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Old 11th November 2008, 09:15 PM   #121
spork
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Originally Posted by technoextreme View Post
I right the first time.
Actually you weren't right any time. I just posted instructions for you to build your own. So you can go do it yourself or you can keep telling us it's B.S.

But keep this in mind - when there are only two people on an elevator, and one farts, everyone knows the score.
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Old 11th November 2008, 09:17 PM   #122
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Originally Posted by ThinAirDesigns View Post
Thabiguy:
Someone needs to break it to techno that Thabi has presented a perfectly good definition of "drag" and it is he/she not Thabi who is confused in this regard. Ok, I'll do it.
JB
I thank you for not reading. Drag forces are opposite of thrust. You could have bothered to read his posts because he was talking about thrust. The drag would be the force of the propeller opposite of that to the direction of rotation.
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Old 11th November 2008, 09:19 PM   #123
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Originally Posted by technoextreme View Post
Thats not drag. Every single time you've said drag you mean thrust. Every single time.
No, I do not mean thrust. I mean drag.

I was mainly speaking about the blower model. The force of the air retarding the movement of the blades is drag, not thrust. You can say that the blades provide forward thrust to the vehicle (which in turn experiences drag as it moves through the air), but this is not what I was talking about.

You can also say that the inertia of the vehicle exerts force on the blades as it pushes them against the wind; this would be thrust. Again, this is not the force I was talking about. I was talking about drag, a force in the opposite direction - force exerted by air on the blades as it retards their movement through the air.
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Old 11th November 2008, 09:29 PM   #124
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Originally Posted by technoextreme View Post
I thank you for not reading. Drag forces are opposite of thrust. You could have bothered to read his posts because he was talking about thrust. The drag would be the force of the propeller opposite of that to the direction of rotation.
You say "Drag forces are opposite of thrust", true. Thabiguy says drag, you claim he is talking about thrust therefore he must be wrong. So in order for you to be right you have to claim he said the opposite of what he said... Hmmm.
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Old 11th November 2008, 09:34 PM   #125
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Quote:
Does it accelerate to be faster than the wind or start there? It would seem to lose power as it approached wind speed, and be limited to under the speed of the wind.
It will accelerate from a dead stop until it is going faster than the wind, and it will continue along faster than the wind until the wind dies. Build one and try it.

Quote:
It's always going to stop because it's going in the wrong direction.
Apparently it doesn't know this.

Quote:
Airplane on a treadmill! Airplane on a treadmill! Airplane on a treadmill! Im going to scream if I hear one more person say that this has nothing to do with airplane on a treadmill I will scream.
Tantrums aside, this has nothing to do with the airplane on a treadmill. Not everything involving a treadmill does.

Quote:
That's a very good reason why the device in the first video can't go faster downwind than wind-speed...
Well there must be an even better reason why it can - because it does.

Quote:
I've a question for everyone, just to make sure I'm not jumping to false conclusions.

When a windmill/propeller is facing directly into the wind, can the force from the wind turning the blades ever exceed the force from the wind pushing the blades backward?
I'm not sure I understand your question, but I think I do. The answer would be no - the blades will never pull themselves forward into the wind steady-state.

Quote:
I'm not a native English speaker. The irony is, even though you imagine I "have no clue what I'm talking about", it's you who weren't right once in this entire topic.
Well your command of the language is better than most natives it seems. And I applaud your choice to use punctuation, spelling, sentences, etc. That's better than most of us Americans for sure.

Quote:
I told you how it fails. DRAG DRAG DRAG DRAG DRAG DRAG DRAG.
Man you almost had me. Probably just one more "DRAG" and you would have convinced me.

Quote:
Look up the definition of DRAG. Read it. Embrace it. Hug it. Kiss it. Because you make the assumption that it doesn't stop the propeller.
They told me all about it when I got my M.S. in aero. They had a pretty different idea about it than you do.

Quote:
You forgot about DRAG. DRAG DRAG DRAG DRAG DRAG DRAG DRAG DRAG. And more drag.
Shoot!!! You're right. Thanks for the reminder.

Now go build the darn thing. I hope you don't implode in a cloud of improbability when it does as advertised. Be sure and use a spotter.
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Old 11th November 2008, 09:36 PM   #126
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Originally Posted by spork View Post
Place it on your treadmill at 10 mph. If it doesn't go straight ahead (and it won't) adjust the steering by bending the soft aluminum tube very slightly. Make sure this doesn't mess up the alignment and cause any drag.

Take a video and post it on youtube.

Don your flamesuit.
Of course I'm going to try your experiment from which the physics has nothing to do with the problem at hand. I've said it. Someone else has said it. The treadmill will work but it has nothing to do with the actual issue of your cart going faster than the wind.
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Last edited by technoextreme; 11th November 2008 at 09:42 PM.
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Old 11th November 2008, 09:43 PM   #127
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Originally Posted by technoextreme View Post
Uggg... I right the first time. It's the problem with the drive ratio. You need to flip direction sometimes and you can't do that with a single belt drive.
Wow, I finally got an answer to the question I asked after his first post, even though he wasn't actually trying to answer any question here.

