The Wind Powered Sail-less Boat

[spork]

Talking about the open air test, how is it possible for the rotor to change sense of turning? :confused: .

I guess I'll just have to learn to accept that you'll never understand that the "open air" test and the "treadmill" test are THE SAME. In fact they're both in "open air". It just happens that in the "treadmill" test we have MUCH better control of the wind speed and direction, the grade of the surface, etc.

[Guest625101138]

Thanks Rick,
Talking about the open air test, how is it possible for the rotor to change sense of turning? :confused:

Cheers.

Guillermo
If you are meaning the situation in the second open air trial where the rotor begins to operate as a turbine you will see it is actually spinning the wheels in reverse. The torque from the rotor is greater than the torque limit resulting from the coefficient of friction and weight on the two front wheels. About 3m after taking off with the rotor forcing the wheels in reverse you see the rotor reverses and becomes a propeller being driven by the wheels.

This is the situation I describe with the turbine boat in post #719:
"I have not done precise calculations on the very low boat speed condition. There is likely to be reverse rotation of the prop when the boat is stopped because the prop has a good reverse flow regime under this condition while the turbine is in a poor regime. But the downwind force will cause the boat to progress downwind such that the reverse flow regime on the prop gets worse and the forward flow regime on the turbine improves. Once this happens the mechanical advantage of the turbine takes over and away it goes, accelerating until there is a force and power balance somewhere higher than windspeed."

You will note by the speed of the litter past the cart there is a strong gust. This puts the rotor in a high power regime which is sufficient to overcome the wheels. Once the vehicle starts moving to reduce apparent wind the rotor torque is reducing and the wheels stop slipping.

Point is you can see the rotor change direction and become a propeller. Once this occurs it is bringing air backwards through the disc. There is clearly no stagnation point or vortex trap that it gets stuck in. It is a pity there is not more litter as you would be able to see it quickly reaches wind speed.

Maybe this is a simple test that could be done with some fine powder being dropped in the wind stream as the vehicle is taking off.

Rick W

[spork]

Maybe this is a simple test that could be done with some fine powder being dropped in the wind stream as the vehicle is taking off.

That particular self-starting demo ended up being a bizarre mixed blessing. On the one hand it underscores some interesting aspects of how this cart operates, but on the other it seems to be the source of a whole new laundry list of concerns.

Rick is absolutely correct that the critical aspect of this particular demonstration is the gust and the wheel slip. I also did a self-start demo with a fan indoors. Perhaps repeating that demo with smoke might show what we want to see.

[Guillermo]

Once the vehicle starts moving to reduce apparent wind the rotor torque is reducing and the wheels stop slipping.

So the wheels slip initially. I see, thanks.
A pity the video is not in slow movement mode, to better realize the rotor and wheels turning.

Cheers

[SamSam]

How can we convince you that the principle of equivalence of inertial frames is real - and applies to treadmills? This is one of the most basic tenets of physics.

Somewhere here someone mentioned Galilian Relativity or something so I looked it up in wiki. Eventually I was led to a site that showed Galileo's method of explaining it, which was a "narration" where you were to imagine various happenings going on in a ship's hold as it sailed along. Examples were weights dropped, people jumping in the air etc. Lastly was the example that smoke from a candle would go straight up in the air. At the end of the story/narration the fellow talking said all these "truths" held good below decks, but were not the same above decks in the airstream.

Reading one thing led to others and even though I don't grasp much of it, isn't below decks 'equivalent inertial frames' and above decks in the wind 'non-inertial frames', which require "ficticious" (not my word) equations to be right?

As far as a powered treadmill being the same as a blowing wind, in some cases that might hold true, but in a wind powered device, which together with DDW, is the priority claim in all this discussion, is it the same? A model sailplane tethered to the front of a running treadmill won't fly, but tethered to a running person it will.

Is it possible that in the treadmill powered cart you are not necessarily going faster than the wind, you are just going faster than the treadmill? Are they the same thing?

[ThinAirDesigns]

As far as a powered treadmill being the same as a blowing wind, in some cases that might hold true, but in a wind powered device, which together with DDW, is the priority claim in all this discussion, is it the same?

Yes.

A model sailplane tethered to the front of a running treadmill won't fly, but tethered to a running person it will.

I guess I don't follow what you are imagining, because tethered properly, the sailplane will fly in both cases.

Imagine a long airport people mover and two light styrofoam models with identical strings say 20ft in length. One string is taped to the floor of the moving sidewalk and one is place in the hand of a person next to the sidewalk . As the people mover is turned on and starts to move at 4mph, the person also starts moving at 4mph. The planes will both be pulled through the air at 4mph and will both fly.

You'll have to explain where my example fails relative to what you are imagining.

Is it possible that in the treadmill powered cart you are not necessarily going faster than the wind, you are just going faster than the treadmill? Are they the same thing?

The cart traveling faster than the belt of the treadmill is truly traveling faster than the wind.

Imagine riding your bike down the road at 10mph with a 10mph tailwind -- you're pumping your legs, and your wheels are turning but you feel absolutely no wind on your face. Now ride on a treadmill set at 10mph -- you're pumping your legs, and your wheels are turning but you feel absolutely no wind on your face.

Without external reference, it is *impossible* for you to tell whether you are on the treadmill or on the street in those above scenarios. This is the point of Galilean relativity.

JB

[spork]

SamSam, it looks like JB beat me to the answers. So I'm definitely not ignoring you, but I think JB covered it. If you'll direct me to the site that said things are different above deck I'll be happy to have a look. I suspect they were saying that things would be different above deck because of the relative wind (in other words a ball thrown straight up wouldn't land in the same place), but that simply means they haven't set up truly equivalent inertial frames. If the ship had a tailwind equal to its speed things would work exactly the same above or below deck. Make sense?

[chabrenas]

It really does look as if the prop on the roadcart autorotates a small fraction of a turn before being driven. Seems too slow for an artefact of the frame rate. Is it taking up slack in the drive train? Maybe even winding up the drive shaft?

Guillermo: I don't accept your proposition that a sail harvests energy from a bigger cross-section of an airflow by traversing across it. In my view, only a bigger sail does that.

I believe that the sail gets more energy from the air (the wind does more work on it) because it is rigidly attached to an object that is immersed in a fluid (or in contact with a solid) that has motion relative to the air mass, and which can apply reactive forces that cause the sail to move in such a way as to increase the relative velocity between the sail and the air mass (i.e. to create an apparent wind which is the vector sum of the transverse motion and the relative motion of the air mass and the second medium).

In a boat, the keel or centreboard provides that force, and on a cart the friction between the wheels and the surface of the solid do so.

[Guillermo]

.... In my view, only a bigger sail does that....
Mike,

For a given size of sails and wind speed, the overall energy gotten from the wind depends on how much mass of wind the sails are using and their efficiency in altering its direction/speed of movement. Mass used depends on relative directions and speeds of craft and wind, and change of wind direction/speed on the sails efficiency for such specific relative movement.

