--- /dev/null
+// inst_vertical_speed_indicator.cxx
+// -- Instantaneous VSI (emulation calibrated to standard atmosphere).
+//
+// Started September 2004.
+//
+// Copyright (C) 2004
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+//
+
+#include <simgear/math/interpolater.hxx>
+
+#include "inst_vertical_speed_indicator.hxx"
+#include <Main/fg_props.hxx>
+#include <Main/util.hxx>
+
+
+// Altitude based on pressure difference from sea level.
+//
+// See http://www.pdas.com/programs/atmos.f90, the tables match exactly
+// environment.cxx (Standard 1976).
+// Example :
+// - at 27900 m the level is 20 km :
+// geopotential altitude 27.9 x 6369 / ( 27.9 + 6369) = 27.778 km.
+// - deltah = 27.778 - 20 = 7.778 km and tbase 216.65 degK.
+// - delta = 5.403295E-2 x exp( -34.163195 x 7.778 / 216.65 ) = 0.016.
+// - pressure = (1 - delta ) x 29.92 = 29.44 inhg.
+// - to construct the tables, round delta to 3 digits.
+
+// altitude ft, pressure step inHG
+static double pressure_data[][2] = {
+ { 0.00, 3.33 }, // guess !
+ { 2952.76, 3.05 },
+ { 5905.51, 2.81 },
+ { 8858.27, 2.55 },
+ { 11811.02, 2.33 },
+ { 14763.78, 2.13 },
+ { 17716.54, 1.91 },
+ { 20669.29, 1.77 },
+ { 23622.05, 1.58 },
+ { 26574.80, 1.49 },
+ { 29527.56, 1.20 },
+ { 32480.31, 1.14 },
+ { 35433.07, 1.05 },
+ { 38385.83, 0.90 },
+ { 41338.58, 0.80 },
+ { 44291.34, 0.69 },
+ { 47244.09, 0.60 },
+ { 50196.85, 0.51 },
+ { 53149.61, 0.45 },
+ { 56102.36, 0.39 },
+ { 59055.12, 0.33 },
+ { 62007.87, 0.30 },
+ { 64960.63, 0.26 },
+ { 67913.39, 0.21 },
+ { 70866.14, 0.18 },
+ { 73818.90, 0.18 },
+ { 76771.65, 0.15 },
+ { 79724.41, 0.12 },
+ { 82677.17, 0.12 },
+ { 85629.92, 0.09 },
+ { 88582.68, 0.09 },
+ { 91535.43, 0.06 },
+ { 94488.19, 0.06 },
+ { 97440.94, 0.06 },
+ { 100393.70, 0.06 },
+ { -1, -1 }
+};
+
+// pressure difference inHG, altitude ft
+static double altitude_data[][2] = {
+ { 0.00, 0.00 },
+ { 3.05, 2952.76 },
+ { 5.86, 5905.51 },
+ { 8.41, 8858.27 },
+ { 10.74, 11811.02 },
+ { 12.87, 14763.78 },
+ { 14.78, 17716.54 },
+ { 16.55, 20669.29 },
+ { 18.13, 23622.05 },
+ { 19.62, 26574.80 },
+ { 20.82, 29527.56 },
+ { 21.96, 32480.31 },
+ { 23.01, 35433.07 },
+ { 23.91, 38385.83 },
+ { 24.71, 41338.58 },
+ { 25.40, 44291.34 },
+ { 26.00, 47244.09 },
+ { 26.51, 50196.85 },
+ { 26.96, 53149.61 },
+ { 27.35, 56102.36 },
+ { 27.68, 59055.12 },
+ { 27.98, 62007.87 },
+ { 28.24, 64960.63 },
+ { 28.45, 67913.39 },
+ { 28.63, 70866.14 },
+ { 28.81, 73818.90 },
+ { 28.96, 76771.65 },
+ { 29.08, 79724.41 },
+ { 29.20, 82677.17 },
+ { 29.29, 85629.92 },
+ { 29.38, 88582.68 },
+ { 29.44, 91535.43 },
+ { 29.50, 94488.19 },
+ { 29.56, 97440.94 },
+ { 29.62, 100393.70 },
+ { -1, -1 }
+};
+
+
+// SI constants
+#define SEA_LEVEL_INHG 29.92
+
+// A higher number means more responsive.
