Feedback on a theory...

[Marc St Louis]

   Eric, a book could easily be written on just the topic of efficiency. Problem is no one seems to understand it well enough to write a complete book on it. Lots of theories floating around, hard to say how accurate or inaccurate they really are. I have my own theories that I have tested to some degree but working with a material like wood tests leave a lot to be desired.

   When it comes to efficiency hysterisis is not the biggest factor, in glass bows it is so small it is negligible. In wood bows it is substantial. In the past couple of years I have done quite a few experiments just aimed at tracking the energy losses in wood bows and trying to figure out how much control we have over them.

   My tests indicated that hysterisis is not as inherent to wood bows as previously thought. The majority of it is induced by damaging the wood cells during the building process. The damage cannot be detected solely by monitoring set but it can be monitored by measuring weight losses in the bow that occur when the draw distance is increased.

    I built some extra wide bows as you are doing just to test hysterisis. I decided to ignore the excess mass and just see what I could come up with. To my amazement the bows came out lower in mass than their much wider counterparts. This can only be explained away by accepting the bows were enduring much more damage than I had previously thought.

    The majority of efficiency losses are lost in the way of limb vibration and distorsion, hysterisis will usually account for about 10% loss, Vibration accounts for the other 20 to 25% losses. Shorter limbs vibrate less thus more efficient. Shorter bows and shorter limbs also store less energy so they are not necessarily faster. I find well made longbows on the longer side will usually outshoot the shorter ones, recurves can be a bit shorter and reach their peak.

  There are tests you can do that will isolate the efficiency losses in a bow and let you know how much is lost to vibration and how much is lost to hysterisis but they are very tedious and time consuming and require a number of repetitions to establish any kind of useful patterns. You can use a no set tillering technique to monitor the condition of the wood and determine how well you executed your design and this will help to reduce the hysterisis to manageable levels.

Steve I would assume that the damage you are talking about is in compression.  If you make the limbs wider then you are increasing the amount of wood that is working in compression but you are also doing the same with wood working in tension.  For a long time I have been of the opinion that what is best for performance, and longevity, is an optimum balance of the 2, this might be easier to control on a self-bow; stave self-bow that is.  I haven't done the amount of performance testing that you have though. 

That short Yew recurve I posted not long ago did not perform as well as it appeared to and quite frankly I have seen that same lack of high performance in other short recurves I have made.  I suspect that short bows perform better with light arrows and the geometry of a longer bow suits heavier arrows better.

[Eric Garza]

Marc, are you referring to the yew recurve you discuss in this thread?

[PatM]

No, Marc posted a shorter one recently.
http://www.primitivearcher.com/smf/index.php/topic,53824.0.html

 Steve, I still think you're barking up the wrong tree with your hysteresis and set theories. I think all the factors that make a good bow come into play and it's the balance of them all that delivers the final performance.

[Badger]

No, Marc posted a shorter one recently.
http://www.primitivearcher.com/smf/index.php/topic,53824.0.html

 Steve, I still think you're barking up the wrong tree with your hysteresis and set theories. I think all the factors that make a good bow come into play and it's the balance of them all that delivers the final performance.

  Pat, I have long since came to that same conclusion. Just because I was able to identify how much of it existed does not mean I fel it is worth pursuing. The tests I did I feel are only worthwhile doing one time. The conclusion is that if you do a real bad job on a bow you might loose a lot because of set. But the difference between a good tillering job and better tillering job are going to be very small. The biggest points I feel that I proved to myself are simply to maintain as much of a starting profile as possible instead of over modifying something and hopeing the finished profile  is what you want. Set causes additional hysteris, less set faster bow. I have made too many bows to take someone elses opinion about barking up the wrong tree on that one.

[PatM]

I just meant it seemed like you were trying to find out the point where there was no hysteresis and work below that. I think you could actually do that but you'd likely have to go to a three inch brace height and a forward handle grip  like a modified flight bow. And a relatively short draw.

[Badger]

 
      Pat, I think where the confusion comes in is here. There is a small group of people around the globe who have a bit of obsession with hysterisis. Not for the sake of making the fastest bow or super bows but just for the sake of identifying losses in everyday bows we build. I had a lot more time on my hands than most of these guys because I am divorced and my kids are all grown. I don't see it as any improvement at all over bows we see here everyday that are well tillered and designed. The whole point is to be able to track the histerisis and learn how to monitor the condition of your wood as you hone your skills, or in my case it I use it to tell me when to stop that a bow is maxed out.

     I built a bow for a young lady this year that maxed out at about 24 or 25" and 40#, she actually shot the bow at about 35# but achieved a distance of 323 yards. Not a real fancy bw, just a slightly reflexed osage self bow. The key was I knew when to stop because I had a solid technique in place that let me know. Thats all it is really about. Special high performance designs are another discussion all together.

[riverrat]

heres what ive come to understand. this is from bows ive made. and bows ive seen. one being a very very old bow, bend through the handle piramid bow about 3 inches dead center of bow flat but tillered so as the crown of the back was matched with the tillering of the belly no cut in for a handle of any sorts. the bow was from puerto rico and was very dark colored and very close rings.tapering to round 3/8 in. wide tips.maybe 48 inches long.i was inspired of the workmanship of this bow quite a bit. had a string on it of skin from some kind of animal. when strung up it felt heavy to draw.well, couldnt imagine the size of arrow needed for that much paradox so i decided to try something im more familiar with , like a somewhat piramid, semi bend through the handle bow with a lensticular type tiller. made it of locust and it drew heavy fast. shot what i thought as of fast. but it had a narrowed handle section. didnt want to build 6 foot arrows to get around the handle. but i found that this works nice. then i read that encyclopidia by Jim Hamm. it had Osage bows made by Osage indians very simular to what i made. its a very good design. very thin limbs. tips pretty rounded. recently i made a not too wide bow, bend through the handle, very narrowed tips, thats thin for most of the bow, cast is awesome. fast far as im concerned with my overly fletched arrows, not evcerything that works has to be flat. look at English long bows, but they are long. shorter bows work better wider im thinking. just my thoughts. Tony