No, you never want the flip the props directions no matter which way the wind is blowing relative to the craft. You always want the prop to blow air out behind the direction of road travel no matter which direction the wind is blowing. If you ever switch directions then you are putting the breaks on the craft.
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Old 11th November 2008, 09:44 PM   #128
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If kinetic energy is being extracted from the wind, it is being extracted by the wind turbine.

The formula for kinetic energy in general is:
1/2 mV2

where m is the mass and V is the velocity through the turbine.
The mass of a volume of air through the wind turbine in one second would be:
(air density) (swept area of turbine)(velocity in linear units per second)

Substituting that into the 1/2mV2

1/2 [(air density)(swept area)(velocity)]velocity2

That reduces to:
1/2 (air density)(swept area)velocity3

Since the volume of the mass I calculated is the volume that goes through the swept area in one second, that's kinetic energy per second, meaning the result has units of power.

(This is actually a way overoptimistic estimate. The power is extracted by slowing the air down. If you don't slow it, you don't extract the energy. If you extract it all, the air is stopped,no longer moving through the turbine, and you can't extract any more energy. So there's a limit to the extractable energy, the Betz limit, and it's about 59% of the kinetic energy in the mass of air moving through the turbine.)

When any of the terms in the equation go to zero, the result goes to zero.
As the wind turbine accelerates downwind, the velocity of the air through it decreases. The power available drops off very rapidly because of the cubed term. As it reaches wind speed, the velocity of air through the turbine goes to zero. Therefore the power the turbine can extract from the air goes to zero.
It doesn't matter much what it's attached to.
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Old 11th November 2008, 09:52 PM   #129
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Originally Posted by technoextreme View Post
Of course I'm going to try your experiment from which the physics has nothing to do with the problem at hand. I've said it. Someone else has said it. The treadmill will work but it has nothing to do with the actual issue of your cart going faster than the wind.
So build the same craft and put it on a tennis court on a good windy day and take good measurements.
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Old 11th November 2008, 09:58 PM   #130
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Originally Posted by TjW View Post
Therefore the power the turbine can extract from the air goes to zero.
Those are some lovely equations you've got there. Were you looking for me to point out where you went wrong, or are you just telling me my cart can't do what I can see it doing?
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Old 11th November 2008, 10:04 PM   #131
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spork, nobody (in this thread at least) disputes what is shown in the treadmill video. In that, the treadmill is serving as the motor, and thrust from the prop pushes the vehicle forward. This is in keeping with what we know of physics.
But that's not what's supposedly happening in the first video. In that, the tailwind is turning the prop, which turns the wheels. But once it reaches wind speed, what turns the prop?
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Old 11th November 2008, 10:08 PM   #132
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Originally Posted by technoextreme View Post
I thank you for not reading. Drag forces are opposite of thrust. You could have bothered to read his posts because he was talking about thrust. The drag would be the force of the propeller opposite of that to the direction of rotation.
I've read them -- he correctly means drag.

JB
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Old 11th November 2008, 10:09 PM   #133
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Originally Posted by TjW View Post
As the wind turbine accelerates downwind, the velocity of the air through it decreases. The power available drops off very rapidly because of the cubed term. As it reaches wind speed, the velocity of air through the turbine goes to zero. Therefore the power the turbine can extract from the air goes to zero.
The thing is that when the device reaches wind speed, the velocity of air going through the propeller is not zero. (ETA: Actually, that wasn't the best way to say it. It's true, in essence, but it probably won't help anyone understand what's going on.)

I feel almost ashamed to promote it again, but if you have a time, check out the blower model that I proposed in post #41. It is conceptually equivalent, but much simpler (and it can also be interpreted as a turbine - a Pelton wheel). I really think people should start with that one, because it's easier to grasp.

If you look at it, you will see that when the device reaches wind speed, the air will still move at non-zero speed with respect to the "turbine", and will still push it forward.

With the propeller, the end effect is the same, but it's less visual.

Last edited by Thabiguy; 11th November 2008 at 10:25 PM.
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Old 11th November 2008, 10:25 PM   #134
ThinAirDesigns
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Originally Posted by JWideman View Post
spork, nobody (in this thread at least) disputes what is shown in the treadmill video. In that, the treadmill is serving as the motor, and thrust from the prop pushes the vehicle forward. This is in keeping with what we know of physics.
But that's not what's supposedly happening in the first video. In that, the tailwind is turning the prop, which turns the wheels. But once it reaches wind speed, what turns the prop?
JWideman, what is happening in both videos is *exactly* the same from a physics perspective.

