Quiz- Critique & Comments

Walter & Group...

 

The following critique contains comments which are well worth heeding.  They help correct certain misunderstandings or misinformation.  They also serve to provide some of the same information as in the quiz and answers, though using different words.  Sometimes they place that information in a different context.  Sometimes they challenge prevailing wisdom.  At the very least they serve to reinforce.

Gordy

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Unanswered question from Aitor Coteron :

Hi Gordy,

This poses an interesting dilemma.

Let's say that we make a cast with constant acceleration:

Since the acceleration is constant from the beginning of the casting stroke up to the point where the deceleration phase starts, how there could be a single point of maximum acceleration?

Regards,

Aitor

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Aitor,

WOW !  A brain teaser. 

We really are interpreting PEAK LOAD as evidence of maximum acceleration as we look at the video frames.

 I don't have an answer for that.  Perhaps it is as Bruce Richards stated....   that true constant acceleration is something he has never actually seen or been able to accomplish ....   a sort of utopic circumstance which is an unachievable goal.

The progressive rod bend actually fits better with my former concept of "accelerated acceleration" since put aside in light of the findings with the Casting Analyzer which support that of "almost" constant acceleration.

I also gave consideration to a progressive rod bend being in response to (almost) constant acceleration ....the tip of the rod lagging behind. The delay being in response to the inertia of the fly line combined with atmospheric resistance.  That might mean that we could have "constant" acceleration of the butt section of the rod, but non-constant acceleration of the rod tip in part due to the rod being flexible.

Gordy

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From Phil Gay :

Gordy,

 

    This is a good thread on casting mechanics.

 

    I'm intriqued by the discussion on question 15.  I make many casts with no discernable stop in the classic sense.  For example my reach cast.  I tell my students to make an L in the aire.  There is a point though where the rod stops accelerating along the intended path of the cast and then starts moving left or right.  It is at that point that rod unload takes place even though the rod did not stop.

 

    I think it is fair to say that the rod will unload when acceleration stops.

 

    Keep up the great work!  Hopefully I'll see you in West Yellowstone.

 

Phil

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Phil...

Agree.  you have pointed out before that your reach cast is a TRUE CAST, not a "CAST/MEND" since you don't have a stop prior to the lateral reach move.   Many others make a cast, stop and then, while the line is still in the air, make the reach move as an aerial mend.  For that I'd call it a REACH MEND.

Many trout fishermen cast all day long without making a crisp stop.  Paul Arden and others have pointed this out. 

Answers the questions :  Can you make a loop if you don't make a defined stop ?   Answer :  YES.

                                        Will the rod unload if you don't make a defined stop ?   Answer : YES.

I agree with your statement that the rod will unload when acceleration stops.  That, of course, is a different "stop" altogether...just means that even thought the rod is still moving, acceleration has ceased.

Gordy

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From Mac Brown :

Hi Gordy,

  

 Number 4 below:

4.)  Can the fly rod bend without acceleration ? I would play the devils advocate and say yes it can bend without acceleration. The reasoning is simple wind or water may have a constant velocity-we all know the rod bends when we hold it still in these conditions. A good example of this-a 3 weight line, 20 mph wind can wind cast all of presentation without the need for a casting stroke at all. Is the rod bent during this type of presentation? Sure it is.

A river with a flow of 8 feet per second. What happens when the fly is on the dangle with 40' of line? Sure the rod bends again.

Keep up the great work Gordy

-mac

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Mac...

 

 

Of course, your answer to # 4.) is correct. Same as the bend of the rod leaned against a barn.  I should have worded the question differently. 

 

Gordy

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From Peter Lami :

 

Gordy,

I teach my students that the "stop" is a sequence of events that begins at peak load and ends at RSP.

 

Peter

On May 19, 2010, at 8:50 AM, Gordy Hill wrote:

Good "short answer".  Actually lots could be written on what happens.  Basically, there is no "stop" as defined by instantaneous cessation of all motion.  The stop is actually one word to describe a compendium of events dominated by rapid deceleration. (Physicists may prefer the term "negative acceleration".   G.

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Peter....

 

Correct for all practical purposes.

 

However:  We might consider the "stop" which is complete a fraction of a second prior to RSP or the one which is sufficiently slow deceleration that it doesn't really come to a stop until after RSP during counterflex. 

 

 The latter could well happen because the rod will go through RSP and the line overtake the rod tip once that tip slows down to a speed less than that of the oncoming line.  A loop will still form, though it will be a wide one because the lack of a crisp well timed stop will lead to a less desirable tip path and tip position at RSP. (Tip farther from the path of the oncoming fly line.)

 

Gordy

 

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Correction to one of Mark Surtees answers :

 

Oops, edit 16

 If you don?t, you will get a big baggy loop and the line will not extend forwards properly.

 Sorry?

 Mark

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From Troy Miller :

 

Hi Gordy -

I'm the black sheep. I deviate from the crowd in my view of "loaded rods". I see a clear distinction between a rod which is bent due to movement (dynamically induced), and one that is stationary (statically induced). Leaning it against a tree, setting up for a bow and arrow cast, holding the rod steady in uniform wind, even just gravitational deflection - these are examples of static loading. Dynamic would be stroking the rod - against its own inertia, the line's inertia, air resistances against the surface of the rod, the line/leader, and parachute effect of the fly. Removal of whatever is inducing the rod load will result in the tendency of the rod to want to straighten (unless other inducements are dominant and keep the rod loaded).

