Primitive Archer
Main Discussion Area => Bows => Topic started by: stuckinthemud on October 16, 2019, 08:02:53 am
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Instinctively, I have always assumed that reflex is good and deflex is bad but recently I have been pondering this, once the bow is braced, it doesn't care what its state was before that, the string will not allow the bow to return to its deflexed or reflexed shape so they have no real effect on anything once the string is released. I think, that what deflex and reflex cause is a heavier or lighter build, a deflexed bow can be overbuilt - lets say you draw 25" and the bow was deflexed 3 inches, then it has little pre-stress so to get a 50lb draw weight you would build it with thicker limbs, it might have a slower cast though, due to the heavier build but it is only bending 22 inches. A 4-inch reflexed bow has bags of pre-stressing so to get it to bend to 50lb at 25inches you would build it relatively light, so you get a faster cast as it is bending 29 inches. How far off am I ?
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Quite a bit since the two are generally used in combination rather than separately.
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I am fine with being a long way off, and d/r bows are something I have always wondered about since the one should cancel the other one out, shouldn't they? I know they can be very very fast, but I don't really understand why, maybe the deflex creates a very highly stressed mid/outer, the limb reflex section is still very thin and bendy, though. Maybe heavier built than they would be without the deflex? Also, they kind of cheat the system as the reflex is visible at brace, so the string is not preventing the bow going into reflex where in a straight limb the string does prevent the bow movement going into reflex. Would all that mean I am not so far off, the deflex allows a heavier build, the reflex is lighter built to bend further??????
Anyway, for my question, might be best if we assume a straight limb deflexed or reflexed at the handle. ;)
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When speaking of wood bows generally speaking you need more mass for higher stress designs than you do lower stress designs. The limbs might be thinner but they will also need to be wider. Reflex adds tension at brace and deflex is mainly to achieve better string angles for more favorable leverages that store more energy.
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Heres how i’m thinking about this, but I haven’t built many r/d bows to speak from experience. Reflex and deflex aren’t exactly opposite so they don’t cancel out. If you reflex near the grip, that can make for a high stacking design while recurves at the tip actually improve string angle. You could totally cancel out your reflex with deflex and still benefit your force draw curve because of string angles.
When the string slams home and the tips stop moving, all that force used to brace the bow isn’t completely wasted. Pre stressing fattens the f/d curve representing more energy stored. This isn’t an efficient use of available stress, but it’s better than not using it at all.
Most horn sinew designs can afford plenty of reflex to fatten the f/d curve, but in a stressed wooden design, there is no leftover stress to throw away. Instead, stress is better applied where it can benefit the arrow more efficiently—during the power stroke and not during bracing, hence the r/d profile.
Contact recurves are a way for r/d bows to still have a fat initial f/d curve by starting off as a short stiff bow but without overstressing the design at full draw like reflex would cause.
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Instinctively, I have always assumed that reflex is good and deflex is bad but recently I have been pondering this, once the bow is braced, it doesn't care what its state was before that, the string will not allow the bow to return to its deflexed or reflexed shape so they have no real effect on anything once the string is released. I think, that what deflex and reflex cause is a heavier or lighter build, a deflexed bow can be overbuilt - lets say you draw 25" and the bow was deflexed 3 inches, then it has little pre-stress so to get a 50lb draw weight you would build it with thicker limbs, it might have a slower cast though, due to the heavier build but it is only bending 22 inches. A 4-inch reflexed bow has bags of pre-stressing so to get it to bend to 50lb at 25inches you would build it relatively light, so you get a faster cast as it is bending 29 inches. How far off am I ?
I think what you're saying is exactly right, with the exception of one thing.
Yes, a bow that starts with its tips in front of the handle will have to bend farther to get to full draw than a bow that starts with its tips behind the handle. If you make both of these bows the same draw weight, the bow with its tips in front of the handle will have lighter and easier to bend limbs.
The part where I disagree with you is when you say it has no real effect on anything once the string is released. It is true that it could potentially have no effect on the bows tiller or geometry throughout its power stroke, but the forces happening will be different. The more reflexed bow has lighter limbs and higher initial string tension. Lighter limbs are easier to move, and the string tension will fatten the f/d curve. Both of these things have an effect on how fast that bow springs back, and how fast the arrow goes.
These things are good, but if you try too hard to get these benefits you just quickly run in to the limits of wood. With highly reflexed designs, you get stuck between needing less wood to get to the draw weight you want, but needing more wood to avoid exploding/crushing.
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so putting the two together in a R/D design means the inners can be built heavier, and the outers built lighter, effectively changing the location in the limbs where working energy is stored?
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so putting the two together in a R/D design means the inners can be built heavier, and the outers built lighter, effectively changing the location in the limbs where working energy is stored?
I understand why you asked that, but I don't think so. It's more about how far the limb can bend overall. Reflexed bows need to bend farther to get to full draw, deflexed bows less far, right? So if you have an R/D design where the tips are exactly in line with the handle, then those limbs just need to bend as much as a straight bow's limbs. Could be flexible where it's deflexed and stiff where its reflexed, or vice versa. Could be flexible near the handle, or could be whip tillered. Just so long as the limbs overall can bend as far as a straight bow's limbs.
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Could be flexible where it's deflexed and stiff where its reflexed, or vice versa. Could be flexible near the handle, or could be whip tillered. Just so long as the limbs overall can bend as far as a straight bow's limbs.
maybe, except energy used to move more limb would reduce efficiency....
as is the case with many things, it's most likely a little of this and a little of that all added up to give an advantage
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Could be flexible where it's deflexed and stiff where its reflexed, or vice versa. Could be flexible near the handle, or could be whip tillered. Just so long as the limbs overall can bend as far as a straight bow's limbs.
maybe, except energy used to move more limb would reduce efficiency....
as is the case with many things, it's most likely a little of this and a little of that all added up to give an advantage
Totally agree. To be clear, I wasn't saying the things I listed were good ideas, or recommending any design over another. Just was talking about concepts and what's possible. If I started talking about what I think is good, that would be a whole other discussion.
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I think Steve is right on the money, I think the designs claim to fame is the superior string angle you could certainly build a reflex bow of the same length & draw that would have much greater early draw weight but would have less performance then the D/R of the same length/draw & mass !
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When speaking of wood bows generally speaking you need more mass for higher stress designs than you do lower stress designs. The limbs might be thinner but they will also need to be wider. Reflex adds tension at brace and deflex is mainly to achieve better string angles for more favorable leverages that store more energy.
I'd like to add to this if I may. Deflex also forces more thickness to be in a limb because it offers a leverage benefit over a straight or reflex limb. As a result, the limb has to be thicker to accomodate a reduced bending radius. That transferes to your reflexed portion so it doesnt end up overly thin and wide, but rather thicker and narrower which drops its mass allowing it to be faster.
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Guys I think the biggest advantage of a deflex in a wood bow reduces set and pushes the working part of the limb out on the bow limbs. That being said I like to load early and not have stack. The trick in wood bows is to prevent set with the reflex only design. I assume we are talking about incorporating both in a bow or just reflex in the bow. Arvin
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I think Steve is right on the money, I think the designs claim to fame is the superior string angle you could certainly build a reflex bow of the same length & draw that would have much greater early draw weight but would have less performance then the D/R of the same length/draw & mass !
I agree with Steve too, I'm pretty sure. (Steve please correct me if I'm wrong about that and we disagree)
Common D/R bow designs definitely have great geometry for efficiency, and offer great string angles. And yeah I agree, it's easy to make a D/R bow that outperforms a reflexed bow of the same length and draw. Some of that is because of limitations of wood, but a lot of it is also those geometric benefits.
My one quibble with what you said is about mass. Assuming the same material, same length, and same draw, I think you'd have a hard time getting a D/R bow's limbs to be the same mass as a reflexed bow's limbs. Not without going with pretty unideal limb dimensions.
Deflex also forces more thickness to be in a limb because it offers a leverage benefit over a straight or reflex limb. As a result, the limb has to be thicker to accomodate a reduced bending radius.
Exactly. And the deflex further reduces the bending radius, requiring a yet more stout limb to get up to draw weight.
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My opinion....Arvin nailed it!
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I think Steve is right on the money, I think the designs claim to fame is the superior string angle you could certainly build a reflex bow of the same length & draw that would have much greater early draw weight but would have less performance then the D/R of the same length/draw & mass !
I agree with Steve too, I'm pretty sure. (Steve please correct me if I'm wrong about that and we disagree)
Common D/R bow designs definitely have great geometry for efficiency, and offer great string angles. And yeah I agree, it's easy to make a D/R bow that outperforms a reflexed bow of the same length and draw. Some of that is because of limitations of wood, but a lot of it is also those geometric benefits.
My one quibble with what you said is about mass. Assuming the same material, same length, and same draw, I think you'd have a hard time getting a D/R bow's limbs to be the same mass as a reflexed bow's limbs. Not without going with pretty unideal limb dimensions.
Deflex also forces more thickness to be in a limb because it offers a leverage benefit over a straight or reflex limb. As a result, the limb has to be thicker to accomodate a reduced bending radius.
Exactly. And the deflex further reduces the bending radius, requiring a yet more stout limb to get up to draw weight.
I think with mass, a R/D gives you less mass. We all know the rule where a bow twice as thick is 8X stringer than one twice as wide. The side affect is that a bow twice as wide is almost twice as heavy ( EXTREEM GENERALIZATION to carry the point ). So when you deflex, you allow the reflex limbs to not need to be so wide, which drops the mass even though you are thicker in the limb to accommodate the reduced bend radius the deflex allows for.
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I think with mass, a R/D gives you less mass. We all know the rule where a bow twice as thick is 8X stringer than one twice as wide. The side affect is that a bow twice as wide is almost twice as heavy ( EXTREEM GENERALIZATION to carry the point ). So when you deflex, you allow the reflex limbs to not need to be so wide, which drops the mass even though you are thicker in the limb to accommodate the reduced bend radius the deflex allows for.
I get what you're saying, but I don't think so. Imagine an R/D bow. Deflex in the handle. Cut it in half and splice it back together so the limbs are straight. Now it's a reflexed bow. Now the draw weight is higher. It probably won't even pull back to full draw anymore without breaking. Scrape some wood off the belly to get it bending more. Make those limbs thinner. Scrape till you get the draw weight down to what it was. Now you have a reflexed bow that's the same draw as the original, but with lighter limbs.
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but to prevent the limbs from taking massive set from the increased reflex they would need to be wider and therefore heavier would they not?
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I mean potentially. But potentially not. We would need to pin down more details to have a better idea. How wide are the limbs? How deflexed is the handle? How high is the draw weight? How long is it?
To say that we would absolutely need to widen the limbs is to say our hypothetical project here is doomed from the start. But I've seen this sort of thing actually done. Cutting an old bow in half, re-splicing at a more aggressive angle, and re-tillering. It worked well. No more wood was necessary on the sides. Keep in mind that by scraping the belly, we are making the limb thinner, and thus more safe and less likely to take set.
But if you imagine a narrow limbed D/R bow that is extremely deflexed at the handle (so we have to change the angle drastically to make it straight at the handle), yeah it probably won't work. But it's just as easy to imagine subtly deflexed and wide enough D/R designs for which it will work. But all that points out is that reflexed bows are less forgiving to make. Which is definitely true. Either way, my point stands.
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I think there are 2 ways to look at it.
1. The geometry and physics behind the D/R design is probably beyond most of us (it's certainly beyond me)!
2.To explain/understand it, I look at it this way:-
The reflex adds early draw weight and improves the string angle approaching full draw. However wood can't take the strain resulting from a big reflex and that's where the deflex comes in, enough deflex is added to nullify the excess strain whilst still maintaining the advantages of the reflex.
Dunno if this explanation really holds water, but it seems intuitively sensible.
Del
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I'm going to hold fast. With the addition of deflex, you drop your bend radius and need to keep the limb thicker to accommodate that. You certainly CAN make it wider instead, but width adds mass, 8x faster than adding thickness. So the results you can get will depend on your built technique.
