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Covered topics /how it works

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James9118
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Re: Covered topics /how it works

#71

Post by James9118 » Fri Aug 14, 2020 9:08 pm

Lasse Karlsson wrote:
Fri Aug 14, 2020 8:09 pm

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
Well how weird is that - we both get the same result. We're both obviously wrong with our real world observations :cool: (my results showed the average untethered cast went further, and my longest single cast was untethered).

Another great test is the unbalanced head experiment. With a #7 I can aerialise a lot of line - probably up towards 100ft. With a #5 I can't do quite as much, but I can still manage a big carry. As such, if I make up a 70ft shooting head out of either a #7 or a #5 it's a piece of piss to aerialise it. However if I have 35ft of #7 at the front and 35ft of #5 at the back, I simply can't do it. I think I know the reason why, but when mentioned previously it's been swept aside.

James

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gordonjudd
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Re: Covered topics /how it works

#72

Post by gordonjudd » Fri Aug 14, 2020 9:09 pm

From 7 years ago, fluffy mpr line throw into the wind
Lasse,
And would you say the loop propagation going down the red portion of that line stalled and did not roll out before it hit the ground in that cast against the wind?
Image

Did you try it with the wind? I would think you would see a difference.

Even though that loop did not roll out it went further than it would have with a tethered cast. Is that the case with your head as well? Thus even though the loop does not roll out the head goes further because it is not encumbered by guide friction on the running line?
Gordy

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Paul Arden
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Re: Covered topics /how it works

#73

Post by Paul Arden » Sat Aug 15, 2020 6:34 am

Hi James,

would you say that for the Untethered loop travelling further it’s because there is lack of Tension from the rings which results in the loop unrolling slower?

For me it’s not all that surprising a result a since as we know shooting heads go further than WF lines go further that DTs. Good exercise too I would imagine :D

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

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Merlin
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Re: Covered topics /how it works

#74

Post by Merlin » Sat Aug 15, 2020 6:51 am

There is no doubt that an untethered cast which rolls over completely goes further than a tethered cast with similar (rather high) launch speed. This is quite obvious. What I am after is to identify conditions which can spoil the rollover, like by making it stall for example, hence the need for a check of the line to restart the rollover process.

The comparison tethered / untethered made with my crudest model (tiny loop, no air drag) shows that whatever the length of the rod leg at release is, the line rolls over completely. But it does not take place at any speed. If the rod leg is half the fly leg at release, then the rollover is rather quick. If the rod leg is very small at release it takes quite a long time for the rollover, which means that the line is going to hit the ground before the end. So the success of a rollover in such conditions is linked to a question of time, which translates into a question of leg length ratio and also likely of launch speed level.

Now that we have the general trends, the incorporation of loop and drag will worsen the situation for the line; this is why I speak of a potential minimum of rod leg length to succeed in rolling over the line in some conditions. There is likely a minimum launch speed associated, and we might see that this minimum is sufficiently low to allow the complete rollover of the line in most conditions. Just wait & see for the upgraded model. Its purpose is to show what the main parameters of the problem are, and get an estimate of their adequate level. Then I think we shall be able to simply explain the rollover of an untethered cast with nothing to hold the line back.

Merlin
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Dirk le Roux
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Re: Covered topics /how it works

#75

Post by Dirk le Roux » Sat Aug 15, 2020 7:38 am

gordonjudd wrote:
Fri Aug 14, 2020 4:16 pm
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.
I don't think it does. There are other feasible explanations for your Teeny morph and I have seen the same morph pattern on dissimilar lines. I suggest we park this detour for another day.

Cheers,
Dirk

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Re: Covered topics /how it works

#76

Post by Dirk le Roux » Sat Aug 15, 2020 9:38 am

James9118 wrote:
Fri Aug 14, 2020 9:08 pm
Another great test is the unbalanced head experiment. With a #7 I can aerialise a lot of line - probably up towards 100ft. With a #5 I can't do quite as much, but I can still manage a big carry. As such, if I make up a 70ft shooting head out of either a #7 or a #5 it's a piece of piss to aerialise it. However if I have 35ft of #7 at the front and 35ft of #5 at the back, I simply can't do it. I think I know the reason why, but when mentioned previously it's been swept aside.
Hi James

With a #7 I can aerialise a lot of line - probably up towards 100ft - what is the #7 mentioned here's length, and is it DT, WF, SH?

if I have 35ft of #7 at the front and 35ft of #5 at the back, I simply can't do it. I think I know the reason why, but when mentioned previously it's been swept aside. I'm curious about this. Could you place a link to the discussion?

All the best,
Dirk

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gordonjudd
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Re: Covered topics /how it works

#77

Post by gordonjudd » Sat Aug 15, 2020 1:47 pm

But it does come into play for the angular momentum of the the distributed mass of the line going around a semi-circular loop.
and
I don't think it does.
Dirk,
Sorry for the detour, but this should be quick.

In that case, what do you get for the angular momentum of the distributed mass having a linear mass density of \(\rho_l\) going around a semicircular loop of radius R with tangential velocity V?

A good place to start is that the angular momentum of a rotating ring is:
The angular momentum of the ring spinning at an angular rate of ω about the axis perpendicular to its plane is L=MR(Rω)=MR²ω.
Gordy

Torsten
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Re: Covered topics /how it works

#78

Post by Torsten » Sat Aug 15, 2020 4:33 pm

Q how does a fly loop unroll?

The loop unrolls, if there exists a velocity difference between the top and the bottom leg of the loop.

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Lasse Karlsson
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Re: Covered topics /how it works

#79

Post by Lasse Karlsson » Sat Aug 15, 2020 4:54 pm

gordonjudd wrote:
Fri Aug 14, 2020 9:09 pm
From 7 years ago, fluffy mpr line throw into the wind
Lasse,
And would you say the loop propagation going down the red portion of that line stalled and did not roll out before it hit the ground in that cast against the wind?
Image

Did you try it with the wind? I would think you would see a difference.

Even though that loop did not roll out it went further than it would have with a tethered cast. Is that the case with your head as well? Thus even though the loop does not roll out the head goes further because it is not encumbered by guide friction on the running line?
Gordy
Yup, the red leader which is extremly fluffy and light didn't manage to roll out before the energy was lost to the headwind. Casting it down wind just made it fly further and straighten out, casting with a sidewind looked like this


Casting with a real leader and flyline makes it roll out nicely. No flying spaghetti monster :(

Cheers
Lasse
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http://www.karlssonflyfishing.com

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Torsten
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Re: Covered topics /how it works

#80

Post by Torsten » Sat Aug 15, 2020 10:03 pm

Side note: a slower moving bottom leg causes tension too.

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