DDWFTTW Turntable Test: 5 Min Video - Is It Conclusive?

[swerdna]

I have built a turntable and “cart” to test the claim of being able to travel directly downwind faster than the wind using only the immediate force of the wind. Here is a video of the test. The turntable is level but looks like it’s on an angle because of the camera angle. The cart ran against the motion of the turntable for over 5 minutes without loosing any speed. Is this conclusive proof of DDWFTTW?

 

[Triple_D]

I'm new here, so I'm not crazy enough to get involved in this debate, but I would like to say that's a pretty cool turntable. Nice job!

 

[Hunterbender]

I have built a turntable and “cart” to test the claim of being able to travel directly downwind faster than the wind using only the immediate force of the wind. Here is a video of the test. The turntable is level but looks like it’s on an angle because of the camera angle. The cart ran against the motion of the turntable for over 5 minutes without loosing any speed. Is this conclusive proof of DDWFTTW?

First of all, interesting design.

I do not see how the fact that the cart ran against the motion of the turntable is a definite proof that DDWFTTW (Downwind Faster than the Wind) exists. Rather, if you can prove that the cart speeds up with respect to the motion of the turntable, then maybe you have a case. Of course, there might be something that I am missing.

In addition, you have not taken into consideration of the possible lift within the device. IF the cart is speeding up, it is completely possible to be an effect of lift rather than some "additional speed".

Personally, I do not think DDWFTW is true, because it contradicts the conservation principles and suggest a perceptual motion machine. But then again, I am only a high school student. My personal belief is that the effect of DDWFTW comes from lift, after all, the birds had been doing it for centuries.

 

[swerdna]

I'm new here, so I'm not crazy enough to get involved in this debate, but I would like to say that's a pretty cool turntable. Nice job!

Thanks. It was fun to build.

 

[swerdna]

First of all, interesting design.

I do not see how the fact that the cart ran against the motion of the turntable is a definite proof that DDWFTTW (Downwind Faster than the Wind) exists. Rather, if you can prove that the cart speeds up with respect to the motion of the turntable, then maybe you have a case. Of course, there might be something that I am missing.

In addition, you have not taken into consideration of the possible lift within the device. IF the cart is speeding up, it is completely possible to be an effect of lift rather than some "additional speed".

Personally, I do not think DDWFTW is true, because it contradicts the conservation principles and suggest a perceptual motion machine. But then again, I am only a high school student. My personal belief is that the effect of DDWFTW comes from lift, after all, the birds had been doing it for centuries.

Unlike all other moving surface DDWFTTW tests I’ve seen this cart is not held against the moving surface to gain propeller thrust. This cart moves freely on the surface and only gets it’s propeller thrust from the wind created when it moves through the still air with the turntable.

Not sure what you mean by “lift”. Can you explain in more detail?

Seems to do the “impossible” to me as well. But as anyone can plainly see, it does it! I like your typo (or humour) “perceptual motion”. It seems to be being continuously positively geared from the speed of the wind and doesn’t have to represent perpetual motion or free energy.

 

[Hunterbender]

Unlike all other moving surface DDWFTTW tests I’ve seen this cart is not held against the moving surface to gain propeller thrust. This cart moves freely on the surface and only gets it’s propeller thrust from the wind created when it moves through the still air with the turntable.

Not sure what you mean by “lift”. Can you explain in more detail?

Seems to do the “impossible” to me as well. But as anyone can plainly see, it does it! I like your typo (or humour) “perceptual motion”. It seems to be being continuously positively geared from the speed of the wind and doesn’t have to represent perpetual motion or free energy.

Hahaha, I was wondering if I should have put LOL next to it. But I guess people got it.

Anyways, here is more about lift
http://en.wikipedia.org/wiki/Lift_(force )
^my personal belief, I don't know if there are any research on its effect on these motion (prob.)


Just wondering, have you seen this setup?

 

[swerdna]

To assimilate actual outside wind conditions as much as possible I have done a test where the cart is held to the turntable with a removable block so the cart initially has to move at the same speed as the turntable. The block is then removed (after about 3 - 4 seconds in video) and the wind then powers the thrust of the propeller to make the cart travel against the motion of the turntable.

Here’s the video -

 

[swerdna]

Hahaha, I was wondering if I should have put LOL next to it. But I guess people got it.