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Interesting conversation. I almost never post but I can’t resist this one. It seams to me that with any reflex your increasing the forces of compression and tension. Most woods are stronger in tension so the belly is at risk of being crushed. The greater of those forces are on the surface area, lessening towards the center. I would believe more mass in width is needed, giving the needed material to resist those forces without crystalling/checking. I suspect It could also minimize the mass in the neutral section of the limb. These are not so much my thoughts as they are my understanding / experience with Steve’s mass principal. I’d love to hear any expansion on this principal in how it pertains to the D/R limbs.
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I'm going to hold fast. With the addition of deflex, you drop your bend radius and need to keep the limb thicker to accommodate that. You certainly CAN make it wider instead, but width adds mass, 8x faster than adding thickness. So the results you can get will depend on your built technique.
My thought experiment was exactly an example of a D/R bow having thicker limbs to accommodate the reduced bend radius. No change in width between the 2 bows. That's what you're saying, right? With no change in width, the thicker limb is heavier. And the thought experiment is realistic, I've seen it done before. Just thinning the limb can be enough to get it happily bending more.
However, adding width does not add mass 8x as fast. The stat is: doubling a bow's thickness makes it 8x as a stiff, while doubling a bows width makes it 2x as stiff. The change in stiffness is the interesting bit there, and nothing is happening at 8x the speed. The change in stiffness is exponential.
But mass gets added linearly with how much volume you add. So long as your bow limb is wider than it is thick, making it a millimeter wider will actually add less mass than making it a millimeter thicker.
So even in the cases where the deflexed bow could never be cut in half and converted in to a reflexed bow because the limbs are too narrow, if we could magically add mass to the sides, let's not get carried away with how much weight that would add. Yes, we all know that for any given stiffness a narrower thicker limb will have less mass than a wider thinner one. But we are not talking about the same stiffness here. Easier to bend limbs tend to be lighter. That's why lighter draw bows tend to have lighter limbs. If the difference in stiffness is significant, I think you'd have to have some pretty extreme paddle bow esque dimensions before the easier to bend limb actually became heavier. And we know that good reflex bows are possible without looking like extreme paddle bows.
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so here is a thought to consider....
if a glass bow is not subject to the same limitations as a wood bow (set), then why do so many glass bow designs incorporate the deflex along with the desirable reflex?
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Willie ask the same question that was in my mind , glass D/R bows where there's no worries about over stressing the materials, but they achieve superior performance over reflexed glass bows of identical mass why? I think because of the superior string angle/leverage same with wood I think another real advantage of the design is you can make a shorter bow for a given draw length vs a strait reflexed bow do to the deflex ! Fred Bear spent a life time perfecting the D/R design !
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Deflex reflex leaves less residual energy in the bow after the loose so they are more user friendly.
Fred didn't actually devote a lifetime to that design. Probably only 30 years if that.
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Fred new his stuff along with a few others. Yes this is all true in a glass bow . The mass ratio between glass limbs and wood are different are they not? The make up of compression strength is also different. So comparing the same design is not a good comparison in my opinion. The stable r-d bows end up with to much mass on the otter limbs imo. Causing shock and slows the bow. This is in a wood bow more than a glass bow. I have built both and prefer Longbows with only reflex plus what ever set you end up with. Again set is the enemy in any wood bow no matter the design! Arvin
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Arvin maybe the glass vs wood was not the best example ,all thought the same design principals are at play with the exception the wood being a less radical bend as a example of that the guys I know that are making some of the BBO, BBH ect are getting some pretty good numbers over a ASL glass bow of the same length and draw/weight if you compared the BBO in the example to the glass ASL full draw profile the string angle on the D/R BBO with the mild D/R is still superior to the glass ASL even with it taking set granted the glass has a slight increase in mass, I'm not arguing that set & mass location doesn't play a roll in the design in the wood D/R ,I'm just saying that the better the string/leverage angle in any bow regardless of material the more superior the performance & Pat is right about the design being user friendly especially with the shorter bows designed for longer then normal draws , there are guys out here playing with some more radical bent bamboo backed bows it would be interesting to see the numbers on those ! I think Steve said the same thing I did in 2 paragraphs vs my long winded version....lol
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Some highly reflexed asiatic style glass bows do put up good numbers. But I agree with PatM, D/R bows are more user friendly. Easier to string, easier to tune, easier to be accurate with, less delicate etc etc. But they also perform well. It's a good choice for commercial fool proof bows.
If you accept what I've been saying about reflexed bows having higher string tension and lighter limbs for the same draw weight (as stuckinthemud said in his original post), it might seem odd that D/R bows can hold their own in performance. As many have been saying, I think it's largely due to the geometry and string angles.
Recurved tips are good, but they don't make the difference here. You can recurve the tips of both reflexed and deflexed bows. The difference maker is the deflex.
I can actually shed some light on the geometric benefits of deflex. It's not terribly mysterious. In fact, I think I can sum it up in one sentence:
A straight line is the most efficient way to cover distance, and deflexed bows are usually less bent at full draw, so the tips end up farther from the handle.
To illustrate:
(https://i.imgur.com/WjkY0bt.jpg)
These two bows have exactly the same limb length, the same brace height, and the same draw length. Yet you can see that the deflexed bow ends up with better string angles, and is acting like a longer bow at full draw. These bows start with straight limbs just to make it simpler, but for basically any limb shape, curved, recurved, whatever, the more overall reflex a bow has, the farther its limbs have to bend. The farther they bend, the more their effective length changes. So the reflexed bow will usually have lighter limbs and higher initial string tension, but the deflexed bow usually has better geometry.
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Thats a great illustration & concept I really like bow B my current test bow has the same geometry in deflex but with working reflex & is one of the best performing bows for being a short bow of 58" drawn to 31" with the string angle of a much longer strait bow its my best performing short bow to date ! The other user friendly trate on these bows is when built right they have very little energy left over and zero detictable hand shock !
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Very interesting discussion, and this is a topic on which the answers have never seemed entirely complete. I came to the the whole D/R party late in the game. After building a handful of them over the current year, it was pretty obvious that the design does offer some real improvements over a reflexed bow. The why has been fairly elusive however. I think Arvin nailed a few of the key aspects so far as I can pin them down. Moving the bend outboard, getting the tips lighter and thereby reducing set, which cripples a bows performance at some level. You simply, so far as I can determine, have less wood moving a shorter distance, which increases the efficiency, coupled with the bow taking less set as a result. That's a winner in and of itself. But it doesn't tell the entire story. Glass bows benefit from the design without reduced set being a factor. I think you can go shorter with a D/R than it's reflexed counter part without suffering the consequences as early. Still not the entire picture though. I don't yet understand the differences (and may never) but I appreciate the discussion.
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Slimbob is right this topic is really interesting to illustrate some of the advantages of the design I will post this bow granted its glass test bow but all the same principals apply & Im planing a similar design in sinew/horn composite with less aggressive bends but I have made 10 of these over the last year different riser/ handle lengths & different working limb lengths & many different power lam wedge tip combo's & and different amount of reflex and tested performance on all but this bow is short for my 31" draw but maintains a great string angle with a total mass of 17oz with all the changes I found every time I effected the string angle in a negetive way the performance drastically decreased ,I think with a beffed up lower limb via a power lam on a bamboo backed bow you could achieve similar results & play with the design to achieve perfect ballance, I would bet set would be low performance would be on the upper end for wood ,but the bow posted has no stack to 32" draw the draw is butter smooth out to my 31" draw for a 58" bow !
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I agree to disagree. I would love to see that design in a selfbow and its cast. You guys are to far ahead of me in the math for me to totally understand the whole string angle stuff. Yet in a selfbow I know my limitations in a reflexed bow to an extent. The wood in a selfbow will only go so far without set depending on the design. Longer limbs vs short limbs and on and on. I am only talking selfbows or even boo backed bows into account here. If the belly crushes we loose. Turning great bow into a good bow. I think we might try some secret sauce on the heat treatment . Ok question? Has anyone ever heated a limb to say 350 degrees and brushed 140-160 degree hide glue onto the limbs and let cool the appropriate time for full cure???? If so what was the affects. If I am so far off the intended post please be kind and say Arvin this one is not for you. :D :BB. Arvin
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Stick Bender, yeah that design you posted includes many things that I would expect to make for excellent string angles, and an excellent bow. By having the limbs start out curved away from the string, they actually effectively get longer when you start bending them. That bow's limbs are pretty straight at full draw, which is great. That gets those tips especially far away from the handle.
You'd want to make it longer for a self bow, but the concept absolutely still applies and is possible. Because those tips only start out a few inches in front of the handle, it will strain the wood similarly to a long bow with a few inches of reflex. Make it as long as you'd need to for a long bow with a few inches of reflex, and you're good to make a self bow with a similar shape to the pictured bow. I'm actually working on a primitive materials bow that is an even more extreme design that uses some of the same principles.
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I agree to disagree. I would love to see that design in a selfbow and its cast. You guys are to far ahead of me in the math for me to totally understand the whole string angle stuff. Yet in a selfbow I know my limitations in a reflexed bow to an extent. The wood in a selfbow will only go so far without set depending on the design. Longer limbs vs short limbs and on and on. I am only talking selfbows or even boo backed bows into account here. If the belly crushes we loose. Turning great bow into a good bow. I think we might try some secret sauce on the heat treatment . Ok question? Has anyone ever heated a limb to say 350 degrees and brushed 140-160 degree hide glue onto the limbs and let cool the appropriate time for full cure???? If so what was the affects. If I am so far off the intended post please be kind and say Arvin this one is not for you. :D :BB. Arvin
Has anyone done this or are you all trying it before you comment??? Well I guess I better build a bow and try it. What is the best source for hide glue?
Arvin
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I havent used this glue for your purpose but its high quality hide glue very good stuff for sinew & so forth !
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Knox gelatin at the grocery. It's the best. Tim Baker started a very similar experiment but lost interest. I'd like to see what you are able to do with it, especially if you build up a thin layer and leave it. You will need some matrix to hold it and keep it from crushing under compression.
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Slimbob is right this topic is really interesting to illustrate some of the advantages of the design I will post this bow granted its glass test bow but all the same principals apply & Im planing a similar design in sinew/horn composite with less aggressive bends but I have made 10 of these over the last year different riser/ handle lengths & different working limb lengths & many different power lam wedge tip combo's & and different amount of reflex and tested performance on all but this bow is short for my 31" draw but maintains a great string angle with a total mass of 17oz with all the changes I found every time I effected the string angle in a negetive way the performance drastically decreased ,I think with a beffed up lower limb via a power lam on a bamboo backed bow you could achieve similar results & play with the design to achieve perfect ballance, I would bet set would be low performance would be on the upper end for wood ,but the bow posted has no stack to 32" draw the draw is butter smooth out to my 31" draw for a 58" bow !
I like this design although when I've thought about it my aim was to have it end up with straight limbs at full draw. That makes the limb lever longest as possible at FD.
String angle--- My gut says that string angle is probably a symptom, not necessarily a cause. You said that anything you did that affected the string angle in a negative way was a bad thing. Is that string angle at FD or through the whole draw? By negative you mean increasing the angle? What kind of things have you found that increase the angle?
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Sleek what is matrix??? My thinking is open the cells up and fill them with hide glue if it’s thin enough. Hoping to make the belly more dance without adding much mass. I started one . How long for full cure on the glue. Guess it depends on the thickness. Arvin
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DC, the bows you make with that design are great, and are a strong testament to how good the design can be. I think you're spot on, straight limbs at full draw is ideal. If your gut says string angle is just a symptom, I'm curious, does it have any feelings about what's the cause?
