belt [Re: Jack T]  
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Scott L Offline
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You would think if would work there would not be much of a need for Aircraft Carriers.... - just big floating conveyor belts

Last edited by Scott L; 08/21/07 10:59 PM. Reason: sp

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#338351 - 08/21/07 11:16 PM Re: The case of the plane and conveyor belt [Re: Scott L]  
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You guys are too smart for me – I thought the entire thing was about the V-22 Osprey...


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#338409 - 08/22/07 08:18 AM Re: The case of the plane and conveyor belt [Re: Lambert Laker]  
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Bowline Offline
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Yeah, but the Osprey is, essentially, a helicopter on take-off.


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#338424 - 08/22/07 08:28 AM Re: The case of the plane and conveyor belt [Re: Bowline]  
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The whole premis is a bit skewed. How can a conveyer moving prevent an air craft from moving? The air around the air craft is its medium for thrust, not the ground. Like the explanation says, this isn't a car. The Conveyer has no influence on the air around the plane. Therefore, it will take off. The wheels will be spinning like mad, but the plane will move forward. Now, if this were a wind tunnel....


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#338436 - 08/22/07 09:12 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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athiker Offline
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What WaterMutt said...absolutely. Like a boat prop in the water an airplane prop bites into the air to create movement through the air. The conveyor belt has no or minimal effect on the surrounding air so the plane takes off. The wheels may need good bearings for the extra-fast spinning for a bit until take-off is achieved. The extra friction might make take-off take a little more time than usual.


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#338453 - 08/22/07 11:02 AM Re: The case of the plane and conveyor belt [Re: athiker]  
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It depends. What airline carrier are we talking about?

No matter, their sure to blame the delay on "weather in Chicago".

#338455 - 08/22/07 11:07 AM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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 Originally Posted By: Rocnat4
It depends. What airline carrier are we talking about?

No matter, their sure to blame the delay on "weather in Chicago".




Yep, and they'll lose your luggage during the test.


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#338457 - 08/22/07 11:15 AM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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 Originally Posted By: Rocnat4
It depends. What airline carrier are we talking about?

No matter, their sure to blame the delay on "weather in Chicago".


boy, isn't that the truth
everything that goes wrong here at Lindburgh Airport is blamed on "weather in Chicago",
i was starting to suspect it was just a big joke amongst the fine workers at our airport,
does it really ever get that rainy or snowy in Chicago ?


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#338476 - 08/22/07 12:00 PM Re: The case of the plane and conveyor belt [Re: FatDog]  
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 Originally Posted By: FatDog

does it really ever get that rainy or snowy in Chicago ?
A couple of times a year.


I'm just happy to be here!



#338493 - 08/22/07 01:01 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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seadog Offline
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I have been on boards where this has gone on for hundreds of replies. Engines do not produce lift, they produce thrust. They can be used to augment lift, such as some STOL concepts, but unless the engine produces more thrust than the mass weight of the plane, it will not take off. An aircraft carrier has to get a minumum wind speed to launch aircraft, even with the tremendouc thrust produced by the jets and the power of the catapaults. If the engines were all that was needed, why have the wings?


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usa1
#338498 - 08/22/07 01:16 PM Re: The case of the plane and conveyor belt [Re: seadog]  
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 Originally Posted By: seadog
I have been on boards where this has gone on for hundreds of replies. Engines do not produce lift, they produce thrust. They can be used to augment lift, such as some STOL concepts, but unless the engine produces more thrust than the mass weight of the plane, it will not take off. An aircraft carrier has to get a minumum wind speed to launch aircraft, even with the tremendouc thrust produced by the jets and the power of the catapaults. If the engines were all that was needed, why have the wings?


I was on a physics message board in which this topic rolled on for 550 pages.


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#338512 - 08/22/07 01:58 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Frantically Relaxing Offline
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To quote Robin Williams (and the pilot of that plane on the conveyor belt attempting to take off in an aircraft generating no forward motion):

"Oh $#**, gravity works!"


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#338514 - 08/22/07 02:00 PM Re: The case of the plane and conveyor belt [Re: Rocnat4]  
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If the effect of the conveyor is that there is insufficient air movement over the wings to provide lift, the plane will not lift into the air. If there is sufficient air speed/movement of air over the weing surfaces, then the plane will lift off of the ground. Why do you think that light planes are tied down at their airports instead of just having their wheels chocked?


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#338516 - 08/22/07 02:13 PM Re: The case of the plane and conveyor belt [Re: Bowline]  
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I guess I am confused at how people think a conveyer belt will prevent an air plane from moving. Also, if the conveyer belt did move the air to prevent the plane from moving, it would have to be moving enough air over the plane to negate the surface pressure on the props, and therefore would create lift on the wings. It would/could go up, but wouldn't move forward.


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#338528 - 08/22/07 02:43 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


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#338535 - 08/22/07 03:17 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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I see a future episode of Myth Busters with the biggest conveyor belt ever built!


I'm just happy to be here!



#338539 - 08/22/07 03:28 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Or a small plane....


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"That's my boat..."
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#338541 - 08/22/07 03:36 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Al Offline
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There are three things necessary for an airplane to fly. Thrust, lift, and drag.

Thrust is required for the aircraft to have FORWARD MOTION, and is accomplished by the engine.

Lift is required for the aircraft to GET OFF THE GROUND, and is accomplished BY AIRFLOW ACROSS THE WINGS.

Drag is required to keep the nose of the aircraft in front of the tail, so that it does not do a loop-de-loop. The tail surfaces create drag in comparison to the nose, thusly keeping the nose pointed forward.

Lose one of these three properties and the plane will not fly.

If the plane is on a conveyor, and the conveyor is going into reverse the same speed that the engine is pulling the airplane forward, so that the airplane does not move on the ground......

There is then no airflow across the wings, which means there is no lift generated by the wings, and then no fly. If otherwise, you would not need wings.

There is not enough airflow generated by the engine to generate sufficient lift. As I said previously, in the case of a Cessna 172, where the engine is predominately below the wings, there will be more airflow under the wings than over, which generates negative lift, and results in the airplane being sucked to the ground.

Only when there is enough lift generated by airflow to counteract the weight of the aircraft AND negative lift generated by the engine, will the airplane lift off the ground.



So its SUFFICIENT airflow over the wings that creates lift, and the engine cannot produce sufficient airflow. Only FORWARD MOTION OF THE WINGS, BEING IN A WIND TUNNEL or something that creates airflow is what creates lift. If a conveyor in reverse prevents forward motion of the WINGS, in the absence of any other sufficient air flow mechanism, there is insufficient lift.

and lastly, even if there were enough lift created by the engine to get the plane off the ground, its likely there would still not enough air flowing across the control surfaces (and for sure the alerons) to fly it.


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2004 Mercury 270 Dinghy.
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#338542 - 08/22/07 03:43 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Al, I fully understand that no air over the wings = no fly. But explain me this, how does a conveyer with contact only to the tires of the air plane stop it from moving?

Also, in your "No Fly" drawing, what is keeping the prop from pulling the plane forward? The conveyer?


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#338544 - 08/22/07 03:49 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Al Offline
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Well then maybe I am reading the scenario wrong.

I took it that the conveyor is going in reverse at the same speed as the airplane is moving forward, which means that the airplane and wings are stationary.

Is this not the case?

But if it takes 100mph of forward movement for the airplane to generate sufficient lift, and if the conveyor is moving at 25mph to the rear, and the airplane is moving at 125mph, and if the conveyor is a mile and half long, then yes, the airplane will take off, because its relative movement to the surrounding air is 100mph.

But if the airplane is moving 100mph forward and the conveyor is moving 100 miles to the reverse, then there is no forward movement of the wings at all, and there is insufficient lift.


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2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#338546 - 08/22/07 03:58 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Al Offline
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Maybe I am seeing your point a bit.

You are saying that the airplane will move forward regardless if the conveyor is moving to the rear?

So lets think about.

So its not really about creating lift, but whether or not the airplane would move forward or not when the same energy is applied to the conveyor as is applied to the engine.

1. if the conveyor moves to the rear, and the airplane engine is off, will the airplane move rearward? I would submit that inertia would initially attempt to keep the airplane steady, but friction from contact with the conveyor would result in the airplane moving to the rear.

Anyone who has pushed a wheelbarrow full of dirt knows this to be true. There is nothing moving the wheels, but it still takes much effort to move the wheelbarrow. Gravity causes a tremendous amount of friction to be applied to the wheel.

2. if the airplane's engine is running, and the conveyor is not, it too will have the initial resistance of inertia attempting to keep it from moving forward, but it will slowly move forward. Again, friction will impede this movement.

3. but if the conveyor is moving to the rear with the same energy as the airplane pushing the plane forward, then the intertia will balance out, but its my guess that friction of the wheels spinning backwards will aid the conveyor, and the airplane will move backwards on the conveyor.

This is because for the wheels to stay static, there is no friction involved, just inertia, so the airplane will move rearward with the conveyor. But to just keep the wheels moving forward to match the rearward movement of the conveyor, friction and inertia must be overcome.

So, rearward movement = overcome inertia.
Forward movement = overcome inertia and friction.

This suggests that it takes more energy to move forward than to maintain status quo.

4. but only when the airplane has enough power to overcome the friction of the wheels spinning backwards, and then can move forward at sufficient speed to create lift will it fly.

Regardless, there has to be forward movement in the airplane for this to happen.

A close scenario might be if you had a treadmill and put a marble on it. If the treadmill were flat, the marble would roll off to the rear.

But if you tilted the treadmill forward so that the marble due to gravity was rolling forward, at some point, the forces would cancel out and the marble would roll without movement.

And if you tilted the treadmill even more forward, gravity would overcome the treadmill and the marble would roll forward off the treadmill.

And its my belief that at that point, there is more energy applied to the marble via gravity than in the rear movement of the treadmill, and that is where friction comes in.

My guess then is that if the forces were equal, then friction would be the tie-breaker and the marble would move to the rear. Only when greater force is applied would the marble overcome friction.

At worst case, equal forces might balance the marble in one spot, but to get it to move forward I believe would require an increase in force.

This is an interesting scenario.


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#338554 - 08/22/07 04:19 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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Scott L Offline
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 Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


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#338556 - 08/22/07 04:23 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Is that the static coefficient of friction, or the dynamic coefficient of friction?

All this brings up another thought. If the conveyor has sufficient friction (read roughness), then it could create drag with the air molucules above it causing the air actually to move past the wing of the plane and quite possibly creating lift. But soon after the plane lifted off the conveyor it would get out of this air stream, lose lift and fall again. If the conveyor created enough wind motion about the wings, the plane might begin to hover a few feet above the conveyor.

Are you ready for 550 pages of posts on this subject?


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#338558 - 08/22/07 04:25 PM Re: The case of the plane and conveyor belt [Re: Al]  
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I think it comes down to the energy created by the air plane to move forward, the energy needed to overcome the friction of the "tires" (and we'll call it that for simplicity, but it does include the tire friction, compression of tire, and bearing friction), and the net amount of energy required to get the plane off the ground. Basically, if the air plane can create the energy needed to get to speed to take off while producing an excess amount of energy equal to or more than the energy to over come the tire friction, I feel that it will take off.

If you really simplify and call all tire friction negligible, that plane is flying.

