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  #1  
Old 02-14-2017, 10:48 PM
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Default Learning how to calculate performance numbers

I hope Iím not opening a can of worms here (just trying to ask and learn)Ö

A good friend of mine (who is also on the board here) got a Border CH recently, and I was trying to learn more about the super recurve concept in general, as well as how to calculate performance numbers, something I havenít really been interested in until as of late.

One website has a review of a CH, featuring a draw force curve and chrono results:

http://peteward.com/2014%20reviews/T...ertHunter.html

I ran the numbers and unless I did something very wrong, the SE/PDF is very impressive, but the dynamic efficiency seems unusually low. Is something off with the guyís numbers, due to a bad chrono or release? Or is something wrong with my math?

Interestingly, the self-reported data for other high end recurves (e.g. Dryad) indicates lower SE/PDF but higher DE.

Is there somehow a tradeoff between the two?

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Old 02-15-2017, 01:51 PM
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Default Re: Learning how to calculate performance numbers

SuperCurves store lots of energy but they over power the mid limb. If you watch jinksters slowmo videoyou will see where that extra energy is going. Heres a quore from my longbow that doesn't store as much energy but its balanced. As developement improves the SC numbers will improve.
OK here's the fd/speed results right at my draw length. Using a release & measured at 53.25# at 29" Stored energy 50.32ftlbs and SE/PDF of 94.5% arrow speed 203 fps for 48.677ftlbs kinetic energy and 96.735% efficiency. Way better than I'd hoped.
Measured finger shot: 53.25# at 29" Stored energy 50.32ftlbs and SE/PDF of 94.5% arrow speed 196fps for 46.309ftlbs kinetic energy and 92.028% efficiency.
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Old 02-15-2017, 03:00 PM
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Default Re: Learning how to calculate performance numbers

Quote:
Originally Posted by BenBow View Post
SuperCurves store lots of energy but they over power the mid limb. If you watch jinksters slowmo videoyou will see where that extra energy is going. Heres a quore from my longbow that doesn't store as much energy but its balanced. As developement improves the SC numbers will improve.
OK here's the fd/speed results right at my draw length. Using a release & measured at 53.25# at 29" Stored energy 50.32ftlbs and SE/PDF of 94.5% arrow speed 203 fps for 48.677ftlbs kinetic energy and 96.735% efficiency. Way better than I'd hoped.
Measured finger shot: 53.25# at 29" Stored energy 50.32ftlbs and SE/PDF of 94.5% arrow speed 196fps for 46.309ftlbs kinetic energy and 92.028% efficiency.
Thanks. I can see lots of wasted energy there in the jinkster video.

http://tradtalk.com/forums/showthread.php?t=82626

Would a good analogy be a high displacement muscle car? Big engine but not efficient compared to other fast cars?
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Old 02-15-2017, 03:06 PM
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Default Re: Learning how to calculate performance numbers

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Originally Posted by BenBow View Post
Something seems a little off with your longbow's numbers.

The arrow kinetic energy calculation seems like it should be (203^2)(533)/ 450,240=48.8 foot-pounds.

Also that seems a bit fast for a 25" draw.

Can you post a higher resolution screenshot? Maybe I'm just reading them wrong from it being pixelated.
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Old 02-15-2017, 07:33 PM
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Default Re: Learning how to calculate performance numbers

FWIW, I ran your numbers through a program I have that uses linear interpolation and came out with 60.2 ft-lb SE. That would improve your efficiency calculation somewhat.

State of tune, and release quality will also have an effect on the results.

And finally, is SE/PDF really relevant? What matters is what is actually delivered. If my bow stores a whole lotta energy but does a crappy job of delivering it, what's the point?
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Old 02-15-2017, 08:13 PM
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Default Re: Learning how to calculate performance numbers

Quote:
Originally Posted by ryddragyn View Post
Something seems a little off with your longbow's numbers.

The arrow kinetic energy calculation seems like it should be (203^2)(533)/ 450,240=48.8 foot-pounds.

Also that seems a bit fast for a 25" draw.

Can you post a higher resolution screenshot? Maybe I'm just reading them wrong from it being pixelated.
The draw length is 29". The KE number is based on Roboto's correction indicating that the correct number is 450,800 not 450,240 especially since 225,400 is used in calculating momentum. I found it calculated 3 different ways depending on how gravity was rounded off. regardless the amount of difference is less than 1% between the two.
Unfortunately a screenshot of the spreadsheet requires better than the norm of a max 640 wide but I'll try and see if 800 will be allowed. It is but not much better which is why I wrote the numbers in the original post. Also using 450,240 gave 48.738 ftlbs where 450,800 gives 48.677 ftlbs or only .061 ftlbs difference.
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Old 02-15-2017, 08:26 PM
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Default Re: Learning how to calculate performance numbers

Also here's a high speed video of the longbow that the FD curve data is from and you can see the bow doesn't waste energy with flapping limbs. But this design is about maxed out as far as performance is concerned
https://youtu.be/1c0CLHOeW84
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Old 02-15-2017, 09:39 PM
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Default Re: Learning how to calculate performance numbers

Here is what I get running your numbers through my bow testing program. I am comparing your results to three other Covert Hunter tests.

