The Wind Powered Sail-less Boat [Archive]

DuncanRox

10-20-2008, 12:11 PM

Hello everyone,

I am an engineering student in the U.K. and have just been given a project to design and create a working model wind powered sail-less boat. Thats right a boat powered by the wind but without a sail. Ha ha...:eek:

Anyway a bit about the project.

The hull is approximately 1.5m x 0.4m (at widest section).
We have 2 hulls and can therefore construct a catamaran design. (likely)
It can hold about 20kg max per hull, without buoyancy aids.

The boat does not need to travel with any significant speed but must be able to complete a short slalom course and make it back to shore if the wind speed drops....therefore some form of energy storage must be implemented, although this comes with a hitch. It must be mechanical energy storage ie flywheel, elastic band or spring.

The contraints of the project allow the use of battery powered servos to ideally operate rudders but this is the only electrical storage permitted.

So far, our team has decided to use a vertical axis wind turbine, probably Darius, to provide the core power. This obviously has the advantages of being able to catch the wind in any direction and it's weight is more evenly distributed than a horizontal axis wind turbine, helping with balance issues.

This is probably the sort of turbine we will construct ourselves due to it's small scale nature and also operate with mechanical power transmission to attach/gear some form of mechanical storage device.

We have not yet constructed any part of our model boat as we are still in the early stages of the analysis. I have therefore made this post to generate some interest in the project and also run our initial ideas past everyone.

So what do you think? Is this possible?

Ha ha, let me know your thoughts!

Thanks,

Duncan

eponodyne

10-20-2008, 09:54 PM

All of the most august sailing associations and racing governing associations have all agreed that kites are not sails.

tom28571

10-20-2008, 10:41 PM

The Darius rotor driving a suitable propeller is probably a good choice. It should have more than two blades to even out the power pulses. A catamaran hull will be more stable but not a lot of stability is needed with the Darius rotor. The catamaran will be much more difficult steering thru the slalom so a monohull with a keel may be better. A flywheel sounds like the simplest storage mechanism but gearing may be an issue to bring it up to speed.

It may be ruled illegal but a small generator-motor driving the flywheel is a simple way around the gearing problem and gets past the prohibition of electrical storage.

The Darius rotor is not self starting, so you have to get past that problem also.

A Savonius rotor is self starting but less efficient.

FranklinRatliff

10-21-2008, 12:33 PM

If you go with screw propulsion, a large diameter slow turning air screw might be more efficient for a low power boat than a water screw.

Stumble

10-21-2008, 04:36 PM

I am not an expert on vertical turbines, but from what little I know I would be very concerned about the system compared to a horizontly propeller for a number of reasons.

Depending on which vertical system you use, these are all significant problems...

Giromills - demand heavy towers which may cause boyancy and balance issues.

Cycloturbines - are very complex and have a lot of moving parts. Leading to corrosion problems, and put a lot of weight far off the centerline of the boat, exaserbating the rocking of the boat.

All of these also have a problem with pulsating forces, since the blades don't produce the same amount of force at any wind angle. Meaning the engine could go into an occillating destructive sequence (see the Tacoma's Narrows Bridge disaster).

I keep thinking that a horrizontly propeller while less flashy is a better design... Not to mention that is should be able to find parts much easier.

tspeer

10-21-2008, 09:49 PM

Not only can it be done, it has been done. The most common method is to have a horizontal axis wind turbine connected via a shaft to the propeller in the water.

A clutch and transmission could be used to couple and decouple with a flywheel for energy storage. The wind turbine could be coupled to the prop without the flywheel, or the wind turbine connected to the flywheel to spin it up, or the flywheel connected to the prop without the wind turbine to power the boat. Modern flywheels are competitive with batteries in terms of energy density. Naturally, any flywheel must be enclosed in a protective case to contain the shards if it should fail, and ideally it would be located so no people are in the plane of rotation.

Revelation II (http://news.bbc.co.uk/2/hi/uk_news/1507825.stm) is one such boat.
http://i.treehugger.com/images/2007-2-21/Windmill-Sailboat.jpg
Such a craft can sail straight into the wind. And, if it weren't for the high resistance of a hull in the water, it could also sail directly downwind, faster than the wind. Which has been demonstrated in practice on land, with the rotor connected to the wheels. When operating faster than the wind, it's actually the wheels that are turning the rotor, and the rotor propelling the craft!

This boat is an 1896 Bembridge Redwing hull fitted with an autogyro sail (http://uk.geocities.com/fnsnclr@btinternet.com/yachts/auto/hist1.htm) in 1933.
http://uk.geocities.com/fnsnclr@btinternet.com/yachts/auto/auto7.gif
You might think it's the same sort of craft. But it's not. The rotor is not connected to anything - it just spins. It's a rotary sail, just like the unpowered rotor of an autogyro is a rotary wing.

Which should give you something to think about - you can use a horizontal axis wind turbine that way, but can you use a vertical axis wind turbine the same way?

And is it more efficient to use the rotor as a sail or to use it as a turbine to drive the prop? Does it depend on which way the boat is traveling or how fast it's traveling?

Windmaster

11-07-2008, 03:32 PM

There's a video of another similar boat on Youtube.
NNbNNSDljGI

Erwan

11-08-2008, 06:02 AM

Hi Duncan,

Just to suggest you to investigate the propulson efficiency of your underwater device.

As your boat will probably be relatively slow, You will probably need a big propeller in the water with low revolution.

There is an alternative solution for low speed.

Imagine a square/ rectangular box open at the front and back sides, just like a matches-box after pulling out the inside part.
This box is underwater and its open ends are in the direction of the water flow of course.

At about a third of its longitudinal axis you have a connection-rod which transmit a rotative motion (the windwill above the deck) into an alternative motion.

This connecting rod moves a flat plate inside the box, of course you have to adjust the box-thickness with "crank" stroke.

The flat plate moving inside the box will move quite similar to a dolphin tail, and the box will limit tip vortex.

My English is far from perfect, so if it seems confused to you, make a drawing of it, everything will be clear.

Regards

EK

Leo Lazauskas

11-08-2008, 08:31 AM

Giromills - demand heavy towers which may cause boyancy and balance issues.

No. Because VAWT mostly have heavy components low down, they do not need heavy towers. The "wings" of the VAWT can also be made of sailcloth so they can be very light.

Cycloturbines - are very complex and have a lot of moving parts. Leading to corrosion problems, and put a lot of weight far off the centerline of the boat, exaserbating the rocking of the boat.

Some have heavy parts, most do not. In most cases they are still lighter than HAWT with their heavy gearboxes and generators.
True, some are complex, as you say, but others are not.

All of these also have a problem with pulsating forces, since the blades don't produce the same amount of force at any wind angle. Meaning the engine could go into an occillating destructive sequence (see the Tacoma's Narrows Bridge disaster).

Yes, that can be a problem, but it can be easily overcome if designed carefully. See, for example,

Variable pitch Darrieus water turbines
B.K. Kirke and L. Lazauskas,
J. Fluid Science and Tech., Vol. 3, No. 3, June 2008, pp. 430-438.
http://www.cyberiad.net/library/pdf/bkll_jfst_vol3_no3_2008.pdf

Although this paper is concerned with VAWT operating in water, the principles for reducing shaking are the same for wind turbines.

All the best,
Leo.

ancient kayaker

11-08-2008, 06:55 PM

Don't forget wings. Here is an intersting site on the wing-sail concept:

http://www.ivorbittle.co.uk/The%20wing-sailed%20yacht%20for%20the%20web.htm

Autodafe

11-09-2008, 05:21 PM

Such a craft can sail straight into the wind. And, if it weren't for the high resistance of a hull in the water, it could also sail directly downwind, faster than the wind. Which has been demonstrated in practice on land, with the rotor connected to the wheels. When operating faster than the wind, it's actually the wheels that are turning the rotor, and the rotor propelling the craft!

Tom, your aero/hydrodynamics is normally so good that I had to do a triple think before coming in with this, but directly down wind faster than the wind is not possible without violation of conservation of energy, on land or water.
If on a perfectly still day such a craft were given a push to get it moving, it would immediately have a headwind and could then accelerate smoothly to its destination. While the free transport sounds nice perpetual motion is a definite no-no.

My mental model for windpower is as follows (note that in this discussion I'm only considering the drive mechanism, eg sails or turbine+propeller, and am ignoring hull drag etc.):
For any sail or turbine 'drag work must be greater than thrust work'. Ideally: thrust=drag and we have 100% efficiency. To paraphrase: the energy we harvest by changing wind momentum over airfoils (thrust) is limited to equal or less than the work required to push our airfoils through the air (drag).

There is hope. Drag and thrust do not have to be applied in opposite directions. Drag acts with the direction of the wind. Depending on the type of sail or turbine we can make thrust act in whatever direction we like, typically in the direction we wish to travel.
However, when we point directly into the wind (or apparent wind, as for dead down wind faster than the wind) thrust and drag are in opposite directions, and as drag>thrust we end up going backwards.

There is, however, another factor that does allow a wind turbine powered craft to sail directly into a head wind, but this does *not* apply for sailing DDW faster than the wind.
Energy = work = force*distance. We know that drag work is greater than thrust work, but if we can get the thrust to be applied over a shorter distance than the drag then thrust force can be greater than drag force. Traveling directly upwind a craft obviously has a longer track through the air (air distance = time*(windspeed+craftspeed)) than its track over the ground (time*craftspeed). Therefore by applying the thrust in the water (or via the wheels for a land craft) a larger force than the air drag can be produced for the same or less energy, and so we can have forward motion.
By contrast if we were traveling DDW our track through the air is shorter than our track over the ground, so any force applied to water or wheels must be less than drag force.

Guest625101138

11-09-2008, 06:26 PM

Tom, your aero/hydrodynamics is normally so good that I had to do a triple think before coming in with this, but directly down wind faster than the wind is not possible without violation of conservation of energy, on land or water.
If on a perfectly still day such a craft were given a push to get it moving, it would immediately have a headwind and could then accelerate smoothly to its destination. While the free transport sounds nice perpetual motion is a definite no-no.

........

Most people struggle with the concept of sailing directly into the wind. Very very few can understand how it is possible to sail directly down wind faster than the wind but it is possible. It does not violate any fundamental laws. It does however rely on relative movement of the air over the water. If there is no relative movement (no wind) then there is no go.

If you want to sail into the wind you extract power from the wind and deliver it to water. Providing the effective gearing between the AIR TURBINE and the WATER PROPELLER is such that the drag on the turbine is less than the thrust on the propeller it will go forward. With a 1:1 mechanical gearing the turbine pitch needs to be at around 1.7 the propeller pitch if you have an efficient design. If you have a higher loss system then the ratio is going to be 2 or even higher.

To sail directly downwind faster than the wind you extract power from the WATER TURBINE and deliver it to the AIR PROPELLER. So the boat can move faster than the airstream over the water with the propeller providing the thrust. Again it gets down to gearing with the water turbine having the larger pitch.

When you get into detail there is no real benefit in optimising a system to sail directly upwind AND directly downwind. The latter would be required so infrequently that it is not worth compromising the upwind ability. Simple solution is to just tack down wind still using the air turbine as the power collector.

Irrespective of the practicality it is not impossible. It does not violate any natural laws. Just hard for most people to think it through. Even conventional sailing boats can have a higher VMG directly down wind than the windspeed but they do not sail directly downwind to achieve it.

Rick W

Autodafe

11-09-2008, 06:35 PM

Thanks Rick, that has cleared up my concern. I saw how the speed differential gave power to windward, but had a brain fart when it came to inverting to problem (extracting power from the water, driving the air rotor) for dead down wind.
I'm happy now, and agree it's possible :)

For most of us sailors tacking downwind is the easier option.

Guest625101138

11-09-2008, 06:51 PM

To get a turbine/propeller system to work well upwind is a design challenge. It needs to have efficient blades and these are inevitably cambered foils. Once you start looking at DDWFTTW then you also need efficient foils but they would have opposite camber. Also for the size of craft I have been looking at the air propeller needs to be much larger than the air turbine to get good results. So I conclude that these practicalities exclude combining the dual ability in a single system.

In fact I do not see much merit in the simple turbine/propeller system with a mechanical linkage. I believe if you treat the turbine as an energy collector, storing to a battery, and this then drives an electric motor you get a nice system. With this sort of system you can store excess power in strong winds rather than wasting it trying to push a hull much faster than it was designed to go. The boat just plods along at a a steady pace with the battery taking excess power when available and delivering more power when needed. You can also store power while sitting at anchor.

Rick W

Windmaster

11-10-2008, 03:30 AM

With a 1:1 mechanical gearing the turbine pitch needs to be at around 1.7 the propeller pitch if you have an efficient design. Rick W
Hi Rick, can you elaborate on this and give and example?

Windmaster

11-10-2008, 03:44 AM

In fact I do not see much merit in the simple turbine/propeller system with a mechanical linkage. I believe if you treat the turbine as an energy collector, storing to a battery, and this then drives an electric motor you get a nice system.
Rick W
There's nothing wrong with this idea, but what do you do if you have any kind of failure? You have no back up. Since it is so simple to mechanically connect the turbine with the prop, why would you not want to do it
? Mechanical connection is such an elegant system. Simplicity is everything in the quest for reliability (KISS). It would be so simple to arrange such a system as a fall-back.
Of course, storage of power whilst moored is a great idea, but with a mechanically connected system it is possible to have the turbine running continuiously (head to wind) at reduced power to relieve anchor loads and prevent downwind drift onto a lee shore.

Guest625101138

11-10-2008, 04:08 AM

Hi Rick, can you elaborate on this and give and example?

For a small boat with a slender hull in windspeed of 5m/s moving directly into the wind.

The turbine has a nominal pitch of 1128mm, the propeller has a pitch of 648mm. Both are operating near 87% efficiency with low slip and low velocity ratio. The connecting shaft is doing 415rpm and mechanical transfer efficiency is 94%. The boat will be doing 4m/s through the water. The boat has a drag of 80N to achieve this speed.

The drag on the air turbine is 150N so total boat drag is 230N.
The total air power applied is 1350W.
The useful power collected from the air turbine is 1183W.
The power delivered to the water prop is 1112W.
Power delivered to the boat to move it is 920W.

This highlights the power transfer requirements. The boat would only need to use 320W to do the same speed without the turbine drag.

So if you take the case where the boat sits at anchor in moderate winds with the turbine delivering at 1000W to a battery you have collected enough energy in 1 hour to operate for 3 hours. This highlights the benefit of storage.

I also add that getting the turbine and propeller to both achieve 87% efficiency is not trivial design either.

Rick W

Guest625101138

11-10-2008, 04:36 AM

A mechanical linkage is not all that simple. In fact it is highly constraining on the boat design. It also really needs to have variable ratio to get the best of the system. In low wind the effective gear ratio has to be more than 2:1.

As a pure sailing system without storage it offers little advantage over a typical sailing vessel. It has curiosity value with the ability to sail directly into the wind. However if you really think about this it does not mean much. Even a power boat will avoid going directly into waves when it can avoid it. Taking seas on the quarter softens the ride quite a lot.

Rick W

Windmaster

11-10-2008, 05:23 AM

For a small boat with a slender hull in windspeed of 5m/s moving directly into the wind.

The turbine has a nominal pitch of 1128mm, the propeller has a pitch of 648mm. Both are operating near 87% efficiency with low slip and low velocity ratio. The connecting shaft is doing 415rpm and mechanical transfer efficiency is 94%. The boat will be doing 4m/s through the water. The boat has a drag of 80N to achieve this speed.

The drag on the air turbine is 150N so total boat drag is 230N.
The total air power applied is 1350W.
The useful power collected from the air turbine is 1183W.
The power delivered to the water prop is 1112W.
Power delivered to the boat to move it is 920W.

This highlights the power transfer requirements. The boat would only need to use 320W to do the same speed without the turbine drag.

So if you take the case where the boat sits at anchor in moderate winds with the turbine delivering at 1000W to a battery you have collected enough energy in 1 hour to operate for 3 hours. This highlights the benefit of storage.

I also add that getting the turbine and propeller to both achieve 87% efficiency is not trivial design either.

Rick W
I wonder if you can clarify two things.
Firstly, you quote pitch settings in mm. and I am really hoping to get an idea of the angle of attack of the blades relative to the rotational axis, for this I need to know the diameters of the turbine and the propeller in your example.
When you talk about turbine drag, which drag are you referring to? the drag against rotation, or the "axial drag" along the line of the rotational axis? Sorry to be a little slow on the uptake on this!

Windmaster

11-10-2008, 05:31 AM

A mechanical linkage is not all that simple. In fact it is highly constraining on the boat design. It also really needs to have variable ratio to get the best of the system. In low wind the effective gear ratio has to be more than 2:1.

Rick W
To clarify, I presume you are saying the airturbine rotates twice for one rev of the prop? (Not sure which way round you mean this). Do you mean that a gear ratio of more than 2:1 is a bad thing?

Guest625101138

11-10-2008, 07:13 AM

I wonder if you can clarify two things.
Firstly, you quote pitch settings in mm. and I am really hoping to get an idea of the angle of attack of the blades relative to the rotational axis, for this I need to know the diameters of the turbine and the propeller in your example.
When you talk about turbine drag, which drag are you referring to? the drag against rotation, or the "axial drag" along the line of the rotational axis? Sorry to be a little slow on the uptake on this!

The blades are based on thin cambered sections. The AoA under design condition ranges across the blade. Usually it ends up slightly negative in the range -1 to -.5 degrees.

The pitch angle is a simple mathematical function related to the geometrical pitch and the radial position:
pitch angle = atan[pitch/(2* pi* radius)]
The maximum radius of the turbine is something like 1.5m. The propeller is about 300mm in radius.

When I refer to drag it is the force applied by the air or water against the direction of travel.

As far as the gearing goes I stated initially for the system described that the turbine and propeller rotated at the same speed. The water velocity past the propeller is 4m/s and the air velocity past the turbine is 9m/s. They are both turning at the same rotational speed. So for roughly the same operating point on the foils the pitch on the air turbine is 1128mm and the pitch on the propeller is 648mm. The foils are not the same and operating conditions are a little different because of the different fluid properties.

Your other question regarding the 2:1 required for low wind speed. You need this sort of ratio because the efficiency of the air turbine drops at low wind conditions so if the gearing is not increased the boat stalls as the turbine cannot generate the torque required to spin the prop. When the wind speed is higher you cannot take advantage of the better overall system efficiency. My best design will operate with gearing as low as 1.4:1 under the most suitable wind conditions.

Having variable gearing means you can actually go faster for the given wind strength than if the gearing was set 2:1. So ability to change the effective gearing between the turbine and the propeller is required if you want to get the best overall performance.

Variable gearing can be achieved with variable pitch prop but these are sub-optimal for all but the design condition. Having variable transmission is a better solution I believe. As the speed builds and the apparent wind increases you can reduce the ratio and go even faster. The limit is the power transfer capability.

Rick W

Martini

11-10-2008, 08:14 AM

well reading all the replies, I take it you have the info you might need, or that i may have been able to help you with...

BUT, going to the UCT mechanical engineering expo of thesis' I found a project with sounds exactly like the one you have.

the wind turbine, was horzontaly mounted (it looked somewhat like a windmill-well the ones you find in South Africa-they pump water from a borehole, this shows this type of 'prop' has a lot of power) and his huls were, well, trimaran. He had a normal propeller to drive the craft forward.

Best of luck with the project

ancient kayaker

11-10-2008, 11:22 AM

Windmaster

11-10-2008, 12:28 PM

Guest625101138

11-10-2008, 03:23 PM

A sailing craft sailing faster than the wind achieves this by tacking, since it must have an apparent wind at an angle off the bow.

Can a fan-driven craft achieve FTTW speed by simply heading directly downwind from a standing start, or must it first achieve FTTW speeds by tacking or using an engine?

Yes. It is complete reverse of the upwind case. You have a water turbine and an air propeller. For 1:1 mechanical connection you need the prop to have roughly half the pitch of the turbine. The downwind system is really incompatible with the upwind system because of the compromises. For example you need a wide gear ratio and you would be restricted to symmetric foils.

As soon as the wind starts pushing the boat the gearing enables the water turbine to overpower the air propeller and the propeller assists in moving the boat forward through the air that is already moving. Ideally you start with a large gear ratio and as the boat picks up speed and the prop gains efficiency you can back off the gearing.

Rick W

Windmaster

11-10-2008, 04:38 PM

As soon as the wind starts pushing the boat the gearing enables the water turbine to overpower the air propeller and the propeller assists in moving the boat forward through the air that is already moving. Ideally you start with a large gear ratio and as the boat picks up speed and the prop gains efficiency you can back off the gearing.

Rick W
According to theory, but in fact it has never happened. If you can do it, you will achieve world fame!
Jack Goodman's demonstration of land-based dwfttw received worldwide admiration, respect from AYRS and and also some disbelief.

Guest625101138

11-10-2008, 05:27 PM

According to theory, but in fact it has never happened. If you can do it, you will achieve world fame!
Jack Goodman's demonstration of land-based dwfttw received worldwide admiration, respect from AYRS and and also some disbelief.

I doubt that world fame will ensue. You have not read through the youtube comments. The world is full of skeptics and most of the comment is negative. A bit like Windmaster's skepticism of anything with a little maths.

It is actually easier to do it on water because the initial friction is zero. Doing it on land is harder because there is static friction. The boat will start moving as soon as there is a slight breeze. As long as the gearing is right it will start accelerating.

The air propeller has to be quite large to be effective because it is operating at quite low velocity. It is not compatible with sailing upwind.

So other than curiosity it has no merit. Boats already sail downwind faster than the wind only they cannot do it directly down wind.

It is interesting to have a look at the speeds that the Aeolus Racing cars get to and compare with land yachts:
http://www.ato.nl/?category=wind&id=30
You can see all that mechanical complexity and performance way below the conventional sail.

By the way, take note of the design of the turbine blades and have a look at the Youtube explanation of the turbine design of the winning machine.

On land the ability to sail at any point has merit but on water you have much more room so does not make a lot of sense.

I believe any useful system for boats will have energy storage. That is where the system outperforms existing sailing vessels - the ease of energy storage.

Rick W

ancient kayaker

11-10-2008, 05:41 PM

Here is a video of a FTTW turbine on a downwind run; it's a model land yacht not a boat but you can see the wind tell tale reverse diection as it speeds up: http://www.youtube.com/watch?v=aJpdWHFqHm0

For further reading there are several threads on turbines:-
Another idea thread http://www.boatdesign.net/forums/projects-proposals/another-idea-1289.html
http://www.boatdesign.net/forums/projects-proposals/windmill-wind-turbine-powered-boats-how-many-out-there-they-viable-14182.html

Guest625101138

11-10-2008, 05:46 PM

This is the Aeolus Race winner:
http://www.youtube.com/watch?v=IWNEXBBAGNw
It gives you an idea of the best turbine blades. The comment made by the student about 1/3rd in is spot on.

The best turbine for a boat would have the same proportions as would the best propeller. When you get foils like this the performance really starts to improve. They can deliver close to 90% of the input power as useful output.

Rick W

Windmaster

11-11-2008, 03:28 AM

I doubt that world fame will ensue. You have not read through the youtube comments. The world is full of skeptics and most of the comment is negative..

Rick W
Well, I have read through the youtube comments. Do you base success or failure on the commenters on Youtube? It's rather sad if you do, I doubt that any of them are informed enough to make serious judgements.

Windmaster

11-11-2008, 03:30 AM

It is actually easier to do it on water because the initial friction is zero. Doing it on land is harder because there is static friction. The boat will start moving as soon as there is a slight breeze. As long as the gearing is right it will start accelerating.
Rick W
So why don't you demonstrate it then? I don't think anyone else in the world believes it is easier on water (have you thought about it?)

Windmaster

11-11-2008, 03:38 AM

I doubt that world fame will ensue. You have not read through the youtube comments. The world is full of skeptics and most of the comment is negative. A bit like Windmaster's skepticism of anything with a little maths.

It is actually easier to do it on water because the initial friction is zero. Doing it on land is harder because there is static friction. The boat will start moving as soon as there is a slight breeze. As long as the gearing is right it will start accelerating.

The air propeller has to be quite large to be effective because it is operating at quite low velocity. It is not compatible with sailing upwind.

So other than curiosity it has no merit. Boats already sail downwind faster than the wind only they cannot do it directly down wind.

It is interesting to have a look at the speeds that the Aeolus Racing cars get to and compare with land yachts:
http://www.ato.nl/?category=wind&id=30
You can see all that mechanical complexity and performance way below the conventional sail.

By the way, take note of the design of the turbine blades and have a look at the Youtube explanation of the turbine design of the winning machine.

On land the ability to sail at any point has merit but on water you have much more room so does not make a lot of sense.

I believe any useful system for boats will have energy storage. That is where the system outperforms existing sailing vessels - the ease of energy storage.

