Down wind faster than the wind

[ThinAirDesigns]

Thanks for the allegory, but I think that the "wind" may perhaps only exist just above the treadmill surface, in a sort of laminar flow kind of way.

Then you are not thinking clearly.

Within the limits of the atmosphere, no matter how tall the flagpole above your porch it will see the same 10mph wind on the treadmill.

JB

 

[humber]

Not really. Only if you are trying to measure how close to actual wind speed the cart gets, not if it can go faster than the wind. Once it exceeds the speed of the wind, a simple visual verification is all that is needed.

Well, no. The result would not be so precise as to allow such a simple binary indicator because there is no such indicator for windspeed itself.
Unless large error margins are allowed, then precision is necessary.

That's like saying that if you have a constant speed input and you want to slow down the output to as low a speed as possible, a precise measuring system is needed to determine how close to infinite the gearing is as the output slows - unless the output stops and then reverses direction without disengaging. Then there is no doubt that the ratio reached infinity and is now coming back down on the other side. Do you see how that applies?

Let's see. A relative measurement, where the discriminator is a change in the sign of the derivative? Complex, and probably error prone. Really, wind measurement is not so easy. Would you accept say, a 10% error margin?

Given the present set of rules, the floor is always open, Humber. I await the physical manifestation of your esoteric cogitations.

No, the floor is the wind. You can be assured that I am never going to build anything, Mender, but I may propose something to test the reaction. I'll keep you in mind.

 

[humber]

Then you are not thinking clearly.

Within the limits of the atmosphere, no matter how tall the flagpole above your porch it will see the same 10mph wind on the treadmill.

JB

Just to make this clear. If you set up the porch on a treadmill of appropriate size, and moved it so that you say there is a wind, you say that I could not tell if it were the same scenario, but stationary with the same velocity real wind?

 

[humber]

Actually humber, you are precisely wrong. In this sunny porch scenario there is exactly no "wind" just above the treadmill surface, just like in all cases where air moves relative to a surface.

H'ethetheth, are you also in agreement with what JB says about the flagpole, and my interpretation of that in my reply?

 

[screensnot]

Just to make this clear. If you set up the porch on a treadmill of appropriate size, and moved it so that you say there is a wind, you say that I could not tell if it were the same scenario, but stationary with the same velocity real wind?

That is the $64k question.

 

[mender]

Humber, you dance divinely but you don't harmonize worth a hoot. Let me know when you are willing to learn a new tune.

 

[humber]

That is the $64k question.

Is it? Do you also say that it is not possible to tell the difference?

 

[humber]

Humber, you dance divinely but you don't harmonize worth a hoot. Let me know when you are willing to learn a new tune.

Mmm, themed answers. Have you ever tried to measure the velocity of a meteorological balloon? Or that of a tennis-ball sized object dragged behind it? Not so easy.

 

[screensnot]

Is it? Do you also say that it is not possible to tell the difference?

I say that it wouldn't make any difference to Spork's cart.

 

[huh34]

Mmm, themed answers. Have you ever tried to measure the velocity of a meteorological balloon? Or that of a tennis-ball sized object dragged behind it? Not so easy.

Have you ever tried to measure windspeed on a porch on a treadmill of appropriate size? So very easy. Doesn't even matter wether the tredmill moves or not.

 

[humber]

I say that it wouldn't make any difference to Spork's cart.

The idea is that the belt is the wind. We have been through this. Every time that this is discussed, it always ends with some example where if I complete the course, I would end up in arithmetic agreement, because that is the inevitable outcome of the assumption that fosters that idea. That's not the the difference at all. In the cart treadmill, there are more differences than that. It is not even logically consistent.

The treadmill belt is said to be an "equivalent frame of reference", but I say that it is a model, and that the limitations of that model will certainly allow me to tell any 'wind' so generated, from the same wind in the real environment. It does not depend on visual clues, or such. They are definitely not the same. Not even close.

 

[humber]

Have you ever tried to measure windspeed on a porch on a treadmill of appropriate size? So very easy. Doesn't even matter wether the tredmill moves or not.

Real windspeed test, not a treadmill. For me, I would want to be sure that I had achieved what I wanted to do, so accuracy of measurement would be important. If the methods that the cart may use are only restricted to the general requirement of "steady state", then I wonder what it is that you are even claiming. No problem to achieve >windspeed under those rules.

 

[huh34]

Real windspeed test, not a treadmill. For me, I would want to be sure that I had achieved what I wanted to do, so accuracy of measurement would be important.

Theoretically, if you had an anemometer of ultimate accuracy, what would you measure on your porch? Based on that result, how would you tell wether you're on a treamill or is it just a quite perfect sailing day with steady 10 mph wind.

If the methods that the cart may use are only restricted to the general requirement of "steady state", then I wonder what it is that you are even claiming. No problem to achieve >windspeed under those rules.