+#define RESPONSIVENESS 5.0
+
+// External environment
+#define MAX_INHG_PER_S 0.0002
+
+
+InstVerticalSpeedIndicator::InstVerticalSpeedIndicator ( SGPropertyNode *node ) :
+ _internal_pressure_inhg( SEA_LEVEL_INHG ),
+ _internal_sea_inhg( SEA_LEVEL_INHG ),
+ _pressure_table(new SGInterpTable),
+ _altitude_table(new SGInterpTable),
+ _speed_ft_per_s( 0 )
+{
+ for (int i = 0; pressure_data[i][0] != -1; i++)
+ _pressure_table->addEntry( pressure_data[i][0], pressure_data[i][1] );
+
+ for (int i = 0; altitude_data[i][0] != -1; i++)
+ _altitude_table->addEntry( altitude_data[i][0], altitude_data[i][1] );
+
+ int i;
+ for ( i = 0; i < node->nChildren(); ++i ) {
+ SGPropertyNode *child = node->getChild(i);
+ string cname = child->getName();
+ string cval = child->getStringValue();
+ if ( cname == "name" ) {
+ name = cval;
+ } else if ( cname == "number" ) {
+ num = child->getIntValue();
+ } else {
+ SG_LOG( SG_INSTR, SG_WARN, "Error in inst-vertical-speed-indicator config logic" );
+ if ( name.length() ) {
+ SG_LOG( SG_INSTR, SG_WARN, "Section = " << name );
+ }
+ }
+ }
+}
+
+
+InstVerticalSpeedIndicator::~InstVerticalSpeedIndicator ()
+{
+ delete _pressure_table;
+ delete _altitude_table;
+}
+
+
+void InstVerticalSpeedIndicator::init ()
+{
+ _serviceable_node =
+ fgGetNode("/instrumentation/inst-vertical-speed-indicator/serviceable", true);
+ _freeze_node =
+ fgGetNode("/sim/freeze/master", true);
+
+ // A real IVSI is operated by static pressure changes.
+ // It operates like a conventional VSI, except that an internal sensor
+ // detects load factors, to momentarily alters the static pressure
+ // (with lag).
+ // It appears lag free at subsonic speed; at high altitude indication may
+ // be less than 1/3 of actual conditions.
+ _pressure_node =
+ fgGetNode("/environment/pressure-inhg", true);
+ _sea_node =
+ fgGetNode("/environment/pressure-sea-level-inhg", true);
+ _speed_up_node =
+ fgGetNode("/sim/speed-up", true);
+ _speed_node =
+ fgGetNode("/instrumentation/inst-vertical-speed-indicator/indicated-speed-fps",
+ true);
+ _speed_min_node =
+ fgGetNode("/instrumentation/inst-vertical-speed-indicator/indicated-speed-fpm",
+ true);
+
+ // Initialize at ambient pressure
+ _internal_pressure_inhg = _pressure_node->getDoubleValue();
+}
+
+
+void InstVerticalSpeedIndicator::update (double dt)
+{
+ if (_serviceable_node->getBoolValue())
+ {
+ // avoids hang, when freeze
+ if( !_freeze_node->getBoolValue() )
+ {
+ double pressure_inhg = _pressure_node->getDoubleValue();
+ double sea_inhg = _sea_node->getDoubleValue();
+ double speed_up = _speed_up_node->getDoubleValue();
+
+ // must work by speed up
+ if( speed_up > 1 )
+ {
+ dt *= speed_up;
+ }
+
+ // limit effect of external environment
+ double rate_sea_inhg_per_s = ( sea_inhg - _internal_sea_inhg ) / dt;
+
+ if( rate_sea_inhg_per_s > - MAX_INHG_PER_S && rate_sea_inhg_per_s < MAX_INHG_PER_S )
+ {
+ double rate_inhg_per_s = ( pressure_inhg - _internal_pressure_inhg ) / dt;
+
+ // IVSI determines alone the current altitude, without altimeter setting.
