Primitive Archer
Main Discussion Area => Bows => Flight Bows => Topic started by: willie on September 26, 2020, 12:00:38 pm
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the following quotes are from https://sites.google.com/site/technicalarchery/home (https://sites.google.com/site/technicalarchery/home)
Kinetic Energy - The energy transferred from the bow to the arrow upon release.
The kinetic energy (KE) of an arrow can be obtained by weighing the arrow with a scale and observing the speed with a chrono, and applying some math.
Potential Energy - The energy stored in the bow at any draw distance. Potential energy is a function of draw force and draw distance.
The Potential Energy of a drawn bow can be obtained by counting squares under a plotted force draw curve or calculating the area.
Should you wish to know how well your bow performs, one can compare potential energy of the bow to the kinetic energy of the arrow. Looking at the equation below, we see our differences or losses broken down and categorized into hysteresis (elasticity efficiency) and energy used move limb mass back to brace height. I should also add that the "Kinetic Energy of the Bow" also includes the string.
Potential Energy of the Bow = Bow Hysteresis + Kinetic Energy of the Bow + Kinetic Energy of the Arrow
On one side of the pond, imperial units are used to describe energy in foot/pounds, while on the other, energy is stated in SI units of Joules. We could also describe hysteresis and limb energy with foot pounds or joules, should we wish.
In the archery world, we like to compare our observed arrow to an imaginary arrow that has the same energy as the bow, and have invented a unit of measure called virtual mass. It is stated in arrow weight. It is the difference in arrow weight, at the same velocity as our actual arrow, that when added to the observed arrow weight, gives the bow and the arrow the same energy. It represents the losses in the bow/string, and is considered to be a unit of measure for bows.
Can this invented unit of measure accurately describe bow/string energy losses?
Can this invented unit of measure accurately describe hysteresis losses?
Can it tell the difference between the two?
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Good definitions and equations, but how is this new unit better than the standard efficiency measure (energy out/energy in) or the standard performance measure (FPS per Pound) accounting for GPP?
Regards,
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Good definitions and equations, but how is this new unit better than the standard efficiency measure (energy out/energy in) or the standard performance measure (FPS per Pound) accounting for GPP?
Regards,
It can not accurately isolate the amount of Hysteresis in a bow but it can be a very good indicator of how much a bow has. Bow and string losses will remain constant while hysterics losses are time sensitive to how fast a sting returns. Variances in virtual mass with different arrow weights will point to hysteresis.
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Variances in virtual mass with different arrow weights will point to hysteresis.
That seems reasonable with wood bows Steve. Was it Klopsteg who invented the idea? I have read where VM was assumed to stay the same within a range of arrow weights. Perhaps the assumption was reasonable in the fiberglass world? and differences were presumed to come from more/less efficient limb designs?
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Willie, one thing interesting about energy losses has to do with limb vibration. To a lesser degree than hysteresis it is also somewhat time sensitive meaning that the faster the bow limbs return the more vibration or limb distortion we get. I have kind of a theory about this. We know the more working limb a bow has the more opportunity for vibration exists. So we need to work toward figuring out the lowest amount of working limb we can get by with before it starts taking set. I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period.
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I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period
like this?
s1 is a 65" 50 # stiff handled pyramid with strain that drops off steadily toward the tips.
(I can quickly re-draw it any way you like)
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Potential Energy of the Bow = Bow Hysteresis + Kinetic Energy of the Bow + Kinetic Energy of the Arrow
The bows efficiency has more losses than only hysteresis. Its has losses through any tiller less than perfect. Not just from set or from moisture, but from less than perfect energy transfer due to whip tiller or limbs not being timed exactly.
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I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period
like this?
s1 is a 65" 50 # stiff handled pyramid with strain that drops off steadily toward the tips.
(I can quickly re-draw it any way you like)
I've tillered my bows for years with the thought of a wave being set up upon string release. The idea being the limbs act as a whip, with the energy flowing and being concentrated as it flows from the inner limbs towards the tips. I have the saying, last to bend, first to release. If all the limbs energy releases at once, like an explosion, the energy does not flow and many losses occur. So I tiller the working limb closer to the tips to bend first as I draw it the bow, and the inner limb to bend last. The inner limb is last to bend on draw but first to release its energy upon string release. This flows like a wave all the way to the tips allowing the most energy efficient delivery of energy possible.
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sleek,
the equation is from the other site. it shows the basics, but does not include all the ways tillering can be done poorly.
Here is the same bow with the strain increasing towards the tips. Is this what you mean? Whether any part of the limb bends first or last as it is drawn is an interesting idea, and might depend on string angles. How it returns to brace could be different, as the arrow is accelerating. maybe.. I think you would have to have a slo-mo camera to actually tell.
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Willie that is pretty close but I like to keep outer limbs stiff to further reduce working limb area.
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sleek,
the equation is from the other site. it shows the basics, but does not include all the ways tillering can be done poorly.
