Primitive Archer
Main Discussion Area => Bows => Topic started by: sleek on September 17, 2017, 04:48:53 pm
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On most my short bows I am getting a stored energy to draw weight ratio of 72-89%. Id like to know how these numbers compare to larger bows? Are these good numbers for stored energy effeciency or too low?
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89% is not bad for a shortbow at all, about average for a mid length bow. The way we have been figuring I found out is not that accurate, add up all the numbers under the curve and divide by 12. It doesn't allow for the slope and will actually be a bit lower I believe. I still do it that way for my own purposes but it really isn't accurate. I need to find out the right way to figure that.
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Thanks Steve. Would we be better off if we measured every half inch and devided by 24? Or am I looking at this in the wrong way?
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There is a formula called Simpson's Rule that boat builders use for figuring the area of oddball shapes. Is that what you're trying to do?
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could just calculate the kinetic energy of a shot arrow. would be a bit easier given just its speed and mass
Custom Thumb Rings has done energy measurements. Peter Dekker's website has a graph somewhere, maybe an excel spreadsheet where you can input draw weight values and it makes a curve ... and finds stored (potential) energy. backyardbowyer has also done such measurements in his blog
the potential energy should be higher than the kinetic energy due to inefficiency (inertia from limb mass, limb vibration, string mass, string stretch)
there are more accurate ways.. there's ways of better approximating integrals like the trapezoid rule. another would be to use software to find a fitting curve and then just make it take the integral.
Thanks Steve. Would we be better off if we measured every half inch and devided by 24? Or am I looking at this in the wrong way?
yes
I'm not the best at physics but. potential energy is sort of like work
(force times distance). Could find the average draw weight over all the
measurements from brace to full draw and then multiply by (draw length -
brace height)?
alternatively the energy is just the integral from brace to full draw with
respect to distance.. so that's basically adding them all, then dividing
such that there's a unit which is not needed if there's a measurement
every inch, which implies given # of data points = powerstroke = draw
length - brace height
((SUM draw_weights) / powerstroke) * powerstroke
SUM draw_weights
more math
PE = mgh due to gravity where m = mass, g = acceleration, h = distance
deriving potential energy in a bow from this
F = ma => a = F/m
PE = m(F/m)d = Fd
but the mass of what? the arrow.. in both cases
if you're dividing by 12, you're just changing the unit to feet from
inches? let's prove this
((SUM draw_weights) / datapoints) * (powerstroke/12)
where datapoints = powerstroke
= (SUM draw weights) / 12
what if every half inch..
((sum draw_weights) / datapoints) * (powerstroke/12)
where datapoints = 2*powerstroke
(sum draw_weights) * 1/(2*powerstroke) * (powerstroke/12)
(sum draw_weights) / 24
yes
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I dont have a chrono or id do kenetic energy....
So to add to this, i am getting an average of 2.5# gained per inch of draw. Its stays consistant through the range of draw.
What is really hurting my stored energy is low initial draw weight. I need to fingure how to increase it. Every time I heat the limbs, take deflex out, reflex the mid limb, or recurve the tips, initial draw weight goes up, but of course, so does the final draw weight. When I tiller it down, initial draw weight always goes back to where it was. The initial draw weight is sad. Down to 5 poinds at 10 inches with a 7 inch brace.
Perhaps if I make long sweeping recurves that work, that will trick the bow into thinking its shorter than it is, the long recurves will apply tension, and still work to add draw length without over stressing the bow.
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https://www.buildyourownbow.com/articles/force-draw-curve-template/
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Loon, i love that link. Than you.
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89% is not bad for a shortbow at all, about average for a mid length bow. The way we have been figuring I found out is not that accurate, add up all the numbers under the curve and divide by 12. It doesn't allow for the slope and will actually be a bit lower I believe. I still do it that way for my own purposes but it really isn't accurate. I need to find out the right way to figure that.
What percent do most good flight bows have?
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110%, like football players ;D ;D ;D ;D
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Slle, flight bows are looking more for high efficiency and low virtual mass. Anything above 95% I think would be considered very good.
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http://www.primitivearcher.com/smf/index.php/topic,59964.msg834378.html#msg834378
Here's a calculator I made to determine stored energy and force curves and stuff like that. The 8th post I explain the equation I use to calculate stored energy. It's the trapezoidal rule https://en.m.wikipedia.org/wiki/Trapezoidal_rule?wprov=sfla1. It should be very accurate. If you open the calculator and plug in your own numbers it will tell you what your energy to draw weight ratio is. Anything over 100% is excellent like mentioned.
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Correction, to the previous post. The way I calculated the area under the curve is not the trapezoidal method but rather the midpoint rule. http://www.dummies.com/education/math/calculus/how-to-approximate-area-with-midpoint-rectangles/. Basically, you find the areas of rectangles by multipling their base (distance between two measurments on the graph) and their hight ( the average midpoint between the two y values you measured) then adding the areas of all rectangles together. The website and I both have examples. I'll post pictures of those now.
