Down wind faster than the wind

[humber]

Well, Spork you should contact this guy:
http://www.reference.com/browse/SMOT&

A few years ago, he was running an alternative energy business. I haven't met him, so I have no evidence, but I feel quite sure that he will take your $100K.

If only I had known how easy it wouldhavebeen.

 

[ThinAirDesigns]

humbert:

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

So, I guess I was wrong after all.

To Brian -- congrats. No shame -- it's truly a frustrating brainteaser.

To humbert -- I guess there's only two guys who "understand" it now.

JB

 

[spork]

So, converting this back to a fixed ground reference, the maximum speed of an idealized version of device (including 100% power transfer at the propeller, no wind resistance, no friction, etc) would be up to twice wind speed.

You're definitely getting closer, but in fact ice boats regularly achieve downwind velocity components of more than 3X the wind speed. Given sufficient efficiency a cart such as ours could do the same.

But I'm glad to see you're willing to look at things critically and consider a new perspective. This thing is not intuitive to most folks. Of course that's what makes it interesting.

 

[spork]

I feel quite sure that he will take your $100K.

If only I had known how easy it wouldhavebeen.

Forget about how easy it "would have been". It's still available. You know how this thing operates and I don't - so it seems like a sure thing for you. Just step up with your own cash and claim mine.

 

[humber]

Yes, but you've already lost one convert. More to come, I expect.

OK, I'll take it. What do I have to do?

 

[Modified]

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.

Even with a small non-zero friction, you can average faster than the wind by re-accelerating occasionally. By connecting several boats through sliding connections, you can build a vehicle that as a whole maintains a steady downwind speed that is faster than the wind. All this happens even if you don't believe that the downwind component of the speed can exceed the wind speed while tacking.

So, by the construction presented, given that it is possible for an iceboat to exceed the speed of the wind in some arbitrary direction, then there exist some non-zero values of iceboat friction and drag such that it is possible to construct a vehicle that can exceed the speed of the wind while traveling straight downwind.

In other words, the fact that the speed of an iceboat can exceed the wind speed (even at some angle to the wind, which is something we can all agree on) implies that a wind-powered vehicle that can travel straight downwind faster than the wind at a steady rate of speed is possible in theory. If you see something wrong with this, what is it?

 

[spork]

Yes, but you've already lost one convert. More to come, I expect.

We did?

OK, I'll take it. What do I have to do?

It's a bet. You have to do the bet thing. You and I each put our $100K into a joint escrow acct. We'll draw up the agreement on the statement of the wager and exactly how it will be decided. Escrow pays all proceeds to the winner.

 

[spork]

In other words, the fact that the speed of an iceboat can exceed the wind speed (even at some angle to the wind, which is something we can all agree on) implies that a wind-powered vehicle that can travel straight downwind faster than the wind at a steady rate of speed is possible in theory. If you see something wrong with this, what is it?

The fact that an ice boat can exceed the wind speed in certain directions doesn't necessarily imply that it can exceed the wind speed in all directions (steady state), or that it's downwind velocity component can exceed the wind speed steady state - only that it can exceed it in bursts.

But we do know from basic aero theory and simple vector analysis that the ice-boat can in fact maintain a downwind velocity component 3X or more the wind speed.

 

[humber]

JWideman has seen the light.

OK. But, what do I have to show, prove or do in order to take the money?
I mean what is the actual task ?
Also, who will be the judge?

 

[spork]

JWideman has seen the light.

So that's the "convert" we lost!? I'm reasonably certain none of us that understand what's going on ever counted him among the enlightened.

OK. But, what do I have to show, prove or do in order to take the money?

You don't have to prove a thing. I have to prove that the cart we built is capable of going directly downwind, faster than the wind, steady state - whether on the open road or a treadmill. For the heck of it I'll also prove that your bizarre theories have no merit. It will be an expensive lesson for you, but I'll try and see you get your money's worth.

 

[casebro]

The propeller vanes are acting like the ice boat sails. The prop shaft axis is down wind, the vanes are tacking across the wind. Easily understood, correct?

So, the prop can have a peripheral speed greater than the wind speed. Actually, propeller airplane prop tips go the speed of sound, but the aircraft ( analogous to windspeed) is much slower. That's why some prop airplanes are so noisy- the prop tips break the sound barrier, causing "sonic booms", shock waves. It's not all exhaust noise.)

