Merged DDWFTTW in a “Real” Wind

[humber]

Only for humber is it not so easy to see how it does that. The front wheel is a little misaligned with the back wheels and steers the cart to one side. I guess how the steering wheel of a car works is still a mystery to humber.


Uh, what?

Mender contradicts you. He says ( in bold text), that the cart goes back with the belt if misaligned. In one video, JB excuses the cart's random motion by saying it has no steering. Are you contradicting him too?
If it were true that misalignment increases the drag force as Mender claims, then once initiated, what is there to stop it from becoming worse? That is what is meant by alignment being unstable. Rather like trying to balance a pencil on its tip.

 

[I Ratant]

Been there, done most of that, can tell you the outcome of each step.
1) Easy to see in person but not a bad idea for a video.
2) Cart falls off the back.
3) With my fan, the bluff force acting on the cart is 10 grams and diminishes with distance (obviously), and the rolling resistance of the cart at speed is about 4 grams. The cart stays at a distance from the fan that balances the forces.
4) The prop's bluff force is reduced as it freewheels; the cart will stay on the belt but will be much closer to the fan..
5) Cart goes flying off the back of the belt
6) a) with only the fan on, the cart moves forward until the forces balance.
b) once the treadmill is above the break-even speed (6.2 mph on my cart) the cart will stay in place without the fan. More belt speed will have the cart moving forward.

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Find a real long treadmill?
The full menu would be entertaining no matter what the length of the treadmill.
The plane-on-the-treadmill showed the independence of the plane (cart) from the belt because of the lack of connection between the propellor and the wheels.
Just seeing how the various modes from no prop to freewheeling prop cart operated on the belt helps when comparing the results when the prop and wheels connected and the fan blowing alone, and with the treadmill and fan going.
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What are you testing with your cart? I skipped quite a few pages so I think I missed your intent.

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I getting lots of motion with the freewheeling prop, but haven't got more than token motion when trying the driven cart. On my 3rd iteration now, trying to eliminate all the sources of friction holding it back... but there's that bummer of the gradient, with the wind it might need being higher than the cart is.
Still hoping for a simultaneous release of both of them.

 

[CORed]

Mender contradicts you. He says ( in bold text), that the cart goes back with the belt if misaligned.

If you are referring to the bolded "it steers itself", it appears to me that he agrees with me, so it surprises me not at all that you say he contradicts me. If he disagrees with me, he can tell me so.

In one video, JB excuses the cart's random motion by saying it has no steering. Are you contradicting him too?
If it were true that misalignment increases the drag force as Mender claims, then once initiated, what is there to stop it from becoming worse? That is what is meant by alignment being unstable. Rather like trying to balance a pencil on its tip.

The "Uh what? response to the second part of your previous post was to indicate that I could make no sense whatsoever of that word salad. The latest post I'm responding to isn't much of an improvement, especially the last few sentences. In any event, how you choose to misinterpret other posters is of little concern to me.

 

[mender]

Mender contradicts you. He says ( in bold text), that the cart goes back with the belt if misaligned.

Oh hard of reading one, not so. Sideways is not the same as back.

The cart, if not aligned properly when released, will make a prompt exit off the side of the treadmill belt.

Try again.

 

[mender]

If you are referring to the bolded "it steers itself", it appears to me that he agrees with me, so it surprises me not at all that you say he contradicts me. If he disagrees with me, he can tell me so.

The Booger double-negative still holds; I agree with you.

 

[mender]

Just seeing how the various modes from no prop to freewheeling prop cart operated on the belt helps when comparing the results when the prop and wheels connected and the fan blowing alone, and with the treadmill and fan going.

Connecting the prop and the wheels changes completely how the cart works and will interact with the air and treadmill. I don't see what you're testing other than the bluff forces.

On my 3rd iteration now, trying to eliminate all the sources of friction holding it back... but there's that bummer of the gradient, with the wind it might need being higher than the cart is.
Still hoping for a simultaneous release of both of them.

I confess, I didn't grok what you were meaning here.

 

[mender]

Your argument fails, because the cart has no steering.

Hmmm.
Your argument fails, because you make it.
Booger logic is interesting. Not terribly effective though.

 

[humber]

Oh hard of reading one, not so. Sideways is not the same as back.


Try again.

Worse. Now you have a cart that slides at all angles. At least with the former claim, you retained some semblance of an argument.
A wind vane is inherently stable. It points into the wind. Move the tail a bit to the left and the increased force on the tail, will return it to the original position, same for motion to the right. The cart is inherently unstable. Move it a bit away from alignment, left or right, and the increased force will turn it more, and down the belt it will go.
That is what both you and Spork found, so tinkered and changed the tyres until that stopped. Proof of DDW....doh.

