Tension Discontinuity /DN

[Graeme H]

... but if you use an inertial frame

And there's my cue to leave this thread.

[gordonjudd]

The topic is pretty difficult. Some speak of a "singular" point within the loop which would correspond to a so called discontinuity in tension.

Merlin,
Is that tension singularity produced by the tension jump that happens at the pinch wheels that are driving the string? Thus to match the shape that you see when a limp, fuzzy length of string is used in a string shooter you have to assume different tension values at that pinch wheels?

Bruce Yeany showed that the shape of the loop you get using a 2m length of fly line in a string shooter is much different than the pear shaped loop you see with a limp string.


To match that duck-head loop shape with its two inflection points in the loop curvature will probably need to take the stiffness of the fly line into account.
Gordy

[Merlin]

Gordy

For sure line stiffness must influence the result, most experiments are using rather soft material. Incidentally stiffer material needs more speed to see a "lift off" of the loop with speed and air drag.

Can you tell me in which direction is the speed in the photo you posted: clockwise or anticlockwise? I would guess it is the second choice (anticlockwise) and that the nose of the duck looks like the one of a dolphin.

Merlin

[Paul Arden]

I mentioned the circular nose loop a few times. A few people have seen it. Basically instead of a dolphin nose it is a small complete circle unrolling at the top of the loop. I often think about it in these discussions.

My question is is it possible to recreate this with the string shooter? Maybe initially looped around a toilet roll holder when it’s turned on and then removed?

Cheers, Paul

[Paul Arden]

One observation I made with Daniel is that I can only really remember seeing the DN appear with top pointed loops. And tight ones.

I like this photo. This me casting in Norway at the Worlds…

What is interesting is a) there is a Dolphin Nose (of course!) but also b) the section of the line that has angular momentum is tiny!

2E1ABFA5-A260-44DC-B24E-A9903BDD9807.jpeg (11.84 KiB) Viewed 1870 times

Even though the loop is relatively wide, the part that is actually rotating is about the size of a fist.

I suppose what I’m wondering in an unscientific way, is if the DN a by-product of angular momentum?

I’ve been meaning to make a String Shooter. You’d think in lockdown I’d have found the time to do this I do at least have the electric motor!

Cheers, Paul

[Lasse Karlsson]

I mentioned the circular nose loop a few times. A few people have seen it. Basically instead of a dolphin nose it is a small complete circle unrolling at the top of the loop. I often think about it in these discussions.

My question is is it possible to recreate this with the string shooter? Maybe initially looped around a toilet roll holder when it’s turned on and then removed?

Cheers, Paul

I can almost make it on command with the MPR line. Have you tried ? Catching it on film has been the hard part, but didnt try in earnest, will do soon..

Cheers
Lasse

[Paul Arden]

I haven’t tried with MPR. For me i believe it’s a disconnect between haul conclusion and butt stop. I can’t do it on demand but also I haven’t spent enough time on it either. If you have semi-mastered it then maybe it’s possible to get a couple of spinning loops in there and not just one?

It must be possible with the string shooter. Those guys making them would love it if it is. Awesome but yes I need to nail this with the rod. I assume there is a circle and a DN? Or does the circle replace the DN? We need to get one on video!

Cheers, Paul

[gordonjudd]

I would guess it is the second choice (anticlockwise) and that the nose of the duck looks like the one of a dolphin.

Merlin,
You are right the loop in that photo had an anti-clockwise rotation.

Bruce had the bottom of the Duck beak on the loop being supported by a chair for some reason. I don't know what the free form shape with no support might have been, but you can see it has two inflection points where the curvature goes inward that are not present in the catenary shapes predicted in the string shooter papers.

Gordy

[gordonjudd]

Even though the loop is relatively wide, the part that is actually rotating is about the size of a fist.

Paul,
Particles do not need to follow a curved or rotating path to have angular momentum. As noted in this note ,

Particles in straight line motion may also have angular momentum if the particle is moving off-axis.

Gordy

[Paul Arden]

Thanks Gordy. I’m not sure how much use that piece of knowledge is to me! Does it have much bearing after the line reaches the point of the loop and becomes the rod leg? I really don’t know.

Where I’m looking at is the radius of the loop. With Merlin’s drawing it’s quite obvious how to measure R. However when you look at Graeme’s videos and the top pointed loop I posted, R would appear to be very much smaller and only really applies to top of the fly leg loop up to the point?

Thanks, Paul