// McCormick lists 299.16/101325/1.22500, but those don't agree with
// R=287. I chose to correct the temperature to 288.20, since 79F is
// pretty hot for a "standard" atmosphere.
-// meters kelvin kPa 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 }};
+// Numbers above 19000 meters calculated from src/Environment/environment.cxx
+// meters kelvin Pa kg/m^3
+float Atmosphere::data[][4] = {{ -900.0f, 293.91f, 111679.0f, 1.32353f },
+ { 0.0f, 288.11f, 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 },
+ {19812.0f, 216.66f, 5644.0f, 0.09073f },
+ {20726.0f, 217.23f, 4884.0f, 0.07831f },
+ {21641.0f, 218.39f, 4235.0f, 0.06755f },
+ {22555.0f, 219.25f, 3668.0f, 0.05827f },
+ {23470.0f, 220.12f, 3182.0f, 0.05035f },
+ {24384.0f, 220.98f, 2766.0f, 0.04360f },
+ {25298.0f, 221.84f, 2401.0f, 0.03770f },
+ {26213.0f, 222.71f, 2087.0f, 0.03265f },
+ {27127.0f, 223.86f, 1814.0f, 0.02822f },
+ {28042.0f, 224.73f, 1581.0f, 0.02450f },
+ {28956.0f, 225.59f, 1368.0f, 0.02112f },
+ {29870.0f, 226.45f, 1196.0f, 0.01839f },
+ {30785.0f, 227.32f, 1044.0f, 0.01599f }};
+
+// 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)
{
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)
// (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;
}
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)
projects / flightgear.git / blobdiff