1 /*******************************************************************************
3 Module: FGAtmosphere.cpp
5 Implementation of 1959 Standard Atmosphere added by Tony Peden
7 Purpose: Models the atmosphere
10 ------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.org) -------------
12 This program is free software; you can redistribute it and/or modify it under
13 the terms of the GNU General Public License as published by the Free Software
14 Foundation; either version 2 of the License, or (at your option) any later
17 This program is distributed in the hope that it will be useful, but WITHOUT
18 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
19 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
22 You should have received a copy of the GNU General Public License along with
23 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
24 Place - Suite 330, Boston, MA 02111-1307, USA.
26 Further information about the GNU General Public License can also be found on
27 the world wide web at http://www.gnu.org.
29 FUNCTIONAL DESCRIPTION
30 --------------------------------------------------------------------------------
31 Models the atmosphere. The equation used below was determined by a third order
32 curve fit using Excel. The data is from the ICAO atmosphere model.
35 --------------------------------------------------------------------------------
37 07/23/99 TP Added implementation of 1959 Standard Atmosphere
38 Moved calculation of Mach number to FGTranslation
39 ********************************************************************************
40 COMMENTS, REFERENCES, and NOTES
41 ********************************************************************************
42 [1] Anderson, John D. "Introduction to Flight, Third Edition", McGraw-Hill,
43 1989, ISBN 0-07-001641-0
45 ********************************************************************************
47 *******************************************************************************/
49 #include "FGAtmosphere.h"
51 #include "FGFDMExec.h"
53 #include "FGAircraft.h"
54 #include "FGTranslation.h"
55 #include "FGRotation.h"
56 #include "FGPosition.h"
57 #include "FGAuxiliary.h"
61 /*******************************************************************************
62 ************************************ CODE **************************************
63 *******************************************************************************/
66 FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex)
68 Name = "FGAtmosphere";
74 FGAtmosphere::~FGAtmosphere()
79 bool FGAtmosphere::Run(void)
81 if (!FGModel::Run()) { // if false then execute this Run()
84 State->Seta(soundspeed);
85 } else { // skip Run() execution this time
91 float FGAtmosphere::CalcRho(float altitude)
93 return (0.00237 - 7.0E-08*altitude
94 + 7.0E-13*altitude*altitude
95 - 2.0E-18*altitude*altitude*altitude);
99 void FGAtmosphere::Calculate(void)
103 float slope,reftemp,refpress,refdens;
105 float htab[]={0,36089,82020,154198,173882,259183,295272,344484}; //ft.
109 } else if (h >= htab[7]){
113 while (htab[i+1] < h) {
120 slope = -0.0035662; // R/ft.
121 reftemp = 518.688; // R
122 refpress = 2116.17; // psf
123 refdens = 0.0023765; // slugs/cubic ft.
137 case 3: // 154198 ft.
141 refdens = 3.01379E-6;
143 case 4: // 173882 ft.
147 refdens = 1.47035e-06;
149 case 5: // 259183 ft.
152 refpress = 0.0222008;
153 refdens = 4.33396e-08;
155 case 6: // 295272 ft.
158 refpress = 0.00215742;
159 refdens = 4.21368e-09;
161 case 7: // 344484 ft.
164 refpress = 0.000153755;
165 refdens = 2.20384e-10;
171 temperature = reftemp;
172 pressure = refpress*exp(-GRAVITY/(reftemp*Reng)*(h-htab[i]));
173 density = refdens*exp(-GRAVITY/(reftemp*Reng)*(h-htab[i]));
175 temperature = reftemp+slope*(h-htab[i]);
176 pressure = refpress*pow(temperature/reftemp,-GRAVITY/(slope*Reng));
177 density = refdens*pow(temperature/reftemp,-(GRAVITY/(slope*Reng)+1));
180 soundspeed = sqrt(SHRATIO*Reng*temperature);
185 float FGAtmosphere::GetTemperature(float altitude)
195 float FGAtmosphere::GetPressure(float altitude)
205 float FGAtmosphere::GetDensity(float altitude)
216 float FGAtmosphere::GetSoundSpeed(float altitude)