Down wind faster than the wind

[humber]

There is nothing to withdraw.
<snip>
.

No, you made that statement. Back it up, or withdraw it.

 

[humber]

Humber's test: replace the propeller with a flywheel, set the cart on the treadmill with the treadmill surface running at 10 mph in the normal direction (front to back or right to left as seen in the small cart videos) and hold it in place until the flywheel gets up to speed, release the cart, run the test for at least one minute and record the result. Next, tilt the front of the treadmill up by 4.4 degrees and repeat the test. Finally, tilt the rear of the treadmill up 4.4 degrees and repeat the test.

I think the cart will be too unstable with a flywheel. It will be on a knife edge. Some damping, in the form of drag, would probably be required to reduce the system Q. I don't claim that the momentum runs out, so the time is not important. The propellor could be replaced with simple drag generator, such as a paddle wheel.

If Humber is correct, the cart will remain in a balanced state on the treadmill belt in all three tests. If he's wrong, the cart will not be able to maintain a steady speed on the treadmill and will move off the treadmill belt to the front or the rear.

Perhaps a direct side by side test of the prop cart vs the humber (silent "b"?) cart would reduce any perceived or actual variances.

We can add some holes so it will whistle while it works.
Yes, as long as the load of the dummy propellor is not so high that it cannot be supported by friction to the belt, I would expect the car to stay still or move up as is normal. Down hill probably. There is so little force, that gravity may win.
A side by side test is a possibility, but if there is no thrust, then how can be said to be an indicator of real world performance? But that is not my main objection. The whole balancing and moving act, is an artifact of a fundamental system flaw. A failure to make an accurate equivalent.

Maybe a direct measurement of the forces experienced by the two carts would help show any differences. A digital scale, some string, some pulleys and two weights could be used to show both fore and aft forces. Tie a string to the front of the cart, mount a pulley on the front of the treadmill and run the string over the pulley so that the end of the string is hanging, tie that end to the weight (500 grams or so) and set the weight on the scale. Do the same at the other end with half the weight but allow the second weight to hang free. Zero the digital scale. Any change in force will be seen on the scale as a change in weight.

Just a suggestion.

Or instead of one test, agree to one test each, in two stages. First stage, as specified, second stage with "corrections" as seen by the other side.

Can't see that working out well but I thought I'd toss it in.

Thanks for those suggestions, Mender. I have thought of a number of load tests, but given that the existing level of force is so low, yet acceptable, it would appear that is not thought to be an issue. It does suggest that the actual amount of force needed at windspeed is highly dependent upon the treadmill surface.

Another means may be to remove any props and measure the drag of the cart against the belt. This would indicate the level of opposing force the 'prop' needs to to provide. More accurately, the 'prop' provides an opposing torque.

 

[H'ethetheth]

Firstly, H'ethetheth, I apologise for not responding to your last post. I will do so a.s.a.p.

That's okay, really. The thread has moved on, and I don't have the time to participate meaningfully in this thread as fast as it's moving now.

On the first point, it is not the "vectorial equivalence" that is the problem. Of course, windtunnels working against a static vehicles exploit the same idea. The treadmill model is wrong, not the principle.

I know that's what you think, but proposing alternative tests that are demonstrably not equivalent to the road situation will not help, I assure you.

The wager that I have with Dan_O, is at least in my understanding, about a wind test. Platt's test is OK, if not a little inconvenient. If no other can be found, then that would seem to be the only choice.

The test I suggested is actually risky from my point of view. It would mean that the cart has already beaten the drag barrier, so that I gave that away in favour of "windspeed" launch. My tethered power test is no good. Platt's circular test is no good. Real wind is too uncontrolled...

I agree that real wind is troublesome, but testing in a windtunnel is only meaningful with a very long test section and no treadmill.

It would not normally be acceptable by anybody's standards to test with the treadmill. On the treadmill, the device under test is the cart, and not the simulator itself.

If TAD want to actually launch the vehicle into the wind at windspeed, then that may be OK, as long as some conditions are met.
The claim is not speed dependent, so any non-trivial speed should do. Perhaps the slowest speed at which the cart will function when on the treadmill? Pull it by wires. As long as it is set free, then the cart should be able to sustain itself. Again, perhaps risky for me if I overlook something. That was the general idea, but I included the treadmill as a compromise. It is not my model, and I don't think it is valid, so I let TAD decide on that matter.

