Primitive Archer
Main Discussion Area => Bows => Topic started by: Knoll on January 09, 2019, 03:22:56 pm
-
Topic or comments re impact of brace height on arrow speed comes up regularly.
I have not seen the subject tested. This fella did.
Impact . . . virtually zippo.
https://www.youtube.com/watch?v=yvjuZL_fdw0
-
I call foul!
IMO it's meaningless for a couple of reasons reasons.
1. It's a modern bow with huge amounts of deflex reflex using F/glass. The high preload/deflection on the limbs at brace (and the shape of the force draw curve) probably means the small change in brace height makes little difference.
2. The brace height is much higher than with a wooden bow and a 1" change in a 7.5" brace is a much smaller percentage change than it would be in a 5.5" brace, which is more typical for a selfbow . Eg 1" in 7.5 is about 13% where from a 5.5" brace it is over 18%
I'm not saying the results are necessarilly different for a self bow... just that this test is doesn't prove the case for a self bow.
Del
-
I'm with Del but I'll stick a self bow in my shooting machine and try it at more like our brace heights. Maybe tomorrow when I get a bunch of crap off my bench ;D
-
What do you guys think of the statement that no bow pushes the arrow more than 19 inches?
-
I'd say that's not true Pat, my f/g recurve for example, braces at 8", measured to the handle of course, it's just a hair over 9.5" to the back of the bow. My draw is 29.5", so it's pushing the arrow 20" from my anchor back to brace.
-
Try these two procedures to establish maximum cast of arrows :
1a.) Start off with a measured to the target (I use 18 meters) . . .
2a.) Start off with “0” point of nock height then mark the place on the target 3a.) Then incremental (1/8” used) to raised of nock height to 1” . . .
4a.) This should give you is a “sweet spot” of maximum cast of the arrows . . .
Using the new nock point:
1b.) Start off with a measured to the target (I use 18 meters) . . .
2b.) Start off with 5” point (“0” point) of brace height then mark the place on the target . .
3b.) Then incremental (1/8” used) to raised of brace height to 8.5” . . .
4b.) This should give you is a “sweet spot” of maximum cast of the arrows . . .
. . . and this is all she wrote . . .
regards,
Scyth
-
Oh I know that math but the statement was in reference to bows of all brace heights and draw lengths.
-
Well I cleaned off the bench. I used a 40#@28" ELB and a 400 gr arrow. The brace height was 6.25". I shot 7 shots- 175,174,175,174,174,174 and 175. I dropped the brace height to 5.25 and shot another 7-177,176,177,176,176,176 and 176. I thought that was pretty convincing but to check I put the brace height back to 6.25 and shot 3 176's in a row. Didn't prove anything. I'll have to do it again. Somebody have any idea what might have gone wrong? When I put the brace height back to 6.25" the speed should have gone down. I'm puzzled.
I'll try my other chrono.
-
Pat are you suggesting that the arrow/string/limbs reach maximum velocity within the first 19" and that even if there is more than 19" of travel the arrow doesn't continue to accelerate, hence no more push?
-
We need more than that Pat. There has to be some kind of conditions for that statement. An 84" longbow with a 36" draw length will obviously(to me at least) have more than a 19" power stroke.
-
It wasn't my idea. There were no conditions attached to the statement AFAIK.
-
OK second try, different chrono. New battery. 6.25 brace height 177,177,177,177,176,177 and 176. 5.25 BH 176,178,178,177,177,177,178. Then I put the BH back To 6.25 and got 177 and got called in for supper. There is a slight difference but it's only an average of .5 fps. That 176 on the second group of numbers bothers me as it was the first shot after I lengthened the string but even if I changed it to 178 the average hardly changed. So 1" in BH doesn't make a lot of difference. Maybe changing fron 5" to 8" might be more noticeable but nobody uses an 8" BH do they ;) ;) ;)
-
Larry Hatfield did a lot of studies on this very subject, and that 19 inches was the number he came up with.Brace the bow were it best suits you as velocity is marginal at best.
-
Thanks for doing that experiment Don. I thought it would make more of a difference than that.
-
What do you guys think of the statement that no bow pushes the arrow more than 19 inches?
That statement is compete and utter nonsense!
Take a warbow (or a Yumi!) for example at 32" draw ... the arrow doesn't leave the string after 19".