I understand your theory on the plane not running on the conveyer running backwards. Given the laws of physics, it will eventually equal the speed of the conveyer, minus wind resistance effects.

I guess my biggest thing is the air plane uses the air around it as its ability to get traction, where as the conveyer is just the gound. Kind of opposite of being in a car driving into a head wind. Ground isn't moving, but the non essential medium of air is moving creating some resistance, similar to the conveyer for the air plane.

Maybe we get one of those JATO's from the guys with the Hobbie, that'll take care of any extra power needed.


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#338569 - 08/22/07 04:47 PM Re: The case of the plane and conveyor belt [Re: Scott L]  
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Once again I follow WaterMutt...unless typing takes too long!

Scott L wrote:
 Quote:
Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.

Scott L:
Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


If someone sits in a hydrofoil air chair, that is tied via a line to a fixed point (rock upstream), thus 'standing still' relative to the bank and earth, but the foil (wing) has water flowing over/around it...then I submit the chair will rise in the water (and the plane will rise in the air as the propeller pulls the plane wings through the air). The wing only cares about wind/water flowing over it to provide lift...either via a head wind/current or moving over the surface of the earth through the medium...not a conveyor belt underneath.

The plane example is not quite the same b/c I believe the plane will move forward in relation to the earth as the prop pulls it through the air. The conveyor belt (setting aside residual air flow...which probably will only help...and extreme friction...there are some pretty good ball bearings out there) is inconsequential. The only reason wheels exist on a plane is to decrease the friction of the plane with the earth as the prop pulls it forward. Wheels roll...and if the bearings are good enough to overcome the increased friction then the plane takes off.

Imagine a sea plane attempting to take off pointed upstream in a river. What is the only thing that will keep it from taking off? Too much friction of the pontoons w/ the water that prevents the plane from getting enough airspeed...or moving over the surface of the earth fast enough assuming no weather wind conditions. I say the conveyor belt can spin to it's heart's content as long as the friction isn't too great a factor, the plane takes off!

550 here we come....


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#338571 - 08/22/07 04:51 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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There is insufficient air flow created by the propeller to create lift on the wings.

Who here is an aerospace or aeronautical engineer? Let's see the hydrodynamics of this equation. (BTW, air is another fluid and conforms to fluid mechanics as a "compressable fluid")

It will not fly, but may hover if there is adequate air flow created by the conveyor belt.


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#338572 - 08/22/07 04:55 PM Re: The case of the plane and conveyor belt [Re: Al]  
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I'm with Al

The argument is that the forward speed of the aircraft is matched by the conveyor, but that the seemingly free wheeling wheels would take the abuse and turn twice as fast (aircraft forward motion + conveyor rearward motion), which would still allow the aircraft to move forward.

What's not taken into consideration is the friction of the wheel contact to the conveyor.
The aircraft would still need to generate enough thrust to overcome the conveyor speed plus the forward speed needed for lift.

An earlier post said something about being on a treadmill on skates and pulling on a rope attached to a wall. The problem with this analigy is that the wall is stationary. If you hold the rope, you will not move on the tread mill and yes, you can pull yourself forward. But if the rope you were holding onto were not attached to something stationary (like air is not), you would move backwards.

You would need to pull aggresively at the rope (or actually move your A@# and skate) to supply enough forward movement to overcome the treadmill.

Like the wheels, the aircraft engines would need to supply enough thrust to overcome forward inertia plus the ever-increasing rearward speed of the conveyor.

So let's say 2x.

If the plane needs 100mph forward motion for lift, and the conveyor is matching 100mph rearward motion, my guess is the engines need to provide 200mph or thrust and would be over rev'd to the point of throwing a rod thru the cockpit killing the pilot and thus not acheiving lift.


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#338573 - 08/22/07 04:57 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Last edited by deepv; 08/22/07 05:00 PM.

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#338575 - 08/22/07 04:58 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Let's go back a minute to the original question. The conveyer tracks the speed of the plane and equals that of the plane, but in opposite direction. Speed of the plane relative to ground, or relative to conveyer, or even relative to how fast it should be going, hmmmmmm.......

Anyway, deepv, I would agree that the prop can not create enough air flow for lift, but I don't agree the plane would be sitting still. I think athiker and I are on the same page here, there isn't enough drag from the conveyer to keep the plane sitting still. The sea plane is a good analogy.


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#338579 - 08/22/07 05:02 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

The original problem statement requires that it be still.


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#338581 - 08/22/07 05:03 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Al Offline
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If the conveyor tracks the speed of the plane in reverse, isn't that by definition mean the plane isn't going forward.

I think that the original scenario may not be adequately explained.


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#338583 - 08/22/07 05:11 PM Re: The case of the plane and conveyor belt [Re: Scott L]  
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Al Offline
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 Originally Posted By: Scott L
 Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


Maybe 5mph relative to the water going behind it, but zero speed relative to the banks, and zero speed relative to airflow.


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1999 Four Winns 268
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#338586 - 08/22/07 05:25 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Last edited by deepv; 08/22/07 05:25 PM. Reason: spelling.

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#338590 - 08/22/07 05:27 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Al Offline
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Would that be with a big "G" or small "g".

No worries on 550 pages, we'll parlay this topic into something else as equally superficial by then.


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#338592 - 08/22/07 05:38 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Like I said initially, the plane will not fly. QED.


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#338595 - 08/22/07 05:43 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Al Offline
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And I don't think you can totally discount friction. Due to gravity, it can be significant. Ever push a caboose?


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#338598 - 08/22/07 05:58 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Agree, friction is the key...I just don't have the ability to gauge how big a factor it is sitting here on my high-friction bum. \:\)

LanierBoater wrote:
 Quote:
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"


Just to revisit the original question. Within the question it is stated that the plane moves. So this much we know.

There is an assumption that the movement is relative to the earth's surface correct? I mean that would be the reference for a spot on the conveyor belt, yes?...the conveyor belt's speed. So that would be the reference for the plane as well.

So the question states the plane moves in one direction, let's say 100 mph, which means the conveyor belt is moving in the other direction at 100 mph. So whatever speed the plane needs to move it can, there is no limitation in the question, it's just that the coveyor belt moves the same speed the other direction. Who cares tho what the conveyor belt is doing, we just care that the plane is moving at take-off speed.



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#338599 - 08/22/07 05:59 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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I studied Mechanical and Aerospace engineering in college. This is not an engineering problem. This is just common sense physics. An airplane flies because the flow of air across the wings creates an imbalanced flow between the top of the wing and the bottom of the wing.To create enough lift to overcome the weight of the aircraft, there is a demand for X amount of wing area at Y speed. This is not an all or nothing factor, as even at low air speeds, some lift is produced, just not enough to overcome gravity.

If a plane has a tailwind, it will get to its destination quicker and with less fuel usage, but if the relative airspeed is lower than the minimum requirement for that aircraft, the plane will not stay in the air. This is why airspeed is a relative factor.

The wheels on an airplane are only a indulgence that recognizes that planes do not stay airborne continuously. They support the airframe when the wings do not.

Answer these questions:

1. If the engine dies while the treadmill is going 100 mph, does the plane stay still?

2. If the plane is turned around on the treadmill and it is cranked up to 100 mph, will the plane fly without the engine?

3. If you take the wheels of the aircraft to where it is setting on the treadmill, and you have rockets/jets that will generate enough thrust to equal the movement of the treadmill, what will happen?


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#338610 - 08/22/07 07:22 PM Re: The case of the plane and conveyor belt [Re: seadog]  
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Im suprised KCook and Seabuddy have not chimed in. I have always been impressed with their fluid dynamics expertise.


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#338617 - 08/22/07 07:43 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Not rightly sure what yer dad burned plane will do but I'm bettin' I can sale a bunch of tickets to watch it do this little stunt to my NASCAR buddies....
....can you make it do a left turn every now and then?.....



By the way, I don't think it will fly....


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#338622 - 08/22/07 07:59 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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I must admit, this kind of thing is way over my head. I'm just a dumb hick farm boy from the middle of Illinoise. But will someone please explain to me how this silly conveyor belt is actually going to stop the plane from moving?


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#338631 - 08/22/07 08:23 PM Re: The case of the plane and conveyor belt [Re: 2Suns]  
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 Quote:
But will someone please explain to me how this silly conveyor belt is actually going to stop the plane from moving?



It won't. The plane takes off. IMO, the wheels/tires and magic conveyor belt have nothing to do with an airplane's ability to create positive thrust.

Last edited by LanierBoater; 08/22/07 08:24 PM.

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#338635 - 08/22/07 08:34 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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WaterMutt, ATHiker and seadog have it right. As long as I got something out of all that $$$ I spend on a couple of engineering degrees, they do... ;\)

The wheels will be spinning over twice as fast as if the plane was taking off from the ground because the conveyer belt is trying to catch up to the plane speed, but it never will unless the brakes are on. I think if you compare the drag from the wheel bearings to the output of the engines, you will see that the plane will move forward almost as fast as without the conveyer belt, right up to the point the bearings melt or the plane leaves the ground!

Like WaterMutt first said, the engines are pushing against the air, not the ground, so the conveyer belt is almost irrelevant, except to the wheels' rotational acceleration. It must be a pretty long conveyer belt...



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#338636 - 08/22/07 08:37 PM Re: The case of the plane and conveyor belt [Re: Al]  
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It would if the wheels where somehow connected to the engine/thrust.

I agree, you can change one word and have a totally different scenerio.


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#338640 - 08/22/07 08:45 PM Re: The case of the plane and conveyor belt [Re: Al]  
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 Originally Posted By: Al
And I don't think you can totally discount friction. Due to gravity, it can be significant. Ever push a caboose?


I think the bigger issue pushing a caboose is inertia. Ever try to stop a caboose?



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#338650 - 08/22/07 09:18 PM Re: The case of the plane and conveyor belt [Re: WayWeGo]  
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If a speedboat were placed into a huge lap pool (narrow swimming pool that produces a current), and the water movement is automatically adjusted to match the boat's speed, but in the opposite direction, will the boat fly?


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#338655 - 08/22/07 09:29 PM Re: The case of the plane and conveyor belt [Re: Jack T]  
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No. Now, if your talking about an air boat (ones that cruise the everglades)...then yes, in theory it would...provided you had the essential dP's present to create lift and ample thrust.





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#338657 - 08/22/07 09:35 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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 Originally Posted By: athiker
Once again I follow WaterMutt...unless typing takes too long!

Scott L wrote:
 Quote:
Originally Posted By: athiker
Again I agree w/ WaterMutt. Yeah, the engine doesn't provide lift, but the the engine turns the propeller, which pulls the airplane through the air, like a prop pushes a boat through water, the subsequent air movement over the shape of the wings lifts the plane into the air.


Scott L:
Yes but a boat facing upriver in order to stay still must prouduce enough forward thrust to negate the riverflow. 5mph riverflow against 5 mph of forward thrust and the the boat stays still relative to the banks - How fast is the boat going ? Relative to what ? 0 relative to the river bank, 5 mph realitive to the water going behind it.


If someone sits in a hydrofoil air chair, that is tied via a line to a fixed point (rock upstream), thus 'standing still' relative to the bank and earth, but the foil (wing) has water flowing over/around it...then I submit the chair will rise in the water (and the plane will rise in the air as the propeller pulls the plane wings through the air). The wing only cares about wind/water flowing over it to provide lift...either via a head wind/current or moving over the surface of the earth through the medium...not a conveyor belt underneath. ......


