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Old 12th November 2008, 01:01 PM   #201
.13.
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Originally Posted by my_wan View Post
Yes, exactly.
Ok. Is spork disagreeing with you or did I misunderstand his post #187?
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Old 12th November 2008, 01:10 PM   #202
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Originally Posted by spork View Post
That is not true. I've shown this in my vector analysis. If you don't care for mathematical proof and experimental results, little can be done.
If the prop rotation is opposite from what the wind alone would spin it when the craft first moves then when the craft exceeds wind speed the apparent direction of wind wrt the prop reverses direction. This would mean the prop is no longer rotating opposite of the wind relative to the prop at this speed.

I'm not real sure what you interpreted in my statement that you quoted. We do have some differences in the interpretation of the equivalency when forces are reversed. The thermodynamics involved does make this a dissipative system so entropy is an issue.

Originally Posted by spork View Post
Please review my vector analysis. It is the foundation upon which I designed the cart.
Your experimental results are not quantitative but they are convincing, at least to me. I've seen lots of diagrams with a few numbers but nothing even close to what I would call mathematical proof. A good mathematical proof for me entails a quantitative description that provides a well defined numerical description of available design choices. This includes the increase/decrease in efficiency as a result of changes in gear ratios, max prop speed, torque distribution, etc. A set of numbers written out to represent the qualitative description does not make it a mathematical proof. I'm working on it but it's far from easy.

Perhaps I missed your best analysis because most of what I've seen simply refer to "tacking" in general and don't even consider individual craft components at all as they pertain to this design. If you could point me to it I would appreciate it and will look closer even if it's not what I'm after. I want to build a human ridable model.
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Old 12th November 2008, 01:33 PM   #203
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Originally Posted by .13. View Post
Ok. Is spork disagreeing with you or did I misunderstand his post #187?
We disagree wrt the equivalency of force direction reversal. In other words I think his treadmill concept is not exactly equivalent to the wind driven case. I do consider it a valid proof of concept but I argue that efficiency can take a larger hit in one case over the other. However, I have had to concede to him that the torque vectors worked in favor of the efficiency of his craft. Something I didn't have worked out when I first debated him on the issue.

My argument can be described in terms of Betz' law. Betz' law states that a theoretically perfectly efficient windmill is limited to 59% efficiency. However, an airplane prop can have a practical efficiency of over 90%. The only difference between them is the direction of the torque vector, wind driven vs motor driven. Physically this is a result of how entropy is dissipated through the system.

We have no substantiative disagreement wrt the legitimacy or operability of his craft in performing as claimed.
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Old 12th November 2008, 01:39 PM   #204
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Originally Posted by ThinAirDesigns View Post
Hello again JW. Did you read my post #134?

If your interested in an exchange on the subject of inertial frames of reference, I would love to have one with you.

If not, that's cool as well.

JB
Originally Posted by Modified View Post
This has been explained numerous times. From the point of view of the vehicle, there is no difference between being on a treadmill in still air and on the ground in wind. Yes, the energy that moves the vehicle forward comes from the treadmill motor. That is irrelevant.
It's not that I don't understand the physics. It's that I've done the experiment, as I'm sure many others have throughout the history of the machine, and it doesn't work.
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Old 12th November 2008, 01:51 PM   #205
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Originally Posted by Modified View Post
This has been explained numerous times. From the point of view of the vehicle, there is no difference between being on a treadmill in still air and on the ground in wind. Yes, the energy that moves the vehicle forward comes from the treadmill motor. That is irrelevant.
It's a proof of concept that a cart with a propeller will move. A proof of concept that a cart with a propeller will go twice the speed of the propeller is to measure the speed at which the device reaches equilibrium which unfortunately is impossible with a regular treadmill.
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Old 12th November 2008, 01:56 PM   #206
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When the device is on the treadmill it can be moved around quite easily.
If these are indeed equivalent frameworks, I wonder how it is that a large scale device could be expected to do any work, like move something.
It's not a lack energy, because it's a treadmill.
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Old 12th November 2008, 02:14 PM   #207
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Originally Posted by technoextreme View Post
It's a proof of concept that a cart with a propeller will move. A proof of concept that a cart with a propeller will go twice the speed of the propeller is to measure the speed at which the device reaches equilibrium which unfortunately is impossible with a regular treadmill.
By what theory would it be possible for a vehicle to be able to go downwind at the exact speed of the wind, but no faster (unless there is zero friction)? "At the speed of the wind" proves "faster than the wind", as far as I am concerned. If you really want to be picky, they could add a small fan at the front of the treadmill.
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Old 12th November 2008, 02:22 PM   #208
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Originally Posted by JWideman View Post
The treadmill videos prove nothing. A motor coupled to a prop is going to create thrust. Nothing groundbreaking about that.
Without storing energy or doing anything more complex than coupling a wheel to a prop, this craft is supposedly traveling faster than the tailwind powering it.
Looking at your plans, this is essentially the same craft I built as kid 25 years ago. That's how I found out about entropy.
Actually it does. I've argued with spork about entropy and absolute equivalence. You can see a summation of it here:
http://www.internationalskeptics.com...13#post4196713
In essence the entropy argument comes down to efficiency rather than legitimacy, but even the sporks craft comes out on the efficient side even in the wind driven case.