Here is the same bow with the strain increasing towards the tips. Is this what you mean? Whether any part of the limb bends first or last as it is drawn is an interesting idea, and might depend on string angles. How it returns to brace could be different, as the arrow is accelerating. maybe.. I think you would have to have a slo-mo camera to actually tell.
How it returns to brace IS and SHOULD be the entire focus and good of you to point that out. The way it returns to brace is ideally controlled by the arrow. The moment you let go of that string, the resistance of your fingers no longer is providing the force that keeps the bow in its drawn shape. Its now the arrows inertia ( at rest, it wants to stay at rest ) and the inertia of the limb ( other things too but too many to easily address ) that slow the rate at which the bow returns to brace. The rate it returns, and the orderly fashion in which it does so, has much to do with its efficiency. Too fast and the wave of energy transfers becomes sloppy, or dirty. The effect Steve mentions of Hysteresis also comes into effect here as well. Him coming up with the idea of time sensitive Hysteresis was a stroke of brilliant insight there.
Hysteresis slows the bows ability to provide power to its load, and becomes part of the load in all honesty. Id bet you could calculate it as such if you were to measure the difference in energy of two different weighted arrows. A heavier arrow is well know to carry more energy than a lighter one, because the it spends more time absorbing the bows energy, vs a lighter arrow. The difference in energy between a heavy arrow and light one could easily be a good indicator of amount Hysteresis in the bow.
Its also noteworthy that the Hysteresis in a bow continues to show up after the arrow is shot. As the limbs relax from the shot the string tension at brace increases. Steve mentioned this same thing earlier. Id like to take a scale ( tensiometer ) rigged to read string tension and see how a bows string tension increases after its been returned to brace, and time it as well.
As for your second drawn bow you show, I dont mean the tips should bend more, or even at all. Im a believer in stiff tips. I mean that the outer working limb ( be it tips or mod limb ) should bend first. One the string angle is increased on them as the bend back, the leverage advantage on them is decreased and they stop bending. The energy of the draw is then focused to the area behind that, and it bends until the string angle relative to it is is beyond any mechanical advantage to cause it to bend further before the wood behind it starts to flex. As it bends, the string angle at the wood closet to the tips becomes even greater loosing even more mechanical advantage, ensuring that the outer wood won't bend any further. I need to get some dial indicators and clamp a bow to a table to test and prove this is how it actually works.
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Willie that is pretty close but I like to keep outer limbs stiff to further reduce working limb area.
more like this?
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Kinetic energy = 1/2mass times speed squared. This means that if you double the speed of an object, you quadruple its energy. This means that a bow shooting twice as fast has four times the kinetic energy in its limbs.
Because heavier arrows cause bows to shoot slower, far less kinetic energy is sunk into accelerating the limbs, which means a larger percentage is put into the arrow.
This explains why light tips are so efficient. Because the limb tips are the fastest moving part of the bow, they take a significantly larger share of energy per Oz to accelerate than mid and inner limb areas.
The kinetic energy of the limbs the moment before departure is not available to the arrow. Instead, it is converted to limb vibration and handshock.
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I'm reading the words, but not quite grasping what they are referring to.
Badger: I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period.
Sleek: So I tiller the working limb closer to the tips to bend first as I draw it the bow, and the inner limb to bend last. The inner limb is last to bend on draw but first to release its energy upon string release. This flows like a wave all the way to the tips allowing the most energy efficient delivery of energy possible.
To me, they appear to be saying the opposites. Am I wrong?
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Didn't we decide that you can't get part of a limb to bend first? More or less, yes but not first or last. If you take any snape limb and move the tip 1/4" the inner part of the limb will move, maybe not much but it will move. Like the Parsons carriage. ;D
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Didn't we decide that you can't get part of a limb to bend first? More or less, yes but not first or last. If you take any snape limb and move the tip 1/4" the inner part of the limb will move, maybe not much but it will move. Like the Parsons carriage. ;D
I haven't abandoned the thought because I simply haven't fount a convincing reason to doubt it. Perhaps instead if saying "bending first" if i were to say, bending faster in terms of release, that could get you closer to my side of the fence? If an arrow relieving a stiff kick in the rear by way of string release will cause the arrow to flex, setting up a wave, then the same logic should apply to the bows limbs. When the arrow is shot, the nock moves either first or faster than the point, i cant say which, causing the arrow to bend until the tip catches up in speed with the nock. I feel strongly this same principle can me made to apply to a bows limbs and do my best to tiller with that in mind.
Id love to be prove wrong, because if so, that means I became more knowledgeable than I am right now as I sit thinking over a bowl of oatmeal. But as I currently sit, I just can't convince myself that it doesn't work that way. This may just continue to be a case where you and I must agree to disagree, and thats ok. Id like to get acess to a super slow mo camera as mentioned to prove this theory, which at this point, is all it is.
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I'm reading the words, but not quite grasping what they are referring to.
Badger: I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period.
Sleek: So I tiller the working limb closer to the tips to bend first as I draw it the bow, and the inner limb to bend last. The inner limb is last to bend on draw but first to release its energy upon string release. This flows like a wave all the way to the tips allowing the most energy efficient delivery of energy possible.