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Don yes I was talking FD/string angle ,a good example of negitive string angle is in Half bows reflexed bow drawing if you have length vs draw length ratio achieving good string angle is not much of a problem the trick is acheving it in short bows with long draw length, in shorter bows with long draw length it becomes a balancing act to still maintain good string angle in the pic there is another 58" bow compared to a osage self lever bow with slightly shimed forward leavers & a BBH thats approaching a neg angle all thought the more whiped BBH is a smooth shooting bow very user friendly the osage pic was under construction pic the tips where thined to the point of flexing and heat treated with 1/2 in forward ! Both natural bows are 68" !
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Ok stick bender which one wins the race. I am guessing the middle bow pic wins.
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Well it depends on what race as far as string angle there all acceptable the osage lever bow & the BBH are with in 2fps of each other the BBH has a better FDC the original 58" posted dwarfs them all both in FPS & FDC , I think for any given design & material there is a balance between working limb and string angle but for a 20 yard hunting bow Im comfortable with them all ! I will take user friendly over speed but try for both , I have bows that ring the bell at some crazy numbers but would not hunt with them, non user friendly ! Adam Korpowicz & Jack B Harrison have great exsplanation on this topic in there books !
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DC, the bows you make with that design are great, and are a strong testament to how good the design can be. I think you're spot on, straight limbs at full draw is ideal. If your gut says string angle is just a symptom, I'm curious, does it have any feelings about what's the cause?
Not really but possibly the actual lever length of the limb. A "lever" is the direct measurement from the fulcrum(grip) to the point of effort(where the string hits the bow) ignoring any bends. With a straight bow the lever gets shorter as the limb bends. Bad. With a reflexed bow the lever gets longer as the bow bends. Better but can be unstable and by the time you get the bow braced you've used up most of the bend. With an RD the deflex gives you your brace height without using up much bend and by moving the tips back it also stabilises the bow some so you can use more reflex. If you can arrange things so that the limb is straightest at FD then I think you would have maximised the lever length.
Also if you can move the the bend toward the grip you can shorten the actual string length. By that I mean the part of the string that isn't touching the bow. Then your braced lever length is short because the lever is measured to where the string hits the bow. This gives you a short lever when the bow is easy to pull and the lever lengthens as you draw it when it gets harder.
That was a lot of typing for a "not really" but those are my thoughts. I get the impression that some others here are swishing roughly the same thoughts around in their heads.
All that said if I understood the physics of bending a beam with a string maybe string angle would mean something ;D
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I really think you nailed it DC. The issue becomes stabilizing the limb from torque. That's where a wider limb comes to help, but with width comes mass, and the thinner limb is also the less efficient limb, so power in vs power our ratio starts dropping even though stored energy goes through the roof. That's the realm we play in.
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And also I think that a design is a design and will work no matter what the material is. It's just how extreme you can go depends on the material. Twisting and set become the limiting factors.
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Ok Arvin has thought common sense here. Since I don’t get the math. I think I agree with DC . String angle is nothing more than string angle. Bow design and length of draw is the important factors to put the energy into the arrow to create cast. As far as width and thickness the Bowyers Bible has gotten pretty close on dimensions to straight stave bows.the rest is keep building till you get it right. That’s what I do. Arvin
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And also I think that a design is a design and will work no matter what the material is. It's just how extreme you can go depends on the material. Twisting and set become the limiting factors.
I totally agree with that Don & Arvin I have 2 bows to finished up but want to make a less aggressive design using maple osage & sinew as lams using the same idea ! But every bow is a test in length , tapper & amount of D/R especially with natural material ! I suspect in will take more then 1 !
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DC, the bows you make with that design are great, and are a strong testament to how good the design can be. I think you're spot on, straight limbs at full draw is ideal. If your gut says string angle is just a symptom, I'm curious, does it have any feelings about what's the cause?
Not really but possibly the actual lever length of the limb. A "lever" is the direct measurement from the fulcrum(grip) to the point of effort(where the string hits the bow) ignoring any bends. With a straight bow the lever gets shorter as the limb bends. Bad. With a reflexed bow the lever gets longer as the bow bends. Better but can be unstable and by the time you get the bow braced you've used up most of the bend. With an RD the deflex gives you your brace height without using up much bend and by moving the tips back it also stabilises the bow some so you can use more reflex. If you can arrange things so that the limb is straightest at FD then I think you would have maximised the lever length.
Also if you can move the the bend toward the grip you can shorten the actual string length. By that I mean the part of the string that isn't touching the bow. Then your braced lever length is short because the lever is measured to where the string hits the bow. This gives you a short lever when the bow is easy to pull and the lever lengthens as you draw it when it gets harder.
That was a lot of typing for a "not really" but those are my thoughts. I get the impression that some others here are swishing roughly the same thoughts around in their heads.
All that said if I understood the physics of bending a beam with a string maybe string angle would mean something ;D
I agree with most of that, and some of it is what I was trying to say earlier. You say that a reflexed bow's lever length gets longer as the bow bends, which seems quite at odds with me saying that reflexed bows usually get extra short as they bend. But I suspect if we further clarify what we mean, we actually agree about most of the underlying principles here. I'm realizing the explanation of my drawing a couple pages back leaves a lot to be desired.
There are two different ways to use the word reflex that I think make the conversation muddled. Reflex can refer to where the limb curves away from the string. But when I talk about "overall" reflex, I'm talking about how far the tips are in front of the handle when unbraced. I'm using it in the sense people use it when they say like, "This bow kept 2 inches of reflex after tillering". They're just measuring how far the tips are beyond the handle, irrespective of the curves the limbs may have taken to get there. I think that difference in language is important to pin down. As D/R bows show us, a bow's limbs can be reflexed along their entire length without the bow having any overall reflex (if the handle is deflexed enough). Similarly, a bow's limbs can be entirely deflexed along their length, like they took set, but the bow could still end up with overall reflex if the handle is reflexed. So these are quite distinct concepts.
In the explanation of my drawing, I should've been more clear, but I was meaning that the farther limbs bend past straight, the shorter their lever length gets. As my drawing shows, increased overall reflex does mean the bow has to bend farther to get to full draw. For most common primitive-type bows, this increased bend means shorter lever length. This is because the main working area is usually pretty close to straight when unbraced, and it starts bending past straight as soon or nearly soon as you start to brace it. Heck most bow's working areas have some string follow, and are bent a little past straight before you even touch it to brace it. This means that the more overall reflex they start with, the farther past straight they will bend, and the shorter lever length they will have. A bow that has overall reflex due to recurves is better off than a bow with reflex with straight limbs, as recurves can counteract some of the loss, but it would always be even better if the main working areas weren't bending so far past straight. Hence some of the benefits of a deflexed handle. I think we agree on all that, right?
But the bow design we've been talking about, the one Stick Bender posted pictures of, doesn't fit in to this usual category. When unbraced, the working area isn't straight or near it, it's significantly curved away from the string. Essentially the whole limb is a working recurve. If we think of the movement of a limb in 3 stages: Pre-straight, straight, past straight, these bow limbs start pre-straight. Their lever length gets longer as they bend toward straight. Then if they go past straight, it starts getting shorter again. The more deflex in the handle, the later this turning point happens.
I agree with all that you said about string contact and the lever length elongating as you draw. That's a recipe for a fat f/d curve. Though I suspect if you take that concept too far and tried to have the string contacting a large proportion of the limb at brace, some other inefficiencies would rear their head. But I won't get in to that now.
Moving on to lever length and string angle, they're closely connected. You'd have to really work to design a bow with a long lever length and bad string angles, so they're mostly two sides of the same coin. So you could look at lever length as the one that matters, and string angle just as a easy quick glance diagnostic. But I'm reluctant to think of string angles as merely a symptom. The direction the string is pulling on the limb pretty directly matters, and the angle that the string makes at your fingers matters too. As the angle at the fingers gets sharper, you put significantly less force on the tips. I don't want to get to math-y, but the pictures here do a good job of explaining. https://roperescuetraining.com/physics_angles.php (https://roperescuetraining.com/physics_angles.php) And you can see in my drawing how much better the angle at the fingers is for the deflex handled bow, even with the same limb length.
Also important to keep in mind is something that stuckinthemud was saying in his original post. Looking at a bow braced and at full draw, you can't easily tell how much overall reflex it has when it's unbraced. Overall reflex/deflex doesn't necessarily matter to the shape of the bow at any point during its use. But I will have to get in to my thoughts on that and why it's interesting at some other time, if anyone is interested.
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First we figure all the ways for a bow to store more energy ignoring stability and stress factors.
Then we post all the tings in a bow that will cause it too loose energy.
And then find ways to compromise and mitigate the losses.
The biggest enemy of efficiency is working limb area because our biggest losses are in limb distortion and vibration, the shorter the working limb area the less opportunity for the limbs to distort on the power stroke. The next biggest source of losses are due to hysteresis which is in direct relation to the amount of set a bow has taken. Reducing set usually means more working limb and adding width and mass to limbs reducing thickness. I haven't found mass to have much negative effects when used in the inner limbs.
As for string angle we use that a couple of ways. A very low string angle at brace gives the accelerating arrow a lot more control over the limbs allowing it to suck more energy out. Maintaining that low string angle for as long as possible makes for a flatter FDC with high starting weight and slow build . It simply stores a lot more energy. The unbraced shape doesn't tell us much about string angles or how much energy a bow might be storing.
As far as priorities in design go I like to give avoiding set the top priority, avoiding vibration second priority( shorter working limb area) and energy storage 3rd priority. If it wasn't for set or the fact that bows break when you bend them too far you could make the perfect bow with about 3" of bending limb. I built a super recurve several years back with maybe a 6 or 8" working limb area. It had about 12" behind the tips and maybe 8 or 10" of string contact with the limbs at brace. The bow was very stable with no twist or torsion issues, it stored about 125% of peak draw force energy and the first few shots were well over 200 fps at 10 grains per pound but it broke down very quickly with each shot.
Usually when we are estimating speed on a bow we are about to build we figure a laminated bow will usually outshoot a self bow with the same profile by about 8 fps. I have found if the self bow doesn't take any set which is very rare the difference is much smaller like maybe 3 fps.
These are some numbers for self bows that I think are pretty typical, I seldom use a reflex deflex in a self bow and usually opt for straight reflex even though I find the r/d to be a tad faster. These are for bows that have taken 1" set between about 64" to 68" long.
Straight self bow about 172 fps, 1" reflex ( tips behind handle) about 175 fps, 2" reflex about 179, 3" reflex up about 184 fps. With less set the numbers will go up a bit and with more set they will go down a bit regardless of having same finished profile. I think the deflex can add about 2 fps to those numbers. I also find the best place to reduce working limb areas is in the outer limbs because they don't add as much to your draw length anyway and keeping outer limbs stiff maintains better string angles. A bow taking set and gaining hysteresis close to the handle will kill a bows performance.
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Good proven info Steve. So are you saying string angle could tell us if our bow design is a good one?
Arvin
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Arvin, I think in most cases controlling set forces us to keep our designs pretty basic. Any bow with stiff outer limbs and some reflex will have decent string angles.
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I think we're pretty much on the same page, probably on the same paragraph. I haven't thought much about working limb length. When I do the material limitations leads me to Turkish hornbows and with my build I'm finding that may not be the way I want to go. Does anyone know if the "Bow Simulator" program will give info like lever length? I can't get it to work on my computer but new computer may not be far down the road.
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I built a super recurve several years back with maybe a 6 or 8" working limb area. It had about 12" behind the tips and maybe 8 or 10" of string contact with the limbs at brace. The bow was very stable with no twist or torsion issues, it stored about 125% of peak draw force energy and the first few shots were well over 200 fps at 10 grains per pound but it broke down very quickly with each shot.
Badger, you've mentioned this bow before. Did you ever try this design again with just a little more working limb?
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I built a super recurve several years back with maybe a 6 or 8" working limb area. It had about 12" behind the tips and maybe 8 or 10" of string contact with the limbs at brace. The bow was very stable with no twist or torsion issues, it stored about 125% of peak draw force energy and the first few shots were well over 200 fps at 10 grains per pound but it broke down very quickly with each shot.
how'd it break?
