Light arrows

[willie]

There is a new LabRadar chronograph that tracks the speed of projectiles up to 50 yards out. I would love to play with one of those. I think much of the initial loss depends on how clean the arrow is released.

Thanks, Alan. I will see if I can find out more about that product. Have you seen one in action?

Am following your latest calcs with interest, as I hope to test some arrows soon.

[avcase]

Here are some calculations to give some idea of how much the material used to make the arrow can affect its potential for ultimate distance. This is just based on a few samples I had around the shop. There is a big range in properties, especially with the softwoods. A friend of mine has this one Douglas Fir arrow that is far superior to the one I measured here.

So here, I kept the shooting at sea level, and varied the temperature and wind.


                      Distance in yards, 42 deg
                     -------------------------------
             Max                   Launch  Sea     Sea    Sea Lvl Sea Lvl
             Dia           Weight  Speed   Level   Level  +10mph   -10mph
Arrow         in.   mm   grains   (fps)   @40°F  @85°F   HdWind     TlWind
-----------  ---    ---  -----    -----   ------   -----   -----   ------
Ipe-Case     0.296  7.5    522     202     313    325      320       331
Sitka Spruce 0.343  8.7    275     251     315    341      330       352
Douglas Fir  0.341  8.7    363     230     320    341      332       350
W. Larch     0.319  8.1    374     227     328    347      339       356
 

[avcase]

That table was a mess. I’ll try an image to see if it is more readable.

[willie]

Alan,
are these arrows all simulations? I assume that they must fit well with you real life collected data. The .319 Larch
is an actual arrow?

[avcase]

This is simulations. So this doesn’t take into account arrow wiggle from a finger release, or initial misalignment due to improper arrow spine.

This is what I am doing:

I have established a reference barreled flight arrow geometry that dictates the geometric proportions for a pretty decent performing flight arrow.

I developed a good approximation of the drag coefficient for this reference arrow.

I then do a spine test on a straight dowel that I intend to make into a new flight arrow. I also measure  the diameter, mass, length, span, and weight used for the spine deflection test.  Finally, I supply the finished arrow length and spine needed, plus some information about the stored energy and virtual mass of the bow.

The program then calculates the shape of the arrow needed to meet the spine and length requirements (based on the reference arrow proportions). It also calculates the new drag coefficient based on the new arrow geometry.  The diameter and mass of the arrows in my example are dictated by the geometry necessary to meet a required spine value.  These all have the same spine. So very stiff materials will generate a thinner arrow and v
ery dense materials will drive up the mass of the arrow. 

The arrow launch speed is dictated by the calculated arrow mass, stored energy, and virtual mass of the bow. Lighter arrows have a faster launch speed, heaveier arrows have a slower launch speed. The distance calculated  is just ballistics.  I can include the effects of temperature, altitude, and wind.

It is really pretty eye opening. It takes about 15 minutes to spine check, weigh, and measure the length and diameter of a dozen dowels made from different materials. After that, it gives instant feedback on which dowel should be the best to meet the requirements.

Alan

[willie]

It is really pretty eye opening.

wow, quite a few features


I am full of questions, but perhaps one at a time?
As far as the arrow calcs go,  Is there a way to input an arbitrary initial velocity of a particular design, for instance one obtained from a chrono, should one want to examine other flight variables besides drag ?

[Selfbowman]

This is simulations. So this doesn’t take into account arrow wiggle from a finger release, or initial misalignment due to improper arrow spine.

This is what I am doing:

I have established a reference barreled flight arrow geometry that dictates the geometric proportions for a pretty decent performing flight arrow.

I developed a good approximation of the drag coefficient for this reference arrow.

I then do a spine test on a straight dowel that I intend to make into a new flight arrow. I also measure  the diameter, mass, length, span, and weight used for the spine deflection test.  Finally, I supply the finished arrow length and spine needed, plus some information about the stored energy and virtual mass of the bow.

The program then calculates the shape of the arrow needed to meet the spine and length requirements (based on the reference arrow proportions). It also calculates the new drag coefficient based on the new arrow geometry.  The diameter and mass of the arrows in my example are dictated by the geometry necessary to meet a required spine value.  These all have the same spine. So very stiff materials will generate a thinner arrow and v
ery dense materials will drive up the mass of the arrow. 

The arrow launch speed is dictated by the calculated arrow mass, stored energy, and virtual mass of the bow. Lighter arrows have a faster launch speed, heaveier arrows have a slower launch speed. The distance calculated  is just ballistics.  I can include the effects of temperature, altitude, and wind.

It is really pretty eye opening. It takes about 15 minutes to spine check, weigh, and measure the length and diameter of a dozen dowels made from different materials. After that, it gives instant feedback on which dowel should be the best to meet the requirements.

