X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FInstrumentation%2Fairspeed_indicator.cxx;h=2b80fbd96c3b9e1c3eef2112e277557beb371f54;hb=863b0c943251fae620406ec8983e5f69e1424731;hp=46eb585c8aab0075e42bc38569cd18ed53c4abee;hpb=0a6d2b75591fa02fb38457b583790fb8c4fa22a2;p=flightgear.git

diff --git a/src/Instrumentation/airspeed_indicator.cxx b/src/Instrumentation/airspeed_indicator.cxx
index 46eb585c8..2b80fbd96 100644
--- a/src/Instrumentation/airspeed_indicator.cxx
+++ b/src/Instrumentation/airspeed_indicator.cxx
@@ -34,15 +34,12 @@ AirspeedIndicator::init ()
         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
@@ -55,12 +52,15 @@ 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 ) * INHGTOPSF;      // dynamic pressure
-
-                                // Now, reverse the equation
-        double v_fps = sqrt((2 * q) / SEA_LEVEL_DENSITY_SLUGFT3);
+        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();