(https://lh3.googleusercontent.com/VFGRbbb3IhEAKOKR-RQSW81ZDGm57LmaCy_r3nlw9vW0WMT4YJjK8VbNVI9aWPvrkvzQiqqIEQ6KFzAU8yNIEa-7qYXyprjLMCcmvNsvFN9UDQFabecx5bej49s64eSxwSF9sqjDFPQ7D3IFCEv-B2XdBeh41Vg1VujJhX2PJDS0W-IxRqWTGnREbHNzVenJfUfhyvDclUWgXCApBgz738_BVbxobK5QhFVT20uAHf9XYSnYW03I5PoPMwxmadsHNZOnYh5x2CSmbExZ0U671GQR6BXRHITIoOFyWvw1fqa-s4u1SGDI2hWw2AtaITeQt-Kc7ypzQXOzrzcHK6HB8GAksZorplhpY1FsEuSY1JOnp9QpBWtwgZSn64AWWuFwpmvBbEN6XwDD3UIUx12BzqWMOUf00XvImoNGCgqTjEZBsrbZ_mWff1QeX2rYhGv3fx2mxQvYMYJvcry5n1UCrdfWGIgJ8DGxWyYeA9VvznTiAG17tj6AD_o_xNfwN76z9b53BQwXYAU2VauleWL4S8Oq32uvzjw_SBfqTpsiMkzf09xQGJGjNRK-A9G565dFfc-U8NJzm1ZTAcUT69z1eGaHJLO-lhyco6mrvid4L1hqHHmP11kcESF--eb0s1ylXd1uEx2D7YDLYBwNYNS_2s-6K2sasw0Gnu9a=w446-h400-no)
(https://lh3.googleusercontent.com/kyl-CdrVBo6CtpSLwnqf-1od42i_9p91TfsxGhN8a3R_bwK_aqwfImrLqCqQeA4oDGC5ksTHddS_gX_-fdE97t_DSExoZtnVXj-G4Y8cWIng_HCifVjefhhgDnBVc0K9zu8Qbm0vT9mEEqcwdhgySSrPskfjVmMucEc7aKSHwxAsjaXsDQacUXtvdTANckAVELa6Cpig4MTcspYuSdrrHB1txp8LIXakbODvOmlOmCTqblJXXm4W4Stvc22qxRxuAW-T18KihNqOpo9h9oY-tr7jskZOzVy0yxF93u1R8W4SiH__oLkGTuWiWX4FFKVKkM2dLJ4-ZVvVmOxCAkHMW6x-LmrcC25E6UdgT5bPHI--2L-aut0HNIMpQdywJ4INcQabvOnchFAutjYiwujbqL_1fVk3mj9OT3CxBT5Gdb61-yw9dsyF3KQJeVg7lND27Xv9rFV_AwtoJE3WOpZ6j-EvCT6y1kLHsFyFzp0Domp_vIs-Tyd_P03fpgYolEQ8b4bsWy2f4txTJcfylu9iyT9_4EyM2az2oPu2faa6UpnZKwXo3DLJs_5wYwLIBon26LJ5OnBgGg9FhU3s-MqWWa8j2-n5KYLH3x93rKCScmyuRbeL96_f7CDwRgFEQNV4SfNIIVa_Q3e4zLdRkcVlj1AVLOzdIfv90i4G=w651-h590-no)
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I believe that's how Simpsons rule works.
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So the old method of adding the numbers and dividing by 12, does that give me higher or lower numbers than I actually have?
And, what percent is it off by in average?
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So the old method of adding the numbers and dividing by 12, does that give me higher or lower numbers than I actually have?
And, what percent is it off by in average?
What numbers are you adding together? The draw weights at each measurement? The final draw length times the final draw weight ÷ 2 then 12? I'm not sure what the old method is.
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Adding up squares on a graph paper then dividing by 12? That will get you in the ball park but not be the most accurate.
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Anything over 100% is excellent like mentioned.
Greg, could you give the short version of how getting results over 100% is possible?
thanks
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I'm late getting in on this discussion, but when you are talking about desiring a high percentage stored energy, like the 95% mentioned for a flight bow, doesn't that come with a shorter life expense?
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Anything over 100% is excellent like mentioned.
Greg, could you give the short version of how getting results over 100% is possible?
thanks
Sorry, I realize this topic is super old, but I just rediscovered the "see new replies to your posts" button and didn't realize willie asked me a question specifically.
