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Old 15th April 2010, 08:52 PM   #1
recursive prophet
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Wind powered prop cart goes directly downwind 2.5x Wind Speed?

A thread that began at JREF back on 11/9/09, Downwind faster than the wind may finally be approaching it's finale after hundreds of pages of debate.

When the discussion began on JREF, much of it centered on whether or not a small prop cart a member-spork-built that could advance up a treadmill was proof that under the right conditions it could go directly downwind faster than the wind. According to his Galilean transformations, all the vector forces were the same. So counter intuitive was this claim, that even one Nobel winning physicist, Dan Kammen, stated he believed it would violate conservation of energy.

As was announced in the original thread last October, spork found a sponsor-Joby Energy-and has now built and tested a drivable wind cart. Since then Google has also become a sponsor, and in late March spork took it to the North American Land Sailing Association (NALSA) meet at Ivanpah Lake in the California desert. They made 3 different runs, one of them self starting, which by their GPS calculations achieved 2.5x wind speed. NALSA official Bob Dill-former holder of the land yacht speed record-observed the test, and they have agreed to certify the cart's performance at their next meet coming later this spring.

Below are links to videos of the 3 trial runs of the sporkmobile. Notice the direction of the streamers attached to a movable bar, and how it out-distances some dust from the truck used to run along with the cart for tracking it's speed and making the videos.

First run: http://www.vimeo.com/10476453
Second run: http://www.vimeo.com/10477373
Last run: http://www.vimeo.com/10476216

For those wishing to learn more about the genesis of this ongoing debate, below are the 3 threads started on various tangents it of it posted here on JREF. Below them are the 7 parts posted on RDF. For a detailed description of the cart's construction including more videos and lot of pictures, there is a link to spork's blog in my sig, along with one to TalkRational where most of the current battle still rages. In the immortal words of Papa John, "What a long, strange trip it's been."

JREF Threads:
http://www.internationalskeptics.com...d.php?t=128483
http://www.internationalskeptics.com...d.php?t=131646
http://www.internationalskeptics.com...d.php?t=130705

RDF Threads:
http://forum.richarddawkins.net/viewtopic.php?t=73123
http://forum.richarddawkins.net/viewtopic.php?t=74154
http://forum.richarddawkins.net/viewtopic.php?t=74988
http://forum.richarddawkins.net/viewtopic.php?t=75643
http://forum.richarddawkins.net/viewtopic.php?t=76400
http://forum.richarddawkins.net/viewtopic.php?t=77451
http://forum.richarddawkins.net/viewtopic.php?t=80402
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Old 16th April 2010, 07:35 AM   #2
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The tests were impressive, but even more impressive is the fact that humber is still at it. When it comes to misunderstanding basic physics, inability to learn, and complete confidence in one's understanding with no basis whatsoever, he is truly an unstoppable machine. I am in awe.
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Old 16th April 2010, 10:41 AM   #3
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I agree....

My sense is it's rather inefficient wind sailer looking at the blade shape and the tower shape.
The design allows it to effective sail close to the wind as the blades sort of act as continuous tacking energy pickup.
But it would be interesting to see without those vertical sails what the performance difference is.

any lateral gusts get picked up as additive vectors.and preserved by the mass of the machine...sort of the way albatrosses and others soar dynamically...

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Old 16th April 2010, 10:49 AM   #4
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Next logical step ought to be an airplane with one prop to power another prop that pulls the plane through the air. Tow it to launch, like a glider, then no fuel for the rest of the flight... Instead of powering a wheel, power an extra prop. hmm., ought to be prototype-able in a land sailer.

Next logical step, merge the two props into one.... needs wing/sail design work...use an engine to get it flying, then shut down engine .

Ya know, this post might have just abrogated a jillion dollars worth of patents. I've made the ideas open source, protected only by my copyrights, if any. If any of this works, I may have just become the most philanthropic man ever.
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Old 16th April 2010, 11:19 AM   #5
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Ha. Yes. I suppose awe isn't entirely inappropriate.

