1 // steam.cxx - Steam Gauge Calculations
3 // Copyright (C) 2000 Alexander Perry - alex.perry@ieee.org
5 // This program is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU General Public License as
7 // published by the Free Software Foundation; either version 2 of the
8 // License, or (at your option) any later version.
10 // This program is distributed in the hope that it will be useful, but
11 // WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // General Public License for more details.
15 // You should have received a copy of the GNU General Public License
16 // along with this program; if not, write to the Free Software
17 // Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
26 #if defined( FG_HAVE_NATIVE_SGI_COMPILERS )
27 # include <iostream.h>
32 #include <simgear/constants.h>
33 #include <simgear/misc/props.hxx>
34 #include <simgear/math/fg_types.hxx>
35 #include <Aircraft/aircraft.hxx>
36 #include <Main/options.hxx>
37 #include <Main/bfi.hxx>
38 #include <NetworkOLK/features.hxx>
40 FG_USING_NAMESPACE(std);
42 #include "radiostack.hxx"
45 static bool isTied = false;
49 ////////////////////////////////////////////////////////////////////////
50 // Declare the functions that read the variables
51 ////////////////////////////////////////////////////////////////////////
53 // Anything that reads the BFI directly is not implemented at all!
56 double FGSteam::the_STATIC_inhg = 29.92;
57 double FGSteam::the_ALT_ft = 0.0;
58 double FGSteam::get_ALT_ft() { _CatchUp(); return the_ALT_ft; }
60 double FGSteam::get_ASI_kias() { return FGBFI::getAirspeed(); }
62 double FGSteam::the_VSI_case = 29.92;
63 double FGSteam::the_VSI_fps = 0.0;
64 double FGSteam::get_VSI_fps() { _CatchUp(); return the_VSI_fps; }
66 double FGSteam::the_VACUUM_inhg = 0.0;
67 double FGSteam::get_VACUUM_inhg() { _CatchUp(); return the_VACUUM_inhg; }
69 double FGSteam::the_MH_err = 0.0;
70 double FGSteam::the_MH_deg = 0.0;
71 double FGSteam::the_MH_degps = 0.0;
72 double FGSteam::get_MH_deg () { _CatchUp(); return the_MH_deg; }
74 double FGSteam::the_DG_err = 0.0;
75 double FGSteam::the_DG_deg = 0.0;
76 double FGSteam::the_DG_degps = 0.0;
77 double FGSteam::the_DG_inhg = 0.0;
78 double FGSteam::get_DG_deg () { _CatchUp(); return the_DG_deg; }
79 double FGSteam::get_DG_err () { _CatchUp(); return the_DG_err; }
81 void FGSteam::set_DG_err ( double approx_magvar ) {
82 the_DG_err = approx_magvar;
85 double FGSteam::the_TC_rad = 0.0;
86 double FGSteam::the_TC_std = 0.0;
87 double FGSteam::get_TC_rad () { _CatchUp(); return the_TC_rad; }
88 double FGSteam::get_TC_std () { _CatchUp(); return the_TC_std; }
91 ////////////////////////////////////////////////////////////////////////
92 // Recording the current time
93 ////////////////////////////////////////////////////////////////////////
96 int FGSteam::_UpdatesPending = 1000000; /* Forces filter to reset */
99 void FGSteam::update ( int timesteps )
103 current_properties.tieDouble("/steam/airspeed",
104 FGSteam::get_ASI_kias);
105 current_properties.tieDouble("/steam/altitude",
106 FGSteam::get_ALT_ft);
107 current_properties.tieDouble("/steam/turn-rate",
108 FGSteam::get_TC_std);
109 current_properties.tieDouble("/steam/slip-skid",
110 FGSteam::get_TC_rad);
111 current_properties.tieDouble("/steam/vertical-speed",
112 FGSteam::get_VSI_fps);
113 current_properties.tieDouble("/steam/gyro-compass",
114 FGSteam::get_DG_deg);
115 current_properties.tieDouble("/steam/vor1",
116 FGSteam::get_HackVOR1_deg);
117 current_properties.tieDouble("/steam/vor2",
118 FGSteam::get_HackVOR2_deg);
119 current_properties.tieDouble("/steam/glidescope1",
120 FGSteam::get_HackGS_deg);
121 current_properties.tieDouble("/steam/adf",
122 FGSteam::get_HackADF_deg);
123 current_properties.tieDouble("/steam/gyro-compass-error",
125 FGSteam::set_DG_err);
127 _UpdatesPending += timesteps;
131 void FGSteam::set_lowpass ( double *outthe, double inthe, double tc )
135 { /* time went backwards; kill the filter */
138 { /* ignore mildly negative time */
142 { /* Normal mode of operation */
143 (*outthe) = (*outthe) * ( 1.0 - tc )
147 { /* Huge time step; assume filter has settled */
150 { /* Moderate time step; non linear response */
151 double keep = exp ( -tc );
152 // printf ( "ARP: Keep is %f\n", keep );
153 (*outthe) = (*outthe) * keep
154 + inthe * ( 1.0 - keep );
160 ////////////////////////////////////////////////////////////////////////
161 // Here the fun really begins
162 ////////////////////////////////////////////////////////////////////////
165 void FGSteam::_CatchUp()
166 { if ( _UpdatesPending != 0 )
167 { double dt = _UpdatesPending * 1.0 / current_options.get_model_hz();
168 double AccN, AccE, AccU;
170 double d, the_ENGINE_rpm;
