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DDW faster than the wind thought experiment:

Most involved here in these discussions acknowledge that it's possible to steady state sail a traditional sailing rig at a fixed angle to the wind where the downwind VMG of the craft is greater than 1x windspeed (even 2x, 3x ...). Those who do not agree with this should review the data collected by NALSA (nalsa.org) on the topic. For those who agree with the above, I present the following thought experiment related to the DDWFTTW propeller driven vehicle that has also been discussed here. The following is presented in the hope of removing some of the related misconceptions and furthering the discussion regarding the section that prillen recently removed.e

Who are these "most"? Much above and below is wrong. Nowhere in the cited refs do I see good claims that the VMG towards the directly downwind point is greater than windspeed. Sure, an ice yacht can do 5 x wind speed but that is across the ground at a very shallow angle to the downwind point. A free floating balloon still beats the water/land/ice yacht to the downwind point. "Most" here seem to think that the angle and the speed can be chosen independently. No! Speed downwind (VMG to the downwind point) will never exceed cos(angle to the wind) x ground-speed. Paul Beardsell (talk) 06:46, 7 June 2010 (UTC)

First, a couple of design basics related to the DDW propeller driven vehicle (DDWPDV). The spinning airfoils are not acting as turbine blades. The blades do not drive the wheels. The spinning airfoils are acting as propeller blades and are *driven by the wheels". The force on the wheels is a braking force and the gearing between the wheel axle and the prop axle transfers this braking force to the spinning blades.

Second, since the topic of this page is "Sailing downwind faster than the wind", some dismiss the DDWPDV saying that it's not "sailing" and thus isn't relevent to the page in any case. The truth is, the airfoils on the DDWPDV are acting in the *exact* manner as the airfoil of a traditional sailing rig with its parent on a 'faster than the wind' downwind reach. Both airfoils are carving helical paths through the air -- the traditional rig is merely carving a helical path of MUCH greater diameter (the diameter of the earth) than those on the DDWPDV.

I will support this above assertion with the following thought experiment:

(I'm not a sailor so pardon me of I misuse a term here or there in the following. Also, as with all thought experiments, there are some simplifications.)

Imagine for a moment a world that rather than being shaped as a sphere is shaped as a cylinder. The cylinder 'world' is laying on it's side in our view and we are standing at the south "end" of the world on top of the cylinder. The entire surface of this world consists of one enormous uninterrupted dry lake bed with one wind blowing from the south to the north. Let's send a land-yacht on a 45 degree reach running to the NW. Without making a single gybe, this craft will 'corkscrew' it's way around the world as many times as needed to reach the far end of the cylinder. We know that if we release a neutral bouyancy floating balloon into the wind at the same time as the land-yacht, by the time the land-yacht has made one circumnavigation of the cylinder world and reappears to us on top it will be significantly farther downwind and 'downcylinder' than the balloon. This of course is just a simple matter of the craft having a downwind VMG greater than 1.0 wind speed .

Nonsense! That is a circular argument (not only a cylindrical one!). You prove the yacht will be ahead of the balloon by assuming that VMG > windspeed. It is not. VMG is never greater than (speed over the ground) * cos(angle to the wind). Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Now, imagine that when the initial craft we sent on it's 45 degree path is halfway around the world (and now on the 'bottom' of the cylinder), we set another identical craft off on an identical 45 degree downwind reaching path. We start this craft off at the same 'longitude' as our craft already in motion. What we now have are two land-yachts on opposite sides of the world, going the exact same speed and carving the same helical path -- all the while remaining exactly opposite of each other on the cylinder. Every rotation they make they cross the DDW path of the drifting balloon and each rotation they get farther and farther ahead of it.

No, they do not. Their landspeed will be max windspeed/cos(angle). They will never ever ovetake the balloon. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Imagine now in this thought experiment that we begin to shrink our cylinder world a bit at a time. We have not changed the speed of the wind nor the speed of the land-yachts. As this 'world' shrinks, all that changes is the diameter of the helical path shrinks and the number of revolutions that the yacht makes in any given period of time increases. Keep shrinking this imaginary world until the wheels of the land-yachts are on such a small cylinder that they are essentially touching each other as they spin dizzyingly around and around -- their sails protruding in opposite directions.

If you are with me so far, you'll see that our two land-yachts are still achieving a downwind VMG of greater than 1.0 -- every time they rotate they increase their advantage over the floating balloon. Also, those sails spinning in a perfect circle are sure looking familiar (propeller anyone?)

Once again, this is the same circular argument! You assume VMG > windspeed is possible, and then you prove this very fact. How convenient! Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Going a step further in this 'morphing' process, let's replace the chassis of both land-yachts with something more simple without making any changes to the spinning sails. We know that both the sails and the chassis are carving a 45 degree helical path so let's dump the frames and wheels of the land-yachts and replace both of those with a single, oversized threaded rod. This rod is equipped with grooves that match the sails 45 degree path and is aligned with the wind, taking the place of the 'pole' of our cylindrical earth. Let's spin on a matching oversized nut and drop the masts into holes in that nut. Now, without ever interrupting the spinning sails nor their downwind VMG >1.0 paths we have created the simplest DDWFTTW vehicle of all -- two spinning airfoils on a nut traversing a threaded rod. At the center of these rotating airfoils, we now have a nut that is going DDW and continuing to press it's advantage over the balloon with every rotation.

(Before taking the last step to our vehicle, it's interesting to note that the sole purpose of the keel mechanism on a traditional sailing rig is to force the airfoil to take an advantageous path through the air. In the case of a 45 degree reach, it's purpose is to ensure that for every foot that the airfoil moves downwind, it also moves one foot to the right (or left). It's this forced diagonal path through the air that creates the apparent wind needed to generate thrust. Of course the purpose of the non-articulated skates of an ice-boat, the wheels on a land-yacht and the threaded rod and nut in our above example serve the same purpose as the keel of the sailboat -- forcing the airfoil to maintain it's path diagonal to the wind.)

Last step: Once we reach the point that we have a pair of spinning airfoils happily pushing the nut DDWFTTW down a threaded rod, we need someway to translate this into a vehicle that can traverse any dry lake bed DDW. Realizing that to do this we only must find a way to force our airfoils to continue on their 45 degree helical path -- a path from which they have yet strayed, we arrange gearing between the wheel axle and the prop axle to ensure that for every foot the wheels roll across the dry lake bed DDW, the airfoil is forced through the air one foot to the side just as before -- and there you have it, DDWPDV -- a DDWFTTW vehicle.