It's been established from the days of Galileo and Newton that motion is relative. There is no physics experiment, no matter how sensitive the instrument, which can determine if the road is still and the air is moving or if the road is moving and the air is still. If you can devise an experiment to do the above -- even if it just involves a silly DDWFTTW cart, and you will be in instant Nobel territory.

I know it seems wrong, but it's the truth.

JW, if you still have issues with the above, I'm happy to help anyway I can. I've got some simple thought demonstrations that might help you.

JB
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Old 11th November 2008, 10:31 PM   #135
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Originally Posted by TjW View Post
If kinetic energy is being extracted from the wind, it is being extracted by the wind turbine.

The formula for kinetic energy in general is:
1/2 mV2

where m is the mass and V is the velocity through the turbine.
The mass of a volume of air through the wind turbine in one second would be:
(air density) (swept area of turbine)(velocity in linear units per second)

Substituting that into the 1/2mV2

1/2 [(air density)(swept area)(velocity)]velocity2

That reduces to:
1/2 (air density)(swept area)velocity3

Since the volume of the mass I calculated is the volume that goes through the swept area in one second, that's kinetic energy per second, meaning the result has units of power.

(This is actually a way overoptimistic estimate. The power is extracted by slowing the air down. If you don't slow it, you don't extract the energy. If you extract it all, the air is stopped,no longer moving through the turbine, and you can't extract any more energy. So there's a limit to the extractable energy, the Betz limit, and it's about 59% of the kinetic energy in the mass of air moving through the turbine.)

When any of the terms in the equation go to zero, the result goes to zero.
As the wind turbine accelerates downwind, the velocity of the air through it decreases. The power available drops off very rapidly because of the cubed term. As it reaches wind speed, the velocity of air through the turbine goes to zero. Therefore the power the turbine can extract from the air goes to zero.
It doesn't matter much what it's attached to.
Yes, this is exactly like my starting point. As it turns out the propeller is acting more like a propeller than a turbine such that efficiency is not limited Betz' limit. Although Betz' law limits absolutely perfect efficiency to 59% airplane propellers often have a practical efficiency of over 90%. The difference is the direction of torque on the prop shaft. When the prop torques the prop shaft Betz' law applies. When the shaft torques the prop it doesn't. The later applies to this craft for the reasons given below.

Wind driven case (no treadmill): The pressure difference front to back of the craft places a forward vector force on the frame of the craft. This forces the craft forward which torques the wheels. This force is then feed through the wheels to increase the props angular speed to maintain (not increase) the pressure difference across the frame of the craft. Although at high speed the wind is much faster front to back of the craft the available power is not increased. The power available to the craft itself is limited to the difference between the air and road, regardless of the apparent air speed relative to the craft. This is accomplished by having the wheel directly tied to the prop so this difference is maintained and all speeds. When the drag from going faster than the wind matches the power available through this air to road difference the craft no longer accelerates, as you indicated. Top speed is reached.

There remains much more slippage in the air to craft interface than the road to wheel interface. However, even here efficiency improves at high craft to air relative speed because the effective density of air is higher relative to the craft. The prop act more like an air screw than a windmill.
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Old 11th November 2008, 10:34 PM   #136
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Originally Posted by Thabiguy View Post
I feel almost ashamed to promote it again, but if you have a time, check out the blower model that I proposed in post #41
I like it. It's very much like a cart I proposed (only by way of explanation)
Attached Images
File Type: jpg simple cart.jpg (12.7 KB, 28 views)
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Old 11th November 2008, 10:49 PM   #137
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Originally Posted by my_wan View Post
When the drag from going faster than the wind matches the power available through this air to road difference the craft no longer accelerates, as you indicated. Top speed is reached.
I feel I should clarify this somewhat. The drag certainly does lower the top speed, but even if there was no unwanted drag at all, the device still wouldn't be able to accelerate indefinitely. The propelling assembly provides forward force only up to a certain speed (vwind / f). At this speed, the propeller is pushing back the air at the same speed as the air is already flowing back (with respect to the device), so the air will no longer exert any force on the propeller. The drag makes the actual limit lower than that, but this is the fundamental limit of the concept.
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Old 12th November 2008, 12:14 AM   #138
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Because of limitations of my OS, machine, and connection, I don't attempt you-tube or any other video downloads: it takes an hour for 5 minutes of unviewable images and chopped audio.

Would someone post some good still shots and also a plan-view (overhead view) diagram showing the road, vehicle, direction of travel, wind direction, and propeller axis orientation with blade angle/rotation direction all included?

