Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on August 10, 2019, 11:40:27 am
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Something I'm not sure of. Lets say I have a bow that increases 2# per inch DW out to 24" DL. Then it starts to stack for the last 4" and instead of gaining 8#, it gains 12#, 4# more than it would have without stack. Does that 4# contribute anything to the bows performance or is it just lost into never never land?
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the 54# bow probably gonna shoot harder than the 50# bow without the stack,, I am just guessing,,
they both would probably shoot about the same 10 gpp.. still just guessing,,
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It seems to me that the stacking portion of the limb is not carrying it's portion of the work thus being dead weight and not increasing but decreasing the performance.
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I don't have hard numbers, but my first bamboo bow which is super stacky only has performance when you pull into the stack and it shows in arrow speed. Makes for terrible consistency if your draw length isn't spot on each time. But it could be an anomaly from it's weird construction.
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I agree with Naibel, the bow does get the benefit of the added draw weight but not as much benefit as it should get because it drops off so rapidly. The bottom line is that a stacking bow simply stores less energy.
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I agree with Naibel, the bow does get the benefit of the added draw weight but not as much benefit as it should get because it drops off so rapidly. The bottom line is that a stacking bow simply stores less energy.
If you cock your head just right that sounds close to what I said ;D ;D You're still going to get the 2# per inch but the 1# from stack doesn't deliver. Or are you saying you will get some of the 1#?
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I agree with Naibel, the bow does get the benefit of the added draw weight but not as much benefit as it should get because it drops off so rapidly. The bottom line is that a stacking bow simply stores less energy.
If you cock your head just right that sounds close to what I said ;D ;D You're still going to get the 2# per inch but the 1# from stack doesn't deliver. Or are you saying you will get some of the 1#?
Yes you get the 1# it just drops off faster, if you start off at 10# and then build to 50 as opposed to starting at 2# and building to 50 there is a sizable difference in stored energy. Just not storing as much energy as a smoother draw.
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Gotcha, thanks. In order to arrive at the same draw weight the mid range on the stacking bow won't be 2# per inch.
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Diminished returns are still returns. The Turkish flight bows max out the stack weight.
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Diminished returns are still returns. The Turkish flight bows max out the stack weight.
A lot of flight bows have been stackers
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Yes but the Turkish ones can safely work into the stack more.
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ok so I am confused and dont understand,,could two same like bows, one that stacked, and one that did not,, shoot the same fps,,,10 gpp,, or what,,
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I don't fool much with stacking bows but my opinion is that they have the potential to be more efficient with very light arrows pound for pound. Loss of efficiency is a major thing with light flight arrows. I have one bow here that does stack at the last 3" a short recurve and I have gotten over 300 fps with it using light arrows.
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That blows my understanding of stack weight.
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That blows my understanding of stack weight.
Was your understanding based on the musings of Tim Baker?
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That blows my understanding of stack weight.
Stack weight is the same as any kind of weight, it just falls off quicker.
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My common sense says that if I keep on pulling on the stacking bow, I will be crushing the belly wood fibers by and by. Unless you are going for the flight bow record, you are better off scraping the belly to make the bow less stacking. As always, all depends on what you are trying to do with the bow. As PatM implied, horns are quite more resilient than wood.
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(lol)
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Stack is a interesting topic to me sense I have a long draw & make short bows these days & Patm made a interesting point about how much of the limb is still working past stack , but I have found that my peak performance (fps) comes right at the point of stack finger release it could be different with a shooting machine , I think when string angle becomes exsesive transfer energy drops quickly , I think a non stackicking 45lb bow would out perform a stacking 47lb bow finger release, but a lot depends on material used & design , but performance doesent always equate to shootability in the bows I have built I find the ones with a larger margine between full draw & stack are more user friendly !
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The 2.3 rule for bow length to draw length is making sense.
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Here is the hard truth about stack weight. It has absolutely NOTHING to do with the compression of wood or anything else related to the bows stress. It has absolutely EVERYTHING to do with the angle. It's a function of leverage and ANY stacking bow can be made to not stack simply by adding recurves. Stack is actually a good thing when shooting lightweight arrows as they can benefit from the very quick dry fire like speeds of a stacked bow in the early inches of release. This is especially true if the bow has low string tension at brace, as up to half the draw weight can take place in the last few inches of draw.