If the requirements would be (my wording not sporks):
1) The cart has to move directly downwind
2) The cart has to move relative to ground faster than the air moves relative to ground
3) The cart has to be able to maintain its desired speed indefinately
4) The cart can utilize only the movement of air relative to ground as its power soure and nothing else

With these rules, is it "no problem" or "impossible" to achieve?

What requirement would you suggest in addition to the ones spork & co have claimed that would satisfy you?

 

[screensnot]

... the limitations of that model will certainly allow me to tell any 'wind' so generated, from the same wind in the real environment. It does not depend on visual clues, or such. They are definitely not the same. Not even close.

I don't care if you have some clever way to determine if you are on a treadmill or not. Or if you can do it in a way that isn't all that clever (GPS, triangulation to the stars, some kind of inertia device).

Spork's cart doesn't know or care if it's on a treadmill or not. If it can move forward on the treadmill, it can go DDWFTTW in exactly the same manner.

 

[tsig]

And yet the trolls never address the oft repeated following:

--------------------
If I simply increased the size of my treadmill enough, I could set you in an easy chair on the porch of a house on a hot summer day and with the treadmill set at 10mph, you would be telling us how sweet the tea was and how nice the breeze was.

The flag on your porch column would stand proud, the wind chimes would be a 'clanging and the shrubs and trees would be swaying -- all because of a treadmill that "can't make wind". And of course you would be arguing strenuously with us that it's REAL wind and would not believe me when I told you that it was all just a treadmill.
--------------------

JB

The idea of proving a wind driven device without using the wind is laughable.

 

[tsig]

Yes. And the velocity difference between the road and the air provides the energy to keep it moving, even when it is moving faster than the wind. Just do the energy calculations and see for yourself. If you can't do the energy calculations you have no basis to argue that the cart can't do what is claimed.

I have not personally seen one of these carts but I have faith in my math and physics that I know it is possible. The energy calculations show that the efficiency of the system needs only to be greater than 50% to maintain its motion at the speed of the wind. The biggest loss is in the efficiency of the propeller and even the Wright Brothers were able to achieve over 60% on their hand made propellers. Modern aircraft propellers are typically over 80% efficient.

I have expressed my faith by offering a wager that independent testing will confirm that a cart can perform as claimed. Do you have similar confidence in your belief?

You have faith I have reality.

 

[ThinAirDesigns]

Just to make this clear. If you set up the porch on a treadmill of appropriate size, and moved it so that you say there is a wind, you say that I could not tell if it were the same scenario, but stationary with the same velocity real wind?

It matters now how sensitive your instrument is. It matters not who you enlist to assist you. It matters not how much money you spend. It matters not how long you take. There is absolutely no experiment which can be performed without external reference which will allow you to determine if your front porch is on a giant treadmill or not.

You must have external reference -- you must be able to look outside the giant box that I have placed around you and convincingly painted to look like the real world.

All you have to do to win the Nobel humber is to device a test that can tell you whether the wind is "real" (your term) or it's a calm day and the treadmill is turned on steady state.

Seize the day humber -- give us the test.

JB

 

[ThinAirDesigns]

The idea of proving a wind driven device without using the wind is laughable.

We would find it laughable as well ... that's why we use real, absolute, verifiable wind -- generated by a treadmill.

JB

 

[H'ethetheth]

H'ethetheth, are you also in agreement with what JB says about the flagpole, and my interpretation of that in my reply?

Yes. For a sufficiently large treadmill there would be no differences that would affect the behaviour of such a cart relative to you on the porch.

The idea is that the belt is the wind. We have been through this. Every time that this is discussed, it always ends with some example where if I complete the course, I would end up in arithmetic agreement, because that is the inevitable outcome of the assumption that fosters that idea.

So at least you don't dispute the math. I guess that's commendable, but that does make your position more mysterious to me. I would like you to go into the nitty gritty here. What exactly is this incorret assumption we make?

The treadmill belt is said to be an "equivalent frame of reference", but I say that it is a model, and that the limitations of that model will certainly allow me to tell any 'wind' so generated, from the same wind in the real environment. It does not depend on visual clues, or such. They are definitely not the same. Not even close.

I want to seriously know your position, so bear with me please. I suspect that you would agree with the following, humber: The wind on the treadmill we think is happening is simply the air dragged along by the belt because of friction.
Am I correct?

 

[tsig]

Because with spinnakers they can project more sail area and thereby get more driving force. For conventional boats, the hull drag increases dramatically when aproaching so called "hull speed". At this point any excessive the force is no no longer driving the boat faster but instead only increasing the wave the hull makes going through water. Thats why the world class sailboats need all the force they can get to go just that bit faster and thats why they use spinnakers. And thats also why they never reach windspeed and therefore can keep utilizing the spinnaker, which is useless upwind.

But why DO iceboats NOT have spinnakers?

But if you can go faster than the wind then you would not need the spinnaker. Ice boats do not have them because it takes too long to set.