Once discounted all loses in the sails, the net amount of captured energy can be more or less effectively used depending on the ability of the interface system (underbody, wheels, skates, etc) in keeping the craft moving in the desired direction with the less possible loses (heel, drag, friction, etc), so how efficient such interface system is in maximizing the desired use of energy. Of course this influences the relative direction and speed between craft and wind, so influencing the amount of mass of wind used, as said before.

I hope to have been able to make myself understand.


Cheers.

[chabrenas]

Guillermo: I agree with both paragraphs of your response.

I also believe that this means that, given a specific wind velocity relative to the water or land mass, the only way to make available more energy than that available from the flux through a projection of the sail profile on a plane normal to the relative motion of air and water/land, you have to increase the velocity of the sail relative to the air mass.

A traditional sailing boat (or ice or land yacht) does this by developing a velocity component normal to that between air and water/land, and hence a resultant velocity relative to the air mass that is greater than the relative motion of the air and the water/land (and we usually call this resultant velocity the 'apparent wind').

Hence, it is this increase in velocity of the sail relative to the air that is the source of the extra energy, not the fact that the sail harvests energy from an area greater than its projection on the plane normal to the relative motion of air and water/land.

[Guest625101138]

Some have difficulty understanding where the power comes from with the propeller. The following shows what energy the air loses in two cases.

Case 1 is a propeller in still air with a vehicle doing 1m/s.

Consider the propeller accelerating the incoming air stream by 0.5m/s so it goes through the disc at 1.5m/s. At this flow rate we will select the prop area to have a mass flow of 100kg/s.

In this case the air is at rest before the vehicle passes but is moving in the reverse direction at 0.5m/s after the vehicle passes.

Energy/s (power) = 0.5 x mass/s x (VAafter^2 - VAinitially^2)
= 0.5 x 100 x (0.5^2 - 0^2)
= 12.5W
So the air has gained 12.5W as the vehicle passed. The only way this can be done is to provide an external power source as the air has gained energy. This energy is what the prop must produce if it could work at 100% efficiency.

Case 2 is the vehicle operating at 4m/s in a tail wind of 3m/s such that the propeller sees EXACTLY the same operating conditions. Air flow into the prop is 1m/s and the air is accelerated rearward at 0.5m/s so passes through at 1.5m/s as before. Mass flow through the disc is the same. The airflow ahead of the vehicle is 3m/s and reduces to 2.5m/s within the prop disc after the vehicle has passed.

Energy/s (power) = 0.5 x mass/s x ((VAafter^2 - VAinitially^2)
= 0.5 x 100 x (2.5^2 - 3^2)
= -137.5W
In this case the air is losing energy at a rate 137.5W. The prop only needs to deliver 12.5W to achieve this result. So there is 125W available to overcome system losses and vehicle drag.

Hopefully this analysis shows in very simple terms where the energy comes from.

Rick W

[markdrela]

Some have difficulty understanding where the power comes from with the propeller. I have an even simpler way to explain it. The attached PDF shows the DDWFTTW situation boiled down to its absolute base minimum:
* The prop and turbine powers are equal.
* The prop sees a slower velocity and therefore has a proportionally larger force than the turbine.
QED.

The naysayers can now throw at this all the losses, inefficiencies, etc that they want. But the simple fact is that if these losses are made low enough, as they always can be, the prop's thrust force will always be greater than the turbine's retarding force. So there's some excess thrust left over to overcome hull drag.

[Joakim]

I have an even simpler way to explain it. The attached PDF shows the DDWFTTW situation boiled down to its absolute base minimum:
* The prop and turbine powers are equal.
* The prop sees a slower velocity and therefore has a proportionally larger force than the turbine.
QED.


Now we have made a loop and came back to where we were 50 pages ago. This didn't help then, probably won't help now, since it seems too hard to understand for most naysayers.

Joakim

[Guest625101138]

Joakim
It seems we now have full agreement that it is possible. The nay sayers have finally been convinced.

If they had have given it some clear reasoning in the first place rather than just offering ill-thought opinions and trying to justify their position it would have been a much shorter thread.

Rick W

[spork]

Joakim
It seems we now have full agreement that it is possible. The nay sayers have finally been convinced.

If they had have given it some clear reasoning in the first place rather than just offering ill-thought opinions and trying to justify their position it would have been a much shorter thread.

Rick W

I'll be happy to provide nay sayers from other forums if you like. We have one guy that is absolutely impervious to reason or logic.

[clmanges]

SamSam wrote:
As far as a powered treadmill being the same as a blowing wind, in some cases that might hold true, but in a wind powered device, which together with DDW, is the priority claim in all this discussion, is it the same? A model sailplane tethered to the front of a running treadmill won't fly, but tethered to a running person it will.

I understand this argument. The man running on the treadmill experiences zero wind velocity, regardless of his groundspeed, so the sailplane (which should be tethered to the man and not the treadmill, btw) also experiences zero windspeed. Take him off the treadmill, and he will run at the same groundspeed, but will now have windspeed equal to that, so the plane will fly.

The problem is that a sailplane is not the same device as the prop-driven cart or boat; the sailplane is not capable of generating its own wind.

[spork]

This is a complete red herring. The equivalent frame is that of the belt, not the structure of the treadmill. Tether the sailplane to the treadmill's belt and it will fly just fine. The belt IS an equivalent frame to the road surface with a wind blowing over it - thus it will behave the same in all respects and give the same result for any experiment.

[sailor2]

A traditional sailing boat (or ice or land yacht) does this by developing a velocity component normal to that between air and water/land, and hence a resultant velocity relative to the air mass that is greater than the relative motion of the air and the water/land (and we usually call this resultant velocity the 'apparent wind').

Hence, it is this increase in velocity of the sail relative to the air that is the source of the extra energy, not the fact that the sail harvests energy from an area greater than its projection on the plane normal to the relative motion of air and water/land.
No, replace word source with cause and I would agree.
Source is still the relative speed between air & ground (or water)
Extra source isn't necessarily even needed, but for any given time intervall, moving laterally, like most iceboats do, increases the source volume and with given density also source mass and thus energysource is greater as well.
Apparent wind is not related to source of energy only the cause of more being available.

[sailor2]

Some have difficulty understanding where the power comes from with the propeller. The following shows what energy the air loses in two cases.

Case 1 is a propeller in still air with a vehicle doing 1m/s.

Consider the propeller accelerating the incoming air stream by 0.5m/s so it goes through the disc at 1.5m/s. At this flow rate we will select the prop area to have a mass flow of 100kg/s.

In this case the air is at rest before the vehicle passes but is moving in the reverse direction at 0.5m/s after the vehicle passes.

Energy/s (power) = 0.5 x mass/s x (VAafter^2 - VAinitially^2)
= 0.5 x 100 x (0.5^2 - 0^2)
= 12.5W
So the air has gained 12.5W as the vehicle passed. The only way this can be done is to provide an external power source as the air has gained energy. This energy is what the prop must produce if it could work at 100% efficiency.

