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Old 11th November 2008, 06:38 AM   #81
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Originally Posted by ponderingturtle View Post
It is so, you are getting more momentum out in a way that you can not put it in, and also increasing the energy as a result.

You are accelerating faster when the only force on you is friction.
If the only force was friction why does it stop working when the propeller is disconnected. In fact any amount of friction reduces it's ability to climb the treadmill so claiming the only force is friction doesn't wash.
http://www.youtube.com/watch?v=LMgDvC5lqsY

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Old 11th November 2008, 06:44 AM   #82
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As for the actual DWFTTW:

I don't think the treadmill proves this concept since it is the driving force in that demonstration.

That being said I think the DWFTTW is possible though. You can get some fraction of the total wind energy to your use. Let's call it E(max). The kinetic energy of the vehicle is E(max) = 1/2mv^2. So v = sqrt[2E(max)/m]. If E(max) is sufficiently large and/or m is sufficiently small then v is greater than wind speed.
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Old 11th November 2008, 06:52 AM   #83
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Originally Posted by Thabiguy View Post
In the same way that the sail, moving with the water, can use its speed against the air to increase its speed against the air. Please try to think about it.
Good point.

Originally Posted by Thabiguy View Post
No, that is just wrong. The energy does not come from nothing - it comes from the kinetic energy of the wind. When two objects are moving with respect to each other (air vs. ground), then braking them against each other releases energy, which can be utilized - in this case, to propel you forward.
Good point.

Originally Posted by Thabiguy View Post
You want a simple example how that works? Imagine yourself in a car on a highway. You are moving at the same speed as the cars in your direction. You take a ball and throw it at a car going in the opposite direction. It bounces from it, then it bounces from a car behind you in your direction, and then you recatch it. Guess what? The ball, when you recatch it, will be travelling forward faster than when you threw it, giving you net increase in momentum and kinetic energy (do the calculation if you don't believe me). The momentum and energy did not come from nowhere - it came from the two cars that the ball hit, slowing them with respect to each other. Your speed is now higher than the speed of other cars in your direction - but you needed the cars going in the opposite direction for this to work.
Very nice analogy.

I'm still chasing a good quantitative analysis. I'm starting with some rather dumb linear assumptions on the grounds that the elements of the basic equation can be substituted with more realistic relationships later in the derivation.
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Old 11th November 2008, 06:56 AM   #84
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Originally Posted by Acleron View Post
Just taking the case of the vehicle reaching the air speed. Then with respect to the propellor, the air is motionless.
The air is motionless with respect to the device as a whole, but not with respect to the blades of the propeller. (It's more obvious in the blower version.) The blades are moving backwards with respect to the air, which makes the air exert forward force on them.

Originally Posted by Acleron View Post
How can it now get any energy to supply to the wheels?
The energy comes from the air being slowed, with respect to the ground, as it pushes the propeller forward.

Originally Posted by Acleron View Post
If the propellor is directly connected to the wheels, which seems the case in the first video, the propellor would now act to stop the wheels.
No, because the air is still pushing forward on the propeller. It's easier to see in the blower version, but it's also true in the propeller version, when f < 1.
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Old 11th November 2008, 07:31 AM   #85
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Originally Posted by .13. View Post
As for the actual DWFTTW:

I don't think the treadmill proves this concept since it is the driving force in that demonstration.

That being said I think the DWFTTW is possible though. You can get some fraction of the total wind energy to your use. Let's call it E(max). The kinetic energy of the vehicle is E(max) = 1/2mv^2. So v = sqrt[2E(max)/m]. If E(max) is sufficiently large and/or m is sufficiently small then v is greater than wind speed.
This is at the root of the debate spork and I had on physicsforums. I still consider it a reasonable proof of concept. However, with the source of energy reversed it doesn't necessarily represent the same efficiency you would get in the wind power source case. However, I will concede to spork that in his design the prop is acting more like a prop than a windmill even in the wind driven case. This allows the prop to go from a 59% theoretically perfect efficiency (Betz' law) to over 90% practical efficiency. I have no doubt that the device can actually work regardless of specific efficiency limitations because you can always just use a larger cross section of wind for more power.

Why doesn't a skeptic here take sporks lead and actually build one. He was told it wouldn't work so he went empirical. Good lead to follow. It needs independent verification as a matter of principle.

