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## Covered topics /how it works

Moderator: Torsten

Paul Arden
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Location: Belum Rainforest
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### Re: Covered topics /how it works

Hi Merlin,

I think there must be an explanation as to why a loop and a flat piece of line behave very differently when in flight. So any explanation of how a loop works can not exclude an explanation about this since it’s integral to the overall function. We even see a positive acceleration of the loop in flight. So if anything needs to be explained to the layman it is this!

Maybe a simple “visual” explanation of how a particle going around a loop results in a force pulling the fly leg would help immensely. I envisage a little ball reaching the loop and being held back. Where does that energy go? It tries to push forwards which results in a force pulling on the line.

Equations are ok so long as there is diagram with an explanation! But I think for most people they need the explanation first and then the equation is used to reinforce/check understanding - they can take it or leave it. In most other aspects of life we rarely use equations anyway but we can still understand how something works. For example I drive a car and I have a pretty good understanding as to how the engine works, whether that’s diesel or petrol. I could even fix them before they became computers with wheels! But I have no idea about the equations that are involved when designing the engine! So I agree - I don’t think that equations are necessary, but if they assist then that’s good.

So that leads me to a question. This is the Physics Forum. What I’m asking for is not highly technical explanations but I am asking for your help and it’s physics! Would it be better to create a sub-forum for this? Mind you, by the sounds of it we might have some very technical discussions in order to formulate the “best answer”. Which incidentally is not some sort of challenge, but rather an answer that is formulated and hopefully agreed on by everyone! So there is a goal

I would be comfortable with this format:
Question in the topic.
Technical discussion.
Final agreed answer. Which will then appear as an answer below the question.

If anyone wants to read the technical discussion they can. The discussions don’t have to be layman discussions by any means.

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

Flycasting Definitions

James9118
Posts: 1239
Joined: Thu Jan 10, 2013 6:59 pm
Location: N.Wales

### Re: Covered topics /how it works

I've been casting today. Horrible conditions for distance but I had a specific test in mind. First set of casts was with a shooting head (one that Tracy uses for training). For the second set of casts I used the same shooting head but cut the running line at my hauling hand, so that for each cast the head and a bit of running line flew out untethered.

Any predictions as to what happened, which went furthest, turnover etc?

I will say that threading the running line back through the rings after every cast was a pain in the arse

James

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

### Re: Covered topics /how it works

we have seen that loop radius makes no difference regarding tension.
Dirk,
But it does come into play for the angular momentum of the the distributed mass of the line going around a semi-circular loop.

You should work this out as a check but I get the angular momentum to be equal to:
$$L=\pi*\rho_l*r^2*v_{tangential}$$

James probably forgot that preserving the nominal angular momentum of the mass going around the loop was used to explain why the loop diameter gets smaller when the larger $$\rho_l$$ of a Tenny 450 line starts going around the loop.

As I remember the reduction in the loop diameter in that case was very close to $$\sqrt(\rho_1/\rho_2)$$

That said I have never seen any reference to angular momentum in all of the papers dealing with computing the fly velocity history involved in the roll out of the loop.

As Merlin noted there are outside torques acting on the loop so angular momentum is not conserved. Computing those torque changes and determining how they would impact the angular momentum of a propagating loop would be unnecessarily complicated. The standard work energy approaches used to develop an ODE approach for modelling the fly velocity history are complicated enough in my book.

Gordy

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

### Re: Covered topics /how it works

Horrible conditions for distance
James,
Were you casting with or against the wind when you released your running line? Drag will have a big impact on the resulting line flight.

It would be interesting to cast in both directions to see the impact that drag has on the loop propagation of a flying loop.
Gordy

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

### Re: Covered topics /how it works

but rather an answer that is formulated and hopefully agreed on by everyone!
Paul,
That is a big ask, and in my experience would be a first for technical discussions on Sexyloops.
Gordy

James9118
Posts: 1239
Joined: Thu Jan 10, 2013 6:59 pm
Location: N.Wales

### Re: Covered topics /how it works

Gordy - hot, sticky, no wind that I could make out.

Torsten
Posts: 194
Joined: Tue Jan 22, 2013 7:34 pm

### Re: Covered topics /how it works

Very nice experiments indeed! But please guys, discuss not everything in one thread. Why not open another thread for the very detailed stuff about untethered casts? (and here the summary only)

I think Paul's idea was a Flycasting Physics FAQ - and that's a pretty good idea - maybe we should collect questions first?

Thanks,
Torsten

Paul Arden
Posts: 13901
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
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### Re: Covered topics /how it works

gordonjudd wrote:
Fri Aug 14, 2020 4:23 pm
Paul,
That is a big ask, and in my experience would be a first for technical discussions on Sexyloops.
Gordy
I know but I’m sure there might be some topics where we can find agreement!! We can deal with the complicated ones afterwards and, as mentioned, if there is disagreement then I’m happy to post several alternatives as the “Best Answer” Anyway, trying to find a common formulated answer (or two!) is actually one of the most compelling reasons to do this!

Sometimes I think of the discussions like twisted rope, Torsten! Since I normally have at least two conversations going on in my head at the same time it’s never really bothered me

And in seriousness, having the Q/A format actually allows discussions to go off on tangents and yet still fulfil their objective. I think forming a list of questions is an excellent idea and it was the topic I was planning to start next after we have ironed out the framework.

Hope you are well!

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

Flycasting Definitions

Lasse Karlsson
Posts: 4161
Joined: Wed Jan 09, 2013 9:40 pm
Location: There, and back again
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### Re: Covered topics /how it works

James9118 wrote:
Fri Aug 14, 2020 3:42 pm
I've been casting today. Horrible conditions for distance but I had a specific test in mind. First set of casts was with a shooting head (one that Tracy uses for training). For the second set of casts I used the same shooting head but cut the running line at my hauling hand, so that for each cast the head and a bit of running line flew out untethered.

Any predictions as to what happened, which went furthest, turnover etc?

I will say that threading the running line back through the rings after every cast was a pain in the arse

James
Done that a heap of times, since this topic seems to surface every few years on SL, the longest I have ever thrown and the straighest was the cut shootingline version so that would naturally be my answer here too

And yes, PITA for sure!

Cheers
Lasse

http://www.karlssonflyfishing.com

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

Lasse Karlsson
Posts: 4161
Joined: Wed Jan 09, 2013 9:40 pm
Location: There, and back again
Contact:

### Re: Covered topics /how it works

gordonjudd wrote:
Fri Aug 14, 2020 4:20 pm
Horrible conditions for distance
James,
Were you casting with or against the wind when you released your running line? Drag will have a big impact on the resulting line flight.

It would be interesting to cast in both directions to see the impact that drag has on the loop propagation of a flying loop.
Gordy
We always start the cast into the wind don't we? Not many throw flylines around when there's hurricane winds higher than the lines launch velocity?

From 7 years ago, fluffy mpr line throw into the wind

Cheers
Lasse