Arrow SpineWork in Progress
The spine of an arrow describes it bendiness. To measure spine the arrow is suspended between 2 points (TODO - how far apart) and a 2lb weight is attached to the centre. The amount of deflection produced by the weight gives the arrows spine (TODO - Deflection/spine graph). Wooden arrows are usually grouped in 5 lb intervals, 25/30, 30/35... The odd thing is that the shafts of the same diameter can have different spines.
Variable 1: arrows have various stiffnesses because wood is a natural material and by nature is variable.
The reason the arrows need to flex is because they have to bend around the arrow handle causing the archers paradox. Arrows for longbows have to go all the way around the handle. Target bows are (close to) a centre shot. That is the arrow is pushed close to straight which minimises the flex.
Variable 2: The amount of deflection to get around the handle varies from bow to bow.
What bends them is the back of the arrow being pushed. The front wants to stand still and the result is that the arrow bends. The heavier the point the greater the inertia.
Variable 3. Heavier points tend to make the arrow behave as though they have a weaker spine.
The way the energy is transferred to the arrow depends on the type of bow. Compounds, recurves and longbows transfer the energy from most efficiently in that order (TODO - Revise this sentence). So draw weight for draw weight a compound needs a stronger spine and a longbow lighter. Some hi-tech bows will have a button that adjusts the position that the arrow goes past the handle. But that is way beyond the wooden arrows we are talking about here.
Variable 4: Bow type affects the spine of the arrow you need.
Arrows that are too stiff tend to fly left, too bendy and they fishtail and recover from leaving the bow slower. Bigger fletchings can help the recovery time.
Variable 5: bigger fletchings tend to make the arrows behave as though the have a stiffer spine.
And last but not least, the way you loose the arrow will make difference. A good loose will let the arrow go just about straight and not deflect it. A sloppy loose will mean more energy will go into pusing the arrow sideways and it will fishtail more.
So how the heck do I get the right arrows?
For perfectionists with bows that can be adjusted the answer is to try shafts with various spines and tune them without fletchings (bare-shaft tuning). Also examine the flight pattern of your arrows using walk back tuning and paper tuning to tune your bow.
All this is beyond the scope of the traditional instictive archer. For traditional archery there are 3 adjustments you can make to the bow that will affect how the arrow behaves:
1. Nocking point
(TODO how to fine tune with paper tuning )
Assuming your bow is tuned and all the above are right the things you should consider when choosing your arrows are.
Step 1 - Get the spine right. There are loads of charts for this. I use the one in the Quicks Catalogue (Link-Ask quicks if I can go direct to their site not just to p78 of catalogue).
Step 2 - Heavy points = big feathers
Get these right at you'll be close enough for instictive archery.