Maximum acceleration is probably pretty much as soon as it is loosed, BUT it is still accelerating.
If the bow stopped pushing after 19 inches we would see the arrow leave the string after that!
I think the bloke doesn't understand the difference between velocity and acceleration.
As an example if you are in a car and yo floor it. Maximum acceleration is pretty much once it gets some grip and overcomes the initial inertia. Then it accelerates smoothly, pretty smooth the rate of acceleration starts to drop off BUT it is still accelerating.... it may still be accelerating when it hits 70mph, but only slowly ... doesn't mean it's stopped being pushed.
Del
-
That's really interesting! So the difference doesn't seem to be that huge. DC, could you do the same test with different arrow weights from maybe 7 to 12 ggp? It would be really interesting to see, if different arrow weights behave differently. Did you use the same string for your tests or different ones?
-
What do you guys think of the statement that no bow pushes the arrow more than 19 inches?
That statement is compete and utter nonsense!
Take a warbow (or a Yumi!) for example at 32" draw ... the arrow doesn't leave the string after 19".
Maximum acceleration is probably pretty much as soon as it is loosed, BUT it is still accelerating.
If the bow stopped pushing after 19 inches we would see the arrow leave the string after that!
I think the bloke doesn't understand the difference between velocity and acceleration.
As an example if you are in a car and yo floor it. Maximum acceleration is pretty much once it gets some grip and overcomes the initial inertia. Then it accelerates smoothly, pretty smooth the rate of acceleration starts to drop off BUT it is still accelerating.... it may still be accelerating when it hits 70mph, but only slowly ... doesn't mean it's stopped being pushed.
Del
You could take that up with Larry but just be aware that he tends to get pouty and belligerent when someone questions his status. ;)
-
Larry and I have been friends for a long time but I would have to disagree with that statement also. I am guessing that he feels the arrow leaves the string before the power stroke is completed. I think in some cases it may on bows with very low early tension but I think most bows are pushing right up to when the bow hits brace height.
I tested speeds with different brace heights quite a bit, I came to the conclusion that if there was a difference it was negligible. This was one of the first things I checked when I got into flight shooting as the popular belief was that lower brace heights give better speeds. A better tuned bow is far more important than any minuscule difference that might be detected.
-
I think Del nailed it down on his first post the reflexed FG bow really has nothing incomon with a self bow braced height wise , There is a much larger brace height window with FG bows I have braced FG bows I have built between 7 1/4 & 9 " with minimal change in arrow speed but I never brace any self bow I have made over7 in. I think arrow flight out trumps arrow speed for me brace height wise !
-
Thank you, DC, for following through with the testing.
-
That's really interesting! So the difference doesn't seem to be that huge. DC, could you do the same test with different arrow weights from maybe 7 to 12 ggp? It would be really interesting to see, if different arrow weights behave differently. Did you use the same string for your tests or different ones?
Yes it was the same string. I've only got two arrows that I use on my shooting machine. They are carbons. Reason is, I do my testing in the garage so there is only seven feet from the bow to the target. The arrows are still going crooked from going around the bow and I've broken more bamboo arrows than I care to mention. So, no, sorry, I'd rather not do more tests.
-
How center shot the bow is likely plays a fair bit into this. Lowering the brace height on a typical selfbow is just going to create interference when shooting the same arrows.
-
Good point. The arrow I was using is very stiff. It's a carbon 300. I just checked the spine and it's 90 some pounds. A tad stiff for a 40# bow ;D ;D
-
what about testing 4 inches to 6 inches with a proper arrow,,
also the 4 inch brace should be a bit less in draw weight, so if it shot the same fps with less draw weight, that would be a difference,,
I have tested many times,, and maybe I am biased,,,, but have seen a 2 -3 fps difference,,
this was not off a machince so my test may not be accurate,,
I did read in volumen one, that it would make a difference as well, ,just saying
your arrow should not be going crooked even at close range
-
As I explained I use a carbon arrow for strength so the spine is way out. I just grabbed an arrow out of the junk bin at the range because I was tired of breaking arrows. Once I get a few limper carbons it may start to sort itself out. Even with my best arrows that fly very true I don't believe they are going straight six feet from the bow. It's got to take longer than that to straighten up. Even when I was shooting properly spined arrows from the machine the arrows always hit the target at an angle.