To me, they appear to be saying the opposites. Am I wrong?
No, he and I are in agreement on the points you are confused about. We just look at it from different ends of the bow for a reference point. His thoughts start from tips to inner limb, mine start from inner limb to tips. Either way, its the progression of energy transfer thats key. Steve, if I misrepresented/understand what you are saying please correct me.
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Right DC. At least on any bow where the string doesn't touch the belly at brace.
The only design I know of to act differently is the Duoflex. Of course this is because the string is sat on the belly of a significant proportion of the limb at brace and this changes as the bow is drawn.
These different limb profiles only work when tied into width taper. Tiller shape is dictated by width profile.
For a straight limb bow eg non recurve the way to the minimum limb distorsion losses is to concentrate the bend in the inner limbs, stiff, narrowed past pyramid taper outer limbs. Tillered like Willies last tiller picture. This tiller gives the longest return path for the tips.
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Didn't we decide that you can't get part of a limb to bend first? More or less, yes but not first or last. If you take any snape limb and move the tip 1/4" the inner part of the limb will move, maybe not much but it will move. Like the Parsons carriage. ;D
I haven't abandoned the thought because I simply haven't fount a convincing reason to doubt it. Perhaps instead if saying "bending first" if i were to say, bending faster in terms of release, that could get you closer to my side of the fence? If an arrow relieving a stiff kick in the rear by way of string release will cause the arrow to flex, setting up a wave, then the same logic should apply to the bows limbs. When the arrow is shot, the nock moves either first or faster than the point, i cant say which, causing the arrow to bend until the tip catches up in speed with the nock. I feel strongly this same principle can me made to apply to a bows limbs and do my best to tiller with that in mind.
Id love to be prove wrong, because if so, that means I became more knowledgeable than I am right now as I sit thinking over a bowl of oatmeal. But as I currently sit, I just can't convince myself that it doesn't work that way. This may just continue to be a case where you and I must agree to disagree, and thats ok. Id like to get acess to a super slow mo camera as mentioned to prove this theory, which at this point, is all it is.
I like the arrow analogy but I still don't think the nock moves first, slower, yes but not first. Anyway That's getting to be semantics.
So the bow is held bent by the string, so the "pressure" is released at the tip. I can see a wave being propagated down the limb. I have to think about what happens next :)
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Right DC. At least on any bow where the string doesn't touch the belly at brace.
The only design I know of to act differently is the Duoflex. Of course this is because the string is sat on the belly of a significant proportion of the limb at brace and this changes as the bow is drawn.
These different limb profiles only work when tied into width taper. Tiller shape is dictated by width profile.
For a straight limb bow eg non recurve the way to the minimum limb distorsion losses is to concentrate the bend in the inner limbs, stiff, narrowed past pyramid taper outer limbs. Tillered like Willies last tiller picture. This tiller gives the longest return path for the tips.
Oh yeah, I'll add that to my thought list.
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@tradecraftsman
nice well written description of the energy losses associated with accelerating the limb at release. limb energy losses do seem like they would be predictable for a given design, and a graph might be plotted to project losses at other velocities.
This might be a way to get a handle on the separation of hysteresis losses from limb kinematic losses.
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Vibration losses don't seem to change as radically as Hysteresis losses.
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You know more about this than I do, (you came up with the mass principal, right?), but handshock is also the result of the limb kinetic energy.
By the way, how do you distinguish between losses for hysteresis and limb kinetic energy in the lab? I'm getting the urge to start experiments myself.
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Virtual mass is based on Limb KE.
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By the way guys - what exactly is it you are trying to work out?
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Mike,
I brought this discussion on virtual mass to a dedicated post, because we were getting off track in http://www.primitivearcher.com/smf/index.php/topic,68878.0.html (http://www.primitivearcher.com/smf/index.php/topic,68878.0.html)
over there, Badger commented....
A glass bow has very little hysteresis so once the virtual mass is established it will remain fairly constant regardless of arrow weight even though efficiency will continue to drop with arrow weight. A wood bow that has taken set will display more hysteresis and because set is time sensitive it increases rapidly as arrow weights go down.
Calculating Virtual Mass does seem useful when hysteresis is constant, and was useful for comparing different glass limb designs when Norb Mulaney made his contributions to the industry, but how useful is calculating VM for natural materiel bows if we need to tease the different losses apart to make improvements?
I think we have learned (or relearned) a lot about limb geometry since klopsteg introduced the VM concept , so our challenge is to use VM or something like it, to learn more about hysteresis.
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I'm trying, I'm really trying but I just seemed to get bogged down. I can't see the direction this is taking me. I know it all works because otherwise you guys wouldn't use it. How about if I was to take a bunch of measurements could someone do whatever it is that you do and tell me a bunch of stuff about my bow? Maybe then I could see what we're trying to do. I'm just taking the last scrapes on a bow so I could use that one. Don't be afraid of saying no :D
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By the way guys - what exactly is it you are trying to work out?
I WAS WRONG IN THE STATEMENT BELOW, BUT AM LEAVING IT BECAUSE IT WAS REFERENCED IN OTHER REPLIES. sorry for yelling :)
Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.
