[MAT]

I don’t build limbs but I have a curiosity question for those that do. When laying up the lams you have a choice of running the fibers parallel to the limb for draw weight, or on the bias (usually 45 degree, as can be seen on many limbs) for torsional stiffness. However lams laid on the bias also increases draw weight. If you run all the lams at 45 degrees until you get to the desired draw weight you would end up at max torsional stiffness, so higher draw weight limbs would be torsionally stiffer (more lams). So do you design a limb for a specific torsional stiffness then just add parallel lams for draw weight (so all limbs would have the same torsional stiffness)? This assumes using the best, or most cost effective materials in the limbs to reach the price point, so not comparing different limbs designs, just different construction techniques using the same materials.

A follow-up question is do you need less torsional stiffness with higher draw weights? With more tension on the fingers does the string deflect less to the side, thus requiring less lateral stability?

 

[Rasyad]

HI Mat,

Very interesting questions on the relationship between draw weight and torsional stiffness. I would like to add in the idea of speed. With more speed there is less time for all the phases of arrow oscillations. In my experience the slower you go the more forgiving the tuning. Over 210 fps and one really has to pay attention to clearance.

My general understanding is that beam thickness (core thickness plus skin thickness) is the primary control of bow draw weight. Speed and efficiency are controlled by the weight or the limb and the mechanical properties of the materials, and geometry. Torsional stiffness (resistance to twisting and to lateral deflection) is mostly a concern at the limb tips where all the beam dimensions are reduced. I am looking forward to following this.

Thanks,

Rasyad

 

[MAT]

The reason I asked this was all the fiberglass bows I know of are all parallel lams, even though you can get cross weave glass cloth. These would be very unstable compared to a CF limb, but does it matter at higher draw weights (I think it does)? My Palmer also has a lam of uni-directional carbon for stability, but it's also parallel (which doesn't help a bit!).

For me the step up to carbon limbs built for stability was noticeable, but these were designed for lower draw weights where maybe it's more important? Or put another way hunters might get the added benefit of more stability with higher draw weights, either by design (more stability can be built it) or less need for it because of draw weight.

 

[rusty craine]

I think the speed come from making the limbs lighter with more curve. The bias ply keeps the super curve tracking. It looks to me like the speed is coming from tension above the neutral plane, thus you have to have torsional stability to track the limb??? Right?

 

[Hank D Thoreau]

I think we will have an answer by morning.

 

[Todd the archer]

My observation is where if everything else is equal a heavier draw weight bow is going to have thicker limbs which are going to have greater torsional resistance.

But often I hear that narrow width limbs are less stable than wide limbs.

So here is my question: Given two bows of equal draw weight, one with thicker but narrower limbs and the other with thinner but wider limbs which one would be more stable?

Todd

 

[Sid]

Todd. your pritty much on the money there.
since the poundage is mostly dictated by the limbs thickness. and since the ts comes from the laminates. as does the poundage. the two are directly linked

 

[Sid]

Two things to remember though. Heavier poundages will have more poundage wishing to jack knife, and heavy bows are also more prone to being pulled or let back down with most techneque errors. (over bowing)

but working on it a little more.
those who shoot the least and newer archers are most likely to have the most poor release. so are in more needy of torsionally stiffer setups.

and the more TS you add, the more mass you add to the limbs structure, which makes the bow less efficent.

choose you TS levels, and market your product is what i say.

we have been gathering data on feedback on TS levels and profile for 16 years.
we have been develping our understanding over this time span. tip deflection is not the be all and end all of TS.

 

[DDD]

Sid, is tip deflection the way you rate the poundage? I have heard of limb deflection, but not tip?
DDD

 

[Sid]

Sid, is tip deflection the way you rate the poundage? I have heard of limb deflection, but not tip?
DDD

http://tradtalk.com/forums/showthread.php?t=30631&highlight=Torsional+stability+Jigs

this might help...

 

[MAT]

We've been down this road before, the more recurve a limb has the more leverage there is to deflect the tips. Total deflection is all that matters since the side loading causing it is the same no matter what shape the limbs are.

But that's not the question, that is do bowyers adjust torsional stiffness based on draw weight, or is the starting point the same? Sid seemed to imply the later. Also he indicated that higher draw weight has more force to deflect the tips? Please explain as the higher draw weight would be pulling the string more inline than a lower weight? It's like trying to swing an empty bucket vs one full of water as I see in my head.