@spork
The limited slip ring I argued before will show the drive train torque coming from the direction of the wheels. This is a good thing as it does give you that ~35 to 40% extra practical efficiency in the prop alone due the the entropy arguement I made. If you forget the prop efficiency and the specifics of the aerodynamic forces it can be thought of as a single force vector on the craft frame itself. This provides the wheel feedback that determines the direction of the torque vectors on the drive shaft. So I stand by the principles of my arguement but must consede the actual numbers from it is working in favor of the efficiency of your design.
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Old 11th November 2008, 07:44 AM   #86
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Originally Posted by my_wan View Post
The limited slip ring I argued before will show the drive train torque coming from the direction of the wheels.
That's correct. And I never argued otherwise. The wheels produce a torque on the axle, which produces a torque on the prop shaft. This is true whether we're on the treadmill or open road. Equally true is the fact that the prop produces a force on the cart through the thrust bearing which produces a force on the wheels, which cause them to spin (against the road surface). This is also true whether we're on the cart or the open road.

The two cases are absolutely indistinguishable by the cart. The equivalency of inertial frames guarantees that this is true.

Quote:
This is a good thing as it does give you that ~35 to 40% extra practical efficiency in the prop alone due the the entropy arguement I made.
Well, you've gone back and forth on that issue twice now. I maintain, as I always have, that we were never missing that magical 35-40% prop efficiency.

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So I stand by the principles of my arguement
And I still stand by the principle of equivalency of inertial frames given to us by Galileo, Newton, and Einstein (and spork).

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Old 11th November 2008, 07:59 AM   #87
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Lets make a simple example of a vehicle that can travel downwind faster than the wind, that we can all agree on. Assume an iceboat with zero drag and blade friction in the forward direction with the sail down. We know iceboats can go several times the speed of the wind at an angle, even if you don't believe the downwind component can be faster than the wind. Get the boat up to speed, then drop the sail and turn downwind, and with zero friction and air resistance it will continue downwind faster than the wind indefinitely. After some time the average speed in the downwind direction will be faster than the wind. With very little friction and drag, the boat will eventually slow down, but there are some non-zero values of friction and drag below which it is possible to average faster than the wind in the downwind direction, by re-accelerating occasionally. So I think we can all agree that in theory traveling downwind faster than the wind is possible.
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Old 11th November 2008, 09:33 AM   #88
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J13, I think we are almostin agreement, but not that the actual device will work.
I would like to stick to the demonstrations for the moment if I may, because here lies a source of confusion.

Spork, try this (thought) experiment. Place the cart so that is runs in the same direction as the belt. Well, it travels at the speed of the belt or perhaps a little backwards. Now hold it with your finger, and allow the propeller to turn, and then release it. It will now move faster than the belt. This has nothing to do with the propeller, because in this direction, the same effect can be achieved with a mass as with the propeller. If you impede the cart briefly, so that it has less opportunity to pick up energy, it will come to a stop before the end of the belt, when the mass (or propeller) stops. So would it the other way, given a chance.

In the other direction, it travels at (almost) the speed of the belt because the propeller itself creates drag. Just like you need a finger to spin the propeller in the first place. Drag 'sticks' the cart to the belt. The propeller doesn't drive the cart, it couples it to the air, so that the belt can drive it. If a momentum-less propeller were possible, the cart would drift backwards, because 100% transfer is impossible, but the initially stored momentum makes up that loss and some, propelling it forward.
Only the stored momentum does work in both cases. Even the sliding will be enough for just a little bit more energy be gained to keep it running. Sorry, but it's an illusion.

In your demonstrations, you are seeing the movie, but not the beginning and the end. Momentum is always conserved. The system must includes all sources of energy, including your input, and run continuously. Many over-energy devices (I know this is not your claim) appear to work when you see only some of the inputs, or for a short time.
The real cart is also a matter of momentum but for another reason. I could try to explain...

My_wan,
It's not skepticism, but physics. This problem is merely the result of intuitive thinking. No shame in that, it led Da Vinci to make many errors.
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Old 11th November 2008, 10:05 AM   #89
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Originally Posted by spork View Post
That's correct. And I never argued otherwise. The wheels produce a torque on the axle, which produces a torque on the prop shaft. This is true whether we're on the treadmill or open road. Equally true is the fact that the prop produces a force on the cart through the thrust bearing which produces a force on the wheels, which cause them to spin (against the road surface). This is also true whether we're on the cart or the open road.