Cheers

Dave
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Old 12th November 2008, 12:45 AM   #139
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Originally Posted by CaveDave View Post
Because of limitations of my OS, machine, and connection, I don't attempt you-tube or any other video downloads

Would someone post some good still shots and also a plan-view (overhead view) diagram showing the road, vehicle, direction of travel, wind direction, and propeller axis orientation with blade angle/rotation direction all included?
Hey, I don't want you to risk a youtube download. I'll be happy to get all that documentation together for you. But that doesn't seem like enough. I could bring the cart by your house, and we'll do the experiment together. When is good for you?
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Old 12th November 2008, 12:54 AM   #140
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Originally Posted by my_wan;4193367
Physics is defined empirically. You are the one assuming you know the physics without actually doing the experiment (empirical test). You are therefore mistaking your intuition for actual physics. That's why this thread is interesting in the first place because the actual physics is counterintuitive, and you fell for your intuition. You even called your experiment a ([I
thought[/i]) experiment when all spork has to do is set the craft on the treadmill backwards and no thought is required. Perhaps you should add that skepticism back into the equation, self skepticism.
Well, it is undeniable that physics is empirical, but that is not the same as simple trial and error, or dare I say it, speculation. You misunderstand me, I think. There is no trial or battles of wills for me. In this case, intuition and Newton's laws are enough to describe what is happening. Counter-intuitive examples, may also be sophisms
How it got beyond that point, is interesting.

Before the Laws of Physics can be declared broken, it is at least necessary to first give them a beating.
If I am wrong, you will be able to tell me so. I ask you to please tell me how the following is flawed.

The real cart shown in the video, works this way.

As I have mentioned, this cart will only run faster than the wind, if the wind is variable. It will tend to run at the peak wind speed. The builder mentions that the wind is variable, and it is obviously so.

Imagine that the cart is running along at walking pace. A gust of wind pushes the cart, so that its velocity is increased by say, 10%. The propeller is directly connected to the wheels, so it too will increase by 10%. Agreed?

The momentum of the body of the cart is therefore increased by 10%, (mv) but that of the propeller also increased by the same amount. If the mass of the propeller is high (as it appears to be), then much more energy is stored than by a cart alone. Note that the kinetic energy is increased by the square of that increase in velocity (1/2mv^2). The cart has now raised its kinetic energy by much more than is needed to maintain its current velocity.
It absorbs more momentum from the wind, because it presents a higher load than a simple cart, but that energy is not dissipated due to simple resistance, but isstored.

If the wind falls again, the overall momentum of the cart will mean that it tends to remain the previous velocity. Do you agree?

The next gust does the same, so the velocity "rathchets up" in this manner until the cart runs closer to the speed of the gusts, than any true average. That is all that this device does. It's a wind-driven flywheel.

I can point to clues and indicators shown in the video, that support this contention, but can tell me why that explanation does not work ?

Spork's model is similar. Its momentum keeps it running in a very similar manner. The belt is the wind. If the cart slows, momentum drives it until some small disturbance allows it to pick up more. That's it.

Newton's law of opposite and equal reaction, means that the cart will certainly not follow the belt backwards, because of the opposing 'thrust' of the propeller.
The cart 'mirrors' its input. Momentum does the rest. If it slows, then energy comes from the stored momentum to maintain that speed.
I agree it appears circular in description. The wheels drive the propeller, which drives the wheels, which drives..... Yes, but it is only a balance of forces.
Find something to upset that balance, and it will move in the appropriate direction. However, there is a bias, because if it slows, the momentum of the flywheel, a reservoir of energy, can be called upon to drive it forward again. It takes what energy it it needs; directly from the belt, or from stored momentum, so as to maintain that balance.
It is visibly so. It slips and slides about due to the low rolling resistance, and its precarious balance. So little work (force x distance) is being done.
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Old 12th November 2008, 01:33 AM   #141
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Originally Posted by spork View Post
Quote:
Originally Posted by CaveDave
Because of limitations of my OS, machine, and connection, I don't attempt you-tube or any other video downloads

Would someone post some good still shots and also a plan-view (overhead view) diagram showing the road, vehicle, direction of travel, wind direction, and propeller axis orientation with blade angle/rotation direction all included?
Hey, I don't want you to risk a youtube download. I'll be happy to get all that documentation together for you. But that doesn't seem like enough. I could bring the cart by your house, and we'll do the experiment together. When is good for you?
You left out the why:
Quote:
it takes an hour for 5 minutes of unviewable images and chopped audio.
Your response seems to indicate you believe I made an unreasonable request.

I don't believe a couple of stills from the video and a photo of a simple sketch or two (I assume one of you have a camera if you make videos) could be that burdensome to provide.

You and your friends came here to convince us of the efficacy of the device, I think it should be your burden to provide the evidence.

Cheers.

Dave
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Old 12th November 2008, 01:35 AM   #142
spork
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Originally Posted by humber View Post
If I am wrong, you will be able to tell me so. I ask you to please tell me how the following is flawed.
Will do.

Quote:
this cart will only run faster than the wind, if the wind is variable.
This is incorrect. The cart will go downwind faster than the wind in a perfectly steady wind. And it will do so steady state. I've done the analysis, and we've built a cart. Neither the math nor the real world backs you up on this.

