/********************************************************************** FILENAME: uiuc_gear.cpp ---------------------------------------------------------------------- DESCRIPTION: determine the gear forces and moments ---------------------------------------------------------------------- STATUS: alpha version ---------------------------------------------------------------------- REFERENCES: based on c172_gear by Tony Peden and others ---------------------------------------------------------------------- HISTORY: 03/09/2001 initial release ---------------------------------------------------------------------- AUTHOR(S): David Megginson #include "uiuc_gear.h" SG_USING_STD(cerr); #define HEIGHT_AGL_WHEEL d_wheel_rwy_local_v[2] static void sub3( DATA v1[], DATA v2[], DATA result[] ) { result[0] = v1[0] - v2[0]; result[1] = v1[1] - v2[1]; result[2] = v1[2] - v2[2]; } static void add3( DATA v1[], DATA v2[], DATA result[] ) { result[0] = v1[0] + v2[0]; result[1] = v1[1] + v2[1]; result[2] = v1[2] + v2[2]; } static void cross3( DATA v1[], DATA v2[], DATA result[] ) { result[0] = v1[1]*v2[2] - v1[2]*v2[1]; result[1] = v1[2]*v2[0] - v1[0]*v2[2]; result[2] = v1[0]*v2[1] - v1[1]*v2[0]; } static void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] ) { result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2]; result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2]; result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2]; } static void mult3x3by3( DATA m[][3], DATA v[], DATA result[] ) { result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2]; result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2]; result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2]; } static void clear3( DATA v[] ) { v[0] = 0.; v[1] = 0.; v[2] = 0.; } void uiuc_gear() { /* * Aircraft specific initializations and data goes here */ static DATA percent_brake[MAX_GEAR] = /* percent applied braking */ { 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. }; /* 0 = none, 1 = full */ static DATA caster_angle_rad[MAX_GEAR] = /* steerable tires - in */ { 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. }; /* radians, +CW */ /* * End of aircraft specific code */ /* * Constants & coefficients for tyres on tarmac - ref [1] */ /* skid function looks like: * * mu ^ * | * max_mu | + * | /| * sliding_mu | / +------ * | / * | / * +--+------------------------> * | | | sideward V * 0 bkout skid * V V */ static int it_rolls[MAX_GEAR] = { 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; static DATA sliding_mu[MAX_GEAR] = { 0.5, 0.5, 0.5, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3, 0.3 }; static DATA max_brake_mu[MAX_GEAR] = { 0.0, 0.6, 0.6, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 }; static DATA max_mu = 0.8; static DATA bkout_v = 0.1; static DATA skid_v = 1.0; /* * Local data variables */ DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */ DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */ DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */ DATA v_wheel_cg_local_v[3]; /*wheel velocity rel to cg N-E-D*/ DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */ DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */ DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */ DATA altitude_local_v[3]; /*altitude vector in local (N-E-D) i.e. (0,0,h)*/ DATA altitude_body_v[3]; /*altitude vector in body (X,Y,Z)*/ DATA temp3a[3], temp3b[3], tempF[3], tempM[3]; DATA reaction_normal_force; /* wheel normal (to rwy) force */ DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */ DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward; DATA forward_mu, sideward_mu; /* friction coefficients */ DATA beta_mu; /* breakout friction slope */ DATA forward_wheel_force, sideward_wheel_force; int i; /* per wheel loop counter */ /* * Execution starts here */ beta_mu = max_mu/(skid_v-bkout_v); clear3( F_gear_v ); /* Initialize sum of forces... */ clear3( M_gear_v ); /* ...and moments */ /* * Put aircraft specific executable code here */ percent_brake[1] = Brake_pct[0]; percent_brake[2] = Brake_pct[1]; caster_angle_rad[0] = (0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal; for (i=0;i 0.) reaction_normal_force = 0.; /* to prevent damping component from swamping spring component */ /* Calculate friction coefficients */ if(it_rolls[i]) { forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i]; abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward); sideward_mu = sliding_mu[i]; if (abs_v_wheel_sideward < skid_v) sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu; if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.; } else { forward_mu=sliding_mu[i]; sideward_mu=sliding_mu[i]; } /* Calculate foreward and sideward reaction forces */ forward_wheel_force = forward_mu*reaction_normal_force; sideward_wheel_force = sideward_mu*reaction_normal_force; if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force; if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force; /* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force); */ /* Rotate into local (N-E-D) axes */ f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle - sideward_wheel_force*sin_wheel_hdg_angle; f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle + sideward_wheel_force*cos_wheel_hdg_angle; f_wheel_local_v[2] = reaction_normal_force; /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */ mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF ); /* Calculate moments from force and offsets in body axes */ cross3( d_wheel_cg_body_v, tempF, tempM ); /* Sum forces and moments across all wheels */ add3( tempF, F_gear_v, F_gear_v ); add3( tempM, M_gear_v, M_gear_v ); } /* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */ /*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear); printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */ } } // end uiuc_engine.cpp