I'm pretty confident on this, but not beyond being corrected if someone knows better than me.
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PatM...primarily, I would say yes. But I would also say that it is based in an intuitive sense. It would seem me that 5 lbs of stack weight would not deliver the same cast or kinetic energy that 3 lbs of ....better leveraged draw weight, at the same drawn distance with the same arrow. I can see that using a very light arrow might enable you to make better use of stack weight, but the energy stored is less. I would think.
It should read 5 lbs of stack weight vs 5 lbs of better leveraged weight.
As to the Turkish bows, my assumption would be that it has more to do with string travel than anything else.
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Sleek,you are correct. Once you go past 90 degrees you start loosing too much leverage. Recurves will also stack but you do pick up some draw length before that happens.
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PatM...primarily, I would say yes. But I would also say that it is based in an intuitive sense. It would seem me that 5 lbs of stack weight would not deliver the same cast or kinetic energy that 3 lbs of ....better leveraged draw weight, at the same drawn distance with the same arrow. I can see that using a very light arrow might enable you to make better use of stack weight, but the energy stored is less. I would think.
5 pounds of energy in an inch of draw is 5 pounds of energy in an inch. It is what is is it could be said. The difference between that 5 pounds being at the end of the draw stroke and it being at the beginning is this: The 5 pounds at the beginning allows all the rest of the draw stroke weight to be built up on top of it ( added up ) allowing for a fatter FD curve and therefore higher energy storage of the bow through the power stroke. That 5 pounds at the end makes the draw curve more anorexic however allows a higher speed of string release, which a light arrow WILL benefit from greatly over a heavier arrow. The heavier arrow can not accelerate due to its mass as quickly as the light arrow, and wont be able to take ad9of that high early energy upon release.
It's similar to a heavy high hp car on the drag strip spinning its wheels, unable to move as fast as its wheels want to go because it's too heavy to accelerate that quickly, vs a rice burner just taking off because its light enough to allow its wheels to push it. It's not the best comparison due to the fact that a heavy high hp car would match its power to its wheel size and throttle etc on take off, but you get the idea.
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Sleek,you are correct. Once you go past 90 degrees you start loosing too much leverage. Recurves will also stack but you do pick up some draw length before that happens.
Recurves can be designed to stack or not stack, if I'm not mistaking Steve? Also, If the wood could take the load, you could make a bow bend until the limbs touched each other and not stack with the right recurves. I wouldn't suggest trying that however it would be a fun novelty... Darn it... now I wanna make one.
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The Indian Crab bows actually are drawn until the limbs start closing in on each other.
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Slimbob, it is not really the stack weight that might help a light arrow, it is the designs used on the bow that have a tendency to stack. The stack itself doesn't help anything.
If a bow stacked for 2" and you broke it down into 1/4" increments it might look like this 42 43 44 45 46.125 47.250 48.375 49.5 7.6 ft # Now if you took a bow with a smoother draw it might read 45- 45.625-46.125-46.750-47.375-48-48.625-49.375=8.84 ft # energy. Not really all that much difference but you can see that it starts higher on the non stacking bow so a lot more energy is lost up front on the stacking bow.
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The Indian Crab bows actually are drawn until the limbs start closing in on each other.
FASSSSCINATING.... I did not know this.
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Slimbob, it is not really the stack weight that might help a light arrow, it is the designs used on the bow that have a tendency to stack. The stack itself doesn't help anything.
If a bow stacked for 2" and you broke it down into 1/4" increments it might look like this 42 43 44 45 46.125 47.250 48.375 49.5 7.6 ft # Now if you took a bow with a smoother draw it might read 45- 45.625-46.125-46.750-47.375-48-48.625-49.375=8.84 ft # energy. Not really all that much difference but you can see that it starts higher on the non stacking bow so a lot more energy is lost up front on the stacking bow.
Interesting though on the idea of it being the design of the bow that causes stacking vs the stacking being part of the design. It does seem we are in agreement however about where the weight gain happens in the draw being a most important factor in how useful the weight gain is?
