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JR's Science Project
Hey fellas. Been away from archery for a few years. Swamp Jr. has a Sci project and decided to do it on arrow penetration upon an object. His hypothesis was that a heavier arrow would penetrate deeper into an object based on KE.
Well the test went as follows: 10 yard shot shooting into block target using a 85 grain tip, 100 grain tip, and 125 grain tip. The same arrow (Easton Acc 3-60's) and bow was used for all tests and the same spot on the target was hit on all shots. The results: 85 gr 3 shot average: 28.75 cm of penetration of the target 100 gr 3 shot average: 32.5 cm of penetration of the target 125 gr 3 shot average: 30.5 cm of penetration of the target Based on our theory, the 125 grain tip should have penetrated the target the most, but did not. I know the logical thing to do is to shoot thru a chronograph and get fps and weight of arrow to figure KE. But the local shop is closed today and the project is due tomorrow [:-]. Can ya'll give me some reasons why our theory did not hold true? |
RE: JR's Science Project
10 yard shot shooting into block target using a 85 grain tip, 100 grain tip, and 125 grain tip. The same arrow (Easton Acc 3-60's) and bow was used for all tests and the same |
RE: JR's Science Project
"The Block" may not be the best material to shoot into.
If some of your shots are going more directly right between the layers of foam instead of hitting the edges as they enter- that can alter your findings. A fresh, solid foam block would be better for each shot- or better yet, ballistics gel. And just doing three shots to make up an average may not be enough either. How about 10? If the spine of the arrow is reacting poorly to the heavier tip, that will degrade your penetration findings also. |
RE: JR's Science Project
I would look at the spine of the arrow. Since you used the same arrow for all 3 heads. Also is the cut Dia the same. I hope you are using the same style broad heads too.
There is a huge dif between the 85 and 100 gr tips this does not sound right for 15 gr dif. I think your test might have a few bugs to work out. |
RE: JR's Science Project
I think the spineis OK. .340 for 27.5" arrow. 29.75" draw length at 68 lbs. At 8.3 grains per inch, that is 228 grains for the shaft only. The same style field tip was used for all tests. I think I will go shoot ten shots per test though, to see if the results vary.
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RE: JR's Science Project
Like mentioned, check spin. The 125 probably had more bend in the arrow, absorbing and releasing some of the bows energy in the arrows elastic potential.
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RE: JR's Science Project
ORIGINAL: Swamp Dawg I think the spineis OK. .340 for 27.5" arrow. 29.75" draw length at 68 lbs. At 8.3 grains per inch, that is 228 grains for the shaft only. The same style field tip was used for all tests. I think I will go shoot ten shots per test though, to see if the results vary. |
RE: JR's Science Project
ORIGINAL: Swamp Dawg I think the spineis OK. .340 for 27.5" arrow. 29.75" draw length at 68 lbs. At 8.3 grains per inch, that is 228 grains for the shaft only. The same style field tip was used for all tests. I think I will go shoot ten shots per test though, to see if the results vary. |
RE: JR's Science Project
Thanks for the replies. I shot ten more shots with each field tip withvery similarresults.
I agree OHbowhntr. The FOC is ideal with the 100 gr tip. This is what I have been using for my hunting set up. Also, Ishot thru thechrono and determined the following. Arrow with 85 grain tip = 383 grains.....................275 fps= 64 ft lbs KE Arrow with 100 grain tip=398 grains.....................271 fps= 65.4 ft lbs KE Arrow with 125 grain tip =423 grains.....................257 fps = 62 ft lbs KE This makes sense that the 100 grain arrow penetrated the deepest with the most KE. I think Indianahunter83 hit the nail on the head. With velocity being squared, it plays a larger factor than the mass in determining KE. Am I missing anything?????? |
RE: JR's Science Project
ORIGINAL: Swamp Dawg Arrow with 85 grain tip = 383 grains.....................275 fps= 64 ft lbs KE Arrow with 100 grain tip=398 grains.....................271 fps= 65.4 ft lbs KE Arrow with 125 grain tip =423 grains.....................257 fps = 62 ft lbs KE This makes sense that the 100 grain arrow penetrated the deepest with the most KE. |
RE: JR's Science Project
Other things to take into account is the actual act of shooting a bow is taking the potential energy of pulling back the bow and passing it on to the arrow in the form of Kinetic energy. I have read somewhere that there is lest energy lost to vibration (and other aspects) when you use a heavier arrow. This being said I think an arrow can be too heavy. Another aspect I think is ignored is momentum. The momentum with the 125 and 100 are very similar however the momentum with the the 85 is much lower. Taking this into account along with the kinetic energy you can probably come up with saying the 100 grain is the best.
