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Swing, Spring, Whip

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Paul Arden
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Swing, Spring, Whip

#1

Post by Paul Arden » Fri Jan 25, 2019 8:54 am

Hi all,

here is a document from Merlin on the Swing, Spring, Whip contributions.

http://www.sexyloops.com/pdf/SwingSpringWhip.pdf

Many thanks,
Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

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Merlin
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Swing, Spring, Whip

#2

Post by Merlin » Fri Jan 25, 2019 5:42 pm

Paul

Thanks for uploading the new version with a corrected color problem in one of the graphics.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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#3

Post by Paul Arden » Fri Jan 25, 2019 6:08 pm

Thanks Daniel. I’m trying to understand this “whip”. Is it like an energy wave that travels up through the rod? Is it due in part to the rod’s tapering? Is it tied to pull-back?

Many thanks,
Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

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Merlin
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#4

Post by Merlin » Sat Jan 26, 2019 7:51 am

Hi Paul

There is a wavey aspect, one rodmaker (Garrison) using the words "wave linear action" to describe the character of his designs inspired by whip motion. Tobias's approach is also something on the wavey side, and this is due to the flexural characteristics of the rod (yes, taper is involved) and to the input (pullback as well) from the caster, and there is the pull angle of the line on the rod to consider.

The article mentionned by Torsten is helpful to get an overview on what is going on. I was recently asked to model a quadruple pendulum (4 piece rod) to analyse its response to an input, but this is awfully difficult and beyond my capabilities. The idea behind was the inertial effect: suppose you hold the quadruple pendulum horizontally and let it go whilst keeping the end butt free to rotate only, the speed at the free end is increasing because of the successive downwards rotation of the pendulums. So there is some energy moving from the lower pendulum (rotating at butt) towards the upper one (the free one) allowing to reach a high speed at tip. This is just a nightmare in terms of modeling.

Merlin
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#5

Post by guest » Sun Jan 27, 2019 7:56 am

Hi Daniel

I’ve made a first pass through your paper and am struggling to find a practical application but I will go through it again. However, I am puzzled by your premise that the whip effect has been known for years:
Today we are aware that there is a « whip » part of energy in a cast. The phenomenon is not easy to describe, it is as if some kinetic energy of the rod was transferred from the butt to the tip, providing extra speed to the tip during the unloading of the rod, and consequently providing extra speed to the line. It is unfortunately extremely difficult to evaluate the corresponding energy from a stroboscopic document or a video. However, this phenomenon has been known by rod makers for years (mid 1930s, see the photo of the booklet attached), some of them referring explicitly to whip behavior as a cornerstone for their design, like Everett Garrison (a Legend in the cane fly rod world). This is not the case for modern rods, although the inertial effect might be known by some, but the lightness of rods put its influence on the low side. If you pay interest to « speed of recovery », then you should have a closer look maybe.
I recall that you didn’t always think this way:

http://www.sexyloops.co.uk/theboard/vie ... 484#p17484
If you want to compare a fly rod with a whip, ask Gordy to explain the difference in physics, it looks like but it is not similar to fly casting.
Your paper doesn’t define the whip effect in a manner I can follow, is it explained in Tobias paper?

Regards

Vince
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#6

Post by Merlin » Mon Jan 28, 2019 11:47 am

Hi Vince

The desription of inertial effects is given in the article posted by Torsten. There are different ways of approaching the issue (e.g. Tobias), and to say the least it is not straightforward.

The (old) post from me is dated 2014, one year before I could solve the MOI/equivalent mass issue. Like we use to say over here, "only fools never change their mind". The inertial effect puzzled me for years. I discovered it in the bamboo fly rods domain many years ago, and I had difficulties to understand what was meant by rodmakers. Once I solved the MOI consistency with equivalent mass definitions and calculation methodology (another kind of nightmare), by analogy with a simple spring, then I realized that there was something behind. It is significant for cane rods, much less for graphite ones, but curiously, modern rods have a large "equivalent mass in mid" proportionaly speaking. Is it by chance? I do not think so, it comes from designers experience I guess.

