Jump to content

An Energy/Ballistics model of the flycast

Rate this topic


Peter Patricelli

Recommended Posts

On 5/6/2022 at 0:21 PM, Peter Patricelli said:

 

 

 

Mr T,

     I just saw your post-question. I dunno who said that.  Me?  Tell me where so I can see the context.

 

      If it was me, then I would hope it was in the following context. The only stored energy in the hanging line is potential energy just as any heavy object lifted against gravity occupies an enhanced POTENTIAL energy to be re-gained when released to gravitational pull, like water stored in a high elevation reservoir later released and used to generate electricity.  In a flycast the energy generated in the loop would elevate grounded shooting line up to the rod tip.....and further into hanging line.  As long as it is in the air, it has potential energy.  But I can't think of many ways I needed a context to say that. 

I don't know if someone said it already (very possible), but it's the only thing that makes sense to me. 

Edited by Mr T
Link to comment
Share on other sites

Then just enjoy flycasting as magic!  It works just as good that way.  How many people really understand the Theory of relativity?  And yet, without it our GPS technologies would be so inaccurate as to be worthless.

Link to comment
Share on other sites

FINALLY.....we have reached the LOOP itself.  We have talked about the levitating effects on the motionless post-loop line of tension between the caster....and the LOOP.  We have talked about levitating effects on the pre-loop line between drag effects down the length of the line to the fly.....lift of inclined line itself....and accelerating force of energy transfer.....at the LOOP.  But WHAT is keeping the loop itself UP THERE?

 

More basic than that.....what IS the loop? The loop is a moving, dynamic wave of fly line transitioning from the final direction and velocity imparted by and through the rod (pre-loop line)....to....an initially stopped, then potentially slower moving (shoot) state (post-loop line). At all times the pre-loop line is moving faster than the post-loop line or the dynamic forces and energy transfers stop. At all times, the loop is ONLY the line being decelerated to lower velocity, exiting the loop with zero or lower velocity on one end, and replaced by new higher velocity on the entrance end. While fly line is flexible, it is relatively non-stretchable, so all forces affecting the connected flyline along its entire length are transmitted equally, through the loop, to the caster.....and to the fly.

 

The loop is an ephemeral, NON-rigid “structure”. Forces on any section do NOT rigidly transmit to all other sections except as an increase or decrease in pulling forces moving as a wave. Lift on the bottom half will not push up the top half. Drag pushing back and down against the top half will NOT directly push the bottom half down.

 

At all times, the velocity of the loop is HALF the velocity of the pre-loop line. That is simple pulley mechanics. Since the energy transfer within the loop creates a constant acceleration force on the pre-loop line, that means the velocity of the loop is, drag forces aside, constantly accelerating.....at half the speed of the accelerating pre-loop line.

 

Ballistics of the loop – an illusion?


The loop is formed at the moment the velocity of the line being accelerated through the rod exceeds the speed of the rod. The loop of the fly line itself is actually preceded by a loop within the rod flexion and even the hand, wrist, and arm. But unlike those structures, once the loop forms at the rod tip, ALL of the line to the fly , whether moving or accelerating, is subject to constant gravitational pull. And all sections, if moving at all, are subject to DRAG. But, while the maybe two or three feet of line initially within the loop are at all moments subject to gravity and drag, the loop line is not a rigid structure. It is a wave phenomenon created by the mechanics and energy transfers within it. Those few feet of line represent an very small fraction of the total length of line. It is a product OF the velocities...or not.....forces.....or not, and the elevations....or not.....of the pre- and post-loop lines. The post-loop line is motionless, has no kinetic energy, and no drag unless/until it begins to fall. AND, on one end, the caster, is a rigid structure holding up that end of the line at elevation.

 

The elevation of the loop is defined by the elevation of the pre-loop line and represents an inflection point of a wave of energy transfer defined by the velocity, mass, and elevation of the pre-loop line. In that sense, the loop has no mass and is not subject to gravity, but is defined by the energy states of the line entering and the line leaving.

 

That said, the “search” for the hidden forces that are “holding up the loop” is not illusory. There is line (mass), changing velocity (momentum and energy) creating forces (accelerations) occurring continuously within it. When we have adequately explored the forces affecting the pre- and post-loop lines......we have already defined what keeps that wave of energy transfer (the loop) on a non-ballistic path.

 

As you may have noticed, all casts are not equal. Some are fast....or slow. Some are flat.....or loopy. That “point of the wave of energy transfer “ can drop....more or less like a rock, or in fact elevate ABOVE the level of the pre-loop line.

 

Is there enough energy (defined by mass and velocity) in the pre-loop line....at the first moment of release......to keep the whole wave system from start to finish off the ground?

 

Back to our (fly line mass equivalent) 2.8 oz dumbbell sinker thrown by our fly rod in a perfect ballistic trajectory. I haven't done it but let's say it goes 100 yards. If we could put that amount of energy into similar mass 90 foot DT fly line, that would represent a perfect throw (not cast) of a fly line 345 feet. What? The center of mass of the sinker is right where it landed.....300 yards. The center of mass of a 90 foot DT fly line is in the exact center of the line....with 45 feet stretched out back, and 45 feet OUT FRONT. That is a LOT of energy. What keeps us from casting anywhere near that distance? DRAG!

 

The two greatest forces acting upon our flycast are gravity, and drag. But the force of gravity is mostly perpendicular to the direction of the cast and presents a limit only when the line hits the ground. So stand on a tall roof. The force of gravity itself does not reduce the velocity or energy of an object thrown horizontally. But DRAG is a force acting on any object with velocity relative to air, and drag force is directly opposite the direction of movement. Drag progressively reduces velocity....and energy....in the cast.

