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Old 12th November 2008, 06:25 PM   #241
ThinAirDesigns
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Originally Posted by Thabiguy View Post
Spork, JB,

if you're reading this: can you please tell me whether I was right in what I was trying to explain to my_wan?

If I'm mistaken in some way, I'd rather find out.
Thabiguy and my_wan, spork and I would love to contribute anyway we can, but the discussion between you very very long (and that's not a criticism).

If you would summerize the point of conflict I'm sure we'd be happy to comment.

JB
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Old 12th November 2008, 06:33 PM   #242
sol invictus
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Originally Posted by JWideman View Post
JB, when I said "I've done the experiment", I was referring to the craft spork posted the plans for. Basically your craft is a prop coupled to a wheel, no weird gearing, no flywheel, just very simple. Had one of those as a kid, couldn't understand why it wouldn't run forever. After all, the wind turns the prop, providing energy to the wheel; the wheel turning provides energy to the prop. That's how I learned about entropy.
But if that's not what is supposedly happening, what is?
What, precisely, did you learn about entropy? Do you think a dust mote caught in the Gulf Stream that circles indefinitely is a violation of the laws of thermodynamics?

All entropy tells you is that the wind will eventually die (think billions of years, after the sun has gone out). Assuming it doesn't go nova and swallow the earth first, that is. It says precisely nothing about this device.

Originally Posted by Brian-M View Post
There's no problem with using stored energy to travel downwind faster than the wind.
OK. But one way to store energy is to hold a propeller into the wind and wind up a spring. Or hold a wheel against the ground you're moving with respect to and do the same.

Quote:
The problem is that the craft in question is not using stored energy, but generating the energy to maintain it's faster than-the-wind velocity from it's own headwind.
No - it's using the fact that the wind moves with respect to the ground. That motion is there regardless of the motion of the craft.

Originally Posted by humber View Post
MHaze,
Well, what I was saying is that is not an inertial frame of reference. This platform is not notional in any way. It's rolling-road model. It's not the wheels that are the ground it's the treadmill belt. Everything is literal. The wheels are wheels, the air is the air, the propeller is the propeller.
I have no idea what you're trying to say. I suggest you learn some basic facts about Lorentz transformations - or Galilean, which are simpler and suffice in this case.

Quote:
I am not saying that a windblown model cannot be, of course not, but that this model is not an indicator of the potential for greater then wind-speed vehicles, other than flywheel driven, of course.
Flywheel, or by jibing, or with a spring - you seem to agree that all of those methods allow travel downwind faster than the wind. Why do you think this is so different?

I haven't seen one single rational objection to this device. Not one of the "skeptics" has identified a single physical principle it violates. The best you seem to be able to do is yell and/or ramble incoherently. As I said before, it's not obvious that this device works from the design. But it does NOT violate any law of physics, it's easy to see how it COULD work, the videos are pretty convincing, and not one real argument has been produced in this thread against it.

Last edited by sol invictus; 12th November 2008 at 06:34 PM.
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Old 12th November 2008, 06:34 PM   #243
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Originally Posted by fsol View Post
So when you say that you have calculations that prove you right, you actually don't have them? or you don't want to show them? or?

It's just that with the tone you are taking when you mention your analysis and how your analysis predicted the performance of the device you built...I dunno, I was expecting something a little more like, umm analysis.
You have me at a complete loss. You clearly seem to be one of the VERY few people that understand this thing completely. I point to my vector analysis and say that along with the necessary description it will prove this is viable. I offer to give that description as soon as anyone wants to discuss it. What tone are you refering to?
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Old 12th November 2008, 06:45 PM   #244
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Originally Posted by Brian-M View Post
I hadn't thought of thinking of the propeller as being used as a sail while below wind-speed, but that doesn't affect what happens when it goes faster than wind-speed.
I've mentioned more than once that this is the exact analog of an ice-boat on a downwind tack. We simply send the sail in a spiraling continuous tack. This is true below the wind speed and above. The blades of the prop act exactly as the sail of the ice-boat with the wheels and transmission providing the same kinematic constraint as the blades of the ice boat.

