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Analysing loop propagation 2

Moderator: Torsten

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Graeme H
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Re: Analysing loop propagation 2

#11

Post by Graeme H » Sun Oct 18, 2020 5:24 am

John Waters wrote:
Sun Oct 18, 2020 2:46 am
Interesting as always Gents, I must have missed it but in a nutshell, what causes the dolphin nose and is the cause the result of rod movement?

John
Maybe when we can talk about it when we catch up for a beer and a cast John. I'd like to discuss it here, but you know, "bollocks" .... :???:

The moderator has decided that discussions about things he doesn't agree with need to be isolated. He doesn't agree with my explanation so I'll keep it to myself.

Cheers,
Graeme
FFi CCI

John Waters
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Re: Analysing loop propagation 2

#12

Post by John Waters » Sun Oct 18, 2020 7:10 am

No worries mate, look forward to that chat and a cast, hopefully next year. I am interested as I was casting some distance a few months back and a mate was saying many of my back casts and some (less) of my forward cast with the 5 weight MED had a dolphin nose. None were noticed when I used my 38 gram or 27 gram shooting head lines the same day. I cast the 5 MED with a different stroke to that used for shorter line events and did not give it a great deal of thought then. However, our 5 km travel limit has been extended to 25 km from tomorrow so I will be able to visit my nearest casting pool for training this week and pay more attention. I want to eradicate it as I suspect there is more resistance on the curved front end than would be on the spearpoint front end.

John

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Paul Arden
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Re: Analysing loop propagation 2

#13

Post by Paul Arden » Sun Oct 18, 2020 9:13 am

Hi John, I’m not sure we really know. There has been quite a few hypothesis over the years. But it’s still open ended as far as I’m aware!

Cheers, Paul
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John Waters
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Re: Analysing loop propagation 2

#14

Post by John Waters » Sun Oct 18, 2020 9:27 am

Thanks Paul,

I had noticed them with my Trout distance and thinking about it maybe only when I have got to my maximum carry, however, that may be my lack of observation. Now that I am allowed to cast again, my interest has been sparked as to whether it is technique or condition caused.

Interesting,

John

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Paul Arden
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Re: Analysing loop propagation 2

#15

Post by Paul Arden » Sun Oct 18, 2020 10:42 am

Hi John, no they are common. You can see them on soft snap casts with a short line for example. I only see them when the nose of the loop is tight and top pointed. The various board members have been discussing them for 20 years :D Back then Bruce Richards was telling us it’s the hallmark of a great caster!

Cheers. Paul
It's an exploration; bring a flyrod.

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Mangrove Cuckoo
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Re: Analysing loop propagation 2

#16

Post by Mangrove Cuckoo » Sun Oct 18, 2020 1:43 pm

John Waters wrote:
Sun Oct 18, 2020 7:10 am
No worries mate, look forward to that chat and a cast, hopefully next year. I am interested as I was casting some distance a few months back and a mate was saying many of my back casts and some (less) of my forward cast with the 5 weight MED had a dolphin nose.

John
John,

That is very interesting.

Around a year ago I was in a position where I could clearly view my backcast loops and I saw a definite dn. It made me stop, and I realized I had never seen one when casting a bc. Then I realized I had never noticed one in anyone's bc.

Then, of course, I tried to repeat it and could not. Nor have I been able to again.

I seldom can see my forward cast loop but am told I commonly have a dn on long casts. My bc loops are often visible as they hook a bit behind me... probably a casting fault.

The above made me think there is something about the mechanics of a bc that does not generate dns... but i guess you prove different.

Out of curiosity, were you blocking on the bc... or casting more like stopless?
"Technique is the proof of your seriousness"

Wallace Stevens

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Merlin
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Re: Analysing loop propagation 2

#17

Post by Merlin » Sun Oct 18, 2020 2:33 pm

Torsten,
First we should define what we mean by "analysing loop propagation" - Do we want to understand an actual cast by means of video analysis and similar tools or do we want to get a better general understanding of the physics behind it?
Personnaly I aim at a fair understanding of physics and support from video analysis to check if we are missing something or not.

Paul,
James’ opinion is that the loop propagates because the fly leg is in flight and the loop front has angular momentum (I believe angular momentum in this case is actually conserved).
And I do agree, we can add the rod leg momentum if the cast is not tethered. If fact we need to consider momentum variations of both legs and loop, including the angular momentum variation of the loop, and sorry, it is not conserved since there are non conservative forces acting on it, like skin drag for example.
Maybe you could do something along the same lines with push me/pull me, or at least try to help find resolution to this core issue.
I see a difficulty in understanding that the fly leg moves forward on its momentum and that this momentum can be changed by the tension at the top of the loop which pulls on the fly leg. It is the same problem for the rod leg if it can move (shoot, pull back, push forward, etc.). The main engine is in the fly leg, the loop is a kind of gearbox through which the rod leg can act if the caster wants to do so.

Graeme,
I'd like someone to explain why the angular momentum in the loop disappears when the tension in the rod leg is removed.
It does not disappear since the loop is able to roll over even if the rod leg is falling down (zero tension). The string like approach is unable to catch a zeroing of the tension during the flight since it directly depends on loop rotation/tangential speed. Here is an example of a push forward and you can see that tension at loop ends varies significantly by comparison to a string like approach.
Push forward 1.JPG
Push forward 1.JPG (26.61 KiB) Viewed 183 times
Push forward 2.JPG
Push forward 2.JPG (42.29 KiB) Viewed 183 times
What is the force causing the change of momentum at the loop front?
There are several: tension at both ends of the loop, drag forces, and momentum of the masses entering and leaving the loop.

