Arrow Weight and KE.

[rinaldo]

I bought an Archery programme which can give you the KE and speed of an arrow, amonst other things when you put in bows specs etc. I found that on bows in the 60 to 70lb draw weight that once you get close to 10grains (arrow weight) per pound of draw weight you start to loose KE.

Eg I shoot a Diamond Victory for hunting set at 68lbs 29" draw with a 480grain arrow this gives me a KE of 80.52
Same set up with a 580 g arrow gives KE of 83, at 680g gives KE 82.59 and 800g gives you KE of 77.51.

The reason I mention this is because I had a friend tell me that a really heavy is always better than a lighter arrow, he was going to run a 1000g arrow at 75lbs for Buff. This is true but only upto a certain point. Post your bow specs and Ill run the figures for you. :shock:

[Piggy]

Rin I'm shooting a 59# recurve shooting 620gn arrows

Thanks Mate

Paul

[rinaldo]

Piggy you didnt put in your draw length so I put in 28" at 59lbs.

KE=69 FTLB

700 gn at 59lb KE=67 ftlb
520 gn at 59lb KE=69.23 ftlb

[AdamK]

Hey Rin,
Bowtec Old Glory (2005 model), 70# at 30 inches shooting a 475Gr arrow.

[rinaldo]

Adam
475g @ 30 =92.31
575g @ 30 =97.16

If your draw length was 28" for the same arrow specs you would get

475g = 80.26
575g = 83.59

Draw length makes quite an impact on the KE.

[Glenn]

Rinaldo I wouldn't be looking at kinetic energy for arrows. Kinetic energy is good for working out the efficiency of a bow but momentum is a much more accurate equation to use for arrows as it is momentum that will translate to penetration. When you do the sums for momentum the heavier arrow at slower speeds will increase giving extra penetration. This is only one area that penetration can be increased, there are several other ways that will help to increase penetration. Your friends set up on the buffalo will have greater penetration than 10grains per pound of bow, I shoot 16 grains per pound for hunting pigs and find this set up perfect, wish I had of done it years ago...Glenn...

[Piggy]

Thanks Rin

[Wareagle]

Rin, don't you need the arrow speed, as well as the arrow weight??

[Howling Dog]

http://www.prairieshack.com/index.html
Try this site for a KE calculator, this site was posted previously ( I forget who by for the 3D ).
Ken :D

[AdamK]

Glenn,

I'm no fissasist, but KE = Arrow mass x Velocity and Momentum = Arrow mass x velocity. In terms of penetration potential for an arrow / bow combination either would be a good indicator.
There does come a point where an increase in arrow weight will have slowed the arrows' velocity down enough that will see a lighter arrow travelling faster (out of the same bow) produce a higher KE or momentum than the heavier arrow.....(I think)

Anyone confirm this .....

Thanks for the calculations Rin. Should be sufficient for Rusa?

[aussiehunter]

adamk beg to differ..

glenn is right in what he is saying.he is a bloke who speaks from knowledge and experience

educate urself by reading dr ashby reports on momentum

been posted numerous times,plus he writes a section or two in archery action most issues

kinetic energy is an energy and momentum is a force which translates to penertration.

momentum is one of the major factors along with broadhead design,shaft thickness,f o c,weight..etc. to do with penertration

and the difference with dr ashby is he does actually testing on our australian asiatic water buffalo, not from a heap of calculations and testings on blocks of wood and foam

http://www.datakey.com.au/steve1/Momentum.pdf

and a complete list of reports from trad gang

http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=24

its a bit of reading,but u will learn a lot if u take the time.

jmho

pat

[Sparra]

:lol: :lol: :lol: And so it begins.....

[aussiehunter]

sparra care to elaborate?

pat :?

[Sparra]

Gaday Pat...This subject has been flogged to death on here a heap of times..Always seems to end up with everyone agreeing to disagree and it's put to bed until someone wakes it up again....

[aussiehunter]

mate i dont see any problem. :?

we dont have those issues on here anymore. :)

passing onto someone the right material to read and educate themselves.

up to them then to make up their own mind, at least they have the right facts.

end of story :)


pat

[Sparra]

lighten up Pat...No one has mentioned a problem...Ya gotta learn to relax....

[Glenn]

You're right AdamK, there is a point where an arrow becomes so heavy that it will become usless. As Pat said broadhead design, shaft thickness and FOC added with momentum will give maxium penetration of a bow-arrow combination...Glenn...

[aussiehunter]

sparra ,mate may i make a friendly suggestion, instead of making a comment like here we go again,which is naturally going to get a reaction,say what ya mean straight up,so there is no misunderstanding.

mate i dont know where it shows im upset, i have replied in a totally polite manner.. :? this smiley means confused..

ok mate?

thankyou

pat :)

[Sparra]

Thanks for the tip Mate...

sparra ,mate may i make a friendly suggestion, instead of making a comment like here we go again,which is naturally going to get a reaction,say what ya mean straight up,so there is no misunderstanding.


