Wind powered prop cart goes directly downwind 2.5x Wind Speed? - Page 23

Ririon · 2nd September 2010, 07:18 AM

Originally Posted by quarky

My little de-rail feels better now. Anyone care to describe the mechanics of 'pumping' a swing? Obviously, it works, but I find the physics somewhat baffling. I have a swing with 2 lines and a spacer, with a single line above that, to the tree branch. It can't be pumped.

Sure it can. If it is longer than a usual swing, you just use a lower frequency. It is an own frequency thing. Unless you immediately start to spin uncontrollably, of course. Then it gets difficult.

BTW: There is a new Japanese computer game out now based on racing office chairs and other less than optimal racing vehicles.

CNY_Dave · 2nd September 2010, 09:47 AM

DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand.

Also desirable because then his hand wasn't dragging through the wet ink.

Dave

quarky · 2nd September 2010, 01:45 PM

cool

GrouchoMarxist · 2nd September 2010, 05:54 PM

Originally Posted by CNY_Dave

DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand.

Also desirable because then his hand wasn't dragging through the wet ink.

Dave

This is a part of the equation I hadn't previously considered.

BowlOfRed · 2nd September 2010, 10:39 PM

Originally Posted by quarky

My little de-rail feels better now. Anyone care to describe the mechanics of 'pumping' a swing? Obviously, it works, but I find the physics somewhat baffling. I have a swing with 2 lines and a spacer, with a single line above that, to the tree branch. It can't be pumped.

There's a way to think of it in two parts (A simplification. You don't really need the first part). The first part is to get the center of mass just a bit off-center from the pivot. Pushing yourself front-back easily does that with air resistance or a bit of friction in the line.

With a bit of motion to the swing, the second part is to use the motion to pump energy into the system. Imagine a swing with a weight at the bottom that can be moved between two positions, one closer to the pivot and one further away. If the weight is moved from the further to the closer position while the swing is at the bottom, work is done to increase the gravitational potential of the weight. By returning to the same position when the swing is away from the bottom, the gravitational potential is decreased again, but not as much due to the angle. So this process can be repeated to drive energy into the system. At very small angles, you can't put much energy in with this mechanism.

I don't know exactly what's happening with the swing you describe, but it could be that it's just got a lot more "wobble" than more common swings. That could make it more difficult to get some initial swing going, so your pumping is very inefficient. But once it's off-center, there should be no difficulty in pushing energy in.

BowlOfRed · 2nd September 2010, 10:50 PM

Hmm. Okay. So I've heard that before and mathematically it's a simple answer (and possible). But while looking for a graphic to append to my post, I found this page that says it's not actually the mechanism used. Makes sense, but I'd never come across it before.

http://www.grinnell.edu/academic/phy...ty/case/swing/

quarky · 3rd September 2010, 06:16 AM

Originally Posted by bowlofred

Hmm. Okay. So I've heard that before and mathematically it's a simple answer (and possible). But while looking for a graphic to append to my post, I found this page that says it's not actually the mechanism used. Makes sense, but I'd never come across it before.

http://www.grinnell.edu/academic/phy...ty/case/swing/

Great link. It explains the matter well. My single line swing allows too much twirl, which tends to neutralize the gains.

CNY_Dave · 3rd September 2010, 05:07 PM

Originally Posted by CNY_Dave

DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand.

Also desirable because then his hand wasn't dragging through the wet ink.

Dave

dang... how'd that end up here?

recursive prophet · 3rd September 2010, 07:56 PM

Originally Posted by D'rok

Are Humber and Harold really and truly gone? They've left the Internet?

Won't somebody please think of the lurkers?

Amen D'rok! We lurks just don't get no respect. Heck, I'll bet traffic on the entire TalkRational site still hasn't recovered from H&H dropping out. I've beseeched humber to come back in emails, but got no reply. I only hope he hasn't been the victim of foul play, and if he has that spork at least has a solid alibi for whenever it happened.

Below is a post from a retired Russian mathematician who believes he sees a way the prop could be redesigned to achieve higher speed for the Blackbird. This one begins Cartville Saga part 17, where he uses a hypothetical iceboat to launch his thesis. If you scroll down from HERE you can follow the discussion, and on the following pages nicvic presents a hodograph to make his case. Only one user on TR-'A.T.'-has had both the patience and maths background to try and understand exactly what his premise is. I'm hoping sol invictus and some of the other cognoscenti here will take a look and see what they make of his claims. Speaking Russian would be a big help.

Originally Posted by nikvic

(K= lift-drag ratio)

I again began to discuss the thesis -

fixed step and transmission
do not allow to achieve maximum speed.

As an analogue treated with ice boat fixed wing and a fixed rate.

The main reason - the angle of attack varies from ~ 160 degrees
to the optimum of ~10 degrees in the process of overclocking.

"Good" value of K - only near the ~10 degrees.

recursive prophet · 5th September 2010, 01:48 PM

I hate doing a double post on this thread, but I’d really like to get some input on what nikvic is asserting on TR. If you CLICK HERE. you can see a description of how the cart works that he cited. I had to fix the link he posted, and his following comments about it appear below. Does anyone remember who wrote this?

Originally Posted by nikvic;

It's all right, but the equations describe only cruising mode. Start-up is described in the language of forces and moments - for the propeller. For the wing enough language forces - so I still have only used this language.
Let Vx <<W, the screw is almost motionless. The air acts on the screw with a force T and moment M.
It is convenient to assume that the transmission is always 1:1, and the equivalent radius of the wheels (including transmission) = R.