Ah? Okay, that's strange. You can't just add random treadmills as a compromise. Nobody here wants treadmills as a matter of principle, it just eliminates the hassle of running after the cart.

 

[John Freestone]

The 'ignore' function is your friend. Click on the trolls name in a post and select "Add to your ignore list". To make the ignore complete, also edit the options in your control panel and set "Hide ignored posts" to yes. Once you have done this, you won't be able to read or respond to the troll without first reversing the steps taken.

Unfortunately, if anyone does respond to the troll you will still see the quoted troll text. Sometimes it is necessary to put the troll feeders on ignore too.

Yeah, thanks Dan. Although I knew that already, someone mentioned the possibility of having humber banned from the thread. I didn't think that was likely to be in the rules, but would at least have the advantage of solving the whole problem at a stroke. I've had myself on ignore for ages.

You continue to make up your own reality. You can't do the math. You can't even keep your vectors pointing in the right direction.

Humber thinks (or pretends to think) that a cart will go faster with a brake, since that's all the prop is doing, balancing the input force of the treadmill. Wrapping a rag round the shaft would do. LOL

I think the cart will be too unstable with a flywheel.

Of course you do. Now that you have pushed your mechanically infantile suggestion enough that people are threatening to actually test it, suddenly you give us the headsup that it would be too unstable. Maybe it will cause a black hole and precipitate the end of the world.

We can add some holes so it will whistle while it works.

Pity the same isn't true for human brains. What is this, Snow White and the Seven Dwarfs?

 

[Michael C]

I think there is only one result that would take him down... and that is none of us responding to his trolling (and therefore ruining) of this thread.

I agree.

I, and I think many others, did have hopes of helping him to understand how this thing works. Many people jump to the wrong conclusions at first, and once somebody is on the wrong track they may need help to do the necessary "rethinking". It's now clear to me that Humber isn't prepared to rethink anything.

I'm no longer going to try to help him see where he goes wrong. I don't need to use the forum to "put him on ignore": I can do my ignoring myself.

 

[ThinAirDesigns]

Now that you have pushed your mechanically infantile suggestion enough that people are threatening to actually test it, suddenly you give us the headsup that it would be too unstable. Maybe it will cause a black hole and precipitate the end of the world.

That's a classic John. I thought I was going to blow milk out my nose while eating breakfast and reading that.

There's always *some* reason that the test can't be defined let alone performed -- but of course I need to tell him *how* I'm going to perform the test before he will tell me what the test is.

JB

 

[humber]

That's okay, really. The thread has moved on, and I don't have the time to participate meaningfully in this thread as fast as it's moving now.

Moved on?. I do not think that is has changed at all. There are several errors in the model. I need not stick to TAD's rules to expose them. One of the many failures that is not directly "equivalence" related, is the logic of its derivation. This results in and ever-so-narrow operating range, that indicates one specific state, and nothing else. That is why is is so "difficult" to test.

I know that's what you think, but proposing alternative tests that are demonstrably not equivalent to the road situation will not help, I assure you.

A stepping stone, perhaps. I can work to define the boundaries by the process of elimination, as by direct proposal.

I agree that real wind is troublesome, but testing in a windtunnel is only meaningful with a very long test section and no treadmill.

Is proof troublesome? Ideas are commonplace. There are lots of those with theories, "concepts"and designs that hope someone else will verify for them. They forget that there are others with ideas, that have proof and supporting secondary evidence, because they are important to them, and not just a means of display. People such as Ynot.
Proof is part of the idea, and the prize. Finding it elusive, may be telling you something.

Ah? Okay, that's strange. You can't just add random treadmills as a compromise. Nobody here wants treadmills as a matter of principle, it just eliminates the hassle of running after the cart.

No, the treadmill AND the cart are the model. They are not independent.
Equivalence not even a part of that model. Equivalency is ubiquitous. That what it implies. The similarities in that regard between a model and the real object may be there, but are trivially true. They are always there.
To base your model upon selected similarities alone, means that the remainder of the equivalency is left behind. I can turn a cat into a rat, if I look only for the similarities.

Windtunnels do not employ "equivalency" to validate their model. That comes with the territory that we all know. Not often heard: 'We need more windage, Jim.'

