1 // airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
2 // Written by David Megginson, started 2002.
3 // Last modified by Eric van den Berg, 09 Dec 2012
5 // This file is in the Public Domain and comes with no warranty.
13 #include <simgear/constants.h>
14 #include <simgear/math/interpolater.hxx>
16 #include "airspeed_indicator.hxx"
17 #include <Main/fg_props.hxx>
18 #include <Main/util.hxx>
19 #include <Environment/environment_mgr.hxx>
20 #include <Environment/environment.hxx>
23 // A higher number means more responsive.
24 #define RESPONSIVENESS 50.0
26 AirspeedIndicator::AirspeedIndicator ( SGPropertyNode *node )
28 _name(node->getStringValue("name", "airspeed-indicator")),
29 _num(node->getIntValue("number", 0)),
30 _total_pressure(node->getStringValue("total-pressure", "/systems/pitot/total-pressure-inhg")),
31 _static_pressure(node->getStringValue("static-pressure", "/systems/static/pressure-inhg")),
32 _has_overspeed(node->getBoolValue("has-overspeed-indicator",false)),
33 _pressure_alt_source(node->getStringValue("pressure-alt-source", "/instrumentation/altimeter/pressure-alt-ft")),
34 _ias_limit(node->getDoubleValue("ias-limit", 248.0)),
35 _mach_limit(node->getDoubleValue("mach-limit", 0.48)),
36 _alt_threshold(node->getDoubleValue("alt-threshold", 13200))
38 _environmentManager = NULL;
41 AirspeedIndicator::~AirspeedIndicator ()
46 AirspeedIndicator::init ()
49 branch = "/instrumentation/" + _name;
51 SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
52 _serviceable_node = node->getChild("serviceable", 0, true);
53 _total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
54 _static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
55 _density_node = fgGetNode("/environment/density-slugft3", true);
56 _speed_node = node->getChild("indicated-speed-kt", 0, true);
57 _tas_node = node->getChild("true-speed-kt", 0, true);
58 _mach_node = node->getChild("indicated-mach", 0, true);
60 // overspeed-indicator properties
62 _ias_limit_node = node->getNode("ias-limit",0, true);
63 _mach_limit_node = node->getNode("mach-limit",0, true);
64 _alt_threshold_node = node->getNode("alt-threshold",0, true);
66 if (!_ias_limit_node->hasValue()) {
67 _ias_limit_node->setDoubleValue(_ias_limit);
70 if (!_mach_limit_node->hasValue()) {
71 _mach_limit_node->setDoubleValue(_mach_limit);
74 if (!_alt_threshold_node->hasValue()) {
75 _alt_threshold_node->setDoubleValue(_alt_threshold);
78 _airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
79 _pressure_alt = fgGetNode(_pressure_alt_source.c_str(), true);
82 _environmentManager = (FGEnvironmentMgr*) globals->get_subsystem("environment");
86 AirspeedIndicator::reinit ()
88 _speed_node->setDoubleValue(0.0);
92 AirspeedIndicator::update (double dt)
94 if (!_serviceable_node->getBoolValue()) {
98 double pt = _total_pressure_node->getDoubleValue() ;
99 double p = _static_pressure_node->getDoubleValue() ;
100 double qc = ( pt - p ) * SG_INHG_TO_PA ; // Impact pressure in Pa, _not_ to be confused with dynamic pressure!!!
102 // Now, reverse the equation (normalize impact pressure to
103 // avoid "nan" results from sqrt)
104 qc = std::max( qc , 0.0 );
105 // Calibrated airspeed (using compressible aerodynamics) based on impact pressure qc in m/s
106 // Using calibrated airspeed as indicated airspeed, neglecting any airspeed indicator errors.
107 double v_cal = sqrt( 7 * SG_p0_Pa/SG_rho0_kg_p_m3 * ( pow( 1 + qc/SG_p0_Pa , 1/3.5 ) -1 ) );
109 // Publish the indicated airspeed
110 double last_speed_kt = _speed_node->getDoubleValue();
111 double current_speed_kt = v_cal * SG_MPS_TO_KT;
112 double filtered_speed = fgGetLowPass(last_speed_kt,
114 dt * RESPONSIVENESS);
115 _speed_node->setDoubleValue(filtered_speed);
118 if (!_has_overspeed) {
122 double lmt = _ias_limit_node->getDoubleValue();
123 if (_pressure_alt->getDoubleValue() > _alt_threshold_node->getDoubleValue()) {
124 double mmo = _mach_limit_node->getDoubleValue();
125 lmt = (filtered_speed/_mach_node->getDoubleValue())* mmo;
128 _airspeed_limit->setDoubleValue(lmt);
132 AirspeedIndicator::computeMach()
134 if (!_environmentManager) {
138 FGEnvironment env(_environmentManager->getEnvironment());
140 double oatK = env.get_temperature_degc() + SG_T0_K - 15.0 ; // OAT in Kelvin
141 oatK = std::max( oatK , 0.001 ); // should never happen, but just in case someone flies into space...
142 double c = sqrt(SG_gamma * SG_R_m2_p_s2_p_K * oatK); // speed-of-sound in m/s at aircraft position
143 double pt = _total_pressure_node->getDoubleValue() * SG_INHG_TO_PA; // total pressure in Pa
144 double p = _static_pressure_node->getDoubleValue() * SG_INHG_TO_PA; // static pressure in Pa
145 p = std::max( p , 0.001 ); // should never happen, but just in case someone flies into space...
146 double rho = _density_node->getDoubleValue() * SG_SLUGFT3_TO_KGPM3; // air density in kg/m3
147 rho = std::max( rho , 0.001 ); // should never happen, but just in case someone flies into space...
149 // true airspeed in m/s
150 pt = std::max( pt , p );
151 double V_true = sqrt( 7 * p/rho * (pow( 1 + (pt-p)/p , 1/3.5 ) -1 ) );
152 // Mach number; _see notes in systems/pitot.cxx_
153 double mach = V_true / c;
155 // publish Mach and TAS
156 _mach_node->setDoubleValue(mach);
157 _tas_node->setDoubleValue(V_true * SG_MPS_TO_KT );
160 // end of airspeed_indicator.cxx