Designing for speed. . . lets talk theory.

[Prarie Bowyer]

    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.

I'm curious for the formulas.

[Carson (CMB)]

I like to think there are a lot of discoveries waiting to be made regarding bow performance.  Flight bows are probably the best place to start looking.  But I don't know that realm all to well, so i will throw out my half-baked ideas regarding bow performance from the materials side of things.  I think sitka spruce needs to enter the discussion...why?  because it is has one of the highest compression strength to mass ratios of all woods.  It just needs some tension strength...which is where sinew comes in.  My only experience with Sitka Spruce is harvesting a couple staves from the top side of a huge horizontal branch, the pieces must have considerable tension strength for a wood known for its compression strength. Once those staves are bows, I will report back.

The other material minded idea I have regarding performance is feathers. Take one of your turkey fletching primaries and bend it.  The main quill has incredible compression and tension strength and has very little mass. I am working on a design that incorporates feather quills.  The only problem is securing them without adding too much mass. 

[Bear Claw]

IMO sinew doesn't add to the performance of the bow it just allows for designs that with wood alone could not be possible or the use of wood that is questionable. Two identical bows, draw weight, mass/ weight, profile, brace height, etc, etc. one backed with sinew one not, theoretically will shoot the same. Everything I have read and experienced with "speed" comes down to a few factors, early draw weight (stored energy), draw length and brace height (transfer of stored energy), bow and tip weight/mass per unit of stored energy (efficient use of stored energy). Some of the best info I have found on this is from research done by Tim Baker.
I am by no means an expert like I said when I started this reply IMO. Lol. I love the exchange of thoughts and ideas in this forum and think that the next breakthrough in bow performance design will come from a forum like this where there is an opportunity to express thoughts with others that love this sport/hobby/way of life as much as I do. Thank you to everyone who contributes to or reads this thread. You are helping keep the tradition alive.
Aaron

[toomanyknots]

IMO sinew doesn't add to the performance of the bow it just allows for designs that with wood alone could not be possible or the use of wood that is questionable.

Well if that is true, why haven't we all just been using rawhide instead of sinew, as it is about 1/100th of the work that a sinew backing takes to put on a bow? As well as a small bit less moisture sensitive. You can also get more usable rawhide on one animal than usable sinew? Why haven't the turks, the arabs, the indians, the mongolians/chinese, the Huns, the egyptians, the assyrians, the koreans, the native american peoples, and countless countless other cultures through out history and up to this very day, why haven't they all used simple rawhide? As rawhide can undoubtedly be utilized as a very effective protective backing when put to use as so. What sinew has going for it where wood is lacking, aside from a higher tension threshold, is a higher resilience, which is the ability to return to its original form after being stretched, where wood  will not return as much and will "follow" the string. That is an advantage where if put to proper use with a proper design that takes advantage of that feature of sinew, than sinew could in fact add to the performance of a bow, could it not?

[Badger]

 Prairie here are ome of the formulas you might work with

FDC- force draw curve is usually expressed in graph form to display how a bow builds energy throughout the drawing process. One side of the graph shows inches drawn and the other side shows draw weight at that particular point

SE- stored energy, usually expressed in foot pounds in America. This is found by measuring the precise draw weight in increments of 1" starting 1" from brace height and all the way to full draw. The sum of all these numbers is divided by 12 to give you the amount of stored energy expressed in foot pounds.

KE- Kinetic energy. In archery we use the kinetic energy to express how much energy has been imparted to the arrow. The formula for finding this is (V2XM/450240)  velocity squaredXgrains of arrow weight, divided by 450240. We would normaly use KE to determine the efficiency of our bows. (KEX100/SE=E)

E- Efficiency, is usually expressed as the percentage of kinetic energy in relation to stored energy. KE times 100 divided by SE =e.

SEPDF- stored energy per draw force is expressed as a percentage of stored energy to draw force. If you have a 50# bow storing 48# energy it would be 48/50= 96% SEDPF

VM, stands for virtual bow mass. This is the amount of mass in the bow that never makes it into the arrow. Most self bows will usually range from about 200 to 250 grains of virtual mass. Virtual mass will tend to stay relatively consistent regardless of arrow weight being shot while Efficiency will drop or rise rapidly with the weight of the arrow being shot. Virtual mass is found by first determing how much stored energy your bow holds and then how much kinetic energy goes into an arrow of known weight. For instance, your bow might store 50# of energy and shoot a 500 grain arrow at 170 fps. You are putting about 32ft pounds of energy into your arrow. 18ft pounds are unaccounted for. If the arrow being sot was 775 grains and was still traveling at 170 fps it would be using 50 ft pounds of energy so in this case your virtual mass is 275 grains.

These are the basic formulas you might find useful, you don't really need any of them but for some it is fun and very eseful when playing with different designs to see which way you are heading, also helps to establish a logical plan of attack when approaching specific problems.

[George Tsoukalas]

Yet, as Tim Baker likes to point out, the bow that won the day at Mojam was a straight limbed, pecan board bow which was slightly whip tillered, I believe. Go figure. Jawge

[Badger]

Jawge, in all fairness if that contest were held today that same bow would not have even been in the running. It would be considered decent but not fast. Tims 66" red oak bows would shoot right with it today. I believe that bow was 76" long. It was a 47# bow shot a 500 grain arrow 164 fps,

[UserNameTaken]

Jawge, in all fairness if that contest were held today that same bow would not have even been in the running. It would be considered decent but not fast. Tims 66" red oak bows would shoot right with it today. I believe that bow was 76" long. It was a 47# bow shot a 500 grain arrow 164 fps,

Maybe it's time for a Bowyer's Bible vol. 5.

[Prarie Bowyer]

woa... processing.

[Matt A]

does anyone remember the speed bow article in primitive archer awhile back?
the man took i believe HHB billets put what looked like 90 degree recurves on the tips and made the tips real thin and got like 242fps!!!!

[Badger]

 Matt, those were lightweight flight arrows, still a good speed if I remember the post. I think it was Mark. Here I think we are talking hunting weight arrows or 10 grains of arrow weight per 1# of draw weight.

[Pappy]

Very interesting topic. I don't worry about speed much but everyone loves to learn a few simple tricks that will make a bow perform and shoot  better.Even us old dogs. if it is easy to incorporate into my bows I will almost always do it,if not and takes to much thinking  and planing I usually won't.  Still I love to listen to the folks that do. Everyone has their own reason and interest in doing what we do and that's Cool in my book.
   Pappy

[Badger]

  Pappy, I think if you are talking practical performance expectations you and a lot of us are already there. Tricking bows out for flight or just for fun to see what we can get is a game in it self. When you stop to think about it we can sum it up in just a few lines. Reasonably thin tips, good tiller, a little reflex, slightly flipped tips for a low string angle,  dry wood, heat treat for a little extra and don't damage the wood as you tiller it out. No matter what we do it won't get a lot better than just covering the basics.

[UserNameTaken]

I was reading about this substance in insect joints, called resilin, that stores a tremendous amount of energy--basically insect sinew. They were joking around calling it flubber (like from the old black and white Disney movie). Thats where modern traditional archery should be headed! We should all be gathering up insects to harvest their sinew and further our advancements in archery! = P

Do a google search on resilin.

[Carson (CMB)]

Heck yeah.  Insect sinew, that is the materials side of things I am talking about.  Might be a pain to harvest, but there are some big bugs in the world.    What about hagfish glue as marine hide glue? 

I guess the title of this thread is designing for speed, so maybe the abstract biological materials stuff is a little off base, but I think there has got to be some good materials out there waiting to be stuck on a bow.  For example, backing bows with bat wings.