The two cases are absolutely indistinguishable by the cart. The equivalency of inertial frames guarantees that this is true.
Not completely equivalent for the reasons I originally specified on physicsforums. The vectorial components have different values in the wind driven and treadmill driven cases. In the treadmill case the initial force vector comes directly from the treadmill to the wheels. In the wind driven case the force vector comes through the frame of the craft itself over and above the prop force vector alone and then feeds back through the wheels. Yes the direction of the vector through the drive shaft is the same so it still doesn't suffer the efficiency limitation from Betz' law but it is still a mistake to assume the vectors are identical. You could easily reinvoke Betz' law by something as simple as changing the gear ratio.

Originally Posted by spork View Post
Well, you've gone back and forth on that issue twice now. I maintain, as I always have, that we were never missing that magical 35-40% prop efficiency.
Not exactly. When Jeff Reid questioned the relevancy of Betz' law I readily admitted that I would have to rethink it before our debate ever started. When I did respond I specifically stated that it was "with qualifications". You went further than simply claiming the the craft wasn't missing the 35-40% efficiency, you claimed via Galilean relativity that the source of power couldn't make a difference. My argument was and still is that it does for the same reason an airplane propeller has an effective efficiency of over 90% while a windmill has a theoretically perfect efficiency of 59%. If Galilean relativity alone is enough to prove equivalency then you can't have two different efficiencies depending on whether the wind is blowing the prop or the prop is blowing the wind as Betz' law states. As I pointed out this is the result of how entropy is dissipated through the system. My argument stands regardless of the fact that the vectors can lined up in such a way to prevent the craft from suffering inefficiencies due to Betz' law.

Originally Posted by spork View Post
And I still stand by the principle of equivalency of inertial frames given to us by Galileo, Newton, and Einstein (and spork).
Here is the claim of equivalency again. You have to be real careful assuming relativistic equivalency of reversal when dealing with dissipative systems. Even though the craft propeller system was spared from Betz' law by the proper direction of the force vector through the drive shaft the force on the frame in the wind driven case is still over twice that of the treadmill driven case. It also means that you need a wind speed greater than the treadmill speed to be equivalent to the power imparted by the treadmill. This is due to only being able to take advantage of a portion of ground wind speed and all of the treadmill speed. The wheels don't slip on the treadmill the way they do in air.

So no I don't take my argument back. More analysis showing the prop alone doesn't suffer the limitations of Betz' law in no way changes that argument.

Point of fact: The "principle of equivalency" has nothing to do with the equivalency of coordinate systems or motion vs at rest. The equivalence principle states only that gravity and acceleration is equivalent or that gravitational and inertial mass are indistinguishable. Velocity is relative, acceleration is not.
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Old 11th November 2008, 10:43 AM   #90
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Originally Posted by humber View Post
Spork, try this (thought) experiment. Place the cart so that is runs in the same direction as the belt. Well, it travels at the speed of the belt or perhaps a little backwards.
No. It would it would do exactly the same thing. If you reversed the wheel to prop gear it would zoom off the belt faster than the speed of the belt. LOL Why a (thought) experiment when all he has to to is do it?

Spork, this would be an easy new video to make.

Originally Posted by humber View Post
My_wan,
It's not skepticism, but physics. This problem is merely the result of intuitive thinking. No shame in that, it led Da Vinci to make many errors.
Physics is defined empirically. You are the one assuming you know the physics without actually doing the experiment (empirical test). You are therefore mistaking your intuition for actual physics. That's why this thread is interesting in the first place because the actual physics is counterintuitive, and you fell for your intuition. You even called your experiment a (thought) experiment when all spork has to do is set the craft on the treadmill backwards and no thought is required. Perhaps you should add that skepticism back into the equation, self skepticism.
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Old 11th November 2008, 11:03 AM   #91
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Originally Posted by Thabiguy View Post
In the same way that the sail, moving with the water, can use its speed against the air to increase its speed against the air. Please try to think about it.
But it is moving against both and useing that force to increase its speed against both.



Quote:
You want a simple example how that works? Imagine yourself in a car on a highway. You are moving at the same speed as the cars in your direction. You take a ball and throw it at a car going in the opposite direction. It bounces from it, then it bounces from a car behind you in your direction, and then you recatch it. Guess what? The ball, when you recatch it, will be travelling forward faster than when you threw it, giving you net increase in momentum and kinetic energy (do the calculation if you don't believe me). The momentum and energy did not come from nowhere - it came from the two cars that the ball hit, slowing them with respect to each other. Your speed is now higher than the speed of other cars in your direction - but you needed the cars going in the opposite direction for this to work.
This is not some issue of redefining coordinate systems.



