Sanding glass weight reduction

[Stagmitis]

Go ahead Roy take a walk on the wild side 

[Crooked Stic]

 

[Kirkll]

[onetone]

Can’t get the link to work. This short video is instructive regarding how narrow limbs can be and remain stable, which glass, belly or back is most likely to fail, etc. Go to YT and enter:
Vegh Sipahi Test 03 in the Search box.

[Kirkll]

Can’t get the link to work. This short video is instructive regarding how narrow limbs can be and remain stable, which glass, belly or back is most likely to fail, etc. Go to YT and enter:
Vegh Sipahi Test 03 in the Search box.

What's your point here?  All that shows is a guy bending and twisting a light weight glass limb until it failed.

[onetone]

No real specific "point" intended.

The bow in the demo is a glass/wood laminate. There was mention made in this thread that limbs can be made quite narrow and remain stable. This bow is a good example of that, in that the limbs are about 1 - 1 1/8" wide, yet it will be stable when braced, even with the significant reflex and the resultant preload, built into the design.

It is interesting that the failure in the glass laminate occurred on the back of the bow and not the belly, when it was catastrophically stressed. I have heard it said that the compression loads are greater in a bow limb than are the tension forces, yet it was the back that failed.

Maybe an engineer in trad gang can offer some insight?

[Kirkll]

There is something about those Turkish designs, and even some of those Korean designs that they use thumb rings on and draw clear past their ears that seem to defy physics.

 The amazing  thing is that even with those Scylla overlays on the tips, that they perform as well as they do with so much tip weight.  The working portion of the limbs come right off the fades and seem to use a reverse taper.

  Theoretically… you shouldn’t be able to even keep a string on one of these things… it just blows my mind….

I think there are a few bowyers that have sucsessfully built these Asian designs that are members here. Maybe they could explain the dynamics on how it works…. Not this kid…..     Kirk

[mmattockx]

It is interesting that the failure in the glass laminate occurred on the back of the bow and not the belly, when it was catastrophically stressed. I have heard it said that the compression loads are greater in a bow limb than are the tension forces, yet it was the back that failed.

Maybe an engineer in trad gang can offer some insight?

I noticed the back lam peeling apart as well. The forces on the tension and compression sides are always the same, as they have to balance. Assuming you have a rectangular limb cross section (ie - not trapped in any way) the stresses are also the same in the lams on both the back and belly. What normally happens is the compression side fails first by buckling when the core material and/or adhesive can no longer hold the belly lam in place and it pulls away from the core.

I can't say why the back failed first in this case, but I can say that isn't a narrow limb in my world. Narrow is defined by the width:thickness ratio and that limb looked to have a ratio similar to most typical recurve limbs. It is possible that the back failed first because the thin limb allowed a massive deflection without overloading the core materials, but that is speculation. I can say that the beam equations used to define bending stresses and strains stop being valid at extremely high deflections, so that may be the story in this case.

If you want to see what I would define as a 'narrow' limb, look at Howard Hill style bows or English long bows where the thickness is often half the width or more.


Mark

[Kirkll]

There is no doubt about deep core narrow limbs still maintaining stability. Stability is never an issue on those long bows….

But the Asian designs that have a huge amount of reflex in the unstrung profile are the ones that mystify me how they can remain stable. Some of those horn bows are a complete circle unstrung, and just stringing them up without them twisting blows my mind…..  look at some of those horse bows they used centuries ago….

Kirk

[onetone]

Mark, thanks for your input, lots to think about there. I agree w/ your definition of "narrow" as a ratio to thickness and the fact that in the demo the width to limb length ratio is similar to a western recurve. I referred to the limb as narrow in the context of the extreme reflex these bows exhibit when unbraced and yet they maintain torsional and longitudinal stability, when braced. Like Kirk, I am intrigued by the extreme design and utility of these Asian bows, particularly the short sipahi Ottoman variations.

I have learned through experience that the brace height is critical to the longitudinal stability of these bows. Set too low and one of the limbs will collapse against the string when shot. Set too high and of course arrow speed drops off.

[mmattockx]

But the Asian designs that have a huge amount of reflex in the unstrung profile are the ones that mystify me how they can remain stable. Some of those horn bows are a complete circle unstrung, and just stringing them up without them twisting blows my mind…..  look at some of those horse bows they used centuries ago….

Yes, they seem sketchy in the extreme. I know how people string them now but it seems unlikely that ancient archers carried around a peg board just to get the string on their bow every morning.


Mark

[Buemaker]

Another thing about these highly stressed Turkish style flight bows, they shoot very light weight arrows, down to 2 grains per pound bow weight. Ivar Malde set 4 records at the Utah salt plains a few years ago and in that class bowstrings of natural materials must be used according to the rules. The strings broke on almost all shots with no ill effects to the bows.

[Buemaker]

I don’t know if this is allowed, but if you go to FB and search for Kviljo Buemakeri you can see some of Ivar’s beautiful bows and some videos of his interesting test shooting with Turkish flight bows.