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_barber_pole(node->getBoolValue("has-barber-pole",false))
28 AirspeedIndicator::~AirspeedIndicator ()
33 AirspeedIndicator::init ()
36 branch = "/instrumentation/" + _name;
38 SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
39 _serviceable_node = node->getChild("serviceable", 0, true);
40 _total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
41 _static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
42 _density_node = fgGetNode("/environment/density-slugft3", true);
43 _speed_node = node->getChild("indicated-speed-kt", 0, true);
45 // barber-pole properties
46 _ias_limit_node = node->getNode("ias-limit",0, true);
47 _mach_limit_node = node->getNode("mach-limit",0, true);
48 _alt_threshold_node = node->getNode("alt-threshold",0, true);
49 _airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
51 string paSource = node->getStringValue("pressure-alt-source",
52 "/instrumentation/altimeter/pressure-alt-ft");
53 _pressure_alt = fgGetNode(paSource.c_str(), true);
54 _mach = fgGetNode("/velocities/mach", true);
58 # define FPSTOKTS 0.592484
62 # define INHGTOPSF (2116.217/29.9212)
66 AirspeedIndicator::update (double dt)
68 if (!_serviceable_node->getBoolValue()) {
72 double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
73 double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
74 double r = _density_node->getDoubleValue();
75 double q = ( pt - p ); // dynamic pressure
77 // Now, reverse the equation (normalize dynamic pressure to
78 // avoid "nan" results from sqrt)
79 if ( q < 0 ) { q = 0.0; }
80 double v_fps = sqrt((2 * q) / r);
82 // Publish the indicated airspeed
83 double last_speed_kt = _speed_node->getDoubleValue();
84 double current_speed_kt = v_fps * FPSTOKTS;
85 double filtered_speed = fgGetLowPass(last_speed_kt,
88 _speed_node->setDoubleValue(filtered_speed);
90 if (!_has_barber_pole) {
94 double lmt = _ias_limit_node->getDoubleValue();
95 if (_pressure_alt->getDoubleValue() > _alt_threshold_node->getDoubleValue()) {
96 double mmo = _mach_limit_node->getDoubleValue();
97 lmt = (filtered_speed/_mach->getDoubleValue())* mmo;
100 _airspeed_limit->setDoubleValue(lmt);
103 // end of airspeed_indicator.cxx