Jeff Reid said: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.
No, the cart will average DDWFTTW if the wind variance is within reason. (It wouldn't work with microbursts every few seconds).zoobyshoe said: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.
Jeff Reid said:No, the cart will average DDWFTTW if the wind variance is within reason. (It wouldn't work with microbursts every few seconds).
zoobyshoe said: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.
Jeff Reid said: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.
ThinAirDesign said: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
ThinAirDesign said:Our current cart beats the wind by over 1.5x.
tsig said: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 said:I know, and for only $50.00 I can find out how wrong I am!
zoobyshoe said:I know, and for only $50.00 I can find out how wrong I am!
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.Subductionzon said: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!
Boy have I got a deal for you! . . .zoobyshoe said: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!
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.pallidin said: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 said: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!
zoobyshoe said: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.
Jeff Reid said: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.
zoobyshoe said: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.)
Jeff Reid said: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.
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).tsig said: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.
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.zoobyshoe said: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.
Jeff Reid said: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.
He was talking about Swerdna's cart. I thought Swerdna was working independently.ThinAirDesign said:Our current cart beats the wind by over 1.5x.
This really isn't a controversial issue. I think that everyone with a decent understanding of physics accepts it, but that doesn't stop those who can't grasp the basic physics behind it from arguing indefinitely.pallidin said: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.
Subductionzon said:OmCheeto, I am sure that Thin Air Design was talking about his and spork's cart. These are the various videos you can find on Youtube under the submitter spork33. swerdna made his cart because of his own doubts that it would work from discussions with spork on another thread. Spork and JB (aka TAD) made a cart that they ran on an everyday treadmill. They did this because of their own interest and doubters like me who said "If you believe it works why don't you make one and run it on a treadmill, that would be a good test and their would be no doubt about it running faster than the wind". Well they did and I was wrong in two ways. First off I thought it would not run as claimed. When it did and I immediately admitted I was wrong and congratulated them I was still wrong since I thought the treadmill demonstration would clearly demonstrate to doubters that it works. It did not, people who may not have had the aeronautical ability to see how this works but still have enough physics knowledge that they HAVE to see the frame of reference equivalence still have problems with this device. I personally know an actual NASA type rocket scientist who's mind boggled at this. He blew it off by saying to me "Well when they have a technical paper that explains this then I will look at it". Though not any where near as important that is like blowing off the Wright brothers flight until he say a paper that described the technical aspects that made their flight possible. Now that I know it can be done I am much more interested in learning how it works, I don't need any more convincing.
It's not the principles I object to: it should be possible. It's the practical side. Archimedes boasted that with a long enough lever and a place to stand he could move the earth. In principle he was absolutely right. There are so many practical impossibilities to his ever being able to do it that the principle become moot.uart said:This really isn't a controversial issue. I think that everyone with a decent understanding of physics accepts it, but that doesn't stop those who can't grasp the basic physics behind it from arguing indefinitely.
I guess it's a little bit like the Physics equivalent the "controversial" Maths issue of :
[tex]0.\bar{9} = 1[/tex]
(that is, zero point 9 repeated equals one)
It's true and not in the least bit controversial to any real mathematician, but search the Maths forum and you'll find no end of "lay" people wanting to argue the point.
zoobyshoe said:I know, and for only $50.00 I can find out how wrong I am!
I thought I was done with the explanations.zoobyshoe said:Can the propeller divert the force in such a way to create the thrust needed for acceleration? Jeff is hard at work on this.
Jeff Reid said:...
OmCheeto said:Viewing the 3 different carts, I can come up with 3 different sets of equations that explain why none of them satisfy the DDWFTTW scenario.
For as far as I can tell, each of them has a slightly different modus operandi, ...
... contrary to vanesch's apparent assertion that they are all somehow equivalent.
So why don't I publish these findings you might ask.
Because I like looking at these devices and figuring out how they work.
I'm now waiting for someone to build a cart that goes 3 times faster than the wind.
Jeff Reid said:I thought I was done with the explanations.
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.
tsig said:According to your second equation when air speed at prop = zero there is no power out.This conditions happens when cart speed = wind speed.
.
Air speed at the prop includes induced wash. When cart speed == wind speed, there is significant induced wash at the prop. There is some sub wind speed where the average speed of air near the prop is zero as it accelerates an apparent tailwind into an apparent headwind, and at this speed, the prop could be considered to be doing no work since the kinetic energy of the air doesn't change, just the direction.tsig said:According to your second equation when air speed at prop = zero there is no power out.This conditions happens when cart speed = wind speed.
The one pound of thrust corresponds to some amount of torque applied to the prop by the wheels. The DDWFTTW carts are configured (effectively geared) so that the force at the prop is greater than the opposing force at the wheels, but the speed at the prop is much less than the speed of the wheels, so that the power output (prop thrust x prop air speed) is less than power input (wheel force x wheel ground speed).If you have one pound of thrust from the propeller then there will also be one pound drag on the wheels since that is where the energy to drive the prop comes from.
I thought you were still calculating the best propeller for the job.Jeff Reid said:I thought I was done with the explanations.
ThinAirDesign said:I'm just not sure how they could *not* be equivalent, as they are all of essentially identical design and operation.
JB
OmCheeto said:Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.
I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.
OmCheeto said:Cart #1 goes in a semi-straight line and is powered by the wind.
Cart #2 goes in a semi-straight line and is powered by a treadmill.
Cart #3 goes in a circle and is powered by a spinning piece of plywood.
I guess, as a "systems thinker", the similarities in cart design are overwhelmed by the differences in how the carts are propelled.
Jeff Reid said:I thought I was done with the explanations.
I haven't looked into optimizing for maximum speed. It's not a speed contest (yet), and except for swerdna's turn table there's no easy way to let the models reach their maximum speed. We're stuck with the selection of slow flyer model props that are available that work well with the relatively slow apparent headwinds (compared to the speed of model airplanes).zoobyshoe said:I thought you were still calculating the best propeller for the job.