Peter Patricelli

An Energy/Ballistics model of the flycast

Rate this topic

47 posts in this topic

Posted (edited) · Report post

The cast of a flyline through the air is a fascinating, complex physical process. At first glance, at a very young age, I was struck by the central feature....from the moment the fly line is thrown through the air past the rod tip....it tends to STAY in the air. Thrown poorly, not very much. Thrown well.....amazing magic. It seems as though gravity is suspended. It is not, of course, but it is obviously resisted, not completely, but with good success for a few seconds. And, portions of the line are moving while others are perfectly still....and still resisting the pull of gravity. That magic persists until all movement stops, and then the line falls like any other object with mass.

 

The question is....what keeps the fly line in the air.

 

Anyone reading this thread will rapidly become aware that it has a history which began in Mike Oliver's “Whole Flyline Challenge” in which Cary Greene made assertions that the line “flew” only because of aerodynamic LIFT and presented a model based upon his beliefs that aerodynamics is the central controlling feature. The central controversy was the assertion that flyline moving through air generates its own lift. That lift resists gravity, and that explains everything. The argument moved then to Cary Greene's thread on “Leader Design – Saltwater and freshwater” where he presents his model again in greater detail. Anyone wishing to examine his model can read his first post in that thread.

 

I am not going to dwell on the past but simply say....if that LIFT truly exists.....it could still only explain a small portion of easily observable and provable features of the cast.

 

There are then at least two models for what is happening: a Lift model based on aerodynamics, and what I am going to call a Ballistic model based upon the kinetic energy and momentum. And we will see which model gets us closer to a complete explanation.

 

To clear away a serious semantics problem. The terms “fly” and “flight” are commonly used interchangeably to describe two vastly different phenomenon. Both are describing an object with mass in motion through the air . A bullet “flies” to it's target. An airplane “flies” to it's destination. Same word, but the differences are enormous. A bullet has no lift at all and drops due to gravity equally whether tossed by your hand or moving at 5000 fps. That is the basis of ballistics. An object appears to resist gravity relative to it's velocity, but fast or slow, it is being accelerated towards earth at all moments. An airplane flies due to aerodynamic LIFT generated by airflow caused pressure differences between opposing sides of it's wings. That is aerodynamic flight. Saying that something 'flies” in the broad sense, does not demand that there be (aerodynamic) LIFT.

 

The second confusing term is “lift” itself. Lots of forces can “lift” a mass off the ground or hold it in the air. I tie a string to something fluffy and run with it. The fluffy “lifts” progressively off the ground with my velocity and stays there as long as I run. The forces are....Drag on the fluffy based on its size, drag on the string based on its diameter, and the velocity I run. The fact that the fluffy is in the air does NOT mean there is aerodynamic LIFT. The fact that the string itself without fluffy would be in the air does not mean there is aerodynamic LIFT on the string.....altho there might be a very small component of that. The overwhelming proportion of “lift” is caused by the tension between the two points of me inducing velocity …....and any/all points of DRAG. Aerodynamic lift and DRAG both require air speed. There is always drag present in any object moving through air, and aerodynamic lift requires air movement as well. DRAG can be present without aerodynamic lift. Aerodynamic lift never exists without DRAG. But.....the force of drag is straight opposite to the direction of movement. The force of aerodynamic lift is perpendicular to the direction of movement. They are therefore, in that perfect state, irrelevent to and independent of each other. Nothing is always perfect, so permutations of a “lifting” force can be mixed, partially aerodynamic lift and partially drag. That is the confusing, complicated part. But we are not going there immediately.

 

Who cares and does any of this really matter? From my side the answer is a resounding YES. From the Ballistic model I can predict quite a large number of phenomenon in the cast that are not easily apparent. More useful, it also predicts the effect of variations in, say, the weight of drag of shooting line. It also predicts whether one could...or could not....flycast on the moon. Without an atmosphere, no aerodynamics, no lift, the Lift model says NO. But with intact mass, velocity, and kinetic energy, the ballistic model says YES. Now......is that useful or what?

 

I am going to conduct this with a series of questions, each focusing narrowly on the three main components of a single forward cast without shoot. I will leave each question there for a day or so for people to think about, analyze, and propose an answer. Then I will give my answer, propose the next question, and we will move on until we have worked our way through that single forward cast from STOP (or loop formation) to finish.

 

Since, however we want to examine it, the physics of fly line moving at velocity is going to be complicated, let's start with, in my mind, the most glaring and dramatic aspect of a fly cast....and..... since the line is motionless..... what should be the most simple.