In general the available power is well defined by the air speed relative to the ground regardless of the motion of the craft. Less efficiency simply means a larger crossection of air for the same power, though this craft does not suffer that potential efficiency loss from my figures. Consider that a windmill is perfectly capable of generating enough electricity to power a small car faster than the wind on the windmill. It cannot be said that there is no power source. This craft tries the rpm of the prop to the rpm of the wheels such that the difference in road to wind speed can still be taken advantage of at speeds greater than the wind. It's not terribly unlike "tacking" in a sailboat.

If the power is available the entropy argument alone can't rule out the craft actually working. The argument that something no more complex than coupling a wheel to a prop doesn't make the case. A sailboat can travel faster than the wind with nothing more complex that a stick tied to a board with a piece of cloth tied to it, just not while traveling in the same direction as the wind. So you need a little stronger argument to claim it doesn't work. You might say we don't have sufficient evidence and the burden is on us. However, claiming unequivocally that it doesn't work is a claim requiring as much evidence as we need, or at least a better argument than entropy.
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Old 12th November 2008, 02:30 PM   #209
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Originally Posted by my_wan View Post
Which is exactly why the wind speed difference wrt craft remains a constant at all speeds. It may not be exactly the "same absolute difference" but close enough and it can be designed so that it does making it even more efficient.
No. The fact that it is not the same difference is essential to the function of the device. This is what you have not understood yet.

Originally Posted by my_wan View Post
So just because the difference is not exact due to design issues that a difference is not maintained at all. Isn't that like admitting that a properly designed craft would work but since this one isn't perfect it can't work?
No, not at all. The difference is directly dependent on the speed of the vehicle. It has nothing to do with whether the craft is built properly or shoddily. It is maintained, but not constant.

Also, I'm not saying that it doesn't work. It works, but not the way you think it works.

Originally Posted by my_wan View Post
Quote one says: "propeller pushes back". Here you say: "the wheels are connected to the propeller so that when the forward speed of the device (wrt ground) is vdev, the propeller tries to move the air forward". The propeller cannot possibly change direction and start moving the air forward without reversing direction of the prop which also reverses direction of the wheels.
Which is why I said to be careful with signs and reference frames. I said that for a reason. Listen well: when the propeller pushes the air backward with respect to the device, the air is moving forward with respect to the ground. Try to read again what I have written, and this time pay extra attention to signs and reference frames.

Originally Posted by my_wan View Post
When the craft first takes off the prop is moving air in the opposite direction of the wind.
With respect to the device, yes. With respect to the ground, no. The air pushed back is moving in the opposite direction of the air wrt device, and in the same direction as the air wrt ground.

If you don't realize this, then you don't understand how the device works.

Originally Posted by my_wan View Post
You only need to watch carefully the video below to see that.
You can't see something very crucial in the video: the speed at which the propeller moves the air backwards, wrt device. This is less than the speed of the vehicle wrt ground. Which is what makes the air moving through the propeller move forward wrt ground.


At this moment, I'm afraid, you're missing the correct understanding of how the device works. This needs to be remedied in order to proceed. I would suggest that you put the propeller version aside for now, and concentrate on the much simpler version of the device, the illustration of which was kindly provided by Spork here.

Answer these questions: if there were no friction and no drag (except air pushing on the blades), would the device accelerate? If yes, would the device accelerate indefinitely? If no, what would the top speed be? And why?

After you understand how the simple version works, we can move back to the propeller version.
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Old 12th November 2008, 02:34 PM   #210
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The cart is the vehicle. The treadmill is the wind. So I'm in the cart?
Put cart A on the treadmill
Put cart B on the treadmill
Can cart B, push cartA ?
Not when it's windy, it seems.