Rick W

Well, if sailing downwind faster than the wind has "no merit" and sailing directly into the wind "does not make a lot of sense" it's hardly worth continuing the conversation.
It's stretching your credibility to the limit when you know all the answers, but cannot show anywhere in practice that your ideas have any validity.
(Maybe you have been misjudged - in that case please direct us to the site where you can show us your ideas actually work.)

Guest625101138

11-11-2008, 04:22 AM

Well, I have read through the youtube comments. Do you base success or failure on the commenters on Youtube? It's rather sad if you do, I doubt that any of them are informed enough to make serious judgements.

Youtube provides a fair reflection of the real world. I expect many of those people commenting made a recent decision on who will be the new leader of the free world. Clearly their understanding of the things around them is important to all of us.

In fact if you go back through any of the threads on turbine powered vessels on this site you will see that even reasonably informed people do not readily grasp the concept. In fact most jump in and say it defeats some natural law without even thinking about it. So I have great reservations about the average joe ever recognising any great achievement with sailing DDWFTTW. It is a long way short of what anyone could realistically consider world fame. In any event it is quite insignificant compared with finding a cure for cancer as an example or even finding a critical part of the jigsaw toward a cure. Sailing DDWFTTW is not going to change mankind forever. It is an interesting curiousity for those intrigued by such things.

In fact until you referenced Mr Goodman's name earlier it had not registered with me and I have often viewed the video and others he has to demonstrate the principle. I think I have a paper on the work but have no idea who authored it. So I doubt you would find many people who could instantly recognise Jack Goodman as being world famous for anything.

So if you have a bent to be world famous I would suggest you not waste time working on a boat that sails DDWFTTW. I do not have interest in being famous or sailing DDWFTTW. There are much faster ways to become famous if that is your ambition although some might land you in jail.

Rick W

ancient kayaker

11-11-2008, 01:42 PM

Whatever happened the the person who started this thread?

TeddyDiver

11-11-2008, 02:31 PM

even reasonably informed people do not readily grasp the concept. In fact most jump in and say it defeats some natural law without even thinking about it. So I have great reservations about the average joe ever recognising any great achievement with sailing DDWFTTW.
I'm not sure wheather I'm reasonably informed or just an avarage joe, but I'd love to see the math (or theory) how it really works. I allready tried kind of ask this in annother thread but none seemed to notice my humble need of wisdom in this particular matter:)

Guest625101138

11-11-2008, 04:31 PM

Joakim

11-11-2008, 04:41 PM

I'm not sure wheather I'm reasonably informed or just an avarage joe, but I'd love to see the math (or theory) how it really works. I allready tried kind of ask this in annother thread but none seemed to notice my humble need of wisdom in this particular matter:)

It's basically very simple, if you just start with basic physics and don't try to look it too complicatedly.

Power P is velocity V multiplied by force F: P = V * F.

Now velocity the propeller sees is the water velocity relative to the vessel and the turbine sees the wind velocity relative to the vessel. This is just the same for sail and keel. All wind driven "things" need a velocity difference between the two: air and water/land/ice.

The transmission between the turbine and the propeller transfers POWER (with some efficiency), thus the power at propeller shaft equals that on the turbine shaft. One is the "generator" and the other the "motor" depending on the situation.

As an example a boat travels 5 m/s in 4 m/s downwind. Now the propeller sees 5 m/s water speed Vp and the turbine sees 1 m/s apparent wind Vt. Without losses thus:

Pt=Pp => Ft * Vt = Fp * Vp => Ft = Fp * Vp / Vt => Ft = 5 * Fp

Thus theoratically we can have 5 times more thrust with the turbine than we have drag by the propeller. The propeller is taking power "out of water" and the turbine is pushing with that power.

Now when we add efficies, say 80% for both and 90% for the transmission, we still get Ft = 2.9 * Fp. Thus we have now Ft-Fp = 1.9 * Fp = 0.7 * Ft to cover drag of the hull and we must design a system that can perform at specified efficiencies and forces at the given condition.

Sounds easy, but when you try to design it, you notice that the turbine needs to be huge to get any meaningfull thrust at 80% efficiency in given conditions. Huge turbine -> huge vessel -> a lot of drag at 5 m/s -> not feasible. By huge I mean 20 m diameter to reach even 100 N thrust at ~80%. And then you need to have less than 70 N drag for the vessel at 5 m/s....

I believe it is far more difficult to build this on water than on land. On water the initial resistance is zero, but at the same time you can not transmit any power at low velocities without a huge propeller and turbine. On land you can use a wheel to extract power with a very good efficiency and you can go fast with little drag, since about all you have is rolling resistance. With a good bicycle the drag is only about 0.004 * mass and it is independent of speed, since we are in almost zero apparent wind. Thus for 100 kg "wind bicycle" the drag can be as low as 4 N and we need only 6 N turbine thrust in the example above.

Joakim

Guest625101138

11-11-2008, 04:59 PM

Joakim
Windmaster rightly insists that we stick with the convention of a propeller absorbing power and a turbine producing power. In the downwind case the turbine is in the water and the propeller is in the air.

You have got the basic physics correct but I disagree with the size of the air propeller. It has to be quite large but no where near the size you indicate for a single person boat.

Rick W

Joakim

11-11-2008, 05:47 PM

You have got the basic physics correct but I disagree with the size of the air propeller. It has to be quite large but no where near the size you indicate for a single person boat.

I think it has to very huge to reach 100 N thrust at 80% efficiency at 1 m/s apparent wind, BUT 80% efficiency is probably not needed. Is it really possible to get 47% efficiency at 323 rpm as you say? At what size?

The power absorbed by the air propeller is too high in your calculation, should be 339 W.

62 N drag is achievable, but you need to keep the total weight at maximum of ~100 kg in order to keep the wetted area under 3 m2 and also the residuary resistance needs to be very very low, thus very slender (= more wetted area). Would this be possible with the propeller and turbine needed?

Joakim

Guest625101138

11-11-2008, 07:38 PM

I think it has to very huge to reach 100 N thrust at 80% efficiency at 1 m/s apparent wind, BUT 80% efficiency is probably not needed. Is it really possible to get 47% efficiency at 323 rpm as you say? At what size?

The power absorbed by the air propeller is too high in your calculation, should be 339 W.

62 N drag is achievable, but you need to keep the total weight at maximum of ~100 kg in order to keep the wetted area under 3 m2 and also the residuary resistance needs to be very very low, thus very slender (= more wetted area). Would this be possible with the propeller and turbine needed?

Joakim

Joakim
I have posted many times on the turbine/prop boats and you are the only poster so far that has demonstrated a sound appreciation of the physics.

I have attached a JavaProp design page for a prop that will achieve close to the numbers I gave at 160N thrust in 1m/s wind. It is spinning much slower than I provided and accordingly the pitch is larger. JavaProp allows for the velocity ratio whereas my analysis does not so at the low apparent velocities my data is inaccurate. However I use slightly better foils than what is available in JavaProp so can get efficiency a percent or so better.

As I said before, once I realised how big the prop needed to be to get reasonable efficiency I did not go any further. It might be that you can do better than I have indicated if you play with prop and turbine size but I would not regard 8m as practical on the boat I was considering. With upwind you find a prop around 3m is about right for this size boat.

You are right about the power absorbed by the propeller for the stated efficiency. The figure I gave was higher than it should have been but is close to the number shown for the slightly lower efficiency prop shown in the attached.

I have not checked which hull I based the hull drag on but, for example, my V11 style hull displaces 100kg, is 7.2m long and has wetted surface of 2.1sq.m. The fibreglass hull and aluminium drive system weighs 23kg and I am currently doing an all carbon fibre version that has estimated weight of 15kg. So It is possible to make a boat with a turbine and prop for the hull drag numbers I have given. The thing is that the upwind boat would be distinctly different to the downwind boat. Now how practical is that.

I have not done analysis across all points of sailing but you have to ask how often do you really want to sail DIRECTLY down wind. It also has a narrow range of operation because above a certain windspeed the hull drag simply does not allow you to get out of the low efficiency region for the propeller so it acts as a rotary sail just retarding forward airflow rather than accelerating it backwards.

Rick W

Guest625101138

11-11-2008, 08:03 PM

Joakim
I should add that in determining the weight of the boat you can see that the power transmission requirements are quite low for the downwind boat. Gearboxes required to handle that power level weigh under 1kg.

The situation for the upwind boat is again quite different in this regard as well. You quickly get up to power levels around 10kW on a small boat. Although the air turbine is much smaller than the air propeller the gearbox to handle the power would actually be quite a lot bigger for the turbine.

Rick W

Joakim

11-12-2008, 04:08 AM

Joakim
I have posted many times on the turbine/prop boats and you are the only poster so far that has demonstrated a sound appreciation of the physics.

So It is possible to make a boat with a turbine and prop for the hull drag numbers I have given. The thing is that the upwind boat would be distinctly different to the downwind boat. Now how practical is that.

Thank you! I have studied quite a bit of physics, which perhaps gives a more open minded view to these things, that sound impossible at first look.

There is no real use for a vessel like this, but it is an interesting subject to think about. How heavy would a 8 m propeller and it's support be? How much wind would it tolerate? Would the boat handle well the moment?

Joakim

Guest625101138

11-12-2008, 04:49 AM

Thank you! I have studied quite a bit of physics, which perhaps gives a more open minded view to these things, that sound impossible at first look.

There is no real use for a vessel like this, but it is an interesting subject to think about. How heavy would a 8 m propeller and it's support be? How much wind would it tolerate? Would the boat handle well the moment?

Joakim

Joakim
Until you play with carbon fibre in a sandwich construction you simply cannot appreciate what the numbers mean. It has unbelievable rigidity and strength for weight. I made a 4mm thick test strip using 200gsm CF and compared with the same size strip using 320gsm fibreglass cloth. Both were made resin rich to give a nice surface finish when formed over plastic so final weigh difference is not huge. The CF ended up around 1kg/sq.m and the fibreglass a little heavier. However the CF panel is roughly three times stiffer than the fibreglass.

If I was making a 4m long blade that tapered from something like 400m at base to 200mm at tip I would use two of these panels back-to-back but only bond the inside CF initially to enable section profile over formers before doing single CF wrap around the outside. I figure I could make such a blade weighing 3kg and it would have more than enough strength. Given the loads are minute once operating, it would be suitable for demonstration purposes.

Moments are going to be nasty but then there is 75kg of movable ballast to offset the worst loading conditions. The particular hull in question is 7.2m long with 225mm beam. It would need wider set outriggers with greater volume to give some safety margin but these do not contribute to drag when going direct down wind.

I would not want to be near those blades in anything over 20kph winds. You would want to stall it before that stage and be careful about getting beam on to wind. I have been on the boat in maybe 60kph wind and at that speed you get concerned that the wind will pick up the boat and roll me and that is sitting right at water level.

I had numbers for a smaller air prop but it needs to operate at higher apparent velocity and I cannot remember if it actually worked or I still had some logic errors in the analysis.

I have posted an Excel spreadsheet on another thread:
http://www.boatdesign.net/forums/attachments/projects-proposals/25268d1221220464-windmill-wind-turbine-powered-boats-how-many-out-there-they-viable-ideal_turbine_boat.xls
that has the equations you provide for the upwind case. It has a little macro that balances operating conditions.

This could be easily be converted for the downwind case but you have to use a much lower air propeller efficiency. I use interactive propeller and turbine models for particular foils but you would be able to use JavaProp for the propeller design. You can make some estimates about the turbine based on a propeller in JavaProp of similar size.

I have components to make a wind turbine but no time right now to get into making it. I expect that I will get back to it in the new year. But the turbine is intended for operation upwind or at anchor to charge batteries. It also has the capability to provide propulsion because I have a full 4-quadrant controller and BLDC motor/generator.

Rick W

TeddyDiver

11-12-2008, 01:52 PM

clmanges

11-12-2008, 03:01 PM

This may be of interest:

http://uk.geocities.com/fnsnclr@btinternet.com/yachts/auto/index.htm

Guest625101138

11-12-2008, 04:16 PM

Thing that troubles me here is the turbine/propeller concept which is here is determined by the apparent speeds of the intermediate. Messing up with energy conservation I'd like to point that in this case water gains more inertia and the air looses some so the apparent truth of a combination of turbine/propeller is in reality a propeller/turbine...
Am I thinking straight or just gear loose:p

For the DDWFTTW boat the turbine in the water extracts power and the mechanical system delivers it to the air propeller. The water is being slowed down a little relative to the boat near the turbine and the air is being accelerated backwards a little relative to the boat. In absolute terms the air slip stream is moving a little slower relative to the water and there is a water slip stream moving in the direction of boat travel.

You might find it easier if you think of the boat clawing its way against a strong current in still air. This is the exact opposite of the upwind condition where the water is static. The current tries to force the boat backwards but the air drag on the big prop and boat superstructure slows it relative to the current. This causes the turbine to spin because the water is now flowing past it and begins delivering power to the propeller and the propeller starts to drive the boat forward through the water. The flow past the turbine increases and the power flow to the turbine increases. This is not as hard to imagine but the boat is now moving in its direction of travel faster than the air, which, of course, is not moving at all.

Now flip this frame of reference so the air is moving over the water.

There is one of the Goodman's videos showing his DDWFTTW on a treadmill. Initially the car is tethered as the treadmill comes up to speed and the prop starts spinning. Once up to speed the car begins to claw its way up the treadmill with power being delivered to the wheels and these in turn driving the prop. The prop generates more thrust than the drag on the wheels by virtue of simple gearing.

Rick W

clmanges

11-12-2008, 10:27 PM

It's taking me a while to grasp this.

Where can I find more information on Goodman or see other videos? I did a search, and only found the one outdoor video, nothing else.

Boston

11-12-2008, 10:48 PM

if its a flywheel then the energy it takes to alter angular momentum is seriously going to foul up your day
one reason flywheels have been nixed in cars is catastrophic failure and random system re stabilization over rough terrain
rough terrain and waves are spelled much alike
but they sure sound similar
same goes for the blades if they find themselves spinning a little fast
might take more energy than you think to redirect them
boat might have a mind of its own when it comes to direction
dont let me discourage you though
I cant wait to see how this pans out
would love to see an animation eventually
B

Boston

11-12-2008, 11:00 PM

Guest625101138

11-12-2008, 11:04 PM

It's taking me a while to grasp this.

Where can I find more information on Goodman or see other videos? I did a search, and only found the one outdoor video, nothing else.

Curtis
This is not the Goodman video but it is similar:
http://www.youtube.com/watch?v=kWSan2CMgos&fmt=18

I think this is easier to wrap your brain around. Providing the gearing is right the wheels will pump power to the propeller and it climbs up the treadmill through reacting on the air. It is not moving all that fast through the air but it is really motoring quite fast on the treadmill.

On the outdoor demonstration it moves too fast to see what is going on.

The proportions on this are better than Goodman's vehicle because it is very light with simple gearing and has a relatively huge propeller.

Once you get this concept on the treadmill you simply have to shift the frame of reference so the wind is moving relatively to the land and the vehicle is advancing faster than the wind. It is a matter of gearing. If the propeller was replaced with a low geared winch drum tied to the front of the treadmill then you would easily understand the idea. You would say it was no big deal.

With the boat you replace the wheels with a water turbine that is simply spinning as the water goes past and pumps power into the air turbine.

Rick W

Boston

11-12-2008, 11:16 PM

dont get mad at me for being a skeptic
but several things
the fluctuations if wind velocity could easily account for the tell tails occasional backwards flutter
that and its proximity to the turbine
also there is energy stored in the turbine that although may for short periods allow for fttw speads
on average
I dont see the system breaking any speed records
stick that thing in water
were pitching and rolling
are energies that will effect an alteration in the axis of rotation and angular momentum
and given that on analysis those energies will need to be deducted from the forward energy of the craft
then Ild say this is not the magic engine I was hoping for
was a fun little gizmo though
B

Boston

11-12-2008, 11:17 PM

Im loving this thread
90% impressive
10% not faster than the wind

the answer is in a spinning something
but what Im dying to see
B

Guest625101138

11-12-2008, 11:23 PM

I would have thought the trick would be accomplished on ice

Im always skeptical of fttw runnin
the extra energy has to have been stored in a spinning something and will not last long
auto gyro might help out some
but its a stretch to say its wind powered and going faster than the wind if its storing that power and then dumping it into the system for a short stretch
on a tack
no problem
a close reach
Im a believer
on a dead run
I need going to need more convincing
sail power alone with no storage device
according to that little darling mentioned previously
the ever handy first law of thermodynamics
that and water resistance
makes it highly unlikely

all that being said
I hope some one does it just to stand science on its ears
best
B

Boston
What I ask people to do once they understand that it DOES work and does not defy any grand laws is make a correcing post just so people that read through these things take a bit more time to understand it rather than not taking any real time to think it through.

If this is not done we just go on with this forever. It is basic physics. Sail powered sail boats have been going faster down wind than the wind for as long as I can remember. And that is in terms of VMG in the direction of the wind. The only feature of the propeller/turbine combination is that it enables DIRECT downwind faster than the wind.

So when the penny drops please take time to post your flash of insight as Tcubed did on #220 here:
http://www.boatdesign.net/forums/projects-proposals/windmill-wind-turbine-powered-boats-how-many-out-there-they-viable-14182-15.html

There are some dumb ideas around and some will not work but this is a somewhat useless idea that does work.

On water you have the advantage of zero friction initially but if you go to the earlier posts you get an idea of the scale of things required to make it work for a single person boat.

Rick W

Boston

11-12-2008, 11:29 PM

there is roughly a one percent loss of energy in a simple gear
a magnetic gear has less but you have to run it in a vacuum to get it to zero
and even then there's arguments to say its not zero
so I have to wonder if a gearing system on a indirect turbine to prop application would be able to eliminate all the friction possibilities plus find energy in the rotation some were to add to the forward motion
I think its bordering on perpetual motion
a sail powered craft runs before the wind by virtue of resistance to the wind
when that resistance reaches zero as the craft approaches wind speed
were you going to get more energy from
inquiring minds
want to know
B

Guest625101138

11-12-2008, 11:45 PM

This is far from perpetual motion. The losses are quite high. If you look through the series of videos on YouTube covering DDWFTTW you will see different vehicles and how they perform. Keeping the vehicle light reduces rolling drag and the propeller relatively large and low pitch (spinning fast) helps the propeller efficiency.

I doubt that anyone could make a system work with windspeed lower than 2m/s because you simply cannot get the required efficiencies. You need this sort of relative movement between ground and air to overcome the loss.

As far as conventional sailing boats go you might gain some insight on how they perform downwind on this thread:
http://www.boatdesign.net/forums/sailboats/tacking-downwind-faster-than-wind-24761.html

Rick W

Boston

11-12-2008, 11:51 PM

Guest625101138

11-12-2008, 11:55 PM

Boston
By the way I do not expect payment for your education just a post acknowledging that it is quite feasible and does not defy any of the known laws.

Rick W

Boston

11-13-2008, 12:11 AM

hey Rick
as far as into the wind is concerned
I didnt mention it cause Im sure its possible
but I really would love to read your research on going faster than the wind on a dead run
I would think you'ld hit a dynamic equilibrium that equals the wind speed minus system friction ( drag )
the air turbine wont spin any faster than air speed allows minus friction
and the water turbine wont spin any faster than the water speed allows minus friction
neither have energy available at dynamic equilibrium
and drawing energy from either only makes that equilibrium a smaller fraction of the ttl energy available
soooo
how does the water turbine add energy to the system with out offering so much drag as to overcome any benefit

Ill get back to you tomorrow
I gotto get going
nice intelligent conversation though
hope all it well
B

Boston

11-13-2008, 12:13 AM

your on
and I owe you a brew for that one as Im laughing my ass off
tell you what
if Im wrong
you tell me your favorite pub
and Ill telli it up and get you a brew on me
k
gotta go
B

Guest625101138

11-13-2008, 12:18 AM

one of the best ways to learn is to be wrong and stand corrected
Im all ears my friend
convince me
maybe I was to quick ( been known to happen before )
I studied physics for a long time and Im just not seeing this one
oh doesnt mean I cant be completely wrong about this
but so far Ive not read a compelling argument
I certainly didnt mean to offend anyone
I actually found the subject really interesting
maybe I missed something
were talking about a simple spinning turbine
either connected to a shaft driving a prop
or simply spinning freely
being able to drive a watercraft faster than the actual wind
no batteries no storage devices

(Tell Tails only read apparent wind)

Im already to be convinced and I will print one huge retraction
send me a video of a boat
and maybe a few details about how it does it
and how they overcome energy loss through random alteration in the angular momentum of spinning components brought on by things like heeling pitching rolling and the like

( takes a lot of energy to redirect the axis of rotation of a gyroscope )

I read this thread word for word
the one about an electric generator operating in port, charging batteries made the most sense
course you might do the same thing with enough solar panels and eliminate all the gyroscopic forces
but thats stored wind power
and given the energy loss of the basic charging system
not real efficient

Have you looked through the videos of the land vehicles on YouTube? Do you believe what is being shown on the treadmills? Are your physics/maths skills good enough to write the equations of motion you see in the application? I need to have some understanding of your level of knowledge so I can peg your education correctly.

Once you have these sorted out post them here and I will check your answers. We can than move on to the land vehicle on fixed ground in a moving air stream. Same thing - post equations of operation and we will move on to the boat situation.

If you know how levers work then you have the basic comprehension to grasp this. I guess there were many who could not believe Archimedes could lift many times his own weight. We are simply dealing with rotary levers here. Some aptly refer to them as screws.

If you want to cheat then Joakim has posted the physics above. I have given precise numbers for a system that will work for a boat based on precise modelling of the foils and hull drag.

If you are really hung up about the system losses with a boat. What you have dome is taken energy from water by accelerating it in the direction of travel and transferring it into the air by slowing the air down a little. So there is evidence of energy being given up. If it was perpetual motion it would be like stopping the treadmill and seeing the thing continue to advance forever. This will not happen. It requires the relative movement of air over ground or air over water.

Rick W

Guest625101138

11-13-2008, 12:43 AM

......
how does the water turbine add energy to the system with out offering so much drag as to overcome any benefit
.....B

The answer is very simple - GEARING or a rotary lever.

Power is force X velocity. Going downwind, the water past the turbine has to be faster than air past the propeller. So if gearing is set to allow the air velocity to be say half the water velocity the force generated by the prop will be twice the force applied to the turbine. The excess force is available to overcome system loss and hull drag.

In practical terms the propeller is not very efficient because the airspeed is quite low so it is not in an ideal operating regime. A boat speed of 4 or 5 m/s is quite fast and is going to need a significant force even with a slender hull so the propeller ends up being a monster in relation to the boat. The scale of propeller to vehicles you see in the video provide a good indication of what is required.

Rick W

Boston

11-13-2008, 01:47 AM

theoretical physics
I just patented plasma insulation
although most of the time I work as a general contractor cause it keeps me fed

the numbers on free spinning wind turbines were dreamed up in the forties
and should be the same as the numbers for a gyrocopter

and I dont really see anything special about a horizontal gyrocopter being pushed uphill by a fan
there doesnt need to be any gearing to the wheals to make that happen

so rather than try and remember the friction formula for an incline plane
and go through all that rot of figuring out the gear friction and turbine speed/wind speed bla bla bla
I think Ill just leave the burden of proof on you
my beer your burden
Im just going to sit back and await convincing
so get cracking cause I might just accidentally drink your beer money
accidentally

as for crunching numbers
I only do it when I have to, and I tend to get paid for it ( if Im lucky )
although
I was playing with Faraday's theorem
E=Hv
found the common denominators with E=mc2 and came up with

Hv
---- = m
c2

if you play with it a little, it basically defines mass as a function of speed "or" frequency

or

being the key operative

so I think Ill understand what ever you send me

but
dont be mad at me if I start asking for considerations of friction with in system
also there is a definite loss of forward motion within any system that demands the redirection of gyroscopic forces
and its a lot of energy
so there could be a reason these things are land models
and not sailing models
as that random motion of the system can be more easily controlled

think of me as a beer buying skeptic
Im not closed minded
just not convinced

I gotta go
B

Guest625101138

11-13-2008, 02:29 AM

and I dont really see anything special about a horizontal gyrocopter being pushed uphill by a fan
there doesnt need to be any gearing to the wheals to make that happen

B

The point is there IS gearing to the wheels and NO fan involved. It is not a gyrocopter. It is a propeller extracting energy from the treadmill through the wheels and applying force to move the vehicle against the treadmill. Very simply it is gearing.

I have provided a series of images that if you work through you will gain understanding. All you need to know is:
Force = Power X Velocity
Turbine has an efficiency of 85%
Propeller has an efficiency of 45%
Mechanical efficiency is 94%
Boat drag is a function of V^2 and is 60N at 3m/s

Current where shown in the attached is 4m/s.

Wind speed where shown is 3m/s.

Rick W

Joakim

11-13-2008, 09:10 AM

how does the water turbine add energy to the system with out offering so much drag as to overcome any benefit

The key you have to understand is that there are two fluids with a velocity difference. Reducing this velocity difference gives you energy.