As you can see, through this entire process the wind never changed directions, the angle of the apparent wind to the airfoils never changed, the speed of the airfoils through the air never changed, the downwind VMG of the airfoils never changed, the lift and drag vectors of any given airfoil section never changed -- in short, other than a slow change in the diameter of the helical path of the airfoil, all remained the same from "sail" to "prop".

Turns out that the airfoils of a traditional sailing rig on a faster than the wind reach and those of the DDWPDV are acting in the same manner -- one can *call* it sailing or not, but it's a distinction without out a difference from an aerodynamic standpoint.

Here is the 'Cliff-Notes' version of the above: The airfoils of the propeller are one loooong and continuous downwind helical reach while the chassis travels DDW. Adjusting the gear ratio between the wheels and the prop is the equivalent of adjusting your ground track on the land-yacht (and thus altering your sails path through the air) and changing the pitch of the propeller is the equivalent of adjusting the angle of the sail on the land-yacht.

Hope this helps:

ThinAirDesigns (talk) 00:11, 26 January 2010 (UTC)

What sophistry! Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Dear ThinAirDesigns, thank you very much for this and your corresponding post on the Sailing page. I had figured out that the propeller on the cart in question had the same function as a sail set at an angle to the wind (just as a rotating helicopter blade has the same function as a wing) but I didn't know how to explain it. Your explanation is very clear and makes perfect sense to me. Would the skeptics now agree that the deleted section can be restored?--Gautier lebon (talk) 17:14, 26 January 2010 (UTC)

Well it is always interesting with a new scope, but I can not see that the thoughts are supported by evidence. As I understand ThinAirDesigns it equals that a wind turbine could generate power in calm weather if it had a foundation that could tilt it from side to side. And I rally can not imagine that happening. The only way I can see it should be possible to sail faster than the wind dead downwind would be to measure the wind speed at the vessel but use a kite much higher up and use the wind shear to generate the driving force. But I do not consider this as a true SFTTWDDW as the kite would fly slower than the wind (and it is only my thoughts – never seen any evidence). Prillen (talk) 20:08, 26 January 2010 (UTC)

Hi prillen. First I would like to say that I am new to WP and want to make sure that I contribute to the discussion according to WP guidelines. Currently I intend for my comments to fall under this quote from the WP talk page guidelines "to discuss how the different points of view obtained from secondary sources should be included in the article, so that the end result is neutral and objective (which may mean including conflicting viewpoints)." With that in mind, I'll continue:

To conclude that the thought experiment that I gave is not supported by evidence, one has to assume that the the plethora of examples shown in operation on YouTube are faked (which of course is always a very real possibility). However, if the only flaw you can find in my example is that "it's not supported by evidence", all you've done is create a circular argument where 'it can't be done therefore the evidence must be faked, therefore your arguments aren't supported by evidence, therefore it can't be done ...'

To break out of this circle, one must first consider the validity of the thought experiment. If the thought experiment is valid, THEN we look at the evidence and say "is it faked"? If the thought experiment has no flaws, one could rationally conclude that while all that YouTube evidence *could* be faked, it need not be and in fact it's easier to just do it than to fake it.

Do you refer to the YouTube video of the model on the treadmill? That does not do what is claimed. Say the wind is 10mph. So we set the treadmill speed to 10mph. What is the speed of the wind which ought to be experienced by mini-you, sitting on the model. Zero! We are travelling downwind at downwind speed. So why is there a dirty great fan behind you? Why does mini-you experience a tail wind on the model on the 10mph treadmill? Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

As an example of this principle: If we logically conclude that an ordinary car has the necessary power and ground clearance to drive over an ordinary speed bump, we might also easily conclude that a video of a car driving over a speed bump to be reasonable evidence of our conclusion. If 10 different people independently video a car driving over the speed bump it starts to look even better as evidence. And certainly if it's easier to produce a video of a car actually driving over a speedbump than to produce one that fakes a car driving over a speedbump, one begins to conclude that the videos may indeed be real evidence. Why would someone fake it after all when it's so easy to actually do?

I believe that extraordinary claims require extraordinary evidence, but the purpose of my thought experiment is to show that there is *nothing* extraordinary about the claim of the DDWPDV, it is merely non-intuitive. For over a hundred years now, reaching ice-boats have been able to achieve downwind VMGs higher than windspeed. For a quarter of a century now sailboats have been able to do the same thing. If you place two of these completely ordinary vessels doing completely ordinary things on opposite sides of a completely ordinary circle (be it the world or a rotating shaft) the reaching sails are not going DDW, but the center point between the two certainly is. Place an object on that center point, or hook an object to that center point, and that object is now going DDWFTTW.

Would you care to explain where in my example the downwind VMG of the airfoils drops below 1.0x windspeed? If we agree that from the outset the two airfoils (on the land-yachts) have a downwind VMG greater than 1.0 windspeed and you don't agree that in the end they are *still* achieving this, there must be somewhere in there you can point to the change.

Also, I'm also not sure where you got the idea from my land-yacht example that a wind generator can be a net producer of power on a calm day (no matter what the foundation does). I certainly hold no such position and in the example I gave, the air is always moving relative to the surface. Also, like you I would not consider your kite example to be true DDWFTTW. To qualify, the wind measured must be the wind used

ThinAirDesigns (talk) 21:40, 26 January 2010 (UTC)

I am sorry but I still do not get your point. As I see it your arguments can just as well be used for sailing "dead" upwind faster than the wind. And you write "I certainly hold no such position and in the example I gave, the air is always moving relative to the surface." but for a vessel moving DDW at the same speed as the wind the relative wind will be zero – just as for a wind turbine on a calm day. Regarding evidence I will off cause except that I am wrong if you provide a reliable source/evidence. And no, I do not consider YouTube as reliable evidence. But it could be interesting to watch them – do you have a link? Prillen (talk) 09:20, 27 January 2010 (UTC)

Dear Prillen, if a vessel moves DDW faster than the wind then the relative wind will not be zero: the vessel will be facing a headwind. Just as an iceboat that starts on a broad reach will accelerate until it sailing into the wind. Regarding sailing dead upwind faster than the wind, consider a boat that has no sails but uses a windmill to power a propeller. There is no theoretical reason why that boat could not advance dead upwind faster than the wind, although it might not be possible in practice given the efficiency of the windmill, the drag induced by the windmill, the efficiency of the propeller, the drag of the water, etc. Regarding the video, please look carefully at the videos that you will find at [1]. Regarding what to do with this, my proposal remains to include in the main article a section on this topic, noting that there is skpeticism, and referring to the talk pages where this discussion has taken place. Surely that is of interest to Wikipedia readers, and surely one can rely on them to make up their own minds, if the text clearly indicates that skepticism may be justified?--Gautier lebon (talk) 12:32, 27 January 2010 (UTC)

Hi Prillen, At the very top of my first entry here (the thought experiment), I stated that my presented exercise was for those who agree that there exist traditional sailing rigs which can achieve downwind VMGs of greater than windspeed while on a broad reach. There have been several highly regarded books and sites referenced which state this, published polars showing craft capable of doing it and at least one international sanctioning sailing organization collecting and publishing data demonstrating it being done in the real world. I'm quite certain that any and all of those sources meet WP standards for inclusion.

