Gordon & Group...
Ally Gowans comments on our last set of messages :
[AG] Hi Gordy,
If Paul can find the physics paper I would be interested to see it too. How others have described the process is always interesting. I think that agree with Paul and you on this one. Tension in the rod leg is derived from the energy in the fly leg being retarded by the rod tip. The fly leg travels on a vector and the rod leg assumes a different vector, the loop is generated by the fly leg as a consequence of the momentum change. If line is shot rod leg tension is reduced and turnover is delayed.
Dusty comments “It seems to me the line would launch the instant the rod tip begins its deceleration, or very shortly thereafter, as the oncoming line overtakes the slowing rod tip.”
The rod tip does not have to decelerate to cause the line to launch its velocity component in the direction of the line momentum just has to be less than the line velocity. Think of a typical “straight” rod tip path. After the “straight” portion of path there comes a rapid change of direction by the rod tip accompanied (of necessity) by a small portion of line pulled out of the path of the “effective” (remaining) line. Because it is no longer pulling the effective mass of line the rod tip may accelerate as it recovers due to loss of loading (you can feel this happen). Looking at microsecond periods the rod tip may be straightening whilst the butt is still bent opposite – the curious transient rod contortions mentioned by Gordy.
Extending this argument suggests that maximum tangential velocity (line velocity) achievable from rod rotation is when a cord between hand and tip ring is approximately perpendicular to the line (in the casting plane). The rod butt angle would of course be considerably further ahead as we know from the usual stopping positions.
Gordy’s definitions of line launch are very good. My only change is to remove any relationship to RSP. This is because line launch and RSP may be well apart or at other times they may be very close. The latter occurs especially with short lines.
Line launch is “the CAST”. RSP is just a state of the rod that has somehow been elevated to importance, in the same way that rod tip speed has.
Launch : To send forth, catapult, or release. (Free from additional input of the caster's rod motion.)
Launch angle : Synonym for CASTING PLANE and TRAJECTORY. (The angle between the direction which will be taken by the traveling loop and the horizon or artificial horizon.)
Line launch direction : The direction in which the line was launched. (Seems that this would determine the direction of the newly forming fly leg of the loop as it overtakes the rod tip.)
Hope this is helpful.
Best wishes,
Ally Gowans
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[GH] I agree that the separation or interval between the point of line launch and RSP can not be a constant or even derivable since it is the product of too many variables one of which (as you point out) is the length of line launched.
Steve Rajeff has called attention to the RELEASE OF LINE BY THE LINE HAND when shooting line as having an impact on line launch. We have so far left that variable out of our discussions.
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[GH] From Fredrik Hedman in response to Paul Arden :
[PA] " No it's the momentum change that creates the tension. I had an physics paper on this somewhere in my hard drive. I'll try to get another copy.
Cheers, Paul "
[FH]
Hi all!
I would very much like to see that paper too. This is however how I have interpreted it from reading some of the posts from a couple of competent physicists on different boards. (I will gladly be corrected if I have got it wrong)
The flyleg usually moves faster than the rodleg (when it doesn't there will be no tension in the loop and that usually ends up in spaghetti). The change in mass in the faster moving part of the line, as it unrolls, will be the source of an accelerating force to act upon it.
This force is together with the one acting on the other end of the line (could be friction in the guides or a static force when not shooting line) is what creates the tension in the line. Therefor you can say that the change in momentum creates tension in the unrolling loop.
Best regards,
Fredrik
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[GH] As the loop travels and unfurls, the fly leg is indeed traveling faster than the rod leg of the loop. The formulae are simple:
With no line shoot : Velocity of the loop = 1/2 the velocity of the fly leg.
With line shoot: Velocity of the loop = Velocity of the fly leg + velocity of the rod leg
2
If the fly leg is traveling at 80 M/sec. and the line is not being shot, the loop velocity is 1/2 80= 40M/sec.
If the fly leg is traveling at 80M/sec. and the line is shot, with the rod leg velocity at 20 M/sec., the loop velocity is 1/2 80+20= 50M/sec.
The velocity of the loop increases as a function of line mass decreasing as the loop unfurls, especially when a tapered line is used. The energy stays the same while velocity increases exponentially (square) as mass decreases. (Heavier line giving way to lighter line as the taper goes through the unrolling loop.)
Where E = energy, M= mass and V= velocity :-
2
E= 1/2 M x V
I look at what happens at the proximal (rod tip) end of the rod leg as resistance to the momentum of the traveling loop. This resistance goes a long way toward providing tension in the system.
If the line were cut free from the rod tip, the loop would (and does) unroll so slowly that it would succumb to gravity and hit the water before finally unfurling. We have done this.
The fact that it unrolls to any extent I think is testimony to the fact that the inertia of the more slowly moving rod leg also contributes to tension in the system.
Is Paul correct about the momentum changing as the loop travels ? Frankly, I don't know. Problem is that as the velocity of the loop increases, its mass is decreasing.... Perhaps one of our physicists can teach me how to compute that.
Gordy
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