Alan


Golly geez! Alan I guess I will just build arrows and throw the crappie arrows away.
Arvin

[avcase]

wow, quite a few features


I am full of questions, but perhaps one at a time?
As far as the arrow calcs go,  Is there a way to input an arbitrary initial velocity of a particular design, for instance one obtained from a chrono, should one want to examine other flight variables besides drag ?
[/quote]

You mean just create a computer model of an arrow and “shoot” it at a certain velocity just to see how far it will go?

What I am really excited about is that

Alan

Alan

[willie]

You mean just create a computer model of an arrow and “shoot” it at a certain velocity just to see how far it will go?

yes

I am building a shooting fixture to hold a set of takedown limbs. I want to play with different limb profiles, different amounts of reflex and deflex, different limb lengths and draw lengths. A primary goal is to also experiment with different arrows, and see what they can do with a mechanical release. Hopefully, results from the fixture will let me see whats possible, and help me set reasonable goals for my own finger release when shooting offhand?, and give me some ideas about bow designs to pursue. I intend to use a chrono, and if possible, shoot for distance at the same time.

Standardizing some arrow parameters and keeping records of the shots was part of the plan. I was hoping you might be willing  to share some arrow designs when I asked about your programs capabilities. It seems like a very nice way to have a baseline when exploring other variables.

[Del the cat]

You have to be wary of computer models, they are basically some fundamental equations with a load of approximations dumped on to to get a match with reality. So the models are made to match reality... reality doesn't start off matching the models.
An anecdote from an engineering forum:-
During high winds in Australia, two power lines touched, arced over, melted and caused a fire that burnt down the farmers barn.
The power company wouldn't pay out because their computer models showed that the insulating spacers prevented the power lines ever touching even in high winds.
The farmer lost his case!
(His lawyer must have been pretty useless....)
Del

[Badger]

  My doug fir didn't test out too bad. 27" long  215 grains, 36# spine, .270 at front and .240 at nock. FOC 1/2". Should be good for a 50# bow, I will cut it to 26". So it will likely finish after sanding at about 200 grains. I am going to make a set from 200 to 260 graduating 10 grains with each arrow

[avcase]

  My doug fir didn't test out too bad. 27" long  215 grains, 36# spine, .270 at front and .240 at nock. FOC 1/2". Should be good for a 50# bow, I will cut it to 26". So it will likely finish after sanding at about 200 grains. I am going to make a set from 200 to 260 graduating 10 grains with each arrow

Steve,
That may be exceptional Flight arrow material!  Would you be willing to do the following?

1) Measure the deflection of one of the square blanks under a weight placed at its center, like a spine test.

2) Check the height and width of the blank in several spots with some calipers.

3) Measure the mass of the blank in grains

Thanks!

[avcase]

You mean just create a computer model of an arrow and “shoot” it at a certain velocity just to see how far it will go?

yes

I am building a shooting fixture to hold a set of takedown limbs. I want to play with different limb profiles, different amounts of reflex and deflex, different limb lengths and draw lengths. A primary goal is to also experiment with different arrows, and see what they can do with a mechanical release. Hopefully, results from the fixture will let me see whats possible, and help me set reasonable goals for my own finger release when shooting offhand?, and give me some ideas about bow designs to pursue. I intend to use a chrono, and if possible, shoot for distance at the same time.

Standardizing some arrow parameters and keeping records of the shots was part of the plan. I was hoping you might be willing  to share some arrow designs when I asked about your programs capabilities. It seems like a very nice way to have a baseline when exploring other variables.

Sure!  I’m Certainly willing to give it a try to see if this approach helps out with getting the most out of your bows.  I don’t claim it will accurately predict an exact distance, but I feel it is very possible to get an idea of the potential of how one arrow stacks up against another for a given bow.  Potential is the key word. Achieving that potential is an entirely different issue.

Alan

[avcase]

You have to be wary of computer models....

I agree. But the nice thing about a computer model is that it will always give the same answer for a given model.  You start with assumptions and then start chipping away at what needs more work Vs. what doesn’t. It should get better and better over time to the point it captures what is really important and shows similar trends as found with the physical tests.

In contrast, actual real physical testing shows what happened for a particular test at a particular point in time. But nothing stays perfectly consistent from one test to another. Temperature changes, moisture content, wind, properties of the materials are not perfectly consistent, etc. but hopefully physical tests can be controlled well enough that it shows some general trends over time.

Alan

[Badger]

  Allen, could you estimate an arrow distance for me.   Ipe, 240 grains, launch speed 216 fps, max dia .220", length 25", spine about 38#.