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