Dissecting the haul

[gordonjudd]

In Graeme’s videos the situation at start is close or fits mechanical waves,

Merlin,
I don't see any point on the line that remains in the same place after the disturbance passed through it as it was before the "wave" came through. Do you see a point on the line where it stayed in place?

The case with the marker on the rope shows what happens for a true mechanical wave. That marker went up an down as the transverse wave (wave vibration was orthogonal to the propagation direction of the wave) passed through it, but it was at the same place after that happened as it was before. I.e. no transport of the medium was involved as expected for a true mechanical wave..
Gordy

[Merlin]

Strictly speaking you are right Gordy, but I try to be magnanimous.

Merlin

[Lasse Karlsson]

Cool, looking forward to that!

I only get flying spaghetti if I introduce tracking flaws. Throwing a shootinghead version of the MPR line indoors, if I start the loop and let go, it unroll fully. If I release it before, and its good, it flies much like a javelin, not going to spaghetti. So I am really looking forward here.

Cheers
Lasse

Hi Lasse,

In post #144 I was able to show a cast that fails without tension in the line. Here's that video again for reference:





At the time I posted, I didn't have any information about the speed of the rod tip prior to loop formation so I was not able to confirm that the failed cast was made with enough line speed to deliver a complete cast, had I not killed it by removing tension.

I can now confirm that the completed cast had a lower maximum rod tip speed than the failed one (~13 m/s for the completed cast, ~15 m/s for the failed cast.) This implies that the failed cast would have rolled out successfully without my intervention.



Successful_Cast.jpg



Failed_Cast.jpg


I'm yet to fully track the line markers, but it's apparent already that when the rod leg markers move forward and tension is lost, the loop no longer moves along the line. This is what we'd predict from examining the loop as a transverse wave.

I'll be interested to apply a moving frame of reference centred on the loop nose here.

Cheers,
Graeme

Hi Graeme

Thanks, I do have a question though, the failed cast is clearly begun long before the line has gotten a chance to straighten in the backcast, you start when the fluff is above the rodtip. Is that also the case for the cast that didn't fail?

Cheers
Lasse

[Graeme H]

Hi Graeme

Thanks, I do have a question though, the failed cast is clearly begun long before the line has gotten a chance to straighten in the backcast, you start when the fluff is above the rodtip. Is that also the case for the cast that didn't fail?

Cheers
Lasse

Hi Lasse,

Yes, I seem to do that on every cast in the clip.

Cheers, Graeme

[Bernd Ziesche]

Hi Graeme,
Looks to me like the fly-leg has a lack of momentum when collapsing. That's what happens when not allowing the previous bc to straighten. Doesn't need an additional reduction in rod leg tension in my exp..
Regards
Bernd

[Graeme H]

I think we have two different things here. In the first case of a wave, it is the wave that propagates. In the second case it is the fly leg that moves and rolls over.

To describe a loop as a transverse wave to me would mean that it’s the wave itself that is responsible for the loop unrolling. However in the case of the loop it appears to be the momentum of the fly leg that is the cause. (Which is why it works on the floor as you point out?).

That’s not to say that there are not aspects of both, or that we can’t view it from one perspective, with difficultly.

Where does angular momentum fit with you?

Cheers, Paul

Back to that part that I skipped last night.

In bold above, there is no "wave turning the loop over". The wave is the loop. That's the point I'm making. Your statement reads to me as "it's the wave turning the wave over".

There is nothing wrong with saying the fly leg momentum is turning the loop over. Newton's laws of motion still apply within wave particle motion. It doesn't matter whether it's a mend or a loop - the opposing forces in a line move the particles within the line in a shape we observe as a wave. It's why those Tracker videos are so instructive: analysing them shows there is no angular momentum to be found because none of the particles are travelling in an ovoid or circular path, much as it might appear that way.

Anyway, there seems to be some confusion about transverse waves being not waves if they transport the medium. Here's an extension of the video I produced last night showing how the wave does indeed transport the medium in every cast we make.






Clearly, the bends in the line I've progressively extended in this video as a transverse wave can transport a fly away from the the centre line of the casting arc. The point here is that if we had an infinite amount of tippet that we could hang from a tree and tied as a dropper on the fly so that the line never ended, we'd transport the fly out to the maximum amplitude of the wave we make and still have connection to the tree. We don't have an infinite amount of tippet, but the wave reaches maximum available amplitude when the loop passes the fly.

As for the point I've seen about the fly not returning to the same place: a front cast is only half the wave. Just like those falling transverse waves from my video of 5 years ago, sweeping to the left (say, "the front cast") is only half the wave. The other half is sweeping back to the right, so that the tip of the fly rod is returned to the original location. That produces a periodicity that we can measure if we want to, and returns the line to a starting position if that seems important.

How does that relate to real casting? The six steps of a PUALD is one full cycle of a cast. The fly returns to the same location is started in. Some might cry semantics, but try making an overhead cast without first making a back cast. False casting 6 times is making three complete waves in the air.

