X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FFDM%2FYASim%2FAtmosphere.cpp;h=92d2fbe56a6e3495762d2c2ffff5c96c42e134e8;hb=c8b8722a14d29e2b4153c39ad4cef0c44a562afd;hp=7e532dd654a7b87d519ab9d0ecb9a01f47ddcce2;hpb=4c422bbe6d3160d4a46058da87942c6317ce3dca;p=flightgear.git

diff --git a/src/FDM/YASim/Atmosphere.cpp b/src/FDM/YASim/Atmosphere.cpp
index 7e532dd65..92d2fbe56 100644
--- a/src/FDM/YASim/Atmosphere.cpp
+++ b/src/FDM/YASim/Atmosphere.cpp
@@ -8,28 +8,35 @@ namespace yasim {
 // R=287.  I chose to correct the temperature to 288.20, since 79F is
 // pretty hot for a "standard" atmosphere.
 //                             meters   kelvin      Pa   kg/m^3
-float Atmosphere::data[][4] = {{ 0,     288.20, 101325, 1.22500 },
-			       { 900,   282.31,  90971, 1.12260 },
-			       { 1800,  276.46,  81494, 1.02690 },
-			       { 2700,  270.62,  72835, 0.93765 },
-			       { 3600,  264.77,  64939, 0.85445 },
-			       { 4500,  258.93,  57752, 0.77704 },
-			       { 5400,  253.09,  51226, 0.70513 },
-			       { 6300,  247.25,  45311, 0.63845 },
-			       { 7200,  241.41,  39963, 0.57671 },
-			       { 8100,  235.58,  35140, 0.51967 },
-			       { 9000,  229.74,  30800, 0.46706 },
-			       { 9900,  223.91,  26906, 0.41864 },
-			       { 10800, 218.08,  23422, 0.37417 },
-			       { 11700, 216.66,  20335, 0.32699 },
-			       { 12600, 216.66,  17654, 0.28388 },
-			       { 13500, 216.66,  15327, 0.24646 },
-			       { 14400, 216.66,  13308, 0.21399 },
-			       { 15300, 216.66,  11555, 0.18580 },
-			       { 16200, 216.66,  10033, 0.16133 },
-			       { 17100, 216.66,   8712, 0.14009 },
-			       { 18000, 216.66,   7565, 0.12165 },
-			       { 18900, 216.66,   6570, 0.10564 }};
+float Atmosphere::data[][4] = {{ 0.0f,     288.20f, 101325.0f, 1.22500f },
+			       {   900.0f, 282.31f,  90971.0f, 1.12260f },
+			       {  1800.0f, 276.46f,  81494.0f, 1.02690f },
+			       {  2700.0f, 270.62f,  72835.0f, 0.93765f },
+			       {  3600.0f, 264.77f,  64939.0f, 0.85445f },
+			       {  4500.0f, 258.93f,  57752.0f, 0.77704f },
+			       {  5400.0f, 253.09f,  51226.0f, 0.70513f },
+			       {  6300.0f, 247.25f,  45311.0f, 0.63845f },
+			       {  7200.0f, 241.41f,  39963.0f, 0.57671f },
+			       {  8100.0f, 235.58f,  35140.0f, 0.51967f },
+			       {  9000.0f, 229.74f,  30800.0f, 0.46706f },
+			       {  9900.0f, 223.91f,  26906.0f, 0.41864f },
+			       { 10800.0f, 218.08f,  23422.0f, 0.37417f },
+			       { 11700.0f, 216.66f,  20335.0f, 0.32699f },
+			       { 12600.0f, 216.66f,  17654.0f, 0.28388f },
+			       { 13500.0f, 216.66f,  15327.0f, 0.24646f },
+			       { 14400.0f, 216.66f,  13308.0f, 0.21399f },
+			       { 15300.0f, 216.66f,  11555.0f, 0.18580f },
+			       { 16200.0f, 216.66f,  10033.0f, 0.16133f },
+			       { 17100.0f, 216.66f,   8712.0f, 0.14009f },
+			       { 18000.0f, 216.66f,   7565.0f, 0.12165f },
+			       { 18900.0f, 216.66f,   6570.0f, 0.10564f }};
+
+// Universal gas constant for air, in SI units.  P = R * rho * T.
+// P in pascals (N/m^2), rho is kg/m^3, T in kelvin.
+const float R = 287.1f;
+
+// Specific heat ratio for air, at "low" temperatures.  
+const float GAMMA = 1.4f;
 
