317 lines
9.4 KiB
C
317 lines
9.4 KiB
C
/***************************************************************************
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TITLE: gear
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----------------------------------------------------------------------------
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FUNCTION: Landing gear model for example simulation
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----------------------------------------------------------------------------
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MODULE STATUS: developmental
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----------------------------------------------------------------------------
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GENEALOGY: Created 931012 by E. B. Jackson
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----------------------------------------------------------------------------
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DESIGNED BY: E. B. Jackson
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CODED BY: E. B. Jackson
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MAINTAINED BY: E. B. Jackson
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----------------------------------------------------------------------------
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MODIFICATION HISTORY:
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DATE PURPOSE BY
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931218 Added navion.h header to allow connection with
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aileron displacement for nosewheel steering. EBJ
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940511 Connected nosewheel to rudder pedal; adjusted gain.
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CURRENT RCS HEADER:
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$Header$
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$Log$
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Revision 1.2 1998/01/19 18:40:29 curt
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Tons of little changes to clean up the code and to remove fatal errors
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when building with the c++ compiler.
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Revision 1.1 1997/05/29 00:10:02 curt
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Initial Flight Gear revision.
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----------------------------------------------------------------------------
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REFERENCES:
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----------------------------------------------------------------------------
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CALLED BY:
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----------------------------------------------------------------------------
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CALLS TO:
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----------------------------------------------------------------------------
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INPUTS:
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----------------------------------------------------------------------------
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OUTPUTS:
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--------------------------------------------------------------------------*/
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#include <math.h>
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#include "ls_types.h"
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#include "ls_constants.h"
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#include "ls_generic.h"
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#include "ls_cockpit.h"
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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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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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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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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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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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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 gear( SCALAR dt, int Initialize ) {
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char rcsid[] = "$Id$";
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/*
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* Aircraft specific initializations and data goes here
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*/
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#define NUM_WHEELS 3
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static int num_wheels = NUM_WHEELS; /* number of wheels */
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static DATA d_wheel_rp_body_v[NUM_WHEELS][3] = /* X, Y, Z locations */
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{
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{ 10., 0., 4. }, /* in feet */
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{ -1., 3., 4. },
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{ -1., -3., 4. }
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};
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static DATA spring_constant[NUM_WHEELS] = /* springiness, lbs/ft */
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{ 1500., 5000., 5000. };
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static DATA spring_damping[NUM_WHEELS] = /* damping, lbs/ft/sec */
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{ 100., 150., 150. };
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static DATA percent_brake[NUM_WHEELS] = /* percent applied braking */
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{ 0., 0., 0. }; /* 0 = none, 1 = full */
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static DATA caster_angle_rad[NUM_WHEELS] = /* steerable tires - in */
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{ 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 DATA sliding_mu = 0.5;
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static DATA rolling_mu = 0.01;
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static DATA max_brake_mu = 0.6;
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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_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 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] = 0.; /* replace with cockpit brake handle connection code */
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percent_brake[2] = percent_brake[1];
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caster_angle_rad[0] = 0.03*Rudder_pedal;
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for (i=0;i<num_wheels;i++) /* Loop for each wheel */
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{
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/*========================================*/
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/* Calculate wheel position w.r.t. runway */
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/*========================================*/
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/* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
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sub3( d_wheel_rp_body_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, temp3b );
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/* plus contribution due to cg velocities */
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add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
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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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if( d_wheel_rwy_local_v[2] < 0. )
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{
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reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
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- v_wheel_local_v[2]*spring_damping[i];
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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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}
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/* Calculate friction coefficients */
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forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
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abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
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sideward_mu = sliding_mu;
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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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/* 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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/* 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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}
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