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  #16  
Old 02-16-2017, 08:59 AM
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Default Re: Learning how to calculate performance numbers

Sid I hope I don't come across as putting you and your team's work down because I'm not. I might be jealous of the challenge and success that lies before you. Keep up the adventure.
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  #17  
Old 02-16-2017, 09:15 AM
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Default Re: Learning how to calculate performance numbers

Quote:
Originally Posted by BenBow View Post
Sid I hope I don't come across as putting you and your team's work down because I'm not. I might be jealous of the challenge and success that lies before you. Keep up the adventure.
Xp10 technology opened pandoras box on bow design for us, back in 1999. To actually get letoff on a single string bow is soo exciting
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  #18  
Old 02-16-2017, 09:33 AM
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Default Re: Learning how to calculate performance numbers

Never too exciting right
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  #19  
Old 02-16-2017, 10:15 AM
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Default Re: Learning how to calculate performance numbers

Thanks for replying everyone.

I originally got interested in this partly due to the post on Border’s Facebook page where someone posted a comment comparing the mystery Border letoff bow to traditional asiatic static recurve bows (commonly called “horse bows” though this term is an anathema to many people who shoot them).

The following is frankenstein data: My attempt to compare known data on the Borders to data that has been publicly published elsewhere on short asiatic static recurves. Take it with a grain of salt, since it obviously wasn’t all measured and put together by the same person, with the same scale, chrono, shooting machine, calculation strategy, etc. It’s just to serve as a springboard for future investigation.

That said, here are a few graph overlays (plus one raw data table, unedited). I’ve scaled either the Border data or horse bow data onto each other’s graphs.







Last edited by ryddragyn; 02-16-2017 at 05:42 PM.
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  #20  
Old 02-16-2017, 10:23 AM
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Default Re: Learning how to calculate performance numbers

My personal thoughts on the above:

1)The Borders are obviously storing much much more energy.
2)The small asiatic bows are much more efficient. But applying a common sense "reasonability" check to their chrono numbers doesn't seem out of the ordinary at all given the testing circumstances, especially with them all being tested at 31" draw. Test a super recurve or even a high end conventional recurve under identical conditions and I wouldn't be surprised if they matched or exceeded those numbers.

From a performance perspective, both are good bows. Perhaps one could analogize this by comparing a high displacement engine to a smaller turbocharged engine.

I have access to both some decent quality asiatic bows and super recurves, perhaps I could do a one-on-one comparison under more controlled conditions.
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  #21  
Old 02-16-2017, 12:01 PM
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Default Re: Learning how to calculate performance numbers

Hmm I think I'l try mine at 31"
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  #22  
Old 02-16-2017, 03:13 PM
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Default Re: Learning how to calculate performance numbers

I see this thread has evolved since I last saw it, but I'll post what I have anyway.

I went a different route to calculate the stored energy. I used the data in the original post (from Pete Ward) and created a chart in Excel. I used Excel to generate a trendline, a third order polynomial was the best fit (I used the data from PWs chart and included the 8" value).



Integrating the equation and evaluating for 21" of displacement (29"-8") produced a total stored energy of 668.252 in*lbf. Converting to standard units shows the bow has a total store energy of 55.688 ft*lbf.





This gives a SE/PDF of 1.09 for the Covert Hunter that Pete Ward reviewed.

Using this to calculate efficiency for the two arrows gives 76.9% for the lighter arrow and 86.9% for the heavy arrow.



I think one reason my calculated stored energy is lower than shown in the original post was the method of calculation. It looks like the original post used a left boundary Reimann sum strategy and added the values for each additional inch of displacement. This is valid method of estimating the area under the curve but since the displacement stops at 29" I don't think the 29" value should be considered since that is actually energy stored from 29"-30" (due to the left boundary method). Leaving out the 29" value gives a stored energy of 697.13 in*lbf, similar to what I got by integrating the Excel equation of the draw force curve (668.252 in*lbf).