Anyways, here is more about lift
http://en.wikipedia.org/wiki/Lift_(force )
^my personal belief, I don't know if there are any research on its effect on these motion (prob.)


Just wondering, have you seen this setup?

Well the cart doesn’t have a wing. Even if it gets some form of lift from the propeller so what? It still appears to effectively travel downwind faster than the wind. And it does it sustainable, I have now tested the cart speed is constant against the turntable for over 10 minutes.

Yes I’ve seen all the Spork & Co videos on another forum and they are what got me interested in this to begin with.

 

[zoobyshoe]

I have built a turntable and “cart” to test the claim of being able to travel directly downwind faster than the wind using only the immediate force of the wind. Here is a video of the test. The turntable is level but looks like it’s on an angle because of the camera angle. The cart ran against the motion of the turntable for over 5 minutes without loosing any speed. Is this conclusive proof of DDWFTTW?

I'm not sure what I'm looking at. The table is turned by a motor. What is turning the propeller on the end of the rotating arm?

 

[swerdna]

I'm not sure what I'm looking at. The table is turned by a motor. What is turning the propeller on the end of the rotating arm?

The wind created by the propeller moving through still air.

ETA - And the wheel rolling against the motion of the turntable surface.

 

[zoobyshoe]

The wind created by the propeller moving through still air.

I watched it three more times. I don't know what this does to your downwind thingy concept, but it's clear that airflow is coming off the spinning table, which is, in effect, a one blade Tesla turbine, dontcha know? I think this airflow is probably turning the propeller. Run the table without the rotating arm and feel anywhere near the periphery of the turntable: you'll feel airflow coming off it. I'm thinking whichever side of the propeller is nearest bottom dead center is getting turned by this air flow while the other one is pulling the propeller forward in the usual way.

 

[OmCheeto]

The wind created by the propeller moving through still air.

Are you sure it's not the frictional force at the pivot point next to the vice grips causing the motor car to move slower than the turn-table, generating a relative speed which at some point causes the propeller to have enough thrust to propel the little car in the direction opposite that of the table.

I do love these FTTW machines. I always scratch my head for a bit when I see them.
I actually like yours the best. You should build a small model and sell it as a novelty.
You might make a million dollars!

Have you seen the motor car that goes faster than the ruler video? It seems to be somehow related to these FTTW devices.

http://www.youtube.com/watch?v=9Yt4zxYuPzI&feature=channel

 

[zoobyshoe]

I actually like yours the best. You should build a small model and sell it as a novelty.
You might make a million dollars!

I think if he reconfigured it a bit he could use it for good rather than evil: to prove than an airplane can take off while sitting on a backwards moving conveyor belt.

 

[swerdna]

Are you sure it's not the frictional force at the pivot point next to the vice grips causing the motor car to move slower than the turn-table, generating a relative speed which at some point causes the propeller to have enough thrust to propel the little car in the direction opposite that of the table.

I do love these FTTW machines. I always scratch my head for a bit when I see them.
I actually like yours the best. You should build a small model and sell it as a novelty.
You might make a million dollars!

Have you seen the motor car that goes faster than the ruler video? It seems to be somehow related to these FTTW devices.

http://www.youtube.com/watch?v=9Yt4zxYuPzI&feature=channel

I’m not “sure” of anything. I built this turntable and cart thinking that it would more than likely disprove the DDWFTTW claim made by others. It seems to me however that it serves to prove the claims rather than disprove.

I don’t see that friction at the centre pivot is any different than the overall friction of rolling resistance of the cart. Can you explain how slight friction at the pivot point would have any effect that is different than the overall friction of the rolling resistance? In my mind the thrust of the propeller shouldn’t exceed the overall rolling resistance of the cart. But apparently it does!

I like mine best as well (but I might have a slight bias). A million dollars you say! . . . Hmmmm

Think I have seen all (if not most) FTTW videos.

ETA - I can also make the cart "hover" with no (or very little) movement against the centre pivot.

 

[OmCheeto]

I think if he reconfigured it a bit he could use it for good rather than evil: to prove than an airplane can take off while sitting on a backwards moving conveyor belt.

With a fast enough belt, we could launch a shuttle all the way to the moon! No more of those toxic solid rockets and explosive hydrogen tanks. Perhaps we could run one up the side of Mt. Everest to give it just the right angle.

