74 lines
2 KiB
C++
74 lines
2 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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// A higher number means more responsive.
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#define RESPONSIVENESS 50.0
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AirspeedIndicator::AirspeedIndicator ()
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{
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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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_serviceable_node =
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fgGetNode("/instrumentation/airspeed-indicator/serviceable",
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true);
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_total_pressure_node =
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fgGetNode("/systems/pitot/total-pressure-inhg", true);
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_static_pressure_node =
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fgGetNode("/systems/static/pressure-inhg", true);
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_density_node = fgGetNode("/environment/density-slugft3", true);
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_speed_node =
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fgGetNode("/instrumentation/airspeed-indicator/indicated-speed-kt",
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true);
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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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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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_speed_node->setDoubleValue(fgGetLowPass(last_speed_kt,
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current_speed_kt,
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dt * RESPONSIVENESS));
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}
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}
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// end of airspeed_indicator.cxx
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