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RE: JR's Science Project
My guess is that the spine is the issue. 3 different tips are not going to all fly in a straight line out of the same arrow. If the arrow doesn't fly perfectly straight, it's not going into the target as far as one that does. I would venture that the 100 gr tip simply matched your static spine the best. The material of the target could also be an issue. Different tip weights will enter the target at different angles. The angle of entry into a target of this material may make a difference.
Also, the arrows should not have been hitting the target in the same spot. The heavier arrow should have hit lower. Penetration will also be affected if hitting near a spot that has been hit before. As for FOC, no way 100 gr tip is optimal for penetration - not even close. The higher the FOC, the greater penetration is - if spine is correct! One thing this test demonstrates, is the importance of matching spine to arrow length, draw weight and tip weight. It's a dynamic formula and when you change one variable, the others have to be adjusted in order to obtain optimum arrow flight. One thing for sure, this test did not verify anything about penetration vs tip weight or KE. Way too many uncontrolled variables. |
RE: JR's Science Project
Very logical explanation.
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RE: JR's Science Project
ORIGINAL: Straightarrow My guess is that the spine is the issue. 3 different tips are not going to all fly in a straight line out of the same arrow. If the arrow doesn't fly perfectly straight, it's not going into the target as far as one that does. I would venture that the 100 gr tip simply matched your static spine the best. The material of the target could also be an issue. Different tip weights will enter the target at different angles. The angle of entry into a target of this material may make a difference. Also, the arrows should not have been hitting the target in the same spot. The heavier arrow should have hit lower. Penetration will also be affected if hitting near a spot that has been hit before. As for FOC, no way 100 gr tip is optimal for penetration - not even close. The higher the FOC, the greater penetration is - if spine is correct! One thing this test demonstrates, is the importance of matching spine to arrow length, draw weight and tip weight. It's a dynamic formula and when you change one variable, the others have to be adjusted in order to obtain optimum arrow flight. One thing for sure, this test did not verify anything about penetration vs tip weight or KE. Way too many uncontrolled variables. What he said.Too many variables to say heavy penetrates better than light. IMO,the spine always gets overlooked and people hurt their penetration when going heavy SOMETIMES. I believe in mass over weight and a perfect spined arrow over just a heavy one. Tip design might be the reason for the results in this test though.;) |
RE: JR's Science Project
ORIGINAL: TFOX ORIGINAL: Straightarrow My guess is that the spine is the issue. 3 different tips are not going to all fly in a straight line out of the same arrow. If the arrow doesn't fly perfectly straight, it's not going into the target as far as one that does. I would venture that the 100 gr tip simply matched your static spine the best. The material of the target could also be an issue. Different tip weights will enter the target at different angles. The angle of entry into a target of this material may make a difference. Also, the arrows should not have been hitting the target in the same spot. The heavier arrow should have hit lower. Penetration will also be affected if hitting near a spot that has been hit before. As for FOC, no way 100 gr tip is optimal for penetration - not even close. The higher the FOC, the greater penetration is - if spine is correct! One thing this test demonstrates, is the importance of matching spine to arrow length, draw weight and tip weight. It's a dynamic formula and when you change one variable, the others have to be adjusted in order to obtain optimum arrow flight. One thing for sure, this test did not verify anything about penetration vs tip weight or KE. Way too many uncontrolled variables. What he said.Too many variables to say heavy penetrates better than light. IMO,the spine always gets overlooked and people hurt their penetration when going heavy SOMETIMES. I believe in mass over weight and a perfect spined arrow over just a heavy one. Tip design might be the reason for the results in this test though.;) |
RE: JR's Science Project
As a matter of principle, are you saying that the same arrow with a 75 gr., 100 gr, and 125 gr. tip - allstriking the targetwith the same KE - and all spined perfect: the 125 gr. (with the greatest FOC) is going to penetrate the most? Thx. Roskoe
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RE: JR's Science Project
If you still have time, You might want to browse bowsite.com, a while back there was a study done for a cape buffalo setup. KE was not the issue when it came to penetration according to the author. If I can remember right, he opted for a 950 grain arrow traveling at 190 fps. The setup that he had, outpenetrated everything that he tested.
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RE: JR's Science Project
As a matter of principle, are you saying that the same arrow with a 75 gr., 100 gr, and 125 gr. tip - all striking the target with the same KE - and all spined perfect: the 125 gr. (with the greatest FOC) is going to penetrate the most? Thx. Roskoe |
RE: JR's Science Project
Heavy arrowsABSORB more of the bows energy than do light arrows.IN GENERAL.
