Vivian Meazza:

I have added <Cd> and <weight> to the input parameters in the submodels.xml
script. Raw data may be used, thus avoiding the need to guestimate <eda>.
Eda remains, but should now be used to enter the proper cross-sectional
area.

src/AIModel/AIBallistic.cxx

@@ -27,6 +27,7 @@
 #include "AIBallistic.hxx"
 
 
+
 FGAIBallistic::FGAIBallistic(FGAIManager* mgr) {
     manager = mgr;
     _type_str = "ballistic";
@@ -111,8 +112,16 @@ void FGAIBallistic::setWind_from_north(double fps) {
 void FGAIBallistic::setWind(bool val) {
    wind = val;
 }
-void FGAIBallistic::Run(double dt) {
 
+void FGAIBallistic::setCd(double c) {
+   Cd = c;
+}
+
+void FGAIBallistic::setWeight(double w) {
+   weight = w;
+}
+
+void FGAIBallistic::Run(double dt) {
    life_timer += dt;
    if (life_timer > life) setDie(true); 
 
@@ -120,12 +129,22 @@ void FGAIBallistic::Run(double dt) {
    double speed_east_deg_sec;
    double wind_speed_from_north_deg_sec;
    double wind_speed_from_east_deg_sec;
+   double mass;
       
-   // the two drag calculations below assume sea-level density, 
-   // mass of 0.03 slugs,  drag coeff of 0.295
-   // adjust speed due to drag 
-   speed -= 0.0116918 * drag_area * speed * speed * dt;
+   // the drag calculations below assume sea-level density,
+   // rho = 0.023780  slugs/ft3
+   // calculate mass
+   mass = weight * lbs_to_slugs;
+   
+   // drag = Cd * 0.5 * rho * speed * speed * drag_area;
+   // acceleration = drag/mass;
+   // adjust speed by drag
+   speed -= (Cd * 0.5 * rho * speed * speed * drag_area/mass) * dt; 
+
+   // don't let speed become negative
    if ( speed < 0.0 ) speed = 0.0;
+   
+   // calculate vertical and horizontal speed components
    vs = sin( pitch * SG_DEGREES_TO_RADIANS ) * speed;
    hs = cos( pitch * SG_DEGREES_TO_RADIANS ) * speed;
 
@@ -133,28 +152,21 @@ void FGAIBallistic::Run(double dt) {
    speed_north_deg_sec = cos(hdg / SG_RADIANS_TO_DEGREES) * hs / ft_per_deg_lat;
    speed_east_deg_sec  = sin(hdg / SG_RADIANS_TO_DEGREES) * hs / ft_per_deg_lon;
    
-   // convert wind speed (fps) to degrees per second
-   
+   // if wind not required, set to zero
    if (!wind){
       wind_from_north = 0;
       wind_from_east = 0;
    }
   
+   // convert wind speed (fps) to degrees per second
    wind_speed_from_north_deg_sec = wind_from_north / ft_per_deg_lat;
    wind_speed_from_east_deg_sec  = wind_from_east / ft_per_deg_lon;
    
- 
    // set new position
-//   pos.setlat( pos.lat() + (speed_north_deg_sec * dt)  );
-//   pos.setlon( pos.lon() + (speed_east_deg_sec * dt)  ); 
- 
- 
-   // set new position
-   
    pos.setlat( pos.lat() + (speed_north_deg_sec - wind_speed_from_north_deg_sec) * dt );
    pos.setlon( pos.lon() + (speed_east_deg_sec - wind_speed_from_east_deg_sec) * dt ); 
 
-   // adjust vertical speed for acceleration of gravity
+   // adjust vertical speed for acceleration of gravity and buoyancy
    vs -= (gravity - buoyancy) * dt;
    
    // adjust altitude (feet)
@@ -170,7 +182,7 @@ void FGAIBallistic::Run(double dt) {
    // set destruction flag if altitude less than sea level -1000
    if (altitude < -1000.0) setDie(true);
 