To speed up the necessary R> M / F. This radius is very large for a positive step screw.

In the clips show how difficult to pick up speed.
For records at cruising equivalent radius can be smaller - and records will be higher.

Some interesting follow up exchanges to nikvic’s above reply were made by him and A.T. in just the last hour or so, which begin HERE. If you’re not a TR member, just post any responses in this thread and I’ll be sure nikvic sees them.

AIRPLANEHUNTER · 10th July 2012, 07:49 AM

I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010.

While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not?

So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it?

If so, can someone point me to the definitive accepted full explanation?

Jack by the hedge · 10th July 2012, 08:07 AM

Welcome to the forum, AIRPLANEHUNTER.

I think the dearth of activity is simply that the small number of vocal individuals who thought it must be impossible eventually ran out of things to say in the face of the evidence.

By coincidence, the team have just recently got through a series of directly upwind tests, and they hope to have a new upwind speed record ratified shortly.

spork · 10th July 2012, 08:11 AM

Quote:

This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not?

We have explained it, documented it in detail, demonstrated it in front of a critical and disinterested 3rd party and any witness that chose to show up, posted detailed build videos so that anyone else could build their own small working model (which several have), and spoken on the topic at AIAA, NASA, Google, Stanford, SJSU, etc.

The science has been done. The math is quite simple. I'm happy explain it here if you like. I have perhaps a dozen different explanations, at least one of which should work for anyone approaching it with an open mind. Or you can read one of the simple analyses like the one I've attached below.

Modified · 10th July 2012, 08:15 AM

Originally Posted by AIRPLANEHUNTER

I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010.

While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not?

So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it?

If so, can someone point me to the definitive accepted full explanation?

The whole question was satisfactorily explained many times, the cranks just refused to accept it. The easiest thing is to look at the "down ruler faster than the ruler" cart, and realize that the dwfttw cart does the same thing, only with a prop interface to the wind instead of a wheel interface to the ruler.

H'ethetheth · 10th July 2012, 08:17 AM

Originally Posted by AIRPLANEHUNTER

I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010.

While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not?

So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it?

If so, can someone point me to the definitive accepted full explanation?

The discussion stopped here because the discussion got too heated, then moderated, and then fizzled and moved to another forum, mostly talkrational. The discussion went on there quite a bit*, though it's mostly a question of two stubborn cooks refusing to accept the mountains of evidence and explanations thrown at them.
Also, the team has now managed to adapt the car for upwind travel and are in the process of having a record ratified for traveling upwind faster than the wind.

The definitive accepted explanation would, I think, consist of the papers by Andrew Bauer, Mark Drela and Mac Gaunaa. The wikipedia article about sailing faster than the wind has links to most of these, I think.

* quite quite a bit: 37 consecutive threads and counting

3point14 · 10th July 2012, 08:17 AM

We're doing this again?!

Ace!

I'll catch up on the thread - Who's decided to be the only one who can see the obvious flaws in the DDWFTTW machine in the face of thought experiments, published papers and an actual working machine.

DrDave · 10th July 2012, 08:56 AM

Originally Posted by 3point14

We're doing this again?!

Ace!

I'll catch up on the thread - Who's decided to be the only one who can see the obvious flaws in the DDWFTTW machine in the face of thought experiments, published papers and an actual working machine.

Facts schmacts. That thing is unpossible!

DC · 10th July 2012, 09:01 AM

the whole thing is a hoax by the windpowered automobile industry.

AIRPLANEHUNTER · 10th July 2012, 02:29 PM

Thank you, Jack, Spork, Modified, and H'ethetheth. I appreciate the generosity of spirit of you gentlemen in sharing with this newbie who is fresh to the whole subject.

I was taking a vacation up to Maine last week and visited an old college roommate who is a life-long one-design sailor. He showed me the video of the Blackbird and as I am a small airplane pilot and amateur aerodynamicist (I majored in music) we talked aerodynamics and physics.

I was fascinated by the implications of the video and I had no problem with down-wind or up-wind travel using a well designed propeller/turbine and an efficient wheel drive system. I grasped that the practical limits of a land-propelled vehicle will be bounded by the traction/friction of the wheels against the ground medium and the overall aerodynamic and mechanical efficiency of the vehicle.

The only thing I am stumbling on is the downwind run transition through the becalmed state. I can see that when ever one has a relative wind it has potential energy that can be extracted. But when the vehicle is completely becalmed, the only energy in the system that I can see is the kinetic energy available from the moving prop or the moving vehicle relative to the ground. Tapping either one of these energy sources would involve some drag and slow the vehicle. I comforted myself by thinking that minor gusts could provide a energy source to tap to accelerate into the relative headwind, but if the wind was indeed absolutely steady, I'm still confused.

So I'm looking forward to reading the paper provided by Spork to get what I am obviously missing here.

Again, many thanks for your kindness to this neophyte.

Jack by the hedge · 10th July 2012, 02:39 PM

That's a question which crops up several times in the threads here, but of course they're so huge that it's hard to find the answers.

The cart is never becalmed, not even as it passes through windspeed. The propeller blades are the part of the cart which the wind bears on, and due to the pitch of the blades, the surface is always effectively moving backwards from the point of view of the air contacting it at any point.