-
I would think the fps gain would have to do with the FDC on any given bow in other words a highly reflexed sinew bow has probably more to gain then a self bow with 1" of set the more early draw tension I think on the glass recurve in the vid the working curve had a lot to do with the neutral gain in fps !
-
That crossed my mind. If you have a ton of early draw weight you will probably gain more speed but my gut says it ain't going to be more than a pound or so. This might mean a yard to a flight shooter which can be a big deal but it won't mean beans to a hunter. Like you said a couple of post back, arrow flight trumps speed.
-
He is referring to his recurve bows
-
my arrows hit the target straight at 6 feet, I shoot inside some,,at very close range,,
wouldnt want you to break any more arrows for sure, ,but having an arrow hit straight at close range is possible,,,for sure,,,my inside target is a bag target,, it wouldnt break an arrow anyway, it has some give to it,, I dont have any experience with carbons,,
all my arrows are wood,, (--)
-
I'll see what I can do. Maybe check all the alignment on the machine but it's more than likely spine or recovery time. Not sure what I can do with that.
-
DC,,no worries ... thanks for all the positive input,, it s does seem reasonable that the longer power stroke of the low brace would have a postivie effect on arrow speed,,,
-
I read that same book Brad and always thought that to be true but I really think it depends on the bow design I recently made a highly reflexed FHLB that ended up at 63lb @30 1/2 I couldnt get the brace down below 8 1/2" with out making limb contact so I was determined to bring it down to 7 1/4 " so I narrowed the limbs & traped both the back and belly got the draw weight down to 57 lb @ 7 1/4 " with the limbs bending more ,I didnt like the way it was shooting even though it wasnt making limb contact and I returned to the 8 1/2 " brace the bow chronyed at the same numbers ether height but shot much better at the higher brace, I cant really exsplain it other then when moved to the higher brace it a loud more of the highly reflexed limb to work negating the extra length, I dont think the lower brace height applies to all bows but just my 2 cents !
-
This is kind of like tuning my model sailboats. You know from the physics of sailing that doing something is a positive thing. What you don't know is how much will it change and will the change be negated be something else that the change will do. It can get very frustrating.
-
Stickbender,, good point,, I think you are right,, and just because someone got a certain result with a bow,, does not mean it is correct for all bows,, for sure,, and DC,, thats a good thought as well,,
maybe with a straight limb self bow it is more applicable,,, I just enjoy getting a bow to shoot smooth with good,, or perfect to my eye,, arrow flight,, and enjoy the rest of the technical stuff, ,but dont let it get me too frustrated,, (f)
-
Very good posts here guys.
Good information.
What this site is all about
You Guys sure can put it in words better than i.
Thanks
DBar
-
I think there is always trade offs with a bow, change one area and it changes in other places it's kind of a balancing act of sorts but a whole hardly agree how the bow shoots regardless what the chrony says is most important , I think that's what makes this bow making fun ,regardless what you read you really don't know tell you make the bow and test it !
-
If it feels good when shot.....its a gooder :) ;)
DBar
-
Hatfield did those tests with Damon Howatt bows that had a lot of early tension built in to them.Most were recurve bows. I don,t think he pulled that number out of the sky.As has been said it may be different with self bows or backed bows or siyah bows etc.Those bows were a very good production bow, maybe the best, and still going strong.Wished he could reply to defend his statement.Might surprise a lot of us.
-
A very interesting topic. Forgive my novice interjection..... but what effect does a higher brace height have on the longevity of a selfbow? Would a higher brace height not place greater stress on the bow during extended periods whilst strung, and result in increased cast-robbing set? A common theme among bowyers I have noticed is that during the tiller process, set becomes more a problem when the bow is first strung at brace height due to the change in the angle of force the string is now applying. From that view point, would a bow being tillered at a lower brace height, and then strung for use at a lower brace height, presumably not be subject to the same force/angular "abuse".
(-P
-
Maybe nonsense,but could a longer power stroke affect penetration?same speed but more kenetic energy?
