Can a cart powered by wind travel faster than the wind itself?

[zoobyshoe]

No, as the device goes down stream...

What force moves the device down stream to begin with? The force of the stream is being turned around to wind it upstream.

 

[vanesch]

In fact, it is easy to see what way the thing will turn: you take the effective point of attachment of the force with the water, and the effective point of attachment of the force on the rope (which is easy: it is along the rope itself). This couple of (balanced) forces will make up a torque, and the direction of the torque will give you the direction in which the system will rotate.

So if the effective interaction point of the water with the wheel is BELOW the rope, then obviously, the torque will work in the sense of the hands of the clock and the rope will wind up, while if the interaction point is ABOVE the rope, it will unwind.

 

[zoobyshoe]

In fact, it is easy to see what way the thing will turn: you take the effective point of attachment of the force with the water, and the effective point of attachment of the force on the rope (which is easy: it is along the rope itself). This couple of (balanced) forces will make up a torque, and the direction of the torque will give you the direction in which the system will rotate.

So if the effective interaction point of the water with the wheel is BELOW the rope, then obviously, the torque will work in the sense of the hands of the clock and the rope will wind up, while if the interaction point is ABOVE the rope, it will unwind.

I have sketched this out for myself for the case of a spool which is larger in diameter than the paddle wheel. (In this case the rope must be all underwater.) If we consider the paddles alone, the force of the water on the paddles still acts to rotate the device such that it will wind itself upstream. The force of the river on the thing as a whole, however, is surely enough to counteract this and will push it downstream, unwinding as it goes. When this happens, the paddles are moot, and do not give it any thrust in excess of the speed of the water. It will be pushed down stream at some speed less than the river speed, unwinding as it goes, paddles contributing nothing to forward speed.

 

[vanesch]

I have sketched this out for myself for the case of a spool which is larger in diameter than the paddle wheel. (In this case the rope must be all underwater.) If we consider the paddles alone, the force of the water on the paddles still acts to rotate the device such that it will wind itself upstream.

You mustn't consider a torque wrt to the center of the wheel, but between the two forces. (well, you can consider the torque wrt the center of the wheel, this will add and then subtract an extra contribution).

The force of the river on the thing as a whole, however, is surely enough to counteract this and will push it downstream, unwinding as it goes.

Well, we make abstraction of "the rest" and consider that only the paddles are in contact with the water, can we ?

 

[zoobyshoe]

Well, we make abstraction of "the rest" and consider that only the paddles are in contact with the water, can we ?

Consider then:
A table whose surface can slide. The x-axis of a milling machine is a good example. We put the wheel assembly on the table with the large diameter spool sticking down into one of the bolt slots. We then affix the "cable" to the wall. The smaller diameter wheels rest on the table surface on either side of the slot. Then we crank the table. Contact between the "water" and the "paddle wheels" will be the only "effective point of attachment."

Sound right?

 

[rcgldr]

Assume the paddlewheel diameter is smaller than the spool diameter and the wire unwinds from under the spool (0 < advance ratio < 1).

Assume the device is not moving and take the simplified case where the initial downstream force on the paddles is equal to the downstream force on the wire. The spool has a larger diameter, resulting in more torque, so the net torque rotates the paddlewheel in the downstream direction, and the paddles themselves upstream. At this point, the downstream force on the paddles is greater than the downstream force on the wire (during acceleration), but the ratio of the the spool diameter to paddle wheel diameter is greater still, so the net torque still results in a downstream rotation of the paddle wheel. As long as the paddlewheel diameter is sufficiently smaller than the spool diameter (advance ratio << 1), the device should work. Slippage of the paddles through the water could be an issue, but it should be less than slippage of a prop through air, so I don't see an issue here.

To compare this with the DDWFTTW cart, the wires are the equivalent of the treadmill or ground, the paddle wheels are the equivalent of the prop, and the paddlewheels interact with relatively dense water, while most of the vehicle travels to relatively thin air. It should be more efficient depending on paddlewheel versus water efficiency.

As previously mentioned, the advance ratio (paddle wheel diameter / spool diameter) puts an upper limit on the theoretical maximum speed, with stationary wires and moving water:

maximum speed = water speed / (1 - advance ratio).

At this maximum speed, the paddle speed equals the downstream speed, so no thrust is generated by the paddle wheels. The actual limit will be less. For example, assume advance ratio is 1/3, then max speed = water speed / (1 - 1/3) = 1.5 x water speed. With respect to the device, at 1.5 times the water speed, the wires move 1.5 times the water speed upstream, the relative water speed is an upstream flow at .5 times the water speed, and the upstream paddle speed = 1/3 of the wire speed = .5 times the water speed, the same speed as the apparent upstream speed at the device so no thrust is generated.

