Draw lengths and KE and penetration

[ks_stickbow]

This is just a question out of curiosity.

IF

I shoot a 26" arrow 500gr and my buddy is shooting 30" arrow at 500gr and we are both shooting 180 fps...are we going to get the same penetration?

assume we both are shooting 50lbs at our draw lengths (mine 26 and his 30), and that both bows are tuned well and blah blah blah..

[jon]

If both arrows are going 180fps and both weigh 500 grains, then both will have the same KE and Momentum. Assumming both are properly tuned to their respective bows, they will have the same penetration.
However, 50# @26" vs 50#@30" will have different levels of stored energy. All else being the same, a longer draw length with the same poundage will impart more energy due to the longer power stroke than the shorter draw length.

[Crash]

Since the KE and momentum would be the same, I would think that the shorter arrow would penetrate better.  It will flex less than the longer arrow upon impact.  It would probably be less difference in a carbon arrow as opposed to a wooden arrow.

[Crash]

Jon, the power stroke is a non issue since both arrows are traveling 180 fps.

[Crash]

Jon, you are correct that all else being equal, a longer drawlength means more power, thus providing more speed.

[John Havard]

Jeff, if you're drawing 50# @ 26" and your friend is drawing 50# @ 30" and if your bows are the same design (they store the same amount of energy from brace height to your respective draw lengths) then he's storing a heck of a lot more energy than you.  

In your "what if" question you ask if your arrows are traveling the same speed would they penetrate the same.  Probably they would.  But with your shorter draw you'll need to store more energy per inch of draw (use a bow with a better design) or shoot a heavier draw weight than your friend in order to store as much energy.  That's the only way your arrow will travel as fast as his.  

This page might help:   http://acsbows.com/bowperformance.html

[ks_stickbow]

Originally posted by John Havard:
Jeff, if you're drawing 50# @ 26" and your friend is drawing 50# @ 30" and if your bows are the same design (they store the same amount of energy from brace height to your respective draw lengths) then he's storing a heck of a lot more energy than you.  

In your "what if" question you ask if your arrows are traveling the same speed would they penetrate the same.  Probably they would.  But with your shorter draw you'll need to store more energy per inch of draw (use a bow with a better design) or shoot a heavier draw weight than your friend in order to store as much energy.  That's the only way your arrow will travel as fast as his.  

This page might help:     http://acsbows.com/bowperformance.html  

Is that under the assumption that we are both shooting the same bows...

I was trying to leave the bow out of the question cause I do not want to start a this bow is better bit.

But if he's shooting say a board bow and getting 180fps... with a 500 grain arrow...I would consider that a pretty good board bow (possible or not I do not know) and if I was shooting a high performance bow like a widow or acs or whatever.

this is really a hypothetical question...this is not a something that happened to me. Just curious if draw length (arrow length) has any impact on an arrow other then the person with the shorter draw has a shorter power stroke and need more poundage to achieve the same speed as a long draw person.

Still don't 100% understand what you guys are saying about the longer draw arrow storing more energy...sine they weigh the same and are traveling the same speed....then again I got a C in engineering physics!

[John Havard]

If the arrows (of different lengths but the same weight) are traveling the same speed then they have the same KE and momentum, so unless they are drastically different in diameter or something that would change how one penetrates versus another then they should penetrate the same amount.

To think about storing energy just draw two triangles - one that goes to 50# @ 26" and another one that goes to 50# @ 30".  Find the area of each triangle and that's a crude demonstration of how much more energy 50# @ 30" provides versus 50# @ 26" provides.  One-half Base * Height equals area, so 50 @ 30" gives 50*15 = 750 inch-pounds of energy stored.  50# @ 26" yields 50*13 = 650 inch-pounds.  Not exact but illustrative of the concept.

[rybohunter]

2 arrows with the same mass and velocity will have the same energy and momentum. To determine which will actually penetrate better is splitting hairs. Diameter, frictional coefficient and probably stiffness come into play. Now assuming diameter & friction are equal, then I don't feel there would be a measurable difference in penetration, unless the difference in stiffness of the 2 arrows was large.

Now the means at which they recieve that energy has a million variables.

[mcgroundstalker]

Hey Jeff... When I ask myself questions like that I end up ...    ... If ya know what I mean. We all know that a "heavy" arrow is best for hunting. Right? O.K. then.......

Ain't it something how an arrow can be stopped by a hanging piece of carpet or a moving sheet of cardboard. So... We as a group must get back to basics by getting in close and shooting at calm/relaxed game.

Please understand my statement is not directed at you but just a general observation and comment.

Have A Great New Year!

... mike ...    ...

[ks_stickbow]

Originally posted by mcgroundstalker:
Hey Jeff... When I ask myself questions like that I end up ...     ... If ya know what I mean. We all know that a "heavy" arrow is best for hunting. Right? O.K. then.......

Ain't it something how an arrow can be stopped by a hanging piece of carpet or a moving sheet of cardboard. So... We as a group must get back to basics by getting in close and shooting at calm/relaxed game.

Please understand my statement is not directed at you but just a general observation and comment.

Have A Great New Year!

... mike ...     ...

Man..My truck spit a spark plug out last night coming home from rabbit slaying....been home bound all day and will be all weekend...I might have a nasty case of cabin feaver...who knows

[Steertalker]

From the parameters you've laid out the math tells you that they both will have the same KE and Momentum the instant they leave the bow...assuming all else is the same, ie BH, fletching/vanes, etc.  However....I would think the longer arrow would out perform, if only incrementally, the shorter arrow because of its longer moment arm giving it a better mechanical advantage which translates into more stability in flight.  In other words, assuming the arrows are properly tuned for their respective bows, the arrow with the longer moment arm and better mechanical advantage will stabilize quicker and be less affected by external forces such as dynamic drag.  All this translates into more retained down range efficiency, albeit, we're probably splitting hairs.  :D        :D  

Brett

[mcgroundstalker]

Did ya have to say "rabbit slayin'"? I can't wait for the 2008 JLMBH in upstate NY!!! Gotta get out of this city, get together with my trad buddies and do some hunting.

Hope ya get your truck fixed real soon.

... mike ...

[ChuckC]

OK Jeff.  You didn't mention some other points.  Are the arrows similar diameter, are the points the same (blunt vs cut on impact broadhead, are both projectiles gonna impact the target at the same angle, are both strikes going into equal substrate (bone, fat, thick skin vs a lighter skin area) etc etc etc.

With what info you gave. my guess is....yes... or close enough to yes that it doesn't matter
ChuckC

[jacobsladder]

i say the arrow that is tuned better and is flying more true will penetrate the best.