Case 2 is the vehicle operating at 4m/s in a tail wind of 3m/s such that the propeller sees EXACTLY the same operating conditions. Air flow into the prop is 1m/s and the air is accelerated rearward at 0.5m/s so passes through at 1.5m/s as before. Mass flow through the disc is the same. The airflow ahead of the vehicle is 3m/s and reduces to 2.5m/s within the prop disc after the vehicle has passed.

Energy/s (power) = 0.5 x mass/s x ((VAafter^2 - VAinitially^2)
= 0.5 x 100 x (2.5^2 - 3^2)
= -137.5W
In this case the air is losing energy at a rate 137.5W. The prop only needs to deliver 12.5W to achieve this result. So there is 125W available to overcome system losses and vehicle drag.

Hopefully this analysis shows in very simple terms where the energy comes from.

Rick W
I disagree. With your assumed 100% efficient prop, you get 137.5 watts of power, not just 125W. Off course there is no 100% efficient prop in reality, but if you assume it in the first case, why not in the second case ?
Substracting something out from 137.5W suggests violation of conservation of energy with 100% efficient prop. All the energy extracted from air has to go somewhere, if you claim 125W is available, what happens to the rest of it ?

[sailor2]

Mike,

For a given size of sails and wind speed, the overall energy gotten from the wind depends on how much mass of wind the sails are using and their efficiency in altering its direction/speed of movement. Mass used depends on relative directions and speeds of craft and wind, and change of wind direction/speed on the sails efficiency for such specific relative movement.

Once discounted all loses in the sails, the net amount of captured energy can be more or less effectively used depending on the ability of the interface system (underbody, wheels, skates, etc) in keeping the craft moving in the desired direction with the less possible loses (heel, drag, friction, etc), so how efficient such interface system is in maximizing the desired use of energy. Of course this influences the relative direction and speed between craft and wind, so influencing the amount of mass of wind used, as said before.

I hope to have been able to make myself understand.


Cheers.
Guillermo, that's the best post by far you have posted in this thread.
Now apply same logical thinking to the rest of it, and you'll see how ddwfttw is possible.

[sailor2]

I understand this argument. The man running on the treadmill experiences zero wind velocity, regardless of his groundspeed, so the sailplane (which should be tethered to the man and not the treadmill, btw) also experiences zero windspeed. Take him off the treadmill, and he will run at the same groundspeed, but will now have windspeed equal to that, so the plane will fly.

The problem is that a sailplane is not the same device as the prop-driven cart or boat; the sailplane is not capable of generating its own wind.
1)The man running on the treadmill experiences zero apparent wind velocity, regardless of his groundspeed, so the sailplane (which should be tethered to the man and not the treadmill, btw) also experiences zero apparentwind speed and the plane will not fly.

2)Take him off the treadmill, and he will run at the same groundspeed downwind as the true wind, but will have zero apparentwindspeed, so the plane will not fly in either case.

Just as principle of equivalent reference frames requires to happen, proving once more, how great and correct and useful that principle is.

[kerosene]

sailor2 beat me -
it is exactly the same case.

Traveling on treadmill is same as traveling downwind at wind speed = apparent wind zero. Exactly same rules apply to the model plane as the DDW-cart

[Guest625101138]

I disagree. With your assumed 100% efficient prop, you get 137.5 watts of power, not just 125W. Off course there is no 100% efficient prop in reality, but if you assume it in the first case, why not in the second case ?
Substracting something out from 137.5W suggests violation of conservation of energy with 100% efficient prop. All the energy extracted from air has to go somewhere, if you claim 125W is available, what happens to the rest of it ?

The only way to get the air to lose 137.5W under the stated conditions is to add 12.5W from the propeller. The conditions for the propeller do not change in either case. This leaves 125W to overcome vehicle drag and transmission losses in transferring said 12.5W power from the wheels back to the air via the propeller. If there is excess power then this will will result in excess thrust accelerating the cart.

Rick W

[clmanges]

Sailor2 wrote:1)The man running on the treadmill experiences zero apparent wind velocity, regardless of his groundspeed, so the sailplane (which should be tethered to the man and not the treadmill, btw) also experiences zero apparentwind speed and the plane will not fly.

2)Take him off the treadmill, and he will run at the same groundspeed downwind as the true wind, but will have zero apparentwindspeed, so the plane will not fly in either case.

Sorry for the confusion; I should have been more specific about the conditions.
In the case I set up, there is no wind velocity; treadmill with man on it are in still air. Then, man running in still air off the treadmill experiences apparent wind equal and opposite to his groundspeed. This relates to the treadmill videos, because there was no ambient wind in those examples, either.

Sailplane tethered to the treadmill's belt -- well, I hadn't thought of it that way, but yes, it will fly -- just long enough to get pulled into the machinery, even though it has zero groundspeed relative to the belt. The belt and the plane both experience a headwind due to their motion relative to the still air, while the man running on the treadmill would not.

Better?

[Guest625101138]

I'll be happy to provide nay sayers from other forums if you like. We have one guy that is absolutely impervious to reason or logic.

What can I say to that - There are slow learners and poor educators. Maybe we have a better mix here.

However it does raise the question on progress with full-scale demonstration and indisputable evidence.

Rick W

[sailor2]

The only way to get the air to lose 137.5W under the stated conditions is to add 12.5W from the propeller. The conditions for the propeller do not change in either case. This leaves 125W to overcome vehicle drag and transmission losses in transferring said 12.5W power from the wheels back to the air via the propeller. If there is excess power then this will will result in excess thrust accelerating the cart.

Rick W
No, under stated conditions 100% efficient prop needs zero watts from the shaft to extract 137.5W from the air. If you add 12.5W from the shaft to keep conditions of the prop the same & 137.5W from the air that's 150W total which have to go somewhere, not 125W !!! That's a scalar addition and both are positive !

The prop doesn't have energy from which to lose at 12.5 Watt rate.
The shaft can deliver that rate if you want, but it's then added to the amount from the air, not substracted. Just like in the first scenario where power delivered from air is negative and again addition of -12.5W & 12.5W = zero total.
The difference of the cases is still 150 Watts.

Read this part from your original post again :
Case1:
Energy/s (power) = 0.5 x mass/s x (VAafter^2 - VAinitially^2)
= 0.5 x 100 x (0.5^2 - 0^2)
= 12.5W

Case 2:
Energy/s (power) = 0.5 x mass/s x ((VAafter^2 - VAinitially^2)
= 0.5 x 100 x (2.5^2 - 3^2)
= -137.5W Case1 - case2 = 150 Watts. The difference of the cases is 150 W

[sailor2]

Sorry for the confusion; I should have been more specific about the conditions.
In the case I set up, there is no wind velocity; treadmill with man on it are in still air. Then, man running in still air off the treadmill experiences apparent wind equal and opposite to his groundspeed. This relates to the treadmill videos, because there was no ambient wind in those examples, either.
Better?
Yes, and that's exactly the case I wrote about and which you just replyed to.
In both cases no apparent wind. No difference if outside or on treadmill.

