1 /***************************************************************************
5 ----------------------------------------------------------------------------
7 FUNCTION: aerodynamics, engine and gear model
9 ----------------------------------------------------------------------------
11 MODULE STATUS: developmental
13 ----------------------------------------------------------------------------
15 GENEALOGY: Equations based on Part 1 of Roskam's S&C text
17 ----------------------------------------------------------------------------
19 DESIGNED BY: Bipin Sehgal
21 CODED BY: Bipin Sehgal
23 MAINTAINED BY: Bipin Sehgal
25 ----------------------------------------------------------------------------
30 3/17/00 Initial test release
33 ----------------------------------------------------------------------------
37 ----------------------------------------------------------------------------
41 ----------------------------------------------------------------------------
45 ----------------------------------------------------------------------------
49 --------------------------------------------------------------------------*/
54 #include "ls_generic.h"
55 #include "ls_constants.h"
56 #include "ls_cockpit.h"
57 #include <FDM/UIUCModel/uiuc_wrapper.h>
60 void aero( SCALAR dt, int Initialize )
67 uiuc_init_aeromodel();
70 uiuc_force_moment(dt);
74 void engine( SCALAR dt, int Initialize )
76 uiuc_engine_routine();
79 /* ***********************************************************************
80 * Gear model. Exact copy of C172_gear.c. Additional gear models will be
81 * added later and the choice of the gear model could be specified at
83 * ***********************************************************************/
84 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 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 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 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 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];
121 v[0] = 0.; v[1] = 0.; v[2] = 0.;
126 char rcsid[] = "$Id$";
129 * Aircraft specific initializations and data goes here
134 static int num_wheels = NUM_WHEELS; /* number of wheels */
135 static DATA d_wheel_rp_body_v[NUM_WHEELS][3] = /* X, Y, Z locations */
137 { 10., 0., 4. }, /* in feet */
141 static DATA spring_constant[NUM_WHEELS] = /* springiness, lbs/ft */
142 { 1500., 5000., 5000. };
143 static DATA spring_damping[NUM_WHEELS] = /* damping, lbs/ft/sec */
144 { 100., 150., 150. };
145 static DATA percent_brake[NUM_WHEELS] = /* percent applied braking */
146 { 0., 0., 0. }; /* 0 = none, 1 = full */
147 static DATA caster_angle_rad[NUM_WHEELS] = /* steerable tires - in */
148 { 0., 0., 0.}; /* radians, +CW */
150 * End of aircraft specific code
154 * Constants & coefficients for tyres on tarmac - ref [1]
157 /* skid function looks like:
163 * sliding_mu | / +------
166 * +--+------------------------>
173 static DATA sliding_mu = 0.5;
174 static DATA rolling_mu = 0.01;
175 static DATA max_brake_mu = 0.6;
176 static DATA max_mu = 0.8;
177 static DATA bkout_v = 0.1;
178 static DATA skid_v = 1.0;
180 * Local data variables
183 DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
184 DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
185 DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
186 DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
187 DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
188 DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
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] = 0.; /* replace with cockpit brake handle connection code */
212 percent_brake[2] = percent_brake[1];
214 caster_angle_rad[0] = 0.03*Rudder_pedal;
216 for (i=0;i<num_wheels;i++) /* Loop for each wheel */
218 /*========================================*/
219 /* Calculate wheel position w.r.t. runway */
220 /*========================================*/
222 /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
224 sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
226 /* then converting to local (North-East-Down) axes... */
228 multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
230 /* Runway axes correction - third element is Altitude, not (-)Z... */
232 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
234 /* Add wheel offset to cg location in local axes */
236 add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
238 /* remove Runway axes correction so right hand rule applies */
240 d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
242 /*============================*/
243 /* Calculate wheel velocities */
244 /*============================*/
246 /* contribution due to angular rates */
248 cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
250 /* transform into local axes */
252 multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
254 /* plus contribution due to cg velocities */
256 add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
259 /*===========================================*/
260 /* Calculate forces & moments for this wheel */
261 /*===========================================*/
263 /* Add any anticipation, or frame lead/prediction, here... */
265 /* no lead used at present */
267 /* Calculate sideward and forward velocities of the wheel
268 in the runway plane */
270 cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
271 sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
273 v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
274 + v_wheel_local_v[1]*sin_wheel_hdg_angle;
275 v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
276 - v_wheel_local_v[0]*sin_wheel_hdg_angle;
278 /* Calculate normal load force (simple spring constant) */
280 reaction_normal_force = 0.;
281 if( d_wheel_rwy_local_v[2] < 0. )
283 reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
284 - v_wheel_local_v[2]*spring_damping[i];
285 if (reaction_normal_force > 0.) reaction_normal_force = 0.;
286 /* to prevent damping component from swamping spring component */
289 /* Calculate friction coefficients */
291 forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
292 abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
293 sideward_mu = sliding_mu;
294 if (abs_v_wheel_sideward < skid_v)
295 sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
296 if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
298 /* Calculate foreward and sideward reaction forces */
300 forward_wheel_force = forward_mu*reaction_normal_force;
301 sideward_wheel_force = sideward_mu*reaction_normal_force;
302 if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
303 if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
305 /* Rotate into local (N-E-D) axes */
307 f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
308 - sideward_wheel_force*sin_wheel_hdg_angle;
309 f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
310 + sideward_wheel_force*cos_wheel_hdg_angle;
311 f_wheel_local_v[2] = reaction_normal_force;
313 /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
315 mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
317 /* Calculate moments from force and offsets in body axes */
319 cross3( d_wheel_cg_body_v, tempF, tempM );
321 /* Sum forces and moments across all wheels */
323 add3( tempF, F_gear_v, F_gear_v );
324 add3( tempM, M_gear_v, M_gear_v );