550 here we come....



Agreed about the lift, but this would equate to the point about planes as to why light aircraft are teathered, not just blocked. A force either downriver water or wind created by nauture will cause a foil to lift, but these are external forces not connected to / or driving the foil.

How about indoor surfing ?

http://www.metacafe.com/watch/51938/indoor_surfing/

In a fast enought down river stream, in theory you could get you boat up on full plane a go nowhere. At a given point, a plane in a strong enought headwind would have full power going and would hover.

Check out how this guy get his plane to hover - Zero lift - all thrust

http://www.fugly.com/videos/3555/hover_plane.html

Last edited by Scott L; 08/22/07 10:26 PM.

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#338680 - 08/22/07 10:24 PM Re: The case of the plane and conveyor belt [Re: Scott L]  
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I rethought my answer. The thrust of the engines will push the plane forward, it's just at 100 MPH of forward speed the wheels will be doing 200 MPH since they are reacting to both the forward motion of the plane and the reverse motion of the conveyor.


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#338709 - 08/22/07 11:14 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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markas Offline
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Yeah, I'm with Parrot Head on this one. I change my mind too, after re-reading the problem statement. Assuming the wheels, wheel bearings etc. can stand up to 2x takeoff speed, then it'll fly. Dang! It made sense the other way yesterday...


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#338720 - 08/23/07 12:23 AM Re: The case of the plane and conveyor belt [Re: markas]  
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You all are considering some magical mistery plane.
To discount the friction of the wheels, might as well discount the wheels all together. Say it's a hovering craft. Doesn't matter which way the conveyor moves, or at what speed.
If we're talking an imaginary plane, then sure, I guess anything is possible.

Forget flight. What about a jet powered 1/4 mile race vehicle?
ie. plane with no wings.
If the track were the same conveyor system, would you say the 1/4 time would be the same, for the same vehicle putting out the same power?
No, it wouldn't. You would need to increase the thrust to overcome the conveyor to achieve the same qtr mile time.

If you're talking a real life plane on this imaginary conveyor system, NO, the plane would not fly because it cannot achieve enough air speed on it's own.


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#338721 - 08/23/07 01:22 AM Re: The case of the plane and conveyor belt [Re: Hockey Family]  
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Do we agree that (A) At the moment before this theoretical 'takeoff', the plane is standing still in relationship to the ground?

Or, are the 'fly' people saying that (B)the plane will actually be moving forward in relationship to the ground?

IF (A), it ain't gonna fly.
IF (B), it might but you're gonna go thru a lot of tires...

#338731 - 08/23/07 05:55 AM Re: The case of the plane and conveyor belt [Re: trooplewis]  
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Al Offline
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This is my last post on this topic.

My assumptions are:

1. the scenario indicates that the conveyor goes into reverse at precisely the same amount as to match the airplane's forward speed.

If true, the airplane is not moving in respect to the ground, but is moving in respect to the conveyor.

2. if there is no movement in respect to the ground then there is insufficient airflow across the wings to lift the airplane into takeoff.

It matters not that air is being generated by the engine. The purpose of the engine is to move the airplane forward to create airflow. The wings make the airplane fly, not the engine.

If you forget about the conveyor for a minute, if you put the output of the engine on the wheels so that the wheels were powered, and took the propeller off, if the wheels could get the airplane moving fast enough, the wings, the wings, the wings, would get the airplane airborne. However, not for long, because you then lose the forward momentum - but it would glide.

So, it still comes down to whether or not the wings are moving in relation to the ambient air. If the plane is not moving in respect to the ground, it is not moving in respect to the ambient air. If it is not moving in respect to the ambient air, the wings are not generating lift. Period!

If the engine was sufficient to move enough air across the wings, then yes the plane would fly off the ground from the conveyor, but it cannot. the air flow is concentrated at the ring root, unless of course you have 6 engines all the way across the wing. If there were 6 engines across the wing, then there might very well be enough to produce lift.

Whether or not it would continue flying would be a matter of sufficient airflow across the control surfaces.

So some of this scenario kind of depends on your perspective of what the plane looks like.

But I don't believe too many airplanes are designed to fly off a conveyor, so its my contention that for most airplanes, the engine cannot by itself produce enough lift to take off.

So here is the absolute proof this cannot happen.

If you were sitting at the end of the runway, applied the brakes, run the engine to maximum power, the engine is applying all of its airflow it can over the wings, the airplane is sitting still, and when you pop the brakes, will it take off? Of course it won't, it simply begins to roll forward, maybe a bit faster, and maybe it will take off a few feet sooner.

And so is the same for the reverse conveyor, given the conveyor is holding the airplane steady in relation to the ground.

Why - because there is insufficient airflow across the wings until the airplane is moving a sufficient speed forward in relation to the ground.

So the answer again, if the conveyor is causing the airplane to have no movement in relationship to the ground, it will not take off.


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#338732 - 08/23/07 06:23 AM Re: The case of the plane and conveyor belt [Re: Al]  
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Clear enough. What I'm struggling with is whether or not the plane is moving with respect to the earth. That is the ambiguous part. On one hand, it can be assumed the intent of the problem is to say that essentially the conveyor offsets the plane's forward motion, but if you read it another way, it says more literally that it moves in the opposite direction at the same speed as the plane moving forward. The former = no fly; the latter = fly.


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#338747 - 08/23/07 07:28 AM Re: The case of the plane and conveyor belt [Re: markas]  
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In order to grasp this...you have to remove any and all relationship of the wheels/conveyor and the planes thrust. The entire "ground" is not moving...just the runway (or conveyor).

Forget wheels/tires. Imagine the runway is a giant frozen pond, and the wheels are ice skates. The plane takes off because the engergy/thrust is focused on something other than the frozen pond and skates.

In theory, the wheels are nothing but ice skates. So, in theory, if the plane's engines are off and its just sitting and someone starts the magic conveyor/runway, the plane will sit still with only the wheels turning right? In other words, the motion of the runway is canceled out by the wheels. So now you are back at zero concerning ground speed. Now add positive thrust from the jets. Assuming you have heavy duty wheel bearings, and rubber...the plane takes off.


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#338750 - 08/23/07 07:38 AM Re: The case of the plane and conveyor belt [Re: markas]  
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 Originally Posted By: markas
Clear enough. What I'm struggling with is whether or not the plane is moving with respect to the earth. That is the ambiguous part. On one hand, it can be assumed the intent of the problem is to say that essentially the conveyor offsets the plane's forward motion, but if you read it another way, it says more literally that it moves in the opposite direction at the same speed as the plane moving forward. The former = no fly; the latter = fly.


That is exactly where I'm at with this whole deal.

Oficially, put me down as "fly" because I don't see how the conveyor will stop the plane from moving. I don't see this conveyor doing anything besides making the wheels on the plane turn twice as fast.

We should be putting one of these conveyors outside every Hometown buffet instead of messing with the runways. Make the fat people jog to their cars. Which begs the question- will the 300 lb women's backwards biceps provide sufficient lift with her arms outstretched to get her in the air, or will the "butt on backwards" cause too much drag? Let's do another 3 pages on that!


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#338764 - 08/23/07 08:20 AM Re: The case of the plane and conveyor belt [Re: Jack T]  
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 Originally Posted By: Jack T
If a speedboat were placed into a huge lap pool (narrow swimming pool that produces a current), and the water movement is automatically adjusted to match the boat's speed, but in the opposite direction, will the boat fly?


This isn't a proper relationship. The boat uses the water as its medium for thrust, and therefore you can zero out the boats movement. To make this relationship, you would have to move the air around the plane. We are moving the ground under the plane, to which it doesn't use for movement.
Put your boat in the pool. Blow air into the front of the boat equal to the boats forward motion. Will the boat's bow hit the pool?


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#338766 - 08/23/07 08:25 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Like Al, I'm giving this one final post.

As I stated previously, if the engine has enough thrust in excess of what it would normally need to take off, to overcome the increased friction on the wheels spinning 2X as fast, the plane will take off. Assuming that your standard air craft does not need 100% power in order to take off, or close to it, I would ASSUME the air craft has the thrust to take off. If not, I think they should come up with more efficient wheel packages.

On second thought, the plane won't take off. It ran out of gas during this discussion.


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#338787 - 08/23/07 09:21 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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I want the Darn Myth Busters show already!!! I don't want to read anymore, i want to see it!!!!!


I'm just happy to be here!



#338795 - 08/23/07 09:49 AM Re: The case of the plane and conveyor belt [Re: BillyB]  
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 Originally Posted By: BillyB
I want the Darn Myth Busters show already!!! I don't want to read anymore, i want to see it!!!!!


Maybe this buy could help out....
http://www.youtube.com/watch?v=PlV8WJ6N3nU


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#338817 - 08/23/07 11:18 AM Re: The case of the plane and conveyor belt [Re: Al]  
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 Quote:
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"


This is poorly worded statement, similar to what you'd see on a college physics midterm and requires that the person solving the problem state their additional assumptions based upon the problem statement. The problem states that the plane is moving and then goes on to state that there is a conveyor that matches the plane's movement in an equal but opposite direction. As soon as the plane moves, the conveyor counters this motion by moving in the opposite direction. My assumption then would be that the plane cannot move relative to the surrounding air or runway adjacent to the conveyor or any other object fixed to the face of the earth due to what is given in the problem statement.


First, about the wheels rotating (which was never in the problem statement and has nothing to do with whether the plane will fly): The conveyor is going in reverse at a speed required to maintain the airplane stationary, then the wheels are not going twice as fast. Here's why:

Assume the plane is producing enough thrust to go 100mph. The conveyor is moving in reverse at a rotational rate sufficient to keep the plane stationary or the angular velocity of 100mph. Becuase the plane does not move as a GIVEN in the problem, the wheels rotate in an equal and opposite direction as the conveyor, or an angular velocity of 100mph.

Furthermore, the plane will not fly becuase insufficient airflow will occur across the wings to creat lift, based upon the additional assumption that the plane does not move.

QED again. (Quite Easily Done or actually: an abbreviation of the Latin phrase "quod erat demonstrandum" (literally, "which was to be demonstrated", and figuratively, "I rest my case"))

My initial answer that it won't fly is on page one of this thread. And being as pigheaded as a pundit, my answer is the only correct answer.


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#338818 - 08/23/07 11:21 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Well that was much better than reading, but still no conveyor belt! That would be the type of plane to test the "myth" on!


I'm just happy to be here!



#338822 - 08/23/07 11:28 AM Re: The case of the plane and conveyor belt [Re: deepv]  
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 Originally Posted By: deepv
 Quote:
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"



Assume the plane is producing enough thrust to go 100mph. The conveyor is moving in reverse at a rotational rate sufficient to keep the plane stationary or the angular velocity of 100mph. Becuase the plane does not move as a GIVEN in the problem, the wheels rotate in an equal and opposite direction as the conveyor, or an angular velocity of 100mph.



