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Upward Force from Form Drag

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Graeme H
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Upward Force from Form Drag

#681

Post by Graeme H » Sat Apr 14, 2018 2:13 pm

VGB wrote:Hats off to you Graeme, I expected more deceleration in the fly leg flight due to drag which shows how little skin drag contributes. We’re you using a fly, if so what was your set up.?
Hi Vince,

Whilst reviewing the clip for Merlin's request, I saw the fluff was still attached to the leader in this clip. It's only small (hard to see) so I don't think it's having a big effect. Sorry for the error.

Cheers,
Graeme
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Upward Force from Form Drag

#682

Post by guest » Sat Apr 14, 2018 6:37 pm

Cheers Graeme, it appears that the fly drag doesn't do much either. I guess if it was large, we would have nice taut fly legs every time.

regards

Vince
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Graeme H
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Upward Force from Form Drag

#683

Post by Graeme H » Sun Apr 15, 2018 9:44 am

Way back in post #297, Gordy posted a couple of images in which he claimed the loop emerging from under or over a net produced lift or drop, depending on the orientation of the loop. The images were screen captures derived from this video.

I asked him to trace markers on the line because the initial starting conditions of the line in each cast were definitely different and his images were produced in a way that represented them to be the same. He has even labeled both of them to show the initial loop traced path of -5 degrees.

I objected because the white traces of the initial loop were duplicated in each cast, implying the only reason the emerging loops had different trajectories was due to different loop orientations. In fact, the white trace in these two images was derived from one cast only. He did not show the initial loop trace of the other cast.

Gordy chose not to correct the error.

These are Gordy's images:
Screen Shot 2018-04-15 at 5.17.48 pm.png
Screen Shot 2018-04-15 at 5.18.02 pm.png

Now that I have some software to trace markers, I can produce the images that Gordy would not produce and correct this obvious error. This first image shows the path of a marker on the fly leg for the loop emerging (reforming) over the net (the upright loop.)
Image

The next image shows the trace of a marker on the line where the loop emerged under the net (the inverted loop)
Image

Note that for each cast, the path of a marker on the fly leg does not significantly alter at any time, even though the initial loop had been destroyed and a new loop had formed. Normal or inverted loop, crash or no crash, the path of a marker on the fly leg is not significantly altered by the loop's existence or orientation.*

The loop is producing neither lift nor drop in the fly leg's trajectory. The fly leg maintains a steady state of motion unless a force acts on it, as per Newton's First Law of Motion.

Cheers,
Graeme

* If anybody would like to check my results, I'll send them the tracker files. You'll need to install the software, but it's free and pretty easy to use.
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Upward Force from Form Drag

#684

Post by guest » Sun Apr 15, 2018 11:58 am

Thanks for that Graeme, do you have the speed record for those markers? I’m interested to see if the collapse of the loop has any impact at all on fly leg behaviour.

Regards

Vince
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Graeme H
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Upward Force from Form Drag

#685

Post by Graeme H » Sun Apr 15, 2018 1:02 pm

Hi Vince,

Unfortunately, I have nothing for those particular markers from before their first loops were destroyed. This image is the point in time when the second loop reformed (inverted). The marker seems to have been slowing fast until just before the loop reformed, when it then slowed at a reduced rate. They might have been slowing faster without a loop than with one, but I haven't analysed enough data points to confirm yet. Tantalising, but not enough yet.

Markers on the fly leg before the crash obviously don't carry on beyond the net. They had an average (and slowing) velocity of about 27m/s, consistent with the first part of the graph shown here.
Screen Shot 2018-04-15 at 8.41.49 pm.png
Cheers,
Graeme
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Upward Force from Form Drag

#686

Post by guest » Sun Apr 15, 2018 1:21 pm

Thanks Graeme, I was hoping to shed light on why a reduction in tension from casting into a headwind causes the fly leg to slow down. I think the loss of tension at the front of the fly leg causes it to go to spaghetti rather than the cast failing being entirely due to drag on the fly leg.

Best get back to tying shit flies to replace the ones stuck in rocks on the river bed.

Regards

Vince
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IANACI - There’s no such thing as absolutes

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Graeme H
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Upward Force from Form Drag

#687

Post by Graeme H » Sun Apr 15, 2018 1:32 pm

Something else to test out, I suppose. I don't know if this experiment is close enough to those particular conditions to explain that question. What I can tell you from a LOT of personal experience with strong head winds is that a high line speed with a good focus of direction is the answer to fixing the problem, regardless of the cause. ;)

(For the record, I have just looked at the other reformed loop. The crash of the initial loop didn't seem to have much effect at all on the fly leg.)
Screen Shot 2018-04-15 at 9.30.09 pm.png
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Upward Force from Form Drag

#688

Post by guest » Sun Apr 15, 2018 1:51 pm

Thinking about it Graeme, the fly leg tension is reconstituted in that experiment when the loop reforms which doesn’t happen in a normal cast into wind.

Regards

Vince
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David Gianfaldoni
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Upward Force from Form Drag

#689

Post by David Gianfaldoni » Thu Apr 19, 2018 9:33 am

Hello everyone,
after watching these videos on youtube I wanted to ask you experts if you think that this phenomenon can be related to the fact that the fly line seems to defy gravity and stay airborne much longer than we would expect when unrolling after the shot, in particular during a distance cast.
Thanks in advance

I apologize if the video has already been discussed here in the past or if it goes out of topic.
(and sorry for my bad english :asleep: )

david

https://www.youtube.com/watch?v=eCMmmEEyOO0

https://www.youtube.com/watch?v=oKb2tCtpvNU

https://www.youtube.com/watch?v=rCw5JXD ... q&index=56

https://www.youtube.com/watch?v=uiyMuHuCFo4

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Paul Arden
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Upward Force from Form Drag

#690

Post by Paul Arden » Thu Apr 19, 2018 11:29 am

Hmmm. Well from that I wouldn't say that they understood it. Ie the top of the slinky has "to send a message" to the bottom of the slinky.

Would it not be that

Cheers, Paul
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