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Walter & Group...
>From Gary Davison:
Gordy,
I like Walter's view point or should I say? I hear his Drum Beat!
His statement makes great sense to me! Thanks for that new term at least for me, Walter.
Center of Mass!
Gary.
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>From Bruce Richards (I added, *):
Gordy, the real problem we're having with "line launch" is that the term is one made up by fly casters, but without clear definition that all have accepted. Some might think LL is when the line is first accelerated, some when rod butt deceleration starts, some at RSP, some when the line clearly overtakes the rod tip, some at max counterflex. All would be right. As with other definitions, we just need to decide. As you well know, not an easy task. *
Gordy, maybe I'm dense, but what's the purpose of "line launch"? It seems to me that it is just a distraction from the really important things instructors need to know to be effective. If we're just chatting about details of casting that's fine, but I'm afraid that some may be thinking this is something they need to know and understand to be good instructors.
As far as I can tell, line launch is just a term made up to label the start of rod butt deceleration. I think we'd be ahead if we talked in depth about the whole of deceleration (angular rod deceleration) rather than just the start. Things truly important to instructors are: rate of deceleration and completeness of deceleration, these things have a big impact on loop size and shape.
Bruce
* LL = Line launch
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[GH] Bruce,
I first became interested in the fact that casters were beginning to talk about, "launching the line" several years ago, despite the fact that I didn't find it used in the fly casting literature.
I don't know when Ally became sufficiently interested in the term that he affixed it to Grunde Lovoll''s schematic which I saw for the first time in 2010. As we know, Soon Lee felt that it was important to know about.
We started talking about the trajectory of the cast when one of the folks interested in physics came up with an alternative term, "LAUNCH ANGLE".
Others related it to the launch of a missile. Our scientific folks showed us the fallacy in that. Still others used analogies such as the launch of an arrow, that of a slingshot, etc., etc.
My own mental picture of "line launch" is that it starts when the movement of the fly rod is no longer needed in order for the line to continue to travel in the general direction of the cast.
That, however, is far from a definition.
As you and I know all too well, we do not yet have agreed upon definitions for things like, "casting stroke", "casting arc (casting angle)", "Stroke length", "drift", "drag", "sweep" etc., either. Despite this we use these other terms freely whenever we discuss fly casting.
I daresay that many of our basic terms came into being by being made up by the fly casters of yore.
Bottom line is that you are correct in that we need agreed upon definitions for this if we are to use the term properly as we discuss fly casting. Same for the basic fly casting definitions many of us worked so hard to develop over the past years.
Is the term, "line launch" simply a useless, "waste basket" term ? We could take the easy path and say it is ..... but since others have been asking about it, I don't think we are wasting time as we inquire about the concept and try to make sense of it.
Gordy
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[GH] From Ally Gowans:
Hi Gordy,
Walter has picked up exactly how the greatly simplified theory based on the centre of gravity (or centre of mass) of the portion of fly line outside the rod tip can be used to explain most casts with a fly line. I have used this methodology to explain casting to my students for many years, some of them have been highly educated physicists, engineers and the like and even though I invite all my students to ask the “why” question if there is any doubt or obscurity I have yet to have the importance of the fly line momentum questioned nor have they required any explanation beyond the centre of mass assumption to convince them. The exact instant of line launch is not important, the direction of line launch is clearly betrayed by the direction of the fly line, which is important.
I have attached a set of sketches that I first sent a good while ago with some other tests. Sketch 2 you performed with the rope and you found the same results as me. If the test is taken a stage further with three different lengths of rope for example you would have found that the longer it is the less influence the pulling force has on its direction.
Best regards,
Ally Gowans
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[GH] Ally,
I did that and found the same thing. Taken to an extreme, if I did it with only 6' of rope, I could change direction. With 40', I couldn't.
Gordy
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From Bill Keister:
Gordy,
In talking about the rope Ally indicated that the first purpose of the rod is as an arm extension. But in talking about the important functions of the flexible aspect of the rod he did not mention the one which I consider the most important. And, that is the translation of rotary motion to linear motion. That is what makes the SLP possible.
The second thought was triggered by Walter's comments about applying force to a fly line relative to its center of mass. Spey casters demonstrate this principle with every snap and circle cast. The single hand caster can demonstrate this principle to themselves as follows. Lay as much fly line as can be comfortably cast on the ground in front of you. With the rod canted about 30 degrees to the side start a smooth lift as you would when making a normal backcast. Keep the energy input low just enough to lift the line of the ground and get it moving toward the backcast. Use much less energy than would be required to complete the backcast. When the rod tip comes even with the caster snap the rod tip straight down toward the ground. You should see the fly line accelerate into the backcast. Next perform the lift in the same manner and when the rod tip comes even with the caster bring the rod tip around in a semicircle so the the motion of the rod tip is 180 degrees from the direction of flight of the fly line. Now make a hard snap forward in the 180 degree direction from the flight of the fly line. Once again the fly line should jump into the backcast. Both of these moves power the fly line with the rod tip moving in a direction other than the direction of the cast.
Overhead casters generally think only of energizing fly lines in the direction of the intended cast. Although energizing the fly line in the direction of the cast is the most efficiently the only thing that is actually needed is to aerolize and then tension the fly line.
Bill
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From Jerald Lewis:
Gordy,
Interesting stuff. I have a question that I think is related to this discussion. Would those extra “waves” that can occur in the rod leg of the loop result from the rod having extra counterflexes and rebounds? I’ve noticed that these waves in the rod leg can occur if I’m gripping the rod too tightly during the cast. Seems like if my grip is too tight, then my hand would not absorb as much energy from the counterflexing/rebounding of the rod after the stop. I think this would cause the tip to bounce more causing the waves in rod leg of the line. Does this sound correct or is there another explanation?
Regards,
Jerald Lewis
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[GH] Jerald,
Before answering, I went out and did some simple experiments :
1. I made casts with my cork grip held tightly throughout the casts. Result: Unwanted vibrations.
2. Then I made the same casts holding the rod gently, then "squeezing to a firm stop". Result: Good rod damping with few vibrations.
3. Tried the same thing with very limber rods. Result: Even more critical to avoid hard grip until the stop sequence.
4. Did them again with large, heavy reel. Result: Still more critical to avoid vibrations.
5. Last- Repeated casts using no reel. Result: Easier to avoid vibrations.
From this, I think we can draw some simple conclusions :
# Best to avoid a super hard "death grip" on the rod during the cast.
# Best to use no tighter a grip on the cork than needed to execute the cast until the start of the stop sequence. At that point a firm grip is needed.
# Limber rods are harder to dampen than stiff ones.
# The reel acts as a counterweight. The heavier the reel, the harder it is to stop the rod efficiently.
Gordy
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