I know that everyone had their own favourite explanation, but I really truly felt that the little LEGO car was a 100% guaranteed argument stopper. It's soooo simple that it took me less than 5 minutes to build a replica after seeing it, and it's pretty hard to disbelieve after actually playing around with a real model (even if it's hand/gear powered rather than wind powered.) I still have the little LEGO car at work, and I show it to people who drop by my office

Last edited by Folly; 16th April 2010 at 11:20 AM. Reason: smiley failure!
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Old 16th April 2010, 11:19 AM   #6
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Quote:
Next logical step o
Sort of called a gyro-copter but TANSTAAFL eh

Some have tried dynamic soaring in a sailplane - not sure if anyone actually has succeeded .....been a while since I flew

Last edited by macdoc; 16th April 2010 at 11:20 AM.
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Old 16th April 2010, 11:23 AM   #7
sol invictus
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Originally Posted by recursive prophet View Post
A thread that began at JREF back on 11/9/09,
11/9/08. Don't sell it short!

Originally Posted by Modified View Post
The tests were impressive, but even more impressive is the fact that humber is still at it. When it comes to misunderstanding basic physics, inability to learn, and complete confidence in one's understanding with no basis whatsoever, he is truly an unstoppable machine. I am in awe.
Seconded.

Originally Posted by casebro View Post
Next logical step ought to be an airplane with one prop to power another prop that pulls the plane through the air.
You do understand why that doesn't work (but this cart does), right?
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Old 16th April 2010, 11:31 AM   #8
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Quote:
(but this cart does), right?
explain away....
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Old 16th April 2010, 11:48 AM   #9
sol invictus
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Originally Posted by macdoc View Post
explain away....
Start with a windmill. Put it on wheels. Feed the power generated by the turbine to the wheels. Now you can drive in any direction, including upwind - which increases the speed with respect to both air and ground.

Start with the cart moving at windspeed. Feed the power generated by the wheels to the propeller, and use it to drive the cart in the direction that increases its speed with respect to both air and ground - which is downwind in this case.

If the first is possible the second obviously is too, the physics is exactly the same. The only hard part is engineering (air is softer than ground).

Something flying in air without contact with the ground cannot do this (unless there are layers in the atmosphere moving at different speeds).
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Old 16th April 2010, 12:14 PM   #10
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Originally Posted by sol invictus View Post
...

Something flying in air without contact with the ground cannot do this (unless there are layers in the atmosphere moving at different speeds).
Drogue chute on a long carbon-fiber tether...
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Old 16th April 2010, 12:58 PM   #11
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Someone PM'd me this the other day and I've been meaning to say this. I was wrong. I don't remember what the hell I said but I pretty sure I was wrong.
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Old 16th April 2010, 01:15 PM   #12
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Quote:
which is downwind in this case.


and just what happens to said turbine when ground speed = windspeed ?

TANSTAAFL
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Old 16th April 2010, 01:46 PM   #13
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Originally Posted by macdoc View Post
and just what happens to said turbine when ground speed = windspeed ?

It (the prop motor) consumes power generated by the wheel turbines to propel the vehicle relative to the wind in some direction (including downwind).

Just as in the low-ground-speed case, the wheel motor consumes power generated by the prop turbine to propel the vehicle relative to the ground in some direction (including upwind).

Quote:
TANSTAAFL

Indeed. If the wind dies down (relative to the ground), you're not going anywhere, in either case.

Respectfully,
Myriad
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Old 16th April 2010, 01:47 PM   #14
sol invictus
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Originally Posted by macdoc View Post


and just what happens to said turbine when ground speed = windspeed ?

TANSTAAFL
What turbine?

The cart doesn't have a turbine, it has a propeller.
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Old 16th April 2010, 02:34 PM   #15
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Don't know if it is applicable in this case, but is there anything like a free body diagram to help explain things? I don't know how to do it, myself.
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Old 16th April 2010, 02:35 PM   #16
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Originally Posted by Modified View Post
The tests were impressive, but even more impressive is the fact that humber is still at it.
Oh god, he's still at it? He's not still trying to claim that balloons can't travel at wind speed because friction through the air slows them down, is he?

