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## Two heads cast at the same time

Moderator: Torsten

gordonjudd
Posts: 1298
Joined: Sat Jan 19, 2013 11:36 pm
Location: Southern California

### Re: Two heads cast at the same time

The line path NEVER mimics the loop shape in a normal tethered cast.
Graeme,
Unless you look at it in moving frame attached to the front of the loop as is done in the Lingard and Gatti-Bono papers. Your own tracking of the markers in a moving frame showed that to be the case. That informative video also shows it had about 3 missing frames that cause the gaps in marker dot paths.

Thanks for taking the time to produce the above video. I know how much time it takes to digitizing video files.

Even Newton knew that the results you get in a moving frame that is moving at a constant velocity and direction (thus an inertial frame of reference) should match the results you get in an earth frame so I don't know why you seem to think a moving frame should not be used to analyze loop propagation.

Gordy

Paul Arden
Posts: 13205
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
Contact:

### Re: Two heads cast at the same time

Hi Graeme,
I believe you have the tapering line always slowing the loop and you write here
Lighter line trying to turn over heavier line, rotation is delayed,
My point is that sometime it accelerates, in fact in your traced loop it also accelerates and when I asked you why you said it was because the leader was not very good.

What I’m really interested in is your explanation as to why a tapered front can cause both acceleration as well as loop deceleration (deceleration is what we mostly want right? ). I know that you disagree with Gordy but I would love to hear your explanation as to why each of these can occur.

Thanks!!
Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

Lee Cummings
Posts: 339
Joined: Tue Feb 19, 2013 12:23 pm

### Re: Two heads cast at the same time

John Waters wrote:
Thu Jun 20, 2019 12:27 pm
Thanks Lee, interesting video.
Just a simple question from me, if you cast each profile with the same rod, one at a time, which one casts further?

John
Hi John

Depends on the conditions, but mainly for here the 70m plus numbers came from casting reversed heads.

Cheers
Lee

Paul Arden
Posts: 13205
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
Contact:

### Re: Two heads cast at the same time

Hi Graeme,

Sorry I just reread your third post. I can see that it’s still being assessed.

Have you had any more thoughts on it since then?

Cheers,
Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

Will
Posts: 292
Joined: Thu Jan 10, 2013 9:44 pm

### Re: Two heads cast at the same time

Hi Merlin

Many thanks for that. Makes sense to me in principle, and explains how tapers can be said to both accelerate and decelerate loops depending on parameters.

Cheers!

Will
Lineslinger
Barrio Pro-team
SGAIC
AAPGAI

"The only advice it is necessary to give the angler… is to avoid any approach to foppery, as trout have the most thorough contempt for a fop…”
WC Stewart

Merlin
Posts: 1372
Joined: Wed Jan 09, 2013 8:12 pm
Location: France

### Re: Two heads cast at the same time

You are welcomed Will.
I hope that Paul can share your views some day

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

John Waters
Posts: 759
Joined: Mon Jan 14, 2013 9:16 pm

### Re: Two heads cast at the same time

Lee Cummings wrote:
Thu Jun 20, 2019 2:59 pm
John Waters wrote:
Thu Jun 20, 2019 12:27 pm
Thanks Lee, interesting video.
Just a simple question from me, if you cast each profile with the same rod, one at a time, which one casts further?

John
Hi John

Depends on the conditions, but mainly for here the 70m plus numbers came from casting reversed heads.

Cheers
Lee
Thanks Lee, in my post about different profiles for the same length and weight of line, I mentioned line designs for wind variations and your observations support that. I just want to affirm we are talking about overhead casting, it does not matter about rod length. Also, have you cast both lines in calm conditions?

Thanks again,

John

Graeme H
Posts: 1762
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Two heads cast at the same time

Paul Arden wrote:
Thu Jun 20, 2019 3:08 pm
Hi Graeme,

Sorry I just reread your third post. I can see that it’s still being assessed.

Have you had any more thoughts on it since then?

Cheers,
Paul
None that have changed my point of view. For the time being, I'm pretty happy with that explanation of why the variation in the behaviour of the leader/fly can be controlled by altering the tension in the rod leg.

If some sensible evidence or thought-provoking ideas are presented, I'll reexamine it. (Once again, thanks James for prompting me to examine the impact angular momentum again.)

Cheers,
Graeme
FFi CCI

Graeme H
Posts: 1762
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Two heads cast at the same time

gordonjudd wrote:
Thu Jun 20, 2019 2:19 pm
Even Newton knew that the results you get in a moving frame that is moving at a constant velocity and direction (thus an inertial frame of reference) should match the results you get in an earth frame so I don't know why you seem to think a moving frame should not be used to analyze loop propagation.

Gordy
Because the loop has no inertia of its own. Only the elements of line within it have mass and velocity.

Let's look at something that can be easily analysed with a moving frame of reference: the valve on the front wheel of Paul's triathlon bike. If someone were to track its path along the road in an Earth frame of reference, it would describe a cycloid.

image003.png (7.35 KiB) Viewed 382 times

That looks pretty nasty. Trying to analyse the physics of the valve's motion from that would be quite difficult.

However, from Paul's point of view on the bike (since he occupies the moving frame of reference), the valve is traveling in a circle around the axel. He can look down and see it going around and around, over and over. The moving FoR is valid here because the wheel on which the valve sits is a solid object, with both mass and velocity (hence inertia) and the separate parts of the wheel do not change their position relative to each other.

That is, they maintain a consistent spatial relationship with each other.

The physics of the valve's motion are fairly easy to analyse from Paul's point of view. It's just 5 grams of metal traveling in a circle around the axle. That's the power of a moving FoR.

When Paul crashes into an Asian Elephant on his training ride (because he's watching the valve on his front wheel), the bike stops moving, wheel stops moving and the valve stops moving. The elephant cannot stop the valve alone and let Paul ride on by. Stopping any part of the wheel stops the whole wheel. A moving FoR is valid here because the hub, spokes, rim, tyre and valve can be considered as a single mass.

The physics of the fly line in motion can't be analysed in the same way. Stopping the loop has no impact on the line in the fly leg. It keeps moving forward. Casting at an Asian Elephant doesn't mean the fly drops as soon as the loop hits the beast. The fly leg has inertia and it keeps piling into the elephant with no loop in sight.

A moving FoR focusing on the loop is not valid because mass is always moving in and out of the object (loop). In physics terms, it's no more a single object than a flock of birds is. Shooting one bird in the flock does not stop the flock from flying past: the bird does not maintain a fixed spatial relationship with those around it. In the same way, stopping a single marker on a fly line does not stop the others behind it from continuing on their path.

Tracking a single point on the line shows that it never follows the form of a loop. To draw it any other way is misleading.

Cheers,
Graeme
FFi CCI

Merlin
Posts: 1372
Joined: Wed Jan 09, 2013 8:12 pm
Location: France

### Re: Two heads cast at the same time

I think Eugene pointed the cycloid path some time ago. But so what? What do we get from angular momentum? Can we assume it is conserved and which practical conclusion can we get from that?

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life