 

Look once again at our 60 foot flycast at mid-turnover. Where is the drag? The post-loop line has zero velocity. The pre-loop line is, minor waves aside, oriented axial to the direction of velocity. The “skin” drag, parallel to the passage of air over 30 feet of surface, significant, but deceasing. And then there is the loop.

 

In this case, the loop is some length of line, traveling twice the speed of the loop itself, being pulled into and up with acceleration, suddenly being pulled down and stopped. What are the forces acting within that “wave of energy transfer”.

 

From the standpoint of drag, the effect of that early top half loop line being pulled vertical, perpendicular to velocity, into draggiest configuration....is to decelerate it's velocity. That force is energy depleting and has no lift, but will force top top half of the loop downward. This is occurring simultaneously and additively with that same line being pulled (accelerated) toward the post-loop line (downward if vertical). The top half of the loop is being pushed back (drag) and pulled back (deceleration force) in the same direction. The drag force there is a small negative to velocity and a small negative to lift. But the deceleration force with high velocity line rushing in still dominates.


Lift forces

 

complex 150 2.jpg
 

Lift forces

 

Now to the lift forces. On the upper face of the loop, rapid moving line is circling downward and the skin friction will create an upward force, lift. That is the first lift effect, but a small one.

 

By mid-loop the forward movement of the line is almost completely stopped while the former forward velocity is now downward. The drag force on the line in the bottom half of the loop is now UPward and back. The easiest way my mind sees this force is by thinking of it as IMPACT. The line is unrolling from above with velocity and climbing the drag resistance of the air impacting it's face. That is the second lift effect.

 

The third lift effect is pure mechanics, and probably the strongest. Back to the basic mechanics of the loop. Rapidly moving line is stopped by the slower or stopped line offset from it's plane. In a vertical loop, that upper pre-loop line is snubbed by the lower line with a downward and back pull. The exact direction of the decelerating force of the lower line morphs (counter-clock-wise in our diagram) as it circles through the loop, but at all times there is a direct downward component, strongest at the top, weakest at the bottom, until the line exiting the loop is in line with the motionless, lower component. At that point IT becomes the snub for pre-loop line entering the loop. For every force, there is a direct, opposite force. The lower line is pulling down on the upper line. The upper line is pulling UP on the lower line. As line is decelerated through the loop, the line entering the loop and the line exiting the loop are PULLING THEMSELVES TOGETHER. The starting offset of the parallel post-loop and pre-loop lines will progressively narrow. Without question, there is the third lifting force here designated as number 3.

 

I am tempted to say that, since ALL of the energy is in the pre-loop line with an accelerating velocity, that, while the forces are equal on both lines, the effect is UN-equal. At a minimum, if the effects were equal the pre-loop line drop would be equal to a rise in the post-loop line. If the effects are UNequal, then the post-loop line is pulled UP more than the pre-loop line is pulled down. As such, in a vertical loop, the effect could be manifest by resistance to gravitational pull, or even a rise. Unquestioningly, there is lift in a vertical loop.


In the second diagram I demonstrate the effects of the upper and lower line being pulled together, and the lower line pulled UP more than the upper.....down. Superimpose on this the continuous downward force of gravity....and you approximate a horizontal path, seeming to defy gravity.

 

 

decel narrow.jpg

 

The obvious question then presents itself , what about a sidearm cast in a horizontal plane?

 

The first thing to be said is that at all times there is a ballistic component to all moving elements of a cast. We throw line, vertically or horizontally, at high speed....and a shortish cast is over in a very short time. The ballistic drop, if it is occurring, is small. Secondly, we make casting adjustments quickly and without thinking. If the first false cast is “too low”, we aim higher....slightly “up” without thinking. And, no one is sidearm casting for distance. There are reasons why?

 

The second fact is that all other “lift elements” of the cast, the elevated anchor at the caster, the initial upward acceleration of the pre-loop line, the drag-lift of the inclined pre-loop line as it approaches the loop (caused by gravitational drop in mid-flight), the tension lift of the post-loop line to the loop....wherever it happens to be......all those factors are exactly the same. The forces narrowing the pre and post-loop line as the loop unfurls will still act in a horizontal plane, just there will not be an anti-gravitational component of direction.

 

In my experiments standing on a bridge and casting at progressive angles below horizontal to completely upside down, I found that, yes, I could still cast. But the most immediate problem was that everything wanted to fall and widen compared to upright. I could bring the pre and post loop lines into parallel and functional, but only by aiming upward at an exaggerated angle.

 

We make casting “adjustments” for everything from wind, line differences in tapers, density, drag resistances, weighted flies, etc. all the time....most of them without thinking about....why? I think that in casting horizontally there will be more drop than there would be casting vertically, correcting for distance and speed.....not because of aerodynamics, but because of mechanics. We make a minor adjustment in angle and aim higher without thinking.

 

I think the mechanics as I have modeled them work, and in a vertical plane, the “deceleration lift” is the major component of answering the original question.....what keeps the loop up? The answer is, the continuous vertical lift to the bottom of the loop caused by it's deceleration force on the higher, moving pre-loop line....and then kept there by the tension of horizontal momentum forces between the elevated loop and the elevated rod tip.


 

Time to stop and digest. The final installment will be a discussion.... with takeaways.