Being Muttheaded, I have to retort. The plane not moving is NOT a GIVEN. In fact, saying the conveyer is moving fast enough to keep the plane from moving is also false, the original statement says the the conveyer moves as fast as the plane is going, only in the opposite direction. Nothing is stated about holding the plane in one place.
In fact, if the plane is held in one place, its speed=0. Therefore the conveyer would also stop, until the plane started to move then so would the conveyer. IMO, it is a complete functiom of available thrust versus the drag created by the wheels.


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#338825 - 08/23/07 11:31 AM Re: The case of the plane and conveyor belt [Re: BillyB]  
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 Originally Posted By: BillyB
Well that was much better than reading, but still no conveyor belt! That would be the type of plane to test the "myth" on!


Billy, go on youtube and search for plane conveyer. A bunch of people have tried this with little to no proper scientific experimention procedres. One guy actually holds the plane still basing that the plane is held in one spot.

I don't think the lack of air to provide lift during stationary positioning is a question here, it is whether the plane will move, and move fast enough to provide lift. I think it will, then again, I tried to blow up DaveR's boat too.....


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#338831 - 08/23/07 11:53 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Nope, I'm too lazy to search UTube. I'll wait for Jamie and Adam to do for real!
I know how it should turn out, I just want to see them do it. ANd hopefully blow something up at the end!


I'm just happy to be here!



#338834 - 08/23/07 12:09 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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I just looked at mythbusters forums. Maybe they'll do it?

I still say the best it'll do is hover if there's enough air movement across the wings created by the conveyor, which is highly unlikely.

Another assumption not stated is that the ground wind speed is 0mph.


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#338841 - 08/23/07 12:23 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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240 Bob Offline
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I'm in the camp that thinks WaterMutt has it nailed. \:\)

The converse of the conveyor belt moving in the opposite direction would be for the conveyor belt to move in the same direction. The conveyor belt would then be moving at the exact speed that the plane moves with a net effect of keeping the wheels for spinning at all, but its not going to help the plane take off any sooner.

The movement of the plane is almost entirely a function of the thrust produced by its engines sucking in air and expelling it (jet engine case) out the other side. The wheels and engines are, more or less, a decoupled system. And the friction produced by the wheels, especially once they are rolling is negligible.

JMDO

#338846 - 08/23/07 01:02 PM Re: The case of the plane and conveyor belt [Re: 240 Bob]  
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So the real problem to solve here is not whether the plane will fly but rather does the problem let the plane move forward in relationship to ground speed.

And the problem does not let us define that, so no answer is possible.

#338847 - 08/23/07 01:05 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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 Originally Posted By: WaterMutt
 Originally Posted By: deepv
 Quote:
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"



Being Muttheaded, I have to retort. The plane not moving is NOT a GIVEN. In fact, saying the conveyer is moving fast enough to keep the plane from moving is also false, the original statement says the the conveyer moves as fast as the plane is going, only in the opposite direction. Nothing is stated about holding the plane in one place.
In fact, if the plane is held in one place, its speed=0. Therefore the conveyer would also stop, until the plane started to move then so would the conveyer. IMO, it is a complete functiom of available thrust versus the drag created by the wheels.


The statement says "A plane is standing on a runway that can move..."

Merriam Webster's definition of standing: "9 a : to remain stationary or inactive." So the plane is not moving relative to the runway. I am 100% correct. QED.


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#338849 - 08/23/07 01:10 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Here's another engineer in my office's answer:

If the velocity of the plane v1 = 200 mph, and the velocity of the conveyer system v2 = -200 mph, the plane cannot take off cause the velocities cancel out, and the plane looks as if it is standing still. No wind velocity or air is hitting the underside of the plane's wing to give it its lift. Change in Pressure = ZERO. The pressure on the top of the wing is in equilibrium with the bottom of the wing. Bernoulli's Equation says the sum of the pressure, (P), the kinetic energy per unit volume (1/2 rho (v sq.)), and gravitational potential energy per unit volume ( rho g y) has the same value at all points along a streamline. P = 1/2 rho (v sq) + rho g y. Depending on the Pressure (P) on the wing the plane goes up or down. In this case the change in pressure = zero, so the plane cannot go up.


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#338850 - 08/23/07 01:12 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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You are right. The plane is standing there, until it starts to move. E.g. The second sentence. "The plane moves in one direction.."

Merriam Webster's definition of moves: "to go or pass to another place or in a certain direction with a continuous motion"

So the plane is moving relative to the runway. I am 100% correct.

Just trying to have some with you. \:\) (note: your response is formated much nicer)

#338851 - 08/23/07 01:20 PM Re: The case of the plane and conveyor belt [Re: 240 Bob]  
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As soon as the plane moves the conveyor moves an equal amount in the opposite direction. Velocity is a vector and two vectors of equal magnitude oriented 180* to each other cancel to create a velocity vector with a magnitude of ZERO and direction of ZERO.

It is a zero sum game.

The plane does not move relative to the runway or the earth for that matter, no wind speed is created across the wings, no pressure differential due to the wing shape is created because there is no wind speed and no lift is created because there is not pressure differential. The plane DOES NOT FLY!!!!!!!!!

How many other ways can I explain this truth?


72% of fatal boat accidents are caused by
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#338853 - 08/23/07 01:26 PM Re: The case of the plane and conveyor belt [Re: 240 Bob]  
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I was going to print this until i realized it would take 47 trees (pieces of paper) to do it.

Guess I will read it from my computer screen shortly. \:\)

PS: this was a post count inflation reply

Last edited by D-Rod; 08/23/07 01:26 PM.

-YOLO
#338854 - 08/23/07 01:27 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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DeepV,

Answer this for me: Imagine you have on a pair of roller skates. Go stand on a treadmill and turn it on. The speed doesn't matter. You will remain at a stand still right?

Then have someone, who is not on the treadmill, come up and push you from behind. You will move forward.


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#338855 - 08/23/07 01:31 PM Re: The case of the plane and conveyor belt [Re: D-Rod]  
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D-Rod, I was just thinking of you. Are you going to pose this to your first year physics professor?

Sure hope so. It's all in the problem statement and the concept of reference plane. I envision a conveyor runway adjacent to or on the overall runway of the airport, so when I say the runway doesn't move, I am using that reference plane as the plane against which the plane does not move. If the reference plane is the conveyor "runway" then yes the plane does move relative to this reference plane. But it still does not move relative to the earth as a reference plane and my arguement holds true.


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#338856 - 08/23/07 01:32 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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 Originally Posted By: LanierBoater
DeepV,

Answer this for me: Imagine you have on a pair of roller skates. Go stand on a treadmill and turn it on. The speed doesn't matter. You will remain at a stand still right?

Then have someone, who is not on the treadmill, come up and push you from behind. You will move forward.


yup and the instantaneous response of the super conveyor will compensate for it and you will stop moving relative to the reference plane of the earth.


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boaters that haven't taken a safe boating course.

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#338857 - 08/23/07 01:37 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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 Quote:
Answer this for me: Imagine you have on a pair of roller skates. Go stand on a treadmill and turn it on. The speed doesn't matter. You will remain at a stand still right?


Go ahead and try it, I betcha you will go backwards if you are not holding onto the handles.


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#338859 - 08/23/07 01:39 PM Re: The case of the plane and conveyor belt [Re: jtheile]  
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Cmon. We are making a lot of assumptions here. Friction force is one of them. Remember, we are talking about the worlds biggest conveyor belt right??


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#338860 - 08/23/07 01:39 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Deepv,

What you are saying is true, assuming that it was the wheels that moved the plane. It is not. It is the jet engines which are not coupled to the wheels. LanierBoater's example is very good. The somebody coming up to push you is the same effect the jet engines create.

#338861 - 08/23/07 01:40 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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If the reference plane is the "runway that can move" then the plane is standing on this runway, so it cannot move relative to the moving runway. As soon as the plane starts to go forward, the runway will go backwards. In order for the plane to stand on the moving runway reference plane, it would actually have to reverse thrust and would be moving backwards relative to the earth's reference plane. It would not fly under these conditions either.

Last edited by deepv; 08/23/07 01:46 PM. Reason: added "and"

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#338862 - 08/23/07 01:43 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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If you stand on a treadmill with skates without holding onto anything, when the treadmill starts, you will move with the treadmill.


As for this question. The title of the post should have been

The RIDDLE of the plane and conveyor belt.

That's all it is. No real answer. You can state that the wording sez the plane moves. So it moves, no matter about the conveyor.

You can ask, if a plane moves forward with enough speed to take off, but is towing an anchor behind it, does it take off?
Of course it does, because the first statement said it does.

With this orig question, you can also figure, the plane moves forward which starts the conveyor moveing backwards, which cancels out (or at least slows) the planes forward movement.
So plane stops moving (or slows), conveyor stops (or slows), then plane moves (speeds up) again which starts the cycle over again.
Never ending movement and stopping (slowing).

Still, plane doesn't lift.


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#338863 - 08/23/07 01:45 PM Re: The case of the plane and conveyor belt [Re: 240 Bob]  
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 Originally Posted By: 240 Bob
Deepv,

What you are saying is true, assuming that it was the wheels that moved the plane. It is not. It is the jet engines which are not coupled to the wheels. LanierBoater's example is very good. The somebody coming up to push you is the same effect the jet engines create.


The wheels have nothing to do with it. It is a problem of defining a reference plane. ALL motion is described relative to a reference plane. I have investigated both the moving conveyor runway as a reference plane and the adjacent runway that is stationary relative to the earth's as a reference plane. In either case, no lift is created on the wings and the plane WILL NOT FLY!!!

Last edited by deepv; 08/23/07 01:49 PM. Reason: Added words in italics for clarification

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#338864 - 08/23/07 01:53 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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Just like evolution, you must except this as a truth.


72% of fatal boat accidents are caused by
boaters that haven't taken a safe boating course.

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#338870 - 08/23/07 02:19 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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 Originally Posted By: deepv
Just like evolution, you must except this as a truth.


Tell that to these guys! All 500+ pages!

Plane on a conveyor


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#338873 - 08/23/07 02:23 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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I saw that. It is really a no brainer, if you think about it from an engineer's mind. So, sleep tight and let us engineers worry about the details without interference of accountants and polititians of course. Get them involved and you might as well forget sleeping.


72% of fatal boat accidents are caused by
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#338874 - 08/23/07 02:24 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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I believe in evolution by not your explanation as truth.


deepv wrote:
 Quote:
As soon as the plane starts to go forward, the runway will go backwards.


The runway will go backwards but the plane is only attached to the runway by its wheels!...and wheels roll across a surface when a force (prop or jet thrust) is pushing on the object that the wheels are attached to.

You state "the plane goes forward"...yes!...like the question states "the plane moves in one direction"...forward in relation to what reference plane?...the earth! The same reference plane for measuring the movement of the conveyor belt...or more specifically a spot on the conveyor belt. We use the same reference plane for both items we are talking about...the conveyor belt and the plane.

"The plane moves in one direction, while the conveyor belt moves in the opposite direction". Isn't that pretty clear? EDIT: You can't move North while the conveyor belt moves South, if you aren't moving! Standing still is not a direction.

It's standing and then it moves...it's right there in the question...relative to what reference plane?...the earth...why would we use any other reference plane?...I think it's the one most think of when they think of movement and speed. It's what we would use to measure a conveyor belt speed I think. When the plane moves fast enough across the earth so that its speed through the atmosphere that surrounds the earth enable the wings to provide enough lift to allow it to take-off into that atmosphere it does so.