We discussed lateral stability ad nauseam, but it seems to have always been from the point of target archers (which I'm not). It might not be as big a deal for hunting weight bows, but I guess that depends on the design? Plus I'm talking individual archers, so they would have the same form issues no matter what bow they shot. If torsional stability is not as important for hunting as target bows then going with the most powerful (fastest) limb would be the logical choice? As Sid said more torsional stiffness is more weight, which is less efficient, but if we don't need it then that's a loss for no gain? Maybe my EBF have too much and suffer a loss of speed because they do? They were based on a target limb which would have been a lower draw weight range. Maybe the way to higher performance is just enough TS for the intended use, freeing up some design limitations to allow for more speed?

To put it another way, maybe target limbs are overkill for hunting? After all most of the hunting bows are fiberglass with very low TS, and they kill a lot of game.

 

[DDD]

What about more preload on lower more efficient limbs?
DDD

 

[Sid]

Mark. you fell into the wording trap again.
you get caught up in the negatives.


how about 200fps at 10gpp no trick setup. real world shooting.
from a bow that is the smoothest bow out there.
1lb gained (or less) from 28 to 29" up to 60lbs in weight.
that has the highest ts of any limb we made todate.

we utterly ignore hysterisis.when it comes to smoothness and bow performance.
we do what we want with ts. so how do you make a limb that is so far universally recived as making hex6 limbs feel stacky by ignoring hysterisis. and how do you get stored energy evens higher than anyone else when your the originator of 45deg carbon for added TS

now heres a flip side to your questions.
since most trad bows are made with simple bow glass. how much TS can they get?
was it a consiquence of materials or a major design paramiter?
can you get 200fps from 9gpp from a non ts glass limb...

how about I say most bowyers using glass dont measure ts. let alone have the technology to quadruple it.

 

[Sid]

What about more preload on lower more efficient limbs?
DDD

what do you mean?

 

[MAT]

now heres a flip side to your questions.
since most trad bows are made with simple bow glass. how much TS can they get?
was it a consiquence of materials or a major design paramiter?
can you get 200fps from 9gpp from a non ts glass limb...

how about I say most bowyers using glass dont measure ts. let alone have the technology to quadruple it.

That's my question, if TS is not a factor in glass limbs used for hunting is it a factor in CF limbs? Can existing CF target limbs be improved by losing some TS to gain speed?

And 200 fps @ 9 ggp is not a big deal, my Palmer fiberglass bow with pretty wood veneers is 196 fps at 9 gpp according to Blacky:

http://www.africanarcher.com/ADS/Bowprofile1.html

What would that bow be if he made it out of CF and foam? These limbs are shorter than most, my 58" bow has a 19" riser (compared to ILF shorts on a 17" riser) so it has a high Dynamic efficiency of 84.5 % . I shot it very well but know the TS is crap, I actually broke the tip doing the twist tip test to compare it to my CF limbs. The string came off so fast and with such little force I am still shocked.

What spured my line of questions was now that you have a hunting specific bow (Covert Hunter) will anyone admit there might be some different design considerations between target and hunting limbs? I would hope so and perhaps this might encourage more limbs for hunters. I know Morrison and Dryad already do, and none of them mention TS (which ironically is needed to build a super RC). But despite the gloom and doom glass limbs are alive and well in hunting bows, and will be for a long time.

 

[bowbuilder]

Mat, Our Max 1 or Max 2 are not possible with glass. TS with the carbon make them possible..... I won't say you can't do a big curve with glass, but it will be a big curve with a smooth draw and slower than anything you have shot. I've been at this awhile now, and spent a lot of money doing it.. I'm done beating a dead horse...IF PERFORMANCE is what your after glass is not in the formula...

Bob

 

[Harpman]

What about more preload on lower more efficient limbs?
DDD

Dan..Are You referring to more pre-load, and then lowering the brace height on the bow?...Jim

 

[DDD]

Dan..Are You referring to more pre-load, and then lowering the brace height on the bow?...Jim

Yes. lowering by string and by lengthen the limb pockets for a target draw length. Just kind of popped in my head.

Jim, remember when we talk about franken bows on finger forum. Where I put a draw specific cam on a non-parallel, non draw specific bow. Manufacture said it wouldn't work but it did. Because it lowered the poundage of a high deflection limb system. I end up with a longer more forgiving quick bow. That I won often with. It kind of jump straight forward at the target. like it was pushing the arrow and throwing it to. It did the push part of the push pull shooting a breeze.

