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Miscellaneous (bead chains, string shooter, whips)

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Paul Arden
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Miscellaneous (bead chains, string shooter, whips)

#1

Post by Paul Arden » Mon Jul 15, 2019 1:08 pm

So it would be an inertial effect? Why not, but there is the rod leg to lift somehow.
One of the 180 rules is a trajectory rule where the backcast target must align the forward target. The closer the front target the higher must be the rear target. I teach to “ring a bell” on the backcast and for the caster to imagine in his mind this bell behind him. In fact this is the very first thing that must go through the anglers mind when making a Snakehead shot (or in fact any cast really. It applies to taking shots, casting into the wind, accuracy targets). Very few casters seem to be able to raise the trajectory of the backcast so the the loop straightens above the horizontal, although they seem to have no problems doing this on the forward cast :p

With short lengths of line it is possible to break this 180 rule. I believe this Is because the tip path is the controlling factor in these conditions. With longer casts the angle of the backcast becomes critical. If the backcast is lower than the forward trajectory this can open the loop. I think there are times when instead of opening the loop it lifts the loop, this is a less extreme example. In certain circumstances it could even be beneficial but mostly I think you’re far better off to stick the backcast aligned to the front target. (I really want to make some videos of these aligned loops and will do so when Graeme is here).

In the case of a Roll Cast it’s physically impossible to align the backcast angle to the forward trajectory unless you are fishing for bats. This is one reason why for very short roll casts I would recommend tilting the rod plane close to the horizontal (the other reason being of course that it’s stealthier and helps keeps the rod out of the fish’s window of vision).

With regards the lifting or straightening of the rod leg I’ve always regarded this as a result of tension from the loop nose to the rod tip. There are also a few bumps/waves running along the rod leg - less with an HT6 of course and a shitload more with a TFO. :p

One experiment I would like to do is to buy, or preferably borrow, some roof guttering and lay the line inside this. It would be possible to set this up at a horizontal angle, level with the rod tip, and make forward casts starting with the line in the guttering. You could make slow and fast casts from an identical backcast position. Unfortunately I don’t have a hardware shop of my own but I know a guy who owns a very nice Chinese restaurant, who’s father owns a hardware shop! It just might be possible and I’ll ask the next time I order sizzling tofu.

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

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Graeme H
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Re: Lift force acting on a fly line

#2

Post by Graeme H » Mon Jul 15, 2019 1:17 pm

Merlin wrote:
Mon Jul 15, 2019 11:11 am
Why not, but there is the rod leg to lift somehow.
Like this?

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Merlin
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Re: Lift force acting on a fly line

#3

Post by Merlin » Mon Jul 15, 2019 1:37 pm

I do not think this has something to do with the video analysed by Dirk.
Remember I am the one who studied sag in details.

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: Lift force acting on a fly line

#4

Post by Graeme H » Mon Jul 15, 2019 1:51 pm

By which you mean there is another mechanism to lift the rod leg?

Perhaps that guy sitting just outside the frame playing a pungi at a cane basket had something to do with it. God I love pungi music! :D

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Re: Lift force acting on a fly line

#5

Post by Merlin » Mon Jul 15, 2019 2:06 pm

It is possible to demonstrate the link in between sag and tension and line acceleration, but not to demonstrate that the same parameters govern the altitude of the loop nose. Have a try if you wish.

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: Lift force acting on a fly line

#6

Post by Graeme H » Tue Jul 16, 2019 5:04 am

Gordy,

Can you please explain how torque and moment are being applied to a flexible string here?

In my ignorance, I am under the belief that torque and moment of inertia are terms applied to inflexible objects subjected to rotational movements. For example, if I apply a perpendicular force of 2 N to a door 50 cm from the hinge, the hinge experiences 1 Nm of torque.

If I apply force of 2 N to the fly line at a distance of 50 cm from the loop nose, the string bends and the loop nose feels no torque force. Where am I getting this wrong?

Additionally, what is the torque of gravity? In what way is it producing a rotational force?