So, each blade is tacking at a speed much greater than the wind. Now it is just a question of how much power the prop has, versus the drag of the whole vehicle. Hmmm, it could certainly go up-wind pretty well . And the faster it goes upwind, the faster the apparent wind, to drive the prop even faster - perpetual motion machine here?

But just how fast can even an ice boat go, down wind? Oh, they go several times wind speed across the wind, but what is their speed made good down wind? Anybody here have a polar chart of wind speed vs hull speed of an ice boat? I only have one of a sail boat. I suspect that ice boats are very low friction, like we would hope in our fan-powered cart. So the efficiency of the ice boat might give a hint of the possibilities of a fan powered cart. And it's diminishing returns as the hull approaches wind speed.

See, even in a cross wind, as an iceboats speed picks up, the apparent wind swings closer to astern, diminishing the gains of going cross wind. So the ice boat has to turn up-wind to maintain the same cross-wind speed. This limits the speed made good in a down wind direction.

Anyway, lets build a cart, prop hooked to wheels. Put the cart on a treadmill. Tether the cart, so it can't roll. Turn on the treadmill motor. The spinning wheels will turn the propeller with some force, which will thrust the cart against it's tethers. Now lets remove the tethers, and use an incline instead. The incline being such that it's slope will equal the drag of the mechanisms. The cart will remain stationary against the rotation of the treadmill. Balancing the treadmill's speed vs the incline, and you just might get motion in the direction opposite the treadmills direction. No wind speed needed. Nor does this prove that the cart can even function in wind at all. Only that a treadmill is a viable way to input power to a fan-propelled cart.

No, still air vs a moving treadmill is NOT the same as moving air vs still pavement. You forgot that the drag of the slope will be exactly equal to the power being input from the treadmill's belt. That power input is what moves the cart 'relative' to the belt.

I think I'll need to see some air speed indicators, hull speedometer, and independent verification before I'll lose my skepticism here.

 

[humber]

When someone familiar with your stuff says:
"The treadmill is merely a misdirection"
That's a win

I still need to know who the judge will be.

As a preliminary step, you can write a Matlab script. You can turn it into an executable, so I can't see the source code. Just the simulation will do.
Simulink is relatively quick. So as to be fair, you can post it on You Tube.
Then there will be no question of plagiarism

Please, define 'steady state'.

ETA:
I just had a thought. I am so sure that the treadmill experiment has no validity, that I will accept proof of concept on that. You have already revealed all there is to know, I understand.
Post the calculations, and a simulation at the Physics Forum, and perhaps we can ask the moderators to take a look at it. If they say that it has potential as the basis of faster than wind travel, then we can go directly to the device.

 

[CaveDave]

Here is a very simple diagram of the craft.
[qimg]http://www.internationalskeptics.com/forums/imagehosting/15393491aaeb9be526.gif[/qimg]
Direction of travel is to the left <----.

Thanks for the drawing, it helps clarify things for me. I assume, even though I can't "see" it from above, that prop. axis, wind direction, and cart travel direction are parallel, despite the many references to "vector diagrams", sail boats and tacking?
(I am more than 90 posts behind, but I am trying to read all, so I may be awhile.)

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

Yes, if only people read Einstein's papers, those that he won the Nobel prize for, perhaps the would learn something about momentum.

The Photoelectric Effect -- the one that started Quantum Mechanics?

Do you mean as in Photon momentum? I don't understand how that relates.

His papers on Relativity, Gravitation, and others did not win Nobel Prizes.

Dave

 

[humber]

Yes, but it's not connected with this matter. It was sarcasm.

 

[my_wan]

I despair of debating with you because you are not debating. You don't even make an attempt. You state your opinion with no supporting argument and then think repeating yourself is debating.

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.

No, I never made that claim. I've described the limits in velocity of this craft many times. I have said the force of a house fly can accelerate an elephant indefinitely in empty space. This device cannot even in principle operate in such an environment.

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".

Number 2 is right, all the time. Particularly when the craft first takes off. I know what I'm saying.

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.

So the wind is by definition going right to left wrt the craft while to prop blows the air left to right wrt the craft and this is the same direction wrt the craft? Only you didn't even bother to make an argument of any sort. You simply responded with, "I know what I'm saying". I don't despair of debating you for your claims I despair of you actually making a case for anything.

*sigh*

You wanted me to answer your question concerning magical notions of zero friction/drag with a (one way?) force that requires drag. I ask you if two real empirical devices are equivalence and ask you about real empirical differences and this is the answer I get.

What I was asking was to ignore practical losses, practical inefficiency. To take it as an ideal model.

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.