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I wish people would call it string tip angle instead of string angle, the latter of which makes no sense at all since it leads newbies to believe it is the angle of the string at the fingers. I was wracking my brain trying to figure out why the math behind what the TBB said wasn't making sense; when you plot the inverse of cosine of half the angle at the finger tips you see a clear hyperbolic graph that shows the mechanical advantage of string tension is highest at brace and gradually lowers as you draw, but nothing that would indicate a sudden increase in draw weight at any point. I had to go back and re-read the TBB carefully to see that it was the angle of the string relative to the limb tips that they were talking about.
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I wish people would call it string tip angle instead of string angle, the latter of which makes no sense at all since it leads newbies to believe it is the angle of the string at the fingers. I was wracking my brain trying to figure out why the math behind what the TBB said wasn't making sense; when you plot the inverse of cosine of half the angle at the finger tips you see a clear hyperbolic graph that shows the mechanical advantage of string tension is highest at brace and gradually lowers as you draw, but nothing that would indicate a sudden increase in draw weight at any point. I had to go back and re-read the TBB carefully to see that it was the angle of the string relative to the limb tips that they were talking about.
You sir have a VERY valid point. I will call it String Tip Angle from now on. Has a good abbreviation as well... STA
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I can’t argue the mechanics of stack as I don’t have a good understanding of it, so I take your explanation at face value. My point is more directed to the results of stack. I’m with Sleek in that it is all about string angle (or mostly). If that is correct then it is the leverage the angle provides that determines it all. So the energy in energy out ratio changes as a result...as the stack increase it takes more energy to draw the bow a given distance, so the energy out does not drop, it just takes more to deliver the same results as earlier in the draw. If the angle was better it would take less energy in to arrive at at a given FPS. So a higher draw weight would be the same energy in (Round about) resulting in a faster arrow than the previous. What am I missing?
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If the angle was better it would take less energy in to arrive at at a given FPS. So a higher draw weight would be the same energy in (Round about) resulting in a faster arrow than the previous. What am I missing?
I dont think you have it quite right here. You are not acknowledging the fact that different weight arrows will gain from different style bows. Also, if a higher draw weight is required to get the same energy in, the FPS will not be higher than the previous unless you have a different weight arrow. It will actually be slower. Higher draw weights with more anorexic fd charts favor a lighter arrow.
Unless I missed what you saying?
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Diminished returns are still returns. The Turkish flight bows max out the stack weight.
A lot of flight bows have been stackers
Steve,
would this be more true about unlimited weight class bows or bows that are shot in specific weight classes?
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I have this FG bow in theory the results should be the same I would think with the caveat that the FG taking more stress but this bow is 58" 46lb @31 at 31" it will do 197 fps with a 9.7 gpp arrow that's the closet I could get to 10 gpp so on average it's 6.3 fps per in. If my math is right it just starts to stack at 31 1/2 " when I draw it to 32" it only gains about 2 fps for the extra 1" & the limb is still working threw out the whole curve , I think the same would happen with wood ? I have not done the test on any of my wood bows for fear of destroying them !
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It just depends how the wood is bending, you still have decent string angle there very close to 90 degrees, if the outer limbs were bending more it would stack sooner.
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I'm not sure if this ties in much but here goes. I made this 57" OS straight bow, tillered it to 40#@26"(I was too chicken to go more ;D) did a FDC and speed test. Pencil line and 166fps @26". Then I recurved it and did the same tests without retillering. It was now 39#@24. Red line and 161fps@ 24". Then I retillered it to 40#@26". Green Line and 170-171fps@26.
You'll notice the dip in the red line at about 35#. I think the bow took a little set right there. Or it could have been one of the tips straightening a bit. I immediately redid the FDC and got the black line. The pencil line shows a little stack at 24". The tip string angle is getting pretty close to 90° there. None of the other lines(now recurved) show any stack if you ignore the dip in the red line.
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Once you pass 90 it noticeably starts stacking. You hadn't passed it yet.
