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

[Brian-M]

Originally Posted by Snixtor

Ah so the propeller is genuinely acting as a propeller, not a turbine (the two terms seem to be getting thrown back and forth a bit, and even interchanged). It's the wheels that are effectively the "turbine", their rotation generating the power to turn the propeller.


Have I paraphrased this correctly above?

Yes.

Originally Posted by Snixtor

If that's the case, then that "push" no longer exists once the vehicle is travelling at the speed of the wind relative to the ground does it? And at faster than wind speed, it has a headwind that is pushing in the opposite direction.

Yes, but at that point the propeller is spinning fast enough to propel the cart by pushing air back against the wind (from the ground's frame of reference), or in the same direction as the headwind (from the cart's frame of reference).

The wind is traveling at X mph (relative to the ground), attempting to keep the cart at x, pushing it forward (tailwind) when it slows down, and pushing it backward (headwind) when it speeds up. But because the wheels are connected to the propeller, the propeller is pushing air backwards at y mph, allowing the cart to maintain forward motion against a headwind.

Originally Posted by Snixtor

Are the basic facts of this machine actually known? Like, which way the propeller is spinning, or is this a case of a machine being demonstrated and everybody speculating as to how it works?

The basic facts are known, and there's nothing secret or unknown about how it works.

Here's a link to Spork's 2008 design for a small working model (I think it's the same one he demonstrates running the "wrong way" along treadmills in many of the YouTube videos), along with a parts list and construction instructions so you can make your own...

http://www.rtfa.net.nyud.net/wp-cont..._plans_147.pdf

I got the link from this site, where Spork and others are discussing the cart.

ETA:

Originally Posted by Snixtor

Is there a particular post that offers explanation? Most of them are "attached part A to part B, here's a photo, doesn't it look great?".

It works exactly the same way my little animated cart would work in real life, except with a propeller connecting to the air instead of a wheel connecting to a belt/ruler.

If you can understand the principles of how that works, the propeller cart is the same. It's just a matter of gearing/leverage.

ETAA: If the belt is moving to the right, pushing the top wheel clockwise, it won't turn clockwise. Instead, the whole cart moves to the right fast enough that the top wheel turns counter-clockwise. The velocity of the cart equals the velocity of the belt plus the counter-clockwise motion of the wheel.

(There are videos where you can see carts built on the same principle in action.)

[Snixtor]

I can see how the treadmill cart with the propeller works. Power is applied to the wheels through the treadmill, which is converted to wind power by the propeller. The treadmill moves at say, 10mph, and the gearing forces air through the propeller at say, 12mph. Pardon my poor terminology, I know "speed" is probably not the right measure, it's acceleration, force, etc. But I'm simplifying.

For frames of reference, the ground is moving from right to left, the air is moving right to left, and the car is moving left to right. The air at one speed, the ground at another.

The device converts wheel power to wind power. The alternative use of it would be converting wind power to wheel power, but as configured for the treadmill experiment, this would need a headwind to generate wheel power. The wind moves right to left, the ground moves right to left at a slower speed.

I can see what you're suggesting by the wind "pressing" against the cart to push it forward, thus rotating its wheels, which in turn rotate the propeller for thrust. But I don't view this as being the same thing as demonstrated on the treadmill. The missing element in the treadmill demonstration is the "tailwind". What would happen if we generated this by placing a fan behind the treadmill and cart? Wouldn't this actually slow the cart down by countering the thrust generated by the propeller?

[recursive prophet]

@Snixtor: The answer is no, it doesn't slow it down but speeds it up. Imagine you are on a long treadmill going 10mph. You will feel a steady apparent wind of that speed as you move along, just as if you were sitting still in a steady 10mph wind.

If you or anyone else wants to look through all the many posts of tests spork has conducted on ddwfttw, just type in spork33 on YouTube search. The one where he blows on it with a fan is called "The Harold Bricer Test," as Harold also believed the fan would slow the cart down. It didn't.

Originally Posted by Brian-M

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?

Indeed he is Brian. Interesting you should ask, as a few days ago at TR I referred to your explanation well over a year ago regarding the molecular pocket around the balloon still being pushed en mass by the wind until it achieved wind speed. He has so many suitors on TR I think he missed my question, so I will soon repost it during one of the threads rare lulls.

My primary interest in this cyber-strand is from an anthropological perspective. I can tell you based on my observations the only threads that achieve real traction are ones where there are opposing positions. I have a feeling in years to come cyber-cultural anthropologists will hold entire conferences based on the humber phenomenon. One way or another, I think it will be acknowledged he had a rare genius in his ability to keep so many bright people who claimed they considered him an idiot coming back for more for a year and a half long period-and counting. You have to see it to believe it.

As humber didn't rejoin the discussion till over 3 months after it started at TR, it took part 1 114 days to reach the 2.5k cut off point. Since then, with humber in tow, the thread has reached that limit on average every 16 days. It's now on part 15, half way to 16.

Personally I find humber's arguments quite intriguing and instructive. They play off all the ways intuition and over-thinking can lead one astray on this subject, while generating a lot of interest and drawing in some very knowledgeable people. All think they can show humber and Harold where they are mistaken. None have succeeded after thousands of pages.

Originally Posted by macdoc

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.

Exactly. Sorry my presentation was unclear.

@Sol Invictus: You never answered my question about your theory spork and humber were the same person, or whether you remembered the story of George P. Burdell. Also, you and others haven't told me if you think 3x ws and beyond is probable?