Last edited by humber; 12th November 2008 at 02:36 PM.
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Old 12th November 2008, 02:47 PM   #211
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Wait... I originally thought this device was supposed to be powered by the wind turning the propeller, like a windmill.

But from what's been written since, it's the propeller pushing the air backwards which supplies the forward momentum which turns the wheels which powers the propeller which pushes the air backwards...

Am I understanding this correctly?

Have I been wasting my time reading this thread about something that's nothing more than a poorly conceived perpetual-motion machine?
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Old 12th November 2008, 02:47 PM   #212
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Originally Posted by JWideman View Post
It's not that I don't understand the physics. It's that I've done the experiment, as I'm sure many others have throughout the history of the machine, and it doesn't work.
I'm going to simply call you on this one.

You've just stated that you've "done the experiment" that proves the treadmill and the street are not the same.

I would bet a large amount of money that you've never:

A: built a device and successfully demonstrated that it climbs a treadmill.

B: then tested the same device to see if it will go downwind faster than the wind in an outdoor setting.

There's a two word statement for what I think of that claim.

I'd be perfectly happy for you to prove me wrong.

JB

PS: talk about a claim ripe for debunking --- geeez!
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Old 12th November 2008, 02:52 PM   #213
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Originally Posted by spork View Post
This vector analysis along with some verbal description can fully describe how the cart works and why it's possible to exceed the wind speed steady state. Look it over and let me know when you want to discuss what it means and how it applies to this cart.
So when you say that you have calculations that prove you right, you actually don't have them? or you don't want to show them? or?

It's just that with the tone you are taking when you mention your analysis and how your analysis predicted the performance of the device you built...I dunno, I was expecting something a little more like, umm analysis.
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Old 12th November 2008, 02:59 PM   #214
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Originally Posted by Brian-M View Post
Wait... I originally thought this device was supposed to be powered by the wind turning the propeller, like a windmill.

But from what's been written since, it's the propeller pushing the air backwards which supplies the forward momentum which turns the wheels which powers the propeller which pushes the air backwards...

Am I understanding this correctly?

Have I been wasting my time reading this thread about something that's nothing more than a poorly conceived perpetual-motion machine?
As I read it, and I could be wrong...

The propeller is a sail. The wind pushes the sail and the cart moves along. Because the wheels are linked to the propeller the propeller starts to turn. This is in the opposite direction than if the rotation was being caused by the wind. The rotating propeller is then meant to act like a sail on a tack (this is the terminology? I don't do sailing) and you can then go faster than the wind.

This is I think what is claimed to happen.
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Old 12th November 2008, 03:00 PM   #215
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OK, who has access to a wind tunnel? This can be easily resolved in a way that will remove all doubt.
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Old 12th November 2008, 03:14 PM   #216
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There are no sails. If the treadmill is the wind, how do you disconnect the propeller?

I don't know how the two are connected, but the treadmill tests could have nothing in common with real world claims of faster than wind travel.

Last edited by humber; 12th November 2008 at 03:17 PM.
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Old 12th November 2008, 03:17 PM   #217
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Originally Posted by my_wan View Post
We disagree wrt the equivalency of force direction reversal. In other words I think his treadmill concept is not exactly equivalent to the wind driven case. I do consider it a valid proof of concept but I argue that efficiency can take a larger hit in one case over the other. However, I have had to concede to him that the torque vectors worked in favor of the efficiency of his craft. Something I didn't have worked out when I first debated him on the issue.

My argument can be described in terms of Betz' law. Betz' law states that a theoretically perfectly efficient windmill is limited to 59% efficiency. However, an airplane prop can have a practical efficiency of over 90%. The only difference between them is the direction of the torque vector, wind driven vs motor driven. Physically this is a result of how entropy is dissipated through the system.

We have no substantiative disagreement wrt the legitimacy or operability of his craft in performing as claimed.
I see. I just got confused again. I thought he disagreed with the direction the wheels would spin. That they wouldn't spin backwards if the wind were spinning the prop freely.

