506 lines
15 KiB
C++
506 lines
15 KiB
C++
// steam.cxx - Steam Gauge Calculations
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//
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// Copyright (C) 2000 Alexander Perry - alex.perry@ieee.org
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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., 675 Mass Ave, Cambridge, MA 02139, USA.
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//
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// $Id$
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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 <simgear/compiler.h>
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#include STL_IOSTREAM
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#include <simgear/constants.h>
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#include <simgear/math/sg_types.hxx>
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#include <simgear/misc/props.hxx>
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#include <Main/fg_props.hxx>
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#include <Aircraft/aircraft.hxx>
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#ifdef FG_WEATHERCM
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# include <WeatherCM/FGLocalWeatherDatabase.h>
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#else
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# include <Environment/environment_mgr.hxx>
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# include <Environment/environment.hxx>
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#endif
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SG_USING_NAMESPACE(std);
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#include "radiostack.hxx"
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#include "steam.hxx"
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static bool isTied = false;
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////////////////////////////////////////////////////////////////////////
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// Constructor and destructor.
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////////////////////////////////////////////////////////////////////////
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FGSteam::FGSteam ()
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:
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the_ALT_ft(0.0),
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the_ALT_datum_mb(1013.0),
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the_TC_rad(0.0),
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the_TC_std(0.0),
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the_STATIC_inhg(29.92),
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the_VACUUM_inhg(0.0),
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the_VSI_fps(0.0),
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the_VSI_case(29.92),
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the_MH_deg(0.0),
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the_MH_degps(0.0),
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the_MH_err(0.0),
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the_DG_deg(0.0),
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the_DG_degps(0.0),
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the_DG_inhg(0.0),
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the_DG_err(0.0),
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_UpdateTimePending(1000000)
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{
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}
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FGSteam::~FGSteam ()
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{
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}
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void
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FGSteam::init ()
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{
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_heading_deg_node = fgGetNode("/orientation/heading-deg", true);
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_mag_var_deg_node = fgGetNode("/environment/magnetic-variation-deg", true);
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_mag_dip_deg_node = fgGetNode("/environment/magnetic-dip-deg", true);
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_engine_0_rpm_node = fgGetNode("/engines/engine[0]/rpm", true);
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_pressure_inhg_node = fgGetNode("environment/pressure-inhg", true);
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}
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void
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FGSteam::update (double dt_sec)
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{
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_UpdateTimePending += dt_sec;
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_CatchUp();
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}
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void
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FGSteam::bind ()
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{
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fgTie("/steam/airspeed-kt", this, &FGSteam::get_ASI_kias);
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fgSetArchivable("/steam/airspeed-kt");
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fgTie("/steam/altitude-ft", this, &FGSteam::get_ALT_ft);
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fgSetArchivable("/steam/altitude-ft");
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fgTie("/steam/altimeter-datum-mb", this,
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&FGSteam::get_ALT_datum_mb, &FGSteam::set_ALT_datum_mb,
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false); /* don't modify the value */
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fgSetArchivable("/steam/altimeter-datum-mb");
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fgTie("/steam/turn-rate", this, &FGSteam::get_TC_std);
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fgSetArchivable("/steam/turn-rate");
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fgTie("/steam/slip-skid",this, &FGSteam::get_TC_rad);
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fgSetArchivable("/steam/slip-skid");
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fgTie("/steam/vertical-speed-fps", this, &FGSteam::get_VSI_fps);
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fgSetArchivable("/steam/vertical-speed-fps");
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fgTie("/steam/gyro-compass-deg", this, &FGSteam::get_DG_deg);
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fgSetArchivable("/steam/gyro-compass-deg");
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// fgTie("/steam/adf-deg", FGSteam::get_HackADF_deg);
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// fgSetArchivable("/steam/adf-deg");
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fgTie("/steam/gyro-compass-error-deg", this,
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&FGSteam::get_DG_err, &FGSteam::set_DG_err,
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false); /* don't modify the value */
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fgSetArchivable("/steam/gyro-compass-error-deg");
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fgTie("/steam/mag-compass-deg", this, &FGSteam::get_MH_deg);
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fgSetArchivable("/steam/mag-compass-deg");
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}
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void
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FGSteam::unbind ()
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{
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fgUntie("/steam/airspeed-kt");
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fgUntie("/steam/altitude-ft");
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fgUntie("/steam/altimeter-datum-mb");
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fgUntie("/steam/turn-rate");
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fgUntie("/steam/slip-skid");
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fgUntie("/steam/vertical-speed-fps");
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fgUntie("/steam/gyro-compass-deg");
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fgUntie("/steam/gyro-compass-error-deg");
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fgUntie("/steam/mag-compass-deg");
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}
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////////////////////////////////////////////////////////////////////////
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// Declare the functions that read the variables
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////////////////////////////////////////////////////////////////////////