I think you have me confused with someone else because I said

And so it begins.....

which is exactly what I meant... :wink: :wink:

cya....

[AdamK]

Pat,
I agree with Sparra. I think I've said it before too.

As I said, I'm no physisist, and I asked for some confirmations...
All (most) rifle balistic information provides quantifications of energy rather than momentum for different projectiles at diffent ranges etc. I was wrong in my stated equation for KE calculations (KE= (0.5mass) velocity2) , but thats what happens when I open my mouth before checking the facts. I'm always happy to be corrected.

Seems as though their may be a couple of schools of thought on the issue. Nick Harvey has published heaps on the best indicator of penetration etc I'll pull out his book and re-read (it has been a while). I'm always happy to read others opinions and to learn from those that know better.

There is something to be said for tone in emails though mate.

Thanks for the links, I will check it out.

[aussiehunter]

sparra forgive me for not quoting ur exact words,,,

adam k.u do whats best for u,

id expeced that those reports would be too long and too much trouble.

go with nick harvey, that makes total sense,thats to do with rifles that kills by massive shock and damage to vitals whilst broadheads kill by massive bleeding.

as for tones mate, try to give u genuine advice

good luck with ur bowhunting

pat

[Willy_R]

What I don't see is the Agree to disagree issue ?

Physics with out set values don't work, i.e. Mass x velocity and what it takes in energy or KE to stop that mass from moving is the final word.

No ifs no buts or maybes ?

Wareagle is right the Speed of the Arrow and the weight of the arrow is the only thing relevant to the KE equation you need at the end of the day.
Weather we are talking Trad or Compound modern bows.

The Speed at which you drive the weight out of your bow is what determines the speed at which it strikes the target in turn the energy dissipated at this exact moment is the measure of KE the greater the weight and speed the greater the KE the greater the penetration.

To these facts there is no argument.

Sure Surface friction and cut on contact broadheads help with penetration to a degree, it just means that the energy is released over a much smaller area for a longer period.
Allowing greater penetration of the matter that the arrow is infact trying to pass through.

This aint perfect so round it off to the nearest 5 if ya like ?

Weight of an arrow; W=mg
where m=mass, g=gravitational constant 32.22 ft/s^2

Mass of an arrow ; m=W/g
but W is measure in grains, convert grains to lbs 1 lb = 7000 grn

m = W(grn)(1lb/7000grn)/32.22 ft/s^2

The basic relationship being used in all calculations is;

Kinetic Energy(KE) = 1/2 * m * v^2 (or one-half times mass(of arrow) times velocity squared)

Normally people just say KE = arrow weight divided by 451,000 something or other times velocity squared, here's where it comes from;

KE = 1/2 X (arrow weight in grains) X (1 lb/7000grn) X v^2 X (1/32.22)

2 X 7000 X 32.22 = 451,080 grn-ft/s^2 and that's where that number comes from.

This formula can be rearranged to solve for arrow speed, if energy input to the arra from the bow is known by the following.

v = sqrt( 2 * KE / m) ( or the square root of 2 times the Kinetic energy divided by mass(of arrow)

[Wareagle]

Onya Willy :D

[AdamK]

Jesus Willy. Thanks I think....

[Friar Tuck]

I suppose if you want to get the perfect equation you would calculate your average hunting shot distance and maximise your bow and arrow set up to generate maximum KE obtainable at that point in time.

[Willy_R]

I suppose if you want to get the perfect equation you would calculate your average hunting shot distance and maximise your bow and arrow set up to generate maximum KE obtainable at that point in time.

Cant we just use fairy dust ? :roll: Works for me ! doesn't it my magical little pixie friends ~~~~~~~~~~~~~ :mrgreen:

I'm off to see the wizard the magical wizard of oz..........tra.....Lah ..lah lar........ 8)

[NormGunston]

Fellas, just got this data back from NormLabs (Inc.)
Well, I'm definitely no fizzicyst either, but I do know that:
i) 3555 G.T.s with 125 g points fly really fast and do not knock over an unsupported Morrell SS bag target.
ii) 3555 G.T.s with 145 g points fly really fast and do not knock over an unsupported Morrell SS bag target.
iii) 3555 G.T.s with 145 g points plus a length of 3 grains per inch Carbon Express weight tubing up the date fly not so fast and wobble an unsupported Morrell SS bag target.
iv) 3555 G.T.s with 175 g points plus a length of 3 grains per inch Carbon Express weight tubing up the date do approx. same speed as a FB Holden and knock a Morrell SS bag target on it's ar$e when the target is hit anywhere above center.
Bow used: 55# recurve. Arrow length: 29", 3 X 5" spiral feathers.
Hope this research helps. If not, print it out and feed it to a goat. :wink:
Ant

[rinaldo]

Guys the program I use has all the bows that have been produced in the last five years or so. It has all the data of the relevant bow so you put in the other variables and it gives you an estinated arrow speed which goes towards the KE. I didnt mean to start a debate on penetration etc, I just found it an interesting bit of information that I thought I would make available. :oops:

[HOOD]

LMAO @ Normy G :lol:

[Willy_R]

But Norm how much fairy dust did you need to get those figures I like about .2grains per inch of fairy dust to get the penetration into the morrells bag ?