Anyway this bolded part makes a lot more sense now (post #153):
Originally Posted by my_wan View Post
Well, let's start at 0 craft speed. Propellers not turning and the wind blowing the craft itself is the only thing to move it. Once the wheels do turn then the prop turns at the same rate. We know the wheels have to be the power right now because if the wind in the prop was the power turning the wheels it would run the craft backward. So now all we have to do is increase prop speed at the same rate and the craft speed and the same relative condition persist. The prop therefore continues to be powered by the wheels and the prop speed only increases enough to maintain exactly the same wind differential even as the craft gains speed. Just because it exceeds ground wind speed does not mean it exceeds wind speed relative to the craft, due to the prop.
Initially this seemed wrong because I didn't realise the direction of the torque. But if I have understood this thus far: The force from the wind pushing against the frame is greater than friction + torque from the prop (which acts against forward motion). And as the cart picks up speed the torque resisting the forward motion decreases.
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Old 12th November 2008, 03:41 PM   #218
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Good grief. It's NOT A FRAME OF REFERENCE it's a MODEL

The TREADMILL is the MODEL of the wind
The PROPELLER must be in the wind, so in the TREADMILL
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Old 12th November 2008, 03:51 PM   #219
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Originally Posted by my_wan View Post
If the prop rotation is opposite from what the wind alone would spin it when the craft first moves then when the craft exceeds wind speed the apparent direction of wind wrt the prop reverses direction.
If I set an ice-boat on a 45 degree downwind tack - but stationary, the wind would initially be filling the sail from the starboard side (assuming a starboard tack), but it would be coming from somewhat aft of beam. The ice boat would self-start and pick up speed until the relative wind was coming from forward of beam, but still from the starboard side. This is precisely the motion of the vectors our prop experiences as the cart picks up speed - whether on the ground in a tailwind or on the treadmill.

Quote:
I'm not real sure what you interpreted in my statement that you quoted. We do have some differences in the interpretation of the equivalency when forces are reversed.
In fact this highlights our difference in understanding of the principle itself. The forces are not reversed.

Quote:
The thermodynamics involved does make this a dissipative system so entropy is an issue.
It's a real world system, so entropy is always an issue.

Quote:
I've seen lots of diagrams with a few numbers but nothing even close to what I would call mathematical proof.
I assure you that my vector analysis along with the appropriate explanations constitutes a mathematical proof. Oddly not a single person has asked me to explain any aspect of it. They'd rather talk about hopping theories and perpetual motion.
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Old 12th November 2008, 03:55 PM   #220
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Originally Posted by JWideman View Post
It's not that I don't understand the physics. It's that I've done the experiment, as I'm sure many others have throughout the history of the machine, and it doesn't work.
Actually, that just shows that you don't understand the physics and were unable to attain successful results in your experiment. I think it's reasonably evident that several of us have shown successful results when we do the experiment.
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Old 12th November 2008, 03:59 PM   #221
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Originally Posted by Brian-M View Post
Have I been wasting my time reading this thread about something that's nothing more than a poorly conceived perpetual-motion machine?
This thing, if it works, is certainly not a perpetual motion machine. Neither is a sailboat, and for the same reason: it uses the wind for power, or more precisely it exploits the difference in velocity between the wind and the sea, so it has an energy input.

For those that think the treadmill is not equivalent to moving at wind speed, pause, take three deep breaths, and think again. As many have pointed out, relativity guarantees they are identical.

For those that think that moving downwind faster than the wind is impossible for a wind powered device, you've obviously never been on a sailboat or a windsurfer. With a bit of jibing it's very easy to do.

Finally, for those that agree with all of the above but aren't sure if this particular device will work, I agree. It's not at all obvious. But the video looks pretty convincing, and no principles of physics are being violated - so why not?

It may help to realize the following: a device at rest with respect to the ground but with the air in motion can use the wind to propel itself either up- or down-wind. A device at rest with respect to the air, but with the ground in motion, can use the motion of the ground to propel itself up- or down-ground. There is a perfect symmetry (apart from the obvious physical differences between ground and air). So if you can convince yourself that a device at rest on the ground/sea can move upwind, you're done. And of course it can - sailboats do it all the time, as can many other devices.

Last edited by sol invictus; 12th November 2008 at 04:03 PM.
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Old 12th November 2008, 04:03 PM   #222
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Talking

Originally Posted by Brian-M View Post
Wait... I originally thought this device was supposed to be powered by the wind turning the propeller, like a windmill.
It's powered by the wind pushing on the propeller, as the wind pushes on the sail of an ice boat - but it the wind does not turn the prop as a windmill.

Quote:
But from what's been written since, it's the propeller pushing the air backwards which supplies the forward momentum which turns the wheels which powers the propeller which pushes the air backwards...

