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Topic: Direct Down Wind Faster Than The Wind (Read 4642 times) previous topic - next topic

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Direct Down Wind Faster Than The Wind
Here's a temporary place to hang your Direct Down Wind Faster Than The Wind Hats!

Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

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Re: Direct Down Wind Faster Than The Wind
Reply #1
I'm here.

Thanks ravenscape!

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Re: Direct Down Wind Faster Than The Wind
Reply #2
Is taking a firm stance on the issue obligatory to being a TR member?
Who even made the rule that we cannot group ducks and fish together for the simple reason that they are both aquatic? If I want to group them that way and it serves my purpose then I can jolly well do it however I want to and it is still a nested hierarchy and you can't tell me that it's not.

  • osmanthus
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Re: Direct Down Wind Faster Than The Wind
Reply #3
It's essential to one's fundamental humanity. Carts is serious bizness.
Truth is out of style

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Re: Direct Down Wind Faster Than The Wind
Reply #4
I got an undeliverable message back from the email to Subduction Zone.  If one of you are in touch with him offsite, maybe give him a link to the new thread.

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Re: Direct Down Wind Faster Than The Wind
Reply #5
It's essential to one's fundamental humanity. Carts is serious bizness.

I think it's more about the divide between people who get something wrong and then change their minds vs people who do not change their minds.

I can never remember for certain.
Was Spork originally a doubter?
I think the vast majority of people do not think that it is possible when they first hear about it.
And some people change their minds after reading more about it.

Others appear to be unable to do so.

On another forum there was the 3 doors question.
There was a guy that could not accept the switching doors strategy.
And he was able to reword the question in such a way that anyone new to the thread would agree with him.
But of course he wasn't asking the original question.  He was asking about things changing behind the doors or something along those lines.

He had one guy agreeing with him, but that guy was able to ask questions and accept the answers.
He asked simply, "what changes?".  I answered, "what you know, changes".
He then understood but the other guy just could not change.


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Re: Direct Down Wind Faster Than The Wind
Reply #6
El Karte thread

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Re: Direct Down Wind Faster Than The Wind
Reply #7
It's impossible.
Love is like a magic penny
 if you hold it tight you won't have any
if you give it away you'll have so many
they'll be rolling all over the floor

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Re: Direct Down Wind Faster Than The Wind
Reply #8
Is taking a firm stance on the issue obligatory to being a TR member?
I hope not. I thought one just had to know the thread existed :shrug:

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Re: Direct Down Wind Faster Than The Wind
Reply #9
... Was Spork originally a doubter? ...
No.

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Re: Direct Down Wind Faster Than The Wind
Reply #10
Was Spork originally a doubter?

I'm the one the originally conceived of this silly thing and posted it as a brain-teaser.  Along with JB, I'm also the one that built it and set the upwind and downwind records with it.  So no - I wasn't a doubter.

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Re: Direct Down Wind Faster Than The Wind
Reply #11
Is taking a firm stance on the issue obligatory to being a TR member?
I hope not. I thought one just had to know the thread existed :shrug:
You don't have to voice your firm stance, just have it.
Who even made the rule that we cannot group ducks and fish together for the simple reason that they are both aquatic? If I want to group them that way and it serves my purpose then I can jolly well do it however I want to and it is still a nested hierarchy and you can't tell me that it's not.

  • MikeB
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Re: Direct Down Wind Faster Than The Wind
Reply #12
Thanks Raven and others for reviving the forum.  Just hanging my hat on the little hook over there now.

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Re: Direct Down Wind Faster Than The Wind
Reply #13
Was Spork originally a doubter?

I'm the one the originally conceived of this silly thing and posted it as a brain-teaser.  Along with JB, I'm also the one that built it and set the upwind and downwind records with it.  So no - I wasn't a doubter.

Then I think you are only very amazing instead of extremely amazing.
Would you agree that almost everyone does doubt when they first hear it?
(especially before a successful cart was built)

  • spork
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Re: Direct Down Wind Faster Than The Wind
Reply #14
Would you agree that almost everyone does doubt when they first hear it?

Yup - that's nearly universal.  Although I'm sometimes not sure whether to be just as dismayed at the people that say "sure - I don't see any reason why a wind powered vehicle can't go downwind faster than the wind".  I sometimes wonder if maybe they didn't even get it wrong right.

  • osmanthus
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Re: Direct Down Wind Faster Than The Wind
Reply #15
I didn't doubt it when I first heard of it, but that was because it had already been demonstrated. It'd be a bit stupid doubting something that obviously works.