They are models, where the medium is air. Sometimes it is water or even particles. Sometimes its the equations of a computer programme.
Equating the velocities does not make for an equivalent model. I would like to see "the math" that supports the claim that it does. Replies to this line of inquiry have invoked the tautological response "everything is relative".

A propellor rotating at 200rpm in wind while driving a cart, is not the same as a propellor being driven to the same speed in still air from the wheels

One has a load, the other not. Propellors need a mass load to transfer energy. They are transducers, converting a sea of momentum into torque. There is none of that to transduce when on the treadmill, so the propellor spins aimlessly about in a netherworld of stray friction.

The traveling is an artifact of that flaw. Focusing on that, is misdirection to cover up the fact that there is no wind, no force, no kinetic energy and no velocity normally associated with a vehicle traveling at 10kph. No. A hitting B is not the same as B hitting A, in this case.

 

[humber]

That's a classic John. I thought I was going to blow milk out my nose while eating breakfast and reading that.

There's always *some* reason that the test can't be defined let alone performed -- but of course I need to tell him *how* I'm going to perform the test before he will tell me what the test is.

JB

John,
Nope. Check my previous remarks. The flywheel are Mender's and Ynot's suggestions.
I have always said a source of drag. Momentum just happens to be associated with rotating masses. While out looking for that blackhole that I hope you find, see if you can find a massless object.

Pity the same isn't true for human brains. What is this, Snow White and the Seven Dwarfs?

Most friction will work. Need to dampen the system, lower its Q, so that is will not be upset by the smallest perturbation.
You could use some.

JB,
The reason being you, and fear of having your toy exposed for what it is.

 

[John Freestone]

That's a classic John. I thought I was going to blow milk out my nose while eating breakfast and reading that.

There's always *some* reason that the test can't be defined let alone performed -- but of course I need to tell him *how* I'm going to perform the test before he will tell me what the test is.

JB

Thanks, JB. We aim to choke.

Yeah, good luck implementing that test of humber's that demonstrates you've been wrong all along. Take special care with the bias of the flywheels and positioning of the bits of rag. I'm sure he'll stand over you pointing out your mistakes as you go along.

 

[humber]

Thanks, JB. We aim to choke.

Yeah, good luck implementing that test of humber's that demonstrates you've been wrong all along. Take special care with the bias of the flywheels and positioning of the bits of rag. I'm sure he'll stand over you pointing out your mistakes as you go along.

No, again. I have accepted your original challenge. I may send it to you, or I may post is anyway.
ETA:
That was Mender's suggestion as to what I might try. It could be that, it is very simple and illustrative. A disk that creates drag but no thrust, would work quite nicely.

John Freestone

Humber thinks (or pretends to think) that a cart will go faster with a brake, since that's all the prop is doing, balancing the input force of the treadmill. Wrapping a rag round the shaft would do. LOL

You are almost there, John. When in a car in a potential energy field, say on a hill, and the car is driven downhill by force from that field, how do you stop?
Perhaps you could use the brake. Ahh, but the wheel thingies won't a be all-a-spinnin'...
Add power and do a burn out. The rolling friction is low because the tyre melts to lubricate the interface.
But then, the road is actually moving below me on the treadmill, so I need not bother.
You pretend to think. Period.

 

[sol invictus]

That was Mender's suggestion as to what I might try. It could be that, it is very simple and illustrative. A disk that creates drag but no thrust, would work quite nicely.

It sounds like you still maintain the absurd position you took at the "beginning" of the thread:

The torque is the tiny difference between the drive from the wheels and the equal and opposite reaction from the propellor*. In an ideal world, these forces would be in balance, resulting in zero torque. It is fundamentally incapable of doing any work. Other ratios are possible, but that simply means that the propellor turns at a different speed in order to create the same result of standing still.

I see - they're always in balance. How odd... would they remain in balance if I aimed the propeller up? What if I applied a resistive brake to the wheels - will the cart remain stationary and its wheels spin at the same rate in that case too?

Changing the orientation of the propellor, will simply change the amount of drag, and therefore the amount of energy absorbed from the belt.
The two forces will always be in balance, not only because of that law, but that the sum of the two forces is that derived form the belt.