-}
+}  // end Run
 
 double FGAIBallistic::_getTime() const {
    return life_timer;

src/AIModel/AIBallistic.hxx

@@ -46,6 +46,8 @@ public:
     void setWind_from_east( double fps );
     void setWind_from_north( double fps );
     void setWind( bool val );
+    void setCd( double c );
+    void setWeight( double w );
 
     double _getTime() const;
 
@@ -63,6 +65,8 @@ private:
     double wind_from_east;  // fps
     double wind_from_north; // fps
     bool wind;              // if true, local wind will be applied to object
+    double Cd;              // drag coefficient
+    double weight;          // lbs
 
     void Run(double dt);
 };

src/AIModel/AIBase.cxx

@@ -43,6 +43,11 @@
 #include "AIBase.hxx"
 #include "AIManager.hxx"
 
+
+const double FGAIBase::rho = 0.023780;  // sea level air density slugs/ft3
+const double FGAIBase::lbs_to_slugs = 0.031080950172;   //conversion factor
+
+
 FGAIBase::FGAIBase()
  :  fp( NULL ),
     model( NULL ),

src/AIModel/AIBase.hxx

@@ -1,4 +1,4 @@
-// FGAIBase - abstract base class for AI objects
+// FGAIBase.hxx - abstract base class for AI objects
 // Written by David Culp, started Nov 2003, based on
 // David Luff's FGAIEntity class.
 // - davidculp2@comcast.net
@@ -62,7 +62,9 @@ typedef struct {
    double buoyancy;           // acceleration in ft per sec2
    double wind_from_east;     // in feet per second
    double wind_from_north;    // in feet per second
-   bool wind;
+   double cd;                 // coefficient of drag
+   bool wind;                 // if true, model reacts to parent wind
+   double weight;             // in lbs
 } FGAIModelEntity;
 
 
@@ -177,6 +179,9 @@ public:
     double _getY_shift() const;
     double _getRotation() const;
 
+    static const double rho;
+    static const double lbs_to_slugs;
+
     int _getID() const;
 
     inline double _getRange() { return range; };

src/AIModel/AIManager.cxx

@@ -203,6 +203,8 @@ FGAIManager::createBallistic( FGAIModelEntity *entity ) {
         ai_ballistic->setWind_from_north(entity->wind_from_north);
         ai_ballistic->setWind(entity->wind);
         ai_ballistic->setRoll(entity->roll);
+		ai_ballistic->setCd(entity->cd);
+		ai_ballistic->setWeight(entity->weight);
         ai_ballistic->init();
         ai_ballistic->bind();
         return ai_ballistic;
@@ -316,3 +318,4 @@ void FGAIManager::processScenario( string filename ) {
   delete s;
 }
 
+//end AIManager.cxx

src/AIModel/AIScenario.cxx

@@ -1,4 +1,4 @@
-// FGAIScenario - class for loading an AI scenario
+// FGAIScenario.cxx - class for loading an AI scenario
 // Written by David Culp, started May 2004
 // - davidculp2@comcast.net
 //
@@ -78,6 +78,8 @@ FGAIScenario::FGAIScenario(string filename)
      en->wind_from_east = entry_node->getDoubleValue("wind_from_east", 0);
      en->wind_from_north = entry_node->getDoubleValue("wind_from_north", 0);
      en->wind            = entry_node->getBoolValue("wind", false);
+	 en->cd              = entry_node->getDoubleValue  ("cd", 0.029); 
+	 en->weight          = entry_node->getDoubleValue  ("weight", 0.030); 
      en->fp             = NULL;
    }
 
@@ -108,4 +110,4 @@ int FGAIScenario::nEntries( void )
   return entries.size();
 }
 
