Primitive Archer
Main Discussion Area => Bows => Topic started by: Kegan on January 09, 2008, 06:31:22 pm
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Let me know what you think:
Heavy tips would be a good thing on longbows shooting way heavy arrows- they have more momentum, and more possible energy to transfer to the arrow. Only think it would work with arrows heavy enough to use up the momentum though. Lighter tips work well on lighter arrows,which i perfect for modern archers. If one wanted to shoot rediculously heavy arrows (for aliens or elephant or what not), thicker tips would contain more possible momentum to be transfered into the heavy arrow. Or would this be a reverse affect and the tips steal all the energy? I don't have any arrows weighing enough to test it or a bow with the proper dimesions. I'm thinking something like 3/4"-1" wide. It'd have to be a heavy bow though.
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The stuff I've been reading in the Bible Vol I discusses how heavier tips steal the umph. I recall a scenario mentioned where the author was contemplating a similar theory only to have the math prove him wrong, maybe not very similar to your thought though - but close. If I find the passage, I"ll post the page. I see your line of thinking though.
-Mike
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Bow making seems easy. This bow theory stuff is hard :P.
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Heavier tips always steal more momentum from the arrow than lighter tips. The limbs need to use up more of their internally stored energy to throw the heavier tips forward, leaving less to throw the arrow forward once the string hits home.
-Eric
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It takes more energy to get the bigger tips moving in the first place and this more than offsets any potential gain which really wouldn't be there since the tips basically hold the string and aren't bending themselves. By getting the tips smaller(as opposed to larger) you are allowing more energy to be transfered by the limbs since there is less weight on the tips to get moving.
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i say, dont sweat the small stuff, when you bring mathmatical questions into play and weighng arrows. is it still primitive archery? ??? bend a stick and if it looks good and feels good, go with it. your bows are already plenty heavy IMO. so extra umph probably isnt needed.
its hard to say sometimes where to draw the line as far as primitive is concerned, but-to each his own opinion. :)
as far as your question is concerned, and this is just the way i would see it, i have no math to back it up. but it seems to me that heavier tips would slow down the speed of the limbs. more mass is more weight gained and arrow dinamics that is lost. also the heavier tips may caiuse more stress on the inner limbs causing more set, and that too would decrease performance. but what do i know, im just a primitive archer..lol ;D i would say, with the thousands of bows that have been build over the modern years, if heavy tips where better for heavy arrows, we would most likley know it and use the info. - Ryan
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I dont think it will cause set at all. The heavy mass in the tips creates more kenetic energy in the tips that stays in the tips. The first problem is that energy is stolen from the arrow by reducing speed. The second is that the energy stays in the bow when the limbs stop moving and goes right up your arm and nocks your teeth out. >:D Can you say strained peas for dinner. Justin
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Man has always looked to improve his lot.....from copper to brass to steel.... from selfbow to composite....necessity will always be the mother of invention.....and usually where theres a will....theres a way.....
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Really heavy tips will cause excessive hand shock. Cast is more affected by the last 6-8 inches than the tips. Narrowing the last 6 inches, but not enough to compromise safety, has a huge effect on cast. Jawge
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In theory bumble bees arent supposed to be able to fly,but they dont seem to know about it,so if the bow doesnt know ...... and too much math will take the fun out of my primitive hobby,so heres the next question in theory,which would hurt more,getting shot with the light weight arra or the heavy one?
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Some of the Eastern Woodlands bows had fairly heavy tips- Seneca designs etc. Perhaps we are more concerned about cast and speed than they were, and durability with rough use (when the bow becomes a club) may have been a quality they valued.
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Hi,
Interesting theory, but I believe casting heavy arrows has more to do with tiller shape. If you're throwing light-weight target arrows, you can have more of an elliptical tiller ( ie. whip tillered), with a non-bending handle. To cast very heavy arrows, you need to tiller to a full compass, bend through the handle type bow, with heavy draw weight. I think of it like throwing a baseball vs. throwing a shotput. To throw a light-weight baseball, you can use your wrist to add the snap at the end. If you want to throw a heavy shot, you need to use your whole arm. Regardless, your hand (or the bow's tips) is still the same size. Heavy tips = slow cast and heavy hand shock. The English warbows were tillered to full compass for a reason... they were casting heavy arrows.