+ // Altimeter setting is 29.92 above 10000 or 18000 ft.
+ // Below this level, the slope is slightly wrong.
+ double altitude_ft = _altitude_table->interpolate( SEA_LEVEL_INHG - pressure_inhg );
+ double slope_inhg = _pressure_table->interpolate( altitude_ft );
+
+
+ double last_speed_ft_per_s = _speed_ft_per_s;
+
+ // slope at 900 m
+ _speed_ft_per_s = - rate_inhg_per_s * 2952.75591 / slope_inhg;
+
+ // filter noise
+ _speed_ft_per_s = fgGetLowPass( last_speed_ft_per_s, _speed_ft_per_s,
+ dt * RESPONSIVENESS );
+ }
+
+ _speed_node->setDoubleValue( _speed_ft_per_s );
+ _speed_min_node->setDoubleValue( _speed_ft_per_s * 60.0 );
+
+ // backup
+ _internal_pressure_inhg = pressure_inhg;
+ _internal_sea_inhg = sea_inhg;
+ }
+ }
+}
+
+// end of inst_vertical_speed_indicator.cxx
--- /dev/null
+// inst_vertical_speed_indicator.hxx -- Instantaneous VSI (emulation calibrated to standard atmosphere).
+//
+// Started September 2004.
+//
+// Copyright (C) 2004
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+//
+
+#ifndef __INST_VERTICAL_SPEED_INDICATOR_HXX
+#define __INST_VERTICAL_SPEED_INDICATOR_HXX 1
+
+#ifndef __cplusplus
+# error This library requires C++
+#endif
+
+#include <simgear/props/props.hxx>
+#include <simgear/structure/subsystem_mgr.hxx>
+
+
+class SGInterpTable;
+
+
+/**
+ * Model an instantaneous VSI tied to the external pressure.
+ *
+ * Input properties:
+ *
+ * /instrumentation/inst-vertical-speed-indicator/serviceable
+ * /environment/pressure-inhg
+ * /environment/pressure-sea-level-inhg
+ * /sim/speed-up
+ * /sim/freeze/master
+ *
+ * Output properties:
+ *
+ * /instrumentation/inst-vertical-speed-indicator/indicated-speed-fps
+ * /instrumentation/inst-vertical-speed-indicator/indicated-speed-fpm
+ */
+class InstVerticalSpeedIndicator : public SGSubsystem
+{
+
+public:
+
+ InstVerticalSpeedIndicator ( SGPropertyNode *node );
+ virtual ~InstVerticalSpeedIndicator ();
+
+ virtual void init ();
+ virtual void update (double dt);
+
+private:
+
+ double _internal_pressure_inhg;
+ double _internal_sea_inhg;
+
+ double _speed_ft_per_s;
+
+ string name;
+ int num;
+
+ SGPropertyNode_ptr _serviceable_node;
+ SGPropertyNode_ptr _freeze_node;
+ SGPropertyNode_ptr _pressure_node;
+ SGPropertyNode_ptr _sea_node;
+ SGPropertyNode_ptr _speed_up_node;
+ SGPropertyNode_ptr _speed_node;
+ SGPropertyNode_ptr _speed_min_node;
+
+ SGInterpTable * _pressure_table;
+ SGInterpTable * _altitude_table;
+};
+
+#endif // __INST_VERTICAL_SPEED_INDICATOR_HXX
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