D'rok · 10th July 2012, 02:51 PM

Originally Posted by H'ethetheth

The discussion stopped here because the discussion got too heated, then moderated, and then fizzled and moved to another forum, mostly talkrational. The discussion went on there quite a bit*, though it's mostly a question of two stubborn cooks refusing to accept the mountains of evidence and explanations thrown at them.
Also, the team has now managed to adapt the car for upwind travel and are in the process of having a record ratified for traveling upwind faster than the wind.

The definitive accepted explanation would, I think, consist of the papers by Andrew Bauer, Mark Drela and Mac Gaunaa. The wikipedia article about sailing faster than the wind has links to most of these, I think.

* quite quite a bit: 37 consecutive threads and counting

Holy hell, humber is still at it.

My God, it's made of stupid.

spork · 10th July 2012, 02:58 PM

Jack's answer is a good one. The cart does not have to "coast" through wind speed or anything like that. It can actually tow a trailer at wind speed all day long - or go uphill. I can't quite get away for a longer explanation at the moment, but I will be glad to later today if you need further explanation.

I suspect the analyses I posted might not give you the intuitive answer you're looking for.

I will leave you with this... A sailboat can tack downwind so as to beat a balloon to a direct downwind point. It can also tack downwind so that it exactly matches the downwind speed component. That's what our prop blades are doing when the vehicle is at wind speed.

AIRPLANEHUNTER · 10th July 2012, 03:08 PM

Originally Posted by Jack by the hedge

That's a question which crops up several times in the threads here, but of course they're so huge that it's hard to find the answers.

The cart is never becalmed, not even as it passes through windspeed. The propeller blades are the part of the cart which the wind bears on, and due to the pitch of the blades, the surface is always effectively moving backwards from the point of view of the air contacting it at any point.

I see your point, but isn't it the propeller contacting/motivating the still air, rather than the still air driving the prop? My confusion is therefore from a pure Newtonian point of view. Since it is the motion of the propeller that would be accelerating the still air, the energy accomplishing that work must be extracted from the kinetic energy stored in the prop or drive system against the ground thus slowing the vehicle. (This assumes a theoretically steady wind. Gusts could do the job...)

But, I don't want to re-ignite this discussion here if it has already been explained, so I'll see what I can find in the resources y'all have provided.

Thanks.

D'rok · 10th July 2012, 03:09 PM

Originally Posted by spork

I will leave you with this... A sailboat can tack downwind so as to beat a balloon to a direct downwind point. It can also tack downwind so that it exactly matches the downwind speed component. That's what our prop blades are doing when the vehicle is at wind speed.

AIRPLANEHUNTER, I am a total noob with no relevant expertise or knowledge, but spork's explanation here is what worked for me. This video makes it crystal clear.

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

AIRPLANEHUNTER · 10th July 2012, 03:11 PM

Originally Posted by spork

Jack's answer is a good one. The cart does not have to "coast" through wind speed or anything like that. It can actually tow a trailer at wind speed all day long - or go uphill. I can't quite get away for a longer explanation at the moment, but I will be glad to later today if you need further explanation.

I suspect the analyses I posted might not give you the intuitive answer you're looking for.

I will leave you with this... A sailboat can tack downwind so as to beat a balloon to a direct downwind point. It can also tack downwind so that it exactly matches the downwind speed component. That's what our prop blades are doing when the vehicle is at wind speed.

Thanks, Spork. Let me read the paper and poke around the internet rather than trouble you at this point. If I strike out, I'll be back!

Cheers.

AIRPLANEHUNTER · 10th July 2012, 03:20 PM

Originally Posted by D'rok

AIRPLANEHUNTER, I am a total noob with no relevant expertise or knowledge, but spork's explanation here is what worked for me. This video makes it crystal clear.

I'll take a look. I'll be back tomorrow.

Thanks to all of you.

quarky · 10th July 2012, 03:35 PM

Frames of reference.

So cool to see this thread revived!
(One of my all-time favorites)

Spork, big greetings to you.
Best to you, and any chance of a link, to get up to speed?

Modified · 10th July 2012, 06:01 PM

To add a bit more by extending the drfttr analogy, suppose we use a greased ruler so that the cart gradually builds up speed. When the cart and the wheel that contacts the ruler are at ruler speed, the wheel surface in contact with the ruler is still slower than the ruler. Similarly, the effective surface of the prop in the dwfttw cart is always moving slower than the wind.

Or this might help... If the prop blade and mechanism were very stiff and you put a greased finger against the leading edge of a prop blade and pushed directly forward, this would force the blade to move against your finger so that the cart would move in the direction of your finger, faster than your finger, until it slipped off the trailing edge of the blade. The wind is in some sense acting like many such fingers.

spork · 10th July 2012, 06:27 PM

Originally Posted by AIRPLANEHUNTER

I see your point, but isn't it the propeller contacting/motivating the still air, rather than the still air driving the prop?

This becomes a bit of a subtle point. It might be best to imagine the road and the air floating through space. Neither the air nor the road is REALLY moving, nor is either one REALLY stationary. Another way to think about it is to look at our treadmill tests. In this case the vehicle advances on a moving treadmill in a room with still air. Now it's not so hard to see how we can be powering the prop.

In this case we can think of the road surface going by powering the wheels. If the retarding force is less than the thrust it can generate through the prop - Bob's your uncle.

The reality is that the cart is exploiting the energy available at the interface of the two media. We can do our analysis in the ground frame, the wind frame. Which thing "powers" it depends on which frame we do our analysis in. But that just tells us something about the nature of energy itself (namely that it's frame dependent).

