src/FDM/LaRCsim/c172_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:  Renamed navion_gear.c originally created 931012 by E. B. Jackson
  16
  17
  18 ----------------------------------------------------------------------------
  19
  20         DESIGNED BY:    E. B. Jackson
  21
  22         CODED BY:       E. B. Jackson
  23
  24         MAINTAINED BY:  E. B. Jackson
  25
  26 ----------------------------------------------------------------------------
  27
  28         MODIFICATION HISTORY:
  29
  30         DATE    PURPOSE                                         BY
  31
  32         931218  Added navion.h header to allow connection with
  33                 aileron displacement for nosewheel steering.    EBJ
  34         940511  Connected nosewheel to rudder pedal; adjusted gain.
  35
  36         CURRENT RCS HEADER:
  37
  38 $Header$
  39 $Log$
  40 Revision 1.2  1999/06/21 03:01:47  curt
  41 Updated for both JSBsim and Tony Peden's c172 flight model.
  42
  43 Revision 1.1.1.1  1999/04/05 21:32:45  curt
  44 Start of 0.6.x branch.
  45
  46 Revision 1.6  1998/10/17 01:34:16  curt
  47 C++ ifying ...
  48
  49 Revision 1.5  1998/09/29 02:03:00  curt
  50 Added a brake + autopilot mods.
  51
  52 Revision 1.4  1998/08/06 12:46:40  curt
  53 Header change.
  54
  55 Revision 1.3  1998/02/03 23:20:18  curt
  56 Lots of little tweaks to fix various consistency problems discovered by
  57 Solaris' CC.  Fixed a bug in fg_debug.c with how the fgPrintf() wrapper
  58 passed arguments along to the real printf().  Also incorporated HUD changes
  59 by Michele America.
  60
  61 Revision 1.2  1998/01/19 18:40:29  curt
  62 Tons of little changes to clean up the code and to remove fatal errors
  63 when building with the c++ compiler.
  64
  65 Revision 1.1  1997/05/29 00:10:02  curt
  66 Initial Flight Gear revision.
  67
  68
  69 ----------------------------------------------------------------------------
  70
  71         REFERENCES:
  72
  73 ----------------------------------------------------------------------------
  74
  75         CALLED BY:
  76
  77 ----------------------------------------------------------------------------
  78
  79         CALLS TO:
  80
  81 ----------------------------------------------------------------------------
  82
  83         INPUTS:
  84
  85 ----------------------------------------------------------------------------
  86
  87         OUTPUTS:
  88
  89 --------------------------------------------------------------------------*/
  90 #include <math.h>
  91 #include "ls_types.h"
  92 #include "ls_constants.h"
  93 #include "ls_generic.h"
  94 #include "ls_cockpit.h"
  95
  96
  97 void sub3( DATA v1[],  DATA v2[], DATA result[] )
  98 {
  99     result[0] = v1[0] - v2[0];
 100     result[1] = v1[1] - v2[1];
 101     result[2] = v1[2] - v2[2];
 102 }
 103
 104 void add3( DATA v1[],  DATA v2[], DATA result[] )
 105 {
 106     result[0] = v1[0] + v2[0];
 107     result[1] = v1[1] + v2[1];
 108     result[2] = v1[2] + v2[2];
 109 }
 110
 111 void cross3( DATA v1[],  DATA v2[], DATA result[] )
 112 {
 113     result[0] = v1[1]*v2[2] - v1[2]*v2[1];
 114     result[1] = v1[2]*v2[0] - v1[0]*v2[2];
 115     result[2] = v1[0]*v2[1] - v1[1]*v2[0];
 116 }
 117
 118 void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
 119 {
 120     result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
 121     result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
 122     result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
 123 }
 124
 125 void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
 126 {
 127     result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
 128     result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
 129     result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
 130 }
 131
 132 void clear3( DATA v[] )
 133 {
 134     v[0] = 0.; v[1] = 0.; v[2] = 0.;
 135 }
 136
 137 void gear( SCALAR dt, int Initialize ) {
 138 char rcsid[] = "$Id$";
 139
 140   /*
 141    * Aircraft specific initializations and data goes here
 142    */
 143
 144 #define NUM_WHEELS 3
 145
 146     static int num_wheels = NUM_WHEELS;             /* number of wheels  */
 147     static DATA d_wheel_rp_body_v[NUM_WHEELS][3] =  /* X, Y, Z locations */
 148     {
 149         { 10.,  0., 4. },                               /* in feet */
 150         { -1.,  3., 4. },
 151         { -1., -3., 4. }
 152     };
 153     static DATA spring_constant[NUM_WHEELS] =       /* springiness, lbs/ft */
 154         { 1500., 5000., 5000. };
 155     static DATA spring_damping[NUM_WHEELS] =        /* damping, lbs/ft/sec */
 156         { 100.,  150.,  150. };
 157     static DATA percent_brake[NUM_WHEELS] =         /* percent applied braking */
 158         { 0.,  0.,  0. };                           /* 0 = none, 1 = full */
 159     static DATA caster_angle_rad[NUM_WHEELS] =      /* steerable tires - in */
 160         { 0., 0., 0.};                              /* radians, +CW */
 161   /*
 162    * End of aircraft specific code
 163    */
 164
 165   /*
 166    * Constants & coefficients for tyres on tarmac - ref [1]
 167    */
 168
 169     /* skid function looks like:
 170      *
 171      *           mu  ^
 172      *               |
 173      *       max_mu  |       +
 174      *               |      /|
 175      *   sliding_mu  |     / +------
 176      *               |    /
 177      *               |   /
 178      *               +--+------------------------>
 179      *               |  |    |      sideward V
 180      *               0 bkout skid
 181      *                 V     V
 182      */
 183
 184
 185     static DATA sliding_mu   = 0.5;
 186     static DATA rolling_mu   = 0.01;
 187     static DATA max_brake_mu = 0.6;
 188     static DATA max_mu       = 0.8;
 189     static DATA bkout_v      = 0.1;
 190     static DATA skid_v       = 1.0;
 191   /*
 192    * Local data variables
 193    */
 194
 195     DATA d_wheel_cg_body_v[3];          /* wheel offset from cg,  X-Y-Z */
 196     DATA d_wheel_cg_local_v[3];         /* wheel offset from cg,  N-E-D */
