Looking for information on building Siyahs

[burtonridr]

Hey everyone,

I'm trying to improve upon a previous build where I made a Mongolian style horse bow, there is probably a more correct name for this style of bow. But, I'm looking for good resources to read up on the construction of the ends of the bow. Maybe Turkish flight bows or Hungarian horse bows? I'm open to any resource that has really good information on design, construction or performance related to the ends of a bow where its primary purpose is to act as a non working lever on a short bow. I'm hoping to learn more about what type of wood was traditionally used for the siyahs, different designs and purpose considerations, etc.

Does anyone have a good link or book they can recommend?

Thanks in advance!

Eric

[PatM]

They are just a piece of wood with some degree of angle or curve either naturally attained or achieved by heating and bending.    All kinds of wood or wood reinforced with horn or bone were used.

  You'll learn how the different angles and lengths work by making and testing.  You can get all sorts of opinions and details on ATARN or their facebook page.

[burtonridr]

Thanks for the ATARN reference, thats kinda what I was hoping for 

[burtonridr]

Just for anyone that is interested in this topic in the future. Here is a summary of what I have learned, based on the reference provided below.

One thing I found interesting is that a bows potential energy, as represented by a draw weight line chart(greater volume to the right of the line = greater potential engery), doesnt always result in greater arrow velocity. Which, if I understand correctly, all else being equal is the only thing that really matters when measuring how well a bow transfers its energy into the projectile. Greater arrow velocity means the bow is putting more energy into the arrow. But, the study also looks at potential energy and efficiency. So there are many instances where a bow design has the most potential energy, but it isnt as efficient, so it doesnt translate into a faster arrow. Why? I'm not sure... Maybe there was a flaw in the study, maybe there is a way to build the bow where it can be more efficient. Maybe it doesnt really matter all that much in the grand schem of things, it flings an arrow, right?

Bridge/ string contact vs no contact:

Bridge/ String contact: Stores more energy than non contact, however it was noted that this didnt translate to a greater arrow velocity, because it is less efficient.

No contact: Stores less energy, however gave a greater arrow velocity, because it is more efficient.

Siyah/ear angle (relative to contact with the limb): Three angles were tested, 0*, 30* and 60*. Where 0* and 30* did not produce string contact while strung and 60* did produce string contact while strung.

0*: Least potential energy, greatest efficiency, slowest arrow velocity(nearly identical to 60*).
30*: Middle of the road potential energy, middle of the road efficiency, fastest arrow velocity.
60*: Greatest potential energy, least efficient, slowest arrow velocity(nearly identical to 0*).

*Note: Something the study doesnt really talk about is stacking at the end of the draw. Shooting a 0* siyah on a short bow would have a lot of stacking toward the end of the draw.

Siyah/ear length: Two different lengths were looked at, 1/2 the overall limb length, and 1/3 the overall limb length. No change was made to the length of the working section of the limb. The original design length of the siyah, I believe, was  1/2 and the siyah was shortened to get the 1/3 length.

1/2: Greater energy potential, less efficient, slower arrow.
1/3: Less energy potential, greater efficiency, faster arrow

*Note: The numbers for this test are relatively close to each other, there wasnt a whole lot of difference. The reason for a longer siyah being less efficient is because it is heavier than the shorter one. Also, it should be noted that with a shorter siyah, even though you gain efficiency, you do loose mechanical advantage and potential energy. The overall length of the limbs in relation to angle of the siyahs come into play when approaching and when at full draw. So there is some give and take in the overall design of the bow and mechanical limitations of the materials being used.


Reference: Functioning of ears and set-back at grip of Asiatic bows, by Bob Kooi
http://www.bio.vu.nl/thb/users/kooi/kooi96.pdf

Also if anyone is interested, there is a great deal of other mathematical and engineering studies located here.
http://www.bio.vu.nl/thb/users/kooi/#soaa%20.

[bownarra]

A gain here.....leads to loss there! Same as all bow making

[willie]

So there is some give and take in the overall design of the bow and mechanical limitations of the materials being used.

give and take.... looking for a sweet spot.

