Wide Loop Inifficiency?

[gordonjudd]

Hi Graeme, by focused 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?

Paul,
Why would the kinetic energy of a nominally straight length of line traveling at some velocity be any different than the KE of a curved length of line traveling at the same speed along its curved path?

Because of loop morph, I would think the KE in the y direction in the curved length of line would not be lost to the lost to the cast. Although the added form drag in the curved line would be higher than the drag losses in a horizontal line.

I agree with Bernd that there are no straight lines in casting and have yet to see a long fly leg that is perfectly horizontal so that all of its KE would be confined in the x direction.

Focused (i.e., confined to one direction) or not, energy is energy.

Gordy

[Paul Arden]

Hi Gordy,

Loop morph can go two ways, it’s not necessarily wide to narrow, but instead, particularly if the tip path is domed, or the backcast misaligned, it can open. Then it’s also quite possible then for the loop to collapse, even with identical KE. In fact it’s rather a common casting fault!

Cheers, Paul

[Graeme H]

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?

Yes but in addition, the cast really must be aimed very well at what it essentially a single point in space.

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.

Why do you think this? What parts of the line are traveling through the air? Can you expand on this?

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.

The highlighted bit is critical. The morphing comes from high tension in the rod leg produced by

• the high line speed in the fly leg travelling at a fixed point in space and
• by maintaining or increasing tension at the other end of the rod leg with the rod tip.

Cheers,
Graeme

[Paul Arden]

Well I think loop morph is a subject that no one truly understands or can predict. Oh I’m looking at an elephant. That’s cool.

Anyway so the reason I think air drag/ skin friction plays a part it is a force acting on the line. It would be odd to me that it didn’t affect loop shape as it unrolled.

The reason I think momentum of the incoming fly leg plays a part is because it has all sorts of directions, it can be travelling up, down, sideways and this is all going to affect the shape of the loop.

Elephant is swimming now.

016CB7CD-C52D-45C1-ADF0-6D499BE97DD0.jpeg (147.82 KiB) Viewed 2371 times

I agree with you that tension plays a role too.

Right gotta get organised. It’s a supplies run day for me.

Cheers, Paul

[Paul Arden]

In town now. So for me anyway, any change in loop shape would be classified as “morph”.

It’s not atypical to see a loop start wide, narrow and then open. I don’t think that’s simply a matter of tension. Mostly I see loops tightening from the bottom and opening from the top. Is that how you see it Graeme?

Cheers, Paul

[Lasse Karlsson]

Its starts wide because the last part of the stroke went downwards and opened it up, it tightens because the majority of the stroke send the majority of the line in more or less the same direction, and it opens up at the end because tension gets low and the line bit at the end came from below and was dragged upwards.

Cheers
Lasse

[Graeme H]

^^^
This.

[Paul Arden]

^^^
This.

Dragged upwards? I’m not sure I understand that bit

Cheers, Paul

[Graeme H]

[Torsten]

Hi Graeme,

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.

I think you mean rather the total momentum, because kinetic energy is a vectorless quantity and can't be focussed in a direction.
And of course, if all mass points of the line are aimed in one direction, you would maximize the total momentum for the given total kinetic energy of a fly line. The direction should be parallel to the line and the line itself straight to minimize the drag (because skin friction is much smaller than form drag). Good loops have often these properties (straight fly leg). Simplest example is the above board logo.

Morphing loops, changing loop shapes, I see two major causes (assuming the above ideal straight fly leg):
(a) Aerodynamic drag (skin friction+form drag)
(b) Tension due to change of momentum at the loop front

I think I've emailed Daniel once a animation from my old model, I've seen some morphing even without aerodynamic drag, but it was much more pronounced when I've turned aerodynamics on. AFAIK Gordy made once a experiment with a leaf blower and got some morphing (?)

Torsten.