James Turner:

[flightgear.git] / src / Instrumentation / airspeed_indicator.cxx

diff --git a/src/Instrumentation/airspeed_indicator.cxx b/src/Instrumentation/airspeed_indicator.cxx
index 27f2f0f175298e1aefd2d9b9cbc0dc6650527763..0196ddbaef9bd20b3d420f1c0f78ae0f868b9af0 100644 (file)
--- a/src/Instrumentation/airspeed_indicator.cxx
+++ b/src/Instrumentation/airspeed_indicator.cxx
@@ -1,4 +1,4 @@
-// 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.
@@ -12,7 +12,15 @@
 #include <Main/util.hxx>
 
 
-AirspeedIndicator::AirspeedIndicator ()
+// A higher number means more responsive.
+#define RESPONSIVENESS 50.0
+
+AirspeedIndicator::AirspeedIndicator ( SGPropertyNode *node )
+    :
+    _name(node->getStringValue("name", "airspeed-indicator")),
+    _num(node->getIntValue("number", 0)),
+    _total_pressure(node->getStringValue("total-pressure", "/systems/pitot/total-pressure-inhg")),
+    _static_pressure(node->getStringValue("static-pressure", "/systems/static/pressure-inhg"))
 {
 }
 
@@ -23,49 +31,45 @@ AirspeedIndicator::~AirspeedIndicator ()
 void
 AirspeedIndicator::init ()
 {
-    _serviceable_node =
-        fgGetNode("/instrumentation/airspeed-indicator/serviceable",
-                  true);
-    _total_pressure_node =
-        fgGetNode("/systems/pitot/total-pressure-inhg", true);
-    _static_pressure_node =
-        fgGetNode("/systems/static/pressure-inhg", true);
-    _speed_node =
-        fgGetNode("/instrumentation/airspeed-indicator/indicated-speed-kt",
-                  true);
-}
-
-void
-AirspeedIndicator::bind ()
-{
-}
-
-void
-AirspeedIndicator::unbind ()
-{
+    string branch;
+    branch = "/instrumentation/" + _name;
+
+    SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
+    _serviceable_node = node->getChild("serviceable", 0, true);
+    _total_pressure_node = fgGetNode(_total_pressure.c_str(), true);
+    _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);
 }
 
-
-#ifndef SEA_LEVEL_DENSITY_SLUGFG3
-# define SEA_LEVEL_DENSITY_SLUGFT3 0.002378
-#endif
-
 #ifndef FPSTOKTS
 # define FPSTOKTS 0.592484
 #endif
 
+#ifndef INHGTOPSF
+# define INHGTOPSF (2116.217/29.9212)
+#endif
+
 void
 AirspeedIndicator::update (double dt)
 {
     if (_serviceable_node->getBoolValue()) {
-        double pt = _total_pressure_node->getDoubleValue();
-        double p = _static_pressure_node->getDoubleValue();
-        double q = pt - p;      // dynamic pressure
-
-                                // Now, reverse the equation
-        double v_fps = sqrt((2 * q) / SEA_LEVEL_DENSITY_SLUGFT3);
-
-        _speed_node->setDoubleValue(v_fps * FPSTOKTS);
+        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 (normalize dynamic pressure to
+        // avoid "nan" results from sqrt)
+        if ( q < 0 ) { q = 0.0; }
+        double v_fps = sqrt((2 * q) / r);
+
+                                // 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));
     }
 }