A very simple analogy is shown in the attachment. You can always replace the rope fixed to floor with a transmission in the "car", which is connected to wheels.

Then you can replace the whole rope with another pair of wheels, which touch the ceiling and are geared to the other wheels touching the floor. Then you are no longer limited to the length of the rope. As a home work you can derive the equation for the speed of the car as a function of the gearing.

When you do these calculation, you are probably not worried about efficiencies, friction and energies, since you don't mind what moves the ceiling and you can assume no slip for the wheels.

Do you agree that the car can move faster than the ceiling (wind) without being perpetual motion. What is the difference between this example and turbine/propeller combination?

Joakim

clmanges

11-13-2008, 12:53 PM

Guest625101138

11-13-2008, 03:49 PM

Rick, thanks for the link to those vids. After watching three of them, I wrote to the guy who posted them, with a couple of comments.

First, I said that some skeptic might think that the whole cart was being blown along by air pressure, and suggested he do a comparison demo with the propeller still on the cart, but disconnected from the gear drive.

Then, I commented that he needed to include scientific measurements, specifically the windspeed at the cart's location, and the rotational speed of the wheels and their diameter. This would allow a simple calculation to compare vehicle speed against windspeed.

I think the biggest problem with understanding this is the way our brains function. Our brains are wired to comprehend natural phenomena just fine and to learn to use that understanding. For example, a person with no training or prior experience can get into a canoe or kayak on moving water, and within a couple hours will learn on their own how to ferry the boat.

Wheels cause problems, because nature didn't invent them. Sure, logs and rocks roll down hills, but take that rolling object away from contact with the ground, and it becomes counter-intuitive. The very most basic: the gyroscope. This one-piece wheel and axle assembly consists of (count 'em) one moving part, in simple rotation, yet causes more brain-spasms than a political campaign (well, maybe some campaigns, anyhow). We just aren't wired to comprehend things that appear to defy gravity or seem to have a mind of their own. Bicycles and motorcycles turn opposite to the way you steer them. The list goes on, and it's no wonder people still believe in magic.

Nature does include flying things like birds, and we can barely comprehend those beyond the level of "tastes like chicken."

So, it's no wonder that DDWFTTW is so controversial. It just doesn't fit in our brains.

I've got a square peg and a round hole in front of me, and I'm seeking the properly sized hammer.

Curtis
Gyroscopes and bicycles staying upright are far more complex physical systems than a turbine driving a propeller to go faster than the wind over water. All you need to know is power equals force times velocity. No need to get into the complexity of corioli effect.

The difference with the bike and the gyroscope is that most toddlers have seen a spinning top and most preschoolers have ridden a bike. They do not understand it but simply have experienced it. The vast majority of people cannot explain why they work. Have a go at telling a complete skeptic that a top can stand upright as long as it is spinning without any external force applied. If you can do that then tell me about gravity. What is this?

We have the situation where the skeptics out there cannot see a monster fan overcoming a little drag on a small hull using power coming from a water turbine and yet most have stepped on board a 500t aircraft that has held itself aloft in that same air. Air is able to produce huge forces providing there is enough area and a bit of velocity.

The analogy that Joakim makes with a vehicle having wheels top and bottom and sandwiched between two surfaces is a good one. I have attached a couple of slides that show this analogy. The direction and speed of travel is solely dependent on the gear ratio. It is not perpetual motion because when the plate stops moving the vehicle will certainly stop moving.

Rick W

clmanges

11-13-2008, 07:16 PM

Boston

11-13-2008, 07:48 PM

well in answer to the three questions in the order they appear
Ild have to say
maybe ( Ild have to see your math on it )
no
and no

Guest625101138

11-13-2008, 07:55 PM

well in answer to the three questions in the order they appear
Ild have to say
maybe ( Ild have to see your math on it )
no
and no

I have framed the problem in a simpler form in post #66. I would expect a grade 5 student to be able to work this out. Once you have got the maths sorted for both cases and provided the correct answers I will add some drag into the system.

Rick W

Guest625101138

11-13-2008, 08:04 PM

I think the issue of wind direction is confusing some people -- it clouds the issue. I understood FTTW better when I completely disregarded wind as a factor in the operation of the device. Just pretend it's dead calm. You push the thing a little to get it going, and the wheels speed up the propeller, which pushes it faster . . . it'll accelerate until drag overcomes further acceleration. This will be the basic case in any wind condition.

Curtis
You have now invented perpetual motion. The system does not work unless the wind is moving relative to the water. There has to be a source of energy input.

Work out the answers to my two problems in post #66. See if you can get correct answers quicker than Boston. We will see who has mastered 5th grade maths. What year are students taught algebra in good old USA?

Rick W

Boston

11-13-2008, 08:13 PM

exactly
but there's no potential in that for fttw or you would have perpetual motion
all your doing is storing the push you put in the system in the gyroscopic action of the propeller
and then watching it wind or oscillate down to equilibrium
I think its the oscillation that's got some folks going over these models

as far as the tread mill gizmo
you are right in that I had misunderstood what they were showing

and I appreciate you explaining it to me
but
but Im still not finding it very convincing
had they not inhibited the forward motion of the device and stored up a gyroscopic energy in doing so
it would not have even developed that cyclical effort it made to find equilibrium
an equilibrium that would not have represented more than the energy of the system minus resistance

Best
B

Boston

11-13-2008, 08:18 PM

wait a minute
I didnt know there was going to be a test and a time trial
you gotto post this again
and ring the bell to get us started
Im not ready
I need a pencil
wait
wait
wait
ok
dam
now were is the site again
something about # 66
what the hell is 66
isnt that some twisted sexual position or something
hang on and Ill ask the girl
might take a while
be right back

Guest625101138

11-13-2008, 08:39 PM

I will award reputation points to whoever posts the right answer first. Here is your opportunity for a big lift in your reputation.

Time starts now. Order of posts will be taken as the earliest finished and has to be the correct answer. You can have as many goes as you like. I will mark the result next week. No cheating using other threads to elicit answers. It has to be your own work

Rick W

Boston

11-13-2008, 08:40 PM

well I didnt see any equations to look at or work out
and Im still thinkin burden of proof is on you
so Im going to sit here and enjoy a cold one
and await the magic equation
its not up to me to dream it up
I dont happen to believe in it
the sum of speed a and speed -a arent going to equal anything more than speed 0
in a system were there is a floating object
a current moving from left to right
and a wind blowing right to left
a drag based propulsion system
will find an equilibrium somewhere in the middle
and it wont be any faster than either individually
nor will its potential energy exceed the sum of the two

if you have something that shows this
Im dying to see it
but so far you guys keep asking me to build a mathematical model of the system
and its not my system to prove
Im not really buying it
soooooooo
Im going to get some more beer
talk to the girl some more
and see what shakes loose
cheers
B

Boston

11-13-2008, 10:43 PM

energy out (A)
energy in (B)
friction F

A =B-F

Boston

11-13-2008, 11:15 PM

B
how does the water turbine add energy to the system

Rick
The answer is very simple - GEARING or a rotary lever.

gearing and leavers add resistance to the system and play with mechanical advantage
they dont actually add energy
matter of fact ttl energy is reduced as the law of conservation of energy is effected by friction

this responce is completely incorrect
no beer for you

90% efficient is a far cry from 110%
and near as I can tell your talking about a system that is more than 100% efficient and it doesnt exist
its called perpetual motion

on a dead run
once a turban powered vehicles speed matches wind speed
the apparent wind at the turban is 0
all it can do at that point is add drag
same goes for he propeller
so equilibrium must be bellow the environmental characteristics
no way that system will exceed wind speed
the more I think about it the less convinced I am
the propeller is no longer powered by the turbine and also adds drag
partly due to having to act against mechanical advantage of the turbine
and partly due to the water resistance
system does not work

oh you will get some motion out of it
but it wont achieve on a dead run fttw speeds

now if you are on a reach then the resistance to sideways slipping and the apparent wind combination will do you some favors
but not on a dead run

speaking of dead
Im tired
need more beer
and stuffed
( had a nice dinner ) ( thanks Bree )
so best
hope all is well
B

Guillermo

11-14-2008, 01:52 AM

Have a look at this video:
http://www.whatheck.com/2007/02/sailing-directly-downwind-faster-than.php

Cheers.

Joakim

11-14-2008, 02:28 AM

on a dead run
once a turban powered vehicles speed matches wind speed
the apparent wind at the turban is 0
all it can do at that point is add drag
same goes for he propeller
so equilibrium must be bellow the environmental characteristics
no way that system will exceed wind speed
the more I think about it the less convinced I am
the propeller is no longer powered by the turbine

You are not reading the posts! There is no problem for the AIR propeller with the apparent wind being 0. It is a propeller pushing air bacwards, just like a airplane propeller when you accelerate starting from zero apparent velocity.

The turbine in the WATER is in this case turning the propeller in AIR not vice versa. The turbine has a lot of apparent velocity, more than the wind speed, if you go faster than wind.

You are thinking this as a sail, which it is not. And actually you can go faster than wind downwind with a sail as well (ask the downwind VMG vs. windpseed from ice sailors), but not without jibing.

If you really know theoretical physics, the answers asked should be easy for you. Actually I think High School physics (at least in Finland) should be enough to solve these.

Joakim

TeddyDiver

11-14-2008, 02:35 AM

Perhaps seeing the DDWFTTW (hope it went right) as an entropy machine is easier (shows how twisted is the way I think) way to understand this. So this turbine/propeller promotes entropy btw the fluids and/or medias and by doing it "borrows" a bit of the energy to accelerate itself to higher energy level until the state of the equilibrum is achieved (in theory anyway) or the hand of god (man running after the machine) stops the process:P

Boston

11-14-2008, 09:32 AM

http://i354.photobucket.com/albums/r420/maxtanks/2008_fara-k15_1.jpg

no Im reading the posts
and I saw the video
Im just not buying it
not trying to piss any one off
just not a believer in perpetual motion
the propeller isnt going to suddenly change direction and add energy to the system
the same mech advantage that drives the wheels off the propeller is the same mech disadvantage that slows it down once it reaches some percentage of wind speed

if this thing is for real
were are the wind tunnel tests
were are the wind speed numbers
were is the vehicle speed numbers
were is the schematic of the device
and were is the data sheet showing average results over number of tests
and were is the confirmation study by an independent researcher

with out the scientific data for all to see
its just a toy rolling down the road
a road
thats bound to not be level
which no road is
and will definitely skew
what
a film of a completely arbitrary non scientific test
and subject to indiscriminate and random winds
with no data stream delta T
please

actually the second law of thermodynamics pretty much covers this one
energy ( heat ) will not flow from a lower state to a higher state with out additional energy ( work ) being applied

if this thing were real we could quit drilling oil or burning coal
and we cant
I wish we could
but it doesn't work

Ill call in a beer at the bar of your choice for each of you guys if
you can show me the scientific data I have requested
I want real data
confirmed
name of university conducting
principals involved
any citations included
supporting articles
publisher
wind tunnel test showing 100+% energy output
an exact description of the device
a full schematic
both raw data and full data analysis
in addition

basically I want to see some scientific data instead of a few renderings and toys that dont prove anything

if there is an actual scientific study this important
then there will also be a confirmation study
Ild be slacking if I didnt take a look at it to
normally they include

confirmational studies verifying previous analysis
name of university conducting confirmation study
principals involved
authors of citations comments if any
authors of supporting articles comments if any
publisher and name of publication
confirmed wind tunnel test showing 100+% energy output
confirmational analysis of schematics
confirmational analysis of test process
bla bla bla

basically I want to see the hole study before I start buying you guys beer
and Ill apologize for having doubted you
all you got to do is bear the burden of proof for what you are saying
Im not trying to be the ogre under the bridge
hell Im waving drinks at you guys hoping you can cough up the data
I just dont think it can happen

on a dead run
a wind powered vehicle
will not go faster than the wind

lunatic

11-14-2008, 09:34 AM

Rotor musings. If a rotor's shroud had radiating supports upwind of the blades blocking the true wind at intervals to change angle of attack at the right Strouhal number, would the blades be virtually flapping in the breeze. If true wind increased in the shroud, blades would need less twist and could have more pitch, rotating lift vector forward for more torque, even at high tip speed ratios. This line of thought requires belief in the Katzmyr effect, hysteresis, negative drag which all have a tenuous place in my mind. The potential stall of the intermittant high angle of attack is avoided by a negative one in the apparent wind of blade travel behind shroud supports maintaining attachment. Would there be any gain in the real world?

Boston

11-14-2008, 10:10 AM

impresive post there Luny
I had to go look up the Katzmyer effect
way to make me think
I found a confirmational study on an original done in the twenties
basically he is looking at the effects of joining a wing and an oscillating flow in harmonic sympathy and seeing if he can add amplitude a to amplitude b and get a+b
which should work in a kinda twisted kinda way since he is not actually dealing with a wave form in the wing
I think its going to very pleasantly confuse this issue
way to go
I really liked the article
thanks
B

oh
it would never work outside a controlled environment as you suggest with the question
Would there be any gain in the real world?

actually Im working on something like this concept with the next generation of plasma insulation
but so far its just a bunch of theory

again
nice post
way to track down a relevant article and note the tenuous nature of the concept
there wasnt much on Katz in the university data base
how is it you are hip to that work
do you do some studies in that field

lunatic

11-14-2008, 11:24 AM

I am just a causal sailor with lots of curiosity and some ability to knock things together in the real world but little theoretical background. Bird flight observation was main inspiration for this concept. You have saved me from the work of a prototype but the mind runs on.

Boston

11-14-2008, 04:46 PM

well it took more than the casual Cat to draw on a near hundred year old study by some Russian scientist that barely shows up in several university data bases
hats off to you
B

Boston

11-14-2008, 05:40 PM

You are thinking this as a sail, which it is not. And actually you can go faster than wind downwind with a sail as well (ask the downwind VMG vs. windpseed from ice sailors), but not without jibing.

my point exactly when I said

now if you are on a reach then the resistance to sideways slipping and the apparent wind combination will do you some favors
but not on a dead run

tacking (Jibing) involves being on a reach
maybe I should have been more specific and said broad reach
but still
I think I got this one covered
although
sideways slipping
was a poor mention of the physics of an object moving through an arc require it to be accelerating or at least not decelerating as fast
basic centripetal force requirement
( newton kids, anyone remember him, funny little hat, gravity, laws of motion guy, Newton )
basically you gain energy when you turn

on a dead run
no jibing or tacking
just an absolute dead run
you will not exceed fttw speeds
asking the guy who doesnt think it can happen to dream up some formula to say it can happen is kinda fundamentally the wrong question
now I can form a summation as to why it wont happen
as I said

energy out (A)
energy in (B)
friction F

A =B-F

seems to me to obey all the basics and still keep it simple
add what ever calculations you want for A,B and F
but thats how they would stack up

I think High School physics (at least in Finland) should be enough to solve these.

seems like basic algebra to me

what I would love to see worked out is a dynamic analysis of energy distribution in a series of tacks running as close downwind as possible, including centripetal forces

but again
its not my burden of proof
whats beer cost in Finland these days
( course I dated a Fin once, girl could drink most of us under the table, so I might be getting myself in a little bit of trouble here )

See if you can get correct answers quicker than Boston.
Rick are you buyin
send me the actual diagram you want worked out and Ill give it a go
what the hell
is it going to be the one with the moving plate with the geared wheeled thing between them
cause Im thinkin
three beers for that one
( happy hour at the appaloosa $2.50 American bar tenders name is Jamie )
( Denver Pale Ail please )

:)
peace people
sailing is just all in good fun
B

clmanges

11-14-2008, 07:46 PM

And now, presented for your approval:

http://www.youtube.com/watch?v=7xL8gRJ5F6k

in which it is shown that an electric treadmill can power a bitty propeller-driven cart in no wind at all!

I'm not sure what this is supposed to have to do with going DDWFTTW . . .

Guest625101138

11-14-2008, 09:21 PM

Curtis
The Youtube video is the same ones I linked earlier. This is simply a reversed frame of reference. The ground is moving and it is using force generated by the prop to move up hill. The fact that it moves uphill shows it is capable of extracting energy from the wheels to generate more thrust from the air than the drag on the wheels.

Back to the analysis so you gain insight--

Just in case you have not understood the problem I posed I will attach the two question sheets again here.

Once you provide the correct answers I will add a little more complexity that includes accounting for the forces and system losses.

The aim of this 5th grade exercise is to see if you can comprehend simple gearing. The understanding gets very simple after that. This is the most challenging aspect of the propeller/turbine system.

The offer of rep points is open to anyone who cares to provide the right answer showing their workings. Only the first right answer will get rep points from me.

Rick W.

bntii

11-14-2008, 09:23 PM

#1 is .67m/s to the right
#2 is 6m/s to the right

front of the class or the dunce cap?
:)

Edit----- assuming belts as pictured... gears will of course reverse the direction of movement.

Boston

11-14-2008, 09:31 PM

Boston

11-14-2008, 09:46 PM

Appaloosa Grill, 535 16th St. Denver • 720-932-1700
owners name is John
just tell em Ill be in tomorrow happy hour
almost seems unfair to get three beers for that
Denver Pale Ail
in case you forgot

soooo
why dont you now work out the energy in foot pounds of the system if the
sliding plate weighs two pounds and the roller device weighs four
given the plate is moving at twenty miles an hour

I think you are in france so that out to keep you busy for a few
Ill knock off one beer if you come up with the right answer
oh
then tell me how much force is required by the system to illicit that twenty miles an hour given there are four wheels each with a 1.5% friction loss and two pullies each with a 1% friction loss

at which point you may get a better understanding as to what Im trying to point out here

best B

Boston

11-14-2008, 10:00 PM

http://i354.photobucket.com/albums/r420/maxtanks/statler_waldorf_02_01.jpg

my God he's an Aussie
I should have asked for more beer
oh well
you will still enjoy all the conversions
cmon
show me what you can do
I want to see you work this out

Boston

11-14-2008, 10:49 PM

mystery question
were are these two pictures taken
and what are they of

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/marstrees.jpg

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/mars_cookies_030731_04.jpg

and now for the real question
why dont you now work out the energy in foot pounds of the system if the
sliding plate weighs two pounds and the roller device weighs four
given the plate is moving at twenty miles an hour

then tell me how much force is required by the system to illicit that twenty miles an hour given there are four wheels each with a 1.5% friction loss and two pullies each with a 1% friction loss

sorry I almost forgot
the part highlighted in red needs to be in ft/lb as well so you can more easily see my next point which is going to be that the energy of the plate that weighs two pounds moving at twenty miles an hour is far less than the energy of the system as a hole at the sixty miles an hour it will end up at

soo were in the equation did you get any additional energy
you didnt
so it doesnt work
does not compute
system slows to a gradual halt over delta T having never attained it max potential
system cannot end up having more energy than it started with unless it contained stored energy in the first place or unless energy was added

if you are in australia you might want the Appaloosa's e mail address so you maybe could just send em your credit card info
that way you wont have to keep making long distance calls to buy all these beers you are going to owe me

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/stupidpictures100.jpg

and the real answer to the question originally posted about how fast the system ends up at if the plate is moving at 2m/s isnt 6m/s
its entirely dependent on the mass of the roller device and the mass of the plate such that the system at speed in a perfectly frictionless enviroment will be nothing more than a relationship between its mass and the ttl foot pounds of the original energy imparted on the additional mass

Body slam
next
B

Boston

11-14-2008, 11:15 PM

bingo

on the 3;1 ratio gear it would be 6m/s except
but there is a major loss because of mass considerations
if the weight of the plate is 2k and its going 2m/s
and the weight of the roller is 2k and its going om/s
then the top speed of this system in a frictionless environment is
given its energy
drum role kids
1m/s
or fifty percent of the original
doesn't mater what the gear ratio's are
although you will lose more to torque effort in the 3:1 system than you will in the 1:3 system

TheUnlogicalOne

11-14-2008, 11:56 PM

Joakim

11-15-2008, 06:23 AM

Can Ricks question really be this difficult? TheUnLogicalOne is quite close already, but even his solving has sign problems. Remember that gearing can have a sign (lower and upper wheels spin in opposite directions) as well as velocity. Try also gearings 1.1:1 and 0.9:1 we will see how Boston reacts to those. What happens at 1:1 gearing?

Boston

How can you think something that is frequently done in ice sailing perpetual motion? They reach the leeward mark much faster than air molecules they "met" at the windward mark. They don't sail dead downwind, but they could tow a sledge that would go dead downwind faster than wind. The rotary motion of the propeller/turbine solves the problems that makes jibing necessary for conventional sail vessels.

Why would someone bother to make scientific tests and publications on something that is obvious to the science community AND has no commercial possibilities. No glory or money to be expected.

Joakim

clmanges

11-15-2008, 10:29 AM

Video looks genuine to me, but who knows. It actually accelerates at a number of points and I've never seen a treadmill that slopes down towards the front. Its possible that the treadmill was adjusted by the camera man to achieve equilibrium.I looked at several of the videos, and in one of them, they used a carpenter's level to show that the treadmill platform was level. Then, they raised the front of the treadmill, showing the device running uphill.
All the treadmill videos are pointless, but you don't get that until #7, where they show that there is no wind blowing on the treadmill from any direction. Therefor, all the driving energy for the cart is being provided by the treadmill; if the treadmill were shut off, the cart would be deprived of input energy and come to a stop as soon as its inertia was depleted.
Therefor, the treadmill vids have nothing whatsoever to do with DDWFTTW.

More presently; I'm still working on Rick's problem.

Joakim

11-15-2008, 01:31 PM

Therefor, the treadmill vids have nothing whatsoever to do with DDWFTTW.

The wind power vehicle doesn't see any difference wether the floor (treadmill) or the wind is moving. Just fix the coordinates to the treadmill and you have downwind and the vehichle is going faster than that downwind despite upphill.

Stopping the treadmill is equal to stopping the wind. Both will obviously stop the vehicle.

Joakim

clmanges

11-15-2008, 01:45 PM

First problem: 1:3 drive

To make matters easier for me, I arbitrarily assigned a dimension to the wheels: a circumference of 2 m.

This means the upper wheel rotates at one rev/sec.
Due to the drive reduction, the lower wheel now rotates at 1/3 rev/sec

1/3 rev/sec times 2 m = 2/3 m/sec, left to right.

****************

Second problem: 3:1 drive

Again, the upper wheel turns one rev/sec.
The lower wheel turns 3 rev/sec

3 rev/sec times 2 m = 6 m/sec, again, left to right.

***************

Now, I'd like to add that there might be some confusion (or a sneaky trick) involved in the presentation of these problems. The illustration shows the gearing as if the ratio were stated as the number of teeth on each gear, which is the way I interpreted the problem in my solution. However, (especially if the detail of the chain drive had not been illustrated) the ratios could be interpreted as the number of input rotations to the number of output rotations. If that were the case, then the results would be just the opposite. I'm not familiar with the convention as to how gear ratios are commonly described, but I would tend to think of input as the first number in the ratio.

Guest625101138

11-15-2008, 04:16 PM

No rep points yet.

Joakim
I am happy to award you the rep points if you care to provide the answer as long as you show the workings so Curtis can understand.

Curtis - the ratios are taken as the chain lead indicates but if you gave the correct answers in reverse I will still give you the points.

The point of this exercise is that if you cannot understand this very simple problem you simply do not have the reasoning ability to understand DDWFTTW. If you do not understand you will only believe if you can experience it. Even if you see it in videos you will be looking for the piece of string or other trick. The solution requires no greater reasoning ability than that expected of a fifth grader.

Rick W

Boston

11-15-2008, 05:15 PM

http://www.boatdesign.net/forums/attachments/boat-design/26915d1226715246t-wind-powered-sail-less-boat-slide6.jpg

if the plate above is moving at 2m/s relative to the geared device
and the gearing is 3:1 the the geared device would be moving at 6m:s relative to ground and the plate would be moving at 8m/s relative to the ground

you are simply saying that you wanted the answer in terms of the plates speed relative to the ground
and we gave an answer that didnt meet your unspecified parameters

you wanted differentiation
we wanted beer

Boston

How can you think something that is frequently done in ice sailing perpetual motion? They reach the leeward mark much faster than air molecules they "met" at the windward mark. They don't sail dead downwind, but they could tow a sledge that would go dead downwind faster than wind. The rotary motion of the propeller/turbine solves the problems that makes jibing necessary for conventional sail vessels.

because they are tacking and were talking about a dead run
and some one said something about a turbine spinning a propeller and the system somehow changing energy flow directions which was laughable
funny thing is
you've admited they dont do it at a dead run several times now in your previous posts
and thats the point Im trying to make

if you assign a weight to the system components
and state which are at rest at time 0 then you should be able to understand that the available energy to the system is x and therefore the system as a hole cannot exceed any speed relative to x

No beer for you

Boston

11-15-2008, 05:28 PM

I noticed every one ignored my conclusion that if the mass of the system components is considered and therefore there kinetic potential then it takes no great reasoning to conclude that regardless of the gearing the ttl systems kinetic energy cannot exceed the sum of its components unless acted on by some additional force

works that same way in the water folks

show me the beef
B

Boston

11-15-2008, 06:06 PM

DDWFTTW.

thats
directly down wind faster than the wind

its what we have been talking about the hole time
and directly down wind ( a dead run )
that turbine
mounted to that boat
when they go
directly down wind
the relative wind speed reduces with the systems speed increase
there is progresively less and less energy available
and the system will eventually reach equilibrium
and that equilibrium will only be some fraction of the wind speed

thank you
( beer thirty )
did you catch the address earlier
cause Im headed down there now

clmanges

11-15-2008, 06:56 PM

Now, I'd like to add that there might be some confusion (or a sneaky trick) involved in the presentation of these problems.
Well Rick, was I right?

you are simply saying that you wanted the answer in terms of the plates speed relative to the ground
and we gave an answer that didnt meet your unspecified parameters
If this is true, then you get no rep points -- or beer.
If you're trying to teach us something, this is a really wrong way to go about it. The lesson we're learning isn't on topic yet.

