Forum Jump :

Author Message

## QuickDagger

Posts: 145
Rank:

Level: Member

Country:
Location:
Occupation:
Age:
In-game name: Dagger

#153899 Posted at 2013-11-01 17:47

Hy friends,

Right now I am on a new ballistics project and I was not able to create a precise MS Excel ballistic simulator for Arma 2. And I would like to ask for your help. Sorry if I haven´t posted this on the BI Forums but for the sake of good and simple organization I´ve chosen to put my sniping related projects right and only here.

I have made some interesting discoveries that I want to share with you.

This site (http://resources.bisimulations.com/wiki/Damage_Modeling:_Simulation) brings some formulas...

For example, if you fire a weapon using the following configs...

class CfgAmmo {
class Dagger_223_77gr_Mk262: Dagger_223 {
airFriction = -0.00094;
coefGravity = 0.64;};}

class CfgMagazines {
class Dagger_223_77gr_Mk262_20Rnd_Mag: CA_Magazine {
initSpeed = 624;
ammo = "Dagger_223_77gr_Mk262";};};

class CfgWeapons {
class Dagger_Test_Rifle: M24 {
magazines[] = {"Dagger_223_77gr_Mk262_20Rnd_Mag"};};};

For the initSpeed of 624 the bullet speeds simulated on the game at different ranges will be:
543m/s @ 250m; 484m/s @ 500m; 424m/s @ 750m and 377m/s @ 1000m.

But, making the math using the formulas:
_acceleration = _velocity*(_speed * _airFriction)
_speed = _speed + _acceleration * _deltaT;

Using ACE and elevating the scope for 16.6 Mils (this is my measured zero for 1000m), the horizontal speed will be:
v * cos (16.6/1,0191082/1000)
the 1,0191082 is the factor to convert NATO Mil´s to trigonometry Mils, which is what MS Excel uses.

Calculating for deltaT = 0.04 and applying the airFriction of -0.00094 your calculations will point a speed of:
490m/s @ 250m; 385m/s @ 500m; 304m/s @ 750m and 240m/s @ 1000m. Wrong values!!!

But, if you make the calculations using BI´s default value of -0.0005 for the airFriction, the simulation will bring:
543m/s @ 250m; 484m/s @ 500m; 424m/s @ 750m and 377m/s @ 1000m. Right values!!!

Conclusion
The game engine is ignoring the airFriction in the configs when calculating the horizontal speeds!!!!

Another problem comes when you try to simulate the y position along the bullets trajectory, which is the bullet drop. BI´s damage modeling simulation tells it considers the ammunition ballistics using the formula:
_acceleration.y = _acceleration.y - _coefGravity * 9.80665;

Doing the calculations, the zero will be around 1100m while in the real simulation it will be at 1000m.

So, I come to the community and ask please for your help on fixing the calculation of bullet drops. Is the formula wrong? Is there a hidden factor? Does BI have a default for drop too?

Any kind of help will be welcome and I thank you in advance! And I promise you will not regret

If you want to try my simulator as well as my testing pbo feel free to download them here: