Author Topic: Bow design and development  (Read 40918 times)

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Offline Stick Bender

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Re: Bow design and development
« Reply #45 on: November 03, 2018, 10:40:03 am »
Ben how long is your riser & power lam ?
« Last Edit: November 03, 2018, 10:50:32 am by Stick Bender »
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Offline Bayou Ben

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Re: Bow design and development
« Reply #46 on: November 03, 2018, 11:38:34 am »
The riser is what I normally consider a powerlam.  Just bamboo/riser/maple/osage.  It’s 10.5”.  Bow is 62 ntn, so I needed more working limb that’s why I made the riser or powerlam a little shorter than my others.

Offline Halfbow

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Re: Bow design and development
« Reply #47 on: November 03, 2018, 06:54:06 pm »
Half bow, my thought behind forward handle and string angle is as you draw the bow back your string angle increases.  If you put let’s say an inch of handle up front as opposed to the belly and you pull your bow back to 28” then you would have the same angle as pulling a traditional belly handle bow 27”.  Not that big of a difference it seems, but it’s definitely something.  And in that same example, a wooden bow has the benefit of less stress, as equivalent to only pulling a belly handle bow 27”.  Those 2 coupled together should result in a less stressed belly with more energy storage.   
A FG bow doesn’t benefit from less stress since it has no memory, so it leads me to believe the string angle on those last few inches are more than insignificant.  Plus on most FG bows with big risers, they are putting closer to 1.5” up front. 
We’ll see though.   These are just unproven thoughts in my head at this point. 

Yes, I'm with you. It will indeed make the string angle that of a 1" shorter draw. But... if you're willing to come with me on a bit of a silly thought experiment here. If all else is equal, say if you were to take an already made bow and saw the handle buldge off the belly and stick it to the back (assume you find a way to do that which doesn't compromise the integrity of the construction). Now your bow's handle has been moved forward an inch, and everything else is untouched.

You have made the bow safer. Drawing to 29" will strain the bow as much as drawing to 28" used to. But it will also make the bow weaker at any given draw length. Drawing to 28" will get you the same poundage as drawing to 27" used to. Also, without changing anything about how the limbs are bending or the length of the string, you have changed your brace height from say 7" to 8". So to get the same length power stroke, you would have to draw it one inch farther anyway. But if you drew to 28" before moving the handle, and to 28" after, you'd find that you'd ended up with a bow with a lighter draw weight and a shorter power stroke.

Maybe you don't want it to be weaker, so you add some thin belly lams to get the poundage back up to where it was. And maybe you don't want a higher brace height so you lengthen the string a bit. You end up with a bow with the same draw weight, brace height, and power stroke length as the original. But for what trade off? Well the most obvious one is that your limbs are heavier now. Also, when you lengthened the string, you let the limbs bend less at brace. So I think you would find that your bow has less string tension at brace than it did in its original form, which means the f/d curve would be less fat than it was originally, which means more stack, and less stored energy. I think moving the handle forward will have near identical effects to deflexing a bow. All the same pluses and minuses.

If you're after good string angle (which I agree is important), wouldn't recurves help a lot more?

But  "simpler" modern designs greatly exceeded the Turkish records.

The Turkish data from Adam K doesn't really show a 200 fps 10gr/p trend.

Modern bows use modern materials. And not just modern bow materials, but modern strings, carbon arrows, etc. This gives an advantage. And also innovations like center shot. This is kind of my point.

So yes, the old Turkish records have been soundly beaten. But even so, I think "greatly exceeded" is a bit of an exaggeration. Setting aside compound bows, the Turk's numbers aren't exactly laughable. And when compared to our attempts at primitive material bows, they're amazing. As far as I'm aware, a modern attempt at a primitive materials bow has yet to beat the old flight records. Generally the primitive bows we are happy to call impressive today are shooting a fraction of the distance.

We are not the inheritors of 100 generations of unbroken bow making knowledge living in a society where you start learning archery as a toddler and live and die by the bow. Our connection to that knowledge got damaged when warfare moved on from archery. Even our attempts at faithfully recreating asiatic composite bows fail to live up to their antique counterparts. However, modern materials have helped us a lot. But it seems to me like we achieved a convenient, easy to maintain, and long lasting modern bow which also preformed admirably, and (mostly) stopped there. When we might have the ability to take performance who knows how much further. I see few people trying to take it in the direction I'm curious to to see.