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I built a super recurve several years back with maybe a 6 or 8" working limb area. It had about 12" behind the tips and maybe 8 or 10" of string contact with the limbs at brace. The bow was very stable with no twist or torsion issues, it stored about 125% of peak draw force energy and the first few shots were well over 200 fps at 10 grains per pound but it broke down very quickly with each shot.
how'd it break?
It didn't break, it broke down from stress, it lost about 15# inside of a dozen shots. I was fortunate to get a couple quick shots out of it. It los about 5 fps with each shot until it went all the way down to 157 from I think about 214.
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The reasons a reflex-deflex design outperforms a straight bow design is more about dynamic efficiency, and to a lesser extent energy storage.
The curvature of the end of the limb effectively stiffens the end of the limb.
If you were able to monitor the kinetic energy in the limb from the moment of release, you would notice that the tip of a straight bow design slows down significantly in the last few inches before the arrow leaves the string. But the mid-limb just keeps carrying forward and doesn’t slow significantly until the arrow is gone. This is wasted kinetic energy that never makes it to the arrow.
In contrast, the deflex-reflex limb end forms an arch that curves away from the direction of travel as it approaches its brace height. This helps resist the mid-limb from carrying forward in the last several inches before the arrow leaves the string. The dynamic stiffening of the end of the limb more effectively forces the conversion of the kinetic energy of the entire limb to the arrow.
Another way to look at it is to think of the end of the limb as a bridge. The most effective bridge forms an arch against the weight it must support. In this case, the “weight” is the decelerating limb mass. A straight bow limb is arching the wrong way, like a saggy beam, and is structurally less effective.
The effect of the curvature of the end of a reflex-deflex bow is similar to the effect of using stiff levers on a straight on a straight bow design bow, except the entire length of the reflex-deflex bow limb is also available for energy storage. So there you have it.
Pictures would probably help.
Alan
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Avcase, that's an interesting concept I haven't thought of before. Do you literally mean the tip slows down while the mid-limb carries forward? That sounds like the limb is becoming more bent as it travels toward brace... Sounds weird. Are you aware of any slow motion videos where the effect is visible?
Edit: After thinking about it a bit more, I have a better visual in my head. I can see something like what you're saying showing up as a sort of wave that starts as the handle and travels toward the tips. The tips don't literally slow down, but rather just go a bit slower than you'd hope. It's easy to imagine how such a thing would lose a lot of energy. But, this seems to speak more to the benefits of recurve than about the benefits of deflex. Wouldn't these advantages be just as present on a recurved bow with a reflexed handle? (Though we would be getting in to horn bow territory there)
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Avcase, that's an interesting concept I haven't thought of before. Do you literally mean the tip slows down while the mid-limb carries forward? That sounds like the limb is becoming more bent as it travels toward brace... Sounds weird. Are you aware of any slow motion videos where the effect is visible?
Edit: After thinking about it a bit more, I have a better visual in my head. I can see something like what you're saying showing up as a sort of wave that starts as the handle and travels toward the tips. The tips don't literally slow down, but rather just go a bit slower than you'd hope. It's easy to imagine how such a thing would lose a lot of energy. But, this seems to speak more to the benefits of recurve than about the benefits of deflex. Wouldn't these advantages be just as present on a recurved bow with a reflexed handle? (Though we would be getting in to horn bow territory there)
Here is a comment I made on a thread a while back that took a similar direction.
Thought experiment: Applying arrow paradox to bow limbs on release. The most motivated part of a bows limb will move first and may move faster than the limbs tips. This loads the other parts of the limbs with energy until all energy is spread equally across the limb. Under slow motion, it probably looks like a wave. If the timing of this wave could be done correctly, the tips would be be at tje crest right when brace heightis hit, snapping the last of the energy into the arrow.
It's in this thread here....
http://www.primitivearcher.com/smf/index.php/topic,65348.0.html
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Allen, they do store more energy. And they tend to be more efficient as long as they remain stiff in the outer limb. If someone tillers amn r/d bow to look like a d bow when braced they loose all the benefits.
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Here is a comment I made on a thread a while back that took a similar direction.
Thought experiment: Applying arrow paradox to bow limbs on release. The most motivated part of a bows limb will move first and may move faster than the limbs tips. This loads the other parts of the limbs with energy until all energy is spread equally across the limb. Under slow motion, it probably looks like a wave. If the timing of this wave could be done correctly, the tips would be be at tje crest right when brace heightis hit, snapping the last of the energy into the arrow.
Yeah that sounds very similar to what I had in mind. Time both limbs right and the wave is canceled the moment the bow hits brace, the energy gone in to the arrow. Mistime it and it becomes a vibration that reverberates through the bow for awhile. ...I have no real idea about this, just spilling thoughts.
If someone tillers amn r/d bow to look like a d bow when braced they loose all the benefits.
What does d bow mean exactly? Do you mean a bow with a deflexed handle? Or like, a straight handle with deflexed limbs? Or maybe just a bow that looks like a letter D when braced?
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Letter D when braced.
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Allen, they do store more energy. And they tend to be more efficient as long as they remain stiff in the outer limb. If someone tillers amn r/d bow to look like a d bow when braced they loose all the benefits.
The shorter the bending section... aka the longer your stiff section on the tips is, the less energy will be wasted in setting up a wave. Still gonna be one, just a lower amplitude, meaning less energy into the wave.
I admit here, I'm into pure theory on this. Just Looking at it as wave propagation, frequency and volume. The longer stiff leave should act as a damper to stop the limb from setting up a wave as easily making more energy available to the arrow.
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Ah ok I'm going to have to disagree with you then, Badger. If someone tillers a deflex-handled bow to look like a D at brace, they won't lose all the benefits. Don't get me wrong, it probably won't be a great bow. They do lose all the benefits of the recurves. But they maintain the benefits of a deflexed handle. There's more benefit to a deflexed handle than simply making it easier to get more recurve/stiffer outer limbs. (Though those things are important)
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Ah ok I'm going to have to disagree with you then, Badger. If someone tillers a deflex-handled bow to look like a D at brace, they won't lose all the benefits. Don't get me wrong, it probably won't be a great bow. They do lose all the benefits of the recurves. But they maintain the benefits of a deflexed handle. There's more benefit to a deflexed handle than simply making it easier to get more recurve/stiffer outer limbs. (Though those things are important)
There are several good things about a pure deflex bow. Efficiency being the best. However, it looses energy storage. A deflex bow is just like a car engine with lower compression ratio. It doesnt require much power to deliver its work. It's a solid reliable, under stressed bow that shoots a heavy arrow quite well. It also is less likely to take set as it bends less.
Now consider this engine with low power, and you wanna boost its performance. Enter the turbo charger. Reflex is like the turbo, perhaps even with a little lag as the tips must catch up to the rest of the limb once released. You take that low compression and shove air down its throat causing it to compress more. Now it has high efficiency AND its power goes up because its storing more energy. The tip/string angle changes providing better leverage, the bend radius increases as you get to the mid limb, and string tension at brace increases.
So, tillering a RD bow to look in profile at FD as a D bow you loose all the benefits of the reflex and are left with a deflexed bow that's like a turbo charged engine with the waist gate stuck open.
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Ok Alan if you can’t measure it how do you know this ? Cause the computer said so. You know I value your knowledge or I would not call you all the time asking for it! If the reflex loads earlier I’m thinking you don’t loose efficiency in the last bit of string travel. This is why I ask about fd curve telling us if the design is better or not. Arvin
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There are several good things about a pure deflex bow. Efficiency being the best. However, it looses energy storage. A deflex bow is just like a car engine with lower compression ratio. It doesnt require much power to deliver its work. It's a solid reliable, under stressed bow that shoots a heavy arrow quite well. It also is less likely to take set as it bends less.
Now consider this engine with low power, and you wanna boost its performance. Enter the turbo charger. Reflex is like the turbo, perhaps even with a little lag as the tips must catch up to the rest of the limb once released. You take that low compression and shove air down its throat causing it to compress more. Now it has high efficiency AND its power goes up because its storing more energy. The tip/string angle changes providing better leverage, the bend radius increases as you get to the mid limb, and string tension at brace increases.
So, tillering a RD bow to look in profile at FD as a D bow you loose all the benefits of the reflex and are left with a deflexed bow that's like a turbo charged engine with the waist gate stuck open.
I mostly agree with you, but you're skipping over what I've been trying to say. Reflex is beneficial for non-deflexed bows too. It is not special to the D/R design. This turbo charger can be effective on many engines. When D/R bows hold their own against fully reflexed bows (even with modern materials with no set, and even when the fully reflexed bows have stiff outer limbs too) you can't explain the D/R bow's excellence by just pointing at the reflexed parts. That's racing two cars with turbo chargers, and saying one won because it had a turbo charger. Deflexed handles offer performance advantages of their own. Those advantages are there whether the reflex is or not.
Sidenote: D/R designs aren't under stressed unless they're overbuilt. Bending a thick piece of wood a little bit stresses the wood just as much as bending a thin piece of wood a lot. You can damage the wood either way. D/R bows aren't inherently less stressed, they're just easier to overbuild without looking overbuilt. (This is at full draw. They are indeed less stressed at brace)
My drawing on page 2 is a D shaped bow with a deflexed handle. Those drawings are carefully drawn with the necessary measurements. I didn't just make it up and draw things where I wanted them to be. I think the differences in lever length and the string angle are important. This helps with energy storage. They're better than a straight bow's too. The advantage may not be enough to make up for the lack of string tension, but they're still there and worth keeping in mind.
It's also worth keeping in mind here that a braced bow's profile doesn't tell you much about its unbraced profile. You could unstring a deflex handled D bow to find its limbs curl up like a Korean horn bow once free. It being a deflexed handled D bow doesn't actually tell you that it has low string tension, or that its limbs aren't reflexed when unbraced. I'd actually love to see more deflex handled horn bows with extreme reflex in the limbs. I suspect a lot of potential lies there.
There seems to be a lack of interest in what I'm saying here, but I don't think it's smoke. I'm open to being wrong, so if my logic is flawed I'd love for someone to point out why. No one who disagrees has really engaged with me yet.
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Halfbow I can only go with my personal experience. The D-R bows just did not work for me but maybe built differently they are better. I don’t design with numbers. I try to visualize stress on the mass and what that might create as far as energy applied to the arrow. Then I build bows. I have had success with the reflexed pyramid design . That’s why I continue to try to remove any set cause the one that took very little is a rocket launcher. Arrows are my top priority as of date.that been said I would like to have another rocket launcher on hand. Just trying to repeat the process. I said some years back pick a wood that suits your climate and is readily available build the same design until you can’t get anymore out of it then try another design. Is any of this important in killing a whitetail ? No!!! My short time in flight shooting has made me think in a different direction . We can definitely learn from math in the design. You just need to know how to do it. Oh well. ;D. Arvin
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Ah ok I'm going to have to disagree with you then, Badger. If someone tillers a deflex-handled bow to look like a D at brace, they won't lose all the benefits. Don't get me wrong, it probably won't be a great bow. They do lose all the benefits of the recurves. But they maintain the benefits of a deflexed handle. There's more benefit to a deflexed handle than simply making it easier to get more recurve/stiffer outer limbs. (Though those things are important)
There are several good things about a pure deflex bow. Efficiency being the best. However, it looses energy storage. A deflex bow is just like a car engine with lower compression ratio. It doesnt require much power to deliver its work. It's a solid reliable, under stressed bow that shoots a heavy arrow quite well. It also is less likely to take set as it bends less.
Your right you don't loose all the benefits but it doesn't shoot as well as a bow that maintains the r'd profile at brace.
Now consider this engine with low power, and you wanna boost its performance. Enter the turbo charger. Reflex is like the turbo, perhaps even with a little lag as the tips must catch up to the rest of the limb once released. You take that low compression and shove air down its throat causing it to compress more. Now it has high efficiency AND its power goes up because its storing more energy. The tip/string angle changes providing better leverage, the bend radius increases as you get to the mid limb, and string tension at brace increases.
