"Consgant acceleration" / Counterpoint / " 'Twixt"

Let me preface this next set of messages by saying that some of these discussions are at the cutting edge of fly casting technology. No "pat" answers and no consensus when our titans seem to clash. As we argue point to counterpoint and back, we all learn. One thing is certain ..................

For MCCI candidates, they go beyond the scope of what you need to know on your forthcoming exams .... so don't be intimidated or confused as you read them. One might look at them as almost at a PhD. level.

I have placed Walter Simberski's fly casting physics papers in the attachments. Though a scientist, he has distilled the information down to make it more understandable. This should help us all. You may wish to archive his articles for future reference.

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" Am I really just compressing a constantly accelerated move into a shorter interval of time ? "

I don?t think so, constant acceleration would be represented by a straight line on graphs like that, whilst the second graph for the overhead shows a bit of a bumpy start, creep maybe, then an almost straight line, the first, the roll cast, plainly doesn?t, both casts are shown over the same time period.

The point is, neither graph would tell me anything about the loop shape or size.

******CA graphs can't predict loop size/shape with 100% accuracy, there are other variables that impact loops beyond rod acceleration. For example, if the previous cast was poor and the line was quite slack, the rod could be accelerated perfectly, but it would be pulling on slack line so obviously the result wouldn't be great. However, rod rebound would be much reduced and that would clearly show so someone skilled in reading the graphs would predict a poor loop in spite of good acceleration. BR

" Bruce Richards has shown that most casters he's studied are more likely to form a small loop when they use translation to delay rotation. "

*****I don't believe that translation "delays" rotation to any significant degree. Good casters will start rotation at the "right time", which they sense naturally. Really good casters might translate their hand some just prior to rotation, to pull some slack from the line, but that will not change when rotation happens significantly. BR

I suspect that normally In overheads, with the possible exception of very short casts, a caster will have to use translation and rotation simultaneously in order to get the right casting stroke length and a SLP, this would be perfectly possible and still achieve near constant acceleration over the period of the casting stroke. But, in the same overhead, if you were to use a period of translational acceleration at the beginning of the casting stroke, which I believe is what we do with roll casts, and rotate late then the acceleration would be non-constant over the period of the casting stroke.

*****You can't really compare overhead to roll casts in this way. When roll casting, the D loop is set by dragging the line back, usually farther back than the comparable "stop" position in an overhead cast. A bigger D loop makes the cast easier, but also puts the rod in a position that is farther back, and lower, than the proper "start" position for the coming cast. To make the cast effectively, the caster will reposition the rod with a slow rotation/translation, this isn't part of the casting stroke, simply a reposition.... BR

Bruce's statement, above, reflects his position that pure translation ("drag") preceeding rotation is outside the CASTING STROKE. Gordy

If Bruce has shown that both constant and non-constant acceleration can be applied to a cast of a fixed length and we get a small loop in both cases it would lead me to believe that there is no specific link between acceleration and loop size.

*****I haven't shown that, to my knowledge. All the great casts we've analyzed had acceleration that was much more constant than lesser casts.

There is a very clear relationship between smooth, constant acceleration and great loops. I've seen no charts of great casts where acceleration wasn't "constant". Understand, we've seen none with perfectly constant acceleration, (a smoothness ration of 1 on the CA), but have seen many that were close.

The smoothness ratio is our measure of acceleration. Ratios of 8 or less result in good loops. Ratios of 4 or less yield great loops, ratios of less than 2 yield needle loops, and is very hard to do!

Bruce

Mark

Mark Surtees

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From Aitor Coteron :

Hi Gordy,

Some comments on acceleration, rod tip path and loops.

If we apply a constant acceleration to the rod butt, since mass doesn't vary during the cast, we are applying a constant force; a constant force loads the rod the same amount throughout the casting stroke. In order to increase the load we need to apply an increasing acceleration. IMHO increasing the acceleration progressively (a constant increase in acceleration) won't result necessarily in a tailing loop.

Aitor Coterón

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Aitor...

First let me say that you are correct, I think, in that a "constant increase in acceleration" as many would look at the term would not result in a tailing loop.

As I now understand the terms after talking with engineers and physicists, acceleration IS increase in velocity as a vector quantity. Constant acceleration is a smooth progression of that increase.

I used to teach "accelerated acceleration" .... but these scientific guys beat me down on that one, so I no longer use that term. They have also explained something I didn't know.... namely that when we do have acceleration which progresses beyond a given rate of increase that the term, "third order progression" applies ... as when describing what happens with rockets. They point out that acceleration IS a rate in the first place.