Comparison charts are in the next post.

Border Mystery Bow BH6.5 = Development Covert Hunter BH 6.5
Border Mystery Bow BH7.0 = Development Covert Hunter BH 7.0
Covert Hunter 68 inch
Border Covert Hunter ryddragyn = Your bow data

The two main panel charts are for the different weight arrows you used in your test.



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Old 02-15-2017, 09:41 PM
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Default Re: Learning how to calculate performance numbers

Here are the comparison charts.

Border Mystery Bow BH6.5 = Development Covert Hunter BH 6.5
Border Mystery Bow BH7.0 = Development Covert Hunter BH 7.0
Covert Hunter 68 inch
Border Covert Hunter ryddragyn = Your bow data

Notice that energy/weight on the fingers is pretty consistent across all bows. The CH and HEX7 limbs store the most energy of any bows I have ever tested, by far.

Also notice that the smoothness curves have the same shape. The smoothness curves are reflective of the geometry of the bow. This is where the CH stands out.

So this indicates that your test results are consistent with what I have found for Covert Hunters. Also, I confirmed your results, though I get 1.18 for SE/PDF but that is probably because you did not account for 0 pounds at brace.

That is probably why our efficiency numbers are slightly off as well.



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Last edited by Hank D Thoreau; 02-16-2017 at 08:49 AM.
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Old 02-15-2017, 09:55 PM
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Default Re: Learning how to calculate performance numbers

These dynamic efficiency numbers are very high. Bear in mind that you get a large bump in efficiency when you use a shooting machine so you have to watch what you are comparing to. Anything 70% and above is excellent. Also note that if your store a huge amount of energy you can sacrifice some efficiency and still have a very fast bow. It looks like you are getting both speed and efficiency.
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  #11  
Old 02-15-2017, 11:27 PM
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Default Re: Learning how to calculate performance numbers

Quote:
Originally Posted by BenBow View Post
Also here's a high speed video of the longbow that the FD curve data is from and you can see the bow doesn't waste energy with flapping limbs. But this design is about maxed out as far as performance is concerned
https://youtu.be/1c0CLHOeW84
Once the arrow leaves the bow. The vibes are inconsiqencial.

Thats like saying the parachute on a drag car makes it really ineffiecient. But it has crossed the line.

Is this 96% efficency bow for sale?

Can anyone buy one?

Last edited by Sid; 02-16-2017 at 12:04 AM.
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Old 02-16-2017, 12:09 AM
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Default Re: Learning how to calculate performance numbers

Quote:
Originally Posted by Hank D Thoreau View Post
These dynamic efficiency numbers are very high. Bear in mind that you get a large bump in efficiency when you use a shooting machine so you have to watch what you are comparing to. Anything 70% and above is excellent. Also note that if your store a huge amount of energy you can sacrifice some efficiency and still have a very fast bow. It looks like you are getting both speed and efficiency.
Petes numbers were with puffballs, fingershot etc etc.
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Old 02-16-2017, 05:23 AM
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Default Re: Learning how to calculate performance numbers

No Sid I just build for family, friends, fun, and the challenge. I'm fighting (and winning) cancer so this hobby gets me of my butt.
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Old 02-16-2017, 05:33 AM
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Default Re: Learning how to calculate performance numbers

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Originally Posted by Sid View Post
Once the arrow leaves the bow. The vibes are inconsiqencil
l beg to differ on that Sid. Those vibrations are stored energy that didn't go into the arrow. My narrow, deep core, simi-static tip d/r longbow is near the limit of it's design but your SC limbs have a lot of potential left. The more of that SE that gets turned in to arrow energy by controlling that limb vibration then it will truely be a super curve. Let's say sign me up for your HEX 10 because now it's like popping the drag chute 3/4s down the track. You have a lot of head room in your design to play with. Enjoy the challenge.

Last edited by BenBow; 02-16-2017 at 06:22 AM.
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Old 02-16-2017, 06:51 AM
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Default Re: Learning how to calculate performance numbers

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Originally Posted by BenBow View Post
No Sid I just build for family, friends, fun, and the challenge. I'm fighting (and winning) cancer so this hobby gets me of my butt.
Congrats on the successes...long may they continue
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