So, tillering a RD bow to look in profile at FD as a D bow you loose all the benefits of the reflex and are left with a deflexed bow that's like a turbo charged engine with the waist gate stuck open.
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There are several good things about a pure deflex bow. Efficiency being the best. However, it looses energy storage. A deflex bow is just like a car engine with lower compression ratio. It doesnt require much power to deliver its work. It's a solid reliable, under stressed bow that shoots a heavy arrow quite well. It also is less likely to take set as it bends less.
Now consider this engine with low power, and you wanna boost its performance. Enter the turbo charger. Reflex is like the turbo, perhaps even with a little lag as the tips must catch up to the rest of the limb once released. You take that low compression and shove air down its throat causing it to compress more. Now it has high efficiency AND its power goes up because its storing more energy. The tip/string angle changes providing better leverage, the bend radius increases as you get to the mid limb, and string tension at brace increases.
So, tillering a RD bow to look in profile at FD as a D bow you loose all the benefits of the reflex and are left with a deflexed bow that's like a turbo charged engine with the waist gate stuck open.
I mostly agree with you, but you're skipping over what I've been trying to say. Reflex is beneficial for non-deflexed bows too. It is not special to the D/R design. This turbo charger can be effective on many engines. When D/R bows hold their own against fully reflexed bows (even with modern materials with no set, and even when the fully reflexed bows have stiff outer limbs too) you can't explain the D/R bow's excellence by just pointing at the reflexed parts. That's racing two cars with turbo chargers, and saying one won because it had a turbo charger. Deflexed handles offer performance advantages of their own. Those advantages are there whether the reflex is or not.
Sidenote: D/R designs aren't under stressed unless they're overbuilt. Bending a thick piece of wood a little bit stresses the wood just as much as bending a thin piece of wood a lot. You can damage the wood either way. D/R bows aren't inherently less stressed, they're just easier to overbuild without looking overbuilt. (This is at full draw. They are indeed less stressed at brace)
My drawing on page 2 is a D shaped bow with a deflexed handle. Those drawings are carefully drawn with the necessary measurements. I didn't just make it up and draw things where I wanted them to be. I think the differences in lever length and the string angle are important. This helps with energy storage. They're better than a straight bow's too. The advantage may not be enough to make up for the lack of string tension, but they're still there and worth keeping in mind.
It's also worth keeping in mind here that a braced bow's profile doesn't tell you much about its unbraced profile. You could unstring a deflex handled D bow to find its limbs curl up like a Korean horn bow once free. It being a deflexed handled D bow doesn't actually tell you that it has low string tension, or that its limbs aren't reflexed when unbraced. I'd actually love to see more deflex handled horn bows with extreme reflex in the limbs. I suspect a lot of potential lies there.
There seems to be a lack of interest in what I'm saying here, but I don't think it's smoke. I'm open to being wrong, so if my logic is flawed I'd love for someone to point out why. No one who disagrees has really engaged with me yet.
I'm very interested in this topic and your points you are making. Dont think that.
I'd like to say your point has been proven by Arvin with his bows. He build and breaks records with his long reflexed only bows. My thought and this isn't proven by me yet but by golly I'm working on it, is that a RD bow can shoot just as well as a reflexed bow, and be shorter. At a certain length deflex doesnt help, and pure reflex is needed. As you go shorter, it's my belief that deflex is needed to keep pace and hold its own , though I dont believe it will out perform a longer reflexed bow. Deflex shines on short bows. I just haven't found the magic number yet.
I am planning on soon starting a long bow and reflexing it until performance gains stop, then deflex it until the improve, then shorten it, reflex it more, then deflex more... rinse and repeat, taking careful notes, and being careful to not allow any set. One I find the specific combination of reflex/deflex/and bow length, I will probably have a bow that holds up to any longer reflexed only bow. After that, arrow performance will be the only thing slowing the bow down.
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Using the car anology I personally think the string angle is the equivelent to the tires you still have to get the power to the road...lol, I don't build bows by numbers ether, theory is theory tell you build the bows to test ,but I built this 3D target bow a while back ,I'm using it as a example in design theory, I built several of the same design and draw weight with the difference being stiffer tips via tip wedges that allowed the tips to not bend and hold there curve creating a better string angle at FD but the performance difference was significant , so the only thing that changed was the string angle I wish I had better pics other then construction pics, I also did test with levered wood bows by angling the lever with out effecting draw weight and got performance not as significant gains as glass but still 3fps ,again nothing changed except string angle unless I'm missing some thing ?
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You stiffened the tips. That moves the bendy part in which improves performance I believe and didn't Alan say that if you can stop the wavy stuff that improves performance.
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You stiffened the tips. That moves the bendy part in which improves performance I believe and didn't Alan say that if you can stop the wavy stuff that improves performance.
Reducing the amount of working limb solves all kinds of design issues. Reduces the limb distortion as well as making the limbs on heavily reflexed bows more stable. The only thing it aggravates is the amount of set a bow might take
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Stick bender I bet that is a fast bow. I like that profile strung and unstrung . Probably has a smooth draw with little shock! Arvin
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Yes it is I designed it as a 3d bow and it's user friendly other materials at play as well , ok maybe I'm using string angle as a barometer to performance but I have done the reverse of lengthening the lowers via shortened power/lam and increased the stack adding mass to gain the same draw weight but good string angle for better performance ? And I really like the theory from Steve on limb frequency because when working with material that can take the stress it's amazing the gains with short bows at long draws & user friendliness I really suspect there is more then just one thing in this design that has no
canned answer to the so called perfect D/R bow but it's certainly the concert between limb length ,deflex,reflex, and the angles and curvature of those as well as many other things but the trick I think is finding the right recipe of those in any given material like I said theory is theory tell you build the bows but every time I change one thing and test it ,I have 5 other questions for the next build but the end result for me must have great string angle & maybe that indicates the right recipe or close to it was involve ,I'm currently building a take down riser so I can experiment quicker with the design, this is a great thread I have learned a lot here , the thing I like is we can share thoughts and ideas !
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I'm silently enjoying this thread.
My next build will be for performance and I've changed the design parameters 3 times as this thread has evolved :OK
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I saw you sand bagging Ben :D I was waiting for you to chime in it will be interesting to see your bow is it a BBO ?
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I saw you sand bagging Ben :D I was waiting for you to chime in it will be interesting to see your bow is it a BBO ?
;D
BBI, Pyramid, r/d. I want it to have almost no set, so I plan to overbuild it, especially the inner limbs.
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Sweet !! sounds good now add a forward handle >:D glad your finding some time to build ! Looking forward to your results !
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Sweet !! sounds good now add a forward handle >:D glad your finding some time to build ! Looking forward to your results !
I really don't have time but I plan to squeak it out in the middle of the night sometime soon.
I like the way forward handles shoot but man they are a PITA to get right...Not sure I'm up for that on this one but we'll see!
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Stick Bender, I love your experiments. I prefer working with primitive materials, but modern ones sure make bow science easier. Have you ever explored the limits of reflex? If you want a challenge, could try something like this:
(https://i.imgur.com/EHb7sGm.jpg)
I call it the extreme reflexed, small working area, stiff ended, straight at full draw D/R bow. ...Still working on the name.
But this seems like the direction of the ideal to me. It gets you the best of all worlds with few drawbacks. Light limbs with very high string tension from the reflex, good harmonics from the stiff outer limbs, good lever length and string angle from the deflexed handle in its finest form (straight limbs at full draw),
The only thing it lacks is ease of make. It would be pretty sadistic. I've never worked with materials that can take it, but you seem like a good man for the job. I don't know the limits of glass, but I know they're high.
Oh, and ease of use would be lacking too. Good luck trying to string the thing. ;D Though it should be easier than some extreme asiatic designs.
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I have built several with that profile, there is a huge amount of tension on the string at brace it it wants to turn the bow inside out, short working area will help to mitigate the torquing but no wood that I know of can stand up to that much bending unless you make it in the 10# or 15# range. I made my osage bow almost 3" wide and had nore working area than the bow in the pic and it almost could take it but not quite.
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i feel like this should be archived once its done! really good discussions here!
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Yeah I'm definitely not proposing that that design be made out of wood. I'm imagining more horn and sinew. I agree, the high string tension will make the stability something to contend with. But considering bows reflexed like this are real:
(https://i.imgur.com/0FDd2wb.jpg)
Nothing seems unrealistic about it to me. Plus, both the small working area and the deflexed handle help to make the design more stable than the bow in that photograph.
Edit: I'd love to see the bows you made with that design. I've never seen one like that.
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I don't think a hornbow or fiberglass bow could hold up to not twisting with that design. Not too hard to brace but once braced the string is under a huge amount of tension. Too much for a bow to stand up to. Maybe with the very small working limb area it might make it. I bet it would be a screamer.
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Allen, they do store more energy. And they tend to be more efficient as long as they remain stiff in the outer limb. If someone tillers amn r/d bow to look like a d bow when braced they loose all the benefits.
Yes, there is some mild cam-like effect that gives a deflex-reflex bow a better force-draw curve. Stiffening the outer limb always helps. Any recurvature present at brace also has a stiffening-like effect. I thought I ran some comparisons several years ago between a straight pyramid-style bow with constant thickness, and a deflex-reflex design with constant thickness. I’ll have to dig that up.
Alan
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The ultra-reflexes horn bows are pretty interesting. They don’t have a particularly impressive force-draw curve, but are extremely efficient due to the small bending area and minimal flex in the outer part of the arms. Much of that unbraced reflex goes away during a conditioning process while it is strung where the bow it tortured into a stable braced position. When unstrung after shooting, most of that reflex is gone.
Alan
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Something interesting about bows with curves in the limbs. They don't bend just according to thickness, every inch of the limb responds to the pull according to its current angle in relation to the string. So if you have a little whoop te do in the limb it will bend more even if it is the same thickness.
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My latest bows have been mostly D/R.
Following this with high interest. Cannot add much but what I recognized in the tillering process, when the string starts to lift from the limb, lets say you are rising brace height, its a very critical part and you loose most of the incredible string tension.
Thanks for all the thoughts
B2W
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yes but one of Marcs fastest bows, is just refelxed,, white lightning I believe
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I don't think a hornbow or fiberglass bow could hold up to not twisting with that design. Not too hard to brace but once braced the string is under a huge amount of tension. Too much for a bow to stand up to. Maybe with the very small working limb area it might make it. I bet it would be a screamer.
To make sure I'm understanding you right, if you had a highly reflexed asiatic design vs the highy reflexed deflex design I drew, tuned the reflex in each to get you the same string tension, you'd expect the asiatic design to be more stable than the deflexed design? Why?
Is it because in the design I drew, at brace the limb follows the string so closely, just not quite touching for such a length? I could see that being problematic. I also imagine it would be okay without getting too ridiculous with limb width... But if it did turn out to be a problem, I have some ideas about how to fix it.
The ultra-reflexes horn bows are pretty interesting. They don’t have a particularly impressive force-draw curve, but are extremely efficient due to the small bending area and minimal flex in the outer part of the arms. Much of that unbraced reflex goes away during a conditioning process while it is strung where the bow it tortured into a stable braced position. When unstrung after shooting, most of that reflex is gone.
Alan
I did not know that! That is interesting. So all the pictures of unbraced bows with touching or nearly touch tips.. those bows have never been braced? Why do you think they went through the effort to build them that way? I imagine that even with horn, it's best not to take an intense amount of set?