No! VMG greater than windspeed towards the directly downwind point is NOT possible on any sea/land/ice yacht. The cited refs do not support such an outlandish claim. So the whole argument vanishes into thin air. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Before directly exchanging comments with you I should have asked your position on that above paragraph. If you do not agree with it, then pretty much all of what I have written will not make sense to you as it is all based on that "traditional sailing rigs can beat the wind to a downwind mark" premise. Do you mind if before we continue, I ask you if you agree with the above paragraph? Thanks ThinAirDesigns (talk) 14:01, 27 January 2010 (UTC)

ThinAir has posted a comment on my user talk page. He draws our attention to the fact that a team of Aero students from San Jose State University, along with their Professor, advisers and generous corporate sponsors have set out to build a device that would definitely prove that it is possible to go downwind, faster than the wind, powered only by the wind(DDWFTTW), steady state, see [2]. This shows that qualified and educated people believe that the feat is not theoretically impossible, although it may be very difficult to achieve in practice.--Gautier lebon (talk) 10:31, 28 January 2010 (UTC)

The world is full of idiots. Linus Pauling won two Nobel Prizes and then staked his considerable reputation on the claim then Vitamin C could cure cancer, baldness and flatulence. Do not accept arguments from authority, academic or commercial! Conservation of energy is a higher authority. Paul Beardsell (talk) 08:01, 7 June 2010 (UTC)

Yes I do agree in the paragraph above. And I agree with Gautier Lebon that a section about the idea should/could be included, but describing it as a subject of discussion and without proof – not the way it was done. But it is interesting with the student project though. Prillen (talk) 12:17, 28 January 2010 (UTC)

OK, I will post a version of the section in question along those lines.--Gautier lebon (talk) 11:07, 2 February 2010 (UTC)

Hi Prillen, and thanks for your response. Above, you say you are unsure of the 'point' to my thought exercise and follow-up post. With your agreement that traditional rigs can achieve steady state downwind VMGs greater than windspeed, and that this achievement is documented according to WP standard the point of my thought exercise is this:

The exercise shows step by step that the airfoils on the DDWPDV are operating in just the same way that the sails on the described (and agreed upon and documented) land-yacht operate. Any documentation deemed WP appropriate for the propulsion of the VMG greater than 1.0 land-yacht is also documentation for the propulsion of the DDWPDV since they are propelled in the identical manner. For this not to be true, someone would need to point out the precise step in my exercise where it goes wrong. To date, no one has even touched on doing so.

If I stick an internal combustion engine in a new and odd looking vehicle, it's WP appropriate to use the same internal combustion engine documention and references as the other application use. Just because I put a normally operating sail on a new and odd looking vehicle (the DDWPDV) doesn't mean that I don't get to use the same sailing documentation as everyone else. Documentation for any tradition rig with a downwind VMG greater than 1.0 windspeed IS documentation for the DDWPDV. (as a note -- It was the realization that the diameter of the circle that a traditional sailing rig follows (the diameter of the earth) could be shrunk to something more manageable that led to the creation of the DDWPDV. True story)ThinAirDesigns (talk) 14:29, 28 January 2010 (UTC)

Deleted thought experiment

Dear Prillen, I see that you have deleted the text that I reproduce below. Can you please explain why you deleted it? I thought that it explained why the claimed device is theoretically possible, and so was worth including.--Gautier lebon (talk) 09:47, 3 February 2010 (UTC)

Consider a boat that has a very large spinnaker and that drags behind it a propeller-driven electric power generator. The spinnaker can be made suffiently large so that the boat sails nearly as fast as the wind despite the drag from the power generator. Suppose that the generated energy is stored in batteries. After a while, the boat can lower its sails and use the energy stored in the batteries to run a propeller to advance faster than the wind. Thus, on average, the boat can proceed dead downwind faster than the wind.

This scenario is highly theoretical and it would be difficult to achieve it in practice because of the high resistance of water. But a wind-powered cart running on wheels, on a flat surface, has much less resistance. Consider a cart that uses a very large spinnaker to run downwind close to the speed of the wind while driving an eletric power generator from its wheels (that is, the wheels are geared to a power generator). If energy from the generator is stored in batteries then, at some point, the spinnaker can be taken down and the energy from the batteries can used to power an electric motor to drive the wheels so as to propell the cart downwind at a speed greater than the wind. Again, on average, the cart can proceed dead downwind faster than the wind.

Dear Gautier lebon you put a lot of energy an enthusiasm in this article - good. But I do not like you add text I think is already discussed, and not agreed upon, to the article. So I deleted the sub-section of the same reasons as earlier: Because then it is not considered as "sailing" faster than the wind. It would be "motoring-faster-than-the-wind" although you would be using stored wind derived energy. That is why I deleted the sub-section. Prillen (talk) 11:04, 8 February 2010 (UTC)

Thank you for the kind words. There were various items that were not agreed, but it seems to me that the validity of the thought-experiment was not challenged. What was challenged is whether it was relevant. I think that we all agree that proceeding dead downwind faster than the wind is not "sailing" in the traditional sense. And the section makes that clear. It is indeed a form of "motoring" faster than the wind, using only energy from the wind. I would be happy to rewrite the material to make it clear that this is what is being described. I still think that it should be included because it expains why the dead downwind cart does not necessarily violate the laws of physics, which is not obvious at first sight. If you agree that some revised text would be appropriate, please let me know, and I will add it. Thank you.--Gautier lebon (talk) 11:20, 8 February 2010 (UTC)

I fear I may be doing this wrong. Trying to leave a comment here -spork-

From the start of this wiki page... "Devices that are powered by sails (such as sailboats, iceboats and sand yachts) can sail (that is, advance over the surface) faster than the wind. Of course they cannot do that by using simple square sails that are set perpendicular to the wind."