-
A very interesting topic. Forgive my novice interjection..... but what effect does a higher brace high have on the longevity of a selfbow? Would a higher brace height not place greater stress on the bow during extended periods whilst strung, and result in increased cast-robbing set? A common theme among bowyers I have noticed is that during the tiller process, set becomes more a problem when the bow is first strung at brace height due to the change in the angle of force the string is now applying. From that view point, would a bow being tillered at a lower brace height, and then strung for use at a lower brace height, presumably not be subject to the same force/angular "abuse".
(-P
If you did loose 1 1/2" power stroke on the bottom end it wouldn't have much effect n arrow speed, less than 1# stored energy in the last inch and 1/2.
-
A very interesting topic. Forgive my novice interjection..... but what effect does a higher brace high have on the longevity of a selfbow? Would a higher brace height not place greater stress on the bow during extended periods whilst strung, and result in increased cast-robbing set? A common theme among bowyers I have noticed is that during the tiller process, set becomes more a problem when the bow is first strung at brace height due to the change in the angle of force the string is now applying. From that view point, would a bow being tillered at a lower brace height, and then strung for use at a lower brace height, presumably not be subject to the same force/angular "abuse".
(-P
You got me thinking. An interesting thing is that the lower the brace height the more tension there is on the string. A 40# bow can have 45# of string tension at brace. This tension actually drops when you draw the bow. Now if the damage done to a braced bow is caused by the string compressing the wood then a lower brace height would cause more compression and more damage. But at the same time a higher brace height bends the bow more. We're back to numbers again, which scenario causes more damage or is it so slight that it doesn't matter. I think i'll go with that ;D
-
The lower brace is still less stress. It just has less leverage to bend the bow so is pushing it together more in a straight line.
-
DC, have you measured string tension on your bows?
I never did but have heard from glass builders that string tension is close to double draw weight in some designs. I thought your bows would have higher string tension.
-
Not on any of the RD's. I have on some of my earlier selfbows. They were just a few pounds over draw weight, nothing like double. maybe I'll try an RD. Once you get the scale in the string it's really weird to draw the bow and watch the scale go down.
-
When I was in Dresden, I saw some ottoman bows that were braced with their original strings. The brace heights were huge compared to modern standards. There must be a reason for it.
So I thought about the pros:
- You can use a greater variety of different arrows (spines), without having tuning problems.
- Ottoman bows have a lot of reflex, which means they can be unstable and twist, if not treated in the right way. A big brace height adds some stability.
- Bows with big brace heights are more accurate.
- The bowstrings of the Dresden bows are really short, which makes them lighter. ->More arrow speed?
- Hand shock is the result of foreward movement of the bow limbs being stoped by the string. With more brace height, the bow limbs don't move so much in the same direction of the arrow. Instead they move more outwards. There should be less handshock then. Has anyone tested this?
The only cons are a higher strain of the material and smaller amount of stored energy. The last point seems to be neglegtable according to badger.
What do you think?
lonbow
-
When I was in Dresden, I saw some ottoman bows that were braced with their original strings. The brace heights were huge compared to modern standards. There must be a reason for it.
So I thought about the pros:
- You can use a greater variety of different arrows (spines), without having tuning problems.
- Ottoman bows have a lot of reflex, which means they can be unstable and twist, if not treated in the right way. A big brace height adds some stability.
- Bows with big brace heights are more accurate.
- The bowstrings of the Dresden bows are really short, which makes them lighter. ->More arrow speed?
- Hand shock is the result of foreward movement of the bow limbs being stoped by the string. With more brace height, the bow limbs don't move so much in the same direction of the arrow. Instead they move more outwards. There should be less handshock then. Has anyone tested this?
The only cons are a higher strain of the material and smaller amount of stored energy. The last point seems to be neglegtable according to badger.
What do you think?
lonbow
The reason is the material they are made of and the design.
Horn and sinew are much more elastic than wood. They need a huge deflection to get the best out of them, hence the vast reflex and high brace.
Del
-
That armament museum in Dresden is awesome. I have some pictures of that bow somewhere that I need to post.
-
DC, have you measured string tension on your bows?
I never did but have heard from glass builders that string tension is close to double draw weight in some designs. I thought your bows would have higher string tension.