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RE: JR's Science Project
ORIGINAL: Swamp Dawg Thanks for the replies. I shot ten more shots with each field tip withvery similarresults. I agree OHbowhntr. The FOC is ideal with the 100 gr tip. This is what I have been using for my hunting set up. Also, Ishot thru thechrono and determined the following. Arrow with 85 grain tip = 383 grains.....................275 fps= 64 ft lbs KE Arrow with 100 grain tip=398 grains.....................271 fps= 65.4 ft lbs KE Arrow with 125 grain tip =423 grains.....................257 fps = 62 ft lbs KE This makes sense that the 100 grain arrow penetrated the deepest with the most KE. I think Indianahunter83 hit the nail on the head. With velocity being squared, it plays a larger factor than the mass in determining KE. Am I missing anything?????? This speed loss MAKES NO SENSE. I am thinking the heavy point is causing problems with the rest and creating some contact issues.You should stiffen the tension of the rest for a heavier arrow. If not that,some other TUNING issue is the culprit. |
RE: JR's Science Project
With the bow shooting the first 2 arrows at those speeds,the arrow SHOULD be shooting 264 fpswith the 125 gr tip,not 257 fps.
These kinds of test should be retuned with EACH different setup. If you are using a loop,the arrow is on the stiff side,if not,the arrow is real close to perfect on spine. |
RE: JR's Science Project
ORIGINAL: indianahunter83 Physics says that energy cannot be created nor can it be lost... energy is just transfered. You first transfer your energy into the bow that transfers its energy into the arrow which is stopped by the friction of the target (thus energy is lost in the form of friction or heat) The arrow would stop its penetration once it lost all of its energy. Because of this IMO if you were to have all of the variabilities the same except for mass and as long as the tips were identical (except for weight) I would expect all arrows to lose their KE at a constant rate and therefore they would have identical penetrance. Add in, the fact that heavier arrows absorb more eneregy from the bow and retain more energy downrange you can see why it has a higher momentum and KE. The heavier arrow should penetrate more if the test is a well controlled one. |
RE: JR's Science Project
I appreciate ya'll chiming in. This test was done in hast partly due to time constraints and partly due to procrastination! I wish I had more time to work the bugs out, but it was due on Tuesday. I doubt the 5th grade teacher will know any better. :)Thanks again.
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RE: JR's Science Project
ORIGINAL: Swamp Dawg I appreciate ya'll chiming in. This test was done in hast partly due to time constraints and partly due to procrastination! I wish I had more time to work the bugs out, but it was due on Tuesday. I doubt the 5th grade teacher will know any better. :)Thanks again. |
RE: JR's Science Project
ORIGINAL: ArrowMike ORIGINAL: Swamp Dawg I appreciate ya'll chiming in. This test was done in hast partly due to time constraints and partly due to procrastination! I wish I had more time to work the bugs out, but it was due on Tuesday. I doubt the 5th grade teacher will know any better. :)Thanks again. Unless she was a physics major in college.[8D] |
RE: JR's Science Project
To start with as someone has already alluded to , any target unless it is made of the gel , there is too much variance to test for penetration differences. But since this was the best to be had for the time constraints it was ok. Even though it said the 125 grain tip didnt penetrate as deep it still had the highest momentum factor of all the different tip configurations.
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RE: JR's Science Project
Hey, either way you look at it, if a 5th grader is doing a science project and a bow and arrow is involved, it's likely a good thing for those of us who love bowhunting and archery!!!!!!!!!!!
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RE: JR's Science Project
If everything were identical, then penetration would be identical. However, in this example each arrow had a different weight, different FOC, different dynamic spine and a different entry angle. Add in, the fact that heavier arrows absorb more eneregy from the bow and retain more energy downrange you can see why it has a higher momentum and KE. The heavier arrow should penetrate more if the test is a well controlled one. |
RE: JR's Science Project
It can but in this instance and most cases,it shouldn't have less ke.
[Hey, either way you look at it, if a 5th grader is doing a science project and a bow and arrow is involved, it's likely a good thing for those of us who love bowhunting and archery!!!!!!!!!!! ]EXACTLY OHbowhntr |
RE: JR's Science Project
ORIGINAL: OHbowhntr Hey, either way you look at it, if a 5th grader is doing a science project and a bow and arrow is involved, it's likely a good thing for those of us who love bowhunting and archery!!!!!!!!!!! |
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