 

Imagine the late stage of a long forward cast carrying a lot of (level belly) line....no shoot. What I see is a long stretch of post-loop fly line (no velocity....no aerodynamics.....no lift) hanging in the air, some of it for up to three seconds....defying gravity. In no more than three sentences..... What is holding it up?

 

I will give you a HUGE hint. Here is a simple video of a construct of that situation.

 

https://www.smugmug.com/app/library?imageKey=7McSFXs

 

 

 

Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

Peter,

 

Changed my mind. This is very interesting stuff no matter how well or badly a person casts.

This information really should be in the domain of two of the worlds casting orgs namely the FFFI and AAPGAI. It would be useful I guess for fly line makers to understand as well.

Hope it does not take too long before you reveal all. The anticipation is growing.

 

Mike

Edited by Mike Oliver

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

It is right there in the video.  How did I get the line to lift off the ground?  Answer that.....and then fill in the blanks.....the _____  is coming from ______. (!!!!!.) (light bulb going off) (insert epiphany here).

 

While you all cogitate.  I want to make clear that I am most interested in the big picture analysis.   At this level, this is not that complicated. A complete analysis by a PhD physicist would reveal about 10-15 mechanisms operating at any one moment, and a roomful of names attached to laws/principles/theories.  Some of them might explain the last two inches at 100 feet.  I'm OK with understanding the first 50 feet....for starters.

 

In the coming journey through the cast, at each step when we identify a mechanism, the next question we should ask ourselves is......OK, but how BIG of an effect is it?  Can I think of actual casting scenarios when the parameters are changed....by wind, a different line, etc. that I notice a difference....or I must make an adjustment to compensate for something.  Can I think of a way to take that mechanism out of the equation?  The big picture view has been for me since 1968 like standing at a river mouth.  I look upstream at the tributary questions and follow them.  This approach has me out there throwing shooting heads....with no shooting line attached, or casting upside down.

 

For example: People can argue endlessly about how much energy and power is stored in a fly rod and how much does that rod stiffness contribute to the distance of the cast. One can invoke discussions of potential and kinetic energy, modulus, taper, resins, etc., etc.. Or.....one can clamp their favorite, longest casting rod (with reel and line-leader-fly) firmly to a picnic bench on a lawn. A rod holder and maybe some duct tape works nicely. Affix the rod in the end-of-power-stroke position, strip off 40 or 50 feet of line, hold the fly, and pull on the fly at cast height level until the pull on the line and the rod flexion begin to get scary.....and let go. The result, to me, was eye-opening......and laughable. It would have taken a computer and consultation with engineers and mathematicians to get an answer on paper. But the result simply lay on the grass in front of me. From an ideal, fully-loaded backcast position, line perfectly straight and suspended,  the fly never made it to the rod. I had to shorten the line drastically, reduce the load that “powerful” rod had to accelerate just to get the fly past the rod.

 

We are NOT going to discuss this here, but I use this as an example of how simple, real life manipulations, like my video above, leads us to serious conclusions.

 

There are real life casting and fishing implications to everything we are going to discuss.

 

I will answer the initial question tonight. I hope someone, or many, will take a shot at it.  And then we are launched. 

Edited just now by Peter Patricelli
 
Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Peter,

I have a brilliant question, how do we find the video?  The first supplied link takes me to the website.  The second link (under the bottom line) takes me to all of your folders on the website and the third to a collection of miscellaneous fly fishing topics.

Mark

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

Thanks for letting me know.  I was hoping to put the video actively in the post., and have successfully done that in the past.  But when I tried this time I was not getting results.  As it sits, when on my computer I open SOL cold, then open the thread, and click on the URL at the end of the first post......I open directly on the video. Clearly that is, at minimum, variable.  Let me try another way.

 

OK, try it now,  I also tried 3 other ways to embed it live in the post.....and none are working.

 

Let me know.

Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Wait, the original link takes you to what website?  If the Smugmug website, then NOW go to Fishing....then Casting.....and look for "CG levitation.mp4".  Should be the last one.

 

Or.....go straight to Smugmug, search for Patricelli.  Once on my website then follow above.

 

Let me know.

Share this post


Link to post
Share on other sites

Hi Peter

 

If a vertical loop somehow produced lift that counteracted gravity the same force would make a side arm cast with a horizontal loop veer to the right (R hand caster) and the rod leg would crash to the ground. 

As pointed out by others elsewhere, it would also make downwind casts fall from the sky and upwind casts soar upward.  It would make casts at altitude, where air density is less, fall faster and travel less far.   

 

None of this happens.

 

So, people. next time some one, no matter how authoritatively, uses physic-babble to 'explain' what THEY don't understand ask them to also explain the above.  

