Barely Above Heavy Bone Threshold Ultra-EFOC Arrow

[AKCrazyhorse]

So I've got a little bit of a dilemna.....I can build one of two arrows here.  One is slightly above heavy bone threshold at 661 grains and 28 % FOC in a thin diameter shaft or I can get a just under threshold, 615 grain total shaft in a standard carbon diameter at 30.6 % FOC.  So which would be the "deal breaker" factor?  Slightly higher FOC (into the ultra FOC realm) or just above heavy bone threshold (dang near ultra FOC)?

[chopx2]

Crazyhorse

Option 1 thin shaft: reduce the rear lever arm.
What size and number of fletching do you use?
If you're not already try 3" low profile feathers on the 661gr arrow. This will increase your FOC. Doesn't take much grain weight off, but because the rear lever arm length each grain is magnified more in the back like a see saw. Search the A&A fletching thread. I think there is a link in this thread to it.

Option a 5/16 shaft: You can stiffen the shaft by building out the arrow side plate thus allowing you to add weight to the point increasing weight and FOC which will give you awesome FOC. I have to build out ALL my cut to center bows to achieve FOC even with .300 spine shafts. Right now I'm tuning a 58# at 29" L/B with .300 shafts and they are 32.6% FOC and still weak so tonight I'm going to build out the side plate even more (to about 1/4-3/16").

[Wolfkiss]

Here's one I encountered many years ago Clay,


 


This particular Funnel web was able to walk under water and nearly crawled up my bare foot when I was fishing for Crayfish in a creek.


Sorry for the poor pic but looking at those fangs it gives you an idea what a bite from one of these would be like      


They are residents of the Sydney area and Blue mountains, so if you are heading up North you will be Ok.

[Ragnarok Forge]

Wolf Kiss,  we will be in the Mackay area and then rolling out into the outback for some hunting with an Aussie gentleman who was generous enough to offer up a stay at his place and hunting on some property he has access to.  He and I both served in the military and in Iraq.    

Tricia and I are really excited to be coming over for a visit in Oz.  We have three weeks planned for the trip the last week of July and first two weeks of August next year.

[chopx2]

Just looking at that picture made me shudder and I'm not squeamish.  

[Rattus58]

Originally posted by Dr. Ed Ashby:
Clint, The arrow setup is in the Current Part 4 Update. Here's the link to it and to the Part 5 Update.

  http://www.tradgang.com/ashby/2008update4.pdf  

  http://www.tradgang.com/ashby/2008update5.pdf  

Ed

What does Arrow MA mean?

What would the effect of a 30% FOC be with a 900 grain arrow?

Much Aloha...

[Dr. Ed Ashby]

MA stands for "Mechanical Advantage". The MA of a "machine" is the ratio of the 'force input' to the 'force output'. (Note that this is a ratio of "Force", not a ratio of Kinetic Energy; yet another reason why KE isn't useful for predicting the 'work' your arrow can accomplish - i.e. the degree of penetration.)

Your broadhead is a 'simple machine', comprised of a series of inclined planes. Your broadhead comprises a part of the larger 'simple machine'; your arrow. Each has its own MA. The approximate MA of a broadhead is relatively simple to calculate. The overall MA of your arrow is more difficult to calculate.

The MA of a simple machine tells you how much the "applied force" is multiplied by use of that particular 'machine'. A MA of 3.0 multiplies the applied force by a factor of three, meaning it allows the applied force of your arrow to do 3 times that amount of "work", when applied against a given 'resistance load'. A word of caution: Don't confuse what some term a "3 to 1 ratio" broadhead with the broadhead's MA; not the same thing.

Hope that helps,

Ed

[Dr. Ed Ashby]

Woops, forgot the second part of your question. Here's what the testing indicates:

(1) At equal arrow weight and equal external arrow dimensions, the higher the FOC the greater the penetration.

(2) At equal arrow weight and equal external arrow dimensions, the higher the arrow's FOC the greater the degree of penetration gain PER EACH 1% OF FOC INCREASE.

(3) At equal external arrow dimensions and equal amounts of FOC, but with differing arrow weights, the greater the arrow weight the greater the average outcome penetration. The difference in average outcome penetration, percentage wise, will be PROPORTIONAL to the percentage of increase in the arrow's force. (Force is measuered by the arrow's momentum. An arrow's 'energy' is not a measure of the arrow's force.) For example: At equal external arrow dimensions and equal amounts of FOC, but with differing arrow weights, the percent increase in the arrow's momentum is closely equivalent the percent of increase in the average outcome penetration; when measured across a large number of shots into real tissues. Often the percentage increase in average penetration will slightly exceed the increase in arrow force. Why? The increased arrow force is being applied by a 'simple machine', which can multiply the arrow's force increase.

