Physics of fly casting / Traveling loop / the STOP

I find Server's dissertation an excellent read. I fully sympathize with the difficulty of trying to

put engineering physics into "layman's" terms. This work is a major effort and I appreciate it.

1. Server gives us some interesting new ways of looking at what happens during the cast.

It reminds me of the first time someone posed the concept to me of whether stepping on

the gas pedal causes the car to shoot forward or it causes the earth to begin moving beneath

the car wheels while the car remains fixed in space. This may seem like a silly thing to

some people but it's one of those thought exercises that gets the mental juices flowing

and has lead to such concepts as the theory of relativity and quantum mechanics.

I beleve it was Einstein who theorized that BOTH occur ... the car moves forward and the Earth tends to move in the opposite direction. (Newton's 3rd law: "For each action there is an equal and opposite reaction") . Problem is that the Earth has so much mass compared to that of the vehicle, that the effect on it is so small it cannot really be measured. As I recall, Einstein also pointed out that the very act of taking measurements can affect the dynamic relationships between two bodies ! G.

2. Sometimes Server states the obvious. Physics is about stating the obvious, proving that

the obvious is true, and building from there.

Well..... sometimes things may not be obvious at all, yet can be proven to be true. G.

3. It would help if Server gave definitions for some of the terms he uses such as hard stop,

swing, and loop formation as he uses them in his dissertation.

4. The same applies to his paradigms. State them explicitly.

5. Remember Newton's first law - Every object in a state of uniform motion tends to remain in that

state of motion unless an external force is applied to it. This means that once we get the rod

butt moving it will only slow down and come to a stop if an external force is applied to it. That

force must come from the hand. Now here is where Server's statement of the obvious becomes

important - if we were applying a force in the opposite direction to stop the rod then the butt

just above the hand would be deflected in the opposite direction - even if we allow for tip lag

we should see an immediate change in the deflection of the rod just above the handle. The

whole concept of when and how we apply force to stop the rod needs to be explored more

To use Dennis Grant's wording, it depends.

When this force is applied, I think, will depend upon the desired final result.

When we do a check haul or a tuck cast it does become obvious. The first is rapid negative acceleration with the line hand, and the tuck cast is usually done with rapid negative acceleration of the rod hand.

In my field (orthopaedic surgery) we use the terms "agonist" and "antagonist" to describe opposing muscular actions upon a joint. Server gets into muscular action just a bit. As I see it, the agonist muscles are those used to make the "swing" whilst the antagonist muscles acting in the opposite direction rapidly come into play as we initiate what we call the "stop" (which I see as rapid negative acceleration of the rod.). This transfer of muscular action is strictly voluntary (volitional) on the part of most casters in most situations. The "stop" of the elite caster who is distance casting may well be almost synaptic !! G.

6. There is no number 6. According to Server's number 6 we should see number 8 but I don't have

a number 8 either. :-)

I'm obviously no physicist, but I thoroughtly enjoy learning as much as I can about the physics of fly casting. This is for my own enjoyment and background information. I'd rarely use it for teaching student fly casters. Sometimes, however, we have to get into just a little physics .......such as when a student asks why we use tapered fly lines. Then we have to use word pictures like, "heavy line turning over light line" and "as the loop unrolls, the heavy line gives way to lighter line; the energy stays the same, so the speed greatly increases....." Gordy

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From Lefty Kreh...

--- I use this example and find that students really understand how the unrolling loop obtains distance. I like to keep things basic and don't want to mention to students scientific terms unless it is absolutely necessary, which it almost never is.

If no line is shot during the cast the fly line loop unrolls like the tracks on a armored tank. The tracks beneath the tank are not moving. What is pulling the tank along are the two forward tracks that are off the ground. A loop does the same and I like the idea the two tracks off the ground resemble a fly line loop as it unrolls.

One more point that I know flies in the face of conventional casting instruction is that I do not like pieces of yarn on the leader when students cast. Yarn acts nothing like any fly--instead is acts just the opposite somewhat like a miniature sea anchor.

Lefty.

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Lefty... I remember your tank track word picture.

I also remember your telling us, "a piece of yarn doesn't cast like a fly". Shortly after that, I learned a trick from Rick Whorwood of Ontario. (Rick is an expert fly tier.) He showed me the "yarn-fly" made by tying a 1" piece from one of the three strands of package yarn (sold at Chrismas season by Hallmark stores.....) to a #14 light wire hook, then cutting the hook off behind the tie. Works a lot better than the yarn itself because it has a lot less air resistance. This "fly" can take a lot of abuse during casting practice. When practicing on water, I can float it with fly dressing or spray. When casting on grass, I like the white material because I can see it better than the red.

When giving classes such as workshops at a conclave, I tie up a bunch of them and give them to the students. They love them and some of them can cast well enough to appreciate the difference.

The official yellow dry fly used at ACA competitions may well be best. It casts well and is bright yellow and easy to see.

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From Bruce Richards:-

Hi Gordy,
Some good comments below... I have to make a couple comments in response to
Troy.

"Bruce said "stopping" is defined as rod deceleration, then yes, it occurs
at peak load, there is no other way it can happen."

I think you can have a fully loaded rod that then is taken through zero
acceleration for an interval (constant speed), during which the rod will
try to unload. Later on in the stroke, you will then decelerate the rod
(reduce the velocity), but you would no longer have a max loaded rod. A
flyrod (which is a loaded spring full of potential energy) will try to
return to RSP as soon as the system reaches steady-state (uniform)
velocity. Maybe even before."

Theoretically, Troy is right. However, what he is describing is not
something I've ever seen, and is most likely not possible for humans to do.
What he suggests is that a caster accelerate the rod to some angular
velocity, say 250 deg/sec, then stop accelerating, but maintain that exact
rate for some period of time, then decelerate. This all has to happen in
about .5 sec. If this was possible then yes, the rod would increasingly
bend when angular acceleration increasing or constant. That bend would be
maintained for the fraction of a second that there was no acceleration or
deceleration, then it would unbend when deceleration started. If it was
possible, it would happen so quickly that it would only be discernible
through scientific measurement, not visually. Noel and I, and many others
who have Casting Analyzers would be able to see this on analzyer charts,
but haven't so far. So, as it relates to the original issue, in casts where
there is no "zero acceleration" during the stroke, rod bend will increase
while there is increasing or constant acceleration. That rod bend will
continue to increase until the rate of acceleration slows (deceleration, or
"stop"). In those casts (which is all casts in my experience), the "stop"
will always start at peak rod load.

Good catch Troy! In physics it is best not to ignore what is possible, even
if it never happens, to be precise. I'm not going to include that in my
instruction though!
Bruce

Scientific Anglers/3M
4100 James Savage Rd.
Midland, MI 48642 USA
Tel: 989-496-1113
Fax: 989-496-3374
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