Primitive Archer
Main Discussion Area => Bows => Topic started by: mmattockx on March 18, 2020, 01:21:04 pm
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It seems that wood bows can be just as fast as laminated fibreglass (or carbon fibre) bows when done properly. I can accept that fact, but I am curious about it. I am an engineer and have a solid grasp of structural design along with mechanics of materials and find this pretty surprising, considering the material property advantages that fibreglass and carbon fibre have over the various bow woods.
Can someone explain the details of how this is possible?
Thanks,
Mark
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My opinion? Its very possible, but rarely happens as often as we hear it about it. I own 45-50 bows from self, to glass to all wood/boo laminated. Nothing holds a candle to a well built glass recurve. Its clear as a bell when you shoot it next to a self bow of equal draw weight arrow after arrow.
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By optimizing the design for the materials you are using.....usually through a whole lot of trial and error! My fastest glass/carbon bows are around 192fps @ 10gpp. My best hornbows are about the same. I know which I prefer making that's for sure!
A lot of glass bows I've actually tested are pretty poor performers but they will do it indefinitely. Neither glass nor carbon excel in compression.
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By optimizing the design for the materials you are using.
that and using the best possible materials utilizing the best possible craftsmanship, etc
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By optimizing the design for the materials you are using.....usually through a whole lot of trial and error!
I understand that, but a fully optimized wood bow shouldn't be able to run with a fully optimized composite bow. Or at least I can't see how it should be able to, based on the materials.
You are correct that neither carbon or fibreglass are that great in compression, but no woods really are, either. A well supported carbon skin should be able to handle stresses that will pulverize any bow wood available. Maybe the composites aren't being optimized for speed, but for other qualities? Or there is lots of bad design out there, as you mention?
It isn't a big deal either way, but it does make me wonder about the deals. The engineer in me wants to know why things happen, not just that they do.
Mark
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This is an interesting question and is an area I have spent a lot of time studying over the last several years. The best possible performance of a bow depends on the the mechanical properties of the materials used to make the bow, and string. It also depends on the testing parameters that the bow is judged against. It turns out that a bow made of suitable bow wood uses the nearly the full potential of the wood it is made out of to provide the structure, and energy storage capacity for a decent 40-50 pound bow drawn to 26-28 inches. This coincides pretty well with the needs of many archers. With a modern low-stretch string, an optimal all-wood now can keep up pretty well with modern composite designs.
For the same draw length and draw weight, modern glass composite designs typically don’t even come remotely close to taking full advantage of the energy storage and structural properties of the glass for a typical 50 pound draw weight at 28” draw length. In order to achieve to push glass as close to its limits as the wood bow, the bow would need to be made so narrow, and so thick, that it will not have enough lateral stability to even function. It will just end up bending sideways. So these glass bows end up much heavier than they theoretically should be.
In contrast, glass is really capable of producing some mind blowing performance when the design of the bow is optimized to take full advantage of its properties. For example, crossbow limbs in excess of 300 pounds of draw weight, and short draw lengths which are capable of sending a hunting weight arrow downrange at 400 fps. These bows are not one shot wonders either. They even carry a manufacturers warranty and these will wear out the one shooting them before the bow limbs give out. A wood bow designed to the same extremely heavy draw weight and shortish draw length would have to be built with such wide and long limbs, that it couldn’t come close to the same level of performance.
Horn and sinew composites are in a similar bucket as the glass bows. If the draw weight is low-to-moderate, and draw length is long, then they don’t perform much better than an all-wood bow. But heavy draw weight designs take much better advantage of the materials and performance really starts to shine.
Carbon fiber is its own unique animal. It depends on how the carbon is configured. Unidirectional carbon has superior structural performance to glass, but it is inferior at storing strain energy. This forces carbon designs to have more working limb than a glass bow. A typical 50 pound at 28” draw bow made with unidirectional carbon is also pushed closer to its material limits compared to a typical glass bow designed to the same draw length and draw weight parameters.
There’s much more to it, but this covers it at a high level.
Alan
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Alan,
Thanks for that explanation. It makes sense if we are getting everything out of the wood bows but are not able to properly take advantage of the composite materials for a hand bow.
