Merged DDWFTTW in a “Real” Wind

[EHocking]

Engines drive props. No engine.
What drives the wheel?

Forward motion of the cart.

From a standstill?

The tailwind.

That was for your benefit. You know, "backwards" roads and so forth.
If the wind is driving the rotor CCW,

It is not.

that means you need something else[/I to drive it forwards, other than the wind on the rotor.

Yep. The wheels, linked to it by gears and a chain.

 

[humber]

The "tacking prop idea" is a helpful analogy for sailors. The propeller isn't doing anything exotic or unusual. It's just doing what propellers do. The analogy of the moving blade to a tacking sail is revealing (to those more familiar with the latter), simple and accurate.

Rum is helpful to sailors too, but one does not expect to find reference to that in an aerodynamics text, but would expect that of such a useful thing as a tacking prop. It appears you are more likely to find the first than the second.

I suspect you haven't checked them all yet. You may find someone's made the analogy before or you may not. I'm not that bothered, personally, but do let us know if you happen to find it in print.

I have not checked everywhere for dinosaurs, so I expect they may well exist.

 

[Jack by the hedge]

But if you pull slowly it stays in place. You can do exactly the same with a simple toy car. Try it. It will drift back a bit.

Yes. Obviously.

That leaves you to explain how much of a difference could there be between that, and not moving back at all, and WTF does that have to do with windspeed travel?

I am struggling to fathom WTF you think it has to do with anything relevant. I guess the moving paper is the moving ground from the cart's frame of reference. (Am I right?) Why your paper suddenly and violently accelerates, I don't know, because that doesn't happen to the cart. From a standstill, and from the cart's frame of reference, the static prop resists the wind - changes the wind's velocity - and (since there's a fixed relationship between the wind and the ground) changes the ground's velocity too. That turns the cart's wheels which begins to turn the propeller.

ETA:
You are almost right. Most of the gimmick is that the expected linear motion - being pulled back- becomes angular motion as the wheels turn. Spin. Not roll up the belt.

No. If you did the whipping-the-paper-away trick with a gearwheel and rack where slip does not happen, it would behave in a similar way.

The rest, including the prop is a matter of engineering the solution, but Spork arrived at it by trial and error and thought he had found gold.

You know, this just looks whiny and resentful, as if you begrudge someone their success because you think they're not clever enough to deserve it. Not an appealing look.

 

[Jack by the hedge]

Rum is helpful to sailors too, but one does not expect to find reference to that in an aerodynamics text, but would expect that of such a useful thing as a tacking prop. It appears you are more likely to find the first than the second.

You apparently missed the bit where I explained why a "tacking propeller" would be referred to in any aerodynamics textbook as a "propeller".

I have not checked everywhere for dinosaurs, so I expect they may well exist.

If a creature was described to a non-scientific audience as a "living dinosaur" would you look to paleontology textbooks to find the properties of living dinosaurs?

 

[humber]

Yes. Obviously.
I am struggling to fathom WTF you think it has to do with anything relevant. I guess the moving paper is the moving ground from the cart's frame of reference. (Am I right?)

How in principle is it any different from the TM belt?

Why your paper suddenly and violently accelerates, I don't know, because that doesn't happen to the cart. From a standstill, and from the cart's frame of reference, the static prop resists the wind - changes the wind's velocity - and (since there's a fixed relationship between the wind and the ground) changes the ground's velocity too. That turns the cart's wheels which begins to turn the propeller.

The movement of the paper is no different from the belt.

No. If you did the whipping-the-paper-away trick with a gearwheel and rack where slip does not happen, it would behave in a similar way.

Again, it's just like the TM. If you were not at first told that the TM represented wind speed travel, would you have though that it would?
Or perhaps you would just see it as a machine traveling against a belt?
You may think that to be surprising, but still not ddw wind travel, I think.

You were almost right with the initial reaction. It is a machine driven by a belt, but it does not travel up the belt, but avoids being dragged back with the belt. Just like the car on the paper, it sits there, as the belt moves underneath the wheels. The trick is what happens after the cart is allowed to spin up on the TM by being held by the hand. That stores momentum in the prop (about 1J)
Through a process of (low friction) intermittent contact with the belt, energy is taken from the belt, to keep that momentum as it is. Cart stays in place.

You know, this just looks whiny and resentful, as if you begrudge someone their success because you think they're not clever enough to deserve it. Not an appealing look.

He has no idea how it works.

 

[A.T.]

And you think that big sail of a prop and the towers can't tack a 20 degree wind?

Any references about your "prop tacking at 20 deg" ?

Rum is helpful to sailors too, but one does not expect to find reference to that in an aerodynamics text, but would expect that of such a useful thing as a tacking prop. It appears you are more likely to find the first than the second.