 

Edited by Peter Patricelli
Link to comment
Share on other sites

You are losing the audience I think because too verbose.  And also the diagram isn't that helpful or doesn't match what actually occurs in later stages of the loop so doesn't explain loop behavior seen in many videos.  Sorry, but there is some good information here that gets completely lost.  A model is only a model.  If it doesn't reflect reality it has to be revised, IMO.

Link to comment
Share on other sites

Kfish,

 

Thanks for the observations.  I mean that.  I agree with you that this is too verbose.  Language, in general, is a tortuous medium to try and describe these things.  I am well aware that it must be agonizing for someone NOT used to thinking about these things to follow along, because it is agonizing for someone who has, on  and off for 60+ years of thinking about them to try and write these things concisely while trying to lay out a step-by-step process of logic. More diagrams, especially in the first few installments would have been helpful.  Physicists would use more mathematical formulas.....which would have left everyone in the dust.  As to the audience, this is dry, "so what" and "who cares" stuff.  There may be 10 people here with the interest and the attention span to actually read it all.  I'm ok with that.  I want it to be as accurate as I can express it, and it will be here for a long time.  And, I have actually learned a lot more than I knew when I started by forcing my brain to plod through it step by step.

 

As to "the diagram isn't that helpful or doesn't match what actually occurs in later stages of the loop so doesn't explain loop behavior seen in many videos."  Can you please be specific?  It is one thing to say "these forces are working in every cast".....and another to say, "this is exactly what is going on in this cast" because of the complexity.  Add tapers, differences in line density/diameter, different tapers, drag forces, shoot or not, etc. and the forces described may be most often cancelled out or just too small to be appreciated.  What seems wrong to you?

 

"If it doesn't reflect reality it has to be revised,"  Some might say....then the earth is flat.  or that light really doesn't bend to gravity.  Sometimes it isn't what do you see most of the time, but what explains what you see on special occasions when the conditions are just right.  Seriously, what are you having trouble with?

 

 

Edited by Peter Patricelli
Link to comment
Share on other sites

O.k. the observation comes from expert casting videos which almost all show that the main line (which is actually post loop line) stays flat, while the still unrolling line (experiencing drag of the fly, and/or leader, and/or indicator) is curved.  What your diagram shows is the loop curving up from below.  Doesn't happen.  The loop below is only slightly curved b/c of sag from middle (affected as it naturally is, by gravity), but compared to the top part of the loop stays mostly straight.  The top part of the loop forms the curved part of the complex "arrowhead" shape that most terminal loops make as the momentum peaks and the loop compresses.  It does compress.  And the statement you make that this compression does not create lift in the lower leg is incorrect.  Just sayin'  I like the bulk of your model as the early phase of the cast is driven by momentum (power of the caster imparted), which once the action is done, determined nearly everything; the middle phase becoming more influenced by gravity (sag) and drag (top part of loop, leader, fly, etc...), but momentum and line tension of static line attached to rod maintained or mostly so (sag).  So that's the part that comports with what I am observing in the real world.  But the fact remains that all these forces and factors exist and play out simultaneously, and over time.

Edited by Killiefish
Link to comment
Share on other sites

Kfish,

      Thanks for that observation.  First of all, "And the statement you make that this compression does not create lift in the lower leg is incorrect."  I don't believe I ever said that.  Please direct me to that.  More, perhaps I am guilty of overstating the lift effect on the lower leg.

 

I say, "For every force, there is a direct, opposite force. The lower line is pulling down on the upper line. The upper line is pulling UP on the lower line.", and "At a minimum, if the effects were equal the pre-loop line drop would be equal to a rise in the post-loop line. If the effects are UNequal, then the post-loop line is pulled UP more than the pre-loop line is pulled down.", and "the continuous vertical lift to the bottom of the loop caused by it's deceleration force on the higher, moving pre-loop line."

 

I considered two options.  Since the forces would be equal, the uplift force on the lower would be the same as the down pull on the upper.  I also considered that there was the possibility that the effect on the lower might be greater.  but then I struggled with how to picture those effects.

 

"In the second diagram I demonstrate the effects of the upper and lower line being pulled together, and the lower line pulled UP more than the upper.....down."

 

Let's both remember that saying there is a lift force does NOT necessarily mean that the line actually elevates.  Many lift forces might exist that never overcome gravitational pull, only slow it down.  That was what I meant by the immediately following sentence, "Superimpose on this the continuous downward force of gravity....and you approximate a horizontal path, seeming to defy gravity."

 

Given the continuous upward pull along with the strong horizontal pull, one might question how much of the slight sag in the lower leg is purely gravity.....or a combination of gravity AND the upward pull stretched out, as it would be.

 

I left the loop shape vaguely semicircular for several reasons.  Like you, I have seen more of an asymmetrical loop, flatter on the bottom and curved on the top, and was tempted to draw it that way.

 

I struggle to understand two things here relating to late loop shape.  I note (and picture) the force of frontal drag on the TOP half of the loop.....and note verbally (and in the figure) it's absence on the lower half.  How THAT sorts itself out with the pulling duties on both halves of the loop., I can't picture in my mind.   I almost drew it as flat on the bottom and inclined, chisel shaped on the upper, but resisted that and chose a safer, earlier shape.   And, what exactly happens to these forces when the upper and lower legs approximate to almost equal heights is unclear. 

 

And, since I have seen it with my own eyes, I can attest that the loop and the lower leg,  in the final acceleration to the leader,  actually can RISE.  But....especially at the end, I cannot attest that either of the other two pictured lifting forces, skin drag 1, and impact 2 weren't singularly or together more responsible than the deceleration lift 3 we are talking about.

