Simple question

[Mangrove Cuckoo]

Generally speaking... does a flyrod unload uniformly?

And, y'all engineers don't have to stop at generally if you don't want to... I don't mind being challenged to think a bit.

[Paul Arden]

Hi Gary,

I’m not one of the engineers What do you mean by uniformly? I often see an S-shape at “RSP” where the butt or middle of the rod has passed through RSP before the tip. I liken unloading more like a wave travelling up the blank. How that progresses has more to do with taper and mass (and maybe some other stuff ). This I suppose is the “whip effect” of the unloading rod mentioned a few years ago.

But I am already out of my element here. Merlin submitted this document some time ago which will clear up any misunderstandings…

https://www.sexyloops.com/pdf/SwingSpringWhip.pdf

Cheers, Paul

[Merlin]

Hi Gary

As I was born in Normandy I can say that the answer maybe "nearly". A rod reacts with multiple modes (usually the first two or three, others are damped very quickly). You may see S shapes, more or less, and it would be an exception that it unbends with only the first mode, something I think one would name "uniform". This is also due to the fact that the caster's input in itself contains several main frequencies which are linked to joints (e.g. shoulder, elbow and wrist).

Some order of magnitudes considering amplitudes. If you define 1 for the first mode, then the second mode would be 1/10, the third 1/100, etc. The rod maily unbends with its first mode. They are all superimposed, and travel along the rod at differents speeds. The higher they are, the faster they damp.

Merlin

[Mangrove Cuckoo]

Paul,

Thanks for the article. That is going to require some time, peach and quiet, and probably some bourbon for me to begin to even try to digest it!

Merlin,

If I take a 4 piece flyrod apart and vibrate each section individually, I suspect each section will have its own particular fundamental frequency. Or am I way off base?

Is the reason why some rods just cast "sweet" because the individual pieces' frequencies are "in tune" with the others?

I had not considered that different people may have unique frequencies in their shoulder joints, elbows and wrists. I knew that everyone has a unique muscle make up of fast and slow twitch fibers, but I had not considered what makes some folks more "graceful" than others... maybe it has to do with frequency and harmonics of the joints.

Last question... I promise!

Using the terms from the article: Can one part of the rod, say a lower section, be in "fling", while an upper section is still in "swing"? Or, is it because they are joined together that they act as a single entity?

That latter situation is kind of what I was asking when I used the term "uniformly".

OK... I will go quietly back into my crazy corner... at least for a while.

[Merlin]

Hi Gary

If I take a 4 piece flyrod apart and vibrate each section individually, I suspect each section will have its own particular fundamental frequency. Or am I way off base?

Yes, of course, but they are very different, up to the point that you may have 4 Hz for the tip and several hundred for the lower butt section. I use to measure the frequencies by starting with tip only, then tip and tip mid, then tip, tip mid and butt mid, and finally the full rod. In that case the numbers are closer together. Unfortunately, one cannot derive a magic recipe for building a sweet rod from those measurements; you can design differently pieces of rod having similar frequency characteristics. The tuning story is rather old; I think it started with the DH rod named “grant vibration” (ca 1895), supposed to offer some harmony all along the rod with the help of acoustics considerations. There is a video of a cast with such a greenheart rod on Youtube and one can see the typical butt action of that rod and its amazing stability (no after vibrations, and this is typical of the design). It is said to use a constant stress level all along the rod and this is something used by some cane rod builders. One can evaluate the speed of sound all along a rod and usually, it is decreasing more or less linearly from butt to tip. Is perfect linearity the big secret of rod design?

Using the terms from the article: Can one part of the rod, say a lower section, be in "fling", while an upper section is still in "swing"? Or, is it because they are joined together that they act as a single entity?

All motions (swing, spring, whip) take place together at different extend and time. The latest in time is the whip effect. It is practically very difficult to separate swing from spring, and there are interactions as you can see in the article. Sections do not behave independently for sure, well or badly designed.

Merlin