173 /**************************
174 There is the possibility that this is the first call.
175 If this is the case, we will emit the feature registrations
176 just to be on the safe side. Doing it more than once will
177 waste CPU time but doesn't hurt anything really.
179 if ( _UpdatesPending > 999999 )
180 { FGFeature::register_int ( "Avionics/NAV1/Localizer", &NAV1_LOC );
181 FGFeature::register_double ( "Avionics/NAV1/Latitude", &NAV1_Lat );
182 FGFeature::register_double ( "Avionics/NAV1/Longitude", &NAV1_Lon );
183 FGFeature::register_double ( "Avionics/NAV1/Radial", &NAV1_Rad );
184 FGFeature::register_double ( "Avionics/NAV1/Altitude", &NAV1_Alt );
185 FGFeature::register_int ( "Avionics/NAV2/Localizer", &NAV2_LOC );
186 FGFeature::register_double ( "Avionics/NAV2/Latitude", &NAV2_Lat );
187 FGFeature::register_double ( "Avionics/NAV2/Longitude", &NAV2_Lon );
188 FGFeature::register_double ( "Avionics/NAV2/Radial", &NAV2_Rad );
189 FGFeature::register_double ( "Avionics/NAV2/Altitude", &NAV2_Alt );
190 FGFeature::register_double ( "Avionics/ADF/Latitude", &ADF_Lat );
191 FGFeature::register_double ( "Avionics/ADF/Longitude", &ADF_Lon );
195 /**************************
196 Someone has called our update function and
197 it turns out that we are running somewhat behind.
198 Here, we recalculate everything for a 'dt' second step.
201 /**************************
202 The ball responds to the acceleration vector in the body
203 frame, only the components perpendicular to the longitudinal
204 axis of the aircraft. This is only related to actual
205 side slip for a symmetrical aircraft which is not touching
206 the ground and not changing its attitude. Math simplifies
207 by assuming (for small angles) arctan(x)=x in radians.
208 Obvious failure mode is the absence of liquid in the
209 tube, which is there to damp the motion, so that instead
210 the ball will bounce around, hitting the tube ends.
211 More subtle flaw is having it not move or a travel limit
212 occasionally due to some dirt in the tube or on the ball.
214 // the_TC_rad = - ( FGBFI::getSideSlip () ); /* incorrect */
215 d = - current_aircraft.fdm_state->get_A_Z_pilot();
217 set_lowpass ( & the_TC_rad,
218 current_aircraft.fdm_state->get_A_Y_pilot () / d,
221 /**************************
222 The rate of turn indication is from an electric gyro.
223 We should have it spin up with the master switch.
224 It is mounted at a funny angle so that it detects
225 both rate of bank (i.e. rolling into and out of turns)
226 and the rate of turn (i.e. how fast heading is changing).
228 set_lowpass ( & the_TC_std,
229 current_aircraft.fdm_state->get_Phi_dot ()
230 * RAD_TO_DEG / 20.0 +
231 current_aircraft.fdm_state->get_Psi_dot ()
232 * RAD_TO_DEG / 3.0 , dt );
234 /**************************
235 We want to know the pilot accelerations,
236 to compute the magnetic compass errors.