 

I don't disagree with you at all.  I WAS uncomfortable with how the diagram showed apparent elevation of the lower leg more than I believed it should, and thusly added the sentence of ""Superimpose on this ...gravity......and you approximate a horizontal path."  It is hard to get words....and diagrams.....to adequately communicate this stuff.

 

And now this discussion here has put that into perspective.  Thanks for that.  My basic goal here is to isolate and identify the major forces and mechanisms, not necessarily fine tune to advanced specificity.  That you have no argument with my forces I take as a good sign.

 

 

Edited by Peter Patricelli
Link to comment
Share on other sites

In trying to do edits I lost fig. 1 and fig, 2 from post #33 and cannot now go back.

 

From the discussion immediately above, fig. 3 shows the presumed effects of the deceleration lift first without the masking effects of gravity and then with the appearance in real life.

 

if anyone can help me get fig, 1 & 2 back in post #33 I would appreciate it.

 

 

 

6284efab7904f_complex1502.jpg.0d1c42c2893b81059b148cf76a1ab7b6.jpg6284efe44a30a_decelnarrow.jpg.3e0882790daded4b095c4f7e9259ba6c.jpg6284ef831a076_decelnarrowcorrected.jpg.d54e989ade166dc0d6851e558ca52cf2.jpg

 

Edited by Peter Patricelli
Link to comment
Share on other sites

"Superimpose on this ...gravity......and you approximate a horizontal path."  Yes, this, I think.  The bottom part of the graphic is more or less correct now, but maybe the uplift from drag differential is more compensated downward to keep the lower leg of the loop still relatively straight.  If there is sag then yes, the bottom leg will appear to be elevated above level, but I think this is mostly an illusion.  So, the only part of your explanation that puzzles me now is the appearance of "lift" at the end of the loops final arrow shape.  Eliminate the "sag" in the middle and the line isn't elevated above level, even in your (new) diagram.

 

The other thing that I think would help is to get rid of the terms "pre-loop line" and "post-loop" line.  Talk about the upper leg and lower leg, or forward edge of the loop.  That will make more sense and not confuse people. 

 

The other thing that could help is if you state that early phases of the cast are dominated by the energy imparted to the line (ballistics, imparting of momentum, and also defining the height and trajectory), loop formation requires tension of the line and that tension must be maintained for loop to persist, momentum plays out, drag comes into it at all stages, gravity does too, but so does inertia of the lower leg which is under tension and mostly static.  Later stages:  gravity takes a bite (sag) and drag increases in influence (maybe several components of drag happening simultaneously but not always increasing or decreasing in sync).  Both gravity and drag have been operating all along but as the momentum peaks, and rebound effect of drag (what you label impact) on lower leg lessens (i.e., the loop unrolls and is more compressed, so less impact, less drag) the result is that the forces are played out or are unable to compensate, momentum lost, energy dissipates, gravity wins and the line either floats down or falls.

Edited by Killiefish
Link to comment
Share on other sites

Ballistics, Energy, and Aerodynamics

 

My goal was to discover and detail the major basic mechanisms of the flycast. Necessarily, that process would consider contributions of the above three factors....plus gravity and drag. The secondary goal was to explore the claim, made elsewhere, that aerodynamics was the over-riding process allowing the flycast to do what it does.

 

In my flyfishing life I have had moments of insight regarding casting mechanics that have led me to this point. Here are three.

 

In 1983 my hometown in the northwest held a “community celebration” with parades and various functions. The owner of the dominant flyshop decided to have a casting contest. With two major fishing rivers confluencing within the city limits, and in striking distance of the most celebrated trout, salmon, and steelhead fishing rivers in the northwest, there was no lack of experienced casters to draw from. The owner pulled off the rack a standard northwest fishing setup, a 9' 9 weight Sage of the then “new” graphite, a 30' fast sinking shooting head, leader and yarn fly.....and monofilament shooting line. All casters used the same setup. The venue was the asphalt parking lot of the flyshop. Casting cold, with no particular practice or warmup, my best cast was 137'.....and the head had not fully turned over, the yarn was behind head line. The two takeaways from that was.....that was 100' of SHOOT.....and that was a mostly ballistical process. Get the head going at maximum speed, haul, and aim high for trajectory. Ballistics.

 

I was seated on the edge of a pond and a friend was casting parallel from a distance toward me to land just past me. My prsence there had nothing at all to do with me studying the mechanics of the loop. He was using a trout outfit, DT line. What I saw was astounding. As the loop passed the midpoint, and especially as it neared the front taper, the the loop narrowed progressively to an edge point, and it's velocity shot forward in an amazing, accelerating crescendo until it hit the leader....which then gently opened up and turned over. And the trajectory of the last ten feet of line, the taper, actually elevated by several inches. What! How? Why?

 

The third is one I have had maybe 5,000 times, and you have had as well...when rather than the usual floating or intermediate line, you string up with a fast sinking line of the same weight and begin to cast. You immediately notice it FEELS different. The line is THINNER. It casts differently. The line seems to be flying faster, your forward and back cadence speeds up.....and you adjust your aim higher. The absurd extreme was the first, and last, and every time in between that I rigged up with a lead core shooting head. Forty years ago that was the ONLY way of REALLY getting DOWN. That was like holding onto the tail of an enraged 30 foot black mamba, desperately trying to avoid being “bit” as it passed by my head. What was the difference? Density and diameter.........affects ballistics and aerodynamics.

