Well, I do, too. And in order to reach an (almost) straight line path I want to achieve a smooth (constant) acceleration.
In my understanding SLP gets more difficult when aiming for a higher rate of accel. near the end of the cast.
Bernd,
This question about different types of acceleration employed by good casters is an interesting one, but you need to define the purpose of the cast before it can be answered any any meaningful way.
Is it to make "good loops" (what ever that might mean) for a 10 meter cast or to get maximum line speed? You might employ entirely different types of acceleration profiles to meet those conflicting requirements.
In terms of the article Tom referenced I would like to see some data that supports the claim that:
We have analyzed thousands of casts in the last 4 years and have found that the best loops are always made with constant rod acceleration. We have analyzed many top casters using very different casting styles, but find that how they accelerate the rod is virtually identical, resulting in great loops.
I have measured the butt phase angle that a number of world class casters making longer casts of 20 meters or so and invariably they tended to have a phase angle vs time that varied as :
Phs=a0 + a3*t.^3. That cubic variation was also measured by Dr. Robson in his paper
Here is an example of the phase and angular velocity profile that Chris Korich (second only to Steve Rajeff in U.S. tournament casting) used to make a forty foot cast.
You can see his angular velocity profile (the green curve) was curved (varied as t.^2) not straight (vary as t.^1) as it would be for constant acceleration.
That means the angular velocity in those casts was varying as t.^2 and the angular acceleration as t.^1 (linearly increasing acceleration)
Even Bruce Richards had a quadratic variation in his measured angular phase velocity in the original "Expert 50" cast as shown below:
That had a linearly increasing angular acceleration as shown here:
So how much difference is there in the actual loop shape Bruce now produces in a 20 meter cast using his "ideal" constant acceleration profile vs his old style employing linearly increasing acceleration? That is the data I would like to see before I climb on the "constant acceleration" bandwagon.
In that regard I would like for someone to actually define what they mean by the "best loop" shape for a 20 meter cast?
Aside from not having a tail would a .2 m semi-minor length in the initial elliptical loop shape at MCF actually be any "better" than a .4 m one? Are we going to define this "best loop shape" after the loop has morphed into some other shape that was caused by drag effects rather than the expert ability of the caster? When it comes down to defining what a "great loop" looks like I think we might be tilting at windmills.
Certainly as discussed here constant angular acceleration is not what you would want to use in distance casting. Paul's acceleration in that cast was increasing as t.^3.3 a far cry from being constant.
In terms of tip path, how "straight" does SLP have to be in order to make a good cast? That is always thrown out as some ideal, but I don't think it is strictly realized in practice. Is the tip path Lasse produced in his distance cast straight enough to qualify for producing some mythical "best loop" shape?
In terms of producing line speed I would think the tip path distance would be much more important than how straight it happened to be.
Who would say if the 3 meter initial loop size that is produced in a the bouncing bomb back cast is a "good loop" or not? I would think that the subsequent loop morph you see with that casting style is going to have a big influence on how you would answer that question.
When you see slow motion videos of the loop formation it appears that a major portion of its size is determined by the tip path from RSP to MCF. Does the caster really have much control on that portion of the tip path?
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
could you explain what you mean by 'butt phase angle' in this instance.
James,
It is just the angle the butt of the rod is pointing relative to the horizontal at some point in time. When you are digitizing video data it is the measurement you need to make in order to see how the butt angle changed with time. You can then take the derivative of that curve to calculate the angular velocity value that is measured directly with the CA.
Here is an example from Lasse's cast where the butt phase angle was measured to be 74 degrees.
At the start of that cast when the rod was horizontal and pointed behind him the angle would have been 0 degrees. The angle when the rod butt was vertical would have been 90 degrees.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
Hi Gordy,
in regard of my main question about the ideal type of acceleration let's focus on two different casts:
a) an average overhead cast with medium line lenghts and
b) a (maximum) distance cast.
Good question about the definition of a "good loop".
I can only define this for myself:
As tight as possible over it's full life cycle + full lenghts and with best possible tension between tip and fly.
The loop we achieve due to the bbbc might be (better to say is ) a good solution to reach high distance for sure. Works well for high line carries.
Why don't we use it for medium distance / medium length of line, too (does anyone)?
I think this is because most of us prefer to see loops which are tight over it's full length and it's full life cycle?!
At least that's what I think.
Very good point about the major portion of loop size formed by the tip path from RSP to MCF.
Let's say we want to achieve proper speed and proper tip path to RSP and in addition to MCF, too.
This to me means:
Tip path to RSP as straight as possible (I agree slighty convex is perfect in truth). CF as small as possible. The speed level has to match the cast's purpose...