[383LQ4SS]

I never followed the original threads since I am a latecomer to JREF...but I read this one and many of the attached links...as well as viewed the videos. Simply awesome! Well done!

Thanks also to those who gave concise yet simple explanations. The main point to make it click for me was that the wheels drove the propeller and not vice versa.

The machine in the vids did seem to have some trouble getting moving. More surface area could be added to the frame in the form of a traditional sail to get the initial push...but of course that would also hinder top speed once the cart was exceeding the wind speed. Of course you could make that sail retractable. Hoist the traditional sail for a fast take off from a stop....lower it for max speed when traveling faster than the wind.

[macdoc]

Quote:

My primary interest in this cyber-strand is from an anthropological perspective. I can tell you based on my observations the only threads that achieve real traction are ones where there are opposing positions.

ain't that the truth ..you should have to wade through the AGW denier swill....

[Snixtor]

Originally Posted by recursive prophet

Imagine you are on a long treadmill going 10mph. You will feel a steady apparent wind of that speed as you move along, just as if you were sitting still in a steady 10mph wind.

Could you rephrase or elaborate on that? It sounds like you're telling me that if I'm running on a treadmill at 10mph I will feel a 10mph headwind.

Originally Posted by recursive prophet

If you or anyone else wants to look through all the many posts of tests spork has conducted on ddwfttw, just type in spork33 on YouTube search. The one where he blows on it with a fan is called "The Harold Bricer Test," as Harold also believed the fan would slow the cart down. It didn't.

I've found a youtube video from spork33 that depicts a "Harold Bricer Test", but it doesn't show what I'm describing. In this they use a fan (with propulsion well in excess of the small propeller on the vehicle) to provide a headwind. I'm talking about putting a fan behind the vehicle, and not one that's so overpowered that it just blows the vehicle in whatever direction its blowing.

[Uncayimmy]

Originally Posted by Snixtor

Could you rephrase or elaborate on that? It sounds like you're telling me that if I'm running on a treadmill at 10mph I will feel a 10mph headwind.

I feel comfortable enough with this whole discussion to say that RP means that if you stood "still" on the treadmill and let it carry you, you'd feel a 10 mph headwind. There were some that argued that a moving platform and still aire were not equivalent to a stationary platform and moving air at the same speed.

[Snixtor]

Originally Posted by UncaYimmy

I feel comfortable enough with this whole discussion to say that RP means that if you stood "still" on the treadmill and let it carry you, you'd feel a 10 mph headwind. There were some that argued that a moving platform and still aire were not equivalent to a stationary platform and moving air at the same speed.

Mm, yeah, so running on a treadmill is equivalent to having a constant tailwind. If you start to move forward on the treadmill, relative to the ground, you start moving faster than this "tailwind", and experience a headwind.

[383LQ4SS]

I wonder if the prop is variable pitch. I would think it needs to be to reach peak performance.

ETA: actually...a variable pitch prop would do alot for this contraption. With the blades set flat...it would accelerate from a stop much easier and faster...but would do no better than a regular flat sail in terms of top speed in relation to the wind. Once moving....slowly increasing pitch will enable it to move faster and faster beyond the surrounding wind speed until too much pitch is added where it would begin to slow again. I am sure with any prop...there will be a "sweet spot" of blade angle for max speed. There should also be one for max acceleration...although that would likely be different at different speeds.

[recursive prophet]

Originally Posted by Snixtor

Could you rephrase or elaborate on that? It sounds like you're telling me that if I'm running on a treadmill at 10mph I will feel a 10mph headwind.

No, just standing on the treadmill, facing in the opposite direction as the cart does. Then the wind becomes a tailwind. That's what keeps the cart moving up the belt. It wouldn't in a vacuum. Same on the big cart. The prop is blowing into the tailwind, and the wheels turn the prop moving it beyond the wind's speed. Don't confuse force and velocity here; F=ma.

Quote:

I've found a youtube video from spork33 that depicts a "Harold Bricer Test", but it doesn't show what I'm describing. In this they use a fan (with propulsion well in excess of the small propeller on the vehicle) to provide a headwind. I'm talking about putting a fan behind the vehicle, and not one that's so overpowered that it just blows the vehicle in whatever direction its blowing.

DOH. Sorry. I conflated it with a test they did to show Harold the cart wasn't really functioning as a turbine and blew into it from the front. But there is a test video on spork33-humber suggested I think-where they blew on the prop from behind and it doesn't really slow it down. Both humber and Harold have also argued it is the ke created from holding the cart against the belt that allows it to advance for a brief period.

A user from here-y'not-made a circular treadmill to show this wasn't the case. It is in the 3rd link for JREF posts in the OP. http://forums.randi.org/showthread.php?t=130705 On this one humber maintained the arm holding the cart on the mill acted as a tether so there was still a transfer from the motor powering the TM. If humber doesn't get into that there, he likely did in the second link which is still on moderated status after the first reincarnation here. As always, humber managed to really draw a crowd, which soon became quite irate.

JMHO, but I think humber has an incredible sense of humor. Hardly a day goes by he doesn't provide a howler. If this thread survives I'll post links from TR to some of the pictures he's photo-shopped. Several show spork in clown outfits working on the big cart and all kinds of other hilarious pictures. I don't see how he keeps coming up with his new material, and he averages like 50 posts a day. Meanwhile spork has become a master of ironic sarcasm and also regularly cracks me up. I truly meant what I had in my earlier sig here-Best Show in the Metaverse.

AND....