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By the way guys - what exactly is it you are trying to work out?
Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.
Virtual mass has very little relation to actual mass
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Virtual mass has very little relation to actual mass
I think kevin has a good point, Steve. My guess is that you are pointing out that arrow mass, or the virtual arrow mass, is not directly comparable to bow mass, as in grains and ounces.
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Virtual mass has very little relation to actual mass
I think kevin has a good point, Steve. My guess is that you are pointing out that arrow mass, or the virtual arrow mass, is not directly comparable to bow mass, as in grains and ounces.
Not at all, virtual mass is a measure of the amount of energy not going into the arrow. It doesn't have much to do with arrow mass or bow mass although bow mass can effect it obviously.
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I gathered some arrows 300,400,500,550 and 560 grains and shot them through the chrono. Then I graphed the results and got a pretty much straight line except for a little jog with the 550 that I can't explain yet. Then I made a heavy Ocean Spray arrow that is 650 grains. I marked on the graph where I thought it would end up and it was right on. Speeds went from 175 to 240 fps. Does this straight line tell me anything?
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That's very interesting, I'd love to see the data. I wish I had a chrono and could do these experiments myself.
Depending on the measurement precision, gentle curves could look flat if their not spread out over a wide enough range of data. What if you shot a 900 or 1000 grain arrow? What about a flight arrow?
The math is looking more and more complex, I fear integrals in the near future... :-\
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I gathered some arrows 300,400,500,550 and 560 grains and shot them through the chrono. Then I graphed the results and got a pretty much straight line except for a little jog with the 550 that I can't explain yet. Then I made a heavy Ocean Spray arrow that is 650 grains. I marked on the graph where I thought it would end up and it was right on. Speeds went from 175 to 240 fps. Does this straight line tell me anything?
From knowing the 300 grains shot the 240 fps I calculated 38.36 foot pounds of energy in the arrow. With the 650 grain arrow doing 175 fps it has 44.19 foot pounds of energy. It illustrates that heavier arrows take more energy away from the bow. That supports whats being said about Hysteresis being time sensitive. The longer the arrow is on the string, the more energy it sucks from it, and the internal frislction of the bow ( Hysteresis ) is reduced.
If you are familiar with non newtonian fluids, you know that they solidify as energy increases through them, providing more resistance to an object trying to move through them. So the slower the object moves through it the easier it can move. Compare that to a bows limbs. They behave in a non newtonian way. The faster they move, the more they dont want to due to internal friction. Im certain inertia of mass has a bit to do with this as well.
If you post the arrow weights and corresponding speed, I can calculate the energy of each arrow, and when you plot that, you may notice the energy is not a linear increase. Id posit that the energy increases tangental to the arrow weight increase.
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Virtual mass has very little relation to actual mass
I think kevin has a good point, Steve. My guess is that you are pointing out that arrow mass, or the virtual arrow mass, is not directly comparable to bow mass, as in grains and ounces.
I was incorrect in my answer and quite honestly,, distracted when I made my reply. Im sorry about that and have edited my reply to note the fact.
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I gathered some arrows 300,400,500,550 and 560 grains and shot them through the chrono. Then I graphed the results and got a pretty much straight line except for a little jog with the 550 that I can't explain yet. Then I made a heavy Ocean Spray arrow that is 650 grains. I marked on the graph where I thought it would end up and it was right on. Speeds went from 175 to 240 fps. Does this straight line tell me anything?
if your graph was based on Virtual mass the predictability would mean little hysteresis. What was your graph based on? You got 240 from a 300 grain arrow? Excellent! I think a clean shot from a 300 grain arrow going 240 fps would get you over 400 yards.
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My graph was just weight vs speed.
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Using virtual mass I came up with these. 400 grains 215 fps 500 grains 195 fps 550 grains 188 fps. How close is this to what you have. I had to estimate your stored energy.
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400 was 215, 500 grains was 200, 550 was 198. I did a 560 and it was 191. I'm thinking that if there was a lot of hysteresis the line would have been curved?? I'm not sure which way. The arrow weight weren't exactly even numbers but they were within a grain or two. I think the 300 was actually 305. It's bed time ;D ;D
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By the way guys - what exactly is it you are trying to work out?
I WAS WRONG IN THE STATEMENT BELOW, BUT AM LEAVING IT BECAUSE IT WAS REFERENCED IN OTHER REPLIES. sorry for yelling :)
Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.
I think you need to set out a theory first then try to prove it or not :)
At the end of the day wood has hysteresis.....you can't change that. Now what do you intend to do about it and what can you do differently that will help 'offset' these losses?
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DC - what was the bow and its parameters? Draw weight and length (from back or belly, if back, how thick handle), brace height (belly or back)? I think that hysteresis is very low, but need those parameters for calculations.
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By the way guys - what exactly is it you are trying to work out?
I WAS WRONG IN THE STATEMENT BELOW, BUT AM LEAVING IT BECAUSE IT WAS REFERENCED IN OTHER REPLIES. sorry for yelling :)
Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.
