1 /***************************************************************************
5 ----------------------------------------------------------------------------
7 FUNCTION: Sums forces and moments and calculates accelerations
9 ----------------------------------------------------------------------------
11 MODULE STATUS: developmental
13 ----------------------------------------------------------------------------
15 GENEALOGY: Written 920731 by Bruce Jackson. Based upon equations
16 given in reference [1] and a Matrix-X/System Build block
17 diagram model of equations of motion coded by David Raney
18 at NASA-Langley in June of 1992.
20 ----------------------------------------------------------------------------
22 DESIGNED BY: Bruce Jackson
24 CODED BY: Bruce Jackson
28 ----------------------------------------------------------------------------
34 931007 Moved calculations of auxiliary accelerations here from ls_aux.c BY
35 and corrected minus sign in front of A_Y_Pilot
36 contribution from Q_body*P_body*D_X_pilot term.
37 940111 Changed DATA to SCALAR; updated header files
41 Revision 1.2 1998/01/19 18:40:24 curt
42 Tons of little changes to clean up the code and to remove fatal errors
43 when building with the c++ compiler.
45 Revision 1.1 1997/05/29 00:09:53 curt
46 Initial Flight Gear revision.
48 * Revision 1.5 1994/01/11 18:42:16 bjax
49 * Oops! Changed data types from DATA to SCALAR for precision control.
51 * Revision 1.4 1994/01/11 18:36:58 bjax
52 * Removed ls_eom.h include directive; replaced with ls_types, ls_constants,
53 * and ls_generic.h includes.
55 * Revision 1.3 1993/10/07 18:45:24 bjax
56 * Added local defn of d[xyz]_pilot_from_cg to support previous mod. EBJ
58 * Revision 1.2 1993/10/07 18:41:31 bjax
59 * Moved calculations of auxiliary accelerations here from ls_aux, and
60 * corrected sign on Q_body*P_body*d_x_pilot term of A_Y_pilot calc. EBJ
62 * Revision 1.1 1992/12/30 13:17:02 bjax
66 ----------------------------------------------------------------------------
70 [ 1] McFarland, Richard E.: "A Standard Kinematic Model
71 for Flight Simulation at NASA-Ames", NASA CR-2497,
74 ----------------------------------------------------------------------------
78 ----------------------------------------------------------------------------
82 ----------------------------------------------------------------------------
84 INPUTS: Aero, engine, gear forces & moments
86 ----------------------------------------------------------------------------
88 OUTPUTS: State derivatives
90 -------------------------------------------------------------------------*/
92 #include "ls_generic.h"
93 #include "ls_constants.h"
97 void ls_accel( void ) {
99 SCALAR inv_Mass, inv_Radius;
100 SCALAR ixz2, c0, c1, c2, c3, c4, c5, c6, c7, c8, c9, c10;
101 SCALAR dx_pilot_from_cg, dy_pilot_from_cg, dz_pilot_from_cg;
104 /* Sum forces and moments at reference point */
107 F_X = F_X_aero + F_X_engine + F_X_gear;
108 F_Y = F_Y_aero + F_Y_engine + F_Y_gear;
109 F_Z = F_Z_aero + F_Z_engine + F_Z_gear;
111 M_l_rp = M_l_aero + M_l_engine + M_l_gear;