So Sid, question.

Lower poundage limbs with high preload would act as if it was the same as higher poundage with lower preload in terms stability?
Of course you really need to have some Ram looking curves plus dependable limbs Which I think you do. Maybe thinking out of the box. But hey why not.
Dan

 

[Sid]

MAT. yes heavy bows do need higher TS.

Not because of what you might think.

People know how to pull a bow back, but on letdown people are not so confident, that are overbowed, tend to grip the bow tight and when they let it down they tend to grip the bow more and let down across their backs and shoulders putting in a lot of torque into the grip of the bow. and this causes Cam derailments as per compound technology.
torsionally stiffer limbs help as the misalignment is pushed more through the grip opposed to the limbs giving way.

more thought:

Lets say the bow has 10lbs (random number) of side load resistance.
A 10lbs bow will be able to take its weight sideways and be ok.

a 20lbs bow if torqued might generate 3lbs of side load. again your ok.

a 80lbs bow might create 10lbs of sideload if mildly torqued, so 10lbs is not enough to stop the limb rotating round.

this second point is different to the first.

the first point is an issue for the 60lbs+ bow weights


as for your question about how much speed would be gained without the TS enhancement.

Well, if you took say anything between 100 GSM and 400gsm of Carbon out a limb, you would pick up about 2-3fps.
not a whole lot in reality.
Your better off using the 100-400gsm to generate more energy. and this is where the bow really takes off.
but its also more stable. since your supporting more string in the string groove.

yes the lever is longer. I fully agree with that. but I think your underestimating what 45deg Carbon can do.
if glass and a wood core as per your broken limb can generate say 5 units of side load resistance. for the same geometry you can generate 70 units with some simple addition of 45 deg carbon. that's not just doubling it. its taking it to the moon and back.
the samick extreme BF limb has mild enhancement., simply because it doesn't need that much more. its taken a stable design, and beefed it up a bit.
how about quadrupling the BF's TS... your question is why? and what would you gain if you did... id agree. We were at that concept in 2001 when we started the Hex2 and hex3 limb design.

We were at that design concept with the ML2 limb.

2007 HEX5 - WCXC (Wood core, CXC laminate, extra high energy recurve ratio)
2007 HEX5 - HCXC ( Hyperflex synthetic core, CXC laminate, extra high energy recurve ratio)
2007 HEX4-WCXC Plus (Wood core, CXC laminate, high energy recurve ratio)
2007 HEX4 - HCXC (Hyperflex synthetic core, CXC laminate, high energy recurve ratio)
2007 CXG (Hyperflex synthetic core, CXC laminate)
2007 CXB (Wood core, CXC laminate)
2004 TXG (Hyperflex synthetic core, TX40 laminate)
2004 TXS (Superflex core, TX40 laminate)
2004 TXB (Wood core, TX40 laminate)
2001 Talisman TX40 Gold (MK2 Hyperflex synthetic core, TX38 laminate)
2001 Talisman TX40 Silver (Superflex synthetic core, TX38 laminate)
2001 Talisman TX40 Bronze (Wood core, TX38 laminate)
1999 ML2 (MK1 Hyperflex synthetic core, glass power structure)
1999 SM Carbon (Wood core, glass power structure)
( ) Carbon (Similar to SM Carbon)
( ) Carbon Premier (Carbons made for Wales Archery)
( ) Merlin Elites (ML2 made for Merlin Archery)
( ) Merlin Classics (Border Carbon)
( ) Carbofast (Similar to SM Carbon)
1998 XP10 Evolution (Synthetic core, glass power structure, stabilization)
1998 XP10 (Wood core, glass power structure, stabilization)
1992 Vision Carbon (Wood core, glass power structure, carbon support)

XP10 stood for CrossX Ply 10. that's 0.010" thick. XP10.

 

[Sid]

196fps trigger shot. 9Gpp
im talking 200fps 10gpps real world finger shot.


but this bow torque on letdown.
we have been boosting riser deflex to help cut this down.

if the grip is infront of the limb pockets, then letdown torque will be harder.
as well as a lovely settled shot feeling that you get from heavy Deflex bows.
(DAS and Widow have this heavy deflex)