 

I have often thought that in the last 60+ years of evolution in rod material, tapers, modulus, weight, etc. that I got maybe, at best, about 5 feet more length in my best, standard fishing cast. But the technology and improvement in LINES, over that same time frame, has gone ballistic......so to speak. And may help some of that better 5 feet! It would seem that, with flylines these days, they can vary the elements of.....memory, flexibility, diameter, density, length, strength, slickness, etc. to an almost infinite extent....on the same line. There is very little to nothing, taper-wise, they cannot accomplish.

 

How much have we discussed “ memory, flexibility, diameter, density, length, strength, or slickness” in analyzing the mechanics above? Very little. But....”density and diameter.........affects ballistics and aerodynamics. I have tried to tease apart what happens in maybe 2+ seconds, the unrolling of a forward or back cast. In those 2+ seconds, what exactly, besides gravity, stays the same? Nothing! The cast is an interplay of continuous increase or decrease, Momentum, drag, energy here become forces and velocity there, mass of one segment switching to the other. Why would we expect that a single level , unchanging in weight and diameter line, different sections of which have vastly different roles in a cast, would be most efficient? We don't. We have gone from level to tapered, then front tapered-level head and running, now front loaded taper to back loaded taper (Wulff triangle Taper), etc. The only thing now left level is the shooting line. Should it be? For example......for someone looking for another foot WAY out there, I can question possible advantages of a lighter last ten to twenty feet...if there is enough energy left in the loop to still get turnover.

 

The point is... the advancement in line technology has widened considerably the options in manipulating the ballistics AND the potential aerodynamics of casting options......for different purposes.

 

Any moving object through air has both ballistic and aerodynamic attributes. Drag is usually considered separately because it affects both ballistics and aerodynamics in an equal, predictable, and measurable way. It is a separate entity. But some drag forces become aerodynamic when they produce a force NOT exactly opposite velocity.

 

Between my only experiences with competitive distance casting, in 1983-5 and the present, distance casting has morphed to longer and longer heads (and special tapers)....and relatively less shoot. While there are non-aerodynamic mechanics in the cast that produce lift (deceleration lift in the loop), the long carry of pre-loop line generating drag-lift (Magnus's force) as an inclined plane becomes a progressively larger factor.

 

Having thrown a lead core head, which is about as ballistic as a rock, I am confident that I could “carry” a 30' head in a vacuum (zero aerodynamics)...and then shoot it (ballistically).....for a new world record. On the other hand, I doubt a distance caster trying to carry 60-70 feet of head could succeed with that, in a vacuum. To the extent that he could would only reinforce the point that the bulk of fly cast is ballistic and energy driven.

 

We have reached the point of realization that there is a NOT just one type of casting. There is ballistic-heavy casting characterized by short heads and greater dependence on shoot, and there is aerodynamic-heavy casting characterized by long heads and shorter dependence on shoot. And there is a continuous spectrum in-between. There are arguable advantages and disadvantages to either mode, depending on who, what, when, where, and why.

 

If we are agreeing that the comparison must be between rods of equal length and line weight, the least arguable are....for the short-headers, the biggest problem is dealing with a lot of loose shooting line and getting a clean shoot. For the long headers...the length of time exposed to complete turnover, and length of line exposed …..to wind.

 

Effect of shoot

 

It would seem that the mechanics of shooting, just the simple release of the running line, would not be complex. Surprisingly, that is not exactly true. I am not going to do a detailed analysis here, other than to say that shoot has complex effects are on EVERYTHING in front of the shooting line. In a controlled, effective shoot, the circulation of line through the loop slows, the acceleration lift in the loop diminishes, the acceleration force pulling from the top of the loop on the pre-loop line diminishes, and the overall speed-up of pre-loop line diminishes. Consequently, the lift forces diminish and the loop develops a more pronounced trajectory in line with gravity. To be effective, there must be sufficient resistance in the process of shooting to maintain efficient loop turnover. The three variables are weight of the running line (inertia), drag resistance through the guides, and height to the rod tip the caster forces the shooting line to climb while being pulled into velocity.

 

The Double Haul

 

If anyone wants to pursue a similar mechanical explanation of the generation of line speed by the double haul, here is a link to an analysis I did years back. The only change I might make now is to point out that the competition casters stress the haul hand be directly in front of the rod and the haul be directly in line with the rod and line. That must get one a marginal extra distance....which matters in competition and where one has free arm space, but I too often find myself in water of a depth that I would be smashing the water or truncating the haul length. I find an angled down and out direction more ergonomically efficient for me for a full day of casting and it allows me to add a whole shoulder rotation for both the haul arm and the rod arm. Again, less tiring for me for hours of casting.

 

http://www.flyfishingfotography.com/fly_casting_dynamics_029.htm

 

Discussion:

 

The flycast is a magic marvel. Who thought to design this thing? The energy of the line launched into the loop is maximally conserved from drag throughout the cast. It achieves that by reducing the amount of line ever exposed at one time to a sideways line of flight. All the line must eventually pass through the draggy loop, but it occurs in only small amounts at a time. Velocity lost is energy lost, and cannot be regained. If all the line were exposed to sideways orientation for even a split second, especially in the early stages when velocity is maximal, the drag effect would be massive and velocity would plummet within a few feet.

