Designing for speed. . . lets talk theory.

[Prarie Bowyer]

Hi guys!

I’m thinking about the factors that contribute to arrow speed OUTSIDE arrow design.  Does sinew add to the performance of a bow or is it only breakage risk reduction?  I’m thinking it does because it’s a tendon.  It’s applied wet and dries which shrinks it.  So it’s under tension when the bow is drawn and It’s trying to return to it’s previous state.
So building a fast bow would be a function of keeping the limbs light and arrow dynamic as possible.  I’ve been using the multi lam approach to conserve valuable Ipe but as I think about it the middle core is an opportunity to improve the design for performance.  Using a light and rigid wood there helps because it’s not “in the way” of the belly wood and less force is lost trying to push that also.
So as I think about it, if one was after a pure performance bow the Sinew on something like a blend of Ipe  (or other seriously hard wood) and carbonized bamboo could be excellent place to start ? ?

What about designs?  Is there some consensus on which bow designs tend produce the fastest arrow speeds?

[cracker]

OOOOO boy what a can of worms this is gonna be I'm gonna make popcorn and grab a 12 pack. Ron

[toomanyknots]

"Does sinew add to the performance"

Why yes it does. From what I know it has a higher resiliency than rubber, and certainly more so than wood.

"What about designs?  Is there some consensus on which bow designs tend produce the fastest arrow speeds?"


I don't really remember what the best performing design was in TBB when they measured a bunch of different bows fps, but I am pretty sure that all the designs were simple traditional designs. I think that people who build flight bows might be able to enlighten you a bit too,  .

[DGF]

Traditional Bowyers Bible, Volume 1, Chapter 3 goes into detail on contributing factors to speed as well as other performance characteristics of  a bow. There's some interesting reading for sure on arrow speed in relation to draw length, brace height, profile, etc. Many of the things I see that make a bow faster seem to make it also less user friendly. ie. Shorter limbs/lower mass, low brace height, higher draw weight.

IMO there is a big difference in speed and performance. I don't care how fast a bow is if it hurts to shoot or I can't hit the side of a barn with it. That said if all you want is speed I'm sure someone out there can take your draw length and max draw weight and figure out the most efficient design for your characteristics.

I look forward to seeing what others have to say on this. Good topic that should put some minds to work.

Dan 

[blackhawk]

Well this is an easy answer.....just do as i do and hit the nitrous button bro 


There is a lot of components big and small that all add up to a fast bow.....proper mass placement in your limbs with any design you choose,design of course(short static reflexed recurves,mollys,R/D bows retaining setback,reflexed bows in any design),maintaining a high early draw weight(which is attained by reflex,and good TILLERING while tillering the bow),draw weight,draw length,perry reflex will add a few fps,tempering woods that gain an advantage in doing so,and the list goes on. You just need to understand what works best for each diff piece of wood and design,and be able to build it in the safe "red zone". Its like a racing engine being revved at high rpms,and if it goes a few higher itll blow. You just need to understand how close to that line you can get without sacrificing durability/breakage. But if all you care about is speed,then who cares,make a one n done and break some speed records(and the bow).

[Buckeye Guy]

Ahhhh Grasshopper (Blackhawk) you learn well!!!

[Badger]

  This thread could go on for days and hopefully will. Their are a few of us that chase speed as part of the hobby. Once a fast design has been established you will see it quickly become popular and lots of other guys will be building the same fast design. No magic to it, many guys here are not measuring the speed of their bows but they are building designs known to be fast so I am sure their are many very fast bows we never really hear reports on.
   Just for the sake of theory you could probably break the speed game down into several categories.

Stored energy, is a product of both design and execution. A bow might have the greatest design potential in the world but if not tillered properly, under built, or overstrained durring the building process the potentail to store energy will quickly disapate,

Efficiency, just means how much of the stored energy in the bow is going into the arrow. Understanding how a bow works helps to make a bow more efficient. A bows job is to accelerate the limbs, the arrows job is to steal as much energy as possible from the limbs and slow the limbs as much as possible before hitting brace height. When we are looking for speed we try and find ways to give the arrow a leverage advantage in slowing the limbs. Long levers with low string angles give leverage back to the arrow. We also want to keep the outer limbs light, not only so they accelerate fast but also so they have less momentum carrying them forward allowing the arrow to have more control over them.. Too much mass in the outer limbs and they will slam home before the inner limb is finished moving and transferring energy to the arrow.

    Hysterisis ( lost energy) is a huge power robber in wood bows.  My own backyard research indicates that hysterisis is a lot more controllable than often reported in some of the old bow building books. I find the best way to control hysterisis is to use a proper design that can be executed without changing the condition of the wood from when it started. Building a bow with 4" reflex so you can finish with one inch is not bad but it will be a lot better if you can maintain 2 1/2 or 3" of that original reflex. Once the wood starts to breakdown internaly the hysteris goes up pretty fast, I imagine internal friction is the culprit but not really sure. So using enough wood to execute a design and using tillering tecniques that will not break the wood down too much durring the process will add a lot of performance.

  For those of you who are interested in working on performance and testing designs their are a few very basic math formulas that are useful  and don't require any special math skills.

[UserNameTaken]

In vol. 4 of the Bowyers Bible, Tim Baker really attacks this subject in Design and Performance Revisited. I think it's the most interesting chapter in the whole series.

According to Mr. Baker:

Sinew is only affective in increasing a bows performance if the bow is highly reflexed.

If the bow is long and straight, combed flax is superior to sinew.

His "mantra" for high performance bows is: Make inner limbs wide or long enough for virtually no set. Make midlimbs wide enough for little set. Make outer-limbs an tips narrow enough for lowest possible mass.

