Merged DDWFTTW in a “Real” Wind

[Subduction Zone]

I Ratant's cart failed because he does not know how a DDWFTTW vehicle works and he used a random attack at the problem. It is very easy to design a cart that does not go directly downwind faster than the wind. You have to know what you are doing to design one that does. It would have helped I Ratant if he had not ignored spork and JB's advice. Instead he antagonized them first, and then complained when they did not follow his whims.

 

[Modified]

Coz that's what Spork says. Qualified people say otherwise.

No, it's because the definition of potential energy must include the way you will use it. You can't just say "PE" and leave it at that. If you are concerned with what happens when you release a stretched spring, you don't care about its gravitational PE. If you are looking at the potential of a rising balloon to do work by rising (by raising a weight, or pulling a string that turns a generator), then gravitational PE alone will not tell you what you want to know.

 

[ridgerunner]

My sentiments exactly.

...
I don't see the value, in and of itself, of a long-running thread. I'd rather read a short thread in which all participants genuinely try to learn or to teach, rather than a long one in which a few people post whatever nonsense they think will get the most replies, and everyone else scrambles to correct errors which have already been corrected innumerable times before. It's hard to find the few bits of good information is the latter sort of thread.

Well said.

...
This forum is a bit like trying to attend class with a maniac in the back row yelling gibberish each time the professor speaks. It's not a very optimal environment.
...

Also, nicely put.

 

[Llyricist]

Aren't the adjustments of the propeller pitch the main reason for variations in acceleration?

There are two places/periods where the acceleration changes suddenly that are probably due to changes in pitch, but otherwise it follows quite smoothly with wind speed changes.

Okay here it is, first up to the end of the test period:

Then after the test period, this data shows a much stronger relationship to relative wind direction, inversely of course.

 

[Dr. Keith]

I know this will sound like I am JAQing off, but I am missing the perspective here of the importance of the angle of deviation. So, in full JAQ mode:

JAQ1: Are there any sail carts that can go 2.8x WS at within 40 degrees of DDW?

JAQ2: If humber is right, and the prop is just a drag element at speeds over WS, are there any sail carts that can achieve 2.8x WS at any angle to DDW with that large of a drag element added to them?

They seem rather streamlined, so I wonder how they would work with such a drag element added.

JAQ3:In other words, how does this speed compare to other sail carts out there?

 

[Llyricist]

In a typical sail cart, you can't start beating a 10 MPH wind unless you are about 45 degrees off. Higher winds allow you to get closer, but still need 25 - 30 degrees off. Iceboats cna doo somewhat better. Here's a polar for one in particular, the wind is coming from the right (0) vb=wind speed:

It should be added that this only shows what happens when the sail is an airfoil rather than a bluff body.

 

[tobermoryphil]

Ice yachts and land yachts can also do around 4 or 5 times the wind speed, when 35 or 40 degrees off DDW, so can have a velocity made good downwind, with tacking, of more than 2.8 times wind speed.

So tow a skater or a VERY light cart, behind one on a VERY long VERY light rope, and they will be able to go DDWFTTW behind the tacking yacht.

So it is possible to visualise DDWFTTW without having to look into the mechanics of the rotating prop's continouously tacking sail airfoil.

ETA: unless of course you are Humber!

 

[humber]

There are two places/periods where the acceleration changes suddenly that are probably due to changes in pitch, but otherwise it follows quite smoothly with wind speed changes.

Not even close, and there is a ton of data that says the cart is no good at all ddw.

 

[Llyricist]

Not even close, and there is a ton of data that says the cart is no good at all ddw.

Keep saying that, maybe one day it will become true.

 

[humber]

Ice yachts and land yachts can also do around 4 or 5 times the wind speed, when 35 or 40 degrees off DDW, so can have a velocity made good downwind, with tacking, of more than 2.8 times wind speed.

So tow a skater or a VERY light cart, behind one on a VERY long VERY light rope, and they will be able to go DDWFTTW behind the tacking yacht.

So DDWFTTW is possible to visualise without having to look into the mechanics of the rotating prop's continouously tacking sail airfoil.

ETA: unless of course you are Humber!

Grasping. There will be no more data posted. NALSA will get it all before you do.
None of you have the mathematical skill to support anything, so go ahead and gossip.

Just to let you know, I have thought of every way you will try to undermine any case against the cart, including the above, so you will find out what that means later on.

 

[tobermoryphil]

Grasping. There will be no more data posted. NALSA will get it all before you do.
None of you have the mathematical skill to support anything, so go ahead and gossip.

Just to let you know, I have thought of every way you will try to undermine any case against the cart, including the above, so you will find out what that means later on.

I believe we are still waiting for your mathematical skills to support your theory of the tacking symmetrical section pylons, and their magical forward thrust from sidewinds.

 

[humber]

Keep saying that, maybe one day it will become true.

You won't know what hit you.

 

[Llyricist]

btw, I should give attribution for that sail cart polar. It comes from:

http://www.tspeer.com/landyachts/performance/Single.html

And it is for a winged sail cart rather than a fabric sail cart, which explains the null downwind.

 

[Llyricist]

You won't know what hit you.

There is a very good reason for that. I tend to know as little total codswallop as possible.

 

[humber]

JAQ3:In other words, how does this speed compare to other sail carts out there?

Poorly. I have reams of data.

And for the LOL, because I can afford to be generous, compare "Rick's Chart" with what Llyricist, the expert has done. Nailed that wind offset....

So many other unflattering details removed.

 

[Dr. Keith]

Ice yachts and land yachts can also do around 4 or 5 times the wind speed, when 35 or 40 degrees off DDW, so can have a velocity made good downwind, with tacking, of more than 2.8 times wind speed.

So tow a skater or a VERY light cart, behind one on a VERY long VERY light rope, and they will be able to go DDWFTTW behind the tacking yacht.

So it is possible to visualise DDWFTTW without having to look into the mechanics of the rotating prop's continouously tacking sail airfoil.

Thanks, that is what I figured.

Do any of those have huge drag elements like the prop (as described by humber)?

 

[Gaspode]

Some posts moved to AAH.

Keep on-topic from now on please. And remember to address the argument, not the arguer.

Replying to this modbox in thread will be off topic  Posted By: Gaspode

 

[Dr. Keith]

btw, I should give attribution for that sail cart polar. It comes from:

http://www.tspeer.com/landyachts/performance/Single.html

And it is for a winged sail cart rather than a fabric sail cart, which explains the null downwind.

Thanks, that is a very cool chart. The winged sail does help me to make better sense of it.

From that graph it seems that the cart has to be more than 60 degrees off DDW to best 2.8x WS in a 10mph wind. Am I reading that right?

 

[Llyricist]

Poorly. I have reams of data.

And for the LOL, because I can afford to be generous, compare "Rick's Chart" with what Llyricist, the expert has done. Nailed that wind offset....

So many other unflattering details removed.
[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=22054&stc=1&d=1304537513[/qimg]View attachment 22054

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=22055&stc=1&d=1304537712[/qimg]

Want to try again and scale the charts properly? It'll still look different but that's because one is averaged data and the other isn't.

 

[Llyricist]

Thanks, that is a very cool chart. The winged sail does help me to make better sense of it.

From that graph it seems that the cart has to be more than 60 degrees off DDW to best 2.8x WS in a 10mph wind. Am I reading that right?

yep, in fact ~60 degrees is where you get your best speeds in the higher winds, and where Jenkins was when he broke the record.