112 M_m_rp = M_m_aero + M_m_engine + M_m_gear;
113 M_n_rp = M_n_aero + M_n_engine + M_n_gear;
115 /* Transfer moments to center of gravity */
117 M_l_cg = M_l_rp + F_Y*Dz_cg - F_Z*Dy_cg;
118 M_m_cg = M_m_rp + F_Z*Dx_cg - F_X*Dz_cg;
119 M_n_cg = M_n_rp + F_X*Dy_cg - F_Y*Dx_cg;
121 /* Transform from body to local frame */
123 F_north = T_local_to_body_11*F_X + T_local_to_body_21*F_Y
124 + T_local_to_body_31*F_Z;
125 F_east = T_local_to_body_12*F_X + T_local_to_body_22*F_Y
126 + T_local_to_body_32*F_Z;
127 F_down = T_local_to_body_13*F_X + T_local_to_body_23*F_Y
128 + T_local_to_body_33*F_Z;
130 /* Calculate linear accelerations */
133 inv_Radius = 1/Radius_to_vehicle;
134 V_dot_north = inv_Mass*F_north +
135 inv_Radius*(V_north*V_down - V_east*V_east*tan(Lat_geocentric));
136 V_dot_east = inv_Mass*F_east +
137 inv_Radius*(V_east*V_down + V_north*V_east*tan(Lat_geocentric));
138 V_dot_down = inv_Mass*(F_down) + Gravity -
139 inv_Radius*(V_north*V_north + V_east*V_east);
141 /* Invert the symmetric inertia matrix */
144 c0 = 1/(I_xx*I_zz - ixz2);
145 c1 = c0*((I_yy-I_zz)*I_zz - ixz2);
146 c2 = c0*I_xz*(I_xx - I_yy + I_zz);
150 c5 = c7*(I_zz - I_xx);
152 c8 = c0*((I_xx - I_yy)*I_xx + ixz2);
153 c9 = c0*I_xz*(I_yy - I_zz - I_xx);
156 /* Calculate the rotational body axis accelerations */
158 P_dot_body = (c1*R_body + c2*P_body)*Q_body + c3*M_l_cg + c4*M_n_cg;
159 Q_dot_body = c5*R_body*P_body + c6*(R_body*R_body - P_body*P_body) + c7*M_m_cg;
160 R_dot_body = (c8*P_body + c9*R_body)*Q_body + c4*M_l_cg + c10*M_n_cg;
162 /* Calculate body axis accelerations (move to ls_accel?) */
166 A_X_cg = F_X * inv_Mass;
167 A_Y_cg = F_Y * inv_Mass;
168 A_Z_cg = F_Z * inv_Mass;
170 dx_pilot_from_cg = Dx_pilot - Dx_cg;
171 dy_pilot_from_cg = Dy_pilot - Dy_cg;
172 dz_pilot_from_cg = Dz_pilot - Dz_cg;
174 A_X_pilot = A_X_cg + (-R_body*R_body - Q_body*Q_body)*dx_pilot_from_cg
175 + ( P_body*Q_body - R_dot_body )*dy_pilot_from_cg
176 + ( P_body*R_body + Q_dot_body )*dz_pilot_from_cg;
177 A_Y_pilot = A_Y_cg + ( P_body*Q_body + R_dot_body )*dx_pilot_from_cg
178 + (-P_body*P_body - R_body*R_body)*dy_pilot_from_cg
179 + ( Q_body*R_body - P_dot_body )*dz_pilot_from_cg;
180 A_Z_pilot = A_Z_cg + ( P_body*R_body - Q_dot_body )*dx_pilot_from_cg
181 + ( Q_body*R_body + P_dot_body )*dy_pilot_from_cg
182 + (-Q_body*Q_body - P_body*P_body)*dz_pilot_from_cg;
184 N_X_cg = INVG*A_X_cg;
185 N_Y_cg = INVG*A_Y_cg;
186 N_Z_cg = INVG*A_Z_cg;
188 N_X_pilot = INVG*A_X_pilot;
189 N_Y_pilot = INVG*A_Y_pilot;
190 N_Z_pilot = INVG*A_Z_pilot;
193 U_dot_body = T_local_to_body_11*V_dot_north + T_local_to_body_12*V_dot_east
194 + T_local_to_body_13*V_dot_down - Q_total*W_body + R_total*V_body;
195 V_dot_body = T_local_to_body_21*V_dot_north + T_local_to_body_22*V_dot_east
196 + T_local_to_body_23*V_dot_down - R_total*U_body + P_total*W_body;
197 W_dot_body = T_local_to_body_31*V_dot_north + T_local_to_body_32*V_dot_east
198 + T_local_to_body_33*V_dot_down - P_total*V_body + Q_total*U_body;
199 /* End of ls_accel */
202 /**************************************************************************/