src/FDM/LaRCsim/navion_gear.c

   1 /***************************************************************************
   2
   3         TITLE:  gear
   4
   5 ----------------------------------------------------------------------------
   6
   7         FUNCTION:       Landing gear model for example simulation
   8
   9 ----------------------------------------------------------------------------
  10
  11         MODULE STATUS:  developmental
  12
  13 ----------------------------------------------------------------------------
  14
  15         GENEALOGY:      Created 931012 by E. B. Jackson
  16
  17 ----------------------------------------------------------------------------
  18
  19         DESIGNED BY:    E. B. Jackson
  20
  21         CODED BY:       E. B. Jackson
  22
  23         MAINTAINED BY:  E. B. Jackson
  24
  25 ----------------------------------------------------------------------------
  26
  27         MODIFICATION HISTORY:
  28
  29         DATE    PURPOSE                                         BY
  30
  31         931218  Added navion.h header to allow connection with
  32                 aileron displacement for nosewheel steering.    EBJ
  33         940511  Connected nosewheel to rudder pedal; adjusted gain.
  34
  35         CURRENT RCS HEADER:
  36
  37 $Header$
  38 $Log$
  39 Revision 1.1  1999/06/17 18:07:34  curt
  40 Initial revision
  41
  42 Revision 1.1.1.1  1999/04/05 21:32:45  curt
  43 Start of 0.6.x branch.
  44
  45 Revision 1.6  1998/10/17 01:34:16  curt
  46 C++ ifying ...
  47
  48 Revision 1.5  1998/09/29 02:03:00  curt
  49 Added a brake + autopilot mods.
  50
  51 Revision 1.4  1998/08/06 12:46:40  curt
  52 Header change.
  53
  54 Revision 1.3  1998/02/03 23:20:18  curt
  55 Lots of little tweaks to fix various consistency problems discovered by
  56 Solaris' CC.  Fixed a bug in fg_debug.c with how the fgPrintf() wrapper
  57 passed arguments along to the real printf().  Also incorporated HUD changes
  58 by Michele America.
  59
  60 Revision 1.2  1998/01/19 18:40:29  curt
  61 Tons of little changes to clean up the code and to remove fatal errors
  62 when building with the c++ compiler.
  63
  64 Revision 1.1  1997/05/29 00:10:02  curt
  65 Initial Flight Gear revision.
  66
  67
  68 ----------------------------------------------------------------------------
  69
  70         REFERENCES:
  71
  72 ----------------------------------------------------------------------------
  73
  74         CALLED BY:
  75
  76 ----------------------------------------------------------------------------
  77
  78         CALLS TO:
  79
  80 ----------------------------------------------------------------------------
  81
  82         INPUTS:
  83
  84 ----------------------------------------------------------------------------
  85
  86         OUTPUTS:
  87
  88 --------------------------------------------------------------------------*/
  89 #include <math.h>
  90 #include "ls_types.h"
  91 #include "ls_constants.h"
  92 #include "ls_generic.h"
  93 #include "ls_cockpit.h"
  94
  95
  96 void sub3( DATA v1[],  DATA v2[], DATA result[] )
  97 {
  98     result[0] = v1[0] - v2[0];
  99     result[1] = v1[1] - v2[1];
 100     result[2] = v1[2] - v2[2];
 101 }
 102
 103 void add3( DATA v1[],  DATA v2[], DATA result[] )
 104 {
 105     result[0] = v1[0] + v2[0];
 106     result[1] = v1[1] + v2[1];
 107     result[2] = v1[2] + v2[2];
 108 }
 109
 110 void cross3( DATA v1[],  DATA v2[], DATA result[] )
 111 {
 112     result[0] = v1[1]*v2[2] - v1[2]*v2[1];
 113     result[1] = v1[2]*v2[0] - v1[0]*v2[2];
 114     result[2] = v1[0]*v2[1] - v1[1]*v2[0];
 115 }
 116
 117 void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
 118 {
 119     result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
 120     result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
 121     result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
 122 }
 123
 124 void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
 125 {
 126     result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
 127     result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
 128     result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
 129 }
 130
 131 void clear3( DATA v[] )
 132 {
 133     v[0] = 0.; v[1] = 0.; v[2] = 0.;
 134 }
 135
 136 void gear( SCALAR dt, int Initialize ) {
 137 char rcsid[] = "$Id$";
 138
 139   /*
 140    * Aircraft specific initializations and data goes here
 141    */
 142
 143 #define NUM_WHEELS 3
 144
 145     static int num_wheels = NUM_WHEELS;             /* number of wheels  */
 146     static DATA d_wheel_rp_body_v[NUM_WHEELS][3] =  /* X, Y, Z locations */
 147     {
 148         { 10.,  0., 4. },                               /* in feet */
 149         { -1.,  3., 4. },
 150         { -1., -3., 4. }
 151     };
 152     static DATA spring_constant[NUM_WHEELS] =       /* springiness, lbs/ft */
 153         { 1500., 5000., 5000. };
 154     static DATA spring_damping[NUM_WHEELS] =        /* damping, lbs/ft/sec */
 155         { 100.,  150.,  150. };
 156     static DATA percent_brake[NUM_WHEELS] =         /* percent applied braking */
 157         { 0.,  0.,  0. };                           /* 0 = none, 1 = full */
 158     static DATA caster_angle_rad[NUM_WHEELS] =      /* steerable tires - in */
 159         { 0., 0., 0.};                              /* radians, +CW */
 160   /*
 161    * End of aircraft specific code
 162    */
 163
 164   /*
 165    * Constants & coefficients for tyres on tarmac - ref [1]
 166    */
 167
 168     /* skid function looks like:
 169      *
 170      *           mu  ^
 171      *               |
 172      *       max_mu  |       +
 173      *               |      /|
 174      *   sliding_mu  |     / +------
 175      *               |    /
 176      *               |   /
 177      *               +--+------------------------>
 178      *               |  |    |      sideward V
 179      *               0 bkout skid
 180      *                 V     V
 181      */
 182
 183
 184     static DATA sliding_mu   = 0.5;
 185     static DATA rolling_mu   = 0.01;
 186     static DATA max_brake_mu = 0.6;
 187     static DATA max_mu       = 0.8;
 188     static DATA bkout_v      = 0.1;
 189     static DATA skid_v       = 1.0;
 190   /*
 191    * Local data variables
 192    */
