src/Instrumentation/airspeed_indicator.cxx

   1 // airspeed_indicator.cxx - a regular pitot-static airspeed indicator.
   2 // Written by David Megginson, started 2002.
   3 //
   4 // This file is in the Public Domain and comes with no warranty.
   5
   6 #include <math.h>
   7
   8 #include <simgear/math/interpolater.hxx>
   9
  10 #include "airspeed_indicator.hxx"
  11 #include <Main/fg_props.hxx>
  12 #include <Main/util.hxx>
  13
  14
  15 // A higher number means more responsive.
  16 #define RESPONSIVENESS 50.0
  17
  18 AirspeedIndicator::AirspeedIndicator ( SGPropertyNode *node )
  19     :
  20     name("airspeed-indicator"),
  21     num(0),
  22     pitot_port("/systems/pitot"),
  23     static_port("/systems/static")
  24 {
  25     int i;
  26     for ( i = 0; i < node->nChildren(); ++i ) {
  27         SGPropertyNode *child = node->getChild(i);
  28         string cname = child->getName();
  29         string cval = child->getStringValue();
  30         if ( cname == "name" ) {
  31             name = cval;
  32         } else if ( cname == "number" ) {
  33             num = child->getIntValue();
  34         } else if ( cname == "pitot-port" ) {
  35             pitot_port = cval;
  36         } else if ( cname == "static-port" ) {
  37             static_port = cval;
  38         } else {
  39             SG_LOG( SG_INSTR, SG_WARN, "Error in aispeed-indicator config logic" );
  40             if ( name.length() ) {
  41                 SG_LOG( SG_INSTR, SG_WARN, "Section = " << name );
  42             }
  43         }
  44     }
  45 }
  46
  47
  48 AirspeedIndicator::AirspeedIndicator ( int i )
  49     :
  50     name("airspeed-indicator"),
  51     num(0),
  52     pitot_port("/systems/pitot"),
  53     static_port("/systems/static")
  54 {
  55     num = i;
  56 }
  57
  58 AirspeedIndicator::~AirspeedIndicator ()
  59 {
  60 }
  61
  62 void
  63 AirspeedIndicator::init ()
  64 {
  65     string branch;
  66     branch = "/instrumentation/" + name;
  67     pitot_port += "/total-pressure-inhg";
  68     static_port += "/pressure-inhg";
  69
  70     SGPropertyNode *node = fgGetNode(branch.c_str(), num, true );
  71     _serviceable_node = node->getChild("serviceable", 0, true);
  72     _total_pressure_node = fgGetNode(pitot_port.c_str(), true);
  73     _static_pressure_node = fgGetNode(static_port.c_str(), true);
  74     _density_node = fgGetNode("/environment/density-slugft3", true);
  75     _speed_node = node->getChild("indicated-speed-kt", 0, true);
  76 }
  77
  78 #ifndef FPSTOKTS
  79 # define FPSTOKTS 0.592484
  80 #endif
  81
  82 #ifndef INHGTOPSF
  83 # define INHGTOPSF (2116.217/29.9212)
  84 #endif
  85
  86 void
  87 AirspeedIndicator::update (double dt)
  88 {
  89     if (_serviceable_node->getBoolValue()) {
  90         double pt = _total_pressure_node->getDoubleValue() * INHGTOPSF;
  91         double p = _static_pressure_node->getDoubleValue() * INHGTOPSF;
  92         double r = _density_node->getDoubleValue();
  93         double q = ( pt - p );  // dynamic pressure
  94
  95         // Now, reverse the equation (normalize dynamic pressure to
  96         // avoid "nan" results from sqrt)
  97         if ( q < 0 ) { q = 0.0; }
  98         double v_fps = sqrt((2 * q) / r);
  99
 100                                 // Publish the indicated airspeed
 101         double last_speed_kt = _speed_node->getDoubleValue();
 102         double current_speed_kt = v_fps * FPSTOKTS;
 103         _speed_node->setDoubleValue(fgGetLowPass(last_speed_kt,
 104                                                  current_speed_kt,
 105                                                  dt * RESPONSIVENESS));
 106     }
 107 }
 108
 109 // end of airspeed_indicator.cxx