So you think if I aim the propeller straight up the cart will remain motionless on the belt. I suggest you think again, and if you find that difficult, imagine the propeller is encased in a container full of thick viscous oil. If there is any resistance in the propeller - which there always will be in still air unless it's not rotating - there is a torque on the wheels. It's precisely like braking a car.

If you still believe that there is an extremely easy test spork and co. could do: replace the propeller with a brake, or just orient the propeller the other way. Hell, just put the cart on the treadmill facing backwards.

In humber's world none of that would have any effect on the cart's behavior. In the real world it will quickly fall of the back end of the treadmill.

So - if you haven't flipflopped and still believe that utter nonsense, say so and maybe they'll oblige by proving you wrong yet again.

 

[H'ethetheth]

A propellor rotating at 200rpm in wind while driving a cart, is not the same as a propellor being driven to the same speed in still air from the wheels

I'm having trouble with your wording here, but it appears you're just rephrasing the statement that the treadmill and the road are not equivalent. This is incorrect, no matter how you rephrase it. I hope to demonstrate that below.

One has a load, the other not. Propellors need a mass load to transfer energy. They are transducers, converting a sea of momentum into torque. There is none of that to transduce when on the treadmill, so the propellor spins aimlessly about in a netherworld of stray friction.

No. The prop accelerates air backward relative to the cart both outside as well as on the treadmill. In fact, seeing how in both cases the cart has a very low velocity relative to the surrounding air, the amount of momentum imparted to the air will be very similar.

The traveling is an artifact of that flaw. Focusing on that, is misdirection to cover up the fact that there is no wind, no force, no kinetic energy and no velocity normally associated with a vehicle traveling at 10kph. No. A hitting B is not the same as B hitting A, in this case.

I'll try to put this to you as clearly I can before giving up. That is, I will have to stop discussing this if you cannot point out the errors in the analysis below, because I can't really explain this any other way.

Okay here goes:

I'm going to assume we can get to wind speed, because that is the state reproduced on the treadmill. If you think this is strange, just imagine we're comparing the treadmill to the situation where we have pushed the cart on the street until it reached wind speed.

(0) The situation where the cart reaches wind speed I define as follows:
Airflow velocities relative to the cart are neglible compared to, say, the tip speed of the propeller blades. I hope you will agree that when the cart travels at wind speed, the airflow velocities relative to the cart are low compared to the speed of the prop tip?
If not, here's an example:
The cart is travelling at 10 m/s, the wind at 10.5 m/s. The gearing between wheel and prop is 1:1 and the prop is twice the diameter of the wheels. That makes the prop tips twice as fast as the cart = 20 m/s. The wind speed experienced by the cart is 0.5 m/s, which is 2,5% of the prop tip speed. If you don't believe me, sit down, draw a picture and do the math.

Good, now consider the universe viewed from the cart, in both situations:

(1) Air is flowing over the cart at speeds much lower than the prop blade speed.

(2) The ground is passing by the cart at 10 m/s, making the wheels spin and therefore the prop.

If you disagree with either of these, please explain why.

Now, (1) implies that the trust of the prop is not significantly affected by the wind flow over the cart and is almost exclusively a function of its rotation speed. Thus, the thrust generated by the propeller is not significantly different between the two situations.
Again, if you do not believe this, try to picture the effect of a vertical gust of wind of 2.5 mph on an aircraft flying at 100 mph. If you do the math, this will change the lift force by roughly 2.5%.

(3) Forces between the ground and wheels remain the same, because the torque required to spin the wheels only depends on the power uptake of the propeller. In both cases, the thrust and the rpm are the same, as established above.

(4) In short, all forces acting on the cart are the same (i.e. not significantly different). Therefore, the treadmill in still air is an equivalent representation of a cart moving on a road in a fairly steady wind at approximately the same speed as the air around it.

If you reply to this post, please limit your reply to the numbered statements, and tell me why and how they are incorrect.

 

[CyCrow]

(snipped word salad with innumerable errors and misconceptions)

Yup, I was right when I gave up on humber a lot of posts ago...

For anyone interested, this is the simplest way I have found to model the cart (basic physics required):

1. For a given ground speed and thrust, calculate the power or energy per time unit available from the wheels.

2. For a given air speed and propeller/drivetrain efficiency, calculate the thrust produced by accelerating a cylinder of air from initial air speed to propeller pitch speed. That is, for a chosen prop diameter and pitch speed, you can calculate the mass of the affected air and its acceleration, giving thrust by F = ma. The energy required to do this at 100% efficiency is given by the difference in the kinetic energy of the air mass before and after acceleration.