Stream of consciousness...

When we squirt a watermelon seed from between our thumb and index finger, which one makes the seed squirt out? Neither one works without the other.

When a sailboat sails across the wind (on a beam reach), what pushes it forward, the keel or the sail? Same answer as above.

Quote:

Since it is the motion of the propeller that would be accelerating the still air, the energy accomplishing that work must be extracted from the kinetic energy stored in the prop or drive system against the ground thus slowing the vehicle.

Much is relative, but we truly are not making use of any stored momentum or kinetic energy. The vehicle works steady-state at, below, or above wind speed.

Quote:

But, I don't want to re-ignite this discussion here if it has already been explained, so I'll see what I can find in the resources y'all have provided.

As you wish, but no one will mind a bit if you're up for discussing it with an open mind.

Originally Posted by quarky

Spork, big greetings to you.
Best to you, and any chance of a link, to get up to speed?

Thanks. I posted a link to Mac's analysis above, and I can also post links to our project blogs - but they don't talk much about the theory - just the build and testing saga. I'm happy to answer questions here, or try and point you to other good stuff. Just let me know what you're looking for.

Originally Posted by Modified

Similarly, the effective surface of the prop in the dwfttw cart is always moving slower than the wind.

This is true, interesting, but difficult for some to picture I fear. It's kind of the barber pole phenomena. It looks like it's always going up - but it clearly doesn't get any higher.

Quote:

Or this might help... If the prop blade and mechanism were very stiff and you put a greased finger against the leading edge of a prop blade and pushed directly forward, this would force the blade to move against your finger so that the cart would move in the direction of your finger, faster than your finger, until it slipped off the trailing edge of the blade. The wind is in some sense acting like many such fingers.

I like this description. It reminds me of my "Jello" description.

Imagine the whole thing is inside a huge block of jello. Now imagine the prop pitch is such that it makes one rotation when the vehicle moves forward 1000'. Now imagine the prop tries to advance only 1 foot through the jello in a single rotation.

So if I push the jello block 1000 feet along the ground, it will push the cart 1000 feet as well. But the prop will have made one rotation inside the jello. So the prop (and therefore the vehicle) will have advanced 1 foot through the jello block. Therefore when the jello (i.e. wind) moved 1000 feet, the vehicle moved 1001 feet! Down jello faster than the jello.

quarky · 10th July 2012, 06:35 PM

Sure...

But what flavor jello, exactly?

spork · 10th July 2012, 11:11 PM

Originally Posted by quarky

Sure...

But what flavor jello, exactly?

Bloody albatross flavor!

Dan O. · 11th July 2012, 08:02 AM

You know, if someone just does the math they don't need the analogy and they can simply eat the jello.

Mmmmm, good albatross!

quarky · 11th July 2012, 02:46 PM

Having read some sea survival journals, I'm guessing that albatross is an acquired taste.

EHocking · 11th July 2012, 03:26 PM

Originally Posted by quarky

Having read some sea survival journals, I'm guessing that albatross is an acquired taste.

Traditionally, an excellent soup.

But second helpings may not sit well...

3point14 · 13th July 2012, 08:05 AM

Originally Posted by quarky

Having read some sea survival journals, I'm guessing that albatross is an acquired taste.

Yeah, but it goes a long way...

A.T. · 16th July 2012, 05:33 AM

Originally Posted by AIRPLANEHUNTER

I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010.

DDWFTTW is so 2010. DUWFTTW is the new thing:

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

But it is the same principle, just backwards. Both directions are analyzed in the paper linked by spork:
http://www.ewec2009proceedings.info/...esentation.pdf

They are also both explained in simple mechanical terms in this video:

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

And here in a more schematic way:

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

spork · 16th July 2012, 05:42 AM

I just got word that our upwind record of 2.1X wind speed has been ratified. It feels good to close that chapter.

2nd September 2010, 07:18 AM	#881
Ririon Cool cat Join Date: Jan 2005 Location: Trondheim, Norway Posts: 2,063	Originally Posted by quarky My little de-rail feels better now. Anyone care to describe the mechanics of 'pumping' a swing? Obviously, it works, but I find the physics somewhat baffling. I have a swing with 2 lines and a spacer, with a single line above that, to the tree branch. It can't be pumped. Sure it can. If it is longer than a usual swing, you just use a lower frequency. It is an own frequency thing. Unless you immediately start to spin uncontrollably, of course. Then it gets difficult. BTW: There is a new Japanese computer game out now based on racing office chairs and other less than optimal racing vehicles.
	__________________ Engineer by day, scientist by night.

2nd September 2010, 09:47 AM	#882
CNY_Dave Thinker Join Date: Dec 2008 Posts: 134	DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand. Also desirable because then his hand wasn't dragging through the wet ink. Dave
CNY_Dave Thinker Join Date: Dec 2008 Posts: 134

2nd September 2010, 01:45 PM	#883
quarky Banned Join Date: Oct 2007 Posts: 20,454	cool
quarky Banned Join Date: Oct 2007 Posts: 20,454

2nd September 2010, 05:54 PM	#884
GrouchoMarxist Cowardly insulter of Buddhism Join Date: May 2008 Location: Surly Bonds correctional facility Posts: 939	Originally Posted by CNY_Dave DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand. Also desirable because then his hand wasn't dragging through the wet ink. Dave This is a part of the equation I hadn't previously considered.
	__________________ I can't believe that having said what I said was interpreted as having been what I said when I said it, because I said it where I said it, when I said it, and who I said it to. Only in America!