Actually, I'm pretty sure it IS possible to sail faster than the wind with a square sail set perpendicular to the true wind. However, the vehicle must be constrained to move at some angle to the wind. Consider an ice-boat on a downwind course 110 degrees off the wind. With a square sail and low enough drag, the ice-boat should maintain a *downwind* vmg of nearly wind speed with this configuration. That will give it a true speed far greater than wind speed. —Preceding unsigned comment added by 75.55.124.115 (talk) 05:21, 8 February 2010 (UTC)

Excellent observation. I will correct the opening sentence.--Gautier lebon (talk) 09:47, 8 February 2010 (UTC)

Is it possible to apply the trigonometry that leads us to believe in reaching downwind (under a fore-and-aft rig) faster than the wind in the vertical plane? Square riggers off the wind set their sails slack so that they are not stalled but have laminar flow from top to bottom, and vertical lift. The boat is certainly constrained to stay in contact with the water surface. --Nigelj (talk) 11:11, 8 February 2010 (UTC)

Of course some part of the boat has to stay in contact with the surface, otherwise you won't get the "wedge" effect and you will simply drift downwind. Also, there is an apparent wind generated in the situation of the 'downwind' iceboat described above. That has to be taken into account, so it would not be efficient to set the square sail perpendicular to the true wind.--Gautier lebon (talk) 08:56, 9 February 2010 (UTC)

New version of thought experiment

I propose to add back the following revised version of the deleted thought experiment. It would appear after the sentence reading "Note that a conventional keelboat's performance is also very much improved by a device other than the sail: its keel". Comments?--Gautier lebon (talk) 09:51, 11 February 2010 (UTC)

That is, consider a device that uses a mechanism in additon to sails to store energy obtained from the wind and then uses the stored energy to propell itself dead downwind.

For example, consider a boat that has a very large spinnaker and that drags behind it a propeller-driven electric power generator. The spinnaker can be made suffiently large so that the boat sails nearly as fast as the wind despite the drag from the power generator. Suppose that the generated energy is stored in batteries. After a while, the boat can lower its sails and use the energy stored in the batteries to run a propeller to advance faster than the wind. Thus, on average, the boat can proceed dead downwind faster than the wind.

This scenario is highly theoretical and it would be difficult to achieve it in practice because of the high resistance of water. But a wind-powered cart running on wheels, on a flat surface, has much less resistance. Consider a cart that uses a very large spinnaker to run downwind close to the speed of the wind while driving an eletric power generator from its wheels (that is, the wheels are geared to a power generator). If energy from the generator is stored in batteries then, at some point, the spinnaker can be taken down and the energy from the batteries can used to power an electric motor to drive the wheels so as to propell the cart downwind at a speed greater than the wind. Again, on average, the cart can proceed dead downwind faster than the wind.

Sorry but "Wikipedia is not a place to publish your own thoughts and analyses or to publish new information." Prillen (talk) 10:10, 11 February 2010 (UTC)

Correct. But it seems to me that the thought-experiment does not fall into any of the forbidden categories. It is not "1. Primary (original) research" nor "2. Personal inventions". It is merely an obvious explanation of why no laws of physics are violated if a wind-driven device moves downwind faster than the wind. I would appreciate comments from others regarding whether the material should be included in the article, or whether it would be more appropriate to add a note referring to the talk page.--Gautier lebon (talk) 09:40, 12 February 2010 (UTC)

There isn't a proper Wiki place yet for well-conceived teaching. That's a pity, because imparting knowledge isn't just statement of facts, but largely helping learners conceptualize, helping them to avoid pitfalls. I heard that in the 1800s calculus was post-graduate work. As pitfalls became understood, it moved to graduate level, then to undergraduate. Now, it's sometimes taught in high school. That clearly demonstrates that there is more to knowledge than presenting the verifiable encyclopedic facts. But yet: that is Wikipedia's charter.

I'd be among the first to be bold and say, "Then change that part of the charter!" Except ... I happen to have years of professional experience editing and writing troubleshooting documents, and my experience suggests there would be significant problems. The problems focus around three primary stumbling blocks: 1) People have a tendency to assume that a major, a breakthrough insight for them ... will also be an insight for others. But in practice, learners have all kinds of misconceptions ... and what is an insight to one person ... is totally obvious to another. The other has some other misconception. 2) People also have a tendency to assume that what is a transparently obvious example will be the same for others. 3) I'm not pointing fingers, this is not directed at the folks who have been in this discussion: Often learners who have had a hard-won insight assume they now understand the whole problem in context. That is, they've considered the social, political, practical ... and every other side. They are in a great mood, happy to share their new understanding. It's a great impulse! Often enough, they don't yet perceive context. So what happens is that these new enthusiasts confidently broadcast their new understanding ... not realizing how limited their perspective remains.

So the problem is both that teaching is important, and that it is far more difficult than typically imagined. Wiki takes the "safe" posture, which is to disallow teaching. Times will change, but for now, that's where we are. Regards to all, Alpha Ralpha Boulevard (talk) 06:26, 13 March 2010 (UTC)

The two vector diagrams

The two big vector diagrams in the article with the respective titles "Upwind" and "Downwind" seem to have the directions of the "true wind" arrows the other way round. For example, in the "Upwind" diagram, the directions of the "boat speed" and "true wind" are both pointing towards the right side of the page. If the boat is travelling towards the same direction as the true wind then it should be travelling downwind, not upwind. 222.153.241.153 (talk) 17:12, 12 February 2010 (UTC)

No, the arrows point in the correct directions for the vector algebra to work: just think of the case when the boat is moving directly upwind or directly downwind.--Gautier lebon (talk) 17:22, 12 February 2010 (UTC)

I think the problem is that the vector diagrams are adding vectors that shouldn't be added. It's a bit like adding torque and horsepower vectorily. We don't want to add boat-speed and wind speed to come up with the apparent wind. What we need to do is add the true wind vector to the negative boat speed vector to get the apparent wind. This is because the negative of the boat speed vector gives you the relative wind over the boat in the frame of the boat when there is no wind. It's simpler to subtract the boat speed vector from the true wind vector to get the apparent wind. I think that would be more conventional and less confusing. ~ spork —Preceding unsigned comment added by 173.13.177.205 (talk) 03:06, 13 February 2010 (UTC)

The true vector addition should be "boat speed" + "apparent wind" = "true wind", which means "apparent wind" = "true wind" + (-"boat speed"). So the two vectors are pointing to the same direction in the vector addition diagram because you are really adding the negative "boat speed", but the original "boat speed" vector and the "true wind" vector" should be point in opposite directions. What we have now in the diagram is that for the upwind situation, the "true wind" and "boat speed" are both pointing towards the right. Now how does it qualify it as the boat going upwind if the wind and boat are going in the same direction. 130.216.172.78 (talk) 07:40, 13 February 2010 (UTC)