3. The ratio of energy available at the wheels and 100% efficiency energy required gives the neccessary prop/drivetrain efficiency to maintain constant speed.

4. The force is variable. Solve for lowest efficiency required by varying pitch speed.

5. If a solution is found that requires a realistic efficiency that can be attained by a real propeller and drivetrain, the cart can maintain DDFTTW travel. QED.

Home assignment for anyone that cares: create a spreadsheet with pretty graphs for required efficiency vs top speed for a given prop diameter.

// CyCrow

 

[CyCrow]

If you still believe that there is an extremely easy test spork and co. could do: replace the propeller with a brake, or just orient the propeller the other way. Hell, just put the cart on the treadmill facing backwards.

Just a friendly correction: Putting the cart on backwards will also reverse the wheel and prop direction, thus still producing thrust against the treadmill/road direction. It will be less efficient as most props are asymetrical and work poorly in reverse, so it may not work at the available treadmill speeds.

// CyCrow

 

[Marcus]

The debate with Humber is a dead end, maybe you guys could get back to designing and implementing a more definitive test.

Since treadmills are out, and wind tunnels are too short, a new improved outdoor test is needed. Perhaps a longer course with better wind measurment and wire guidance for lateral motion, as was suggested for the treadmill.

 

[ThinAirDesigns]

The debate with Humber is a dead end, maybe you guys could get back to designing and implementing a more definitive test.

Since treadmills are out, ... <snip>

You lost me at that point Marcus. There's nothing more "definitive" about a non-treadmill test. In fact, the treadmill test is the *most* definitive as it allows for the tight control and repeatability unrivaled in the great outdoors.

Having said that, an outdoor test is rather easy to do but hard to do well -- that is covering all the bases for documentation purposes is absolutely non-trivial.

JB

 

[screensnot]

The treadmill was a good idea to show the operation of the cart in the most controlled circumstance.

Of course, if you can't see the equivalency of a cart on a treadmill and a cart being pushed by the wind down the road, it only provides more confusion.

 

[Dan O.]

The treadmill was a good idea to show the operation of the cart in the most controlled circumstance.

Of course, if you can't see the equivalency of a cart on a treadmill and a cart being pushed by the wind down the road, it only provides more confusion.

The problem with outdoors is that there are variations in the wind that can confuse the results. We can block the variation by putting a moving shield around the cart that is moving at the average speed of the wind. The only wind inside the shield will be the average wind speed.

The cart will create air circulation within the shielded zone. To minimize the effect of these induced circulations, that shielded area should be large in comparison to the cart. For a cart the size of Spork's small cart, a shield the size of a room would be appropriate.

A work platform could be extended at the base of the shield up to the area just around the cart. To make access to the cart easier, a raised section of artificial road could be constructed above the shield platform and geared so that the top surface is stationary relative to the road.

The cart can be tested on this raised section in the comfort and controlled environment of the shield. Since this is in the real wind there is no question of equivalency as there is with a treadmill.

 

[screensnot]

...We can block the variation by putting a moving shield around the cart that is moving at the average speed of the wind. The only wind inside the shield will be the average wind speed.

The cart will create air circulation within the shielded zone. To minimize the effect of these induced circulations, that shielded area should be large in comparison to the cart. For a cart the size of Spork's small cart, a shield the size of a room would be appropriate.

A work platform could be extended at the base of the shield up to the area just around the cart. To make access to the cart easier, a raised section of artificial road could be constructed above the shield platform and geared so that the top surface is stationary relative to the road.

The cart can be tested on this raised section in the comfort and controlled environment of the shield...

That sounds like a lot of work/materials. Let's just use a treadmill.

Oh, wait.

 

[spork]

If you still believe that there is an extremely easy test spork and co. could do...

In the interest of full disclosure, I doubt I'll be doing any test humber requests of me. I simply don't read much of his nonsense, and can't follow what I do. If someone such as sol thinks humber has a test that's either useful or entertaining, I'll certainly consider doing it to their specs.

The debate with Humber is a dead end...

The debate with humber seems to be the true proof of perpetual motion.