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double
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FGSteam::get_ALT_ft () const
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{
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return the_ALT_ft;
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}
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double
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FGSteam::get_ALT_datum_mb () const
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{
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return the_ALT_datum_mb;
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}
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void
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FGSteam::set_ALT_datum_mb (double datum_mb)
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{
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the_ALT_datum_mb = datum_mb;
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}
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double
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FGSteam::get_ASI_kias () const
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{
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return fgGetDouble("/velocities/airspeed-kt");
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}
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double
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FGSteam::get_VSI_fps () const
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{
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return the_VSI_fps;
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}
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double
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FGSteam::get_VACUUM_inhg () const
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{
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return the_VACUUM_inhg;
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}
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double
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FGSteam::get_MH_deg () const
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{
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return the_MH_deg;
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}
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double
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FGSteam::get_DG_deg () const
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{
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return the_DG_deg;
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}
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double
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FGSteam::get_DG_err () const
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{
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return the_DG_err;
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}
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void
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FGSteam::set_DG_err (double approx_magvar)
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{
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the_DG_err = approx_magvar;
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}
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double
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FGSteam::get_TC_rad () const
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{
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return the_TC_rad;
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}
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double
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FGSteam::get_TC_std () const
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{
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return the_TC_std;
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}
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////////////////////////////////////////////////////////////////////////
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// Recording the current time
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////////////////////////////////////////////////////////////////////////
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/* tc should be (elapsed_time_between_updates / desired_smoothing_time) */
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void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
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{
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if ( tc < 0.0 )
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{ if ( tc < -1.0 )
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{ /* time went backwards; kill the filter */
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(*outthe) = inthe;
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} else
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{ /* ignore mildly negative time */
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}
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} else
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if ( tc < 0.2 )
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{ /* Normal mode of operation; fast approximation to exp(-tc) */
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(*outthe) = (*outthe) * ( 1.0 - tc )
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+ inthe * tc;
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} else
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if ( tc > 5.0 )
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{ /* Huge time step; assume filter has settled */
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(*outthe) = inthe;
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} else
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{ /* Moderate time step; non linear response */
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double keep = exp ( -tc );
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// printf ( "ARP: Keep is %f\n", keep );
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(*outthe) = (*outthe) * keep
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+ inthe * ( 1.0 - keep );
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}
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}
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#define INHG_TO_MB 33.86388 /* Inches_of_mercury * INHG_TO_MB == millibars. */
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// Convert air pressure to altitude by ICAO Standard Atmosphere
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double pressInHgToAltFt(double p_inhg)
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{
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// Ref. Aviation Formulary, Ed Williams, www.best.com/~williams/avform.htm
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const double P_0 = 29.92126; // Std. MSL pressure, inHg. (=1013.25 mb)
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const double p_Tr = 0.2233609 * P_0; // Pressure at tropopause, same units.
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const double h_Tr = 36089.24; // Alt of tropopause, ft. (=11.0 km)
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if (p_inhg > p_Tr) // 0.0 to 11.0 km
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return (1.0 - pow((p_inhg / P_0), 1.0 / 5.2558797)) / 6.8755856e-6;
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return h_Tr + log10(p_inhg / p_Tr) / -4.806346e-5; // 11.0 to 20.0 km
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// We could put more code for higher altitudes here.
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}
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// Convert altitude to air pressure by ICAO Standard Atmosphere
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double altFtToPressInHg(double alt_ft)
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{
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// Ref. Aviation Formulary, Ed Williams, www.best.com/~williams/avform.htm
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const double P_0 = 29.92126; // Std. MSL pressure, inHg. (=1013.25 mb)
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const double p_Tr = 0.2233609 * P_0; // Pressure at tropopause, same units.
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const double h_Tr = 36089.24; // Alt of tropopause, ft. (=11.0 km)
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if (alt_ft < h_Tr) // 0.0 to 11.0 km
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return P_0 * pow(1.0 - 6.8755856e-6 * alt_ft, 5.2558797);
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return p_Tr * exp(-4.806346e-5 * (alt_ft - h_Tr)); // 11.0 to 20.0 km
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// We could put more code for higher altitudes here.