Originally Posted by casebro View Post
Next logical step ought to be an airplane with one prop to power another prop that pulls the plane through the air.
Won't work. The Down Wind Faster Than The Wind cart works by exploiting the difference in velocity of two mediums, in this case the ground and the wind. An airplane/glider only has wind-speed to work with.

ETA:

Originally Posted by macdoc View Post
and just what happens to said turbine when ground speed = windspeed ?
Since the theoretical maximum speed of the cart in ideal conditions is a fixed multiple of windspeed (relative to the ground), when windspeed equals zero the theoretical maximum possible speed of the cart equals zero.
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Old 16th April 2010, 02:48 PM   #17
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Quote:
What turbine?

The cart doesn't have a turbine, it has a propeller
SIGH

your're at THAT stage of misunderstanding??

turbine = propeller...see myriad

••

a sailplane exploits rising air masses to climb - there is also theoretical dynamic soaring which is hard to sketch out - basically the attitude and ( ideally the wing configuration ) works in such a way as to gain altitude from swooping

( move downwind in a low friction dive, then loop very smoothly into the wind ( preferably a gust ) and trade speed for altitude in a high lift, low speed attitude, repeat.

See albatross et al..

any turbulent medium can find these pockets of energy gain....kayakers do it as well in a different manner.

BUT
TANSTAAFL

When down wind speed and land speed are identical....no energy...turbine/propeller/windmill stops...

Vector gains from angled surfaces do gain which is why ice boats for instance can gain incredible speeds...there MUST be a vector at play no matter how small the angle.

all else is woo..

••

BrianM - my question was rhetorical/sarcastic.

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Old 16th April 2010, 02:51 PM   #18
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Originally Posted by recursive prophet View Post
In the immortal words of Papa John Robert Hunter, "What a long, strange trip it's been."
Fixed that for you.
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Old 16th April 2010, 03:44 PM   #19
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Before I forget again, it appears the BBC is interested in doing a segment on the Sporkmobile,* and the Discovery Channel is sending out a crew to spork's shop this weekend. I have a strong feeling after the NALSA certification this fascinating saga will get a lot more press.

It began with a 16g model prop cart that could go up a treadmill, and for those new to this topic I would recommend watching this 7 minute YT video spork posted about 2 years ago. It does a good job of laying out the the history of DDWFTTW going back to Bauer in the sixties, and shows the cart advancing on the treadmill. http://www.youtube.com/watch?v=xHsXcHoJu-A

*This was the name used for the sporks model here, but at TR in was dubbed by a denier Harold Bricer (who is amazingly similar to Christoph from jref) as the Big Ugly ********** Cart, or BUFC. Now they have abandoned that handle; likely at the bequest of their sponsors. There was an article on their Ivanpah runs in Sail Magazine and the explanation for BUFC probably didn't amuse them. So spork and jb have dropped that name and haven't decided on new one yet.

Wanted to respond to some replies to several here, but something weird is up with the quote feature-I keep getting the same one I began with not the one I'm clicking. Anyway, humber truly is unique. As Sol pointed out over a year ago-and thanks for catching my typo on 09 dude-humber was wrong way to consistently. Even a broken watch is right twice a day after all. He was either a master troll, or spork! Remember this topic is on part 15 and has over 45 thousand replies there!! This on a site that sees about one sixth the traffic that JREF does.

I'm sure Sol recalls his theory that humber was actually spork. It certainly would provide a motive for his tenacity. The thread quickly died on RDF after humber was banned. Only the shadow knows...

Did I ever tell you about the connection between spork and George Burdell, sol? Spork got his BS at Georgia Tech. Do Google that name if you don't remember. I'll have more on this later. It makes for an interesting backdrop for your initial theory. It still seems pretty unlikely, but would be a classic MF if true. I love this whole circus, and only wish I could make up stuff like this. I'm basically just the thread text janitor, as I have little else to offer other than my appreciation of humber, spork, and virtually ALL the mad carters.

Thanks to those sharing your thoughts, and I will soon post a link to this thread on the one at TalkRational. It truly has become a recursive cyber-strand

@billw-thanks for the correction. I just always think of walking in the coastal jungles of northern Colombia listening to Truckin on my headphones when I think of those words.
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Old 16th April 2010, 03:46 PM   #20
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Originally Posted by macdoc View Post
TANSTAAFL

When down wind speed and land speed are identical....no energy...turbine/propeller/windmill stops...

