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Wind powered prop cart goes directly downwind 2.5x Wind Speed?

recursive prophet

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recursive prophet
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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/forums/showthread.php?t=128483
http://www.internationalskeptics.com/forums/showthread.php?t=131646
http://www.internationalskeptics.com/forums/showthread.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
 
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.
 
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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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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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 :p
 
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recursive prophet said:
A thread that began at JREF back on 11/9/09,
Click to expand...

11/9/08. Don't sell it short!

Modified said:
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.
Click to expand...

Seconded.

casebro said:
Next logical step ought to be an airplane with one prop to power another prop that pulls the plane through the air.
Click to expand...

You do understand why that doesn't work (but this cart does), right?
 
macdoc said:
explain away....:popcorn1
Click to expand...

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).
 
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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macdoc said:
and just what happens to said turbine when ground speed = windspeed ?
Click to expand...


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).

TANSTAAFL
Click to expand...


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

Respectfully,
Myriad
 
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.
 
Modified said:
The tests were impressive, but even more impressive is the fact that humber is still at it.
Click to expand...

Oh god, he's still at it? :bwall 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? :scared:

casebro said:
Next logical step ought to be an airplane with one prop to power another prop that pulls the plane through the air.
Click to expand...

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:

macdoc said:
and just what happens to said turbine when ground speed = windspeed ?
Click to expand...

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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What turbine?

The cart doesn't have a turbine, it has a propeller
Click to expand...
SIGH :boggled:

your're at THAT stage of misunderstanding??

turbine = propeller...see myriad:rolleyes:

••

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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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 F****** Cart, or BUFC. Now they have abandoned that handle; likely at the bequest of their sponsors.:D 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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macdoc said:
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..
Click to expand...

Anddddddd.... here we go again :D


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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