src/Instrumentation/airspeed_indicator.cxx

   1 // airspeed_indicator.cxx - a regular VSI.
   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 AirspeedIndicator::AirspeedIndicator ()
  16 {
  17 }
  18
  19 AirspeedIndicator::~AirspeedIndicator ()
  20 {
  21 }
  22
  23 void
  24 AirspeedIndicator::init ()
  25 {
  26     _serviceable_node =
  27         fgGetNode("/instrumentation/airspeed-indicator/serviceable",
  28                   true);
  29     _total_pressure_node =
  30         fgGetNode("/systems/pitot/total-pressure-inhg", true);
  31     _static_pressure_node =
  32         fgGetNode("/systems/static/pressure-inhg", true);
  33     _speed_node =
  34         fgGetNode("/instrumentation/airspeed-indicator/indicated-speed-kt",
  35                   true);
  36 }
  37
  38 #ifndef SEA_LEVEL_DENSITY_SLUGFG3
  39 # define SEA_LEVEL_DENSITY_SLUGFT3 0.002378
  40 #endif
  41
  42 #ifndef FPSTOKTS
  43 # define FPSTOKTS 0.592484
  44 #endif
  45
  46 #ifndef INHGTOPSF
  47 # define INHGTOPSF (2116.217/29.9212)
  48 #endif
  49
  50 void
  51 AirspeedIndicator::update (double dt)
  52 {
  53     if (_serviceable_node->getBoolValue()) {
  54         double pt = _total_pressure_node->getDoubleValue();
  55         double p = _static_pressure_node->getDoubleValue();
  56         double q = ( pt - p ) * INHGTOPSF;      // dynamic pressure
  57
  58                                 // Now, reverse the equation
  59         double v_fps = sqrt((2 * q) / SEA_LEVEL_DENSITY_SLUGFT3);
  60
  61         _speed_node->setDoubleValue(v_fps * FPSTOKTS);
  62     }
  63 }
  64
  65 // end of airspeed_indicator.cxx