 

Similarly, energy and momentum are digested in small increments at a time, and still used efficiently to maintain the mechanics of the system. The lost momentum in the loop becomes the opposing (to the caster) force that keeps the post-loop line from crashing to the ground. The kinetic energy to be lost by line (mass) and velocity being stopped in the loop is actually conserved by accelerating forces on the pre-loop line, pulling it straighter against drag, accelerating it's velocity in an up-angled direction entering the loop. As a result, there is so much energy, even after pulling into motion the shooting line, that, as the loop nears the end of the line that … we have to diminish it by draggy elements such as thinner taper, leader, and fly. And at the end of all that, out there aways, the whole system is still hanging in the air. AMAZING!

 

Understanding what is happening lets us vary and tinker with options with each element, and make knowledgeable decisions and adjustments to solve a particular problem. Going to be wading deep and using a weighted fly......a short head line and a short leader will help keep the backcast from hitting water. Using a very wind-resistant, light fly, go up a line weight, shorten the leader, use slower cadence to give the line, moving more slowly, time to straighten. Using a heavy, sinking head and very light running line but not getting full turnover......use a heavier shooting line, the weight of which in being pulled into motion will strengthen the loop and increase it's speed and energy to the end.

 

Each element has options. With regard to the “head”, whether that be 25 feet or 50 feet, there are options of weight, density, diameter, taper, and even slickness. Considering the concepts of ballistics and aerodynamics, for competition distance casting, which is favoring long heads and long carry, I would guess that thin, dense (sinking) fly line is NOT used because the aerodynamic-heavy casting would favor wider diameter for the weight (lower density).....and therefore floating lines. That would favor more lift during the longer carry.

 

I note that competition distance lines also now have an aggressive, front-loaded taper. That would/will INcrease the pulling forces within the loop at the later stages of turnover when energy and momentum are running low. A head with a back-loaded taper (such as Triangle Taper) will favor other moments in a cast, such as roll casting.

 

In thinking about leader options one can just shift all the mechanics and principles from the line to the leader......with the single caveat that the smaller diameter and diminishing mass means common drag suddenly heavily outweighs the remaining energy and momentum. The leader is the brakes to the freight-train. Apply the brakes too early with smaller diameter (think mass here) butt....and the drag overwhelms the momentum and turnover fails. You choose where in the leader and how much braking you want where by the taper. The stiffness of the leader also forces it to open up from what might be a very narrow line loop at the transition.....causing more drag earlier. Since I have experienced it, a too stiff leader may simply refuse to be bent by the remaining velocity and drag forces and simply flop over as a 4 foot long, slightly curved entity.

 

The contribution of the fly in the cast varies with the balance of ballistics (weight) and aerodynamics (drag...more or less). A draggy fly that you want to fully turnover will need more energy maintained until very close, a shorter, butt-heavy, short tippet leader. Or.....one can “tune” the fly by adding weight in the tying (or manufacture) to get a more favorable momentum. And, there is the sparse, heavily weighted fly that has enough speed and mass, and little enough drag, that when the loop hits the leader, the fly's ballistic trajectory is enough to reach the turnover distance....straightening a too-light exhausted leader.....rather than the other way around. It all depends on what you want or need in terms of presentation.

 

I would guess that the vast majority of fly fishing is done in situations where full turnover of the leader and straight initial presentation of the fly are relatively unimportant.....or counterproductive. A weighted nymph cast onto current, for example, will dive to some depth straight down rather quickly if the tippet is slack compared to straight and tight....having to pull the leader, flat orientation (draggy) down with it. On the other hand, situations that demand predictability and accuracy, or stealth, require a very fine-tuned system and a balance between the last vestiges of velocity and energy delivered through the turned-over leader......and the ballistic/aerodynamic properties of the fly.

 

Finally....we get to the shooting line. The weight, stiffness, memory, and drag (more or less) of the shooting line play a crucial role in any cast where one wants, and uses.....shoot. As to the cast mechanics, what matters is weight (inertia), drag through the guides, and height. There must be enough counter-force through the post-loop line to keep the loop working dynamically....all the way to the end. Too light and the loop fails in mid or late turnover when the shooting line speed approximates the pre-loop line speed. Too heavy and distance is lost by excessive resistance.

 

Although this is a small element, it must be said that drag through the guides, while potential achieving the goal of providing “enough” resistance, is a loser compared to getting that resistance from a slightly heavier, but slicker line. Drag through the guides is energy lost forever. Resistance from slick, slightly heavier line becomes momentum acted upon only by air drag....much less. Competition caster might get another foot with that one. Raising one's rod high at the very end of shoot also provides extra inertia if one feels the need to slow the shooting line at the very end to ensure leader turnover for distance.

 

Other factors NOT related to the mechanics of the cast also come into play with shooting line, such as memory (coiling), stiffness (reducing tangling), resistance to being blown about by wind (weight), density (floating or sinking), etc.. For these reasons I, who use head systems frequently, carry not just a variety of heads I can swap out on the water, but several reels with different shooting lines.

 

What is interesting to me is that, to my knowledge, so far shooting line is the only part of the whole system where one density-diameter-weight is still felt to “suffice” through it's whole length. There are no “tapered” shooting lines When one applies a cast analysis as we have done for the other elements, we have infinitely variable leader tapers, a wide range of front-end taper length, and a wide range of front, belly, or back dominant head tapers. But we ask different roles for different areas of the shooting line in the cast. The “front” of the shooting line must provide enough inertia (weight) to maintain the dynamic cycle through the loop. That resistance through the rest of the shoot will consist of inertia of the (level diameter) line and guide-drag (both of which are stable throughout), and the air-drag of the now-moving shooting line. That drag becomes progressively greater with the lengthening (and increased velocity) of the moving post-loop line AND shoot-line. Is that additional resistance/drag force a positive out at the last 1/3 or ¼ of the shoot? If one were throwing with a fishing setup pretty consistently 80' with a 30' head, that would be a shoot of 50'. What if the last 15' were a lighter line?