[Brian-M]

Originally Posted by Snixtor

I can see how the treadmill cart with the propeller works. Power is applied to the wheels through the treadmill, which is converted to wind power by the propeller. The treadmill moves at say, 10mph, and the gearing forces air through the propeller at say, 12mph.

Yes. That's exactly how the cart works, on the treadmill or off it.

Originally Posted by Snixtor

For frames of reference, the ground is moving from right to left, the air is moving right to left, and the car is moving left to right. The air at one speed, the ground at another.

I think you might be mixing up frames of references here (unless by "the air is moving right to left" you're referring to the air coming from the propeller, in which case you're right, but I'll throw in the explanation anyway).

Take a huge treadmill in a room with no air movement.

For someone hovering over the treadmill in the balloon, the air is still and the "ground" (treadmill belt) is moving from right to left.

But for someone standing on the treadmill, the "ground" (treadmill belt), the "ground" (treadmill belt) is still and the air is moving from left to right.

It would be equally correct to say that the "ground" is moving and the air is still as it would be to say the "ground" is still and the air is moving, depending on whether you're looking at the system using the "ground" or the air as your frame of reference.

If you step outside and stand on an actual road with the wind blowing, the same thing applies. It would be equally correct to say the ground is moving and the air is still as it would be to say the ground is still and the air is moving, depending on whether you're looking at the system using the ground or the air as your frame of reference.

As far as the laws of physics are concerned, all frames of references are equally valid. Just think of the earth itself as a giant treadmill.

(Of course, the fact that the earth is curved and the surface is moving in a circle changes things a little, but not enough to have any effect on the scale we're talking about.)

Originally Posted by Snixtor

What would happen if we generated this by placing a fan behind the treadmill and cart? Wouldn't this actually slow the cart down by countering the thrust generated by the propeller?

Since the propeller is pushing back against the tailwind in order to push itself forwards (every action has an equal and opposite reaction), the more wind behind the cart the faster it goes. The cart is powered by the difference in the velocities of the air and the "ground". You're just giving it more power.

Putting the cart on a treadmill in a room with still air is exactly the same as putting it in a wind tunnel. Putting an object on a treadmill moving 10km/h right to left is exactly the same as putting that object in a wind tunnel with the wind moving 10km/h left to right.

Putting a fan behind the cart on the treadmill is the same as turning up the speed of the treadmill.

[Brian-M]

Originally Posted by recursive prophet

Indeed he is Brian. Interesting you should ask, as a few days ago at TR I referred to your explanation well over a year ago regarding the molecular pocket around the balloon still being pushed en mass by the wind until it achieved wind speed.

*sigh* It strikes me as bizarre that he can't grasp such a simple concept. I'm almost tempted to think that he actually does understand, but refuses to admit it out of pure stubbornness.

(I can't remember how the subject came up. Was it about whether or not any cart could, in theory on a frictionless surface, achieve wind-speed? Or was it about using bubbles as a measure of windspeed, and that the cart could be demonstrated as traveling faster than the wind by out-racing them?)

Originally Posted by recursive prophet

One way or another, I think it will be acknowledged he had a rare genius in his ability to keep so many bright people who claimed they considered him an idiot coming back for more for a year and a half long period-and counting. You have to see it to believe it.

I believe it. I spent far too long arguing with him as it is. What finally prompted me to stop was when the internet filter at work started blocking JREF, and as I didn't have a connection at home back then I had to get on through an over-priced internet cafe. I realized I was paying a lot of good money to argue with him, and that really brought home how absurd it was spending so much time arguing with him. Like a very bad version of a Monty Python sketch...

YouTube Video This video is not hosted by the JREF. The JREF 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

The "getting hit on the head lessons" would have been less painful.

[recursive prophet]

Sure wish I'd known you were going to post such a clear reply to Snixtor's questions, Brian. As you can see I really suck at explaining this stuff. Anyway, I'll leave you in Brian's capable hands Snixtor. I will tell you you're not alone in having trouble seeing the total equivalence between the treadmill and a cart in the wind. I don't believe my_wan, who started this discussion here-first link in OP-ever fully accepted that, and he's pretty sharp. Humber used to just say sporks cart had a wind allergy.

Heh, yeah humber really has a gift for frustrating people. The trick to appreciating him is suspension of disbelief. It's a lot like enjoying sci-fi. I'm happy to consider that despite all the evidence humber might be right. Hey, as far as I know only one Nobel physicist has weighed in on this-Dan Kammen. And HE said in an email to one of sporks fans that it would violate conservation of energy; same as humber and Christoph. Yes, I realize he's a busy guy and probably gave it about 2 minutes thought, is all. Still... See what I mean? Let others do the teaching and enjoy watching them get frustrated. spork mostly does that any more. He even makes funny sarcastic remarks like..."Ya know-I have good feeling about this. I think you've almost got humber convinced." :rofl:

[Uncayimmy]

Originally Posted by Snixtor

Mm, yeah, so running on a treadmill is equivalent to having a constant tailwind. If you start to move forward on the treadmill, relative to the ground, you start moving faster than this "tailwind", and experience a headwind.

There is no tailwind. Think of a people mover in an airport. The track is moving 5 mph relative to the air. When you stand on it, you start moving 5 mph relative to the air. Likewise, one could do that math and say that you and the track were stationary and the air was moving. Same results in the calculations.

If you turn around and start walking at 5 mph in the opposite direction of the track, you are stationary relative to the air. There is no headwind or tailwind.

[Snixtor]

Originally Posted by recursive prophet

equivalence between the treadmill and a cart in the wind

Which leads well to my next question...