I think you need to set out a theory first then try to prove it or not :)
At the end of the day wood has hysteresis.....you can't change that. Now what do you intend to do about it and what can you do differently that will help 'offset' these losses?
I think you may have missed where I stated I posted that while distracted. I thought this question I was answering was referencing actual mass, on another thread. I really made myself look foolish there.
As for what to do about Hysteresis, I feel with out the ability to provide a concrete argument, that it can be dealt with via efficient energy transfer..The way nature does it is via wave transmission. Im pretty set on my wave theory and seeing as how it works in so many other applications, I feel a limb tillered to release its energy via a sine wave, flowing from handle towards tips, will minimize hysteresis loses best.
I do reserve the right to be wrong...
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By the way guys - what exactly is it you are trying to work out?
I WAS WRONG IN THE STATEMENT BELOW, BUT AM LEAVING IT BECAUSE IT WAS REFERENCED IN OTHER REPLIES. sorry for yelling :)
Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.
I think you need to set out a theory first then try to prove it or not :)
At the end of the day wood has hysteresis.....you can't change that. Now what do you intend to do about it and what can you do differently that will help 'offset' these losses?
Bownarrow, I did some extensive testing several years ago on hysteresis. What prompted the tests was seeing how much more efficient shorter draw bows were. Wood has almost no hysteresis until fibers start to get crushed ( set) the virtual mass testing was used to isolate hysteresis from vibration losses. As it turns out it is one of the biggest controllable losses.
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DC - what was the bow and its parameters? Draw weight and length (from back or belly, if back, how thick handle), brace height (belly or back)? I think that hysteresis is very low, but need those parameters for calculations.
50#@28" from the back, handle 1 1/2" thick, BH 6" back.
A little more accurate arrow weights and speed
306-240 and 236
405-215
501-200
548-198
556-191
653-175
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It looks like your 650 grain arrow was a little slower than it should have been and your 548 grain arrow was too fast.
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I'm going to do this test again with a couple of shots for each weight. The 548 was a definite jog in the graph. The 650 is just an arrow that I threw together to get a heavy one. It doesn't have any fletching and hit the target sideways. I think I got an error on the second chrono with it.
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I did it again and the changes aren't worth typing. The 548 dropped 4fps and the 667(fletched added 4 grains) came up by 2 fps. My second chrono seems to be about 5 fps slower for some reason.
I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[
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I did it again and the changes aren't worth typing. The 548 dropped 4fps and the 667(fletched added 4 grains) came up by 2 fps. My second chrono seems to be about 5 fps slower for some reason.
I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[
Consider that the weight of the arrow allows the harmonics ( wave theory ) of the bow to be maximized. That weight arrow 548 grain, allows the return wave of the bow limbs to perfectly sync up, delivering the most efficient energy flow possible.
In support of this consider an off balance tire. It will vibrate worse up to a certain speed and then smooths out to be unnoticeable at a specific rpm, then as you pass that rpm range you get bad vibrations again. All these other arrows don't allow your bow to be in its proper vibration range. But the one heavily arrow puts it right there, picking up ALL the bows energy.
I know its just a theory of mine, but it explains a lot, and has worked for me in getting good performance from my bows. Also, there is usually 2 ranges that fall 180° ( i think ) from eachother that allow good performance. You may find another arrow weight that also joggles the graph, either by more or less, but i dont think the same amount as this arrow.
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It is strange. I've run the test twice and even with the the readings from the second chrono being different that hump for the 548 one is there. If your wave theory is right wouldn't you think that the 556 one would show some improvement?
The 501,548 and 556 are all the same Tiger shafts. the 501 and 556 are both 60# spine and the 548 is 55#. Could that one be getting a cleaner launch?
I think I'll sand down the 556 to 55# spine. I'll take 5 shots before and 5 shots after.
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That 550 arrow has 47.87 foot pounds of energy, which is more than the heavier arrow has at 44.19 foot pounds with 650 grains. If it were only hysteresis as an energy loss factor, this energy difference wouldn't make any sense. For certain, sometimes else is working to allow this random arrow to absorb more energy contrary to standard thought.
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It is strange. I've run the test twice and even with the the readings from the second chrono being different that hump for the 548 one is there. If your wave theory is right wouldn't you think that the 556 one would show some improvement?
The 501,548 and 556 are all the same Tiger shafts. the 501 and 556 are both 60# spine and the 548 is 55#. Could that one be getting a cleaner launch?
I think I'll sand down the 556 to 55# spine. I'll take 5 shots before and 5 shots after.
Certainly a cleaner launch is a very good possibility and could completely explain this. I assumed you had all the arrows spined for the bow so similar flight would be hoped for. If you can try different spines all in the same weight range that would be an interesting test. Are they arrows all hitting the target fairly straight?
I wouldn't expect the 556 to show much if any improvement, because i don't know where the harmonic range on this, or any, bow is. and chances are, its a narrow range. The difference from 548 to 556 is 8 grains, and thats enough to make a noticeable difference in flight distance.