SO: CONSTANT ACCELERATION DOES MEAN A CONSTANT INCREASE IN VELOCITY IN A PARTICULAR DIRECTION (VECTOR QUANTITY) AS OPPOSED TO A SCALAR (NON DIRECTIONAL) QUANTITY.

With CONSTANT ACCELERATION, we do have progressive rod load and, therefore, increasing rod bend.

Gordy

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From Jerry Puckett :

Gordy,

Would you entertain the thought of "Progressive Acceleration."

Jerry

Gerald L. Puckett

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Jerry ...    Acceleration IS progressive .... so the term might well be considered redundant.

Gordy

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                                                           COUNTERPOINT

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From Paul Arden :

Hi Guys,

"A bunch of Creep". What if the rod started in the "proper start postition"? What is the proper start position anyway?

I don't think that the purpose of the early part of the roll cast stroke is to establish the start position. I think it gets line in the D-loop moving forward without losing the anchor. Better to make this action with translation as opposed to rotation - otherwise you'll be in the wrong start position.

I don't agree with Constant Acceleration - as you know Bruce. Even your constant acceleration graphs have a distinct curve to them. Constant would mean a straight line?

Cheers, Paul

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                                                              RETURN TO POINT

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From Bruce Richards :

"proper start position" would be the rod angle needed to make the desired loop. Too far back and the loop is too big, too far forward and it will crash.

Paul, you are fixated on constant acceleration.

I have NEVER said that constant acceleration was necessary to make great casts, I'm not even sure it is possible. BUT, the closer you get to it, the better the loop.

Bowling a 300 game isn't possible for me either, but the closer I get to it the better the game, right? I'm sure you get this....

Bruce

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                                                             ' TWIXT POINTS

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Paul....

I don't know that there is a "proper start position" ... I see it as a range of positions. Could argue that forever, so I won't.

Your third paragraph re. Constant Acceleration relative to Bruce's opinion, I think is in part derived from your own way of looking at the casting stroke as opposed to his. You place that initial translation within the stroke and he doesn't. Once you look at the curve after eliminating the contribution by translation, it straightens out a lot. Completely ?   NO.

After looking at lots of these curves, my own take is in between your's and Bruce's. Just as we talk about a "straight line path of the rod tip yielding a small loop" when we really mean a slightly convex rod tip path or "almost straight" path, so with acceleration ...... I see it as "almost constant" for small loops. Never perfect except, perhaps, on occasion with some of our supercasters who can often achieve razor sharp loops.

Gordy

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From Jim Valle who learned from the fish as he takes it from physics to what he observes and feels.  He and I are, "betwixt & between " :-

Gordy and Group,

Re: Acceleration in the Casting Stroke

Take a lesson from the fish?

Ever watch a fish just cruising , gentle back and forth movement of the last ½ of his body?.wooosh ?woooosh

However when he wants to really accelerate he applies a real thrust to his caudal fin ?.at the end.. pow!

Casts are like that?. All part of the same movement ?just more emphasis at the end if you want it to go?.

Pantomime this using your forearm, wrist, hand and fingers ? you?ll recognize the movement!.. Maybe feel it too!

Keep it Simple?

RE: Roll Casts

I think there is a lot to be considered, people make excellent roll casts in many ways and that is why it seems illusive and complicated.

Personally I like the ? Reach Out and Touch Someone? or the stroke length approach, this is translation and rotation. Sends out a nice tight horizontal loop just like a forward cast, SLP and all that. Line is tensioned, directed and given momentum in the translation phase, speed and distance ( and loop size) are mostly determined in the rotation phase. Both phases affect tracking and accuracy. (This is the method I prefer to teach because it is the forward cast motion and emphasizes stroke length)

I have seen others make excellent roll casts Floyd Franke comes to mind? using a downward, elbow leading, chopping action that makes a beautiful tight loop aimed on a slightly declining angle.

There are many other variations.

In my opinion this is all about Balancing all the variables into a controlled motion that may include adjusting stroke length , power (rod load), tip path, line plane, and length and firmness of the stop? all modified for the particular rod and individual caster?s physiology.

Gordy uses a ?compressed burst of power? to get a tight roll cast loop?. Ok that?s his adaptation, supposes he was to use less power and a longer stroke? Try it. Change your trajectory?. Why are horizontal roll casts easier to make? Think about the D loop and relationship of the tip starting position in vertical and horizontal roll casts.   Try some roll casts with a spey rod with 70? + of line out of the tip?. You will find it.

Feel the Cast,

Hope that helps,

Jim

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