I think that we are all saying the same thing. In the diagram, the vector labelled "boat speed" is actually the apparent wind induced by the boat's motion. That is of course pointing in the opposite direction of the boat's motion. That has to be vector-added to the true wind in order to get the total apparent wind. I would welcome suggestions regarding text to add to clarify and avoid confusion.--Gautier lebon (talk) 11:01, 13 February 2010 (UTC)

I think we can only do it accurately if we lable the current "boat speed" vector "negative boat speed". It's very difficult to explain it without saying it's a negative vector because the rigorous vector addition involves the addition of a negative vector.222.153.225.5 (talk) 15:38, 13 February 2010 (UTC)

>> I would welcome suggestions regarding text to add to clarify and avoid confusion

I would suggest the vector be labeled "relative wind resulting from boat speed". I think this would be less confusing and more accurate. spork —Preceding unsigned comment added by 75.55.124.115 (talk) 09:36, 14 February 2010 (UTC)

Seems like a good suggestion to me. I'm tied up for the next 2 weeks, so I might not get around to it right away (it is more troublesome to change the graphics than just the text), but I will do it in due course.--Gautier lebon (talk) 14:14, 14 February 2010 (UTC)

Finally it seemed to me difficult to add the full explanation to the charts without cluttering them up too much, so I've added a sentence in the text before each chart to explain what the vector "boat speed" stands for. Please let me know if you think that this is not sufficient.--Gautier lebon (talk) 15:00, 16 February 2010 (UTC)

Prillen's edit of 23 February 2010

The following vector diagram includes impossible combinations of speeds and angles. The max speed of a frictionless sail craft over the surface is cosine(alpha)*(true wind speed). That is exactly the same speed towards the windward point as a free floating balloon. Like it or not. Nothing is for free. You cannot independently choose the speed over the surface and the angle to the wind - they are dependent on each other according to the (max speed)=(cosine alpha)*(true wind speed) formula. All arguments below make that mistake. They are not independent variables. Paul Beardsell (talk) 17:24, 6 June 2010 (UTC)

I am removing the diagram from the article, therefore! Paul Beardsell (talk) 17:25, 6 June 2010 (UTC)

I feel that Prillen's edit of 23 February 2010 (deleting the vector diagrams) is not appropriate. As discussed above, the vector diagrams are correct, and text was added clarifying the labels on the vectors. If someobody thinks that the diagrams are not correct, then it seems to me that the topic should either be first discussed on this discussion page, and/or a different version of the diagram should be produced to replace then one that is claimed to be incorrect. However, I would like some reactions before reverting to the previous version that contained the diagrams.--Gautier lebon (talk) 14:40, 1 March 2010 (UTC)

I think a diagram would be very helpful in explaining these concepts and should be part of the article. How about this diagram?

--Paul (talk) 20:01, 1 March 2010 (UTC)

Paul, this is a good diagram, and I think that we can include it. But it does not replace the original diagrams. The purpose of the original diagrams was to show how elementary trigonometry can be used to derive the numbers shown in the tables. Without those diagrams, it seems to me hard to understand what is going on.--Gautier lebon (talk) 16:11, 2 March 2010 (UTC)

Hi. I did not delete the diagrams, nor the text. I merely commented them out as the diagrams are wrong. The section should be included, but as long the diagrams are wrong it is better commented out, but if somebody could fix (I do not do graphics) the diagrams it would be an welcome improvement. The suggestion Paul brings forth is better than the exiting file, but it is a pity it does not show the increasing boat speed with vectors. The vectors are about the same length although the text states different boat speeds. Perhaps the arrowheads for boat speed should only be an indicator of boat direction an placed under the "130.0°" and be a little larger and hence the small arrowheads on the boat speed vector removed? And the small arrows pointing at the vectors seems redundant. Prillen (talk) 09:04, 2 March 2010 (UTC)

Commenting them out is the same as deleting them, because nobody can see them any more. Which means that they cannot understand how the tables are computed. In my opinion, the proper procedure would have been to open a discussion item. You say that the diagrams are wrong, but you do not say in what way. I agree that the label "boat speed" was misleading, but this was corrected in the text. Please tell me exactly what you think is wrong and I will either fix it, or explain why I don't think a fix is needed. Regarding Paul's suggestion, please see my comment above.--Gautier lebon (talk) 16:11, 2 March 2010 (UTC)

Commenting the section out was a way of saying "the section is not right as it is now, but is important and should be included" - and you are right the proper way is to start a discussion. But here it is! Regarding the diagram Paul made I still think it replace this diagram from the section above the one in question here.

UPDATE: the displayed drawing is the new version, see below; the comment that follows refers to the old version. The problem with the the vector diagrams is the direction of the vectors and the lack of direction on the apprarent wind vector. If we take the "Upwind" diagram shown above. As it is drawn now the wind is from ca. SSW (210°) and boat is sailing directly east (course 90°) and that mean the boat is sailing downwind or more precise a broad reach! So the "True wind" vector might be wrong, but if we assume the "True wind" and "boat speed" vectors are correct the title is wrong and the "apparent wind" vector is wrong. The apparent wind would be something like SE (135°). And I think the "True wind = 1" should be removed or relation with boat speed and apparent wind should be added. The same problems apply to the "downwind" diagram. Prillen (talk) 09:24, 3 March 2010 (UTC)

Dear Prillen, thank you very much for your constructive comments. I see that the diagrams need to be clarified to state that the vectors are not showing compass directions, merely relative directions. The boat is moving in some direction, at a certain angle to the wind, and into the wind. The vector labelled "boat speed" actually shows the relative wind generated by the boat as it moves upwind. I added text that makes that clear. The label "true wind = 1" indicates that the other vectors are shown as multiples of the true wind. No numbers are shown for the other vectors, because they are indicative. I don't have a problem with removing the "1" from the "true wind" label, I can include the explanation in the text. So it seems to me that the chart is not incorrect, but can be misunderstood as you did. Would you agree that the problem can be solved by adding text to clarify what the diagram is meant to show? If you agree with the principle, I will add text and restore the diagrams, and we can then fine-tune the text. I will also add Paul's chart, which is valuable, but does not have the same purpose as mine, which is to show how vector algebra and elementary trigonometry can be used to derive the various quantities.--Gautier lebon (talk) 16:39, 4 March 2010 (UTC)

Ok, I think that make a bit more sense – "Boat speed" means "wind-generated-by-boat-speed"? And then the apparent wind vector is pointing up to the right and the title is then correct. Is this the way it should be interpreted? But if that is the case I still think is it not so intuitive because of the "wind-generated-by-boat-speed" vector. A "boat speed" vector is a lot more intuitive and easily understood by most people. And in other words; I think the diagrams should be changed, not the text. Prillen (talk) 08:06, 5 March 2010 (UTC)