The claim here is that if the you are on a treadmill going some speed and have wind blowing in the same dirrection of motion at a lower speed it will accelerate at the sources.
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Old 11th November 2008, 11:09 AM   #92
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Originally Posted by Modified View Post
Just connect two sailboats, iceboats, or land yachts with a long sliding bar with a seat in the middle, and let them tack back and forth in opposite directions. The seat and the center of mass of the system could move straight downwind faster than the wind, or move straight upwind.
The nature of vector addition might well kill this. The boats might be moving faster than the wind, but is the down wind component of their velocity faster than the wind?
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Old 11th November 2008, 11:10 AM   #93
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I don't think this will be resolved until you've posted the plans as promised, spork.
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Old 11th November 2008, 11:24 AM   #94
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Originally Posted by my_wan View Post
If the only force was friction why does it stop working when the propeller is disconnected. In fact any amount of friction reduces it's ability to climb the treadmill so claiming the only force is friction doesn't wash.
http://www.youtube.com/watch?v=LMgDvC5lqsY

You can see all of spork's videos here:
http://www.youtube.com/user/spork33
Does it accelerate to be faster than the wind or start there? It would seem to lose power as it approached wind speed, and be limited to under the speed of the wind.
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Old 11th November 2008, 11:29 AM   #95
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Originally Posted by ponderingturtle View Post
But it is moving against both and useing that force to increase its speed against both.
Are you not going against both when the OP craft gets faster than the wind?

Originally Posted by ponderingturtle View Post
This is not some issue of redefining coordinate systems.
If the ball started with you and came back to you then the coordinate system was never redefined. The one and only coordinate system was yours and you never even accelerated. Yet the ball came back to you faster than the ball left you.

Originally Posted by ponderingturtle View Post
The claim here is that if the you are on a treadmill going some speed and have wind blowing in the same dirrection of motion at a lower speed it will accelerate at the sources.
Are you talking propeller created wind or just wind? What is "the sources"? I can't even see a claim here much less admit it's the OP claim.
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Old 11th November 2008, 11:35 AM   #96
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Originally Posted by ponderingturtle View Post
Does it accelerate to be faster than the wind or start there? It would seem to lose power as it approached wind speed, and be limited to under the speed of the wind.
Watch the first video, without the treadmill. That's what it really does.
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Old 11th November 2008, 11:57 AM   #97
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Originally Posted by my_wan View Post
Think again. The headwind at above wind speed turns the prop in the same direction it takes to increase the speed of that wind in the same headwind direction.
Yeh gods you have no idea how a screw works do you...... What you are describing is a violation of basic mechanics. Headwind-One direction. Tailwind-Other direction. It's always going to stop because it's going in the wrong direction.
Originally Posted by my_wan View Post
Physics is defined empirically. You are the one assuming you know the physics without actually doing the experiment (empirical test). You are therefore mistaking your intuition for actual physics. That's why this thread is interesting in the first place because the actual physics is counterintuitive, and you fell for your intuition. You even called your experiment a (thought) experiment when all spork has to do is set the craft on the treadmill backwards and no thought is required. Perhaps you should add that skepticism back into the equation, self skepticism.
Please don't delude yourself into thinking you are doing any better. The fact that you replied to my draw the free body diagram suggestion with a assinine remark means that you just as guilty of gullibility than anyone else.
Quote:
Humber, think of the treadmill as an engine that drives the propeller.
Airplane on a treadmill! Airplane on a treadmill! Airplane on a treadmill! Im going to scream if I hear one more person say that this has nothing to do with airplane on a treadmill I will scream. I SAID THAT ALL THE WHILE. THE LITTLE CART EXPERIMENT PROVES NOTHING BECAUSE IT RELIES ON THE PHYSICS BEHIND AIRPLANE ON A TREADMILL AND NOTHING ELSE. The cart experiment is invalid. Wrong. Faulty assumption. Your not getting power from the ground so why even make such an experiment in the first place.
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Old 11th November 2008, 12:49 PM   #98
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Originally Posted by technoextreme View Post
Yeh gods you have no idea how a screw works do you...... What you are describing is a violation of basic mechanics. Headwind-One direction. Tailwind-Other direction. It's always going to stop because it's going in the wrong direction.
Yet you still don't seem to get the fact that the wheel and prop are directly tied to each other. If you turn it around the wheels turn the other way but that means so does the prop because they are tied together. The craft alway always blows air in the opposite direction that it moves, forward or backward. Move it one direction the prop blows one way, move it the other direction the prop blows the other direction. Turned the other way the craft would go faster than the wind backward. Think an airplane can do that?
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Old 11th November 2008, 01:07 PM   #99
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Originally Posted by technoextreme View Post
Airplane on a treadmill! Airplane on a treadmill! Airplane on a treadmill! Im going to scream if I hear one more person say that this has nothing to do with airplane on a treadmill I will scream. I SAID THAT ALL THE WHILE. THE LITTLE CART EXPERIMENT PROVES NOTHING BECAUSE IT RELIES ON THE PHYSICS BEHIND AIRPLANE ON A TREADMILL AND NOTHING ELSE. The cart experiment is invalid. Wrong. Faulty assumption. Your not getting power from the ground so why even make such an experiment in the first place.
I'm not sure what you are trying to say here. Wether you agree with my post (or rather a single sentence) or not. The sentence you quoted was from a post that was specifically written in an attempt to explain why the vehicle accelerates forward on those treadmill videos.
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Old 11th November 2008, 01:42 PM   #100
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Originally Posted by .13. View Post
I'm not sure what you are trying to say here. Wether you agree with my post (or rather a single sentence) or not. The sentence you quoted was from a post that was specifically written in an attempt to explain why the vehicle accelerates forward on those treadmill videos.
I'm agreeing with you. Im just pointing out you gave the same explanation as airplane on a treadmill.
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Old 11th November 2008, 02:08 PM   #101
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Originally Posted by my_wan View Post
Yet you still don't seem to get the fact that the wheel and prop are directly tied to each other. If you turn it around the wheels turn the other way but that means so does the prop because they are tied together.