That leaves the question of does the plane have enough power to move it through the surrounding air to achieve take-off speed. Nothing in the question limits the planes power.

EDIT: I don't pretend to have the engineering brainpower that has been employed re: the question, but I think I can read the question and the question says the plane moves and doesn't limit how fast it does so. Who am I to argue? \:\)




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#338877 - 08/23/07 02:40 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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 Originally Posted By: deepv
 Originally Posted By: WaterMutt
 Originally Posted By: deepv
 Quote:
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"



Being Muttheaded, I have to retort. The plane not moving is NOT a GIVEN. In fact, saying the conveyer is moving fast enough to keep the plane from moving is also false, the original statement says the the conveyer moves as fast as the plane is going, only in the opposite direction. Nothing is stated about holding the plane in one place.
In fact, if the plane is held in one place, its speed=0. Therefore the conveyer would also stop, until the plane started to move then so would the conveyer. IMO, it is a complete functiom of available thrust versus the drag created by the wheels.


The statement says "A plane is standing on a runway that can move..."

Merriam Webster's definition of standing: "9 a : to remain stationary or inactive." So the plane is not moving relative to the runway. I am 100% correct. QED.


Yep, and it also says the plane moves in one direction. that fact that the plane is standing is at time=0, start of experiment. By your assumption that the plane is sitting with velocity=0, would mean that the friction created by the wheels at speed=s is equal to the energy created by the plane's thrust. That is extremely inefficient wheels.


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#338878 - 08/23/07 02:40 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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Go take a hike!! (just kidding, of course)

So you agree to using the earth (runway on which the plane is standing in the problem statement) as the reference plane.

As soon as the plane moves relative to the earth, the conveyor moves in the opposite direction and the velocities of the conveyor and the plane cancel so the plane stands still (or remains stationary) relative to the earth. Because it does not move relative to the earth there is no air flows across the wings and no lift is created. The plane WILL NOT FLY. This again is not dependent on how much power the plane has or the wheels or the friction between the wheels and the conveyor or the friction of the bearings in the wheels or skates or skateboards or treadmills or ropes or boats in currents or... All of these are superfluous and not necesary to solve this problem. The conveyor system can detect motion of the plane independent of either any of this and compensate by moving in the opposite direction. If we chose the earth as the reference plane and the airplane does not move relative to the chosen reference plane this is the only answer that there is.


QED

Last edited by deepv; 08/23/07 02:45 PM. Reason: Changed "either" to "any of this"

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#338882 - 08/23/07 02:54 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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By the way, if the airplane's forward speed is 100 mph and the conveyor's rear speed is 100mph in the reverse direction, the wheels are turning 100mph, not 200mph.

Figure that out and you will have your answer.

I built a conveyor and airplane and confirmed it today...... \:\)


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#338884 - 08/23/07 02:55 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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So we have the world's biggest conveyer it would seem. Now, I am going to introduce the world's biggest winch. Now, my winch is say 1 mile in front of the airplane and mounted to the earth's reference plane. The cable goes to the plane. I begin to pull the plane and the conveyer reacts and goes the opposite direction at the same speed in which I pull it. Now, does the plane stop and stop my winch?


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#338886 - 08/23/07 02:57 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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 Quote:
As soon as the plane moves relative to the earth, the conveyor moves in the opposite direction and the velocities of the conveyor and the plane cancel so the plane stands still (or remains stationary) relative to the earth.


True,if the plane's ground speed was generated by the wheels. It is not.


-------------------------------
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#338887 - 08/23/07 03:01 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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deepv,

First, sorry I miquoted you a bit in "the plane goes forward"...its not exactly what you said which correctly quoted in the quote box.

Second, I would love to "go take a hike"...come on weekend!

Finally, I think your error, and oh yes it is an error , is in giving the conveyor belt powers that are not given in the question.

 Quote:
The conveyor system can detect motion of the plane independent of either and compensate by moving in the opposite direction.


Compensate?

 Quote:
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?


The question has no reference to the ability of the conveyor belt to "compensate" for the speed of the plane to hold it still. It only says the belt "tunes the speed of the conveyor belt to be exactly the same ( but in the opposite direction). ie) The plane is moving at X mph North and the belt is moving at X mph South.

You put a penny on the belt under the plane at the same time you start this crazy experiment and put a flag into the earth next to the plane and conveyor belt. Start he plane and belt, have them move in opposite directions for 1 minute. The distance from the flag to the penny and the flag to the plane will be the same...because they both are tuned to move at the same speed, but in the opposite direction !!




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#338889 - 08/23/07 03:08 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Love the winch idea WaterMutt, great. And I think it plays into this confusion that the conveyor belt can do whatever it must to stop the plane from moving across the earth. I just don't think that is in the question. It just moves, just like the plane moves...only in the opposite direction.

Rock on...I'm back to work, or hiking, or boating...or something...


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#338891 - 08/23/07 03:14 PM Re: The case of the plane and conveyor belt [Re: Al]  
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 Originally Posted By: Al
By the way, if the airplane's forward speed is 100 mph and the conveyor's rear speed is 100mph in the reverse direction, the wheels are turning 100mph, not 200mph.

Figure that out and you will have your answer.

I built a conveyor and airplane and confirmed it today...... \:\)


I'm sure no one will argue that.


Joe
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#338894 - 08/23/07 03:21 PM Re: The case of the plane and conveyor belt [Re: jtheile]  
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Who ever said this was like a physics exam question with the need to clarify all assumptions, that was the most correct statement made here today. MCF=80%


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#338902 - 08/23/07 04:35 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Tune = Compensate


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#338911 - 08/23/07 05:20 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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I'm no mental giant, but it would seem to me that the thrust of the engines would cause the plane to move forward irregardless of what the wheels are doing on a conveyor belt. The only thing a conveyor belt would do is spin the wheels faster in trying to move the plane backwards. Duh!


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#338917 - 08/23/07 05:51 PM Re: The case of the plane and conveyor belt [Re: jtheile]  
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 Originally Posted By: jtheile
 Originally Posted By: Al
By the way, if the airplane's forward speed is 100 mph and the conveyor's rear speed is 100mph in the reverse direction, the wheels are turning 100mph, not 200mph.

Figure that out and you will have your answer.

I built a conveyor and airplane and confirmed it today...... \:\)


I'm sure no one will argue that.




I just might-- *grin* --because it seems to me that in the above scenario, if the wheels AREN'T going 200 mph, then they must be going ZERO mph (the conveyor and plane speed cancel each other out)

But then---and this may have been brought up already but I'm too lazy to read and find out---the wheels will be moving the same speed as the airplane is moving. But how fast they're ROTATING is a different matter! \:\)


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#338919 - 08/23/07 06:06 PM Re: The case of the plane and conveyor belt [Re: Frantically Relaxing]  
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Al, if the plane has a forward speed of 100 mph, and the conveyor belt is going 100 mph in the opposite direction, then the wheels are going at the same rate as if the plane was moving 200mph.

Now riddle me this. If the purpose of the plane on the treadmill is to keep the plane from forward motion, why not just put a rope from the plane to a stationary object that cannot break? Does anyone believe that the plane would fly? Replace the wheels with concrete blocks. Same question?

Look at how they test planes and cars in a wind tunnel. One of the main things tested in both cases is aerodynamics. With airplanes it is to see how much lift is generated by the flow of air over the entire plane. With a car, the test is for balancing the airflow over the car so that it does not fly. If you were to look at the numbers, the average car has only a couple of pounds of pressure on the road above a certain speed. You can actually make a car fly if it is designed too aerodynamically. The problem is that once the source of momentum is removed, the air drag will reduce the air speed to non-flying status.


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#338922 - 08/23/07 06:27 PM Re: The case of the plane and conveyor belt [Re: seadog]  
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 Originally Posted By: seadog
If the purpose of the plane on the treadmill is to keep the plane from forward motion,


The conveyor CAN'T keep the plane from going forward. When it tries to, it just spins the plane's wheels faster and the plane moves forward because of the engine's thrust.


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#338929 - 08/23/07 06:57 PM Re: The case of the plane and conveyor belt [Re: cny boater]  
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 Originally Posted By: cny boater
I'm no mental giant, but it would seem to me that the thrust of the engines would cause the plane to move forward irregardless of what the wheels are doing on a conveyor belt. The only thing a conveyor belt would do is spin the wheels faster in trying to move the plane backwards. Duh!


CNY and I are in the same camp.....


...only what is the difference between regardless and irregardless?

And since it is our camp if you want to join us you must bring firewood or beer.....

Last edited by Parrott_head; 08/23/07 06:57 PM. Reason: Pall Mall Can't Spall...

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#338930 - 08/23/07 07:00 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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#338931 - 08/23/07 07:21 PM Re: The case of the plane and conveyor belt [Re: cny boater]  
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Good Lord, this has gone on for 6 pages?

#338932 - 08/23/07 07:33 PM Re: The case of the plane and conveyor belt [Re: KCook]  
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 Originally Posted By: KCook
Good Lord, this has gone on for 6 pages?


Check the link I gave o n the previous page.


-------------------------------
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#338945 - 08/23/07 08:38 PM Re: The case of the plane and conveyor belt [Re: seadog]  
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 Originally Posted By: seadog
Al, if the plane has a forward speed of 100 mph, and the conveyor belt is going 100 mph in the opposite direction, then the wheels are going at the same rate as if the plane was moving 200mph.


Nope.

The airplane does not have a forward speed of 100mph, it has a forward speed of 0 mph.

The statement said that the conveyor matched the airplane's speed exactly, but in reverse. Therefore the airplane cannot have any forward speed since 100 + -100 = 0

Think of your logic for a minute.

If the airplane is going down the conveyor at 100mph and the conveyor is not moving, it is going 100mph in relationship to the ground. But if the conveyor then kicks in, going 100mph in reverse, unless the airplane is already producing sufficient lift, and if its means of support are the wheels, then it cannot maintain its position, and must slow down to 0 forward speed in relationship to the ground - even though it is still going 100mph in relationship to the conveyor.

If on the other hand, you are suggesting it maintains the 100mph forward speed in relationship to the ground when the conveyor kicks in - where did the additional energy come from?


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#338949 - 08/23/07 08:51 PM Re: The case of the plane and conveyor belt [Re: Al]  
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Al Offline
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Remember the scenario:

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

Since the scenario does not specify that the airplane is going forward, but only in a direction, all of you take-off guys are then 50% wrong to begin with, because if the airplane is in reverse, and while reverse thrust might not be that fast, the plane will not fly in reverse, regardless of the reverse speed.

Therefore, at best, you take-off guys can only be 50% correct, which means, take off cannot be assured (regardless of the forward speed controversy).

Case closed, goodnight!

(you guys better not mess with my logic, I flunked a Mensa test once)






Since this is irrefutable evidence, no since in dragging this out another 500 pages.


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#338952 - 08/23/07 09:04 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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 Originally Posted By: Parrott_head


CNY and I are in the same camp.....



And since it is our camp if you want to join us you must bring firewood or beer.....


I'm coming, too. You guys like Blatz Lite?


