Arrow Mass/Spine Ratio

cestria

Member
Fonz Awardee
A bit of a long question but please bear with me.
I’m specifically thinking of flight arrows here but the general principle relates to all arrows particularly wooden arrows.
I’ve come across an old film of a guy in the states called Bill Sweetland on YouTube giving a talk to a group of archers about compressed cedar arrows (https://www.youtube.com/watch?v=I8oUCNE4ulQ), very interesting to listen to. In the film, he makes mention of the weight/spine ratio being extremely important to achieve good arrow flight, and that Paul Klospeg wrote about it in the 1920’s in “his book”. I’ve got a copy of Klospeg’s book "Composite Bow" and have found the reference that Sweetland seems to refer to but there is very little information other than a general statement suggesting for any one bow there is an ideal weight of arrow.
I’ve also seen on YouTube (https://www.youtube.com/watch?v=J__NRSNv45g) a good explanation of arrow ballistics where it is explained that for every bow there should be an ideal mass weight of arrow to achieve maximum distance.
So to my question, other than being able to find a range long enough to try flight arrows (extremely difficult where I live), has there been any work done to find an ideal mass weight of arrow for a particular bow draw weight?
I’m aware of general guidance from bowyers about grains/pound of draw weight but know that is more to do with bow longevity rather than getting the most from the bow.
Any help or pointing in the right direction would be greatly appreciated, thanks.
 

geoffretired

Supporter
Supporter
Sounds interesting. I'm wondering if ideal weight for a given bow, would also vary with draw length, not just draw weight.Would the ideal arrow weight be the same for a 28" draw reaching 30lb at that draw and a 30" draw reaching 30lb at its longer drawlength?
 

jbridges

New member
I spent some time studying arrow ballistics and even built a wind tunnel in my guarage. In brief arrow mass affects several things simultaneously. These are:
1) the efficiency of a bow to transfer elastic potential energy to kinetic energy goes up for heavier arrows and down for lighter arrows.
2) for a given amount of kinetic energy, the velocity of the arrow goes down the heavier the arrow and up for a lighter arrow.
3) once the arrow is in the air, drag slows it down. A lighter arrow slows down faster than a heavy one.

If you have a look at the following webpage you will find some interactive models of a bow and arrow. Look at the the 'How to ...' menus you will find out how to set the sliders for all the different parameters. I have not exhaustivly tested thd models but they tie up with my English longbow. I can predict my point of aim to within 1 yard.

I hope you find the reference interesting. Any constructive feedback most welcome.

URL is www.efaafieldarcher.com/resources/
 
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Deleted member 7654

Guest
Draw weight is a crude and near useless measure.
As an example I have a 70# self Osage bow with 24" draw that will outshoot a 120# warbow with 32" draw.
The guidelines and rules of thumb are pretty much useless when it comes to flight shooting.
E.G I've made flight arrows of 50# spine shot very effectively from 120# Warbows. They would of course explode if they had heavy points which would provide too much inertia to their acceleration and would cause them to bend too much.
It is so complicated that the serious flight archer would probably build a shooting machine for testing.
This post from my blog shows the trade off between velocity, and energy.
Bowyer's Diary: Mass Velocity and Energy
For the arrow you want minimum diameter for minimum drag, but you need sufficient stiffness and mass too.
So many variables, and it can be all ruined by a sluggish loose.
I have the problem of trying to find a shooting ground too... just lost one due to grumpy farmer syndrome...
Del
 

cestria

Member
Fonz Awardee
The more I learn about Flight the more I realise how complicated it is and how there is so much more to understand. I've heard said that arrow flight is so complicated that even the best brains and computers NASA have can't calculate the process without assuming some of the variables. Nevertheless Del the Virtual Arrow Flight Simulator is an impressive resource for those wishing to experiment with some of the variables to see if theory aligns with reality, thanks Jamie for the link
 
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Deleted member 7654

Guest
Yes, the arrow flight simulator is V good, but of course in reality you can't change one factor without effecting others.
E.G increasing arrow mass shows increasing range... great we've found the holy grail.... but unfortunately, increasing arrow mass will also reduce the initial velocity.
Bottom line is we need to do the testing to get the figures to plug into the simulator.
But yes it's good and yes I've book marked it! :)
Del
 

jbridges

New member
I'm glad you both like it. Feel free to share with others and if you have some ideas for other archery related calculators or some improvements to what is there, let me know.
 

gtek

Member
I've heard said that arrow flight is so complicated that even the best brains and computers NASA have can't calculate the process without assuming some of the variables.
This hasn't been true since the mid 90's. I have flight simulator programs which my company created that are perfectly consistent with real world measurements, and which can cope with minor release differences from shooter to shooter. There is at least one commercial program that also does an outstanding job on this.
 
