// airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
// Written by David Megginson, started 2002.
+// Last modified by Eric van den Berg, 09 Dec 2012
//
// This file is in the Public Domain and comes with no warranty.
#include <math.h>
+#include <simgear/constants.h>
#include <simgear/math/interpolater.hxx>
#include "airspeed_indicator.hxx"
#include <Main/fg_props.hxx>
#include <Main/util.hxx>
+#include <Environment/environment_mgr.hxx>
+#include <Environment/environment.hxx>
// A higher number means more responsive.
_mach_limit(node->getDoubleValue("mach-limit", 0.48)),
_alt_threshold(node->getDoubleValue("alt-threshold", 13200))
{
+ _environmentManager = NULL;
}
AirspeedIndicator::~AirspeedIndicator ()
void
AirspeedIndicator::init ()
{
- string branch;
+ std::string branch;
branch = "/instrumentation/" + _name;
SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
_total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
_static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
_density_node = fgGetNode("/environment/density-slugft3", true);
-
- _sea_level_pressure_node = fgGetNode("/environment/pressure-sea-level-inhg", true);
- _oat_celsius_node = fgGetNode("/environment/temperature-degc", true);
-
_speed_node = node->getChild("indicated-speed-kt", 0, true);
_tas_node = node->getChild("true-speed-kt", 0, true);
_mach_node = node->getChild("indicated-mach", 0, true);
_airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
_pressure_alt = fgGetNode(_pressure_alt_source.c_str(), true);
}
+
+ _environmentManager = (FGEnvironmentMgr*) globals->get_subsystem("environment");
}
void
_speed_node->setDoubleValue(0.0);
}
-#ifndef FPSTOKTS
-# define FPSTOKTS 0.592484
-#endif
-
-#ifndef INHGTOPSF
-# define INHGTOPSF (2116.217/29.9212)
-#endif
-
void
AirspeedIndicator::update (double dt)
{
return;
}
- double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
- double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
- double r = _density_node->getDoubleValue();
- double q = ( pt - p ); // dynamic pressure
+ double pt = _total_pressure_node->getDoubleValue() ;
+ double p = _static_pressure_node->getDoubleValue() ;
+ double qc = ( pt - p ) * SG_INHG_TO_PA ; // Impact pressure in Pa, _not_ to be confused with dynamic pressure!!!
- // Now, reverse the equation (normalize dynamic pressure to
+ // Now, reverse the equation (normalize impact pressure to
// avoid "nan" results from sqrt)
- if ( q < 0 ) { q = 0.0; }
- double v_fps = sqrt((2 * q) / r);
+ qc = std::max( qc , 0.0 );
+ // Calibrated airspeed (using compressible aerodynamics) based on impact pressure qc in m/s
+ // Using calibrated airspeed as indicated airspeed, neglecting any airspeed indicator errors.
+ double v_cal = sqrt( 7 * SG_p0_Pa/SG_rho0_kg_p_m3 * ( pow( 1 + qc/SG_p0_Pa , 1/3.5 ) -1 ) );
// Publish the indicated airspeed
double last_speed_kt = _speed_node->getDoubleValue();
- double current_speed_kt = v_fps * FPSTOKTS;
+ double current_speed_kt = v_cal * SG_MPS_TO_KT;
double filtered_speed = fgGetLowPass(last_speed_kt,
current_speed_kt,
dt * RESPONSIVENESS);
_speed_node->setDoubleValue(filtered_speed);
- computeMach(filtered_speed);
+ computeMach();
if (!_has_overspeed) {
return;
}
void
-AirspeedIndicator::computeMach(double ias)
+AirspeedIndicator::computeMach()
{
-
- // derived from http://williams.best.vwh.net/avform.htm#Mach
- // names here are picked to be consistent with those formulae!
-
- double oatK = _oat_celsius_node->getDoubleValue() + 273.15; // OAT in Kelvin
- double CS = 38.967854 * sqrt(oatK); // speed-of-sound in knots at altitude
- double CS_0 = 661.4786; // speed-of-sound in knots at sea-level
- double P_0 = _sea_level_pressure_node->getDoubleValue();
- double P = _static_pressure_node->getDoubleValue();
+ if (!_environmentManager) {
+ return;
+ }
+
+ FGEnvironment env(_environmentManager->getEnvironment());
+
+ double oatK = env.get_temperature_degc() + SG_T0_K - 15.0 ; // OAT in Kelvin
+ oatK = std::max( oatK , 0.001 ); // should never happen, but just in case someone flies into space...
+ double c = sqrt(SG_gamma * SG_R_m2_p_s2_p_K * oatK); // speed-of-sound in m/s at aircraft position
+ double pt = _total_pressure_node->getDoubleValue() * SG_INHG_TO_PA; // total pressure in Pa
+ double p = _static_pressure_node->getDoubleValue() * SG_INHG_TO_PA; // static pressure in Pa
+ p = std::max( p , 0.001 ); // should never happen, but just in case someone flies into space...
+ double rho = _density_node->getDoubleValue() * SG_SLUGFT3_TO_KGPM3; // air density in kg/m3
+ rho = std::max( rho , 0.001 ); // should never happen, but just in case someone flies into space...
- double DP = P_0 * (pow(1 + 0.2*pow(ias/CS_0, 2), 3.5) - 1);
- double mach = pow(5 * ( pow(DP/P + 1, 2.0/7.0) -1) , 0.5);
+ // true airspeed in m/s
+ pt = std::max( pt , p );
+ double V_true = sqrt( 7 * p/rho * (pow( 1 + (pt-p)/p , 1/3.5 ) -1 ) );
+ // Mach number; _see notes in systems/pitot.cxx_
+ double mach = V_true / c;
// publish Mach and TAS
_mach_node->setDoubleValue(mach);
- _tas_node->setDoubleValue(CS * mach);
+ _tas_node->setDoubleValue(V_true * SG_MPS_TO_KT );
}
// end of airspeed_indicator.cxx
projects / flightgear.git / blobdiff