BTW: Not every broadhead on the market has a MA exceeding 1.0, though most traditional broadheads do. A broadhead with a MA below 1.0 REDUCES the 'work output' an arrow carrying a given amount of force can do. When measured across a large number of shots into real tissues, increasing arrow force by a given amount, WHILE USING A BROADHEAD WITH A MA BELOW 1.0, results in an average penetration increase SIGNIFICANTLY LESS than the percentage of increase in arrow force.

Ed

[slivrslingr]

Never thought I would get a physics lesson on an archery forum, LOL!  Thanks for the great info and work you do Dr. Ed!  

[chopx2]

Dr. Ashby...where were you freshman year!

I might have gotten better grades if they applied physics to something I cared about like bowhunting!

[Rattus58]

Hi Dr. Ed....

Ok... here goes....  

1) How do you calculate the MA of a Broadhead or is it published in your wonderful works.

2) Arrow weight and FOC... You said that a heavy arrow is as effective as a lighter (though heavy) arrow with a 30% FOC. You just now are saying that the FOC with 30% is commensurately better and so I'm assuming (I'm somewhat slower to have lights go off sometimes... ok.. maybe more often than that... )that a 700 to 900 grain arrow with a 30% FOC will have a commensurately greater penetration than an arrow somewhat more modest with 30%.

I've tried to explaine Kinetic Energy and Momentum to my kids in that Kinetic Energy might get it there, but momentum gets it done. What I mean by that is that as with heavy bullets, it doesn't matter how it gets there, it's what happens when it does, and it's the energy contained within the projectile that provides penetration.

I know a superfast arrow or bullet can sometimes provide enough speed to penetrate, but usually at the expense of a good wound channel.

I'm learning how to make arrows from some of the trees we grow here in Hawaii and that leaves me to anothter question for you...

It was you I think mentions that when the arrowshaft is smaller than the ferrule, then penetration is improved. I'm not sure how this works, even my wood arrows are tapered into the ferrule and the shaft itself is larger than the ferrule. However, the argument seems to be saying that a tapered shaft (FOC aside) might have better penetration.

[Rattus58]

Dang... something happened there.... Tapered shafts... what happens if you taper towards the arrowhead as well as towards the nock? Would that improve penetration any (again FOC notwithstanding)?

Much Aloha...  :cool:

[Dr. Ed Ashby]

Rattus58,

The mechanical advantage of a wedge depends on the ratio of its length to its thickness. Where a short wedge with a wide angle does the job faster, it requires more force than a long wedge with a smaller angle. For the purposes of simple comparison of one broadhead to another, and assuming similar profiles for the ferrules on both broadheads, you can just use the MA of the main blade, which is a wedge. I borrowed the directions for the MA of a wedge from a University of Arkansas web site.

“The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.” Note that that the “Slope” is the length ALONG ONE EDGE of the wedge. The “Thickness” would be the width of the broadhead.

Here’s what the Study data indicates about the FOC effect on average outcome penetration into tissues, expressed differently.With arrows having equal external dimensions (same broadhead, same shaft diameter and material), equal quality of arrow flight and total arrow integrity (remembering that FOC’s measurable penetration effect does not show up until a FOC of 19% is reached):

(1)   Having a greater degree of FOC allows a lighter arrow to equal the penetration of a heavier arrow having a lesser amount of FOC. How much difference in weight there can be becomes a function of both the amount of FOC difference between the two arrows and the starting point for the FOC change (the FOC of the heavier, lower FOC arrow). That’s because the rate of penetration gain becomes greater the higher the FOC gets. In other words, a change from 30% to 31% FOC yields a greater penetration increase than does a change from 20% to 21% FOC, or from 26% to 27%. The upcoming 2008 Update, Part 6 will have an analysis of what the data suggest is the degree of change that can be achieved by Ultra-EFOC, as well as a brief review of what a similar analysis of the 2007 testing EFOC data indicated.

(2)   When arrow FOC is equal but arrow weight is different the arrow having the greater weight will have greater penetration.

You definitely want the diameter of your arrow’s shaft to be less than the diameter of the broadhead’s ferrule. All else equal between two arrows, the difference in average outcome penetration between a shaft diameter smaller then the broadhead’s ferrule and a shaft diameter greater than the diameter of the broadhead’s ferrule is 40%. That’s HUGE!