Quote:
That is all that this device does. It's a wind-driven flywheel.
You're simply incorrect. The math and the real world do not back you up here.

Quote:
I can point to clues and indicators shown in the video, that support this contention, but can tell me why that explanation does not work ?
The explanation doesn't work because it simply isn't correct. Whether gusts will tend to increase the speed of the cart is not at issue. What is at issue is how fast the cart will be going. And it's already going faster than the wind. This is shown by analysis and experiment.

Quote:
Spork's model is similar. Its momentum keeps it running in a very similar manner. The belt is the wind. If the cart slows, momentum drives it until some small disturbance allows it to pick up more. That's it.
I love it! We'll call this "small disturbance drive". How many miles per small disturbance can we get?

Quote:
Newton's law of opposite and equal reaction, means that the cart will certainly not follow the belt backwards, because of the opposing 'thrust' of the propeller.
Well, that's interesting. In that case it's a real pisser that JB and I spent so many hours before succeeding. I guess our earlier attempts weren't aware of Newton's second law - because they managed to follow the belt backwards.

Quote:
The cart 'mirrors' its input. Momentum does the rest. If it slows, then energy comes from the stored momentum to maintain that speed.
I agree it appears circular in description.
"circular"? not so much. Utter nonsense based on your unfounded opinion? More like it.

Quote:
if it slows, the momentum of the flywheel, a reservoir of energy, can be called upon to drive it forward again. It takes what energy it it needs; directly from the belt, or from stored momentum, so as to maintain that balance.
You're making my brain hurt.

You know what's a much more likely theory? The analysis that we've presented. The analysis that actually predicts exactly what we see both on the open road and the treadmill. There's really no need to appeal to negative energy crystal pyramid flywheel flux inverters.
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Old 12th November 2008, 01:35 AM   #143
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To add to the general hubbub, the force is drag and not thrust.
However, it is not necessary to make that distinction, but that one is the opposite of the other. That's agreed, I think.

Try a cart that has sails and skids rather than wheels. If the friction between the skids and the belt is zero, then in a vacuum, it could be moved about at will.
Add air, and the sail will create a drag force in opposition to any attempt to move it forward or backwards along the belt.
The propeller provided drag, because it opposes movement along the belt.
Call that thrust then, but be consistent with that definition.
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Old 12th November 2008, 01:41 AM   #144
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Originally Posted by CaveDave View Post
I think it should be your burden to provide the evidence.
If convincing you mattered to me, the burden would definitely be mine. I care just enough to meet you 99% of the way. We did the analysis, built two carts, tweaked them for days, tested and demonstrated them indoors and out, took many videos, posted them on youtube, and have spent countless hours trying to help explain the simple truth of how and why this little parlour trick works just fine without violating every law of physics.

If you don't care to let your computer download a youtube video, you're going to miss all the truly globe changing breakthroughs you would otherwise experience (because that's where they all are).
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Old 12th November 2008, 01:48 AM   #145
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Spork,
Note that I was referring to the original video with the windsock. You have not explained why that is not an adequate explanation.

You are claiming to have a video of a vehicle like your model that exceeds windspeed. I take it that this was conducted in a wind tunnel with verified constant speed? Please, show me this. I would be astonished.

The math does not back up the idea. It contradicts. In fact, it's based upon the assumption that zero is not zero.
If you would have me believe that the videos are 'proof' then you must also supply a plausible means of operation.

See previous post regarding drag.

It's a prediction based upon a false assumption that supports itself. Seeing is not necessarily believing.
It is not at all fair to say, "See, it works" if you are the only judge on the matter and have complete control of the experiment.
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Old 12th November 2008, 02:07 AM   #146
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Originally Posted by humber View Post
Spork,
Note that I was referring to the original video with the windsock. You have not explained why that is not an adequate explanation.
It's not about coming up with an "adequate explanation". The object is to arrive at the correct explanation. Your explanation simply isn't correct. There's nothing about it that's correct. If I tell you the moon orbits the earth because the sky is blue, how will you counter that brilliant argument? Here's how - you should tell me that my "explanation" is simply B.S.

Quote:
You are claiming to have a video of a vehicle like your model that exceeds windspeed. I take it that this was conducted in a wind tunnel with verified constant speed? Please, show me this. I would be astonished.
I believe the videos are linked in this thread.

Quote:
The math does not back up the idea. It contradicts. In fact, it's based upon the assumption that zero is not zero.
Do you have a random word generator you use to come up with this stuff?

Quote:
If you would have me believe that the videos are 'proof' then you must also supply a plausible means of operation.
The videos are what they are. Take them as you like. The fact that you don't like, or can't follow, the explanations doesn't mean they haven't been offered.

Quote:
See previous post regarding drag.
No

Quote:
It is not at all fair to say, "See, it works" if you are the only judge on the matter and have complete control of the experiment.
I've told you how to build one of these things. You may choose to do so. You may even succeed. You might then become a believer. But I have no hope or expectation that you'll ever understand how it works.