Boston

11-15-2008, 10:51 PM

now I think its fare since we answered your question that you answer one of mine

why doesnt someone actually show the system they claim will go
directly down wind faster than the wind
along with an analysis of how it does it
and prove the rest of us wrong in the process

hmmmm
shouldn't be that difficult should it

if that ones to difficult maybe someone could answer this one

why is no one is willing to address the ratio of reduced energy available as a function of apparent wind vs vehicle acceleration on a dead run since that is the key issue limiting vehicle speed on a dead run

really people if you want to prove a point then simply show us all the magic machine that can accomplish the impossible
and quit with the living room tread mills and the physics 101 questions

show me the beef

were is the film of your craft going faster than the wind on a dead run
why is there no impericle data on the process being presented
why are we being shown silly irrelevant models instead of an analysis of the vehicle that will achieve this mythical accomplishment

there is ample data concerning the efficiency of down wind tacking angles
were is yours concerning dead running

once again I am not the ogre under the bridge
or the man poking needles at the kids balloons
what I am is practical
and I am not being presented practical evidence to support this claim

I will buy the first person to do so
all the beer they can drink
in a one hour period of time
at the bar of there choice
Im not offering kudo's or flowers or big sloppy kiss to whoever can show me the space ship
just a good old fashioned celebration drunk

oh
and there was no sneaky trick
or attempt at teaching
we just took the obvious solution given the lack of parameters
and frankly made the hole thing look pretty silly
( oh, I just got back from the pub )
( I asked, and no one from Sweden called in a tab for me )
( very depressing since I did get the answer given that the plates movement relative to what, was not specified )

someone is just trying to deviate from the original statement that it was possible to go directly down wind faster than the wind
which it isnt
with some irrelevant gear ratio distraction

all the irrelevant models, tread mills and we kicked its ass gearing ratios later isnt going to change anything

the ice racers go at about a 45deg angle to the wind for a reason
course no one here wants to notice that part of the process
but thats how they do it

btw
the ice yachting speed record if I remember right is about 110 or 120 or something in there, mph or maybe knots its been a while since I looked
dam fast
but not directly down wind kids
they dont even pretend to go directly down wind

they are always on a reach of some kind and always will be

love B

peace people
all in good fun
at some point we are all wrong from time to time
grace
is when you can be wrong and can admit it
its how we learn
if Im wrong
show me the system you think can accomplish direct down wind faster than the wind
if Im not
you will not be able to
I strongly suspect the next post will not include a diagram or a film of a vehicle doing so

TeddyDiver

11-16-2008, 03:50 AM

I will buy the first person to do so
all the beer they can drink
in a one hour period of time
at the bar of there choice

Sorry bro, but you think anyone is going to invest big bucks and time away from family/work/sailing just to prove you the case and earn some free beer :D

Joakim

11-16-2008, 08:26 AM

Boston

You agree that an ice racer can reach the downwind mark faster than the wind. Thus it is not perpetual motion going faster than the wind dead downwind. This physical fact does not change wether one goes directly from A to B or by jibing.

Why doesn't the sledge towed by a ice racer suffice as going dead downwind faster than wind? The sledge can be steered dead downwin and it only uses wind with a help of a ice racer. The mechanism an ice racer uses could also be build into the sledge, but very likely the ice racer would be more efficient and thus faster.

It is obvious that using a normal sail powered vessel it is impossible to go dead downwind faster than the wind, just as it is obvious that it is impossible to go dead headwind. Both can be accomplished by tacking or with a propeller turbine combination. Why do you believe in going dead headwind, but not in going dead downwind faster than the wind?

The design of a turbine propeller vessel and the physics behind it is already shown on the 3rd page of this thread. And the videos on treadmills shows that in practice for anyone having basic understanding of physics.

The gearing calculations are far from silly, since a propeller is a gear that "connects" fluid to the vessel. There can be slip (=gear ratio not constant) and efficiency is not very good, but it still is a gear.

Accelerating from zero velocity to faster than the wind dead downwind, the water turbine is turning the air propeller all the time. The handness of the air propeller is such that it would turn the wrong way, if wind would turn it. So at very low speed it doesn't turn at all and it acts as a sail. With sufficient water velocity the propeller starts to turn the turbine and nothing special happens when the wind speed is reached, just as nothing special happens when a ice racer reached wind speed as VMG.

Joakim

TeddyDiver

11-16-2008, 01:50 PM

Actually in some of the videos the air propeller did turn wrong way a bit, maybe half a turn, before the water turbine overcame, so B made a point there.
Later, after gaining some speed, it seemed like smth similar to happen, which actually is an effect of frame speed of the video camera and turbine speed..

Windmaster

11-16-2008, 01:55 PM

Here is the latest video on youtube.
It explains everything.

http://www.youtube.com:80/watch?v=_fBDcchw5nw

Let's face it, it is hardly worth arguing with "flat earthers".

What is amazing, is that some who claim to be scientifically trained, cannot grasp a simple concept of moving interfaces.

Tiny Turnip

11-16-2008, 02:21 PM

Some of the images that helped me 'get' the principle of a turbine vessel going DDWFTTW:

1. Imagine the whole vessel but with no water propeller being blown down wind, moving at, or close to the same speed as the wind, in still water. The air blades will not be rotating, or rotating very slowly, as there is little difference between vessel velocity and air velocity.
There is considerable relative difference between vessel velocity and the stationary water however.

2. then consider putting the water propeller on the end of the Shaft. The 'considerable' velocity of the stationary water relative to the vessel will spin the water prop, and drive the Air blades. The air blades will spin, clawing their way forward through the air which is relatively stationary with respect to the vessel, and thus pull the vessel forward faster than the wind.

3. Of course there are many complex losses in the system, and my rusty physics prevents me from readily tacKling the detail, but the fact that energy is lost *does not matter* to the *principle*, it just affects the efficiency.

The vessel is a machine allowing work to be applied in a different way. The gears on a bicycle allow us to apply the work we do pedalling to go much faster, further than we can walking, or even pedalling round a wheel of the same diameter as the pedal cranks, like a stunted penny farthing. (high wheeler?) The bicycle can do this *even *though *the *gearing *means *additional *energy *losses *in *the system*.
(I'm sure the losses in the bicycle system are small compared with the turbine vessel, but the principle remains)

Guest625101138

11-16-2008, 04:02 PM

Day two and still no rep points awarded.

Once again I will post the question sheets.

As is convention, velocity provided is with reference to the fixed ground surface and the answer has to be given with respect to the ground reference.

Happy to have anyone provide the correct answers. First correct answers get rep points.

Rick W

Guillermo

11-16-2008, 04:06 PM

No sailboat can travel faster than the wind if going dead-downwind. No windmill can either sail faster than the wind, be it moving a prop, wheel or whatever. That's a fake.

The amount of power transferred to a wind turbine is directly proportional to the area swept out by the rotor, to the density of the air, and the cube of the wind speed.

The power P in the wind is given by:

P = 1/2 π α ρ r^2 v^2

where P = power in watts., α = an efficiency factor determined by the design of the turbine, ρ = mass density of air in kilograms per cubic meter, r = radius of the wind turbine in meters, and v = velocity of the air in meters per second.

As the wind turbine extracts energy from the air flow, the air is slowed down which causes it to spread out. Albert Betz, a German physicist, determined in 1919 that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section, that is α can never be higher than 0.59 in the above equation. The Betz limit applies regardless of the design of the turbine.

This equation shows the effects of the mass rate of flow of air traveling through the turbine, and the energy of each unit mass of air flow caused by its velocity. As an example, on a cool 15 °C (59 °F) day at sea level, air density is 1.225 kilograms per cubic metre. An 8 m/s (28.8 km/h or 18 mi/h) breeze blowing through a 100 meter diameter rotor would move almost 77,000 kilograms of air per second through the swept area. The total power of the example breeze through a 100 meter diameter rotor would be about 2.5 megawatts. Betz' law states that no more than 1.5 megawatts could be extracted.

Cheers

Joakim

11-16-2008, 04:55 PM

No sailboat can travel faster than the wind if going dead-downwind. No windmill can either sail faster than the wind, be it moving a prop, wheel or whatever. That's a fake.

You should have read page #3! I'm sure you know enough physics to understand this. It's not a windmill, it's an air propeller.

Use your equation for the water turbine to calculate how much power is available there and then calculate how much is needed for the air propeller.

Joakim

Guest625101138

11-16-2008, 05:01 PM

No windmill can either sail faster than the wind, be it moving a prop, wheel or whatever.

Cheers

Guillermo
You are correct with the above statement. But this is not what we are debating.

We have a WATER TURBINE extracting power from the water and delivering it to the AIR PROPELLER producing thrust.

If you have a go at answering the questions I have posed in post #110 above you will likely gain the necessary understanding to realise that sailing DDWFTTW is indeed possible and those various land vehicles are no trick.

You will do yourself a disservice if you do not try to understand what is going on. It simply requires an open mind and some reasoning power, roughly that of a fifth grader.

Rick W

Guillermo

11-16-2008, 05:17 PM

As an example a boat travels 5 m/s in 4 m/s downwind. Now the propeller sees 5 m/s water speed Vp and the turbine sees 1 m/s apparent wind Vt. Without losses thus:

Pt=Pp => Ft * Vt = Fp * Vp => Ft = Fp * Vp / Vt => Ft = 5 * Fp

Thus theoratically we can have 5 times more thrust with the turbine than we have drag by the propeller. The propeller is taking power "out of water" and the turbine is pushing with that power.
That makes no sense to me. You're asuming a boat is sailing faster downwind than the wind to demonstrate it can sail faster downwind than the wind. That's circular. And you're saying it's possible to extract energy from nothing. The only physics where it's possible to extract energy from nothing is on quantum mechanics, not in everydays life.

The cart thing, which video I posted (as well as several others) before, is neatly a fake. Bringing its reasoning to the extreme it is like saying that if in absence of wind we push the cart fast enough it will create its own wind and run forever. If that's not perpetual movement, let God come here and see it. I'm with Boston in this one.

Cheers.

Guillermo

11-16-2008, 05:19 PM

You will do yourself a disservice if you do not try to understand what is going on. It simply requires an open mind and some reasoning power, roughly that of a fifth grader.
Unluckily I'm not a fifth grader but a humble Naval Architect.
Let me ask you: Could it be possible you're doing a disservice to yourself?

Cheers.

Guest625101138

11-16-2008, 05:33 PM

Unluckily I'm not a fifth grader but a humble Naval Architect.
Let me ask you: Could it be possible you're doing a disservice to yourself?

Cheers.

Guillermo
No. I have taken the time to understand it.

The original demonstration was done by Mr Goodman as Windmaster has pointed out. There are published papers on his work. I applaud his efforts to demonstrate it and it is encouging to see others making similar vehicles. It is only a matter of time befor it is demonstrated on the water if it has not already been done. It is not that hard to do. There is no magic. There is no need for perpetual motion.

I have posed a very simple problem that will help you understand what is going on. If you cannot work out the answers then find a fifth grader and ask them to give it a go. Someone with an open mind and not prejudiced about what is and is not possible.

Rick W

philSweet

11-16-2008, 06:15 PM

Rick.

case 1. yes, to the right, at 0.5m/s
case 2 yes, to the right, at 1.5 m/s

Guillermo

11-16-2008, 06:36 PM

I have taken the time to understand it.
OK. Let's see how your fifth grade mind works. Could you please set out the energy balance of the system for me to understand? Perhaps I'm missing something.

Cheers.

philSweet

11-16-2008, 06:39 PM

Rick,
first post requested workings.

case 1 (2m/s -v) = 1/3v
case 2 (2m/s -v) = 3v

sorry for the distraction, I caught the second post and have just caught up with the discussion from the first one.

Jim_Hbar

11-16-2008, 09:21 PM

Phil:

I agree with your first post, where;

case 1. yes, to the right, at 0.5m/s
case 2 yes, to the right, at 1.5 m/s

But in the follow up post,
case 1 (2m/s -v) = 1/3v
case 2 (2m/s -v) = 3v
I believe you have inadvertently reversed your equations.

My explanation -

Consider the "buggy" as a free body - If the input velocity is called Vin, and the output velocity Vout, and the ratio of Vin/Vout = N

One can write the following equations:
Vin + Vout = 2m/s
Vin = N x Vout

Substituting Vin results in (1+N)Vout = 2 m/s

Now, in Case 1, N = 3 and in Case 2, N= 1/3

So, Case 1, 4Vout = 2 m/s or Vout = .5 m/s

and case 2, 4/3Vout =2 m/s or Vout = 1.5 m/s

BTW Vout = the speed of the buggy

This whole discussion reminds me of the high-school science experiment, where one pulls on the thread wrapped around a spool... And most do not understand when the spool wraps up the thread, and moves faster than the thread is pulled..

philSweet

11-16-2008, 10:03 PM

Good grief! My equasions are reversed.

masalai

11-16-2008, 10:29 PM

Joakim

11-17-2008, 02:40 AM

That makes no sense to me. You're asuming a boat is sailing faster downwind than the wind to demonstrate it can sail faster downwind than the wind. That's circular. And you're saying it's possible to extract energy from nothing. The only physics where it's possible to extract energy from nothing is on quantum mechanics, not in everydays life.

The cart thing, which video I posted (as well as several others) before, is neatly a fake. Bringing its reasoning to the extreme it is like saying that if in absence of wind we push the cart fast enough it will create its own wind and run forever. If that's not perpetual movement, let God come here and see it. I'm with Boston in this one.

Sad to read this, since I have read your many posts with good respect and really should be understandable for a NA. I hope you can open your mind and think beyond limitations of a sail.

I didn't assume the vessel was going faster than the wind, I just calculated the force balance in that situation and it clearly shows that having clearly more thrust than drag is possible, thus it would be easy to maintain such a speed. Now you can calculate some intermediate situations you think are uncrossable.

You really don't seem to understand the cart thing. It gets it's driving force from the velocity difference of the treadmill and air. It will not work without that velocity difference just as no sailing vessel will move through water in any direction without a velocity difference between air and water.

Can you have a velocity through water if the geographic wind velocity is zero but there is a 5 kn current? Is it different from sailing in 5 kn wind without current? Will you notice any difference in your instruments or sailing performance (except GPS)? Compare this to treadmill.

Joakim

Guest625101138

11-17-2008, 04:24 AM

Phil and Jim
I am not awarding half points. You have to have both answers correct in terms of direction and velocity. Hint - it is possible for the vehicle to travel in the opposite direction to the direction of the sliding plate.

It is good to see someone actually putting their mind to it. I appreciate your effort and with a bit more thinking you should get it. I am certain if you understand this simple problem you have the keys to work out sailing directly into the wind and faster than the wind down wind.

Joakim - offer still open to you. At least there are some actually using their reasoning ability.

Rick W

Joakim

11-17-2008, 06:06 AM

Joakim - offer still open to you. At least there are some actually using their reasoning ability.

I don't want to spoil others change for thinking. I already asked for the equation in post #64 and prior to asking did the simple maths.

Joakim

philSweet

11-17-2008, 09:15 AM

The device as drawn cannot travel in the direction opposite to the plate.

by inspection-

1. for buggy velocity < 2, upper idler must turn cw
2. v > 2, upper idler must turn ccw
3. v < 0, lower idler must turn ccw
4. v > 0, lower idler must turn cw

as drawn, upper idler and lower idler must both either travel cw or both ccw. Thus only 0 < v < 2 are feasible (case 1 and 4 satisified) cases 2 and three cannot both be satisified.

clmanges

11-17-2008, 09:42 AM

Case 1:
Plate moves 2 m/sec relative to cart
Cart moves 2/3 m/sec relative to ground
Plate moves 2 2/3 m/sec relative to ground, from left to right

Case 2:
Plate moves 2 m/sec relative to cart
Cart moves 6 m/sec relative to ground
Plate moves 4 m/sec relative to ground, from right to left, since cart is outrunning plate by the difference of the two speeds.

There, is that better?
You should have stated the question properly to begin with.

philSweet

11-17-2008, 10:16 AM

clmanges, no, it is not better. regarding your case two, apply the logic from my preceding post.

if plate is moving from right to left at four m/s and cart is moving at six m/s (right to left implied), then upper idler is going cw and the lower one ccw. the device is not shown this way, thus, regardless of whether the 2 m/s is taken to be relativ to the cart or the ground, your case two is not correct.

Tiny Turnip

11-17-2008, 10:54 AM

Rick states that the plate velocity is 2m/s relative to the ground, not the trolley.

I am finding this one very difficult to grasp, and have been giving it a lot of careful, step by step thought. In both Rick's pictures, I find the top left wheel wanting to rotate at a rotational (angular?? rusty physics again) velocity different that is from that of the plate when is in contact with it, and and so I get concerned about the nature of the interface between plate and wheel - slippery, or high friction/mechanical?

In Rick's case 2, if you follow the gearing round, the trolley wants to scoot to the right at 6m/s, but this would mean top left wheel rotating anti clockwise.If it is driven by the plate, we already know it is rotating clockwise at 2m/s angular/rotational velocity. So I don't think it goes anywhere, and probably doesn't drive, whether it is a high or low friction interface. Or, does it resolve into 2m/s to the right?

Jim, you state that in your analysis, the output velocity is the buggy velocity. Could you enlarge on what you mean/take by input velocity please?

as Vin + Vout = 2m/s, then you are not referring to the plate velocity as the input velocity?

Joakim's illustration in post#64 I understand very readily.

The velocity of Joakim's cart seems to me would vary depending on the relative positions of cart, ground and 'wind'.

Tcubed

11-17-2008, 11:39 AM

Solving for no slip both top and bottom-

In the first case;

V=2-3v

Thus v=0.5

In the second case;

V=2-v/3

so v=1.5

Where v is M/s to the right relative to stationary plane

Now let me see what happens if the belt is twisted so the wheels turn in opposite directions....

Tcubed

11-17-2008, 11:55 AM

Tiny Turnip

11-17-2008, 12:11 PM

much happier now. Thankyou

Joakim, Unlogical, Phil, Jim and Tcubed. and of course Rick.

just frustrated that I am quite comfortable intuitively with the DWFTTW turbine, and I'm now happily following the maths that you gentlemen have put together (the fact that a twisted chain can be expressed with as a -ve ratio is a big help) but unless the chain is twisted I'm stumped.

clmanges

11-17-2008, 12:36 PM

!@#$%^&*()_+

You should have stated the question properly to begin with.Yeah, and I should have read it properly . . .

Joakim

11-17-2008, 03:15 PM

And the easy formula for the velocity respective to ground is:

V = W / (1 + G),

Where V is the velocity, W is the wind and G is the gearing ratio. Depending how G is defined it could also be -G, 1/G or -1/G.

Now you can see, that with postive G you can not go faster than the wind downwind and also not at all to headwind. This is the normal "sailing region" where your speed comes from drag ratios when going dead downwind.

With negative G these limitations are removed and you can reach any speed by choosing G close to -1. Higher speeds require very good efficiencies, which sets limits to the speed of a propeller turbine system.

For propeller/turbine negative G means, that the propeller and the turbine have same handness and rotate to same direction. In dead downwind situation this means that both would "try to go forward".

I think Ricks rep points should go to TheUnlogicalOne, since in his post #94 he actually has it right. I didn't check the belt/chain causing the wrong sign for gearing and was only expecting the -1 and +3 m/s answers, which are more relevant for this discussion.

Joakim

Boston

11-17-2008, 04:46 PM

so I left this alone for a few days to see what would shake loose
hoping to hear how folks would answer the questions I proposed
and not one true believer stepped up to the plate

I must admit I was looking forward to reading how the problem of reduced energy in, results in increased energy out
no mater what the system or gearing involved

I may have missed a post so Ill look again but I didnt notice anyone addressing the previously suggested problems with the hole perpetual motion theory

address the ratio of reduced energy available as a function of apparent wind vs vehicle acceleration on a dead run since that is the key issue limiting vehicle speed on a dead run

actually I think Teddy sorta did
but it was the same kind of smart ass answer I would have given
so it only sorta counts

if he sends me an address Ill buy him half a pint for being the only one to even make a pretense at the real issue behind why this doesnt work

Joakim's questions though had a lot of validity so I think it deserves a mention

You agree that an ice racer can reach the downwind mark faster than the wind. Thus it is not perpetual motion going faster than the wind dead downwind. This physical fact does not change wether one goes directly from A to B or by jibing.

actually there is a huge difference between tacking, running on a reach
and running directly down wind

tacking you have the alterations in the apparent wind
and the addition of centripetal forces

on a reach you have the difference in relative wind and actual wind

on a dead run
you got nothin
but the actual wind speed and a hole lot of friction

yes an ice racer can go faster than the wind powering it
but not directly down wind
do they hit the down wind mark faster than the wind itself ?
Ive never really looked into it
given that they are on such a high angle of attack
Ild have to have a diagram of there course relative to wind, wind speed and there course time and distance
Im betting it's possible, given how insanely fast those things are
but to be fair you would have to extrapolate the course as the hypotenuse of a right triangle and the wind as side "a"
if you consider the vehicle is on a 45deg angle to the wind just for the sake of argument
the vehicle would have to travel at 1.41x the speed of the wind, to hit the mark directly down wind from the start, on its 45deg course, at the same time as the wind

but the reason for this is the apparent wind is not o when the vehicle hits actual wind speed
therefor there is energy still available to offset the system friction
high school physics folks
( lets see who is first to mention my high school grammar )

course we can hoist a few anyway
but your going to have to do a lot better than the tread mill trick before Im buying

I saw some great stuff in here
but not one person could post a flicker of the mythical monster
not a shred of evidence, mathematical or actual presented
just an insistence that it works

oh and the tread mill thingy was not level
if you look at the bubble of the level they placed on the frame

nor is there any accredited independent support of the rubber band cart
no wind speed data
no cart speed data
pretty much proves that the wind can blow beach ball into the surf
and why didnt they show the road ahead of the thing at any time during the flick
hmmmmmmm

its really basic
energy out, cannot exceed energy in, minus friction

friction being the key word
if you can show that friction can be reduced to a negative on both sides of the equation at some tipping point of dynamic instability over delta t
then you got me
I was wrong
but the problems presented so far dont even come close to doing so

oh and the ice racers are definitely, not going "directly down wind"
and this hole thing is about "directly down wind"

also there is a lot to be said about powering the wheels to turn the turbine and the gear ratio's involved verses powering the turbine and turning the wheels
after all
if you take a mechanically advantaged system and run it in reverse
dont you get mechanical disadvantage ?

as for flat earthers
can anyone tell me were these pictures are taken
and what they are of
as if that isnt enough of a hint

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/marstrees.jpghttp://i29.photobucket.com/albums/c262/bostonpyramidbuilder/mars_cookies_030731_04.jpg

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/marsfor3.jpg

Guest625101138

11-17-2008, 05:40 PM

If the machine is geared such that the wheels turn in opposite directions, then with the gear ratio of the first example

we have v=2+3v

so v=-1 (this is the case of the boat sailing straight upwind, as in going at one meter per second in the direction opposite the top plate)

and with the second gear ratio

we have v=2+v/3

so v=3 (and this would represent the boat sailing downwind faster than the wind, it is going one meter per second faster than the plate)

With all due respect Rick, didn't you mean to demonstrate how this models the turbine boat's behaviour? So did you not originally mean for the wheels to turn opposite each other?

Tcubed
You even anticipated what I should have posted. You will find your rep has gained.

I have attached solutions for all four cases. To hopefully make it easier for some to understand I have introduced the wheel rpm but it is eventually substituted.

So I will need to back track and see if some of the earlier posters gave the correct answers to my forward geared problem and award points retrospectively. (Hopefully my 5th grade teacher would have forgiven me for having a sign incorrect.)

The point of this exercise is that the vehicle can travel in the opposite direction to the plate and also move faster than the plate in the same direction.

I will post the next stage of the problem shortly.

Rick W

Tcubed

11-17-2008, 06:16 PM

Thanks Rick.

