Speed... Curiosity only

[PlanB]

Not saying anything about effectiveness of various weight arrows in hunting. Just what happens as the string accelerates with the arrow, here:

The speed of the limbs can limit the amount of energy transmitted to a light arrow because it accelerates faster than a heavy arrow, and receives less energy in the latter part of the travel in the bow. The faster the limbs, the less this is a factor.

[Stick Bender]

You guys got me going on this, Just ordered a chronny get it in a week , I was just thinking & wondering I would think every bow using wood is kind of unique to that paticular bow & bows like firearms have sweet spots for length & powder charge & such , so I guess my point is one size probably doesent fit all, some bows probably are more efficent with light arrows & some heavy ?

[Del the cat]

Yeah, I think a bit of time making up a set of arrows from say 300 to 800 grain every 100grain should make for some interesting testing.
That's only 6 arrows but it should provide some good data. the hard thing is getting consistent chrony results. I've often toyed with the idea of making a shooting machine. it's not too difficult, but it would be one more thing cluttering up the garage.
Del

[Badger]

  Del, the kind of testing you are talking about where you use arrows from 200 grains to 800 grains is where you become keenly aware of "virtual mass"
Nearly all wood bows have quite a bit of hysterisis which is exaggerated by lighter arrows. I used to do a lot of testing but quit a couple of years ago. I came to the conclusion that if a bow holds the profile and has a decent design I will just take it out and see how far I can shoot it.

[Emmet]

Lite vs heavy can get vague sometimes as far as what heavy is.
 Just my experience shooting, heavy or lite doesn't change much on targets or trees when hit out to 20 yards but 60-80 yards the heavy arrow wont stick enough to support their own weight. The lite ones out penetrate contrary to the ole heavy penetrates better way of thinking. I haven't tried extreme lite to compare. My best long range arrow weight for 50# self bow is 430g-480g with 125g tips with a foc around 13-14. 8-9 grains per pound. If hunting and short distance I may go on the heavy side, Maybe 10 gpp

[BowEd]

Tracker0721.....I like em all really.Something to be said for a softer initial draw bow too as far as accuracy goes,[swweeeeet]and as far as noise goes your heavier arrow will make less noise from your bow with things being equal here tillered properly wise.I know I've overshot deer and they spook closer to me for the next shot,,,,lol.You can be accurate with any weight arrow I think,if shot enough.At least with me it's that way.So many things go into this it's crazy.You got to figure these things out for yourself.Making your own equipment and testing gives you an advantage knowing in your gut what's what and what works no matter what the so called experts say.The common denominaters will be there.Welcome to the craze!!!!!!!!

[BowEd]

One thing too yet if it's field point penetration your talking about is that a 5/16" shaft will penetrate farther then a 23/64" shaft too.

[bigcountry]

I think some are getting energy and momentum mixed up a bit.  Energy out of a "system" should not change much but is dominated by velocity.  Hence why velocity is squared. 
...

What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum
Del

Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup.  And with all things being equal, will out penetrate high lighter setup.  what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity.  That's just physics.

But there is no bow built that will cause an arrow to suffer from those effects.  Hydrostatic shock is outa the realm of possibility even today, April 1st!

I don't believe hydrostatic shock is part of this equation.  I am just talking pure momentum for an object to hit a medium.  I myself have hit deer with a 420 arrow launched at 145fps  that barely went into one lung.  Maybe it hit a rib in a funny fashion, but also have seen an arrow so slow in flight, you think you could catch it, enter a deer and disappear, like going thru butter. 

[bradsmith2010]

if the deer is spinning out of the way,, penetration can be effected,, almost like you had bad arrow flight,,  sometimes we don't pull the bow as far as we think we did in the heat of the moment( especially shooting down),,,,that will have an effect on penetration,,, sometimes our test or experience is biased,,,  there is always someone that thinks the lighter arrow penetrates better, and that is their experience ,,I am sure it did on some particular test,,or could in some cases,, I like the shooting into water analogy ,,you can see very easy that the heavy fish arrow penetrates better,, and thats basically what happens when you shoot an animal,,it is great to explore the efficiency of the Primitive bow,,,  different designs,, and see how far or fast they will shoot,,,,and in explaining what we think ,, we always learn something ,, or adjust our knowledge base as we learn something new,,

[JW_Halverson]

I think some are getting energy and momentum mixed up a bit.  Energy out of a "system" should not change much but is dominated by velocity.  Hence why velocity is squared. 
...