 

[swerdna]

It’s a gimmick so there’s got to be a buck in it. Maybe I should have a talk with my Irish friend Pat Pending. Hmmmmm . . . world domination . . . evil it is!

 

[OmCheeto]

I’m not “sure” of anything. I built this turntable and cart thinking that it would more than likely disprove the DDWFTTW claim made by others. It seems to me however that it serves to prove the claims rather than disprove.

I'm not even sure what they are trying to prove.

I don’t see that friction at the centre pivot is any different than the overall friction of rolling resistance of the cart.

Why did the cart move slower than the turntable when you started it then?

Think I have seen all (if not most) FTTW videos.

That one was faster than a ruler though. And the maker has a British accent. And he has prequels and sequels. I've watched them all.

 

[swerdna]

I'm not even sure what they are trying to prove.

That it is possible to sustain ably travel directly downwind faster than the wind only using the immediate speed of the wind.

Why did the cart move slower than the turntable when you started it then?

Not just because of friction at the centre pivot but also because of all the friction of the cart and resistance of the still air. Un-tethered three wheel carts can do the same thing.

That one was faster than a ruler though. And the maker has a British accent. And he has prequels and sequels. I've watched them all.

But the demonstration was that ruler = wind.

 

[OmCheeto]

That it is possible to sustain ably travel directly downwind faster than the wind only using the immediate speed of the wind.

I've yet to see that.

Not just because of friction at the centre pivot but also because of all the friction of the cart and resistance of the still air. Un-tethered three wheel carts can do the same thing.

Your next model should be on stationary ground with a wind tunnel.

But the demonstration was that ruler = wind.

And the puppets were incredible.

 

[Hunterbender]

Just because there isn't wings doesn't mean lift doesn't occur. Helicopters, for example, doesn't have wings but they rely on the concept of lift to fly. After all, the cart does have a propeller.

And once again, I don't see how a cart moving against the turntable definitely proof that a sail can go faster than the wind that propels it.

 

[zoobyshoe]

The wind created by the propeller moving through still air.

ETA - And the wheel rolling against the motion of the turntable surface.

Re: your edit, are you saying the wheel is connected to the propeller by a flexishaft?

 

[swerdna]

Re: your edit, are you saying the wheel is connected to the propeller by a flexishaft?

By a flexible cable.

 

[swerdna]

Wind is air moving relative to something and/or something moving relative to air. If you ride a bike on a calm day you are effectively riding into a headwind. The cart moving with the turntable in calm air is moving in a wind no less than a cart stationary on the ground in an outside wind. It really doesn’t matter how the wind is created. It all boils down to the relative motion of air and something. The turntable surface moving relative to calm air is effectively the same as air moving relative to stationary ground in an outside scenario.

 

[schroder]

If this proves DDWFTTW, then so does a crankshaft, a right-angle drill, and the hands on a clock. In fact, any machine which redirects motion would be equally a “proof”. Sorry, I don’t see anything revolutionary here, but it is a nice turntable.

 

[schroder]

I just want to add that it is more than just a “nice turntable”. I can appreciate, as much as anyone, a really nice bit of mechanical workmanship. You obviously put a fair amount of time and effort into this. Many years ago I used to do hub integration design work on large satellite antennas with many precision rotating parts, moving cables and waveguides and it required a lot of mechanical skills as well as electrical work. You would be good at that sort of system integration. Back on topic; No this does not prove DDWFTTW. I think it comes closer to your original goal, which was to disprove it! What it shows is force redirection in mechanical systems is nothing unusual. A cart running on a treadmill, powered by a treadmill is no more unusual than any other type of force redirection, including your turntable. It has little or nothing to do with a cart going directly downwind, powered by nothing but the wind. What is happening here is that the force generated by the turntable against the wheel is greater than the rolling friction, which is obvious or the wheel would not roll! By stepping up the velocity of the turntable, that force can be made great enough to drive a propeller with enough force to also be greater than the rolling friction. That enables the cart to move in the opposite direction as the turntable. Nothing unusual is happening here at all. What I do find interesting about your design is that it leaves open the possibility to test for the runaway condition, or the terminal velocity, which obviously could not be done on the treadmill. Unfortunately, this probably falls under the category of “destructive testing” and I doubt if you want to do this with your new machine! But theoretically, if you increase the turntable velocity enough, the wheel and propeller should try to accelerate until either frictional forces or air turbulence become the only limiting factors. Things would get very interesting as you near the critical terminal velocity!