-
+// end scenario.cxx

src/Systems/submodel.cxx

@@ -13,6 +13,8 @@
 #include <AIModel/AIManager.hxx>
 
 
+const double SubmodelSystem::lbs_to_slugs = 0.031080950172;
+
 SubmodelSystem::SubmodelSystem ()
 {
     
@@ -124,6 +126,8 @@ SubmodelSystem::release (submodel* sm, double dt)
   entity.wind_from_east = IC.wind_from_east;
   entity.wind_from_north = IC.wind_from_north;
   entity.wind = sm->wind;
+  entity.cd = sm->cd;
+  entity.weight = sm->weight;
   ai->createBallistic( &entity );
  
   if (sm->count > 0) (sm->count)--; 
@@ -161,7 +165,7 @@ SubmodelSystem::load ()
      sm->trigger        = fgGetNode(entry_node->getStringValue("trigger", "none"), true);
      sm->name           = entry_node->getStringValue("name", "none_defined");
      sm->model          = entry_node->getStringValue("model", "Models/Geometry/rocket.ac");
-     sm->speed          = entry_node->getDoubleValue("speed", 0.0);
+     sm->speed          = entry_node->getDoubleValue("speed", 2329.4 );
      sm->repeat         = entry_node->getBoolValue  ("repeat", false); 
      sm->delay          = entry_node->getDoubleValue("delay", 0.25); 
      sm->count          = entry_node->getIntValue   ("count", 1); 
@@ -171,11 +175,13 @@ SubmodelSystem::load ()
      sm->z_offset       = entry_node->getDoubleValue("z-offset", 0.0); 
      sm->yaw_offset     = entry_node->getDoubleValue("yaw-offset", 0.0); 
      sm->pitch_offset   = entry_node->getDoubleValue("pitch-offset", 0.0);
-     sm->drag_area      = entry_node->getDoubleValue("eda", 0.007);
+     sm->drag_area      = entry_node->getDoubleValue("eda", 0.034);
      sm->life           = entry_node->getDoubleValue("life", 900.0);
      sm->buoyancy       = entry_node->getDoubleValue("buoyancy", 0);
      sm->wind           = entry_node->getBoolValue  ("wind", false); 
      sm->first_time     = false;
+     sm->cd             = entry_node->getDoubleValue("cd", 0.295);
+     sm->weight         = entry_node->getDoubleValue("weight", 0.25);
 
      sm->trigger->setBoolValue(false);
      sm->timer = sm->delay;
@@ -217,6 +223,8 @@ SubmodelSystem::transform( submodel* sm)
   in[1] = sm->y_offset;
   in[2] = sm->z_offset; 
   
+  IC.mass = sm->weight * lbs_to_slugs;
+   
 // pre-process the trig functions
 
     cosRx = cos(-IC.roll * SG_DEGREES_TO_RADIANS);

src/Systems/submodel.hxx

@@ -29,6 +29,7 @@ public:
  typedef struct {
   SGPropertyNode* trigger;
   SGPropertyNode* prop;
+  
   string             name;
   string             model;
   double             speed;
@@ -47,6 +48,9 @@ public:
   double             buoyancy;
   bool               wind;
   bool               first_time;
+  double             cd;
+  double             weight;
+//  double             mass;
  } submodel; 
 
  typedef struct {
@@ -65,6 +69,7 @@ public:
   double     total_speed_down;
   double     total_speed_east;
   double     total_speed_north;
+  double     mass;
  } IC_struct;  
 
     SubmodelSystem ();
@@ -105,6 +110,8 @@ private:
     double x_offset, y_offset, z_offset;
     double pitch_offset, yaw_offset;
 
+    static const double lbs_to_slugs; //conversion factor
+
     SGPropertyNode* _serviceable_node;
     SGPropertyNode* _user_lat_node;
     SGPropertyNode* _user_lon_node;
@@ -128,3 +135,4 @@ private:
 
 #endif // __SYSTEMS_SUBMODEL_HXX
 
+