At least I believe you ! Cos ya didn't quote 100+ GT safaris with 85 grain expandable heads ,outa a 80# long bow .

Well done goat will starve tonight !

[Glenn]

Good one Norm, that's all the proof I need...Glenn...

[NormGunston]

Hate to flog the dead horse- just weighed an arrow- 29" G.T. 3555, standard insert, 175g field point, 28" Carbon Express 3 grains per inch weight tube, 3 X 5" feathers: Only 510 grains!! My arrows snuk off to Gloria Bloody Marshall!!
Ant

[interceptor]

A couple of mates up here are shooting the 100+ big game shafts out of their Hoyts (70# and 80#) When they have weight tubes in them they fly like crap and wont paper tune worth a damn. They are taking the weight tube out as we managed to get them flying pretty good. Strangely enough one of the lads said that they could not get more than half an arrow length of penetration on good pigs when they used the weighted arrow? This may be caused by the bad arrow flight?

Cheers Noel

[FentonW]

Can someone out there give us the K.E figure for a .22 rifle? When you compare that to the K.E of an heavy arrow shot out of either longbow, recurve or compound the .22 should blow through any animal on the planet compared to the humble old bow. Then do the math on momentum and compare the two and you will get a true sense of potential for penitration. I have watched these debates alot over the years and mostly there is two schools of thought, hopfully there will always be two (Or more) schools of thought as well. How else are we going to listen and possibly learn. I am a big believer in momentum for bowhunting. I have been hunting Cape York boars for far to many years and have seen them eat up light arrows time and time again not to believe in it. Just my thoughts.
Cheers, Fenton.

[Glenn]

Yes Noel I would say that bad arrow flight is one of the reasons for their bad penetration. The reason I like to use wood arrows is that I can determine where I want the weight to be. It's one thing to add weight but it has to be in the right place...Glenn...

[Friar Tuck]

The physics of KE does not always represent the reality of field testing. If for example you test a small diametre arrow and specific broadhead in a target, say a foam 3D target it will get better penetration than a large shaft - friction.

This is far less when hitting an animal where the internal part of the animal is lubricated with blood etc.

My personal opinion is that arrow flight is far more important as the faster an arrow becomes stable the less KE and Momentum it loses. The intitial KE of an arrow may be faster in Bow A than in Bow B but in the first 10 feet of flight should bow A be underspined or overspined it is possible that the arrow from bow B maintains a higher KE due to the arrow from bow A fishtailing and losing KE. Given that alot of hunters here are shooting from 5 - 40 feet the faster stabilisation of an arrow seems to be of greatest benefit.

[aussiehunter]

take the time to read dr ashbys reports on momentum, f oc and 99% of ur questions will be answered.

ive posted the link before,we have more info in previous posts and archery action has had numerous articals of him in there for months.

but nothing replaces good shot placement with a razorsharp broadhead tipped shafts ,shot into the vitals of ur game out of a well tuned bow,,

i had my partner shooting out of her 40lb mathews mustang,26.5 inch draw using goldtips 600 pros tipped with razor sharp 115g blackstumps plus inserts,total head weights 145approx..they would punch completly through the large boars here,had one of her shots that enetered behind back ribs on left side and exited out right front shoulder.


jmho

pat :)



pat :)

[Friar Tuck]

It is worth reading the articles Pat posted. 8)

[aussiehunter]

nah...its a totally waste of ur time :wink:


pat :)

[Tj]

OK had to through my two bob’s worth in. KE (1/2 mass x velocity squared) is what is used for calculating the energy contained in a projectile due to its velocity. This is very useful for things like bullets and such like that work by transferring this energy to the target. One example of this is hydrostatic shock where the energy from a high velocity bullet forms a shock wave that dissipates outwards from the wound site bursting cells along the way.

And here lies a difference between how high powered rifles and bows kill. Bows rely on slicing a neat channel through an animal, to cause hemorrhage. This strait channel allows blood to drain away quickly causing a swift death (one of the disadvantages of a bullet that relies hydrostatic shock alone is that the damaged tissue can block the wound and slow or even stop the blood loss). To do this you need the arrow to penetrate as far as possible, ideally achieving a pass-through which will provide another path for the blood to exit the body. So when it comes to calculations it may be better to be interested in an arrows ability to continue to pass through an animal rather than the amount of energy it can transfer. Momentum describes a body’s tendency to continue in its direction of travel, exactly what you want to know.

But at the end of the day this is all theory and if you achieve a pass-through a deer/goat/pig is not going to notice which set of formula you used.

[jpbon]

what is the site that calculates arrow speed?

cheers

jpbon