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Author Topic: "The Study" - need YOUR ideas NOW!  (Read 975 times)

Offline AZStickman

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Re: "The Study" - need YOUR ideas NOW!
« Reply #20 on: March 28, 2003, 11:54:00 AM »
I think you have it covered but broadhead length to width ratios as it relates to penetration and blood trails.... and broadhead materials of construction......which will affect proper sharpening and durability......also wouldn't fletching combinations possibly factor in..... 4 fletch v.s 3 fletch and differing fletch lengths..... Terry
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Offline bob@helleknife.com

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Re: "The Study" - need YOUR ideas NOW!
« Reply #21 on: March 28, 2003, 02:43:00 PM »
Dr. Ashby,

Your study seems so over whelming to me.  So much data, so many variables...with tools designed over 10,000 years ago.  Interesting paradox!

Digressing a tad.  The holy grail of current archery thought is two holes are better than one.  Seems I have read that some early American archery pioneers felt that it was best if the arrow stayed in the animal and allowed to "work" as the critter fled.  Wonder how they came to that conclusion?  Perhaps they talked to some native Americans and that information was conveyed to them?

I wonder if there is any correlation between recovery or ease of recovery of animals on pass through shots vs. arrows that stayed in the animal.

Warmest regards.

bob@helleknife.com
Beware of all enterprises that require a new suit.

Don't give up what you want most for what you want now.

Offline Dr. Ed Ashby

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Re: "The Study" - need YOUR ideas NOW!
« Reply #22 on: March 28, 2003, 05:39:00 PM »
Russ ... somewhere, further along in the study, I hope to do a lot of "look'n" at arrow shafts as a factor, not only by type of material, but by FOC and by profile (straight, tapered, double tapered).

These 'individual factor' studies will have to be very 'focused', where all remains constant except for the varable being looked at, and a lot of shots have to be taken with each 'parameter' to get a valid result.  That means they are well down the road in the study, so don't be looking for that answer to drop out too soon - but I hope to get there, Lord willing, and the creek don't rise.  I too, hope to find the 'shaft answers', and, if I do, it could well change the arrow I hunt with too!

By the very definition, momentum is the correct formula for penetration.  It is the straight line force vector of a body in motion which must be met by an equal amount of resistance before a body in motion comes to rest.  Kinetic Energy is the entirity of energy of a body in motion and, for an arrow in flight, would include such things as the flexional energy, the sound energy, the rotational energy, and the heat energy, as well as the directional force vectors.

The reason for the "re-visit" is that so many still subscribe to, and rely upon, kinetic energy readings as an indicator of the arrow's 'potential'.  In some locations it is even used as the legal 'benchmark' for hunting set-ups to be legal for certain classes of game.

This dispute needs to be settled.  All the data I have so far indicates that Kinetic Energy should not be used as an indicator for penetration.  In all the studies I've done so far, it has no "significant' correlation at all.  The hope is that the case can be made so overwhelming that absolutely no question can remain, and we can all move on to the more important issue, coming up with something that really is valid.

Now, as momentum is the correct formula for straight line energy vs resistance, and assuming it does prove to have a sufficient level of correlation to penetration in this study, it will be used as the 'starting point', the 'impact force' (and 'impact force' is only A PART of what is needed for a final 'model').

The next phase will be to analize the resistance factors.  This is where the 'noodling' factor will enter, as will shaft drag, shaft size vs ferrule diameter, mechanical advantage of the broadheads, cut resistance, etcetera.  The 'changed momentum formula' you refer to is not really a 'change',it is a modeling - looking at the 'moment of momentum', the vairable force applied over the time period of action of a body in motion before it comes to rest.

The moment of momentum is one factor I hope to look at - the effect of like arrows of equal mumentum, but where one has higher mass and lower velocity and the other lower mass at higher velocity.  As the mass remains a constant throughout the penetration, the heavier arrow will have a longer 'moment' of force - therefore it will act 'longer' but, as it is moving slower, just how far will it be able to travel in that 'extra time of action"?  Which will go farther before expending all the energy and coming to rest against tissues of "X" amount of intrensic resistance?  Conventional wisdom says the heavier one will, but is that correct?  Could this be a factor in the reported 'carbon arrow penetration paradox'?  I have no idea yet!

Using the basic definition of momentum from physics, it is clear that all the factors influencing the resistance being met have to be delineated in order to come up with a predictable penetration factor.

If it can be varified that momentum is the correct 'starting point', and the other factors can then be 'quantified' somehow, it should be possible to develope an 'arrow profile formula' that should give a very close correlation to actual measured penetration under field condition.  This was what the TPI was about, and it appeared to have a very close correlation in it's one and only test so far done.  That test, however, was way to limited to be certain that it was correct.  Much, much, more needs to be done towards development of a relaible model.

Bob ... One of the many things being looked at this time will be the types of correlations between shot locations, penetration, exits and non-exits and the degree of lethality (recovery rates, distance traveled before collapse, degrees of blood trails, and a host of other factors).  The question you raise of an arrow remaining in and continuing to cut is one that has lingered long, and it must be look at critically.

