Emory,

That's true, but as we know, static measurements can tell you plenty about the dynamic characteristics of an item. I can calculate how much lift any particular airfoil will generate at any airspeed,and I can do it by static methods alone. The action is certainly dynamic, but I don't have to actually put it in a dynamic situation to tell you how it's going to work.

For most of what we do with a fishing rod, and need or prefer to know, our static measurements are more than sufficient. I won't argue that the addition of a relative scale based on resonant frequency would provide some extra information that many of us might find very helpful.

............

Question from the peanut gallery,

Would an items natural resonant frequency be different if measured A=From end of object, or B= From some fulcrum or pivot point along the same object? (As in location of reel seat on a rod) And if so how would this enter into the issue.

It would change yes, but just like in other systems, you'd have to a constant - a particular place to support the blank from, whether it be at the very end, or a percentage of the total blank. If you didn't, your results really wouldn't be relative in nature and much of the usefulness of any such system would go out the window.

.........

Sing....You've got their attention my friend, excellent question !

Guys....Google Search the words : fly rod evaluation and calibration

Or : [home.att.net]

....Info from Cal Poly that will lead to many other links and lines of thought on this issue.

Fun reading for the inquireing mind !

Bob Meiser

Emory,
At resonace frequency the rod deflects at the largest amplitude, and if you change your wiggling frequency while keeping the same strength, the deflection amplitude WILL decrease. Resonance freqeuncy is a driving frequency. If you're wiggling at a higher or a lower rate, you will feel like the rod does not like it! :) And you're right, I'm confining myself to wihtin the first harmonic range. Like I said, avoid the "node".

Bill,
Wow, 12 Hz, that's very fast!!!! I can' t count that fast! I haven't fished a non-fly rod for years. Remind md what they feel like. :)

And gang,like I mentioned in an earlier thread, while I understand the correlation of natural frequency to the material's mechanics, I don't agree that the natural frequency alone indicates the action, performance, or power of a rod. But it sure is fun to wiggle a rod!

... off to Vancouver for two days. Too bad it's not a fishing trip. I'll be suffering from withdrawal from reading this forum. :(

-Sing

Sing,
I agree completely with what you say about increasing the "wiggling frequency" and the deflection amplitude as long as you start your wiggling at a frequency below the resonance and then move up to the resonance. If you start your wiggling at a frequency above the resonance then the rod/blank will tend to resonate at the second harmonic.
When watching the typical person pick up a rod and wiggle it, most often they will wiggle it so that it is oscillating at a frequency above the resonance. Very often the tip will be moving in one direction while the center of the rod is going in the opposite direction or the second harmonic. I think that this is probably what you meant by "node".
By the way, I did not say that resonance frequency ALONE will tell you everything you want to know about a rod/blank. Obviously it will not. I think that the measurement of resonant frequency is best used in conjunction with the other static measurements. However, I think that I did say that it would tell you more than any other single measurement and that all of the characteristics of a rod/blank will affect or show up in the resonant frequency.

We should remind ourselves of the basic physics that we are all appealing to here, the mass-spring oscillator. There is a simple equation which relates the spring constant, the mass that is loading the spring, and the oscillation frequency. One thing it tells us is that if we keep the ratio of spring constant to mass the same, the frequency doesn't change. Said another way, if we up the mass load and the spring constant proportionally, the frequency doesn't change. So a 10 wt rod is noticably stiffer and heavier than a 5 wt rod of the same length, yet they can have the same frequency and thus require moves with about the same timing to cast them. This is likely as close as we can get to an objective measurement of the feel of a rod. We already measure spring constant in form of the CC measurement, which essentially is the spring constant scaled by the length of the rod. Combine that with resonant frequency and you really know a lot about a rod.

Now a rod is admittedly a more complex oscillator than a simple mass-spring system. Mass distribution and stiffness (spring constant) vary along its length. However by restricting attention to just what the tip is doing, I have found that a simple mass-spring model fits pretty well. I can go into details on the subject off-line if anyone cares to email me. The CC measurement makes essentially the same restriction of interest to what the tip does in respone to a static load, and any number of casting gurus will tell us that it's how the tip moves is what counts.

Mike

Mike,
I am in complete agreement with you. One could argue that when we measure the power of a rod we are measureing the spring constant.
However, normally when we measure spring constant we assume a linear relationship between the mass and the deflection and this is of course not the case with a rod/blank. To get around this variable the CC system deflects the blank/rod a fixed distance, 1/3 the length.

If you have done some work in this area I would be very interested in looking at what you have done. I have also done some work in this area and would like to exchange thoughts with you.