What you say makes sense, but isn't actually quite right.
Look at the graphs I plotted...
Yes energy out doesn't change much, once you have a heavy enough arrow
You'd think the velocity squared would dominate... but below that optimum weight. it doesn't!
Again see the graph... with the lightest bolt I got over 200fps, but the energy (and momentum) was far less than the heaviest arrow.
That's the whole point of doing all those tests and plotting the graph.... to see where common sense and intuition breaks down and and the actual performance of the system takes over.
The optimum is the arrow that is getting close to that maximum energy, whilst having the highest velocity, and thus most momentum, which is what I think you were alluding to.
Taking it to the limit, the arrow with zero mass is fastest, but it has no energy or momentum
Del

Really, its whatever floats your boat, but in the fella's example of his two results momentum is higher with 770gr setup.  And with all things being equal, will out penetrate high lighter setup.  what many are not factoring in the fact is harder you hit a medium, the harder it hits back. The surface tension changes with velocity.  That's just physics.

But there is no bow built that will cause an arrow to suffer from those effects.  Hydrostatic shock is outa the realm of possibility even today, April 1st!

I don't believe hydrostatic shock is part of this equation.  I am just talking pure momentum for an object to hit a medium.  I myself have hit deer with a 420 arrow launched at 145fps  that barely went into one lung.  Maybe it hit a rib in a funny fashion, but also have seen an arrow so slow in flight, you think you could catch it, enter a deer and disappear, like going thru butter.

Soooo many factors come into play on that shot that the list would bring the internet down! My first arrow into a deer was a 650 grain ash arrow moving about 140 fps, razor sharp two blade fixed broadhead....and the arrow was wagging back and forth from a bad release!  It was wagging like a hungry dog watching a hotdog eating contest!!!  I hit just behind the ribs in the paunch and didn't get good penetration.  It taught me to not hunt with a bow until I had more control over the myriad of variables. 

And so we argue back and forth, throwing out anecdotes and and science and opinion and experience.  Hopefully, we all learn something and commit to MORE PRACTICE!  Because no matter what your arrow choice, it is pointless (pun intended, this is me, remember?) if you are not capable of hitting vitals with overwhelming regularity! 

Good hunting, folks!

[Del the cat]

Just for the record.
I've just taken the trouble to go through my data and work out momentum for all the different weights. (It's allright, I don't expect any thanks )
Momentum keeps increasing with arrow weight. (I was expecting there to be a peak somewhere )
But there must come a point where although it has more momentum it is too slow to shoot accurately or indeed reach the target.
In my data, at the highest weight (approx 2000grain), the bolt was only travelling at about 40fps!
So it's up to the individual to find their own 'boat floating' trade off between speed/momentum/energy.
Del

[bradsmith2010]

thanks Del that is interesting,,,with wood arrows,, they will self limit,, you can only get so much weight per arrow,,

[PlanB]

Thanks Del, expected or not!

[Newindian]

This has probably already been said but I breezed through and thought I'd throw it out there. Kinetic energy=(.5)mv^2  momentum=mv. When calculating efficiency use energy, which should increase with arrow eight presumably because it increases the impulse. However momentum is the actual measurement of how much "motion" the arrow has and is directly related to penetration. Kinetic energy doesn't relate directly to penetration, the misconcetption that it dose leads archers to favor higher velocities (v^2) resulting in less than optimal penitration.
 In short make your hunting arrows as heavy as you feel comfortable with.
(Apologies if I'm being redundant)
And I've noticed that y'all seam very interested in finding a happy ground between momentum and Kinetic energy, but unless your arrow is super sonic there is no reason to consider kinetic energy.

[PlanB]

My target doesn't seem to care much about penetration, so I'm interested in some other aspects of dynamics. A couple of them are the curve of the rate of acceleration of the arrow nock, and where in the firing cycle it reaches max velocity.