However, I was definitely a bit WTF, and immediately wanted to know how the bloody thing worked. Which took a few explanations and a bit of head scratching, but ended up making perfect sense. Buggered if I could explain it now though. I've sorta forgotten the details.
Truth is out of style

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Re: Direct Down Wind Faster Than The Wind
Reply #16
Would you agree that almost everyone does doubt when they first hear it?

Yup - that's nearly universal.  Although I'm sometimes not sure whether to be just as dismayed at the people that say "sure - I don't see any reason why a wind powered vehicle can't go downwind faster than the wind".  I sometimes wonder if maybe they didn't even get it wrong right.


The reason I originally doubted it was my own ignorance and stupidity (hard to admit but true).  I didn't realize how much my fundamental physics was lacking in terms of energy concepts.  Had I simply realized that energy for mechanical systems is reference frame dependent and the mechanism for this working utilized a principle to always exploit the comoving media, it probably wouldn't have come as any surprise that it could work as long as the mechanism was efficient enough.

But being the dullard that I was, the first question I asked (which still seems to be the rut some are mired in) was, "How can it gain any energy when there is no relative wind?"  Once that was understood and the efficiency was demonstrated, it isn't all that difficult.

But it is counterintuitive and that first step towards awareness is a doozy! ;D
Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

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Re: Direct Down Wind Faster Than The Wind
Reply #17
I just received two requests to give talks about the downwind cart 30 minutes apart.  This hasn't come up in years.

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Re: Direct Down Wind Faster Than The Wind
Reply #18
I just received two requests to give talks about the downwind cart 30 minutes apart.  This hasn't come up in years.

Who to?
Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

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Re: Direct Down Wind Faster Than The Wind
Reply #19
St. Francis Yacht Club and Zee.aero


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Re: Direct Down Wind Faster Than The Wind
Reply #20
I just received two requests to give talks about the downwind cart 30 minutes apart.  This hasn't come up in years.
Yesterday I visited the physics department in one of the biggest German Universities (Free University of Berlin), during an open house day where they show cool science stuff to the public. One of the demos was this one build to educate their students about DDWFTTW:

https://www.youtube.com/watch?v=2JL_7cx7lnc

They also knew about the Blackbird and noted that it was the most impressive demo of the concept.

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Re: Direct Down Wind Faster Than The Wind
Reply #21
I just received two requests to give talks about the downwind cart 30 minutes apart.  This hasn't come up in years.
Yesterday I visited the physics department in one of the biggest German Universities (Free University of Berlin), during an open house day where they show cool science stuff to the public. One of the demos was this one build to educate their students about DDWFTTW:

https://www.youtube.com/watch?v=2JL_7cx7lnc

They also knew about the Blackbird and noted that it was the most impressive demo of the concept.


Nice piece of demo apparatus.  It's been shown to work linearly, angularly, On stationary surfaces relative to the earth, on moving surfaces relative to the earth, and all worked.  What's not to like?

As the Mythbusters would say:


Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

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Sailcart Simulator
Reply #22
Once again, here is a link to my sailcart simulator which clearly demonstrates how the aerodynamic force acting on a sailing craft can provide a net forward thrust at speeds well in excess of windspeed. The Kddw number is the ratio of the craft's downwind velocity component divided by the windspeed. Force vectors are shown in RED and velocity vectors are shown in GREEN except for the all-important apparent wind velocity vector which is shown in BLUE.

The simulation is a Flash application written using the (old pre-Adobe) Macromedia Flash MX development platform.

Sailcart Simulator

Instead of running this in your browser using a flash plugin, for best viewing I recommend downloading the executable which has an embedded Flash 6 player. Here are the hashes for the known good sailcart.exe file (Rev:20160518_2000) for those who may be (rightfully) paranoid about downloading an executable file:
CRC32: 9CD509B3
MD5: BD36F9322F96BEC92E55FB54D5029574
SHA-1: CFCE2692C1BF1CE35117AD444B02C07B0A3E8EBF


EDIT: Note that the simulated sailcart employs a wing having a N.A.C.A. 0009 airfoil. I got the Cl and Cd data from the attached figure (from 1931).
  • Last Edit: June 15, 2016, 07:28:28 AM by ridgerunner

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Re: Direct Down Wind Faster Than The Wind
Reply #23
That's really good. Thanks.
Love is like a magic penny
 if you hold it tight you won't have any
if you give it away you'll have so many
they'll be rolling all over the floor

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Re: Direct Down Wind Faster Than The Wind
Reply #24
"If you pick up a starving dog and make him prosperous he will not bite you. This is the principal difference between a dog and man."
― Mark Twain 🔭