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Upward Force from Form Drag

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Paul Arden
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Upward Force from Form Drag

#731

Post by Paul Arden » Sun Apr 22, 2018 12:32 pm

I might make the tech forum only viewable by Board Members and when results are ready we can publish to the general public.

What do you think?

Cheers, Paul
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Flycasting Definitions

crunch
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Upward Force from Form Drag

#732

Post by crunch » Sun Apr 22, 2018 9:10 pm

Now after seeing the String Shooter I believe the "skin drag effect" is significant to keep the line loop not falling as much as gravity would. "The wheel effect" still is the main power which acelerates the line loop speed and there fly leg skin drag has negative effect to fly leg speed.

Esa

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Upward Force from Form Drag

#733

Post by guest » Mon Apr 23, 2018 5:46 am

gordonjudd wrote:
It doesn't do that as you can see the loop remains aligned in a vertical plane even though the angle of the shooter was changed as shown here:
Image
Esa

The same issue applies to the skin shooter as to the cast. In the normal plane, lift has to generate a 1g upward force, to oppose the 1g downward force of gravity to maintain a level position. When you turn the loop such that Gravity is no longer opposing the skin drag generated aerodynamic lift, the “lifting” force due to skin drag generated by the loop should start to accelerate the loop around at a rate of 1g.

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Vince
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Upward Force from Form Drag

#734

Post by guest » Mon Apr 23, 2018 6:10 am

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#735

Post by guest » Mon Apr 23, 2018 8:15 am

crunch wrote: "skin drag effect" is significant to keep the line loop not falling as much as gravity would
I suspect this statement is indicative of why we are not making any headway with this subject because the term "significant" is subjective. Nobody denies that skin drag exists and that in a loop it is in opposition to gravity but we have been debating its significance for years.

If I make a cast with a defined length of line, I can see no discernible difference in time of flight due to how fast I make the loop rotate. A pullback cast doesn't appear to float in the air more than a non- pullback cast with the same length of line, even though it is rotating much faster than a loop where I do not pull on the rod leg. I can look at a raft of distance casts and see loop rotation stop without visibly effecting the time of flight:
collapse.jpg
Please can someone explain and demonstrate with a fly cast why the skin drag in the downward facing portion of the loop is significant and how I can exploit it.

regards

Vince
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David Gianfaldoni
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Upward Force from Form Drag

#736

Post by David Gianfaldoni » Mon Apr 23, 2018 11:43 am

Thank you very much Merlin and thank you all!
I imagined that the behavior of the slinky had very little to do with the fly lines and their cast, but when in the video the physicist responds to the question (1:47) "this is applicable to other objects…” saying "is applicable especially in sports etc etc …" I thought his comment very interesting because in fact the fly line constantly sends “messages” through the rod to me during the cast and its flight, or rather besides the time to reverse the cast I can predict pretty well if (how long) it will remain in flight as expected or not before landing in the water as on the ground.
However sorry if all this has brought you completely off topic here.

There are many things that I can’t explain to me and so sometimes I really think the line is magic!
That's why I follow your discussions here with great interest. :yeahhh:
Thanks again
david

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#737

Post by Graeme H » Mon Apr 23, 2018 2:18 pm

sometimes I really think the line is magic!
David, if you want Magic, you came to the right place. We got lots here. :D

Cheers,
Graeme
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#738

Post by guest » Mon Apr 23, 2018 2:23 pm

And photos that prove the existence of magic
cottingley-fairies-520x406.jpg
cottingley-fairies-520x406.jpg (65.62 KiB) Viewed 2358 times
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Upward Force from Form Drag

#739

Post by crunch » Mon Apr 23, 2018 5:22 pm

VGB wrote:
Esa

The same issue applies to the skin shooter as to the cast. In the normal plane, lift has to generate a 1g upward force, to oppose the 1g downward force of gravity to maintain a level position. When you turn the loop such that Gravity is no longer opposing the skin drag generated aerodynamic lift, the “lifting” force due to skin drag generated by the loop should start to accelerate the loop around at a rate of 1g.

Regards

Vince
Vince, what we see in this line shooter device video is very close the stationary moment of a line loop cast. The skin drag finds a balance and line loop stays upright. If whole device is lift to a direction "fly leg" goes I believe whole line loop angle would change when line loop wheel "bites" to air molecules more. And during the acceleration there comes a "sexy loop" or at least line loop will widen when the rod leg tension lessens.

In video when they push the line and move the device angle they "cast" Mends and Tailing Loops and open loops. Mends and TLs which stay quite long time and I believe it is because of line skin friction which is high against line weight until line loop balance again comes.

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#740

Post by guest » Mon Apr 23, 2018 6:43 pm

Hi Esa

I will have to respectfully disagree.

The string shooter video is of a loop of line that is continuously driven at the rod leg equivalent, a fly cast is a open length of line where the rod leg is constrained by the rod which provides a reaction force. In the fly line, the energy in the rod leg is very low, in the string shooter, the rod leg energy is very high. In a fly line loop, (assuming semi circular loop etc), the line at the top of the loop is moving at the fly leg speed, falls to 70% at 90 degrees around the loop and has zero speed by the time it reaches the rod leg. In the string shooter, the line in the loop is travelling at more or less the same speed all the way round. Dynamically the 2 cases are very different. In the string shooter, I see a top leg that is launched with some momentum that starts to fall until it is caught by tension due to the external force provided by the motor, I do not see any special effects caused by skin drag.

The mends and TL in the video are transverse waves, the same as a fly line. If I change the plane of a fly cast it stays in that plane. In Gordys picture, the string shooter loop stays vertical, despite the change of plane.

James asked a question about 60 pages ago; if a loop develops lift why doesn't his loop veer off when he casts horizontally. He has grown a beard and looks like Robinson Crusoe, while he waits for an answer. Today I spent about an hour casting at a bird feeder in a tree at about head height with #2 and #10 lines and the MPR both vertically and horizontally. I did not see any unexpected lift in any cast. I also tried pullbacks to increase the rotational speed of the loop and it made no difference. I may buy a mill end fly line, roughen it with sandpaper and cast wide loops with a pullback cast to see if I can get it to rise but I am not holding my breath.

Regards

Vince
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