That's a very good reason why the device in the first video can't go faster downwind than wind-speed. If it started going faster than the wind, the headwind would be pushing the prop in the opposite direction, slowing the whole thing down.


I've a question for everyone, just to make sure I'm not jumping to false conclusions.

When a windmill/propeller is facing directly into the wind, can the force from the wind turning the blades ever exceed the force from the wind pushing the blades backward?
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Old 11th November 2008, 03:02 PM   #102
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Originally Posted by technoextreme View Post
I'm agreeing with you. Im just pointing out you gave the same explanation as airplane on a treadmill.
I see. I just got confused by the frustrated tone of your post.
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Old 11th November 2008, 03:58 PM   #103
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Originally Posted by ponderingturtle View Post
But it is moving against both and useing that force to increase its speed against both.
That's correct. The boat sailing against the wind increases its speed against both the water and the wind. The car in my car-and-ball example increases its speed against all other cars. And the OP device increases its speed against both the air and the ground.

Such speed increase is perfectly valid. You should concentrate on the aforementioned examples and think about them really hard, until you're sure you completely understand what's going on in them.

Originally Posted by ponderingturtle View Post
This is not some issue of redefining coordinate systems.
Indeed, it is not some issue of redefining coordinate systems. The speed increase is real. Do the math. Check it for yourself.

Originally Posted by ponderingturtle View Post
The claim here is that if the you are on a treadmill going some speed and have wind blowing in the same dirrection of motion at a lower speed it will accelerate at the sources.
I don't know what "accelerate at the sources" means, but if you are on a treadmill going some speed and have wind blowing in the same direction at a lower speed, yes, you can use the wind to accelerate forward. If you stop for a while and think about it, you will realize that the boat sailing against the wind does exactly that.

Originally Posted by technoextreme View Post
Im going to scream if I hear one more person say that this has nothing to do with airplane on a treadmill I will scream.
This has nothing to do with airplane on a treadmill. Scream all you want; when you're done screaming, it will still be true.

Last edited by Thabiguy; 11th November 2008 at 04:01 PM.
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Old 11th November 2008, 04:22 PM   #104
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Originally Posted by ponderingturtle View Post
The nature of vector addition might well kill this. The boats might be moving faster than the wind, but is the down wind component of their velocity faster than the wind?
Traveling upwind is possible, and that is effectively traveling downstream faster than the water (you can do that "for real" going downriver on a windless day). The air and the water are just two streams. So by symmetry it should be possible in a sailboat or something very much like it.