[Guest625101138]

No, under stated conditions 100% efficient prop needs zero watts from the shaft to extract 137.5W from the air. If you add 12.5W from the shaft to keep conditions of the prop the same & 137.5W from the air that's 150W total which have to go somewhere, not 125W !!! That's a scalar addition and both are positive !

The prop doesn't have energy from which to lose at 12.5 Watt rate.
The shaft can deliver that rate if you want, but it's then added to the amount from the air, not substracted. Just like in the first scenario where power delivered from air is negative and again addition of -12.5W & 12.5W = zero total.
The difference of the cases is still 150 Watts.

Read this part from your original post again :
Case1 - case2 = 150 Watts. The difference of the cases is 150 W

The calculation of the work is unrelated to the difference between case 1 and case 2. It is simply the rate of energy either added to or taken from the air stream as calculated from the velocity changes and the mass flow rate in either case.

In the second case the air certainly gives up 137.5W.

However the rate of work being done by the air on the vehicle IS 150W. This is the sum of what the air loses and what the prop contributes. So you are correct in that the 12.5W is already allowed for in the 137.5W.

Rick W

[clmanges]

Yes, and that's exactly the case I wrote about and which you just replyed to.
In both cases no apparent wind. No difference if outside or on treadmill.

Let me try this again. Air speed relative to ground is zero in both cases. On the treadmill, the man -- and the plane he's pulling -- both experience zero wind velocity; even though they both have some speed relative to the treadmill belt, neither they, nor the surrounding air, are moving relative to the fixed ground.
Off the treadmill, the man is then moving at some speed relative to the ground, but the air is not, so the man sees a headwind, and so does the plane.

Try using the frame of reference of the surrounding air or the fixed ground, since neither is moving relative to the other.

[ThinAirDesigns]

It seems we now have full agreement that it is possible. The nay sayers have finally been convinced.

LOL Rick -- that's a bit optimistic as 3 of the primary critics when you gave up on this thread and when I restarted this tread are still critics:

Guillermo
Boston
3dYachts


JB

[Guest625101138]

LOL Rick -- that's a bit optimistic as 3 of the primary critics when you gave up on this thread and when I restarted this tread are still critics:

Guillermo
Boston
3dYachts


JB

Yeah; but they have gone away either not prepared to say they were completely wrong or simply not wishing to continue digging holes and embarrassing themselves any more. I take their silence as acceptance of the feasibility of sailing DDWFTTW.

There is also the pilot on the DDWFTTW thread who has gone away and not returned. At least he offered concrete calculations to show his reasoning that enabled the misunderstandings to be specifically identified.

It would be nice to get a thank you for taking the time to correct their misguided opinions but that is difficult for some when they have strongly defended an ill-thought opinion and later realised they were totally wrong.

If you had not revived the thread they would have lived in blissful ignorance and not realised the joke until it becomes well known, accepted knowledge. So they have you to thank for now being better informed on this curious slice of sailing technology.

I look forward to your post with a clip slowing a full-scale buggy easily exceeding wind speed directly downwind.

Rick W

[sailor2]

Let me try this again. Air speed relative to ground is zero in both cases. That's the flawed assumption which leads incorrect conclusion by you that principle of equivalent IRF:s doesn't work.
In reality it works just fine without flawed assumptions. When you use it correctly the airspeed relative to the reference frame is the same in all cases by definition. An assumption not in agreement to that is flawed by definition.

[sailor2]

1) In the second case the air certainly gives up 137.5W.
2) However the rate of work being done by the air on the vehicle IS 150W.
3) This is the sum of what the air loses and what the prop contributes.
4) So you are correct in that the 12.5W is already allowed for in the 137.5W.
Rick W
Assuming power from shaft being 12.5 Watts :
1) I agree.
3) The sum is indeed 150 W, not 125W as initially claimed.
2) the rate of work being done by the air on the vehicle is what the air loses, nothing to do with the sum including other sources than air.
4) If something was alreade allowed for and you didn't take that into account then the error would have been 12.5W not 25W as it was. (150 instead of 125)
Don't understant this 4th statement anyway.

In both cases:
If prop is 100% efficient, then there are no swirl losses, no tangential force between blades & air, and no torque due to that. Therefore no power from shaft. Assumed 12.5W from shaft and 100% efficiency are in cotnradiction.

[Guest625101138]

.....
In both cases:
If prop is 100% efficient, then there are no swirl losses, no tangential force between blades & air, and no torque due to that. Therefore no power from shaft. Assumed 12.5W from shaft and 100% efficiency are in cotnradiction.

The power out of the prop is 12.5W. The is the power required to accelerate the air.

Mechanical efficiency is defined as Power Out/ Power In. With 100% efficiency both power In and Out are 12.5W. The prop has to do this work. 100% efficiency does not mean it is doing no work. It just means it has no conversion losses. So the shaft power to the prop is 12.5W and converts all this to accelerating the airflow through the disc. There is no swirl, viscous drag or induced drag. JUst perfect conversion from rotation to thrust by accelerating air through the disc.

Rick W

[sailor2]

The power out of the prop is 12.5W. The is the power required to accelerate the air.

Mechanical efficiency is defined as Power Out/ Power In. With 100% efficiency both power In and Out are 12.5W. The prop has to do this work. 100% efficiency does not mean it is doing no work. It just means it has no conversion losses. So the shaft power to the prop is 12.5W and converts all this to accelerating the airflow through the disc. There is no swirl, viscous drag or induced drag. JUst perfect conversion from rotation to thrust by accelerating air through the disc.
Rick W
Accelerating air in the direction of initial flow means losing energy into air as induced losses by definition. See PDF Marc Drela posted to see that.
If you want 100% propulsion efficiency, no amount of air can be accelerated linearly at all, since that would mean induced losses. You would have to have no slip at all. Therefore I initially assumed 100% efficiency meant thermodynamic efficiency instead. Perhaps you didn't mean that either. So what efficiency did you mean ?!?!?!?!?

"With 100% efficiency both power In and Out are 12.5W." And depends how power out is defined. In ground IRF we are using the power out is 150W if power in is 12.5W. Does that mean the efficiency is 1200% ? I wouldn't define it that way since the power out comes from air by the prop, it's not converted from rotation to linear.

"JUst perfect conversion from rotation to thrust by accelerating air through the disc." does not mean 100% propulsion efficiency as induced losses are there. It means more than just 100% thermo eff. as swirl losses are zero. And why assume that both powers are 12.5 W why not both as zero Watts ? That would avoid some of the contradictions, so some logic would still be there.
If that's what you mean then you need a new definition for efficiency instead of just saying 100% and you also assume conservation of rotation energy is invalid. What's the point of analysing by math if laws of physics are assumed to not hold ?

