//
// This file is in the Public Domain and comes with no warranty.
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
#include <math.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 ()
_static_pressure_node = fgGetNode(_static_pressure.c_str(), true);
_density_node = fgGetNode("/environment/density-slugft3", 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);
+
// overspeed-indicator properties
if (_has_overspeed) {
_ias_limit_node = node->getNode("ias-limit",0, true);
_airspeed_limit = node->getChild("airspeed-limit-kt", 0, true);
_pressure_alt = fgGetNode(_pressure_alt_source.c_str(), true);
- _mach = fgGetNode("/velocities/mach", true);
}
+
+ _environmentManager = (FGEnvironmentMgr*) globals->get_subsystem("environment");
+}
+
+void
+AirspeedIndicator::reinit ()
+{
+ _speed_node->setDoubleValue(0.0);
}
#ifndef FPSTOKTS
current_speed_kt,
dt * RESPONSIVENESS);
_speed_node->setDoubleValue(filtered_speed);
+ computeMach(filtered_speed);
if (!_has_overspeed) {
return;
double lmt = _ias_limit_node->getDoubleValue();
if (_pressure_alt->getDoubleValue() > _alt_threshold_node->getDoubleValue()) {
double mmo = _mach_limit_node->getDoubleValue();
- lmt = (filtered_speed/_mach->getDoubleValue())* mmo;
+ lmt = (filtered_speed/_mach_node->getDoubleValue())* mmo;
}
_airspeed_limit->setDoubleValue(lmt);
}
+void
+AirspeedIndicator::computeMach(double ias)
+{
+ if (!_environmentManager) {
+ return;
+ }
+
+ FGEnvironment env(_environmentManager->getEnvironment());
+
+ // derived from http://williams.best.vwh.net/avform.htm#Mach
+ // names here are picked to be consistent with those formulae!
+
+ double oatK = env.get_temperature_degc() + 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 = env.get_pressure_sea_level_inhg();
+ double P = _static_pressure_node->getDoubleValue();
+
+ 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);
+
+ // publish Mach and TAS
+ _mach_node->setDoubleValue(mach);
+ _tas_node->setDoubleValue(CS * mach);
+}
+
// end of airspeed_indicator.cxx