Limb Stability

[**DONOTDELETE**]

Here's my take on it Bob... i've been testing about 4 different Matrix Carbon lay ups myself and have had various results. if you can get the right Matrix design on the very back of the limb it helps both speed and stability. if you put it both belly and back the torsional stability (side to side) jumps 50%....

But.... getting that dad burn stuff to to hold up without shearing the core it's glued to isn't easy. I'm looking into getting a hybrid matrix using carbon and S-glass laid up next go round.

The only way I'm getting both speed and stability and having these things hold together is using a double carbon and putting a thin layer of glass under the belly carbon..... it's expensive though.

with the added stability you can narrow the width profile and trim mass weight & get rid of the parachute effect...... THEN you can get both....

The prototyping is never ending as we get newer materials available.... give me a call sometime Bob... I'd love to swap some tech info with you some time....  Kirk

[last arrow]

OK, help me out.  If stability can not be measured, how do you know you have it, or more importantly don't?  

Based on the above posts, it is clear that materials affect stability, what other design elements affect it also?

Thanks in advance for your explanation.

[Bob Morrison]

If you go to pick up your bow by the tip and it flips apart in your hand, you have very little side to side stability. If you rest your bow tip on your knee and it folds up,,, very little end to end stability. This does not mean your bow will not shoot just fine, it will be less forgiving. I'm have been hunting with a test longbow limbs that fold up on my knee, They shoot fine and I've taken one deer with them... Switching to test recurve today. Gluing up a set of real stable longbow today, hope it does the same as the recurve did.

[FerretWYO]

I am with most others and as you mentioned, for me Stability means forgiving. I am very interested to see what your working on Bob.

[BobCo 1965]

Do not try this at home. It is just for concept sake.

 http://s1097.photobucket.com/albums/g343/Borderbows/?action=view¤t=00048.mp4

[**DONOTDELETE**]

There are two types of stability in bow limbs. "Vertical stability"  and "torsional" stability.

They can both be measured by the bowyer with the use of weights and dial indicators if you want to get technical. But the only time that method would be incorporated, or useful is in comparing two identical limbs using different materials for an increase or decrease.

Having good torsional stability is very important, and effects the tracking of the limbs through the draw cycle. When you see photos of bowyer's with a tiller stick of 18" holding the bow at half draw while they look down the limbs.... this is what they are looking at. the limb tracking. if the limbs are stayng perfectly straight through the complete draw cycle. this would mean it is tracking well.  

The question that is most commonly asked is, when the torsional stability becomes borderline weak, can the tracking, and more importantly the consistency of the shot be effected by a less than perfect release.... the answer is yes... BUT... and i say BUT.... it requires a much better than average archer to detect the difference in most cases.

a bow that doesn't track well at all will be noticeably inconsistent to most archers.


"Vertical stability" on the other hand is one of those things that is criticized unjustly my many. There are many very high performance bows out there that are considered vertically unstable that you can flat out drive tacks with.... if the timing of the limbs are perfect, and there is enough preload to stop those limb tips dead it has no effect on accuracy at all.... I could name a half dozen on the market that are competing in IBO wold competition that many guys would deem vertically unstable....and these same bows are taking the titles.

Where you run into a disagreement on this is that some feel that slight inconsistency of finger placement on the string at full draw will have more effect on the timing of a bow that is vertically unstable.... this inconsistency isn't noticed too much on the line, as it is when shooting in different body positions out of a tree stand or when canting the bow to extreme angles.

With a bow that has very stiff outer limbs and excellent vertical stability, it would be very difficult to alter how those limbs are bending by shifting the applied pressure to the string with your fingers.....

this vertical stability issue is, and always will be debatable.IMO

i hope this helps

[WildmanSC]

Originally posted by Jason R. Wesbrock:
I'll gladly take stability over speed, but thankfully, such decisions aren't and either/or situation any longer. My main recurve sports Winex limbs, and they are by far the most stable (and quite fast) limb I've used.

Jason,

Your draw length makes for excellent speed no matter what!       But, you're right, you want limb stability along with the speed.

I loved the article you wrote in the October/November TBM.  Very touching and I can identify with your sentiments.

Bill

[Sixby]

What Kirk Said, And if you ever want to try a bow that is super fast , verticaly and horizontaly stable then try one of his bows.

On the other hand I want both stability and speed and work to get the extra stability so that I can slimline those limbs and knock that weight down.

