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., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
61 USA or view http://www.gnu.org/copyleft/gpl.html.
63 **********************************************************************/
65 #include <simgear/compiler.h>
67 #include "uiuc_gear.h"
69 #if !defined (SG_HAVE_NATIVE_SGI_COMPILERS)
74 #define HEIGHT_AGL_WHEEL d_wheel_rwy_local_v[2]
77 static void sub3( DATA v1[], DATA v2[], DATA result[] )
79 result[0] = v1[0] - v2[0];
80 result[1] = v1[1] - v2[1];
81 result[2] = v1[2] - v2[2];
84 static void add3( DATA v1[], DATA v2[], DATA result[] )
86 result[0] = v1[0] + v2[0];
87 result[1] = v1[1] + v2[1];
88 result[2] = v1[2] + v2[2];
91 static void cross3( DATA v1[], DATA v2[], DATA result[] )
93 result[0] = v1[1]*v2[2] - v1[2]*v2[1];
94 result[1] = v1[2]*v2[0] - v1[0]*v2[2];
95 result[2] = v1[0]*v2[1] - v1[1]*v2[0];
98 static void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
100 result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
101 result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
102 result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
105 static void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
107 result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
108 result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
109 result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
112 static void clear3( DATA v[] )
114 v[0] = 0.; v[1] = 0.; v[2] = 0.;
121 * Aircraft specific initializations and data goes here
124 static DATA percent_brake[MAX_GEAR] = /* percent applied braking */
128 0., 0., 0., 0. }; /* 0 = none, 1 = full */
129 static DATA caster_angle_rad[MAX_GEAR] = /* steerable tires - in */
133 0., 0., 0., 0. }; /* radians, +CW */
135 * End of aircraft specific code
139 * Constants & coefficients for tyres on tarmac - ref [1]
142 /* skid function looks like:
148 * sliding_mu | / +------
151 * +--+------------------------>
158 static int it_rolls[MAX_GEAR] =
163 static DATA sliding_mu[MAX_GEAR] =
164 { 0.5, 0.5, 0.5, 0.3,
167 0.3, 0.3, 0.3, 0.3 };
168 static DATA max_brake_mu[MAX_GEAR] =
169 { 0.0, 0.6, 0.6, 0.0,
172 0.0, 0.0, 0.0, 0.0 };
173 static DATA max_mu = 0.8;
174 static DATA bkout_v = 0.1;
175 static DATA skid_v = 1.0;
177 * Local data variables
180 DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
181 DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
182 DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
183 DATA v_wheel_cg_local_v[3]; /*wheel velocity rel to cg N-E-D*/
184 DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
185 DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
186 DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
187 DATA altitude_local_v[3]; /*altitude vector in local (N-E-D) i.e. (0,0,h)*/
188 DATA altitude_body_v[3]; /*altitude vector in body (X,Y,Z)*/
189 DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
190 DATA reaction_normal_force; /* wheel normal (to rwy) force */
191 DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
192 DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
193 DATA forward_mu, sideward_mu; /* friction coefficients */
194 DATA beta_mu; /* breakout friction slope */
195 DATA forward_wheel_force, sideward_wheel_force;
197 int i; /* per wheel loop counter */
200 * Execution starts here
203 beta_mu = max_mu/(skid_v-bkout_v);
204 clear3( F_gear_v ); /* Initialize sum of forces... */
205 clear3( M_gear_v ); /* ...and moments */
208 * Put aircraft specific executable code here
211 percent_brake[1] = Brake_pct[0];
212 percent_brake[2] = Brake_pct[1];
214 caster_angle_rad[0] =
215 (0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal;
218 for (i=0;i<MAX_GEAR;i++) /* Loop for each wheel */
220 // Execute only if the gear has been defined
224 /* printf("%s:\n",gear_strings[i]); */
228 /*========================================*/
229 /* Calculate wheel position w.r.t. runway */
230 /*========================================*/
233 /* printf("\thgcg: %g, theta: %g,phi: %g\n",D_cg_above_rwy,Theta*RAD_TO_DEG,Phi*RAD_TO_DEG); */
236 /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
238 sub3( D_gear_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
240 /* then converting to local (North-East-Down) axes... */
242 multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
245 /* Runway axes correction - third element is Altitude, not (-)Z... */
247 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
249 /* Add wheel offset to cg location in local axes */
251 add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
253 /* remove Runway axes correction so right hand rule applies */
255 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
257 /*============================*/
258 /* Calculate wheel velocities */
259 /*============================*/
261 /* contribution due to angular rates */
263 cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
265 /* transform into local axes */
267 multtrans3x3by3( T_local_to_body_m, temp3a,v_wheel_cg_local_v );
269 /* plus contribution due to cg velocities */
271 add3( v_wheel_cg_local_v, V_local_rel_ground_v, v_wheel_local_v );
273 clear3(f_wheel_local_v);
274 reaction_normal_force=0;
275 if( HEIGHT_AGL_WHEEL < 0. )
276 /*the wheel is underground -- which implies ground contact
277 so calculate reaction forces */
279 /*===========================================*/
280 /* Calculate forces & moments for this wheel */
281 /*===========================================*/
283 /* Add any anticipation, or frame lead/prediction, here... */
285 /* no lead used at present */
287 /* Calculate sideward and forward velocities of the wheel
288 in the runway plane */
290 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
291 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
293 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
294 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
295 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
296 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
299 /* Calculate normal load force (simple spring constant) */
301 reaction_normal_force = 0.;
303 reaction_normal_force = kgear[i]*d_wheel_rwy_local_v[2]
304 - v_wheel_local_v[2]*cgear[i];
305 /* printf("\treaction_normal_force: %g\n",reaction_normal_force); */
307 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
308 /* to prevent damping component from swamping spring component */
311 /* Calculate friction coefficients */
315 forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i];
316 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
317 sideward_mu = sliding_mu[i];
318 if (abs_v_wheel_sideward < skid_v)
319 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
320 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
324 forward_mu=sliding_mu[i];
325 sideward_mu=sliding_mu[i];
328 /* Calculate foreward and sideward reaction forces */
330 forward_wheel_force = forward_mu*reaction_normal_force;
331 sideward_wheel_force = sideward_mu*reaction_normal_force;
332 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
333 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
334 /* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force);
336 /* Rotate into local (N-E-D) axes */
338 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
339 - sideward_wheel_force*sin_wheel_hdg_angle;
340 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
341 + sideward_wheel_force*cos_wheel_hdg_angle;
342 f_wheel_local_v[2] = reaction_normal_force;
344 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
345 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
347 /* Calculate moments from force and offsets in body axes */
349 cross3( d_wheel_cg_body_v, tempF, tempM );
351 /* Sum forces and moments across all wheels */
353 add3( tempF, F_gear_v, F_gear_v );
354 add3( tempM, M_gear_v, M_gear_v );
361 /* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */
363 /*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear);
364 printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */
370 // end uiuc_engine.cpp