So, this percentage is a ratio: Stored energy (in ft-lbs) divided by draw weight. 100% doesn't mean maximal energy stored. It just means the stored energy value happens to match the draw weight value. Modern compound bows are well over 100%, like 200% and even more. It's very much possible to get over 100%. 100% would be a straight line on a force curve like this:
(https://lh3.googleusercontent.com/TD_W1CFXHCyKhSXDShKMJ0ZZxGtT__SqAMb4ciXc_ZpX9aMc58chq36OZLWEhGohPR32fOVzXcAW9sXRRiodprcfkstVLHoT79jqCJow2t0QrpEIBGC038natlYMi3CqnfaJJ0a8jjQGxnQAmfV8-WOXulDMBRet9OXdZrLeeIoOpsMbffXaW1LURcW5qQUZe7DZxPX3m2OzuZoXiTY60QAOz4u99OvD4Xp1m7ZTigSEGF8qG5_e2mX8gI2IW6UbAK350K2u0VV9MUwk4TsH074SK5iQW6r-Ox5fQOPFMV1rdskqW0JYdN0d9OLBympC9owweRT0KZLUCW1Cmeilqu0jbd9WjVkgo6ZGYfR-WXJkuXyJLwzUMnV0gXUbaQP7HPOHiD86wptOaSlf4VCt1FPTG1Qjiwl1oeXgBUQKpZLj6Ev5eDLUrWoxPV5P8a3VTqP1XgRVFWCYh2ygfcp-12Bzm9nNHdj7FDoamE09wX5X3uy09_Uk9D7PetPgJFK_SeSZo4LlIXmrdYVHJ3BiKudlunndr2WzfBvI7wl-YnYKYsE7av3WE8DAj9v8PvCOh1COuRTgfpYBoIkRVLshJlrs3QJ_59YjE9txTNuX6KwUTBaL38ySrkvlMdMCGs_KkT76jprquvjZiLT9LzPhFRrYZBUCHjPvkg=w1026-h432-no)
I just picked Simson's bow #100 to illustrate that it's very possible to get over 100% with a "primitive bow". ( I chose his because he's one of the few that actually posts force curve data). Here's a picture of it to recall your memory (hopefully Simson doesn't mind)
(http://primitive-bows.com/wp-content/uploads/2018/01/osage-Nr-100-7-von-40-768x576.jpg)
And here is his force curve. I didn't know his arrow speed, but I calculated that at 65% efficiency and 10gpp it would be 183 fps, which seems very reasonable if not slow for a bow of this caliber. But that's not the point. Notice the box that says stored energy per draw weight. This bow is at about 115% SE/DW.
(https://lh3.googleusercontent.com/33jPWcV4H9ub0i4_ZrPIXztqxhcZxDPGJg-WcxHYE-pSqRYjkLBds8bV57NES1ZjXi0nTov_UNiCEcehzBp5ao98faLAmRYvhI8zqJunDQcK3uD_SQ0LbH_J2f6lWapFA7VQ3hqdDv7doCue1aaQ2isQKjY80iwagbJKiTHINbCzRurZscQKF5r2JhyaZQjQ-0VcTF2-dWYNykSekaf9Aoio-6ZOQmei7LCmDoT8mrKa382f8Afrxr_74Pgb4KCBWexND6G5gS6oaWn42k3VsME8F6V0PmVfoZ5NMqMEvJiYnoI5fttc7nNfZ-HBKQwxNXwCjbLrmj1940kNv0jTbiBz1z9qtg8YAGRKjy1bkH88X1OcD_Sy6Xnmh0ip8xKPL_cfARCDN8DID4PfZ0aLlBpAkrMx00skyWFpCA8erZb1zxwNHPJMwTZIkYgEKkv3BEwgZUcwt7X6-1-Apqo1LXuKyyn3rq24aCvBDcvLHJg1wXryr77nnvGTnUEtlG0fJ-fryiUcG-ryC6ipgDmguQX6PSXfKcZhJPt0ThdzWHatLq_wVTDF2eYCOSyjL88yA6VMwwoeDasBeUlVzQaOVehe7k7r4vNwVvSQvMzWpIWBKrB4jdMntZfNZNlhgVHCAuXzrxnixJT02sJ65vWJP9-U3hEyjXH4cg=w1058-h418-no)
Now compare that to a compound bow I have which has a SE/DW of 233%
(https://lh3.googleusercontent.com/p1JR1_eWDHS6LD-GlzRzQ92LLjgo0Af1LMcyFitpLT4MJ4AX8PRucq6KEHs5-q3r6ZMKmnZeRYjHeeKcwSnJjxzkkKJabKSG3UPmxqq7RY7tM7QVgzL05SKLlWsT_nEbGmaUWhvH64r38c_-sDs7O8nf4Baa3udfrlIqH7svdddmgKwmAVjrWlXwd_AtKIArpIK3GtOvUFgjeBItQIHvSULjimUzY0mL4umkea0SBY2HIPNzAJFkt-eaEQfXZxYkqm2a0Tmofxh8D-C4n2LhEWAFUcLRWUkLJCbd0Wf19-4SH8-_ID2jszfSkX9-IkWVspYD_XlNu-_W18At4qdEX5XUvBl4RdaiIV0URMTlX8lSK0I-5BkvcSbo4ah4mRqHfsOLNOoElQXmwsaXWknXAiZNXmYonCeQQmp6Icb2uJEz5V75GgffVUf-1EnQSKQQWZ6UuME81q5hDkDWjxtvBF_xPicfbaULKGi85GFZ-BSj0tA9h8nEq9wXRa6ogujQUDvzpPHBXnKMaBKmmsQzdTZ3tsD_7wCAURadP8hw7kXesVPl5pydI-NaGZdHH5n0muVdp7OGFX-sKlLgnspX5eg3Jy2_H3VbrDLkYqPmx22iujCBWyN2wMGXdB4velpC_QY_QDoLwCtawkdeX8nPoRdlw22QuHSqpg=w1065-h428-no)
As well as too this bow I made a while ago at a SE/DW ratio of 55% (which isn't anything to brag about). However, it has an extreme overdraw at 25" (28" shown in picture) despite it's length of 43" with a non-working handle. It stacks badly!
