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Walter & Group...
[GH] One last message before going into summation and then into our new topic.
As an engineer sees it, from Eric Cook :
Hi Gordy,
Good discussion going here.
In the comments section on the video page, Aitor mentions "...the difference is that the taper in the line tip gives much less dramatic results.". Aitor also points out that the initial layout of the bead chain greatly influences the resulting direction of the casts bead chain. From that, I'm sure he realizes that this demonstration is a worst case scenario for showing the line not following the rod tip (very good though, I might add).
I would like to point out one thing about the video and the simulation method for everyone to keep in mind. I would think Aitor has already considered this, but I didn't see mention of it through the discussion. The simulation scale is a bit skewed. Granted, I am making a few guesses here at dimensions and Aitor may clear up those guesses with a few measured parameters.
Just from looking at the video, I estimate the length of the "rod" to be about 4 inches. That is 27 times shorter than a 9 foot fly rod so I used that as a base for the similitude. With that in mind and figuring the length of the tile in the video to be about 12 inches, the stroke length in scale is greater than 25 feet! I have no idea the comparison of the mass of the bead chain he used to the relative length of fly line (my guess is scaled to around 40-45 feet). The rod arc looks to be around 60 degrees and 60 degrees is 60 degrees no matter the scale but with the reduction of rod length, a reduction in tip acceleration is also seen. Therefore, less a in the F=m*a, so there is little chance in influencing the direction of the bead chain in the end, considering its starting layout (momentum wins).
All in all, I think Aitor shows an excellent example of the other factors in influencing resulting line layouts.
How about "the casts line goes in the direction of the resultant force vector"? ...yeah, I didn't think you would buy into that one.
Eric
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[GH] Eric,
Never thought of those relationships. Still- a good experiment, I think. Exaggeration sometimes helps make a point when teaching.
I think we've about beat the #@%^&* out of this topic !
Gordy
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[GH] From Guy Manning :
Aitor Writes: “Guy says that the links closer to the "rod" tip influence those in the chain end. He fails to see that the influence is reciprocal…”
This was all obvious and was covered where I wrote something about excluding outside influences which Aitor and others apparently missed. I was not attempting to make a scientifically correct analysis how a fly line acts as it travels through space. I was giving an example of something I tell students to help them understand how we get flat line legs out of a curved tip path. Beyond that simple explanation the topic is out of the venue of what an instructor is expected to know, specialized information and frankly boring.
In an effort to ”understand” the physics of casting some of the scientific minded seem to have taken a God position over the past few years, deconstructing any and all phrasing and turning any slightly misused element into an attack against the other persons understanding of the process. This with no firsthand knowledge of the other person ability to teach affectively or the information’s actual relevance to teaching. The end result is a body of confused information being pushed around as fact. One person’s idea of how the physics work become law for all the other “science minded” people because these others can’t refute it. Last I heard, for something to be considered science, it had to go through a peer verification/review process, otherwise it was held up as questionable. One person’s statement doesn’t prove anything, regardless of their background, and to be presenting something as fact based upon one person’s opinion is asking for trouble. Peer review means having others of the same specialty looking at the information, not having an electrical engineer perform a review on work of a structural engineer. Even then they can’t agree among themselves all of the time. What they accept as “law” one day can be shown incorrect the next. An example is studies done on the amount of work contributed by the rod. For years the estimate of X% by Perkins (I don’t remember the number but it was at least 50%) was accepted, now it has been shown to be much less by Lovell I believe it was.
Bead chain experiments are fine if they apply to the point one is trying to make. It may have been changed but the original comments on the bead chain video didn’t seem to apply to what one was observing. I repeated the experiment a number of months back. I used better controls and moved a rod along a straight edge, without rotation to insure accuracy. What I discovered was that if I had the chain parallel to the tip path it barely cleared the tip, and only because of the tension between the chain links pulled it slightly above the tip path. Which is fine. But if I put the chain at an angle 30 degree below horizontal before the stroke, it would rise to a position of 30 degrees above horizontal at the end of the stroke prior to turnover. The same occurred if I used 45 or 60 degrees. The chain would always rise to its opposite angle or 180 degrees, regardless of the angle of the tip path. So it seems the video didn’t really apply.
So what!
What has all this to do with the fact that some people use an analogy that the line follows the tip or not? If you were to have asked knowledgeable people up front, scientific minded or not, I don’t think there would be any doubt that most would have stated the line didn’t truly follow the tip. But they also might have added that those words are good teaching tools. Any half-way observant person is going to see there is no such thing as a straight line path of the tip and that the majority of the line doesn’t follow the tip.
Mark puts it well when he writes:
“ From a teaching perspective there is absolutely nothing the matter in saying that the tip path influences the path of the line, it obviously does and it is easy to demonstrate on the ground or indeed in the air how it does so. In this sense this sort of statement is not dissimilar to Al Crises “Zoomies” or “painting a rainbow” or Mels “Whuump” or dozens of others that we could think of, indeed, asking a student to imagine “that the line followed the rod tip” in order to get better control of the tip path is obviously a really effective way of getting the idea across. Nothing the matter with that whatsoever because no-one in their right mind is going to talk about mass distribution and Walters finite element analysis in an effort to get the concept over....it’s too complicated. The problem arises because this fairly uncontroversial means of communicating a concept to a student seems to have been converted into an absolute truth about the dynamics of a cast which is regularly reproduced by instructors as a real explanation of what is actually happening to the line.”
Too much of this stuff is NOT NEEDED to teach or communicate with any but the engineer casting geek. Frankly, it has taken a lot of the enjoyment out of casting for
me. My apologies for the second paragraph as it references discussions held in another forum and many reading this may not see the points.
Guy Manning
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[GH] Guy,
No apologies needed or accepted for your second paragraph. I daresay many others have had these thoughts. My own articles written for the medical journals had to be subjected to strict peer review before being accepted.
So happens, I love physics .... but I see the "other side" as well. In my mind the romance, fluidity, passions and enigmas of fly casting still live.
If these lively contentious discussions make the blood boil; perhaps that's not a bad thing. I guarantee it's making our Master candidates THINK.
After once demonstrating a distance snap cast, I was asked about the paradox provided by the rod tip going in one direction resulting in the line going almost 180 degrees in the opposite direction. I pretended to look very wise and said, "It's the nature of the beast !"
Reminds me of the late Mel Krieger and his "poets" and "engineers".
Gordy
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