-// airspeed_indicator.cxx - a regular VSI.
+// airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
// Written by David Megginson, started 2002.
//
// This file is in the Public Domain and comes with no warranty.
#include <Main/util.hxx>
+// A higher number means more responsive.
+#define RESPONSIVENESS 50.0
+
+
AirspeedIndicator::AirspeedIndicator ()
{
}
fgGetNode("/systems/pitot/total-pressure-inhg", true);
_static_pressure_node =
fgGetNode("/systems/static/pressure-inhg", true);
+ _density_node = fgGetNode("/environment/density-slugft3", true);
_speed_node =
fgGetNode("/instrumentation/airspeed-indicator/indicated-speed-kt",
true);
}
-#ifndef SEA_LEVEL_DENSITY_SLUGFG3
-# define SEA_LEVEL_DENSITY_SLUGFT3 0.002378
-#endif
-
#ifndef FPSTOKTS
# define FPSTOKTS 0.592484
#endif
AirspeedIndicator::update (double dt)
{
if (_serviceable_node->getBoolValue()) {
- double pt = _total_pressure_node->getDoubleValue();
- double p = _static_pressure_node->getDoubleValue();
- double q = ( pt - p ) * INHGTOPSF; // dynamic pressure
+ double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
+ double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
+ double r = _density_node->getDoubleValue();
+ double q = ( pt - p ); // dynamic pressure
- // Now, reverse the equation
- double v_fps = sqrt((2 * q) / SEA_LEVEL_DENSITY_SLUGFT3);
+ // Now, reverse the equation (normalize dynamic pressure to
+ // avoid "nan" results from sqrt)
+ if ( q < 0 ) { q = 0.0; }
+ double v_fps = sqrt((2 * q) / r);
- _speed_node->setDoubleValue(v_fps * FPSTOKTS);
+ // Publish the indicated airspeed
+ double last_speed_kt = _speed_node->getDoubleValue();
+ double current_speed_kt = v_fps * FPSTOKTS;
+ _speed_node->setDoubleValue(fgGetLowPass(last_speed_kt,
+ current_speed_kt,
+ dt * RESPONSIVENESS));
}
}