Math question

[BUCKSHOT]

I never was the greatest at Math so perhaps one of you folks on here can straighten this out for me!

If you take the formula for determining FOC and change it around, is there a way to determine a missing value so that if you need to change your arrow you can determine the change value for that component before you make a change to your arrow?

FOC=[(Arrow Ballance Point divided by Total Arrow Length) - .5"] x 100

For example in the above the FOC is the unknown, if you insert the value for FOC that you would like to achieve, how would the rest of the formula be configured to give you an unknown such as the arrow length?

[wildwindom]

ya

[awshucks]

Whew! Can't answer that question, but I fooled around some changing my FOC, and a 1" piece of threaded rod screwed into nock weighs 25 gr and lowered my FOC by 5% on 431 gr GT's.

[Doe Master]

the problem buckshot is the balance point also changes as the length is increased so it is a sliding scale . So as one changes it adversely effects the other values . As for the formula I have always used
(difference of balance point divided by arrow length only) times 100=foc

( 2.5/20)x100=12.5%

[pokynojoe]

Yes, you can substitute values into the equation if you're looking for an unknown, as an example:

Let's say you have a 12% FOC and a 20" arrow and you want to know what the balance point should be, well:

Let "x" be the balance point:

12= [(x/20)-.5]x100
.12=x/20-.5
.62=x/20
12.4=x

As you can see, your balance point would be 12.4". Now will check:

FOC=[(12.4/20)-.5]x100
FOC=[.62-.5]x100
FOC=.12x100
FOC=12% Eureka!

Hope this helps.

Regards
Joe

[BUCKSHOT]

Thanks!

[Hipwader]

Where were you guys when I was trying to pass highschool math..lol

[ALINALBERTA]

A question for you,anyone. For the length of arrow in the formula, do you or do you not measure to the tip of the point(or broadhead) from the nock or just to the end of the insert and ignore the point???

Thanks,Al.

[BUCKSHOT]

Ignore the tip as far as the length value!



Include the tip to get your ballance point!

[BOB VANDRISH]

Buckshot,are you sure about not including the tip when you measure the length,but including it when you determine balance point?
All the diagrams that I have seen include the tip for length and balance.
I am playing around with some of my bolts,to try and find out why a 3 blade fixed blade Innerloc broadhead does not fly the same as a target head,and I am convinced it is all to do with the wrong FOC.
I am using Easton 2219 bolts,with 5" plastic vanes and 100 gr broadheads.
That throws the FOC down to under 5%.
I can go to 125 gr heads,and 4" feathers,and that will shift it a long way forward,which is the way that I need to go.
100 gr mechanicals,with the same set up are fine.
Your comments,please.

[ComfyBear]

I agree with Bob V. The total length SHOULD include the head, since it's part of a complete arrow. If one were to use two broadheads both weighing 100gr, but one is longer than the other, then the FOC is going to be different. Since the head is an extension of the arrow

[BUCKSHOT]

You know honestly, I have always used a total arrow length of 18" not including the head.
I will pick bj's brain tommorrow and find out for sure!
I hope I didn't inadvertently mislead anybody!

Back at ya' tommorrow!

[Iglooman]

There are three types of people in this world those that can count and those that can't

[pokynojoe]

Interesting, Buckshot's graphic representation of the FOC formula would most certainly be valid for a given length of shaft, and it's relationship to the balance point of that shaft. Although, hunting heads come in different lengths, a 100gr head of any configuration, should not move the balance point, it would remain the same. To move the balance point forward, relative to a given length of shaft, you would have to add weight to the front end or reduce the weight on the rear end. Given a 3" length hunting head or a 2" length hunting head, one could, if one chooses to do so, include that length when calculating there FOC and get different percentages even with the heads the same weight. However what would that number mean? The balance point would still be the same. It seems to me, what your trying to do by increasing or decreasing your FOC is in effect, moving the balance point either forward or back. But then again, I could be completely wrong about all of this, it happens from time to time.

Joe

[BUCKSHOT]

I finally have the answer Al!
There are a ton of calculators on the net, many of which use different methods to determine FOC.
It is amazing how many formula's there are that can be used!
I guess I will keep using the formula I pictured as the drawing explains and not include the length of the head! If you do the calculation with the head included the difference is so minimal it will hardly affect the outcome!

One thing that I was directed to and which stirred this whole thing for me in the first place, is an Excel formula which allows you to insert the critical information about an arrow i.e front end weight, arrow length, arrow weight e.t.c this will effectively allow you to change a given component on your arrow to determine the change in FOC without actually changing the arrow untill you do the math on paper, that's a figure of speech. The calculator will do the math for you!
I thought that was really neat because you could save a lot of time experimenting and determine precisely what you need to change in a jiffy!

I am going to try and figure out how to pass on this calculator to others whom may be interested because it is so neat and easy to use!