[Guest625101138]

The power put in by the prop can be determined by the mass flow through the disc by the velocity change.

In either case this is:
Power = 0.5 x 100kg/s x 0.5m/s^2
= 12.5W

This formula is identical to the original analysis that Mark Drela provided.

I am using the prop mechanical efficiency as 100% as defined in any text book you care to look at. That means 12.5W applied to the air will require 12.5W applied to the prop shaft. This obviously cannot be achieved but again is the same assumption that Mark Drela offered before he applied the efficiencies for the various components.

In case 2 the power flows are 150W applied by the air. 12.5W of this is contributed by the prop leaving 137.5W given up by the air. That power goes into mechanical losses in the power transfer system, overcoming vehicle drag and accelerating the vehicle if any is left over.

The whole aim of the exercise was to show that once there is relative movement of the air over the ground a small power input from the prop can result in a large power reduction in the air flow. It makes the point that the energy comes out of thin air. There is no perpetual motion involved.

Rick W.

[sailor2]

The power put in by the prop can be determined by the mass flow through the disc by the velocity change.

In either case this is:
Power = 0.5 x 100kg/s x 0.5m/s^2
= 12.5W

This formula is identical to the original analysis that Mark Drela provided.

I am using the prop mechanical efficiency as 100% as defined in any text book you care to look at. That means 12.5W applied to the air will require 12.5W applied to the prop shaft.
Rick W.O.K. I did find only 6 hits on the google and one of them is from a book:
http://books.google.fi/books?id=Ns5PtVDNfK8C&pg=PA169&lpg=PA169&dq=%22mechanical+efficiency+of+the+propeller%22&source=bl&ots=k8dUzp3fo6&sig=RNB1EAjaXO_CQBoEPhYl1WMwGi4&hl=fi&sa=X&oi=book_result&resnum=1&ct=result
Engineering analyses of flight vehicles by Holt Ashley
It seems to define prop mechanical efficiency exactly the same as propulsive efficiency in one of the problems, not mentioned in anywhere else in the book. That means that 100% is acheaved only if there is no slipstream and no swirl. Assuming 0.5 m/s slipsream therefore contradicts 100% efficiency assumption,
since some energy goes into accelerating air with slipstream reducing that efficiency from 100%.
I can not read every book in this planet to find out if any of them uses some other definition.
Definition of thrust power = The power usefully expended on thrust, equal to the thrust (or net thrust) times airspeed.
Airspeed is defined as relative speed of free stream air to the plane.

[clmanges]

That's the flawed assumption which leads incorrect conclusion by you that principle of equivalent IRF:s doesn't work.
In reality it works just fine without flawed assumptions. When you use it correctly the airspeed relative to the reference frame is the same in all cases by definition. An assumption not in agreement to that is flawed by definition.
I'm starting to think that this reference frame thing may have driven some people to insanity . . .
As I stated, "Air speed relative to ground is zero in both cases."

This is not a "flawed assumption." It is a condition of the experiment. It is the environment in which the activity takes place.
It's quite easy to set up such a thing in real life; all you need is a big, empty building with all the doors and windows closed and the ventilation system turned off. Treadmill off in a corner, and a little track for the runner to use when he's not on the treadmill.

Man on treadmill: the man and his tethered airplane experience no wind, despite their groundspeed (relative to the treadmill belt). In this case, the only thing experiencing windspeed is the belt on the treadmill, since it's the only thing in motion relative to the air. The treadmill belt feels a tailwind. Plane gets no headwind, thus no lift.

Man off treadmill, running on ground: man with plane moves relative to ground, while the air does not. Man with plane see headwind, plane flies.

What frame of reference do you use that would change the above outcomes?

[ThinAirDesigns]

I'm starting to think that this reference frame thing may have driven some people to insanity . . .

Me too.

As I stated, "Air speed relative to ground is zero in both cases."

This is not a "flawed assumption." It is a condition of the experiment. It is the environment in which the activity takes place.
It's quite easy to set up such a thing in real life; all you need is a big, empty building with all the doors and windows closed and the ventilation system turned off. Treadmill off in a corner, and a little track for the runner to use when he's not on the treadmill.

Man on treadmill: the man and his tethered airplane experience no wind, despite their groundspeed (relative to the treadmill belt). In this case, the only thing experiencing windspeed is the belt on the treadmill, since it's the only thing in motion relative to the air. The treadmill belt feels a tailwind. Plane gets no headwind, thus no lift.

Man off treadmill, running on ground: man with plane moves relative to ground, while the air does not. Man with plane see headwind, plane flies.

What frame of reference do you use that would change the above outcomes?

I'm not sure what your getting at clmanges, you're correct in your above described outcomes, but in your scenarios, you haven't change frames, you've changes entire scenarios. In your comparison, you haven't take the same story and looked at it through another 'frame', you've started telling a different story.

A: If I were outdoors in a 6mph wind and were to run straight downwind at 6mph towing the plane, the plane would most certainly get no wind and thus no lift.

B: I use your scenario with the man running 6mph on the treadmill in the enclosed room -- the plane would most certainly get no wind and thus no lift.

A and B are equivalent frames -- both men are running 6mph and neither feels any wind.

Your own two comparisons fail as equivalent because on the treadmill, the runner has a tailwind that matches his groundspeed (both 6mph). When the runner runs 6mph across the floor of the large enclosed building, he has no 6mph tailwind to cancel out the runners motion and thus sees a 6mph headwind.

Again, not exactly sure what point your attempting to make, but just wanted to point out that even though your 'outcomes' were correct, if you were attempting to use those outcomes as results from 'equivalent frames', your conclusion is flawed.

JB

[Guest625101138]

O.K. I did find only 6 hits on the google and one of them is from a book:
http://books.google.fi/books?id=Ns5PtVDNfK8C&pg=PA169&lpg=PA169&dq=%22mechanical+efficiency+of+the+propeller%22&source=bl&ots=k8dUzp3fo6&sig=RNB1EAjaXO_CQBoEPhYl1WMwGi4&hl=fi&sa=X&oi=book_result&resnum=1&ct=result
Engineering analyses of flight vehicles by Holt Ashley
It seems to define prop mechanical efficiency exactly the same as propulsive efficiency in one of the problems, not mentioned in anywhere else in the book. That means that 100% is acheaved only if there is no slipstream and no swirl. Assuming 0.5 m/s slipsream therefore contradicts 100% efficiency assumption,
since some energy goes into accelerating air with slipstream reducing that efficiency from 100%.
I can not read every book in this planet to find out if any of them uses some other definition.
Definition of thrust power = The power usefully expended on thrust, equal to the thrust (or net thrust) times airspeed.
Airspeed is defined as relative speed of free stream air to the plane.