On the treadmill, the power is being provided by the treadmill, through the wheels, to the propeller, pushing against the air. To swap the reference frame, to say that the air is moving and the ground is "still" would mean that the air pushes against the propeller which turns the wheels. In this case, it's a headwind that drives the carts wheels.

In the treadmill experiment, what is the tailwinds effect on the cart? My thinking is that it's reducing the drag, but it's not providing any thrust. The volume of air behind the treadmill isn't aiding the cart in moving forward, it's just providing some resistance from it moving backwards.

[Snixtor]

Originally Posted by UncaYimmy

There is no tailwind. Think of a people mover in an airport. The track is moving 5 mph relative to the air. When you stand on it, you start moving 5 mph relative to the air. Likewise, one could do that math and say that you and the track were stationary and the air was moving. Same results in the calculations.

If you turn around and start walking at 5 mph in the opposite direction of the track, you are stationary relative to the air. There is no headwind or tailwind.

I understand what you're saying, but I think you've misinterpreted what I've said. Running on a treadmill going 10mph in the gym you have no airflow relative to your body, but a 10mph relative to the ground. It's the equivalent of running outside with a 10mph "tailwind". If you're on the gym treadmill and run off the front of it (oops), you outrun this effective tailwind and experience a headwind. I'm sure we're on the same page there, just mixing terms and examples.

[Christian Klippel]

Originally Posted by Snixtor

Which leads well to my next question...

On the treadmill, the power is being provided by the treadmill, through the wheels, to the propeller, pushing against the air. To swap the reference frame, to say that the air is moving and the ground is "still" would mean that the air pushes against the propeller which turns the wheels. In this case, it's a headwind that drives the carts wheels.

The cart does not care where the power comes from. It interfaces the belt and the air, nothing else. It works on the difference of velocity between belt(ground) and air. On the treadmill, the treadmills motor provides the difference. Outside, the big fusion reactor in the sky (aka. the sun) provides it. If the cart would be stationary on the belt (that is, the belt dragging it through the air), it would experience a tailwind, not a headwind.

Originally Posted by Snixtor

In the treadmill experiment, what is the tailwinds effect on the cart? My thinking is that it's reducing the drag, but it's not providing any thrust. The volume of air behind the treadmill isn't aiding the cart in moving forward, it's just providing some resistance from it moving backwards.

Note that the treadmill experiments show the situation where the cart is brought up to windspeed already, and then released. It then accelerates further. The reason for that is that a treadmill is simply too short to allow for a self-start scenario. The equivalent outside would be a car or truck pushing the vehicle to windspeed, on the treadmill it is a hand holding the cart until the wheels/prop are up to speed.

Greetings,

Chris

[D'rok]

Originally Posted by macdoc

ain't that the truth ..you should have to wade through the AGW denier swill....

As a lurker in these and the AGW threads, I gotta say...you're in with the swill on this one.

Honestly. Not trying to put you down. Take a step back and examine your righteous certainty in this context. You're not dealing with Poptech here - these are real scientists and real engineers doing real work. Take a look at Spork's youtube videos and other related videos, read Drela's paper, and, if you can stomach it, wade through some of the threads.

Or don't. Just a friendly prod, is all. You do good work in the AGW threads.

[macdoc]

and if you read what I wrote you will see that I don't deny the phenomena - I deny the statement of what it is describing...

a) any use of a treadmill or turntable is useless crap as you have an outside power source of practically unlimited torque.

Quote:

directly downwind 2.5x Wind Speed?

That's the TANSTAAFL statement.

b) you won't be getting a laminar flow.

Harnessing turbulence is no great breakthrough..it's "interesting" to play with....no real world significance that I can ascertain.

Tell us, why the sail construction on the vertical poles??

There are all sorts of designs to capture wind energy

http://blog.modernmechanix.com/2007/...lightest-wind/

http://openlearn.open.ac.uk/mod/reso....php?id=254231

[sol invictus]

Originally Posted by recursive prophet

@Sol Invictus: You never answered my question about your theory spork and humber were the same person

I wouldn't have bet on that at straight odds even before, and it seems considerably less probable now. Spork appears to be a real person with a real job and real interests; to maintain a humberian persona over such a long time he'd have to be psychopathic beyond the point where I think he could function efficiently. But anything is possible...

Quote:

or whether you remembered the story of George P. Burdell. Also, you and others haven't told me if you think 3x ws and beyond is probable?

I'd forgotten about Burdell, but this would go well beyond that. As for 3x... that's purely a question of engineering. Directly dw vehicles have a major advantage (over sailcarts or boats) in that the apparent wind they see at Nx wind speed is only (N-1)x. So 3x wind speed may well be possible; the cart will see only a 2x apparent wind, which makes air resistance less of an issue.

So I'd say yes, I think it's possible, and probably will be achieved soon (if it hasn't already) by spork and co.

[sol invictus]

Originally Posted by macdoc

and if you read what I wrote you will see that I don't deny the phenomena - I deny the statement of what it is describing...

Your posts are generally incoherent to the point that it's very difficult to determine what you think.

Quote:

a) any use of a treadmill or turntable is useless crap as you have an outside power source of practically unlimited torque.

You mean, like the wind?

Quote:

That's the TANSTAAFL statement.

b) you won't be getting a laminar flow.

Nonsense.

Quote:

Harnessing turbulence is no great breakthrough..it's "interesting" to play with....no real world significance that I can ascertain.

