walks with a gimp

Sylvan,, sorry but I spotted the reason the one arrow dosen't "fit" It's a 356.4 grain arrow,, not a 365.4 grain arrow[&:] It should read "a 356.4 grain arrow going 297 fps" I only have about 10 grains of added weight in the tied in nock set and two elinimator buttons on my string besides the string silencers

Blodg

Sylvan, I am supposed to pick up my Allegiance tomorrow (Tuesday). I plan to measure the stored energy and calculate the dynamic efficiency. I do believe that BowTech's binary cam may have a level of efficiency, especially at the shorter draw lengths, that may have never been seen before. I will post results in a few days and it may help with your calculations.

I am also going to graph the force draw curve versus a typical 1 Cam so we can compare this "front loaded" draw cycle.

Kanga

Sylvan.

here are some numbers from my Allegiance.
60lb 28" draw string loop hush kit and 2 elininator buttons slid to to the bottom serving.

birth cert 60.9lb 28" draw 300 gr arrow 303fps with hush kit 1 brass nock and 2 eliminator buttons.

400gr arrow 265fps unfortunately I did not take any of my lighter arrows to put through the crono as I was more interested in what it would do with my hunting arrows.

Sylvan

Blodg,

I will be very interested in your results!

Sylvan

walks with a gimp,

I added a corrected line to the original table using your new number. That measurement still looks a bit odd...

pdq 5oh

Sylvan, not being an engineer, I can only apply logical thinking to arrive at my conclusions. I agree with you re: the front loading being more to my/archers in general liking. At that point, the larger muscles in my back are doing the majority of the work. We do become less efficient as our arms bend more. I also like the absence of the hump to roll the cam over into the wall. This part of the curve most likely helps with the low levels of noise from the E cam bows. Also in reducing recoil/vibration. The efficiency of these cams is, IMO, higher than we've seen in the past. Possibly having no cables attached to the limbs helps in this regard. But what can be seen is this, better speed at short draw lengths, with heavier arrows, and lower poundage. We are not seeing the typical losses of speed when these factors are considered.

Sylvan

pdq 5oh,

You could very well be right on the money with your conclusions. I am not very knowlegeable regarding the subject of dynamic efficiency as it relates to the shape of the force draw curve. In fact I'm being generous to my self, I'm actually pretty ignorant here. I've always looked at it from the perspective of overall stored energy and overall dynamic efficiency. It would be facinating to be able to measure efficiency as the arrow accelerates through the power stroke. That sort of data could give some confirmation regarding your ideas.

You might be right as well regarding Bowtechs effiency's being something not seen before. This new binary design is a brand new concept and I have no direct experience testing any Bowtech bows. My skepticism regarding the high efficiencies is purely the result of never having seen such high numbers with those weight arrows either by my measurements or any published measurements I've seen. It would be like if somebody just told me they measured the gas milege on their v8 pick up and got 40 miles/gal. I'd be skeptical but then again I could just be lagging behind in the technology. I can remember a time that I would be skeptical if somebody told me they were getting 20 miles/gal with their passenger car.

Anyway, if I can get some more confirmation as to whether or not the numbers I've seen on this forum are anywhere near close, I will be buying a new bow. If you or anybody knows of testing done (like you see in Bowhunting World) on the binary cam bows I'd love to know about it.

Sylvan

Ausie-guy wrote: 88 grains of virtual mass produces an SEP of 1.30 which is what jerry and walks with a gimp settled in on so for comparison i picked the 88. Your measurement is interesting in that it calculates to 77% efficiency for those conditions which is right in line with what I would expect. A little odd though is if I use these numbers to predict the velocity for a 400 grain arrow I get 270.2 which is abit faster than what you got. If I understand your post correctly though, the 303 measurement was from Bowtech and you measured the 265 so maybe this could be accounted for by small differences in conditions

Kanga

Yes Bowtech got the 303 with a 300gr arrow I got 265 with a 400gr arrow.
Now I am not exactly sure if the crono I used is accurate or when it was last calibrated.

Unfortunately it is a long drive from Texas to Oregon to use their crono

Sylvan

Ausie-guy,

I wouldn't worry about it, it's only around a 5 ft/sec difference and out of 270 that's still a pretty small deviation. The other thing to think about is that the 88 grains virtual mass I used is only an educated guess (though I think a pretty good one) and the prediction for the speed of the 400 grain arrow is based on that and the accuracy and conditions of Bowtech's measurement. I wouldn't accuse them of inflating their speed (which would make the prediction low) but manufacturers are notorious for doing everything they can to get a few more feet/sec. They have been known to frequently shoot arrows without fletching. They will honestly quote the arrow weight but will conveniently forget to mention that it isn't fletched and a 400 grain fletched arrow will launch a bit slower than a 400 grain unfletched arrow.