Swing, Spring, Whip

[gordonjudd]

So if we take each piece of 1cm mass and assign an instantaneous centre of rotation to each section, a bending rod will have many instantaneous centres of rotation.

Vince,
Exactly, because the rod is not a rigid body different sections of the rod will have different instant center of rotation as well as the different angular velocity values that Tobias has pointed out.

And to get the K.E. of the rod you would have to use those different rotation center values (and different omega and mass values along the length of the rod) to calculate the correct K.E. of the moving rod using the rotational dynamics energy value of K.E.=sum(1/2*I*omega.^2) values.

Gordy

[VGB]

Gordy

No you don't have to use individual ICR, you just use a single reference frame as Tobias has. ICR are only suitable for use on a rigid body and you can't just ignore that point.

Vince

[Torsten]

Gordy,

I think Vince is right; ICR applies only to rigid bodies.

I think Tobias means with the rotation center the element with the highest rotation speed along the blank.
I'd rather move this discussion to the relevant thread, but I've found not the one about Tobias acrticle.

[Merlin]

I think Tobias means with the rotation center the element with the highest rotation speed along the blank.

Hi Torsten

I do not think so for having discussed the point with Tobias and Dr Schmitt. A good candidate corresponding to the criteria above is the point of maximum bending moment. It does not comes from the butt, rises towards the tip and then go down in the butt as described by Tobias. It starts from the tip, goes down along the shaft and rises again towards the tip.

IMHO the difficulty to define the "rotation center" mentionned by Tobias explains why no one can start a theoritical approach of it.

The "pirouette effect" corresponds to the chord and its effect on the MOI of the rod, it eases the loading of the rod but uneases the unloading. The "whip" effect does influence favourably the tip speed as the rod butt decelerates, just as it promotes kickback at the beginning (incidentally, Tobias does not show "red circles " for that phase of the cast in his video, it is limited to unloading).

I do not think that this figurative approach can lead to a mechanical understanding which can be translated into a few equations showing possible clues.

Merlin

[Bernd Ziesche]

Hi everyone,
thanks for sharing all the fine info. Not easy to follow though.

Tobias,
when I look at all your drawings tip path RSP0 to RSP1 is dead straight. Putting aside that this in my point of view is a wrong theoretical ideal in order to shape a tight loop, let's assume a signifcant more curved tip path pre RSP1 already.
The rod tip obviously (following the investigations done by slomos yet) still speeds up between MCL all the way until RSP1. Grunde (and others) proved that pretty well.
Does this speed up effect the hole fly line in the same way or does it mainly work on the first part of line just behind the tip (when curving downwards)?
Lasse,
any conclusions here from casting with those markers on your line?

To all,
was there ever any measurement of a) how much force it takes to put in max rod bend compared to b) how much force against the tip the line outside the tip provides in that accel. part between MCL and RSP1?
Shouldn't we just measure those forces to get a more precise idea of where the energy stored in the rod really goes?

No offense now!
Following all this stuff for years it somehow seems to me yet no one feels 100% safe to know all details about this energy flow? (Please step in, if I got this impression wrong!)

Thanks,
Bernd

[Merlin]

Hi Bernd

I'm afraid I do not understand your goal with your question. Did you read the pdf quoted in post # 1?

Merlin

[Bernd Ziesche]

Hi Merlin,
Yes, I have, but not understanding all of it. Reading your fine article it left the impression on me, that modeling all these effects in one model must be very difficult and high variabel? I was wondering, how the kinetic energy of the fly line was calculated. Was it calculated for the hole line, a certain part of line? When I follow the angle between the middle part of fly line and the tip direction when all three effects (swing, spring and whip) take place, I am not understanding yet, what this means to the relationship between the kinetic energy at tip position relativ to the kinetic energy for every part of fly line. Isn't that essential in modeling to get percentages for the impact of each effect?
(Little confused though)
Regards
Bernd

[Merlin]

Hi Bernd

The model considers that the whole line has the same speed up to the launch point, it does not considers the shaping of the loop, nor the flight of the line, it concentrates on the rod in fact (it was made for rod design).

The illustrations in the article show variability: in between rods, in between carries for a given rod, etc. The aim was to give typical orders of magnitude, knowing that things can change with casting conditions (and there are quite a few).

I'm not after pinpoint accuracy when using it, I just need consistent variations along mechanical laws.

Merlin

[Paul Arden]

Finally had more of a chance to go though and think about this some more. What would happen if instead of having a tapered tod you had a level rod? The whip
effect would increase?

(Just trying to get my head around this!)

Thanks, Paul

[Merlin]

Hi Paul

A whip is a very very soft tapered fly rod. The following illustration confirms that the amplitude of the whip effect comes along with softness:

whipbroom.JPG (29.76 KiB) Viewed 4166 times

The absissa "1" corresponds to a standard rod.

Merlin