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Gentlemen,
How is this possible? if an aluminum and a carbon arrow have the same kinetic energy (1/2mV2) the carbon "hits harder"??

KE measured in ft-lbs is universal and makes no adjustment based on composition. 100 lbs of feathers and 100 lbs of rock have the same KE (in a vacuum)

Is there a better measure of "arrow effectiveness" than ft-lbs?

Does anyone do a gelatin test to study the external ballistics of arrows?

The reasoning given to me regarding the "hits harder" is that carbon, being stiffer, transfers more energy.

Do not read into this more than is written, don't get into specific bow/arrow combinations. For all intents and purposes they could be shot from an air-rifle.

Thanks for the help,
Jim G,
 

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There are those that are proponents of the maintained momentum measurement but from what I understand it's not universally (sp) accepted. There's been a lot of explanations as to why carbon shafts penetrate better, the most popular seems to be the smaller shaft diameter. This explanation makes sense to me at least and we could easily test it's voracity using some of the new carbon fat shafts (26/64" diameter) vs. the smaller diameter std. carbon shaft to see if the theory holds up.
 

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Redheaded Stepchild
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Basically the only thing I can see is that while your Energy at impact is the same, with a smaller diameter carbon that force is being distributed across a smaller area resulting in a higher pounds per square inch of pressure on the area of impact. Don't see where it's going to be that drastically different but there may be a negligble difference. Also, since the point making the impact is the broadhead and not the shaft itself, and they should be the same in both cases if you want to compare apples to apples then it shouldn't matter. Now upon impact I could see an aluminum arrow slowing down faster due to the larger surface area being acted upon which would result in it bleeding off it's KE faster than a smaller carbon arrow.
 

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i like russ believe in the diameter theory but i also believe that the fact that the carbon is wrapped tighter than an aluminum and causes less friction when contacting the skin of the animal is also part of the reason and if you shoot both you will find that the aluminum has a tendency to go off the string and occeslate sorry for the spelling getting old to quickly. but the impact from the aluminum is where there is a loss of k.e. due to the flexability of aluminums and the spine is better on a carbon arrow. when i say better it is due to the wrapping of the arrow
rob k
rob k
 

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X's R Us
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Could be because the carbon is usually stiffer so less energy is lost from flexing when it hits the target.
 

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There is some research that tends to lean towards Carbs not ocsillating as much as alums. on impact. As far as penetration goes,when you have a 2314 or a 2413 or there abouts going thru a critter,you have alot of friction,the shaft is bigger around than the head. You launch a 18/64'' dia. +- carbon,its all head,very lil resistance on the shaft. I can tell you when a 470 gr. 28.5" 2314 hits a hog on the shoulder from 20 yds at 250ish fps ,it really flexs's on impact.Momentum and penetration straightens it all right out.The term ''Deflection" which I believe Easton uses and they measure and rate thier shafts spine this way.Go to a 2315 (almost 30 gr heavier),noticably less deflection on impact.Carbons also,at least on impact seem to bend or oscillate less than the light alums.
 

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"Basically the only thing I can see is that while your Energy at impact is the same, with a smaller diameter carbon that force is being distributed across a smaller area resulting in a higher pounds per square inch of pressure on the area of impact. "


How do you figure? If I'm shooting the same broadhead on a carbon or aluminum arrow, how does that work? The surface area at impact is the same.
 

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Paradox: Your energy at the exact point of impact is truely determined by the size of the broadhead and that will be the same for each shaft if you are using the same broadhead. Where the small dia Carbon has the advantage is on the followup force it takes to drive the arrow shaft through the hole that your broadhead just made. The flesh will tend to close in around the shaft as it penetrates causing surface friction and lost KE. If you look at a block target for example it stops a arrow SOLELY with friction against the sides of the shaft NOT resistance to the point penetrating. The smaller the shaft the smaller the surface area and less drag along the sides so it retains more energy longer no matter what the size of the head of the shaft is.
 

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Punch_Master

I can accept you answer, but I don't think that's what potato749 meant. What you explained is what everybody else is saying, a smaller shaft penetrates because of less surface area.

I wanted clarification because I run into this same argument in my neck of the woods. They are trying to tell me that carbons just penetrate better because a smaller shaft concentrates the initial impact force on a smaller area (the point of the broadhead). That's untrue if you're comparing the same broadhead. Sixty-five pounds of KE is 65 pounds of KE whether you're shooting a thunderhead (or whatever) on a carbon or aluminum. The surface area of the trocar tip is the same.
 

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Redheaded Stepchild
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Little clarification on my point from earlier.....if they were talking about a carbon giving more punch on impact the only way it would work is if you were shooting a point the same size as the OD of the shaft. But if you compare each with the same point no matter what style it is as long as the point is the same size there should be no difference no matter what size shaft you are shooting. The only difference should be like I said earlier after impact due to the larger surface area of the aluminum offering more for friction to act upon leading to the speed dropping quicker which drops the KE. The thing is though that since the larger part of the KE for the aluminum is the mass and it stays constant throughout the impact (in ideal case) then the slightly increased loss in velocity at least in my mind :)
I tend to think theres more to the fact that the carbons don't flex as much on impact imparting the force of the mass directly behind the impact point instead of oscillating back and forth like an aluminum is more likely to do......all I got to say :)
 

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I noticed that when i put on MAGNOCKS that my carbon hit the target a lot harder Sooo i think it has a lot to do whet the flexing or NOT FLEXING THAT GIVES YOU MORE KE just my 2 cents

runawaysXs:D
 

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Hey Paradox...