(https://lh3.googleusercontent.com/EwLM5lKXwmQR_Lsdz0d-YkQNYuTJrXtyeSkF4zHA2wgo5sL1vV9ZIc7xH7RZFrB4fRabykC4b_rkLGBeEm1ERNx5XJphRglGk5hcV1_hSP96rPKIU-YpI1cFqspO6kocb16VxWpUopB_-ge12fDtHkirNuh-g1y3k-2nRSlc2YuhKUtHoYkKh6lZDGXDEPyGsDkqMgWD365YVOpK4sGVUD65P6TNciscxrql28ZqYTAlHlDEj_TzBc3Wq9TvVAHxoLlqYkxjPNuIVaImk8oG1Px7kC2q8-MIzd4TYNuuLB0xkehbORQzpk4aOgs5txflVj1pmukMI5QmfZ5-6LeRjMPgFV39zMOLDJMdZ16Hkr_R7eZh4K5W7uLKJwVZa5_fHJmr8ugA-LdVL3olHEt8pID62RhLR1fhhYA4W3f33Z0Hv6krgMKWRVKjRC4k2v_X_F3HGv_wcgqnx3YT8jN8MRY-2bLd7YrNoPKHGyliBkbVAsRqfsr8i0cHzqIS5vPe9psOLDsyjGVrC5UfHNnnHcI63zYYrrgM5zpnsJSwWxMPxEhPl6OtC4HdvYM3xBftt0ZhAaB6_05nYvKVk_kFPWsUYqqaZ3pjNYXrpqrS-0Oe5aGvN7rqKodnlHeoSxEYPzGU-ck5yt7RwV8R5P0bOjWvL1_MOobgxA=w1065-h422-no)
(https://lh3.googleusercontent.com/h87VpcRgCXXc9uqCSHZpV0NNi2Gxd5qki_uqjYtS3ahpsdYEXBUGqoYr5NNiz_-MR7j8c997VkYZFoViZpK1cazTzOXBrX7PVFwZfd2YXYVro264_gPFxjA_wgOdK482YkeNli7v8CngFwqG81BKYzW0lMCesR2al3_kSuYs-lAN9CZ_JK7f5qu9NOpbr5E_2WYr0OTCKmUY_7GMaDFf9YEPH09MVQl2PZlmPnx9agWrkwGBAsiceqCYsztw03TYmO3lGWMCkGnf_6rbpk9cwuTQFvstP8BE59dkqiqzh1jGmP6NtSpNz0eMwUBUUFluWLdt9_oJRXoK1KSw5u4GzTp75O0t0fYlr2iubEAD-rCsZhrEyUY1RPsmkbbZsBHPBQU10_GTsMHdytuRk44rt01b-jiaiAy2XqKmuxghauajEPT875RQdZ5Q32N91sDgy5ArkvWEPF_mcfZCvx5GhAvlfe7xBHo-LtTnTVB3sPMwPy8wS9H0qjHMQX4CVab-1JdrE4JB4GCqHgn5sxltiNNevH_ZUBJPcIIyeYHbyp5MoTySrL5T6XV5Dsa5Y-lRyvUCiKHPdjBGjJpTOmV2BUaELd32M8bFrHZkzMbNfcoPSo7ZVxu9KyPokgcCQ_3a62mtqlAwDWNHaX5676msTeB7YaTEld3rPQ=w507-h449-no)
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thanks, Greg. that was better than the short version.
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Anything over 100% is excellent like mentioned.
Greg, could you give the short version of how getting results over 100% is possible?
thanks
Sorry, I realize this topic is super old, but I just rediscovered the "see new replies to your posts" button and didn't realize willie asked me a question specifically.
So, this percentage is a ratio: Stored energy (in ft-lbs) divided by draw weight. 100% doesn't mean maximal energy stored. It just means the stored energy value happens to match the draw weight value. Modern compound bows are well over 100%, like 200% and even more. It's very much possible to get over 100%. 100% would be a straight line on a force curve like this:
(https://lh3.googleusercontent.com/TD_W1CFXHCyKhSXDShKMJ0ZZxGtT__SqAMb4ciXc_ZpX9aMc58chq36OZLWEhGohPR32fOVzXcAW9sXRRiodprcfkstVLHoT79jqCJow2t0QrpEIBGC038natlYMi3CqnfaJJ0a8jjQGxnQAmfV8-WOXulDMBRet9OXdZrLeeIoOpsMbffXaW1LURcW5qQUZe7DZxPX3m2OzuZoXiTY60QAOz4u99OvD4Xp1m7ZTigSEGF8qG5_e2mX8gI2IW6UbAK350K2u0VV9MUwk4TsH074SK5iQW6r-Ox5fQOPFMV1rdskqW0JYdN0d9OLBympC9owweRT0KZLUCW1Cmeilqu0jbd9WjVkgo6ZGYfR-WXJkuXyJLwzUMnV0gXUbaQP7HPOHiD86wptOaSlf4VCt1FPTG1Qjiwl1oeXgBUQKpZLj6Ev5eDLUrWoxPV5P8a3VTqP1XgRVFWCYh2ygfcp-12Bzm9nNHdj7FDoamE09wX5X3uy09_Uk9D7PetPgJFK_SeSZo4LlIXmrdYVHJ3BiKudlunndr2WzfBvI7wl-YnYKYsE7av3WE8DAj9v8PvCOh1COuRTgfpYBoIkRVLshJlrs3QJ_59YjE9txTNuX6KwUTBaL38ySrkvlMdMCGs_KkT76jprquvjZiLT9LzPhFRrYZBUCHjPvkg=w1026-h432-no)
I just picked Simson's bow #100 to illustrate that it's very possible to get over 100% with a "primitive bow". ( I chose his because he's one of the few that actually posts force curve data). Here's a picture of it to recall your memory (hopefully Simson doesn't mind)
(http://primitive-bows.com/wp-content/uploads/2018/01/osage-Nr-100-7-von-40-768x576.jpg)
And here is his force curve. I didn't know his arrow speed, but I calculated that at 65% efficiency and 10gpp it would be 183 fps, which seems very reasonable if not slow for a bow of this caliber. But that's not the point. Notice the box that says stored energy per draw weight. This bow is at about 115% SE/DW.