Well surprise surprise! I have two spring scales. One 50 # and one 77# It pinned them both. I was using my fastest bow https://www.primitivearcher.com/smf/index.php/topic,64730.0.html
42#@28" and on the 77# scale it went past the 77 and right out to the end of travel of the scale so it's more than double the draw weight. I could only get it to a low brace so that would make the reading higher and the string was still laying on the belly quite a bit. Not sure what that would do. I have my digital scale that goes to 300 but I'm not sure if I could push the button and get it braced before it timed out. I'll probably give it a try. The spring scales have about 2" of spring travel so you have to pull it way past brace height to get it braced. The digital has a load cell(think that's what it's called) in it so it stays a constant length. That will help.
Anyway I am very surprised. Can this be tied directly to early draw weight? Is this high string tension the reason this bow is fast? Or am I doing something wrong to get such high numbers?
-
The biggest problem I have with skinny strings on flight bows is that they break at brace especially if I have a low brace. Never too much unless it starts twisting your bow in half like it does on bows with long straight outer limbs with about 10" of near string contact with the limb.
-
I managed with the digital. It was a bear to get it braced for some reason. Anyway I got two readings at 4" BH the string tension was 100# and at 8" it was 90#. I guees what you heard was right Ben. :) Still surprised me but the last time I did this was around when I started six years ago. That time I got 45# or so on a 40# bow. Guess I'm makin' them better ;D ;D
-
Nice Don. I would say you are much better at making bows than you were when you started. Not many people in the world can make wooden bows hit the numbers you are getting.
I've seen them setup with a turnbuckle connected to the scale so that it's easy to adjust for different brace heights.
The guys that are recording string tension report that with only a few exceptions high string tension bows are good performers. There's obviously more than just string tension, but if I ever get more into chasing speed, I surely will be recording it.
-
Can this be tied directly to early draw weight? Yep, I would say so
Is this high string tension the reason this bow is fast? One of the reasons
Or am I doing something wrong to get such high numbers? I doubt it, that's consistent with the numbers that they report.
-
wow :BB
-
I had a turnbuckle in there but it was a cheapy and with that much strain on it I couldn't move it. If I decide to make this a regular thing I would get a better one. I doubt that it would be a regular thing though because the chrono is right there, it's easier to use and I think it would tell me the same thing. The string tension would tell me that this bow may be fast but the chrono would verify it. I can't see a way of using the string tension as a tool.
"The guys that are recording string tension report that with only a few exceptions high string tension bows are good performers."
It would be interesting to know what the exceptions were :D
-
wow :BB
Yeah, those were my sentiments exactly :)
-
"The guys that are recording string tension report that with only a few exceptions high string tension bows are good performers."
It would be interesting to know what the exceptions were :D
Too much mass is the 1st thing that comes to mind.
The times when string tension and speed line up, yes, I agree it wouldn't be that helpful. But it would be nice to understand those exceptions like we mentioned; you got good speed but string tension wasn't all that high, and vice versa.
The string tension tells you if you are storing good energy, and the chrono tells you if you are transmitting it to the arrow efficiency. Not necessarily the same.
-
Good one. I'll think about that.
-
The effect of brace height on bow performance is pretty interesting. It is true that a bow will give the most energy storage for a lower brace height. How much does depend on the bow design, and it can be pretty significant. But the reason many bows quiet down at a higher brace height and do not lose much, if any speed, is because the efficiency of the higher braced bow also improves. If you could track how much limb mass is moving for each inch of draw, you would find that there is more limb mass moving farther for each inch of draw for the first several inches of draw for a low brace height, compared to a bow at higher brace. You can think of it like two cars in a race. One has a more powerful engine, but can’t shift past 3rd gear, the other car has a less powerful engine, but can keep shifting to a higher gear.
There comes a point where higher and higher brace height does no good. For natural material bows, the higher braced bow is being held under higher bending stresses with no relief.
Alan
-
You can quickly test how string changes as the bow is drawn by plucking the bow string while drawing it and hearing how the pitch goes down. Lower pitch equals lower tension. This leads to some others interesting phenomena.
How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot! How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string. ;)
Alan
-
How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot! How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string. ;)
Alan
So to open up another can of worms :BB: if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?
-
I just brace my bows at the lowest brace eight at which good arrow flight is achieved. That for me is silent flight where only the back of the feathers is seen.
The only thing to gain, for me, at raising the brace height beyond that, is more wear and tear on my bow.
