Do we have any engineers in the house?

[Badger]

Man you guys are confusing me with all this , guess I will just go back to letting them fly to the target on their own just like always Haha
Good read anyway Steve
keep on searching!
thanks
Guy

  Sometimes I get bored and like to stir the pot a bit. I am not adverse to poking some of my buddies here as well. I enjoyed the conversation.

[loefflerchuck]

Hmmm? Recently I've been making more short bows center shot. At first it was because horn limbs were not the same length and I did not want to cut them. Then I liked how they shot better and started doing it with wood bows too. When I tiller a equal length limb bow I put the tiller stick in the center of the handle. When I tiller a center shot bow I put the stick on the top of the handle where the arrow passes(still in the center). Now you have me thinking maybe it's just that and if I try a equal limb bow tiller at the top of the handle it will also be a improvment. ??

[Selfbowman]

I don't know if I tiller correctly or not ? I tiller by pulling my bow string on scale 1/2" below knocking point and pulled by hand at throat of handle just below the shelf. I do however not cut my shelf till I get the bow close to weight desired in case I need to flip the bow to hit weight easier and correct tiller at same time. My bows usually bend pretty good though. Arvin

[redhawk55]

This topic reminds me a lot of my research of asymmetrical bows:

https://redhawk55.wordpress.com/2010/08/22/asymmetrical-bow-designs-vol-1-what%C2%B4s-harmony/

I' ve to add a reply to a discussion about asymmetrical bows in the Paleoplanet- forum: http://paleoplanet69529.yuku.com/reply/224548/t/Re-old-designs-reloaded-asymmetrical-bows.html#.V3zNQ6Z76bg

The exact Golden Ratio is 1.618, but as a common sense a 2/3:1/3 ratio is usual. The question is, if this ratio is referred to the really working parts of the limbs or does it mean the location of the nocking point. I havenīt checked it yet.
Due to my knowledge the nocking point of a Yumi bow is located 1/3 apart from the bottom tip of the bow.
Itīs not at all true that short or asymmetrical bows are used only by mounted or kneeling archers, they take advantage from those bow- design, but there is enough evidence that short or asymmetrical bows were used by foot soldiers too. Think of the Parthians, what about the short West Coast-Indian bows................................?

Almost every excavated asymmetrical bow I had the oppurtunity to study measures 121- 140cm in length, the excavated arrows were measuring at least 54cm and at most 66cm in length and almost all of them were barreled. It is obvious that the "asymmetrical bowyers " have laid out the shorter lower limb 0.5-1cm wider than the longer upper limb. A lot of fitting bow- cases and quivers(Goritoi) had been excavated too.

For a first test I made 2 easy to do D- bows out of the same black locust-stave, with a length of about 120cm and about 20lbs drawweight. I shot the same arrow with these bows, almost no difference in speed. But the f/d-curve of the asymmetrical bow results in a higher energy- storage.
A typical f/d- curve for an asymmetrical bow increases steeply in its first third then it flattens a bit. My experience is that the an energy- storage of 85- 95% is usual for this design. The last asymmetrical bow Iīve done seems to store about 110%, cause this means such a high storage Iīll recheck it again.
Speed is comparatively low to the stored energy, efficiency is 53- 73%
Exact numbers will be posted soon.

Shooting an asymmetrical bow is at first a strange experience, cause you feel a kind of imbalance when drawing it. But soon this is compensated ,when the arrow is released and the upper limb moves a bit down. If you are used to the "loose grip" youīll soon enjoy such a designed bow.
This design is an additional option for every self- bowyer, have a look at asymmetrically grown woods.

2 pics of the first asymmetrical selfbow I did. It is made of Black locust. It measures in length in width, the upper limb measures 67cm in length, the lower limb measures42cm in length. It draws 22lbs at 22", speed with a 280grains arrow is about 110f/s.


Thinking back I' m still wondering why there is such a heavy loss of energy? I think that' s the point where Steve and my research are meeting?
Any ideas?

Michael

[Selfbowman]

Red hawk I am no engineer but I think speed is lost in the physical mass of the wood and its placement. The better we lighten the ends and keep the draw weight up the better cast we will get. Hitting the happy medium is our goal without breaking the bow. That been said. I believe we may be able to achieve this with as even limb length and center shot not only in respect to spine but but tip to tip may be the key. I had a friend build several bows that where right and left handed . The site window was in the middle.left handed your hand would be on one end right handed your hand would be on opposite end . These shot very well. I think a cross bow is the best example of total center shot bow. No hand placement to deal with. Am I way off track here guys if so tell me so. Arvin

[Badger]

  Michael, two of our biggest losses come from hysteresis and vibration. Vibration can be minimized by keeping the weight down in the outer limbs and also reducing the amount of working limb available to vibrate. I also believe that the tapers we use on a bow also effect this. I have noticed that in most cases bows with elliptical tillers tend to have less shock. The hysteresis is mostly a bi product of compression damage to the limbs so using an adequate design to handle the draw weight and length helps a lot here.

[bubbles]

A bow spends most of its time at FD with hands in the string right? The shot is a tiny speck of time in a shot sequence.  I figured that's why you tiller so it looks good in the hand. Because most of a bows life it is being pulled and held with hands on the string.

[scp]

Can asymmetrical bows be better than symmetrical bows? I doubt it, but there is a video that says so.

With a high speed camera and two medieval bows, weapons experts compete to see which bow was the ultimate medieval weapon.
From: JAPANESE BOW: BUILT TO KILL
http://bit.ly/1rwOr2W

[Badger]

A bow spends most of its time at FD with hands in the string right? The shot is a tiny speck of time in a shot sequence.  I figured that's why you tiller so it looks good in the hand. Because most of a bows life it is being pulled and held with hands on the string.

  Thats fair logic and one of the main reasons I feel is justified. The differnce between tillering for the released bow and the drawn bow are fairly small anyway and can be easily adjusted for.

[Badger]

Can asymmetrical bows be better than symmetrical bows? I doubt it, but there is a video that says so.

With a high speed camera and two medieval bows, weapons experts compete to see which bow was the ultimate medieval weapon.
From: JAPANESE BOW: BUILT TO KILL
http://bit.ly/1rwOr2W

   I don't think it makes a lick of difference if the bow is tillered right, the limbs could be 2 feet difference in length and still shoot fine.

[scp]

That video does not mention the draw length. I think it's just a case of longer draw length storing more energy. I wonder how they have missed such a simple fact.

[Dances with squirrels]

'Slightly' asymmetrical bows are better in some ways. The bow's longitudinal center, string hand fulcrum, and dynamic balance point can all very close to each other, in fact they can all be perfectly aligned, essentially one and the same, which makes for redeeming qualities that are impossible to obtain with symmetrical bows. I think I already covered that in a previous post.... or maybe it was the other thread.

Steve, I do think it matters.... degree of limb length discrepancies that is. Once the difference in length gets beyond a certain point, it becomes impossible to balance them just by making one stronger than the other. Study the unbraced profile of the Yumi and you'll soon pick up on some of the measures the bowyers take to achieve some semblance of balance.

[Badger]

  I have played around quite a bit with asymetrical bows using drasticaly different length limbs. It does get a little tick sometimes but once they are ballanced properly they shoot fine. As long as the arrow draws straight back and the limb mass is appropriately distributed there is no problem tuning them.