(https://lh3.googleusercontent.com/33jPWcV4H9ub0i4_ZrPIXztqxhcZxDPGJg-WcxHYE-pSqRYjkLBds8bV57NES1ZjXi0nTov_UNiCEcehzBp5ao98faLAmRYvhI8zqJunDQcK3uD_SQ0LbH_J2f6lWapFA7VQ3hqdDv7doCue1aaQ2isQKjY80iwagbJKiTHINbCzRurZscQKF5r2JhyaZQjQ-0VcTF2-dWYNykSekaf9Aoio-6ZOQmei7LCmDoT8mrKa382f8Afrxr_74Pgb4KCBWexND6G5gS6oaWn42k3VsME8F6V0PmVfoZ5NMqMEvJiYnoI5fttc7nNfZ-HBKQwxNXwCjbLrmj1940kNv0jTbiBz1z9qtg8YAGRKjy1bkH88X1OcD_Sy6Xnmh0ip8xKPL_cfARCDN8DID4PfZ0aLlBpAkrMx00skyWFpCA8erZb1zxwNHPJMwTZIkYgEKkv3BEwgZUcwt7X6-1-Apqo1LXuKyyn3rq24aCvBDcvLHJg1wXryr77nnvGTnUEtlG0fJ-fryiUcG-ryC6ipgDmguQX6PSXfKcZhJPt0ThdzWHatLq_wVTDF2eYCOSyjL88yA6VMwwoeDasBeUlVzQaOVehe7k7r4vNwVvSQvMzWpIWBKrB4jdMntZfNZNlhgVHCAuXzrxnixJT02sJ65vWJP9-U3hEyjXH4cg=w1058-h418-no)
Now compare that to a compound bow I have which has a SE/DW of 233%
(https://lh3.googleusercontent.com/p1JR1_eWDHS6LD-GlzRzQ92LLjgo0Af1LMcyFitpLT4MJ4AX8PRucq6KEHs5-q3r6ZMKmnZeRYjHeeKcwSnJjxzkkKJabKSG3UPmxqq7RY7tM7QVgzL05SKLlWsT_nEbGmaUWhvH64r38c_-sDs7O8nf4Baa3udfrlIqH7svdddmgKwmAVjrWlXwd_AtKIArpIK3GtOvUFgjeBItQIHvSULjimUzY0mL4umkea0SBY2HIPNzAJFkt-eaEQfXZxYkqm2a0Tmofxh8D-C4n2LhEWAFUcLRWUkLJCbd0Wf19-4SH8-_ID2jszfSkX9-IkWVspYD_XlNu-_W18At4qdEX5XUvBl4RdaiIV0URMTlX8lSK0I-5BkvcSbo4ah4mRqHfsOLNOoElQXmwsaXWknXAiZNXmYonCeQQmp6Icb2uJEz5V75GgffVUf-1EnQSKQQWZ6UuME81q5hDkDWjxtvBF_xPicfbaULKGi85GFZ-BSj0tA9h8nEq9wXRa6ogujQUDvzpPHBXnKMaBKmmsQzdTZ3tsD_7wCAURadP8hw7kXesVPl5pydI-NaGZdHH5n0muVdp7OGFX-sKlLgnspX5eg3Jy2_H3VbrDLkYqPmx22iujCBWyN2wMGXdB4velpC_QY_QDoLwCtawkdeX8nPoRdlw22QuHSqpg=w1065-h428-no)
As well as too this bow I made a while ago at a SE/DW ratio of 55% (which isn't anything to brag about). However, it has an extreme overdraw at 25" (28" shown in picture) despite it's length of 43" with a non-working handle. It stacks badly!