 

Fly lines stay aloft because of momentum in the fly leg and tension in the rod leg.  The tension exists because the momentum of the fly leg is pulling against the line attached to the rod tip...through the rod leg.  Release the tension and the line, loop and all, falls. 

 

 Drag does add to this tension, but not via lift.  Likewise, drag slows the drop of the straight line (like it would a falling leaf) but this is not lift. 

 

And I don't know squat about physics.

 

G  

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

5 hours ago, Peter Patricelli said:
...

While you all cogitate.  I want to make clear that I am most interested in the big picture analysis.   At this level, this is not that complicated. A complete analysis by a PhD physicist would reveal about 10-15 mechanisms operating at any one moment, and a roomful of names attached to laws/principles/theories.  Some of them might explain the last two inches at 100 feet.  I'm OK with understanding the first 50 feet....for starters.

 

I will answer the initial question tonight. I hope someone, or many, will take a shot at it.  And then we are launched. 

Edited just now by Peter Patricelli
 

I gave it a shot, in the other thread, oops.  People there are still arguing lift vs drag. My observations re: haul timing are relevant if you want to suspend the fly line in the air longer, but not necessarily increase line speed beyond 50ft or extend distance, as the distance casters do, well beyond 100ft at least on the Earth (on the Moon, distance is probably easy with a stick and a string).  What's the next Q?

Edited by Killiefish

Share this post


Link to post
Share on other sites
7 hours ago, Peter Patricelli said:

...

For example: People can argue endlessly about how much energy and power is stored in a fly rod and how much does that rod stiffness contribute to the distance of the cast. One can invoke discussions of potential and kinetic energy, modulus, taper, resins, etc., etc.. Or.....one can clamp their favorite, longest casting rod (with reel and line-leader-fly) firmly to a picnic bench on a lawn. A rod holder and maybe some duct tape works nicely. Affix the rod in the end-of-power-stroke position, strip off 40 or 50 feet of line, hold the fly, and pull on the fly at cast height level until the pull on the line and the rod flexion begin to get scary.....and let go. The result, to me, was eye-opening......and laughable. It would have taken a computer and consultation with engineers and mathematicians to get an answer on paper. But the result simply lay on the grass in front of me. From an ideal, fully-loaded backcast position, line perfectly straight and suspended,  the fly never made it to the rod. I had to shorten the line drastically, reduce the load that “powerful” rod had to accelerate just to get the fly past the rod.

...

I remember many moons ago when you produced and posted a video of this experiment on another board. The results and your message were eye opening for sure.

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

I believe that most of what is shown in the video above supports my answer in the other thread.

 

"The unfurling of the loop produces the downward pressure, and its a rolling phenomenon - it (drag, air resistance opposing the downward pressure) suspends, in sequence, the entire path of the loop, and also maintains tension of the line behind.  At the end of the loop unfurling there is no further downward pressure or linear tension, and the line either falls, i.e. floats down, or overshoots and dumps."

 

So regardless of other forces at work, gravity (constant), etc..., the early part of the cast (up to around ~50ft) is energy imparted to the line by the rod (ballistics), as affected by drag, with line tension also playing a role.  Sloppy casting that allows loss of tension ruins the effect.  Overshooting ruins the effect, causing early loss of "floating" and hence "hang time" or continued moving forward supported by air resistance from below (drag).  The rapid loss of elevation of that marked point on the line at the end occurs when forward motion slows and tension lessens, also as less of the loop is folded above there is less downward pressure, and interestingly the air pressure or drag/rebound effect at the end declines non-linearly.

 

 

Edited by Killiefish

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

Gentlemen, gentlemen, gentlemen.  Divide and conquer.  If we keep our initial pass through to small elements at a time that everyone can understand....without controversy, then the whole becomes more visible to all. Trying to explain it all in one place, especially when there are more hidden elements to be discovered can lead you into shifting sand.  And for some, if light bulbs are going off, please save them until we get to that issue.  One step at a time.

 

DAQ, thanks for remembering that.  I wish I knew where that video was.

 

Numbskull, great video.  Thanks.    Most of what I have learned and will present here came before the internet, so I have never followed Sexyloops, for example.  It is entirely possible there is information or videos that might argue with what I present here.  I sure hope someone calls me on it.

 

The question was: "What I see is a long stretch of post-loop fly line (no velocity....no aerodynamics.....no lift) hanging in the air, some of it for up to three seconds....defying gravity. In no more than three sentences..... What is holding it up?"