In answer to what do you do design wise to add stability.

Stability works from the bottom of the stack to the top.
You can use slightly thicker glass on the belly and gain stability. Most bowyers go the opposite way.
You can trap to the back. It does the same thing by removing glass from the back.
You can thicken the core and use less glass. A thick core adds a lot of stability. This is why longbows are inheriently more stable than flat longbows and recurves.
You can shorten the recurve.
You can adjust tapers
You can adjust preload.

I worked really hard to develope a limb that could be belly mounted and have a 7 14 in brace height. If you ask a Talon 11 owner they will say it was worth it. The problem was to get the stability at a lower brace. I did this because I hate compromising. I want a bow that gets the stability but will also keep the arrow on the string to get maximum thrust and use the energy that the limb has without wasting it.
I just could not see having to have an 8 3/4 inch brace height and losing an inch and a half of powerstroke.

Its quite a subject and one that Bob is wise to be delving into.

God bless you all, steve

[Friend]

Totally ignorant here with regard to practical experience but will relay my interpretation from reading.

Much R&D has and is still invested by World Class limb builders in order to reduce limb torsion as generated by the finger release.
Much of the speed increases have been a welcome bi-product as a result by the successful endeavor to reduce torsion.

Also, have read that the static limbs are some of the most challenging limb designs for reducing torsion, thus reliance on man made materials have taken precedence.

[**DONOTDELETE**]

Originally posted by BobCo 1965:
  Do not try this at home.  It is just for concept sake.

  http://s1097.photobucket.com/albums/g343/Borderbows/?action=view¤t=00048.mp4  

That bow in the video has excellent torsional stability. but i wouldn't   EVER do that to a bow. That's absolutely abusive right there.   :mad:   Who ever would do that to a bow is nuts!   :rolleyes:  

if you want to compare one bow to another. you hang weights off the tip with the bow unstrung and measure the deflection.

[Bob Morrison]

Kirk, I saw a picture of a scale that can be used for limb deflection. And it looks like I can use a spine tester to accomplish the same thing. pic was on different site.

[Sixby]

Friend:Also, have read that the static limbs are some of the most challenging limb designs for reducing torsion, thus reliance on man made materials have taken precedence.

I agree in part. However the designing and r and D is anything but manmade material. We do have to learn or know how to utilize that material , whatever it is. Personallhy I use a lot of wood. I like certain woods even better than foam for cores in some designs...
However if I were to build a bow to go to Alaska or Aftika I belive I would recommend a complete composit limb because of the imperviousness to weather .

God bless you, Steve

[BobCo 1965]

Originally posted by Kirkll:
 

Originally posted by BobCo 1965:
  Do not try this at home.  It is just for concept sake.

   http://s1097.photobucket.com/albums/g343/Borderbows/?action=view¤t=00048.mp4  

That bow in the video has excellent torsional stability. but i wouldn't   EVER do that to a bow. That's absolutely abusive right there.    :mad:    Who ever would do that to a bow is nuts!    :rolleyes:    

if you want to compare one bow to another. you hang weights off the tip with the bow unstrung and measure the deflection. [/b]

FWIW the test was done at and by Border Bows (Hex6 limb), I think they knew what they were doing.  

[**DONOTDELETE**]

[/QUOTE]FWIW the test was done at and by Border Bows (Hex6 limb), I think they knew what they were doing.      [/QB][/QUOTE]

You honestly think so eh?  I wonder if they would honor their warranty if you did that to one of their bows?   NOT!

I'm not questioning the fact that that particular bow has incredible torsional stability. but... putting that video on a public forum with no explanation except "Don't try this at home" is nuts!  You know someone is going to ruin a perfectly good bow trying that...

it's stupidity is what it is... IMO.

[Lee Robinson .]

deleted...double post.

[Lee Robinson .]

As far as that bow in the vice picture, I would be interested in knowing what the draw weight of the bow is. A heavier draw bow would handle that test much better than would a light weight bow.

That said...yes, stability is much more important than is speed...as it doesn't matter how fast one misses. A problem in the archery field though is stability is a much more subjective measure than is speed. Speed is easy to measure. Take a given draw weight, a given draw length, and a given arrow weight...and we can determine speed and efficiency. Unfortunately though, not many archers have form and accuracy good enough to determine a good stable bow...so too often speed becomes the target priority.