Last edited by spork; 12th November 2008 at 02:09 AM.
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Old 12th November 2008, 02:10 AM   #147
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Originally Posted by spork View Post
I love it! We'll call this "small disturbance drive". How many miles per small disturbance can we get?
Well, that's interesting. In that case it's a real pisser that JB and I spent so many hours before succeeding. I guess our earlier attempts weren't aware of Newton's second law - because they managed to follow the belt backwards. "circular"? not so much. Utter nonsense based on your unfounded opinion? More like it.
No. Newton's law of opposite and equal reaction mean that thrust and drag are opposing forces, but it also means that the decision as to which is which is arbitrary. That is not necessary to any equations on the matter. A force is a force, just the sign changes.
Convention has it, that thrust is the force that comes from some motivator.

The belt drives the wheels and propeller. When the propellor's mass absorbs energy, then it appears it drag. When that same mass returns energy it is thrust. The choice of name is arbitrary, as long as the distinction is consistent. That's the flaw in your argument and calculations.


I cannot find a links to your experiments other than the treadmills. Where are they, please?
Your videos are not only presented for viewing, but you claim a means of operation, and describe a critics a "genius". Not so facile, is it?

Last edited by humber; 12th November 2008 at 02:20 AM.
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Old 12th November 2008, 02:16 AM   #148
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Why am I getting a completely innaccurate remedial course in dynamics from a person so hard of thinking?

Originally Posted by humber View Post
That's the flaw in your argument and calculations.
My flawed arguments and calculations resulted in a very real vehicle that does exactly what those calculations predicted. And now that I offer you a paint-by-numbers approach to repeating these experiments yourself with little or no trial and error - I get the most bizarre lecture about how dynamics works. What I don't hear is "you're darn right I'm going to build one - and prove you wrong".
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Old 12th November 2008, 02:38 AM   #149
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Originally Posted by spork View Post
Why am I getting a completely innaccurate remedial course in dynamics from a person so hard of thinking?
<snip>
Spork,they are subjective assertions.
Your videos are evidence that something is happening. If I were to build one, I would fully expect to get the same result. What is being argued, is why that happens, and how it relates to support for a machine of this type that can actually travel faster than the wind.

So, do you have links for a machine that does that in a controlled constant- wind environment?
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Old 12th November 2008, 03:07 AM   #150
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Originally Posted by Thabiguy View Post
I feel I should clarify this somewhat. The drag certainly does lower the top speed, but even if there was no unwanted drag at all, the device still wouldn't be able to accelerate indefinitely. The propelling assembly provides forward force only up to a certain speed (vwind / f). At this speed, the propeller is pushing back the air at the same speed as the air is already flowing back (with respect to the device), so the air will no longer exert any force on the propeller. The drag makes the actual limit lower than that, but this is the fundamental limit of the concept.
I'm glad to finally get any sort of clarification. Now take a close look at this sentence:

"At this speed, the propeller is pushing back the air at the same speed as the air is already flowing back (with respect to the device), so the air will no longer exert any force on the propeller."

The thing missing here is the fact that as the speed of the craft increases so does the speed of the propeller. Therefore the propeller will always push the air faster than the air is already moving by the same difference in speed as it was at lower speeds. If the propeller had the same RPM at all speeds then you would be right, but it doesn't. The wheels are geared directly to the propeller so that as the craft gains speed so does the propeller. This gearing is such that the difference in propeller speed always exceeds the wind speed relative to the propeller by the same amount at all speeds. This difference is the same amount as the air speed relative to the ground.

There are some practical engineering issues that makes this description less than mathematically perfect yet it remains qualitatively accurate. Hopefully you can see how the constant speed difference (power source) I kept talking about applies to the propeller vs wind speed relative to the propeller now. Please try to remain as clear as you where in the post quoted above.
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Old 12th November 2008, 03:27 AM   #151
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Originally Posted by CaveDave View Post
Because of limitations of my OS, machine, and connection, I don't attempt you-tube or any other video downloads: it takes an hour for 5 minutes of unviewable images and chopped audio.

Would someone post some good still shots and also a plan-view (overhead view) diagram showing the road, vehicle, direction of travel, wind direction, and propeller axis orientation with blade angle/rotation direction all included?

Cheers

Dave
Here is a very simple diagram of the craft.

Direction of travel is to the left <----.
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Old 12th November 2008, 03:29 AM   #152
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Originally Posted by my_wan View Post
I'm glad to finally get any sort of clarification. Now take a close look at this sentence:

"At this speed, the propeller is pushing back the air at the same speed as the air is already flowing back (with respect to the device), so the air will no longer exert any force on the propeller."

