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
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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)*/
193 DATA reaction_normal_force; /* wheel normal (to rwy) force */
194 DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
195 DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
196 DATA forward_mu, sideward_mu; /* friction coefficients */
197 DATA beta_mu; /* breakout friction slope */
198 DATA forward_wheel_force, sideward_wheel_force;
200 int i; /* per wheel loop counter */
203 * Execution starts here
206 beta_mu = max_mu/(skid_v-bkout_v);
207 clear3( F_gear_v ); /* Initialize sum of forces... */
208 clear3( M_gear_v ); /* ...and moments */
211 * Put aircraft specific executable code here
214 percent_brake[1] = Brake_pct[0];
215 percent_brake[2] = Brake_pct[1];
217 caster_angle_rad[0] =
218 (0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal;
221 for (i=0;i<MAX_GEAR;i++) /* Loop for each wheel */
223 // Execute only if the gear has been defined
227 /* printf("%s:\n",gear_strings[i]); */
231 /*========================================*/
232 /* Calculate wheel position w.r.t. runway */
233 /*========================================*/
236 /* 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 if( HEIGHT_AGL_WHEEL < 0. )
279 /*the wheel is underground -- which implies ground contact
280 so calculate reaction forces */
282 /*===========================================*/
283 /* Calculate forces & moments for this wheel */
284 /*===========================================*/
286 /* Add any anticipation, or frame lead/prediction, here... */
288 /* no lead used at present */
290 /* Calculate sideward and forward velocities of the wheel
291 in the runway plane */
293 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
294 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
296 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
297 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
298 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
299 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
302 /* Calculate normal load force (simple spring constant) */
304 reaction_normal_force = 0.;
306 reaction_normal_force = kgear[i]*d_wheel_rwy_local_v[2]
307 - v_wheel_local_v[2]*cgear[i];
308 /* printf("\treaction_normal_force: %g\n",reaction_normal_force); */
310 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
311 /* to prevent damping component from swamping spring component */
314 /* Calculate friction coefficients */
318 forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i];
319 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
320 sideward_mu = sliding_mu[i];
321 if (abs_v_wheel_sideward < skid_v)
322 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
323 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
327 forward_mu=sliding_mu[i];
328 sideward_mu=sliding_mu[i];
331 /* Calculate foreward and sideward reaction forces */
333 forward_wheel_force = forward_mu*reaction_normal_force;
334 sideward_wheel_force = sideward_mu*reaction_normal_force;
335 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
336 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
337 /* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force);
339 /* Rotate into local (N-E-D) axes */
341 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
342 - sideward_wheel_force*sin_wheel_hdg_angle;
343 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
344 + sideward_wheel_force*cos_wheel_hdg_angle;
345 f_wheel_local_v[2] = reaction_normal_force;
347 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
348 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
350 /* Calculate moments from force and offsets in body axes */
352 cross3( d_wheel_cg_body_v, tempF, tempM );
354 /* Sum forces and moments across all wheels */
356 add3( tempF, F_gear_v, F_gear_v );
357 add3( tempM, M_gear_v, M_gear_v );
364 /* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */
366 /*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear);
367 printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */
373 // end uiuc_engine.cpp