Are you applying this theory of lift?

Cheers,
Graeme
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gordonjudd
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Re: Lift force acting on a fly line

#7

Post by gordonjudd » Tue Jul 16, 2019 12:20 pm

Can you please explain how torque and moment are being applied to a flexible string here?

In my ignorance, I am under the belief that torque and moment of inertia are terms applied to inflexible objects subjected to rotational movements.
Graeme,
Here is a refresher for you to study that describes how torque balance in the wind gauge wind gauge experiment determines the tilt angle.
http://sexyloops.co.uk/archivedboard/vi ... 29#p243521

I repeated that experiment with .2m length of fly line and the theory remains the same since the line takes on a nominally straight shape when facing a uniform stream of air. Drag and gravity forces are balanced all along the length of the line so it still takes on a straight shape (aside from possible end effects) even though it is flexible.

Gordy

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Graeme H
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Re: Lift force acting on a fly line

#8

Post by Graeme H » Tue Jul 16, 2019 2:06 pm

gordonjudd wrote:
Tue Jul 16, 2019 12:20 pm
Graeme,
Here is a refresher for you to study that describes how torque balance in the wind gauge wind gauge experiment determines the tilt angle.
http://sexyloops.co.uk/archivedboard/vi ... 29#p243521
Thanks Gordy. I've read that (again) but I'm no closer to an answer. Forget about it.

From your calculations, could you devise a scenario in which a line cannot be cast because it doesn't have enough lift? Can you supply parameters of a "line" which has too much density or too little form drag and thus we would not be able to "cast" it? So far, all line weights between 0wt floating and 14wt sinking lines have proven to be amenable to casting, and that seems like a huge range of form drag/line density ratios to deal with. So let's push it to the extreme, eh?

For example, would the numeric modelling show it would be theoretically impossible to cast a loop in a 15 metre length of light-weight chain?

I'm up for the challenge. It may need to wait until I return from Malaysia (or not) but I'll be happy to test your lift theory at the extremity.

Cheers,
Graeme
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Re: Lift force acting on a fly line

#9

Post by gordonjudd » Tue Jul 16, 2019 3:48 pm

For example, would the numeric modelling show it would be theoretically impossible to cast a loop in a 15 metre length of light-weight chain?
Graeme,
I tried casting a shorter length of metal bead chain but my rod could not handle its heavy mass.

I have cast about 5 m of plastic bead chain as shown in a clip that was posted previously.

As has been mentioned before i think the momentum flux in the y-direction that is produced when the fly leg is tilted down by some angle is another source of lift. In the Rowen's cast that lift was about 4 times larger than the lift on inclined section of line.

That y momentum flux concept has not yet been commented on by Merlin, Torsten and Dirk who understand the physics of variable mass systems better than I do, so you might take it with a grain of salt.

Gordy

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Walter
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Re: Lift force acting on a fly line

#10

Post by Walter » Tue Jul 16, 2019 3:58 pm

gordonjudd wrote:
Tue Jul 16, 2019 3:48 pm
For example, would the numeric modelling show it would be theoretically impossible to cast a loop in a 15 metre length of light-weight chain?
Graeme,
I tried casting a shorter length of metal bead chain but my rod could not handle its heavy mass.

I have cast about 5 m of plastic bead chain as shown in a clip that was posted previously.

As has been mentioned before i think the momentum flux in the y-direction that is produced when the fly leg is tilted down by some angle is another source of lift. In the Rowen's cast that lift was about 4 times larger than the lift on inclined section of line.

That y momentum flux concept has not yet been commented on by Merlin, Torsten and Dirk who understand the physics of variable mass systems better than I do, so you might take it with a grain of salt.

Gordy
Gordy

That’s beginning to sound a bit like an inertial propulsion drive. Mssrs Dean and Thornton salute you.
"There can be only one." - The Highlander. :pirate:

PS. I have a flying tank. Your argument is irrelevant.

PSS. How to generate a climbing loop through control of the casting stroke is left as a (considerable) exercise to the reader.

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