Dear Prillen, thank you for your positive comment. I will now rewrite the section and restore it. In the meantime, I looked at Bethwaite's book again, and found a citation that supports the diagram: I will include that. I will also change the diagrams to try to clarify, aligning with the diagrams at apparent wind. The diagram is correct in terms of vector algebra, but you have to understand that the "boat speed" vector actually represents what you say above. I look forward to your comments on the new version. It isn't hard for me to modify the diagram, I just am not sure what would be best. Regarding "true wind speed = 1", I need that because the formulas use that value for true wind speed, in order to avoid an extra variable and extra complications. I will also explain that in the cover text.--Gautier lebon (talk) 14:46, 5 March 2010 (UTC)

Gautier lebon I see your problems with the algebra, but I think it is better to leave the "boat-speed" vector out of the drawing and explain it in the text to clarify the diagram. The apparent wind vector still miss the direction arrowhead. And why not call "alfa" and "beta" for "awa" and "twa"? Prillen (talk) 13:11, 8 March 2010 (UTC)

Thank you for your comments. I've aligned the diagrams to the one that appears in the apparent wind article. Isn't it better to maintain consistency with other Wikipedia articles? If yes, we should maintain the "boat speed" vector. I didn't put an arrow-head on the apparent wind vector because it is obvious and it would further clutter an already rich diagram. But it would be trivial to add. Since I'm a mathematician by training, I tend to use alpahs and betas for angles. That is pretty common.--Gautier lebon (talk) 17:52, 9 March 2010 (UTC)

I haven't been following this discussion in detail, but looking at the diagrams now, I wonder if they could be clearer still. What we want to show is vector subtraction between the boatspeed and the wind to find the apparent wind, am I right? For clarity and intuitive viewing, I wouldn't introduce the head-wind-due-to-boatspeed vectors, as these are artificial and just represent minus(boatspeed), which enables the subtraction. I would show boatspeed proceeding left to right across the bottom of both diagrams (L to R is more intuitive to us westerners I think) and the wind impinging onto it as a vector from above, ending at the right-hand end of the boatspeed vector in both cases. In both cases, the triangle is the same shape, just remove the extra head-wind lines and labels, move the arrow-heads to the other ends of both other lines and leave the labels 'boat speed' and 'true wind' where they are. There is another intuitiveness benefit in that, to my eye, it then looks in both cases as if the boat is actually "at" the right-hand corner where the two vector-heads meet, and the vectors show how, in the most recent unit of time, the boat and the wind actually reached this point. I hope my explanation makes sense - it's always hard to describe a drawing. I've just sketched the two new diagrams here and they both look fine to me that way. Arrows trailing after each other - vector addition; arrows meeting at a point - vector subtraction. You have arrows pointing off in different directions - they look to me like your going to do addition using a parallelogram diagram, but then you draw the 'wrong' diagonal in, and my eye gets confused. Is this any help? --Nigelj (talk) 19:54, 9 March 2010 (UTC)

Nigel, thank you for your helpful comments. I'm all in favor of redoing the diagrams so that they are easier to understand. I thought that what I had originally done is pretty much what you describe now, but I'm probably missing something. I have to confess that I don't quite understand what you propose. Could you scan your handwritten chart into a PDF and post it to this discussion page? I could then use that as a model to modify my diagrams? I do agree that vector algebra can be confusing, I was just helping my 15-year old daughter last night. And it isn't helped by the fact that there are different ways of doing things, with and without parallelograms, as you say.--Gautier lebon (talk) 12:30, 10 March 2010 (UTC)

I've been bold. I don't own a scanner, so rather than create new upload file locations, I edited the previous versions of your two files to show what I mean. This means that my versions have currently gone live into the article. Please feel free to revert them if you don't agree it's an improvement. If you do like the approach, there are some small errors in the position of the windspeed vector on the 'downwind' diagram that meant that I couldn't get the arrowhead to the end of the line without it disappearing. In the end, both of these diagrams will need to be changed to SVGs for clarity and that might be the best time to fix that. --Nigelj (talk) 13:36, 10 March 2010 (UTC)

Dear Nigel, thank you for having taken that initiative, I think it is helpful. But now we are back where we started: people will probably misunderstand the diagrams, since they won't understand that the true wind vector is being added to the not-shown head wind vector that is induced by boat speed. I suggest that we leave it like this for a little time, so see if we get any more comments. If nobody complains, then I'm satisfied. And then I will fix it up the details as you propose above.--Gautier lebon (talk) 13:56, 11 March 2010 (UTC)

I have now updated the charts as agreed.--Gautier lebon (talk) 16:03, 25 March 2010 (UTC)

Dead downwind faster than the wind

For those interested in this esotheric topic, please take a look at [3]. The graduate students have done it. Their device advances against a treadmill, meaning that it can progress dead downwind faster than the wind.--Gautier lebon (talk) 14:08, 11 March 2010 (UTC)thttp://tech.slashdot.org/story/10/06/06/0518216/Google-Backed-Wind-Powered-Car-Goes-Faster-Than-the-Wind

No! Maybe it is possible to do what is claimed but those students have proven nothing using the treadmill. Were (minitiarised) you sitting on the device on the treadmill you would not be experiencing a headwind but a tailwind. In order to travel downwind faster than the wind you must experience an apparent headwind as a passenger. If the students took the prop/fan off their model and simply put a flat square sail perpendicular to the wind it would still go uphill on the treadmill. What a joke that experiment is! Those postgrad students should be stripped of their undergraduate degrees. Paul Beardsell (talk) 14:05, 6 June 2010 (UTC)

A device with a flat sail would not be able to progress against a treadmill. Surely that is obvious. What happens in the experiment is that the treadmill causes the wheels to turn, which causes the propeller to turn. The propeller creates a backwards-moving stream of air, which is sufficient to cause the cart to advance against the treadmill. This is the equivalent of progressing dead downwind at the speed of the wind.--Gautier lebon (talk) 11:29, 11 June 2010 (UTC)

Your remarks are unsubstantiated and offensive. These students conduct systematic and exciting experiments. MrBeanBob (talk) 00:09, 8 June 2010 (UTC)

Those students are either fools or hoaxters! And you are taken in. Why, if the model is going faster than the tailwind, does mini-you on the model still experience a tailwind from the fan on the ground behind the treadmill. What should be experienced is an apparent head wind. I would like to substitute their model with mine. It has no rotating propeller but just a flat card as a sail to be pushed along by the fan on the floor! It performs much better in THEIR experiment than does their own model! Paul Beardsell (talk) 11:47, 8 June 2010 (UTC)