But you don't even need that. See my last iceboat example. If you can travel faster than the wind at some angle, then you can average faster than the wind in the downwind direction, by turning downwind and coasting with sails down, if you have low enough friction and drag. Now connect the sliding bar again and you have a system that can average faster than the wind in the downwind direction. Connect four boats with a more complex sliding system and you can maintain a steady downwind speed that is faster than the wind. Not practical in real life, but nothing wrong with it given semi-ideal components.
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Old 11th November 2008, 05:49 PM   #105
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Originally Posted by Thabiguy View Post
The air is motionless with respect to the device as a whole, but not with respect to the blades of the propeller. (It's more obvious in the blower version.) The blades are moving backwards with respect to the air, which makes the air exert forward force on them.



The energy comes from the air being slowed, with respect to the ground, as it pushes the propeller forward.



No, because the air is still pushing forward on the propeller. It's easier to see in the blower version, but it's also true in the propeller version, when f < 1.
And I thought we had a really interesting discussion. Never mind. When somebody cannot see that enregy in cannot exceed energy out there is no argument.
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Old 11th November 2008, 06:46 PM   #106
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Originally Posted by Acleron View Post
And I thought we had a really interesting discussion. Never mind. When somebody cannot see that enregy in cannot exceed energy out there is no argument.
*sigh*
Sometimes I wonder what is sadder - if it's woos who claim they invented machines that violate the law of conservation, or if it's people who miscomprehend a perfectly valid mechanism to the point of claiming it violates the law of conservation.

I think you have a little more chance of finding out that you're wrong than the woos. Good luck.

This should be a lesson to all skeptics, including myself: never be so full of yourself to think that you cannot be dead wrong about something.
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Old 11th November 2008, 06:53 PM   #107
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Originally Posted by Thabiguy View Post
*sigh*
Sometimes I wonder what is sadder - if it's woos who claim they invented machines that violate the law of conservation, or if it's people who miscomprehend a perfectly valid mechanism to the point of claiming it violates the law of conservation.
I don't think you correctly used the word drag once in this entire topic.
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Old 11th November 2008, 07:25 PM   #108
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Originally Posted by technoextreme View Post
People who have no clue what they are talking about is sadder. I don't think you correctly used the word drag once in this entire topic.
That's possible; I'm not a native English speaker. The irony is, even though you imagine I "have no clue what I'm talking about", it's you who weren't right once in this entire topic.

If you want to find out how the device operates, I can help to explain. If you think you can show that the device doesn't work, I can answer your arguments. And if you just want to hold on to your misconceptions, well, I hope you have a good time holding on to them.
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Old 11th November 2008, 07:51 PM   #109
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As this is an educational forum, I'll try and offer something useful to those who have a hard time wrapping their minds around the OP device, but are willing to give it a try.

Roadmap to comprehension:

1. This is a counter-intuitive gadget. There are many working mechanisms that are counter-intuitive, and may appear to violate the laws of physics, but don't. This is one of them.

How to proceed: do not trust your instinct. Your gut judgement can be misleading. Instead, go the rigorous way. Use math. Apply the laws of physics. Check your assumptions, check your results. Do not try to come up with proofs supporting your beliefs - instead, be inquisitive and try to find out what is actually going on. If it works, how exactly does it work? If it doesn't work, how exactly does it fail?

2. Realize that downwind travel faster than the wind is not violating the law of conversation.

How to proceed: realize that there already are existing machines that do just that. There are many examples in this thread. Concentrate on understanding how these existing machines work. Concentrate on understanding why these existing machines do not violate the law of conversation.

3. Verify that the OP device happens to be one of those devices that can travel faster than the wind.

How to proceed: try to understand how it works. It's not easy, but if you go through this thread, you may find posts that will help you. Ask questions; people will explain. You might even try to build the device yourself.
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Old 11th November 2008, 07:52 PM   #110
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Originally Posted by Brian-M View Post
That's a very good reason why the device in the first video can't go faster downwind than wind-speed. If it started going faster than the wind, the headwind would be pushing the prop in the opposite direction, slowing the whole thing down.
It doesn't slow it down, it only slows down how fast it accelerates until the wind is resistance gets so high it can't accelerate anymore.

Originally Posted by Brian-M View Post
I've a question for everyone, just to make sure I'm not jumping to false conclusions.