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Unless I am misinterpreting DC’s chart, it confirms what I said...I think. The straight limb bow shoots 166 FPS at 26”. When recurved it shot 170 FPS at 26”. The bow had to be retillered so wood was removed to accomplish that. So bow with less wood shot faster and I will assume with the same arrow. String angle changed, energy in was less, energy stored and delivered was higher. I know that early string tension has some effect on this but this again tends to confirm my point. What am I missing?
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It looks to me like it just stored more energy with a better force draw curve. The mass removed to retiller I am pretty sure was small
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I think it was about 5 scrapes on one limb and 10 on the other. It's too bad it didn't hold the red line. I've glued a bit of a belly splint on the suspected weak spot so it may recover. Then I'm going to try to get 28"@40# out of it so I may scrape most of the splint off or it may be a garden stake. ;D
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I smoothed the splint out. It is about 1/16" thick and about 5" long right at the base of the recurve. Did another FDC and the line dropped about halfway between the black and red line. Speed went up to 175fps@26". Worth doing ;D. I'll do some chores and then tiller it to 27", do an FDC etc and then tiller it to 28"
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thanks DC,, thats so interesting, :)
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Your results fly in the face of the thought that recurving causes more stress and ultimately slower performance from the same bow.
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Your results fly in the face of the thought that recurving causes more stress and ultimately slower performance from the same bow.
That's one reason I'm going to try to get it to 28". Just to see if it does fall off with more stress. I'm going to guess that it's much like stack, limited gains but gains just the same.
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As long as the bow can handle the stress the recurves will always add to the speed. Many times a bow will already be over stressed and have taken set so the builder will recurve the tips hoping to offset the set. In this case it backfires and just takes more set.
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So 26" was the peak. 27 dropped to 173 and 28 was 175. It's taking some serious set, 2-3 inches I guess. So this much bend is too much for OS I think. Maybe 61-62 inches long rather than 57 would be the sweet spot. The recurves aren't very aggressive either. Looks like the bottom limb could have bent a little more. Actually the top limb should have bent a little less. Back to chores ;)
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One thing I have always liked about you DC is you put your talk and your ideas in to action rather then just rely on theory because there are times when you build a bow that it performs differently then expected, there is really only one way to find out & you do it (--)
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Well said and I agree. Mucho.
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I certainly appreciate your willingness to experiment!
I think with the set the bow was taking, any gains or losses from the further draw length and string tip angles will be lost or unobservable due to the set.
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I agree with Stickbender, you are doing some good research work. I used to do a lot more but not as motivated as I was. How much is the mass in that bow and what was the starting reflex?
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493 grams and it was pretty much straight with a bit of deflex dogleg in each limb. I steamed that out but a bit of it came back. Pic is after sitting for a day. I'm trying to think of kinda the next step. I could reflex the limbs and bring it back to 40# or deflex the handle but deflexing would drop the draw weight and any results would be meaningless. I could do both. Deflex the handle and reflex the limbs trying for the same total reflex as it has now. that may preserve the draw weight. I'll have to decide if it's taken to much set.
Thanks for all the nice thoughts but the motivation is mostly trying to find something to do in the shop that doesn't result in another bow hanging on the wall. There's almost 60 hanging there now and it just starts to feel pointless to make another. The horn bow is taking no daily time, it's mostly waiting.
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Very nice work DC, thanks for posting!
-Taylor
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Here's the next step. It's got 5" of reflex and about 5° of deflex. I was trying to get the same reflex as I had before but I over did it. Some will pull out. Tiller seems OK on the long string. See if I can get it braced :D
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Got it braced but the string alignment got messed up when I reflexed it. I'm correcting that now. I should have picked a stave with no sideways bend for this. It's coming back to haunt me.
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What? There is such a thing?
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OK string alignment is good enough. Put it on the tree and it went to 40#@28 with no tillering. That's the same DW as when it was straight. Most of the 5" reflex pulled out. It now has 1 1/2" total reflex which is very close to what it was when it was straight. It now shoots 181fps@10gpp.
When I pulled it to 28" before I deflexed the handle it was starting to take some serious(I thought) set. I think deflexing took some strain off the bow letting it hold a bit of the reflex I heated in. It was 175fps before so it looks like just changing it to RD got me 6fps.