 

[rcgldr]

Some close up pictures of the various components, especially the wheel - prop interface would be nice. What is the wheel diamter and prop pitch? (The advance ratio is effective prop pitch / wheel circumference).

A cart running on a treadmill, powered by a treadmill is no more unusual than any other type of force redirection, including your turntable. It has little or nothing to do with a cart going directly downwind, powered by nothing but the wind. What is happening here is that the force generated by the turntable against the wheel is greater than the rolling friction, which is obvious or the wheel would not roll! By stepping up the velocity of the turntable, that force can be made great enough to drive a propeller with enough force to also be greater than the rolling friction. That enables the cart to move in the opposite direction as the turntable.

I don't understand your point here. You have a set of forces. Aerodynamic drag and rolling resistance exert a backwards force, while air accelerated by the propeller exerts a forward force. Equilibrium is occurring with the cart advancing against the motion of the turntable. Using the cart as a frame of reference, which way are the ground (turntable) and surrounding air moving relative to the cart?

Why did the cart move slower than the turntable when you started it then?

Inertia. The turntable initially accelerates faster than the cart and the attached arm. Eventually sufficient speed differential between the turntable and the (virtually) non-moving air allow the prop to generate enough thrust to decelerate the backwards movement, continuing to accelerate until it reaches it's terminal forwards velocity for a given turntable speed.

 

[Phrak]

swerdna, whatever you have, it's a real brain teaser. Is the propeller driving the wheels, or are the wheels driving the propeller?

I have a suggestion to make to discover which way it is. Break the torsion shaft or cable in a convenient place and insert a piece of pliable rubber material. How the material twists will determine which is driving which. You will need to put some lengthwise stripes on it to tell which way it twists. And take closeup pics of it at rest and in action!

 

[rcgldr]

Is the propeller driving the wheels, or are the wheels driving the propeller?

The wheel is driving the propeller. The thrust speed from the propeller is slower than the speed of the wheel. We've been calling (effective thrust speed / wheel speed) advance ratio, and it needs to be < 1 for a downwind cart, > 1 for an upwind cart.

 

[schroder]

I don't understand your point here. You have a set of forces. Aerodynamic drag and rolling resistance exert a backwards force, while air accelerated by the propeller exerts a forward force. Equilibrium is occurring with the cart advancing against the motion of the turntable. Using the cart as a frame of reference, which way are the ground (turntable) and surrounding air moving relative to the cart?

Well then I will try and clarify my point: In this video, we see the turntable turning in the CW direction, looking from the top. Initially, due to a combination of inertia, static resistance between the wheel and the table and resistance at the pivot point of the support arm, the wheel is caused to move in the same direction as the table. But the wheel is not static on the table; it is turning due to the rolling interface and is going anti-clockwise, as viewed from the center of the table. The wheel is driving the propeller via a flexible drive shaft, and the propeller is turning anti-clockwise as viewed when it is on the left side of the table. I have looked at the pitch under magnification and have determined that the pitch is such which will result in a propeller force into the stationary air which will drive the cart in the opposite direction the turntable is moving. This is evident at approximately 13 seconds into the video, when the propeller thrust is finally sufficient to overcome the drag forces and the cart begins to move in the opposite direction as the table. It is acting as a propeller, driven by the wheel and NOT as a turbine driven by any apparent wind generated by moving CW on the table. This is a most important point! All the energy is being provided by the turntable to the wheel, which transfers some of that energy to the prop which then provides the force to drive the cart in the opposite direction on the table. This actually increases the energy at the wheel, because the relative velocity between the cart and the table has increased. There is absolutely nothing out of the ordinary happening here and such force reversals are occurring in countless machines everywhere in the world.
Now, to try and extrapolate what is happening here, to a DDWFTTW situation is not valid. First of all, you should disconnect the flexishaft between the wheel and the propeller, and run the exact same experiment again. This will simulate the same cart in a wind environment, with the wind coming from the rear and trying to drive the cart ddw. The wheel will only serve as a drag in this case and not provide any drive force. I confidently predict that the cart will be dragged along with the table in a CW direction until the apparent wind generated is sufficient to turn the propeller. However, with the given pitch of the prop, the wind will turn the propeller in the opposite direction that we see in the video! It can not do anything else! With the propeller, actually windmill, now turning in the opposite way, in order for the cart to advance downwind the flexishaft would need to be connected through a gear reversal in order to drive the wheels in the same direction as before. This should be done. NOW you would have a true configuration which can be compared with a DDW situation. But when you run the test in this configuration, you will soon find that the cart can never advance against the turntable! You cannot mix and match reference frames in order to get the result you want to see. The cart on the table must be configured exactly the same as the cart in the wind. No changes are allowed or you totally invalidate any correlation between reference frames. I hope you now understand my point.