Am I understanding this correctly?
Not quite - but not terribly far off. The wind does push on the prop (actually it provides lift over the airfoil of the prop. But it is the kinematic constraint of the wheels and transmission that causes the prop to turn - and this is clearly a key element. It's really far more easy to envision it when laid out flat (i.e. the ice boat on a downwind tack) rather than through the blades of the prop rotating about an axis and geared to the wheels. That just makes the problem more fun (and a little harder to believe). My vector diagram explains it through the ice boat analogy.

Quote:
Have I been wasting my time reading this thread about something that's nothing more than a poorly conceived perpetual-motion machine?
We think its a very nicely conceived perpetual-motion machine
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Old 12th November 2008, 04:05 PM   #223
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Originally Posted by ThinAirDesigns View Post
I'm going to simply call you on this one.

You've just stated that you've "done the experiment" that proves the treadmill and the street are not the same.
I've stated no such thing.
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Old 12th November 2008, 04:10 PM   #224
humber
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You have got to be kidding me.

It's NOT A FRAME OF REFERENCE it's a MODEL

The TREADMILL is the MODEL of the wind
The PROPELLER must be in the wind, so in the TREADMILL

There's a second magical wind. Please, tell me, without saying you have tried it, do you explain where the second wind comes from?
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Old 12th November 2008, 04:12 PM   #225
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Originally Posted by Thabiguy View Post
No. The fact that it is not the same difference is essential to the function of the device. This is what you have not understood yet.
If there is a difference there is usable power, period. Even if the difference isn't fully maintained.

Originally Posted by Thabiguy View Post
No, not at all. The difference is directly dependent on the speed of the vehicle. It has nothing to do with whether the craft is built properly or shoddily. It is maintained, but not constant.
Again you have admitted the difference is maintained whether constant or not. If the is a difference there is usable power.

Originally Posted by Thabiguy View Post
Also, I'm not saying that it doesn't work. It works, but not the way you think it works.
Do you have any idea how many different ways you can describe the same thing and they all be equally valid? There are at least 3 different formulation of thermodynamics alone that are equally as valid.


Originally Posted by Thabiguy View Post
Which is why I said to be careful with signs and reference frames. I said that for a reason. Listen well: when the propeller pushes the air backward with respect to the device, the air is moving forward with respect to the ground. Try to read again what I have written, and this time pay extra attention to signs and reference frames.
Ok, that's actually a perfectly valid statement but in what way does it relate to the argument I made? You didn't even relate it to any specific claim.


Originally Posted by Thabiguy View Post
With respect to the device, yes. With respect to the ground, no. The air pushed back is moving in the opposite direction of the air wrt device, and in the same direction as the air wrt ground.
This was in response to me saying:
"When the craft first takes off the prop is moving air in the opposite direction of the wind."
When the craft first takes off wrt the ground and wrt the device is the same thing. Remember this, the speed of the craft is almost but not quiet zero here. Look at the diagram:
<-- Craft moves to the left
You say:
1) The air pushed back is moving in the opposite direction of the air wrt device.
2) The air pushed back is the same direction as the air wrt ground.
Number 2 is dead wrong. It will be right once the craft exceeds the ground air speed but the single sentence you quoted and responded to specifically labeled it, "when the craft first takes off".

Originally Posted by Thabiguy View Post
If you don't realize this, then you don't understand how the device works.
You do of course now realize that the statement you want me to realize as the truth is dead wrong. If not reread my response one quote up with the diagram.

Originally Posted by Thabiguy View Post
You can't see something very crucial in the video: the speed at which the propeller moves the air backwards, wrt device. This is less than the speed of the vehicle wrt ground. Which is what makes the air moving through the propeller move forward wrt ground.
Uugh....

Originally Posted by Thabiguy View Post
At this moment, I'm afraid, you're missing the correct understanding of how the device works. This needs to be remedied in order to proceed. I would suggest that you put the propeller version aside for now, and concentrate on the much simpler version of the device, the illustration of which was kindly provided by Spork here.
Trying to say that is how the original craft works is like drawing a paddleboat and saying that is how a sailboat works. If these things are equivalent then wouldn't you say a propeller and a windmill are equivalent? Why the do propellers often get over 90% efficiency when a windmill is limited to less than 59% efficiency?