By the time they had diminished from 50 to 8, the other dwarves began to suspect "Hungry.”-Gary Larson
#338962 - 08/23/07 09:55 PM Re: The case of the plane and conveyor belt [Re: 2Suns]  
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Al Offline
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Al  Offline
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Vagabond Wanderer from Mich.
OK, I said I was going to leave this alone......


The US Navy has just built a new super carrier, the USS GoFast that has the capability of traveling at 120mph.

During the initial sea trials, the carrier got up to a speed of 120mph, at which time Capt "Crash" Kane, in an attempt to tickle the fancy of one said Navy nurse, decides in all his bravado to take off his aircraft towards the stern of the carrier.

So, he taxis out to the bow of the carrier, turns to the stern of the ship, and signals "watch this"......

Stop the video one second.

We know that with the ship going 120mph in the seas, Capt Crash Kane has a 120mph tail wind; air going in reverse over the wings.

OK, start the video again.

The Capt next pulls his portable Garmin GPS out that his parents got him for Christmas, and notices that he is going 120mph to the reverse. He thinks about it for a moment, then oh yea, that is the speed of the boat. Man, this GPS will be cool next summer on my yacht, he thinks.

The brave Capt rolls his mustache, does a whoop-de-whoop that Slim Pickens would be proud of, and mashes the throttles forward.

The plane rushes down the runway.....

The first thing that Crash notices odd is that as the airplane picks up speed, the GPS speed indicator begins to show his reverse speed is lower, then lower, then no reverse speed at all.

Oh yea, he thinks, I am going down the runway at the same speed the boat is moving forward..... duh!

he then promptly crashes into the sea.

But wait, you say, he was going 120mph.

Yea, he was racing down the deck at 120 mph, but he had a 120mph tailwind, so unfortunately, he did not develop any lift over the wings because he took off with the wind, not into the wind.

So the board of inquiry determined that Crash Kane sped down the runway towards the stern of the ship at 120MPH, with his wheels turning at the same 120mph rate of speed. However, since the carrier had a forward speed of 120MPH, his relative speed to the the tail-wind was 0mph, which meant he did not have any airflow across the wings.

It was then concluded that since the first crash of the Wright Brothers, its been long known by pilots that you lose lift when taking off with the wind, and that posthumously, Crash Kane had well deserved his "handle".

In effigy, one of Crash Kane's fellow pilots came up with this little riddle.........


President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#338967 - 08/23/07 10:04 PM Re: The case of the plane and conveyor belt [Re: Al]  
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trooplewis Offline
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Think of the machine they use to dyno-tune your car. Wheels are cradled in it, much like the 100mph conveyor belt, engine is cranking along, speedo says 60mph.

Are you going 60 mph? Wheels are spinning, car is not moving...

Conveyor belt is moving, plane is not flying.

#338970 - 08/23/07 10:17 PM Re: The case of the plane and conveyor belt [Re: trooplewis]  
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markas Offline
Captain
markas  Offline
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Western PA
Check these related links out. Apparently there's nothing new under the sun. You can google 'plane and conveyor belt' and get a lot - this is just the tip of the iceberg. Seems like generally there is agreement the plane flies.

http://en.wikipedia.org/wiki/Airplane_-_Treadmill_Conundrum

http://www.kottke.org/06/02/plane-conveyor-belt

http://www.airliners.net/discussions/tech_ops/read.main/136068/

http://forum.physorg.com/index.php?s=62a...25&#entry249664

http://www.straightdope.com/columns/060203.html


1992 Maxum 1900 XR bowrider
1991 GMC K1500 pickup
1 great kid
1 great wife
#338985 - 08/23/07 10:45 PM Re: The case of the plane and conveyor belt [Re: markas]  
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cny boater Offline
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If you put a car with wings on the conveyor, it's not taking off because the driving force is the wheels.

Put Superman with a rope tied to the plane and have him pull the plane on the conveyor. The plane takes off. Jet engine thrust is the same as Superman with a rope.

I wonder how many planes have "taken flight" while tethered to the tarmac in an airfield during a windstorm?


Bob
2002 Cobalt 226 350 MPI B1

[Linked Image]
#338987 - 08/23/07 10:46 PM Re: The case of the plane and conveyor belt [Re: cny boater]  
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cny boater Offline
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BTW, I'm gathering up some stuff for Smores here at Camp CNY!


Bob
2002 Cobalt 226 350 MPI B1

[Linked Image]
#338992 - 08/23/07 10:53 PM Re: The case of the plane and conveyor belt [Re: cny boater]  
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BillyB Offline
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Alright. I'll bring some burgers!


I'm just happy to be here!



#338997 - 08/23/07 11:03 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Parrott_head Offline
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Cool....beer, firewood, smores, burgers....Camp CNY is looking pretty dern good....

...now if we could just get that idiot in the plane to switch his engines off we could sing camp songs....

"In the boarding house where I live,
everything is growing old.
Long, gray hairs are in the butter,
and the bread has turned to mold.
When the dog died we had sausage,
when the cat died, catnip tea.
When the landlord died I left there,
spare ribs were too much for me"


Former owner of a 2002 Four Winns 234 FunShip
'16 F250 4x4 Oil Burner
"Hey, if I'm a Vice Admiral, which vice do I get to claim?"
#339000 - 08/23/07 11:26 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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Skibrain Offline
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Enough about airplanes.

If you had a river with a current moving at 20 mph, could you tie a rope to a bridge over the river and go waterskiing? If you fell and let go of the rope, would the local laws require the observer on the bridge to raise an orange "skier down" flag?

#339001 - 08/23/07 11:27 PM Re: The case of the plane and conveyor belt [Re: Parrott_head]  
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trooplewis Offline
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 Quote:
I wonder how many planes have "taken flight" while tethered to the tarmac in an airfield during a windstorm?


Yup, as long as you have wind, you could do that.

markas's wikipedia link above says this:
 Quote:
The solution comes from the fact that unlike the wheels of a car, the wheels of an aircraft are not motorised and that the aircraft's forward motion relative to the ground is created by the thrust of its engine(s), not the spinning of its wheels. With the treadmill moving in the opposite direction to the plane but at the same speed as the aircraft is moving relative to the rest of the world, the plane still takes off as normal, but with its wheels spinning at twice the speed they would otherwise be spinning at.
So the plane is moving forward at it's normal rate of speed, and takes off as normal, but the wheels are moving twice as fast as normal because the conveyor belt is moving backward...

Nah, I like the plane standing still on the runway on a 100mph belt.

#339021 - 08/24/07 05:37 AM Re: The case of the plane and conveyor belt [Re: trooplewis]  
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Al Offline
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The whole answer to the question is momentum.

If the airplane rolls down the conveyor before the conveyor starts, then there is forward momentum and

But if the airplane and conveyor begin simultaneously, its hard to say, because there are too many factors in this dynamic situation to predict the outcome; real world factors such as air pressure, air density, dew point, whether or not the pilot stayed at a Holiday Inn last night, and so on.

The real problem is that the question is not adequate. Momentum is the real key. if the speeds are truly balanced, then inertia is the tie-breaker.

And as I said, the conveyor did not say movement of the airplane forward, it just said movement of the airplane in one direction. As I stated before, if the airplane went in reverse, flight could not be accomplished, so by definition, regardless of what it does in the forward motion, the airplane cannot take off, if it is going in reverse.



President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#339036 - 08/24/07 08:02 AM Re: The case of the plane and conveyor belt [Re: Al]  
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WaterMutt Offline
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No one has addressed my giant winch, my winch is saddenned by this.

Next, if the airplane is not moving, why would the conveyer be moving???


Malibu Wakesetter 23XTI
Bryant 214 Limited (gone, but not forgotten)

"That's my boat..."
-Forest Gump

#339063 - 08/24/07 09:29 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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athiker Offline
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Its a new day so a new attempt!

Al, make your aircraft carrier deck infinitely long and you'll have yourself a nice flight. You mention that the he see's the reverse speed dropping towards zero as he moves down the carrier deck, what makes it stop at zero? Certainly not the movement of the deck, as the jets thrust is from its jets engines vs the atmosphere. If it moves from neg 120 mph at all, then the engines are strong enough to overcome the intial maximum tailwind...so it's just a matter of time till take-off.

Al also wrote:
 Quote:
And as I said, the conveyor did not say movement of the airplane forward, it just said movement of the airplane in one direction. As I stated before, if the airplane went in reverse, flight could not be accomplished, so by definition, regardless of what it does in the forward motion, the airplane cannot take off, if it is going in reverse.


The plane is going in reverse? I guess you could pose the question, "Could Tiger woods hit a golf ball over 100 yards?" and answer..."Not if he doesn't want to." Just why would the plane be in reverse?...is it a stretch to make the assumption that the question assumes the plane is trying to take-off?


 Quote:
it just said movement of the airplane in one direction.


This to me is the key issue. It not only says the plane is moving in one direction, it says it is moving in the opposite direction of the conveyor belt. I still do not understand how standing still is a direction and further how it can be the opposite direction of any other direction.

Watermutt, for the record I liked your winch idea. \:\)




2000 Cobalt 206 5.7L EFI Alpha 1
#339066 - 08/24/07 09:38 AM Re: The case of the plane and conveyor belt [Re: athiker]  
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seadog Offline
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Al, my logic is good, it is the interpretation of the statement that is in question. If the plane has a forward speed of 100 mph, that can be taken to be ground speed and not relative speed. And there is no one that can convince me that the plane will fly unless the wind speed over the wings exceeds the minimum takeoff velocity.


03 Crestliner 2485 LSi 4.3 MPI
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usa1
#339067 - 08/24/07 09:45 AM Re: The case of the plane and conveyor belt [Re: seadog]  
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jtheile Offline
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Is it February already?


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Four Winns 225 Sundowner
#339068 - 08/24/07 09:52 AM Re: The case of the plane and conveyor belt [Re: seadog]  
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WaterMutt Offline
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 Originally Posted By: seadog
..... And there is no one that can convince me that the plane will fly unless the wind speed over the wings exceeds the minimum takeoff velocity.


I don't think anyone will argue that. In fact, i think this discussion has become whether or not the plane will move. I think if you can prove the plane moves, you can prove the plane will EVENTUALLY take off. That is where the problem lies. Is the run way long enough for the plane to build speed over and above the resistance of the wheels spinning twice as fast as they typically would? That is my position on it.

I did stop by the local municipal airport on the way home last night, I lifted up a corner on some little plane, and spun the wheel. It seemed to move pretty easily. I would have checked another, but the Shepherds are pretty fast over there.


Malibu Wakesetter 23XTI
Bryant 214 Limited (gone, but not forgotten)

"That's my boat..."
-Forest Gump

#339072 - 08/24/07 10:05 AM Re: The case of the plane and conveyor belt [Re: jtheile]  
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WayWeGo Offline
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Many of you are confused about what you should use for a reference.

For a plane to fly, it needs to move fast enough relative to the AIR to produce sufficient lift to counteract the force of gravity on its' mass. Al's carier analogy is a good example of this.

Starting with a reference of the air (and assuming no significant wind), the plane engines fire up, produce thrust, and move the plane forward RELATIVE TO THE AIR. At the same time, the conveyor begins moving the ground surface backwards at the same rate RELATIVE TO THE AIR. Since the plane is moving forward relative to the air the wheels start spinning. Because the conveyor is moving backwards relative to the air, the wheels are spinning twice as fast as if there was no conveyor. At some point, the plane reaches a velocity that supports enough lift, and it leaves the surface of the conveyor.