After hanging around a lot of hunt camps for lots of years, one of the things I'm absolutely certain of is that a 'body hit' animal that runs off with the arrow still in it is much more likely to be the 'lost animal' than one that has a 'body hit' pass-through shot.  The question remains, "Why"?  Was it broadhead failure?  Inadequate penetration?  (These two often go 'ahnd in hand'.)  This continuing occurrance of a higher frequency of 'lost with the arrow in it' makes me wonder how valid the 'continues to do damage' theory is.

Yet another factor that enters into this 'remaining in' issue is that the Indians used stone points, which often shatter inside the animal, making multiple secondary missiles.  What is their effect?  From all the bullet wound dissections I've done over the years (which VASTLY outnumber all the arrow shots I ever even seen, or even heard about, might less dissected), I think it is more likely that it is these secondary missiles that do the damage, rather than a factor of the arrow remaining in and continuing to cut.

We WILL be doing some testing with stone points during this study.  The individual tasked with this portion of the study is an experienced hunter with stone points, and he has already brough up the subject of the damage done as the point shatters.  That shattering is the 'norm' not the exception, and would creat numerous secondary wound channels, and a 'cone of destruction' similar to an expanding rifle bullet.  He is also an experienced rifle hunter, and describes some stone point shot animals dropping "as though hit by a bullet".  Interesting stuff, huh?

AZStickman ... got 'ya covered on ALL those!

Thanks Russ, Bob, Stick ... your doing a great job.  I need these 'brain rattlers' just to keep me aware of where we are and where we're trying to get to with the studies.

Ed

Offline Kevin Bahr

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Re: "The Study" - need YOUR ideas NOW!
« Reply #23 on: March 28, 2003, 09:16:00 PM »
Well, Dr. Ashby, since hairs are being split, how about broadhead blade to nock alignment, any angle better than others as far as penetration goes?  And one big one that always seems to get stuck in my craw, how about some professional arguments on why one should not use mechanical broadheads.  THanks in advance.  Kevin Bahr

Offline Kevin Bahr

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Re: "The Study" - need YOUR ideas NOW!
« Reply #24 on: March 28, 2003, 09:19:00 PM »
Just kidding on my first question Doctor.  But serious on the second.  I have had bad experiences with open on impact heads shot by others and I need some professional, scientific study-backed reasons to quote when speaking about them to others.  Thanks again.  K. Bahr

Offline Dr. Ed Ashby

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Re: "The Study" - need YOUR ideas NOW!
« Reply #25 on: March 28, 2003, 10:06:00 PM »
Hi Kevin,

Best never to take anything for granted!

I HAVE looked at broadhead to nock alignment pretty extensively, and the answer is ... it makes no differance at all.  Now, I didn't look at it out of curosity, I did it so that there WOULD BE hard data to verify what was obvious from the outset.

The arrow rotates in flight, so we really have no choice in the orientation of broadhead impact angle.  Also, the torque is too low for the arrow to continue rotation once tissue is entered.  The wound channel will show no change in orientation of the head's impact position from entrance to exit UNLESS it is deviated by impact with a heavy tissue, such as bone  (This, by the way, is another 'plus' for the single blade broadheads.  When they hit rib(s) they frequently glance off and turn to pass between the rids, thus conserving their energy for deeper penetration into the underlying soft tissues.)

Mechanicals WILL be in the testing - several different ones will be extensively tested.

Thanks - it's not always bad to 'split hairs'.  Often it's the fastest way to get answers ... by getting to the 'roots' of problems ... just to prove it really was only a good 'color job' all along!

Ed

Offline bayoulongbowman

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Re: "The Study" - need YOUR ideas NOW!
« Reply #26 on: March 30, 2003, 06:42:00 PM »
Dr. Ed , How about the sharpness of the broadhead isnt that one of most important and cutting on impact..maybe parallel to taper shat could develope more Kenitic Energy if its matched with the LBs . of the bow correctly...TY mark
"If you're living your life as if there is no GOD, you had  better be right!"

Offline Dr. Ed Ashby

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Re: "The Study" - need YOUR ideas NOW!
« Reply #27 on: March 30, 2003, 09:01:00 PM »
bayoulongbowman - Thanks for the post.  'Edge' is one of the factors that I'll be tracking, both the angle it is sharpened at and the type of edge sharpening finish technique used.  I hope to try cross-correlation to a number of factors (if there proves to be ANY correlation), penetration, edge durability, percentage of exits, degree of blood trail, etcetera.

Some initial 'overall durability' testing will be done, using the manufacturer's edge angle.  This is to forestall any criticism that the head(s) might have performed better if used 'as intended' by the manufacturer.

Will also be tracking type of shaft, by both material (includung, for woods, the specific wood type) and by shaft profile (parallel, tapered, double tapered).

Thanks, and KEEP THINKING!

Ed

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