Mark
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You could have just explored how woods as diverse as ERC and Ipe can do the same things more or less. No need to even mention glass and carbon. ;)
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You could have just explored how woods as diverse as ERC and Ipe can do the same things more or less. No need to even mention glass and carbon. ;)
In the end, it's all really the same question of optimizing the design for the material used. I promise not to speak of those devil materials again.
Mark
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Should I ever decide to learn how to use my my chronograph for a comparison shoot, I will be sure to disguise the "devil bows" by appropriate pseudonym! I have one of each, but I am a hoarder of sorts, and sentimentality gets into the situation! Science, my boy, science! You have tweaked my interest! (lol) (SH) >:D
Hawkdancer
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Science, my boy, science! You have tweaked my interest! (lol) (SH) >:D
Hawkdancer
I will be interested to hear of your results if you do the test. It isn't that hard to find info, though. DC (among others here) seems to regularly make bows that shoot into the high 180fps range at 10gpp and there is lots of data floating around showing that higher end target recurves aren't much better than that with the same 10gpp. That is a heavy arrow by target standards, though, and they may have more of an advantage with the lighter arrows they typically shoot (more like 9gpp or less) but I can't say.
Mark
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Many of the higher end recurves arn't designed for speed as much as they are built for accuracy and smoothness for the target shooters. the fg speed demons probably just moved on to wheelbows
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How can one bow be more 'accurate' than another? :)
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One has properly matched arrows and one doesn't :)
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He meant to say that other bows are less accurate, not that target bows are more accurate. ;)
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What Pearl said.
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I agree with Alan's post. I have built a few Osage selfbows that
get real close to 50# glass bow records. That being said
The consistency of the glass bows are easier to achieve by far.
Arvin
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He meant to say that other bows are less accurate, not that target bows are more accurate. ;)
yes, bows designs maximized for speed may not always let the arrows leave as smoothly as others. the trade off shows in flightshooting where both speed and smoothness count.
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When I'm using my shooting machine I always pull the arrow out of the target before shooting again. The chances are too high of hitting the other arrow. I have to keep moving the target or after two or three shots the arrows start to go though the target. I don't think there is any such thing as an inaccurate bow. If you could hold the bow absolutely the same way and use the same arrow every shot they would pretty much all go in the same hole. That's my thinkin' and I'm stickin' to it ;D ;D
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Has anyone ever tested a shooting machine with built in human error? if the release or grip mechanism had vibrating components the arrows would spread into measurable groups.
The grouping size is more a measure of something like ‘forgiveness’ but I think it’s what people intuitively mean when they say a bow is accurate. Obviously bows don’t have an inherent accuracy quality, but bows and archers together do. If the archers errors are standardized by a machine then bows could be compared and measured in this aspect
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You go ahead and do that ;D ;D I'll sit back. Good luck trying to build a machine with unlimited repeatable adjustments. ;D ;D ;D I'm having enough trouble building a clamp to hold the bow the same each shot.
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Having made both wood & glass & glass /carbon bows I would agree design is key in what ever medium you use but my best glass/carbon bow bests my best wood bow by 20 fps but does that mean any thing ? Its not really apples to apples because the wood bow would never survive the hybrid glass/carbon design , my best glass/carbon is well over 200 fps at my 31" draw , I think if you compare strait limb LB designs with wood vs glass or glass/carbon the playing feild is narrowed and in some cases the wood would out perform the glass or glass/carbon bows ! Thats just my personal opinion having made both !
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That seems a reasonable take on it )P(
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Brad I agree it's reasonable, most guys I know that are making the ASL or HH follow glass bows are doing between 139fps & 170 fps , they don't really buid the bows for speed but for shooting quality's & they are amazingly smooth shooters but most shot in well maid self bows & certainly reflexed self bows will easily out perform that in fps !
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If you took random test samples of glass recurve bows that have been made in the last 50 years, and compare them to random test samples of selfbows that have been made in the last 50 years ,and backed bows in my opinion, and on "AVERAGE" the glass bows would be smoother drawing,faster, and more durable. Some guys on leather wall who make glass bows would like to think their glass bows will compare in every way to wheel compound bows.In the real world that is not going to happen any time soon. JMO. I have a passion for all kinds of bows, and own, and shoot self bows,backed bows, recurves, compound, and cross bows, and am not bias.