1 /***************************************************************************
5 ----------------------------------------------------------------------------
7 FUNCTION: Landing gear model for example simulation
9 ----------------------------------------------------------------------------
11 MODULE STATUS: developmental
13 ----------------------------------------------------------------------------
15 GENEALOGY: Renamed navion_gear.c originally created 931012 by E. B. Jackson
18 ----------------------------------------------------------------------------
20 DESIGNED BY: E. B. Jackson
22 CODED BY: E. B. Jackson
24 MAINTAINED BY: E. B. Jackson
26 ----------------------------------------------------------------------------
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.
40 Revision 1.3 1999/07/31 02:57:36 curt
41 Improvements to Tony's c172 model.
43 Revision 1.1.1.1 1999/04/05 21:32:45 curt
44 Start of 0.6.x branch.
46 Revision 1.6 1998/10/17 01:34:16 curt
49 Revision 1.5 1998/09/29 02:03:00 curt
50 Added a brake + autopilot mods.
52 Revision 1.4 1998/08/06 12:46:40 curt
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
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.
65 Revision 1.1 1997/05/29 00:10:02 curt
66 Initial Flight Gear revision.
69 ----------------------------------------------------------------------------
73 ----------------------------------------------------------------------------
77 ----------------------------------------------------------------------------
81 ----------------------------------------------------------------------------
85 ----------------------------------------------------------------------------
89 --------------------------------------------------------------------------*/
92 #include "ls_constants.h"
93 #include "ls_generic.h"
94 #include "ls_cockpit.h"
96 void sub3( DATA v1[], DATA v2[], DATA result[] )
98 result[0] = v1[0] - v2[0];
99 result[1] = v1[1] - v2[1];
100 result[2] = v1[2] - v2[2];
103 void add3( DATA v1[], DATA v2[], DATA result[] )
105 result[0] = v1[0] + v2[0];
106 result[1] = v1[1] + v2[1];
107 result[2] = v1[2] + v2[2];
110 void cross3( DATA v1[], DATA v2[], DATA result[] )
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];
117 void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
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];
124 void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
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];
131 void clear3( DATA v[] )
133 v[0] = 0.; v[1] = 0.; v[2] = 0.;
136 void gear( SCALAR dt, int Initialize ) {
137 char rcsid[] = "$Id$";
142 * Aircraft specific initializations and data goes here
147 static int num_wheels = NUM_WHEELS; /* number of wheels */
148 static DATA d_wheel_rp_body_v[NUM_WHEELS][3] = /* X, Y, Z locations */
150 { 10., 0., 4. }, /* in feet */
154 static DATA spring_constant[NUM_WHEELS] = /* springiness, lbs/ft */
155 { 1500., 5000., 5000. };
156 static DATA spring_damping[NUM_WHEELS] = /* damping, lbs/ft/sec */
157 { 100., 150., 150. };
158 static DATA percent_brake[NUM_WHEELS] = /* percent applied braking */
159 { 0., 0., 0. }; /* 0 = none, 1 = full */
160 static DATA caster_angle_rad[NUM_WHEELS] = /* steerable tires - in */
161 { 0., 0., 0.}; /* radians, +CW */
163 * End of aircraft specific code
167 * Constants & coefficients for tyres on tarmac - ref [1]
170 /* skid function looks like:
176 * sliding_mu | / +------
179 * +--+------------------------>
186 static DATA sliding_mu = 0.5;
187 static DATA rolling_mu = 0.01;
188 static DATA max_brake_mu = 0.6;
189 static DATA max_mu = 0.8;
190 static DATA bkout_v = 0.1;
191 static DATA skid_v = 1.0;
193 * Local data variables
196 DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
197 DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
198 DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
199 DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
200 DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
201 DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
202 DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
203 DATA reaction_normal_force; /* wheel normal (to rwy) force */
204 DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
205 DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
206 DATA forward_mu, sideward_mu; /* friction coefficients */
207 DATA beta_mu; /* breakout friction slope */
208 DATA forward_wheel_force, sideward_wheel_force;
210 int i; /* per wheel loop counter */
215 * Execution starts here
218 beta_mu = max_mu/(skid_v-bkout_v);
219 clear3( F_gear_v ); /* Initialize sum of forces... */
220 clear3( M_gear_v ); /* ...and moments */
223 * Put aircraft specific executable code here
226 /* replace with cockpit brake handle connection code */
227 percent_brake[1] = Brake_pct;
228 percent_brake[2] = percent_brake[1];
230 caster_angle_rad[0] = 0.03*Rudder_pedal;
232 for (i=0;i<num_wheels;i++) /* Loop for each wheel */
234 /*========================================*/
235 /* Calculate wheel position w.r.t. runway */
236 /*========================================*/
238 /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
240 sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
242 /* then converting to local (North-East-Down) axes... */
244 multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
246 /* Runway axes correction - third element is Altitude, not (-)Z... */
248 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
250 /* Add wheel offset to cg location in local axes */
252 add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
254 /* remove Runway axes correction so right hand rule applies */
256 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
258 /*============================*/
259 /* Calculate wheel velocities */
260 /*============================*/
262 /* contribution due to angular rates */
264 cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
266 /* transform into local axes */
268 multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
270 /* plus contribution due to cg velocities */
272 add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
275 /*===========================================*/
276 /* Calculate forces & moments for this wheel */
277 /*===========================================*/
279 /* Add any anticipation, or frame lead/prediction, here... */
281 /* no lead used at present */
283 /* Calculate sideward and forward velocities of the wheel
284 in the runway plane */
286 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
287 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
289 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
290 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
291 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
292 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
294 /* Calculate normal load force (simple spring constant) */
296 reaction_normal_force = 0.;
297 if( d_wheel_rwy_local_v[2] < 0. )
299 reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
300 - v_wheel_local_v[2]*spring_damping[i];
301 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
302 /* to prevent damping component from swamping spring component */
305 /* Calculate friction coefficients */
307 forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
308 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
309 sideward_mu = sliding_mu;
310 if (abs_v_wheel_sideward < skid_v)
311 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
312 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
314 /* Calculate foreward and sideward reaction forces */
316 forward_wheel_force = forward_mu*reaction_normal_force;
317 sideward_wheel_force = sideward_mu*reaction_normal_force;
318 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
319 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
321 /* Rotate into local (N-E-D) axes */
323 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
324 - sideward_wheel_force*sin_wheel_hdg_angle;
325 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
326 + sideward_wheel_force*cos_wheel_hdg_angle;
327 f_wheel_local_v[2] = reaction_normal_force;
329 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
331 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
333 /* Calculate moments from force and offsets in body axes */
335 cross3( d_wheel_cg_body_v, tempF, tempM );
337 /* Sum forces and moments across all wheels */
339 add3( tempF, F_gear_v, F_gear_v );
340 add3( tempM, M_gear_v, M_gear_v );