(https://lh3.googleusercontent.com/EwLM5lKXwmQR_Lsdz0d-YkQNYuTJrXtyeSkF4zHA2wgo5sL1vV9ZIc7xH7RZFrB4fRabykC4b_rkLGBeEm1ERNx5XJphRglGk5hcV1_hSP96rPKIU-YpI1cFqspO6kocb16VxWpUopB_-ge12fDtHkirNuh-g1y3k-2nRSlc2YuhKUtHoYkKh6lZDGXDEPyGsDkqMgWD365YVOpK4sGVUD65P6TNciscxrql28ZqYTAlHlDEj_TzBc3Wq9TvVAHxoLlqYkxjPNuIVaImk8oG1Px7kC2q8-MIzd4TYNuuLB0xkehbORQzpk4aOgs5txflVj1pmukMI5QmfZ5-6LeRjMPgFV39zMOLDJMdZ16Hkr_R7eZh4K5W7uLKJwVZa5_fHJmr8ugA-LdVL3olHEt8pID62RhLR1fhhYA4W3f33Z0Hv6krgMKWRVKjRC4k2v_X_F3HGv_wcgqnx3YT8jN8MRY-2bLd7YrNoPKHGyliBkbVAsRqfsr8i0cHzqIS5vPe9psOLDsyjGVrC5UfHNnnHcI63zYYrrgM5zpnsJSwWxMPxEhPl6OtC4HdvYM3xBftt0ZhAaB6_05nYvKVk_kFPWsUYqqaZ3pjNYXrpqrS-0Oe5aGvN7rqKodnlHeoSxEYPzGU-ck5yt7RwV8R5P0bOjWvL1_MOobgxA=w1065-h422-no)
(https://lh3.googleusercontent.com/h87VpcRgCXXc9uqCSHZpV0NNi2Gxd5qki_uqjYtS3ahpsdYEXBUGqoYr5NNiz_-MR7j8c997VkYZFoViZpK1cazTzOXBrX7PVFwZfd2YXYVro264_gPFxjA_wgOdK482YkeNli7v8CngFwqG81BKYzW0lMCesR2al3_kSuYs-lAN9CZ_JK7f5qu9NOpbr5E_2WYr0OTCKmUY_7GMaDFf9YEPH09MVQl2PZlmPnx9agWrkwGBAsiceqCYsztw03TYmO3lGWMCkGnf_6rbpk9cwuTQFvstP8BE59dkqiqzh1jGmP6NtSpNz0eMwUBUUFluWLdt9_oJRXoK1KSw5u4GzTp75O0t0fYlr2iubEAD-rCsZhrEyUY1RPsmkbbZsBHPBQU10_GTsMHdytuRk44rt01b-jiaiAy2XqKmuxghauajEPT875RQdZ5Q32N91sDgy5ArkvWEPF_mcfZCvx5GhAvlfe7xBHo-LtTnTVB3sPMwPy8wS9H0qjHMQX4CVab-1JdrE4JB4GCqHgn5sxltiNNevH_ZUBJPcIIyeYHbyp5MoTySrL5T6XV5Dsa5Y-lRyvUCiKHPdjBGjJpTOmV2BUaELd32M8bFrHZkzMbNfcoPSo7ZVxu9KyPokgcCQ_3a62mtqlAwDWNHaX5676msTeB7YaTEld3rPQ=w507-h449-no)
I didn't see your old posts, I plan to download your calculator. On bows where I have gotten 120% with a 28" draw it usually has involved massive recurves and lots of reflex. 100% can be had with minor reflex and gently flipped stiff outer limbs. Stored energy is a very poor predictor of performance as most everything we do to store more energy has a negative effect on efficiency. Overall high energy storing bows do usually tend to be faster but not by as much as you might expect.
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I didn't see your old posts, I plan to download your calculator. On bows where I have gotten 120% with a 28" draw it usually has involved massive recurves and lots of reflex. 100% can be had with minor reflex and gently flipped stiff outer limbs. Stored energy is a very poor predictor of performance as most everything we do to store more energy has a negative effect on efficiency. Overall high energy storing bows do usually tend to be faster but not by as much as you might expect.
It's definitely not the only thing that matters for sure. You can see the compound bow I posted had a SE/DW of over 200% yet could only spit out an arrow the same grains as 10 times it's max (not final wright) at 160 fps. Even estimating it's speed at 10 gpp of 196 fps, it isn't that far out of reach for the top wood bows half that ratio. The compound is actually a really old bow, probably from the late 70s or 80s. As you can see it's efficiency is pretty low. I don't have some good wood bows to test out, but I'm guessing they are more efficient than it by a lot. That is the other factor: efficiency.
Those two things are what determines the speed of a bow. You have to have both. If you you had a horrible force curve like my bow, it doesn't matter if it had 100% efficiency. If it's a stacky mess it's going to be slow regardless. On the otherhand, if it has loads of stored energy but is highly inefficient, it will be like my compound.
It's interesting that you bring up the point that the things that make bows store more energy also tend to make it less efficient. So it becomes a balancing game where you try not to optimise one at the expense of the other. There are things you can do to increase efficiency: lighter tips, non-stretch string, minimizing set, etc. I wan't to point out, like you said, by designing large hooks which give you good energy storage, also causes higher stress on the working limbs increasing the chance of set as well likely increasing tip weight since the recurves/siyahs are static. These are just a couple of examples
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Of course I don't mind!
I foloow this thread with great interest, have to reread the most. I haven't understood everything, math and physics in English isn't my thing.
But I'm hooked!!
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You guys make my head hurt. ??? :-\ :BB (SH)
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You can see the compound bow I posted had a SE/DW of over 200% yet could only spit out an arrow the same grains as 10 times it's max (not final wright) at 160 fps. Even estimating it's speed at 10 gpp of 196 fps, it isn't that far out of reach for the top wood bows half that ratio.