I'm not holding up Turkish bows as the greatest design possible or anything. With modern knowledge and science we can point out improvements. But I think the asiatic composites were on to something. They were chasing some universal concepts that I think are simply true. I could talk about many examples, but just to pick one: the more reflex, the more energy a bow will store at the same draw weight. I really don't see any way around that. If anyone is finding that adding reflex is causing worse performance, the issue is probably with the materials. Wood will obviously fail or break down in such high stress designs. Perhaps fiberglass isn't good for the job either. If tests show that fiberglass bows are slower when bent that far (I haven't actually seen these results, but it seems plausible to me), then fiberglass has some kind of internal friction or some inefficiency when bent so extremely. That's not an argument against the high reflex concept, that's just an argument that fiberglass is not the ideal material for the ideal fast bow.

Maybe no material in the universe can spring back from extreme bends as well as horn and sinew. That would be interesting to know in itself. I'd enjoy it if there were true. Go nature. That would indeed suggest that the old asiatic composites got nearly all the performance out of highly reflexed bows as ever could be. But if anyone were to suggest that, I'd be immediately skeptical. Nature is amazing, but modern material science is too. There's got to be some material or combination of materials that can bend that much, store that much energy, and be lighter/spring back faster. And it's hard to imagine how such a bow wouldn't be breaking records in its category.
« Last Edit: November 03, 2018, 08:03:09 pm by Halfbow »

Offline DC

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Re: Bow design and development
« Reply #48 on: November 03, 2018, 07:38:24 pm »
I redid the experiment I mentioned back a bit. The first two pictures show the setup. Two 30" limbs, same taper, one straight and one I heat treated some reflex into. Two slots cut into the 2x4, one straight and one at an angle to make deflex. A bunch of nails 1" apart so I can pull the "bow" 1" and then mark it. This is a half bow. Don't feel that i need the other half.
  I put a limb in the slot and adjusted the string length for equal brace height. Then I marked the tip. Moved the string down one nail and marked the tip again. Repeat 27 times. Then I measured the lever length from the base of the limb to the first mark and again to the last mark.
  The second picture is the results. Line "B" (I screwed up the labeling, sue me ;D)is the straight limb in the straight slot. Lever length is 28 1/8" at brace and 27 3/16" at FD.
Line "A" is the reflexed limb in the straight slot. Lever length is 28" at brace and 27 3/4" at FD
Line "C" is reflexed limb in the deflexed slot. Lever length is 27 1/2" at brace and 28" at FD
The lever length is shorter a full draw on the straight limb. The lever length is about the same on the straight handled reflex limb. The deflex reflex lever length is longer at full draw. It's not a big difference but there is 5% dif between the best and worst.

Offline Badger

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Re: Bow design and development
« Reply #49 on: November 03, 2018, 07:57:48 pm »
    There is a lot you can do with horn and sinew that you simply cannot do with wood. With regular hunting arrow weights the horn sinew bows are not all that much better than well made wood bows but with light flight arrows and short bows they can excel even though not many shooters today are getting the distances that are possible a few are getting some pretty impressive distances. The record shot by the sultan has been called in question and I myself am not convinced it was a real shot. But we do know it was very possible.

Offline Stick Bender

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Re: Bow design and development
« Reply #50 on: November 03, 2018, 08:06:45 pm »
Asiatic composite bows have awesome performance with the highly reflexed design & there's guys around here making them with great performance but a lot of the old ones where in the 100 lb plus class the old adage if you want the bow to go faster pull it farther or make it heavier with the right design apply's  I don't think modern materials would have a issue taking the stresses of that much reflex & I know there are guys making them but never really saw any performance stats on them ,like you said maybe not the best design for the material , I think what's not discussed a lot with design is consistency & durability and the horn composite bows certainly have it , I think every material has it's idealized design the trick is finding it , I think chasing speed can be over rated ,I have some very fast bows but don't like some of them the way they shoot the bow to me has to be smooth drawing user friendly ,accurate ,durable type bow for me to like it , I think one size or one material or one design doesn't fit all , it seems to me from bows I have built there is always trade offs in design !
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Offline Del the cat

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Re: Bow design and development
« Reply #51 on: November 04, 2018, 01:34:54 am »
@ DC
Nice experiment,write up and pics... thanks for posting :)
Del
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Offline DC

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Re: Bow design and development
« Reply #52 on: November 04, 2018, 09:15:05 am »
Thanks Del, I was thinking about it last night and I'm wondering if leverage has anything to do with performance. It crossed my mind that because you're using the same lever to store the energy as you are to harvest the energy there might not be a gain.

Offline Del the cat

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Re: Bow design and development
« Reply #53 on: November 04, 2018, 10:10:34 am »
Thanks Del, I was thinking about it last night and I'm wondering if leverage has anything to do with performance. It crossed my mind that because you're using the same lever to store the energy as you are to harvest the energy there might not be a gain.
Even if it's the same lever there may be a gain if the variation is F/D curves gives a smoother acceleration to the arrow... even if the area under the curve is the same, maybe slight changes give a smoother more efficient power delivery and leave less in the bow.
I like your word "Harvest" ... they may have the same energy stored, but the D/R presumably harvests it better :)
Del
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Offline Badger

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Re: Bow design and development
« Reply #54 on: November 04, 2018, 10:34:52 am »
   In recent years I have kind of gotten away from the maximum speed thing but it does still fascinate me. At some point when you reach the higher levels perfection of execution starts to play in more significantly. I was trying to find this list I made several years ago that attempted to isolate all the ways we could store more energy, all the things that rob energy and all the things that improve efficiency.