More nonsense. To my knowledge there are no wind-powered devices that operate that way. Turbulence is usually a problem for them; for example that's why windmill turbines are generally positioned upstream of the tower they are attached to.

As for "real world" applications, you don't consider this cart to be an object in the real world?

[D'rok]

Originally Posted by macdoc

and if you read what I wrote you will see that I don't deny the phenomena - I deny the statement of what it is describing...

a) any use of a treadmill or turntable is useless crap as you have an outside power source of practically unlimited torque.


That's the TANSTAAFL statement.

b) you won't be getting a laminar flow.

Harnessing turbulence is no great breakthrough..it's "interesting" to play with....no real world significance that I can ascertain.

Tell us, why the sail construction on the vertical poles??

There are all sorts of designs to capture wind energy

http://blog.modernmechanix.com/2007/...lightest-wind/

http://openlearn.open.ac.uk/mod/reso....php?id=254231

http://i106.photobucket.com/albums/m...307_1_026i.jpg

You're applying the wrong expertise to the wrong problem. Turbulence has nothing to do with what is happening. And the treadmill is a valid proof of concept. Where's the turbulence there? Why do you think it is different in principle than a steady wind? Why does the cart move up the treadmill? As silly as it is, the faster than the ruler video shows why.

The science types can explain it better than I.

As an aside, the treadmill experiments helped my liberal arts brain get a basic grasp of relative motion.

[macdoc]

No a treadmill is not "proof of concept" and no I'm not going to explain nor wade into the nonsense.
You are on your own if you choose to be deluded.

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there

TANSTAAFL



This from the 50s
http://www.dcss.org/bauer_cart.jpg

[D'rok]

Originally Posted by macdoc

No a treadmill is not "proof of concept" and no I'm not going to explain nor wade into the nonsense.
You are on your own if you choose to be deluded.

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there

TANSTAAFL



This from the 50s
http://www.dcss.org/bauer_cart.jpg

Yes the cart requires wind (or a treadmill) to move. Duh.

As to the rest. Well...arrogant ignorance rocks!

Best.

[sol invictus]

Originally Posted by macdoc

No a treadmill is not "proof of concept" and no I'm not going to explain nor wade into the nonsense.
You are on your own if you choose to be deluded.

Evidently by spending your time arguing with AGW deniers, you have adopted their way of thinking - be unwilling to consider any evidence, ignore the laws of physics as understood for the last 400 years (that is what you are denying by ignoring the equivalence of the cart on the treadmill to a cart in the wind), then salt liberally with unwarranted arrogance.

Quote:

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there

And there's a tasty strawman for desert. No one disagrees with that - the cart does not work without wind.

[Modified]

Originally Posted by macdoc

No a treadmill is not "proof of concept" and no I'm not going to explain nor wade into the nonsense.
You are on your own if you choose to be deluded.

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there

The equivalent situation would be the cart on the treadmill with a treadmill-speed headwind (no wind with respect to the surface). The cart would behave exactly the same with respect to the surface there as in your example: it would stay at surface speed if at surface speed and return to surface speed after being pushed.

[Christian Klippel]

Imagine science would work like macdoc. Then we would still have the sun revolving around a flat earth. Because anything else would be TANSTAAFL.

Lucky for us that this is not how science works.

Greetings,

Chris

[Myriad]

I don't understand macdoc's point about turbulence either. While the operation of the propeller (and the cart itself, in the wind) will inevitably create some turbulence, that is not to the cart's advantage, and no turbulence is necessary (or desirable) in the initial conditions either.

Since all of the cart's mechanisms will, as far as I can tell, work at any Reynolds number, it might help to imagine starting with a 1 mm/sec flow of oil down a duct, and a slow moving cart with a slow moving propeller that goes down-oil faster than the oil. No turbulence before or after. (Traction for the wheels against the duct would be an engineering issue but doesn't affect the principles. I'd suggest making the oil stationary, a simple oil bath, and simulate "down-oil motion in moving oil with wheel traction against a stationary duct" by replacing the wheels with a spool with thread wrapped around it, and pulling the thread backward from outside at the same 1 mm/sec. Down-oil faster than the oil propulsion would be demonstrated by the device moving away from the thread puller, while unwinding more thread from its spool than is taken up by the pulling spool. All with no fluid turbulence. But that might revive all those tiresome treadmill arguments.)

Respectfully,
Myriad

[Myriad]

Originally Posted by macdoc

This from the 50s
http://www.dcss.org/bauer_cart.jpg

So, it worked in the 50s but it wouldn't work today?

Respectfully,
Myriad

[ynot]

At the very beginning the wind pushes against the frame of the cart and propeller but never directly spins the propeller as a turbine.

The wind indirectly spins the propeller via the rotation of the wheel(s) to create thrust against the wind. This is possible using appropriate gearing.

When the cart reaches and exceeds the speed of the wind the propeller is still thrusting against air in the direction of the wind.

Effectively the propeller acts as a sail with thrust.

[Snixtor]

Originally Posted by Christian Klippel

The cart does not care where the power comes from.

The cart may not, but we clearly do.

Originally Posted by Christian Klippel

It interfaces the belt and the air, nothing else. It works on the difference of velocity between belt(ground) and air.

Absolutely, but what is that difference? On the treadmill, the cart wheels are turned by the treadmill, the wheels turn the propeller, the propeller pulls air past the cart. If we change our frame of reference, its not the ground that is moving, but the air that is moving. But in which direction is the air moving? Massively from the front of the cart to the back of the cart. To "reverse" the reference, you need a headwind, relative to the carts direction on the ground, not a tailwind.