 

[swerdna]

In fact, it is easy to see what way the thing will turn: you take the effective point of attachment of the force with the water, and the effective point of attachment of the force on the rope (which is easy: it is along the rope itself). This couple of (balanced) forces will make up a torque, and the direction of the torque will give you the direction in which the system will rotate.

So if the effective interaction point of the water with the wheel is BELOW the rope, then obviously, the torque will work in the sense of the hands of the clock and the rope will wind up, while if the interaction point is ABOVE the rope, it will unwind.

I think you’re spot on. Whether the paddlewheel rolls up (Fig1) or down (Fig3) the cable or neither (Fig2) depends if the force of the water is above or bellow the point where the cable leaves the spool. So will this design ever be able to travel DDSFTTS? (S = Stream)

http://www.accommodationz.co.nz/images/ratios.bmp

 

[rcgldr]

paddlewheel rolls down (Fig3) the cable. So will this design ever be able to travel DDSFTTS?

Yes. If the cable unwinds from the bottom of the spool, below the paddles, the device is advancing against the water (0 < advance ratio < 1). If the spool were reversed so the cable unwound from the top of the spool it would move downstream, but slower than the water, regardless of the relative diameters (advance ratio < 0).

 

[zoobyshoe]

My curiosity got the better of me and I made a model using a spool of thread with a dowel pushed through the hole. For the water I cut a slot in a cardboard box. The spool goes in the slot and the dowel's ends ride on the box. With the thread tied down, I pushed on the box. This gives the spool a thrust according to the ""advance ratio"", but too much. It gets so much momentum that it rolls faster than the water can keep up, unrolling more thread than it should so that the thread tension is lost. It comes to rest and sits there at water speed doing nothing till it's carried far enough downstream to restore the tension. Then it gets another impulse. Then it loses tension. And so on. It sort of works. In spurts. It's much like my prediction about the cart, which was that it might be able to temporarily go faster than the wind on momentum, but then it would slow back down to wind speed.

 

[rcgldr]

It sort of works. In spurts.

In the case of the spool on the box, there's nothing significant to dampen out the motion caused by jerks on the thread. For the DDWFTTW carts, the momentum of the components, and the drag related factors provide enough damping that the cart doesn't oscillate noticably on a treadmill. In a real outdoor test with a wind that varied, the carts momentum would tend to smooth the motion due to momenum, alternating between powered mode and coast mode.

The water based device should have plenty of damping from the water. It apparently wasn't an issue with the Brennan torpedo which relied on wire tenstion to both propel and steer it.

 

[zoobyshoe]

In the case of the spool on the box, there's nothing significant to dampen out the motion caused by jerks on the thread. For the DDWFTTW carts, the momentum of the components, and the drag related factors provide enough damping that the cart doesn't oscillate noticably on a treadmill. In a real outdoor test with a wind that varied, the carts momentum would tend to smooth the motion due to momenum, alternating between powered mode and coast mode.

Well, it seems from this that you acknowledge that you're going to end up with a speed oscillation of + and - wind speed that almost surely will give your cart an average speed = average wind speed, not FTTW. Yes? No?

 

[rcgldr]

Well, it seems from this that you acknowledge that you're going to end up with a speed oscillation of + and - wind speed that almost surely will give your cart an average speed = average wind speed, not FTTW.

No, the cart will average DDWFTTW if the wind variance is within reason. (It wouldn't work with microbursts every few seconds).

 

[zoobyshoe]

No, the cart will average DDWFTTW if the wind variance is within reason. (It wouldn't work with microbursts every few seconds).

Isn't the whole thing kind of pointless if all you end up with is something like average cart speed exceeds average wind speed by .0000000006785 %?

What people want to see is the cart zipping downwind so obviously faster than the wind it blow their socks off. They want to see the cart under the ruler, with wind.

 

[ThinAirDesign]

Isn't the whole thing kind of pointless if all you end up with is something like average cart speed exceeds average wind speed by .0000000006785 %?

What people want to see is the cart zipping downwind so obviously faster than the wind it blow their socks off. They want to see the cart under the ruler, with wind.

Our current cart beats the wind by over 1.5x. That's just a bit more than .0000000006785%

Additionally, it only goes through windspeed once on the way to that speed rather than oscilate back and forch above and below it as you describe.

JB

 

[tsig]

It is more difficult, and I previously questioned if the propeller related losses (induced wash, slip ratio, angular movement of air, tip vortices, ...) would exceed what is needed to accomplish DDWFTTW. The videos have convinced me that DDWFTTW with a propeller works.

You stated that my last explantion wasn't simplified enough.