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.

What you described was not an ideal model of anything. It required assuming the effects required for the devices operation doesn't exist but that they do exist in some (uni?)directional sense when you want them. What about the wheels? If they are frictionless/dragless, even if the prop turned them do they have any effect on the craft motion or just spin freely on the ground? An ideal model in physics depends on taking the limit on a well defined physical aspect, not removing physical effects except when you want them. That's what pseudoscience does.

It bears no resemblance at all to the empirical fact that a tiny persistent force can accelerate a massive object to arbitrarily high speeds in space. Do you deny that the persistant force of a fly can do this to an elephant in empty space?

This has no relevance to what I was saying.

Nothing in this whole Universe has any relevance to what you were saying. That was the point. You can claim the fly force accelerating an elephant does but your fairy tale properties removes by definition the very effects the device depends on except when you want them to exist.

I apologize for assuming that you were here to discuss.

When asked to clarify what you mean you simply repeat yourself. When admitted assumptions are made about what you were trying to say you say "wrong". When you do say something that is wrong by definition, not physics, you respond with, "I know what I'm saying". Well maybe I don't but that response gives me no clue. *sigh* is not a clue. When asked to explain why other devices work as they empirically do you respond that it has nothing to do with it. The you invent grossly different devices with no empirical precedence and assume magical fairy properties and claim it has everything to do with it. It is you that is not actually discussing anything.

 

[my_wan]

Thanks for the drawing, it helps clarify things for me. I assume, even though I can't "see" it from above, that prop. axis, wind direction, and cart travel direction are parallel, despite the many references to "vector diagrams", sail boats and tacking?
(I am more than 90 posts behind, but I am trying to read all, so I may be awhile.)

Yes, they are parallel. The "tacking" used by sailors is used as an example model of how ground wind speed vs apparent wind speed relative to a craft can produce craft velocities greater than the wind speed relative to the ground. By itself it doesn't prove this craft works but it does prove that the principles behind the effect is physically sound.

I'm very sure this device works and even more sure that it can be made to work as advertised. I do have some differences with some pro people here concerning the equivalency of a bidirectional analysis of force vectors, but only wrt efficiency. However, the craft has a well defined direction of torque on the individual craft components and the way these vectors compliment in my analysis is showing the craft should come out on the extreme high end of efficiency.

 

[my_wan]

my_wan says that the maximum speed of the device is only limited by practical considerations (such as drag on the device as it moves at higher than wind speed), and that no matter how fast the device is going, it would always be (in theory) able to utilize the power of the wind for further acceleration, if it weren't for the drag etc. (I hope I have not misrepresented what he says. If I have, I apologize, and invite him to offer his own summary.)

Close but with qualifications. It is always possible to add a tiny amount of speed but it is a exponentially diminishing return. By doubling the cross-section of wind for more max velocity you fall way short of doubling the max velocity. This is because the resistance of an object to motion through a fluid increases as the cube of the velocity. So even though it is always possible for any given design to be improved to add some amount of top end speed, larger prop cross-section, etc., there remains an approximate practical limit.

 

[Thabiguy]

So the wind is by definition going right to left wrt the craft while to prop blows the air left to right wrt the craft and this is the same direction wrt the craft? Only you didn't even bother to make an argument of any sort.

In fact, I explained with great detail why that is. You just didn't understand my explanation. Perhaps I didn't explain it clearly enough.

Let me try again. The craft is travelling right to left, wrt ground, at 4 mph. The wind is going right to left, wrt ground, at 8 mph (and also right to left, wrt craft, at 4 mph). The prop blows the air left to right wrt the craft, at 2 mph.

What direction is the air blown by the propeller travelling, wrt ground? In the same direction as the air, or the opposite direction of the air?

Does this make statement number 2 true, or false?

When asked to clarify what you mean you simply repeat yourself.

Does this clarify what I mean? If not, what is still unclear to you?

ETA: I'm sorry, I mistyped one of the directions when I was typing this post. The error is now corrected. If you have read it before, please read the post again.

 

[my_wan]

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):


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.

This is at the root of my differences with the other pro people here but it seems you have nailed it quiet well here. I got the torque direction wrong myself before I started analyzing it.

 

[my_wan]

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?

It's not the "propeller pushing the air backwards which supplies the forward momentum". At below wind speed it is the wind blowing the craft itself downwind with force. The prop is then powered with some of this force through the wheels so the the wind relative to the craft remains faster than the wind relative to the ground even when the craft exceeds ground wind speed.