Angular acceleration is not the same type of vector that you're thinking of. A vector is defined by magnitude and direction. This can be linear or angular. For linear motion, an acceleration could be something like 4 feet per second per second to the north. For angular, it could be something as simple as 30 degrees per second per second in a counter-clockwise direction. Linear and angular both can have a magnitude and direction. Hope this is clear...

Troy

 

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Troy...

 

Makes good sense. I didn't know angular change could be expressed that way Thanks !

 

Helps to have you engineers aboard.

 

Gordy

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Mike Heritage sends a couple of his answers and comments.  My comments in italics  G :

 

I won't anwer them all as so many have already replied, I'm just glad to see I was right on most of them. However, one or two had me a bit perplexed. For instance;

 

3.)  When, during the cast, is the rod top moving at its fastest rate ? Just before RSP

 

#3.)  Yes.  For most casters the caster initiates the stop, then about 1/10th of a second later the rod tip moves through RSP.  In that approximate time the rod tip is moving fastest. G.

14.)  You are given a series of pictures of the caster and fly rod taken as multiple frames shot as the cast is made.  You are asked to pick out the one which demonstrates the point of maximum acceleration.  How do you choose it ?

 

Wouldn't that be the same answer? Picking the point that shows the most bend wouldn't necessarily be the point of most load because of the angular change as the rod rotates.

 

#14.)  The point of max load is pretty close to RSP only because it takes so little time for the rod to go from max bend to RSP.  It has been pointed out that we really cannot measure true acceleration by looking at rod bend alone, but I specified "a series of pictures".  If we have only frames showing the rod, then the closest we can come to picking the one representing max acceleration is to pick the one with the greatest rod bend.     G.

 

16.)  Your student asks you, "Why do I have to make a stop at the end of my cast ?".  What do you tell him ? I take it '' because I told you'' won't cut the mustard.

 

#16.)  Like the mother who says to her child who asks "why do I have to do that ?" .... "Because I said so" just won't fly here.   G.

 

  Mike

 

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From Guy Manning :

 

You write: Your answer may be more correct than the one usually given, which is "angular acceleration at the rod butt".  I've wondered about that in view of the fact that acceleration is a vector quantity whereas angular change has been described as the resultant of an infinite number of vectors.  We'll need input from physicists on that one for a final answer. 

 

I have never heard the term ?angular acceleration at the rod butt? used and that would be incorrect. The analyzer can only measure changes in the angle of the rod but, which includes periods of deceleration and periods of no motion.  It does measure ?angular rotation of the rod butt?. I think you will find that true in  everything that Bruce Richards has written or said.  If you look at the documentation it mentions using an ?angular rate gyro? to obtain measurements.

 

Guy Manning

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Guy....

 

Thanks for helping to clear that up.  As I go back and review what Bruce wrote, I find that you are correct.  I had sent him a message asking him about that in view of the fact that I have had casters who work with the CA teach that bit about "angular acceleration".  Bruce has been away from his computer during the past few days and has not had a chance to answer me.

 

As I think about it, the very name of the "angular rate gyro" does imply the measurement of the rate of angular change during rotation.

 

Gordy

 

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From Lewis Hinks :

 

Hi Gordy,

 

 

 

    In the latest quiz, on what the casting analyzer measures, the owners manual for my analyzer says the following:

 

   

"The sensor capsule contains a tiny microelectromechanical (MEMS) sensor known as an "angular rate gyro" which senses the rate at which you rotate your fly rod while casting. This rotation rate, or what we simply call the "rod speed", represents approximately 90% of the motion you give to the fly rod during normal casting. More specifically, about 90% of the speed developed by the tip of the fly rod results from your rotating this very long (9 foot!) lever. The remainder derives from translating your hand.

So think of the sensor as a speedometer. However, rather than measuring linear speed in the units of miles (or kilometers) per hour, this sensor measures angular speed and in the units of degrees per second, what we again call simply the "rod speed". By measuring and then storing your rod speed during casting, we produce your unique "casting signature" which forms the basis for analyzing your casting stroke. An example casting signature is shown below for one forward cast followed by one back cast. The figure also introduces the major parts of the fly cast that are automatically analyzed by the software; see Terminology and Example Casts to learn more."

So, would the answer, "measuring rod speed" be acceptable?

 

Great quiz, I had the answers, but have been on the road for work almost steady the last week.

 

Lewis

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Lewis...

 

I think Guy has the answer to your question:  "....it does measure 'angular rotation of the rod butt' "

 

Gordy

 

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From Jim Higgins :

 

Gordy

 

Question 18.  If you set a fly rod on a table and you do nothing it will do nothing.  The "straighten" assumes that the rod is bent during a casting stroke and the question was not asked that way.

 

Jim Higgins

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Jim...   True.   We could also look at it this way :  That fly rod can't do anything at all except exist unless something is done to it first.  If we take that position, then the only thing the rod can "do" on its own is to respond to an outside force.  Still remains that it can only straighten or resist bending.

Gordy

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