The only way that the plane will stay stationary relative to the ground is if the brakes are on or the engine does not produce enough thrust to overcome the static friction in the wheel bearings plus the drag of any headwind.

To work this problem relative to the gound is a quite obtuse method and noone here has accounted for all the significant factors.

Can we go boating now??? You know, now that I mention it, boating is a good idea, so I am going to take the afternoon off and see how my boat performs with different currents and winds !!! ;\)



1975 Trojan F36 Convertible, Twin Chrysler 440's
2014 West Marine AL360 Inflatable, 1966 Mercury 6HP, 1992 Mercury 20HP
#339118 - 08/24/07 12:53 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Hockey Family Offline
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OC - SoCal
 Originally Posted By: LanierBoater
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

Lots of "experts" on both side of the fence. What say you?


===============================================================
plane (pln) KEY

NOUN:

- A carpenter's tool with an adjustable blade for smoothing and leveling wood.
- A trowel-shaped tool for smoothing the surface of clay, sand, or plaster in a mold.
===============================================================

The plane will fly only as far as it was thrown.


HF
2006 Monterey 214FS
Volvo/Penta 5.0 GXi SX
#339120 - 08/24/07 12:59 PM Re: The case of the plane and conveyor belt [Re: Hockey Family]  
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deepv Offline
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72% of fatal boat accidents are caused by
boaters that haven't taken a safe boating course.

[Linked Image][Linked Image]
#339212 - 08/24/07 07:15 PM Re: The case of the plane and conveyor belt [Re: Skibrain]  
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markas Offline
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Western PA
 Originally Posted By: Skibrain
Enough about airplanes.

If you had a river with a current moving at 20 mph, could you tie a rope to a bridge over the river and go waterskiing? If you fell and let go of the rope, would the local laws require the observer on the bridge to raise an orange "skier down" flag?


And do you need an observer?


1992 Maxum 1900 XR bowrider
1991 GMC K1500 pickup
1 great kid
1 great wife
#339229 - 08/24/07 08:43 PM Re: The case of the plane and conveyor belt [Re: markas]  
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Budinski Offline
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Houston
Just when you thought this horse was dead, I saw it twitch. I just want to complete the story.

A number of you are right, or at least close to being right. The relative wind (air flow) over an airfoil (wing) is what produces the low pressure above the wing that we call LIFT. And the most common way to get that air to flow over the wing is to introduce forward motion of the wing. That’s why airplanes roll and helicopters’ blades turn. The faster the airfoil moves through the air—or the air moves past the airfoil—the more lift is produced. When enough lift is produced to overcome the affect of gravity, the aircraft leaves the ground.

In the 1970’s NASA wanted to increase helicopters' speed while retaining their vertical take-off capabilities. They tried many things, and one of the innovative ways they thought of was truly amazing. They wanted to make a 4-bladed rotor extra stiff so that it could be slow down during flight to become a wing. To achieve fast airflow over an airfoil was slowing to a stop, they delivered compressed air out of the leading edge over the top of the wing and had the trailing edge of the wing with a slot in it which sucked air in. That way they thought that they could create lift from the wing/rotor at all times—even if the rotor wasn’t spinning.

You can see the X-wing experimental aircraft at this site:
http://www.dfrc.nasa.gov/gallery/Photo/X-Wing/Medium/EC86-33555-2.jpg

It was a neat idea; however, the Russians beat NASA to it when they retrofitted one of their HIND helicopters with this advanced technology. So NASA gave up on this innovative idea.

You can see it flying at this site: http://www.youtube.com/watch?v=jQDjJRYmeWg

So, hopefully this horse is dead…or is it?


2000 Sea Ray 180 BR
2000 SeaArk 15
2000 Expedition
#339230 - 08/24/07 08:46 PM Re: The case of the plane and conveyor belt [Re: Budinski]  
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markas Offline
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Western PA
Wait...the type of plane was not specified - 'state your assumptions' - what about assuming the plane is a Harrier or some other VTOL?


1992 Maxum 1900 XR bowrider
1991 GMC K1500 pickup
1 great kid
1 great wife
#374472 - 01/28/08 11:25 AM Re: The case of the plane and conveyor belt [Re: markas]  
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Just Bob Offline
Cap'n of all things wet
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OK, not trying to ressurect an old debate, but I just noticed that Mythbusters will be testing this out on Wednesday night January 30th at 9PM on the Discovery channel.

We will FINALLY know the answer to this question!


"Annabo": 2005 Larson Senza 206 w/5.0L Bravo III
#374500 - 01/28/08 01:08 PM Re: The case of the plane and conveyor belt [Re: Just Bob]  
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BillyB Offline
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Alright!!!! Thanks for the heads up!


I'm just happy to be here!



#374503 - 01/28/08 01:22 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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deepv Offline
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Nooooooooo......!!!!!!!!!!!!!!!!!


72% of fatal boat accidents are caused by
boaters that haven't taken a safe boating course.

[Linked Image][Linked Image]
#374511 - 01/28/08 01:44 PM Re: The case of the plane and conveyor belt [Re: deepv]  
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WaterMutt Offline
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Whether they agree with my answer or not, I put NO faith in the Mythbusters and thier antics.


Malibu Wakesetter 23XTI
Bryant 214 Limited (gone, but not forgotten)

"That's my boat..."
-Forest Gump

#374514 - 01/28/08 01:54 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Admin Offline
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Cyberland
I tried sitting through that show once. Lasted about 10 mins.

I do not believe it worthy of being taken seriously or as "fact".


Mike

BoatingABC.com
My imaginary friend thinks you have serious problems.
#374515 - 01/28/08 01:56 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Just Bob Offline
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 Originally Posted By: WaterMutt
Whether they agree with my answer or not, I put NO faith in the Mythbusters and thier antics.

Really? I find that they seem to really try to test the myth as accurately as possible, and then if/when they disprove it, they have fun going overboard to show exactly what it would take to achieve the myth.

Like the other day, they tried to see if firing a 9mm pistol into a propane tank would blow it up, and it didn't, so they ended up firing incendiary rounds from a 50 round per second machine gun. It blew up after that...


"Annabo": 2005 Larson Senza 206 w/5.0L Bravo III
#374518 - 01/28/08 02:12 PM Re: The case of the plane and conveyor belt [Re: Just Bob]  
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Frantically Relaxing Offline
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I like mythbusters, and believe they try their best to prove/disprove things. However, I myself am proof one of their busted myths is wrong---the one where they tried to prove whether or not a person could crash thru glass and walk away relatively unhurt (like in the movies)---they built a jelly dummy, and 'proved' that going thru 1/4" thick glass would hack a person up big time, and therefore it was BS that Eddie Murphy could just walk away from being thrown thru that window in 'Beverly Hills Cop'...Well, when I was 6 years old I crashed thru the 1/4" thick glass door at the local bowling alley (running, and missed the door handle!) and ended up face first in a pile of shattered glass---all that happened was a 1/2" gouge across my nose and a cut on my thumb. And not another scratch...

That said -- ;\)

The plane will fly. \:\)


[Linked Image]
#374522 - 01/28/08 02:24 PM Re: The case of the plane and conveyor belt [Re: Frantically Relaxing]  
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FatDog Offline
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Lakeside, CA
 Originally Posted By: Frantically Relaxing
......... Well, when I was 6 years old I crashed thru the 1/4" thick glass door at the local bowling alley (running, and missed the door handle!) ....

i watched a buddy at college do the same thing, unknowingly run through the glass door and hit the ground, all without a scratch,
it should have been a commercial for budweiser, as that played an active role, but maybe thats not the sort of image they are going for,

mythbusters was better before they got all those junior assistants on the show,
but those guys sure do have access to a bunch of cool equipment and ideas, it can be pretty enjoyable


22' Launch, VP 8.1
pugs, boxer, bulldog

"Let us cross over the river and sit under the shade of trees." ...... General Thomas 'Stonewall' Jackson
#374524 - 01/28/08 02:25 PM Re: The case of the plane and conveyor belt [Re: Frantically Relaxing]  
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BToran Offline
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BToran  Offline
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yeah, yeah, yeah. but what if monty hall was flying the plane while everyone debated whether a contestant was better off with door number one or door number two and at the same time, the flight attendant was flipping coins while everyone debated whether the chances were increased or decreased that it would land on heads or tails? seems to me, in that situation, time would slow to the point of it being inconsequential, and we'd all realize the exact same thing at the exact same space/time moment.......it's winter, we're bored, and it just doesn't matter.

oh, and the monkey on the rope....he'll still stink.


Bruce Toran
Former Owner of a 1996 Carver 320 Voyager
-----------------------------------------
"Don't Eat Anything Bigger Than Your Head"
#374527 - 01/28/08 02:31 PM Re: The case of the plane and conveyor belt [Re: BToran]  
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Admin Offline
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Admiral

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Cyberland


Give that man a cigar! We have a winner!.


Mike

BoatingABC.com
My imaginary friend thinks you have serious problems.
#374543 - 01/28/08 03:09 PM Re: The case of the plane and conveyor belt [Re: Admin]  
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WaterMutt Offline
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WaterMutt  Offline
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Massachusetts
My problem with Mythbusters is they do things thier way, and it might not be the right way that it should be done. AFter doing it one way and failing after several attempts, the myth is busted. Also, thier scientific methods aren't overly scientific typically. I don't know, may be I am all wased up on the idea, but I don't follow thier methods.


Malibu Wakesetter 23XTI
Bryant 214 Limited (gone, but not forgotten)

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#374545 - 01/28/08 03:11 PM Re: The case of the plane and conveyor belt [Re: Admin]  
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I do not see how Mythbusters can create a scenerio that can duplicate the original set of circumstances.
Until that happens, its like discussing politics. You can't prove your point.


-------------------------------
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#374549 - 01/28/08 03:17 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

Tell me they won't build a conveyer belt, stick a plane on it, and try to make the plane take off. I bet they'll even do it on the same full size scale.


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#374558 - 01/28/08 03:35 PM Re: The case of the plane and conveyor belt [Re: Just Bob]  
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In any case, I am interested in how they interpret the question.


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#374560 - 01/28/08 03:44 PM Re: The case of the plane and conveyor belt [Re: Just Bob]  
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 Quote:
Tell me they won't build a conveyer belt, stick a plane on it, and try to make the plane take off. I bet they'll even do it on the same full size scale.


In the words of John McEnroe: "You can NOT be serious".


-------------------------------
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#374566 - 01/28/08 04:03 PM Re: The case of the plane and conveyor belt [Re: Just Bob]  
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 Originally Posted By: Just Bob

Tell me they won't build a conveyer belt, stick a plane on it, and try to make the plane take off. I bet they'll even do it on the same full size scale.


Uummm, how else would they test the myth if they don't do it that way??


I'm just happy to be here!



#374572 - 01/28/08 04:14 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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 Originally Posted By: BillyB
 Originally Posted By: Just Bob

Tell me they won't build a conveyer belt, stick a plane on it, and try to make the plane take off. I bet they'll even do it on the same full size scale.


Uummm, how else would they test the myth if they don't do it that way??