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Kegan,
Interesting question.
Imagine you were throwing baseballs. According to your theory you should be able to throw a really heavy ball further it you wore a glove that was really heavy. The extra momentum of your hand should throw it further? I think not. I think you may well find a lot of the momentum stayed in your arm and hurt like hell and the heavy ball would go further if you kept your hand as light and fast as possible.
Is thinking about bow design primitive? In my opinion it is. There are so many different primitive bow types, showing than people have thought hard and found new ways of making efficient hunting weapons all round the world. Those different designs didn't just happen, they were thought about and created through experimentation.
Primitive isn't stupid. Primitive is graet craftsmanship and intelligent thought leading to effective simple self made bows and arows.
JMHO,
Mark
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Thanks guys! I was trying to think about whether the old Cherokee warbows pictured in TBB vol. II. I don't know abiout the mathmatical stuff behind it- just "how the stick bends", at least some of it. Thanks for all the input ;D! It just seems that flight bows wouldn't be able to shoot heavy arrows. I dunno. Just thinkin' ;D.
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Kegan, Just because it is simple doesn't mean its easy! (Marc St Louis) I try to keep it as simple as possible. My pea brain doesn't work well with complicated stuff. ;) Pat
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kegan. generaly speaking a bow that is faster with one arrow will be faster with another. But when you go to extremes of light of heavy it can start to change. The best way I hear it explained was by using a term they call virtual mass. Virtual mass is basicaly used to account for all the energy unaccounted for in the arrow. A typical self bow will have close to 200 grains of virtual mass, meaning if it were 100% efficient it would shoot an arrow the same speed as it normaly does with an arrow 200 grains heavier. A flight bow might have a virtual mass of maybe 80 grains. The virtual mass in a bow has a lot to do with how fast it's dry fire speed will be. A bow with low vitual mass will normaly not store as much energy as a bow with the higher virtual mass but can accelerate a very light arrow( under 200 grains) very quickly. By the same token for a very heavy arrow more energy storage might be needed even at the cost of adding some virtual mass, which usually means heavier limbs. Steve
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The amount of potential energy stored in the drawn bow is the same no matter what the wieght of the tips. The trick is to get as much of that energy transfered to the arrow as practical for a given application. The less energy expended moving the limbs (and tips) the more energy is available to move the arrow.
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The amount of potential energy stored in the drawn bow is the same no matter what the wieght of the tips. The trick is to get as much of that energy transfered to the arrow as practical for a given application. The less energy expended moving the limbs (and tips) the more energy is available to move the arrow.
Ahhhh, now I get it. Makes pefect sense now :)!
Okay, new question, conpletely unrelated- how do you quiet a bow without a soft strike plate ????
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If the bow is not recurved and if the bow and arrows are well matched the bow will be quiet. You do not need a strike plate because the arrow should not make a noise against the bow and the string should not make a noise agasinst the limbs.
Mark in England
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I always thought that a strike plate was to protect the wood of the handle/riser area. I have made some out of antler and seen them made of tortoise shell and they were quite hard which to me would equal noise!
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Huh. I always thought that little "tak" agaisnt the bow was a bad thing for hunting ???.
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Cool thread guys. My take on things is if the bow shoots the arrow accurately, quietly and with enough force to kill a deer
then its good enough for me. ;D
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Kegan,
Tim Baker raises the exact question you raised. He says it is analogus to comparing the power of a golf club compared to a freight train. The freight train has more power but the golf club is way faster. If you think about it though, there is a weight of 'arrow' that a freight train--however slow it may be--would shoot faster than a golf club. Ha, ha.
In answer to your second question--If your arrows are perfect, Perfect, PERFECT in spine they will barely touch the bow as they clear the strike plate.
