Slo-bo

If an arrow starts losing speed, ie. energy, as soon as it leaves the string, then the KE is constantly dropping as the arrow continues it's flight, correct? So that to say you are shooting a certain speed bow in conjuction with a certain weight arrow so you have an arrow with "X" amount of KE is truly a misleading statement, right? If part of the formula for KE is arrow speed, and the arrow is constantly losing said speed, then in order to compare one bow/arrow combo to another as far as KE, the chrony would have to be the exact same distance from each bow, yes? So when the statment is made that you need, or should have, "X" amount of KE in order to use mechanical heads, or to hunt elk or whatever, "X" amount of KE at what distance?
By the way, I never took physics, and didnt always pay attention in class like I should have!!

PABowhntr

Good discussion gentleman. Some excellent posts so far and I really don't have anything to add to the original question beyond what FL stated.

I would say though that I think KE is probably the best "general measuring tool" when it comes to penetration.

One can usually state that a bow generating 70 lbs of KE will outpenetrate a bow generating 50 lbs of KE even if everything else isn't equal (ie...bow tune...broadhead style or sharpness, etc) but we can't always state that a bow with a fixed blade broadhead will always outpenetrate a bow shooting an expandable head. There are too many other factors that might be involved.

KE is the biggest determiner but everything else listed above plays a part.


















Edited by - PABowhntr on 08/14/2002 13:28:58

pdq 5oh

I agree with amosgreg, 45# of KE is 45# at 5 yd or 45 yd. I still feel a heavier arrow will penetrate deeper, at the same KE. On deer sized game I don't see the arrow weight being such an issue, as on an elk or grizzly. The deer is much narrower, the elk much thicker across the chest. The elk and grizzly offer much more resistance to the arrow than the deer, slowing the arrow faster. The heavier arrow will resist being slowed better than the lighter one, all else being equal.

Phil.

TheArcheryProgram

I will try and sum this up as simply as I can based on all the good posts so far.

First of all the arrow is in constant deceleration even before it leaves the string. If you ever look at a draw cycle curve you should be able to clearly see the point at which this happens.

Secondly I agree whole hardily that the shot placement is about 90% of the penetration equation.

Now to answer the original question. Penetration is best quantified by looking at momentum. KE is nothing more than number value of how much energy the arrow can deliver.

Think of momentum this way....we all agree that a heavy and light arrow will produce almost identical KE shot from the exact same bow right? The difference comes in downrange where-as the arrow that can maintain the most of its starting speed will also retain more KE right? Momentum is very similar.....its really a way to quantify a moving bodies resistance to change. This does not always mean that the heavier projectile will have more momentum when shooting through an animal though! A lighter narrower smaller arrow may actually win out based purely on the fact that the medium in which you are shooting through (animal flesh) will have less effect (drag) on the smaller surface area to slow it down. This is very similar to the effects of air on an arrow, and it coralates the speed and KE loss downrange.

I hope this helps....

Happy Shooting!




>>>------Tony Virnoche------>>>
>>>---The Archery Program--->>>

WV Hunter

Slo-bo....I think the answer to what you are asking is...the KE is measured at the initial launch of the arrow....very similar to the muzzle velocity on a rifle. And it then begins to decrease with the loss of speed downrange. So to say that it has X amount of KE....that would be basically at the bow, not at 40 yds(or whatever distance downrange). I guess "they" base the minimum amounts required, based on an average loss of velocity...? Not really sure, but it could definitely vary a whole lot depending on the setup.

Phil, I agree with you on the heavier arrow.

Slo-bo

WV Hunter, my point exactly! I believe it would be an easy mis-conception for someone to fall into, that because they have a "chart" KE of X right out off the bow, that they retain that at 20, or 30 yards. I knew when I first read BobCo's post, this would be an interesting one!

Edited by - Slo-bo on 08/14/2002 14:28:11

Arthur P

Air resistance also increases in proportion to the square of a projectile's speed. So, a fast arrow will lose proportionally more speed over a given distance than a slower arrow launched with an equal amount of KE.

Take a 350 grain arrow at 300 fps and a 700 grain arrow at 212 fps and go to the ballistics program. Both arrows carry 70 fpe from the bow. At 30 yards, the 350 grain arrow has slowed to 285 fps (-5%) and lost 7 fpe (-10%). The 700 grain arrow is going 207 fps and carries 66 fpe, a loss of only 5 fps (-2.4%) and 4 fpe (-5.7%). And the 700 grain arrow is carrying a whopping 31% more momentum at 30 yards than the light arrow.

I assume the resistance in hide, flesh and organs as the projectile passes thru an animal also increases in proportion to the square of the projectile's speed. If the heavy arrow penetrates air with less resistance, then it has to penetrate better in flesh.

Personally, I think far too many people put way too much importance on speed and flat trajectory over typical hunting distances when they should be more concerned about getting their arrow to the animal with as oomph as possible. But then, how deep do you have to bury the arrow in the dirt on the far side of the deer?

silentassassin

My light fast arrows sure seem to pass through deer awful quick. I have on video me shooting a pretty good buck and the arrow hitting him right in the heavy part of the opposite shoulder on the way out. Shooting mechanicals and light arrows mind you with a complete pass through. I plan on shooting Montecs this year but this whole thing is meaningless. What the question is really is how far will your arrow bury up in the dirt if you hit them in the right place. Everyone go out and practice putting the arrows where they are supposed to and the rest will fall into place. The indians killed them with wood bows and wood arrows and stone broadheads. Don't you think this arguement is splitting hairs?

Protect your hunting rights, "Spay or neuter a liberal."

amosgreg

Thanks TheArcheryProgram!
I am glad this didn't degenerate into something ugly as I enjoyed the thread and thinking about the issues.

It would be real interesting to chrono various arrows at a number of ranges and do the math to see what is really happening out at longer hunting distances with hunting set-ups.

Anyone want to?

Greg



"Getting close to the game is the joy of Bowhunting for me, the harvest is a bonus."

Live 15 ft Python after eating a small Antelope!

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