Originally Posted by Thabiguy View Post
Answer these questions: if there were no friction and no drag (except air pushing on the blades), would the device accelerate? If yes, would the device accelerate indefinitely? If no, what would the top speed be? And why?
That's not even a question. Can air push on both sides of the blade? Apparently not sense there is no drag. Except you seem to assume the blade has drag because you are baiting me with indefinite acceleration. Do you realize that the speed of air has little to do with the speed of air molecules except statistically? No friction? Never mind, too messy. Didn't you mean to start this paragraph with, "Riddle me this"? This makes as much sense as asking what would happen if an unstoppable object hit an immovable object. No matter whether I get it right or wrong in your imagination you would then claim it means something real. Get real!!!

Originally Posted by Thabiguy View Post
After you understand how the simple version works, we can move back to the propeller version.
So I guess I need to figure out what really would happen when an unstoppable object hit an immovable object. Then I could be as smart as you...

Don't debate with me anymore..
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Old 12th November 2008, 04:15 PM   #226
Brian-M
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Originally Posted by fsol View Post
As I read it, and I could be wrong...

The propeller is a sail. The wind pushes the sail and the cart moves along. Because the wheels are linked to the propeller the propeller starts to turn. This is in the opposite direction than if the rotation was being caused by the wind. The rotating propeller is then meant to act like a sail on a tack (this is the terminology? I don't do sailing) and you can then go faster than the wind.

This is I think what is claimed to happen.

I hadn't thought of thinking of the propeller as being used as a sail while below wind-speed, but that doesn't affect what happens when it goes faster than wind-speed.

Originally, I thought he meant the headwind was supposed to turn the propeller, which would then turn the turn the wheels, moving it forwards. The problem with this is, the force of the headwind pushing the craft backwards would always be greater than than the rotational force imparted to the propeller pushing the craft forwards (by the connection to it's wheels).

For traveling upwind, this can be compensated for through gearing by sacrificing speed. However, since it's traveling downwind, reducing speed reduces headwind, which would then reduce speed even further, which would reduce headwind further... and so on, making it physically impossible to maintain the faster-than-wind speed.

From later posts, it looks like he means the spinning of the propeller would push the air backwards, providing the craft with a forward thrust which turns the wheels faster, which would then turn the propeller faster, which would provide more forward thrust... and so on.

If so, he's forgetting that the energy imparted to the propeller to produce this forward thrust is taken from forwards momentum of the craft itself, so he's subtracting forward momentum in order to spin a propeller to provide forward momentum. Somehow he thinks he can get more power out of the propeller than the propeller takes from the craft via the wheels.
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Old 12th November 2008, 04:18 PM   #227
sol invictus
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Originally Posted by humber View Post
You have got to be kidding me.

It's NOT A FRAME OF REFERENCE it's a MODEL

The TREADMILL is the MODEL of the wind
The PROPELLER must be in the wind, so in the TREADMILL

There's a second magical wind. Please, tell me, without saying you have tried it, do you explain where the second wind comes from?
I assume you're talking to me? You're asking what the analogue of the propeller is for the ground?

It's the wheels, of course. The motion of the ground relative to the device makes the wheels spin, just as the motion of the air makes the propeller spin.

Maybe it would be easier to think about if you imagine a boat with two propellers, one in the air and one in the water, connected so that they must rotate together. Or if you don't like that, a zeppelin floating in the air right at an interface: the air above it is moving with respect to the air below it. In all these cases, there is a nearly infinite supply of energy available in the relative motion of these two fluids, and one simply needs to tap it somehow.

Last edited by sol invictus; 12th November 2008 at 04:20 PM.
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Old 12th November 2008, 04:36 PM   #228
ThinAirDesigns
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Originally Posted by JWideman View Post
I've stated no such thing.
JW, there are strange things afoot here :-)

I attempted to explain that there's an ironclad principle of physics which states that there is NO experiment which can discern the difference between this device on the treadmill and this device on the street.

You responded:
Quote:
It's not that I don't understand the physics. It's that I've done the experiment, ...

I have no idea what to say so I will say only this -- I can only go by the words you write.

JB
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Old 12th November 2008, 04:41 PM   #229
humber
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Nevermind
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Old 12th November 2008, 04:47 PM   #230
mhaze
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Originally Posted by humber View Post
There are no sails. If the treadmill is the wind, how do you disconnect the propeller?

I don't know how the two are connected, but the treadmill tests could have nothing in common with real world claims of faster than wind travel.
The treadmill eliminates the issue of wind at a slant angle to the prop. In that case, I think we could all agree for a large variety of wind impact angles, the prop could pick up more energy than what is required to overcome forward drag for movement "forward".