When all else is equal between two arrows, a tapered shaft out penetrates a parallel shaft, and a parallel shaft out penetrates a barrel tapered shaft. Here’s where you can read more about this.

 http://www.tradgang.com/ashby/2004update2.pdf

 http://www.tradgang.com/ashby/2007update8.pdf

 http://www.tradgang.com/ashby/Momentum%20Kinetic%20Energy%20and%20Arrow%20Penetration.htm

Hope that helps,

Ed

[chopx2]

Dr. Ashby,

Not wanting to be obtuse (i.e. low MA [mental ability]) but I assume tapered meaning the larger diameter at the BH end of the arrow.

Do you know of any other tapered carbon shafts other than Grizzlystiks?

[Rattus58]

Originally posted by Dr. Ed Ashby:
 Rattus58,

“The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.” Note that that the “Slope” is the length ALONG ONE EDGE of the wedge. The “Thickness” would be the width of the broadhead.

(1)   Having a greater degree of FOC allows a lighter arrow to equal the penetration of a heavier arrow having a lesser amount of FOC. How much difference in weight there can be becomes a function of both the amount of FOC difference between the two arrows and the starting point for the FOC change (the FOC of the heavier, lower FOC arrow). That’s because the rate of penetration gain becomes greater the higher the FOC gets. In other words, a change from 30% to 31% FOC yields a greater penetration increase than does a change from 20% to 21% FOC, or from 26% to 27%. The upcoming 2008 Update, Part 6 will have an analysis of what the data suggest is the degree of change that can be achieved by Ultra-EFOC, as well as a brief review of what a similar analysis of the 2007 testing EFOC data indicated.

(2)   When arrow FOC is equal but arrow weight is different the arrow having the greater weight will have greater penetration.

You definitely want the diameter of your arrow’s shaft to be less than the diameter of the broadhead’s ferrule. All else equal between two arrows, the difference in average outcome penetration between a shaft diameter smaller then the broadhead’s ferrule and a shaft diameter greater than the diameter of the broadhead’s ferrule is 40%. That’s HUGE!

When all else is equal between two arrows, a tapered shaft out penetrates a parallel shaft, and a parallel shaft out penetrates a barrel tapered shaft. Here’s where you can read more about this.

  http://www.tradgang.com/ashby/2004update2.pdf  

  http://www.tradgang.com/ashby/2007update8.pdf  

  http://www.tradgang.com/ashby/Momentum%20Kinetic%20Energy%20and%20Arrow%20Penetration.htm  

Hope that helps,

Ed

Again, I cannot thank you enough. I've some wood drying right now that I'm going to cut into shafts. How would I, unless I cut the shaft to a smaller diameter to start with, effect with a wood arrow, a ferrule diameter smaller than my shaft. My Cedar/Ash shafts are 23/64" right now and the ferrules look like they are max maybe 5/16" maybe less even.... (Snuffers).

Will a taper from the Broadhead, as already asked, work to improve this situation... and how does a taper of the tail help if any?

Again, Thank you profusely for your insight and knowledge that you share with us...

Much Aloha,

Tom

[AKCrazyhorse]

Doc,

I asked this question a page or two back but am wondering what your personal preference would be.  I can build two arrows that will tune perfectly for my set up .  One is just under heavy bone threshold (about 620 grains with an FOC of right on 30%.  The other is just over the threshold at 661 grains with a 28%foc.  This is done with a axis 500 shaft, 100 grain insert, 300 grain broadhead vs. a beman mfx same insert same broadhead.  If your choices were limited to these two shafts, which would you pick for game up to and including african plains species?

[AKCrazyhorse]

Oh yeah, and I've already switched to a bare minimum of wrapped cresting and a small RAYZR type feather so the only real variable in the set up is the model of shaft and the grains per inch.

[Dr. Ed Ashby]

AKCrazyhorse, for me, personally, the choice would be simple. I always try to plan for the worst hit that MIGHT occur. The heavy bone threshold has been so persistant in all testing that I won't hunt big game with an arrow below 650 grains. Though having higher FOC increases the arrow's penetration once a heavy bone is penetrated testing shows that the degree of FOC has no effect on the arrow weight required to breach a heavy bone. I'd use the 28% FOC, 661 grain arrow.

Ed

[AKCrazyhorse]

Good enough for me doc.  thanks

[Rattus58]

Originally posted by Dr. Ed Ashby:
AKCrazyhorse, for me, personally, the choice would be simple. I always try to plan for the worst hit that MIGHT occur. The heavy bone threshold has been so persistant in all testing that I won't hunt big game with an arrow below 650 grains. Though having higher FOC increases the arrow's penetration once a heavy bone is penetrated testing shows that the degree of FOC has no effect on the arrow weight required to breach a heavy bone. I'd use the 28% FOC, 661 grain arrow.

Ed

Any thoughts on the wood arrow/ferrule dimension question?

Aloha...