 

[quarky]

Am I getting this right:
Humber's objection to the ddw test is that steering (in a straight line) is, in effect, tacking?
Because the actual wind is never coming in a straight line?
If this is the gist of it, wouldn't a wind tunnel test solve it?

 

[humber]

Am I getting this right:
Humber's objection to the ddw test is that steering (in a straight line) is, in effect, tacking?

If the cart stays on a fixed course and the wind changes, that is the same as if the wind stays fixed and the cart changes. Both produce the same tacking effect.

Because the actual wind is never coming in a straight line?
If this is the gist of it, wouldn't a wind tunnel test solve it?

A wind tunnel test is possible, but apparently don't meet the demands of the cart: too short etc.
But, that does not mean the windtunnel may be substituted by a storm.
The wind condtions over lake beds, and the two in question, are known to be variable. The run is too short to prove steady state, and that was also known prior to the trial, though the matter of length has always been a primary objection to the wind tunnel.
The first trials were at Ivanapah, and only limited testing had been undertaken up until then. The dyno is a useless farce, so said nothing.
On arrival at Ivanpah, TAD said they had forgotten the wheels, but later said it was all a joke. That was a ruse to buy some time so that the cart could be tested. If it should fail, stick with the wheel excuse. Fortunately for them, the variable wind worked to their advantage. Now they learned what to look for in the next test.


The steering on the TM is another matter, because the TM has nothing to do with ddw. The process which produced it, is trial and error, where the outcome is to defeat the inherent instability of the cart, and not a logical process that results on proof of DDW.
The theory is full of holes, ad hoc, and assessed by acceptance.
The trial is the result of trial and error and selective outcome.

The claim is propped up by three pillars with the same shaky foundations. Smoke and mirrors.

 

[mender]

That is what both you and Spork found, so tinkered and changed the tyres until that stopped.

Again, no. The frame of the little cart is tweaked until the cart runs in as straight a line as possible; the tires are selected to have more than the minimum amount of grip needed to keep them from slipping. With both conditions met, the cart runs on the belt for quite a while (see appropriate video for an impressive 2 1/2 minute run).

These two conditions are easy to test, and have been, repeatedly, for your edification. Simply refusing the evidence is a weak ploy at best.

 

[humber]

Again, no. The frame of the little cart is tweaked until the cart runs in as straight a line as possible; the tires are selected to have more than the minimum amount of grip needed to keep them from slipping. With both conditions met, the cart runs on the belt for quite a while (see appropriate video for an impressive 2 1/2 minute run).

These two conditions are easy to test, and have been, repeatedly, for your edification. Simply refusing the evidence is a weak ploy at best.

The cart would not at first stay on the belt, so you contacted Spork, who told you how to tinker until it slides, so takes up intermittent contact with the belt, and avoids being dragged by the belt. A result of a transmitted virus.
Not one valid measurement, but a false conclusion.

 

[mender]

The cart would not at first stay on the belt, so you contacted Spork, who told you how to tinker until it slides, so takes up intermittent contact with the belt, and avoids being dragged by the belt. A result of a transmitted virus.
Not one valid measurement, but a false conclusion.

New game, Booger; see if you can argue your case without changing the facts.

Go.

 

[ridgerunner]

Am I getting this right:
Humber's objection to the ddw test is that steering (in a straight line) is, in effect, tacking?
Because the actual wind is never coming in a straight line?
If this is the gist of it, wouldn't a wind tunnel test solve it?

Extensive "wind tunnel" tests have already been performed using a treadmill, which exactly simulates the situation where an object is traveling downwind at the speed of the wind. Using a real wind tunnel is problematic because you would need a very, very long one since this craft must be connected to the ground while going downwind, (and into an apparent headwind when faster than the wind). The craft making progress on a treadmill is the best proof of its ability to beat the wind. (It even makes progress uphill.)

But nothing will solve Humber's objections. Humber is a troll and is only here to incite people's reactions.

 

[I Ratant]

Connecting the prop and the wheels changes completely how the cart works and will interact with the air and treadmill. I don't see what you're testing other than the bluff forces.



I confess, I didn't grok what you were meaning here.

