Generic Loop Shape

[Walter]

You've probably seen this figure 2 from the Perkins-Bono paper, "Effects of Loop Shape on the Drag-Induced Lift of Fly Line".

My question, at this point, is whether we believe any of those shapes actually representative of the most common loop shape, or shapes, that we typically see when casting? I've modified the "climbing" loop shape a bit to make it pointier, by increasing the distance from A to B, and removed a vertical constraint on the two circular portions to see if this could be used as a generic shape for discussion purposes. I'm curious what people think about this. Thanks!

[Graeme H]

I'm loathe to use the labels applied in that diagram to describe the loop shape. The first two imply loop shape produces an effect that is not shown to occur.

I see the 1st, 3rd* and 4th shapes often. I don't think I can recall seeing the 2nd shape and I can't imagine a rod tip path that would produce that shape when the fly leg is the upper leg.

* The 3rd shape is a stylised version of the very common elliptical loop shape. In the real world, I have not seen anything with straight sections A-C and D-F.

Cheers,
Graeme

[Walter]

Back when we did engineering drawings by hand we made ellipses using segments of a small circle for the pointy ends and segments of a larger circle for The AC and DF sections.

Personally, I think the wedge shape and elliptical shapes are most common. Circular loops would be a subset of the elliptical loops.

[easterncaster]

On any given weekend, on any given trout stream:

[Paul Arden]

I’ve seen 2 very often. I remember Herb called it the “rat’s snout loop”. It was very typical from APGAI instructors in the UK when I first joined. Henry Lowe who I spent a lot of time with, mostly threw these. High backcast, 12.30-10 arc. I never saw them falling however.

Over the years I think maybe it’s perspective, tip path and of course trajectory.

Cheers, Paul

[Paul Arden]

Obviously there is a lot of stuff in this that is wrong. It was written in April 1999 before the Board existed.
https://www.sexyloops.com/flycasting/tloopshape.shtml
(Nice misspelling of damping )

It was in fact a NZ fishing magazine and the author was Herb Spannagl who I later met and was on the Board for many years. He was the guy later who named and popularised the Tongariro Roll Cast.

Cheers, Paul

[VGB]

On any given weekend, on any given trout stream:

And Stillwater. Usually, preceded by an open back cast loop.

[Mangrove Cuckoo]

Sorry if this is slightly off topic but I wanted to share something I recently encountered in case any of y'all were not aware.

Visiting a local fly fishing nut and he hands me this cheap plastic toy with line attached. It was a loop generator like one I saw discussions about here on SL. The string is a continuous loop and a tiny battery drives a motor that keeps it spinning.

I only played with it for a few minutes, but the predominant loop shape was a dolphin nose. The only way I could form a narrow and pointed loop was to aim it straight up.

I can get the manufacturer name or where he purchased it if anyone is interested.

[Merlin]

Hi Walter

There are some calculation issues in this paper, I sent a note to Paul on this topic in April 2022. It is possible to develop a generic calculation for loops made of three circles with various position as indicated in that note.

Merlin

[Walter]

Thanks Daniel,

I don’t intend to use any of the calculations in that paper. I’m currently looking at velocity profiles around the loop for the tethered cast, shooting cast and pull back. I’ll probably use that information to look at things like angular momentum but I don’t think I’ll be looking at lift again.

I’m not sure if I’ll present any of it but if I do I was hoping to avoid the “real world loops don’t look like that” comments by letting people decide beforehand which shape or shapes they would accept as typical real world shapes. It seems that there are no right answers.