Quote:
From later posts, it looks like he means the spinning of the propeller would push the air backwards, providing the craft with a forward thrust which turns the wheels faster, which would then turn the propeller faster, which would provide more forward thrust... and so on.
I don't think I'd word it that way, but that's the gist of it.

Quote:
If so, he's forgetting that the energy imparted to the propeller to produce this forward thrust is taken from forwards momentum of the craft itself, so he's subtracting forward momentum in order to spin a propeller to provide forward momentum. Somehow he thinks he can get more power out of the propeller than the propeller takes from the craft via the wheels.

I'm not forgetting anything. It's just that I understand exactly how this thing can exploit the energy of the wind relative to the ground - and you can't. This has you claiming that the very object I built must be an example of perpetual motion.
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Old 12th November 2008, 06:46 PM   #245
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Originally Posted by ThinAirDesigns View Post
If you would summerize the point of conflict I'm sure we'd be happy to comment.
I say that even under ideal conditions (no unwanted friction, no unwanted drag) the device would not accelerate indefinitely, but only up to a certain, well-defined multiple of wind speed (depending on the transmission between the wheels and the propeller), at which the wind will no longer exert forward force on the propeller, making it impossible to accelerate further (unless the device is adjusted to change the transmission).

my_wan says that the maximum speed of the device is only limited by practical considerations (such as drag on the device as it moves at higher than wind speed), and that no matter how fast the device is going, it would always be (in theory) able to utilize the power of the wind for further acceleration, if it weren't for the drag etc. (I hope I have not misrepresented what he says. If I have, I apologize, and invite him to offer his own summary.)
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Old 12th November 2008, 06:52 PM   #246
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Originally Posted by humber View Post
Brian-M, Mhaze. At least 3 of us understand.

Perhaps, but it clearly isn't you three. In fact I can tell you more or less definitively, JB, Sol, TheBigGuy, and I clearly understand the mechanics of this. Some others have parts of it right.
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Old 12th November 2008, 06:54 PM   #247
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Originally Posted by Thabiguy View Post
The important force is the force of the air pushing the propeller forward.
And the force of air pushing the propeller backwards.
Originally Posted by Thabiguy View Post
Other than that, it's ground friction, internal friction, lateral drag on the propeller as it rotates...
And the force of air pushing the propeller backwards.
Quote:
The force that is key to accelerating above wind speed is the force of the air pushing the propeller forward.
But the force of air also pushes the propeller backwards.
Quote:
Flywheel, or by jibing, or with a spring - you seem to agree that all of those methods allow travel downwind faster than the wind. Why do you think this is so different?
Because it's a screw. If you start running straight into the wind you develop a force that is opposite to the cart. Half the people here have no idea how a screw works. Half the people here have no idea about frames of references. Pick your butchering of science. I was in the frame of reference group but then I just realized that you will see the same problems no matter what frame of reference you jump to.
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Old 12th November 2008, 06:56 PM   #248
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Originally Posted by Thabiguy View Post
Spork, JB,

if you're reading this: can you please tell me whether I was right in what I was trying to explain to my_wan?

If I'm mistaken in some way, I'd rather find out.

Sorry for the delay. Yes you are completely right. You are one of the VERY few people that seem to understand even the subtle aspects of this thing.

I honestly consider it a fairly simple (if unintuitive) thing, based on the simpler analogies. While it's hard to imagine there could ever be this much debate about it is astonishing. But I have to remind myself that people argued about the plane on a treadmill (which was infinitely simpler still).

I am beginning to find more people on the forums that do understand the physics and aero behind it, and some that are getting closer. But that number is still quite small.

Probably the most amazing thing is that there are still so many people that claim it can't be done. Hell, we've described how to build the thing and offered to send them to critics. I can only assume these are the same folks that don't believe we've put men on the moon.
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Old 12th November 2008, 07:03 PM   #249
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No, think Mythbusters. Any time that their plane is NOT touching the belt, is its real-world speed, agree? When it is in the air, you can turn off the treadmill, agree? If the plane does a hop, when it lands, it will land at some speed relative to the belt. This might be only a little slower. I say this to demonstrate, that when the plane is on the belt, it IS its real world speed, when it takes off, that's its real-world speed too. You must agree.

