[Matt B]

in reply to: Math Question; #138675

Not really, but in personal, practical terms it probably will work for you to compare performance of different bows.

A bow with a lower brace height will have a longer power stroke, so to most of us, it would seem “more efficient” because it shoots the same arrow faster with the same draw weight. In reality, it has more stored energy and may or may not be more efficient.  “Efficiency” requires comparing the stored energy (area under the force-draw curve) to the delivered energy (KE of arrow, just how you calculated it). But, to compare bows, all with the same draw length (you shooting) you can use your method. Should probably call it a “comparison quotient” or something rather that “efficiency” just to be accurate and not draw criticism from mathematical types.

 

 

[Matt B]

in reply to: Math Question; #138612

The stored energy would be the “area under the curve” if you graph the draw weight versus length. So, if you, hypothetically, started at zero force and drew (power stroke) 24″ and ended with 50# draw weight, the area under the curve would be 50 ft-lbs. (25# average X 2′) This would be a very rare situation, but if you actually had this bow draw force curve, your formula would work.

If you had a bow scale, you could take a measurement at each inch or two of draw length, graph it to your draw weight, and make a pretty simple graph and calculate the area under the curve. If that’s too much math, if you did it on square graph paper, with pounds on the vertical axis and inches on the horizontal, you could just count the squares under the graph line and be pretty darn close to the stored energy.

Then you could shoot the bow through a chronograph and calculate the kinetic energy and get efficiency from that.

I hope this helps.

Matt

[Matt B]

in reply to: Ahhh.one of those days #138303

Our Amarillo “PDBH” trad play day is always fun. The great weather we had Saturday made it even better. I encourage any of y’all withing driving distance of Amarillo come join us. It is a very relaxed,  very fun shoot.

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