Main Discussion Area > Flight Bows
Light arrows
willie:
--- Quote ---It is really pretty eye opening.
--- End quote ---
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:
--- Quote from: avcase on February 21, 2018, 05:30:24 pm ---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
--- End quote ---
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:
--- 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?
--- End quote ---
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! :o
(His lawyer must have been pretty useless....)
Del
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