The real world speed, of the cart is not its speed relative to the belt, but relative to the ground. That is how fast it is going. It's exactly as Briam_M described. Your using the wind to stay (almost) stopped.

You are on the same ground as the belt, but at different velocities, same inertial reference, save for that small difference we attribute to Einstein, which is infinitesimally small at that speed. You are not standing on the belt, but on the static ground. That is your observer's view.

Do you think that the plane jumps from -takeoff speed, to +takeoff speed instantaneously?

What you see, IS the cart's speed. What you are seeing, is the cart's inability to remain at zero velocity. Also, the frictional components cannot be scaled to a bigger real-world value in any useful way. The cart is like a nearly floating gyroscope. See how it twists?

Tell me I'm wrong.
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Old 12th November 2008, 07:04 PM   #250
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Perfect Thabiguy. Perfect.

JB

Originally Posted by Thabiguy View Post
I say that even under ideal conditions (no unwanted friction, no unwanted drag) the device would not accelerate indefinitely, but only up to a certain, well-defined multiple of wind speed (depending on the transmission between the wheels and the propeller), at which the wind will no longer exert forward force on the propeller, making it impossible to accelerate further (unless the device is adjusted to change the transmission).

my_wan says that the maximum speed of the device is only limited by practical considerations (such as drag on the device as it moves at higher than wind speed), and that no matter how fast the device is going, it would always be (in theory) able to utilize the power of the wind for further acceleration, if it weren't for the drag etc. (I hope I have not misrepresented what he says. If I have, I apologize, and invite him to offer his own summary.)
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Old 12th November 2008, 07:07 PM   #251
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humber:
Quote:
What you see, IS the cart's speed. What you are seeing, is the cart's inability to remain at zero velocity. Also, the frictional components cannot be scaled to a bigger real-world value in any useful way. The cart is like a nearly floating gyroscope. See how it twists?

Tell me I'm wrong.
-

When a door is left open that wide is must be taken.

You're wrong.

JB
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Old 12th November 2008, 07:22 PM   #252
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Originally Posted by sol invictus View Post
What, precisely, did you learn about entropy? Do you think a dust mote caught in the Gulf Stream that circles indefinitely is a violation of the laws of thermodynamics?

All entropy tells you is that the wind will eventually die (think billions of years, after the sun has gone out). Assuming it doesn't go nova and swallow the earth first, that is. It says precisely nothing about this device.
Sorry, I sometimes say things that suggest a more direct connection than I mean to imply. My childish experiment led me to learn why perpetual motion doesn't work, which included the lesson on entropy.

Originally Posted by spork View Post
Originally Posted by Brian-M
From later posts, it looks like he means the spinning of the propeller would push the air backwards, providing the craft with a forward thrust which turns the wheels faster, which would then turn the propeller faster, which would provide more forward thrust... and so on.
I don't think I'd word it that way, but that's the gist of it.
Quote:
This has you claiming that the very object I built must be an example of perpetual motion.
Brian-M was describing perpetual motion.
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Old 12th November 2008, 07:23 PM   #253
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Originally Posted by sol invictus View Post
No - it's using the fact that the wind moves with respect to the ground. That motion is there regardless of the motion of the craft.

No... if this was simply a wind-powered device that travels upwind (or downwind), I'd agree with you.

From what he's claiming (or from what I think he's claiming) is this:

Code:
<------< Wind (Slow)
<------------< Speed (Fast)

      X|
       |
  O------O
Ground (Still)
Traveling faster than, but in the same direction as the wind on a fixed surface, which is logically equivalent to putting it on a treadmill on a windless day like this:


Code:
Wind (none)
<------< Speed (slow)

      X|
       |
  O------O
>------> Ground (slow)

Traveling against a treadmill on a windless day.
Apparently, he thinks it should accelerate to the left.