Boston, i'm starting to think either 1; if you laid off the beer awhile your mind might clear up a little bit and you could understand, or 2; you do actually understand and like to wind people up.

It is true that in a turbine boat, if the air prop is turning the water prop then it cannot go faster than the wind downwind. However, if the water prop is turning the air prop then the boat can go faster than the wind downwind.

You seem to understand that a sailyacht tacking downwind can have a VMG dead to leeward faster than the wind. You correctly point out that the ice boat at 135 degrees to the true wind needs to go 1.4142 times the real wind (cos45=sqrt2) , ice boats have been known to reach V/W of close to three, making for near twice the speed of the wind downwind..

In a turbine boat, only the boat itself is going straight downwind, all the dynamically active parts are moving at angles to the real wind just like the boat tacking downwind (or upwind)

Guillermo, The energy available is a function of the relative velocities of the two fluid mediums. The energy lost is a function of the aero/hydrodynamic functioning of the boat (+ a bit of mechanical losses in the case of the turbine boat) . There is nothing in the energy equations that categorically limits boat speed at any angle to always be less than the real wind velocity-or more accurately the velocity differences between the two fluids.

Boston, your ambiguous images are intriguing, they could be some aerial shots of some kind...I'm trying to see what if any connection there might be with this thread.

Guest625101138

11-17-2008, 06:19 PM

Curtis
Do you agree with what Tcubed provided and my more detailed solutions?

We need to move on now to introduce some real world losses in the system. Can you answer the attached question?

Rick W

Guest625101138

11-17-2008, 06:37 PM

Lost my first post, and I can't be bothered to make this one as nice as the first.

1:3 gearing gives 0.5 m/s
3:1 gearing gives 1.5 m/s

Used the cart as a frame of reference, meant that the total velocity of the top/bottom of the wheels was 2m/s.

so V(lower)+V(upper)=2m/s

1:3 => V(lower)=1/3*V(upper)

substituting => V(lower) + 3*V(lower)=2m/s
V(lower)=0.5m/s
This means the cart (over glorified ball bearing) moves at 0.5 m/s relative to the ground.

3:1 => Just substitute V(lower)=3*V(upper) instead.

Video looks genuine to me, but who knows. It actually accelerates at a number of points and I've never seen a treadmill that slopes down towards the front. Its possible that the treadmill was adjusted by the camera man to achieve equilibrium.

TheUnlogicalOne
You will find your rep enhanced. I believe you were the first to provide the correct answer to the original questions. My apologies for not recognising it sooner.

It was not until Tcubed posted that I realised I needed the gearing reversed in my DDWFTTW analogy. My excuse is that I was thinking of the boat situation where there is no need to reverse gear unless the pitches are reversed and I was looking for -1 and 3.

By all means have a go at the next stage of the problem. Hopefully by working through this logically more will understand it is not witchcraft, a trick or perpetual motion but very simple physics.

Rick W

Tiny Turnip

11-17-2008, 06:45 PM

go on then- starter for ten.
if vehicle velocity is constant, no +/- acceleration, system is in equilibrium.
input force = total system losses, i.e. 6n.

pictures are Microscopic: mould/fungi, spores, eggs, possibly.

Guest625101138

11-17-2008, 06:54 PM

I do not have much knowledge on how rep points work but I will continue to award to correct answers as long as I have them available.

I do not think I will be able to award Tcubed or TheUnligicalOne until I have awarded others. If you do feel inclined to answer, wait a day or so until others have had a go at the next step of the problem.

I really appreciate your contribution as it helps others realise that those who can think logically have little difficulty understanding that sailing DDWFTTW is possible.

Rick W

clmanges

11-17-2008, 07:17 PM

Curtis
Do you agree with what Tcubed provided and my more detailed solutions?

We need to move on now to introduce some real world losses in the system. Can you answer the attached question?

Rick W

Yes; the solution was tying me in knots though (about 35 knots DDW, to be specific).

I'd like to make clear here that I never doubted that DDWFTTW could be done; I just wasn't able to untangle the knot of how.

Also -- and I haven't seen anyone else mention this -- that, if you can go DDWFTTW, you can also go directly upwind, because, once you are doing the first, you're already doing the second. Exceeding the tailwind automatically puts you into a headwind condition.

On to the next thing.

Tcubed

11-17-2008, 07:31 PM

Wait a couple of days for rep? um if you feel like i deserve them you can always give em in a couple of days......

The reaction force of the top tyre against the ceiling is three times greater than the reaction force of the bottom tyre against the floor due to the gearing.

Call it f So 3f-f = 6N

Therefore f = 3 N

So the force required to move the top plate is 9 N and the reaction force on the floor is -3 N .

9-3 = 6 so we have equilibrium.

I assumed the drag force to be acting independently of either plate.

masalai

11-17-2008, 08:04 PM

Not meaning to interrupt but this may help http://www.boatdesign.net/forums/forum-questions-suggestions/forum-rules-code-conduct-11083-14.html post 205....
It's currently set for:

* User Spread: (How many different users must you give reputation to before you can hit the same person again?) 25
(there was a fear early on that the user reputation system would create a problem of cliques so this number was set fairly high to prevent this)
* Daily Reputation Clicks Limit: 10
*
* Minimum Post Count: (How many posts must a user have before his reputation hits count on others?) 50
(so new users to the forum can basically send you a note of approval or disapproval (over 5 posts needed for any negative) but only members with at least 50 posts will affect your numerical reputation number at all.)

Guest625101138

11-17-2008, 08:34 PM

Yes; the solution was tying me in knots though (about 35 knots DDW, to be specific).

I'd like to make clear here that I never doubted that DDWFTTW could be done; I just wasn't able to untangle the knot of how.

Also -- and I haven't seen anyone else mention this -- that, if you can go DDWFTTW, you can also go directly upwind, because, once you are doing the first, you're already doing the second. Exceeding the tailwind automatically puts you into a headwind condition.

On to the next thing.

Curtis
I know you have believed in the concept but there is a difference between seeing and believing and truly understanding. Hopefully by working through this logically will actually help you understand what is going on.

So we are agreed that the vehicle can do 3m/s when the plate is only doing 2m/s! With the help of others we have finally got agreement on that even with my confusing the whole story with gear reversal.

We already have two answers to the next part of the problem. They are different. Is either TT or Tcubed correct?

We will move on once you have understood this part.

Rick W

clmanges

11-17-2008, 09:54 PM

Okay, I agree with TT's statement:
if vehicle velocity is constant, no +/- acceleration, system is in equilibrium.
input force = total system losses, i.e. 6n.
From there, I get lost. You know how things look smaller as you get farther away from them? Well, it's been over 35 years since I've done more than a few minutes at a time worth of math or physics . . . so, to your post #138, I meant to say, yes, I agree, but no, I can't answer the next question.
Maybe it would be better for everyone else if I just step aside and watch for a while . . . just be thorough in showing your work, and maybe I'll catch up. (Creak, creak . . .)
Your show, you call it.

Tcubed

11-17-2008, 10:21 PM

I should probably clarify slightly about the signs in my last post. The top wheel is rotating ccw and exerting 9 N force to the left, which must therefore be countered by maintaining 9 N force to the right in the top plate.

The bottom wheel is being turned by the ground cw with 3 N force

Furthermore, energy analysis; work done by motion of machine 6*3=18 NM/s = 9*2=18 NM/s by moving plate. The bottom plate is not moving so it is not 'working'.

Guest625101138

11-18-2008, 12:36 AM

Curtis
I have attached the answer sheet to the force question.

You will see that Tcubed has it right.

The sheet also has the next question which Tcubed has already anticipated.

Each of these little steps is intended to take you through the logic. Not much point though if you are not following it.

Rick W

Boston

11-18-2008, 12:55 AM

Boston, i'm starting to think either 1; if you laid off the beer awhile your mind might clear up a little bit and you could understand, or 2; you do actually understand and like to wind people up.

lmao
thats great
there is a light
as for beer
if Magueijo can work out variable light speed theory on a cocktail napkin
three sheets to the wind on a night out with a few friends in the local pub
( oh it took him years to work out all the kinks but the basic idea he got while face down on the bar, not bad since it solves the need for the cosmological constant in the field equations )
then I think I can ride this wind thing till anyone actually breaks down and mathematically explains the tread mill
( which is the only tangible albeit tentative piece of evidence Ive seen yet )

I havnt tried to work it out yet but the basic formula should be easy for the tread mill trick
I hate playing my own devils advocate
its like debating both sides of a loosing argument

It is true that in a turbine boat, if the air prop is turning the water prop then it cannot go faster than the wind downwind.

bingo
my point exactly
we are talking wind powered not water powered aren't we

However, if the water prop is turning the air prop then the boat can go faster than the wind downwind.

of course it can
if the water is already moving faster than the wind and in something like the same direction
in which case you might as well float a balloon down a river in a dead calm

and wouldn't that be a water powered craft going faster than the wind
what about hydrothermal powered
can we shoot a lab rat out of old faithfull faster than the wind
course you can
but thats not wind powered

You seem to understand that a land yacht tacking downwind can have a VMG dead to leeward faster than the wind. You correctly point out that the ice boat at 135 degrees to the true wind needs to go 1.4142 times the real wind (cos45=sqrt2) , ice boats have been known to reach V/W of close to three, making for near twice the speed of the wind downwind..

but we are talking a wind powered vehicle going directly down wind

In a turbine boat, only the boat itself is going straight downwind, all the dynamically active parts are moving at angles to the actual wind just like the boat tacking downwind (or upwind)

yes if the boat is traveling at some angle to the wind
then the turban will power the boat
not very efficiently
but it will
but set it on a dead run course and
the turban on the boat is going to realize the same apparent wind reduction relative to down wind speed that no one is willing to address yet

a platform traveling directly down wind
with a device (wind turban) mounted on the platform angled to the wind
will realize the same reduction of apparent wind relative to speed
as the platform itself
therefor the directly down wind traveling oscillating turban
wont work
you dont have the energy available to flap your arms fast enough

if you are draggin a sled behind the ice boat
and Swedish rowing the ice boat ahead of it
then yup
the sled may end up faster than the wind
( I can hear people gasping now )
but
your engine didnt meet the parameters
the question is
can a wind powered vehicle traveling directly down wind go faster than the wind
and the engine isnt going directly down wind if its rowing away out front somewhere
so that model doesnt meet the criteria of directly down wind

if anyone wants to break parameters
and now say that a lead ball can be dragged down wind faster than the wind by a wind powered engine going at some angle to the wind
then I hang my head in shame
but if we stick with the original of
direct down wind faster than the wind, wind powered craft
then Im still holding my breath

Guillermo, The energy available is a function of the relative velocities of the two fluid mediums. The energy lost is a function of the aero/hydrodynamic functioning of the boat (+ a bit of mechanical losses in the case of the turbine boat) . There is nothing in the energy equations that categorically limits boat speed at any angle to always be less than the real wind velocity-or more accurately the velocity differences between the two fluids.

I couldnt agree more
( but dont tell anybody )
glad we could find some common ground

however if I might add
and Im totally giving it away here
the energy available at the transition to faster than wind speeds will no longer be significantly dependent on the variation of the mediums relative velocities to one another but as a function of the friction variations of the systems driving components relative to the mediums upon who's friction those driving mechanisms are dependent
given that at some point in order to pass this test the relative wind velocity must pass through zero
I believe the system will find stability if going directly down wind before crossing the light speed barrier because the amount of energy available to the system is directly proportional to the variation in either mediums relative speed to the system
not relative to one another
and since water is significantly more dense than air
it will win in a friction contest any day

happy thought kids

Boston, your ambiguous images are intriguing, they could be some aerial shots of some kind...I'm trying to see what if any connection there might be with this thread.

just tell me what you think the pictures look like
and no its not that relevant
but you will be dam surprised

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/marstrees.jpg

Boston

11-18-2008, 01:05 AM

turban ?
given my goofy sense of humor
you guys are sure being quiet about my grammar skills

Tcubed

11-18-2008, 06:24 AM

and Im totally giving it away here
the energy available at the transition to faster than wind speeds will no longer be significantly dependent on the variation of the mediums relative velocities to one another but as a function of the friction variations of the systems driving components relative to the mediums upon who's friction those driving mechanisms are dependent
given that at some point in order to pass this test the relative wind velocity must pass through zero
I believe the system will find stability if going directly down wind before crossing the light speed barrier because the amount of energy available to the system is directly proportional to the variation in either mediums relative speed to the system
not relative to one another
and since water is significantly more dense than air
it will win in a friction contest any day

There's no point arguing with Mathematics, so i'm anxiously waiting for the mathematical analysis backing your flowery language.

The thing with saying wind powered or water powered is actually a bit misleading- it's just a way of trying to help the mind over some counter intuitive parts of the problem.

The ice boat is moving due to the balance of forces between sails and skates, so it is no more wind powered than it is ice powered. It needs both and relative movement between both to work. Another similar example is a glider ; is gravity or wind powering it? Again both are needed. With a sailboat too, is it sail or keel powered, again it is the resultant vector forces of the two combined which create forward acceleration until reaching speeds at which (due to increasing resistance and drag) the vectors balance each other out and no further acceleration is realised i.e. constant speed. Where it not for the buildup of resistance a sailboat would accelerate indefinitely.

The images are (my new best guess) rot starting in wood and spores.

philSweet

11-18-2008, 11:37 AM

Boston,

Regarding turban powered boats. I'd just like to mention that you can extract more power from a moving flow using a turban at the surface than you can using a turbine in free flow (far from surface). The latter runs afowl of the Bentz Limit introduced by Guillermo earlier in this thread. The former does not! The Bentz limit defines the best you can do in a WORST CASE senario. A futher pleasant confusion?

Boston

11-18-2008, 12:50 PM

Regarding turban powered boats. I'd just like to mention that you can extract more power from a moving flow using a turban at the surface than you can using a turbine in free flow (far from surface). The latter runs afowl of the Bentz Limit introduced by Guillermo earlier in this thread. The former does not! The Bentz limit defines the best you can do in a WORST CASE senario. A futher pleasant confusion?

MR Sweet
it makes sense
a submarine encounters the most resistance at something like one half its diameter bellow the surface
( something like, its been about thirty years since I was in a fluid dynamics class )
so its more efficient to travel either breaking water or at depth
and so the area of greatest drag for any submerged object is a function of its depth
basic physics 101 again

Boston

11-18-2008, 01:36 PM

Where it not for the buildup of resistance a sailboat would accelerate indefinitely.

Mr T

and so the fundamental error in theory that is perpetual motion

in any environment frictionless or not there is a fixed amount of available
energy and so the ability to accelerate indefinitely is never a possibility

no system is 100% efficient and so it is not possible to even reach the equivalent of actual wind speed on a dead down wind course let alone exceed it in a wind powered craft

There's no point arguing with Mathematics, so i'm anxiously waiting for the mathematical analysis backing your flowery language.

I just think the burden of proof is on the true believers
Im the skeptic here
so Ill wait this thing out and see if any one can explain the rubber band fan

but I will throw a believer a bone and say
the drag of the wheels
the air resistance of the prop and all the friction in between
must be exceeded by the alteration in air pressure required to move the toy forward

four relatively simple components of the magic equation

Guest625101138

11-18-2008, 06:07 PM

......
the drag of the wheels
the air resistance of the prop and all the friction in between
must be exceeded by the alteration in air pressure required to move the toy forward

.

Boston
This is the first time you have demonstrated any propensity to actually think about the problem rather than offering drivel.

There is a huge air propeller that would move almost at the speed of the wind if it was not turning. This would also move the boat through the water close to windspeed. This is easy to understand. The boat moves a little slower than the wind but is moving almost at wind speed through the water. So we could be 90% of the way there without any clever bits.

We are simply adding a small turbine that extracts a little extra power from the water to advance the prop forward through the airstream. The propeller offers the advantage over a sail here because the force on the sail drops to zero when boatspeed matches the airspeed. The propeller can continue to provide thrust while moving forward through the air - nothing new there. That is what propellers do.

The challenge is to add power to the propeller so it will spin forward to maintain thrust in the airstream.

Because the air is already moving relative to water the speed through the water is faster than the speed through the air. This means the force required to generate the required power from the turbine is considerably less than the thrust from the propeller. This extra thrust is required to keep the boat going.

In simple terms that you might comprehend:
For the air propeller:
Prop Power = BIG FORCE x small velocity
For the water turbine:
Turbine Power = little force x BIG VELOCITY

The pressure difference to create this propeller force is not much because we are talking about a huge propeller. In the original example I gave for a single person boat I needed an 8m diameter propeller to generate the required force. But it is spinning quite slowly because it only has to move slightly faster than the air to achieve DDWFTTW.

You will notice with the various land vehicle domonstrations that they have quite large propellers for the size of the vehicle. The proportion of the air propeller would be even greater for a boat that actually works.

The key aspects are that the propeller enables us to generate large thrust force while advancing slowly through the airstream. That thrust is much greater than the force acting on a turbine in the water to spin the propeller because the turbine is advancing through the water much faster than the prop is advancing through the air.

Rick W

Boston

11-18-2008, 10:36 PM

rather than offering drivel.

if drivel is arguing the impossibility of perpetual motion
then drivel it is

and speaking of drivel

There is a huge air propeller that would move almost at the speed of the wind if it was not turning.

if the propeller was not turning
how can it almost go the speed of the wind

just a question kids
course a few simple questions got Socrates dead if I remember my history

The challenge is to add power to the propeller so it will spin forward to maintain thrust in the airstream.

the basic problem of all over unity devices
how to blink and derive the extra power

the propeller you are so attached to is in equilibrium or decelerating the instant it hit a relative wind speed proportional to its drag coefficient
soooooo
whats making anything accelerate if the system is in neutral or deceleration
and you didnt mention anything about a slipping differential yet

In simple terms that you might comprehend:
I would again refer you to the following

the energy available at the transition to faster than wind speeds will no longer be significantly dependent on the variation of the mediums relative velocities to one another but as a function of the friction variations of the systems driving components relative to the mediums upon who's friction those driving mechanisms are dependent
given that at some point in order to pass this test the relative wind velocity must pass through zero
I believe the system will find stability if going directly down wind before crossing the light speed barrier because the amount of energy available to the system is directly proportional to the variation in either mediums relative speed to the system
not relative to one another

speaking of dont understand
I didnt notice any rebuttal to the my previously quoted statement
also

The key aspects are that the propeller enables us to generate large thrust force while advancing slowly through the airstream. That thrust is much greater than the force acting on a turbine in the water to spin the propeller because the turbine is advancing through the water much faster than the prop is advancing through the air.

represents a fundamental misunderstanding of the physics involved as the hole system at the time of the mythical moment can only be in equilibrium or deceleration due to the drag coefficients of both the air and water turbine being what they are relative to that of the vehicle itself

although
The boat moves a little slower than the wind but is moving almost at wind speed through the water. So we could be 90% of the way there
you do seem to realize the vehicle will hit equilibrium at some point before reaching dead down wind wind speed

and Im dying to find out what these earth shattering
clever bits.are

but please
Im actually loving this thread
we have managed to take on a slightly antagonistic approach to one another
and we need to keep that in check
although pleasant banter is the heart of a healthy debate
I actually hope you come up with something to convince me
I seek a greater understanding at all times
( if you are all that much interested in physics Im surprised you never asked about my patent on plasma insulation )
and Im probably a lot more open minded than you are thinkin right about now
so do go on

however
the model you are analyzing
Im curious
did you make that diagram
and if not were did you find it
Ive got an anvil to drop on it once you guys are done playing

Tcubed

11-18-2008, 11:09 PM

Mr Boston says <<I just think the burden of proof is on the true believers
Im the skeptic here>>

He also put forward the premise;
<<the energy available at the transition to faster than wind speeds will no longer be significantly dependent on the variation of the mediums relative velocities to one another but as a function of the friction variations of the systems driving components relative to the mediums upon who's friction those driving mechanisms are dependent
given that at some point in order to pass this test the relative wind velocity must pass through zero
I believe the system will find stability if going directly down wind before crossing the light speed barrier because the amount of energy available to the system is directly proportional to the variation in either mediums relative speed to the system
not relative to one another>>

To which i say there is a deep flaw in reasoning, so that makes me a skeptic of this 'premise' and therefore,
according to your own words, the onus falls on you, Boston, to demonstrate to me its truth.

However, since you haven't been able to follow the elementary algebra in the model i would be surprised to see some meaningful supporting maths coming from you at this late a stage.

Now on a more serious note, i would like anyone with maths abilities to join me in the following extension to the problem;
Take the same model as Rick originally presented, but add the third dimension. I.e. include all cases of motion at different relative angles to the direction of motion of the top plate. (this would represent different headings relative to the wind)

Again, break it into two parts, first the general formula for all angles and gear ratios, and then secondly, including an arbitrary resistance vector opposing the velocity vector of the model.

I will work on this over the next few days myself.

philSweet

11-18-2008, 11:58 PM

Boston,

is the following what you had in mind with regards to the treatment of four forces?

A graph with 2 lines on it -

The first line is the resultant of forces above the water line, namely windage on the hull and force due to the fan.
The second line is the resultant of forces below the waterline, namely hull drag and the force due to the water wheel.

IF the first line is above the second line for all velocities 0 < v < windspeed
AND the device travels only downwind , are we getting close?

You seem want to rule out tacking. No flying of kites that tack back and forth, and you seem disiclined to consider the case of the yacht Hydroptere tacking back and forth in a floating drydock and towing it with a rope. Taken to its limits, this could prove very tedious conceptually. I just want to confirm that a fan is an acceptable device. Tacking involves changing control surfaces and a fan does not. Is this a reasonable distinction?

kerosene

11-19-2008, 02:50 AM

As I see it the wind turbine acts as a big wing/sail as in a helicopter (rotary wing) which initially pushes the vehicle downwind, and since the wheels are connected this then rotates the wind turbine but the rotation must be in the other direction to force the turbine to blow air aft (backwards) once this occurs then the craft is pushed by the velocity of the air produced by the air turbine driven by the wheels and also by the tail wind also pushing the "rotating wing/sail area" and something does not quite add up as what changes the wind turbine rotational direction from a driven force to make the wheels turn to a driving force by the movement of the wheels causing the wind turbine to become a fan which pushes the vehicle????? Now I am confused - which is easy to do.....

You almost got it. I am quoting because it was almost the best worded explanation here.

My re-treatment (co-author Masalai mutilation by me without permission :D )

Propeller acts as a big wing/sail as in a helicopter (rotary wing). Initially the propeller is at rest (no spinning). When the wind cathces the prop (and the rest of the craft) it pushes the vehicle downwind.

Logical so far.

Since the turbine is in the water (we assume still water btw) it starts to spin - forcing the propeller to spin too. As the propeller blows air against the wind it causes bigger force on the boat. rest is sort of obvious.

No with all the extra resistance of water and all that crap it might seem against gut feel. That is why the cart version is more obvious.

Lets try again

Propeller acts as a big wind cather and when spinning as a propller (doh). Initially the propeller is at rest (no spinning). When the wind cathces the prop (and the rest of the craft) it pushes the vehicle downwind.

Logical so far.

Since the wheels are on the ground they start to spin - forcing the propeller to spin too. As the propeller blows air against the wind it causes bigger force on the cart.

Now how would it NOT work.

Lets stop the experiment at different phases.

1. still craft little friction on the gearbox and wheel. wind. Surely it has to start moving - if it didn't it would fight the wind with no outside force.

2. cart starts rolling pushed by the wind. Propeller starts spinning (it has to or the wheels would skid but that wouldn't make any sense)

3. We have a cart rolling that is blowing wind against the wind. What stops it from reaching and passing the speed of the wind? You would need brakes to do so.

I probably failed like many before me in simplifying somewhat simple dilemma.

And Guillermo - drop the arrogance a notch - just so happens that this time you were wrong and if I hadn't read about 1000 very valuable posts from you I might question your character :D

masalai

11-19-2008, 02:58 AM

kerosene, Now I have a swollen head, but thanks, and permission granted, so long as you do not upset Guillermo.... An autogyro is a good example of a rotary wing in action...

clmanges

11-19-2008, 09:09 AM

1. still craft little friction on the gearbox and wheel. wind. Surely it has to start moving - if it didn't it would fight the wind with no outside force.

2. cart starts rolling pushed by the wind. Propeller starts spinning (it has to or the wheels would skid but that wouldn't make any sense)

3. We have a cart rolling that is blowing wind against the wind. What stops it from reaching and passing the speed of the wind? You would need brakes to do so.

Someone should chisel this in stone. Big, like visible from orbit. Then pick the stone up and drop it on those youtube jerks for not having said so in the first place.
Thank you.