Id like to see the speed differences as the grains go up one at a time, then down from 548 one at a time. That would help you dial right in and you may even be able to plot the results of the wave as a wave. You should be able to if my theory is correct.
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Foiled! I started scraping down the shaft and realised that I was removing weight as well as spine. I took off 10 grains of arrow and lost 2.5-3# of spine. I gained about one or two fps which 10 grains of weight could explain so that's a bust. I've never really worried about spine as it didn't seem to have that much effect in the speed and it's a PITA to have to make equal spined arrows in every weight. This is where the mathematical method would shine because you can change one thing(I think). I think where the cleaner launch would help is in equalising the two chronos readings.
The arrows are hitting the target pretty straight.
With a real arrow you can't change the weight without changing the spine and vice versa. Maybe you could increase the weight by wrapping tape around the middle of the arrow so it wouldn't change the spine but then you'd have to wonder if the bumpy surface going across the bow would have any effect. More thinking required :D
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Foiled! I started scraping down the shaft and realised that I was removing weight as well as spine. I took off 10 grains of arrow and lost 2.5-3# of spine. I gained about one or two fps which 10 grains of weight could explain so that's a bust. I've never really worried about spine as it didn't seem to have that much effect in the speed and it's a PITA to have to make equal spined arrows in every weight. This is where the mathematical method would shine because you can change one thing(I think). I think where the cleaner launch would help is in equalising the two chronos readings.
The arrows are hitting the target pretty straight.
With a real arrow you can't change the weight without changing the spine and vice versa. Maybe you could increase the weight by wrapping tape around the middle of the arrow so it wouldn't change the spine but then you'd have to wonder if the bumpy surface going across the bow would have any effect. More thinking required :D
Wrap tape around the nock end. If you can do ALL your weight adjustments back there, spine won't be an issue.
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It takes a lot of tape. Half the length of the arrow is just a few grains and I'm not so sure that putting the weight on the back doesn't increase the spine. If weight on the front decreases it, I dunno.
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It takes a lot of tape. Half the length of the arrow is just a few grains and I'm not so sure that putting the weight on the back doesn't increase the spine. If weight on the front decreases it, I dunno.
We are over thinking this. The arrow doesn't care how much it weighs. So, don't add weight to the arrow, add it to the string right at the nock area using split shot fishing weights. The bow will handle it fine, just a little hand shock, but it will force the bow to push the correct weight, and you won't have a variable in spine to worry about.
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I've got chores to do so it's going on the back seat. It's the Vancouver Island Wooden Bow Makers Gathering this weekend. Got to get the trailer(RV) ready ;D
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I've got chores to do so it's going on the back seat. It's the Vancouver Island Wooden Bow Makers Gathering this weekend. Got to get the trailer(RV) ready ;D
Have fun man! Thats awesome yall have an event, lots of folks dont. Im prepping to go out of state on a big hunt with my son for his first hunt. He has made his bow for this specific hunt. Going on an 8,000 acre ranch for trophy bucks. Otherwise I'd try to do the testing myself. When I get back, I will build a shooting machine. to do some testing also. I do appreciate your willingness to do all these experiments. Your dedication to precision and testing is invaluable.
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I guess that spot in the bag got a little soft :-[ :-[ :-[ :-[
Damn. the door looks pretty good otherwise. though.
are you shooting with one of your best bows? It could be there is not much hystersis to detect :)
maybe test some really light arrows, and then repeat the test with an otherwise similar bow, but is doggy with set, when you have a chance. I will try to plot any data you generate on a graph this evening to see if we can "see" any hysteresis.
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Consider that the weight of the arrow allows the harmonics ( wave theory ) of the bow to be maximized. That weight arrow 548 grain, allows the return wave of the bow limbs to perfectly sync up, delivering the most efficient energy flow possible.
In support of this consider an off balance tire. It will vibrate worse up to a certain speed and then smooths out to be unnoticeable at a specific rpm, then as you pass that rpm range you get bad vibrations again. All these other arrows don't allow your bow to be in its proper vibration range. But the one heavily arrow puts it right there, picking up ALL the bows energy.
I know its just a theory of mine, but it explains a lot, and has worked for me in getting good performance from my bows. Also, there is usually 2 ranges that fall 180° ( i think ) from eachother that allow good performance. You may find another arrow weight that also joggles the graph, either by more or less, but i dont think the same amount as this arrow.
This is an very good analogy and very true. You will see this if you very carefully test a bow over a wide range of arrow weights. In a plot of virtual mass versus arrow weight, the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan
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Waves involve the transport of energy without the transport of matter. In conclusion, a wave can be described as a disturbance that travels through a medium, transporting energy from one location (its source) to another location without transporting matter.
:)
DC just make some selfnocked test arrows. You can fine tune the weight quite a bit without affecting spine. You can also get sticky backed lead strips. Airgun pellets are another way to alter weigh easily. Use screw on field points and drop the melted lead in the head (soften spine + add weight). Sanding just the middle will reduce spine without affecting weight much. Stiffen an arrow whilst reducing weight - sand both ends, don't touch the middle.
Many ways to play about with arrow dynamics.