Vector gains from angled surfaces do gain which is why ice boats for instance can gain incredible speeds...there MUST be a vector at play no matter how small the angle.

all else is woo..
Anddddddd.... here we go again


Sorry, you're flat wrong here. The propeller of the cart isn't powering the wheels - it's the other way around.

You're going downwind at windspeed, and your wheels are generating power to spin the propeller, increasing the cart's speed wrt the ground, and so increasing the available power. The wheels are breaking, the propeller is pulling. Generally speaking, the propeller will win.

Eventually, drag forces and wheel losses equal the propeller's forward force, and you reach equilibrium. i.e. top speed.

If you want to talk physics, any sail craft is extracting energy and momentum by slowing a mass of air wrt the ground. A propeller is much more effective at this than a sail, which is why a spinnaker approach loses out to the prop cart.

There are no wind direction changes, no turbulence vortices, nothing but an even, smooth wind to extract energy from.
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Old 16th April 2010, 03:56 PM   #21
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Originally Posted by macdoc View Post
Vector gains from angled surfaces do gain which is why ice boats for instance can gain incredible speeds...there MUST be a vector at play no matter how small the angle.

all else is woo..

That's why propellers have angled surfaces.

To get from the ice boats to the downwind cart without woo, just follow these simple steps.

Step 1 is to acknowledge that ice boats can not only sail at speeds faster than the wind speed, they can sail steady-state (without exploiting gusts, momentum from turns, etc) such that the downwind component of their velocity is faster than the wind. This can be verified from ice-sailing sources.

Once that's understood, all that's needed is to transform an ice boat into the downwind "cart" in a series of steps, each of which preserves the essential mechanics of the scenario.

So, step 1 is an iceboat sailing at a downwind angle in a steady wind on an infinite ice surface. The directly downwind component of its velocity is faster than the wind; it's speed of course is faster still.

In step 2, wrap the ice surface into a tube (larger in radius than the height of the iceboat's mast), with the iceboat inside. The wind flows continuously down the tube; the boat on its slanted downwind course now sails a helix in the tube. (Ignore gravity; if you must, assume zero gravity and that the centrifugal force of the spiral course is sufficient to keep the boat's blades pressed against the ice enough for them to work as normal.)

In step 3, add a second ice boat. It is identical to the first, and it sailing the same way, but it is positioned 180 degrees around the tube from the first one. If either ice sailor looks straight "up" he's looking straight down on the other boat.

In step 4, lengthen the two boats' masts so that they connect in the center, rigidly attaching the two boats together.

In step 5, add a threaded rod running down the center axis of the ice tube. This rod passes through a hole in the two masts where they join in the center. The threads have the same pitch (number of turns per meter) as the helical path the ice boats are sailing along.

In step 6, add screw threads to the hole in the masts, that match the threaded rod. Since the hole threads and the rod threads have the same pitch as the path the the boats were traveling anyhow, this will not (aside from adding a bit of friction which we can ignore for the moment, for reasons explained in the next step) alter the courses or impede the movement of the boats.

In step 7, we remove the runners from the ice boats. They no longer contact the ice. However, the screw threads serve the same function that the runners used to, of keeping the boats' course on the most efficient angle. There is no longer any runner friction, but the friction of the central bearing replaces it. Since in principle either can be minimized, call it even.

In step 8, we remove the ice tube, since it no longer plays any part (except maybe to contain the wind in a zero gravity environment, so if it helps, assume the tube is replaced with a much larger tube, still containing the same wind velocity along it.)

In step 9, we introduce a long strip of flat pavement parallel to the tube. The pavement is far enough from the threaded rod that the two boats stay about half a meter away from it at their closest approach. At the same time, we also re-introduce a gravitational field that attracts the boats toward that pavement. Since the boats are still held "up" by the threaded rod, and they counter-balance one another, this does not affect their motion.