The important thing to derive from "under the ruler faster than the ruler", is that when he holds the ruler still and moves the ground, the ground is going in the same direction, relative to the cart, as when he moved the ruler. Ruler to the right, ground to the left.

On the treadmill, relative to the cart, in which direction is the air moving? It is moving from the front of it, to the back, thanks to its propeller. If we are not moving the ground from the front of the cart to the back of the cart, we must instead move the air from the front of the cart to the back of the cart. Much as with "under the ruler", he could move the ruler to the right, or the ground to the left.

Originally Posted by Christian Klippel

Note that the treadmill experiments show the situation where the cart is brought up to windspeed already, and then released. It then accelerates further.

And what provides that acceleration? The rotation of the wheels. And what provides the rotation of the wheels? Its forward motion. And what provides its forward motion? The wind pushing on the back of it. Once it is going faster than that wind, its no longer pushing on the back of it. The physics then enter a closed system where:
What is making the cart move forward? the propeller
What is making the propeller spin? the wheels, due to the carts forward motion.
What is making the cart move forward? - etc.

It would effectively be boot-strapping itself (many of us will have heard this term, whereby a man stands on the ground, then pulls upwards on the laces of his boots, thus pulling himself into the air and levitating).

I'm convinced there's something wrong with using the ruler above the cart to represent the air. My first clue is that the cart under the ruler doesn't need a boost to get going. The system doesn't change the rules at a certain speed, the same principles apply at any speed.

[Brian-M]

Originally Posted by macdoc

No a treadmill is not "proof of concept" and no I'm not going to explain nor wade into the nonsense.
You are on your own if you choose to be deluded.

I'd like to hear your reason as to why the treadmill is not "proof of concept". It should be good for a laugh. Come on, tell us why you think that such a very basic and long-standing principle of physics as "there are no preferred frames of reference" is invalid, and why we are deluded if we think it applies.

Motionless surface with moving air exactly the same thing as motionless air and moving surface. It's the same thing from different frames of reference. Just because you can't grasp this simple fact doesn't make it "nonsense".

Originally Posted by macdoc

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there

The cart on the treadmill has a difference between ground speed and air speed to exploit. Put the cart on the floor where the same difference between air speed and ground speed exists and it will move... exactly the same way it does on the treadmill. It's been demonstrated to do this in real life. It's a proven fact, not just some wild theory.

[r-j]

Some people never let the facts get in the way of the truth.

[macdoc]

Not sure bm understands the irony of his statement

[Brian-M]

Originally Posted by Snixtor

Absolutely, but what is that difference? On the treadmill, the cart wheels are turned by the treadmill, the wheels turn the propeller, the propeller pulls air past the cart.

It would be equally valid to say that on the street, the cart wheels are turned by the earth moving under the cart, so no difference between that and the treadmill there.

Originally Posted by Snixtor

If we change our frame of reference, its not the ground that is moving, but the air that is moving. But in which direction is the air moving? Massively from the front of the cart to the back of the cart. To "reverse" the reference, you need a headwind, relative to the carts direction on the ground, not a tailwind.

If the cart is facing in the right direction to move to the right, then by placing it on the ground, you have a tailwind moving from left to right, relative to the ground. From the back of the cart to the front of the cart until the cart reaches windspeed.

If the cart is facing in the right direction to move to the right, then by placing it on the treadmill, you have a tailwind moving from left to right, relative to the belt. From the back of the cart to the front of the cart until the cart reaches windspeed.

Exactly the same physics, no reversal of wind needed. Of course, as the cart starts to go over wind-speed, then you do get a headwind, from front to back relative to the cart in both cases, which reduces the maximum speed of the cart.

Originally Posted by Snixtor

The important thing to derive from "under the ruler faster than the ruler", is that when he holds the ruler still and moves the ground, the ground is going in the same direction, relative to the cart, as when he moved the ruler. Ruler to the right, ground to the left.

Moving the ground under a still ruler is the same difference as moving the ground (treadmill belt) under still air.

Originally Posted by Snixtor

And what provides that acceleration? The rotation of the wheels. And what provides the rotation of the wheels? Its forward motion. And what provides its forward motion? The wind pushing on the back of it. Once it is going faster than that wind, its no longer pushing on the back of it. The physics then enter a closed system where:
What is making the cart move forward? the propeller
What is making the propeller spin? the wheels, due to the carts forward motion.
What is making the cart move forward? - etc.

But remember, the air is not stationary relative to the ground, and the propeller is "pushing" back against the wind. If the wind is traveling 10km/h to the right, and the propeller is pushing air 5km/h to the left, then you have the same effect on the moving prop as would a 15km/h wind on an immobile prop.

Originally Posted by Snixtor

I'm convinced there's something wrong with using the ruler above the cart to represent the air. My first clue is that the cart under the ruler doesn't need a boost to get going. The system doesn't change the rules at a certain speed, the same principles apply at any speed.

The difference between the ruler-cart and the propeller cart is friction. The ruler driven cart has a very high level of friction and energy transfer between the ruler and the top-wheel even when stationary. The propeller driven cart has a very low level of friction and power transfer between the air and the propeller when stationary.

Using a very slippery ruler would be a better analogy for the wind.

[recursive prophet]

Originally Posted by macdoc

hint - put said cart on floor....does it move? ..no
even with a push does it continue? no
start from there.

