src/FDM/LaRCsim/ls_gravity.c

   1 /***************************************************************************
   2
   3         TITLE:  ls_gravity
   4
   5 ----------------------------------------------------------------------------
   6
   7         FUNCTION:       Gravity model for LaRCsim
   8
   9 ----------------------------------------------------------------------------
  10
  11         MODULE STATUS:  developmental
  12
  13 ----------------------------------------------------------------------------
  14
  15         GENEALOGY:      Created by Bruce Jackson on September 25, 1992.
  16
  17 ----------------------------------------------------------------------------
  18
  19         DESIGNED BY:    Bruce Jackson
  20
  21         CODED BY:       Bruce Jackson
  22
  23         MAINTAINED BY:  Bruce Jackson
  24
  25 ----------------------------------------------------------------------------
  26
  27         MODIFICATION HISTORY:
  28
  29         DATE    PURPOSE                                                 BY
  30
  31         940111  Changed include files to "ls_types.h" and
  32                 "ls_constants.h" from "ls_eom.h"; also changed DATA types
  33                 to SCALAR types.                                        EBJ
  34
  35
  36 $Header$
  37 $Log$
  38 Revision 1.1  1999/06/17 18:07:34  curt
  39 Initial revision
  40
  41 Revision 1.1.1.1  1999/04/05 21:32:45  curt
  42 Start of 0.6.x branch.
  43
  44 Revision 1.3  1998/08/06 12:46:39  curt
  45 Header change.
  46
  47 Revision 1.2  1998/01/19 18:40:26  curt
  48 Tons of little changes to clean up the code and to remove fatal errors
  49 when building with the c++ compiler.
  50
  51 Revision 1.1  1997/05/29 00:09:56  curt
  52 Initial Flight Gear revision.
  53
  54  * Revision 1.2  1994/01/11  18:50:35  bjax
  55  * Corrected include files (was ls_eom.h) and DATA types changed
  56  * to SCALARs. EBJ
  57  *
  58  * Revision 1.1  1992/12/30  13:18:46  bjax
  59  * Initial revision
  60  *
  61
  62 ----------------------------------------------------------------------------
  63
  64                 REFERENCES:     Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
  65                                 Control and Simulation", Wiley and Sons, 1992.
  66                                 ISBN 0-471-
  67
  68 ----------------------------------------------------------------------------
  69
  70                 CALLED BY:
  71
  72 ----------------------------------------------------------------------------
  73
  74                 CALLS TO:
  75
  76 ----------------------------------------------------------------------------
  77
  78                 INPUTS:
  79
  80 ----------------------------------------------------------------------------
  81
  82                 OUTPUTS:
  83
  84 --------------------------------------------------------------------------*/
  85 #include "ls_types.h"
  86 #include "ls_constants.h"
  87 #include "ls_gravity.h"
  88 #include <math.h>
  89
  90 #define GM      1.4076431E16
  91 #define J2      1.08263E-3
  92
  93 void ls_gravity( SCALAR radius, SCALAR lat, SCALAR *gravity )
  94 {
  95
  96         SCALAR  radius_ratio, rrsq, sinsqlat;
  97
  98         radius_ratio = radius/EQUATORIAL_RADIUS;
  99         rrsq = radius_ratio*radius_ratio;
 100         sinsqlat = sin(lat)*sin(lat);
 101         *gravity = (GM/(radius*radius))
 102                 *sqrt(2.25*rrsq*rrsq*J2*J2*(5*sinsqlat*sinsqlat -2*sinsqlat + 1)
 103                                 + 3*rrsq*J2*(1 - 3*sinsqlat) + 1);
 104
 105 }