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 **********************************************************************/
69 #include <simgear/compiler.h>
70 #include <simgear/misc/sg_path.hxx>
71 #include <Aircraft/aircraft.hxx>
72 #include <Main/fg_props.hxx>
74 #include "uiuc_gear.h"
81 #define HEIGHT_AGL_WHEEL d_wheel_rwy_local_v[2]
84 static void sub3( 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 add3( DATA v1[], DATA v2[], DATA result[] )
93 result[0] = v1[0] + v2[0];
94 result[1] = v1[1] + v2[1];
95 result[2] = v1[2] + v2[2];
98 static void cross3( DATA v1[], DATA v2[], DATA result[] )
100 result[0] = v1[1]*v2[2] - v1[2]*v2[1];
101 result[1] = v1[2]*v2[0] - v1[0]*v2[2];
102 result[2] = v1[0]*v2[1] - v1[1]*v2[0];
105 static void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
107 result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
108 result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
109 result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
112 static void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
114 result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
115 result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
116 result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
119 static void clear3( DATA v[] )
121 v[0] = 0.; v[1] = 0.; v[2] = 0.;
128 * Aircraft specific initializations and data goes here
131 static DATA percent_brake[MAX_GEAR] = /* percent applied braking */
135 0., 0., 0., 0. }; /* 0 = none, 1 = full */
136 static DATA caster_angle_rad[MAX_GEAR] = /* steerable tires - in */
140 0., 0., 0., 0. }; /* radians, +CW */
142 * End of aircraft specific code
146 * Constants & coefficients for tyres on tarmac - ref [1]
149 /* skid function looks like:
155 * sliding_mu | / +------
158 * +--+------------------------>
165 static int it_rolls[MAX_GEAR] =
170 static DATA sliding_mu[MAX_GEAR] =
171 { 0.5, 0.5, 0.5, 0.3,
174 0.3, 0.3, 0.3, 0.3 };
175 static DATA max_brake_mu[MAX_GEAR] =
176 { 0.0, 0.6, 0.6, 0.0,
179 0.0, 0.0, 0.0, 0.0 };
180 static DATA max_mu = 0.8;
181 static DATA bkout_v = 0.1;
182 static DATA skid_v = 1.0;
184 * Local data variables
187 DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
188 DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
189 DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
190 DATA v_wheel_cg_local_v[3]; /*wheel velocity rel to cg N-E-D*/
191 // DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
192 DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
193 DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
194 // DATA altitude_local_v[3]; /*altitude vector in local (N-E-D) i.e. (0,0,h)*/
195 // DATA altitude_body_v[3]; /*altitude vector in body (X,Y,Z)*/
200 DATA reaction_normal_force; /* wheel normal (to rwy) force */
201 DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
202 DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
203 DATA forward_mu, sideward_mu; /* friction coefficients */
204 DATA beta_mu; /* breakout friction slope */
205 DATA forward_wheel_force, sideward_wheel_force;
207 int i; /* per wheel loop counter */
210 * Execution starts here
213 beta_mu = max_mu/(skid_v-bkout_v);
214 clear3( F_gear_v ); /* Initialize sum of forces... */
215 clear3( M_gear_v ); /* ...and moments */
218 * Put aircraft specific executable code here
221 percent_brake[1] = Brake_pct[0];
222 percent_brake[2] = Brake_pct[1];
224 caster_angle_rad[0] =
225 (0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal;
228 for (i=0;i<MAX_GEAR;i++) /* Loop for each wheel */
230 // Execute only if the gear has been defined
239 /*========================================*/
240 /* Calculate wheel position w.r.t. runway */
241 /*========================================*/
243 /* printf("\thgcg: %g, theta: %g,phi: %g\n",D_cg_above_rwy,Theta*RAD_TO_DEG,Phi*RAD_TO_DEG); */
245 /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
247 sub3( D_gear_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
249 /* then converting to local (North-East-Down) axes... */
251 multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
254 /* Runway axes correction - third element is Altitude, not (-)Z... */
256 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
258 /* Add wheel offset to cg location in local axes */
260 add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
262 /* remove Runway axes correction so right hand rule applies */
264 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
266 /*============================*/
267 /* Calculate wheel velocities */
268 /*============================*/
270 /* contribution due to angular rates */
272 cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
274 /* transform into local axes */
276 multtrans3x3by3( T_local_to_body_m, temp3a,v_wheel_cg_local_v );
278 /* plus contribution due to cg velocities */
280 add3( v_wheel_cg_local_v, V_local_rel_ground_v, v_wheel_local_v );
282 clear3(f_wheel_local_v);
283 reaction_normal_force=0;
284 static const SGPropertyNode * gear_wow
285 = fgGetNode("/gear/gear[0]/wow", false);
286 static const SGPropertyNode * gear_wow1
287 = fgGetNode("/gear/gear[1]/wow", false);
288 static const SGPropertyNode * gear_wow2
289 = fgGetNode("/gear/gear[2]/wow", false);
290 fgSetBool("/gear/gear[0]/wow", false);
291 fgSetBool("/gear/gear[1]/wow", false);
292 fgSetBool("/gear/gear[2]/wow", false);
293 if( HEIGHT_AGL_WHEEL < 0. )
294 /*the wheel is underground -- which implies ground contact
295 so calculate reaction forces */
297 //set the property - weight on wheels
300 // fgSetBool("/gear/gear[0]/wow", true);
304 // fgSetBool("/gear/gear[1]/wow", true);
308 // fgSetBool("/gear/gear[2]/wow", true);
311 /*===========================================*/
312 /* Calculate forces & moments for this wheel */
313 /*===========================================*/
315 /* Add any anticipation, or frame lead/prediction, here... */
317 /* no lead used at present */
319 /* Calculate sideward and forward velocities of the wheel
320 in the runway plane */
322 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
323 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
325 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
326 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
327 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
328 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
331 /* Calculate normal load force (simple spring constant) */
333 reaction_normal_force = 0.;
335 reaction_normal_force = kgear[i]*d_wheel_rwy_local_v[2]
336 - v_wheel_local_v[2]*cgear[i];
337 /* printf("\treaction_normal_force: %g\n",reaction_normal_force); */
339 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
340 /* to prevent damping component from swamping spring component */
343 /* Calculate friction coefficients */
347 forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i];
348 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
349 sideward_mu = sliding_mu[i];
350 if (abs_v_wheel_sideward < skid_v)
351 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
352 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
356 forward_mu=sliding_mu[i];
357 sideward_mu=sliding_mu[i];
360 /* Calculate foreward and sideward reaction forces */
362 forward_wheel_force = forward_mu*reaction_normal_force;
363 sideward_wheel_force = sideward_mu*reaction_normal_force;
364 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
365 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
366 /* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force);
368 /* Rotate into local (N-E-D) axes */
370 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
371 - sideward_wheel_force*sin_wheel_hdg_angle;
372 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
373 + sideward_wheel_force*cos_wheel_hdg_angle;
374 f_wheel_local_v[2] = reaction_normal_force;
376 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
377 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
379 /* Calculate moments from force and offsets in body axes */
381 cross3( d_wheel_cg_body_v, tempF, tempM );
383 /* Sum forces and moments across all wheels */
385 fgSetBool("/gear/gear[1]/wow", true);
388 add3( tempF, F_gear_v, F_gear_v );
389 add3( tempM, M_gear_v, M_gear_v );
396 /* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */
398 /*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear);
399 printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */
405 // end uiuc_engine.cpp