250 lines
7.3 KiB
C++
250 lines
7.3 KiB
C++
// inst_vertical_speed_indicator.cxx
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// -- Instantaneous VSI (emulation calibrated to standard atmosphere).
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//
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// Started September 2004.
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//
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// Copyright (C) 2004
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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//
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include <limits>
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#include <simgear/math/interpolater.hxx>
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#include "inst_vertical_speed_indicator.hxx"
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#include <Main/fg_props.hxx>
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#include <Main/util.hxx>
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// Altitude based on pressure difference from sea level.
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//
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// See http://www.pdas.com/programs/atmos.f90, the tables match exactly
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// environment.cxx (Standard 1976).
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// Example :
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// - at 27900 m the level is 20 km :
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// geopotential altitude 27.9 x 6369 / ( 27.9 + 6369) = 27.778 km.
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// - deltah = 27.778 - 20 = 7.778 km and tbase 216.65 degK.
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// - delta = 5.403295E-2 x exp( -34.163195 x 7.778 / 216.65 ) = 0.016.
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// - pressure = (1 - delta ) x 29.92 = 29.44 inhg.
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// - to construct the tables, round delta to 3 digits.
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// altitude ft, pressure step inHG
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static double pressure_data[][2] = {
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{ 0.00, 3.33 }, // guess !
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{ 2952.76, 3.05 },
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{ 5905.51, 2.81 },
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{ 8858.27, 2.55 },
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{ 11811.02, 2.33 },
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{ 14763.78, 2.13 },
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{ 17716.54, 1.91 },
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{ 20669.29, 1.77 },
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{ 23622.05, 1.58 },
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{ 26574.80, 1.49 },
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{ 29527.56, 1.20 },
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{ 32480.31, 1.14 },
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{ 35433.07, 1.05 },
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{ 38385.83, 0.90 },
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{ 41338.58, 0.80 },
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{ 44291.34, 0.69 },
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{ 47244.09, 0.60 },
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{ 50196.85, 0.51 },
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{ 53149.61, 0.45 },
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{ 56102.36, 0.39 },
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{ 59055.12, 0.33 },
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{ 62007.87, 0.30 },
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{ 64960.63, 0.26 },
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{ 67913.39, 0.21 },
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{ 70866.14, 0.18 },
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{ 73818.90, 0.18 },
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{ 76771.65, 0.15 },
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{ 79724.41, 0.12 },
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{ 82677.17, 0.12 },
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{ 85629.92, 0.09 },
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{ 88582.68, 0.09 },
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{ 91535.43, 0.06 },
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{ 94488.19, 0.06 },
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{ 97440.94, 0.06 },
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{ 100393.70, 0.06 },
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{ -1, -1 }
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};
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// pressure difference inHG, altitude ft
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static double altitude_data[][2] = {
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{ 0.00, 0.00 },
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{ 3.05, 2952.76 },
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{ 5.86, 5905.51 },
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{ 8.41, 8858.27 },
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{ 10.74, 11811.02 },
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{ 12.87, 14763.78 },
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{ 14.78, 17716.54 },
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{ 16.55, 20669.29 },
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{ 18.13, 23622.05 },
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{ 19.62, 26574.80 },
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{ 20.82, 29527.56 },
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{ 21.96, 32480.31 },
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{ 23.01, 35433.07 },
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{ 23.91, 38385.83 },
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{ 24.71, 41338.58 },
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{ 25.40, 44291.34 },
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{ 26.00, 47244.09 },
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{ 26.51, 50196.85 },
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{ 26.96, 53149.61 },
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{ 27.35, 56102.36 },
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{ 27.68, 59055.12 },
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{ 27.98, 62007.87 },
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{ 28.24, 64960.63 },
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{ 28.45, 67913.39 },
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{ 28.63, 70866.14 },
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{ 28.81, 73818.90 },
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{ 28.96, 76771.65 },
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{ 29.08, 79724.41 },
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{ 29.20, 82677.17 },
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{ 29.29, 85629.92 },
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{ 29.38, 88582.68 },
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{ 29.44, 91535.43 },
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{ 29.50, 94488.19 },
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{ 29.56, 97440.94 },
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{ 29.62, 100393.70 },
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{ -1, -1 }
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};
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// SI constants
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#define SEA_LEVEL_INHG 29.92
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// A higher number means more responsive.