J. D.
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True JD, but you could not possibly move the freight train the same distance as the golf club with the same expenditure of energy.
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If your arrows are perfect, Perfect, PERFECT in spine they will barely touch the bow as they clear the strike plate.
J. D.
That statement is about as true as any, but under hunting conditions barely touching or barely making noise can be to much. Even if it don't make noise when released, the arrow makes noise when being drawn since it has to slide about 20" across the arrow rest. Use a soft strike plate. Justin
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This has been much discussed. I think Tim's (Baker) latest theory is that extra limb mass increases "hysteresis," a term used to describe essentially what Steve calls virtual mass, although it is measured in efficiency terms versus arrow mass terms. Basicially the idea is that extra limb mass causes the limbs to bend or vibrate upon the loose, robbing energy to friction (the internal friction of anything that bends).
The most interesting realization I made during the discussions was this, the kinetic energy related to (extra) limb mass IS transferred to the arrow at the end of the power stroke. The idea being, the limbs kinetic energy is delivered to the arrow at an increasing rate as the angle the string makes with the arrow is increased, this provides the mechanical advantage necessary to "leverage" the relatively high mass of the limbs at low speed to the relatively low mass of the arrow at high speed. Essentially, the string angle iacts as a set of "gears." As the limb ends speed approach zero, the arrow nock speed is still accelerated due to this gearing. This tends to muddy the waters when it comes to judging which is the best, low mass or high energy storage.
But when it's all said and done, lower limb mass is "better" in all practical applications. The old saying that a longbow throws heavy arrows "better" (than a recurve) is a misconception. Yes, it throws heavy arrows better than it throws light arrows, just like every other bow. But it doesn't throw heavy arrows better than a more efficient bow or higher energy storing bow (ie. recurve).
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Hysteresis isn't the equivalent to virtual mass. Hysteresis is how different the return trip is, from the draw. As such, its a component of VM since in figuring our your VM you roll everything involved together by determining arrow speed and mass. You determine stored energy from your F/D curve and what isn't carried off by the arrow, is what is left. What is left is converted to an equivalent arrow mass that is your VM, its just a way to express "what is left".
Interesting point about string angle and its effect on energy transfer. It'd be interesting to measure arrow speed as it accelerates during the loose. Limb speed doesn't really approach zero till it hits the wall though. But the effects of string angle would mean that there'd be slight differences between short and long bows, and that brace height would have some slight effects in addition to power stroke. Power stroke would probably swamp out the effect of string angle though.
I purposely avoided this thread as long as I could. But I just couldn't help myself.
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DCM, I don't think the kinetic energy of the limbs it transfered at the end, KE is only transfered while the limbs are moving. The speed of the arrow squared times the weight of the arrow is the KE we really want. That is why the speed robbing mass is so bad. The other energy is left in the limb tips until the string brings it to a screeching halt, then it goes through the handle of the bow into your arm. To throw a heavier arrow better you need all the extra mass in the bending portion of the limb where it can work. There the extra weight of the arrow wont slow the limb down because the limb has the extra mass working for it (freight train). If the mass is not working it is bad. If the weight of the tips was allowed to travel beyond the handle and stop on its own it may make a little difference, but only once it is beyond the straight profile. Justin
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Lennie,
I concede to your better explanation of the contribution of hysteresis to vm. Only wanted to direct folks attention to the "hysteresis is everything" idea, which I think it the theme of Tim's work in TBB IV. Certainly it was the thrust of the conversation he hosted at PP.
Justin,
Agreed. Only trying to make the point that at the lower end of the power stroke it is plausible that both the spring energy remaining in the limbs and their kinetic energy might contribute to accelerating the arrow.
It's an interesting question, whether the arrow is in fact still accelerating at the end of the power stroke, and if so I must wonder how the very low, say 10#, 7#, 5# of force only could account for this acceleration, particularly in light of the fact that it's "purchase" or leverage against the arrow is ever decreasing. Were it not, still accelerating, clear it would have to be decellerating at a rate faster than the limbs, which hardly seems likely given their relative mass and friction. Seems like one of the math wiz fellars convinced me KE was contributing at the end of the power stroke.
