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## Analysing loop propagation

Moderator: Torsten

Merlin
Posts: 1472
Joined: Wed Jan 09, 2013 8:12 pm
Location: France

### Re: Analysing loop propagation

Wave, energy or momentum, it depends of the type of approach, qualitative or quantitative.

I consider wave as a qualitative one. I agree that a mend is a transverse wave but the loop is not, the displacement is not perpendicular to the medium. The string analogy may be a trap since it does not handle “dynamics”. I mean that most of the time string studies refer to “stranded waves”, some type of “steady state” situation by opposition to a situation where accelerations and decelerations take place. The whip analogy looks better, but it is far from being that simple. Maybe the loop is a “longitudinal wave” in some aspect; anyway it is a strange wavy flying object.

If we aim at quantification then we have to use momentum variation in time (horizontal, vertical, angular) and energy balance. There must be a number of equations equivalent to the number of unknowns (among them: leg speeds, rod leg sag, line inclination at both ends of the loop, loop radius, etc. ) and you usually have to use simplifying assumptions or software able to handle a number of ODEs simultaneously. For example, morphing is included within the angular momentum problem but to make that easily usable for a simple model you assume that the loop does not morph. Such quantitative approach involves tension in the line, this tension varying along the line itself.

If you consider “tension” as something more global, then you are back into the qualitative approach (remember Berlin?).

You need something qualitative for teaching and it should ideally be based on a quantitative approach, as accurate as possible. Tension could be an example of a parameter linking both approaches.

You cannot solve the loop propagation technical problem by wave only, momentum only or energy only appraoches, IMHO.

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

Paul Arden
Posts: 13829
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Location: Belum Rainforest
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### Re: Analysing loop propagation

Thank you. Those last couple of answer were very helpful for me

I agree Merlin, wave length and frequency don’t make much sense applied to an unrolling loop. So in order to quantify it we need to use other methods.

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

Flycasting Definitions

gordonjudd
Posts: 1372
Joined: Sat Jan 19, 2013 11:36 pm
Location: Southern California

### Re: Analysing loop propagation

A jerk is readable in Gordy's pull-back cast rod leg velocity and at the same time an opposite direction jerk is readable in the fly leg velocity - centripetal force explains it for me.
Dirk,
Not only is it readable, the jerk derived from the measured velocity profiles in that pull back cast can be calculated as shown below.

Since the calculated correlation coefficient between those two jerk curves was only 12%, I don't think you can cherry pick a time range that fits with your centrifugal force theory while ignoring the 88% of the time when there is no correlation between the two jerk curves.

Invoking jerk as an explanation for the delay in the fly legs velocity increase relative to the start of the pull back is a derivative too far for me.

Gordy

Graeme H
Posts: 1911
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation

Is this a loop or a wave?
Screen Shot 2020-09-15 at 5.28.51 pm.png (25.01 KiB) Viewed 399 times
Cheers,
Graeme
FFi CCI

gordonjudd
Posts: 1372
Joined: Sat Jan 19, 2013 11:36 pm
Location: Southern California

### Re: Analysing loop propagation

Is this a loop or a wave?
Graeme,
For lack of a better term I would say it is an example of one of the many different shapes you see in a "fly wave."

It has a different shape than the "whip wave" that Dr. McMillan analyzed. However in both cases the mass of the medium is transported as the wave propagates down the medium.

That mass transport does not happen in the many types of mechanical waves described in the literature. A transverse wave is a good example of a mechanical wave.

Gordy

Graeme H
Posts: 1911
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation

gordonjudd wrote:
Tue Sep 15, 2020 2:19 pm
That mass transport does not happen in the many types of mechanical waves described in the literature. A transverse wave is a good example of a mechanical wave.
And yet in every static image we show of a mechanical wave, the medium is displaced, including the ones you've just posted. In the case of a transverse wave, we show the medium deviating from the centre line of the graph. If the medium has mass, then the mass has been momentarily transported perpendicular to the direction of wave propagation.
For lack of a better term I would say it is an example of one of the many different shapes you see in a "fly wave."
Well, yeah, that's not a great term. It means nothing to anybody.

Is the picture showing a wave or is it a loop? Don't be too hard on yourself - I don't know how anybody can answer the question. I'm simply pointing out the inconsistency in the argument that every bend travelling along a fly line is called a transverse wave except one. In isolation, it is not possible to determine if I've shown a loop or a "real" transverse wave.

The fact that we are making this distinction between the two otherwise identical bends travelling through a medium means something is wrong with the model of a wave that we have in mind. That implies a change of perspective is required.

Cheers,
Graeme
FFi CCI

Lasse Karlsson
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### Re: Analysing loop propagation

Graeme, quite difficukt to determine anything from your blown up picture, but I think I know where you want to go with it.

If a transverse wave displaces matter while it travels, but brings it back when it leaves, how can a loop be called a wave, when it moves matter from one point and leaves it at another?

Cheers
Lasse

http://www.karlssonflyfishing.com

***Bring Mark back!!!!!! ***

Graeme H
Posts: 1911
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation

Lasse Karlsson wrote:
Wed Sep 16, 2020 7:33 am
If a transverse wave displaces matter while it travels, but brings it back when it leaves, how can a loop be called a wave, when it moves matter from one point and leaves it at another?

Cheers
Lasse
I think you might have missed a post of mine earlier. The full cycle of the wave returns the fly to its starting point, as in a PUaLD cast.

But to answer your question: look at an aerial mend. when you land the line on the water, the line has a bend in it. That line was not returned to the starting point but we all agree that's a transverse wave.

Cheers,
Graeme
FFi CCI

Graeme H
Posts: 1911
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation

Which of one of these actions marks the transition from a wave to a loop?

Cheers,
Graeme
FFi CCI

Dirk le Roux
Posts: 461
Joined: Thu Sep 19, 2013 5:09 pm
Location: Pretoria, South Africa

### Re: Analysing loop propagation

Graeme,

I find the fly leg behaviour part of this clip extremely fascinating. Thanks for doing this one!

Cheers,
Dirk