 

In other words, would a progressively front-loaded taper to the shooting line, based on the projected average length of shoot, actually get another small increment of distance? Might be something for competition casters to tinker with.

 

In the end, these days we have an amazing degree of flexibility and options in assembling a complete setup for fishing....or competition casting. Understanding the mechanics of the cast allows us to make informed adjustments with the rods, lines, leader and flies we have on hand to best match the demands of the situation, the fish, and the environment.

 

And, when the fish aren't biting, sometimes we can, as I do, just stare in amazement at the cast itself.

 

 

 

Edited by Peter Patricelli
Link to comment
Share on other sites

The above makes sense to me with the exception of late stage lift.  You observe lift (from drag), I see minor compensation of sag, if anything, and the line is not further elevated above the avg. level of the pre-loop line (overall height of lower leg).  The apparent "lift" effect or counter impact could be due to several things:  1. the compression of the loop forcing the lower leg of the line down against an air mass, 2. the entire front face of the loop is now more sharply angled and hence more aerodynamic, or 3. the caster adjusts the trajectory angle by making the last rod movement up, and this increases tension of the late stage loop, which as I state in another thread is a way to reduce the effects of middle st(age) sag.  If only (or mostly) based on 3 then there is no actual lift, only minor compensation of sag.

Edited by Killiefish
Link to comment
Share on other sites

Kfish,

"You observe lift (from drag), I see minor compensation of sag,"

By definition, "lift" is ANY degree of force in an anti-gravitational direction, even if no actual movement upward results.  "compensation of sag" ....unclear to me what you mean by "compensation".  Do you mean more of a curve or do you mean a flattening of the curve.  An upward lift of the far end at the bottom of the loop, together with the outward pull from the momentum being stopped, would cause an elevation of the far end, resulting in a "sag" appearance.  That is what I model in figure 2.  The "sag" that is observed undoubtedly has a drag component, but is also likely to look slightly deeper because of a far end lift component.

 

"and the line is not further elevated above the avg. level of the pre-loop line (overall height of lower leg"    If the upper and lower lines are actually falling slowly simultaneous with a lifting effect.....you would not necessarily see an elevation above.  But....I have seen it with my own eyes.  Anything that counteracts gravity is "lift".

 

"The apparent "lift" effect or counter impact could be due to several things:  1. the compression of the loop forcing the lower leg of the line down against an air mass". 

I think you are stating here exactly what I have as "impact lift" .  How big that is is very hard to judge and would vary with the velocity of the line....which is changing.  "Compression" is a confusing word.  "Narrowing: we both agree on.  Compression conjures up direct interaction.  The upper line can never directly compress against the lower, since they are connected only by a semi-circle of floppy line.  They can only PULL against each other.

 

"2. the entire front face of the loop is now more sharply angled and hence more aerodynamic,"

 

I agree that there is a direct drag force on the top half of the loop forcing it to flatten.  the bottom half of the loop is mostly stopped and the direction of movement is mostly downward...thus what I call "impact lift".  We both agree that the face of the loop is asymmetrical...and flatter on the top half.

 

"3. the caster adjusts the trajectory angle by making the last rod movement up, and this increases tension of the late stage loop, which as I state in another thread is a way to reduce the effects of middle st(age) sag."

If you are saying that lifting the rod late in the turnover as the loop nears the end lifts sag in the post-loop line....then sure, just as pulling straight back would.  But but that does not negate the considerable lift apparent in the trajectory of the loop.

 

If you are trying to argue that there is no lift at all....you will never win that one.   Since the (I will use your terms) upper line is moving more or less straight....and is stopped with a downward pull, then there is NECESSARILY an EQUAL upward pull on the line doing the pulling.  THAT line on the bottom of the loop is out there hanging in air with no velocity at all.  It is not tied to the ground.  It could never move the upper line downward without being pulled upward.  And the fact is that, most visible in the early and mid-stage, clearly the upper line with velocity enters high, with velocity, and exits low, without.  That deceleration mechanism is operating then and throughout the whole sequence...unless or until the loop somehow turns over.  Just because the loop narrows....even to 1/4 inch....that mechanism and lift still existsif there is any vertical offset of the two lines.  And...note that I said that in a horizontal cast, there would be no lift.....and in fact some drop.

 

 

Link to comment
Share on other sites

I mean a flattening of the curve.  I don't think I see an actual gain in elevation of the lower leg, late loop wedge stage.  I do see some compensatory tension or inertial force operating at the end to overcome some of the sagging in the middle.

 

But I understood that you were stating that there is some other drag related lift that raises the level of the post loop line above its prior, mostly flat level.  My understanding of what you were saying you observed as "lift" may have been wrong.  Optically, you might see any uptick in line elevation but it's relative to sag.   If there is drag related lift it is associated with what I am calling parts 1. and 2.  By compression I mean tightening up of the two legs of the loop.  And the line is not entirely floppy, especially saltwater diameter floating lines, and lines that are above, say ~6wt.  Compression (narrowing) of the two legs of a stiffer line would exert a force on the lower leg that is independent of the line pull or tension.  Also the upper leg is curved not flat if there is drag from the leader and fly, as you do suggest.  That curve is not symmetrical at the late stages. 