This stuff can cook one's brain.
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I don't believe that hysterisis is as significant as many would try to have us believe. I would just guess about 5%. The most significant factor I have found, right along with outboard mass on the limbs is how much we have changed the wood durring the tillering process. Experimenting around I am convinced that wood is every bit as fast as fiberglass until the wood starts to get some memory of being bent, At this point it is all downhill. I have seen self bows shooting at 24" what the very best selfbows shoot tat 28". Those same bows showed no improvement and even lost speed when tillered out to 28" just because the wood started breaking down even though it wasn't all that visible in the bow taking much set. Steve
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Steve, I'd either allocate that to extra mass (crushed wood) or hysteresis ("rubbing" wood). But I agree. I still think simple Newton physics accounts for most of the "lost" energy, that is KE left in, invested in depending upon the exact point in time, the bow, string and archer after the arrow leaves the string. In a way this could be called "hysteresis," because it is not retained as either PE or KE.
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Didn't know you were quoting Baker, I'd have been more reverent. I haven't been to play on the other site lately, not enough time or interest. It'll be an interesting new volume I'm sure.
Steve, your idea that wood is best prior to being over-stressed goes right along with hysteresis. One way to get hysteresis is to overstress something. On the pull, you change the material so that it isn't the same on the loose. If its not terribly overstressed it can fully recover, just not in the space of time of the loose. I'd agree that wood that hasn't been damaged by training, certainly performs best. I understand you flight shoot people don't bother breaking your bows in prior to competition for this reason. I do think there's competing factors though. If you make a bow that shows no set after shooting in, it is likely overbuilt and underperforms even though it has undisturbed wood. and if a bow takes an inordinate amount of set (>2") then you probably lose what you gained in efficiency, by reducing the performance of the wood (per unit mass). A little mashing of the spring wood to the point it has a similar density to summer wood, is all you probably want.
It'd be interesting to be able to look at the effects on a piece of wood in training to be a bow, at a cellular level. I just don't know how you'd prep the sample without altering it.
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So far, most of my questions have been anwsered here's what I got:
1. Big tips, wouldn't help enough to make them worth it.
2. The Cherokee Warbows efficiency is explained by Steve- not abusing the wood as much. Seems they found the best balance for their needs.
3. Theories hurt the head alot more than those extra few yards/fps are worth ;).
But I'm still unclear on the strike plate. I've seen alot of harder amterial strike plates. But in order to get away without a strike plate you need perfect arrows. I'm still need some more help here :-\.
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What noise? Oh you mean the kawomp! when the arrow hits the target and you say "tat the spot" :o Sorry, I couldn't resist. :)
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But I'm still unclear on the strike plate. I've seen alot of harder amterial strike plates. But in order to get away without a strike plate you need perfect arrows. I'm still need some more help here :-\.
Most bows arent hunting bows so the little bit of noise dont matter. If you are making a hunting bow I suggest a soft strike plate. Justin
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If your arrows are perfect, Perfect, PERFECT in spine they will barely touch the bow as they clear the strike plate.
J. D.
That statement is about as true as any, but under hunting conditions barely touching or barely making noise can be to much. Even if it don't make noise when released, the arrow makes noise when being drawn since it has to slide about 20" across the arrow rest. Use a soft strike plate. Justin
Agreed Justin. It is important to note, however, that well-matched hunting arrows will not smack the bow as it clears the strike plate thus will be quieter regardless of the material used at the pass. In fact, the arrow wont touch the bow at all after it begins to paradox. This is yet another desirable characteristic of a matched set of arrows.
J. D.
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True JD, but you could not possibly move the freight train the same distance as the golf club with the same expenditure of energy.
Oh I know Gordon. I'm just silly enough to point out extreme at which the analogy breaks down. ;D Most of us aren't going to be shooting 2,000 lb. arrows. We'll give Mark Stretton a couple more years to prove us wrong. ;D
J. D.
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But I'm still unclear on the strike plate. I've seen alot of harder amterial strike plates. But in order to get away without a strike plate you need perfect arrows. I'm still need some more help here :-\.