1/4 scale model airplanes. Pretty big in their own right, should be enough to test the theory.

and--the only way a conveyor turning the wheels backwards would stop a plane from going forwards is if turning the wheels caused the plane to go backwards in the first place, which they won't do. There. No money need be wasted on a TV show.

;\)


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#374574 - 01/28/08 04:25 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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 Originally Posted By: WaterMutt
My problem with Mythbusters is they do things thier way, and it might not be the right way that it should be done. AFter doing it one way and failing after several attempts, the myth is busted. Also, thier scientific methods aren't overly scientific typically. I don't know, may be I am all wased up on the idea, but I don't follow thier methods.



So? It's just a lot of fun to watch! Anytime the blow something up or utterly destroy it, I'm a happy man. I don't think this show is really about the science.


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#374576 - 01/28/08 04:35 PM Re: The case of the plane and conveyor belt [Re: casualboater]  
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thats it ... blowing some stuff up under the guise of science, but its fun to watch,

afterall, the last truly scientific show came to an end once they got Gilligan, the professor, and those two hot babes off the island


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#374579 - 01/28/08 04:38 PM Re: The case of the plane and conveyor belt [Re: casualboater]  
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 Originally Posted By: casualboater
 Originally Posted By: WaterMutt
My problem with Mythbusters is they do things thier way, and it might not be the right way that it should be done. AFter doing it one way and failing after several attempts, the myth is busted. Also, thier scientific methods aren't overly scientific typically. I don't know, may be I am all wased up on the idea, but I don't follow thier methods.



So? It's just a lot of fun to watch! Anytime the blow something up or utterly destroy it, I'm a happy man. I don't think this show is really about the science.


Never said I wasn't jealous of getting to rubble-ise a bunch of perfectly good stuff. I just don't place much emphasis on thier conclusions is all.


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#374587 - 01/28/08 04:49 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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 Quote:
Until that happens, its like discussing politics. You can't prove your point.



Lanierboater mentioned politics!! Lock the thread!

#374588 - 01/28/08 04:51 PM Re: The case of the plane and conveyor belt [Re: mambajack]  
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I was going to chime in but I don't want to repeat anything and I don't have time to read 17 pages. For what it's worth, Plane takes off, Monkey stinks, and Monty Hall's one rich old dude.


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#374594 - 01/28/08 05:16 PM Re: The case of the plane and conveyor belt [Re: AnchorYanker]  
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I see the plane lifting off then crashing. I suspect they will have a BIG fan of some type.

#374598 - 01/28/08 05:48 PM Re: The case of the plane and conveyor belt [Re: Heyboer]  
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FR has it, IMHO. Unless the internal friction of the wheel bearings cannot handle the additional speeds.

The wheels will be traveling at 2x rate of the orginal take off speed.

Example, plane normally takes flight at 300mph.

On the belt, the wheels will be traveling at 600mph. I think. It might be 1200mph. Let me think about that a little more.

Obviously, that isn't going to happen with stock wheels, so therefore the plane is not taking off until that part is corrected.

Fix that and the plane will take off.

D-Rod.

PS: Here's the routing number 0000000000 and account number 1234567 for you to deposit your contributions too.


-YOLO
#374607 - 01/28/08 06:11 PM Re: The case of the plane and conveyor belt [Re: Heyboer]  
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 Originally Posted By: Heyboer
I see the plane lifting off then crashing. I suspect they will have a BIG fan of some type.


Maybe they'll do two conveyers and two planes aimed at each other. That'd be cool...


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#374618 - 01/28/08 06:39 PM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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 Originally Posted By: WaterMutt


Maybe they'll do two conveyers and two planes aimed at each other. That'd be cool...


Oh yeah, now you've got me really hoping!!


I'm just happy to be here!



#374660 - 01/28/08 08:45 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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I trust MythBusters WAY more than any personality I have seen so far in the presedential debates. I hope the plane stays on the ground...

#374768 - 01/29/08 12:30 PM Re: The case of the plane and conveyor belt [Re: trooplewis]  
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Without reading all of this, it's easy. An airplane needs air speed to fly. Conveyor belt creates air speed only off the friction of the "belt". Not significant.

Airplane would not fly.

An airplane with zero ground speed and a head wind ( or wind tunnel) equal to or greater than it's take off speed can "fly" under power. It could even have negative ground speed. flying backwards in relation to the ground.

#374774 - 01/29/08 12:59 PM Re: The case of the plane and conveyor belt [Re: Skibrain]  
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nevermind....

Last edited by WaterMutt; 01/29/08 01:00 PM.

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#374781 - 01/29/08 01:04 PM Re: The case of the plane and conveyor belt [Re: Skibrain]  
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Skibrian, why do you think the plane will have zero ground speed? The conveyor belt only has the ability to move "wheels", not the plane. If the engines are producing thrust, the plane can move forward on the conveyor belt at any speed. There simply has to be enough thrust to overcome the wheel friction, right?

Think of it like this, if you tied a huge chain the the airplane and ran the conveyor belt, the plane's wheels would move but the plane would not move in the direction of the belt. The engine's thrust can work the same as the chain. When powered up, the engine's thrust can be greater than what is needed to hold the plane stationary, therefore the plane accelerates.

If the belt's speed increases as the plane moves forward, that just means the plane's wheel's are moving twice as fast. Again, assuming the gear assembly can handle double the speeds, and the friction is small enough that the engines can overpower, the plane should lift off in approximently the same distance it would normally take.

The plane will need the 2 miles or whatever is needed to lift off. There is no way to keep the plane stationary and have it take off. But, that is not what this question asks, right?

D


-YOLO
#374848 - 01/29/08 03:26 PM Re: The case of the plane and conveyor belt [Re: D-Rod]  
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Got it. I was not paying attention.

#374850 - 01/29/08 03:27 PM Re: The case of the plane and conveyor belt [Re: D-Rod]  
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I just saw the commercial for that show on Wednesday and thought of this thread.

The plane will fly in the stated theoretical problem.

I can imagine that that the control loop for the conveyor could be a problem for them on TV though. By definition, it will be a feed-back loop and will present issues with regard to sensor selection, processing cycle time, and prime mover acceleration ramp.

I also wonder how they will handle the dimensional analysis and similitude challenges for the experiment. I am not sure that the assumption of "divide everything by the same number" is a valid modeling approach given the subject matter.

#374974 - 01/30/08 08:51 AM Re: The case of the plane and conveyor belt [Re: Scott L]  
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I have not read all the replies regarding this topic. I sent the initial question to my uncle who is a retired commerical airline captain, who flew 737 for 30 years with not putting even a dent in his planes. I also sent this to my brother who is not a retired but is a captain for the same airline as my uncle.

This is what my uncle said:
"I need more info before answering. What is the planes speed? Lift must occur which is a result of speed based upon weight, temp, and altitude. If the conveyer is moving the wing fast enough, then lift will occur and flight will follow.


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#375225 - 01/30/08 10:31 PM Re: The case of the plane and conveyor belt [Re: trooplewis]  
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Anyone watching Mythbusters?


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#375226 - 01/30/08 10:33 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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Yep. Pretty obvious what was going to happen. And he explained it very well with the RC car on the treadmill.


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#375233 - 01/30/08 11:00 PM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Some had it figured out. I definitely wasn't the first to mention the correct prediction.

Interesting nonetheless.


-YOLO
#375263 - 01/31/08 01:50 AM Re: The case of the plane and conveyor belt [Re: D-Rod]  
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Oh sure. My dish network is kaput, can't watch-- and you guys don't bother saying WHAT the results were?
;\)


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#375292 - 01/31/08 08:12 AM Re: The case of the plane and conveyor belt [Re: Frantically Relaxing]  
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We'll let Deepv tell you. QED.


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#375294 - 01/31/08 09:19 AM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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I missed the show. I would like to hear a synopsis of what happened. If they used an RC car driven by wheels, it only supports my thoughts of missedbusters.


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#375298 - 01/31/08 09:28 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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Mutt, they showed an RC car staying in perfect pace with the treadmill and then turned it off and let it freewheel. Then they push the RC car with their hand and it moved forward. That was a teeny tiny part of the episode, and it was done to try to illustrate to people that the drive thrust of an aiplane is not the wheels. It's the thrust washer of the propeller.

So in short, the little remote control plane they used first, took off easily.

Then they went to an airport and got a guy with an Ultralight plane that could take off in 85 feet. The pilot thought he'd sit still on the conveyor! (remind me to not have him as my pilot!). Their "converyoer belt" was a large strip of tarp that they pulled the opposite direction with a Toyota pickup. The truck took off, the plane revved up and moved in the oppostie direction and became airborne off the conveyor belt. Myth BUSTED! (the myth was it wouldn't move or take off)
The only thing they didn't show was how much longer, if at all it took the plane to acheive flight. But that wasn't the point.

Last edited by BillyB; 01/31/08 09:30 AM.

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#375300 - 01/31/08 09:34 AM Re: The case of the plane and conveyor belt [Re: BillyB]  
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Thanks, Billy. Sounds like they were on track with that one, not that they need or should heed my help. I'm kind of bummed I missed the episode. But Military Channel was doing the 10 best Bombers of all times and i wanted to see where the B-1 came in. Didn't make the top 10, I should have watched the MB. Maybe MB should have used a B-1 in thier experiment. i wonder what would be left of the Toyota?


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#375301 - 01/31/08 09:37 AM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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and it only took 19 pages of posts for us to get a definitive answer. imagine if it was never tested on tv. thank you, myth busters, for allowing us to get back to what's really important..........determining if monty is gonna give away a goat or a car.


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#375315 - 01/31/08 10:12 AM Re: The case of the plane and conveyor belt [Re: BToran]  
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A few clips courtesy of YouTube for those w/o Tivo that missed it:

http://youtube.com/watch?v=S377HwOthjo

http://youtube.com/watch?v=0ul_5DtMLhc&feature=user

Do a YouTube search for: mythbusters conveyor ...and you will get other versions. I saw one for the RC plane tests but lost it, a lot of them aren't as nice quality as the 2 links above.

BTW, as a side note the cockroaches will not inherit the earth in the event of a nuclear war...some may survive but the Flour Beetle will kick @@@! ;\) (it was the other show segment)


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#375317 - 01/31/08 10:30 AM Re: The case of the plane and conveyor belt [Re: WaterMutt]  
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 Originally Posted By: WaterMutt
Maybe MB should have used a B-1 in thier experiment. i wonder what would be left of the Toyota?


WM, there was talk at the end about "next time maybe we can super size it w/ a jet!"...so maybe! Thanks for the heads up on the show airing Just Bob.

Of course this doesn't settle question interpretation and wording issues, etc....but I think this is how most interpreted the question. Like BillyB wrote, the fact that the pilot even thought his plane would sit still is telling.


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#375969 - 02/01/08 11:14 PM Re: The case of the plane and conveyor belt [Re: athiker]  
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I think they just need a faster conveyor belt...

#569986 - 01/09/18 03:43 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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In case anyone wants to see it, I have video of a plane on a conveyer belt. Mythbuster exhibit at pur local science museum.


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#569987 - 01/09/18 06:24 PM Re: The case of the plane and conveyor belt [Re: LanierBoater]  
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If speed of conveyor is unlimited it will eventually approach the speed of light. The plane will fly, but not in three dimensional space, but in time. Congratulations board, you have developed the first theoretical time machine.


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