Sailing downwind faster than the wind: resolved?

[Subductionzon]

It's technically called rolling friction. With fairly constant rolling friction, power loss increase directly with the velocity.

Yes, power will increase directly with velocity, but that is a direct outcome of W=F*D. With W being work, F the force of friction, and D the distance that you travel. Swedna seemed to have a problem with overcoming the force of friction which I pointed out is a constant. Once you overcome it you do not get more, but if you speed up more of your power goes into friction.

 

[swerdna]

The claim that the combination of the speed of the wind and the opposing thrust of the propeller causes the vehicle to travel faster than the wind is incorrect.

(1) All of the energy to move the vehicle comes from the wind.

(20 All of he energy to spin the propeller comes from the wind.

(3) The energy produced by the spinning propeller is less than the energy taken from the wind to create it because of friction.

(4) The combined energy of the wind and the propeller is therefore less than the speed of the wind.

Not only could this vehicle not exceed the speed of the wind, it couldn’t even achieve it. The same vehicle with a sail the same area as the sweep of the propeller would perform better as there would be less friction involved.

There’s no free lunch and there’s no free energy.

 

[mender]

So you didn't read my post.

The vehicle has demonstrated beyond a doubt that it moves DDWFTTW. I also took a lot of time to explain why there is no issue with energy. Ignoring the facts while making statements does not alter anything.

This doesn't use free energy.

 

[schroder]

Shroder, I can answer your last question: there is no travesty of physics going on.

It is a basic but not obvious use of surplus energy to generate surplus speed. Exchanging force and velocity. Leverage. Mechanical advantage. Gearing.




It's a simple energy balance. It's not so simple to see how it works.

Why don't you add VOODOO to your above list. The game is over. You must really have a vested interest in this to blow so much smoke. Were you planning on selling them as Christmas stocking stuffers? It's over, your hoax is exposed. No more free advertising on this forum.

 

[ThinAirDesign]

Why don't you add VOODOO to your above list. The game is over. You must really have a vested interest in this to blow so much smoke. Were you planning on selling them as Christmas stocking stuffers? It's over, your hoax is exposed. No more free advertising on this forum.

There's nothing to sell and thus nothing to advertise.

It's a physics brainteaser and a darn good one -- it elicits immediate, strong and emotional responses such as yours which are ultimately demonstrably wrong.

It's just good clean fun with physics.

To anyone who want's to build one of these 'VOOODOO' devices, I'm happy to provide a parts list and any build advice requested. I would only ask that in exchange for my input you promise to video and post the results *no matter the result*.

JB

PS: One good thing to remember is that the person who presents a brainteaser usually has inside information.

 

[mender]

Why don't you add VOODOO to your above list. The game is over. You must really have a vested interest in this to blow so much smoke. Were you planning on selling them as Christmas stocking stuffers? It's over, your hoax is exposed. No more free advertising on this forum.

No, I'm only trying to help you understand this. You don't want to. No game, no product, no haox, just physics. Report this thread if you feel the need. At this point I'm sure that the moderators are quite aware of the content.

Why don't you try reading my post and doing the experiments that I suggest? You might find something of interest.

 

[Subductionzon]

Why don't you add VOODOO to your above list. The game is over. You must really have a vested interest in this to blow so much smoke. Were you planning on selling them as Christmas stocking stuffers? It's over, your hoax is exposed. No more free advertising on this forum.

If this is a hoax how did they get the cart to move faster than the wind directly down the wind? Or don't you understand physics well enough to see that the treadmill is equivalent to a perfect tailwind.? If you cannot understand something as simple as frame of reference there is no point trying to explain the aerodynamics of sailing to you.

 

[rcgldr]

Can the thrust if the propeller ever exceed the rolling resistance caused to create that thrust?

Yes, I already explained this in earlier posts. Effective gearing between the driving wheels and the propeller muliptly the force and divide the speed. The reducion in speed works because the propeller is interacting with the slower (relative to the cart) moving air, while the wheels interact with the faster (relative to the cart) ground.

Vw = speed of wind
Vc = speed of cart
Vp = speed of induced wash from prop
Fp = force from prop
Fc = force from cart wheels
Fd = overall losses (drag) related to forward speed of cart

Speed of air through the prop = induced wash + relative air speed = Vp + (Vc-Vw)
The power input = Fc x Vc
The power output = Fp x (Vp + Vc - Vw)
The power loss = Fd x Vc
The net force on the cart = Fp - (Fc + Fd)

Vc can be > Vw, Fp can be > Fc, with power output still well below power input as long as Vw is greater than zero (a tailwind). The gearing factor (diameter ratios between wheels and prop, gearing at the differential, prop pitch), multiplies the force and divides the speed. The reduction in speed is relative to the ground though, but the prop is interacting with the air, so although its speed is a fraction of it's ground speed, if the gearing ratio is not excessive, the prop speed is still positive relative to the air it interacts with, Vp + (Vc-Vw) > 0.