When a windmill/propeller is facing directly into the wind, can the force from the wind turning the blades ever exceed the force from the wind pushing the blades backward?
No, but force and speed are two entirely different things. When the forward force of the craft matches the winds resistive force the craft stops accelerating and simply stays at that velocity. When the craft is very near wind speed the resistive forces are very small but the force is quiet large because even though the wind speed is low relative to the craft the wheels must forcefully turn which then forcefully turns the prop. If the resistive force didn't keep increasing with speed the craft would eventually accelerate ever nearer light speed. In fact in space you can accelerate an elephant with the constant force output of a house fly to near light speed given enough time. That is the principle of how ion drives work. It is also true that the craft can't exceed the ground air speed + the average air speed of air coming out of the prop. Ground air speed + prop air speed is faster than wind speed alone though.

ETA: Reason why force and velocity is not the same: f=ma or force equals mass times acceleration, not velocity. Without friction zero force is required to maintain a relative velocity. Force is only needed to increase or decrease velocity relative to something.
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Old 11th November 2008, 08:19 PM   #111
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Originally Posted by Thabiguy View Post
If you want to find out how the device operates, I can help to explain.
No you can't because you don't even know the definition of drag, what it is, and why it's important to this discussion.
Quote:
How to proceed: do not trust your instinct. Your gut judgement can be misleading. Instead, go the rigorous way. Use math. Apply the laws of physics. Check your assumptions, check your results. Do not try to come up with proofs supporting your beliefs - instead, be inquisitive and try to find out what is actually going on. If it works, how exactly does it work? If it doesn't work, how exactly does it fail?
I told you how it fails. DRAG DRAG DRAG DRAG DRAG DRAG DRAG. Look up the definition of DRAG. Read it. Embrace it. Hug it. Kiss it. Because you make the assumption that it doesn't stop the propeller.
Quote:
How to proceed: realize that there already are existing machines that do just that. There are many examples in this thread. Concentrate on understanding how these existing machines work. Concentrate on understanding why these existing machines do not violate the law of conversation.
No. The only examples given really utilize tacking which isn't related to this discussion.
Quote:
No, but force and speed are two entirely different things. When the forward force of the craft matches the winds resistive force the craft stops accelerating and simply stays at that velocity.
You forgot about DRAG. DRAG DRAG DRAG DRAG DRAG DRAG DRAG DRAG. And more drag.
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Old 11th November 2008, 08:29 PM   #112
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Originally Posted by technoextreme View Post
No you can't because you don't even know the definition of drag, what it is, and why it's important to this discussion.
Drag is the aerodynamic analogue of friction. It is a force resisting movement through a fluid.

I have explained that drag is essential to the operation of the device, and how. If you think you have some additional knowledge that I don't have about the importance of drag to this discussion, then please, do not just state that I don't know it, but tell us what it is.
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Old 11th November 2008, 08:34 PM   #113
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Originally Posted by technoextreme View Post
I told you how it fails. DRAG DRAG DRAG DRAG DRAG DRAG DRAG. Look up the definition of DRAG. Read it. Embrace it. Hug it. Kiss it.
You are not making any sense. That's like saying that a bicycle cannot work, because of FRICTION. And instead of explaining how friction prevents a bicycle from working, just shouting "FRICTION, FRICTION, FRICTION."

In order to show how drag prevents the device from working, you have to show how drag prevents the device from working. Not just shout "DRAG, DRAG".
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Old 11th November 2008, 08:36 PM   #114
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Originally Posted by technoextreme View Post
You forgot about DRAG. DRAG DRAG DRAG DRAG DRAG DRAG DRAG DRAG. And more drag.
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Old 11th November 2008, 08:38 PM   #115
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Originally Posted by Thabiguy View Post
Drag is the aerodynamic analogue of friction. It is a force resisting movement through a fluid.

I have explained that drag is essential to the operation of the device, and how. If you think you have some additional knowledge that I don't have about the importance of drag to this discussion, then please, do not just state that I don't know it, but tell us what it is.
Thats not drag. Every single time you've said drag you mean thrust. Every single time. How am I supposed to take anyone seriously that can't understand the difference between thrust and drag?
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Old 11th November 2008, 08:42 PM   #116
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Originally Posted by ponderingturtle View Post
The nature of vector addition might well kill this. The boats might be moving faster than the wind, but is the down wind component of their velocity faster than the wind?

Yes, the downwind component can be 3X or more the wind speed. There is plenty of GPS data to back this up. This is not in contention. It's an every day thing for ice-boat racers.