I am curious whether the physics you cite would hold true for bows utilizing different materiels (in designs most effective for those materiels)


for instance   would a siyah length to working limb length proportion or siyah angle best for a highly reflexed bow constructed with lots of sinew and horn be the same physics for a straighter bamboo bow of a more conventional construction.

[burtonridr]

So there is some give and take in the overall design of the bow and mechanical limitations of the materials being used.

give and take.... looking for a sweet spot.

I am curious whether the physics you cite would hold true for bows utilizing different materiels (in designs most effective for those materiels)


for instance   would a siyah length to working limb length proportion or siyah angle best for a highly reflexed bow constructed with lots of sinew and horn be the same physics for a straighter bamboo bow of a more conventional construction.

Thats a good question, it might not hold true for different materials. I would think with bamboo it might hold true if the design helps reduce weight at the tips and/or can provide mechanical advantage.

[willie]

Thats a good question, it might not hold true for different materials. I would think with bamboo it might hold true if the design helps reduce weight at the tips and/or can provide mechanical advantage.

Do you have a link or pic of your previous horsebow or a bow of the design you are researching?

 

[burtonridr]

I wasnt going to get into it to much because it is a PVC bow and not a traditional. But here is a pic. Full disclosure, I never thought PVC could perform as good as it does. But, I just moved and I dont have a my tools really unpacked or a space to work setup yet, so in my darkest desperation to build another bow I tried PVC. It makes the absolute worst bow imaginable if it is something like a long bow, but you chop the ends off and replace it with a light weight wood siyah while keeping the working limbs pretty small and it performs pretty darn good. A lot of what I have learned building traditional bows translates to working with PVC, it is super forgiving and easy to make changes if you goof up, plus its cheap.

Ok sorry, dont mean to try to sell it lol.... Probably banned for life for discussing PVC here. 

The black bow is the previous one I built 46.5" NTN unstrung, draws 65lb at 28". It shoots surprisingly fast and smooth.

The white one is the unfinished one I'm working on, I've been tweaking things to get more potential power, but I like the draw weight at 45-50lbs. The draw curve is for the white bow. This one is 46" NTN unstrung, draws 47lbs at 28".

Last night I made a small change of the siyah angle by maybe 15* and took some of the reflex out (making it more straight limbed unstrung). It made some improvement on the curve. I got it to go from 14lbs at 10" to 18lbs at 10". Its noticeably more difficult to string.

[willie]

I wasnt going to get into it to much because it is a PVC bow ..... Probably banned for life for discussing PVC here. 


Last night I made a small change of the siyah angle by maybe 15* and took some of the reflex out (making it more straight limbed unstrung). It made some improvement on the curve. I got it to go from 14lbs at 10" to 18lbs at 10". Its noticeably more difficult to string.

I think its fine in the campfire section, so It might get moved, but its really an interesting design question.

If  I understand correctly, you have made improvements in the "shape" of the draw curve at 10" with a less aggressive bend?

a couple of questions

1. is the final draw weight remained the same?
2. are the limbs lifting off the string at about the same point or did that change?


interesting way to try out ideas, I might have to give this modern materiel a try to do a stability test on something different.....

[burtonridr]

I think its fine in the campfire section, so It might get moved, but its really an interesting design question.

If  I understand correctly, you have made improvements in the "shape" of the draw curve at 10" with a less aggressive bend?

a couple of questions

1. is the final draw weight remained the same?
2. are the limbs lifting off the string at about the same point or did that change?


interesting way to try out ideas, I might have to give this modern materiel a try to do a stability test on something different.....

The improvement was in the shape of the curve, in that it moved the curve up. (see attached image of the draw curve that I recorded prior to making the changes.)

1. The Draw weight might have increase by 1 lb, tough to tell with the scale that I have.
2. The point where the string contacts the siyah did change. Before it was contacting very close to the nock, now it is contacting very close to where the siyah attaches to the limb. I wish I would have taken a photo before I made the change.

[bassman]

I have been making some bows with siyahs lately. I don't cut the v splice. Mine just mount on the top of the limb tip. 5 1/4 inches long with a 3 inch rise seems to be working out for me.