Home › Forums › Friends of FOC › Arrow length as substitute for more FOC
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Does anyone have substantial experience with using greater arrow length on wooden arrows to improve flight stability?
Assume you keep draw weight at 55 or lower (and you don’t have arms like an orangutan.) 😉 I’m wondering whether stiffer and longer arrows with moderately heavy points can improve stability enough to satisfy practical requirements? (Yeah, I love the idea of maximizing FOC and I’ve seen the results personally. I’m just not fond of carbon or aluminum as shaft material and all that they entail.)
BTW, this IS rocket science: Why Rockets Have Fins
(Maybe I should clarify preemptively that by “stiffer” I am referring to static spine, not dynamic. Hope that keeps the ‘Net hounds off my trail. 😉 )
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Never really thought about it. My DL is 28″+ so conventional wisdom says my arrows should be 29 or 29.5. That, however isn’t so. My arrows are 31″ from bop to nock throat. at that length with 5.5″ feathers and 125gr. medieval field points there is no fish tailing or purposing this is from a 53# 66″ LB.
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Hmmm, this sounds like a Physics 101 professor’s “logic trap”, to wit: All else held equal (and in tune), (A) increased FOC increases arrow flight stability thus accuracy, and (B) a longer lever arm (longer arrow with same point weight) increases effective head weight thus FOC, therefore (C) a longer shaft, all else held equal, increases flight stability thus accuracy.
Alas, it ain’t quite that simple since at some point of length no amount of realistically achievable shaft stiffness can canx the increased flexibility of the shaft. But then, ALL arrows, even the shorties, suffer archer’s paradox yet still are accurate if well tuned.
So, a real good question for which I have no answer but share your curiosity. Hoping EA and some of our resident physicists will clue us in.
What I do know is that I like around an inch of extra length between front of bow and back of head, and use the heaviest heads I can arrange, and have never had a problem. So, assuming that several inches of extra shaft length provides no real benefit (since we can more easily achieve EFOC by increasing head weight rather than shaft length), and given that overly long arrows have other problems (like projecting beyond the bottom of the bow when in a bow quiver, complicating placing the bottom of the bow on the ground … or if in a back quiver, sticking up high and getting snagged on brush, etc.), I guess my bottom line is “What’s the point?” for extremely long shafts? We can now buy first-rate broadheads up to 300 grains and add more yet with shaft sleeves, WoodyWeights, etc. Still, it’s a good question and good questions are always good fun. 😛
This line of inquiry becomes more pertinent when thinking about spears and atlatl “darts,” and it so happens I plan to build and learn to use an effective atlatl system this year.
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Back when I was really primitive, I’d use river cane arrows that were, sometimes, up to a foot longer than my draw length. Even with very lightweight bone tips (for small game), these arrows had good flight.
I think longer arrows are, in general, more accurate. But, increasing the shaft length wouldn’t gain you any of the penetration bennifits of EFOC.
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Just for curiosities sake, I cut a 2″ piece of 11/32 cedar shaft and weighed it. I know different shafting woods weigh differently per inch but these 2″ weigh only 21 gr. so that ain’t going to be like putting 50 gr., 100 gr., etc up front on carbon shafting. Playing with weight and length and spine can be tricky with wood arrows especially with before center shot bows. Just me thinking.
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R2 wrote: Just for curiosities sake, I cut a 2″ piece of 11/32 cedar shaft and weighed it. I know different shafting woods weigh differently per inch but these 2″ weigh only 21 gr. so that ain’t going to be like putting 50 gr., 100 gr., etc up front on carbon shafting. Playing with weight and length and spine can be tricky with wood arrows especially with before center shot bows. Just me thinking.
It’s not penetration that I have in mind here (except to an incidental and nearly trivial degree) and certainly not any enhancement of FOC. It’s Archimedes’s lever that I have in mind here, not Thor’s hammer.
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R2 wrote: Excuse me for being the only one to have made reference to FOC, since the title includes FOC.
I think you may have misunderstood what I was saying. I wasn’t dismissing what you said, only trying to clarify that I was looking at using greater arrow length than in a “standard” setup as a partial substitute for increasing FOC.
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No prob! I guess 21 gr. is pretty much partial. 😀 Extra length to me though means more wiggles to contend with in the archers paradox. Stiffer spine, longer length, something to play with.
A couple of inches extra arrow sticking out could be a problem in some hunting situations.
Be well.!
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In ‘flight stability’ it’s not the length of the arrow that matters, it’s the relative relationship between the forward and rear leaver arms, and the degree of force exerted on each. Lengthening your arrow, without adding additional point weight, is going to lower the FOC, because you are adding additional weight to the rear leaver arm.
With a given shaft material, when length is added without adding point weight, it does lengthen the rear leaver arm but, because it shifts the gravitational center to the rear (lowering the FOC) it also lengthens the forward lever arm. As long as there is still some positive FOC there will be some degree of flight stability.
The degree of dynamic stability demonstrated in flight will depend of the balance of forces exerted on each of the lever arms. For example, a field point exerts very little wind sheer pressure on the forward lever arm, and would require less pressure on the rear lever arm to achieve a given degree of stability, but a broadhead will exert far more wind sheer on the forward lever arm, requiring more pressure on the rear lever arm to achieve the same degree of flight stability.
It must be recognized that it is not only the broadhead and fletching that exerts pressure on the leaver arms. As an arrow deviates from the flight direction the surface area of the shaft also exerts pressure on the rear leaver arm, providing some additional steering effect; but that’s also true for the forward lever arm, except that the force is a destabilizing one. As long as there is positive FOC the differential in ‘shaft pressure’ will be in favor of the rear lever arm. The degree of this ‘shaft pressure’ differential is also reflected by the relative position of the gravitational center; ergo, it, too, is reflected by the FOC of the projectile in flight.
I always found that longer arrows shot better for me when using field points, but not with broadheads, and the flight got worse as the degree of broadhead wind sheer increased. Now, I tune my EFOC/UEFOC arrows by altering the shaft length, and many of these are longer than my minimum arrow length but the added length is not what is creating the great stability, it is the FOC. Ideally I would want the shaft as short as usable because it would give greater FOC, at any given point weight. However, the benefits of EFOC/UEFOC is squandered without quality arrow flight so arrow length will be wherever it tunes best, even if I have to sacrifice a bit of FOC.
In a nut shell, it’s the relationship between the forward and rear leaver arms that you need to be looking at when seeking flight stability, and it’s the degree of FOC that reflects this relationship. Hope that’s the info you were looking for.
Ed
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That is one heckuva handy response, and I’ll probably tape it to my bathroom mirror for a few weeks … or months. Thanks!
I’ve seen references elsewhere to the difficulties inherent in modeling arrow flight. Seems like some brain power and CPU capacity would be better devoted to that pursuit than creating yet another social media service. At least for those of us here. 😉
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Years ago I tested it with wood arrows (Northern Pine) around 500grain with 125grain field point, going from 28″ to 25″ BOP.
25grain more point weight (without shortening the arrow) or shortening the arrow by 1″ (with same point weight) produced 1% more FOC (until a certain point which I don’t remember).
It also depends on the weight of the shaft. So it could be more or less then I found.
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