Tuning Carbons (Physics101) Am I thinking correctly?

[fatman]

I have some CX250's on order from 3R.  Currently shooting 58@28 (approx 55 at my 27), hybrid longbow cut past center w/ FF...
My question is, once I get the insert/BH combo that flies well, shouldn't I be able to add weight (weed whacker line, aquarium tube) without affecting the tune?  Since the internal weight isn't attached to the inside of the shaft, it shouldn't alter the spine of the shaft;  and since it's free-floating, it shouldn't affect the "flex" upon release...is this sound thinking?
Your comments, opinions, and SWAG's are greatly appreciated - fatman

[R H Clark]

I've only used the tubes made for CX arrows.I've used the 2 and 3 gpi tubes and can't tell any difference when bareshafting with or without.

[McDave]

Whatever you do to the arrow will affect the tune.  Obviously, if you add weight to the front or back, it will affect the tune the most.  But if you add an equal amount of weight to the front and back, it will increase the spine of the arrow.  If you add weight uniformly throughout the whole shaft, like a tube that extends from front to back, it will affect the spine the least, but I still think it would change the spine enough that you would want to tune for it.

[ISP 5353]

If you add weight to an already tuned arrow it will affect the tune.  BY adding it internally it may not affect it too much, but it will change it some.  With a heavier arrow you are using more power from the bow just to start the arrow momentum.  This may affect the arrow paradox around the riser resulting in a change of the dynamic spine.  Good luck.  Just give it a try and see.

[snag]

I purchased some of the Heritage CEs and they tuned up great with similar poundage. I added 100gr. inserts and 125gr tips. The total weight of the arrows are 605-610gr. For a 55# bow I was real happy with this weight and FOC. What kind of weight are you trying to achieve?

[bowfiend]

I've added weight tubes to a tuned arrow and it didn' work out for me. Maybe it can be done, but it really weakened the spine for my setup.

[fatman]

wow, you guys are on this like a buzzard on a meat wagon; thanks for the replies, I'm sure we're not done here...
snag, I'm looking to achieve around 625gr or so....sounds like it should work out OK....

[Russ Clagett]

I tuned my perfect then added weight tubes, now they dont fly quite as good, so it must affect the spine some.

I would build the arrow to exactly the way and weight you're going to shoot, then tune the bow to the finished arrow.

[Steve O]

The tubes won't affect the STATIC spine of the arrow (like on a spine tester), but will affect the DYNAMIC spine (shot out of the bow) IMO.

[Jeff Strubberg]

Yep.

Now, if you don't get carried away, you can generally add some weight in the form of a weight tube and be OK.  You can never escape physics, though.

Here's what happens.  We know that all objects have intertia.  An object at rest tends to stay at rest, one in motion tends to stay in motion.  This is a function of mass.

More weight = more mass.  More mass means it takes more energy to overcome inertia and start the arrow moving.  Here's where it starts to matter where the weight is added.  

If you front load the arrow, the tip now weighs considerably more than the tail.  When you drop the string, the tail of the arrow is ready to move sooner than the tip.  The only way this can happen is if the shaft between the two flexes.  More flex is the same thing as saying less spine.

If the weight is evenly distributed up and down the shaft, the arrow moves more as a whole and less flexing occurs.  Still, we have to deal with the increased inertia.  The only way we can apply more energy to the arrow from a closed system like a bow is by applying the same amount of enery over a longer time.  Simply put, the bow string must move farther before the arrow starts to move.  Again, the arrow has to flex.  Not as much as in a front loaded arrow, but more than with a lighter shaft.

The cliff notes version is that heavier shafts, however they are acheived, require more spine to remain relatively straight through the longer push required to get them moving.  Front loading exaggerates the problem because the tail of the arrow is ready to move before the tip is.

There you go.  A really lousy explanation of why more weight requires more spine.  

[JC]

Originally posted by Steve O:
The tubes won't affect the STATIC spine of the arrow (like on a spine tester), but will affect the DYNAMIC spine (shot out of the bow) IMO.

I'm 90% in agreement with Steevo on this one. But, with some of the heavier tubes (like the 5 and 8 gr/in) I do notice a very slight difference on my cup-cake spine-o-meter between tubed and empty shafts. More of a variance than I get between arrows of the same lot.

Some guys say they can't get them to fly differently with tubes...I can't get them to fly the same. They definately work, but when I used them, I had to retune with tubes inserted to get the arrowflight I wanted.

[swampbuck]

I'm planning on front loading the one's I just ordered.I'd like 250 up front since thats what my BH's are which should put an arrow in the wieght range your talking.I shoot 57@28" drawn 28

[Shawn Leonard]

I do not think it reall y effects spine on a spine tester but it does effect flight, no doubt and you will need to re-tune them, if ya want 625 out of those arrows it will not be too hard as You will need to leave them long(due to your 27" draw) and have to add lots of point weight. I dare say you need them at least 29"s long and inthe ballpark of 275 grains up front, give or take a bit. Shawn

[Shawn Leonard]

I should of just read JC's post, which I repeated with a suggested starting point. Shawn