fly/flightgear
1
0
Fork 0
Code Activity

Tweaks to add an altitude indicator adjustment.

Browse source
This commit is contained in:
curt 2001-01-23 07:17:47 +00:00
parent 1bc2a66b1c
commit 1c000fef96
3 changed files with 65 additions and 20 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

66
src/Cockpit/steam.cxx
View file

@ -53,9 +53,16 @@ static bool isTied = false;
double FGSteam::the_STATIC_inhg = 29.92;
double FGSteam::the_ALT_ft = 0.0;
double FGSteam::the_ALT_ft = 0.0; // Indicated altitude
double FGSteam::get_ALT_ft() { _CatchUp(); return the_ALT_ft; }
double FGSteam::the_ALT_datum_mb = 1013.0;
double FGSteam::get_ALT_datum_mb() { return the_ALT_datum_mb; }
void FGSteam::set_ALT_datum_mb ( double datum_mb ) {
the_ALT_datum_mb = datum_mb;
}
double FGSteam::get_ASI_kias() { return FGBFI::getAirspeed(); }
double FGSteam::the_VSI_case = 29.92;
@ -104,6 +111,9 @@ void FGSteam::update ( int timesteps )
isTied = true;
fgTie("/steam/airspeed", FGSteam::get_ASI_kias);
fgTie("/steam/altitude", FGSteam::get_ALT_ft);
fgTie("/steam/altimeter-datum-mb",
FGSteam::get_ALT_datum_mb, FGSteam::set_ALT_datum_mb,
false); /* don't modify the value */
fgTie("/steam/turn-rate", FGSteam::get_TC_std);
fgTie("/steam/slip-skid", FGSteam::get_TC_rad);
fgTie("/steam/vertical-speed", FGSteam::get_VSI_fps);
@ -124,6 +134,7 @@ void FGSteam::update ( int timesteps )
#undef DF2
/* tc should be (elapsed_time_between_updates / desired_smoothing_time) */
void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
{
if ( tc < 0.0 )
@ -135,7 +146,7 @@ void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
}
} else
if ( tc < 0.2 )
{ /* Normal mode of operation */
{ /* Normal mode of operation; fast approximation to exp(-tc) */
(*outthe) = (*outthe) * ( 1.0 - tc )
+ inthe * tc;
} else
@ -152,6 +163,24 @@ void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
}
#define INHG_TO_MB 33.86388 /* Inches_of_mercury * INHG_TO_MB == millibars. */
// Convert air pressure to altitude by ICAO Standard Atmosphere
double pressInHgToAltFt(double p_inhg)
{
// Ref. Aviation Formulary, Ed Williams, www.best.com/~williams/avform.htm
const double P_0 = 29.92126; // Std. MSL pressure, inHg. (=10135.25 mb)
const double p_Tr = 0.2233609 * P_0; // Pressure at tropopause, same units.
const double h_Tr = 36089.24; // Alt of tropopause, ft. (=11.0 km)
// return (P_0 - p_inhg) * 1000.0; // ### crude approx. for low alt's
if (p_inhg > p_Tr) // 0.0 to 11.0 km
return (1.0 - pow((p_inhg / P_0), 1.0 / 5.2558797)) / 6.8755856e-6;
return h_Tr + log10(p_inhg / p_Tr) / -4.806346e-5; // 11.0 to 20.0 km
// We could put more code for higher altitudes here.
}
////////////////////////////////////////////////////////////////////////
// Here the fun really begins
@ -287,24 +316,20 @@ void FGSteam::_CatchUp()
*/
the_ENGINE_rpm = controls.get_throttle(0) * 26.0;
/**************************
This is just temporary, until the static source works,
so we just filter the actual value by one second to
account for the line impedance of the plumbing.
*/
set_lowpass ( & the_ALT_ft, FGBFI::getAltitude(), dt );
/**************************
First, we need to know what the static line is reporting,
which is a whole simulation area in itself. For now, we cheat.
We filter the actual value by one second to
account for the line impedance of the plumbing.
*/
the_STATIC_inhg = 29.92;
i = (int) the_ALT_ft;
double static_inhg = 29.92;
i = (int) FGBFI::getAltitude();
while ( i > 9000 )
{ the_STATIC_inhg *= 0.707;
{ static_inhg *= 0.707;
i -= 9000;
}
the_STATIC_inhg *= ( 1.0 - 0.293 * i / 9000.0 );
static_inhg *= ( 1.0 - 0.293 * i / 9000.0 );
set_lowpass ( & the_STATIC_inhg, static_inhg, dt );
/*
NO alternate static source error (student feature),
@ -312,6 +337,21 @@ void FGSteam::_CatchUp()
NO slip-induced error, important for C172 for example.
*/
/**************************
Altimeter.
ICAO standard atmosphere MSL pressure is 1013.25 mb, and pressure
gradient is about 28 ft per mb at MSL increasing to about 32 at
5000 and 38 at 10000 ft.
Standard altimeters apply the subscale offset to the output altitude,
not to the input pressure; I don't know exactly what pressure gradient
they assume for this. I choose to make it accurate at low altitudes.
Remember, we are trying to simulate a real altimeter, not an ideal one.
*/
set_lowpass ( & the_ALT_ft,
pressInHgToAltFt(the_STATIC_inhg) +
(the_ALT_datum_mb - 1013.25) * 28.0, /* accurate at low alt. */
dt * 10 ); /* smoothing time 0.1 s */
/**************************
The VSI case is a low-pass filter of the static line pressure.
The instrument reports the difference, scaled to approx ft.

5
src/Cockpit/steam.hxx
View file

@ -72,6 +72,10 @@ public:
// Engine Gauges
static double get_VACUUM_inhg ();
// Atmosphere
static double get_ALT_datum_mb ();
static void set_ALT_datum_mb(double datum_mb);
// Hacks ... temporary stuff
static double get_HackVOR1_deg ();
static double get_HackOBS1_deg ();
@ -83,6 +87,7 @@ public:
private:
static double the_ALT_ft;
static double the_ALT_datum_mb;
static double the_TC_rad, the_TC_std;
static double the_STATIC_inhg, the_VACUUM_inhg;
static double the_VSI_fps, the_VSI_case;

14
src/Main/main.cxx
View file

@ -1058,18 +1058,18 @@ static void fgMainLoop( void ) {
double mp_factor;
if ( cur_fdm_state->get_engine(0) != NULL ) {
mp_factor =
cur_fdm_state->get_engine(0)->get_Manifold_Pressure() / 28;
cur_fdm_state->get_engine(0)->get_Manifold_Pressure() / 100;
} else {
mp_factor = 1.0;
mp_factor = 0.3;
}
// cout << "mp = "
// << cur_fdm_state->get_engine(0)->get_Manifold_Pressure()
// << endl;
/* cout << "mp = "
<< cur_fdm_state->get_engine(0)->get_Manifold_Pressure()
<< endl; */
double volume = mp_factor;
double volume = 0.3 + mp_factor;
if ( volume < 0.3 ) { volume = 0.3; }
if ( volume > 2.0 ) { volume = 2.0; }
if ( volume > 1.0 ) { volume = 1.0; }
// cout << "volume = " << volume << endl;
pitch_envelope.setStep ( 0, 0.01, pitch );