Sorry for the distracting step back, I thought someone could critique my math and tell me it I did something incorrectly. I didn't foresee the switch to a comparison between SRs and asiatic bows when I started working.
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  #23  
Old 02-16-2017, 03:38 PM
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Default Re: Learning how to calculate performance numbers

Easy,

I do my calculations both analytically, using the best fit polynomial, and numerically. They are usually pretty close. My first derivative is done both ways. My displayed energy is numerical because the answer is the same as the analytic. The differences come from setting the boundary conditions. That impacts both methods of calculation. Where you set your zero point makes a difference. I have a way of doing it that allows me to drive my database, graphs, and pull downs for selecting bows. It may introduce some minor issues. The thing to recognize is that the error in precision is fairly large for efficiency. How you integrate the DFC to get energy being a smaller contributor. Estimating stored energy actually in the bow when the shot was made is a much larger factor. You can reduce that by using a shooting machine, but that does not reflect "real life" and will result in a much higher efficiency.
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  #24  
Old 02-16-2017, 05:19 PM
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Default Re: Learning how to calculate performance numbers

This is a great thread snd solid civil discussion...and I like that so?...I think I'll add a couple of my backyard level opinions based on experience here...

First?..

BenBow: I believe we've had this discussion before where you cited "Wasted Energy" (as ref. from my amateur level slomo vid) where once again you're citing a case of...

"An Over-Powered Mid-Limb"

where my contention is still the same in that...

why do you say "Over-Powered Mid-Limb" as though it were a bad thing?

Because of course the mid-limb is over-powered...if it weren't?...I wouldn't be holding only 45#s on my fingers of a bow that yields the equivalent of a 52# conventionally profiled limb and?...

It's those front end loaded big hooks that begin the draw by piling on the pounds from first tug which then transition from nearly dead horizontal too almost straight up vertical rendering a leverage advantage unto me where I'm only holding 45#'s worth of the 52#s worth of energy now stored in what you're appropriately calling...my over-powered mid-limb.

And you know what my new Hex7.5 limbs are going to do?...They are going to Over-Power my mid-limbs even more and I say...

Bring It On!

Under certain specified parameters?...Borders boasts achieving 1.17LBs of SE for every (1) pound of DW the archer invests while their Hex7.5's have achieved 1.25 Ft/Lbs for every (1) pound of DW the archer invests where in my minds eye?....achieving such would be pretty much impossible without...

"Over-Powering Something Somewhere"

as at some point?...the numbers dictate that a leverage advantage has been designed into the limbs...via big hooks fashioned from modern materials.

I spent a couple years going through all sorts of bow configurations in an attempt to replicate (or at least "come close too") what Borders has achieved with their Hex7 CH and?...failed miserably...as in..."Not Even Close"

My efforts and research got the attention of a Bowyer bud of mine...Steve Jewett of Bushmen Bows where he invited me to collaborate with him on a no holds barred radical new bow design (where his works are concerned) and this is what we came up with...where I tried to bilk the Asiatic 5curve design for all it was worth that culminated in a bow who's max DL is 26"s...a one off...which is now Steve's Personal Bow...His Scythian WarBow....(what he calls it)...

Check out the preload in this little monster...



The tip ends came out nearly static "Over-Powering" a very small working area just south of the fades...



It scaled nearly 63 1/2#s@26"s...



and this is me shooting a 26" long .400 spine VAP drawn too...26"s...



Now...that arrow only weighed 425grs making for about 6.75GPP but we were still very impressed to get 201fps with only a 26" length of draw..BH was 6 3/4".

what's it all mean?...heck if I know cause when we got done?...

Just buying a Borders Hex7 CH was way easier!

and preformed so well?...I ordered a 2nd one.
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  #25  
Old 02-16-2017, 07:01 PM
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Default Re: Learning how to calculate performance numbers

This is good jinkster. Just think if that wasted energy is converted into arrow energy you'd get 62 ftlbs out of your 45#. There's nothing wrong with the HEX 7.5s just save your pennies for the HEX 10s.
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