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Upward Force from Form Drag

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Graeme H
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#61

Post by Graeme H » Sat Feb 17, 2018 9:52 am

Merlin wrote:If you shoot a video, you will see a marker on the inclined section going down nearly vertically (the red arrow).
Hi Merlin,

I tried to shoot the video but I was standing too far from the camera and could not make out the marks on the line.

In the same session I also shot another series of casts to show fly leg momentum, these much closer to the camera. Some of these were "sexy loop" shapes before they crashed into the net/board, so I think we can see that your conclusion of the mark moving down and very slightly forward is supported. Forward velocity in the inclined section of the sexy loop is very close to 0m/s relative to the ground.



Cheers,
Graeme
FFi CCI

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guest
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#62

Post by guest » Sat Feb 17, 2018 10:28 pm

Some great video there Graeme, thank you
Bright but shite

IANACI - There’s no such thing as absolutes

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Geenomad
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#63

Post by Geenomad » Sun Feb 18, 2018 11:52 am

Nice Graeme. Thanks.

Cheers
Mark
"The line of beauty is the result of perfect economy." R. W. Emerson.
https://thecuriousflycaster.com

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Merlin
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#64

Post by Merlin » Sun Feb 18, 2018 8:15 pm

This is the magic of sorcerers Graeme. :sorcerer:
Nice video. Amazing dolphin nose generation for tiny loops which reminds bed chains in similar conditions. My guess is that it is related to line stiffness.

:pirate:

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

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Graeme H
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#65

Post by Graeme H » Sun Feb 18, 2018 11:15 pm

Merlin wrote:This is the magic of sorcerers Graeme. :sorcerer:
Nice video. Amazing dolphin nose generation for tiny loops which reminds bed chains in similar conditions. My guess is that it is related to line stiffness.

:pirate:

Merlin
I suspect so too but I have three competing models in mind at the moment so I need to device some experiments to remove at least one, preferably two or more of those models. :)

The problem with the stiffness model is that it happens in slow casts with wider loops than what we've seen here. Wider loops should not approach the radius where line stiffness comes into play.

The other two things I have in mind are a standing compression wave and the inertia of the line mass resisting the acceleration due to "rapid" change of direction.

Devising experiments that disprove any or all of these hypotheses should keep my mind occupied for a while. :pirate: The inverted loops with dolphins noses absolutely removes the possibility of them being caused by gravity interacting with tension forces.

Cheers,
Graeme
FFi CCI

anjill
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#66

Post by anjill » Mon Feb 19, 2018 3:55 am

Hi Graeme,

Great video. :worthy: Standing compression wave would be my guess.

Regards,
Tony.

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gordonjudd
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#67

Post by gordonjudd » Mon Feb 19, 2018 4:30 pm

Amazing dolphin nose generation for tiny loops which reminds bed chains in similar conditions. My guess is that it is related to line stiffness.
Merlin,
Until you get to a ball on ball situation what is the stiffness of bead chain?

The image that Alejandro captured of the dolphin nose shape when he pulled a length of bead chain is blurred, but it appears there are still spaces between the balls.
Image

Dr. McMillen says the DN shape is related to the viscoelastic properties of the line, but I don't know if bead chain can be classified as a viscoelastic material either.
Standing compression wave would be my guess.
Tony, I don't know what a standing compression wave might be, but how can you get compression in a flexible string?
Gordy

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Graeme H
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#68

Post by Graeme H » Mon Feb 19, 2018 11:02 pm

2C42DDCC-FCCA-49F7-9D9A-FE1675891C8E.jpeg
Fly line has stiffness. This is a 6wt MED. The 8 in the video is stiffer again.

Cheers,
Graeme
FFi CCI

TrevH
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#69

Post by TrevH » Tue Feb 20, 2018 2:07 am

Where can I find a copy of Dr McMillen’s work? I would be interested to read it (hope there’s not too
much complicated maths in it :D )

Isn’t viscoelasticity a kind of stiffness? We know bead chain has stiffness and the effect that has in forming the loops we see in siphoning bead chain.

Cheers
Trev

anjill
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#70

Post by anjill » Tue Feb 20, 2018 8:42 am

Hi Gordy,
Tony, I don't know what a standing compression wave might be, but how can you get compression in a flexible string?
Gordy
I'd align it, accelerate it (as in the fly leg of a loop) and then restrict it's forward motion (as in causing it to form a narrow loop).I reckon the rearwards elements would be pushing on the forward elements. I've actually never heard the term but I like the sound of it. Maybe Graeme made it up.

Regards,
Tony.

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