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Walter & Group...
[GH] From Guy Manning :
Ally Gowans writes:
Each element of line travels according to the forces applied to it. This includes those from the rod tip and those from momentum of adjacent line elements and external influences.
This is important to understand and seems to be missed by most. Each segment of line is influenced by the one in front of it. As the rod proceeds forward through the stroke, the line immediately following will imitate its path. In other words, line farther back in the “chain” of line segments will tend to imitate the path of the line segment immediately preceding it.
Keeping in mind that the tip does not travel in an actual straight line but a curve; at that point in the stroke where the tip travels the straightest line, a line segment (let’s call it segment X) will be influenced into a particular trajectory and azimuth. If sufficiently far from the influence of the tip, and barring other outside influences, the line segment X will want to continue along that same trajectory and azimuth. The line segments following X will then be influenced toward the same trajectory and azimuth. So even if line segment Y and Z have a curved profile at the moment we observe segment X, the curve will be removed from segments Y and Z as they proceed through the position in space of X .
An analogy I use in teaching instructors is it is like forcing water through a hose. Lay 49 feet of hose in a coil and leave only the last foot pointed in a direction. Instantaneously turn on the water., The water will move in the trajectory and azimuth of the last foot of hose. Not only that but all of the water in the curved part of the hose will tend to follow the path of the first foot of water as it exits the end of the hose.
Of course outside influences like late tip path and gravity etc. all influence what actually happens. The line will not travel its entire length within the same point in space. But the concept works for teaching.
Guy Manning
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[GH} Guy,
This fits Ally's description. Also, that of the Mosser/Bachman Loop Kinematics Diagram where the fly line is treated as a chain of particles *
Although I have not yet found the reference, I also recall Dr. Greg Spolek describing the fly line in terms of what he called, "coupled plane pendula" as he looked at the fly line in terms of flexibly linked segments. **
In contrast, he, at another time, wrote a paper on the mechanics of the moving fly line seen as a flexible tapered cylinder. ***
* THE TECHNOLOGY OF FLY RODS by Don Phillips, 2000, p. 90.
** Greg Spolek, PhD., Professor Mechanical Engineering, Portland State University, Portland, Oregon.
*** The Mechanics of Flycasting: The Flyline, by Greg A. Spolek, 1986, American Association of Physics Teachers, pp. 832-835.
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[GH] From Walter Simbirski :
Hi Gordy,
I'm not sure what Ally's background is but he seems to have a good grasp of engineering principles and is able to provide excellent insights without going all techy. His idea of looking at multiple centers of
mass forms the basis of finite element analysis - basically breaking up a continuous system that would
require extremely complex mathematics to solve (if it could be solved) into a finite number of elements
that interact. The analysis of the individual elements, if properly chosen, is greatly simplified and then the
interactions can be treated as a separate analysis. This forms the basis for much of the computer generated
modeling we see these days.
This is indeed cool stuff.
Walter
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[GH] Ed Chamberlain asks some questions :
Gordy,
Need to ask for assistance from my buddies, Eric and Mac, to explain the physics of this observation. Appears to me we are talking different principles and in fact the original video does not demonstrate nor disprove line following the rod tip. The rod in video does not bend and itself is not following a SLP. Starting and stopping the video it appears the line begins its motion in the original direction of movement of the rod tip then as the rod drops the entire line follows an almost tangential path. Only when there is a STOP (or just before) does a loop, sort of, form. Watching the line, one notices there is not an actual parallel loop rather an anchor at rod tip with the line moving in a tangential plane until pulled down by the rod anchor into an "L" shaped non-parallel loop (and the physics applied here I suspect is the one at play with the snap cast when the line begins movement in one direction [large mass] and the quick snap of energy directed 180 degrees from original movement pulls the anchor down and accelerates the larger mass of line in the original direction of movement). Not sure exactly what this all demonstrated other than the bend in the rod works with other casting factors to achieve the SLP, which in turn helps achieve parallel lops. By using a non-flexing rod in the video, I think the entire premise (line doesn't follow rod tip path) may be flawed.
The SLP and parallel loops play a key part of Lefty's teaching point I suspect. Even the curve cast and change of planes has the rod bending and the rod tip moving (if not accelerating) and stopping along a path the line will follow. Mac's point of fly and rod legs responding differently to applied forces and transverse waves is all very true, but still operates with a bent rod.
Mac, what does dropping the loops off the barn roof do to the theory and loop shape? :-)
Regards, Ed Chamberlain MCCI
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[GH] Bill Kiester sends his answers to our 3 questions :
Gordy,
My thoughts.
Questions:
1. Does the line always follow the rod tip ?
No. Over the past several years I have become more and more aware that where the line goes on the forward cast is a function of where it started from. To simplify things lets think of the fly line as the head and the running line. At the beginning of the cast the head (representing most of the mass) is hanging up there in the air. The running line connects it to the rod tip. As the rod starts forward the head is pulled forward by the running line. If the rod begins to deviate left or right from a straight line path away from the head the head will still be pulled forward by the running line. The change in direction cannot be transmitted through the running line. Only the tension can be transmitted so the head continues to be pulled forward in what is almost a straight line. If this process was not taking place we would not have the horizontal tracking issues which cause a left or right kick of the tip of the fly line at the end of the forward cast.
2. How can the same motion described above with the keystrokes yield 2 totally different line layouts with curves landing to the left or the right at will??
I am not sure I totally understand the cast being described by Mac. I am assuming that the tail of the > can be to the left of right and is in a horizontal plan. If this is the case I would suggest that what is happening is that a component of the loop is being directed horizontally by the > and the pull back overpowers the cast. This will cause the tip of the fly line to kick into a left or right curve. This will only work if the > is completed before a loop has formed.
3. When we make a snap cast, the line suddenly goes in the opposite direction to that of the last movement of the rod tip. How does that happen?
What is needed to make a cast is to remove the slack from the fly line (which implies starting with the line straight) and then tensioning the fly line. In overhead casts the cause and effect are fairly obvious. The direction of the rod movement and the intended line movement are all lined up. This is not so obvious in snaps.
Snaps start with the line laid out straight with little or no slack. An initial move (referred to as a lift in Spey Casting) starts the line in a given direction. If the lift is done relatively slowly and then the snap is done very rapidly in the opposite direction so that the rod tip move in the opposite direction only a foot away from the oncoming line an acceleration I the oncoming line can be very clearly seen.
OK so what is happening? I find it difficult to internalize that that much force is being transmitted around the loop. But what must be happening is that the snap dramatically increases the tension in the line. That tension (force) is being transmitted through the loop because the centrifugal force applied to the line moving through the loop is sufficient to maintain the integrity of the loop and therefore the tension in the line. Most spey snaps move the rod in the opposite direction from the line trajectory but it does not have to be that way. A neat thing to do is make controlled easy false casts with a single handed rod. On one of the forward cast stop the rod at a right angle to the path of the cast. Then instead of initiating the backcast snap the rod vertically down to the ground. The move is neutral to the casting direction but the backcast is accomplished. (I am still trying the then make the forward cast by drifting the rod tip vertically up and snapping it down again to complete the forward cast.)
Spey casters know more about energizing fly lines than overhead casters ever dreamt of.
Bill
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