(Correct me if I have misunderstood the claim.)
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Last edited by Brian-M; 12th November 2008 at 07:30 PM. Reason: Spacing
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Old 12th November 2008, 07:25 PM   #254
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Really. Put the cart on the belt as usual and get it moving forward.
Kick the underside of the treadmill, so as to make the cart jump.
At what speed is it traveling, at the moment it leaves the belt?

Answer: Very slowly.
What's the 'windspeed'? Answer: Belt speed, -belt speed.

ETA:
Imagine a small aircraft on the belt. Launch it against the belt, so that it takes off. Hide behind the bench so that you can't see the belt. How fast is it going? The speed at which it just left the belt.
Same with cart, hide so that you cannot see. How fast is it going, slowly to the right.
Put an object on the belt, how fast is it going. Belt speed to the left.

Let's say the belt speed is 10 knots. Imagine the cart in a 10 knot wind. It would be blown along at whatever speed. This is not a simulation of a cart in wind. It's the speed above zero. It would be, windspeed if attached to the belt, then the propeller would be driven at windspeed.

Last edited by humber; 12th November 2008 at 07:43 PM.
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Old 12th November 2008, 07:29 PM   #255
spork
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Originally Posted by Brian-M View Post
Traveling against a treadmill on a windless day.
Apparently, he thinks it should accelerate to the left.

(Correct me if I have misunderstood the claim.)

I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.
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Old 12th November 2008, 07:47 PM   #256
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Originally Posted by spork View Post
I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.

That's what I thought. I'd be interested in seeing the video.
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Old 12th November 2008, 07:53 PM   #257
spork
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Originally Posted by Brian-M View Post
That's what I thought. I'd be interested in seeing the video.

Normally I'd assume you're joking, but after 3 days on this forum I'm not going to make such assumptions.

Search on spork33 on youtube. I've got a pile of videos on this.
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Old 12th November 2008, 08:04 PM   #258
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The wind on the cart, is not a tail wind, but a simulated headwind. Just like Mythbusters.
It simulates the wind blowing from propeller to tail. So it is for the cart. Its progress is not against belt zero, but it is the (-windspeed + forward speed)
It's going backwards. That is, how a real cart would behave in a real 10 knot headwind, but blown backwards. Or can it make it's own wind-powered effort against a headwind as that would suggest.

Last edited by humber; 12th November 2008 at 08:15 PM.
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Old 12th November 2008, 08:13 PM   #259
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Originally Posted by spork View Post
I'm not going to parse the ascii art, but I can tell you what mine DOES do. It will advance on a treadmill in a room with no wind.

Come to think of it - maybe I can get some video showing this. Maybe post it on youtube.
Yes but it will also stop accelerating at one point. That is whats important. That's the proof in the pudding. And that's what missing.
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Old 12th November 2008, 08:19 PM   #260
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Originally Posted by technoextreme View Post
Yes but it will also stop accelerating at one point. That is whats important. That's the proof in the pudding. And that's what missing.
Yes, it will stop accelerating at some point. But that point is at a speed faster than the wind - downwind. This is clearly true and clearly demonstrated, and the only point we set out to make.
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Old 12th November 2008, 08:24 PM   #261
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Originally Posted by spork View Post
Yes, it will stop accelerating at some point. But that point is at a speed faster than the wind - downwind. This is clearly true and clearly demonstrated, and the only point we set out to make.
No it isn't. You never provide any measurements.
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Old 12th November 2008, 08:34 PM   #262
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Originally Posted by humber View Post
MHaze,
Well, what I was saying is that is not an inertial frame of reference. This platform is not notional in any way. It's rolling-road model. It's not the wheels that are the ground it's the treadmill belt. Everything is literal. The wheels are wheels, the air is the air, the propeller is the propeller. Just like on Mythbusters.

So, only the labels are changed. But, the body of the treadmill is connected to real ground, so the belt is also real ground. Call the air the ground if you like. No matter, as long as you realise what that means.