 197     DATA d_wheel_rwy_local_v[3];        /* wheel offset from rwy, N-E-U */
 198     DATA v_wheel_body_v[3];             /* wheel velocity,        X-Y-Z */
 199     DATA v_wheel_local_v[3];            /* wheel velocity,        N-E-D */
 200     DATA f_wheel_local_v[3];            /* wheel reaction force,  N-E-D */
 201     DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
 202     DATA reaction_normal_force;         /* wheel normal (to rwy) force  */
 203     DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle;      /* temp storage */
 204     DATA v_wheel_forward, v_wheel_sideward,  abs_v_wheel_sideward;
 205     DATA forward_mu, sideward_mu;       /* friction coefficients        */
 206     DATA beta_mu;                       /* breakout friction slope      */
 207     DATA forward_wheel_force, sideward_wheel_force;
 208
 209     int i;                              /* per wheel loop counter */
 210
 211   /*
 212    * Execution starts here
 213    */
 214
 215     beta_mu = max_mu/(skid_v-bkout_v);
 216     clear3( F_gear_v );         /* Initialize sum of forces...  */
 217     clear3( M_gear_v );         /* ...and moments               */
 218
 219   /*
 220    * Put aircraft specific executable code here
 221    */
 222
 223     /* replace with cockpit brake handle connection code */
 224     percent_brake[1] = Brake_pct;
 225     percent_brake[2] = percent_brake[1];
 226
 227     caster_angle_rad[0] = 0.03*Rudder_pedal;
 228
 229     for (i=0;i<num_wheels;i++)      /* Loop for each wheel */
 230     {
 231         /*========================================*/
 232         /* Calculate wheel position w.r.t. runway */
 233         /*========================================*/
 234
 235             /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
 236
 237         sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
 238
 239             /* then converting to local (North-East-Down) axes... */
 240
 241         multtrans3x3by3( T_local_to_body_m,  d_wheel_cg_body_v, d_wheel_cg_local_v );
 242
 243             /* Runway axes correction - third element is Altitude, not (-)Z... */
 244
 245         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
 246
 247             /* Add wheel offset to cg location in local axes */
 248
 249         add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
 250
 251             /* remove Runway axes correction so right hand rule applies */
 252
 253         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
 254
 255         /*============================*/
 256         /* Calculate wheel velocities */
 257         /*============================*/
 258
 259             /* contribution due to angular rates */
 260
 261         cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
 262
 263             /* transform into local axes */
 264
 265         multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
 266
 267             /* plus contribution due to cg velocities */
 268
 269         add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
 270
 271
 272         /*===========================================*/
 273         /* Calculate forces & moments for this wheel */
 274         /*===========================================*/
 275
 276             /* Add any anticipation, or frame lead/prediction, here... */
 277
 278                     /* no lead used at present */
 279
 280             /* Calculate sideward and forward velocities of the wheel
 281                     in the runway plane                                 */
 282
 283         cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
 284         sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
 285
 286         v_wheel_forward  = v_wheel_local_v[0]*cos_wheel_hdg_angle
 287                          + v_wheel_local_v[1]*sin_wheel_hdg_angle;
 288         v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
 289                          - v_wheel_local_v[0]*sin_wheel_hdg_angle;
 290
 291             /* Calculate normal load force (simple spring constant) */
 292
 293         reaction_normal_force = 0.;
 294         if( d_wheel_rwy_local_v[2] < 0. )
 295         {
 296             reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
 297                                   - v_wheel_local_v[2]*spring_damping[i];
 298             if (reaction_normal_force > 0.) reaction_normal_force = 0.;
 299                 /* to prevent damping component from swamping spring component */
 300         }
 301
 302             /* Calculate friction coefficients */
 303
 304         forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
 305         abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
 306         sideward_mu = sliding_mu;
 307         if (abs_v_wheel_sideward < skid_v)
 308             sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
 309         if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
 310
 311             /* Calculate foreward and sideward reaction forces */
 312
 313         forward_wheel_force  =   forward_mu*reaction_normal_force;
 314         sideward_wheel_force =  sideward_mu*reaction_normal_force;
 315         if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
 316         if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
 317
 318             /* Rotate into local (N-E-D) axes */
 319
 320         f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
 321                           - sideward_wheel_force*sin_wheel_hdg_angle;
 322         f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
 323                           + sideward_wheel_force*cos_wheel_hdg_angle;
 324         f_wheel_local_v[2] = reaction_normal_force;
 325
 326             /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
 327
 328         mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
 329
 330             /* Calculate moments from force and offsets in body axes */
 331
 332         cross3( d_wheel_cg_body_v, tempF, tempM );
 333
 334         /* Sum forces and moments across all wheels */
 335
 336         add3( tempF, F_gear_v, F_gear_v );
 337         add3( tempM, M_gear_v, M_gear_v );
 338
 339     }
 340 }