In step 10 we add a three-wheeled cart that is in contact with the pavement. We also add some struts that extend from the cart to a bearing around the central threaded rod. The bearing where the threaded rod goes through the boats' masts pushes against the cart's bearing, pushing the cart along at the same downwind speed as the boats.

In step 11, we remove the hulls of the boats, since the pilots can now ride in the cart instead.

In step 12, we remove the threaded rod. Instead, we add linkages and gears from the main axle of the cart to the bearing around which the boats' masts rotate, with the gearing arranged so that the angle that the boats' mast rotates for a given rotation angle of the cart's wheels is the same as it was before.

And we now have the downwind cart. Note that from the start to the finish, the fundamental device that makes it work remains the same: a surface moving laterally at an angle to the wind, whose downwind movement is constrained to maintain a certain ratio to its lateral movement. At the start the surface is an iceboat sail and at the end it's a propeller blade. At the start the mechanism that enforces the ratio of lateral to downwind movement is the iceboat's blades and at the end it's the gearing between the wheels and the propeller. But the basic dynamics stay the same.

If you still have difficult accepting this, please point out in which step I introduced the woo.

Respectfully,
Myriad
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Last edited by Myriad; 16th April 2010 at 04:08 PM. Reason: replace "spiral" with "helix/helical" for clarity
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Old 16th April 2010, 03:59 PM   #22
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when ground = windspeed = zero energy to be harvested...

this is getting hilarious.

tell us oh wise one....does the cart move when there is no wind`?
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Old 16th April 2010, 04:05 PM   #23
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Myriad

You mean that's why wind turbines have angled surfaces....propellers have them to maximize thrust and reduce tip vortice losses - not vector gain.

Answer the question....will the cart move with no wind?

Does a ice boat go faster downwind or across the wind...?

then you will know where you introduced the woo.
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Old 16th April 2010, 04:16 PM   #24
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Gday all,

Very interesting

But one thing strikes me as odd - perhaps I misunderstood, or something, but...

The wind is apparently driving the angled-blade of the propeller to turn it and thus drive the wheels, right?

But looking closely at the video #2 at e.g. 1:25, the angled-blade of the propeller appears to be turning the wrong way - as if it is driving against the wind - implying it is powered from the cart, not the wind.

Or have I completely missed something :-)
?

But then, in video #3, after they lose the chain apparently - it free-wheels the OTHER way - the way I would expect.


K.

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Old 16th April 2010, 04:19 PM   #25
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Originally Posted by Kapyong View Post
Gday all,

Very interesting

But one thing strikes me as odd - perhaps I misunderstood, or something, but...

The wind is apparently driving the angled-blade of the propeller to turn it and thus drive the wheels, right?

But looking closely at the video #2 at e.g. 1:25, the angled-blade of the propeller appears to be turning the wrong way - as if it is driving against the wind - implying it is powered from the cart, not the wind.

Or have I completely missed something :-)
?


K.
Yes, you missed something. The wheels turn the prop. The bluff body area of the cart and prop is large enough so that the wind can initially push it forward. That causes the wheels to spin, which in turn spin the prop.

Greetings,

Chris
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Old 16th April 2010, 04:23 PM   #26
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Ah, thanks....

Silly me.
And somehow I missed ArmillarySphere's clear explanation too :-(

K.

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Old 16th April 2010, 04:24 PM   #27
Myriad
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Originally Posted by macdoc View Post
Myriad

You mean that's why wind turbines have angled surfaces....propellers have them to maximize thrust and reduce tip vortice losses - not vector gain.

That would be my cue to answer with the laughing dog, except I don't do that.

A flat propeller produces no thrust.


Quote:
Answer the question....will the cart move with no wind?

If by no wind you mean zero wind speed relative to the ground, no, it will not move. Who ever said it would?

If by no wind you mean zero wind speed relative to the cart, if the wind is moving relative to the ground the wheels are resting on, the cart will move. For instance, on a treadmill in still air, the cart will begin to move in the direction opposite the treadmill. There are many videos showing this with small carts.

Quote:
Does a ice boat go faster downwind or across the wind...?