   Energy losses are for the most part confined to hysteresis and vibration or distortion of the limbs. 
   Energy storage is for the most part a product of geometry.

   Adding length to the bow is the easiest way to increase energy storage but not always a very efficient method. Adding reflex and curves to increase tension and lower string angles are probably a more efficient method but also carry a risk of added vibration. This is where we tend to experiment the most and get a lot of mixed results. The more curves in a bow limb the more complicated it gets. Every inch of the limb responds to its particular string angle relationship throughout the draw. Some of the forward handle bows or heavily deflexed bows with curves at the ends do a good job of keeping string angles low throughout most of the draw but also require a lot of working limb which gives the bow more opportunity to distort or vibrate toward the end of the power stroke. Reducing outer limb mass cuts back on the momentum the limbs carry and gives the arrow a little more control over the bow limbs.

     I think what is most fascinating is how we can try different strategies, not just different designs but strategies that have to be executed through designs. My favorite strategies involve limiting the amount of working limb as much as possible reducing opportunity for vibration. This carries a higher risk of set and hysteresis so it often requires wider working limb areas and flawless tillering in those areas. It also lends it self well to more conservative designs not using as much curve in the limbs or excessive reflex.

      My favorite method which I have never come close to perfecting and I think in the long run will prove out to be the most effective involves limb tapers matched to the curves in the bow which will allow for the limb to uncoil kind of the same way a fly line uncoils when cast. This is where the last part of the limb to uncoil is toward the tips. I still believe this design would allow for more working limb with less vibration and be more efficient. It would also allow bigger curves and more net reflex.

      Hysteresis in our bows is almost entirely a product of set and is one of our biggest losses. All we can do here is keep set low by using dry wood and making sure we have enough working limb and wide enough limbs along with flawless tillering.   

Offline DC

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Re: Bow design and development
« Reply #55 on: November 04, 2018, 10:51:42 am »
I'm jumping from pillar to post here but do you think it matters when the arrow reaches maximum acceleration? Is it better for the arrow to get a big kick at the begining and then "coast" or is a nice smooth increase in acceleration with the big kick at the end better? I'm thinking about the positive effect of early draw weight here. Also compound bows have that funny F/D curve and they are fast. I have no idea how a person could use this info in a selfbow but it is info. :D

Offline Del the cat

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Re: Bow design and development
« Reply #56 on: November 04, 2018, 11:05:48 am »
I'm jumping from pillar to post here but do you think it matters when the arrow reaches maximum acceleration? Is it better for the arrow to get a big kick at the begining and then "coast" or is a nice smooth increase in acceleration with the big kick at the end better? I'm thinking about the positive effect of early draw weight here. Also compound bows have that funny F/D curve and they are fast. I have no idea how a person could use this info in a selfbow but it is info. :D
Think of two identical dragsters on the track, one with an experienced driver and one with a rookie ... which would you bet on?
Too much kick up the pants wastes a lot of energy flexing the arrow more than necessary. The smoother acceleration curve is more efficient... a regular bow doesn't coast the arrow, it is accelerating through the whole power stroke, but the rate of acceleration is decreasing.
So at the start you have the most force, but the arrow also has most inertia being stationary.
A compound gets the arrow moving and increases the acceleration as the arrow speeds up ... back to the dragster analogy.
Note I've prob' take a bit of a liberty with some of the terms I use but it's the idea I'm try to express rather than an exact analysis.
Del
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Offline DC

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Re: Bow design and development
« Reply #57 on: November 04, 2018, 11:13:41 am »
Thanks Del, that was my gut feeling. I wonder if you had a compound that stored the same amount of energy as a self bow if it would still be faster.

Offline Badger

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Re: Bow design and development
« Reply #58 on: November 04, 2018, 11:30:29 am »
    A compound isn't really a true bow.

Offline Del the cat

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Re: Bow design and development
« Reply #59 on: November 04, 2018, 11:50:50 am »
Thanks Del, that was my gut feeling. I wonder if you had a compound that stored the same amount of energy as a self bow if it would still be faster.
I'd guess yes as the limbs would travel a shorter distance so would be quicker and the acceleration would be smoother, prob have a longer draw too with a few extra inches of low weight hold off (or whatever it's called )
But I think we need to stop thinking and have a beer instead ;)
Del
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