 193
 194     DATA d_wheel_cg_body_v[3];          /* wheel offset from cg,  X-Y-Z */
 195     DATA d_wheel_cg_local_v[3];         /* wheel offset from cg,  N-E-D */
 196     DATA d_wheel_rwy_local_v[3];        /* wheel offset from rwy, N-E-U */
 197     DATA v_wheel_body_v[3];             /* wheel velocity,        X-Y-Z */
 198     DATA v_wheel_local_v[3];            /* wheel velocity,        N-E-D */
 199     DATA f_wheel_local_v[3];            /* wheel reaction force,  N-E-D */
 200     DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
 201     DATA reaction_normal_force;         /* wheel normal (to rwy) force  */
 202     DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle;      /* temp storage */
 203     DATA v_wheel_forward, v_wheel_sideward,  abs_v_wheel_sideward;
 204     DATA forward_mu, sideward_mu;       /* friction coefficients        */
 205     DATA beta_mu;                       /* breakout friction slope      */
 206     DATA forward_wheel_force, sideward_wheel_force;
 207
 208     int i;                              /* per wheel loop counter */
 209
 210   /*
 211    * Execution starts here
 212    */
 213
 214     beta_mu = max_mu/(skid_v-bkout_v);
 215     clear3( F_gear_v );         /* Initialize sum of forces...  */
 216     clear3( M_gear_v );         /* ...and moments               */
 217
 218   /*
 219    * Put aircraft specific executable code here
 220    */
 221
 222     /* replace with cockpit brake handle connection code */
 223     percent_brake[1] = Brake_pct;
 224     percent_brake[2] = percent_brake[1];
 225
 226     caster_angle_rad[0] = 0.03*Rudder_pedal;
 227
 228     for (i=0;i<num_wheels;i++)      /* Loop for each wheel */
 229     {
 230         /*========================================*/
 231         /* Calculate wheel position w.r.t. runway */
 232         /*========================================*/
 233
 234             /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
 235
 236         sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
 237
 238             /* then converting to local (North-East-Down) axes... */
 239
 240         multtrans3x3by3( T_local_to_body_m,  d_wheel_cg_body_v, d_wheel_cg_local_v );
 241
 242             /* Runway axes correction - third element is Altitude, not (-)Z... */
 243
 244         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
 245
 246             /* Add wheel offset to cg location in local axes */
 247
 248         add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
 249
 250             /* remove Runway axes correction so right hand rule applies */
 251
 252         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
 253
 254         /*============================*/
 255         /* Calculate wheel velocities */
 256         /*============================*/
 257
 258             /* contribution due to angular rates */
 259
 260         cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
 261
 262             /* transform into local axes */
 263
 264         multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
 265
 266             /* plus contribution due to cg velocities */
 267
 268         add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
 269
 270
 271         /*===========================================*/
 272         /* Calculate forces & moments for this wheel */
 273         /*===========================================*/
 274
 275             /* Add any anticipation, or frame lead/prediction, here... */
 276
 277                     /* no lead used at present */
 278
 279             /* Calculate sideward and forward velocities of the wheel
 280                     in the runway plane                                 */
 281
 282         cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
 283         sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
 284
 285         v_wheel_forward  = v_wheel_local_v[0]*cos_wheel_hdg_angle
 286                          + v_wheel_local_v[1]*sin_wheel_hdg_angle;
 287         v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
 288                          - v_wheel_local_v[0]*sin_wheel_hdg_angle;
 289
 290             /* Calculate normal load force (simple spring constant) */
 291
 292         reaction_normal_force = 0.;
 293         if( d_wheel_rwy_local_v[2] < 0. )
 294         {
 295             reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
 296                                   - v_wheel_local_v[2]*spring_damping[i];
 297             if (reaction_normal_force > 0.) reaction_normal_force = 0.;
 298                 /* to prevent damping component from swamping spring component */
 299         }
 300
 301             /* Calculate friction coefficients */
 302
 303         forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
 304         abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
 305         sideward_mu = sliding_mu;
 306         if (abs_v_wheel_sideward < skid_v)
 307             sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
 308         if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
 309
 310             /* Calculate foreward and sideward reaction forces */
 311
 312         forward_wheel_force  =   forward_mu*reaction_normal_force;
 313         sideward_wheel_force =  sideward_mu*reaction_normal_force;
 314         if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
 315         if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
 316
 317             /* Rotate into local (N-E-D) axes */
 318
 319         f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
 320                           - sideward_wheel_force*sin_wheel_hdg_angle;
 321         f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
 322                           + sideward_wheel_force*cos_wheel_hdg_angle;
 323         f_wheel_local_v[2] = reaction_normal_force;
 324
 325             /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
 326
 327         mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
 328
 329             /* Calculate moments from force and offsets in body axes */
 330
 331         cross3( d_wheel_cg_body_v, tempF, tempM );
 332
 333         /* Sum forces and moments across all wheels */
 334
 335         add3( tempF, F_gear_v, F_gear_v );
 336         add3( tempM, M_gear_v, M_gear_v );
 337
 338     }
 339 }