An ice boat goes fastest when angled downwind. As I said, in such configurations, high-performance ice boats go fast enough that the downwind component of their velocity is faster than the wind speed. Such an ice boat can get from a starting point to a point directly downwind faster than a balloon in the same wind.

I encourage you to verify this from ice boating sources.

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Then you will know where you introduced the woo.

Which step, please.

Respectfully,
Myriad
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Old 16th April 2010, 04:26 PM   #28
Christian Klippel
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Originally Posted by macdoc View Post


when ground = windspeed = zero energy to be harvested...
You are aware of the concept of frames of reference? You know that all motion is relative? You know how a lever works?

Do you think that if there is difference in speed between a surface and a medium, that as soon as an object reaches the speed of the medium everything comes to an halt, relative to the object?

Originally Posted by macdoc View Post
this is getting hilarious.
This topic tends to, yes. But not for the reasons you might think.

Originally Posted by macdoc View Post
tell us oh wise one....does the cart move when there is no wind`?
No one ever claimed that. The cart works because it has interfaces to two mediums (road and air) which are at different velocities.

Maybe it would help if you read a little about the topic.

Greetings,

Chris

Edit: For a simple equivalent of the situation check out this video:

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


Tell us, how can it move faster than the thing driving it, if what you claim would be true? If you accept that video, then tell us why the situation in the wind should be different?

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Old 16th April 2010, 04:39 PM   #29
casebro
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Originally Posted by sol invictus View Post
11/9/08.

You do understand why that doesn't work (but this cart does), right?
It's just drag on the prop vs drag on the 'wheel'. Substitute another prop for the 'wheel', add wings.

Wind direction to ground shouldn't matter. Once the cart reaches wind speed, it ought to be free to change direction. Might need to twist the 'prop tower' to do it, keep the prop axis paralell to the apparent wind direction. Haven't you ever been on a sail boat? As cross wind speed picks up, the apparent wind moves closer to the bow. Sails need to be adjusted accordingly, that is when the 'wing' function of the sail becomes most visible. A variable pitch prop makes an airplane more efficient, propably need one to make anything practical in this application.
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Old 16th April 2010, 04:41 PM   #30
Kapyong
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macdoc -

I am pretty sure you are stuck in the very same misunderstanding I was.

(Because I used to insist that this was absolutely impossible, and I was 100% sure of it. I forced myself into being tentative in my post above, but I was thinking that I had caught them out with a hidden power source in the cart :-)

There IS a power source in the cart - the WHEELS.

The gearing is the OPPOSITE to what you think it is - step back, unclench, look and think - the 'aha' moment should come :-)

The WHEELS drive.
NOT the prop.


K.
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Old 16th April 2010, 04:42 PM   #31
Brian-M
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Originally Posted by Kapyong View Post
But one thing strikes me as odd - perhaps I misunderstood, or something, but...

The wind is apparently driving the angled-blade of the propeller to turn it and thus drive the wheels, right?

But looking closely at the video #2 at e.g. 1:25, the angled-blade of the propeller appears to be turning the wrong way - as if it is driving against the wind - implying it is powered from the cart, not the wind.

Or have I completely missed something :-)

The propellers do turn against the wind (the opposite direction the wind is trying to turn them). They're pushing the wind backwards. (Well, I haven't watched that video, but I'm assuming it works the same as the models in the original thread.)

The wind does not turn the propeller. The wind pushes the cart forward, and the forward motion of the cart turns the propeller. The propeller pushes the wind backwards, which pushes the cart forwards even more, which makes the propeller turn even faster, which pushes the wind back harder, which pushes the cart forward even more.

ETA: Looks like I was a little late on this answer. But I got distracted by something else while writing my reply.
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Old 16th April 2010, 04:52 PM   #32
Christian Klippel
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Originally Posted by Brian-M View Post
The wind does not turn the propeller. The wind pushes the cart forward, and the forward motion of the cart turns the propeller. The propeller pushes the wind backwards, which pushes the cart forwards even more, which makes the propeller turn even faster, which pushes the wind back harder, which pushes the cart forward even more.
Whereas it is important to clarify that the power taken up at the wheels is more than the power expended at the prop. This is due to prop efficiency, gearing losses, etc. For that reason it is required that there is a difference in velocity between the ground and the air. Otherwise it would run in still air, once pushed, which of course is impossible.