SE/DW
if the compound max draw is 48#, is not that what you should used in the SE/DW calculation? do folks in the compound world actually use this metric? 233% seems to be about the dropoff more than anything else.
It's interesting that you bring up the point that the things that make bows store more energy also tend to make it less efficient. So it becomes a balancing game where you try not to optimise one at the expense of the other.
is the compound more efficient?
is high early draw weight more efficient?
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Willie, high early draw weight bows are usually fast because they store a lot of energy. How efficient they are depends on several other things. How much hysteresis was created in the limbs do to cell damage in the wood and how much distortion is the limb experiencing prior to releasing the arrow. High energy storing designs will typically have lower string angles which are much better at slowing the limbs and sucking out the energy near the end of the power stroke but if they have too much working limb available to distort it will often loose some energy by flexing in the inner limbs. If the recurves on a bow are bulky and heavy reducing working limb area is the only way to control the distortion.
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so if there is any efficiency advantage to a compound, it is because of the low hysteresis of the limb rather than any particular shape in the force draw curve?
I have always wondered if having so much energy available later on in the powerstroke makes a difference?
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The newer compounds are pretty efficient, I think the older ones lost a lot more through their pulley systems than the newer ones do. I really don't know squalt about compounds but I know they have very little limb movement.
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Kooi's papers address the energy storage versus efficiency battle. The gains are obviously pretty marginal but considered worthwhile when you are going for absolute max performance.
A lot of people still trumpet the F/D curve as telling the whole story of a bows potential.
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The newer compounds are pretty efficient.......... I know they have very little limb movement.
the smaller movement would show a gain in efficiency due to a smaller hysteresis loss, but we often cite hysteresis losses as being around 10%.
even if a compound was 0 %, would that explain all the difference a compound has? efficiency wise?
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With compounds, they have come a long way. All the stuff that made them quieter makes them very efficient. Parallel limbs, for one.
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SE/DW
if the compound max draw is 48#, is not that what you should used in the SE/DW calculation? do folks in the compound world actually use this metric? 233% seems to be about the dropoff more than anything else
Well the ratio is based on final draw weight, which is usually the highest in traditional bows, but yes compounds are the exception. I suppose if you based it off that it wouldn't be quite so ridiculously high. If I use the max draw weight instead if final I get a SE/DW of 105% which is still good, but nothing fantastic. Compou d people (not that I am one, or know of any) probably don't use this value because they aren't into building compounds. I think only the engineers who make the bows for the company would care, and even then it's a less useful tool for them than it is for us.
is the compound more efficient?
is high early draw weight more efficient?
Compounds aren't inherently more efficient because of high early draw weight. The force curve and efficiency are two very different things. Just because you have one doean't necessarily mean you have the other. Sure they may frequently show up together, good energy storage and good efficiencg, in those cases you have a great shooter on your hands. Jowever, it's also possible to have one or the other as I gave example of before (although I would add that poor force curves will tend to lead to poor efficiency as well because if you have a bow that stacks bad it most likely is overbending to get those bad string angles. Therefore extreme set is likely which induces more hysterias).
So yes, modern compounds may be more efficient (remember my old one from the 80s wasn't efficient). But they may not necessarily be more efficient because of their good force curve and early draw weight. I'm guessing it has more to do with their materials and design that reduces weight, and minimilizes the distance the limbs have to bend.
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I took an fdc on one this morning 77#@28". I plan to retiller down to 70# and flip the tips just a bit and am curious how much it will affect the FDC. Starting at 7" and ending at 28" the fdc reads like this. 6-11-14-17-20-24-27-29-32-35-39-43-47-51-54-57-60.5-64-67-70-73.5-77. I figured it using the method of just adding up the numbers for inch pounds and then dividing by 12 for foot pounds. I cam up with 76.5 I believe. Curious what the actual number is. Going to retiller and flip tips now.
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interesting experiment , standing by for the news at 6
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I finished the heat treat and recurve process, it picked up a lot of weight. I had about 1 1/4" reflex at that time and now I have about 3 1/2, I hope to keep about 2 3/4. Try to get it tillered back down tomorrow.
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I finished her up this morning 70#@28" 67" N/N. I picked up almost 4 percentage points on the FDC with the recurves and I suspect I will pick up a little efficiency as well because it is lowering the string angle some. The bow maintained 2 3/4" reflex so I lost 3/4" which I am happy with. No change after sitting for an hour which is a very good sign and usually indicates very low hysterisis. Best case scenario I think the bow could hit 184 to 185 with 10 grains. Anything over 180 I would be tickled pink with. I need to rebuild my shooting machine as I can't draw 70# anymore. So once I test it out I will report back with some photos. I am really curious as to how efficient it will be with much lighter 450 grain arrows I have to shoot in the broadhead event.
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Could you post the new force curve numbers. I'm going to calculate your old one's but it would be nice to see the difference. Keep us updated on the speed.
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Could you post the new force curve numbers. I'm going to calculate your old one's but it would be nice to see the difference. Keep us updated on the speed.