.
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I am interested in this because it's something opposite from common encounters. Windmilling props are not beneficial.
And here's a prop hooked up to move something, but... it moves the thing the "wrong" way.
To get a handle on what happens when, I started with the cart on wheels, and the prop freewheeling.
Then noted what occurred.
The prop rotates/windmills as a normal prop does, and creates only drag doing this. Just like real life. This drag moves the cart downwind...only.. the direction the cart faces, or the orientation of the prop on the shaft machs nichts to that. Downwind it goes.
Fixing the prop so it can't rotate, same thing.
The prop in that configuration is a sail.
On the treadmill running to oppose the motion of the cart pushing it away from the fan, the car will move downwind regardless of the treadmill belt speed.
It needn't run off the far end of the belt, the motion can be restrained to keep it on the belt.
The cart should keep the thread tight.
Connecting the prop and the wheels moves the whole thing out of simple aerodynamics and forces the interaction with the ground.
Then, the usual rotation of the prop with the wind becomes tricky.
That rotation is "wrong". Turning the prop in the expected windmilling rotation direction, the cart backs up.
So there's an initial resistance to moving, when only the air's effect and the rotation of the prop are considered. But... the prop being constrained from rotating in the expected direction by the connection to the wheels and the ground can act as a sail, and without rotating, the wind force on the prop can overcome the rolling friction of the wheels, and the cart begin to move downwind. The wheels then relieve the rotation constraint on the normal direction the prop would naturally rotate when windmilling, and the cart accelerates. The combined effect of the sail force and the wheels driving the cart add to each other until the ground speed can exceed the wind speed, and the propellor begin to operate as a propellor instead of a sail.
This point still makes my head hurt.
I'd kinda expect the cart to get to wind speed and no faster.
That it goes faster is obvious.
Why it should.. that ain't so obvious.
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The Treadmill-airplane test.
http://www.youtube.com/watch?v=4owlyCOzDiE
Note the added marks on the belt..

 

[Llyricist]

The cart would not at first stay on the belt, so you contacted Spork, who told you how to tinker until it slides, so takes up intermittent contact with the belt, and avoids being dragged by the belt. A result of a transmitted virus.
Not one valid measurement, but a false conclusion.

In some universes, rubber is slippy-er than plastic.

 

[humber]

New game, Booger; see if you can argue your case without changing the facts.

Go.

You contacted Spork when the magic cart did not work. You posted that you did that.

 

[Michael C]

Am I getting this right:
Humber's objection to the ddw test is that steering (in a straight line) is, in effect, tacking?
Because the actual wind is never coming in a straight line?
If this is the gist of it, wouldn't a wind tunnel test solve it?

Yes, if we built a wind tunnel long enough the cart would work in it. But anybody who understands what a wind tunnel is primarily used for should understand that using a treadmill in still air is a better way to test the performance of the cart at wind speed or just above it.

The term "wind tunnel" might convey the impression that wind tunnels are used to test the way things perform in the wind, but in fact most of the time a wind tunnel is being used to test the way an object (a plane, for example) moves through still air. It doesn't make any difference if the plane moves through the air or if we move the air over the plane. As long as all relative velocities are the same, the forces (thrust, lift, whatever) will be the same.

When we want to test if the cart can accelerate above wind speed, we can put it on the ground in the direction of the wind, measure the speed of the wind and measure the speed of the cart. Or we can go inside, in a room with still air, and put the cart on a treadmill moving backwards at the speed of the wind. When the cart is neither advancing nor moving backwards on the treadmill, it's moving at the speed of the wind. If it advances on the treadmill, it's going faster than the wind.

If we wanted to test the performance of the cart at a steady speed of, say, 2x the speed of the wind, we could combine treadmill and wind tunnel. Let's say we want to see if the cart can do a steady 20 km/h in a 10 km/h wind. We set the treadmill to be moving backwards at 20 km/h and blow air through the tunnel from front to back at 10 km/h. If the cart now runs stationary on the treadmill, it's running at 20 km/h with respect to the ground and 10 km/h with respect to the air: this is the exact same situation as a cart on the road doing a steady 20 km/h in a 10 km/h wind.

Humber wil of course take great pains to tell you that these situations aren't equivalent, arriving at his conclusions by getting the relative velocities mixed up.

And one more thing: if somebody went to all the trouble of building a very long wind tunnel and was able to show that the cart ran through it faster than the air going through it, humber would come up with some objection: it was measured wrong, or the walls of the wind tunnel were somehow forcing the cart to go faster than it otherwise would, or it's a wind tunnel and not real wind anyhow, or some other crazy excuse that only humber could imagine.

 

[Michael C]

.
.So there's an initial resistance to moving, when only the air's effect and the rotation of the prop are considered. But... the prop being constrained from rotating in the expected direction by the connection to the wheels and the ground can act as a sail, and without rotating, the wind force on the prop can overcome the rolling friction of the wheels, and the cart begin to move downwind. The wheels then relieve the rotation constraint on the normal direction the prop would naturally rotate when windmilling, and the cart accelerates. The combined effect of the sail force and the wheels driving the cart add to each other until the ground speed can exceed the wind speed, and the propellor begin to operate as a propellor instead of a sail.

You're still on the wrong track here. The propeller is already working as a propeller when the cart is going under wind speed. The wheels are never, ever driving the cart.

 

[I Ratant]

What creates the initial downwind motion?
The sail effect, or the prop drag effect?