Greetings,

Chris
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Old 16th April 2010, 05:05 PM   #33
Kapyong
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Gday,

Originally Posted by Brian-M View Post
The propellers do turn against the wind (the opposite direction the wind is trying to turn them). They're pushing the wind backwards. (Well, I haven't watched that video, but I'm assuming it works the same as the models in the original thread.)

The wind does not turn the propeller. The wind pushes the cart forward, and the forward motion of the cart turns the propeller. The propeller pushes the wind backwards, which pushes the cart forwards even more, which makes the propeller turn even faster, which pushes the wind back harder, which pushes the cart forward even more.

ETA: Looks like I was a little late on this answer. But I got distracted by something else while writing my reply.
Thanks Brian,
another clear explanation :-)

I really hope some others get to share my experience to day - that was a real blast. To be wrong, and then to clearly realize I was wrong, and exactly HOW and in such a clear and obvious fashion - that was a fantastic emotional ride - it's hardly EVER so clear-cut (right now I'm in morning caffeine mode.)

It's one thing to argue, and maybe be wrong about some abstract meanings in Paul, or the future of oil, or the origins of the Bible, or the politics of XXX.

But to be so clearly wrong, and to fail to understand so many times - that really really shook me. All those smart people so convinced there are right - nah, somehow they are ALL wrong.

Honestly - I was thinking I was the first one to catch them out faking a video - I was gunna be hailed as a clear-thinking hero, Brian and Hans and bluskool would be in awe of my insight, James Randi would congratulate me personally ... maybe there'd be cars and women and fame (obviously there is more than caffeine at work here - Hey - it's the weekend :-)


So,
to anyone who keeps coming back to this :

"once you reach the speed of the wind - that's it, there's no more energy or whatever"

Stop right there, and imagine the propeller going the OTHER way - just think that, and see if the 'aha' happens for you like it did for me.

(You're subtracting the wind speed, when you should be adding it.)

(back to Battleground europe now, I hear grenades nearby :-)


K.
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Old 16th April 2010, 05:13 PM   #34
Brian-M
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Originally Posted by Kapyong View Post
I really hope some others get to share my experience to day - that was a real blast. To be wrong, and then to clearly realize I was wrong, and exactly HOW and in such a clear and obvious fashion - that was a fantastic emotional ride - it's hardly EVER so clear-cut (right now I'm in morning caffeine mode.)

I had the same experience in the original DDWFTTW thread. Spork's explanations based on ice-boats made no sense to me. It's not until I actually saw a video of a model cart running up a treadmill that I began to think about it in a different way, and realize that I was wrong.
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Old 16th April 2010, 05:46 PM   #35
ArmillarySphere
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Glad to be of service

Some other clues:

If the prop was the power source, you'd expect top power when the cart was still (maximum wind wrt the cart) and zero power at windspeed. Just the opposite occurs, since it's the groundspeed wrt the cart that is of interest. At standstill, the prop-driving force is zero, since the wheels aren't turning. At windspeed, we have plenty of "engine" power, since while the wind is still wrt the cart, the wheels are spinning like mad and have plenty of power to turn the prop.

Which increases the turn rate, which increases the ground speed, which increases the wheel spin, which turns the prop faster...

Another simile:

Disconnect the wheels from the prop. Add a pair of pedals driving the prop, and Pepe the Mad Pedalier. You now have a man-powered prop cart.
Pepe will always crank the pedals at the same rate the wheels are turning. What will happen at windspeed? Why should Pepe care what speed the wind is going - he only cares about the wheels!
Obviously, with this setup, Pepe will be going to hit terminal velocity, horizontally.

Now add a handbrake, which Pepe will pull in rough proportion (~v^2 or thereabouts, I think) to how much he has to crank. Turns out this puts a limit to how fast he can go, when the breaking is equal to the prop's pull.

