369 lines
11 KiB
C++
369 lines
11 KiB
C++
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/**********************************************************************
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FILENAME: uiuc_gear.cpp
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----------------------------------------------------------------------
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DESCRIPTION: determine the gear forces and moments
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----------------------------------------------------------------------
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STATUS: alpha version
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----------------------------------------------------------------------
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REFERENCES: based on c172_gear by Tony Peden and others
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----------------------------------------------------------------------
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HISTORY: 03/09/2001 initial release
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----------------------------------------------------------------------
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AUTHOR(S): David Megginson <david@megginson.com
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----------------------------------------------------------------------
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VARIABLES: [TODO]
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----------------------------------------------------------------------
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INPUTS: [TODO]
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----------------------------------------------------------------------
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OUTPUTS: [TODO]
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----------------------------------------------------------------------
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CALLED BY: uiuc_wrapper.cpp
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----------------------------------------------------------------------
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CALLS TO: none
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----------------------------------------------------------------------
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COPYRIGHT: (c) 2001 by David Megginson
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
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USA or view http://www.gnu.org/copyleft/gpl.html.
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**********************************************************************/
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#include <simgear/compiler.h>
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#include "uiuc_gear.h"
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SG_USING_STD(cerr);
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#define HEIGHT_AGL_WHEEL d_wheel_rwy_local_v[2]
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static void sub3( DATA v1[], DATA v2[], DATA result[] )
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{
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result[0] = v1[0] - v2[0];
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result[1] = v1[1] - v2[1];
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result[2] = v1[2] - v2[2];
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}
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static void add3( DATA v1[], DATA v2[], DATA result[] )
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{
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result[0] = v1[0] + v2[0];
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result[1] = v1[1] + v2[1];
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result[2] = v1[2] + v2[2];
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}
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static void cross3( DATA v1[], DATA v2[], DATA result[] )
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{
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result[0] = v1[1]*v2[2] - v1[2]*v2[1];
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result[1] = v1[2]*v2[0] - v1[0]*v2[2];
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result[2] = v1[0]*v2[1] - v1[1]*v2[0];
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}
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static void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
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{
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result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
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result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
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result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
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}
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static void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
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{
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result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
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result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
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result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
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}
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static void clear3( DATA v[] )
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{
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v[0] = 0.; v[1] = 0.; v[2] = 0.;
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}
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void uiuc_gear()
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{
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/*
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* Aircraft specific initializations and data goes here
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*/
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static DATA percent_brake[MAX_GEAR] = /* percent applied braking */
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{ 0., 0., 0., 0.,
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0., 0., 0., 0.,
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0., 0., 0., 0.,
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0., 0., 0., 0. }; /* 0 = none, 1 = full */
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static DATA caster_angle_rad[MAX_GEAR] = /* steerable tires - in */
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{ 0., 0., 0., 0.,
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0., 0., 0., 0.,
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0., 0., 0., 0.,
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0., 0., 0., 0. }; /* radians, +CW */
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/*
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* End of aircraft specific code
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*/
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/*
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* Constants & coefficients for tyres on tarmac - ref [1]
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*/
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/* skid function looks like:
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*
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* mu ^
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* |
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* max_mu | +
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* | /|
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* sliding_mu | / +------
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* | /
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* | /
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* +--+------------------------>
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* | | | sideward V
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* 0 bkout skid
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* V V
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*/
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static int it_rolls[MAX_GEAR] =
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{ 1, 1, 1, 0,
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0, 0, 0, 0,
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0, 0, 0, 0,
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0, 0, 0, 0 };
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static DATA sliding_mu[MAX_GEAR] =
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{ 0.5, 0.5, 0.5, 0.3,
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0.3, 0.3, 0.3, 0.3,
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0.3, 0.3, 0.3, 0.3,
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0.3, 0.3, 0.3, 0.3 };
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static DATA max_brake_mu[MAX_GEAR] =
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{ 0.0, 0.6, 0.6, 0.0,
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0.0, 0.0, 0.0, 0.0,
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0.0, 0.0, 0.0, 0.0,
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0.0, 0.0, 0.0, 0.0 };
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static DATA max_mu = 0.8;
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static DATA bkout_v = 0.1;
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static DATA skid_v = 1.0;
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/*
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* Local data variables
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*/
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DATA d_wheel_cg_body_v[3]; /* wheel offset from cg, X-Y-Z */
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DATA d_wheel_cg_local_v[3]; /* wheel offset from cg, N-E-D */
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DATA d_wheel_rwy_local_v[3]; /* wheel offset from rwy, N-E-U */
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DATA v_wheel_cg_local_v[3]; /*wheel velocity rel to cg N-E-D*/
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DATA v_wheel_body_v[3]; /* wheel velocity, X-Y-Z */
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DATA v_wheel_local_v[3]; /* wheel velocity, N-E-D */
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DATA f_wheel_local_v[3]; /* wheel reaction force, N-E-D */
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DATA altitude_local_v[3]; /*altitude vector in local (N-E-D) i.e. (0,0,h)*/
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DATA altitude_body_v[3]; /*altitude vector in body (X,Y,Z)*/
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DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
