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Analysing loop propagation

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Dirk le Roux
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Re: Analysing loop propagation

#61

Post by Dirk le Roux » Thu Sep 24, 2020 2:55 pm

Graeme H wrote:
Wed Sep 23, 2020 10:31 pm
If all we ever do is mathturbate here on a forum, it makes no difference if the loop is a wave or not. However, it has real world consequences for me when I cast and teach, so exploring the concept is not a frivolous pursuit. I use it every time I cast.
Well put, Graeme!

I, for one, would be very interested in your exposition of that list. :???:

Cheers,
Dirk

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Merlin
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Re: Analysing loop propagation

#62

Post by Merlin » Thu Sep 24, 2020 7:04 pm

• Morphing loops
• How snap casts work
• Check hauling (forced turnover)
• Explaining how pull back works

I am impatiently waiting for your (interpretation of the) explanations Graeme. I do not care about the name used to qualify the loop (at least we can all agree it can be named a loop), and I am particularly attentive to the hidden mechanisms behind those phenomenon :sorcerer:

All is in N laws application, the problem being to write them.

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

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Graeme H
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Re: Analysing loop propagation

#63

Post by Graeme H » Thu Sep 24, 2020 10:24 pm

The explanations nearly all require an understanding of how the speed of progression of a wave through string can be controlled using tension.

The others focus on the mass density of the string and how it affects the transmission of that wave.

You know, mechanical impedance and all that shit ...

(It's a long weekend here this weekend. Maybe I'll put something up in the teaching forum. I'm sure it was all covered by @Berlin many years ago, before he left in frustration.)

Cheers,
Graeme
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Paul Arden
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Re: Analysing loop propagation

#64

Post by Paul Arden » Thu Sep 24, 2020 11:15 pm

Berlin/Carl didn’t leave in frustration. He got married and moved to Canada. I know he left the casting world and had a complete change of life. For a while he actually disappeared off the planet and not only the Board!

Different physics Board members back then, but they all disagreed with his “wave packet” theory and whiplash. The casters also disagreed with whiplash for distance casting down the tape - and we’ve moved a lot further down the tape since then! But you have to remember when Carl was first on the Board this was over 20 years ago - we didn’t really understand anything back then. Casting was mostly a big spring. I think he would get pinned down fairly quickly now.

Back then, to give you just one example, we didn’t even understand how tailing loops formed and all the drawings of them were false. The double intersection came from Mac Lord who was filming them and the wave progression from Alejandro some years later.

In particular I remember Frank, Berlin and I had a huge 100 page argument, on whiplash of course (Frank called it “whipshit” :laugh:). The thread was nonsense. Absolutely full of contradictions. Unfortunately that’s on two Boards back - which reminds me I must have a look at restoring that one.

Cheers, Paul
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Graeme H
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Re: Analysing loop propagation

#65

Post by Graeme H » Fri Sep 25, 2020 12:03 am

Paul Arden wrote:
Thu Sep 24, 2020 11:15 pm
He got married and moved to Canada.
A sure sign of frustration!

:D
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Paul Arden
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Re: Analysing loop propagation

#66

Post by Paul Arden » Fri Sep 25, 2020 4:29 am

Hi Graeme,

Let’s have some art. Here is a transverse wave progression, travelling up the page. (It’s your gravity cast but inverted).
4B761A69-E558-4524-9082-8F537106D6EF.jpeg
4B761A69-E558-4524-9082-8F537106D6EF.jpeg (41.09 KiB) Viewed 190 times
In order for these waves to progress up the page there needs to be resistance. The line needs to be tethered. Or suspended by gravity. In other words there needs to be resistance on the line end from the top for this upwards /transverse wave propagation.

Let us take the scenario below and instead of two big tip paths I return to making the smaller ones above again...
D28DDDBD-0D4D-4B74-B2F3-32C543B63371.jpeg
D28DDDBD-0D4D-4B74-B2F3-32C543B63371.jpeg (31.23 KiB) Viewed 190 times
If we were looking at a transverse wave travelling up the page, I should be able to go from 2 to 1. On a floor say, that wave would be pushing upwards away from the rod tip and allow us to do that. But that doesn’t happen. What actually happens is that the line stays level with the rod tip and ends up in a mess. There is no upwards wave propagation.

Cheers, Paul
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Graeme H
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Re: Analysing loop propagation

#67

Post by Graeme H » Mon Sep 28, 2020 3:20 am

Paul wrote:If we were looking at a transverse wave travelling up the page, I should be able to go from 2 to 1. On a floor say, that wave would be pushing upwards away from the rod tip and allow us to do that. But that doesn’t happen. What actually happens is that the line stays level with the rod tip and ends up in a mess. There is no upwards wave propagation.
I need to assume when you say "On a floor say, that wave would be pushing upwards away from the rod tip and allow us to do that." you may away from you and not upwards (i.e. vertically above the floor.)

You're not accounting for gravity when you lay your loop on the floor. Of course it's going to end up in a mess around the rod tip because you have no force acting to move it away from the rod tip. I don't know how many times I need to say it, but I'll say it again: gravity must be accounted for in this discussion!

Now, if you do actually mean "upwards" in the vertical sense, is this the scenario you're talking about:



Yes, it would end up in a mess if that was done with the rod tip on the floor. You need to allow the wave somewhere to go. Here, we can see the waves descend under the influence of gravity. In a cast, we always throw the line upwards to some extent to allow for gravity, even if we don't recognise we are doing so. That's an instinctive calculation based on our experience (e.g. when was the last time you allowed for gravity when throwing a dart at triple 20?) If you disagree with that, please find some footage of false casting with a loop above the rod tip height in which the line is not launched upwards to some extent.

Image

This is pretty much the same thing as this video, isn't it?



Can you see the wave moving upwards through the string while it is tethered?

When the tether is released, the string falls but the wave is still moving through it. Yes, the line is falling and so is the loop.

If we make the string move upwards before we make the wave, the string does not fall as quickly and the wave does not collapse around the rod tip as it would in your scenario.

Cheers,
Graeme
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Paul Arden
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Re: Analysing loop propagation

#68

Post by Paul Arden » Mon Sep 28, 2020 4:31 am

My backcasts are certainly higher than yours however gravity is undeniable :D

[media] [/media]

If the waves were transverse in the horizontal plane they should push outwards no? That’s why I brought up the floor experiment.

Cheers, Paul
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Graeme H
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Re: Analysing loop propagation

#69

Post by Graeme H » Mon Sep 28, 2020 5:14 am

Paul Arden wrote:
Mon Sep 28, 2020 4:31 am
If the waves were transverse in the horizontal plane they should push outwards no? That’s why I brought up the floor experiment.

Cheers, Paul
Yep, they do push outwards. They stay out there as long as there is tension stopping them coming back at us. When they are small enough, we'd call them wiggle mends. When they are big enough, we'd call them casts.

If the floor wasn't there holding them up against the force of gravity, they'd fall as they do in the first video I posted in my last post or to water as they do in a wiggle mend.

So, how does the floor experiment help?

Cheers,
Graeme
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Paul Arden
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Re: Analysing loop propagation

#70

Post by Paul Arden » Mon Sep 28, 2020 6:14 am

They don’t stay out there without tension at 90 degrees to the rod tip direction :p In other words without that tension they fail to propagate as transverse waves.

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

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