Question about Dr. Ashby's article on TBM

[NorthShoreLB]

Wanderful piece he wrote on the latest TBM, wish more people will take in consideration his studies about the heavy arrow advantage.

...Now there's something that I quite don't understand,...if 2 arrows are of the same overall weight and both fly the same, why would the one with more FOC penetrate better ?

I'm not going against this being one that loves extreme FOC, but I'd like to understand why, maybe some of you technical brain people can explain it to me.

Thanks

Manny

[Strutter]

Not sure but may be the one with a high FOC will begin penetrating immediately upon impact and the one with less will have to wait for the arrow shaft to flex a bit before starting to penetrate.  Hope that makes sense.

Rob

[Fallguy]

I it because the majority of the weight is closer to the point so there is less shaft to deflect on impact with the target.

[Jason Jelinek]

The shaft with extreme FOC will flex less upon impact.  Arrow flex upon impact causes drag.  Extreme FOC arrows will have less flex and less drag leaving more energy to penetrate.

Jason

[NorthShoreLB]

That makes sense, thanks !!!

[Biggie Hoffman]

man that's really splitting hairs.....

[John Havard]

Actually Biggie that's what I used to think, too.  But Bob Morrison described a test to me in which he took the same bow and the same arrows and the same BH, but in one arrow he put a heavy insert behind the BH and in the other he added weight inside the shaft.  Both arrows weighed exactly the same amount, were the same shaft and the same BH - just one had high FOC and the other carried the weight through its entire length.  He then shot both arrows 12 times each into 7/8" marine plywood. All 12 shots with the "normal" FOC arrow produced a bounce-off.  All 12 shots with the high FOC arrow stuck into the plywood with (as I recall) 3 or 4 having the BH protruding out the back side of the plywood panel.  Bob would be the first to admit that there are still uncertainties in his test which were impossible to resolve.  But the results speak pretty strongly to the benefits of not having the tail end of the arrow paradoxing when it strikes the game we're trying to penetrate.  

I thought it was an interesting experiment with very interesting results.

[Biggie Hoffman]

yeah I've heard of test like that but I don't think it proves anything. Plywood is a laminated hard suface, it has give to it, bounce etc,
So many test nowadays are flawed. Especially allot of the broadhead tests. Most broadhead destruction is "after the fact" and means little as far as a clean kill. I mean anyone can destroy a broadhead so what? Know what I mean?

[Bjorn]

Unless I am mistaken the tests described by John were repeated by DR. Ashby on animals with similar results. Unfortunately it is difficult to achieve high FOC with wood like you can with carbon and aluminum cause it is so hard to get that stiff a woodie.

[Dr. Ed Ashby]

Yes, the extra penetration is a result of reduced shaft-flex at impact and during penetration.

The Prologue to the 2007 Updates gives a more complete explination of the 'why and how' Extreme FOC arrows achieve this reducion in shaft flex, and resultant shaft-drag. However, there also is a bit more to understanding how important a penetration factor Extreme FOC is, and how to achieving the most from its conserved energy (and, yes, energy applies here).

Less shaft-flex means conserved arrow-energy, which also means more retained arrow force (momentum).

The more efficientently your entire arrow setup is able to use (apply) the conserved energy and arrow force (momentum), the longer the TIME fator of the arrow's IMPULSE OF FORCE will be.

Against any given tissue resistance, it is the IMPULSE OF FORCE that determines the final amount of penetration.

The formula for the impulse of force is the net arrow force (momentum) applied during penetration MULTIPLIED by the the time period that the force is applied.

Since the ADDITIONAL impulse (and resulting extra penetration) that results from less shaft flex is a PRODUCT derived from MULTIPLYING the conserved force (the 'extra retained momentum') by the ENTIRE time period of the impulse, the penetration increase will be a far greater than suggested solely by the amount of reduced-resistance (or retained arrow force) that results from reducing the shaft flex and drag.

On all except a total abrupt-stop impact, the extra retained momentum also extends the TIME FACTOR of the impulse of force. This further contributes a geometrical increase to the arrow's resulting penetration.

Extreme FOC's total penetration increase is IN FACT far greater than the SUM of the force saved and the increase in the time of impulse; it is the product of them. Each MATHEMATICALLY MULTIPLIES the other to derive the outcome penetration. Understanding this is the key requirement to understanding arrow penetration; and knowing how your arrow's setup impacts its termianl performance.

The Part 4 2007 Update will have penetration results from two sets of arrows as precisely matching in all dimensions except FOC as I could achieve - including flawless flight - from a 54# straight-end longbow. They are as startling as those John relates above - perhaps even more so.

There will also be a comparison of penetration results from this 54# bow's Extreme FOC arrows and 'normal and high' FOC arrows from both the 70# and 82# longbows used in testing. Only 'comparable shot' data is used; for shot range, shooting angle, impact angle and location, and animal size. For these 'matching shots', comparison is made against 'all single blade' broadheads and those with the same BH as the lighter bow's Extreme FOC arrows. There will also be a comparison of Extreme FOC arrows from each of the three bows.

It's fascinating stuff and, bottom line, Extreme FOC makes a very, very significant contribution to arrow penetration when everything else about the arrows matches exactly. Exactly how much difference does it make? You'll have to read Part 4 and 5 Updates!

Ed

[SteveB]

Originally posted by Biggie Hoffman:
man that's really splitting hairs.....

Biggie - lets us get deeper in the dirt    

Steve

[bearhair]

One aspect of high FOC that I don't quite have straight in my head is that a high FOC doesn't equate to super heavy overall arrow weight, does it?  One can acheive the same high FOC using a 150gr point on a light shaft as using a 250gr point on a heavier shaft.  Of course you'd have to play around with different spined shafts given the difference in point weights.