3rd September 2010, 06:16 AM	#887
quarky Banned Join Date: Oct 2007 Posts: 20,454	Originally Posted by bowlofred Hmm. Okay. So I've heard that before and mathematically it's a simple answer (and possible). But while looking for a graphic to append to my post, I found this page that says it's not actually the mechanism used. Makes sense, but I'd never come across it before. http://www.grinnell.edu/academic/phy...ty/case/swing/ Great link. It explains the matter well. My single line swing allows too much twirl, which tends to neutralize the gains.
quarky Banned Join Date: Oct 2007 Posts: 20,454

2nd September 2010, 10:39 PM	#885
BowlOfRed Muse Join Date: Jul 2010 Location: Silicon Valley Posts: 535	Originally Posted by quarky My little de-rail feels better now. Anyone care to describe the mechanics of 'pumping' a swing? Obviously, it works, but I find the physics somewhat baffling. I have a swing with 2 lines and a spacer, with a single line above that, to the tree branch. It can't be pumped. There's a way to think of it in two parts (A simplification. You don't really need the first part). The first part is to get the center of mass just a bit off-center from the pivot. Pushing yourself front-back easily does that with air resistance or a bit of friction in the line. With a bit of motion to the swing, the second part is to use the motion to pump energy into the system. Imagine a swing with a weight at the bottom that can be moved between two positions, one closer to the pivot and one further away. If the weight is moved from the further to the closer position while the swing is at the bottom, work is done to increase the gravitational potential of the weight. By returning to the same position when the swing is away from the bottom, the gravitational potential is decreased again, but not as much due to the angle. So this process can be repeated to drive energy into the system. At very small angles, you can't put much energy in with this mechanism. I don't know exactly what's happening with the swing you describe, but it could be that it's just got a lot more "wobble" than more common swings. That could make it more difficult to get some initial swing going, so your pumping is very inefficient. But once it's off-center, there should be no difficulty in pushing energy in.

2nd September 2010, 10:50 PM	#886
BowlOfRed Muse Join Date: Jul 2010 Location: Silicon Valley Posts: 535	Hmm. Okay. So I've heard that before and mathematically it's a simple answer (and possible). But while looking for a graphic to append to my post, I found this page that says it's not actually the mechanism used. Makes sense, but I'd never come across it before. http://www.grinnell.edu/academic/phy...ty/case/swing/

3rd September 2010, 05:07 PM	#888
CNY_Dave Thinker Join Date: Dec 2008 Posts: 134	Originally Posted by CNY_Dave DaVinci didn't write with mirrored letters as any kind of a 'code', it is simply the most logical way for a lefty to reproduce the letters the same way using the same motions, but with the other hand. Also desirable because then his hand wasn't dragging through the wet ink. Dave dang... how'd that end up here?
CNY_Dave Thinker Join Date: Dec 2008 Posts: 134

3rd September 2010, 07:56 PM	#889
recursive prophet Graduate Poster Join Date: May 2008 Location: Escondido, CA Posts: 1,135	Originally Posted by D'rok Are Humber and Harold really and truly gone? They've left the Internet? Won't somebody please think of the lurkers? Amen D'rok! We lurks just don't get no respect. Heck, I'll bet traffic on the entire TalkRational site still hasn't recovered from H&H dropping out. I've beseeched humber to come back in emails, but got no reply. I only hope he hasn't been the victim of foul play, and if he has that spork at least has a solid alibi for whenever it happened. Below is a post from a retired Russian mathematician who believes he sees a way the prop could be redesigned to achieve higher speed for the Blackbird. This one begins Cartville Saga part 17, where he uses a hypothetical iceboat to launch his thesis. If you scroll down from HERE you can follow the discussion, and on the following pages nicvic presents a hodograph to make his case. Only one user on TR-'A.T.'-has had both the patience and maths background to try and understand exactly what his premise is. I'm hoping sol invictus and some of the other cognoscenti here will take a look and see what they make of his claims. Speaking Russian would be a big help. Originally Posted by nikvic (K= lift-drag ratio) I again began to discuss the thesis - fixed step and transmission do not allow to achieve maximum speed. As an analogue treated with ice boat fixed wing and a fixed rate. The main reason - the angle of attack varies from ~ 160 degrees to the optimum of ~10 degrees in the process of overclocking. "Good" value of K - only near the ~10 degrees.

5th September 2010, 01:48 PM	#890
recursive prophet Graduate Poster Join Date: May 2008 Location: Escondido, CA Posts: 1,135	I hate doing a double post on this thread, but I’d really like to get some input on what nikvic is asserting on TR. If you CLICK HERE. you can see a description of how the cart works that he cited. I had to fix the link he posted, and his following comments about it appear below. Does anyone remember who wrote this? Originally Posted by nikvic; It's all right, but the equations describe only cruising mode. Start-up is described in the language of forces and moments - for the propeller. For the wing enough language forces - so I still have only used this language. Let Vx <<W, the screw is almost motionless. The air acts on the screw with a force T and moment M. It is convenient to assume that the transmission is always 1:1, and the equivalent radius of the wheels (including transmission) = R. To speed up the necessary R> M / F. This radius is very large for a positive step screw. In the clips show how difficult to pick up speed. For records at cruising equivalent radius can be smaller - and records will be higher. Some interesting follow up exchanges to nikvic’s above reply were made by him and A.T. in just the last hour or so, which begin HERE. If you’re not a TR member, just post any responses in this thread and I’ll be sure nikvic sees them.
	Last edited by recursive prophet; 5th September 2010 at 02:33 PM.