It is clear that you have not looked at the videos of the outside runs, made after the treadmill experiments. Indeed the cart accelerates until it encounters a headwind. This can be seen from the telltales on the cart, as well as from the speed data (charts) that are posted on the web page.--Gautier lebon (talk) 11:29, 11 June 2010 (UTC)

On Monday, March 22, 2010 the San Jose State University project overwhelmingly succeeded in demonstrating 'direct downwind faster than the wind' on the Ivanpah dry lakebed south of Las Vegas, Neveda. There were numerous NALSA (North American Land Sailing Association) officials in attendance and one NALSA BOD member (Bob Dill) was there for every run and collected his own rough wind and GPS data. All collected video and data corroborate the personal witnesses. To be clear, this was NOT a NALSA sanctioned event but was presented as a demonstration to the NALSA BOD that the vehicle was capable of ddwfttw. After the demonstration, the team is working out the details with NALSA for rules and instrumentation related to an upcoming official NALSA ratified test and record. The team expects to be able to certify a record according to these upcoming rules in the range of 3 times the speed of the wind powering the craft. www.fasterthanthewind.org ThinAirDesigns (talk) 18:52, 25 March 2010 (UTC)

I propose three cheers for ThinAir and his colleagues. Will anybody join me?--Gautier lebon (talk) 16:23, 26 March 2010 (UTC)

Thanks Gautier. There were many long nights. Still a few more coming up to get the ratified record. ThinAirDesigns (talk) 08:04, 27 March 2010 (UTC)

Without even saying sailing dead downwind faster than the wind is impossible (it is impossible) one can rightly pour scorn as I do above on the treadmill experiment. Let's say it is possible and that it has been done. So, what is the theroretical maximum speed. There seems to be no limit. No limit, something's wrong, no prize. Energy from nowhere. Paul Beardsell (talk) 16:20, 6 June 2010 (UTC)

The energy comes from the wind. It is used to drive the machine forward. The maximum speed depends on how much energy can be captured from the wind and on the resistance on the surface and on the resistance induced by the apparent head wind. There is no free lunch here and no claim that a device can achieve infinite speed.--Gautier lebon (talk) 12:35, 7 June 2010 (UTC)

Dead downwind faster than the wind: Formatting & References

I am concerned that this section of the article is running afoul of WP policy in several areas. First, it appears that some edits are coming directly from ThinAirDesigns. This appears to be a violation of WP COI policy.

The discussion in this section as a whole, and the sources cited, are questionable at best. This is both in terms of content, style, and use of references. As this has also (at least in the past) been a controversial topic, I'm also concerned that there may be a [[Wikipedia:Neutral_point_of_view|NPOV] issue here as well.

Per WP policy on [original thought], a WP article talk page is not a notable or or authoritative reference suitable for use in the article.

Much of the rest sounds like a description of personal experience at the event. This is not appropriate. "Primary sources or sources affiliated with the subject are generally not sufficient for a Wikipedia article," see Wikipedia:Reliable_sources. Rather, "Articles should be based on reliable, third-party, published sources with a reputation for fact-checking and accuracy." (Wikipedia:Verifiability) Please see Wikipedia:Notability and Wikipedia:No_original_research as well. --Oskay (talk) 20:03, 31 March 2010 (UTC)

For the record, to my knowledge, so far I haven't made a single edit on any WP article on any topic, ever. Again to my knowledge I have only commented on the discussion page. *IF* one can find an edit or addition on a WP article made by me, it was not intentional and was made when I thought I was on the discussion page. I'm pretty darn certain the record will support my assertion that I stick to the discussion page. ThinAirDesigns (talk) 20:47, 31 March 2010 (UTC)

The edit of the article dated 18:54, 25 March 2010 was performed under the account ThinAirDesigns. This was a significant edit to the article, adding the claim that the students had "overwhelmingly succeeded in demonstrating" this phenomenon. ThinAirDesigns, can you please clarify your relation (if any) to this research group? Oskay (talk) 00:59, 1 April 2010 (UTC)

I went and checked Oskay, and you are correct. For some reason I mistakenly posted that on the article page rather than the intended discussion page. I apologize as I had no intention nor realization of such until now. I have avoided editing (or at least *intended* to void editing) this topic because,

A: I am not a regular WP contributor and as such am not familiar with the rules to do such.

B: Until our team gets a record ratified by NALSA (in internationally recognized sanctioning body for wind powered land speed records) I frankly don't know if any of our findings meet WP standards. The fact that this is a project undertaken by a reputable and accredited University may or may not meet WP standards. Perhaps you know ... I do not.

C: We expect in the next few months to have a NALSA record ratified, so I've got no to reason to press the issue considering the relatively short time to this upcoming event.

As to my relationship with the San Jose State University project, I am a Guest Professor for the duration of this effort(this semester and last) and one of two SJSU defined Managers of the project.

Again Oskay I apologize for the edit to the actual article -- being new to WP I lost my way in the edit process. ThinAirDesigns (talk) 01:29, 1 April 2010 (UTC)

Dear Oskay: you are correct, ThinAir mistakenly posted the same material to both the talk page and the main article. I quickly corrected that, posting to the main article a somewhat modified version of what is on the San Jose team web site. Please note that there are now two independent sources showing that a cart using a propeller linked to its wheels can progress dead downwind faster than the wind. Surely this is worth inclusion in Wikipedia? Regarding "no physical law is violated", that is not original research, it is a fact, otherwise the device could not work. I agree that it is not an obvious fact, that is why I wanted to include the thought experiment explaning why no physical laws are violated. But there was resistance to including that thought experiment, so it appears only here on the talk page. Could you please make specific comments, apart from the various in-line comments that you have already provided, that would allow us to clean the article up and resolve the dispute?--Gautier lebon (talk) 11:22, 1 April 2010 (UTC)

What's needed for clean up should be very clear if you read the WP guidelines on style, notability, and references that I initially linked to.

The majority of the recent edits have been directly taken from material provided by first-hand sources. Whether ThinAirDesigns edited the material personally or whether someone else copied information from this discussion page or their blog is somewhat immaterial (except for the possible COI/NPOV issue): it's still first-hand experiences that are being described here. Wikipedia is not a publisher of original thought. The guidelines explicitly state that "Wikipedia should not offer first-hand news reports on breaking stories. Wikipedia is not a primary source."

In the absence of reliable, third-party references and verification, the San Jose team's efforts -- while interesting and possibly of historic value -- should be carefully portrayed so as not to give undue weight. Right now, that whole section of the article is a discussion of the San Jose team efforts-- this absolutely, without question, undue weight with respect to the full article.