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I have never tried a bow to that exstream but guys on the horn bow side have tried it ,I think BowEd is posting one there soon ,I credit him on a lot of my knowledge on D/R design ,I have made a couple 64" bows posted below that have extream early draw weight ,I cringe to string , you could easely get hurt if it went wrong but they are among my fastest bows the problem with highly reflexed D/R & angular bows is you have to brace higher to keep from flipping the string so there is always a ballance point , what hasn't been discussed in detail here is front view profile by altering it you can control the bend, also I have found that D/R bows that unwind with less stiff tips may not be the best in FPS but they are very accurate user friendly bows the one I posted earler is by far my most accurate hunting bow it hade no wedges , I think it would be easer & quicker to exsperment with bamboo backed wood bows with adjustable forms vs having to make a new form every time !
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Stick Bender, I didn't mean to belittle the work that goes in to making glass bows. I just meant science is easier. Fewer variables and more consistent results.
Yeah in my early bow making days, I had a quite reflexed bow flip on me so hard it jammed my wrist. Could've been worse, I've read historic accounts of people dying while trying to string highly reflexed asiatic warbows. High reflex and instability can be scary as hell. And they definitely tend to be less accurate. Less forgiving. But I'm on conceptual mission for the fps here. ;D
In light of these stability concerns, I will whip up a new design idea. Will have to wait until later though.
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No worries I didn't take it as belittling I was just saying adjustable form vs individual forms is easier and wood/bamboo bows are more economical to make , it makes exspermenting easeier !
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No worries I didn't take it as belittling I was just saying adjustable form vs individual forms is easier and wood/bamboo bows are more economical to make , it makes exspermenting easeier !
That is a nice bow you posted, I bet it is fast. Bows like that have tons of pressure pushing outwards at brace, like if you set the bow on one end and just pulled straight down on the string it would be extremely tight.
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I don't think a hornbow or fiberglass bow could hold up to not twisting with that design. Not too hard to brace but once braced the string is under a huge amount of tension. Too much for a bow to stand up to. Maybe with the very small working limb area it might make it. I bet it would be a screamer.
To make sure I'm understanding you right, if you had a highly reflexed asiatic design vs the highy reflexed deflex design I drew, tuned the reflex in each to get you the same string tension, you'd expect the asiatic design to be more stable than the deflexed design? Why?
Is it because in the design I drew, at brace the limb follows the string so closely, just not quite touching for such a length? I could see that being problematic. I also imagine it would be okay without getting too ridiculous with limb width... But if it did turn out to be a problem, I have some ideas about how to fix it.
The ultra-reflexes horn bows are pretty interesting. They don’t have a particularly impressive force-draw curve, but are extremely efficient due to the small bending area and minimal flex in the outer part of the arms. Much of that unbraced reflex goes away during a conditioning process while it is strung where the bow it tortured into a stable braced position. When unstrung after shooting, most of that reflex is gone.
Alan
I did not know that! That is interesting. So all the pictures of unbraced bows with touching or nearly touch tips.. those bows have never been braced? Why do you think they went through the effort to build them that way? I imagine that even with horn, it's best not to take an intense amount of set?
Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.
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Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.
Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:
(https://i.imgur.com/q7hjIoD.jpg)
That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?
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I wonder what that tension is, and how it compares to other bows. If a bow could be made that duplicates the string tension of a horn bow, throughout its draw length, seems its performance could be duplicated in wood only.
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Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.
Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:
(https://i.imgur.com/q7hjIoD.jpg)
That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?
I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs
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Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.
Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:
(https://i.imgur.com/q7hjIoD.jpg)
That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?
I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs
100% agree, and the straighter the limbs are at brace, the higher the string tension.
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I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs
Ah so I pretty strongly disagree with you there. Not to say that the flat profile of the limbs doesn't matter, but the reflex will be a huge part of the string tension at brace.
I've posted a relevant pic on these forums before.. let me dig it up.
(https://i.imgur.com/WS8TKHx.jpg)
Ok bow C is fanciful, but it works fine to show my point. These 3 bows are the same draw weight. They have identical profiles while braced and at full draw. But they are very different when unstrung.
It should be pretty obvious that bow A will have low string tension at brace. It barely has to bend to get to brace. Imagine the experience of stringing it. If it were any more deflexed, the string would be slack.
Add a bit more reflex to bow A, scrape the belly some, and you get straight bow B. You'd have to use a bit more muscle to string this one. When you string it, you bend the wood halfway to its final full-draw bend. That string is taught.
Just keep going. Adding reflex. Making the limbs weaker to maintain the same draw weight. Hope your materials are real good.
Eventually you get to bow C. To brace bow C, you have to bend the bow like 80% its final bend. That thing is wicked straining to go back. With like 80% of its might. The string tension will be enormous. With this bow, the stress the wood (or more realistically: some other material) feels from brace to full draw doesn't even change that much.
I put it to you that the difference reflex makes to string tension at brace isn't subtle, but huge.
Edit: Disclaimer. I'm not advocating any of these designs, just illustrating a concept.
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I wonder what that tension is, and how it compares to other bows. If a bow could be made that duplicates the string tension of a horn bow, throughout its draw length, seems its performance could be duplicated in wood only.
I think string tension throughout the draw would be an interesting thing to pay attention to, but I think you'd have a really hard time mimicking a horn bow's string tension with a wood bow. And if you managed it, it would be just one factor of many that effect performance.
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String tension is NOT a function of how much the bow has bent. This is evidenced by string tension drops as the bow is drawn. String tension is a factor of the mechanical advantage offered over the limbs by the angle at the tips, not by how far the tips bent to get to brace.
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It would be interesting to see a working proto type of Halfbows drawing or even a milder version I'm not that smart numbers wise but I built enough bows to intuitively know the problems with the build (not saying it can't be done) I'm speaking building ,my guess is there would be stability problems & wood only ,would not work in my mind ,A horn/wood/sinew could take the stress but stability ? , carbon,stabil core,glass,wood would could take it but the problem would lie with material thickness vs stability it would have to have very thin lams & zero taper or max.001 the bend would have to be controled by the front view , the problem in my mind is how to get a stabile bow that's doesn't have a 300 lb draw weight...lol even minor miss alignment would be exponentially multiplied in stability , deflexing the bow adds issues but it would be a great bow if you could get one to fly would be my guess , but a milder version would defiantly be possible in a short bow !
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String tension is NOT a function of how much the bow has bent. This is evidenced by string tension drops as the bow is drawn. String tension is a factor of the mechanical advantage offered over the limbs by the angle at the tips, not by how far the tips bent to get to brace.
When a bow is drawn, there are many factors that change and interact in interesting ways. A substantial one has nothing to do with the angle at the tips, but the angle at the fingers. The one I linked earlier. https://roperescuetraining.com/physics_angles.php The fingers are like the weight in those pictures. The table and the graph show the force multiplying effects of a near straight string. This is a big part of why string tension is higher earlier in the draw, and why draw weight gets higher the further you draw.
The angle at the limb tips plays its part too, though I think people usually measure it in a pretty uninformative way. But yes, sometimes the limb has more leverage over the string than other times and that makes a big difference.
But the thing that's true throughout all of it is: String tension has everything to do with how hard the poor string is being pulled. And how hard the limbs are stressing against it is absolutely a part of that.
When comparing a braced bow to other braced bows, straight string to straight string, a lot of the factors that change around interestingly during draw don't come in to play. Like the angle at the fingers.
All 3 of those bows will end at full draw with the same string tension. They will not begin with the same string tension. Not remotely.
Again this is not to say that other factors don't matter a lot. I'm just saying, let's not discount the effect of reflex here.
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Halfbow, I think we are talking about string tension in the context of a bows stability at brace, not string tension as it affects the draw. Any bow resembling anything like a "C" when braced will likely be stable. If it resembles a triangle it will be much less stable because of the forces pulling the limbs together have no where to go without distorting the limbs, there is no clear path the limbs have to follow as in a bow with a "C" shape. Kind of like pushing straight down on a poll, you have no idea which way it is going to bend. I tried building some deflexed inverted limb bows just to see how they would do. The string tension was still too high at brace for the bows to be stable and the bows had no reflex at all.
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Steve the pole thing is what I was thinking also. Did not know how to say it though. Well done. Arvin
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Badger, I'm with you there. Pulling down on a pole is what I was trying to describe when I asked if it was because the limb was running quite parallel with and close to the string for so long at brace.
I'm unsure about how much that kind of braced profile increases initial string tension, as would be measured by a scale, but I can see how the profile could even make less string tension too much. Revised design that I think will be more stable, coming soon.
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...... But I'm on conceptual mission for the fps here. ;D
Half,
I am kinda curious for what purpose you you seek max fps with primitive mat'ls?
hunting?
flight?
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Badger, I'm with you there. Pulling down on a pole is what I was trying to describe when I asked if it was because the limb was running quite parallel with and close to the string for so long at brace.
I'm unsure about how much that kind of braced profile increases initial string tension, as would be measured by a scale, but I can see how the profile could even make less string tension too much. Revised design that I think will be more stable, coming soon.
It is a huge amount of string tension, I have had it break strings as soon as I braced them that were fine for normal 50# bows.
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Half,
I am kinda curious for what purpose you you seek max fps with primitive mat'ls?
hunting?
flight?
Time travel of course. If you ever find yourself stuck in the stone age, you ain't going to be building computers, planes, or lightbulbs. But you might be able to build the most efficient bow the world has ever seen.
Really though, primitive materials because I like knowing I can make things from my environment. I'd love to get in to flight archery, but really the main reason is I think it's an unusually fascinating puzzle, and I like puzzles. A bent stick with a string seems so simple... until you start really thinking about it.
Also, I think that understanding concepts is inherently valuable. Even if the most efficient possible design is torture to shoot, understanding the concepts behind it will be helpful for making knowledgeable decisions about what trade-offs to make, and for making better usable bows.
It is a huge amount of string tension, I have had it break strings as soon as I braced them that were fine for normal 50# bows.
That's very interesting, and it does expand my understanding of string angle at the tips. (Though I stand by my point about reflex mattering a lot for string tension too)
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Alright here's mkII. It may not look like much, but this was quite difficult to arrive at. Playing around with design becomes a real pain when you have an end goal as precise as straight limbs at full draw.
(https://i.imgur.com/WmCQ02w.jpg)
Fair warning, skip the next 3 paragraphs if you don't care about fiddly details. Here's my thought process:
My first thought for how to increase stability was to get the string contacting the outer limbs at brace. Where the string contacts the limb is mostly taken out of the stability equation, and the bow behaves like a shorter bow until the string gets lifted off the limb during draw.
But I also knew I wanted to the limbs to be straight at full draw. It's not especially easy to achieve both these things. If I had just made the limbs more dramatically curved at brace, I could've gotten good string contact, but then the brace height would get too low. This meant I had to increase the deflex at the handle, as this way the limbs are angled more directly toward the string and can contact it sooner. But that meant I had to make the bow shorter. If I didn't, the limbs wouldn't bend far enough to be straight at full draw. So the challenge was to deflex the handle enough to get good string contact while maintaining brace height while avoiding making the bow absurdly short.
After I got the string to contact the outer limbs, I started to worry about efficiency losses there. The string doesn't have much leverage on the limb when it's right up against it. With it contacting so much of the limb, that could turn in to a real problem. When shooting, after releasing, when the bow hit brace, the string wouldn't have enough leverage to stop those outer limbs. They'd just continue moving forward past brace position, violently stretching the string. A lot of energy would go in to the bow instead of the arrow. To deal with this, I added some string bridges along the outer limbs. This is kind of like thickening the outer limbs. They'll be much far stiffer for the price of the minimal mass of the bridges. They give the string much better leverage over the limb. They also offered the benefit of lengthening the string and raising the brace height. This longer string meant I had to lengthen the limbs, or the draw length would be too long, which meant I had to decrease the deflex in the handle, which was convenient because I now had some extra room to do so thanks to the extra brace height. So adding string bridges caused a slightly longer and less deflexed bow, which is what I was wanting. Thanks string bridges.
(https://i.imgur.com/csd8SXM.jpg)
With it on top of my old design, you can see how much shorter it is. You can also see it's suffered a significant downgrade to the string angle at the fingers. But on the other hand, we've added the benefits of less mass from shorter limbs, and the string let off. The string coming off the bridges during the draw should fatten the f/d curve.