However, if the prop is exactly head on to the wind, then as the vehicle increases speed, the relative wind increases and with this to a first approximation, lift increases as the square of the speed while drag as the cube. Effective thrust decreases, instead of increases. Result: As the vehicle accelerates against the wind, it must slow down and slow down until it is going slower than the wind.

That is not even taking into account frictional losses in the drivetrain. There is a bit more here related to prop bite/camber/airfoil but these will not affect the conclusion.

By the way, one of the tests on the treadmill was invalid - this is the one where the machine starts about 18" from the wall and moves forward away from the wall. This provides a semblance at start up of what is called "ground effect" for aircraft.
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Old 12th November 2008, 04:56 PM   #231
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JB, when I said "I've done the experiment", I was referring to the craft spork posted the plans for. Basically your craft is a prop coupled to a wheel, no weird gearing, no flywheel, just very simple. Had one of those as a kid, couldn't understand why it wouldn't run forever. After all, the wind turns the prop, providing energy to the wheel; the wheel turning provides energy to the prop. That's how I learned about entropy.
But if that's not what is supposedly happening, what is?
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Old 12th November 2008, 05:15 PM   #232
Brian-M
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Originally Posted by Modified View Post
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.

Of course traveling downwind faster than the wind is possible. I do this all the time in my car, using stored energy from fossil fuels. I could do the same thing in an electric car using stored energy generated from the wind. Your iceboat example uses stored energy to do this too (in this case, it's stored as kinetic energy perpendicular to the direction of the wind). With zero friction, any idealized hypothetical vehicle can maintain this high speed indefinitely.

There's no problem with using stored energy to travel downwind faster than the wind.

The problem is that the craft in question is not using stored energy, but generating the energy to maintain it's faster than-the-wind velocity from it's own headwind.

It's velocity creates a headwind that is used to generate power to maintain and increase it's velocity.

That's like running a light bulb from an array of solar panels powered by the light produced by the same light bulb.

ETA: Generating energy from the headwind (or the wheels) reduces velocity. Basically, you're harnessing the kinetic energy of the craft itself. Using energy extracted from it's own kinetic energy to increase it's kinetic energy never results in more kinetic energy than you began with. (In real life, it results in less kinetic energy than you started with.)
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Old 12th November 2008, 05:40 PM   #233
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I believe it works, and the key is the lift-to-drag ratio of the rotating airfoils (i.e. propeller). There is no doubt that energy is available in the differential motion of the ground and the air. Another key is the gearing and pitch speed of the propeller, which must match the desired top speed, which is related to wind speed.

So the top speed will be limited by the wind speed, the lift-to-drag ratio of the prop, and the friction and drag forces. There is a lot of similarity to ice boats in this respect. The prop is in effect a continuously downdind-tacking airfoil.

As an aside, another unintuitive example of extracting energy from relative motion is dynamic soaring: http://en.wikipedia.org/wiki/Dynamic_soaring The record is 365 mph, the wind speed was naturally much lower.

// CyCrow
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Old 12th November 2008, 05:45 PM   #234
ThinAirDesigns
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Originally Posted by mhaze View Post
By the way, one of the tests on the treadmill was invalid - this is the one where the machine starts about 18" from the wall and moves forward away from the wall. This provides a semblance at start up of what is called "ground effect" for aircraft.
Very observant mhaze.

For the record, that video was not done by us, but rather one of our biggest critic who after seeing our first cart decided he would try it for himself.

He was surprised and we were delighted.

JB
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Old 12th November 2008, 05:49 PM   #235
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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 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.
Then answer the question I posed. If the vehicle is at the wind speed, what forces are acting on it?
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Old 12th November 2008, 05:49 PM   #236
Thabiguy
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Originally Posted by my_wan View Post
Do you have any idea how many different ways you can describe the same thing and they all be equally valid? There are at least 3 different formulation of thermodynamics alone that are equally as valid.
It's not a question of describing the equivalent thing differently. We are saying different things. You are saying that the device can, in theory, accelerate indefinitely (for a given construction). I'm saying that it can't, even in theory.

Originally Posted by my_wan View Post
You say:
1) The air pushed back is moving in the opposite direction of the air wrt device.
2) The air pushed back is the same direction as the air wrt ground.
Number 2 is dead wrong. It will be right once the craft exceeds the ground air speed but the single sentence you quoted and responded to specifically labeled it, "when the craft first takes off".
Number 2 is right, all the time. Particularly when the craft first takes off. I know what I'm saying.