10th July 2012, 07:49 AM	#891
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010. While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not? So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it? If so, can someone point me to the definitive accepted full explanation?
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Last edited by AIRPLANEHUNTER; 10th July 2012 at 07:51 AM. Reason: grammer

10th July 2012, 08:07 AM	#892
Jack by the hedge Safely Ignored Join Date: Oct 2009 Posts: 5,421	Welcome to the forum, AIRPLANEHUNTER. I think the dearth of activity is simply that the small number of vocal individuals who thought it must be impossible eventually ran out of things to say in the face of the evidence. By coincidence, the team have just recently got through a series of directly upwind tests, and they hope to have a new upwind speed record ratified shortly.

10th July 2012, 08:15 AM	#894
Modified Illuminator Join Date: Sep 2006 Location: SW Florida Posts: 4,062	Originally Posted by AIRPLANEHUNTER I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010. While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not? So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it? If so, can someone point me to the definitive accepted full explanation? The whole question was satisfactorily explained many times, the cranks just refused to accept it. The easiest thing is to look at the "down ruler faster than the ruler" cart, and realize that the dwfttw cart does the same thing, only with a prop interface to the wind instead of a wheel interface to the ruler.

10th July 2012, 08:17 AM	#895
H'ethetheth fishy rocket scientist Join Date: Aug 2004 Location: among the machines Posts: 2,341	Originally Posted by AIRPLANEHUNTER I have just recently been made aware of this DDWFTTW issue and the Blackbird vehicle. It seems that the discussion was hot and heavy for several years and then seems to have essentially stopped since the fall of 2010. While I have my own opinions as to what is going on aerodynamically and mechanically, I am very interested in seeing ongoing research and other vehicles testing the original claims in the spirit of true scientific inquiry. This controversy should be solved in time as new data and repeatable experimentation are brought forward and achieve consensus acceptance from skeptics. This is how science works, is it not? So why do we have an apparent dearth of activity on the blogs and forums. Have all of the loose ends been tied up and the whole question satisfactorily explained and I can't find it? If so, can someone point me to the definitive accepted full explanation? The discussion stopped here because the discussion got too heated, then moderated, and then fizzled and moved to another forum, mostly talkrational. The discussion went on there quite a bit, though it's mostly a question of two stubborn cooks refusing to accept the mountains of evidence and explanations thrown at them. Also, the team has now managed to adapt the car for upwind travel and are in the process of having a record ratified for traveling upwind* faster than the wind. The definitive accepted explanation would, I think, consist of the papers by Andrew Bauer, Mark Drela and Mac Gaunaa. The wikipedia article about sailing faster than the wind has links to most of these, I think. * quite quite a bit: 37 consecutive threads and counting
	Last edited by H'ethetheth; 10th July 2012 at 08:19 AM.

10th July 2012, 08:17 AM	#896
3point14 Pi Join Date: Nov 2005 Location: London ish Posts: 3,600	We're doing this again?! Ace! I'll catch up on the thread - Who's decided to be the only one who can see the obvious flaws in the DDWFTTW machine in the face of thought experiments, published papers and an actual working machine.
	__________________ Cull the delusional.

10th July 2012, 08:56 AM	#897
DrDave Guest Join Date: Apr 2005 Location: Geneva Posts: 3,110	Originally Posted by 3point14 We're doing this again?! Ace! I'll catch up on the thread - Who's decided to be the only one who can see the obvious flaws in the DDWFTTW machine in the face of thought experiments, published papers and an actual working machine. Facts schmacts. That thing is unpossible!

10th July 2012, 09:01 AM	#898
DC dedicated aphilatelist Join Date: Mar 2008 Location: Switzerland Posts: 21,675	the whole thing is a hoax by the windpowered automobile industry.
	__________________ AGW is a fact, including the A, face it

10th July 2012, 02:29 PM	#899
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Thank you, Jack, Spork, Modified, and H'ethetheth. I appreciate the generosity of spirit of you gentlemen in sharing with this newbie who is fresh to the whole subject. I was taking a vacation up to Maine last week and visited an old college roommate who is a life-long one-design sailor. He showed me the video of the Blackbird and as I am a small airplane pilot and amateur aerodynamicist (I majored in music) we talked aerodynamics and physics. I was fascinated by the implications of the video and I had no problem with down-wind or up-wind travel using a well designed propeller/turbine and an efficient wheel drive system. I grasped that the practical limits of a land-propelled vehicle will be bounded by the traction/friction of the wheels against the ground medium and the overall aerodynamic and mechanical efficiency of the vehicle. The only thing I am stumbling on is the downwind run transition through the becalmed state. I can see that when ever one has a relative wind it has potential energy that can be extracted. But when the vehicle is completely becalmed, the only energy in the system that I can see is the kinetic energy available from the moving prop or the moving vehicle relative to the ground. Tapping either one of these energy sources would involve some drag and slow the vehicle. I comforted myself by thinking that minor gusts could provide a energy source to tap to accelerate into the relative headwind, but if the wind was indeed absolutely steady, I'm still confused. So I'm looking forward to reading the paper provided by Spork to get what I am obviously missing here. Again, many thanks for your kindness to this neophyte.
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Last edited by AIRPLANEHUNTER; 10th July 2012 at 02:33 PM.