I'm honestly not sure which of those 2 bows to expect to be better performance-wise. I think that string angle is really important, but the little bow has strong advantages on its side too. I want to experiment. But, I am at least pretty confident this new bow is more stable.
I drew in quite a lot of unbraced reflex again. But note that that is the easiest part of the design to change. It's basically the only thing you can change without throwing everything else in to disarray. So if it's too much reflex for you or your materials, you can just lessen it. Unbend those working areas a bit. If you went far enough unbending them, you could even make this bow have the same braced and unbraced profile. Get that slack string, if that's what you're in to.
Note that with a bow this short, I think wood would have a hard time even without the extreme unbraced reflex. I think we are in horn/sinew or modern material land here. ..But possibly a modified version of this design could be a wooden paddle bow?
But that said, I think this odd short little guy would be good. Excellent string angles for its length, light limbs (especially if you keep a lot of unbraced reflex), fat f/d curve, and more stable than my previous design. It would need a hefty string though.
Tell me what I'm missing guys.
P.S. Yes, I know the handle is a pinnacle of ergonomics. ;D
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There is another issue I am going to throw at you. When you go to tiller the bow at brace you will have high string angles coming out of the handle so that will want to bend first, you will have a tendency to weaken the stiff area with low string angles to get them bending and then suddenly when they start to bend their string angle will increase and they will bend too much. It is a real balancing act trying to get it right
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Good post. I like it because it parallels kinda where my thoughts were going. I was thinking about a lot of string contact as a good thing but I hadn't thought about how the unsupported outer limb would behave when the bow was released. It would basically be a dry fire. As much as I don't like bridges(aesthetics mostly) they do seem like an answer.
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There is another issue I am going to throw at you. When you go to tiller the bow at brace you will have high string angles coming out of the handle so that will want to bend first, you will have a tendency to weaken the stiff area with low string angles to get them bending and then suddenly when they start to bend their string angle will increase and they will bend too much. It is a real balancing act trying to get it right
I was/am having a lot of trouble with this. What I find helped was using a long long string. It puts some strain on the outers while tillering and kind of keeps them in line. You have to be careful and conscious of what a long string can do but it helped me with the "all of a sudden" issue I was having.
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There is another issue I am going to throw at you. When you go to tiller the bow at brace you will have high string angles coming out of the handle so that will want to bend first, you will have a tendency to weaken the stiff area with low string angles to get them bending and then suddenly when they start to bend their string angle will increase and they will bend too much. It is a real balancing act trying to get it right
Thanks, definitely something to watch out for. I'm sure such a thing takes practice, but you may have saved me some frustrations.
Good post. I like it because it parallels kinda where my thoughts were going. I was thinking about a lot of string contact as a good thing but I hadn't thought about how the unsupported outer limb would behave when the bow was released. It would basically be a dry fire. As much as I don't like bridges(aesthetics mostly) they do seem like an answer.
DC, a test you did awhile ago helped me to understand the geometry of bending limbs. You may remember when you were tracing the arc various limbs made at the tip as they bent. That was really interesting, and is what eventually lead me to realize the benefits of straight limbs at full draw.
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Really though, primitive materials because I like knowing I can make things from my environment. I'd love to get in to flight archery, but really the main reason is I think it's an unusually fascinating puzzle, and I like puzzles. A bent stick with a string seems so simple... until you start really thinking about it.
Also, I think that understanding concepts is inherently valuable. Even if the most efficient possible design is torture to shoot, understanding the concepts behind it will be helpful for making knowledgeable decisions about what trade-offs to make, and for making better usable
Half
Lots of good ideas being explored here, and the concepts are challenging. Since we lost Stuckinthemud after he third post, I don't suppose it would be inappropriate expand the discussion to point out that raw speed does not always equate to long cast or accurate arrow placement.
BTW, are these conceptual bows "geared" towards lighter arrows? Or arrows of any particular type?
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Alright here's mkII. It may not look like much, but this was quite difficult to arrive at. Playing around with design becomes a real pain when you have an end goal as precise as straight limbs at full draw.
(https://i.imgur.com/WmCQ02w.jpg)
Fair warning, skip the next 3 paragraphs if you don't care about fiddly details. Here's my thought process:
My first thought for how to increase stability was to get the string contacting the outer limbs at brace. Where the string contacts the limb is mostly taken out of the stability equation, and the bow behaves like a shorter bow until the string gets lifted off the limb during draw.
But I also knew I wanted to the limbs to be straight at full draw. It's not especially easy to achieve both these things. If I had just made the limbs more dramatically curved at brace, I could've gotten good string contact, but then the brace height would get too low. This meant I had to increase the deflex at the handle, as this way the limbs are angled more directly toward the string and can contact it sooner. But that meant I had to make the bow shorter. If I didn't, the limbs wouldn't bend far enough to be straight at full draw. So the challenge was to deflex the handle enough to get good string contact while maintaining brace height while avoiding making the bow absurdly short.
After I got the string to contact the outer limbs, I started to worry about efficiency losses there. The string doesn't have much leverage on the limb when it's right up against it. With it contacting so much of the limb, that could turn in to a real problem. When shooting, after releasing, when the bow hit brace, the string wouldn't have enough leverage to stop those outer limbs. They'd just continue moving forward past brace position, violently stretching the string. A lot of energy would go in to the bow instead of the arrow. To deal with this, I added some string bridges along the outer limbs. This is kind of like thickening the outer limbs. They'll be much far stiffer for the price of the minimal mass of the bridges. They give the string much better leverage over the limb. They also offered the benefit of lengthening the string and raising the brace height. This longer string meant I had to lengthen the limbs, or the draw length would be too long, which meant I had to decrease the deflex in the handle, which was convenient because I now had some extra room to do so thanks to the extra brace height. So adding string bridges caused a slightly longer and less deflexed bow, which is what I was wanting. Thanks string bridges.
(https://i.imgur.com/csd8SXM.jpg)
With it on top of my old design, you can see how much shorter it is. You can also see it's suffered a significant downgrade to the string angle at the fingers. But on the other hand, we've added the benefits of less mass from shorter limbs, and the string let off. The string coming off the bridges during the draw should fatten the f/d curve.
I'm honestly not sure which of those 2 bows to expect to be better performance-wise. I think that string angle is really important, but the little bow has strong advantages on its side too. I want to experiment. But, I am at least pretty confident this new bow is more stable.
I drew in quite a lot of unbraced reflex again. But note that that is the easiest part of the design to change. It's basically the only thing you can change without throwing everything else in to disarray. So if it's too much reflex for you or your materials, you can just lessen it. Unbend those working areas a bit. If you went far enough unbending them, you could even make this bow have the same braced and unbraced profile. Get that slack string, if that's what you're in to.
Note that with a bow this short, I think wood would have a hard time even without the extreme unbraced reflex. I think we are in horn/sinew or modern material land here. ..But possibly a modified version of this design could be a wooden paddle bow?
But that said, I think this odd short little guy would be good. Excellent string angles for its length, light limbs (especially if you keep a lot of unbraced reflex), fat f/d curve, and more stable than my previous design. It would need a hefty string though.
Tell me what I'm missing guys.
P.S. Yes, I know the handle is a pinnacle of ergonomics. ;D
I'm very certain that your string bridges will do the exact same thing as deflex.
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String bridges won't stiffen the tips. They may stiffen tiny parts of it but not the entire area.
Are you aware that Karpowicz did a fair bit of experimenting with this design and Hickman also in the past?
Someone on ATARN made this design also.
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Half
Lots of good ideas being explored here, and the concepts are challenging. Since we lost Stuckinthemud after he third post, I don't suppose it would be inappropriate expand the discussion to point out that raw speed does not always equate to long cast or accurate arrow placement.
BTW, are these conceptual bows "geared" towards lighter arrows? Or arrows of any particular type?
Definitely. As with most things, optimizing for one thing means trade offs in other areas (though not always). But again, I think these underlying concepts are useful to understand.
As to your question about arrows, I too am curious about people's thoughts on that. My thoughts are to take the dry fire speed of the bow (something you'd never want to test, but nonetheless a real and interesting data point) then figure out how easily it gets slowed down by the weight of an arrow. I suspect this bow will have a very fast dry fire speed, but due to the light limbs it may be more easily slowed down by heavier arrows. However, I'm not sure how much the extreme reflex affects this, but I bet it does.
I'm very certain that your string bridges will do the exact same thing as deflex.
The same thing as deflex? I don't follow. Can you explain more?
String bridges won't stiffen the tips. They may stiffen tiny parts of it but not the entire area.
Are you aware that Karpowicz did a fair bit of experimenting with this design and Hickman also in the past?
Someone on ATARN made this design also.
Stiffen tiny parts of it? Hahaha that's an amusing thought. Yes, I agree, the bridges themselves don't do much to stiffen the limb. It's the elevated string under tension.
Think of a cable backed bow. If you put bridges along the back to elevate the cable, the limbs get much stiffer, and not just tiny parts of them. ;D I know this not just because it makes sense (which it does, you're essentially thickening the limb by moving the tension side farther out), I also know it first hand because I've done it. My bow here uses the same concept flipped around.
On a braced bow, the only thing stopping it from returning to its unbraced profile is the string and its tension. Elevating the string off the limb gives it better leverage over the limb, and makes it harder for the limb to bend away from it. This is useful at the end of the powerstroke when the outer limbs have a lot of momentum. Without string bridges the string would be right up on the outer limbs, and thus wouldn't have much leverage to stop them. At best the string would get stretched, reducing the efficiency of the bow.
Stiffness may be a poor choice of words on my part here. Obviously this "stiffness" only applies in one direction, and only while the string is actually on the bridges. The bridges do nothing for the stiffness during most of the draw, which is fine.
I was unaware of other people trying things like this. That's kind of awesome. I did some searching, but was unable to find Karpowicz's version, or the one on ATARN. I did find a drawing of the Hickman design. I can see why you'd make a comparison, mine and his both have severe deflex in the handle and straight limbs at full draw. But I wouldn't call it the same design. That's as bad as saying all straight bows have the same design.
Just so everyone knows what we're talking about:
(https://i.imgur.com/BYgHe8z.png)
A big difference is that his design has very similar braced and unbraced profiles. Little extra unbraced reflex. I'd expect that design to have much lower string tension at brace. Also my design has a smaller working area and stiff outer limbs (even without the string bridges). I think small working area and stiff outer limbs are significant for all the reasons Badger says they are.
Also, to me that design is just begging to have string bridges. I'd expect that bow to have a fantastic f/d curve, but to be inefficient at putting that energy in to the arrow because the string can't effectively stop the limbs' momentum.
I do, however, think he's on to something with the long unbending handle. This gets you the string angles of a longer bow but with the short light limbs of a shorter bow. I was thinking of doing something like that on my design, but decided to leave it for another time.
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This is a long and interesting discussion. The straight-limb-fulldraw-theory now really took my attention. Therefore I just wanted to remark that this summer I accidentaly started to do bows with straight limbs at fd. I did a trilam glueup on my old angular-form of ash-ash-yew. actually I wanted the the limbs to form more of an arc a at full draw when ran out of belly lam and created straight limbs at full draw. I just have to say that it really was shooting tremendous (b2w can testify i think...). It finally failed at the fades due to beginners problems - using just white wood glue (all repairs finally failed).
I then did the r/dbirch which shoots well but didn^t hold much reflex.
I'm on another glue up now including enough belly wood for any f-d-tiller. What do you think the final f-d should lookalike for optimized performace and comfort. To where should I aim tillering Off course without overstressing the wood (--)
My thouhts about straight fd are that it takes a lot of non working wood on the limbs to keep the limbs stable (bad). Having the bend mainly on the inners gives perfect string angle (good). The reflexed unbraced profile gives good string tension at brace. Just my thoughts...Cheers
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Half
Lots of good ideas being explored here, and the concepts are challenging. Since we lost Stuckinthemud after he third post, I don't suppose it would be inappropriate expand the discussion to point out that raw speed does not always equate to long cast or accurate arrow placement.