I think it is sectional density that determines the punch transfered by the projectile. I know for bullet comparisons two identical weight bullets that travel at the same speed and thus holding identical KE, the true marksman usually leans to the bullet with higher sectional density because of its ability to shed drag better downrange and transfer energy better on impact.

I have really just begun reading on this topic recently because it is that time of the year again. :)

I have run across some formulas and will see if thay can be used for archery and see if it correlates as to why people say carbons penetrate better.

See yah at Brunners Wednesday?
 

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OK I couldn't resist!!!!

Sectional Density is described as the weight of the projectile in pounds divided by the diameter squared in inches.

I ran two typical arrows...

a 2312 weighing 400 grains and a carbon arrow also weighing 400 grains. They had diameters of .359 & .296" respectively.

Doing the math shows the following:
The 2312 has a sectional density of .442
The Carbon arrow has a sectional density of .648.

For the sake of argument in modern ballistics for rifles a higher SD (sectional density) is generally thought as having better penetration with all other things being equal.

Maybe this can FINALLY put this to rest?!!!! ;)
 

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I've seen some high speed video footage at http://www.goldtip.com/video/highspeedexplorer.html of carbon and aluminum arrows in flight. Due to the vibration dampening characteristics of carbon arrows the oscillations are reduced quicker so that the arrows is traveling straighter and thus more of the energy goes straight down the shaft for more penetration. The newer layered carbon shafts are not that much smaller than aluminum, but I'm sure that helps too.

Targetnut
 

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I believe it is simply a function of carbons ability to dampen vibration. Take two similar spined aluminum and carbon arrows and tap them on your hand. You can feel the aluminum bounce like a spring. This results in lost energy, and thus lost penetration.

The friction factor may be true in 3D targets but not in an animal where typically 3 blades are cutting slits 120 degrees apart and releaving the friction force. Also the blood and fat act as a lubricant.

Since broadheads would have the same size I don't think the cross sectional density affects penetration. It does explain why an arrow penetrates the bucket of sand and a 44 magnum with much more KE does not. If I remember correctly this also has a relation to the projectiles length?

No physicist around, should be a text book problem!
 

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PJ-

Shape has no effect on SD.....only the diameter and the weight.

The interesting thing that I am seeing with this whole SD thing is that you can can get a much lighter carbon arrow (300 grains) which exhibits the same SD as a 2312 weighing 440 grains!

Now shoot them out of the same bow and for all practical purposes you will have equal KE....(lets not argue this point, it's close enough!)

The SD theory would indicate that each arrow would penetrate the same! Now change the weight of the carbon arrow to 400 grains and the SD jumps substantially higher than the aluminum arrow. This would indicate the carbon arrow having much better penetration potential than the aluminum! This also seams to hold true in my own observations.

Just tonight I was shooting two different Carbon arrows with different diamters. The target was a 8" thick slab of styrofoam. Both arrows had G5 Montecs. The narrower arrow penetrated farther through the styrofoam every single time. I realize this is pretty un-scientific, but here are the arrows used. Carbon Express CXL250....Carbon Express CX200 3D PRo.

If the whole carbon thing held true then the heavier arrow should have penetrated better in the above test. The CXL250 weighed 345 grains with an SD of .379, and the CX200 weighed 335 grains with an SD of .585
The CX200 went WAY farther through the styrofoam!

The more I read and calculate the more I am convinced this is the real answer.
 

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runawaysXs said:
I noticed that when i put on MAGNOCKS that my carbon hit the target a lot harder Sooo i think it has a lot to do whet the flexing or NOT FLEXING THAT GIVES YOU MORE KE just my 2 cents
If you look at vibration in the arrow, it takes a small amount of energy. For example, if you have a 0.5" spine, and the arrow bends 1" (say), then the energy put into vibration is about 0.4 foot pound. But a 310gr arrow at 280fps is around 108 ft pounds, so the vibration holds much less than 1% of the energy (if I did this right).

If your Magnocks actually do penetrate better, my guess is that it's because your bow is tuned better, and the arrow strikes normal to the target upon impact.

kgk
 

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Kinetic energy is a wonderful thing - when you have a lot of it.

I used to work in ammunition design. At one point I was working with a .45 ACP round that would go 2200 fps out of a standard gov't model. The bullet was really light, so had almost no recoil (low momentum), but it would shoot through two kevlar vests at short range. A customer had an accidental discharge once into a wall with this stuff. The bullet stopped in the 2nd layer of sheet rock. I have also seen autopsy photos where the wound volume was about one gallon. That is high KE, low momentum does for you.

Arrows are just the opposite. They depend on momentum for penetration and cutting. The KE on an arrow has almost no effect. Faster arrows have higher momentum and higher KE, so it might look like it is the KE that does the damage, but it isn't. Until you have an arrow that kills with a shock wave, you have a kill-by-momentum arrow.

Hard targets are a different story. . .

Scott
 

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"Could be because the carbon is usually stiffer so less energy is lost from flexing when it hits the target."

That's pretty much how I see it...


- georgestrings
 

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Carbon Express did some testing on this. Granted they might be biased but if you watch the video it is obviouse the alluminum flexes alot more at impact then the carbon arrow does. thus shedding energy.

I don't believe the diameter of the arrow has much to do with it. If you are shooting a 3 blade broadhead or more the hole it cuts is bigger then any arrow. Two blade might be different.

tony a smaller diameter penetrates more on styrofoam because it is compression friction that stops the arrow. If you do not compress the styrofoam as much it does not produce the same amout of friction to slow the arrow down.
 
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