10th July 2012, 02:39 PM	#900
Jack by the hedge Safely Ignored Join Date: Oct 2009 Posts: 5,421	That's a question which crops up several times in the threads here, but of course they're so huge that it's hard to find the answers. The cart is never becalmed, not even as it passes through windspeed. The propeller blades are the part of the cart which the wind bears on, and due to the pitch of the blades, the surface is always effectively moving backwards from the point of view of the air contacting it at any point.

10th July 2012, 02:51 PM	#901
D'rok Free Barbarian on The Land Join Date: Dec 2006 Posts: 6,237	Originally Posted by H'ethetheth The discussion stopped here because the discussion got too heated, then moderated, and then fizzled and moved to another forum, mostly talkrational. The discussion went on there quite a bit, though it's mostly a question of two stubborn cooks refusing to accept the mountains of evidence and explanations thrown at them. Also, the team has now managed to adapt the car for upwind travel and are in the process of having a record ratified for traveling upwind* faster than the wind. The definitive accepted explanation would, I think, consist of the papers by Andrew Bauer, Mark Drela and Mac Gaunaa. The wikipedia article about sailing faster than the wind has links to most of these, I think. * quite quite a bit: 37 consecutive threads and counting Holy hell, humber is still at it. My God, it's made of stupid.
	__________________ "War exists within the continuum of politics, in which play is continuous, and no outcome is final, save for a global thermonuclear war, which might be." - Darth Rotor "Life, like a Saturday afternoon, finds its ruination in purpose." - MdC

10th July 2012, 02:58 PM	#902
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356	Jack's answer is a good one. The cart does not have to "coast" through wind speed or anything like that. It can actually tow a trailer at wind speed all day long - or go uphill. I can't quite get away for a longer explanation at the moment, but I will be glad to later today if you need further explanation. I suspect the analyses I posted might not give you the intuitive answer you're looking for. I will leave you with this... A sailboat can tack downwind so as to beat a balloon to a direct downwind point. It can also tack downwind so that it exactly matches the downwind speed component. That's what our prop blades are doing when the vehicle is at wind speed.
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356

10th July 2012, 03:08 PM	#903
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Originally Posted by Jack by the hedge That's a question which crops up several times in the threads here, but of course they're so huge that it's hard to find the answers. The cart is never becalmed, not even as it passes through windspeed. The propeller blades are the part of the cart which the wind bears on, and due to the pitch of the blades, the surface is always effectively moving backwards from the point of view of the air contacting it at any point. I see your point, but isn't it the propeller contacting/motivating the still air, rather than the still air driving the prop? My confusion is therefore from a pure Newtonian point of view. Since it is the motion of the propeller that would be accelerating the still air, the energy accomplishing that work must be extracted from the kinetic energy stored in the prop or drive system against the ground thus slowing the vehicle. (This assumes a theoretically steady wind. Gusts could do the job...) But, I don't want to re-ignite this discussion here if it has already been explained, so I'll see what I can find in the resources y'all have provided. Thanks.
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5

10th July 2012, 03:11 PM	#905
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Originally Posted by spork Jack's answer is a good one. The cart does not have to "coast" through wind speed or anything like that. It can actually tow a trailer at wind speed all day long - or go uphill. I can't quite get away for a longer explanation at the moment, but I will be glad to later today if you need further explanation. I suspect the analyses I posted might not give you the intuitive answer you're looking for. I will leave you with this... A sailboat can tack downwind so as to beat a balloon to a direct downwind point. It can also tack downwind so that it exactly matches the downwind speed component. That's what our prop blades are doing when the vehicle is at wind speed. Thanks, Spork. Let me read the paper and poke around the internet rather than trouble you at this point. If I strike out, I'll be back! Cheers.
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5

10th July 2012, 03:20 PM	#906
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5	Originally Posted by D'rok AIRPLANEHUNTER, I am a total noob with no relevant expertise or knowledge, but spork's explanation here is what worked for me. This video makes it crystal clear. I'll take a look. I'll be back tomorrow. Thanks to all of you.
AIRPLANEHUNTER New Blood Join Date: Jul 2012 Posts: 5

10th July 2012, 03:35 PM	#907
quarky Banned Join Date: Oct 2007 Posts: 20,454	Frames of reference. So cool to see this thread revived! (One of my all-time favorites) Spork, big greetings to you. Best to you, and any chance of a link, to get up to speed?
quarky Banned Join Date: Oct 2007 Posts: 20,454

10th July 2012, 06:01 PM	#908
Modified Illuminator Join Date: Sep 2006 Location: SW Florida Posts: 4,062	To add a bit more by extending the drfttr analogy, suppose we use a greased ruler so that the cart gradually builds up speed. When the cart and the wheel that contacts the ruler are at ruler speed, the wheel surface in contact with the ruler is still slower than the ruler. Similarly, the effective surface of the prop in the dwfttw cart is always moving slower than the wind. Or this might help... If the prop blade and mechanism were very stiff and you put a greased finger against the leading edge of a prop blade and pushed directly forward, this would force the blade to move against your finger so that the cart would move in the direction of your finger, faster than your finger, until it slipped off the trailing edge of the blade. The wind is in some sense acting like many such fingers.
	Last edited by Modified; 10th July 2012 at 06:05 PM.