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

Torsten
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Re: Analysing loop propagation 2

#18

Post by Torsten » Sun Oct 18, 2020 5:59 pm

I'd like to discuss it here, but you know, "bollocks" .... :???:
The moderator has decided that discussions about things he doesn't agree with need to be isolated. He doesn't agree with my explanation so I'll keep it to myself.
Don't be offended, I'm sure I'm talking sometimes a lot of bollocks. I found only that the other thread went a bit too much off-topic (at least the whole discussion about the term loop) so I thought it would be a good idea to start a new one.
Would someone like to reframe the question of analysing loop propagation without using the word "propagation?" Since we're now excluding discussion of waves but keeping an open mind to all other possible explanations, the thread title no longer seems appropriate.
The Wiktionary is often a good source:
https://en.wiktionary.org/wiki/propagation
(physics) the act of propagating, especially the movement of a wave

"propagate"
https://en.wiktionary.org/wiki/propagate
To cause to spread to extend; to impel or continue forward in space

Although often used in combination with waves it's useful for the fly line too - if we're looking for alternatives:

Dynamics
https://en.wikipedia.org/wiki/Dynamics_(mechanics)
Dynamics is the branch of physics developed in classical mechanics concerned with the study of forces and their effects on motion.

So we could use alternatively the wording "Loop Dynamics".

Related to "Dynamics" are the terms "Kinematics" (geometry of the motion) and "Kinetics" (forces causing the motion).
https://en.wikipedia.org/wiki/Kinematics



(Statics)
https://en.wikipedia.org/wiki/Statics
* I think we can ignore statics, because it deals only with systems without acceleration.

--

OK, more (maybe) useful concepts:

External effects acting on the fly line

Gravity
https://en.wikipedia.org/wiki/Gravity


Aerodynamics
https://en.wikipedia.org/wiki/Aerodynamics

Drag
https://en.wikipedia.org/wiki/Drag_(physics)

Form Drag
https://en.wikipedia.org/wiki/Parasitic_drag#Form_drag
-> We can expect this mainly when the line moves perpendicular to the airflow, e.g. at the loop front

Skin friction drag
https://en.wikipedia.org/wiki/Skin_friction_drag
-> acts e.g. along the entire fly leg of the loop

Lift-induced drag
https://en.wikipedia.org/wiki/Lift-induced_drag

-> the lift force due drag a controversial topic here, but possible for parts of the line which move forward and are tilted too



--

Further concepts for modelling a fly line:

Hooke's law
https://en.wikipedia.org/wiki/Hooke%27s_law


* We have used this law for modelling the interaction fly line - rod with the mass-spring model

Internal Friction
https://en.wikipedia.org/wiki/Friction# ... l_friction


* Internal friction can be relevant because the fly line is deformed

Damping (ratio)
https://en.wikipedia.org/wiki/Damping_ratio


--

I'll collect next time a few more concepts that we need and then combine all this stuff to a simple model of a fly line.

John Waters
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Re: Analysing loop propagation 2

#19

Post by John Waters » Sun Oct 18, 2020 10:15 pm

Hi Gary,

Thanks for your reply, it is interesting because it is a term I had not heard of before I started casting the long carry events but it is a real line shape in that world. I just returned home from a cast, my first since 9th June. It was an interesting session. I started with the 5 weight MED distance and then planned to cast the 27 and 38 gram lines. I say "planned" because that is as far as I got with the 38 gram line. I was buggered after casting the 5 weight so I lost interest in the rest of the session rather quickly.
My objective was my backcast and I noticed a few dolphin nose casts on my longest carries. Given my lay-off, my technique was not flash so if it is technique driven, I am sure there where a few technique deficiencies present today to cause a dolphin nose.
I'll see how it goes from now on.
For the 5 MED line I now use a stopless cast because I have difficulty controlling a 90 foot carry with a blocked stroke. Up to 75 feet, I have no problems with a blocked stroke but over that length I get increasing sag in my backcast and at 90 feet I hit the grass on the forward stroke on a few occasions with a blocked stroke. That 15 feet gap becomes more impactful in strong winds blowing into my backcast. For the shorter shooting head lines I use a blocked stroke.

John

PS I think there is a tablet you can take for sag, maybe the solution will be a pharmaceutical one.

Torsten
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Re: Analysing loop propagation 2

#20

Post by Torsten » Mon Oct 19, 2020 9:05 pm

More concepts ..

Wave
https://en.wikipedia.org/wiki/Wave
"In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities, sometimes as described by a wave equation. "
"Mechanical and electromagnetic waves transfer energy, momentum, and information, but they do not transfer particles in the medium. "

If both ends of a string are fixed, this concept seems to be applicable to me ..
https://en.wikipedia.org/wiki/String_vibration

.. but this is not the case for the loop - also if the fly line is the medium, the whole medium would move?

I'd maybe use the wave concept for the mend or if there are indeed transversal waves in the loop.

Transverse wave
https://en.wikipedia.org/wiki/Transverse_wave
"In physics, a transverse wave is a moving wave whose oscillations are perpendicular to the direction of the wave or path of propagation."

Unlikely for the loop (propagation), but right for the mend.


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