Tidying loose ends

[geoffretired]

Tarkwin wanted advice on new arrows and the thread took off into the world of science etc etc. I was fascinated by the posts and baffled by some (my lack of understanding). I do enjoy the scientific explanations and try to follow as well as I am able. What I take away from that thread, has to be in useable form. Useable for me, that is. Pushing a car or a roller skate with a piece of wood makes sense to me. Pushing a car with a bamboo or a steel bar does too.
I would like to make a list of simple analogies/ideas that I can carry in my head, for when they are next needed. If my list is incomplete or flawed, I would be glad if corrections could be posted.
Heavy,thin arrows will drift less at long distance in the wind.
Choose the spine that best matches your poundage and arrow length.
Tune for nocking point and centre shot in that order.
Adjust bow poundage to improve the matching of the arrows if need be.

Recurves are more sensitive to spine matches/mismatches than compounds.

In the next section, I am assuming one change and all else remains the same.

Changing point weight alters amplitude of vibration but not frequency.
Changing insert length will change frequency.( if the weight changes so will amplitude)
Changing bow poundage changes amplitude not frequency.
Changing string weight changes amplitude.
Changing centre shot changes amplitude.

If we add weight to the point, we increase the amplitude. We also slow the arrow, I believe. Does that mean the arrow, as it passes the rest, is in a slightly different phase of its vibration? Could that account for the results some archers see when they change point weight.?);

[joetapley]

Geoff
Each to his own I suppose but I don't favour your approach. Far too many archers and coaches already with no understanding and a head full of memorised sound bites. In archery there are very few black & white answers they're usually some shade of grey. Almost by definition a soundbite is going to be wrong or at best only a half truth. Much better to acquire the understanding, then there is no need for soundbites, you can explain things, maybe well or poorly but this is always going to be better option.

Avoiding soundbites is also relevent for inspiring confidence for those you coach. My normal reaction to those speaking soundbiteeze is "this guy hasn't a clue". An attempted explanation, even if you disagree with it, will generate a lot more respect.

[geoffretired]

Thanks, Joe. I know what you are saying. Believe it or not, I agree with you!
So often , when we communicate it takes me three or more attempts to get my message clear. Blame me for that. You will know that I do try to understand at a level that is deeper than soundbites. I am against them, too.And for the same reasons you are. My soundbites are for my ears only. If I have the soundbite wrong: it means I have the big picture wrong. In my work, I had to get used to filling myself with information and then delivering that to others. I had to understand the information or I could never pass it on. Once I'd understood it I made notes and then the soundbites. I could then carry the information to the students, in my head. I suppose it is like compressing files on a computer, but I'm guessing there.
I don't use soundbites with others, it's not my style. I say more than I should perhaps.( you may have noticed from my posts); ) Like you, I appreciate the "grey areas" and try, when explaining, to give more than my own views.
I think, in truth, our approaches match. I just use a different storage/retrieval system.

[Rik]

Originally Posted by geoffretired

Changing bow poundage changes amplitude not frequency.

That sounds wrong to me. If you increase the tension on a guitar string, the vibrations you get are a higher frequency... Granted you don't change the characteristics of the shaft by changing the bow poundage, but you do alter the forcing behaviour of the bow, which I suspect will govern how the shaft reacts for most of the period before it leaves the bow...
I ought to dig into Kooi's papers and see if I can get a grip on the theory, but just the thought of it makes my eyes start to glaze...

[joetapley]

Kooi, B.W. & Sparenberg, J. A. 1997. On the Mechanics of the Arrow: Archer's Paradox.
Journal of Engineering Mathematics 31(4):285-306

[geoffretired]

Rik,I was thinking along the lines of a guitar string or similar. "Increasing poundage increasing amplitude" came from my thinking that big pluck, little pluck gives loud and quiet versions on the same note. Same note/frequency, different volume level/amplitude.
Joe, I see, from the graph, the weakest arrow slapping the pressure point.
Am I right that the middle stiffness arrow contacts the pressure point too, or did I mis read the graph?

[joetapley]

Just verifying Rik's comment (answer already given by Max on original thread). Increasing axial stress in the arrow shaft (heavier shaft/pile or increased draw weight) results in the shaft bending more and more slowly.

As regards your windrift soundbite reference to the Easton spine chart suggested as a better aproach in relating trends in arrow properties to arrow performance.
http://www.eastonarchery.com/spineWeight/target/

Am I right that the middle stiffness arrow contacts the pressure point too, or did I mis read the graph?

The ends of the lines represent the nock position as it passes the button (occurs at different times of course). The middle arrow is the best match and clears the button. The stiff arrow sort of indicates why people recommend stiff arrows - you get clearance even if the tuning is crap.

Mmm to clarify the horizontal axis is the time in seconds. The vertical axis is the displacement of the nock from the bow centreline in metres.

[geoffretired]

Right, Joe. I think I'm there this time. Two arrows have nocks that cross the centre line of the bow but not at the point where they are passing the button.
The softest one is still the wrong side of the centre line as its nock reaches the button but the middle one gets back over on the safe side.

[joetapley]

You've got it. The following picture represents the arrow configuration at the moment the arrow leaves the string. It's at maximum bend (around the riser) with the nock just on the "wrong side" of the bow centreline. As the arrow moves forward the rear moves away from the bow (hopefully) clearing all the obstructions. The weak arrow doesn't make it and the back end clobbers the riser. The stiff arrow is clear of the bow but the rear end is wagging so contact is a possibility. (Incidentally the configuration of the arrow at the moment it leaves the string is the only sensible definition of arrow alignment. Talking about alignment while the arrow is on the string is meaningless).

[geoffretired]

Thanks again, Joe. Great picture.