1 /**********************************************************************
3 FILENAME: uiuc_gear.cpp
5 ----------------------------------------------------------------------
7 DESCRIPTION: determine the gear forces and moments
9 ----------------------------------------------------------------------
13 ----------------------------------------------------------------------
15 REFERENCES: based on c172_gear by Tony Peden and others
17 ----------------------------------------------------------------------
19 HISTORY: 03/09/2001 initial release
21 ----------------------------------------------------------------------
23 AUTHOR(S): David Megginson <david@megginson.com
25 ----------------------------------------------------------------------
29 ----------------------------------------------------------------------
33 ----------------------------------------------------------------------
37 ----------------------------------------------------------------------
39 CALLED BY: uiuc_wrapper.cpp
41 ----------------------------------------------------------------------
45 ----------------------------------------------------------------------
47 COPYRIGHT: (c) 2001 by David Megginson
49 This program is free software; you can redistribute it and/or
50 modify it under the terms of the GNU General Public License
51 as published by the Free Software Foundation.
53 This program is distributed in the hope that it will be useful,
54 but WITHOUT ANY WARRANTY; without even the implied warranty of
55 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
56 GNU General Public License for more details.
58 You should have received a copy of the GNU General Public License
59 along with this program; if not, write to the Free Software
60 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
62 **********************************************************************/
68 #include <simgear/compiler.h>
69 #include <simgear/misc/sg_path.hxx>
70 #include <Aircraft/aircraft.hxx>
71 #include <Main/fg_props.hxx>
73 #include "uiuc_gear.h"
75 #define HEIGHT_AGL_WHEEL d_wheel_rwy_local_v[2]
78 static void sub3( DATA v1[], DATA v2[], DATA result[] )
80 result[0] = v1[0] - v2[0];
81 result[1] = v1[1] - v2[1];
82 result[2] = v1[2] - v2[2];
85 static void add3( DATA v1[], DATA v2[], DATA result[] )
87 result[0] = v1[0] + v2[0];
88 result[1] = v1[1] + v2[1];
89 result[2] = v1[2] + v2[2];
92 static void cross3( DATA v1[], DATA v2[], DATA result[] )
94 result[0] = v1[1]*v2[2] - v1[2]*v2[1];
95 result[1] = v1[2]*v2[0] - v1[0]*v2[2];
96 result[2] = v1[0]*v2[1] - v1[1]*v2[0];
99 static void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
101 result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
102 result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
103 result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
106 static void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
108 result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
109 result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
110 result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
113 static void clear3( DATA v[] )
115 v[0] = 0.; v[1] = 0.; v[2] = 0.;
122 * Aircraft specific initializations and data goes here
125 static DATA percent_brake[MAX_GEAR] = /* percent applied braking */
129 0., 0., 0., 0. }; /* 0 = none, 1 = full */
130 static DATA caster_angle_rad[MAX_GEAR] = /* steerable tires - in */
134 0., 0., 0., 0. }; /* radians, +CW */
136 * End of aircraft specific code
140 * Constants & coefficients for tyres on tarmac - ref [1]
143 /* skid function looks like:
149 * sliding_mu | / +------
152 * +--+------------------------>
159 static int it_rolls[MAX_GEAR] =
164 static DATA sliding_mu[MAX_GEAR] =
165 { 0.5, 0.5, 0.5, 0.3,
168 0.3, 0.3, 0.3, 0.3 };
169 static DATA max_brake_mu[MAX_GEAR] =
170 { 0.0, 0.6, 0.6, 0.0,
173 0.0, 0.0, 0.0, 0.0 };
174 static DATA max_mu = 0.8;
175 static DATA bkout_v = 0.1;
176 static DATA skid_v = 1.0;
178 * Local data variables
181 DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
182 DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
183 DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
184 DATA v_wheel_cg_local_v[3]; /*wheel velocity rel to cg N-E-D*/
185 // DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
186 DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
187 DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
188 // DATA altitude_local_v[3]; /*altitude vector in local (N-E-D) i.e. (0,0,h)*/
189 // DATA altitude_body_v[3]; /*altitude vector in body (X,Y,Z)*/
194 DATA reaction_normal_force; /* wheel normal (to rwy) force */
195 DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
196 DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
197 DATA forward_mu, sideward_mu; /* friction coefficients */
198 DATA beta_mu; /* breakout friction slope */
199 DATA forward_wheel_force, sideward_wheel_force;
201 int i; /* per wheel loop counter */
204 * Execution starts here
207 beta_mu = max_mu/(skid_v-bkout_v);
208 clear3( F_gear_v ); /* Initialize sum of forces... */
209 clear3( M_gear_v ); /* ...and moments */
212 * Put aircraft specific executable code here