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Deleted member 7654

Guest
This hasn't been true since the mid 90's. I have flight simulator programs which my company created that are perfectly consistent with real world measurements, and which can cope with minor release differences from shooter to shooter. There is at least one commercial program that also does an outstanding job on this.
These will cope with a wooden flight bow and wooden arrows?
Links?
Del
 

little-else

Supporter
Supporter
AIUK Saviour
I'm with Del on this one, draw length versus draw weight is far too crude, if you look at the archers around at Agincourt they were all short arses (reference to one of the knights there being exceptionally tall at 5'8")and so their bows would be shorter and thus having greater impulse energy on release for the same draw weight as a typical modern longbow. Their arrows would be shorter too, giving less drag for the same cross sectional area of the arrow when compared to a taller person with a longer draw length. this would also allow for a thinner shaft for a particular pile weight and that again reduces the drag. As wooden arrows are not isometric how you fletch them compared to the grain will also have an impact so you will get arrow to arrow variations that will make a computer model very limiting.
Standard mass v velcity charts are useful for bullets and long range rifle shooters go for down range velocity so use a heavy bullet with a low drag that is still supersonic at say 1200 yds and dont worry about the trajectory or to a certain extent the accuracy of the round at short ranges. Most ballistic data is collected for game shooters who want the maximum transfer of energy at shorter ranges (say 50-200yds) so go for higher velocity round to make use of the V2 part of the bullet energy. So, for flight archery you basically have to start with the tables and then go from there rather than try and keep to the data given. Accuracy isnt that important but a set of arrows should have some consistency to them. The balance of the arrow is also very important as you are launching it at an angle where the shear forces of the wind/air will affect it so much more than at your usual 9 dgeree arc for twanging at 100yds. Not having looked into the models perhaps someone could say whether this is taken into account. That is why many people use tapered or barrelled shafts and small piles. A standard 3 point bend test for spining isnt really good enough for these unless you make your test rig to suit.
Empirical results are probably the only ones that will tell you so suck it and see
 

jbridges

New member
Not having looked into the models perhaps someone could say whether this is taken into account.
Hi Little-else. I can't speak for other models of arrow flight, only my own. It is pretty simple and is intended purely to help understand the basics rather than predict anything with precise accuracy. Having created models of other dynamic systems in my day job, I have come to the conclusion that there is no point creating a model for the purposes of prediction unless you are unable to validate/prove the assumptions in the model are correct. I'm an amature archer whose ability to measure, get data and whos needs for prediction is very limited. ktec's company may have invested considerable money and time in their models because they have a need. They perhaps have that need because it saves development time or provides a competative advantage. If so it is highly unlikely that such accurate models would be made available to the public and their competitors. Further more I doubt I personally would be able to paramertize such a model.
So I suspect you are limited as to what is available. Feel free to try mine. There are short blogs trying to explain how to paramerterize it. If you find it does not stack up with your own measurements please let me know and do tell me if there are other factors you would like to be able to play with and I will give some thought as to whether I could realistically add it. If you think people would care, I could easily try and explain the maths behind my model so archer's could better understand it's limitations. When I talk to archers about this stuff it is not normally too long before their eyes get that distant look.
 

Rik

Supporter
Supporter
... gtek's company may have invested considerable money and time in their models because they have a need...
I guess you could say that... So far as I know GT still works for Hoyt and was involved in the design of the X10 shafts... :)

Incidentally, I still have a copy of the old Easton Arrow Flight Simulator program. Obviously out of date now...
 

cestria

Member
Fonz Awardee
Like Del I wonder how commercial arrow flight simulators cope with the variances you get with wooden shafts. I can see how GTek's model works with carbon, aluminium and composite material because of the uniform nature of the shafts but my woodies are all different. I didn't mention in my opening post that the flight classes my wife and I contest most are English longbow and American flatbow which require the use of wooden shafts.
My thoughts are slightly different to my wife's in how we make up our arrows, she prefers to go more down the standard bullet point and plastic over nock (though highly modified), where i'm playing around with various insert points and pin nocks to enable drastic barrelling of the shaft. Obvious we both think we are both right so testing is the answer but we're limited to where we can test fly. One reason to look for as much information as i possibly can on arrow characteristics is to help us determine if the paths we are on stand any chance of being the right path as there are so few flight tournaments to try for real.
 

jbridges

New member
Like Del I wonder how commercial arrow flight simulators cope with the variances you get with wooden shafts. I can see how GTek's model works with carbon, aluminium and composite material because of the uniform nature of the shafts but my woodies ....
cestria, I think you are expectig too much from an arrow flight simulator. They allow you to study the effects of one variable at a time, perhaps on arrow range if you are interested in flight shooting. But fundamentally there will always be assumptions baked into the maths. For example, my simple model allows you to vary initial velocity, arrow mass, arrow drag and angle of elevation. I assume that centre of gravity has no effect and also assume the ground is flat, air density is constant etc. My suspicion is that there are factors that have a greater effect in the distance an arrow will travel than material variability and I suspect it is these factors you should look to identify as they are design parameters you can try and change to get the greatest distance. I would love an ordered list of arrow parameters that affect flight distance if you have one. Might modify my model to try and include.
 
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