A conservative setup might only try to achieve DDWFTTW by a ratio of 1.2. In a 10mph wind, the cart would move at 12mph, resulting in a 2 mph working air speed for the propeller. If the effective gearing for wheel speed to prop speed was 2:1, then the prop speed would be 6mph, and the induced wash speed, Vp - (Vc-Vw) = 4mph. If the gearing was 1.5:1, the prop speed would be 8mph, induced wash speed: = 6mph. The actual force from the prop depends on the change in air speed due to the prop times the mass flow, and this force propels the cart forwards. The force at the driving wheels (Fc) is the prop force minus all the losses in the system (rolling friction, aerodyanic drag of the cart, prop inefficiencies).

If someone gets some actual numbers for the mini-cart, and prop, here's a link for some prop math:

http://www.grc.nasa.gov/WWW/K-12/airplane/propanl.html

 

[schroder]

“It is a basic but not obvious use of surplus energy to generate surplus speed. Exchanging force and velocity. Leverage. Mechanical advantage. Gearing.”

That is Voodoo. That is your theory? This thread has been reported and Admin can do what they want with it. This is not worth any more of my time.

 

[ThinAirDesign]

Or don't you understand physics well enough to see that the treadmill is equivalent to a perfect tailwind.?

Sub, that one has clearly been asked and answered.

Schroder has got it in his head that it matters *how* the relative motion is created. It's a case of the watermellon seed being squeezed apparently by only one finger.

JB

 

[swerdna]

Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.

Conservation of energy is not just a good idea . . . it’s the law!

 

[Subductionzon]

Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.

Conservation of energy is not just a good idea . . . it’s the law!

Alright, I will ask you the same question I asked shrodeer. You saw the various videos of the carts working on the treadmill, how did they hoax them since they are obviously running faster than the wind? And for frame of reference an ant on the treadmill for the short time before it ran underneath could not tell the difference between being on the treadmill with a 10 mph wind blowing towards the front of it or being on an open field with a 10 mph wind. C'mon people the frame of reference part of this is the extremely easy.

One question, how many people who do not think the treadmill is a perfect representative of a 10 mph tailwind thought the plane would not take off? Be honest now.

 

[ThinAirDesign]

Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.

And we agree with that clever guy completely.

Conservation of energy is not just a good idea . . . it’s the law!

And we think it's a very good law.

Somehow folks who think this device must be over-unity forget the potential energy between the two moving mediums. This device slows that relative motion and uses the extracted energy to overcome a bit of prop drag, a very very small bit of rolling friction and bearing drag, and an even smaller bit of aero drag created by the chassis moving some tiny amount more than the wind.

We don't need very much and there is a lot available. This surplus is demonstrated easily by the 3-4x VMG that traditional sailing rigs can achieve. We after all are only looking for 1.01 to visibly prove the point.

JB

 

[ThinAirDesign]

This thread has been reported and Admin can do what they want with it.

As has been demontrated earlier in this thread, the moderators of this forum agree with us as to both the theoretical concept and the validity of treadmill testing.

This is not worth any more of my time.

Only you can determine that.

Best wishes

JB

 

[swerdna]

Alright, I will ask you the same question I asked shrodeer. You saw the various videos of the carts working on the treadmill, how did they hoax them since they are obviously running faster than the wind? And for frame of reference an ant on the treadmill for the short time before it ran underneath could not tell the difference between being on the treadmill with a 10 mph wind blowing towards the front of it or being on an open field with a 10 mph wind. C'mon people the frame of reference part of this is the extremely easy.

One question, how many people who do not think the treadmill is a perfect representative of a 10 mph tailwind thought the plane would not take off? Be honest now.

It was always obvious to me that the plane would take off (honestly). The plane gets all of it’s propeller energy from an onboard motor and not from the ground. The difference with the vehicle on the treadmill is that it does get all of it’s propeller energy from what is essentially the ground.

 

[Subductionzon]

It was always obvious to me that the plane would take off (honestly). The plane gets all of it’s propeller energy from an onboard motor and not from the ground. The difference with the vehicle on the treadmill is that it gets all of it’s propeller energy from what is essentially the ground.

Close, it gets its energy from the difference in speed between the moving treadmill and the still air (or the difference in speed between the ground and the wind if you are outside). It is a subtle difference but a very important one.

 

[mender]

I'd like to address the power issue. I'll likely need some help on this. I'll list where I'm getting info so that it can be checked for validity.

I'm going to use the wind power chart found on this site:

http://www.windpower.org/en/stat/unitsw.htm#anchor1345942

It lists the power of the wind at regular intervals. 10 mph converts to 4.4m/s. The wind power is 313.6 w/m2 at 8 m/s. Dividing 4.4 by 8 and cubing then multiplying by 313.6 shows that at 4.4 m/s there is 52.18 watts available.

