Fly Line Tapers
- This topic has 21 replies, 17 voices, and was last updated Jan 29, 2009 at 12:07 am by
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Hey guys –
I am doing preliminary research on a follow up article to “Cooking Up Some Lines” for American Angler. I have already had my mind basically blown by Bruce Richards of SA, who did his best to cram the physics behind fly line casting into my thick head. I will synthesize the stuff Bruce and the other folks I am talking to have to say in the ultimate article, but I thought I would throw out these talking points. This may lead to some questions you have which I can answer in the article.
– Fly lines create lift, but not like an airplane. An airplane achieves lift through the twin forces of a vacuum on the back of the wing and the speed of air flowing under the wing creating a cushion, forcing the plane up. Fly line loops also create lift, but it has more to do with drag than a vacuum. Because the drag running along the length of the loop as it unrolls (skin drag) is greatly less than the drag on the front of the loop as it unrolls (form drag), the force exerted on a fly line is primarily backwards (slowing the line down). However, because the top leg of the loop also rolls downwards as the loop unrolls (that is, if you imagine a particular point on the line, when it hits the front of the loop, it moves downwards to the bottom leg as the line unrolls), the force of drag also exerts upward pressure, because it pushes back against the line as it tries to go down. Thus, the pressures on a fly line loop are up and back, creating lift.
– Fly lines accelerate rapidly as their tapers unroll, but this acceleration is matched by even stronger air resistance. As the energy in the fly line is concentrated by the diameter of the line growing thinner (as all fly lines do at the tip, where they taper to a point), that energy must go somewhere. It turns out that it is expressed as a huge speed increase. Theoretically, in a vacuum, as a fly line unrolled from some mass to almost none, its tip speed would approach the speed of light. HOWEVER, we don’t cast in a vacuum. It turns out that air resistance quadruples for every doubling in the speed of an object passing through that air. Thus, as the fly line tip wants to accelerate, the air resistance pushing back on it grows ever stronger, slowing the line down. Controlling this force is a major point in tapering; when do you want the line to slow? Shouldn’t a distance line slow down much later than a line meant to unroll at close range? These are the things I’ll explain in the article.
– Finally, last talking point since your minds are probably as blown as mine was, but what happens when the line has no taper? Level fly lines, we all know, whip around like crazy when they unroll and are hard to aim. This is because the absence of a taper at the tip means all of the energy being unrolled down the line suddenly comes to a hard stop. Yes, the line tip never accelerates with that forward taper unrolling, but at the same time, the counterbalancing air pressure never works its quadrupling magic to slow the tip down. So basically the tip crashes to a hard stop; the energy must go somewhere, and it is imparted into an unpredictable whipping/crashing/bounce back behavior. This is why shooting heads which have no taper on the front end tend to “crash out.”
Ok, mull that over.
Zach
Z-
I have a thought about explaining these concepts with pictures, just a thought and might not be practical.
For what it is worth, all the physics in the world didn’t keep Mr. Richards from hooking
me in the face on the Battenkill a couple years ago.All of my casts approach the speed of light anyway, so it really doesn’t matter whether its in a vacuum or not.
This is darn interesting!
I’ve NEVER read anyone talking about the difference in diameter of various brands of fly line. Obviously all with the same line weight.
SA’s lines seems to be among the thinnest, while Cortland lines are the thickest. This difference in diameter will encounter different air resistance. This will cause the fly rod to feel a lot ‘slower’ or ‘faster’.
Anyone considered/wondered “hey my rod feels different…” while casting a different brand line than you usually use?
Yeah… Great! Thanks, Zach. I really was looking forward to sleeping tonight, but now I’ll be awake till the wee hours pondering this post!
Really looking forward to your article, though – you’ve penned some of the best I’ve read.
Best Regards,
Beechy
You may already have it Zach, but Bruce Richard’s Modern Fly Lines from Lefty’s Little Library series is a great source for anyone interested in fly line design and construction. The chapter on tapers and their effects on casting, and of course fishing, is a real head spinner….. 😮 😀
Morsie
For your article, it might be really informative if you took a couple of SA lines with different tapers and use them to illustrate these mind-numbing principles. For example, they make GPX with a 5′ front taper and Expert Distance with a 12′ front taper.
A graphic might color-code the line-speeds, say, from a 60′ cast as each part of the head reaches the front of the loop. Including a leader and fly might be cool for showing whether there are any differences in the tapers in accuracy of fly placement.
Just a wild guess, my guess it that the big difference might arise not at a constant distance, but if you compared, say 30′ to 60′ casts.
SA likely has something comparable internally, wonder if they’ll share.
The science of how and why things work the way they do is pretty interesting. If you can take the science and bring it to a point where a user can make a practical decision about what line would word with a given rod is really helpful although manufacturers suggest what line will work under most conditions. I had 4 or 5 lines for a 5 weight once and the rod cast all of them well but it changed the “feel” a great deal.
I would think it really comes down to trial and error a lot of the time, a good fly line is more of a recipe than a creation of computer model. Computer modeling would be really valuable to fine tune things but some person has to quantify and evaluate the qualities of a taper for its intended purpose which is more art than science.
Zach,
I don’t pretend to know anything near as much about fly line as does Bruce. I wrote this some time back before I really got interested in the subject. It is an attempt in my words of explaining what taper does. I still maintain that the average caster would have trouble in differentiating between different dry fly tapers. More extreme taper variations for throwing big heavy bugs or sink tips are probably noticable though. I don’t know much about them.
Try this. It is just a novice approach at the subject.
http://www.hatofmichigan.org/uploads/Mechanics_of_Fly_Casting_2.pdf
Bob
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