#include "AIManager.hxx"
-const double FGAIBase::rho = 0.023780; // sea level air density slugs/ft3
+const double FGAIBase::e = 2.71828183;
const double FGAIBase::lbs_to_slugs = 0.031080950172; //conversion factor
void FGAIBase::update(double dt) {
ft_per_deg_lat = 366468.96 - 3717.12 * cos(pos.lat()/SG_RADIANS_TO_DEGREES);
ft_per_deg_lon = 365228.16 * cos(pos.lat() / SG_RADIANS_TO_DEGREES);
+
+ // Calculate rho at altitude, using standard atmosphere
+ // For the temperature T and the pressure p,
+
+ if (altitude < 36152) { // curve fits for the troposphere
+ T = 59 - 0.00356 * altitude;
+ p = 2116 * pow( ((T + 459.7) / 518.6) , 5.256);
+
+ } else if ( 36152 < altitude && altitude < 82345 ) { // lower stratosphere
+ T = -70;
+ p = 473.1 * pow( e , 1.73 - (0.000048 * altitude) );
+
+ } else { // upper stratosphere
+ T = -205.05 + (0.00164 * altitude);
+ p = 51.97 * pow( ((T + 459.7) / 389.98) , -11.388);
+ }
+
+ rho = p / (1718 * (T + 459.7));
}