Down wind faster than the wind

[.13.]

Yes, exactly.

Ok. Is spork disagreeing with you or did I misunderstand his post #187?

 

[my_wan]

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.

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.

 

[my_wan]

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.

 

[JWideman]

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

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.

 

[technoextreme]

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.

 

[humber]

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.

 

[Modified]

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.

 

[my_wan]

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/forums/showthread.php?postid=4196713#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.

 

[Thabiguy]

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.

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.

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 v_dev, 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.

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.

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.

 

[humber]

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.

 

[Brian-M]

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?

 

[ThinAirDesigns]

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!

 

[fsol]

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.

 

[fsol]

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.

 

[BenBurch]

OK, who has access to a wind tunnel? This can be easily resolved in a way that will remove all doubt.

 

[humber]

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.

 

[.13.]

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):

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.

 

[humber]

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

 

[spork]

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.

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.

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.

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.

 

[spork]

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.