I need some indication on how the wind power numbers were arrived at, specifically is the wind slowed to a percentage of the original wind speed when the wind turbine removes the energy? Also, I request that someone (like Jeff) looks at this site to see whether this calculator can be used:

http://members.jcom.home.ne.jp/4223215501/staticthrust.htm

Next, I need some more numbers on JB's cart. I need the force readings on a gram scale when the cart is on the treadmill and the treadmill is moving at 2.5, 5.0, 7.5, and 10.0 mph both with the prop connected and disconnected. Also, I need a better idea of the rpm of the prop at those speeds. As I mentioned, I counted about 20 revolutions in four seconds when the cart was at 2.7 mph, but it's hard to be sure over the internet.

Finally, a confirmation on these specs: prop is a 14 x 8 slow flight (part or model number?), overall cart weight is 169 grams, steady state is achieved on level treadmill is 2.7 mph, incline needed to resist advancing at 10 mph is 4.4 degrees. I'd like the incline for 5.0 and 7.5 mph as well if possible.

Please let me know if and when you can assist me in this. This may be another part of the puzzle that is needed. I know that an actual test is a better proof of the concept but this may help others accept what they see.

 

[molinaro]

Gearing only moves things faster it doesn’t create extra or new energy. In fact because of friction gearing always reduces energy. Some clever guys worked all this out many years ago.

Conservation of energy is not just a good idea . . . it’s the law!

It's one thing to be able to state a principle in physics. It is something entirely different to be able to use it when appropriate.

I do not agree with any of your points in this thread.

 

[mender]

Quick note, found that the wind is slowed by 2/3 of the original speed, and that Betz' law states that at most 59% of the energy can be harnessed. That reduces the wind speed to 3.3 mph when a maximum of 30.8 watts per square meter is harvested.

 

[ThinAirDesign]

Quick note, found that the wind is slowed by 2/3 of the original speed, and that Betz' law states that at most 59% of the energy can be harnessed. That reduces the wind speed to 3.3 mph when a maximum of 30.8 watts per square meter is harvested.

Hey Mender, you might wish to double check on that Betz' law deal. It's my understanding that it applies to turbines and not props. I'm pretty sure prop efficiency can be significantly higher than that.

Not suggesting what the efficiency of our prop is -- just that Betz' may not apply to our application.

JB

 

[mender]

JB, you may be right. I'll use the lower number for now since it is based on the difference in air speed before and after the wind turbine (2 cubed over 3 cubed or 16/27) and only references the speed, not the efficiency of the wind turbine itself. I suspect that the propeller efficiency will be part of the other side of the equation.

Here's a good site explaining some of this:

http://www.windturbine-analysis.netfirms.com/index-intro.htm

 

[rcgldr]

Gearing only moves things faster it doesn’t create extra or new energy.

Gearing also moves things slower. It's how your car operates. In 1st gear the overall gear ratio is high, about 10:1, the engine rotates 10 times every time the driven tires rotate once. The tire speed is reduced by a factor of 10, but the torque is multiplied by a factor of 10 and the power is identical if there are no losses. Assuming a realistic loss of about 15%, then the torque from the engine is multiplied by 8.5. If the car is in top gear, then the gear ratio is around 3:1, the speed is divided by 3, and with the 15% loss factor, the torque is multiplied by 2.55.

The point here is that gearing was used to multiply the torque output of the engine, but at a slower speed, and taking losses into account.

Getting back to the wind cart, the fact that the speed of the air that the prop interacts with is much slower than the speed of the ground that the wheels interact with, allows a gearing effect that reduces speed but increases force, even though power output is less than power input.

http://www.grc.nasa.gov/WWW/K-12/airplane/propanl.html

Assume the wind is 10mph, the cart is going downwind at 12mph, and the required additional induced wash to generate the force to overcome all the drag factors is 3mph. The air speed through the prop is 5mph, so an effective gear factor of 2:1 between wheel speed and prop air speed would be enough, and with a 30% loss, the force at the prop would be 1.4 times the force at the wheels.

 

[russ_watters]

Yes, swerdna, you have hit the nail on the head. The standard explanation put forth by the people who are promoting this nonsense on this forum is “the cart extracts its energy from the air-ground interface” as if that is an explanation. Exactly how does the cart do this? Let's remove the air-ground interface and have a frictionless cart that floats in mid-air. Now the wind blows and it moves with the wind at wind velocity. It cannot possibly go any faster than wind velocity under those circumstances (what is it going to work against?) Now introduce the magical air-ground interface. In order for the wheel to add any drive force against the ground it must have friction with the ground; no friction, no drive force. If it has friction with the ground, that is additional drag and the cart must slow down so it is now moving at less than wind velocity. It is that simple. Unless you believe that a wheel dragging on the ground, which requires friction to get it turning, can also provide a drive force at the same time it is being driven! Can we now put a stop to this travesty of physics?

You are describing the scenarios wrong. You motion vectors do not match what is being claimed/what is happening: you have it backwards. Since the craft is moving faster than the wind, the wind can't be powering the wheels. The wheels are powering the propeller to create thrust to move ahead of the wind. You need to draw a diagram. Or better yet: look at the one I already drew!

This thread is going nowhere and is therefore locked. I may reopen it if you respond to the query I made with the diagram a few pages ago. You can send me a PM.