With respect to "original research," there is a big problem here as well. I added that inline tag because the reference given was this talk page I don't know how you could possibly argue that a WP talk page is a verifiable third-party reference, or that a discussion page here is an authoritative reference on the laws of physics. Also, per WP guidelines, Wikipedia should not be used for discussion forums. A thought experiment does not belong here. These talk pages are for discussing the article itself, not for debating the substance of the article.

"there are now two independent sources showing that a cart using a propeller linked to its wheels can progress dead downwind faster than the wind." And there are hundreds of sources showing perpetual motion machines in operation. That doesn't make either more or less verifiable, does it?

"Surely this is worth inclusion in Wikipedia?" I didn't say it was unworthy, just that you need to do it correctly. You don't need to make that kind of implication. Come on: It's an encyclopedia, not a press release. Read some other WP articles, read the guidelines about WP style and the WP core content guidelines, and fix it up. Why are we debating this? Oskay (talk) 00:24, 3 April 2010 (UTC)

Dear Oksay, thank you for your very helpful comment. Indeed, I had read the various guidelines more carefully before your last post, and I now understand your point and agree with it. It seems to me that the material at [4] can be referred to under the guideline "Self-published ... sources may be used as sources of information about themselves", see Wikipedia:Reliable_sources#Self-published_sources_.28online_and_paper.29. That is, it should be made clear that the reference only supports what the source says. Regarding the thought expertiment, I still think that it should go in the main article, because it shows why the device in question does not necessarily violate the laws of physics, which is not the case for perpetual motion machines. But there was resistance to including the thought experiment. For now, I propose the following rewrite of the section. Please let me know what you think of this.--Gautier lebon (talk) 07:27, 3 April 2010 (UTC)

A team of aeronautics students from San Jose State University, along with their professor and advisers, have reported that they set out at the end of 2009 to definitively determine whether it was possible to build a vehicle which can go directly downwind, faster than the wind, powered only by the wind, steady state.

At first, it would seems impossible to sail dead downwind faster than the wind: a wind-driven machine cannot progress dead downwind faster than the wind using only sails. This is because the apparent wind will be zero if the speed of the boat equals the speed of the wind, so the boat cannot possibly go any faster than that.

However, in theory, it can sail dead downwind faster than the wind using only energy obtained from the wind while moving (that is, it does not need to stock energy while in the port). Some sort of mechanical device can be used to transfer energy from the surface on which the machine is moving in order to increase the speed of the machine. Some might say that this is not sailing properly speaking, because the boat's speed is influenced by devices other than the sails. However, it is 'sailing' in the sense that the boat is propelled only by energy obtained from the wind. Note that a conventional keelboat's performance is also very much improved by a device other than the sail: its keel.

And indeed it has been claimed that a cart can be built that would use a propeller linked to its wheels (without batteries or electrical power generators) to sail dead downwind faster than the wind. Such a cart has been built and demonstrated. At first, this was considered to be a hoax, but it was subsequently considered to be a legitimate demonstration of what is theoretically possible. Indeed, as explained above, sources indicate that high-performance sailboats and iceboats can sail downwind at speeds greater than the wind, in the sense that their velocity made good downwind is faster than the wind (that is, they will arrive at the downwind mark of a course faster than would a balloon released from the upwind mark). Thus there is no reason to conclude that any fundamental law of physics is violated by a device that progressed dead downwind faster than the wind.

The team from San Jose University claim to have built a vehicle based on the same principle: a cart whose wheels are linked to a propeller. The team reported testing their vehicle on 7 and 8 March 2010 on a motor-driven moving belt (treadmill), showing that it would avance against the belt, which means, according to the team, that it can progress dead downwind faster than the wind. On 24 March 2010, the team reported that it ran the vehicle on the Ivanpah dry lakebed south of Las Vegas, Nevada, showing that it could accelerate dead downwind from a standstill and reach velocities well in exceed of wind speed. That is, according to the team, the vehicle was progressing dead downwind faster than the wind. The team reported that there were North American Land Sailing Association (NALSA) officials in attendance and one NALSA Board of Directors member (Bob Dill) was there for every run and collected his own rough wind and GPS data. This was not a NALSA sanctioned event but was presented as a demonstration to the NALSA Board of Directors that the vehicle was capable of progressing dead downwind faster than the wind. The team reports that it is currently working out the details with NALSA for rules and instrumentation related to an upcoming official NALSA ratified test and record. The team says that it expects to be able to certify a record according to these upcoming rules which should show dead downwind velocity in the range of 3 times the speed of the wind powering the craft.

It is important to stress that even as the wind-powered cart referred to above is actually going "upwind", it would not move at all if the wind speed relative to the ground is zero. In other words, it requires the wind to be moving in the same direction as it does for it to work. If, for example, an initially moving cart enters a region where the wind speed relative to the ground is zero, it would eventually stop due to energy dissipation (e.g. friction) even as it is heading "upwind" within the region. The wind-powered cart referred to above therefore would not necessarily violate the laws of conservation of energy, nor is it a perpetual motion machine, as it harnesses its energy from the kinetic energy contained in the wind. If enough of the wind energy is harnessed, the machine can (at least in theory) use it to propel itself, even at speeds faster than the wind. The cart is an example of a device that, while respecting the laws of physics, appears at first sight to be in perpetual motion: a so-called apparent perpetual motion machine.

I have to say that I'm a bit confused by some of the WP rules on sources that have been brought up above. I don't currently have the time to research these rules and I certainly don't claim any standing to argue with them, but it appears from the discussion that for whatever reason, this source may be considered more reliable somehow than the original source. http://sailmagazine.com/racing/running_faster_than_the_wind/ ThinAirDesigns (talk) 13:56, 6 April 2010 (UTC)

You can report that such'n'such web site says this works but you cannot have WP say it works. Conservation of energy. Paul Beardsell (talk) 22:37, 6 June 2010 (UTC)

Conservation of energy is not a mantra that can be used to dismiss actual observed data. Paul has not explained how conservation of energy would be violated. Indeed it is not. The energy comes from the wind, and is potentially very large. The device in question uses energy from the wind to overcome the resistance of the surface and the resistance from the induced apparent headwind. That would violate conservation of energy only if the energy required to overcome the resistances were greater than the energy obtained from the wind. Where are the equations to show that this is the case? Or the citation to the relevant calculations? Why is the unsupported assertion by one Wikipedia editor sufficient to overcome the patient work of many others, others who provided citations? Why is one editor's opinion that multiple concordant citations are all wrong sufficient to deprive Wikipedia readers of the chance to obtain the information in question?--Gautier lebon (talk) 12:31, 7 June 2010 (UTC)