Tiny Turnip

11-19-2008, 09:47 AM

A little OT, but pursuing extraordinary wind powered machines:

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/3_eY22R0TWE&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/3_eY22R0TWE&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

more film of Theo Jansen's work at http://www.strandbeest.com/film.html

I particularly like the Animaris Currens Ventosa walking clip. there is more on Youtube of course.
It is clear that some of the machines are not wind powered, (the 'rhinoceros' for instance) and it really is difficult to get a sense of how they are actuated, though the embedded clip has a shot of Jansen apparently assembling wind powered pneumatics, I think. So, presented largely for inspiration, suspension of disbelief, and enjoyment.

philSweet

11-19-2008, 10:21 AM

Here is a sketch of a device. It is contrived so that there is no reversal in force, torque, or rotation as it accelerates. It is shown at rest. the fan is free to pivot forward or aft.

TheUnlogicalOne

11-19-2008, 06:38 PM

Tcubed

11-19-2008, 07:04 PM

Well at last i see someone who thinks along the same track as i.

This to me is by far the most interesting part of the analysis of the turbine boat so far. How does the "gearing" vary with heading and V/W......???? At what angles is critical and what happens at critical angles.

Although it is no doubt possible to make a boat with fixed pitches and gearings get to ddwfttw in a straight line, in practice i'm certain that real boats outfitted with this system would not start heading straight downwind when at a standstill. It would not be the quickest way to accelerate , basically.

For this system to function well realistically, it needs full pitch control in both screws as well as fully variable gearing between them.

I have been analysing the basic problem as per my previous post to precisely that end, and am trying to simplify the equations to give V in terms of G , W and alpha , As well as give G in terms of V , W and alpha.

So far i've got G in terms of V , W and beta and am going over it again and will convert it to w.r.t. alpha soon.

(alpha is angle between real wind vector and machine's velocity vector, beta is apparent wind angle)

I'm glad we could get this discussion back on track and usefull, instead of wasting time trying to convince people incapable of following mathematical logic.

Guest625101138

11-19-2008, 08:38 PM

Just trying (and possibly failing) to be helpful here, but there is something that seems to have been forgotten. While its not required I tend to think practically and if I can see how it could be done in reality it makes things easier.

The air prop/turbine either has to be able to swing around or reverse pitch for this to work from a stand still effectively. (at least this is my gut feeling, can't be bothered to work it out, and it would depend on gearing) If not, the wind would possibly "pull" the craft straight back. Not a bad ability but not the desired out come.

If the prop could rotate freely to face any heading, like a windmill with a tail, then it should be fairly straight forward. Start out perpendicular to the wind and accelerate up to the required speed, then turn down wind. If you are traveling faster than the wind at an angle (which I think is agreed is possible) when you change direction the prop would swing to face forwards (where if the boat where stationary it would face back into the wind).

I'm not entirely sure what this "required speed" would theoretically be. It is the point where, depending on gearing, more power is available from the water relative to the boat than in the air relative to the boat.(the "relative to the boat" is important I think?) Its probably below the wind speed but that would cause practical problems for the free turning prop as it would want to swivel back the wrong way and act as a brake until the boat was slowed down again.

Unless you could change the gearing on the fly and manually control the direction/pitch of the prop the boat would not easily accelerate from a stand still to faster than the wind in a straight line. It would have to be pushed by the wind up to a certain speed, like a floating brick, where the water prop stops stalling, and if the gearing is good with low resistance it might actually reverse direction.

I'm sure I'm out to lunch on at least a few points here, but I was bored during lunch and couldn't think of anything more productive to do.

TUO
I essentially agree with what you say. I have concluded that most of the time the upwind set up would be used. For any practical purposes the difference between the upwind boat and the DDWFTTW boat would exclude their combination in a single system. It is somewhat like trying to make a spinnaker a good upwind sail or making a flat cut jib a good directly downwind sail.

As for getting the thing moving downwind I would expect the following to occur.

Think about the propeller blades and turbine blades connected on a common shaft with the propeller having a pitch of 1m and the turbine having a pitch of 3m. The propeller blades will present almost flat surface to the line of the hull. The turbine blades will have a much flatter angle to the line of the hull.

With everything at rest the wind past the blades will be trying to turn the propeller backwards but they are in a stall condition with AoA maybe 80 degrees. They might give a slight nudge backwards but this will be strongly resisted by the turbine blades churning in the water - effectively rotating paddles given their angle to the line of the hull.

The wind is exerting force on the propeller and the boat superstructure so it starts to move forward. Remember that a boat does not have static friction so the slightest force starts it moving. The windspeed past the propeller reduces so its tendency to turn backwards is reduced. Water is now moving past the turbine blades. The AoA of these blades is only around 40 degrees at rest so they will be generating maximum lift and high torque. This torque will overcome the counter torque from the propeller and begin to turn it forward.

So we now have both the turbine and the propeller spinning in the forward direction. The local slip steam at the propeller blades is going backwards relative to the boat although the far field apparent wind is still moving forward faster than the boat. So the propeller is now creating its own localised apparent wind due to its forward rotation.

The boat speed will continue to build until the power produced by the turbine balances the power absorbed by the propeller plus the drag on the hull and air drag on the boat when it exceeds the wind speed.

If you wanted to demonstrate a boat it is easy enough to do an unmanned model. I would use a long slender hull about 20ft long and maybe 6" beam with two small stabiliser. Make a propeller using carbon fibre 4m in diameter and pitch around 1m. Mount this near the bow. Make a steel turbine 0.6m in diameter with a pitch of 3m. Mount this at the stern. Connect turbine to propeller with a 1/4" spring steel shaft. The shaft would need three intermediate supports to prevent vibration.

You need a large prop to get any reasonable efficiency because the wind speed is so low. You need a long slender hull so the wave drag does not rise too quickly. The single curved shaft supported on bearings will have very low losses.

You then need to find a place where the wind is blowing steadily around 10 to 15kph. Set the boat at the start of a course that has small waves and let it go. You could video the exercise showing a ribbon being blown backwards and post here but the skeptics will remain skeptics and continue to look for the trick because they simply lack open minds and the ability to reason.

I would applaud the effort for curiosity sake. Windmaster might even claim you to be world famous.

Actually I am impressed that there are so many more people now building the DDWFTTW wheel vehicles to satisfy their curiosity. I expect it will only be a matter of time before someone tries a boat.

Rick W.

Guest625101138

11-19-2008, 09:09 PM

.........

For this system to function well realistically, it needs full pitch control in both screws as well as fully variable gearing between them.

I have been analysing the basic problem as per my previous post to precisely that end, and am trying to simplify the equations to give V in terms of G , W and alpha , As well as give G in terms of V , W and alpha.

So far i've got G in terms of V , W and beta and am going over it again and will convert it to w.r.t. alpha soon.

.......

Tcubed
I have full VPP models for turbine/propeller boats that are modelled on actual blade profiles and foil polar data over the full range of Re# used in the analysis. I expect if you do the same you will conclude that you cannot find a workable solution that covers all bases irrespective of what you do with variable pitch and variable transmission .

In my view the best solution for a practical boat is using electric motors/generators in combination with batteries for storage and solar cells for a little extra energy input in calm weather. The only benefit in making the air turbine able to operate as a propeller is as a back-up to the water prop. Similarly it is unlikely that the water prop would ever be used as a turbine.

The ability for DDWFTTW is of such limited value that it is not worth while contemplating other than for curiosity value.

Rick W

Tcubed

11-19-2008, 09:30 PM

I'm aware that you are a proponent of this system to be used in conjunction with energy storage systems and i agree that on the whole that is doubtless the most pragmatic setup, despite the energy losses.

I'm also aware that optimization across all scenarios is impossible without organically morphing foils, which are as yet beyond the wonders of high tech engineering.

However i admire the simplicity of the directly mechanical setup and am analyzing the mechanics of it in a simplistic way so far. I have solved the first part and would appreciate someone going over it to check i have not made a mistake and if the equations can be reduced further as they are quite complex. I don't feel like attemting to type the workings in here as i'll be at it for hours. I guess i'll fotograph the paper and post that (tommorow) .

I believe that gaining full understanding of this phenomenon is beneficial to better understanding some of the subtleties of regular sailing craft.

The data you have i would naturally be very interested to see.

Boston

11-19-2008, 11:22 PM

http://www.boatdesign.net/forums/attachments/boat-design/26982d1226961353-wind-powered-sail-less-boat-slide7.jpg

please people, I know I am treating this a little harshly, but when I see this kind of blatant failure to comprehend the most basic tenants of physics
its just hard to not snicker a little

these numbers are laughable
folks must be talking fig newtons
cause the newtons we use in physics are dependent on mass and velocity
not just velocity

if you want math, try this ( its about as basic as it gets )

N=kgV/s2

this is some really basic stuff but apparently it needs to be explained
Ill give you a hint although all the hints Ive dropped so far have been ignored
N = newtons

energy
as measured in newtons is directly proportional to velocity and mass
not just velocity

if you need to ask questions
dont
this is pathetically obvious

I attempted to add mass to the equation early on
knowing that the system wouldn't survive the proof if I did
its max speed potential can only be its kinetic energy minus friction once distributed to all moving components of the system
something else I pointed out earlier

but it got ignored

anyone wonder why

why would the proponents of this system refuse to address an obvious proof of the system

keeping it simple the max energy of this system
if the plate and the cart both weigh the same ( say 2kg each )
and if the cart starts out at 0m/s and the plate at 2m/s
is 1kgm/s
doesn't mater what the gearing is
we will consider torque in a moment

I pointed the mass component out earlier
but because it screws up the results
and because there were obviously preconceived results
and because the lesson in perpetual motion insisted on ignoring mass entirely
the folks on the band wagon insisted on ignoring my comments

which is one of many reasons your model
your understanding of the most basic physics
and your conclusions
are laughable
in the real world
we have mass
I want a few of you folks to drop a large rock on your big toe a few times
till you learn about mass

also
this model
ignores delta T and
if you consider delta T then you find a system in perpetual acceleration
doesnt work without perpetual increasing the available energy
(is the word perpetual anathema around here, cause its what this thing represents)
its a simple fact that in any system
the faster you go
the more friction
the less energy you have available as positive velocity
so again
the system only provides diminishing returns in the real world
if it constantly wants to accelerate from the fixed energy source of the plate
( ok so now Im about to be told the wind takes the place of the plate and the top roller is the wind turbine )
( makes no difference, run that directly down wind and it'll still hit the same relative wind barrier Ive been pointing out from the go )
( run it across the wind like the ice racers do and all the moving crap makes you slower than they any day )

if you were to actually graph the results of the energy requirement of the system over time you would find they are required to increase exponential

why do you think I wouldnt play the game in the first place when I gave you the proof considering for mass

next problem
torque
your torque considerations are completely fictional since you ignored mass considerations
and
the energy of the rotational velocity of the wheels is directly subtracted from the forward motion of the vehicle
and no
Im not going to explain that one
its way to advanced for a class that's just learning that N is in some way related to mass and not just velocity
and not something just wrapped around a fig

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/iMhdksPFhCM&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/iMhdksPFhCM&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

You seem want to rule out tacking. No flying of kites that tack back and forth, and you seem disiclined to consider the case of the yacht Hydroptere tacking back and forth in a floating drydock and towing it with a rope. Taken to its limits, this could prove very tedious conceptually. I just want to confirm that a fan is an acceptable device. Tacking involves changing control surfaces and a fan does not. Is this a reasonable distinction?

( this model you suggest doesn't work )
( for the reasons previously specified )
( your welcome to use a fan all you want )

at this point I dont care how you can do it
as long as the vehicle is going directly down wind
you win the beer
Im actually hoping someone can come up with something
but so far

http://i29.photobucket.com/albums/c262/bostonpyramidbuilder/3_Bugs-Portrait.jpg

Boston

11-20-2008, 12:09 AM

Guest625101138

11-20-2008, 12:28 AM

........

if you want math, try this ( its about as basic as it gets )

N=kgV/s2

this is some really basic stuff but apparently it needs to be explained
Ill give you a hint although all the hints Ive dropped so far have been ignored
N = newtons

.....g

Boston
Can you please explain what you mean by this equation. I accept the N means Newtons - a force.

what is the k, g, V and S???

Rick W

Guest625101138

11-20-2008, 12:32 AM

3dyachts

11-20-2008, 12:39 AM

Hi all,

I just had the patience to go all the way this looong thread (reading diagonally at times!). And I was feeling a bit depressed, so l was looking for something a little mind blogging!

I am ASTOUNDED!

This started with an interseting question: how to loose a war that has already been fought sort of thing. Effectively, nothing - by far - beats the speed obtainable by simple foils that a "sail" is, sitting on another foil that fights against leeway (and eventually provides lift), if no other power source than present wind is used,.

Accumulation is then a good answer to the question that was primarily asked, since it was not excluding "internal" power source.

But then this discussion about the capabilities of rotating foils (call them props, turbines, or else) or other means of using directly or undirectly wind energy by anything that could not be called a sail somehow diverted to this icredible discussion about Directly Down Wind Faster Than The Wind.

May I first say that any discussion that pretends to resolve a problem should be - basically - about the same problem for everyone? If one says Directly Downwind, that is not even at a fraction of an angle: that is directly Downwind. Period.

We all know that the ice sledges can go much faster than the wind. NOT Directly Downwind! We all know that diverse experiments have been conducted that show possible to go strictly directly upwind: the result is a desolation, and tacking is much faster altogether, but it works.

But then, an impressive number of numbers have been written down to demonstrate that what has NEVER worked does actually work! Show one! Do not say "it works, I demonstrate it, but that...hmmm...wait...we think it works..we are sure it does...but...hmmm...well: so long must admit it DOES not!"

Sorry guys: if, with the basic scientific attitude of following strictly the question as it is written down: DDFTTW: it does not work. Tacking downwind: it works. No matter how you will angle your "wind catching contraption": if the vehicle moves strictly down wind, it will never go faster than the wind. None can be shown. These little vehicles nicely rolling along the road have to be at an angle to the wind.

Write figures, go round in circles, even do these (sorry: ridiculous!) little sliding ceiling comparison (got to have totally misunderstood the problem to put that here!!!) : NOTHING has been demonstrated!

Care joining the team for a beer?

kerosene

11-20-2008, 12:50 AM

2 things.
1.
If taking downwind makes it possible to go faster down wind can I make a machine that is a broad frame in which a device takes back and forth (down wind) and pushes that cage directly downwind?
If it is acknowledged that there is no weird science or perpetual motion in traveling faster than the wind when tacking it is only reasonable to extrapolate that it is possible to break those components and go straight down wind without braking any laws of physics. Obviously normal wing can't do that as its loses the flow on its surface.

2. If you suggest that the small carts are working because they are actually traveling of the wind then how do you explain the treadmill experiment. After all the starting phase of a treadmill experiment is as if vehicle is rolling (directly) downwind exactly at the speed of the wind (no apparent wind).

Call diagrams ridiculous at least Rick is taking time trying to explain his point.

And about the practicality of all this. Fully agree traditional wing beats these contraptions clearly - its more of a mental exercise on a dilemma that is counter intuitive and thus gets slammed by people like you.

masalai

11-20-2008, 12:59 AM

2c - besides, I am enjoying the discussion, learning something and having a beer... Keep the discussion going it is interesting....

Boston

11-20-2008, 01:28 AM

MR 3dyachts

team beer is ready for some new members anytime

also
I notice the timbre of my threads has gotten a little sarcastic
for that I apologize
Im just frustrated that the basics of physics are being so flaunted
and that the perfectly valid questions I raised earlier in this discussion were so studiously ignored

Rick if you are working in newtons
and dont know what a newton is
how much validity can possibly be found in your equations
Idont mean that to sound harsh
but it's true

I just am not going to explain basic physics
its late
I had a crap day
and Im just about out of beer

I will however explain theoretical physics
what theoretical physics does is dream up equations about things that for the most part dont exist but maybe could
it doesnt necessarily propose a solution for those equations
but it does insist that the equations balance with proofs to show the validity of those equations
in doing so it requires that all common denominators be resolved and that a consistent and generally obvious question be answered by the proof
to also show the validity of that proof
one that must also be answered by the original equation
it would be something like the conservation of energy proof I proposed for that model you first posted

as an example

in relativity old uncle Albert found a flaw
everyone said he was nuts
and he went on to be considered over the hill
but he dreamed up the field equations to try and resolve the problem
( by the way folks thought he was nuts for doubting his own discovery )

the field equations are the example Im going to use here

they could not be resolved unless you provide an arbitrary number called the cosmological constant
the cosmological constant is an imaginary number that makes up for the flaw in relativity and allows the field equations to be resolved
and yet
everyone clung to relativity with a death grip
really pissed off All
now
about a million years later
folks are starting to notice that quantum mechanics and relativity dont jive
( ok they new that from the start but they've lately given up on waiting for a reason why they dont jive )
along comes a guy named Joao
old Jo dreams op variable light spead theory and resolves the field equations
way to go Jo
thing is now every one who staked there rep on relativity
( which is still good up to the plank limit by the way )
hates Jo
why
why would they hate a guy with a name like Joao
and not just admit they were wrong in the first place
they are scientists
shouldnt they be interested in truth

thing is we all put our ego's on the line with some of our beliefs
and some of those turn out to be wrong
its a grim admission

so when there is only one of me
and ten of you
it doesnt mean I must be nuts
it could just mean
that I know a little more than you are giving me credit for

might just be time to admit that model is seriously flawed
when you have insisted on a calculating units or measurement in the model that dont exist in the model

and Ill still buy you a pint
it was entertaining
I dont care who is right or wrong

Boston

11-20-2008, 01:43 AM

oh #$%@
I just noticed I put v instead of m

it should read
N=kgm/s2

told you I had a crap day
way to put my head on the chopping block
its basically the same thing
but not
oops
B

just I didnt look it up and then I went back and read the question again
I realized I had mixed the American equation with the conversion equation

its E=mv2/2
and N=kgm/s2

I think
been a long time since I used any of this crap

Boston

11-20-2008, 01:51 AM

hmmmmmm
its kg moving at m per sec
I think I still wrote that wrong
but it represents V no matter
and you should be able to recognise the error in a heartbeat
hell I think its what caused one of the mars landers to crash
oh well
its dam late
or at least that would be Nasa's excuse

Guest625101138

11-20-2008, 02:18 AM

Guest625101138

11-20-2008, 02:35 AM

The attached clips are not going to make much difference in the debate but it might help those who grapple with the understanding.

This is a highly imperfect little vehicle, built in 5 minutes, that does work. The wheel slip and flexible belt drive adds a dimension of reality that might trigger understanding in those prepared to open their minds. The vehicle is inverted to achieve the different operations.

It does show that you can build a vehicle that will advance directly against the force that it causing its motion. It also shows that the vehicle can advance faster than the media that it pushing it. Both examples work through the wonders of gearing. No witchcraft, no strings and no perpetual motion; just gearing.

Rick W

3dyachts

11-20-2008, 02:39 AM

Gee! I just had a lunch and a short nap, and there's been three new posts! (one lengthy one from Boston must have been pre-written: he has had too many beers and couldn't think/ write THAT fast!) . That's what I could call a lively thread!

Kerosene: I don't know if "people like you" is adressed to me, but "people like me" like things to be exact, whether immediately percievable of a bit mind boggling. "People like me" aslo like things to be well understood.

What I would have liked to hear about more in this lengthy thread is: energy.

The little cart between two surface is nothing really different from what you have in a planetary reduction gear for example. Energy has not much to do in it besides fighting inertia at the start, and frictions all along. Demonstrates nothing for what we are talking about. There ias different speed between different objects, no change in speed of one object and not in energy.

A little reminder, now:

When talking about using wind (or water flow) energy, we are talking of moving off their track ponderable molecules, which makes them loose speed so that their kinetic energy is converted into an other form, via a foil followed by a mechanical transmission (kinetic energy to be used later via a flywheel, or immediately), or converted into electrical converted eventually into chemical to be re-converted into electrical later, and then be converted into mechanical (talking losses?), etc...etc...

Air molecules: it is their kinetic energy we can collect, that's all the wind has to offer. To collect it, we must slow them down. Not stop them: they must continue to flow: we must divert them. Movement is induced by the force applied on the surface of the foil by a difference in pressure, but kinetic energy= quantity of movement * mass: E=1/2 M*v2 (not to be confounded with E= Mc2) in induced - in this case - by the reduction in speed of a mass of fluid. That is how all foils work (wings, sails, propeller blades, etc... )

A turbine immersed in water just does that too.

A propeller does the opposite: it accelerates a fluid.

In this "DDTW..." thingy, energy is taken from an immersed turbine. To be able to divert the water flow and turn (remember that it is the relative speed that counts: whether it is the fluid that is moving referring to the ground, or the craft, it is the relative speed which can be called flow in both instances), it has to have a force (thrust) applied , otherwise it will just go along with it, and not turn (stay still if the water is still). The thrust applied converts the kinetic energy it gets from the water via the turbine into turning an aerial propeller which accelerates air and , which "in turn" propels the craft through the water (by providing the thrust). That's what a propeller is supposed to do...!

This means not only that the propeller must give a bigger thrust than the force the turbine has to apply into the water for moving through it, but that the energy it gets to turn and accelerate the air (which, remember, all comes from what the turbine gets from moving through this water) has to be higher than what this turbine can get by moving through the water.

Where do you get the energy from??????

Another beer, please!

Guest625101138

11-20-2008, 03:36 AM

......
Sorry guys: if, with the basic scientific attitude of following strictly the question as it is written down: DDFTTW: it does not work. Tacking downwind: it works. No matter how you will angle your "wind catching contraption": if the vehicle moves strictly down wind, it will never go faster than the wind. None can be shown. These little vehicles nicely rolling along the road have to be at an angle to the wind.

....

3dyachts
Can you explain what magic causes the direction of airflow to change over this vehicle as evidenced by the direction the ribbon trails:
http://www.youtube.com/watch?v=aJpdWHFqHm0&feature=related

Before you give some half-baked ignorant response like your other input, remember the fellow doing this demonstration, Jack Goodman, is highly regarded by AYRS, a group that has made significant contributions to the development of yachts. Also be reminded that it was not so long ago that ignorant people thought the world was flat and the sun revolved around the earth. It has a lot to do with your frame of reference. So clear your mind, be prepared to have your conventions challenged and read this brief article:
http://www.ayrs.org/DWFTTW_from_Catalyst_N23_Jan_2006.pdf

By the way the vehicle analogy is an extremely good one as it has all the key elements required to understand what is going on. It really is that simple - just gearing.

Rick W

kerosene

11-20-2008, 03:45 AM

ha - good job rick on your aparatus. Nice to see that we are all so enthusiastic on this one.

Here is my video presentation of a tacking machine:
http://vimeo.com/2294997

Don't take it too literally maybe the tacking angle and wing (sail) is aligned wrong - that is not the point. The point is that if it is possible to travel downwind way faster than the wind - as seems to be agreed - then wouldn't this machine be able to go _directly_ downwind faster than the wind?

If so then we can at least put the perpetual motion arguments aside

Updated with youtube video:
http://www.youtube.com/v/IMEerIkOVZ0&hl=en&fs=1

Guest625101138

11-20-2008, 04:09 AM

ha - good job rick on your aparatus. Nice to see that we are all so enthusiastic on this one.

Here is my video presentation of a tacking machine:
http://vimeo.com/2294997

Don't take it too literally maybe the tacking angle and wing (sail) is aligned wrong - that is not the point. The point is that if it is possible to travel downwind way faster than the wind - as seems to be agreed - then wouldn't this machine be able to go _directly_ downwind faster than the wind?

If so then we can at least put the perpetual motion arguments aside.

I cannot view the video. It tells me it is a private video when I go to the link.

Rick W

kerosene

11-20-2008, 04:27 AM

This means not only that the propeller must give a bigger thrust than the force the turbine has to apply into the water for moving through it, but that the energy it gets to turn and accelerate the air (which, remember, all comes from what the turbine gets from moving through this water) has to be higher than what this turbine can get by moving through the water.

Where do you get the energy from??????

Another beer, please!

First - sorry if I came of rude earlier. I will try to explain again. Please try to read with fresh eyes (lets hope the beer has freshened them).

(again I prefer cart because turbine associates losses and resistance in less intuitive sense)

"Where do you get the energy from?????? "

From the wind. Lets again assume the cart is rolling. Wind is nice 5 m/s
Cart rolls 4 m/s in the direction of the wind. What are the forces?

Clearly the apparent wind of 1 m/s puts some force on the cart AND the propeller is spinning so it will push it forward too.

NAAYYY. some say - the wheels will cause resistance (after all they have to spin the prop) surely it will slow down.

hmmm.... why on earth would it slow down - the only for acting on it is the wind. All frictions are rather meaningless. Just image the machine going slower than the wind. Clearly the wind wants to push it to reach the apparent wind 0 (cart going 5 m/s)

But if the cart reaches closer the apparent wind (which is reasonable considering that there are not that much losses) it means that the prop is spinning and it wants to go faster.

It indeed is the wind making this all happen.

I really think the best way to understand how it works is to try to justify why the cart would travel SLOWER than the wind (and lets ignore losses and efficiencies for the sake of clarity).