I think constant acceleration results in less rod bend compared to constant increasing acceleration when reaching the same max speed level in both casts. Is that correct?
If so wouldn't constant acc. result in less cf, too?
Let me add something I have in mind in regard of teaching:
When I tell a student to aim for constant increasing acceleration he might think to start with slow acceleration and end up with fast acceleration (which would be correct anyway).
I am pretty sure this can easily result in too slow acceleration in the beginning or in other words in a waste of maybe the first third of the arc.
And for the distance cast wouldn't I want to start with maximum possible acceleration? Maximum possible to control of course...
If you will measure my acc. in truth to be more close to constant increasing, fine. But if I would aim for that doesn't it mean I should not aim for highest (possible to control) acc. in the beginning of the arc?
Because how should I increase if I start with my maximum possible acceleration?
This is probably difficult to answer? ... successful teaching vs. physical side of the story (something like that).
In regard of Paul's distance cast ... he brings in a huge amount of delayed rotation via wrist (and I think - Paul? - finger movement) close to the end of the acceleration. So if we measure his angular change of the butt section of course this won't be constant as I understand it.
How about force application here, Paul? Do you increase force application close to the end of acceleration or is it more about high fore application from the beginning and just being more effective in creating speed near the end by using more of the force to rotate your stick?
(Hope this doesn't sound too weird now! :kungfo: )
I think constant acceleration results in less rod bend compared to constant increasing acceleration when reaching the same max speed level in both casts. Is that correct?
Bernd,
The amount of rod bend will depend on the angular acceleration and drag effects on the rod. Thus if the acceleration increases more as the the rod butt is near the vertical then the rod hand drop required to get a flatter tip path would be less for the larger acceleration value.
The line speed will depend on the area under the force over distance curve. Any number of different varying angular acceleration curves could result in the same area as a constant acceleration curve for a conventional cast. I don't know that one would be any better than another as long as they were smoothly varying and did not cause the tip to go through a dip as some point and create a tail.
And for the distance cast wouldn't I want to start with maximum possible acceleration?
I assume you mean translational acceleration here as we know you want to delay the angular acceleration for as long as possible to preserve the angle the rod can be accelerated.
In terms of applying force over distance I would think you would want to match up the maximum rod hand translation speed (not acceleration) when the force on the line was near its maximum value at MRF. Whatever acceleration profile was required to make that happen would be the thing to shoot for. You have another constraint that the rod hand must be dragged forward at the beginning of the cast so that no slack is produced in the trailing line. That might limit the actual type of acceleration profile that can be used. I would look at what world class casters do as I do think that good athletes do tend to self-optimize when it comes to perfecting sports motions.
You can see that Lasse's rod hand speed was decreasing throughout the cast. It would be interesting to see what other good casters do.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
Bernd,
See attached link for description of a cycloid http://mechanical-design-handbook.blogspot.com/2009....am.html
When the camshaft in your car open and closes the valve train this is the preferred cam curve to prevent the valve train from destroying itself. The addition of a constant velocity portion allows more valve opening in the same time frame. The harmonic allows the valve to decelerate without jumping off the cam which will cause shock and near immediate failure.
As acceleration increases rod load increases resulting on more rod deflection and a reduction in effective rod length reducing velocity of the swept arc at the rod tip. If acceleration is constant deflection remains constant with an increase in velocity at the rod tip. If acceleration goes to zero deflection decreases increasing effective rod length giving more tip swept velocity. The key IMO is how the acceleration is applied. Too much power, too abruptly increases rod deflection without the payback in speed increase.
Too little acceleration results in running out of stroke without reaching high velocity.
The amount of power any of us has is finite. The rod strength is finite. How the rod and caster work with each other is where the potentials are.
It would be interesting to see what other good casters do.
Here is a plot of the rod hand velocities for Chris Korich's shooting head cast.
He has a much different profile than Lasse's. Max rod flex in this cast was near the t=-.13 time point as shown below:
His maximum hand speed had a fairly broad hump around the time where the acceleration force on the line was at a maximum. This is what I would expect to see for an optimum hand speed profile that would maximize the work energy applied to the line. I.e. he moves the rod tip over the largest distance with his rod hand while the deflection force from the rod is near its maximum value.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
I aim to hit it as hard and as late as possible. I have no idea how to make constant acceleration and don't believe in it. I'd need to practise with an accelerometer to learn it, and from my readings with such a device it appears that I absolutely don't do this for distance.
I don't know how to make my body move linearly with constant acceleration let alone move an object rotationally with constant acceleration... And rotation combined with translation to give constant acceleration all starts to get incredibly complicated! So I don't even know where to begin in trying to teach it.
I think constant acceleration results in less rod bend compared to constant increasing acceleration when reaching the same max speed level in both casts. Is that correct?