I guess what I'm getting at is I see alot of threads where guys give positive feedback concerning high FOC but it always seems they also have heavy arrows as well (200 or 250 gr points).  So to utilize the advantage of high FOC do you also need heavy overall arrow weight or can one get the advantages of high FOC by coming up with a point/shaft combo that keeps overall arrow weight a little more moderate?

Not trying to debate heavy versus light, just wondering if regardless of overall arrow weight one should try and acheive a high FOC (assuming one believes there are advantagwes to high FOC)..

[Dr. Ed Ashby]

Stephen, you are absolutely correct. In fact, using penetration averages, all the data indicates that extreme FOC's DEGREE of penetration gain - percentage wise - is greater the lighter the arrow becomes and the lower the arrow's force becomes.

However, that can be misleading. DO NOT confuse DEGREE of BENEFIT with the TOTAL AMOUNT of benefit. Higher mass arrows have higher penetration to begin with, so it takes more inches-of-penetration-increase to represent the same percentage of gain that a low mass arrow attains.

Also, you need to consider the number of penetration barriers encountered (ie: just entrance-side skin and ribs, or both entrance and exit-side ribs/skin) and the limits of measurable penetration (penetration is measured as depth of the wound channel through tissues, and penetration beyond that is not accurately measurable). In the buffalo testing, on all shots from reasonable shooting angles, an exceedingly high portion of all structurally-intact Extreme FOC arrows having a mass-weight above the heavy bone threshold fully traversed the thorax to reach the off-side ribs.

Arrow mass becomes a more critical factor on heavy bone impact, and the amount of FOC has not demonstrated any effect on the heavy bone threshold.

All that notwithstanding, Extreme FOC is decidedly a desirable penetration-enhancing feature on arrows of lighter mass; greatly enhancing soft tissue and light-bone penetration.

Ed

[NorthShoreLB]

Good reading  

...since it's hard to achieve high FOC on woodies, (unless we start using those alluminum arrow adapters, ....than we can get up to 375gr point ,..just got some and I'll try them soon)

I assume than, from following this studies, that would be better using alluminum or carbon shafts.

[Dr. Ed Ashby]

NSLB - At Extreme FOC levels (above 19%), I've found it very difficult to get the quality of flight I want when using aluminun shafting. Carbon shafting is much easier to get great Extreme FOC flight with, at least in my experience.

I think the difference has to do with carbon's flexional characteristics - and that may also be one reason carbon-fiber poles replaced both metal and fiberglass ones in Pole Vaulting.

Think about the amount of weight FOC (and how much it shifts) on a vaulting pole during the verious stages of the vault - and the fast recovery the carbon-fiber pole makes from a state of extreme flexion!

Ed

[p1choco]

I have never read through a whole report so maybe I'm missing something.  I don't ever think I've seen actual picture results and I am still unsure as to how the data is recorded.  What I mean by that is how does Dr. Ed know how much has penetrated?  He says, "In Buffalo testing..." is he actually shooting at a whole live Buffalo?  Is it a side of hanging Buffalo or maybe bones encased in ballistic gelatin with Buffalo hide over it?  Another question I have is how do traditional arrow penetration compare to compound arrow penetration with BH or mechanical BH's flying at 280+ fps?

[vermonster13]

He shoots fresh killed buffs. All that matters here is how traditional tackle works. Compound comparisons are outside the scope of this forum. Lots of good stuff in the reports if you do read them. Even for long time trad shooters.

[NorthShoreLB]

....hmmm, so Ed you'll be suggesting to shoot carbons to get best results, any particular brand?

I'm getting good flight out of my 71# Hill (without cut in arrow pass) with 27 1/2" BOP 2117 legacys and 430gr up front.

[p1choco]

I understand that the compound comparisons may be outside the scope of this forum, but I think it would be nice to see what's happening on the opposite side of the spectrum as a comparison.  Lighter, less FOC etc.  If we're are getting down to the technical science and we're talking performance with penetration, I like to weigh the scales.  Dr. Ed seems to be the only one writing up the reports, so pretty much whatever he says is gold.  Once upon a time the world was flat.  Coming from a world of studying ballistics on long guns and pistols, I'm trying to adjust to the world of trad and get on the same page as Dr. Ed.  I think I'll take my time and read through all the reports and look for answers to my questions there.

[Dr. Ed Ashby]

Reynaldo, seek and ye shall find.

The study's testing has included bows of all types; something necessary to reach the stratospheric KE levels (of the bow world). Testing of the KE/Momentum relationship to outcome penetration in tissues with normal and high FOC arrows has involved IMPACT KE levels up to 94 foot pounds. That information is among the study updates and associated articles to be found here on TradGang, along with comparisons against the terminal tissue performance of both normal/high FOC and Extreme FOC arrows from traditional bows.

In just the last couple of months, I've had offers from a top wheel-bow shooter and hunter and a couple of light draw-weight trad bow shooters to further investigate (on whitetails and hogs) the Extreme FOC effect at the higher impact KE/momentum levels; and this is greatly appreciated. Very similar arrows are being used by each.

I'm also seeking a correlation of the penetration ratios between higher-mass (above threshold value) Extreme FOC arrows from lower draw weight traditional bows with that obtainable with lower mass (below threshold) Extreme FOC arrows at higher velocity; and trying to ascertain if Extreme FOC has any significant demonstrable effect on the heavy bone threshold, as velocity is increased.

It is also likely this testing will provide more insight into the relative penetration-importance of the time of impulse, as opposed to the increasing the force component of the impulse.

Only time and the results will be able to provide an accurate answer.

Ed