There is little impetus. The impetus between an operator, and the cart is the same that would be felt in the real world. Because, it is the real world.
Friction aside, the bigger one is as easy to move around as the little one. The only impetus lies in the difference between the forces controlling the cart itself, and how they are coupled to the belt by friction through the wheels. Moreover, the impetus is the momentum stored in the propeller.

I am not saying that a windblown model cannot be, of course not, but that this model is not an indicator of the potential for greater then wind-speed vehicles, other than flywheel driven, of course.

Brian-M, Mhaze. At least 3 of us understand.
Yes.

This example should be used in college Aerodynamics 101 as an example of thrust, momentum, lift and drag. But at the end of the course, not by any means when these concepts were introduced.

Last edited by mhaze; 12th November 2008 at 08:36 PM.
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Old 12th November 2008, 08:56 PM   #263
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Tell me, please, just before you release the cart, do you feel wind coming from the direction of the propeller? No. Then neither does the cart. No tail wind.

Wind from the direction of the front of the cart? No head wind. Just the scarcest pull of the difference between those two "winds". The one that could be, should be, generated were it to be moving along with the belt, and an imagined one. The difference of that imagined calculation is the difference of those two. It's movement is an indicator of it's inability to remain at zero velocity. It's a cat trying to climb up a slippery pole, and barely succeeding.
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Old 12th November 2008, 08:59 PM   #264
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Originally Posted by technoextreme View Post
No it isn't. You never provide any measurements.
You don't need a digital readout to tell whether the cart is advancing or retreating on the belt - at least I don't.
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Old 12th November 2008, 09:00 PM   #265
sol invictus
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Originally Posted by humber View Post
No, think Mythbusters.
I have no idea what you're talking about. There was a thread here about planes on treadmills, in which many people said wrong things. I'm guessing mythbusters did the experiment? Why did they bother - the answer was completely obvious.

Originally Posted by Brian-M View Post
Traveling against a treadmill on a windless day.
Apparently, he thinks it should accelerate to the left.
The claim is that the cart will accelerate against the direction the treadmill is trying to carry it (at least if you start it at rest with respect to the air). The mechanism is easy to understand - the belt spins the wheels, which spin a propeller, which moves the plane. It could move it either way depending on how you connect and orient the propeller. Big deal.

Originally Posted by humber View Post
Really. Put the cart on the belt as usual and get it moving forward.
Kick the underside of the treadmill, so as to make the cart jump.
At what speed is it traveling, at the moment it leaves the belt?

Answer: Very slowly.
Relative to the air and ground, yes.

Quote:
What's the 'windspeed'? Answer: Belt speed, -belt speed.
Huh?

You seem to be profoundly confused about reference frames. There is no such thing as absolute velocity - get that out of your head. There is only relative velocity. The speed of the cart with respect to the ground is totally irrelevant in the treadmill experiment. All that matters are the relative speeds of air, cart, and belt.
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Old 12th November 2008, 09:14 PM   #266
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Originally Posted by spork View Post
You don't need a digital readout to tell whether the cart is advancing or retreating on the belt - at least I don't.
That doesn't prove anything. Give me the velocity that proves your little cart works.
Originally Posted by sol invictus View Post
I have no idea what you're talking about. There was a thread here about planes on treadmills, in which many people said wrong things. I'm guessing mythbusters did the experiment? Why did they bother - the answer was completely obvious.

The claim is that the cart will accelerate against the direction the treadmill is trying to carry it (at least if you start it at rest with respect to the air). The mechanism is easy to understand - the belt spins the wheels, which spin a propeller, which moves the plane. It could move it either way depending on how you connect and orient the propeller. Big deal.
I love how you complain about people getting stuff wrong when you were not even concerned enough to know what we are talking about. No one is disputing the cart won't accelerate. And if they are well they are really horribly wrong. The claim is that the acceleration means that it's traveling faster than the wind which is a big no.
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Old 12th November 2008, 09:22 PM   #267
humber
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Originally Posted by sol invictus View Post
You seem to be profoundly confused about reference frames. There is no such thing as absolute velocity - get that out of your head. There is only relative velocity. The speed of the cart with respect to the ground is totally irrelevant in the treadmill experiment. All that matters are the relative speeds of air, cart, and belt.
Mythbusters example was not appropriate then. I have another.