 

[Phrak]

The wheel is driving the propeller. The thrust speed from the propeller is slower than the speed of the wheel. We've been calling (effective thrust speed / wheel speed) advance ratio, and it needs to be < 1 for a downwind cart, > 1 for an upwind cart.

What are thrust speed and advance ratio?

 

[zoobyshoe]

By a flexible cable.

So, to be perfectly clear: there is always a direct causal link between the rotation of the propeller and the rotation of the wheel? Turing either one in either direction always causes the other to turn?

 

[swerdna]

Thinks for the replies. This cart was only meant to be a prototype but it worked so well I though I would publish the results. The cart I was going to build (and still might) would have two identical carts directly opposite each other and sharing the same tether. The whole weight would be on the two wheels and no weight on the centre pivot. This design would be very balanced and would reduce and negative effects from such things as the turntable not being perfectly level and centre pivot friction.

I’m just a backyard inventor so don’t tend to get too technical. But here are a few basic specs . . .

The wheel is 8.5cm diameter
The circle traveled by the wheel is 120cm diameter
The prop is 12 x 6 slow air
Shafts run on roller bearings that have been washed of grease
Cable is from my son's BMX brake system
Hose clamps are optional

Here’s a mug shot . . .

 

[swerdna]

So, to be perfectly clear: there is always a direct causal link between the rotation of the propeller and the rotation of the wheel? Turing either one in either direction always causes the other to turn?

Yes.

 

[zoobyshoe]

Yes.

Thanks. It's also more obvious in the nice close-up shot. The workmanship does look excellent, incidentally.

I take it the diameter of the table is 48 inches. What is the diameter of the hole in its center? The table is mounted on a bicycle wheel, is that correct?

 

[swerdna]

Thanks. It's also more obvious in the nice close-up shot. The workmanship does look excellent, incidentally.

I take it the diameter of the table is 48 inches. What is the diameter of the hole in its center? The table is mounted on a bicycle wheel, is that correct?

Centre hole is 22.5 inches and table diameter is 48inches.

Yes it is simply attached to a bicycle wheel. Thanks but I don’t think hose clips qualify as “excellent workmanship”.

The shafts are threaded rod and the cable is attached to their ends by cutting a thin slot down their diameter, spreading the two halves apart, inserting the cable end then and then closing the slot by winding a nut up the thread to squeeze the cable (my son’s idea).

 

[rcgldr]

What are thrust speed and advance ratio?

Thrust speed is the speed of the air through the propeller. Advance ratio is the ratio of speed of the air through the propeller divided by the speed of the ground (relative to the cart). Another way to look at this is the distance the prop would move forward for every revolution of the driving wheel, this is equal to effective prop pitch / (gear ratio x wheel circumference).

The wheel is 8.5cm diameter. The prop is 12 x 6 slow air

Prop pitch is 6 inches per revolution, wheel circumference is 10.5 inches. Advance ratio would be < (6 / 10.5) < .57 depending on the ratio of effective pitch / physical pitch. The prop also has an advance ratio, (actual air speed) / (prop surface speed), and the effective pitch is the (actual air speed) / (rate of rotation of the prop). The physical pitch of the prop advances 6 inches per revolution, but the air flow through the prop will be less than 6 inches per revolution.

I've simplified the prop advance ratio description, as the real thing is a bit more complex. The prop operates in it's own induced wash, and in the imediate vicinity of a typical propeller, there's little change in air speed, mostly just an increase in pressure. Normal prop wash pressure is higher than ambient, so the air continues to accelerate aft of the propeller until it's pressure returns to ambient. The speed of the air at the point when it's pressure returns to ambient is called the exit velocity. For a typical propeller, the air speed through the prop is the 1/2(ambient speed + exit speed). I not sure how much difference there is between effective pitch and actual pitch for the DDWFTTW models, other than it's probably small.

