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Vivian Meazza:

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I've finished the variation of Cd with Mach number.
The calculations are only applicable to ballistic
objects, and then strictly one shape: non boat-tailed bullets/shells, so
I've put them in AIBallistic rather than AIBAase. For all inputs, Cd
should be the sub-sonic value, so bullets will need changing.

I've just posted a graphical analysis here:

http://myweb.tiscali.co.uk/vmeazza/FlightGear/cd_mach.pdf
This commit is contained in:
ehofman 2004-10-02 12:02:04 +00:00
parent 3bb349179d
commit 1af8736df6
1 changed files with 14 additions and 3 deletions

15
src/AIModel/AIBallistic.cxx
View file

@ -123,19 +123,30 @@ void FGAIBallistic::setMass(double m) {
void FGAIBallistic::Run(double dt) {
life_timer += dt;
// cout << "life timer 1" << life_timer << dt << endl;
if (life_timer > life) setDie(true);
double speed_north_deg_sec;
double speed_east_deg_sec;
double wind_speed_from_north_deg_sec;
double wind_speed_from_east_deg_sec;
double Cdm; // Cd adjusted by Mach Number
// Adjust Cd by Mach number. The equations are based on curves
// for a conventional shell/bullet (no boat-tail).
if ( Mach < 0.7 ) { Cdm = 0.0125 * Mach + Cd; }
else if ( 0.7 < Mach && Mach < 1.2 ) {
Cdm = 0.3742 * pow ( Mach, 2) - 0.252 * Mach + 0.0021 + Cd; }
else { Cdm = 0.2965 * pow ( Mach, -1.1506 ) + Cd; }
// cout << " Mach , " << Mach << " , Cdm , " << Cdm << endl;
// drag = Cd * 0.5 * rho * speed * speed * drag_area;
// rho is adjusted for altitude in void FGAIBase::update,
// using Standard Atmosphere (sealevel temperature 15C)
// acceleration = drag/mass;
// adjust speed by drag
speed -= (Cd * 0.5 * rho * speed * speed * drag_area/mass) * dt;
speed -= (Cdm * 0.5 * rho * speed * speed * drag_area/mass) * dt;
// don't let speed become negative
if ( speed < 0.0 ) speed = 0.0;
@ -181,8 +192,8 @@ void FGAIBallistic::Run(double dt) {
} // end Run
double FGAIBallistic::_getTime() const {
// cout << "life timer 2" << life_timer << endl;
return life_timer;
}
// end AIBallistic