The amount of rod bend will depend on the angular acceleration and drag effects on the rod. Thus if the acceleration increases more as the the rod butt is near the vertical then the rod hand drop required to get a flatter tip path would be less for the larger acceleration value.
As acceleration increases rod load increases resulting on more rod deflection and a reduction in effective rod length reducing velocity of the swept arc at the rod tip. If acceleration is constant deflection remains constant with an increase in velocity at the rod tip. If acceleration goes to zero deflection decreases increasing effective rod length giving more tip swept velocity. The key IMO is how the acceleration is applied. Too much power, too abruptly increases rod deflection without the payback in speed increase.
Too little acceleration results in running out of stroke without reaching high velocity.
The amount of power any of us has is finite. The rod strength is finite. How the rod and caster work with each other is where the potentials are.
Seems to me as if we are almost in one line here.
It seems to be inpossible to say which kind of acceleration should be the ideal one? Instead it seems to depend on many factors how one adds his kind of acceleration to the whole system + process.
Gordy, "drag effects" does that include inertia of line & rod?
You pointed out the rod butt near vertical to be the critical point in moving the tip along SLP. I think the critical point is (more exactly) when the tip passes the vertical position above rod hand. Trajectory being horizontal that is of course. Agree?
Paul,
I fully agree with you: It's inpossible to reach constant accelereration in truth. Seems to me as if this is the same with SLP. Agree?
What is your current advice to your students about how force application during the cast / how acceleration during the cast should be done?
Can we agree that
"Don't decrease the rate of acceleration before it's maximum. Always keep it smooth."
would be a good advice?
Regarding force application my general hint to beginners and advanced students would be to avoid sudden burst of power during acceleration.
It's impressive how many different views are still available when it comes to how to accelerate a fly rod.
One could think this wouldn't be an important point at all.
Don't decrease the rate of acceleration before it's maximum
Nope, that doesn't make any sense! It's completely impossible to decrease your rate of acceleration before it is maximum!
What is your current advice to your students about how force application during the cast / how acceleration during the cast should be done?
I don't talk about acceleration. And the approach and advice varies from pupil to pupil and what they are trying to achieve. I'm much more likely to give analogies that to talk about acceleration. "Try dunking a basketball", "pulling a bell", "think heavy" etc etc.
Hi Paul,
I remember the FFF offering a DVD "The 15 most common casting errors" by Jason Borger.
One of the errors is adressed to be a "two stage" cast.
This would mean to have a significant decrease in accel. before reaching maximum as I understand it.
Anyway I agree it rarely happens.
So it should be better to say something like:
Aim for smooth acceleration.
If a change in the rate of acceleration is needed always keep it smooth.
Here is what Bill & Jay Gammel offered in their 5 e broschure:
"The power should be applied slowly at first, gradually increasing to a peak at the end of a stroke."
I also remember John van Dalen saying: "No power before midnight (vertical rod position)". For the roll cast this was.
I personally think this may be contraproductive to those who tend to have (too) slow acceleration in the beginning of the stroke. And this shows up quiet often in my experience.
In case I am with Bruce here who states to aim for smooth "constant" acceleration.
Gordy, "drag effects" does that include inertia of line & rod?
Bernd,
As noted in Wikipedia:
In common usage the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass)
Thus "drag effects" is not related to mass but is just related to the form and skin drag imposed on the rod (or line) that is proportional to the velocity squared of the rod's (line's) movement through the air.
There is also an inertial bending effect in the rod that will depend its acceleration (primarily angular acceleration). If you have not tried this, take the line off of the rod and simulate a casting motion. You will be surprised how much bend there is even when there is no bend that is associated with acceleration the line.
You will see some impressive amounts of counterflex in doing that experiment as well.
I am with Bruce here who states to aim for smooth "constant" acceleration.
I would agree with smooth, but would not be concerned with the "constant" part of that statement. You would have to show me that constant acceleration produces a "better" (what ever that might actually mean) loop in making short fishing casts. I have observed that many world class casters produce linearly increasing angular acceleration in their 40-50 casts so I am not going to worry about my "smoothness" factor as long as I do not see the onset of a tailing loop in my casts.
For sure constant acceleration is exactly the wrong thing to do in distance casting where the goal is to produce the highest possible line speed.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
Hi Gordy,
thanks for clarifying. I was just wondering if you missed inertia of line + rod here... .
I have tried how much I can load a rod just by moving it without any line rigged up. It's impressive.
Seems as if we would need a casting robot to really see the differences in constant vs. non constant acceleration.
So I leave it as:
smooth acceleration
If a change in the rate of acc. is needed, keep it smooth.
Thanks for the help!
:kungfo: )
.