238 AccN = current_aircraft.fdm_state->get_V_dot_north();
239 AccE = current_aircraft.fdm_state->get_V_dot_east();
240 AccU = current_aircraft.fdm_state->get_V_dot_down()
242 if ( fabs(the_TC_rad) > 0.2 )
243 { /* Massive sideslip jams it; it stops turning */
245 the_MH_err = FGBFI::getHeading () - the_MH_deg;
247 { double MagDip, MagVar, CosDip;
248 double FrcN, FrcE, FrcU, AccTot;
249 double EdgN, EdgE, EdgU;
250 double TrqN, TrqE, TrqU, Torque;
251 /* Find a force vector towards exact magnetic north */
252 MagVar = FGBFI::getMagVar() / RAD_TO_DEG;
253 MagDip = FGBFI::getMagDip() / RAD_TO_DEG;
254 CosDip = cos ( MagDip );
255 FrcN = CosDip * cos ( MagVar );
256 FrcE = CosDip * sin ( MagVar );
257 FrcU = sin ( MagDip );
258 /* Rotation occurs around acceleration axis,
259 but axis magnitude is irrelevant. So compute it. */
260 AccTot = AccN*AccN + AccE*AccE + AccU*AccU;
261 if ( AccTot > 1.0 ) AccTot = sqrt ( AccTot );
263 /* Force applies to north marking on compass card */
264 EdgN = cos ( the_MH_err / RAD_TO_DEG );
265 EdgE = sin ( the_MH_err / RAD_TO_DEG );
267 /* Apply the force to the edge to get torques */
268 TrqN = EdgE * FrcU - EdgU * FrcE;
269 TrqE = EdgU * FrcN - EdgN * FrcU;
270 TrqU = EdgN * FrcE - EdgE * FrcN;
271 /* Select the component parallel to the axis */
272 Torque = ( TrqN * AccN +
274 TrqU * AccU ) * 5.0 / AccTot;
275 /* The magnetic compass has angular momentum,
276 so we apply a torque to it and wait */
278 { the_MH_degps= the_MH_degps * (1.0 - dt) - Torque;
279 the_MH_err += dt * the_MH_degps;
281 if ( the_MH_err > 180.0 ) the_MH_err -= 360.0; else
282 if ( the_MH_err < -180.0 ) the_MH_err += 360.0;
283 the_MH_deg = FGBFI::getHeading () - the_MH_err;
286 /**************************
287 This is not actually correct, but provides a
288 scaling capability for the vacuum pump later on.
289 When we have a real engine model, we can ask it.
291 the_ENGINE_rpm = FGBFI::getThrottle() * 26.0;
293 /**************************
294 This is just temporary, until the static source works,
295 so we just filter the actual value by one second to
296 account for the line impedance of the plumbing.
298 set_lowpass ( & the_ALT_ft, FGBFI::getAltitude(), dt );
300 /**************************
301 First, we need to know what the static line is reporting,
302 which is a whole simulation area in itself. For now, we cheat.
304 the_STATIC_inhg = 29.92;
305 i = (int) the_ALT_ft;
307 { the_STATIC_inhg *= 0.707;
310 the_STATIC_inhg *= ( 1.0 - 0.293 * i / 9000.0 );
313 NO alternate static source error (student feature),
314 NO possibility of blockage (instructor feature),
315 NO slip-induced error, important for C172 for example.
318 /**************************
319 The VSI case is a low-pass filter of the static line pressure.
320 The instrument reports the difference, scaled to approx ft.
321 NO option for student to break glass when static source fails.
322 NO capability for a fixed non-zero reading when level.
323 NO capability to have a scaling error of maybe a factor of two.
325 the_VSI_fps = ( the_VSI_case - the_STATIC_inhg )
326 * 10000.0; /* manual scaling factor */
327 set_lowpass ( & the_VSI_case, the_STATIC_inhg, dt/6.0 );
329 /**************************
330 The engine driven vacuum pump is directly attached
331 to the engine shaft, so each engine rotation pumps
332 a fixed volume. The amount of air in that volume
333 is determined by the vacuum line's internal pressure.
334 The instruments are essentially leaking air like
335 a fixed source impedance from atmospheric pressure.