215 percent_brake[1] = Brake_pct[0];
216 percent_brake[2] = Brake_pct[1];
218 caster_angle_rad[0] =
219 (0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal;
222 for (i=0;i<MAX_GEAR;i++) /* Loop for each wheel */
224 // Execute only if the gear has been defined
233 /*========================================*/
234 /* Calculate wheel position w.r.t. runway */
235 /*========================================*/
237 /* printf("\thgcg: %g, theta: %g,phi: %g\n",D_cg_above_rwy,Theta*RAD_TO_DEG,Phi*RAD_TO_DEG); */
239 /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
241 sub3( D_gear_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
243 /* then converting to local (North-East-Down) axes... */
245 multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
248 /* Runway axes correction - third element is Altitude, not (-)Z... */
250 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
252 /* Add wheel offset to cg location in local axes */
254 add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
256 /* remove Runway axes correction so right hand rule applies */
258 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
260 /*============================*/
261 /* Calculate wheel velocities */
262 /*============================*/
264 /* contribution due to angular rates */
266 cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
268 /* transform into local axes */
270 multtrans3x3by3( T_local_to_body_m, temp3a,v_wheel_cg_local_v );
272 /* plus contribution due to cg velocities */
274 add3( v_wheel_cg_local_v, V_local_rel_ground_v, v_wheel_local_v );
276 clear3(f_wheel_local_v);
277 reaction_normal_force=0;
278 static const SGPropertyNode * gear_wow
279 = fgGetNode("/gear/gear[0]/wow", false);
280 static const SGPropertyNode * gear_wow1
281 = fgGetNode("/gear/gear[1]/wow", false);
282 static const SGPropertyNode * gear_wow2
283 = fgGetNode("/gear/gear[2]/wow", false);
284 fgSetBool("/gear/gear[0]/wow", false);
285 fgSetBool("/gear/gear[1]/wow", false);
286 fgSetBool("/gear/gear[2]/wow", false);
287 if( HEIGHT_AGL_WHEEL < 0. )
288 /*the wheel is underground -- which implies ground contact
289 so calculate reaction forces */
291 //set the property - weight on wheels
294 // fgSetBool("/gear/gear[0]/wow", true);
298 // fgSetBool("/gear/gear[1]/wow", true);
302 // fgSetBool("/gear/gear[2]/wow", true);
305 /*===========================================*/
306 /* Calculate forces & moments for this wheel */
307 /*===========================================*/
309 /* Add any anticipation, or frame lead/prediction, here... */
311 /* no lead used at present */
313 /* Calculate sideward and forward velocities of the wheel
314 in the runway plane */
316 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
317 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
319 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
320 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
321 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
322 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
325 /* Calculate normal load force (simple spring constant) */
327 reaction_normal_force = 0.;
329 reaction_normal_force = kgear[i]*d_wheel_rwy_local_v[2]
330 - v_wheel_local_v[2]*cgear[i];
331 /* printf("\treaction_normal_force: %g\n",reaction_normal_force); */
333 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
334 /* to prevent damping component from swamping spring component */
337 /* Calculate friction coefficients */
341 forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i];
342 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
343 sideward_mu = sliding_mu[i];
344 if (abs_v_wheel_sideward < skid_v)
345 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
346 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
350 forward_mu=sliding_mu[i];
351 sideward_mu=sliding_mu[i];
354 /* Calculate foreward and sideward reaction forces */
356 forward_wheel_force = forward_mu*reaction_normal_force;
357 sideward_wheel_force = sideward_mu*reaction_normal_force;
358 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
359 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
360 /* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force);
362 /* Rotate into local (N-E-D) axes */
364 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
365 - sideward_wheel_force*sin_wheel_hdg_angle;
366 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
367 + sideward_wheel_force*cos_wheel_hdg_angle;
368 f_wheel_local_v[2] = reaction_normal_force;
370 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
371 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
373 /* Calculate moments from force and offsets in body axes */
375 cross3( d_wheel_cg_body_v, tempF, tempM );
377 /* Sum forces and moments across all wheels */
379 fgSetBool("/gear/gear[1]/wow", true);
382 add3( tempF, F_gear_v, F_gear_v );
383 add3( tempM, M_gear_v, M_gear_v );
390 /* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */
392 /*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear);
393 printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */
399 // end uiuc_engine.cpp