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}
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////////////////////////////////////////////////////////////////////////
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// Here the fun really begins
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////////////////////////////////////////////////////////////////////////
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void FGSteam::_CatchUp()
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{
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if ( _UpdateTimePending != 0 )
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{
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double dt = _UpdateTimePending;
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double AccN, AccE, AccU;
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/* int i, j; */
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double d, the_ENGINE_rpm;
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/**************************
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Someone has called our update function and
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it turns out that we are running somewhat behind.
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Here, we recalculate everything for a 'dt' second step.
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*/
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/**************************
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The ball responds to the acceleration vector in the body
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frame, only the components perpendicular to the longitudinal
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axis of the aircraft. This is only related to actual
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side slip for a symmetrical aircraft which is not touching
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the ground and not changing its attitude. Math simplifies
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by assuming (for small angles) arctan(x)=x in radians.
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Obvious failure mode is the absence of liquid in the
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tube, which is there to damp the motion, so that instead
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the ball will bounce around, hitting the tube ends.
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More subtle flaw is having it not move or a travel limit
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occasionally due to some dirt in the tube or on the ball.
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*/
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d = -current_aircraft.fdm_state->get_A_Z_pilot();
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if ( d < 1 ) d = 1;
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set_lowpass ( & the_TC_rad,
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current_aircraft.fdm_state->get_A_Y_pilot () / d,
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dt );
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/**************************
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The rate of turn indication is from an electric gyro.
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We should have it spin up with the master switch.
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It is mounted at a funny angle so that it detects
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both rate of bank (i.e. rolling into and out of turns)
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and the rate of turn (i.e. how fast heading is changing).
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*/
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set_lowpass ( & the_TC_std,
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current_aircraft.fdm_state->get_Phi_dot ()
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* SGD_RADIANS_TO_DEGREES / 20.0 +
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current_aircraft.fdm_state->get_Psi_dot ()
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* SGD_RADIANS_TO_DEGREES / 3.0 , dt );
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/**************************
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We want to know the pilot accelerations,
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to compute the magnetic compass errors.
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*/
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AccN = current_aircraft.fdm_state->get_V_dot_north();
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AccE = current_aircraft.fdm_state->get_V_dot_east();
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AccU = current_aircraft.fdm_state->get_V_dot_down()
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- 9.81 * SG_METER_TO_FEET;
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if ( fabs(the_TC_rad) > 0.2 /* 2.0 */ )
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{ /* Massive sideslip jams it; it stops turning */
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the_MH_degps = 0.0;
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the_MH_err = _heading_deg_node->getDoubleValue() - the_MH_deg;
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} else
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{ double MagDip, MagVar, CosDip;
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double FrcN, FrcE, FrcU, AccTot;
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double EdgN, EdgE, EdgU;
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double TrqN, TrqE, TrqU, Torque;
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/* Find a force vector towards exact magnetic north */
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MagVar = _mag_var_deg_node->getDoubleValue()
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/ SGD_RADIANS_TO_DEGREES;
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MagDip = _mag_var_deg_node->getDoubleValue()
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/ SGD_RADIANS_TO_DEGREES;
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CosDip = cos ( MagDip );
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FrcN = CosDip * cos ( MagVar );
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FrcE = CosDip * sin ( MagVar );
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FrcU = sin ( MagDip );
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/* Rotation occurs around acceleration axis,
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but axis magnitude is irrelevant. So compute it. */
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AccTot = AccN*AccN + AccE*AccE + AccU*AccU;
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if ( AccTot > 1.0 ) AccTot = sqrt ( AccTot );
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else AccTot = 1.0;
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/* Force applies to north marking on compass card */
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EdgN = cos ( the_MH_err / SGD_RADIANS_TO_DEGREES );
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EdgE = sin ( the_MH_err / SGD_RADIANS_TO_DEGREES );
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EdgU = 0.0;
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/* Apply the force to the edge to get torques */
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TrqN = EdgE * FrcU - EdgU * FrcE;
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TrqE = EdgU * FrcN - EdgN * FrcU;
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TrqU = EdgN * FrcE - EdgE * FrcN;
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/* Select the component parallel to the axis */
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Torque = ( TrqN * AccN +
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TrqE * AccE +
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TrqU * AccU ) * 5.0 / AccTot;
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/* The magnetic compass has angular momentum,
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so we apply a torque to it and wait */
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if ( dt < 1.0 )
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{ the_MH_degps= the_MH_degps * (1.0 - dt) - Torque;
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the_MH_err += dt * the_MH_degps;
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}
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if ( the_MH_err > 180.0 ) the_MH_err -= 360.0; else
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if ( the_MH_err < -180.0 ) the_MH_err += 360.0;
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the_MH_deg = _heading_deg_node->getDoubleValue() - the_MH_err;
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}
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/**************************
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This is not actually correct, but provides a
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scaling capability for the vacuum pump later on.