 float Atmosphere::getStdTemperature(float alt)
 {
@@ -46,9 +53,12 @@ float Atmosphere::getStdDensity(float alt)
     return getRecord(alt, 3);
 }
 
-float Atmosphere::calcVEAS(float spd, float pressure, float temp)
+float Atmosphere::calcVEAS(float spd,
+                           float pressure, float temp, float density)
 {
-    return 0; //FIXME
+    static float rho0 = getStdDensity(0);
+    float densityRatio = density / rho0;
+    return spd * Math::sqrt(densityRatio);
 }
 
 float Atmosphere::calcVCAS(float spd, float pressure, float temp)
@@ -69,8 +79,8 @@ float Atmosphere::calcVCAS(float spd, float pressure, float temp)
         // (1+(mach^2)/5)^(gamma/(gamma-1))
         cp = Math::pow(1+0.2*m2, 3.5);
     } else {
-        float tmp0 = ((144/25.) * m2) / (28/5.*m2 - 4/5.);
-        float tmp1 = ((14/5.) * m2 - (2/5.)) * (5/12.);
+        float tmp0 = ((144.0f/25.0f) * m2) / (28.0f/5.0f*m2 - 4.0f/5.0f);
+        float tmp1 = ((14.0f/5.0f) * m2 - (2.0f/5.0f)) * (5.0f/12.0f);
         cp = Math::pow(tmp0, 3.5) * tmp1;
     }
 
@@ -82,15 +92,44 @@ float Atmosphere::calcVCAS(float spd, float pressure, float temp)
     return Math::sqrt((7*p0/rho0)*(tmp-1));
 }
 
-float Atmosphere::calcDensity(float pressure, float temp)
+float Atmosphere::calcStdDensity(float pressure, float temp)
 {
-    // P = rho*R*T, R == 287 kPa*m^3 per kg*kelvin for air
-    return pressure / (287 * temp);
+    return pressure / (R * temp);
 }
 
 float Atmosphere::calcMach(float spd, float temp)
 {
-    return spd / Math::sqrt(1.4 * 287 * temp);
+    return spd / Math::sqrt(GAMMA * R * temp);
+}
+
+float Atmosphere::spdFromMach(float mach, float temp)
+{
+    return mach * Math::sqrt(GAMMA * R * temp);
+}
+
+float Atmosphere::spdFromVCAS(float vcas, float pressure, float temp)
+{
+                                // FIXME: does not account for supersonic
+    float p0 = getStdPressure(0);
+    float rho0 = getStdDensity(0);
+
+    float tmp = (vcas*vcas)/(7*p0/rho0) + 1;
+    float cp = ((Math::pow(tmp,(7/2.))-1)/(pressure/p0)) + 1;
+
+    float m2 = (Math::pow(cp,(1/3.5))-1)/0.2;
+    float vtas= spdFromMach(Math::sqrt(m2), temp);
+    return vtas;
+}
+
+void Atmosphere::calcStaticAir(float p0, float t0, float d0, float v,
+                               float* pOut, float* tOut, float* dOut)
+{
+    const static float C0 = ((GAMMA-1)/(2*R*GAMMA));
+    const static float C1 = 1/(GAMMA-1);
+
+    *tOut = t0 + (v*v) * C0;
+    *dOut = d0 * Math::pow(*tOut / t0, C1);
+    *pOut = (*dOut) * R * (*tOut);
 }
 
 float Atmosphere::getRecord(float alt, int recNum)