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OK string alignment is good enough. Put it on the tree and it went to 40#@28 with no tillering. That's the same DW as when it was straight. Most of the 5" reflex pulled out. It now has 1 1/2" total reflex which is very close to what it was when it was straight. It now shoots 181fps@10gpp.
When I pulled it to 28" before I deflexed the handle it was starting to take some serious(I thought) set. I think deflexing took some strain off the bow letting it hold a bit of the reflex I heated in. It was 175fps before so it looks like just changing it to RD got me 6fps.
Fantastic experiment and nice results as well. I'm a very firm believer in the advantages of deflex.
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I think the total reflex has to stay the same so I'm thinking it has to be reflex deflex rather than just deflex. That said, I've never made a straight limbed deflex bow. Have you?
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That was a very valuable test you did there it clearly demonstrated the benefits to D Flex. D Flex put the limb in the right position to start bending right out of the handle right from the start it makes for a little higher energy storage and takes the strain off of some of the Lim
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I think the total reflex has to stay the same so I'm thinking it has to be reflex deflex rather than just deflex. That said, I've never made a straight limbed deflex bow. Have you?
I have made a few, with up to 2 inches of deflex, one was about 3 weeks ago. I have not had occasion to chrono them, but they do make solid shooting bows. Never made a slow one, I'd say from experience around 170s.
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That was a very valuable test you did there it clearly demonstrated the benefits to D Flex. D Flex put the limb in the right position to start bending right out of the handle right from the start it makes for a little higher energy storage and takes the strain off of some of the Lim
Do you think that the deflex has to be combined with reflex in order to be effective or is it a "one is good, two is better" thing?
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That was a very valuable test you did there it clearly demonstrated the benefits to D Flex. D Flex put the limb in the right position to start bending right out of the handle right from the start it makes for a little higher energy storage and takes the strain off of some of the Lim
Do you think that the deflex has to be combined with reflex in order to be effective or is it a "one is good, two is better" thing?
I know you are asking Steve, but I'd like to offer an opinion. It's to me, as if you were to modify your intake on your car so it breathes better, now it runs more efficiently, but without ALSO modifying your exhaust to handle the extra air you put in the engine you wont see the full benefit of your intake mods.
I believe deflex allows a bow to be more efficient, and reflex adds to it by allowing the extra efficiency to be used in extra power.
Basically deflex allows for a more efficient bow, reflex allows for more energy storage. Either can be used singularly. A bow built with only reflex must be wider and have more mass to reach the level of performance that a deflex reflex bow can offer. A deflex bow can offer more efficient cast per draw weight, but its low initial string tension reduces the total energy stored in a bow.
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Don did you get a better string angle as result of the D/R ? My guess is you did !!!
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Good question. I guess I should have taken more FD photos. I'm trying to visualise it but my brain doesn't work first thing in the morning.
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Good question. I guess I should have taken more FD photos. I'm trying to visualise it but my brain doesn't work first thing in the morning.
That's one benefit to reflexing a deflexed bow, is the string angle increase especially at brace.
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DC if you have anywhere you can shoot is there any chance you could take a couple of those bows out and shoot them with nine-grain and 10 grain arrows just to see how far they go?
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I wish ;D We have only managed one flight shoot a year. In the dead of winter. Any open land is probably dairy or hay. I'm looking though.
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I think with the D/R design you have a lot of advantages a couple being able to make a much shorter bow less mass for longer draw less stacking ,superior early draw weight and superior string angle thru out the arc even minor changes in string angle can make big changes in performance but one thing I have noticed is the more exstream the D/R becomes the less user friendly the bow can become ,the best shooters for me are the more mild D/R all though not as fast but more accurate & stable and the more taper in the limbs the more angular the brace & draw profile becomes that takes away from performance , I think there is a happy medium for any given material used just finding it is the trick !
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Good point you bring up stick Bender one of the ways you can counter that instability is by reducing the amount of working limb. But then you have the issue of the bow taking too much set. I built a boat several years ago gray extreme that address all these issues when I get back home I'll see if I can write about it and maybe post a picture