Simpler still description:

Prop power input = force at wheels times ground speed at wheels
Prop power output = force at prop times air speed at prop

The power input is used to create the torque and angular velocity used to drive the prop. The prop generates a higher force but at a lower speed than the wheel + ground interface. A tailwind allows the prop to interact with air that is moving slower than the ground (using the cart as a frame of reference), so that the slower speed at the prop still results in a net upwind thrust.

The net upwind thrust opposes the tailwind, slowing the wind down significantly below cart speed, allowing the cart to operate DDWFTTW.

So are you saying that the prop output is greater that it's input? More power out than power in is impossible no matter what the gearing.

 

[zoobyshoe]

Our current cart beats the wind by over 1.5x. That's just a bit more than .0000000006785%

Additionally, it only goes through windspeed once on the way to that speed rather than oscilate back and forch above and below it as you describe.

JB

I know, and for only $50.00 I can find out how wrong I am!

 

[OmCheeto]

Our current cart beats the wind by over 1.5x.

Oh! I missed the video for that one! Can you re-post it please.

 

[vanesch]

So are you saying that the prop output is greater that it's input? More power out than power in is impossible no matter what the gearing.

No, the prop. MOMENTUM transfer output is greater than the wheel momentum input, but the prop. ENERGY output is less (per unit of time).

Now, momentum transfer per unit of time = force. The reason why it is possible to have a higher momentum output (force) with less energy than the input is because the medium on which it acts has a lower velocity.

 

[Subductionzon]

I know, and for only $50.00 I can find out how wrong I am!

I am fairly sure that spork published a parts list, he also has made a series of how to build it yourself videos. So you might be able to do it for even less. You do not have to send your hard earned money to him. We can show how wrong you are wholesale!

 

[OmCheeto]

I know, and for only $50.00 I can find out how wrong I am!

For a hundred dollars, I'll send you plans for one that goes faster than them all. You'll be the new king of the DDWFFTTW world!

 

[zoobyshoe]

I am fairly sure that spork published a parts list, he also has made a series of how to build it yourself videos. So you might be able to do it for even less. You do not have to send your hard earned money to him. We can show how wrong you are wholesale!

Hmmm. Tempting... Tell you what: send me $500.00 to cover my video study time, shopping and construction time, gas for the truck, electricity for shop lighting and power tools, and I'll do it. Actually, make it $3000.00: I'm going to need a radar gun and an accurate anemometer. Those are going to take time to figure out how to use, and I'll need to hire assistants to man them. There'll be training time. I might need a radio controlled steering mechanism. Coffee and donuts, all that. Days of locations scouting and wind chasing: make it $5000.00.

For a mere $5000.00 you can prove how wrong I am!

 

[pallidin]

I am rather curious as to why this issue has not been settled.

This phenomena expression, including all variants, is readily testable and arguably affordable; thus well within the confines of even basic scientific inspection.

There should be a definitive, "this is how it works/doesn't work" answer.

But I'm not seeing that.

 

[swerdna]

Hmmm. Tempting... Tell you what: send me $500.00 to cover my video study time, shopping and construction time, gas for the truck, electricity for shop lighting and power tools, and I'll do it. Actually, make it $3000.00: I'm going to need a radar gun and an accurate anemometer. Those are going to take time to figure out how to use, and I'll need to hire assistants to man them. There'll be training time. I might need a radio controlled steering mechanism. Coffee and donuts, all that. Days of locations scouting and wind chasing: make it $5000.00.

For a mere $5000.00 you can prove how wrong I am!

Boy have I got a deal for you! . . .

Pay me just half the $5000.00 (a mere $2500.00) and I will continue to spend my time and money doing all the making, testing, filming, and posting the results for you.

But wait, there’s more! . . .

10% discount for prompt payment!

 

[swerdna]

I am rather curious as to why this issue has not been settled.

This phenomena expression, including all variants, is readily testable and arguably affordable; thus well within the confines of even basic scientific inspection.

There should be a definitive, "this is how it works/doesn't work" answer.

But I'm not seeing that.

That’s something I’ve always been curious about as well. I’ve only been studying this principle since November 2008 but some have been doing it for many years. Some say it has been conclusively proven and others are refusing to accept the proof provided. The lack of testing in “real” wind or even water I also find curious.

 

[zoobyshoe]

Boy have I got a deal for you! . . .

Pay me just half the $5000.00 (a mere $2500.00) and I will continue to spend my time and money doing all the making, testing, filming, and posting the results for you.

But wait, there’s more! . . .

10% discount for prompt payment!