What are the wind and ground speeds of your hand. Both zero.
That's odd, because the cart barely deviates from this when on the belt.
There is no wind to be felt upon the hand, from either direction.
Uuum...no wind at all.

It's just the model's reaction to being driven by a belt.

Last edited by humber; 12th November 2008 at 09:25 PM.
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Old 12th November 2008, 09:30 PM   #268
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Originally Posted by humber View Post
What are the wind and ground speeds of your hand. Both zero.
What if I'm driving down the road at 20 mph and I happen to have a 20 mph tailwind. I stick my hand out the window. What wind does my hand feel? Zero.
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Old 12th November 2008, 09:32 PM   #269
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Originally Posted by spork View Post
What if I'm driving down the road at 20 mph and I happen to have a 20 mph tailwind. I stick my hand out the window. What wind does my hand feel? Zero.
Right. Now go faster. You have now have a head wind which will now case the propeller to act like a giant break.
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Old 12th November 2008, 09:47 PM   #270
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Originally Posted by technoextreme View Post
Right. Now go faster. You have now have a head wind which will now case the propeller to act like a giant break.

Ahhh - that explains why our cart always fails to advance on the treadmill. There's our problem right there.
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Old 12th November 2008, 09:50 PM   #271
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Originally Posted by spork View Post
Ahhh - that explains why our cart always fails to advance on the treadmill. There's our problem right there.
No. A basic understanding of physics is your problem. The cart in all scenarios never fails to go up the treadmill. It will stop accelerating which your movies never actually prove except when it's on an incline but that's the wrong force.
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Old 12th November 2008, 09:52 PM   #272
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Originally Posted by technoextreme View Post
I love how you complain about people getting stuff wrong when you were not even concerned enough to know what we are talking about. No one is disputing the cart won't accelerate. And if they are well they are really horribly wrong. The claim is that the acceleration means that it's traveling faster than the wind which is a big no.
No. Either you didn't read what I wrote, or you don't understand the concept of relative motion.

Hold the cart in place at the center of the treadmill, letting its wheels spin. That situation is identical to one in which the cart is rolling across the ground at precisely the wind speed.

Now let the cart go. If it accelerates against the direction of the treadmill, as it does in the video, that is identical to the cart accelerating in the wind direction, so that it ends up going faster than the wind.
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Old 12th November 2008, 09:56 PM   #273
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Originally Posted by humber View Post
What are the wind and ground speeds of your hand. Both zero.
That's odd, because the cart barely deviates from this when on the belt.
There is no wind to be felt upon the hand, from either direction.
Uuum...no wind at all.
Yes - that's the precisely the point.
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Old 12th November 2008, 10:00 PM   #274
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Originally Posted by technoextreme View Post
No. A basic understanding of physics is your problem. The cart in all scenarios never fails to go up the treadmill. It will stop accelerating which your movies never actually prove except when it's on an incline but that's the wrong force.

Excellent. Then you should take me up on my $100K wager. We'll do the test your way.
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Old 12th November 2008, 10:03 PM   #275
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Originally Posted by spork View Post
What if I'm driving down the road at 20 mph and I happen to have a 20 mph tailwind. I stick my hand out the window. What wind does my hand feel? Zero.
Yes, but then you are already at windspeed. The premise is that, when placed on the belt, the cart is already at windspeed - at launch.

I only 'realised' this, when thinking about a test for JB. It's not only
incapable of doing any real work, but that there are no real winds other than a very slight wind blowing over the propeller.
It all comes from the belt, as we have being trying to tell you. It got lost in detailed discussions about oscillations and so forth. It creates its own drag.

The Mythbuster's example is of a propeller driven vehicle travelling on a belt that is moving moving backwards or forwards, but it actually has wind blowing across it, no matter what direction you choose as wind.