I guess that means "no".

 

[Jack by the hedge]

How in principle is it any different from the TM belt?

In the violence of its acceleration. Otherwise it's a fair analogy.

The trick is what happens after the cart is allowed to spin up on the TM by being held by the hand. That stores momentum in the prop (about 1J)
Through a process of (low friction) intermittent contact with the belt, energy is taken from the belt, to keep that momentum as it is. Cart stays in place.

Suddenly it appears you understand how the cart works. Of course it relies on the air in the room not moving at the same velocity as the treadmill. There has to be a difference in their velocities as that's what powers the cart. The cart on the treadmill even seems, from your description, to be efficient enough that it can extract sufficient power when only driven for a certain percentage of the time (when the wheels are in effective contact with the belt).

He has no idea how it works.

So, you're still saying he doesn't deserve the glory of having actually done it. Because he didn't do it properly, with all the proper math. Because he's not as smart as... well, someone else.

I wish you could see how that stuff looks. It's really toe-curlingly embarrassing.

 

[CORed]

How in principle is it any different from the TM belt?


The movement of the paper is no different from the belt.


Again, it's just like the TM. If you were not at first told that the TM represented wind speed travel, would you have though that it would?

Of course I would

Or perhaps you would just see it as a machine traveling against a belt?
You may think that to be surprising, but still not ddw wind travel, I think.

That might be what you think, but I'm not as ignorant as you

You were almost right with the initial reaction. It is a machine driven by a belt, but it does not travel up the belt, but avoids being dragged back with the belt. Just like the car on the paper, it sits there, as the belt moves underneath the wheels. The trick is what happens after the cart is allowed to spin up on the TM by being held by the hand. That stores momentum in the prop (about 1J)

the Joule is a unit of energy, not momentum. However it is obvious that although you know the words, you have no grasp of the concepts.

Also, in many of the videos, the cart clearly travels up the belt, until it is held or pushed back

Through a process of (low friction) intermittent contact with the belt, energy is taken from the belt, to keep that momentum as it is. Cart stays in place.

Priceless entertainment. Tell me humber: How does this intermittent contact work? Antigravity? Do you realize that the process you describe is every bit as impossible as you think ddwftw travel is? Of course you don't.

He humber has no idea how it anything works.

 

[A.T.]

Not quite. He thinks that it is possible. And describes a few means, some of which I have posted, but he thinks the "obvious" means is that the prop "slows down" the headwind and that drives the wheel.

Since humber is not only quote mining the NASA engineer here, but outright lying about what he said I will post the entire e-mail from:
http://talkrational.org/showthread.php?p=1257363#post1257363

Hello (RP),

My name is (NASA #2), and (NASA #1) forwarded your email dialog to me, along with some attachments from one of the naysayers of the DWFTTW cart physics. I have been an applied aerodynamics researcher at NASA Ames for 31 years. In addition, I grew up racing sailboats, then after starting work at Ames, left sailboat racing to race sailplanes, also for the last 31 years.

So I am well-acquainted with the performance of sailboats at downwind headings not directly downwind, and it is true that for sailboats, there is a significant benefit to boat speed to do that, primarily from the aerodynamic characteristics of sails. However, that effect is not in play to any appreciable degree on the DWFTTW cart, and if anything, acts to diminish the thrust on the propeller. Drawing the vector diagram of the relative wind (apparent wind) as the sum of the cart speed and the wind speed, it can be seen that if the wind direction swings, the apparent wind increases. If the wind angle approaches 90 degrees, the apparent wind speed will be roughly equal to the ground speed, and the cart will stop. The cart gets its power from the DIFFERENCE between the apparent wind speed and the ground speed, requiring that the apparent wind be LESS than the ground speed.

Interesting that the writer (Humber) in his attempt to make an argument for why the cart can not go DWFTTW, he states exactly why it DOES:
“the prop is said to travel less distance through the air, than the cart travels over the ground, but of course,
work =force*distance, and must be the same at the wheel as at the propeller.”

His statement is true, that for a given interval of time, the work done by the prop must be equal to the work input from the wheels, (excepting for losses). The fact that the prop travels less AIR distance in that time than the wheels travel in GROUND distance is exactly WHY the propeller thrust can be greater than the wheel drag. There are, of course, significant losses in the system, and Mr. Cavallaro’s example problem provides realistic estimates for those, demonstrating that even with those losses, there is excess thrust at the propeller to accelerate the vehicle despite the wheel drag. The only thing that limits the cart speed is the escalation of those losses to the point where there is no longer sufficient power to create the excess thrust. When the thrust equals the drag, the cart will move at constant speed.