This video isn't a "perfect" stability test, but the perfect test would require an archer with very consistent near perfect form that makes no changes in their perfect form without an intentional decision to do so. Without this ability, it is difficult to obtain a controlled objective test. SO...for this reason, I produced this video to illustrate SOME characteristics of stability and another way of observing traits that are often associated with stability. I hope this video is beneficial.

Thanks for viewing.

 http://keepitsimplearchery.webs.com/apps/videos/videos/show/14179600-limb-stability-demo

[**DONOTDELETE**]

I looked far and wide for the video i did on testing vertical stability and i cannot find that ting to save my life.

Hey Lee, In your test procedure in the video it's rather hard to see the limbs flexing really well. and doing your test using the weight of the bow itself doesn't really show you what you need to see, and it wouldn't work too well with a heavy riser target bow with 35 pound limbs.

If you put the bow in a vice at the riser.  you can grab the string with your hand and pull it towards the tips back and forth and see how easily it moves. this is much easier to feel the movement. most guys describe vertically unstable bows as "Floppy limb bows".....

here is the rub... and where all the disagreement starts. First and foremost important, beyond a shadow of a doubt.... is that vertical stability cannot be measured accurately at brace height.... period.....

how stiff the limb is at brace height has nothing to do with how easily you can alter the pressure point on the grip at full draw. a 40 pound bow still has 40 pounds of pressure on those limbs at anchor. Shifting from a high to low pressure point on your grip , or rotating high or low pressure to the string, effects a stiff limb bow exactly the same as it does a bow that seems floppy at brace......

it's a total misconception that stiffer limbs are harder to change the pivot point on, or more forgiving in that regard than a floppy limb bow.

i know... i know... I'll get arguments over that statement till dooms day arrives.    :rolleyes:   But it's true.

i've got a film somewhere with a couple different bows on the tiller tree cranked down to full draw, while i rotate the finger pressure on the string using a string hook 2.5" wide shaped like your fingers are at full draw..... regardless of what those limbs feel like at brace whether they are stiff, or floppy, it still takes the identical amount of pressure at full draw to rotate the grip, or the finger hook. 50 pounds is 50 pounds at full draw....

So now a guy has got to ask... So what difference does poor vertical stability have on a bows performance..... it's limb bulge at the end of the power stroke.....That limb bulge is the center of the working limb continuing forward after the limb tips stop. this robs the stored energy that could be transferred into the arrow shaft, and adds vibration to the bow.

Even shooting the stiffest of bows like a Howard Hill style. until you learn to locate your grip in the perfect pivot point applying even pressure on the grip, the dad burn thing will shake your teeth loose..... the reason the shock is more pronounced on that style of bow is that there is so much more mass in the outer limbs the string has to somehow stop, and never really succeeds because there isn't enough string tension or preload in a D style bow.
So the guys that shoot them well learn to heel down on the grip, and they shoot heavier shafts. simple as that.

The bottom line is those floppy limb bows are just as accurate and forgiving as the stiff limb bows if they are timed right, only they have a bit more vibration and rob part of the stored energy..... as a bowyer i hate leaving stored energy on the table like that.  


How's that for a long winded response.    :rolleyes:

[SL]

I'm not a bowyer but I do shoot a lot and have owned a bunch of bows. It seems to me a lot of the stability issues can be minimized with the grip.
 For instance I shoot a certain recurve because the grip fits me so well and I can flat hit with his bows(not stating names). The bow has wide limbs which I assume is helping the stability, it also has some limb bulge. Just curious of your thoughts on how the grip effects the stability from y'alls point of view.
  I realize like the spine of an arrow- there is static and dynamic stability as well as torsional and vertical. That being said I shoot heavier bow in the 55 to 65 range so I guess that helps.
SL

[SL]

That last sentence didnt come out right. I know the bow is either stable or not-but can a unstable bow be made stable with the right grip from a shooting standpoint?
Ok- I'll shut up now  

[Rob DiStefano]

i've got a "barn burner" of an aggressive r/d longbow that's 60" in length.  that puppy flat out hauls a 10gpp arrow the fastest i've ever seen.  but it can't hold a candle to the stable shootability of a 64" mild r/d longbow - now that bow could pretty much shoot itself with consistent accuracy ... and with a "forgiving" nature when i screw up my form, to boot.  oh yeah, gimme consistent accuracy over speed any day, thank you.