A:"And why can those ice boats go so fast?"
B:"- well they go off an angle."
A:" But but they steal energy from nowhere?? "
B:"Oh no they don't need to steal energy from anywhere - they go off an angle and thus the apparent wind on the sail is higher"
A:"Why can't they go faster than the wind straight down wind?"
B:"Because there would be no flow on the sail - no apparent wind"
A:"hmm... but they still go faster than the wind"
B:"yes OFF THE ANGLE"

A:"but the cart cant go faster than the wind?"
B:"Not straight"
A:"Even if its sails were spinning and they had higher apparent wind?"

B:":eek: :confused: "

SLOWLY:
Any work we take away from the cart is used to push it forward, any work that we take from the wheels wants to slow it down, if its slower than the wind the wind keeps pushing it.

Joakim

11-20-2008, 04:28 AM

This means not only that the propeller must give a bigger thrust than the force the turbine has to oppose to the water for moving through it, but that the energy it gets to turn and accelerate the air (which, remember, all comes from what the turbine gets from moving through this water) has to be higher than what this turbine can get by moving through the water.

Where do you get the energy from??????

First of all I think it is much easier to think about powers and forces. If you want energies, just multiply power with time.

The power flowing through water turbine is 0.5 * massflow * V^2, where V is the vessel speed through water and massflow is the waterflow through turbine disk area. For a 0.5 m propeller at 5 m/s this power would be 12 kW.

To capture part of this power the propeller causes drag. Power captured by this drag is V * F * ETA0, where F is the drag force and ETA0 is the efficiency of the propeller (80% easily achievable). V*F is the actual impulse to water and 1-ETA0 goes into turbulence and heat.

Propeller will cause a wake, thus it will have a "tube of water" travelling to the same direction as the vessel, but much slower, since we only need perhaps 500 W. With 80% efficiency the drag is 0.25 N/P, thus 500 W can be taken with 125 N drag at 5 m/s.

Now the thurst vs. power of the air propeller depends very much on the apparent air speed. As an example one 8 m propeller could give the following thrusts at 450 W power (90% transmission efficiency)

Air speed (m/s), Thurst (N)
0, 300
0.5, 300
1, 190
1.5, 160
2, 130

As you can see there is a lot of thrust at 0-0.5 m/s air speed, thus in 4.5-5 m/s wind for this 5 m/s water speed, but already in 4 m/s wind the thurst is only 65 N more than the drag of the propeller. Thus the drag of the hull needs to be less than 65 N to go 5 m/s at 4 m/s wind, but it can be as big as 175 N to reach 5 m/s at 4.5 m/s wind.

Thus it should be rather easy to make a vessel that goes just slightly faster than the wind, but why whould someone bother to built one.

If you don't beleive in the thrust vs. apparent wind numbers think of the air propeller in still air (apparent wind = 0). Say it pushes air bacwards at 2 m/s. For a 8 m diameter disk this means the power input to air would be 0.5 * massflow * Va^2 = 0.5 * PI * 4^2 * 1.2 * Va * Va^2 = 240 W. And the momentum of the airmass pushed would be massflow * Va = 200 N. Thus we got 200 N thrust with 240 W input to air. For this 240 W input we need more than 240 W at the shaft.

When the propeller has a apparent wind forward, say 2 m/s, you still need still need the same added momentum, but now the mass flow is more. If you now add 1 m/s to apparent wind, the power input is 450 W and the momentum is only 180 N. This is quite an inaccurate way to think of a propeller, but it gives you a clue what happens to the power and thrust with increasing apparent velocity.

As a summary:

From high speed you can take a lot of power with small drag

With small power you can cause a big thrust to low speed.

Joakim

Windmaster

11-20-2008, 04:55 AM

I have no idea why you would offer this video with regard to the current discussion. It shows an air turbine that is driving a water propeller. The DDWFTTW boat we are discussing has a water turbine driving an air propeller. Very significant difference in operation.

Rick W

He posted it because he also believes that a boat driven by a wind turbine cannot progress steadily directly upwind. Thinking he sees it is "decelerating" he believes this validates his belief.
If he believed that a wind-turbine boat could make steady progress directly towards the wind - it would also mean he had to believe that a boat driven by a water-turbine and powered by a prop could sail downwind faster than the wind, and that contravenes his preconcieved notion.

3dyachts

11-20-2008, 06:45 AM

3dyachts
Can you explain what magic causes the direction of airflow to change over this vehicle as evidenced by the direction the ribbon trails:
http://www.youtube.com/watch?v=aJpdWHFqHm0&feature=related
Rick W

Rick: there is no magic there, effectively.

With the environment around this experiment, you can expect the airflow to be disturbed in both strenth and - moreover - direction. That is not a wind tunnel.

If you read me, and other posters, carefully, you will see that we insist on the word: "strictly".

The airflow around this propeller - and it is a propeller in the strict meaning of it: it does "propulsion" as you can see by its pitch - is not constantly and strictly perpenducular to it's plane, but changing. This craft is not going permanently directly downwind, but as the wind behind it changes direction all the time, is on one tack or another, depending on the direction of the wind .

The beauty, effectively, of this little craft's propeller is that, once the initial push has given an apparent wind further forward than when it was stopped, it gives a "lift" (somehow comparable to a gyroplane's one - but don't take that strictly) with rapidly changing wind direction from - I would guess - both sides alternately in this messy wind tunnel. It deviates the wind flow backwards many times, as the ribbon shows ...which ribbon also shows the very disturbed air flow.

You have to understand that it does not matter that the general direction of the car maybe downwind: whether it is the car that actually tacks in a constant wind flow, or the wind that makes it equivalent to a broad reach, thuis craft is not going directly downwind in the "strict" meaning of it. So, being effectively "tacking", this propeller gets turning faster and faster - up to a certain limit! - and transmits TO the wheels (and not the contrary) a propulsive power that, combined with the lift of the propeller, makes the car get to a speed higher than true wind. The wheels are driven by the propeller, they do not drive the propeller (whatever the author of this experiment says).

All in all, this only resolves around a simple debate:
A/ can a wind powered "vehicle" whose general track is downwind but is actually tacking (whether it's the wind or the vehicle that tacks referring to the "reference surface") can be called going faster than the wind?
Of course: yes, since it will be faster than an object left free floating in this wind.
B/ can a wind powered vehicle whose direction is strictly and permanently the same as the wind go faster than this wind: No

3dyachts

11-20-2008, 06:56 AM

3dyachts
Before you give some half-baked ignorant response like your other input,...... Rick W

Now, Rick: (this is personal: no need for others to read)

Your agressive and insulting attitude is a clear sign of your frustration when you face your incapacity to defend your position in any other way than this not very convincing method.

Good bye

3dyachts

11-20-2008, 07:18 AM

From the wind. Lets again assume the cart is rolling. Wind is nice 5 m/s
Cart rolls 4 m/s in the direction of the wind. What are the forces?

Clearly the apparent wind of 1 m/s puts some force on the cart AND the propeller is spinning so it will push it forward too.

Little mistake there, Kerosene: If you look at it's pitch, you will see that the propeller, in the youtube video, is "propulsive", which means that, when it turns, it gives a forward thrust. It is connected to the wheels so that, while turning (in a propulsive direction) it also communicate to these wheels a rotation that makes this craft move forward.

With this pitch, and before receiving an initial external thrust, it would start spinning the other way with the wind behind it, and the transmission to the wheels make the craft go...in astern. With properly designed wind turbine (should not be called a propeller anymore) and efficient transmission, such craft can go directly into the wind, yes. Slowly, sure, but can!

But if the cart reaches closer the apparent wind (which is reasonable considering that there are not that much losses) it means that the prop is spinning and it wants to go faster.

It indeed is the wind making this all happen.

It's the wind, indeed!

There is a limit, though: the propeller can only be pulling the craft forward (and also sending propulsive energy to the wheels) with the wind blowing inside a rather limited sector one side or the other.

A:"And why can those ice boats go so fast?"
B:"- well they go off an angle."
A:" But but they steal energy from nowhere?? "
B:"Oh no they don't need to steal energy from anywhere - they go off an angle and thus the apparent wind on the sail is higher"
A:"Why can't they go faster than the wind straight down wind?"
B:"Because there would be no flow on the sail - no apparent wind"
A:"hmm... but they still go faster than the wind"
B:"yes OFF THE ANGLE"
A:"but the cart cant go faster than the wind?"
B:"Not straight"
A:"Even if its sails were spinning and they had higher apparent wind?"
B:":eek: :confused: "

That's just what it is: at an angle.

3dyachts

11-20-2008, 07:24 AM

Here is my video presentation of a tacking machine:
http://vimeo.com/2294997

Don't take it too literally maybe the tacking angle and wing (sail) is aligned wrong - that is not the point. The point is that if it is possible to travel downwind way faster than the wind - as seems to be agreed - then wouldn't this machine be able to go _directly_ downwind faster than the wind?

Kerosene: hi again.

Iam sorry, but this machine will not go faster than the wind with a steady flow as indicated in this (clever!) computer animation....but if the wind is at an angle, the thingy will stay nicely on one side, and perhaps...? ;)

Guest625101138

11-20-2008, 07:24 AM

Rick: there is no magic there, effectively.

With the environment around this experiment, you can expect the airflow to be disturbed in both strenth and - moreover - direction. That is not a wind tunnel.

If you read me, and other posters, carefully, you will see that we insist on the word: "strictly".

The airflow around this propeller - and it is a propeller in the strict meaning of it: it does "propulsion" as you can see by its pitch - is not constantly and strictly perpenducular to it's plane, but changing. This craft is not going permanently directly downwind, but as the wind behind it changes direction all the time, is on one tack or another, depending on the direction of the wind .

The beauty, effectively, of this little craft's propeller is that, once the initial push has given an apparent wind further forward than when it was stopped, it gives a "lift" (somehow comparable to a gyroplane's one - but don't take that strictly) with rapidly changing wind direction from - I would guess - both sides alternately in this messy wind tunnel. It deviates the wind flow backwards many times, as the ribbon shows ...which ribbon also shows the very disturbed air flow.

You have to understand that it does not matter that the general direction of the car maybe downwind: whether it is the car that actually tacks in a constant wind flow, or the wind that makes it equivalent to a broad reach, thuis craft is not going directly downwind in the "strict" meaning of it. So, being effectively "tacking", this propeller gets turning faster and faster - up to a certain limit! - and transmits TO the wheels (and not the contrary) a propulsive power that, combined with the lift of the propeller, makes the car get to a speed higher than true wind. The wheels are driven by the propeller, they do not drive the propeller (whatever the author of this experiment says).

All in all, this only resolves around a simple debate:
A/ can a wind powered "vehicle" whose general track is downwind but is actually tacking (whether it's the wind or the vehicle that tacks referring to the "reference surface") can be called going faster than the wind?
Of course: yes, since it will be faster than an object left free floating in this wind.
B/ can a wind powered vehicle whose direction is strictly and permanently the same as the wind go faster than this wind: No

3dyachts
So you accept there is no trick in the clip. The vehicle actually moves downwind in the general direction of downwind faster than the wind but fortunately the wind is veering around so it is actually tacking in the wind rather than the wind being directly or "strictly" behind. The designer and builder has it wrong and is deluded when he makes the observation:
"It prefers to go straight downwind ......."
Maybe he is not being "strict" enough with his wind direction.

So you are saying the only way you would accept this would be if testing was carried out in a wind tunnel where there is no means of having this very fortunate wind oscillation that keeps an "apparent" tack rather than a "strict" downwind.

So you have explained that one by the good fortune of wind variation.

How do explain what you see here with the vehicle climbing up the treadmill:
http://www.youtube.com/watch?v=1pSYALWQ-nI
It cannot be explained by "apparent" tacking in the wind because the air is still.

Rick W

3dyachts

11-20-2008, 07:39 AM

First of all I think it is much easier to think about powers and forces. If you want energies, just multiply power with time.
"Multiply"..?????
Hum...sorry ...(I talk in low voice so that "the others" could not hear): Mass is mass. Speed is distance per time (meter per second for example). Mass multiplied by speed (Kilograms per meter per second) is kinetic energy. Mass multiplied by speed multiplied by time (Kilograms per meter per second squared) is acceleration. To have acceleration, you need power.
Power will be in Watts, horse-power...what you like...: see their definition!

The rest of the "demonstration" becomes less convincing when started with such a "missteake"!

Guest625101138

11-20-2008, 07:41 AM

Little mistake there, Kerosene: If you look at it's pitch, you will see that the propeller, in the youtube video, is "propulsive", which means that, when it turns, it gives a forward thrust. It is connected to the wheels so that, while turning (in a propulsive direction) it also communicate to these wheels a rotation that makes this craft move forward.

With this pitch, and before receiving an initial external thrust, it would start spinning the other way with the wind behind it, and the transmission to the wheels make the craft go...in astern. With properly designed wind turbine (should not be called a propeller anymore) and efficient transmission, such craft can go directly into the wind, yes. Slowly, sure, but can!

..

3dyachts
This demonstrates you are almost there. IT IS A PROPELLER. The driving power for the PROPELLER is coming from the wheels.

If the gear ratio was changed so the wheels could overpower the air screw it would be an air TURBINE driving the wheels and it would move into the wind not away from it.

This is the significance of the little vehicle and sliding plate analogy that I have shown. It shows that by varying the gear ratio you can make it go against the direction of the plate or faster than the plate moves forward. All by virtue of simple gearing.

When you finally understand this I expect an apology for claiming I made a personal attack. I was simply being frank about your poorly thought out foray into the debate without really thinking through what had been posted.

Rick W

3dyachts

11-20-2008, 08:07 AM

3dyachts
How do explain what you see here with the vehicle climbing up the treadmill:
http://www.youtube.com/watch?v=1pSYALWQ-nI
It cannot be explained by "apparent" tacking in the wind because the air is still.

Rick W

Hahahaha! I like it when people take the pain to make these little "miracle" things that do confuse many! This one will have needed quite some adjustments, but is very nicely done, indeed!

But there is no miracle there! The only thing that is confusing is the level gauge: it shows clearly that the bubble is towards the "right" side, meaning up, but also that there is an angle between the level gauge and the treadmill showing that it's "left" side is up compared with the level gauge...!???!
Anyway: the author makes it clear that his little thingy is going to go "uphill"!

So, it's just a very well worked out equilibrium:

In one direction (downhill), which is the direction of the movement of the surface onto which this thingy is, the carpet "pulls" the wheels, which "react" by the torque they get from the propeller and some friction). In the opposite direction, the propeller "pulls" the thingy "forward" (to the left= uphill). Nicely balanced between weight, frictions, prop thrusts, angle if the prop shaft, and speed and angle of the threadmill!!!.

Would the prop not have enough thrust, or the threadmill too much angle, or be too slow (mind that this has some funny "reverse" consequences, eventually!), or too heavy, the thingy would have fallen back down. Or adjusted the other way gone forward up the top... and fall down!

And you know what the full fun would have been: to have a little bit of wind (in either direction) to add more complexity!!!

Joakim

11-20-2008, 08:45 AM

"Multiply"..?????
Hum...sorry ...(I talk in low voice so that "the others" could not hear): Mass is mass. Speed is distance per time (meter per second for example). Mass multiplied by speed (Kilograms per meter per second) is kinetic energy. Mass multiplied by speed multiplied by time (Kilograms per meter per second squared) is acceleration. To have acceleration, you need power.
Power will be in Watts, horse-power...what you like...: see their definition!

The rest of the "demonstration" becomes less convincing when started with such a "missteake"!

Could you please show me where I made a mistake?

You don't agree energy E = P * t, in SI units E: [Ws] =[J], P: [W]=[J/s], t: [s]???? When I said 12 kW of power flows through the propeller disk, you can calculate that in one second there has flown 12 kJ and in one hour 12 kWh.

Mass multiplied by speed is NOT energy, it's momentum [kgm/s]. Kinetic energy is 0.5*m*V^2: [kgm^2/s^2] = [Nm].

You seem to mix "multiply" and "per" so badly that I don't know what you mean by your definition of acceleration. Please show them in mathematical form.

Joakim

Boston

11-20-2008, 08:47 AM

well said 3D
and no it wasnt prewritten
 I really can write and hoist a few at the same time
its called multi tasking
buy the way
the energy consideration is what Ive been trying to get across here for quite some time

What I would have liked to hear about more in this lengthy thread is: energy.

I also mentioned all of this before as well and it only got ignored

But there is no miracle there! The onlt thing that is confusing is the level guage: it shows clearly that the bubble is towadrs the "left" side, meaning "right" side up, but also that there is an angle between the level gauge and the treadmill showing that it's "left" side is up compared with the level gauge...!???!

matter of fact
if you mention anything that deviates from the dream
your going to get ignored or insulted

for instance

I have already deduced that you believe simple maths is crap. People usually do not like what they do not understand.

Before you give some half-baked ignorant response

The attached clips are not going to make much difference in the debate but it might help those who grapple with the understanding.

Rick
I would love to see em but I have a high security computer that doesnt like there format
could you please reformat and post again
Ild love to grapple and grok the mythical monster you seem to believe in so vehemently

it seems maybe you missed this post ( so I will repost it ) because you sure seem to have deliberately ignored it

and I have to wonder who is having trouble understanding when you fail to address a single error in your model

http://www.boatdesign.net/forums/attachments/boat-design/26982d1226961353-wind-powered-sail-less-boat-slide7.jpg

please people, I know I am treating this a little harshly, but when I see this kind of blatant failure to comprehend the most basic tenants of physics
its just hard to not snicker a little

these numbers are laughable
folks must be talking fig newtons
cause the newtons we use in physics are dependent on mass and velocity
not just velocity

if you want math, try this ( its about as basic as it gets )

N=kg.M/s2

this is some really basic stuff but apparently it needs to be explained
Ill give you a hint although all the hints Ive dropped so far have been ignored
N = newtons

energy
as measured in newtons is directly proportional to velocity and mass
not just velocity

if you need to ask questions
dont
this is pathetically obvious

I attempted to add mass to the equation early on
knowing that the system wouldn't survive the proof if I did
its max speed potential can only be its kinetic energy minus friction once distributed to all moving components of the system
something else I pointed out earlier

but it got ignored

anyone wonder why

why would the proponents of this system refuse to address an obvious proof of the system

keeping it simple the max energy of this system
if the plate and the cart both weigh the same ( say 2kg each )
and if the cart starts out at 0m/s and the plate at 2m/s
is 1kgm/s
doesn't mater what the gearing is
we will consider torque in a moment

I pointed the mass component out earlier
but because it screws up the results
and because there were obviously preconceived results
and because the lesson in perpetual motion insisted on ignoring mass entirely
the folks on the band wagon insisted on ignoring my comments

which is one of many reasons your model
your understanding of the most basic physics
and your conclusions
are laughable
in the real world
we have mass
I want a few of you folks to drop a large rock on your big toe a few times
till you learn about mass

also
this model
ignores delta T and
if you consider delta T then you find a system in perpetual acceleration
doesnt work without perpetual increasing the available energy
(is the word perpetual anathema around here, cause its what this thing represents)
its a simple fact that in any system
the faster you go
the more friction
the less energy you have available as positive velocity
so again
the system only provides diminishing returns in the real world
if it constantly wants to accelerate from the fixed energy source of the plate
( ok so now Im about to be told the wind takes the place of the plate and the top roller is the wind turbine )
( makes no difference, run that directly down wind and it'll still hit the same relative wind barrier Ive been pointing out from the go )
( run it across the wind like the ice racers do and all the moving crap makes you slower than they any day )

if you were to actually graph the results of the energy requirement of the system over time you would find they are required to increase exponential

why do you think I wouldnt play the game in the first place when I gave you the proof considering for mass

next problem
torque
your torque considerations are completely fictional since you ignored mass considerations
and
the energy of the rotational velocity of the wheels is directly subtracted from the forward motion of the vehicle
and no
Im not going to explain that one
its way to advanced for a class that's just learning that N is in some way related to mass and not just velocity
and not something just wrapped around a fig

might just be time to admit that model is seriously flawed
when you have insisted on calculating units of measurement in the model that dont exist in the model

and Ill still buy you a pint
it was entertaining
I dont care who is right or wrong

Boston

11-20-2008, 09:05 AM

guys the energy of a moving body is defined through consideration of its mass and its velocity

for instance
E=mc2
or if you really want to get confused
E=hV

there is a number of ways you can write this
but in the end
its mass and velocity

3dyachts

11-20-2008, 09:06 AM

3dyachts
This demonstrates you are almost there. IT IS A PROPELLER. The driving power for the PROPELLER is coming from the wheels.

If the gear ratio was changed so the wheels could overpower the air screw it would be an air TURBINE driving the wheels and it would move into the wind not away from it.

Sorry: wrong again!

It is a propeller, indeed, and it does it's propulsion although the craft may be going at a higher speed than air in it's average direction through the fact that the wind is most of the time at an angle with it's disc, not perpendicular.

And then it not only propels the craft forward, but also does transmit some of this power (or energy: depends if you're fighting friction and acceleration, or simply cosntant motion) to the wheels which help this forward motion. Reciving the wind at an angle, it acts as a propeller which has a "lift" (remember the comparison with gyroplanes) AND as a turbine tranferring power to the wheels.

There is also something which, having indicated to me this funny treadmill video, should not have escape your attention: it is the comparative diameter of the wheels.

Doesn't your acute mechanical sense tell you that it would be a little difficult to the tiny wheels of Mr. goodman's "DDW..." thingy to transfer any torque to the big prop above? And these are not rubber on rubber like on the treadmill, but on gravels and irregular tarmac!

My poorly thought out foray, you said????

Joakim

11-20-2008, 09:11 AM

energy
as measured in newtons is directly proportional to velocity and mass
not just velocity

keeping it simple the max energy of this system
if the plate and the cart both weigh the same ( say 2kg each )
and if the cart starts out at 0m/s and the plate at 2m/s
is 1kgm/s
doesn't mater what the gearing is
we will consider torque in a moment

Please tell me how on earth can you measure energy in newtons? Since when is energy directly proportional to velocity?

As you should already understand this gearing cart is supposed to model a turbine/propeller craft in water/air interface or a propeller/wheel cart in air/road interface. Thus the fixed/ground is road/water and the "plate" is air flowing at wind velocity.

Please calculate the mass of air flowing around a lake of your choice and compare that to the mass of any vessel. Do you think it has enough kinetic energy to accelerate a vessel/cart.

Also keep in mind that there is a weather system that keeps up the wind velocity. It is the weather system (=sun) that provides the energy needed or the blower in a wind tunnel.

Joakim

Joakim

11-20-2008, 09:26 AM

for instance
E=mc2
or if you really want to get confused
E=hV

There is no relevance in this discussion to quantum physics, theory of relativity nor electromagnetic waves, all of which I have studied quite a bit. So please stop posting this BS.

This is just plain classical mechanics: http://en.wikipedia.org/wiki/Classical_mechanics
http://en.wikipedia.org/wiki/Newton's_laws_of_motion

Joakim

Joakim

11-20-2008, 09:55 AM

Was this here already? http://www.ayrs.org/DWFTTW_from_Catalyst_N23_Jan_2006.pdf

There are even some force and efficiency measurements.

Joakim

philSweet

11-20-2008, 02:07 PM

Boston and others,

Regarding your energetic defense of physical laws- you complain that we seem to be violating one when we carry a bucket of energy from the water to the air. Look at what happens to visible light when we do this. It refracts. It is in the nature of energy to do so across free surfaces. It appears to violate physical laws, but it doesn't. If you wish to carry energy accross the free surface, please include a refraction coefficient, or its analog, appropriate to the frame of reference being discussed. Or just do what we do- choose a frame of reference such as dynamics, in which only forces, not energy, need be transfered. If you want an energy model for the DDWFTTW proposition, please provide a convenient frame of reference for the workings such as Rick has done for the dynamic system. Will the velocity of wind and water appear in this frame of reference? If not, how can they create a limit to anything?

An infinite number of mathematicians walk into a bar. The first one orders a beer. The second orders half a beer. The third, a quarter of a beer. The bartender says "You're all idiots", and pours two beers.