Just Google mechanical efficiency. Here are a couple of examples:
http://en.wikipedia.org/wiki/Mechanical_efficiency
http://www.britannica.com/EBchecked/topic/371842/mechanical-efficiency
http://encyclopedia2.thefreedictionary.com/Mechanical+efficiency
Hope this helps.

Rick W

[spork]

Just Google mechanical efficiency. Here are a couple of examples...

It seems clear to me that you two are now down to debating the definition of "efficiency" or "mechanical efficiency" (or whatever). The "mechanical efficiency" you're using Rick is a much broader one. Both definitions have a place (and are useful for given applications). But arguing definitions is no fun. I recommend that we agree on the meaning of what you're trying to say (which I think most of us understand and accept), and not worry about what to call it. Just a suggestion.

[Guest625101138]

It seems clear to me that you two are now down to debating the definition of "efficiency" or "mechanical efficiency" (or whatever). The "mechanical efficiency" you're using Rick is a much broader one. Both definitions have a place (and are useful for given applications). But arguing definitions is no fun. I recommend that we agree on the meaning of what you're trying to say (which I think most of us understand and accept), and not worry about what to call it. Just a suggestion.

I never intended to debate the meaning of mechanical efficiency.

My intention was to show in the simplest possible way the propensity for wind over the ground to give up energy simply by applying a little extra energy from a propeller. The aim was to answer the question - where does the energy come from? The answer in this case is "from thin air" of course.

Rick W

[sailor2]

It seems clear to me that you two are now down to debating the definition of "efficiency" or "mechanical efficiency" (or whatever). The "mechanical efficiency" you're using Rick is a much broader one. Both definitions have a place (and are useful for given applications). But arguing definitions is no fun. I recommend that we agree on the meaning of what you're trying to say (which I think most of us understand and accept), and not worry about what to call it. Just a suggestion.
My point was and still is that although mechanical efficiency is always defined as power out / power input, but despite of that power out can have more than one reasonable definitions for a prop. As a result just saying 100% efficiency is too fuzzy expression to use if one wants to teach somebody something.
It's unfortinate that Rick refuse to realize that, because his teaching methods would otherwise be one of the best. Sad really.

Ps. I wasn't debating what the definition is or should be, just pointing out it wasn't ( and still isn't ) properly defined like it should have been.
Hope Rick now looks closely the bold part of your statement quoted above to understand what it was all about since you seem to agree more than one definition exists for props. Thanks for pointing that out.

[sailor2]

I'm starting to think that this reference frame thing may have driven some people to insanity . . .
As I stated, "Air speed relative to ground is zero in both cases."

This is not a "flawed assumption." It is a condition of the experiment. It is the environment in which the activity takes place.
...
What frame of reference do you use that would change the above outcomes?
It's not a condition of an experiment in 2 different frames. It's 2 different conditions of 2 different experiments in either the same or different frames of reference.

Of course no IRF would change the outcomes of your 2 different scenarious.
JB alredy correctly responded for the same issues, perhaps you could read it carefully.

[clmanges]

It's not a condition of an experiment in 2 different frames. It's 2 different conditions of 2 different experiments in either the same or different frames of reference.

Of course no IRF would change the outcomes of your 2 different scenarious.
JB alredy correctly responded for the same issues, perhaps you could read it carefully.

I did read JB's post carefully; almost replied to it, but decided to let my brain cool off a little first.

I'll take the blame for the misunderstanding here; somewhere along the way I failed to properly comprehend "equivalent reference frames." Silly me, I thought that a reference frame was the same thing as "point of view." I need to work on that a bit more, I guess.

Maybe I need a "Relativity for Dummies" book.

[gketterman]

This is way off topic, but you folks have had so much fun debating this issue I guess you will have a lot of fun with this one too. Would you believe a model sailplane that goes 371 mph?

This video is all about the guy with the record and how obsessed he is with the pursuit; http://www.vimeo.com/2375301

The sound is the impressive part and this video has the best sound; http://www.youtube.com/watch?v=AQoVBvQacwE&feature=related

[Guest625101138]

This is way off topic, but you folks have had so much fun debating this issue I guess you will have a lot of fun with this one too. Would you believe a model sailplane that goes 371 mph?

This video is all about the guy with the record and how obsessed he is with the pursuit; http://www.vimeo.com/2375301

The sound is the impressive part and this video has the best sound; http://www.youtube.com/watch?v=AQoVBvQacwE&feature=related

Greg
If you go back to post #226 you will see that Tom Speer has provided a nice little paper on dynamic soaring. Mark Drela and others go on from there to discuss it in some detail.

Rick W

[chabrenas]

Bet there'll be plenty of people capable of misinterpreting the PDF, and plenty of others who start arguments that don't address its contents.

You still need to write the words that go with the diagram - i.e. the script for a presentation to an audience - in the same clear-cut manner. Shall we continue fro another 50 pages? (:=? It could be time well spent.

[Guest625101138]

For this long running past topic there is a series of tests in a home made wind tunnel that is hard to dispute:
http://www.youtube.com/watch?v=GC-EoGbdyzE&NR=1


Rick W

[PanAmMan]

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.


So when you boat is going zero speed relative to the water the water prop generates zero power / lift and therefore provides zero power to the wind prop.

When the boat is going faster than the water prop it is extracting energy from the bat speed (drag) to push the boat with the wind prop (loss of efficiency).

the only time this works is in an ultra low drag environment where the relative wind or water over the blade produces (local) wind / water speeds faters than the net relative speed of the boat. These are usually very uncommon (transient) conditions rarely seen even in racing multi hulls and hydrocats. they frequently ccheat by converting intertia into the necissary relative motion for short periods of time. all sailboats do this when they tack. But very very few can maintain that "effect" for more than a few min.

it is true that very large sails act as a force multiplier which can be converted to a relative speed increase but if it were easy or relaible we would see 14knt oil tankers all over the world... LOL

[Guest625101138]

So when you boat is going zero speed relative to the water the water prop generates zero power / lift and therefore provides zero power to the wind prop.

When the boat is going faster than the water prop it is extracting energy from the bat speed (drag) to push the boat with the wind prop (loss of efficiency).

the only time this works is in an ultra low drag environment where the relative wind or water over the blade produces (local) wind / water speeds faters than the net relative speed of the boat. These are usually very uncommon (transient) conditions rarely seen even in racing multi hulls and hydrocats. they frequently ccheat by converting intertia into the necissary relative motion for short periods of time. all sailboats do this when they tack. But very very few can maintain that "effect" for more than a few min.

it is true that very large sails act as a force multiplier which can be converted to a relative speed increase but if it were easy or relaible we would see 14knt oil tankers all over the world... LOL

You should go over to this thread and take up sporks bet if you are confident it does not work:
http://www.boatdesign.net/forums/propulsion/ddwfttw-directly-downwind-faster-than-wind-25527-10.html

Rick W

[ThinAirDesigns]

San Jose State University Aero Professor and Stanford Phd Dr. Nikos Mourtos along with a team of students and advisors have taken on a project to construct and document DDWFTTW in a more thorough way than ever before. Their goal is to achieve a documented 2x windspeed DDW.

