The Wind Powered Sail-less Boat

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!

 

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

 

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

 

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

Rick W

 

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:" "


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.

 

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

 

Reason for posting the upwind turbine clip

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.

 

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

 

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

 

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!

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.

That's just what it is: at an angle.

 

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...?

 

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

 

"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
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

 

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!!!