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Up until now I have just used two carbons with a variety of tip weights and it's worked just fine. I just ignored the spine. Now I've got this one arrow that seems faster for some reason and it's opened a can of worms. I did try scraping the middle to lower the spine but it did affect the weight enough to make me doubt whether it was the weight or the spine that was making the improvement. I wasn't expecting that. It may be the Tiger arrows. They are heat treated I believe and maybe that makes them less responsive to scraping. I dunno. Anyway the shooting machine is all packed in the trailer for the Gathering so it's all stop for a few days. I'll be making a good old knotty yew self bow. It will be nice not to think about speed for a few days. :D
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the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan
Alan, would you be willing to speculate or comment about any limb designs features that may affect these harmonics? or how one could "tune" their design to a particular weight arrow? This goes a bit beyond making tips lighter or stiffer I presume.
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When you think about it all you can do is leave wood on or take it off. The question is where?
Oh, I guess you can prebend it or not.
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the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan
Alan, would you be willing to speculate or comment about any limb designs features that may affect these harmonics? or how one could "tune" their design to a particular weight arrow? This goes a bit beyond making tips lighter or stiffer I presume.
I know 6ou weren't asking me, but as far as I've got so far in my wave theory is that the wave exists and the best flying arrow weight needs to be found for the bow, I haven't figured a way to tune the bow to the arrow yet, though I'd imagine it has to do with bow length or working limb length as it applies to wave length. I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.
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I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.
How about trying to see the limbs in action with some sort of way to "record" an arrow release?
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I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.
How about trying to see the limbs in action with some sort of way to "record" an arrow release?
I want to go to a college with a high speed camera and do some recording with different weight arrows to see how they affect the harmonics of the bows limb.
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Tuomo did a lot of work with HS photography, maybe he can comment if something as subtle as a wave in a returning limb is something he has seen, or could be detected with photography.
https://www.youtube.com/channel/UCmVczwYUfq6sQQjCmKd2q5Q/videos (https://www.youtube.com/channel/UCmVczwYUfq6sQQjCmKd2q5Q/videos)
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Maybe if I make the bow large enough, like, ridiculous proportions, the wave would be large enough and slow enough to see easily.
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Maybe if I make the bow large enough, like, ridiculous proportions, the wave would be large enough and slow enough to see easily.
I don't thin a very efficient bow would have much of a wave. It is usually just refereed to as vibration but I think of it more as dis torsion. Unless you are talking about a wave that occurs during the power stroke before the arrow has left the bow. I estimated DC's stored energy at 55# more of a guess than an estimate. But based on that he only has about 125 grains of virtual mass which is almost nothing. Extremely efficient bow.
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Unless you are talking about a wave that occurs during the power stroke before the arrow has left the bow. I estimated DC's stored energy at 55# more of a guess than an estimate. But based on that he only has about 125 grains of virtual mass which is almost nothing. Extremely efficient bow.
It is my understanding Kevin is proposing a "wave" during the powerstroke, but an investigation might detect it as a vibration or low frequency sound. Sonar is just a reflected sound wave, and you would be surprised what can be learned from looking at the returned "picture". It is not at all a pic that looks anything like the real thing, but can be quite useful if interpreted correctly.
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The power stroke wave is exactly what I am referring to. I think I will refer to it as a power stroke wave theory to provide clarification from now on, PSW for short.
Willie, I like your thought process and would like to engage every possible way to disprove my idea as possible to be certain I dont look for false positives due to my own bias.
Badger, in my line of thought, the limb distortion that undoubtedly exists as we all see it often, in my opinion, can come from a frustrated wave, or, dirty wave, due to improper arrow weight, and more commonly, poor tiller that instead of setting up a proper wave on release, sends out instead, a blast of.... static? Maybe I'll just call it noise. So then, instead of the bow limbs being properly tuned, like a harmonically tuned exhaust in a car, its just wasted power getting released in an chaotic way.
Again, as usual, I reserve the right to be wrong and would welcome it.
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If the arrow doesn't use all the energy the remaining energy has to go somewhere. Low string angles make the arrow effectively heavier and help it to sap more energy out of the bow and I think we both agree that tiller shape can have an effect on that also. If set can be avoided shorter working areas in the limb will usually solve that problem.
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Tuomo did a lot of work with HS photography, maybe he can comment if something as subtle as a wave in a returning limb is something he has seen, or could be detected with photography.
Yes, I made a videos of shooting heavy and light arrows but it was very difficult to see any kind of valuable information, except that with heavy arrows bow limbs are returning slower. I think this video can tell something, at least about the importance of tiller:
https://www.youtube.com/watch?v=xGgWZYny9RM
This is an very good analogy and very true. You will see this if you very carefully test a bow over a wide range of arrow weights. In a plot of virtual mass versus arrow weight, the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan
Weight may be one thing but I believe that spine and the properties of the arrows are also very important. I made some years ago testing and found that same weight bamboo arrows were about 1 fps faster than wood (pine) arrows. Maybe CF arrows are also ittle faster than wooden arrows? But, there seems to be three arrow variables: arrow mass, arrow (dynamic) spine and arrow material stiffness (elastic modulus).