Follow their blog at www.fasterthanthewind.org

Remember that in the blog format the latest posts show up on top. To view the entries from the start, click on the "2009" link on the right (below the list of followers) and scroll to the bottom.

Enjoy.

JB

[Guest625101138]

For those who doubted the physics:
http://www.youtube.com/watch?v=7SYvg40NHtc


Rick W

[spork]

And a couple more clips from the same outting.

We muted the audio where we were talking specifically about our downwind speeds beyond windspeed because we didn't think it would be responsible to post unofficial numbers without at least discussing with NALSA and our sponsors. More than likely we will wait and post numbers when we have proper instrumentation that is blessed by NALSA.

Second run: http://www.youtube.com/watch?v=aDzWh9J1dk4&feature=channel
last run: http://www.youtube.com/watch?v=c5VlX-xEk00&feature=player_embedded

[Jeremy Harris]

How can anyone doubt such an incredibly simple bit of physics?

My guess is that some must have a problem with understanding some really basic principles and manage to confuse velocity, force and power. Anyone who goes back to basic schoolboy physics (think of Newtons Laws and the basic equations governing force, velocity, time and power), works out the power needed for any vehicle to travel at a given velocity and then calculates the practically extractable power in a given swept area of wind at a known velocity can very quickly see that going downwind faster than the wind is perfectly possible and doesn't need any complex experiments to prove.

There isn't really a issue over the relative wind velocity vs the relative vehicle velocity, provided that you can continue to extract enough power from the wind to meet the vehicle power demand. The only issue is one of being able to extract enough power to overcome the vehicle total resistance.

Why is something so fundamentally simple causing so much debate? Surely it should have been self-evident from the first instant it was raised?

Jeremy

PS: Reminds me of a rather dim acquaintance who came up to me years ago and accused me of speeding in an urban area. His argument was that I had to be going over 30 mph as he was doing 30mph behind me, just to keep up with me in the traffic........................

[spork]

How can anyone doubt such an incredibly simple bit of physics?

My guess is that some must have a problem with understanding some really basic principles and manage to confuse velocity, force and power. Anyone who goes back to basic schoolboy physics (think of Newtons Laws and the basic equations governing force, velocity, time and power), works out the power needed for any vehicle to travel at a given velocity and then calculates the practically extractable power in a given swept area of wind at a known velocity can very quickly see that going downwind faster than the wind is perfectly possible and doesn't need any complex experiments to prove.

There isn't really a issue over the relative wind velocity vs the relative vehicle velocity, provided that you can continue to extract enough power from the wind to meet the vehicle power demand. The only issue is one of being able to extract enough power to overcome the vehicle total resistance.

Why is something so fundamentally simple causing so much debate? Surely it should have been self-evident from the first instant it was raised?


While I'm inclined to agree with you, I can only tell you that we know of several Physics and Aero PhD's and professors that assure us it's quite impossible. One of whom teaches at my alma mater (GA Tech) sadly enough, another is a nobel prize laureate at Berkeley, and still several others.

It's surprising just how much even highly educated people will substitute intuition for science - and refuse to hear another thing on the topic.

ETA: ... and these videos won't change their minds.

[Jeremy Harris]

While I'm inclined to agree with you, I can only tell you that we know of several Physics and Aero PhD's and professors that assure us it's quite impossible. One of whom teaches at my alma mater (GA Tech) sadly enough, another is a nobel prize laureate at Berkeley, and still several others.

It's surprising just how much even highly educated people will substitute intuition for science - and refuse to hear another thing on the topic.

ETA: ... and these videos won't change their minds.

As a scientist I can understand this to some extent. What seriously concerns me is that a significant number of people in my profession have seemingly moved away from the fundamental principles that govern the scientific method and have lost that essential spark of curiosity in the process.

A colleague of mine and I often have the same conversation regarding this lack of curiosity and willingness to accept unproven statements as fact amongst some of our colleagues. He's fond of quoting this fairly well-known proverb: "The mind is like a parachute, it works best when open" (author unknown).

I suppose that the opposite of closed thinking and blind acceptance of ideas as fact can be a bit irritating, though. I know that I annoy people by not always accepting things they have shown (to their own satisfaction) to be true, without doing at least some experiments of my own to confirm their findings. My wife sometimes gets infuriated by my need to understand why things happen.......................

Jeremy

[spork]

He's fond of quoting this fairly well-known proverb: "The mind is like a parachute, it works best when open"

Some of our skeptics prefer the alternative "the mind is like a parachute - use ONLY in an emergency" (and this is NOT an emergency).

[ThinAirDesigns]

http://sailmagazine.com

http://sailmagazine.com/racing/running_faster_than_the_wind/

[ThinAirDesigns]

NALSA DDWFTTW ratification reports are now up: www.nalsa.org

And a great article by Kimball Livingston, an editor at Sail Magazine:

http://kimballlivingston.com/?p=3971

[Windmaster]

NALSA DDWFTTW ratification reports are now up: www.nalsa.org

And a great article by Kimball Livingston, an editor at Sail Magazine:

http://kimballlivingston.com/?p=3971

Nowhere in the above article or anywhere on the Faster than the Wind website can I see mention of Jack Goodman - a member of the Amateur Yacht Research Society who, with his downwind faster than the wind model (on youtube here: http://www.youtube.com/watch?v=aJpdWHFqHm0) showed that it was possible.

I don't think Jack was the originator of the idea (which has been talked about on AYRS channels for many years) but he was the first to build a model, film it, and demonstrate that it worked.

I am willing to be corrected on this if I have got the timescale wrong, but it seems a shame that in all the ballyhoo, the first demonstrator of this concept should be forgotten and not given any mention.

[ThinAirDesigns]

Nowhere in the above article or anywhere on the Faster than the Wind website can I see mention of Jack Goodman - a member of the Amateur Yacht Research Society who, with his downwind faster than the wind model (on youtube here: http://www.youtube.com/watch?v=aJpdWHFqHm0) showed that it was possible.

I have no control of the article, but Jack is featured prominently on the faster than the wind website -- check out the very third post:

http://www.fasterthanthewind.org/2009/10/machinist-and-internet-hoax_03.html

I don't think Jack was the originator of the idea (which has been talked about on AYRS channels for many years) but he was the first to build a model, film it, and demonstrate that it worked.

You are correct, Jack was not the originator, nor the first to build one (see the very first post on our project blog)

By all accounts so far it was first done in the the '60s by a team of engineers from Douglas Aircraft, but even they weren't the ones who came up with the idea and as they did it to settle a bet between friends, they didn't document their exploits in a way that satisfied very many critics.

AMO Smith (google him), the Supervisor of Aerodynamics Research and Chief Aerodynamics Engineer at Douglas and one of his wind tunnel engineers, Dr. Andrew Bauer discovered the idea in a paper presented by a midwestern student who was was angling for a summer internship.