 

[Phrak]

Thrust speed is the speed of the air through the propeller. Advance ratio is the ratio of speed of the air through the propeller divided by the speed of the ground (relative to the cart). Another way to look at this is the distance the prop would move forward for every revolution of the driving wheel, this is equal to effective prop pitch / (gear ratio x wheel circumference).

Prop pitch is 6 inches per revolution, wheel circumference is 10.5 inches. Advance ratio would be < (6 / 10.5) < .57 depending on the ratio of effective pitch / physical pitch. The prop also has an advance ratio, (actual air speed) / (prop surface speed), and the effective pitch is the (actual air speed) / (rate of rotation of the prop). The physical pitch of the prop advances 6 inches per revolution, but the air flow through the prop will be less than 6 inches per revolution.

I've simplified the prop advance ratio description, as the real thing is a bit more complex. The prop operates in it's own induced wash, and in the imediate vicinity of a typical propeller, there's little change in air speed, mostly just an increase in pressure. Normal prop wash pressure is higher than ambient, so the air continues to accelerate aft of the propeller until it's pressure returns to ambient. The speed of the air at the point when it's pressure returns to ambient is called the exit velocity. For a typical propeller, the air speed through the prop is the 1/2(ambient speed + exit speed). I not sure how much difference there is between effective pitch and actual pitch for the DDWFTTW models, other than it's probably small.

Thank you, Jeff. That all makes some sense. For werdna's particular set-up you would want to factor in the relative diameters of the tracks taken by wheel and propeller. For each revolution, the propeller travels further than the wheel for every revolution. It's equivalent to adding a pair of gears between propeller and wheel.

 

[rcgldr]

advance ratio ... For werdna's particular set-up you would want to factor in the relative diameters of the tracks taken by wheel and propeller. For each revolution, the propeller travels further than the wheel for every revolution. It's equivalent to adding a pair of gears between propeller and wheel.

I didn't take that into account. When the "cart" is moving, the apparent wind at the radius of the propeller is greater than the apparent wind at the wheel. The net effect would be to reduce the overall effective advance ratio because the prop spins at the same speed as the wheel, but operates in a faster apparent wind.

 

[zoobyshoe]

... apparent wind.

Since wind direction is a critical factor is this quest for directdownwindblahblah, I am still thinking air is being propelled off the spinning table. It's not spinning fast, but it's pretty large, and might be moving enough air to upset the notion we can take the sedentary room air as a reference point, especially since the prop is right in the stream of any air that is coming off the disc (table). I'm thinking that you might have some insight into determining how much air the disc might be moving. Is there such a formula as "air displaced by a spinning disc" or similar?

 

[swerdna]

I may have a design that will test the principle without using a treadmill or turntable (or maybe it‘s just a stupid idea) . . .

Build a cart with an onboard motor powered prop at it’s rear end so it‘s driven forward by the thrust of the wind it creates (wind powered cart). At the front end put the DDWFTTW prop and drive wheel but don’t connect them together. Run the cart in calm conditions and measure it’s top speed. Then connect the DDWFTTW prop and drive wheel and repeat the test. The connected cart should run faster than the non-connected. A valid test?

 

[zoobyshoe]

I may have a design that will test the principle without using a treadmill or turntable (or maybe it‘s just a stupid idea) . . .

Build a cart with an onboard motor powered prop at it’s rear end so it‘s driven forward by the thrust of the wind it creates (wind powered cart). At the front end put the DDWFTTW prop and drive wheel but don’t connect them together. Run the cart in calm conditions and measure it’s top speed. Then connect the DDWFTTW prop and drive wheel and repeat the test. The connected cart should run faster than the non-connected. A valid test?

This is my first taste of this whole controversy, but elsewhere here at PF I have gotten the notion that the trick is to go downwind, faster than the wind, powered only by the wind. Did I misunderstand the issue?

 

[rcgldr]

Since wind direction is a critical factor is this quest for directdownwind, I am still thinking air is being propelled off the spinning table.

Any air off the spinning table would be in the same direction as the spinning table, opposing the forward motion of the cart, not assisting it.

Build a cart with an onboard motor powered prop at it’s rear end so it‘s driven forward by the thrust of the wind it creates (wind powered cart). At the front end put the DDWFTTW prop and drive wheel but don’t connect them together. Run the cart in calm conditions and measure it’s top speed. Then connect the DDWFTTW prop and drive wheel and repeat the test. The connected cart should run faster than the non-connected. A valid test?

