1 // airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
2 // Written by David Megginson, started 2002.
4 // This file is in the Public Domain and comes with no warranty.
8 #include <simgear/math/interpolater.hxx>
10 #include "airspeed_indicator.hxx"
11 #include <Main/fg_props.hxx>
12 #include <Main/util.hxx>
15 // A higher number means more responsive.
16 #define RESPONSIVENESS 50.0
18 AirspeedIndicator::AirspeedIndicator ( SGPropertyNode *node )
20 _name(node->getStringValue("name", "airspeed-indicator")),
21 _num(node->getIntValue("number", 0)),
22 _total_pressure(node->getStringValue("total-pressure", "/systems/pitot/total-pressure-inhg")),
23 _static_pressure(node->getStringValue("static-pressure", "/systems/static/pressure-inhg")),
24 _has_overspeed(node->getBoolValue("has-overspeed-indicator",false)),
25 _pressure_alt_source(node->getStringValue("pressure-alt-source", "/instrumentation/altimeter/pressure-alt-ft")),
26 _ias_limit(node->getDoubleValue("ias-limit", 248.0)),
27 _mach_limit(node->getDoubleValue("mach-limit", 0.48)),
28 _alt_threshold(node->getDoubleValue("alt-threshold", 13200))
32 AirspeedIndicator::~AirspeedIndicator ()
37 AirspeedIndicator::init ()
40 branch = "/instrumentation/" + _name;
42 SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
43 _serviceable_node = node->getChild("serviceable", 0, true);
44 _total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
45 _static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
46 _density_node = fgGetNode("/environment/density-slugft3", true);
47 _speed_node = node->getChild("indicated-speed-kt", 0, true);
49 // overspeed-indicator properties
51 _ias_limit_node = node->getNode("ias-limit",0, true);
52 _mach_limit_node = node->getNode("mach-limit",0, true);
53 _alt_threshold_node = node->getNode("alt-threshold",0, true);
55 if (!_ias_limit_node->hasValue()) {
56 _ias_limit_node->setDoubleValue(_ias_limit);
59 if (!_mach_limit_node->hasValue()) {
60 _mach_limit_node->setDoubleValue(_mach_limit);
63 if (!_alt_threshold_node->hasValue()) {
64 _alt_threshold_node->setDoubleValue(_alt_threshold);
67 _airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
68 _pressure_alt = fgGetNode(_pressure_alt_source.c_str(), true);
69 _mach = fgGetNode("/velocities/mach", true);
74 # define FPSTOKTS 0.592484
78 # define INHGTOPSF (2116.217/29.9212)
82 AirspeedIndicator::update (double dt)
84 if (!_serviceable_node->getBoolValue()) {
88 double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
89 double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
90 double r = _density_node->getDoubleValue();
91 double q = ( pt - p ); // dynamic pressure
93 // Now, reverse the equation (normalize dynamic pressure to
94 // avoid "nan" results from sqrt)
95 if ( q < 0 ) { q = 0.0; }
96 double v_fps = sqrt((2 * q) / r);
98 // Publish the indicated airspeed
99 double last_speed_kt = _speed_node->getDoubleValue();
100 double current_speed_kt = v_fps * FPSTOKTS;
101 double filtered_speed = fgGetLowPass(last_speed_kt,
103 dt * RESPONSIVENESS);
104 _speed_node->setDoubleValue(filtered_speed);
106 if (!_has_overspeed) {
110 double lmt = _ias_limit_node->getDoubleValue();
111 if (_pressure_alt->getDoubleValue() > _alt_threshold_node->getDoubleValue()) {
112 double mmo = _mach_limit_node->getDoubleValue();
113 lmt = (filtered_speed/_mach->getDoubleValue())* mmo;
116 _airspeed_limit->setDoubleValue(lmt);
119 // end of airspeed_indicator.cxx