Merlin
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#7

Post by hshl » Mon Jan 28, 2019 1:33 pm

Hi Vince,
VGB wrote: Your paper doesn’t define the whip effect in a manner I can follow, is it explained in Tobias paper ?
Franz- Josef and I tried to clarify the "inertial" as well as the "whip effect" in section F1 of my paper, especially by drawing the figure XIII (see attachment). We think this figure contains both effects.

To be not misunderstood I would like to mention, that everything I continue to write can just be a tendency due to the complexity of the fly cast.

Simply spoken the inertial effect is visualized by the shortening of the chord length between the grip and the tip of the fly rod, I gave an estimation about this effect in annex 2 of my paper. Franz- Josef and I used the term “pirouette effect” instead of “inertial effect” in order to visualize, that already this shortening must lead to an additional tip speed. I guess there are various explanations for the same effect.

Up to 1:16 the video "center of the rotation mass in fly casting" is mainly about the pirouette effect, inertial effect respectively, the rest of the running time is mainly about the "whip effect". Simply spoken the whip effect is visualized be the additional / further shortening of the chord length between the tip of the fly rod and the upward moving "center of the rotating mass" (see this older video from 2014 too. There the whip effect is explained from 1:10, before the pirouette effect).

I can remember that after a long discussion Franz- Josef and I decided to draw the course of the "center of the rotating mass" back towards the grip during the retraction of the fly rod (see figure XIII – this visualizes the self deceleration process of the fly rod as the moment of inertia increases again). But as the whip effect represents a somehow independent component which is difficult to describe, we strongly assume that this effect still pumps some KE into the tip during the center of the rotating mass moves back towards the grip deceleration the butt section. This "whip effect" corresponds most with the "upmoving circle" or "wave" illustration. Therefore Franz- Josef gave some further explanations in annex 3 of my paper. But how it works in detail is beyond the scope of my investigations. As mentioned before, there are questions left. It remains exciting.

Cheers, Tobias
Attachments
figure_XIII_experimental_investigations_on_the_fly_rod_deflection.JPG
http://www.passion-fliegenfischen.de/_en
All in its proper time ...

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#8

Post by Graeme H » Mon Jan 28, 2019 2:46 pm

Hi Tobias,

I've always tried to teach my students that they need to be moving the whole rod - also known as translation - in addition to the rotational phase of a cast. That avoids a "windscreen wiper action". How does such instruction fit with Figure XIII?

Have you overlaid your figures with strobe images of actual rods being cast? I don't know if it's even possible to get a SLP for the tip without translation so I'm interested to find out your thoughts.

Cheers,
Graeme
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#9

Post by Lasse Karlsson » Mon Jan 28, 2019 2:58 pm

True SLP is the holy grail, something we strive for but will never achieve. I'd love for drawings of casts to actually render a true cast from the right perspective. Would make life easier as an instructor without the students having impossible expectations ;)

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Lasse
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#10

Post by hshl » Mon Jan 28, 2019 3:05 pm

Hi Graeme,
Graeme H wrote:I've always tried to teach my students that they need to be moving the whole rod - also known as translation - in addition to the rotational phase of a cast. That avoids a "windscreen wiper action". How does such instruction fit with Figure XIII?
Good point and you pointed out an assumption I had to make to keep my investigations simple. Figure XIII is reducing the casting stroke to the rotary motion only and in fact my investigated casting stroke includes a significant translatory motion at the beginning.

So how I recomment to cast is shown on the attachment. With this video I also tried to work out some motion properties which should benefit the described energy transfer. However, this video is only a kind of approximation. Fell free to continue.

Cheers, Tobias
Attachments
redistribution_effect-simple.jpeg
http://www.passion-fliegenfischen.de/_en
All in its proper time ...

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