 

The closest correct answer is:  " Fly lines stay aloft because of momentum in the fly leg and tension in the rod leg.  The tension exists because the momentum of the fly leg is pulling against the line attached to the rod tip."

 

But....as stated, it is not exactly true....because of incompleteness, not error.  That is why I encourage keeping it as simple and limited as possible...exactly as I ask the question.

 

My one sentence answer is:  The post-loop line stays aloft  because of tension between restriction of line movement from the rod side....and the pull generated in the loop as the velocity of the pre-loop line is stopped IN THE LOOP."

 

Momentum is not the whole answer to that tension.

 

In 1968 I was trying to explain to myself what was holding the motionless line up.....and couldn't do it.  SO, to try and stir other brain pathways I took a reel and did exactly what the video shows.  I fixed the reel at roughly cast height, stripped off a length of line, and then recreated the picture of the line hanging there by pulling on the line to stretch it with tension.  I looked at it and thought, this is so simple, there are only three elements here.  One end is fixed, the line is stopped, and it is hanging between the fixed point and... MY HAND.....PULLING!.  In a cast, my hand pulling would be the LOOP.....PULLING?  Why would the loop be pulling?

 

That started all focus on the LOOP....where it belongs.  How, why was there PULL in the loop?  Because, taking the complex and almost inscrutable loop as a opaque black box, whatever can be said about what happens in there,  a big loop, small loop, sharp loop, drag, yada, yada, yada, the irreducible truth is that line, with MASS and VELOCITY (MOMENTUM = MASS X VELOCITY) goes in one side.....and comes out the other....MOTIONLESS!!    That cannot happen without an opposing force, and that force is pulling and maintaining tension on the motionless line,

 

And then, to more careful analysis:  The only line being stopped is the line IN the loop, so the loop forces being generated as a result are limited to the mass and velocity of that relatively small amount of line as it passes through the loop.  Given the same initial line speed at loop formation, a large loop will slow more  line.....longer, or a narrow, sharp loop will slow a small amount of loop....rapidly, but the resulting pull IS THE SAME.  With regard to momentum, if the line weight/per inch is stable (level line), the pull is exactly the same (except for drag losses in velocity) in the turnover of the first foot (when there is very little line to be held up) as it is way out there in the turnover of the last foot of line (again, based on level line).  When the loop begins digesting lighter line (taper) , then leader, the pull diminishes.  Sooooo, we are asking the constant pulling loop to progressively hold up a longer and progressively heavier hanging line at the end.  BIG TASK....way out there.  ALL of it, the weight of the line and the pulling tension is felt as a constant pull by the caster, and the reduced pull of lighter line tells him when the backcast is ending....without looking.

 

The second big implication:  The speed of the loop progression AND pull depends upon the speed difference between pre-loop line and post-loop line (in our scenario that is zero).  If the post-loop line speed is the same as pre-loop line speed, the loop as a curved line may persist, but it is the speed of decelerating line moving through that creates the pull. Without speed through the loop a functional, dynamic, pulling  loop is dead. The cast falls apart.

 

The most efficient loop, and the most energy at the end,  is with no shoot.  But by necessity we must.....some.  When we release the shooting line then the necessary resistance to create tension must fall to the inertia of accelerating the shooting line, the resistance going through the guides, and the height in lifting that line up to the level of the held rod.  Lifting the rod higher adds to that resistance at any point.  Shoot can easily be overdone with too light, too slick shooting line that allows too little resistance and too much acceleration.  The result is a weaker and weaker loop and sufficient energy for final turnover becomes questionable, or impossible.

 

I could go on.  That simple system and Momentum = mass x velocity, is, in a dynamic loop, sneakily complex.

 

Two months after I discovered all this in 1968 I was writing this up, and questioning in writing how changing a long taper in the belly would affect loop efficiency when I saw an ad by the Wullfs for a radically new line....the Triangle Taper.  Who can find the statement in their readily available literature that relates to all this?

 

With regard to the basics of a cast unfolding through turnover, that is all I had for about 20 years.  I knew it was true, but it didn't seem to me that was enough to explain both holding up a very long "carry".....or CARRY and then long SHOOT.  I knew there was more, but didn't know where.

 

The other obvious question was....what is holding up the LOOP itself? (We will ask that last)

 

Sooooo....at the risk of abandoning simplicity, let's look for more energy.  In our three piece cast, pre-loop line, loop, post-loop line, We have a good start on understanding post-loop line.  What is the behavior of Pre-loop line?  From the moment of loop formation, pre-loop line, most of it initially behind the caster, is falling, but NOT falling at a rate consistent with gravity.  It is tethered by the loop on one end, and UN-tethered on the other.  There is clearly drag present.   Two ways of asking the same question.  What is the second force keeping it aloft.....or.....is the line entering the loop "coasting" at the same velocity of the line at loop formation, minus drag to that point.?  One sentence or one word, for the first question, or two sentences for the send question.