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DATA reaction_normal_force; /* wheel normal (to rwy) force */
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DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle; /* temp storage */
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DATA v_wheel_forward, v_wheel_sideward, abs_v_wheel_sideward;
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DATA forward_mu, sideward_mu; /* friction coefficients */
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DATA beta_mu; /* breakout friction slope */
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DATA forward_wheel_force, sideward_wheel_force;
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int i; /* per wheel loop counter */
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/*
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* Execution starts here
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*/
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beta_mu = max_mu/(skid_v-bkout_v);
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clear3( F_gear_v ); /* Initialize sum of forces... */
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clear3( M_gear_v ); /* ...and moments */
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/*
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* Put aircraft specific executable code here
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*/
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percent_brake[1] = Brake_pct[0];
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percent_brake[2] = Brake_pct[1];
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caster_angle_rad[0] =
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(0.01 + 0.04 * (1 - V_calibrated_kts / 130)) * Rudder_pedal;
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for (i=0;i<MAX_GEAR;i++) /* Loop for each wheel */
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{
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// Execute only if the gear has been defined
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if (!gear_model[i])
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continue;
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/* printf("%s:\n",gear_strings[i]); */
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/*========================================*/
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/* Calculate wheel position w.r.t. runway */
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/*========================================*/
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/* printf("\thgcg: %g, theta: %g,phi: %g\n",D_cg_above_rwy,Theta*RAD_TO_DEG,Phi*RAD_TO_DEG); */
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/* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
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sub3( D_gear_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
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/* then converting to local (North-East-Down) axes... */
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multtrans3x3by3( T_local_to_body_m, d_wheel_cg_body_v, d_wheel_cg_local_v );
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/* Runway axes correction - third element is Altitude, not (-)Z... */
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d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
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/* Add wheel offset to cg location in local axes */
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add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
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/* remove Runway axes correction so right hand rule applies */
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d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
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/*============================*/
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/* Calculate wheel velocities */
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/*============================*/
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/* contribution due to angular rates */
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cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
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/* transform into local axes */
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multtrans3x3by3( T_local_to_body_m, temp3a,v_wheel_cg_local_v );
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/* plus contribution due to cg velocities */
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add3( v_wheel_cg_local_v, V_local_rel_ground_v, v_wheel_local_v );
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clear3(f_wheel_local_v);
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reaction_normal_force=0;
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if( HEIGHT_AGL_WHEEL < 0. )
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/*the wheel is underground -- which implies ground contact
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so calculate reaction forces */
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{
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/*===========================================*/
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/* Calculate forces & moments for this wheel */
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/*===========================================*/
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/* Add any anticipation, or frame lead/prediction, here... */
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/* no lead used at present */
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/* Calculate sideward and forward velocities of the wheel
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in the runway plane */
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cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
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sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
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v_wheel_forward = v_wheel_local_v[0]*cos_wheel_hdg_angle
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+ v_wheel_local_v[1]*sin_wheel_hdg_angle;
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v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
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- v_wheel_local_v[0]*sin_wheel_hdg_angle;
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/* Calculate normal load force (simple spring constant) */
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reaction_normal_force = 0.;
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reaction_normal_force = kgear[i]*d_wheel_rwy_local_v[2]
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- v_wheel_local_v[2]*cgear[i];
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/* printf("\treaction_normal_force: %g\n",reaction_normal_force); */
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if (reaction_normal_force > 0.) reaction_normal_force = 0.;
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/* to prevent damping component from swamping spring component */
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/* Calculate friction coefficients */
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if(it_rolls[i])
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{
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forward_mu = (max_brake_mu[i] - muGear[i])*percent_brake[i] + muGear[i];
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abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
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sideward_mu = sliding_mu[i];
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if (abs_v_wheel_sideward < skid_v)
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sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
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if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
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}
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else
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{
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forward_mu=sliding_mu[i];
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sideward_mu=sliding_mu[i];
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}
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/* Calculate foreward and sideward reaction forces */
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forward_wheel_force = forward_mu*reaction_normal_force;
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sideward_wheel_force = sideward_mu*reaction_normal_force;
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if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
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if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
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/* printf("\tFfwdgear: %g Fsidegear: %g\n",forward_wheel_force,sideward_wheel_force);
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*/
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/* Rotate into local (N-E-D) axes */
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f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
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- sideward_wheel_force*sin_wheel_hdg_angle;
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f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
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+ sideward_wheel_force*cos_wheel_hdg_angle;
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f_wheel_local_v[2] = reaction_normal_force;
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/* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
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mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
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/* Calculate moments from force and offsets in body axes */
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cross3( d_wheel_cg_body_v, tempF, tempM );
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/* Sum forces and moments across all wheels */
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add3( tempF, F_gear_v, F_gear_v );
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add3( tempM, M_gear_v, M_gear_v );
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}
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/* printf("\tN: %g,dZrwy: %g dZdotrwy: %g\n",reaction_normal_force,HEIGHT_AGL_WHEEL,v_wheel_cg_local_v[2]); */
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/*printf("\tFxgear: %g Fygear: %g, Fzgear: %g\n",F_X_gear,F_Y_gear,F_Z_gear);
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printf("\tMgear: %g, Lgear: %g, Ngear: %g\n\n",M_m_gear,M_l_gear,M_n_gear); */
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}
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}
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// end uiuc_engine.cpp
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