On the topic of the small deviations in wind speed and the effect that has — first of all, remember that what is important is the direction of the “apparent wind”. This is also true of sailboats, of course; by sailing at an angle to the wind (reaching angle) the sail performs better as a wing rather than just a drag device. The faster the boat goes, the more the apparent wind swings to reduce the angle of flow onto the sail into the useful range to operate as a wing, providing more ‘lift’ force that has a large component in the direction of motion. Choosing the optimum reaching angle for a sailboat is complex because it involves not only the vector combination of the boat speed and wind speed to find the apparent wind, but also the performance ‘polar’ of the sails – the amount of lift and drag force they produce as a function of angle to the apparent wind. But, for the DWFTTW cart, any reaching angle increases the apparent wind component into the propeller, which reduces its thrust.

One other possibility is worth discussing — that it could be the time-variation of the wind direction, rather than simply the fact that the wind is not DDW. There are examples of similar effects in nature that would give some reason to consider this. For example, what is called “dynamic soaring” -- the maneuvering in a wind gradient field (regions where there is a consistent pattern of different wind speed) that allows birds (and gliders) to soar by extracting energy out of the wind gradient field. This is the life-blood of the albatross, and to some extent, the frigate bird. The world record for a radio-controlled glider in dynamic soaring is something close to 400 mph! In the case of the DWFTTW cart, it might be possible to extract a very slight amount of extra energy from the time variation of the wind – I will at least give it additional thought. But it is certainly not the dominant effect, which is much more simple and, (dare I say...) obvious.

One other observation on the wind data — I am not familiar with the instrumentation used to measure the wind speed in the plots that are presented. The high frequency ( 5hz) oscillations in the wind direction look to me to be partly due to an artifact of the instrumentation. Several possible ways that this would happen occur to me, but each is dependent on assumptions of how the measurements were made, so until I know that, I would not elaborate further on those effects. In any case, they are of very little significance compared to the actually very simple situation of why the cart can go about 3x the wind, down wind.

A quick thought on what additional measurements might be made to help persuade naysayers: Is there sufficient skepticism in the assertion that the propeller is pulling and the wheels are dragging, that some well-placed force measurements might be convincing? Probably the simpler thing would be to build one with electric generator at the wheels and motor at the prop, and show what direction the current is flowing. Even simpler is to just examine the drive chain while it is running, and see which side of the drive gears the chain is tight on. When you pedal a bike, the top leg of the chain is tight -- if the wheel of a bike is forcing the pedals to turn, the bottom leg of the chain is tight. On the DWFTTW cart, this simple test makes it easy to see that the wheels are indeed driving the prop.

It’s funny to me how hard people work to contrive an alternative explanation for something that is actually fairly simple: The propeller thrust is greater than the wheel drag, because the apparent (relative) wind speed is slower than the ground speed. The power (work per unit time) available from drag on the wheels is D x V_g. The power required by the propeller is T x V_a. As long as V_a is less than V_g, then T must be greater than D, ignoring system losses, so that the power absorbed matches the power developed.

I can’t help make an analogy to someone that would argue with Einstein’s proposition that gravity is just the curvature of space-time because they don’t understand it, rather than accept that they don’t understand it and try to fill their knowledge gap.

I respect your efforts to try to reconcile these things, and to try to impose some level of civility into the technical discussion. I often try to do the same. I sometimes find that when the conversation is reduced to simultaneous monologues, it is best to sigh and give up, and until now, I have not spoken out on the DWFTTW. I laud your tenacity.

There are those that get quoted as expressing a certain opinion, and the quote persists long past the time that that opinion is still held. I’m quite certain that if you give me 5 minutes at the chalk board with a Nobel laureate physicist, I can convince him of the validity of the analysis for the DWFTTW cart. I have encountered this before in reverse — someone comes to us with a crackpot idea, and when we naysay it, they site the affirmation of some prize physicist who made a polite and supportive comment during a brief meeting, but who would easily be persuaded later by sound argument that the idea is without merit.

When Mr. Cavallaro is here, I will raise this hypothesis about the effect of small variations in wind direction. I think we can quickly dispel it on his demonstration treadmill by moving the fan in small amounts to one side, and I expect to see the cart slow down.

Best Regards,
(NASA #2).

 

[spork]

Since humber is not only quote mining the NASA engineer here, but outright lying about what he said I will post the entire e-mail from:
http://talkrational.org/showthread.php?p=1257363#post1257363

It's difficult to find a post in which humber does not lie.

 

[jduffy77]

Yevgheni has never commented on it.
The video says 3W. Too bad.

Sigh, more lies Humber. The video says no such thing. Your hero Yev has posted at least twice today alone regarding the props thrust.

Engines drive props. No engine.
What drives the wheel? From a standstill?
Spontaneous motion?

The prop powered by the wind generates thrust Humber, wake up! Its not even very complicated.