The thing missing here is the fact that as the speed of the craft increases so does the speed of the propeller. Therefore the propeller will always push the air faster than the air is already moving by the same difference in speed as it was at lower speeds. If the propeller had the same RPM at all speeds then you would be right, but it doesn't. The wheels are geared directly to the propeller so that as the craft gains speed so does the propeller. This gearing is such that the difference in propeller speed always exceeds the wind speed relative to the propeller by the same amount at all speeds. This difference is the same amount as the air speed relative to the ground.

There are some practical engineering issues that makes this description less than mathematically perfect yet it remains qualitatively accurate. Hopefully you can see how the constant speed difference (power source) I kept talking about applies to the propeller vs wind speed relative to the propeller now. Please try to remain as clear as you where in the post quoted above.
My_wan, it seems that you are making the same mistake as others.
Not F1-F2 = 0, But F1+F2 =2.

The 'speed' of the wind is not the direct issue, but whether it releases to, or absorbs energy from the environment. The gearing works both ways. It allows perhaps more energy to be absorbed, say through higher efficiency, but that very mechanism reduces the potential motive force by the same amount.
At an exaggerated scale, the propeller is passing through a sea of tennis balls of varying kinetic energy. It is not the 'speed' that counts but the propellers capacity to absorb or release momentum from those tennis balls.
So it seems to me, that this is ignored, and the sign of the force, is decided on the basis that it is supports or denies a working device.
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Old 12th November 2008, 04:02 AM   #153
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Originally Posted by humber View Post
My_wan, it seems that you are making the same mistake as others.
Not F1-F2 = 0, But F1+F2 =2.

The 'speed' of the wind is not the direct issue, but whether it releases to, or absorbs energy from the environment. The gearing works both ways. It allows perhaps more energy to be absorbed, say through higher efficiency, but that very mechanism reduces the potential motive force by the same amount.
At an exaggerated scale, the propeller is passing through a sea of tennis balls of varying kinetic energy. It is not the 'speed' that counts but the propellers capacity to absorb or release momentum from those tennis balls.
So it seems to me, that this is ignored, and the sign of the force, is decided on the basis that it is supports or denies a working device.
Good point. I'll use this sentence of yours to represent what you said: "The gearing works both ways." Yes it in fact does. It is also a fact that by changing gear ratios and other parameters you can make it work both ways in practice. So the question then is which direction does the torque actually come from in practice given the plans spork published?

Well, let's start at 0 craft speed. Propellers not turning and the wind blowing the craft itself is the only thing to move it. Once the wheels do turn then the prop turns at the same rate. We know the wheels have to be the power right now because if the wind in the prop was the power turning the wheels it would run the craft backward. So now all we have to do is increase prop speed at the same rate and the craft speed and the same relative condition persist. The prop therefore continues to be powered by the wheels and the prop speed only increases enough to maintain exactly the same wind differential even as the craft gains speed. Just because it exceeds ground wind speed does not mean it exceeds wind speed relative to the craft, due to the prop.

The way I got through this part in my thinking was to consider the drive shaft run into a ring with a flange. The drive shaft has a peg so it turns freely in the ring until it hits the flange. This mean the peg will be on one side if the wheels power the prop and on the other side if the prop powers the wheels. It can't be both at the same time unless you want to call it Schroedinger's craft, LMAO. Anyway.. there is a clear direction that the forces propagate through the craft and I'm not just picking the one that seems to make sense. I even had to concede the Betz' Law issue to spork in a previous debate for this very reason.
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Last edited by my_wan; 12th November 2008 at 04:03 AM. Reason: Changed "I'll this this sentence" to "I'll use this sentence"
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Old 12th November 2008, 05:04 AM   #154
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Originally Posted by my_wan View Post
Good point. I'll use this sentence of yours to represent what you said: "The gearing works both ways." Yes it in fact does. It is also a fact that by changing gear ratios and other parameters you can make it work both ways in practice. So the question then is which direction does the torque actually come from in practice given the plans spork published?

Well, let's start at 0 craft speed. Propellers not turning and the wind blowing the craft itself is the only thing to move it. Once the wheels do turn then the prop turns at the same rate. We know the wheels have to be the power right now because if the wind in the prop was the power turning the wheels it would run the craft backward. So now all we have to do is increase prop speed at the same rate and the craft speed and the same relative condition persist. The prop therefore continues to be powered by the wheels and the prop speed only increases enough to maintain exactly the same wind differential even as the craft gains speed. Just because it exceeds ground wind speed does not mean it exceeds wind speed relative to the craft, due to the prop.

The way I got through this part in my thinking was to consider the drive shaft run into a ring with a flange. The drive shaft has a peg so it turns freely in the ring until it hits the flange. This mean the peg will be on one side if the wheels power the prop and on the other side if the prop powers the wheels. It can't be both at the same time unless you want to call it Schroedinger's craft, LMAO. Anyway.. there is a clear direction that the forces propagate through the craft and I'm not just picking the one that seems to make sense. I even had to concede the Betz' Law issue to spork in a previous debate for this very reason.
Perhaps you are thinking that this is about your debate with Spork?
As far as I can see, the videos show a completely understandable and predictable trifle.