Unfortunately, no one remembers who the student was (they didn't get the intern position) so credit for the actual invention will apparently remain nebulous for all time.

Bauer believed the student was correct and AMO believed DDWFTTW to be impossible. They made a bet and Bauer assembled a small team, built and sucessfully tested the device. AMO paid off on his bet and by all acounts it was near 40 years before anyone physically tried it again (Goodman).

http://3.bp.blogspot.com/_XtHg_q76Tgs/SsUfmgmFJqI/AAAAAAAAABA/Bk6e13mXMQA/s400/Bauer.jpg

I am willing to be corrected on this if I have got the timescale wrong, but it seems a shame that in all the ballyhoo, the first demonstrator of this concept should be forgotten and not given any mention.


We give Jack HUGE credit everywhere we go and are in regular phone and email contact with him to this day. Check out the video that we did when we were trying to get this on MythBusters:

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

In history if we are remembered in any way with regard to DDWFTTW, it will be because we truly were the first group who documented it well enough to bring most rational people around. Before us most folks still called Goodman and Bauer crackpots and hoaxers -- now it's only the moonshot denier types who will never be convinced.

JB

[Windmaster]

You're right, you have accorded Jack (and Bauer) some credit.
It was only in the article that Kimball Livingston did not mention it.
He has been in touch with me and points out that he did not have space to go into a complete history of the subject - which is true I suppose.

[jcolvin]

Just jumping in here, I'm a physics BSc, also a glider pilot and sailboat owner. I was ready to call "hoax" when I first saw this, since I just could not visualize how the machine gets energy from the prop when the prop is seeing zero apparent wind. What made it "click" for me (and I don't see anyone else mentioning this, which is weird..perhaps I missed it somewhere in the lengthy thread), is that it is not the turbine driving the wheels but the wheels driving the turbine. When you first see this machine you automatically assume that wind flowing through the turbine drives it (and then the question...how does it work when the machine is going same speed as the wind). But then watch it start from a standstill...the turbine goes in the *opposite* direction that it should if wind were driving the turbine directly (ie, if the turbine was working like a wind-powered generator). Clearly, the wheels are driving the turbine, not the other way round; thanks to the magic of gearing, torque from the wheels is greater than the opposite torque the wind is exerting on the turbine blades. Once I saw this, it became apparent how it could work; before that clicked, I was mighty sure that it was just plain impossible.

bravo!

[Windmaster]

Just jumping in here, I'm a physics BSc, also a glider pilot and sailboat owner. I was ready to call "hoax" when I first saw this, since I just could not visualize how the machine gets energy from the prop when the prop is seeing zero apparent wind. What made it "click" for me (and I don't see anyone else mentioning this, which is weird..perhaps I missed it somewhere in the lengthy thread), is that it is not the turbine driving the wheels but the wheels driving the turbine. When you first see this machine you automatically assume that wind flowing through the turbine drives it (and then the question...how does it work when the machine is going same speed as the wind). But then watch it start from a standstill...the turbine goes in the *opposite* direction that it should if wind were driving the turbine directly (ie, if the turbine was working like a wind-powered generator). Clearly, the wheels are driving the turbine, not the other way round; thanks to the magic of gearing, torque from the wheels is greater than the opposite torque the wind is exerting on the turbine blades. Once I saw this, it became apparent how it could work; before that clicked, I was mighty sure that it was just plain impossible.

bravo!

That's quite right, so it's really better to describe the "turbine" as a propeller. Lots of people have mentioned it and to those who understand it, it's quite obvious.

[Richard Miller]

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
Hi Erwan;
Have you actually tried this? The theorie sounds great. I wonder how well it would work in practice? It's a dolphin's tail in a box. It gives you the large contact with the water that's required for good velosity. See the posts that talk about large propellers in the water. Richard: PS Your English is just fine. I understood everything. PPS: Peter, go to your shop & try this.

[New Dawn Fades]

Hi, I see this thread is now 55 pages long and so I don't want t start a new one.

I have seen it written that a windmill powered prop will run a boat at about half wind speed in any direction, so basically what I'm looking for here is a sort of cost/benefit analysis from those of you who have been following this thread for all these years.

This would be going on an aprox 40' aluminum blue water cat that is yet to be designed.

For example, it sounds like the boat will be slower than one with sails and yet it can sail directly into the wind, so that helps a lot to make up some speed difference.

I assume that a good windmill will cost less than a moderate quality set of sails and that it will last longer and be easier to handle.

Of course there is one great benefit that sails can't provide, and that is mass quantities of electrical power available when you are stopped or drifting. I'm planning on having a mini welding shop on the boat (welder in the hull, welding on deck =) to earn some $$ in remote areas as I understand there is frequently the need for welding and metal fabrication.

[New Dawn Fades]

Hi Erwan;
Have you actually tried this? The theorie sounds great. I wonder how well it would work in practice? It's a dolphin's tail in a box. It gives you the large contact with the water that's required for good velosity. See the posts that talk about large propellers in the water. Richard: PS Your English is just fine. I understood everything. PPS: Peter, go to your shop & try this.

Due to my association with aircraft design, instinct tells me you can't come anywhere near the efficiency of a decent prop with any kind of paddle device

[Windmaster]

Hi, I see this thread is now 55 pages long and so I don't want t start a new one.

I have seen it written that a windmill powered prop will run a boat at about half wind speed in any direction, so basically what I'm looking for here is a sort of cost/benefit analysis from those of you who have been following this thread for all these years.

This would be going on an aprox 40' aluminum blue water cat that is yet to be designed.

For example, it sounds like the boat will be slower than one with sails and yet it can sail directly into the wind, so that helps a lot to make up some speed difference.

I assume that a good windmill will cost less than a moderate quality set of sails and that it will last longer and be easier to handle.

Of course there is one great benefit that sails can't provide, and that is mass quantities of electrical power available when you are stopped or drifting. I'm planning on having a mini welding shop on the boat (welder in the hull, welding on deck =) to earn some $$ in remote areas as I understand there is frequently the need for welding and metal fabrication.

Sounds like a great idea! Go for it!

[New Dawn Fades]

That's very nice, but I'm looking for a cost comparison.

Also, I'm thinking it would be good to have the windmill run a generator/motor to either provide power or run a water prop. The water prop would have an identical generator/motor, that way either one could drive the other one and either could provide electric power.

[Windmaster]

That's very nice, but I'm looking for a cost comparison.

Also, I'm thinking it would be good to have the windmill run a generator/motor to either provide power or run a water prop. The water prop would have an identical generator/motor, that way either one could drive the other one and either could provide electric power.

That's theoretically sound, but difficult in practice. I've seen a patent about it.

[CaptBill]

Use the power to charge up a flywheel then pull the power off the flywheel. You can power any other devices from the flywheel too so no batteries. Plus the flywheel, mounted optimally, will make an excellent stabilizer