what do all the testing numbers really mean?

[wasapt]

I like to read Blacky's bow test reports  and see the nice photo's but really I am not up on what all the numbers mean and how to use the information to evaluate a bow. I am good with the speed feet per second and also the kinetic energy but what is " stored energy?" and " dynamic efficientcy?"

[John Havard]

Bryce, how a bow performs enables a bowyer to judge the efficacy of his/her bow design.  How much energy it stores per pound of draw (SE/PDF) and how much of that energy is delivered to the arrow versus being wasted when the string is loosed is dynamic efficiency (DE).  

Probably of much less interest to the average archer but of supreme importance to a bowyer working on a new bow design.

If you're interested to learn more here's a link that will explain things further:

http://acsbows.com/bowperformance.html

John

[Old York]

SE/PDF means

Stored Energy ÷ Peak Draw Force?

[John Havard]

SE/PDF means Stored Energy per Pound of Draw Force.  It's a measure of energy storage efficiency.  A typical number might be something like .85 ft-lbs of energy per pound of draw force.  An exceptional number would be something over 1.00 ft-lbs of energy per pound of draw force.

Using the example numbers above the less efficient bow would store 50#.85 = 42.5 ft-lbs.  The more efficient bow would store 50 ft-lbs.  It all depends on how well they are designed.  Obviously a bow that stores more energy per pound of draw has more energy to give to the arrow when the string is released.

[overbo]

Bryce,
By the looks of that polar bear.You need not worry about those #'s

[wasapt]

Thanks Overbo, he was a thrill to chase. I'm having a painting made of the moment he jumped into the dog team and I jumped off the sled to nock an arrow. I want to shoot a Brown bear with a vintage Bear bow, I'm just trying to learn more about how to evaluate the performance of the old bows other than a chronograph and how they feel to shoot.
John, is there a simple way to calculate stored energy and dynamic efficientcy when I know the speed of the arrow and arrow weight and draw weight?

[Tree man]

If you keep reading Blacky's reports you will probably begin to grasp the numbers better. Blacky's work is top notch and yields a real basis of comparison between bows......on the other hand it is also true that in one sense the numbers don't mean diddly squat. If  you can shoot a bow and it makes arrows fly where you wish the efficency numbers and force draw curve don't REALLY matter.

[John Havard]

Bryce, you can calculate stored energy by recording the precise draw weight at each inch of draw from brace height to full draw.  The sum of those inch-pounds of draw force is a decent approximation of stored energy (just divide by 12 to convert to ft-lbs).  

You know the ft-lbs of the arrow if you know its speed and precise weight.  So, DE is equal to the arrow's energy divided by the stored energy.  It tells you what percentage of the stored energy goes into the arrow and what percentage of the stored energy is wasted by accelerating the dead mass of the limbs and the string forward (along with other wasted energy in the form of sound/vibration).

A well-designed bow will have both high energy storage efficiency as well as high dynamic efficiency.

I used to collect and test old Bear bows.  If you're interested I can look up the numbers for SE/PDF and DE for most every year of Kodiaks from '59 through '69.  But as I recall they're pretty much all the same.  Find one you enjoy shooting and like Tree man says, put it in the boiler room.