Most bows arent hunting bows so the little bit of noise dont matter. If you are making a hunting bow I suggest a soft strike plate. Justin
Justin's got the answer to your question. Keep them as quite as possible. You'll dampen almost all of your noise with a good, soft strike plate. Tune your bow's brace height and spine your arrows carefully for silent death. :)
J. D.
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Ahh, now I get it ;D!
Thanks everyone- you've all been a ton of help :)!
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Interesting discussion. Well worth remembering who said what.
I put big/long tips on my rigid recurves so I can get more string. Also, laminates can be worked in different ways to achieve different characteristics. And relatively speaking, the shorter the working limb, the faster the recovery.
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Ok.....
What about harmonics? Limb balance. Could not one limb recover differently than the other? Would that not be a source of vibration upon shooting?
Just a thought.....
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Pitts, as per some discussion about just what you are mentioning I did some experiments a few years back. I spliced a broken but fast recurve to a slow straight bow limbs and handle. No particular extra vibration. I even built a bow about 9 feet long with one limb about 2 1/2 feet long and the other limb about 6 ft long, didnt seem to make much difference. Biggest cause of vibration I have seen and I almost hate to say it is overbuilt limbs. Another thing about vibration I have noticed is that many times perfectly tillered bows bending evenly throughout the entire limb will sometimes be the worst tooth jarring bows around. I think the perfect tillers would often have allowed the bows to be much narrower and lighter thn they actually are and it will often creat a "soft" bow that shocks hard when it hits home. Steve
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Pitts, as per some discussion about just what you are mentioning I did some experiments a few years back. I spliced a broken but fast recurve to a slow straight bow limbs and handle. No particular extra vibration. I even built a bow about 9 feet long with one limb about 2 1/2 feet long and the other limb about 6 ft long, didnt seem to make much difference. Biggest cause of vibration I have seen and I almost hate to say it is overbuilt limbs. Another thing about vibration I have noticed is that many times perfectly tillered bows bending evenly throughout the entire limb will sometimes be the worst tooth jarring bows around. I think the perfect tillers would often have allowed the bows to be much narrower and lighter thn they actually are and it will often creat a "soft" bow that shocks hard when it hits home. Steve
Wow Steve, that's a lot of bow building wisdom packed into one paragraph. Brilliant experiments, too.
I have often wondered (casually) about harmonics. I have an acquaintance who is a gifted, hobbyist luthier. He told me once that every piece of wood that he puts on his guitars is individually tuned to a perfect 'G' note. Thus the entire structure of the instrument is designed to resonate in perfect harmonic balance. The result of perfect, harmonic balance?--Louder guitar! I'm thinking, the principle is essentially the same in both disciplines. We are both trying to store and release energy as efficiently as possible. The principle that makes a wooden instrument louder may make a bow more efficient. Not that I could begin to prove it.
J. D.
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Badger,
Thats some interesting experiments....
I wonder then if maybe it's not the limbs shape (in relation to each other) per se......but more it's tillered balance.
Interesting thoughts J.D.
I have wondered myself if there was a way to tiller the limbs in such a way that the negative harmonics of the limbs slamming back to their homes, would be absorbed or turned to a positive harmonic outcome.......maybe the weight of the handle plays a part.....wish there was a computer graphics program we could plug these forces into to see what a simulation might bring to light...
See what enginering school will do to you.....
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pitts, there is a program online you cna download by Allen Case, who is also a friend of mine. The program is called super tiller. Allen is also somewhat of a musician and has similar theories about harmonics in a bows limbs. I think I do to but don't know enough about harmonics to really discuss it LOL. I can tell you one thing interesting, a good flight bow will never have any perceptable handshock even shooting arrows as low as 3 grains per pound, even dryfiring the bow for that matter. Normaly weight is added to a bow to absorb the shock but flight bows are feather light in the hand to start with. Steve