BTW, are these conceptual bows "geared" towards lighter arrows? Or arrows of any particular type?
You didn't loose me, I'm really enjoying this, but I learned long ago, there's times to speak and times to sit and listen ;)
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Halfbow,
The Hickman extreme Recurve design had a pretty incredible force-draw curve. I believe it may have had a brief moment in the draw where the draw weight decreased as the bow was drawn. The problem was that efficiency was very poor because the string hadn’t no leverage on the unsupported limb and all that’s forward energy remained in the limbs at the end of the shot. This evening symptom of this would be a huge amount of limb flapping post-shot. Modern “Super Recurves” are very similar to this design, except they are using modern composite sizes to keep the limb mass to a minimum. The efficiency is still poor, but the energy storage makes up for it when shooting heavier hunting type arrows.
The idea of using string to prevent this limb flap has been kicked around for years, but I haven’t seen much development work yet to make this work on a real bow yet. I hope you will pursue this!
Alan
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Thanks Alan. Yeah the flapping is exactly what I was imagining. But I wouldn't have guessed the draw weight actually decreased, that's amazing. But good to hear I'm thinking along the right lines.
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Think of a cable backed bow. If you put bridges along the back to elevate the cable, the limbs get much stiffer, and not just tiny parts of them. ;D I know this not just because it makes sense (which it does, you're essentially thickening the limb by moving the tension side farther out), I also know it first hand because I've done it. My bow here uses the same concept flipped around.
I can agree with you about the stiffening effects of a cable backed arrangement, as I have had some similar results.
As for the concept flipped around, I will have to take your word for it until I can give it some more thought or see the concept demonstrated better.
Stuck, glad your still here and OK with the "thinking out loud" direction this thread has taken.
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It's sounding that there are a few things that are good to a point and then start being bad. What you have to a design is a bow that has all these things peak at the same time. So all you have to do is figure out what these things are and when and how they peak. Then assemble a bow that has them all happen at the same time. Sounds pretty straight forward to me. You guys get busy on that and report back. ;D ;D ;D ;D ;D
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The problem was that efficiency was very poor because the string hadn’t no leverage on the unsupported limb and all that’s forward energy remained in the limbs at the end of the shot.
Alan, could you elaborate that topic? I can see what is happening (have made a few too-much-reflex-*****bows) but I can't get what is science behind low efficiency and flip-flopping. What exactly means "no leverage on the unsupported limb"? Why is so much limb's forward energy remained in the limbs? Every bow has moving limbs, which have some forward (in direction of arrow) kinetic energy and momentum - but what is the process of energy transfer to the arrow?
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Tuomo, I may be able to help answer. A different context might make the concept more intuitive.
The leaning tower of Pisa is finally falling over. You see it start to slowly lean more and more. Thinking quickly, you get out your rope and manage to lasso the top. You're going to try to stop its fall. Maybe you just barely caught it before the point of no return.
Now would you choose to stand next to it and pull down on the rope to try to stop it?
(https://i.imgur.com/MqK9pOG.jpg)
Or would you choose to stand away from it.
(https://i.imgur.com/hrdQxND.jpg)
One of these gives you more leverage.
All bow limbs have forward momentum throughout the power stroke. Ideally that momentum is stopped instantly at the end of the power stroke, when the bow hits brace. Any movement in the bow limbs after the arrow has left the string is indicative of energy that could have gone in to the arrow, but didn't. So you really want those limbs to stop. The string is the only thing there to stop them.
But some string angles offer better leverage to stop them. If the string has poor leverage, it will get stretched out as the limbs keep moving forward despite it. In the first pic, imagine the tower falling, lifting the guy off the ground, his weight barely making a difference. The force that would lift him is the same force that would stretch a bow string.
The now longer string means the limbs can travel past the intended brace position (related to: longer string means lower brace). Eventually, assuming the string doesn't break, it will stop stretching, the limbs' forward momentum will finally die, the string will elastically rebound, and the limbs will go back, oscillating back and forth for a bit around the intended brace position, flapping.
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Nice diagram, very neatly explains why I need a much stronger string when I'm tillering reflexed bows at low brace than I do at full brace - thought it was just that by the time I got to full brace I'd reduced the draw weight but I guess not
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Good explanation even Arvin understood. Thanks.
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I like the cracks in the tower nice touch :)
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Isn't the arrow gone by the time all this happens? I understand that the limbs will still flap around and all but how would this get more energy in to the arrow.
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Halfbow - thank you for the nice explanation, figures were nice!
But, as DC stated, "Isn't the arrow gone by the time all this happens?" Before the string is at brace height, energy is transferring to the arrow.
It is about efficiency - what is the physics behind poor efficiency of super recurves, as Alan said?
Bow stores energy and after release some of energy goes to arrow and some dissipates as losses:
-hysteresis - bow related constant, should not depend recurves
-string elasticity - should be not a problem with modern materials (or??)
-recoil - not a problem, if bow is heavy
-air drag - not a problem
-bow limb mass and related forward momentum - not a problem, if limbs are light enough
Any of those losses are not related in any way to recurves. I am not sure is poor efficiency of super recurces related to bow geometry or is it material related? If we would have perfectly rigid (non-elastic) string, would we have a problem?
So, the problem may be in energy transfer. I can imagine, that shooting a bow which has a bit loose string (brace height just under zero) is not nice and efficiency may be poor - I should try. Although the bow stores more energy when it is braced normal way. As Halfbow said "All bow limbs have forward momentum throughout the power stroke. Ideally that momentum is stopped instantly at the end of the power stroke, when the bow hits brace. Any movement in the bow limbs after the arrow has left the string is indicative of energy that could have gone in to the arrow, but didn't. So you really want those limbs to stop. The string is the only thing there to stop them.".
Hickman said (as we know by experience also): "The arrow velocity increases with increase in bracing height up to a certain point, after which is slowly decreases with additional increase in bracing height." So, the efficiency of the bow also increase with brace height.
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One thing that's been known about D/R design for years is that in most cases these bows are most efficient when there within a 1/2"-1" of stacking especially with guys making lighter draw weight bows I'm wondering if that plays in to length vs draw length & the limb frequency /vibration theory Steve mentioned but I'm sure each material used has it's variants on the theory to, really only one way to find out ;D Halfbow I enjoy your drawings !
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So, the problem may be in energy transfer.
Yes
but what is the process of energy transfer to the arrow?
energy is transferred from the limb to the arrow via the string. the string and arrow slows the return of the limb compared to a "dryfire" without the arrow.
as the sketches above indicate, the force the string exerts on the limb at the end of the power stroke has minimal effect on the return of the limb, so remaining energy in the limb is not transferred efficiently, leaving excess energy in the limb to be dissipated by vibration.
Remember all that high early draw strength/energy we wished to have? It wants to return to the string at the end of the powerstroke.
Creating a limb with more high early draw reaches a point of diminishing returns if limb is reflexed too much.
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Half bow,
Good diagram!
If the leaning tower with the string laying along side it is stiff, then it’s momentum will still be forced down the string. In the case of a bow, the forward momentum of the limb is transferred to the arrow as long as the bow/ tower does not buckle, and the string can take the load.
A bow shouldn’t experience a sudden stop at the end of the return stroke. The limb tip of a very efficient bow will typically start slowing down in the last 1/3rd of the return stroke. Because of the changing string angle, the arrow will keep gaining speed and the limb continues to slow down until the bow reaches its dynamic brace height and the arrow nock separates from the string. So it is more of a tug on the string over a period of time rather than sudden stop at the end.
Alan
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The problem was that efficiency was very poor because the string hadn’t no leverage on the unsupported limb and all that’s forward energy remained in the limbs at the end of the shot.
Alan, could you elaborate that topic? I can see what is happening (have made a few too-much-reflex-*****bows) but I can't get what is science behind low efficiency and flip-flopping. What exactly means "no leverage on the unsupported limb"? Why is so much limb's forward energy remained in the limbs? Every bow has moving limbs, which have some forward (in direction of arrow) kinetic energy and momentum - but what is the process of energy transfer to the arrow?
The bow design with the best force-draw curves are extreme full-working recurves. This requires the entire length of the limb to flex as the bow is drawn back. But this flexibility doesn’t work as well on the return stroke unless the limbs can be made from a zero mass material. What happens is that the flexible limb will buckle and oscillate on the return stroke in reaction to the increasing string tension. To use Halfbow’s diagram of the leaning towers, it is like the diagram of the string laying against the tower and trying to hold it in place, except the tower is made of rubber, and it buckles under the tension of the rope.
The limb flapping and vibration is visible after the arrow has left the bow, but this is just a symptom that indicates some energy remained in the limbs, not the arrow.
Alan
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We have enough guys working on fast boats right now That'll Walk the talk type event would be very interesting. Suppose we set a date approximately one year from now at one of the big gatherings Maybe mojam. We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
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We have enough guys working on fast boats right now That'll Walk the talk type event would be very interesting. Suppose we set a date approximately one year from now at one of the big gatherings Maybe mojam. We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
Count me in.
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We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
Steve, with that little difference in FPS using a shooting machine, wouldn't you want to compare cast distance also?
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We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
Steve, with that little difference in FPS using a shooting machine, wouldn't you want to compare cast distance also?
That's an event on it's own already, and more to do with archer and arrow. This would be pure power if the bow, and I'm ALLLL about that
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Thank you Alan, Halfbow, willie and so on – I got it!
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Guys I built a reflex glass bow to the same design as my pyramid selfbow design.it was a dog! So my point here is the material must play into the equation. That being said in a osage pyramid bow which you have close to perfect deminishing mass there is virtually no shock. I’m thinking distribution of the mass is important as the reflex or deflex. Arvin
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I agree with Arvin distubution of mass is key all of my D/R glass & carbon bows are pyramidal front view !
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That's an event on it's own already, and more to do with archer and arrow.
I should be more clear with my suggestion, Sleek.
When I mention cast, I am not proposing a flight for max distance evaluation.
The cast of the arrow could also be evaluated in a shorter distance, say 50 or 75 yards or so. Maybe looking at the arrow drop at the target, when the machine is set for level or 5 degrees above the horizontal (for instance). Speeds would still be recorded directly in front of the machine but observing downrange performance could tell a bit about "bow caused" instability factors in arrow flight. Just move the backstop further back to enable more observations. Admittedly, this would not account for different arrows abilities to recover differently, but if a shooting machine is to be used and release factors will be minimized, so could arrow differences also if a few modern type arrows were for the testing.
I have a project where I intend to use one inexpensive guitar pickup at the target and another at the machine to help determine actual time of flight. The distance divided by time would yield an average velocity over a practical distance
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We have enough guys working on fast boats right now That'll Walk the talk type event would be very interesting. Suppose we set a date approximately one year from now at one of the big gatherings Maybe mojam. We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
I'd join in!
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We have enough guys working on fast boats right now That'll Walk the talk type event would be very interesting. Suppose we set a date approximately one year from now at one of the big gatherings Maybe mojam. We set up a shooting machine and address could mail their bows in ahead of time. My guess would be Rd recurves would win which speed between 188 to 190. I would guess that straight reflex bows would be slightly behind them maybe two or three feet per second. This would be for laminated bows and I would guess that self bows would be about 5 feet Behind These
I'd join in!
Me too :)
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Im pretty sure I read a post by Marc that white lightning shot 190,,reflexed no deflex,,
do you think the reflex deflex has a speed advantage in general,, I could be wrong I am going by memory :D
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Im curently building a reflex only , retro flip tips 57" osage/sinew Laubin inspired bow Im induesing 4" of reflex to start & going to take tiller out to at least 28"-29" I guarantee its going to stack more then if it was a D/R but I will let you know on performance I could make both types to compare its really the only way know vs a paper bow , we need working examples !