Somebody please help me understand why if you put an aluminum footing on a carbon arrow, the dyn. spine increases? I thought adding weight to the end of the arrow reduces the spine, not increases it. For example on Stu Millers calulator:
Goldtip 3555 black
27.5 inches
200 grain point
15 grain insert
15 grain nock
3x5 inch feathers= D.Spine of 60.8
If I add a 2 inch aluminum footing of 25 grains, the D.Spine increases to 72.8!
Am I doing something wrong or what?
Somebody explan this to me....PLEASE!
Wish I could help, but I don't put footings on my arrows.
Sorry.
Because it effectively makes the arrow shorter. Not by actually decreasing the length but by shortening the amount of the arrow that can flex.
Spine increases as the stiffness of the shaft increases. Spine decreases as the point weight increases. A 2" piece of aluminum arrow shafting doesn't weigh very much, but does increase the stiffness of the shaft as a whole somewhat by making the front 2" inflexible. I would assume the increase in shaft stiffness more than offsets the increase in point weight.
I have found it makes no difference in arrow flight unless you shoot short shafts. I shoot full length shafts and two inches of footing does not impact the spine at all. With shorter shafts it can have a greater impact.
McDave and Buckeye hit it on the head, when you add a 2" footing on to your arrow you are making that 2" non-flexable there fore turning your 27.5" arrow into a 25.5" arrow as far as spine goes. The same goes for incerts. The calulator uses the standered incert lenght for its calulations, if you use a long 100 grain incert you need to put the diferance in incert lenght in the footing box.
How about adding 1.5 inch footing that`s what I do and spine goes down on stu`s calculator.
A 1" footing is all I use.
Thanks ya'll...now I understand! :notworthy:
QuoteOriginally posted by Bill Carlsen:
A 1" footing is all I use.
Me too and I've never seen a bit of difference how my arrows shoot with or without the footing.
QuoteOriginally posted by Guru:
QuoteOriginally posted by Bill Carlsen:
A 1" footing is all I use.
Me too and I've never seen a bit of difference how my arrows shoot with or without the footing. [/b]
With a 1" footing you should not see a difference as a standerd incert is just shy of 1" so that first 1" is already rendered non-flexable by the incert.
Just throwing that out there for the guys that might not understand why a 1" footing would not make a differance.
pops is right even with brass inserts.
If you are using 100 brass inserts you have about 1 1/4" inside the shaft and 1/4" in front of the shaft. If anything with a 1" footing your spine should decrease the tiniest bit due to the extra weight. If you are using 50 grain brass inserts you have 3/4" inside and 1/8 in front. This should cancel out the 1" footing and should make no noticeable difference in spine.
I 2nd 1" footing and no difference.