If one only ever attempts to analyse half the cycle, it's always going to be an uphill battle with the big picture. We'll be stuck in the weeds.

Both sides of the story

WavesInAir.jpg (19.47 KiB) Viewed 311 times

Cheers,
Graeme

[Lasse Karlsson]

Hi Graeme

Thanks, I do have a question though, the failed cast is clearly begun long before the line has gotten a chance to straighten in the backcast, you start when the fluff is above the rodtip. Is that also the case for the cast that didn't fail?

Cheers
Lasse

Hi Lasse,

Yes, I seem to do that on every cast in the clip.

Cheers, Graeme

Hi Graeme

Could you verify? Seems doesn't really cut it, as Bernd points out, wasting strokelength due to slack in the system will alter the outcome. It smells a bit like Paul trying to prove a soft rod tails when a stiff rod throws a nice loop, and having the starting point being two very different outlays

Will try to replicate your findings as soon as we have some sun here.

Cheers
Lasse

[Graeme H]

Hi Graeme,
Looks to me like the fly-leg has a lack of momentum when collapsing. That's what happens when not allowing the previous bc to straighten. Doesn't need an additional reduction in rod leg tension in my exp..
Regards
Bernd

I understand momentum to be the product of mass and velocity (itself a vector) The fly leg on the failed cast is faster than the fly leg on the successful cast at the moment of launching and the "launch angle" is not significantly different. I haven't overlaid the tracks from each cast just yet, but I'll do so now. (Edit: all the data I digitised yesterday seems to be lost due to the unconventional saving system Tracker employs. I'll do this rework later when I've got time.)

Importantly, the velocities of the respective fly legs during the cast progression will be different, even with the same launch speed. This is established with Tracker and is actually one of the fundamental evidentiary data sets that supports this concept. The horizontal component of fly leg velocity increases as the loop progresses in a normal cast. That happens because the tension from the rod leg is pulling the line in the fly leg (see that snap cast video for visual proof, or ask for the tracker fly leg velocity results from any cast except these collapsed ones, where it does not accelerate.)

In these collapsed casts, the fly leg does not accelerate in the horizontal direction. It acts as a true ballistic object, gradually losing horizontal velocity, perhaps from losses due to air drag.

This is the main point of considering the loop as a wave: By controlling tension after loop formation, we can improve the cast after we've "completed the stroke". If slack is the enemy of the cast, tension is its best friend! (Note the slack between the reel and the stripping guide in the failed cast ...)

Anybody who wants the original videos from the phone (warts and all) can PM me here and I'll send you a link to download it. There are lots of examples of these casts in the files, including the series of casts made from the other direction in case wind was cited as a reason for the collapse. Many of the casts I didn't have faith in because I felt like I had unconsciously undercooked the cast. Some of the best examples occurred at the start and end of the clip, where Apple for some reason known only to themselves, speeds up the video to normal speed instead of keeping slo-mo.

Anyway, since it seems so hard for all to to see the just how dramatically different the cast results are, I will shoot it again so that the back cast and the front cast are all visible. There will only be tip speeds in the Tracker though because video resolution is already at the limit on these ones. Going twice as wide will prevent line tracks being digitised.

Please, do not take my word for it. This experiment is repeatable in any (land) location of the world. You guys can do it for yourself. Just make sure you have dialled in the slowest possible cast you can successfully achieve before attempting it. The reason the loop collapses is the removal of tension. If your fly leg is faster than you can move the rod tip forward, the fly leg will reinstate tension in the rod leg as you attempt to kill it.

Cheers,
Graeme

[Paul Arden]

In bold above, there is no "wave turning the loop over". The wave is the loop. That's the point I'm making. Your statement reads to me as "it's the wave turning the wave over".

Surely a wave travelling through a flyline is not the same as the flyline taking the shape of a wave? A wave moves because it’s a wave. A loop unrolls because the fly leg has momentum.

Unfortunately it’s very difficult to make experiments that appease everyone. As can be seen by Lasse’s comments on mine. I find it very difficult to stall an unrolling loop. It needs to be cast at a very slow speed to begin with. Lasse on the other hand is still wrong.

Cheers, Paul

[Graeme H]

Hi Graeme

Could you verify? Seems doesn't really cut it, as Bernd points out, wasting strokelength due to slack in the system will alter the outcome. It smells a bit like Paul trying to prove a soft rod tails when a stiff rod throws a nice loop, and having the starting point being two very different outlays

Will try to replicate your findings as soon as we have some sun here.

Cheers
Lasse

I get the point. I'll be happy to send you a link to the original videos if you feel like scrolling through them.

But as noted above, it's easy to replicate for yourself. Both casts need to be VERY slow though, or the fly leg tightens the rod leg as you try to introduce the slack.

Cheers,
Graeme