That was for your benefit. You know, "backwards" roads and so forth.
If the wind is driving the rotor CCW, that means you need something else[/I to drive it forwards, other than the wind on the rotor.

That's what the wheels are for. You can't make a ddwfttw balloon except in the Humberverse.

 

[CORed]

It's difficult to find a post in which humber does not lie.

A minor quibble. Ther are many posts in which humber makes no sense whatsoever, so it's impossible to tell whether he is lying or not.

 

[D'rok]

Since humber is not only quote mining the NASA engineer here, but outright lying about what he said I will post the entire e-mail from:
http://talkrational.org/showthread.php?p=1257363#post1257363

That email is a very lucid and understandable explanation.

 

[spork]

A minor quibble. Ther are many posts in which humber makes no sense whatsoever, so it's impossible to tell whether he is lying or not.

There is no doubt he posts plenty of complete nonsense, but he also posts many absolute outright lies - and he does it over and over. He doesn't get a pass on lying just because he posts so much nonsense, just as he doesn't get a pass on being malicious just because he has been diagnosed with Alexia.

 

[mike3]

It's just hard (impossible) for humber to understand.

In which case it'd probably be best to just quit debating with him altogether, since it's an impossibility to get anywhere.

 

[A.T.]

Since humber is not only quote mining the NASA engineer here, but outright lying about what he said I will post the entire e-mail from:
http://talkrational.org/showthread.php?p=1257363#post1257363

That email is a very lucid and understandable explanation.

It is the same correct explanation that was given by spork and others before:

The cart gets its power from the DIFFERENCE between the apparent wind speed and the ground speed, requiring that the apparent wind be LESS than the ground speed.
...
The propeller thrust is greater than the wheel drag, because the apparent (relative) wind speed is slower than the ground speed. The power (work per unit time) available from drag on the wheels is D x V_g. The power required by the propeller is T x V_a. As long as V_a is less than V_g, then T must be greater than D, ignoring system losses, so that the power absorbed matches the power developed.

In fact, humber's crank-fellow on TR said that it sounds just like written by spork. While humber implied that NASA is useless and he now wants to hear the opinion of Boeing engineers about it. But now humber goes to another forum and lies about what the NASA guy actually said. Pathetic.

 

[humber]

In the violence of its acceleration. Otherwise it's a fair analogy.

Mender performed a test where the cart was dropped onto the belt, to show that it could withstand a sudden start.

Suddenly it appears you understand how the cart works. Of course it relies on the air in the room not moving at the same velocity as the treadmill.

How about it's just spinning in still air?

There has to be a difference in their velocities as that's what powers the cart. The cart on the treadmill even seems, from your description, to be efficient enough that it can extract sufficient power when only driven for a certain percentage of the time (when the wheels are in effective contact with the belt).

Do you say that a dog is a cat because they both have 4 legs? Just because the relative speed is zero, does not mean that is the same condition as wind speed. The small car on the piece of paper meets all requirements of the test, but it's nothing like the same car traveling at speed in the wind.

So, you're still saying he doesn't deserve the glory of having actually done it. Because he didn't do it properly, with all the proper math. Because he's not as smart as... well, someone else.

Well JBTH, "glory" is the very reason the cart exists. Spork claims to be a "scientist" but they don't go on the internet and abuse everyone who disagrees with them, nor show total ignorance of math and technology.

But, that is not the point. It was found by trial and error, and through sheer ignorance, mistaken for a genuine model of a cart in the wind rather than the machine that stays in place as I have described. In the wind, there will be forces that are not on the TM. So, you have been deceived into sharing that mistake.

I wish you could see how that stuff looks. It's really toe-curlingly embarrassing.

Not to me.

 

[humber]

Any references about your "prop tacking at 20 deg" ?

I guess that means "no".

There are no references to tacking props, because that is BS.
There are tacking boats.

 

[humber]

Since humber is not only quote mining the NASA engineer here, but outright lying about what he said I will post the entire e-mail from:
http://talkrational.org/showthread.php?p=1257363#post1257363

And?

 

[humber]

There is no doubt he posts plenty of complete nonsense, but he also posts many absolute outright lies - and he does it over and over. He doesn't get a pass on lying just because he posts so much nonsense, just as he doesn't get a pass on being malicious just because he has been diagnosed with Alexia.

Desperate. I am more articulate than you by a large margin, but you think that a supposed word disorder prevents me from taking your trinkets apart?
That I have transmitted Alexia to Drs Camp, Allain, Whiteman and Kammen?


But, on the matter of lying, can ask Modified. He was here from the start.

Modified, did we ever discuss the idea of the distance the prop moved through the air and the distance the cart moved over the ground? The "air lever"?

Force? work? power? Or were they issues introduced by Christoph and me?