152 lines
5 KiB
C++
152 lines
5 KiB
C++
// airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
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// Written by David Megginson, started 2002.
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//
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// This file is in the Public Domain and comes with no warranty.
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#include <math.h>
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#include <simgear/math/interpolater.hxx>
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#include "airspeed_indicator.hxx"
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#include <Main/fg_props.hxx>
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#include <Main/util.hxx>
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#include <Environment/environment_mgr.hxx>
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#include <Environment/environment.hxx>
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// A higher number means more responsive.
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#define RESPONSIVENESS 50.0
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AirspeedIndicator::AirspeedIndicator ( SGPropertyNode *node )
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:
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_name(node->getStringValue("name", "airspeed-indicator")),
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_num(node->getIntValue("number", 0)),
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_total_pressure(node->getStringValue("total-pressure", "/systems/pitot/total-pressure-inhg")),
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_static_pressure(node->getStringValue("static-pressure", "/systems/static/pressure-inhg")),
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_has_overspeed(node->getBoolValue("has-overspeed-indicator",false)),
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_pressure_alt_source(node->getStringValue("pressure-alt-source", "/instrumentation/altimeter/pressure-alt-ft")),
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_ias_limit(node->getDoubleValue("ias-limit", 248.0)),
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_mach_limit(node->getDoubleValue("mach-limit", 0.48)),
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_alt_threshold(node->getDoubleValue("alt-threshold", 13200))
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{
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_environmentManager = NULL;
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}
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AirspeedIndicator::~AirspeedIndicator ()
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{
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}
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void
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AirspeedIndicator::init ()
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{
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string branch;
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branch = "/instrumentation/" + _name;
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SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
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_serviceable_node = node->getChild("serviceable", 0, true);
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_total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
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_static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
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_density_node = fgGetNode("/environment/density-slugft3", true);
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_speed_node = node->getChild("indicated-speed-kt", 0, true);
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_tas_node = node->getChild("true-speed-kt", 0, true);
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_mach_node = node->getChild("indicated-mach", 0, true);
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// overspeed-indicator properties
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if (_has_overspeed) {
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_ias_limit_node = node->getNode("ias-limit",0, true);
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_mach_limit_node = node->getNode("mach-limit",0, true);
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_alt_threshold_node = node->getNode("alt-threshold",0, true);
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if (!_ias_limit_node->hasValue()) {
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_ias_limit_node->setDoubleValue(_ias_limit);
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}
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if (!_mach_limit_node->hasValue()) {
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_mach_limit_node->setDoubleValue(_mach_limit);
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}
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if (!_alt_threshold_node->hasValue()) {
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_alt_threshold_node->setDoubleValue(_alt_threshold);
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}
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_airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
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_pressure_alt = fgGetNode(_pressure_alt_source.c_str(), true);
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}
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_environmentManager = (FGEnvironmentMgr*) globals->get_subsystem("environment");
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}
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#ifndef FPSTOKTS
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# define FPSTOKTS 0.592484
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#endif
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#ifndef INHGTOPSF
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# define INHGTOPSF (2116.217/29.9212)
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#endif
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void
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AirspeedIndicator::update (double dt)
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{
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if (!_serviceable_node->getBoolValue()) {
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return;
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}
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double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
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double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
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double r = _density_node->getDoubleValue();
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double q = ( pt - p ); // dynamic pressure
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// Now, reverse the equation (normalize dynamic pressure to
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// avoid "nan" results from sqrt)
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if ( q < 0 ) { q = 0.0; }
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double v_fps = sqrt((2 * q) / r);
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// Publish the indicated airspeed
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double last_speed_kt = _speed_node->getDoubleValue();
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double current_speed_kt = v_fps * FPSTOKTS;
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double filtered_speed = fgGetLowPass(last_speed_kt,
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current_speed_kt,
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dt * RESPONSIVENESS);
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_speed_node->setDoubleValue(filtered_speed);
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computeMach(filtered_speed);
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if (!_has_overspeed) {
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return;
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}
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double lmt = _ias_limit_node->getDoubleValue();
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if (_pressure_alt->getDoubleValue() > _alt_threshold_node->getDoubleValue()) {
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double mmo = _mach_limit_node->getDoubleValue();
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lmt = (filtered_speed/_mach_node->getDoubleValue())* mmo;
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}
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_airspeed_limit->setDoubleValue(lmt);
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}
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void
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AirspeedIndicator::computeMach(double ias)
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{
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if (!_environmentManager) {
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return;
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}
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FGEnvironment env(_environmentManager->getEnvironment());
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// derived from http://williams.best.vwh.net/avform.htm#Mach
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// names here are picked to be consistent with those formulae!
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double oatK = env.get_temperature_degc() + 273.15; // OAT in Kelvin
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double CS = 38.967854 * sqrt(oatK); // speed-of-sound in knots at altitude
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double CS_0 = 661.4786; // speed-of-sound in knots at sea-level
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double P_0 = env.get_pressure_sea_level_inhg();
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double P = _static_pressure_node->getDoubleValue();
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double DP = P_0 * (pow(1 + 0.2*pow(ias/CS_0, 2), 3.5) - 1);
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double mach = pow(5 * ( pow(DP/P + 1, 2.0/7.0) -1) , 0.5);
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// publish Mach and TAS
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_mach_node->setDoubleValue(mach);
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_tas_node->setDoubleValue(CS * mach);
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}
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// end of airspeed_indicator.cxx
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