No, because the cart relies on a tailwind relative to the ground, using prop to accelerate air upwind against the tailwind, allowing the cart to go DDWFTTW. The goal here is to go faster than the wind, not to minimize power consumption. The connected cart consumes more power than the unconnected cart.

The only viable alternatives to a treadmill or spining wheel is a long wind tunnel where the wind speed and direction are stable. An outdoor test could be subject to gusts of wind combined with a flywheel effect.

 

[zoobyshoe]

Any air off the spinning table would be in the same direction as the spinning table, opposing the forward motion of the cart, not assisting it.

That's what I'm wondering: if it's not actually traveling upwind rather than downwind.

 

[rcgldr]

This is my first taste of this whole controversy, but elsewhere here at PF I have gotten the notion that the trick is to go downwind, faster than the wind, powered only by the wind.

Powered by the difference between wind speed and ground speed. The DDWFTTW carts use the wheels to drive a prop to generate a small amount of thrust to oppose the tailwind, allowing the cart to go faster than the wind. The speed of the thrust is a fraction of the speed of the wheels, and this effective gearing multiplies the thrust at the prop so it's larger than the force at the wheels, minus some losses in conversion of power. The speed reduction factor is greater than the thrust muiltiplcataion factor due to losses, so power output is less than power inputs, meaning it's not a perpetual motion machine.

As a though experiment example, imagine a cart with an advance ratio of .5, the thrust from the prop is 1/2 the speed of the ground (wheel) speed. At 10 mph, the prop produces 5 mph of upwind thrust. With a 10 mph tailwind, perhaps the cart could go 12 mph forwards, producing 6 mph of upwind thrust to oppose the tailwind, but using up 4 mph of the "excess" thrust speed to overcome the drag factors.

 

[rcgldr]

Any air off the spinning table would be in the same direction as the spinning table, opposing the forward motion of the cart, not assisting it.

That's what I'm wondering: if it's not actually traveling upwind rather than downwind.

That's the point of the cart, to travel forward faster than the wind, using the difference between wind speed and ground (turntable in this case) speed to power it. The cart can't travel upwind in a no wind situation, it requires a tailwind with respect to the ground it travels on as a power source.

 

[swerdna]

Any air off the spinning table would be in the same direction as the spinning table, opposing the forward motion of the cart, not assisting it.

No, because the cart relies on a tailwind relative to the ground, using prop to accelerate air upwind against the tailwind, allowing the cart to go DDWFTTW. The goal here is to go faster than the wind, not to minimize power consumption. The connected cart consumes more power than the unconnected cart.

The only viable alternatives to a treadmill or spining wheel is a long wind tunnel where the wind speed and direction are stable. An outdoor test could be subject to gusts of wind combined with a flywheel effect.

But if the DDWFTTW prop was reversed from normal wouldn’t the headwind effectively become a tailwind for that prop? All test that aren’t carried out in actual outside downwind conditions are representative assimilations (some may be valid, some not). The cart would be traveling into more of a headwind than the “original” but this may be compensated for by the fact that it doesn’t gradually receive less power from the wind and always receives full wind power. The headwind that is a tailwind for the prop is also greater and always there but in the "normal" scenario the tailwind disappears when the cart reaches wind speed.

 

[swerdna]

That's the point of the cart, to travel forward faster than the wind, using the difference between wind speed and ground (turntable in this case) speed to power it. The cart can't travel upwind in a no wind situation, it requires a tailwind with respect to the ground it travels on as a power source.

The cart in an outside wind test would be traveling upwind after it exceeds the speed of the wind as well.

 

[OmCheeto]

The cart in an outside wind test would be traveling upwind after it exceeds the speed of the wind as well.

??

 

[zoobyshoe]

That's the point of the cart, to travel forward faster than the wind, using the difference between wind speed and ground (turntable in this case) speed to power it. The cart can't travel upwind in a no wind situation, it requires a tailwind with respect to the ground it travels on as a power source.

I understand what you are saying: once faster than downwind speed is achieved it would be traveling upwind.

However, just to be crystal clear: the only power source allowed is the wind. Correct?

 

[swerdna]

??

Isn't traveling upwind effectively the same as traveling into a headwind?