Originally Posted by my_wan View Post
You do of course now realize that the statement you want me to realize as the truth is dead wrong. If not reread my response one quote up with the diagram.
No. The statement that I want you to realize is actually true. The problem is that you think it is false, and it is not.

Originally Posted by my_wan View Post
Trying to say that is how the original craft works is like drawing a paddleboat and saying that is how a sailboat works. If these things are equivalent then wouldn't you say a propeller and a windmill are equivalent? Why the do propellers often get over 90% efficiency when a windmill is limited to less than 59% efficiency?
*sigh*

Originally Posted by my_wan View Post
That's not even a question. Can air push on both sides of the blade? Apparently not sense there is no drag.
What I was asking was to ignore practical losses, practical inefficiency. To take it as an ideal model.

Originally Posted by my_wan View Post
Except you seem to assume the blade has drag because you are baiting me with indefinite acceleration. Do you realize that the speed of air has little to do with the speed of air molecules except statistically? No friction? Never mind, too messy.
I have absolutely no idea what you're talking about here. What I asked you was a perfectly valid question. There is no "bait". It's all about understanding the physics of the model.

Originally Posted by my_wan View Post
Didn't you mean to start this paragraph with, "Riddle me this"? This makes as much sense as asking what would happen if an unstoppable object hit an immovable object. No matter whether I get it right or wrong in your imagination you would then claim it means something real. Get real!!!
Again, I have absolutely no idea what you're talking about. I can only conclude that you must have misunderstood what I was asking you. I asked you to consider it as an ideal model.

Originally Posted by my_wan View Post
So I guess I need to figure out what really would happen when an unstoppable object hit an immovable object. Then I could be as smart as you...
This has no relevance to what I was saying.

Originally Posted by my_wan View Post
Don't debate with me anymore..
I apologize for assuming that you were here to discuss.
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Old 12th November 2008, 05:55 PM   #237
humber
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MHaze,
Well, what I was saying is that is not an inertial frame of reference. This platform is not notional in any way. It's rolling-road model. It's not the wheels that are the ground it's the treadmill belt. Everything is literal. The wheels are wheels, the air is the air, the propeller is the propeller. Just like on Mythbusters.

So, only the labels are changed. But, the body of the treadmill is connected to real ground, so the belt is also real ground. Call the air the ground if you like. No matter, as long as you realise what that means.

There is little impetus. The impetus between an operator, and the cart is the same that would be felt in the real world. Because, it is the real world.
Friction aside, the bigger one is as easy to move around as the little one. The only impetus lies in the difference between the forces controlling the cart itself, and how they are coupled to the belt by friction through the wheels. Moreover, the impetus is the momentum stored in the propeller.

I am not saying that a windblown model cannot be, of course not, but that this model is not an indicator of the potential for greater then wind-speed vehicles, other than flywheel driven, of course.

Brian-M, Mhaze. At least 3 of us understand.

Last edited by humber; 12th November 2008 at 05:59 PM.
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Old 12th November 2008, 06:08 PM   #238
Thabiguy
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Originally Posted by Acleron View Post
Then answer the question I posed. If the vehicle is at the wind speed, what forces are acting on it?
The important force is the force of the air pushing the propeller forward. Other than that, it's ground friction, internal friction, lateral drag on the propeller as it rotates... You could list more forces, like gravity pulling the vehicle down, force exerted by the ground on the vehicle as it doesn't let it fall down, forces between individual components of the vehicle... It's difficult to answer your question when I don't know where you're going and what is therefore of interest to you.

The force that is key to accelerating above wind speed is the force of the air pushing the propeller forward.

Again, it's more apparent if you consider the simplified model, posted here. When the device moves at wind speed, the key force is the force of the air pushing the blades forward (as the blades are moving at half the wind speed).
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Old 12th November 2008, 06:14 PM   #239
Thabiguy
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Spork, JB,

if you're reading this: can you please tell me whether I was right in what I was trying to explain to my_wan?

If I'm mistaken in some way, I'd rather find out.
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Old 12th November 2008, 06:18 PM   #240
ThinAirDesigns
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humber:
Quote:
Moreover, the impetus is the momentum stored in the propeller.
Anyone can come up with theories humber -- coming up with one that can be *tested* and falsified is the basis of scientific research.

I'll ask again for you to provide me with a test which can be executed which will prove your theory right and our theory wrong.

Please?

JB
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