If you put the cart on a belt, and have an external wind generator, then that is a different story.

ETA:
But we have told you that we fully expect that to happen. It has no relation to wind, but demonstrates that a propeller is capable of creating enough drag to stop itself on a belt, in vague manner.

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Old 12th November 2008, 10:08 PM   #276
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Originally Posted by sol invictus View Post

Hold the cart in place at the center of the treadmill, letting its wheels spin. That situation is identical to one in which the cart is rolling across the ground at precisely the wind speed.
Nope. Nice try though but that cart aint moving at all with respect to the air. Hence no drag which is present when the car actually moves.
D = Cd * A * .5 * r * V^2
Thus they are not equivalent frames of reference when you let the car go. Admittedly, you do get to that point eventually which is the point of zero acceleration.
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Old 12th November 2008, 10:12 PM   #277
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The wind from the propeller, cannot be equated to wind. There is never any full-speed wind over any part of the cart. It responds to all sorts of thrusts, resistances and torques as a reaction to being driven, but nothing else.

Air can be thought of as viscous fluid, certainly for small objects. Replace the air with an imagined syrup, what drags on what? You will see a cart immersed in syrup, with the propeller making a local disturbance, but the cart remains essentially fixed to that disturbance. It does not travel through the bulk of the syrup, but moves about a fixed point, determined by the propeller's local drag 'hook'.
Whatever claims you have for faster than windspeed travel, it does not relate to this experiment.
If you could build such cart, it would essentially stand still in the wind.

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Old 12th November 2008, 10:33 PM   #278
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This is an absolute train wreck. I just don't understand. You guys haven't designed, built, or tested one of these. All you've seen are videos of them - the very videos that you claim don't prove anything - because who could possibly tell what's happening off screen and who knows what trickery is being played. You clearly have no training in physics or aero. But somehow from absolutely no evidence at all (this is what you tell me) you're able to correct JB, theBigGuy, Sol, and myself.

I can't speak for the others, but I have an M.S. in aero, and MANY years of flying everything that flies from R/C models to hang gliders, to small planes, sailplanes, helis... I know JB's background with flight is very impressive as well. I strongly suspect TheBigGuy and Sol have training in physics or Aero.

But you three can correct us all with no evidence or background whatever - based only on truly bizarre "theories" you make up on the fly?

Build the stupid cart. I posted the parts and directions. You could have built 10 of them in the time you spewed all this misinformation on this forum. Having done absolutely nothing at all - your words carry absolutely no weight at all. Knowwhatimean?
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Old 12th November 2008, 10:43 PM   #279
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You guys almost had me.
Work = thrust - drag
If thrust equals drag, no work is being done. The treadmill is merely a misdirection.
Nice try.
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Old 12th November 2008, 11:19 PM   #280
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Originally Posted by spork View Post
Normally I'd assume you're joking, but after 3 days on this forum I'm not going to make such assumptions.

Search on spork33 on youtube. I've got a pile of videos on this.

Sorry, I'd forgotten you'd mentioned the videos before.
The one in this video is clearly accelerating as you said it should...

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE



I think I owe apologies all around. After thinking about what was happening in the video and the forces involved, I realized where I was going wrong in my mind.

Early on in the thread, I mentioned it would be possible for a wind-powered device to travel upwind, but would have to gear-down to achieve this, and so would be limited to travelling at less than wind-speed.

When I started looking at this from the viewpoint of a treadmill, with the air as the stationary reference-point things suddenly flipped around in my mind, and I realized the same principle would work in this situation too, but with ground and air reversed.

So, instead of pushing against the ground to move at less than wind-speed against the wind, this device would be pushing against the air to move at less than ground-speed against the ground.

So, converting this back to a fixed ground reference, the maximum speed of an idealized version of device (including 100% power transfer at the propeller, no wind resistance, no friction, etc) would be up to twice wind speed.

So, I guess I was wrong after all.

(I doubt anyone else would think of it in exactly this way... I suspect I'm operating with a non-standard brain. )
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