It does not bother me at all. However, I am back on the road tomorrow and off-line fro a while, so it does bother me to come back and find that you have taken a pot shot several pages back.
If you understood the model (it is not voodoo as you seem to think), then you would realize it is a fair comparison. As Merlin noted you can simulate the impact of a non-flexible broomstick (or an inextensible string) in his model by using very high spring constant in the model.
but just stiffening the spring does not turn it into a comparable broomstick.
The function of a simple harmonic oscillator is not so simple (especially when it has an accelerating forcing function) so it is difficult for non-technical people to understand its operation and concepts.
It is difficult to understand the maths not the concepts.
Rotate the rod, tip travels further than the butt in the same time and therefore faster...completely get that. True if its rigid...not true if it's bendy apparently... I don't get that at all...
Not sure I understand your question here
If the model doesn't account for system energy losses and doesn't account for the reduction in lever length due to the bend then the output data, whatever it may be, is going to be overstated isn't it, or am I going mad ?.
Not at all, its a matter of fidelity and intent. Most models make simplifications to make them manageable. The losses do not usually matter if you are talking general trends, it only matters if you start making decimal place type claims.
The change in lever length is a bit different and I have not seen that explicitly addressed, only the effects of with and without springs.
Rotate the rod, tip travels further than the butt in the same time and therefore faster...completely get that. True if its rigid...not true if it's bendy apparently... I don't get that at all...
The reaction of the tip to a forcing function at the butt can run an entire gamut of scenarios. For one thing we have kickback of the tip if we apply a sharp sudden input at the butt. In this case the tip actually moves in the opposite direction for a brief period. If the rod ovalizes and collapses at this point the tip may never catch up to the butt. As an analogy think of the casting exercise of pretending you have a spider on the end of a stick and you want to throw that spider as far from you as possible - if you apply too much force too quickly the spider simply falls off the stick and lands on your head. If that spider is connected to the end of the stick by a very weak and stretchy elastic you will eventually get enough stretch in the elastic to finally get the spider to move and then he/she will eventually catch up and overtake the stick.
A lever in which the effort is placed between the fulcrum and the load.
We usually consider our elbow as the fulcrum, the load is the line, and the point where effort is applied is our hand. Given this the rod is always a third class lever whether it bends or not. If you are thinking of a third class lever as one that multiplies movement then for a real world rod this is also true except in very limited situations and timeframes such as when you have kickback at the beginning of your stroke.
Back to one of your earlier statements:
If the model doesn't account for system energy losses and doesn't account for the reduction in lever length due to the bend then the output data, whatever it may be, is going to be overstated isn't it, or am I going mad ?.
You are not going mad. Just as the postulated SHO model cannot take kickback into account so too does it overlook many other real world issues, some of which you have identified. Like any other model if you don't state assumptions or boundary conditions then the model has about as much value and use as used toilet paper. One can try to deny the universal nature of Newton's Laws to overcome the other universal law of garbage in garbage out or call it hand waving or bad physics but in the end we are still left trying to find a use for our used toilet paper.
I know what a third class lever is Walter....my query was in response to this from Gordy
He says...
I think that we can agree that the broomstick functions as a third class lever, but because of the more complicated dynamic response of the spring in the rod to external forcing accelerations the rod (even to first order) does not.
You say...
..... the rod is always a third class lever whether it bends or not.
I happen to agree with you.
The point being that, if you are correct, then there is a payoff between the positive benefits of a bend for the management of tip velocity, which isn't in any particular dispute bar the losses detail, and the negative effects of the bend by shortening the rod as a third class lever.
Yeah - he's strangely quiet about that just like he is about Newton's laws being breakable. Unfortunately he is unable to edit away those statements at this point.
We've discussed the effects of effective rod length on the third class lever. The question that goes along with that is how the ability to maintain slp adds to the cast. Unfortunately I don't know if anybody has been able to characterize the bend shape of a typical rod in order to determine the tradeoff... :O
Yep, well, I think I can have a go at answering Springers original question...
The reason I ask is that if fly casting is all about such high percentages of leverage then why is it that heavier loads cast better with rods which bend deeper? Im thinking in particular about long bellied lines and skagit with a DH rod and spey cast
If we cast with a very stiff or rigid rod then we get a convex tip path during rotation. In order to keep the tip tracking as straight as possible we have to have a compensatory change in the hand path, if this becomes dramatic then it can negatively effect how we are able to apply force at the butt.
With a rigid rod this change will become increasing extreme the bigger the casting arc you require. So for short casts, low load, not much force, its just about manageable but the heavier the load gets and the more force you need, the less manageable your hand path becomes and the less control you have over how force is directed at the tip.