336 The regulator provides a digital limit setting,
337 which is open circuit unless the pressure drop is big.
338 Thus, we can compute the vacuum line pressure directly.
339 We assume that there is negligible reservoir space.
340 NO failure of the pump supported (yet)
342 the_VACUUM_inhg = the_STATIC_inhg *
343 the_ENGINE_rpm / ( the_ENGINE_rpm + 10000.0 );
344 if ( the_VACUUM_inhg > 5.0 )
345 the_VACUUM_inhg = 5.0;
348 > I was merely going to do the engine rpm driven vacuum pump for both
349 > the AI and DG, have the gyros spin down down in power off descents,
350 > have it tumble when you exceed the usual pitch or bank limits,
351 > put in those insidious turning errors ... for now anyway.
353 if ( _UpdatesPending > 999999 )
354 the_DG_err = FGBFI::getMagVar();
355 the_DG_degps = 0.01; /* HACK! */
356 if (dt<1.0) the_DG_err += dt * the_DG_degps;
357 the_DG_deg = FGBFI::getHeading () - the_DG_err;
359 /**************************
360 Finished updates, now clear the timer
364 // cout << "0 Updates pending" << endl;
369 ////////////////////////////////////////////////////////////////////////
370 // Everything below is a transient hack; expect it to disappear
371 ////////////////////////////////////////////////////////////////////////
374 double FGSteam::get_HackGS_deg () {
375 if ( current_radiostack->get_nav1_inrange() &&
376 current_radiostack->get_nav1_has_gs() )
378 double x = current_radiostack->get_nav1_gs_dist();
379 double y = (FGBFI::getAltitude() - current_radiostack->get_nav1_elev())
381 double angle = atan2( y, x ) * RAD_TO_DEG;
382 return (current_radiostack->get_nav1_target_gs() - angle) * 5.0;
389 double FGSteam::get_HackVOR1_deg () {
392 if ( current_radiostack->get_nav1_inrange() ) {
393 if ( current_radiostack->get_nav1_loc() ) {
394 // localizer doesn't need magvar offset
395 r = current_radiostack->get_nav1_heading()
396 - current_radiostack->get_nav1_radial();
398 r = current_radiostack->get_nav1_heading() - FGBFI::getMagVar()
399 - current_radiostack->get_nav1_radial();
401 // cout << "Radial = " << current_radiostack->get_nav1_radial()
402 // << " Bearing = " << current_radiostack->get_nav1_heading()
405 if (r> 180.0) r-=360.0; else
406 if (r<-180.0) r+=360.0;
407 if ( fabs(r) > 90.0 )
408 r = ( r<0.0 ? -r-180.0 : -r+180.0 );
409 // According to Robin Peel, the ILS is 4x more sensitive than a vor
410 if ( current_radiostack->get_nav1_loc() ) r *= 4.0;
419 double FGSteam::get_HackVOR2_deg () {
422 if ( current_radiostack->get_nav2_inrange() ) {
423 if ( current_radiostack->get_nav2_loc() ) {
424 // localizer doesn't need magvar offset
425 r = current_radiostack->get_nav2_heading()
426 - current_radiostack->get_nav2_radial();
428 r = current_radiostack->get_nav2_heading() - FGBFI::getMagVar()
429 - current_radiostack->get_nav2_radial();
431 // cout << "Radial = " << current_radiostack->get_nav1_radial()
432 // << " Bearing = " << current_radiostack->get_nav1_heading() << endl;
434 if (r> 180.0) r-=360.0; else
435 if (r<-180.0) r+=360.0;
436 if ( fabs(r) > 90.0 )
437 r = ( r<0.0 ? -r-180.0 : -r+180.0 );
446 double FGSteam::get_HackOBS1_deg () {
447 return current_radiostack->get_nav1_radial();
451 double FGSteam::get_HackOBS2_deg () {
452 return current_radiostack->get_nav2_radial();
456 double FGSteam::get_HackADF_deg () {
459 if ( current_radiostack->get_adf_inrange() ) {
460 r = current_radiostack->get_adf_heading() - FGBFI::getHeading();
462 // cout << "Radial = " << current_radiostack->get_adf_heading()
463 // << " Heading = " << FGBFI::getHeading() << endl;