Boston

11-20-2008, 04:21 PM

being wrong is one thing
being a poor sport
is just bad form

why the deflecting argument
instead of just a simple admission
the numbers have proven to be bunk
the model shown to be flawed
the concept shown to defy the simple laws of physics
and the gearing shown to be irrelevant on a dead down wind run

on the previous questions on force vs energy
the term energy and the term force are for all practical purposes interchangeable
while I would say we are talking NEWTON'S
that would be measured in kilograms moving one meter per second squared
when talking gearing expressed as a unit of energy or force
and what is energy or force
I think professor Mellendorf said it best

It is difficult to say whether potential energy causes force or vice versa.
Potential energy seems to be stored in the force between objects. If a
force causes an object to speed up, potential energy in the force becomes
kinetic energy in the object. If a force causes the object to slow down,
the reverse occurs. If a force only causes the object to change direction,
there is no transfer of energy. The force causes the transfer of potential
energy, but not necessarily its existence. We do not really know the answer
to this question.

argue with him if you chose

now go study up on flywheels and see if you gain a better understanding

but this pathetic argument in semantics is classic to people not willing to admit error
you cant just assign newton's to the equation with out defining mass
period
otherwise they are some kind of fig newton
and you still havnt addressed the flaws pointed out in the system

I was serious about buying in my previous
right wrong I just though Ild extend an olive branch
but instead of hoisting a few and making nice
you guys are showing some really bad form here

my point earlier about E=mc2 is that energy can be expressed in about a million ways
so whats the point about arguing which
when the subject is about DDWFTTW
eh

its ok to be wrong folks
Im wrong
your wrong
we are all wrong from time to time
hell
Ive made several silly errors in my argument against this thing
thing still doesnt work but I made mistakes to
so what
I was wrong
not so hard to admit
now you try it
just think of how relaxing the day is to have learned something and moved on
for everything Edison got rite
he got a hole lot wrong as well
peace people
I think we have beaten this horse to a bloody pulp
and I for one am not interested anymore
B

Guest625101138

11-20-2008, 04:29 PM

Joakim, Tcubed, Windmaster and all the others that have joined me in this bit of fun I think it is time to let the cat out of the bag. It is getting beyond a joke now and I have other things to get on with.

We might have eventually convinced Boston if 3dyachts had not weighed in late with his detailed observations. Although he did not get the Goodman cart right. His explanation on that IS crap. It just uses batteries. It had me fooled until I saw the original publication date of the article was April 2005. Also I do not think ALL the treadmill carts use the same trick with the "spirit" level (The "spirit" is clear set silicone rubber - the trouble people go to try to trick others). I believe some simply have fans running behind the carts so there is already air movement.

Anyhow Boston I think we had you tottering until you got a bit more support. Maybe if we could have convinced Guillermo to play along early on we might have fooled you. You're right of course. It is all about ENERGY. I thought Joakim's idea with the little cart and bringing gearing in on the act was plausible but you kept pushing - show me the energy balance. We cannot of course as this would prove it could not possibly work. Don't bother looking at the videos of my little cart. As 3dyachts pointed out they are just nonsense - nothing to do with the nub of the reality - energy.

I hope you are not put out by our elaborate ruse but we were just having some entertainment. Hopefully you do not feel it was at your expense. If you are upset with our sport then I apologies.

Rick W

Boston

11-20-2008, 04:34 PM

I was wondering why you guys wouldn't see reason
no worries
all in good fun

oh
and no
you didnt have me convinced at any time
wasnt even close
but you did have me fooled
I though you guys seriously believed in this thing
B

masalai

11-20-2008, 04:36 PM

Got me suckered too.... Good fun but and still an interesting read ... as I have said elsewhere - "never let the truth get in the way of a good story" don't know whose quote that is but I am using it :D:D:D:D:D

"You must spread some Reputation around before giving it to Rick Willoughby again." so I am constrained by rules..... Thanks from an old fart....

philSweet

11-20-2008, 06:34 PM

An infinite number of mathematicians walk into a bar. The first one orders a beer. The second orders half a beer. The third, a quarter of a beer. The bartender says "You're all idiots", and pours two beers.

Yes, it was in bad taste, and I appologize. I was trying point out the sillyness of doing things the hard way, but missed the mark.

Boston

11-20-2008, 06:41 PM

not really
I was actually on the way out the door to hoist a few
when I heard the comp chime
no flies on you mate
was a pretty funny joke all in all
I kinda got a bang out of it once I was let in on it
B

3dyachts

11-20-2008, 10:46 PM

We might have eventually convinced Boston if 3dyachts had not weighed in late with his detailed observations. Although he did not get the Goodman cart right. His explanation on that IS crap. It just uses batteries. ........ It is all about ENERGY. ...... As 3dyachts pointed out they are just nonsense - nothing to do with the nub of the reality - energy.

I hope you are not put out by our elaborate ruse but we were just having some entertainment. Hopefully you do not feel it was at your expense. If you are upset with our sport then I apologies.

Rick W

Well done! it really got me hooked up....but not fooled (excepted in thinking you really believed in all that! )

Then, first, may I ask how "real" was the original question that started the thread, ? Since it is that which got me hooked-up to start with, it "may" have been a pity that an interesting question got sunk because this April's fool game...!

Second is that, would there have been reality in the little cart video, I gave what I think is the only possible reponse to the accelaration of this cart: side wind. This is no BS.

Third is that: Sorry, but I do not see where was the slightest need to be "on the verge" of insults to someone who jumped in against this obvious DDTWF... nonsense affirmation ???
Gives this "joke" a bad taste.....!

kerosene

11-20-2008, 11:16 PM

I don't understand Rick why would they need a fan on the treadmill experiments as they are anyway totally irrelevant to the dilemma at hand...

Also - your cart example of having the board as a sliding non-exhaustible force that you could extract more speed from that it has. What was the relevance in the first place? Its not like wind is made out of plywood...

kerosene

11-21-2008, 12:21 AM

First - I am sorry but I cannot quit.

Originally Posted by Joakim View Post
First of all I think it is much easier to think about powers and forces. If you want energies, just multiply power with time.

"Multiply"..?????
Hum...sorry ...(I talk in low voice so that "the others" could not hear): Mass is mass. Speed is distance per time (meter per second for example). Mass multiplied by speed (Kilograms per meter per second) is kinetic energy. Mass multiplied by speed multiplied by time (Kilograms per meter per second squared) is acceleration. To have acceleration, you need power.
Power will be in Watts, horse-power...what you like...: see their definition!

The rest of the "demonstration" becomes less convincing when started with such a "missteake"!

3dyachts suggests that mutiplying power with time would NOT be energy. It very much is so. kW (kilowatt) is unit of power kWh (kilowatthour) is unit of energy - an can be expressed in joules if so wanted.

I am rusty with my physics as I do not need it these days too often.

F=m*a
(m=mass [kg], a=acceleration [m/(s*s)])

Kinetic energy is
E=(1/2)* (m * v * v)

(m=mass [kg], v=velocity [m/s])

it really does seem that joakim's formulas have no mistakes but your do.

I am still waiting a real explanation why it is possible to reach faster than downwind speeds (in actual travel) for an iceracer but not an apparatus of my video.

http://www.youtube.com/watch?v=IMEerIkOVZ0
http://www.youtube.com/watch?v=IMEerIkOVZ0

Boston

11-21-2008, 02:44 AM

try and let it go
it was a good joke on me
and im ok with it
whats life if we cant laugh at ourselves every once in a while
although
I do kinda miss beating the crap out of there arguments
it was so full of holes I was loving it
( going to have to do better than that kids )

the ice racers are actually dam efficient
they move tangential to the wind such that they realize an apparent wind at true wind speed
if you notice they have only two moving bits
the mast and the steering blade
any motion in the frame is directly subtracted from the forward motion of the vehicle so suspension is limited as much as possible
even the sail on the speedsters are solid vertical wings
the more rigged the better
gears would only slow it down
no matter how you arrange em
its back to basic physics for the fromula to explain it
which I dont remember off the top of my head
but look at the formula class cars
stiffest suspension they can carry
tight steering

dont get stuck on math games
its they theory that has to jive before any numbers need be crunched
I would never have admitted theoretical physics to these guys but that they had gotten stuck on a simple theory problem
not a math problem
or at least I thought they had
B

3dyachts

11-21-2008, 04:01 AM

Yes, sorry Kerosene, there was mistake in my post too! (late at night)
Kinetic energy needs a mass somewhere!
Acceleration does not. OK.
a.s.o...

Now, just like others, I am tired of this discussion which, actually, proved to be a not so funny joke due to some reactions (...) a bit difficult to understand.

Still, if you don't see how an ice-boat - or a windsurf board - goes so easily so fast: take a piece of soap, and squeeze it between your two hands, or better between two flat polished panes, nearly parallel, of whatever that is: see how fast it escapes!!!

One of your hands (or of the panes) is the wind, the other one are the skates (with a firm lateral grip in the ice) or the fin of the board, fighting against leeway.

You will see that the more your two panes are parallel, you will need less movement of one pane toward the other to get the soap escaping fast, and the more angle they have they will have to move closer to each other to make the soap escape slower and slower.

Think it out, but sorry: I am just too busy (and now bored by it) to continue this discussion.

Boston

11-21-2008, 04:14 AM

dont let a few poor sports get to you 3D
it was kinda funny in that dry English humor way
a few people
probably out of the loop
just got a little excited when they didnt understand the drivel that was intended to confuse and the people trying to unconfuse the drivel
I thought it kinda brought out the best in some
and the worst in a few others

Im just surprised no one actually bought me beer
I was right on target the hole way
I say they owe me a pint for being a good sport
and another for seeing the energy deficiency in there efforts from the word go
but no worries
there's a few nitwits in every pile
and after all
this is a big pile
B

3dyachts

11-21-2008, 11:51 AM

I was right on target the hole way

B

the "hole" way!!!???!

Now, yep: you owe me a double, you!

:p :)

Boston

11-21-2008, 03:15 PM

oh Im sure thats not the only thing I spelled wrong mate
its kinda my trademark

I hadnt really thought about DDWFTTW till some yoyo suggested it

http://i354.photobucket.com/albums/r420/maxtanks/mobiusgears500.jpg

and it was down hill from there
I didnt guess that they had a battery in that thing
but I did suggest that it was a fake
I also suggested that it was a simple matter of adding up the energies or frictions cant remember which
on both the tread mill trick and the gears thing to show it doesnt work
and I kicked there buts on there considerations of the physics involved
besides

at this point most of them are to embarrassed to show there smiling faces
either that or they are still rolling on the ground laughing

so I gotta wonder how many of em were in on it and how many were serious
I think they had a lot of people believing
there were thousands of reads on that post

it was fun
rubbing there noses in the physics
its been fun knowing it was all just a gag
and yerp
I think I was the only one who from the go consistently said
wont work guys
thats a few rounds my way if you ask me
no flies here mate

on a side note
I was over on the hydropter thread and noticed they were bickering about the kiting kids kicking the pants off the +50 record
and how they wont recognize them as the speed holders
funny
guy spends a hundred million on a boat to hit +50
and some stoner with a surf board and a kite nails it spending what
a few hundred
now that's funny
I suggested a head to head race
didnt go over very well
ya think

I want to see it
B

masalai

11-21-2008, 03:24 PM

Such strong denials seems to admit to some susceptibility and self defence at taking some of the bait.... :D:D:D:D

Boston

11-21-2008, 03:43 PM

oh Im guilty of that
as I said
I hadnt considered it before
so I had to think it through no doubt
but come on now
I pegged it
its not so hard to admit
you can fool some of the people some of the time
but :D

and it was dam funny guys
thanks for the laughs

Boston

11-21-2008, 03:53 PM

now If you will excuse me for a minute
Ive got to go find the kite boys and see if I can get em to challenge the hydropter guys
seems there is a little difference of opinion as to who holds the speed record
and frankly Ild love to see sea biscuit all over again

what a great name for the kite boarder to take on
yow

god I hope I can make this happen
what if we were to start a race fund
a few bucks from us all
as prize money
winner take all

does that violate site rules in any way
to suggest a race and start a prize fund
some one clue me in
cause Im not trying to violate any rules here
I just want a nice sportsman like race between David and Goliath
would be the event of the century
world news stuff
Im calling CNN
maybe they can pull this off

Tcubed

11-21-2008, 04:45 PM

Yeah that sure was funny, i'm still laughing now. I guess there's always someone who's kind enough to call an end to a prank.

Sorry if i was a bit harsh at times, had to sound authentic you know......

We all knew it couldn't go on indefinitely, especially when E=mc2 was mentioned....

Boston

11-21-2008, 04:48 PM

to funny
was a great time

Guillermo

11-22-2008, 05:09 AM

lunatic

11-22-2008, 09:21 AM

More rotor musings. I assume true wind is affected by a spinning rotor's downwash before it becomes part of blades' apparent wind. I have a rather messy image of two colliding air masses, in a neater abstraction, opposing downwash would reduce upwash resulting in a negative (ground?) effect. The use of high speed twistedly bladed rotors with highest opposing downwash is dominant, but still not close to Betz limit. Is the problem in the wake, or might it be up front.

Joakim

11-22-2008, 09:42 AM

**** you, Rick! :D (And Joakim, Tcubed and others)
I thought (and very surprised, indeed!) you were seriously supporting the damn DDWFTTW thing!

All the best.

And we were. Love to here your current opinion.

Joakim

tspeer

11-22-2008, 01:48 PM

I should be ashamed of myself for lobbing such a piece of red meat as DDWFTTW into a pool of alligators like this forum just to watch the action! ;-)

The attached file is rather off topic, but it is an elegant analysis of another form of wind-powered travel that can go down-wind 40% faster than the wind. Enjoy.

Windmaster

11-23-2008, 10:34 AM

An Albatross, or a glider, or any aircraft can certainly travel downwind faster than the wind. It needs to move through the airmass in order to stay aloft.

It's speed over the ground directly downwind = its flying speed + the windspeed.

I don't think anyone could dispute that.

But you never know on here!....:?:

Tcubed

11-23-2008, 11:29 AM

Thank you Speer for that beautiful attachment.

I had long known of the capacity for energy extraction across a sheared flow like that but had never come across an in depth analysis of it.

I had also observed the phenomenon being used by seabirds- not only albatrosses use the technique, although they must undoubtedly be the masters of it.

The technique is actually even more powerful than as described in the analysis due to ground effect. This allows the bird to drastically increase its L/D during a portion of the upwind part of the cycle. This applies in flat water as well.

Naturally, when there is wind there is also waves and (this is alluded to in the presentation) this allows the bird to time its cycles with the upwind portion of the waves and further enjoy the lift off of them.

It is interesting to note that the upwind portion of the wind is not necessarily the backs of the waves. In the waning part of a weather system the wind decreases to a value inferior of that of the celerity of the wave trains created previously by the stronger winds.

There is yet another phenomena which i saw used in a calm (when there is no wind shear) and that is simply flying down the faces of old swells. By adjusting flight speed to coincide with the celerity of the swell the bird remains in the lift area and "surfs" down it, at least until that swell reaches the end of its group and decays.

The upshot of all this is that there are many ways to extract energy from a velocity gradient and the speed of the object is limited by its own efficiency, unbounded by the actual velocities, or velocity differences within the energy giving flow.

markdrela

11-23-2008, 11:45 AM

I had also observed the phenomenon being used by seabirds- not only albatrosses use the technique, although they must undoubtedly be the masters of it.
Naturally, when there is wind there is also waves and (this is alluded to in the presentation) this allows the bird to time its cycles with the upwind portion of the waves and further enjoy the lift off of them. I think what you're describing is "slope lift", which is not what the albatross uses. It uses the horizontal wind shear -- the vertical velocities near the waves are relatively insignificant.
The most spectacular example of Dynamic Soaring today is done by RC sailplanes. This is done on the downwind side of a hill, by circling through the shear layer which comes off the hill crest, much like an albatross circles in the surface boundary layer shear. The current DS speed record is 371 mph, in roughly a 40 mph wind. Here's one video as an example:
http://www.youtube.com/watch?v=Vi0hrjqU15I

Tcubed

11-23-2008, 12:34 PM

That's right, which is why in the presentation Barnes specifies waveless seas, so as to analyze dynamic soaring independently from slope lift effects.

In reality the bird soars dynamically, but also takes advantage of the slope lift where and when possible. So the bird really has a range of options from which to maximize it's energy efficiency.

Boston

11-23-2008, 12:51 PM

Boston

11-23-2008, 03:10 PM

it would be so easy to get sucked into this again
thank god I dont know Jack about birds

as for why can the rc go so fast
think circular flight pattern on an oblique plane in a steady updraft
normally angular momentum is defined as
J=mvr
( dam I hope I remembered that right )
but this case is not simple angular momentum as there are two drivers in the system
gravity and wind
not sure I can but maybe I can dream up a defining equation for the amazing speed that rc is gaining in these conditions
I think the energy in a flywheel is defined as on half its moment of inertia times its angular velocity squared ( squared part is the kicker )
basically
E=1/2AvI2
ok doesnt write very well on this computer
now two things about that number
angular velocity is measured about a radian with a fixed center of rotation
and we dont have a fixed center of rotation
so there are multiple centripetal forces at work
both I think would result in the squaring of the velocities they impart
( not sure thats a fair way to handle it but it feels right )
( feel free to help if you know the proper calculation )
dam I havnt tried to work this king of thing out in a while
ok so
there is a oblong instead of circular flight pattern but Im going to work it out like it was a flywheel with an imaginary increase in the length of some of the radians with out an increase in time for those radians because they center of rotation is altering relative to ground not relative to wind
( if that makes any sence to anyone else feel free to applaud )
because the wind is pushing this thing at whatever wind speed is faster with each loop
so Im going to try to add for the wind boost at perpendicular to wind
and emagine its neutral on the dead down wind and up wind runs
into and upwind there is no relative gain but the velocity caried out of each turn should carry along just fine
also there is a gravity gain with each loop 9.91N I think for the drop in altitude considering mass and that the uphill climb can be attributed to wind direction and lift
so thats 9.91N
measured in
drum roll people
NEWTONS
ok gotta go flip laundry
brb

Boston

11-23-2008, 03:20 PM

ok
dam I got sucked in again
complex orbital mechanics was one of my favorites
the short answer is that oblong pattern is helping out a lot
the oblique nature of the pattern is adding some
the wind itself is the main driver and is driving him faster with each circuit competed
the gravitational force is adding some
so
hella fast
hows that for a technical explanation

guess laundry brought me back to reality eh
love B

dam I just remembered
its called hyperbolic excess velocity and there is some formula that some one is about to rub my nose in that covers the concept

Hella fast

Tcubed

11-23-2008, 03:29 PM

Ummm.... Actually that sailplane is flying in an area of sink, not updraft.

Boston

11-23-2008, 03:33 PM

did any one notice the smog in the background of that flicker
wow

markdrela

11-23-2008, 03:46 PM

i as for why can the rc go so fast
think circular flight pattern on an oblique plane in a steady updraft
...
but this case is not simple angular momentum as there are two drivers in the system
gravity and wind In RC Dynamic Soaring, updrafts and gravity are both are irrelevant. There is no updraft on the downwind side of the hill where DS is done, and the airloads are vastly greater than the gravity forces. The plane is driven entirely by the horizontal velocity difference across the shear layer.

One can make a crude force/power analogy of DS and conventional sailing:
* The wind shear layer is like the air/water interface, but smeared vertically somewhat.
* When the glider is above the shear layer its wings act like sails.
* When the glider is below the shear layer its wings act like the keel.
* Both the DS glider and the sailboat extract power from the velocity difference across the shear layer or air/water interface.
One difference is that the "sail" and "keel" driving forces on the DS glider are intermittent, while on a sailboat they are steady.

One could imagine a flying fish doing "dynamic soaring" in a strong wind storm. The fish leaps into the air against the wind, spreads its fins/wings and does a 180 deg turn, dives back into the water with fins mostly folded, does a 180 deg turn underwater, leaps back into the air, etc. If its drag is low enough, the fish could do this by inertia alone, without any muscle power.

Joakim

11-23-2008, 04:05 PM

In RC Dynamic Soaring, updrafts and gravity are both are irrelevant.

Is gravity really irrelevant? As a first thought I would think gravity is very necessary, since it used to gain speed. Is it not important that there is gravity and thus you are able to gain potential energy while going against the wind?

I think there always has to be a connection between the two different velocities/fluids. In DDFTTW it is the transmission between the propeller and turbine and in soaring it is the gravity. I may be wrong about soaring, since I haven't yet understood it well enough.

Joakim

markdrela

11-23-2008, 04:39 PM

Is gravity really irrelevant? As a first thought I would think gravity is very necessary, since it used to gain speed. Is it not important that there is gravity and thus you are able to gain potential energy while going against the wind? The high and low points of the orbit are about 50m apart vertically. That translates to a change of 500 J/kg in potential energy. When the glider is going at 160 m/s (360 mph), its kinetic energy is 12800 J/kg. So the potential energy changes are just a few percent of the kinetic energy, i.e. negligible. Another way to look at it: When a 160 m/s glider drops down the 50 meters without drag, its new speed from the extra energy is only 163 m/s --- not a significant change.

I think there always has to be a connection between the two different velocities/fluids. In DDFTTW it is the transmission between the propeller and turbine and in soaring it is the gravity. The only requirement is that there is a zero net force vector, in order to produce a steady state operation. In DS, the net force vector is zero when averaged over the orbit, since the orbit center stays in place, and doesn't accelerate away.

Boston

11-23-2008, 05:03 PM

since the orbit center stays in place, and doesn't accelerate away.
I gotto wonder about that
if you look at any attempted circular pattern in a cross wind up draft
or call it what you may you would get some slipping relative to ground
thus my thought there would be an excess hyperbolic velocity
also since the velocities of the radian is squared it actually would add significantly
I think
I didnt crunch any numbers
but
seems like it aught to be
B

could be why there plane broke

Tcubed

11-23-2008, 06:33 PM

That's a nice analogy you've offered and should help people imagine what is going on. The plane is almost "bouncing" between being a keel and being a sail.

However, to be slightly pedantic, there will always be sink to leeward of a mount like that. The amount of sink will depend naturally on the specific topography,flow separation etc.. The sink is adverse to soaring so the pilot must be fairly proficient at getting into DS mode or he'll lose the model down the slope.
But yes, once at speed the sink becomes a relatively unimportant factor.

Boston

11-23-2008, 09:19 PM

no doubt wind shear is the main driver
but
although my bet is they crunched a lot of numbers before they decided to make the wings and connecting surfaces x thick
thing is if you look through, there is a video of the plane breaking
not surprising since complex orbital mechanics is a mind bender it may have been forgotten in the calculations
and if I remember calculating the induced or excess hyperbolic velocity is a problem taught in diffy Q not even sure they had that in vector analysis
top end of math kids
the theoretical physics and electrical engineering folks all took it
but not sure the basic structural engineer is required to take it
not even sure a aeronautics engineer would have taken it
its not a class for a week of heart
and frankly
Ive forgotten virtually all of it
but
it will add some to the energy of the system
its one reason there is a turn involved in dynamic soaring
other than the obvious
sooooo
Im out
thanks for the entertainment
was great
B

Joakim

11-24-2008, 02:31 AM

The high and low points of the orbit are about 50m apart vertically. That translates to a change of 500 J/kg in potential energy. When the glider is going at 160 m/s (360 mph), its kinetic energy is 12800 J/kg. So the potential energy changes are just a few percent of the kinetic energy, i.e. negligible. Another way to look at it: When a 160 m/s glider drops down the 50 meters without drag, its new speed from the extra energy is only 163 m/s --- not a significant change.

The glider needs to have a side force in order to "get thrust" from the wind, that is going much slower than the glider. I guess at that point the side force comes from acceleration due to turning, but in the beginning it must have started with gravity. With that 500 J/kg you can achieve a initial speed of ~30 m/s. How many loops you need to get that 160 m/s?

How much does the speed (kinetic energy) change during each loop. I guess the speed is at maximum just before diving into boundary layer and at minimum before getting back to high wind.

Joakim

markdrela

11-24-2008, 11:00 AM

The attached diagram shows what happens in DS.

Windmaster

12-13-2008, 09:04 AM

Here's an interesting video about this:

http://www.boingboing.net/2008/12/12/downwind-faster-than-1.html

Don't be put off - stay with it - its not for children!

masalai

12-13-2008, 04:06 PM

Windmaster, The debate has raged and Rick & a few admitted to a hoax but I am still confused as I have limited theoretical training and failed in advanced maths so I stick to computing - which is just "talking in another language"...

If the mythbusters get to play with this concept - do please post on BD.net - in "Drivel" if busted and a link there if "plausible" It could keep many of us occupied and entertained for a looooong time... Thanks...

ThinAirDesigns

12-23-2008, 08:16 PM

Hello all.

I can see that I'm late to this party, but thought I would weigh in anyway.

I'm JB and I'm the guy you see in the MythBuster's Challenge video. My partner and I have built over 10 of these DDWFTTW carts and demonstrated them many times.

In spite of the humor of Rick's last posts here, there is no hoax. There is no CGI. There is not string pulling the cart. There is no perpetual motion. There is only long used traditional sailing principles wrapped in a clever, unfamiliar and unintuitive package.

The packaging truly allows the vehicle to travel directly downwind, faster than the wind, powered only by the wind, steady state.

I can offer the math. I can offer analogies. I can offer explanations from simple to complex. Happy to answer any questions.

It's real, it does what we say it does and it can be demonstrated upon request. We present it not as something useful (it's really not), but as a physics brainteaser that confounds some pretty bright people.

We are currently in the design/build process of a ride-along vehicle with which we will be attempting to exceed the downwind velocity of the wind by more than 2x, all while traveling DDW. As the windspeed gets exceeded by such a multiple, it make people look more and more silly when they say it can't even be equaled, let alone exceeded.

Fire away.

JB

PS: Nice to see Mark Drela here -- you're reputation precedes you (courtesy of JJcotes and many, many others -- and of course your work)