Of course after a couple thou pages most possible arguments have already been made ad nauseum mac, and this one has been mentioned many times by deniers. You have to accept that from the RF of the cart on the TM that everything in the room is at WS. Hope I can find the humber photo-shop gem where he puts signs on objects in spork’s shop saying “At Wind Speed.”

I won’t take the time to recap that discussion, but will hopefully find some links where it is explained far better than I could even approach and post them for you. I really would like to see you follow up on this, and would be willing to bet you’ll see the light if you do. You can’t imagine how many I’ve seen even more adamantly positive than you that ddwfttw is an over unity farce who became converts in a few pages. I for one would be extremely grateful if you’d continue to post your viewpoints, just to see if it happens with you. You’re a smart guy, and I’m always on the lookout for more support for humber’s claims. I’m a dull bulb on a very bright marquee. While many of his diatribes seem to contain elements of truth, the Humberverse is still difficult for me to grok even though spork thinks I summer there. Help me understand your reasoning and we all might learn in the process.

I would ask everyone to notch up the civility just a bit wrt any who question the claims put forth in the OP. I’m trying to get Kammen and Drela to join this discussion, which I wouldn’t dream of doing at TR. If you want to be part of a gloves off slugfest, take it there. (Link on my sig) It’s the wild west of cyberspace, and loads of fun. But academia wouldn’t even want to be mentioned there, let along participate. So take a deep breath and the high road. He who ignores snide remarks always scores more points. It’s all pure glasperlenspiel after all.

Originally Posted by sol invictus

I wouldn't have bet on that at straight odds even before, and it seems considerably less probable now. Spork appears to be a real person with a real job and real interests; to maintain a humberian persona over such a long time he'd have to be psychopathic beyond the point where I think he could function efficiently. But anything is possible...

Especially in the realm of virtual reality, eh sol? I definitely agree it’s a long shot, and that spork is the real deal. I had an hour long Skype chat with him a year or so back, and no question he’s a heavy hitter. Yet I know next to nothing about humber or Harold, though I’ve exchanged many emails with humber and PM’s with Harold/Christoph. At some point I’ll reveal my different theories, including a few tidbits I know about the whole scene that others don’t. But I’m pretty sure the whole George Burdell legend plays a more significant role than you suspect due to spork’s connection with it. Many possibilities.

Originally Posted by Myriad

I don't understand macdoc's point about turbulence either. While the operation of the propeller (and the cart itself, in the wind) will inevitably create some turbulence, that is not to the cart's advantage, and no turbulence is necessary (or desirable) in the initial conditions either.

I think what macdoc has in mind is that under the right conditions the cart could ride the transients between gusts. humber made a good case-at least for the great unwashed like me-that this was exactly what happened in Bauer's experiments.

The wind has a 20 second gust at 25mph, then drops back to say 10mph. At that point the cart's mass will have enough ke to exceed that speed for how long? Beats me, but I'm sure sol could maths it out. This is one of the reasons spork build the treadmill model; a steady state apparent wind. There is a video of it running on the ground in the YT spork33 collection, including a race with a turbine cart. These tests were mostly in response to arguments made by Harold and humber, who claimed the turbine would win. It didn't, but of course H&H found some ostensible flaws in how the test was conducted. Laurel and Hardy Do a Science Test was the title on one of humbers more hilarious parodies.

I really hope someday a lot more people read this saga. You learn a lot of interesting science from those trying to explain to humber how he fails to grasp reference frames; relative motion; air foils; prop vector analysis; GPS tracking; Galileo; Newton;.... You get the picture. And you get to laugh as you learn!! There are a few silly seasons, but I've never read anything anywhere that elicited as many belly laughs.

I like your oil analogy Myriad, and something like it has been discussed before. However, after two thousand pages of replies between the 3 sites everything starts to get fuzzy and hard to find for the search challenged like me. I'm in my dotage, and tend to conflate a lot; to wit the Harold Bricer Test. But I know at least one chemistry buff posted a fluids model. If I come upon it I'll send a link.

Liking your exchanges with Brian, Snixtor; keep asking questions. And hi to the yguy. Glad to see you here. Your dialogue at TR with cold one and spork on billiard balls was a classic. Definitely admire your style.

[macdoc]

Quote:

Quote:

Originally Posted by Myriad
I don't understand macdoc's point about turbulence either. While the operation of the propeller (and the cart itself, in the wind) will inevitably create some turbulence, that is not to the cart's advantage, and no turbulence is necessary (or desirable) in the initial conditions either.

I think what macdoc has in mind is that under the right conditions the cart could ride the transients between gusts. humber made a good case-at least for the great unwashed like me-that this was exactly what happened in Bauer's experiments.

Under all real world wind conditions - there will always be vectors and using a treadmill for anything involving this is hilariously wrongheaded..

The turbulence is not from the vehicle tho prop tip vortices may have some sort of impact on efficiency...
..think about vectors and how energy is gained to drive the speed above the wind speed.....and why nothing happens sitting on the floor.

Visualize instantanteous high efficiency tacking as to why turbulence allows energy harvesting.
How is that ship I posted working? ..it can absorb energy from various directions...

In a laminar flow it simply will not happen in the same manner as that flow is smooth and uni-directional....

for starters the windspeed in the real world is an average of the gusts....it's one reason they state .....60 kph wind gusting to 80 kph....well it's ALWAYS gusting up and down....there is likely no laminar flow in nature.

Unless you can see why the treadmill with its ..for practical purposes in these kind home experiments...infinite torque...you'll flounder.

[jsfisher]

So what would be a valid experiment to distinguish between your explanation and others?