Link to comment
Share on other sites

Kfish,

 

"I do see some compensatory tension or inertial force operating at the end to overcome some of the sagging in the middle."

 

The tension on the post-loop line created by stopping the pre-loop line velocity comes only from the line IN the loop.  Through the early stages of the cast that is certainly constant and stable.  In that early stage the acceleration force on the pre-loop line is relatively small...and pulling on a whole lot of line.....and line drag.  From mid to late stage all that begins to change as the amount and drag of the pre-loop line starts diminishing rapidly.  THEN a real acceleration in velocity starts becoming a factor.  The loop is also diminishing in size (how much line is being decelerated at any one time.....force would go down)....but the velocity on top AND the velocity of the loop ( 1/2 pre-loop velocity) is also increasing.  Does that all equal out....or increase? (that would be the only source of "compensatory tension or inertial force operating at the end to overcome some of the sagging in the middle".  In the latest stage, when the loop is very narrow, but accelerating rapidly, it gets even harder to call.  The velocity is great, but the mass getting even smaller (front taper).  Do we feel an increasing tug on the rod at the end?  I have pondered that from the start.  I would love to have another increasing outward force to hold up the post-loop line, but my conservative nature keeps me from calling that as certain. 

 

"But I understood that you were stating that there is some other drag related lift that raises the level of the post loop line above its prior, mostly flat level.  My understanding of what you were saying you observed as "lift" may have been wrong."

 

That is what I am calling drag lift 1 and even more impact lift 2 on the diagram.  And yes, the last end taper line and even the butt of the leader actually elevated.  It was not an illusion of increased sag.  At that late stage, with the offset above and below the loop only inches...or less, the potential for deceleration lift 3 (in the diagram) becomes very limited....at best.  And in that configuration the actual flexibility/stiffness of the line  becomes a factor.  That is why I am suggesting that in the very end lift forces 1 and 2 may be dominant and #3 becoming irrelevant.  But those lift forces are separate (perpendicular) to the outward tension force discussed in the paragraph above.  Don't get the two mixed up. 

 

"Also the upper leg is curved not flat if there is drag from the leader and fly, as you do suggest.  That curve is not symmetrical at the late stages. "

 

I don't know whether you are talking about "upper leg"....of the pre-loop line.....or of the loop itself.  "if there is drag from the leader and fly".  There is ALWAYS drag from the leader and the fly.....not IF.  "That curve is not symmetrical at the late stages."  WHAT....asymmetrical curve?

 

IF we're talking about pre-loop line and not loop, then I think most commonly the combination of gravity and drag has the pre-loop line slightly below the top of the loop, curved concave UP.  BUT....at the same time the top of the loop is also being pulled DOWN by the loop itself.  THAT would create a curve convex UP.  The two would tend to cancel, unless one is more dominant that the other.....and the amount of drag on the far end quite variable.....and perhaps determinative.

 

Don't get lost  in little details here and miss the big picture.  The initial question was...."What keeps the whole cast UP.  There are no lack of forces trying to bring it down, the most obvious starting with G and then D.....and then T(ime).   And then maybe 10 more smaller ones. I can make a diagram of "downward forces" that would make it seem that the whole thing is impossible.  But we both know that is NOT what happens.  The overall sum of lifting forces has to be greater than the downward....in each and every section.....or they would be dropping like rocks.  Goal #1 is to identify each and every lifting force we can be sure of, where it operates and when.  Then we can speculate about which are strongest...and when in the cycle.  Identifying downward forces does very little for the conversation.   "The bumblebee cannot fly",  There are a slew of them.

 

A precise diagram supposes that we have calculated ALL of the up and down forces and know exactly what and why for that particular cast, line taper, weight, drag, fly drag, velocity, etc..  That is far beyond me......and you.  It is happening too fast and there are too many shifting variables.  And almost every cast looks somewhat different to me,  BIG PICTURE here.  I am about done.

Link to comment
Share on other sites

5 hours ago, Peter Patricelli said:

"["Also the upper leg is curved not flat if there is drag from the leader and fly.... That curve is not symmetrical at the late stages. "

 

I don't know whether you are talking about "upper leg"....of the pre-loop line.....or of the loop itself.  "if there is drag from the leader and fly".  There is ALWAYS drag from the leader and the fly.....not IF.  "That curve is not symmetrical at the late stages."  WHAT....asymmetrical curve?]"

Yes I should have said because there is drag, not if.  

 

The curve I am referring to in this case is the entire front of the loop.  In Numbskull's video one can see that the loop becomes flatter, pointier, over time.  Also the curve of the loop starts out symmetrical and becomes more wedge shaped with the apex closer to the top of the loop (upper leg).

 

I give up....what are you holding out as your answer to the original question.  Inertia?  A loop when forming is moving but the lower leg of the fly line is static.  A body at rest will remain at rest....and the still moving loop's energy keeps it up until it runs out.  A body in motion stays in motion.  The body in motion keeps the energy sufficient for the time needed to allow the body at rest to stay at rest, despite the other downward forces acting on it.

 

Lower leg - body at rest, until other forces win (gravity acts)

Loop as it unrolls - body in motion, runs out of gas and has to cease moving

Drag - a force acting upon it - keeps the loop from unrolling too quickly, and also adds "lift" (but minor), and there are several draggy components acting.

Gravity - a force that always acts, and ultimately wins.

Edited by Killiefish
Link to comment
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


×
×
  • Create New...