Similarly, there is a point where the rod is so long that although we have all the benefits of it as a third class lever, we are completely unable to compensate for the consequent convexity of the tip path at any load or arc and so force on the line at the tip is not directed the way we want it.
The bend in a rod has the effect of shortening its length and thus reduces the extremity of the required changes in hand path. So, for a long rod the more it bends the easier it is to manage at the butt and the more effective your force application.
Even though this reduces the benefits accruing from leverage, it is compensated for by the benefits accruing from the bendy rod as a spring which Merlins model goes some way to explain.
For any rod, there is a bell curve of non-linear spring values with an optimal range that will fit a particular style of casting or in fact the biomechanical preferences, or abilities, of a particular caster.
There is a downside as the rod gets bendier and bendier and a downside when the rod gets stiffer and stiffer, depending on its length.
So for a very long DH rod and heavy loads the range of optimal spring values is skewed towards the bendy whereas for a shorter rod and heavy loads the range is skewed towards the stiff.
This is why the big guns applying high loads with a 9' use a very stiff rod and the big guns applying high loads with an 18' use a bendier one...
A few information about the models: losses are in (but negligible for comparison purposes as Vince said), the lever effect is in also.
Vince: the broomstick is represented by the red lines in the Lincast model, you can find circumstances where the broomstick is better than the flexible lever... guess why.
To illustrate discussions about the lever effect, I can tell you about an experience I made some time ago. I simulated a tricky cast with a significant change in tip path due to a hard wrist torque effect. I spended a lot of time to simulate that carefully with my most sophisticated model (shoulder, elbow and wrist rotations are simulated, and translation too). I incorporated best guess of instantaneous center of rotation, and at the end of the day I found something fair enough. That was making my day but I decided to see what the basic simple model was predicting. I then realized that its prediction in terms of line speed was better. Since that time I do not make a headache of where the center of rotation is and if the flexibility of the rod deeply affects the line speed.
One difficulty with the SHO, maybe the main one, is to understand that the energy stored in the spring is not used to improve line speed. This energy is used in facilitating the deceleration of the rod, is transformed into kinetic energy at RSP, then in counter flex. To me it has very little direct impact on line speed.
The real efffective action of the spring is indirect, it creates an extra force at rod tip, and this force is moved by the caster generating energy in the line. The miracle is that all this can be done in a given space frame and time frame compatible with our physical ability.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
Merlin wrote:One difficulty with the SHO, maybe the main one, is to understand that the energy stored in the spring is ... used in facilitating the deceleration of the rod ...
Hi Merlin
By this, do you mean that you have to use less force to stop the rod? If so, is this the same as the weight in Aitor's experiment hitting the floor with less force?
Merlin wrote:Vince: the broomstick is represented by the red lines in the Lincast model, you can find circumstances where the broomstick is better than the flexible lever... guess why.
Hi Merlin
Unfortunately I have not had time to use Lincast but I suspect I know the answer to your question:
In my youth I used to build valve and transistor based oscillators, as I've just had to remind my son when he acclaimed the use of bootstraps in computers.
Stoatstail50 wrote:Yep, well, I think I can have a go at answering Springers original question...
Similarly, there is a point where the rod is so long that although we have all the benefits of it as a third class lever, we are completely unable to compensate for the consequent convexity of the tip path at any load or arc and so force on the line at the tip is not directed the way we want it.
Again back to Springer's question, is a two-handed rod an example of a first class lever?
It depends. I can use it as a 1st class or a 3rd class depending on how I apply force. I can also switch between the two during a cast. I can also switch on the forward and backward strokes.
I'm sure there are a number of people who will say that there is only one proper way to maximize efficiency or to get the maximum distance but lever classification is just an arbitrary designation and is just as much of a red herring in double hand casting as translation and rotation is in single hand casting. For what it's worth a baseball bat is considered to be a third class lever.
Stoatstail50 wrote:Yep, well, I think I can have a go at answering Springers original question...
The reason I ask is that if fly casting is all about such high percentages of leverage then why is it that heavier loads cast better with rods which bend deeper? Im thinking in particular about long bellied lines and skagit with a DH rod and spey cast
There is a reason for using a softer rod when spey casting.
As graphically explained here the fly leg of a D/V loop in a spey cast doesn’t load the rod. This means that, for the same line and distance, an overhead cast will put more load in the rod than a spey cast. Different casters favor different bend profiles (hence the ample range of rod actions available) and the rod “bendiness” which suits our style and anatomy in overhead casting will be too stiff for spey.
Also, the bigger casting angle available allows for more line speed with the same force.
Aitor is not like us, he is Spanish, and therefore completely mad.
Cheers, Paul
No discutas nunca con un idiota, la gente podría no notar la diferencia.
Immanuel Kant
