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Wide Loop Inifficiency?

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tinpusher
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Wide Loop Inifficiency?

#1

Post by tinpusher » Sun Jun 06, 2021 5:50 pm

Many discussions I've found on why a wide loop doesn't travel as far lists wind resistance as the main reason. It seems to me the number one issue is transference of energy not being in a singular focused direction. Thoughts?

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Graeme H
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Re: Wide Loop Inifficiency?

#2

Post by Graeme H » Mon Jun 07, 2021 3:02 am

tinpusher wrote:
Sun Jun 06, 2021 5:50 pm
Many discussions I've found on why a wide loop doesn't travel as far lists wind resistance as the main reason. It seems to me the number one issue is transference of energy not being in a singular focused direction. Thoughts?
I agree with you.

A tight loop is an indication that you've focused the energy correctly. For me, the proof of that is that a wide loop will become narrow of its own accord ("morph"), but only if you focused that energy. If you didn't, the loop remains wide and may even fail.

Cheers,
Graeme
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Merlin
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Re: Wide Loop Inifficiency?

#3

Post by Merlin » Mon Jun 07, 2021 7:56 am

Hi Graeme

A few questions since I am not sure I understand the concepts mentionned in this thread:

1) how do you "focuse" energy in practice?

2) what mechanism morphs the loop and then focuse its energy?

Tinpusher mentions direction, and to me it comes from the rod tip trajectory, would that mean that the cast is somehow out of plane for a wide loop?

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

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Paul Arden
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Re: Wide Loop Inifficiency?

#4

Post by Paul Arden » Tue Jun 08, 2021 2:45 am

Hi Doug,

I’m not really qualified to answer this one, so I’m also going to ask a question or two as well :)

Assuming that the wide loop has a straight fly leg that is aligned to the target and that the only difference is loop width, then wouldn’t the wide loop experience more drag losses? (Form drag)

I assume also, in the case of a very wide loop, there are more drag losses because of skin drag on the line within the loop itself.

Personally I think a straight fly leg is far more important than loop width. I also think line speed is a more dominant factor than loop width. However one adjustment we can make to control the acceleration of a sink tip line is to open the loop.

Is there a tension difference between wide and tight loops, all else being equal?

Thanks,
Paul
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Paul Arden
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Re: Wide Loop Inifficiency?

#5

Post by Paul Arden » Tue Jun 08, 2021 2:07 pm

This answers my questions... http://www.sexyloops.com/flycasting/mer ... %20use.pdf

Thanks Merlin!
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gordonjudd
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Re: Wide Loop Inifficiency?

#6

Post by gordonjudd » Wed Jun 09, 2021 4:24 pm

Is there a tension difference between wide and tight loops, all else being equal?
Paul,
As given in Merlin's analysis, The nominal tension in a circular loop is equal to rho_l*v_tangential.^2. V_tangential is equal to .5(Vf-Vr). Thus to first order the tension for a wide loop and a narrow loop having the same tangential velocity of the line going around the loop would be about the same.

There is probably some tension difference when you take acceleration of the loop into account as Merlin notes:
From this equation we can see that this formula represents an oversimplification of the situation studied here,
but I suspect he is the only one that understands the details of how second order effects impact the tension difference as the line goes around the loop.

Gordy

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Paul Arden
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Re: Wide Loop Inifficiency?

#7

Post by Paul Arden » Wed Jun 09, 2021 5:42 pm

Maybe the details Gordy, but I think the overall picture of drag losses in the wide loop is quite easy to visualise.
There is a difference in tension coming from the loop size because tensions at loop ends are influenced by drag forces, and a larger loop means more drag, more angular momentum, etc. I think Doug introduced a concept saying the same thing than: have a straight fly leg flying in the right direction (so called focused energy). Drag affects the flight and as you say this can be controlled by line speed: high speed also generates more drag but at the end of the day the line can go further, you just spent more energy to get the desired result by comparison to a smaller loop.
Merlin writes it more eloquently!

From a practical casting perspective while there is a difference, so long as the fly leg is straight, I think that the differences are pretty small. But also large enough to use them for when making adjustments, eg sink tips.

How are you Gordy? It’s been a while! I hope that you are very well :) :)

Cheers, Paul
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John Waters
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Re: Wide Loop Inifficiency?

#8

Post by John Waters » Thu Jun 10, 2021 1:43 am

As always Daniel, great analytical perspective on casting. You've got me rethinking my views on line tapers.

Stay safe,

John

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Graeme H
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Re: Wide Loop Inifficiency?

#9

Post by Graeme H » Fri Jun 11, 2021 6:45 am

Merlin wrote:
Mon Jun 07, 2021 7:56 am
Hi Graeme

A few questions since I am not sure I understand the concepts mentionned in this thread:
We've been through this ad infinitum. If you don't understand it by now, I'm not going to add to your confusion.

Cheers,
Graeme
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Paul Arden
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Re: Wide Loop Inifficiency?

#10

Post by Paul Arden » Fri Jun 11, 2021 8:47 am

Hi Graeme, by focussed energy I assume you mean a reasonably straight fly leg aimed at target with a starting position of a fully straight line and a correctly aligned backcast?

I think loop morph is a result of aerodynamics (drag forces) as well as momentum of various parts of the line approaching the loop front.

Wide/narrow loops are often difficult to compare because sometimes it’s like comparing apples with durian (and no one in their right mind would do this); when we increase line speed by increasing force, counterflex will initially open the loop, but we have higher line speed that more than compensates.

But even so, comparing wide and narrow loops, that are otherwise identical, both with straight fly legs aligned to the target, I can only assume that the narrow loop is more efficient. It’s just that the other factors may be more significant eg higher line speed.

However it’s also an important tool. On a long carry we want to start with a wider loop because it’s going to otherwise morph into a collision. And of course if we have an ugly sinktip line we use a wider loop so that it doesn’t accelerate into oblivion. :)

Cheers, Paul
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