Whip effect

[Paul Arden]

Hi Merlin,

I’ve been reading “whip effect” in your calculations. Spring/lever/whip.

Whip is new to me, what is it please?

Thanks!
Paul

[Merlin]

Hi Paul

Since the word was introduced by members of the finnish caster’s club, it would be nice to get an explanation from them, using caster’s vocabulary and not engineer’s one

Many thanks in advance to Sakke or Esa.

Merlin

[Paul Arden]

Hi Daniel,

Is this second node Frequency unloading the rod caster as you understand it? Just trying to follow where you are? I have a new hat for Sakke

Cheers, Paul

[Torsten]

Hi Paul,

this phenomen describes the energy transfer of the rod mass in motion to the fly line. The hyphothesis is, that the kinetic energy of the lower part of the rod is transferred to towards the tip and then also to the line. Tobias did some investigations, see [1]. So the mass distribution of the rod plays a major role here.
I'm guessing it's not that easy to model; you would need a FEM model or a multi-body simulation for that.

Thanks,
Torsten

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[1] http://www.passion-fliegenfischen.de/_e ... -momentum/

[Paul Arden]

Thanks Torsten. That’s very interesting and reminds me about a conversation back in around 2003 when it was questioned whether a rod could unload during the casting stroke (with regards the stopless/170).

So on a practical course which properties of the rod (apart from a flexible butt) would you experiment with to enhance the effect? Is pull-back a method of forcing this behaviour? If so there are sacrifices/compromises in rod action. I’d be happy to organise some experimental blanks.

Cheers, Paul

[Merlin]

Hi Paul

A rod does unload before the end of the casting stroke. The whip effect is some kind of tranmission of angular momentum from butt to tip during the loading and unloading of the rod.

When I started modeling that with the "sprig and marble" model, it could not involve anything but one mode, and the inertial effect is the source of SDM, kick back or forward, without explicitely involving a higher mode. There is some way to optimize it by tuning the relative importance of the three corresponding equivalent masses (a good headache).

With a SH rod, higher frequences can be excited by our wrist. Typically the second clamp free mode. You do not need that with a DH rod, the frequency range is lower. Now the question is to know whether using the second CF mode (or the first FF one) with a DH rod allows constraining the loop size because of the rebound of the rod, which takes place on that other mode, with a rotation around a node in the tip. This is why I asked that question to DH casters.

Merlin

[sms]

I use overhang and early release to control the loop size, so it is not related to rebound amount.

[Merlin]

Thanks Sakke

There is no advantage in higer modes then. Here is a picture of the energy distribution for SH (glass) rods having various stifnness but the same mass (just as if it was possible to change only the modulus of glass):

SWL intermediate.JPG (29.63 KiB) Viewed 4958 times

The abscissa is N/m. S= spring energy, W = whip energy and L = lever energy.

Merlin

[Torsten]

Hi Paul,

So on a practical course which properties of the rod (apart from a flexible butt) would you experiment with to enhance the effect? Is pull-back a method of forcing this behaviour? If so there are sacrifices/compromises in rod action. I’d be happy to organise some experimental blanks.

A steep (mass) taper would pronounce this effect, just like real whips.
See as example this: https://www.youtube.com/watch?v=U5mPcPn81-M

We don't have measurements for this effect yet, I'm guessing it's as difficult to show as the tension in the line
Daniel's model shows a smaller effect for SH than for DH rods.

I think we have such a 17ft. T120 glass/carbon monster in our training room - maybe it makes sense to compare.

[gordonjudd]

the kinetic energy of the lower part of the rod is transferred to towards the tip and then also to the line.

Torsten,
What is the mechanism for the energy transfer from the rod to the line?

Is there an actual transfer of energy from one medium to another as there would be for a transverse wave in a string with two different impedances or does the whip effect result in a higher tip (and hence line) velocity).

Since the impedance of the rod is so much different than the line I don't see how there could be much direct transfer of energy from the rod to the line as there would be in a transmission line having a smaller impedance discontinuity.
Gordy