[Slackbunny]

Its all about finding the sweet spot between speed, durability, and comfort. I don't care how fast a bow shoots, if I feel my shoulder letting go when I draw it, or if it slaps my wrist everytime I'm probably going to leave it on the rack and opt for a more comfortable bow. If its too slow, I'm probably never going to use it in a real hunting situation which is always my goal for every bow I build. And if its not durable I'm probably only going to get to use it a few times.

But if we're talking exclusively about speed, I would guess that a short, bendy handle, reflexed, sinew backed, pyramid design with recurves or flipped tips, and a tempered belly would make for a screamer. And then you need to find a stave that can handle it all, which is easier said than done.

Also you would probably do well to leave out any tip overlays. They probably don't add enough weight at the tips to notice on most regular bows, but I bet its measurable on a racing bow. You want those limbs to throw forward as little weight as possible.

[Badger]

  The fastest recurves I have tested wer Mark St Louis at about 190 fps, 10 grains per pound drawing 28", Not sure of the length but I think about 58" with stiff handles. The fastest r/d Longbows were about 66" to 67" long, stiff handles also about 190 fps. I think Marks bows had about 4" reflex and the long bows about 2 1/2" reflex. These were backed bows. Same design self bows usuall run about 10 fps slower than the backed bows.

[LivingElemental]

Definitely bowyers bible... I own the first and second volumes, the first of which goes into some pretty good depth on design and performance. Mass of working wood, fiber strength, elasticity, plus backing. I'm not sure if they mention, or if I just came to the conclusion that sinew and bamboo would be the best performance enhancing. It also mentions torque of the bow. Say, you have a slick wood handle on a snaky bow that will turn a little in your hand, that is wasted energy. One of the authors mentions that something that will mold to the hand perfectly is a bundle of dead plant fiber wrapped in cloth. Im interested to see the masterpiece this thread produces.

[toomanyknots]

When we are looking for speed we try and find ways to give the arrow a leverage advantage in slowing the limbs. Long levers with low string angles give leverage back to the arrow. We also want to keep the outer limbs light, not only so they accelerate fast but also so they have less momentum carrying them forward allowing the arrow to have more control over them.. Too much mass in the outer limbs and they will slam home before the inner limb is finished moving and transferring energy to the arrow.

Using that knowledge you have pointed out it has to be obvious that strong light non-working siyahs (like mulberry or hackberry) at around a 45 degree angle or whatever the optimum angle to result in the optimum string angle at fulldraw (bout 90 degress, right?) would be part of the answer. The next would be to figured out how to get the best compression strength and spring back from the over worked limbs while trying to keep mass down to the utter absolute necessary minimum. (...It seems very close to the final answer being a horn bow...  )

[toomanyknots]

His "mantra" for high performance bows is: Make inner limbs wide or long enough for virtually no set. Make midlimbs wide enough for little set. Make outer-limbs an tips narrow enough for lowest possible mass.

I always thought it would be an easy mantra to remember if he just summed it up as:

"Make a pyramid bow"

LOL,

In vol. 4 of the Bowyers Bible, Tim Baker really attacks this subject in Design and Performance Revisited. I think it's the most interesting chapter in the whole series.

According to Mr. Baker:

Sinew is only affective in increasing a bows performance if the bow is highly reflexed.

I can't agree with that at all. Sinew + hideglue will sometimes highly reflex a bow with no reflex anyway so that is kinda a weird statement in general, it is rare for me to have a bow that is sinewed that ever has any set even if it started out with set. I have sinewed alot of bows flat, (some even slightly deflexed from set when I first started out, ) and had them all gain reflex over a couple months if not a couple weeks. Now if wood is temperamental depending on the elements, then sinew is like wise 100 times over. So one day when there is alot of moisture in the air, the bow will not shoot all that great. But in the winter when it is dry as a bone, the bow will shoot like lightning. I think these things have to be considered as they can make a great difference for or against performance in regards to sinewed bows, and there is no real middle ground with a sinewed bow I think, when it comes to performance one day verses the next. The turks were smart to hot box their bows the night before shooting. I think the chinese did the same? AND THE MAIN reason ( this is really my only relevant point againt tim bakers statement above,  ) is that he is assuming the bow is a typical flatbow style or recurve bow where the bow will be at least 75 percent or so covered with sinew. Where the extra weight the sinew adds on the ends can slow the bow down... But if the bow were say a Hun style of bow where only like 50 percent or so of the bow was covered in sinew and the rest siyah, then you lose most of that outer mass added by the sinew and only gain the good attributes of a sinewed inner limb? Inner limbs can have mass (like being wider) and not affect performance as negatively, as they don't really move that much... 

[blackhawk]

But a hornbow doesnt gain much advantage over other designs untill over around 60 pounds toomany.

Slackbunny...tip overlays are a must because of how narrow the tips are where the string nocks..all my tips are 1/4"-3/8" where the string nocks..if your were to cut ctring grooves you wood cut the tips right off....and there isnt any noticeable difference having them on,cus the tips themselves are so narrow,and the overlays wont even weigh a tenth of an ounce(i know cus i tried weighing them before gluing them on)

Thanks for explaining more in detail than me steve you have a way with words better than me...and i was waiting for you to jump in

[toomanyknots]

But a hornbow doesnt gain much advantage over other designs untill over around 60 pounds toomany.

The term "horn bow" covers a broad spectrum of bows of many designs sizes and drawlengths, which by default must perform differently from one an other, and cannot all be dumped into one category in regards of performance. At least I would think so? But I really don't know...