I was referring to your general arguments for a real machine.

OK, it seems that you are proposing a rectifying mechanism. That would work, but not without storage. That is, energy is accepted one way, stored, 'turned around' and added to the motive force. Spronk's design has this built in, but he refuses to see it.

Anyway, you can use the vehicle shown in the original video.

There are few such rectifying mechanisms in this machine, but the most obvious are the wheels. Wouldn't you use low rolling-resistance wheels, as found on solar-powered craft?
The propeller's precession, forces the rear wheels to engage with the road; the front will tend to lift, which probably accounts for its dragster-like design.

What this means is that when the vehicle is being driven by the wind, a large amount of energy is absorbed. On the other hand, when the wind drops, it can coast on the stored energy while releasing less to the environment than it previously stored. It accumulates and stores as it goes along.
If the propeller were also to be used to charge a battery and then drive a motor, would that qualify as a contender ?

Last edited by humber; 12th November 2008 at 06:14 AM. Reason: clarification
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Old 12th November 2008, 05:28 AM   #155
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Originally Posted by spork View Post
Why am I getting a completely innaccurate remedial course in dynamics from a person so hard of thinking?



My flawed arguments and calculations resulted in a very real vehicle that does exactly what those calculations predicted. And now that I offer you a paint-by-numbers approach to repeating these experiments yourself with little or no trial and error - I get the most bizarre lecture about how dynamics works. What I don't hear is "you're darn right I'm going to build one - and prove you wrong".

So, we can see your calculations where?
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Old 12th November 2008, 05:53 AM   #156
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Originally Posted by ThinAirDesigns View Post
It's been established from the days of Galileo and Newton that motion is relative. There is no physics experiment, no matter how sensitive the instrument, which can determine if the road is still and the air is moving or if the road is moving and the air is still.
Set up two wind tunnels. One has a solid floor and airflow the other has a treadmill with no airflow. Put a cart in each. Turn on the ariflow and the treadmill. Hold the carts above ground and make sure both of their wheels has zero angular velocity. Drop them on the ground. They will travel to opposite directions. Right?

Originally Posted by my_wan View Post
Well, let's start at 0 craft speed. Propellers not turning and the wind blowing the craft itself is the only thing to move it. Once the wheels do turn then the prop turns at the same rate. We know the wheels have to be the power right now because if the wind in the prop was the power turning the wheels it would run the craft backward.So now all we have to do is increase prop speed at the same rate and the craft speed and the same relative condition persist. The prop therefore continues to be powered by the wheels and the prop speed only increases enough to maintain exactly the same wind differential even as the craft gains speed. Just because it exceeds ground wind speed does not mean it exceeds wind speed relative to the craft, due to the prop.
Why? <- refers to emphasised statement.

Last edited by .13.; 12th November 2008 at 05:57 AM.
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Old 12th November 2008, 05:57 AM   #157
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And the video of wind-powered craft operating in a controlled constant-wind environment ?
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Old 12th November 2008, 06:05 AM   #158
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Originally Posted by .13. View Post
Why? <- refers to emphasised statement.
I know why. He thinks propellers work in only one direction. The only reason why the cart doesn't go backwards is because the forces equalize and the cart stops accelerating. I'm not disputing the cart doesn't move but his mystical magical description ignores the fact that with the headwind the propeller starts acting like a generator in the wrong direction thus counteracting the force of the wheels.
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Old 12th November 2008, 06:27 AM   #159
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Yes, there appears to be little acceptance of qualitative descriptions along the lines of opposing forces. If only Einstein had not used the word "Relativity".

Last edited by humber; 12th November 2008 at 06:52 AM.
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Old 12th November 2008, 07:19 AM   #160
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Originally Posted by .13. View Post
Why? <- refers to emphasised statement.
The emphasized statement was:
"if the wind in the prop was the power turning the wheels it would run the craft backward".
Now look at the diagram I drew:
Direction of travel is to the left <----.

Notice that when the wheels rotate as shown the prop ejects air to the right while the wind travels to the left. Now if this wind is what turned the propeller the ejected air would necessarily be in the same direction as the air turning it, but it's not. If the air output is reversed from that shown the wheels must also turn in the opposite direction, because they are directly connected, making the craft go right instead of left as shown. Since the craft does go left the prop must be driven by the wheels and not visa versa. So there's you "why" on the emphasized statement.

Originally Posted by technoextreme View Post
I know why. He thinks propellers work in only one direction. <snip>
That's an impossible position to maintain as much as I stressed to you the direct connection between the wheels and the prop. The above argument demonstrates just how aware I am that the prop can go both directions but that that also means the wheels must also go the other direction running the thing backward. Turn the wheels one way the prop blows air one way. Turn the wheels the other way the prop blows air the other way. Doesn't get simpler than that.
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