Head at the rod tip increasing counterflex?

[nicholasfmoore]

Hi Paul,

Different C/F however… that difficult for me to say. With the head in the rings compared to running line - I think so. It’s like having a heavier rod tip. Heavier tips give more CF.

That makes much more sense than the head at the tip, now you've said it! Would you say that the reason for the increase in tightness is mainly due to the head being at the top of the loop?

Something I have noticed is that heavier lines on a given rod can sometimes result in better damping (head in the tip).

I've experienced that with some barstool rods, a lighter line often results in a tremendous cf wave no matter how lightly you hold the rod

Feel is a different thing, but we never get anywhere here when that comes up

True!

All the best

[gordonjudd]

I was wondering if the head at the rod tip contributes to making more counterflex than normal in relation to loop size?

Nick,
Doesn't Lasse's video show the reverse is true? It appears to me the peak counterflex increases as the length of the running line outside the tip increases.

If you want to get some really big counterflex values, try casting the rod with no line attached. I was amazed at how big the counterflex can be when no energy is transferred to a line.


Gordy

[Paul Arden]

That is amazing Gordy. I remember this when you posted it. So if I understand this correctly you have more rod bend at MCF than at MCL?

Cheers, Paul

[Viking Lars]

I don't believe that C/F is affected much by head in/away from the tip ring. But as Paul says, there's a clear difference in loops shape and I've always believed this to be a result of C/F not affecting the the head as it morphs from straight into a loop. Ie. the effect of the counterflex is absorbed by the thin running/shooting line which is unable to affect the head due to its low weight.

Lars

[gordonjudd]

So if I understand this correctly you have more rod bend at MCF than at MCL?

Paul,
That is true. With no line I was also surprised by how large the inertial bending of the rod happened to be.

The bendforms are different, but quantifying the bend as being equal the perpendicular difference from the rod tip to the broom stick butt projection from the butt angle, then the deflection at MCL was 1.66 m while it was 1.60 m at MRF.

Gordy

[Paul Arden]

Thanks Gordy. That’s actually quite staggering. How do you account for that? Did you also record MCF2?

Cheers,
Paul

[gordonjudd]

How do you account for that?

Paul,
Merlin probably has some quantifiable numbers, but I think without a line there is nowhere for the KE of rod at RSP1 to go other than into counterflex. With a line some of the energy goes into the mass of the line as the loop is being formed and thus the remaining energy left in the rod produces a smaller counterflex.

I think that is also why the counterflex with a large overhang the initial loop is formed in the small mass of the running line in Lasse's videos is larger than the counterflex you get when the loop is formed in in the larger rho_l of the head.

I suspect the reason the loop diameter gets smaller as the heavier rho_l of the head starts going around the loop is primarily due to the conservation of angular momentum. It is not strictly conserved since there are outside forces acting on the loop but I would think the r2/r1 radius values would be proportional to the cube root of the rho_l1/rho_l2 ratios of the running line and the head.

Gordy

[Paul Arden]

Thanks Gordy, certainly that fits the pattern. That would also explain why the opposite occurs and the loop opens when the front taper reaches the loop?

How would you explain loop diameter decreasing with a DT for example?

Perhaps an explanation for the MCF being of similar displacement to MCL is that you were adding force at some point while the rod was unloading? I’m sure there must be losses through air resistance. Alternatively is there a small degree of pull-back?

I also remember at the time being impressed by how much the rod flexed at MCL without the line. I had failed to appreciate what happened afterwards!!

Cheers, Paul

[gordonjudd]

How would you explain loop diameter decreasing with a DT for example?

Paul,
The angular momentum of a circular loop is equal to pi*rh0_l*r.^3*omega. If you assume omega=v_tan/r for a circular loop and that v_tan is equal the loop velocity over the ground for a tethered cast then there would be a r.^2 dependence on the loop radius for nominal change in the rho_l of the line or the loop velocity to keep the angular momentum of the loop about the same over some small time range.

Thus if the loop velocity over the ground stayed the same you would expect the r2/r1 radius values would be proportional to the square root of the rho_l ratios given by the line taper. That would hold for a sink tip line with different line densities as well so I should have referenced the square root of the rho_l ratios in the above post, not the cube root.

When the loop velocity increases at the end of the cast then the relative increase in the v_tan term could be larger than the decrease in the rho_l values related to the line taper and thus the loop diameter would decrease as the loop velocity increases at the end of the cast. That is a hand waving argument than needs to be supported (or refuted) by some measurements related to what happens to the loop diameter at the end of the cast for a tapered line.

Note the use of the conservation of the angular momentum is related to my simple minded intuition on factors that might impact the dynamics of the loop. It is not strictly valid since there are outside forces acting on the loop. You won't see the conservation of angular momentum referenced in many papers related to the shape of a propagating loop although James may have some references that I have not seen.

Hendry also predicted a sizeable decrease in the diameter of the loop based on the change in the vertical momentum of the loop due to drag forces. He predicted the loop diameter would decrease from .5 m to .25 m for a level line with a dia= 1.4 mm, rho_l of .0012 Kg/m, l= 40 foot and an initial loop velocity over the ground of 30 m/s. He also makes no reference to the angular momentum of the loop in his thesis.

Perhaps an explanation for the MCF being of similar displacement to MCL is that you were adding force at some point while the rod was unloading?

That is true. It is quite easy to get large angular butt velocities in a rod with no line.

Gordy

[Paul Arden]

Too late for this one Gordy! I’ll read it again with morning coffee Thanks!! Paul