Lowering it only results in very poor flight.
I think it is amazing that one can make a bow and vary optimum brace height.
Jawge
-
How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot! How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string. ;)
Alan
So to open up another can of worms :BB: if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?
What you gain on the roundabout, you loose on the swings.
Any extra push at the end has already been lost when at full draw the string has stretched slightly so the bow isn't actually drawing as far as it would with a non stretch string.
Del
-
Would the string stretch at full draw when we already know the pressure on it actually drops? ;)
-
How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot! How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string. ;)
Alan
So to open up another can of worms :BB: if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?
The mass weight factor of FF compared to B50 makes the diff.
-
Exactly BowEd, at the same weight both types of strings perform about the same.
I think another issue with lower brace heights is that in the final few inches of the stroke the limbs are carrying some momentum that still needs to be sucked out into the arrow. I find around 5" to 6" brace height usually gives me the best results as far as performance goes. I like about 6 1/2 for shooting.
-
Im wondering if draw length plays a roll in it to ,I draw 30 1/2 to 31" depending on the handle and almost all my natural material bows shoot best for me around 7" give or take for a 32" arrow !
-
6-61/4brace for me. But I do cut shelf just shy of center. About a 1/8" . This allows a stiffer arrow which has better cast. Need at least 6" of brace even with shelf cut this depth to get the best arrow flight . Hunting arrow or flight arrow. Just my experience. Arvin
-
Would the string stretch at full draw when we already know the pressure on it actually drops? ;)
Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.
Alan
-
So the energy from an overstretched string does'nt get to the arrow.Interesting.
-
Would the string stretch at full draw when we already know the pressure on it actually drops? ;)
Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.
Alan
Errrr.
I think there is some bonkersness creeping in.
If we take it to the limit a near rigid bow and a rubber string (much more elastic).
I think it shows the string stretches.
Del
-
Here are 4 bows I have extensively tested for for brace height vs speed vs shootability the top down osage leaver bow mild reflex ,BBO Lb ,moderate D/R Glass bow & exstream D/R glass/carbon bow the natural bows both 68" the unaturals both 64" the 2 natural LB had maybe a varience of 2 fps playing with the brace height from 6-71/4" the trad bows the 64 moderate D/R had a almost non detectable 1 fps & the exstream D/R had virtualy none the trad bows where braced between 7-9" every one of those bows shoot nicer at the longer brace height all where finger realease between 30 1/2-31" varied weights between 48-57lb, ok nothing scientific just a hands on test but to me it seems at least there wasnt enough fps gain to make a difference in a hunting bow they where all shot with FF plus or D97 string !
-
Good test Ritch.The results are about what's stated in the TBB.I never have tested that yet.Nice self bow I might add....Ha Ha.
-
Would the string stretch at full draw when we already know the pressure on it actually drops? ;)
Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.
Alan
Errrr.
I think there is some bonkersness creeping in.
If we take it to the limit a near rigid bow and a rubber string (much more elastic).
I think it shows the string stretches.
Del
I don't think it's bonkerness, if string tension increases with lower brace heights then it would follow the tension decreases more and more the further the bow is drawn. There was a time where I was trying to figure out at what point the string is under the most tension, and if there was a way to calculate that tension. Long story short it is incredibly difficult physics, with changing vectors, round bending adding near infinate angle and leverage changes, etc. I think theconclusion was that tension at brace was the highest tension, especially when the bow is slamming home but there wasn't a way I could figure out how much more that max "slowing limb momentum" tension was compared to normal brace tension. You would think resting tension would be greatest at full draw, but due to angle changes and leverage the tension actually decreases.
Subsequentaly you can't use the string tension changes at different draws to determine the stress on the limbs. We all know the stress on the limbs at full draw are more than at brace, despite there being less string tension.
-
In regards to a bow only pushing an arrow 19" then it would follow that longer draws would shoot at similar speeds as shorter draws, but it is well documented that longer draws, even for comparative draw weights, shoot faster if the bow doesn't get damaged from it. So I think that's hogwash. There might be some truth in it though, that the first inches of recovery accelerate the arrow more than the last couple of inches.
-
I thought the main reason stretch was bad in string was because the string's recovery is different than the limbs, thus causing interferring frequencies, muddying the release, or robbing some of the limb's recovery.