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#define RESPONSIVENESS 5.0
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// External environment
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#define MAX_INHG_PER_S 0.0002
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InstVerticalSpeedIndicator::InstVerticalSpeedIndicator ( SGPropertyNode *node ) :
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_name(node->getStringValue("name", "inst-vertical-speed-indicator")),
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_num(node->getIntValue("number", 0)),
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_internal_pressure_inhg( SEA_LEVEL_INHG ),
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_internal_sea_inhg( SEA_LEVEL_INHG ),
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_speed_ft_per_s( 0 ),
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_pressure_table(new SGInterpTable),
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_altitude_table(new SGInterpTable)
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{
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int i;
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for ( i = 0; pressure_data[i][0] != -1; i++)
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_pressure_table->addEntry( pressure_data[i][0], pressure_data[i][1] );
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for ( i = 0; altitude_data[i][0] != -1; i++)
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_altitude_table->addEntry( altitude_data[i][0], altitude_data[i][1] );
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}
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InstVerticalSpeedIndicator::~InstVerticalSpeedIndicator ()
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{
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delete _pressure_table;
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delete _altitude_table;
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}
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void InstVerticalSpeedIndicator::init ()
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{
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SGPropertyNode *node = fgGetNode("/instrumentation", true)->getChild(_name, _num, true);
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_serviceable_node =
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node->getNode("serviceable", true);
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_freeze_node =
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fgGetNode("/sim/freeze/master", true);
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// A real IVSI is operated by static pressure changes.
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// It operates like a conventional VSI, except that an internal sensor
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// detects load factors, to momentarily alters the static pressure
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// (with lag).
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// It appears lag free at subsonic speed; at high altitude indication may
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// be less than 1/3 of actual conditions.
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_pressure_node =
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fgGetNode("/environment/pressure-inhg", true);
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_sea_node =
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fgGetNode("/environment/pressure-sea-level-inhg", true);
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_speed_up_node =
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fgGetNode("/sim/speed-up", true);
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_speed_node =
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node->getNode("indicated-speed-fps", true);
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_speed_min_node =
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node->getNode("indicated-speed-fpm", true);
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}
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void InstVerticalSpeedIndicator::reinit ()
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{
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// Initialize at ambient pressure
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_internal_pressure_inhg = _pressure_node->getDoubleValue();
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_speed_ft_per_s = 0.0;
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_internal_sea_inhg = _sea_node->getDoubleValue();
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}
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void InstVerticalSpeedIndicator::update (double dt)
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{
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if (_serviceable_node->getBoolValue())
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{
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// avoids hang, when freeze
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if( !_freeze_node->getBoolValue() && std::numeric_limits<double>::min() < fabs(dt))
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{
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double pressure_inhg = _pressure_node->getDoubleValue();
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double sea_inhg = _sea_node->getDoubleValue();
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double speed_up = _speed_up_node->getDoubleValue();
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// must work by speed up
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if( speed_up > 1 )
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{
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dt *= speed_up;
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}
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// limit effect of external environment
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double rate_sea_inhg_per_s = ( sea_inhg - _internal_sea_inhg ) / dt;
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if( rate_sea_inhg_per_s > - MAX_INHG_PER_S && rate_sea_inhg_per_s < MAX_INHG_PER_S )
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{
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double rate_inhg_per_s = ( pressure_inhg - _internal_pressure_inhg ) / dt;
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// IVSI determines alone the current altitude, without altimeter setting.
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// Altimeter setting is 29.92 above 10000 or 18000 ft.
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// Below this level, the slope is slightly wrong.
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double altitude_ft = _altitude_table->interpolate( SEA_LEVEL_INHG - pressure_inhg );
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double slope_inhg = _pressure_table->interpolate( altitude_ft );
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double last_speed_ft_per_s = _speed_ft_per_s;
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// slope at 900 m
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_speed_ft_per_s = - rate_inhg_per_s * 2952.75591 / slope_inhg;
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// filter noise
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_speed_ft_per_s = fgGetLowPass( last_speed_ft_per_s, _speed_ft_per_s,
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dt * RESPONSIVENESS );
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}
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_speed_node->setDoubleValue( _speed_ft_per_s );
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_speed_min_node->setDoubleValue( _speed_ft_per_s * 60.0 );
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// backup
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_internal_pressure_inhg = pressure_inhg;
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_internal_sea_inhg = sea_inhg;
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}
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}
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}
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// end of inst_vertical_speed_indicator.cxx
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