Quote:
I don't think this will be resolved until you've posted the plans as promised, spork.
Fair enough. I can't imagine that will resolve it, but at least it will make it possible for anyone to try it.

I don't have it all laid out, but it's pretty darn straightforward. Hopefully this will be enough for anyone that wants to try it:

Get:
- A set of GWS 4" wheels (LXHHZ7) from any R/C hobby shop
- The 90 degree gear drive from a T-Rex 600 R/C heli and the torque tube that drives it.
- A 14" x 10" GWS plastic slow-flyer prop (same hobby shop)
- A 5 mm carbon tube for the axle
- A relatively soft aluminum tube from the hardware store (Orchard Supply Hardware in our case)
- A little bitty tail wheel.

- Remove the tail rotor drive shaft from the T-Rex 600 tail rotor gearbox and replace it with the 5mm carbon axle.
- Carefully drill out the hubs of the GWS wheels to fit the 5mm axle, and stick them on.
- Mount your aluminum tube to the bottom of the gear box (get creative) and bend it to form an arc like you see on JB's model (Make sure you have the gear box oriented such that pushing the cart forward causes the prop to spin clockwise when viewed from behind).
- Mount the tailwheel on the bottom of the arc'd aluminum tube
- Make a bearing support on the top of the arc'd aluminum tube to support the aft end of the torque tube.
- Drill the hub out on the GWS prop in order to fit it on the torque tube, and stick it in place (curved surface forward).
- Make sure everything spins VERY freely - spray the gears with silicone lubricant if necessary. You can even clean the lube out of the bearings to reduce the drag.

Place it on your treadmill at 10 mph. If it doesn't go straight ahead (and it won't) adjust the steering by bending the soft aluminum tube very slightly. Make sure this doesn't mess up the alignment and cause any drag.

Take a video and post it on youtube.

Don your flamesuit.

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Old 11th November 2008, 08:46 PM   #117
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Originally Posted by technoextreme View Post
No. The only examples given really utilize tacking which isn't related to this discussion.
Why is it not related? That's somewhat like saying a motorboat and a car is unrelated. Yet they both depend on an internal combustion engine for power. In sailing "tacking" works because wind speed + boat speed make the effect wind relative to the boat faster than the ground wind speed. This craft works because the ground wind speed + the propeller wind speed is faster relative to the craft than the ground wind speed alone.

The sailboat is still moving against the wind even if at an angle. Why wouldn't drag stop that from working?
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Old 11th November 2008, 09:04 PM   #118
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Uggg... I right the first time. It's the problem with the drive ratio. You need to flip direction sometimes and you can't do that with a single belt drive.
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Old 11th November 2008, 09:10 PM   #119
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Thabiguy:
>Drag is the aerodynamic analogue of friction. It is a force
>resisting movement through a fluid.

techno:
>Thats not drag. Every single time you've said drag
>you mean thrust. Every single time.

Someone needs to break it to techno that Thabi has presented a perfectly good definition of "drag" and it is he/she not Thabi who is confused in this regard. Ok, I'll do it.

techno, "thrust" is not the aerodynamic analogue of friction -- drag is.

techno, "thrust is not a force resisting movement through a fluid -- drag is.

techno, just to cover it better, apples are not oranges, green is not red, light is not dark and "thrust" is not the aerodynamic analogue of friction.

Just sort of wanted to throw the thrust thing in there with some other obvious tid-bits.

JB
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Old 11th November 2008, 09:14 PM   #120
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Originally Posted by technoextreme View Post
Thats not drag. Every single time you've said drag you mean thrust. Every single time. How am I supposed to take anyone seriously that can't understand the difference between thrust and drag?
Is the air resistance around your car thrust or drag?

Let's compare. Thabiguy said:
Originally Posted by Thabiguy View Post
Drag is the aerodynamic analogue of friction. It is a force resisting movement through a fluid.
You responded:
Originally Posted by technoextreme View Post
Thats not drag. Every single time you've said drag you mean thrust. Every single time.
Here is what wiki says:
Originally Posted by http://en.wikipedia.org/wiki/Drag_(physics)
In fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a solid object through a fluid (a liquid or gas). The most familiar form of drag is made up of friction forces<snip>
Ok maybe wiki is off so let's check NASA.

Quote:
Drag is the aerodynamic force that opposes an aircraft's motion through the air. <snip> Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). <snip> We can think of drag as aerodynamic friction
So how is Thabiguy wrong? He used exactly the same definition as wiki and NASA.
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