Replace Pepe with a differential connecting the wheels to the prop and there you go.
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Old 16th April 2010, 06:00 PM   #36
Modified
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Originally Posted by Brian-M View Post
Oh god, he's still at it? He's not still trying to claim that balloons can't travel at wind speed because friction through the air slows them down, is he?
I didn't read enough of the threads to find out, but I think he's made that claim too often and too clearly to pull a "that's not what I really meant" (an "I was wrong" is, of course, completely out of the question).
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Old 16th April 2010, 06:07 PM   #37
Modified
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Originally Posted by Brian-M View Post
I had the same experience in the original DDWFTTW thread. Spork's explanations based on ice-boats made no sense to me. It's not until I actually saw a video of a model cart running up a treadmill that I began to think about it in a different way, and realize that I was wrong.
I'd say that because I knew that sailboats can go upwind, I started off thinking this is possible and probably true. The wind and water are both streams; "upwind" equals "downstream faster than the stream"; if you can outrace one stream, you can probably do so for the other.
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Old 16th April 2010, 06:15 PM   #38
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So what's the theoretical limit on overall speed - is it bounded by friction? I guess you would achieve that with a hypothetical frictionless geartrain mechanism, since there always needs to be friction between wheels and ground to have something to push against.

ETA: 'nother question - could you achieve the same effect by deriving power for the propeller not from the wheels, but from a second passive (i.e. feeder) propeller of different efficiency to the first one?
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Old 16th April 2010, 06:34 PM   #39
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First, hi to Chris, Brian, and Modified. I remember each of you well from the original thread. Welcome to all others, some I recall posted on the earlier reincarnation but weren't among the regular punters.

Kudos on remembering that MichaelC spool video Chris. I should have included it in the OP. For a good chuckle, take a look at the comments under Michael's YT posts. He has developed a fan club of people in love with his voice and classic Oxford accent. They want him to keep talking no matter what the subject. Reading any book has been suggested-nay begged. It's a hoot. Michael is still very active on the TR thread, and I rib him about perhaps being able to convince humber with his melodious tones.

@Macdoc: Here's a link to a long comment today by Harold Bricer at TR: http://talkrational.org/showthread.p...554#post894554 Along with humber he supports your over unity POV, so you will probably find this post of interest.

Rats!! I forgot to mention we have a poll going on TR on what the NALSA test will reveal wrt percentage of windspeed. I'm one of the most conservative guessers, with a prediction of just 1.2 * ws. Spork's prediction was PI, and after Ivanpah he was far more confident it would be at least 3X ws. That seems unrealistically high to me, as even ice boats only exceed 3X ws by a bit going downwind, and then not directly but on a broad reach. I'd like to hear what others here at JREF think about this. And thanks to all for your input.

This just in: Here's a link to an interview spork did Thursday on The Bloomberg Report: http://www.facebook.com/video/video.php?v=382130502502 This one is about his day job, but I thought given he is in the center of the ddwfttw debunk the myth campaign some would find it of interest. I'm not actually a sports fan, but all here who are should give it a look.
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Old 17th April 2010, 12:34 AM   #40
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Quote:
3X ws by a bit going downwind, and then not directly but on a broad reach.
that would be correct

Quote:
he supports your over unity POV,
I'm not clear on why you think I support over unity....unless you are saying he supports my view of "over unity" being impossible without a vector.
Your post is not clear and I have no idea nor do I care who Humber is.

from your link
Quote:
There is NO way around this and anyone who tells you differently is a perpetual motion, over unity crank! There is NO way for a cart to go directly down wind faster than the wind powered by the wind!
this is correct
That said, birds and fish exploit turbulence all the time with micro-vectoring but they are so incredibly efficient at extracting energy they can do that...

•••

and to others....don't peddle pseudo Eureka moments just because you still don't get the very basic physical principals.

•••

Floyt
Quote:
So what's the theoretical limit on overall speed - is it bounded by friction?
assuming you throw out the directly downwind absurdity you then get into sailing theory with length of the hull in water as a major factor in speed ( the longer the vectoring edge the more energy gain ) against drag and sail efficiency.

This has implications for the directly downwind nonsense and should be required reading.
http://web.mit.edu/2.972/www/reports...sail_boat.html

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