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When we have a real engine model, we can ask it.
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*/
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the_ENGINE_rpm = _engine_0_rpm_node->getDoubleValue();
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/**************************
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First, we need to know what the static line is reporting,
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which is a whole simulation area in itself.
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We filter the actual value by one second to
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account for the line impedance of the plumbing.
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*/
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#ifdef FG_WEATHERCM
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sgVec3 plane_pos = { cur_fdm_state->get_Latitude(),
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cur_fdm_state->get_Longitude(),
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cur_fdm_state->get_Altitude() * SG_FEET_TO_METER };
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double static_inhg = WeatherDatabase->get(plane_pos).AirPressure *
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(0.01 / INHG_TO_MB);
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#else
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double static_inhg = _pressure_inhg_node->getDoubleValue();
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#endif
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set_lowpass ( & the_STATIC_inhg, static_inhg, dt );
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/*
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NO alternate static source error (student feature),
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NO possibility of blockage (instructor feature),
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NO slip-induced error, important for C172 for example.
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*/
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/**************************
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Altimeter.
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ICAO standard atmosphere MSL pressure is 1013.25 mb, and pressure
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gradient is about 28 ft per mb at MSL increasing to about 32 at
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5000 and 38 at 10000 ft.
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Standard altimeters apply the subscale offset to the output altitude,
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not to the input pressure; I don't know exactly what pressure gradient
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they assume for this. I choose to make it accurate at low altitudes.
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Remember, we are trying to simulate a real altimeter, not an ideal one.
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*/
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set_lowpass ( & the_ALT_ft,
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pressInHgToAltFt(the_STATIC_inhg) +
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(the_ALT_datum_mb - 1013.25) * 28.0, /* accurate at low alt. */
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dt * 10 ); /* smoothing time 0.1 s */
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/**************************
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The VSI case is a low-pass filter of the static line pressure.
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The instrument reports the difference, scaled to approx ft.
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NO option for student to break glass when static source fails.
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NO capability for a fixed non-zero reading when level.
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NO capability to have a scaling error of maybe a factor of two.
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*/
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the_VSI_fps = ( the_VSI_case - the_STATIC_inhg )
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* 10000.0; /* manual scaling factor */
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set_lowpass ( & the_VSI_case, the_STATIC_inhg, dt/6.0 );
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/**************************
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The engine driven vacuum pump is directly attached
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to the engine shaft, so each engine rotation pumps
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a fixed volume. The amount of air in that volume
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is determined by the vacuum line's internal pressure.
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The instruments are essentially leaking air like
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a fixed source impedance from atmospheric pressure.
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The regulator provides a digital limit setting,
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which is open circuit unless the pressure drop is big.
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Thus, we can compute the vacuum line pressure directly.
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We assume that there is negligible reservoir space.
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NO failure of the pump supported (yet)
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*/
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the_VACUUM_inhg = the_STATIC_inhg *
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the_ENGINE_rpm / ( the_ENGINE_rpm + 10000.0 );
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if ( the_VACUUM_inhg > 5.0 )
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the_VACUUM_inhg = 5.0;
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/*
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> I was merely going to do the engine rpm driven vacuum pump for both
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> the AI and DG, have the gyros spin down down in power off descents,
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> have it tumble when you exceed the usual pitch or bank limits,
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> put in those insidious turning errors ... for now anyway.
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*/
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if ( _UpdateTimePending > 999999 )
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the_DG_err = fgGetDouble("/environment/magnetic-variation-deg");
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the_DG_degps = 0.01; /* HACK! */
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if (dt<1.0) the_DG_err += dt * the_DG_degps;
|
||
the_DG_deg = _heading_deg_node->getDoubleValue() - the_DG_err;
|
||
|
||
/**************************
|
||
Finished updates, now clear the timer
|
||
*/
|
||
_UpdateTimePending = 0;
|
||
} else {
|
||
// cout << "0 Updates pending" << endl;
|
||
}
|
||
}
|
||
|
||
|
||
////////////////////////////////////////////////////////////////////////
|
||
// Everything below is a transient hack; expect it to disappear
|
||
////////////////////////////////////////////////////////////////////////
|
||
|
||
double FGSteam::get_HackOBS1_deg () const
|
||
{
|
||
return current_radiostack->get_navcom1()->get_nav_radial();
|
||
}
|
||
|
||
double FGSteam::get_HackOBS2_deg () const
|
||
{
|
||
return current_radiostack->get_navcom2()->get_nav_radial();
|
||
}
|
||
|
||
|
||
// end of steam.cxx
|