10th July 2012, 06:27 PM	#909
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356	Originally Posted by AIRPLANEHUNTER I see your point, but isn't it the propeller contacting/motivating the still air, rather than the still air driving the prop? This becomes a bit of a subtle point. It might be best to imagine the road and the air floating through space. Neither the air nor the road is REALLY moving, nor is either one REALLY stationary. Another way to think about it is to look at our treadmill tests. In this case the vehicle advances on a moving treadmill in a room with still air. Now it's not so hard to see how we can be powering the prop. In this case we can think of the road surface going by powering the wheels. If the retarding force is less than the thrust it can generate through the prop - Bob's your uncle. The reality is that the cart is exploiting the energy available at the interface of the two media. We can do our analysis in the ground frame, the wind frame. Which thing "powers" it depends on which frame we do our analysis in. But that just tells us something about the nature of energy itself (namely that it's frame dependent). Stream of consciousness... When we squirt a watermelon seed from between our thumb and index finger, which one makes the seed squirt out? Neither one works without the other. When a sailboat sails across the wind (on a beam reach), what pushes it forward, the keel or the sail? Same answer as above. Quote: Since it is the motion of the propeller that would be accelerating the still air, the energy accomplishing that work must be extracted from the kinetic energy stored in the prop or drive system against the ground thus slowing the vehicle. Much is relative, but we truly are not making use of any stored momentum or kinetic energy. The vehicle works steady-state at, below, or above wind speed. Quote: But, I don't want to re-ignite this discussion here if it has already been explained, so I'll see what I can find in the resources y'all have provided. As you wish, but no one will mind a bit if you're up for discussing it with an open mind. Originally Posted by quarky Spork, big greetings to you. Best to you, and any chance of a link, to get up to speed? Thanks. I posted a link to Mac's analysis above, and I can also post links to our project blogs - but they don't talk much about the theory - just the build and testing saga. I'm happy to answer questions here, or try and point you to other good stuff. Just let me know what you're looking for. Originally Posted by Modified Similarly, the effective surface of the prop in the dwfttw cart is always moving slower than the wind. This is true, interesting, but difficult for some to picture I fear. It's kind of the barber pole phenomena. It looks like it's always going up - but it clearly doesn't get any higher. Quote: Or this might help... If the prop blade and mechanism were very stiff and you put a greased finger against the leading edge of a prop blade and pushed directly forward, this would force the blade to move against your finger so that the cart would move in the direction of your finger, faster than your finger, until it slipped off the trailing edge of the blade. The wind is in some sense acting like many such fingers. I like this description. It reminds me of my "Jello" description. Imagine the whole thing is inside a huge block of jello. Now imagine the prop pitch is such that it makes one rotation when the vehicle moves forward 1000'. Now imagine the prop tries to advance only 1 foot through the jello in a single rotation. So if I push the jello block 1000 feet along the ground, it will push the cart 1000 feet as well. But the prop will have made one rotation inside the jello. So the prop (and therefore the vehicle) will have advanced 1 foot through the jello block. Therefore when the jello (i.e. wind) moved 1000 feet, the vehicle moved 1001 feet! Down jello faster than the jello.
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356

10th July 2012, 06:35 PM	#910
quarky Banned Join Date: Oct 2007 Posts: 20,454	Sure... But what flavor jello, exactly?
quarky Banned Join Date: Oct 2007 Posts: 20,454

10th July 2012, 11:11 PM	#911
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356	Originally Posted by quarky Sure... But what flavor jello, exactly? Bloody albatross flavor!
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356

11th July 2012, 08:02 AM	#912
Dan O. Philosopher Join Date: Feb 2007 Posts: 8,767	You know, if someone just does the math they don't need the analogy and they can simply eat the jello. Mmmmm, good albatross!
Dan O. Philosopher Join Date: Feb 2007 Posts: 8,767	__________________ Permanent solution to national fiscal problems: Collect UNDIEs from dead rich people. (link)

11th July 2012, 02:46 PM	#913
quarky Banned Join Date: Oct 2007 Posts: 20,454	Having read some sea survival journals, I'm guessing that albatross is an acquired taste.
quarky Banned Join Date: Oct 2007 Posts: 20,454

11th July 2012, 03:26 PM	#914
EHocking Illuminator Join Date: Apr 2004 Posts: 4,410	Originally Posted by quarky Having read some sea survival journals, I'm guessing that albatross is an acquired taste. Traditionally, an excellent soup. But second helpings may not sit well...
EHocking Illuminator Join Date: Apr 2004 Posts: 4,410	__________________ "A closed mouth gathers no feet" "Ignorance is a renewable resource" P.J.O'Rourke Prayer: "a sophisticated way of pleading with thunderstorms." T.Pratchett "It's all god's handiwork, there's little quality control applied", Fox26 reporter on Texas granite Forum Birdwatching Webpage

13th July 2012, 08:05 AM	#915
3point14 Pi Join Date: Nov 2005 Location: London ish Posts: 3,600	Originally Posted by quarky Having read some sea survival journals, I'm guessing that albatross is an acquired taste. Yeah, but it goes a long way...
	__________________ Cull the delusional. Last edited by 3point14; 13th July 2012 at 08:35 AM.

16th July 2012, 05:42 AM	#917
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356	I just got word that our upwind record of 2.1X wind speed has been ratified. It feels good to close that chapter.
spork Graduate Poster Join Date: Nov 2008 Posts: 1,356