Module: FGAtmosphere.cpp
Author: Jon Berndt
+ Implementation of 1959 Standard Atmosphere added by Tony Peden
Date started: 11/24/98
Purpose: Models the atmosphere
Called by: FGSimExec
HISTORY
--------------------------------------------------------------------------------
11/24/98 JSB Created
+07/23/99 TP Added implementation of 1959 Standard Atmosphere
+ Moved calculation of Mach number to FGTranslation
+********************************************************************************
+COMMENTS, REFERENCES, and NOTES
+********************************************************************************
+[1] Anderson, John D. "Introduction to Flight, Third Edition", McGraw-Hill,
+ 1989, ISBN 0-07-001641-0
********************************************************************************
INCLUDES
#include "FGPosition.h"
#include "FGAuxiliary.h"
#include "FGOutput.h"
+#include "FGDefs.h"
+#include "FGMatrix.h"
+
+static const char *IdSrc = "$Header$";
+static const char *IdHdr = ID_ATMOSPHERE;
/*******************************************************************************
************************************ CODE **************************************
*******************************************************************************/
-FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex)
+
+FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex),
+ vWindNED(3),
+ vWindUVW(3)
{
- Name = "FGAtmosphere";
+ Name = "FGAtmosphere";
+ h = 0;
+ Calculate(h);
+ SLtemperature = temperature;
+ SLpressure = pressure;
+ SLdensity = density;
+ SLsoundspeed = sqrt(SHRATIO*Reng*temperature);
+ useExternal=false;
+ vWindUVW(1)=0;vWindUVW(2)=0;vWindUVW(3)=0;
+ vWindNED(1)=0;vWindNED(2)=0;vWindNED(3)=0;
}
bool FGAtmosphere::Run(void)
{
- if (!FGModel::Run()) { // if false then execute this Run()
- rho = 0.002377 - 7.0E-08*State->Geth()
- + 7.0E-13*State->Geth()*State->Geth()
- - 2.0E-18*State->Geth()*State->Geth()*State->Geth();
-
- State->SetMach(State->GetVt()/State->Geta());
- } else { // skip Run() execution this time
- }
- return false;
+ //cout << "In FGAtmosphere::Run(void)" << endl;
+ if (!FGModel::Run()) { // if false then execute this Run()
+ //do temp, pressure, and density first
+ if (!useExternal) {
+ //cout << "Atmosphere: Using internal model, altitude= ";
+ h = Position->Geth();
+
+ Calculate(h);
+ } else {
+ density = exDensity;
+ pressure = exPressure;
+ temperature = exTemperature;
+ //switch sign of wind components so that they are
+ //in aircraft reference frame. The classic example is
+ //takeoff or landing where you always want to fly
+ //into the wind. Suppose that an aircraft is
+ //taking off into the wind on the runway heading
+ //of pure north. Into the wind means the wind is
+ //flowing to the south (or negative) direction,
+ //and we know that headwinds increase the relative
+ //velocity, so to make a positive delta U from the
+ //southerly wind the sign must be switched.
+ vWindNED *= -1;
+ vWindUVW = State->GetTl2b()*vWindNED;
+ }
+ soundspeed = sqrt(SHRATIO*Reng*temperature);
+ //cout << "Atmosphere: soundspeed: " << soundspeed << endl;
+ State->Seta(soundspeed);
+
+
+ } else { // skip Run() execution this time
+ }
+ return false;
}
-float FGAtmosphere::CalcRho(float altitude)
+
+void FGAtmosphere::Calculate(float altitude)
{
- return (0.002377 - 7.0E-08*altitude
- + 7.0E-13*altitude*altitude
- - 2.0E-18*altitude*altitude*altitude);
+ //see reference [1]
+
+ float slope,reftemp,refpress,refdens;
+ int i=0;
+ float htab[]={0,36089,82020,154198,173882,259183,295272,344484}; //ft.
+ // cout << "Atmosphere: h=" << altitude << " rho= " << density << endl;
+ if (altitude <= htab[0]) {
+ altitude=0;
+ } else if (altitude >= htab[7]){
+ i = 7;
+ altitude = htab[7];
+ } else {
+ while (htab[i+1] < altitude) {
+ i++;
+ }
+ }
+
+ switch(i) {
+ case 0: // sea level
+ slope = -0.0035662; // R/ft.
+ reftemp = 518.688; // R
+ refpress = 2116.17; // psf
+ refdens = 0.0023765; // slugs/cubic ft.
+ break;
+ case 1: // 36089 ft.
+ slope = 0;
+ reftemp = 389.988;
+ refpress = 474.1;
+ refdens = 0.0007078;
+ break;
+ case 2: // 82020 ft.
+ slope = 0.00164594;
+ reftemp = 389.988;
+ refpress = 52.7838;
+ refdens = 7.8849E-5;
+ break;
+ case 3: // 154198 ft.
+ slope = 0;
+ reftemp = 508.788;
+ refpress = 2.62274;
+ refdens = 3.01379E-6;
+ break;
+ case 4: // 173882 ft.
+ slope = -0.00246891;
+ reftemp = 508.788;
+ refpress = 1.28428;
+ refdens = 1.47035e-06;
+ break;
+ case 5: // 259183 ft.
+ slope = 0;
+ reftemp = 298.188;
+ refpress = 0.0222008;
+ refdens = 4.33396e-08;
+ break;
+ case 6: // 295272 ft.
+ slope = 0.00219459;
+ reftemp = 298.188;
+ refpress = 0.00215742;
+ refdens = 4.21368e-09;
+ break;
+ case 7: // 344484 ft.
+ slope = 0;
+ reftemp = 406.188;
+ refpress = 0.000153755;
+ refdens = 2.20384e-10;
+ break;
+ }
+
+
+ if (slope == 0) {
+ temperature = reftemp;
+ pressure = refpress*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
+ density = refdens*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
+ } else {
+ temperature = reftemp+slope*(altitude-htab[i]);
+ pressure = refpress*pow(temperature/reftemp,-GRAVITY/(slope*Reng));
+ density = refdens*pow(temperature/reftemp,-(GRAVITY/(slope*Reng)+1));
+ }
+
+ //cout << "Atmosphere: h=" << altitude << " rho= " << density << endl;
}
+
+
+
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