[Myriad]

Originally Posted by Snixtor

And what provides that acceleration? The rotation of the wheels. And what provides the rotation of the wheels? Its forward motion. And what provides its forward motion? The wind pushing on the back of it. Once it is going faster than that wind, its no longer pushing on the back of it. The physics then enter a closed system where:
What is making the cart move forward? the propeller
What is making the propeller spin? the wheels, due to the carts forward motion.
What is making the cart move forward? - etc.

It would effectively be boot-strapping itself (many of us will have heard this term, whereby a man stands on the ground, then pulls upwards on the laces of his boots, thus pulling himself into the air and levitating).

I'm convinced there's something wrong with using the ruler above the cart to represent the air. My first clue is that the cart under the ruler doesn't need a boost to get going. The system doesn't change the rules at a certain speed, the same principles apply at any speed.

E pur si muove (ocius quam ventus)!

Let's look again at the situation when the cart is moving at just below wind speed. The wheels are turning, so the propeller is turning. If the propeller blades were flat, with zero pitch (making the propeller just a funny-shaped sail, whether it's spinning or not), then the wind is (just barely) pushing on the propeller and the cart frame, the drag from the road and the propeller mechanism acting on the wheels is (just barely) pushing back on the wheels. At that point, just below the wind speed, we're at equilibrium, so the cart does not accelerate.

(If the same condition were simulated on a treadmill, the cart would drift slowly backward on the treadmill. The force applied by the still air against the cart frame and the propeller-shaped sail would be not quite enough to hold the cart in place, just as outside in the wind, the wind force is not quite enough to push the cart all the way to wind speed.)

Now we add some pitch to the propeller, so that (relative to the cart) it pushes air backward when it spins. The propeller must continue spinning because the wheels are spinning. So the propeller is adding some additional thrust, accelerating the cart toward windspeed... and beyond...

And this is where a lot of people's woo meters, understandably, but mistakenly, go off! ALERT! ALERT! IMPOSSIBLE! OVER UNITY! WOO!

Because of course, for the cart to accelerate past wind speed, it has to gain kinetic energy. Specifically, it has to gain more kinetic energy from the thrust generated by the spinning propeller that it loses from the wheels doing the work of spinning the propeller. And that's impossible.

Except, it isn't.

Because spinning the propeller, which is what the wheels do, isn't what actually provides the thrust. What provides the thrust is the tail wind, the same tail wind that pushed the cart from a standing start, pushing against the spinning propeller.

What the spinning of the propeller does is provide a dynamic surface that's moving at the right speed for the wind to push against. For the wind to push the cart, it needs a surface to push against that's effectively moving slower than the wind. That means, when the cart is moving downwind near, at, or beyond wind speed, the dynamic surface must be moving slower than the cart with respect to the ground, and backward with respect to the cart. An angled surface moving across the wind -- such as a propeller blade or an ice boat's sail -- can do that.

[Lengthy digression:] There are other less elegant ways to do it. Here's a cart that uses simple sail drag (represented by the parachutes) to move faster than the wind:



When this cart moves to the right relative to the ground, the parachute at the top also moves to the right relative to the ground. But it doesn't move to the right as fast as the cart does, because it's being wound to the left (relative to the cart) by the movement of the wheels and rope.

Pushing the parachutes forward moves the cart forward (faster than the parachute) in exactly the same way that, in the "faster than the ruler" video, the ruler pushing forward on the top of the large wheel moves the cart forward faster than the top of the wheel.

So, when the cart is moving at wind speed, the parachutes are moving backward with respect to the cart, and therefore slower than the wind. So the wind can still push forward on the parachutes, accelerating the cart.

That's a different (and cruder) kind of "dynamic surface moving at the right speed for the wind to push against when the cart is moving at or beyond wind speed" than the propeller, but it serves the same function. [end of lengthy digression]

In still air, if you propel a vehicle with a propeller, the kinetic energy of the vehicle derives from the energy put into the propeller, which creates thrust acting over a distance. Given inevitable inefficiencies, the vehicle's resulting kinetic energy be less than the energy put in. That's why you can't just link the wheels to the propeller, give it a push, and expect it to accelerate or even keep going.

But in the downwind cart, the thrust is provided by the wind, not the energy used to spin the propeller. So one cannot assume (and it turns out it is not correct to say) that the propeller must take away more energy from the cart's KE (via the wheels) than can possibly be imparted to the cart's KE from the propeller's thrust. When the cart is moving near wind speed, the power needed to spin the propeller is less than the power of the wind pushing on the spinning propeller. The cart actually does gain kinetic energy and hence goes faster. The wind is slowed and loses kinetic energy.

Respectfully,
Myriad

[recursive prophet]

This is spork's ready for prime time cart: The Blackbird. It was just posted on his blog. I think any interested in this topic really should check it out via the link in my sig, and sign on to follow it. They've done a terrific job documenting the entire construction process, including test videos. A great read also.

@Myriad: Some intriguing posts here; thanks for sharing. I look forward to reading mac and Sniks response to your latest. I'm also hoping sol, Brian, and others will comment on it it. Kinetic energy transfer seems to be at the core of this debate, along with drag and thrust. My initial impression is that some of your thinking circumvents the aggregate consensus, but I'll leave that for the cognoscenti here to analyze. In my chosen roles as janitor, facilitator, and observer, I've learned not to overreach my limited capabilities. Very interesting explanation, no matter.

@staff: I have permission from spork to post this picture from his blog and can document this if required. Thanks.