 

 

 

 

 

Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

9 hours ago, Peter Patricelli said:

 

....is the line entering the loop "coasting" at the same velocity of the line at loop formation, minus drag to that point.? 

Hi Peter

 

Your question is ambiguously phrased.  Does "entering" mean about to enter or already in?  And "velocity" requires a direction designation, otherwise one is referring to "speed".

 

 The line ABOUT to enter the loop is "coasting".  As soon as it enters the loop its FORWARD velocity begins to drop and reaches zero at the loop front.  Forward velocity remains at zero thereafter.  The loop itself does not continue to pull it forward.  Rather the loop itself just moves on like a wave between the rod leg and fly leg.  A point on the line does move towards the rod leg while in the loop, so it has a DOWNWARD velocity (for a vertical loop) until it joins the rod leg.         

 

And for your other question,  trajectory matters.

 

Peter, I'm impressed that you figured this all out alone in 1968.   It is a shame you weren't (and aren't) participating in the SL forum where truly smart guys (not me!) have been dissecting everything about a fly cast for decades....and still are.  You would have fit right in.

 

I think, however, you are making things overly complex by attributing a life of sorts to the loop.  Yeah it is a fascinating phenomenon but it does not drive the cast.  Rather, it is just the result of the forces driving the cast.  One force is the momentum imparted to the line and carried by the fly leg and the other force is the pullback by caster still holding the rod (let go of the rod and the momentum of the fly leg would pull it forward).  Two opposing forces working against each other through a medium (the line) creates tension, and that is carried by the rod leg.   The loop is just where momentum becomes tension.   It matters because when casting we all focus on the loop (or the rod) whereas we should be focusing on the fly leg that drives the whole process.

 

G

 

 

 

   

Edited by numbskull

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

G,

 

"Your question is ambiguously phrased.  Does "entering" mean about to enter or already in?  And "velocity" requires a direction designation, otherwise one is referring to "speed".

 

 

I did not want to give away the answer too easily, so I phrased it with some ambiguity to achieve that goal.....without putting too much thought into variations of phrasing that might achieve that without causing confusion.

 

Any mass that has entered the loop is already, by definition, accelerating, just an any small point of mass on a spinning wheel that is any measurable radius off the center is accelerating, continuously, in the direction of the center.....or it would fly off in a straight line.

 

I could have said, pick an inch of line, just six inches before it hits the loop.  Is it coasting with constant velocity/speed? (Take your pick) To me, at least, in the simple context in which I am using it, they say the same thing.  Am I wrong in that?  I think this is semantics, I but have enough to do without argueing about that.  In this case I meant velocity TOWARD the loop.....but I thought that was obvious .

 

As for your last paragraph....hold onto that thought until you see where I am going.  It also occurs to me....and I am instantaneously in love with this analogy:  Before you sits a delicious plate of coq au vin, a masterpiece of culinary art.  How did this come to be?  What do you want to look at first, the ingredients.....or the kitchen?

 

Here is a more specific wording of the Questions 2.:

 

Consider the line ABOUT to enter the loop. Besides DRAG, what is the second force keeping it aloft.....or.....is the line about to enter the loop "coasting" at a constant speed toward the loop (minus drag to that point)? 

 

One sentence or one word for the first question, or two sentences for the second question.

 

You are standing ten feet back from a lookout point on the Grand Canyon......inching forward.

 

Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

I forgot to put this picture in with the answer to question 1.  The red line is the pre-loop line with momentum.  The blue line is the motionless, post loop line.  In order to stop the momentum in the red line, there MUST be an opposite pulling force, modulated through dynamics within the loop, represented by the left green arrow.   The ONLY line generating that force is the black line within the loop itself.  That force is constant so long as the loop is processing line of equal weight, regardless of loop size or shape. The opposing pull (right green arrow) is the resistance of the held line through the rod tip.  The tension between those points pulls   the line into tension and prevents it from falling due to gravity.  Imagine that blue line getting longer as the loop progresses.  The job for the loop, with only the single, unvarying force (when we consider momentum only) gets harder and harder.

 

It there enough force?  What is holding up the loop itself?  Only the first is Question 2.  The last is Question 3.....so ignore for the moment.

 

Sorry I didn't put this in above.

 

 

 

 

Momentum levitation small.jpg

Edited by Peter Patricelli

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to register here in order to participate.

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.