Zero is 6" 0-5-10-14.5-19-22.5-26-28.5-31-33.5-36-39-42-44.5-47-49.5-52-55-58-61.5-65-67.5-70
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Alright here's what I calculated
Before re-tiller
(https://lh3.googleusercontent.com/dhadyM-LjDl_2R3wRyQNrP8Fy8q9dPvAJGSXmX6eBvaM8KUp-8yNd4HACQ-9qhG3b_Zv1T_houp-2tduRK5zajRq3-SKf9wViWTcGhvXRbeMuHvVkU5jgOzWJRo5gH7mpWxo60D6IveP9KzW0IgPV3ECOtSAsG7rcvHasX8p8M5CKJup6af8jYKga44pDjYYsqYVjV9GX-o_5KXO9x3s3Hm0qheVRf6edby0IqGIX_k5VacBEWu258mzBbFgkxfFuquqK3wDcE3jXI4xXnGo4bodS190PxGGviwwmfWKtHrYkgW4egRemOFFpvJFFBn8QWo_fhb762OKsKLRuEJWyZpUEnEm_gfJu3LYig0loNXoTK0rKg4tHoUO5KRPc22nT-0JoSMejjvjH0ZeWJ_--cSJDSR98CV_7FKDmbnMmg9ocdDiOrwgb_YKJMEOhk-5UzoQ0pKLoI5nc3R96Cv2upd5daC8RZs9wtjkzyJhqqFH8bCavbCFRKVVQ1cZrBcRPgf7ztTPDripCuPtvqT8xWq-shc4jZBfzo_m7wgcPHB5sbNRpp0glEh-mNQJDx_5cNQxQlj7wRgICknf8d8ng5an3xjsrjhT6huNxdCG=w885-h408-no)
And after re-tiller
(https://lh3.googleusercontent.com/szllZoEW-LP_KVbjffXD6SlHlRhxppx43mra3OFaL6LLqYtLx22v23UG83HHgGN_EH-xY1YK2j70w6JzfWSq8r2zsd7t2WIPI4-lcG0Rkr3FhbI-c072-BRRAfyiaZ7e8IC2qQ48LNc-QbbIEpSH0OihhEWA36Den4T7qfPn7DsNbdbPIny4tMg0ZN-S5d5w8yxPvMBiDJ_8dlAi8fv5y7hTIOuq4FsTV5MJHfMbXLv1YGZVIbFnXGQeMlDH8Ka_pNLb4WPCzjbv_SHFMCrqJa7KZHHWVAQuRgO38AjrVujCxvuRlpHBZWBCqCo2VTo-qGyWO8BwSJh4EOLkKUw7CluaU7dDMYWMBcy2Ls5f7-5mJiZoWi0nmGyiVLUEIJH_LnK2r05JL9H54fLc0Gn1CAvfm4YRff1YRAkZ1x-5_vccGWBw90CdqX3elabBGfCzYNxtZIG4-suIrrmkL8lOePF-G-fybNNoWsKMkuKPlJdeN35KErY5E5MdvnMqGBVRSxkQP2tz7NI4HgbVkkJONSCZdw2RV1f5qfchgAL0W-NxTeXNKA42MeLrdMSGwgfr4Nc0rQbj4EY_ImMGBGAYMDguz52sDheIzU6s8JLk=w884-h407-no)
So on your first one I calculated a stored energy a little less than what you get when you add all the numbers and divide by 12: 73.3 vs 76.5 Ft-Lbs. that's only a difference of 4.4% so I think it's safe to say that it gets a good estimate, however, that method won't work if you have measurements anything other than every inch (I like to do it every 2 inches for example, but some people may like to uses centimeters or something too).
If you have an efficiency of 65% I'm estimating a velocity of around 170 fps. however, I'm guessing that you'll have an efficiency better than that, since it seems to be your speciality. If you get in the 180 fps you'll be more than 72% efficiency. I'm eager to see what you get. keep us posted.
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Greg
I see that your new spreadsheet also has calcs for virtual mass and efficiency. There have been a few questions posted recently (at least about virtual mass), would be willing to explain how you actually make those calcs in the example above?
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Greg, the virtual mass on a primitive wood bow can be tricky as the hysteresis is time sensitive. In other words we have more hysteresis with lighter faster arrows than we do with slower heavier arrows so it is very difficult to extrapolate speeds of various weight arrows using the virtual mass method. It is possible to isolate and identify a good portion of the hysteresis from other more typical vibration losses but it is a lot of work. When the integrity of the wood has been only minimally compromised during the tillering process the hysteresis can be very low and when it has been more typically compromised it can easily exceed 10% power losses.
I have found several ways to increase efficiency. Some of the obvious ways are to build shorter bows, efficiency goes up but stored energy goes down and the bow is at higher risk of taking set increasing hysteresis. By building a bow using a no set tillering method where the integrity of the wood is constantly being monitored you get an instant jump of up to 10% this is huge. The other method is to time the unfolding of the limbs so that the inner limbs hit home first and it rolls out toward the tips. This puts much less load on the arrow to try and slow down the limb tips at the end of the power stroke and eliminates a lot of the opportunity for the limb to vibrate or distort. You can pick up as much as 10% here also and even with a longer 68 to 70" bow still realize up to 80% efficiency if everything goes just right. I am thinking about 75% with a 10 grain arrow on the bow shown above but won't know until I test it.