I've been thinking. I'm going to need a wind tunnel. Prolly need a jet engine for that. That brings it all up to...I don't know, let's say $500,000.00

 

[zoobyshoe]

My curiosity got the better of me and I made a model using a spool of thread with a dowel pushed through the hole. For the water I cut a slot in a cardboard box. The spool goes in the slot and the dowel's ends ride on the box. With the thread tied down, I pushed on the box. This gives the spool a thrust according to the ""advance ratio"", but too much. It gets so much momentum that it rolls faster than the water can keep up, unrolling more thread than it should so that the thread tension is lost. It comes to rest and sits there at water speed doing nothing till it's carried far enough downstream to restore the tension. Then it gets another impulse. Then it loses tension. And so on. It sort of works. In spurts. It's much like my prediction about the cart, which was that it might be able to temporarily go faster than the wind on momentum, but then it would slow back down to wind speed.

In the case of the spool on the box, there's nothing significant to dampen out the motion caused by jerks on the thread. For the DDWFTTW carts, the momentum of the components, and the drag related factors provide enough damping that the cart doesn't oscillate noticably on a treadmill. In a real outdoor test with a wind that varied, the carts momentum would tend to smooth the motion due to momenum, alternating between powered mode and coast mode.

I figured out a completely dry way to dampen it: push it uphill.

I found a board and elevated one end a couple/three inches. To insure the dowel had traction I put two pieces of tape, sticky side up, on either side of the slot. Then I put the spool/wheel unit on the box and taped the end of the thread to the floor. Then I pushed the water uphill.

It seems, ladies and gentlemen, this embodyment works.

The box moved 27.8 cm and the spool/wheel unit moved 34.7 cm.

-----------------

I think the cart under the ruler does much better but this one could be vastly improved with larger wheels. The "wheels" are .78 cm in diameter and the spool is 3.67 cm in diameter for a ratio of 1:4.7. Obviously something like 1: 1.5 is going to be way better.

(I also realized I could have dampened it with tape alone.)

 

[swerdna]

I figured out a completely dry way to dampen it: push it uphill.

I found a board and elevated one end a couple/three inches. To insure the dowel had traction I put two pieces of tape, sticky side up, on either side of the slot. Then I put the spool/wheel unit on the box and taped the end of the thread to the floor. Then I pushed the water uphill.

It seems, ladies and gentlemen, this embodyment works.

The box moved 27.8 cm and the spool/wheel unit moved 34.7 cm.

-----------------

I think the cart under the ruler does much better but this one could be vastly improved with larger wheels. The "wheels" are .78 cm in diameter and the spool is 3.67 cm in diameter for a ratio of 1:4.7. Obviously something like 1: 1.5 is going to be way better.

(I also realized I could have dampened it with tape alone.)

Bet it didn’t cost more than $1.00. $499,999.00 left in the kitty. (well done)

 

[rcgldr]

Prop power input = force at wheels times ground speed at wheels
Prop power output = force at prop times air speed at prop

The power input is used to create the torque and angular velocity used to drive the prop. The prop generates a higher force but at a lower speed than the wheel + ground interface. A tailwind allows the prop to interact with air that is moving slower than the ground (using the cart as a frame of reference), so that the slower speed at the prop still results in a net upwind thrust.

The net upwind thrust opposes the tailwind, slowing the wind down significantly below cart speed, allowing the cart to operate DDWFTTW.

So are you saying that the prop output is greater that it's input? More power out than power in is impossible no matter what the gearing.

No, I'm saying the prop outputs more force, but at a slower still speed, and if you compare power output (prop thrust x air speed) versis power input (wheel force x ground speed), the power output is less than the power input. The tailwind interacts with the slow upwind thrust from the prop to generate a forwards force on the cart, greater than the opposing force from the ground onto the driven wheels (related to the torque load from the prop).

 

[rcgldr]

Isn't the whole thing kind of pointless if all you end up with is something like average cart speed exceeds average wind speed by .0000000006785 %? What people want to see is the cart zipping downwind so obviously faster than the wind it blow their socks off. They want to see the cart under the ruler, with wind.

Swerdna's turntable video shows that. The angular speed (rate of rotation) for Swerdna's cart was about -1/2.3 times the rate of the turntable, so relative to the turn table, the cart advances 3.3 revolutions while the wind advances 2.3 revolutions, about 1.4 times the wind speed.

 

[OmCheeto]

Swerdna's turntable video shows that. The angular speed (rate of rotation) for Swerdna's cart was about -1/2.3 times the rate of the turntable, so relative to the turn table, the cart advances 3.3 revolutions while the wind advances 2.3 revolutions, about 1.4 times the wind speed.

I see. So when TAD said:

Our current cart beats the wind by over 1.5x.

He was talking about Swerdna's cart. I thought Swerdna was working independently.