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If there is a wave you would want it to dissipate by the time it reached the end of the limb? Somehow when I think of the wave I always think of it as starting at the tip and running toward the handle. If it's not dissipated you get hand shock.
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Sleek, have you considered the possibility there might be more going on with the arrow than the bow if one arrow outshines the others on the graph?
Arrows have the primary flexing or "wave" deflection we see in slow motion where spine seems to be the biggest factor, but a close examination of the arrow shows a number of different things going on. Click the settings gear icon in this video and lower the playback speed to .25. Starting at 5:12 you will see the arrow doing a variety of flexing before it leaves the bow.
How the bow transfers the energy into the arrow might make a difference in how the limbs react and ultimately how effectively the energy is transferred.
https://www.youtube.com/watch?v=96KGWC0PB6s (https://www.youtube.com/watch?v=96KGWC0PB6s)
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I've looked at those until I'm cross eyed. To me it looks like a low spined arrow has a slower "wave" and if it is low enough the fletching hits the bow. I really can't see what goes wrong with a too stiff arrow. Anyone help me?
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Too stiff will often hit the bow and kick left
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Alan, would you be willing to speculate or comment about any limb designs features that may affect these harmonics? or how one could "tune" their design to a particular weight arrow? This goes a bit beyond making tips lighter or stiffer I presume.
I like to try to find ways to minimize the interaction of various harmonics on the shot. The best ways to do this is to push secondary vibration modes to as high a frequency as possible. This is done by following the familiar advice of focusing the bending area over as small an area as possible and using a string with maximum tensile stiffness. Otherwise, it is a matter of being aware that these interactions exist. A long thin flexible limb design should be more troublesome. A full working recurve with very flexible tips is probably going to be the most susceptible to bad behavior over a very wide range of arrows.
Alan
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Thanks Alan. I was playing around with some take down limbs in the riser fixture recently and was reminded of just how much limb vibration occurs when the tips do not come home at the same time.
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The out of sync vibration does feel bad at the handle. There can be very high lost energy even if the limbs are perfectly in sync. It is dominated by a little different mode shape, which is the mid limb popping forward and back.
Alan
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What do you think of this one? This is a plot of virtual mass for a wide range of arrow mass. This is a pretty heavy draw weight modern composite longbow design. I was trying to do everything I could to get it to throw light arrows as efficiently as possible to equal a static recurve that I had built earlier, but it was not cooperating. The plot for the static recurve was almost the opposite of this, with the lowest virtual mass for the lightest arrow, and higher virtual mass for a heavier arrow.
(https://live.staticflickr.com/65535/50537876997_af365c235f_o_d.jpg)
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Odd but still a low virtual mass.
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I was trying to get the virtual mass extremely low. I was throwing every trick I knew of to maximize efficiency with a 3ggp arrow, but fell short of my goal. This particular design has stiffened lever-like limbs with a smaller bending area centered near the handle fades.
It makes sense why this happens. There are a couple natural frequencies in the bow limb and combination of the bow limb and properties of the string which either fall in or out of phase with the launch of the arrow. The big dip is driven by the natural frequency of the middle of the bow limb between the fades and string. This frequency is lower for a long-limbed longbow than it is for a shorter limbed static recurve, and this shifts the bigger dip in the plot so that the lowest virtual mass coincides with heavier arrows. It isn’t easy to change this very much without compromising other desirable properties of the bow such as smoothness of the bow or energy storage versus draw.
Alan
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The plot for the static recurve was almost the opposite of this, with the lowest virtual mass for the lightest arrow, and higher virtual mass for a heavier arrow.
(https://live.staticflickr.com/65535/50537876997_af365c235f_o_d.jpg)
Alan,
would you be kind enough to post the plot of the static recurve? or at least post a typical curve?
the curve above is non typical? or the static recurve is non typical?
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would you be kind enough to post the plot of the static recurve? or at least post a typical curve?
the curve above is non typical? or the static recurve is non typical?
Each bow design will behave a little different. This is typical for this particular bow, but at 114#@31”, this bow is not representative of what a typical archer would shoot! What I find very interesting is that I find it more challenging to design a light 35#@28” longbow with lower virtual mass numbers.
I need to disclose that this bow is made using modern composites and modern string material. It just happens to be one that I am currently working on so I have the performance data readily available. The main point I am illustrating here is that virtual mass can be a useful method to predict arrow speeds for over a narrow range of arrow masses, but it has its limits. I still find virtual mass useful in other ways because it provides a little more insight into bow behavior than pure bow efficiency. The plot of efficiency versus arrow weight for the same bow is quite different. See below. I have observed many instances where I was testing a flight bow and I would find a particular light arrow mass where the bow seemed to quiet down with less post shot vibration. In the meantime, I have been trying to figure out ways to find ways to tie design characteristics for targeting a minimal virtual mass at a specific range of arrow mass.
Alan
(https://live.staticflickr.com/65535/50541508893_4eddec4391_o_d.jpg)