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  2002/09/10 01:14:02  curt
  39 Initial revision
  40
  41 Revision 1.1.1.1  1999/06/17 18:07:34  curt
  42 Start of 0.7.x branch
  43
  44 Revision 1.1.1.1  1999/04/05 21:32:45  curt
  45 Start of 0.6.x branch.
  46
  47 Revision 1.3  1998/08/06 12:46:39  curt
  48 Header change.
  49
  50 Revision 1.2  1998/01/19 18:40:26  curt
  51 Tons of little changes to clean up the code and to remove fatal errors
  52 when building with the c++ compiler.
  53
  54 Revision 1.1  1997/05/29 00:09:56  curt
  55 Initial Flight Gear revision.
  56
  57  * Revision 1.2  1994/01/11  18:50:35  bjax
  58  * Corrected include files (was ls_eom.h) and DATA types changed
  59  * to SCALARs. EBJ
  60  *
  61  * Revision 1.1  1992/12/30  13:18:46  bjax
  62  * Initial revision
  63  *
  64
  65 ----------------------------------------------------------------------------
  66
  67                 REFERENCES:     Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
  68                                 Control and Simulation", Wiley and Sons, 1992.
  69                                 ISBN 0-471-
  70
  71 ----------------------------------------------------------------------------
  72
  73                 CALLED BY:
  74
  75 ----------------------------------------------------------------------------
  76
  77                 CALLS TO:
  78
  79 ----------------------------------------------------------------------------
  80
  81                 INPUTS:
  82
  83 ----------------------------------------------------------------------------
  84
  85                 OUTPUTS:
  86
  87 --------------------------------------------------------------------------*/
  88 #include "ls_types.h"
  89 #include "ls_constants.h"
  90 #include "ls_gravity.h"
  91 #include <math.h>
  92
  93 #define GM      1.4076431E16
  94 #define J2      1.08263E-3
  95
  96 void ls_gravity( SCALAR radius, SCALAR lat, SCALAR *gravity )
  97 {
  98
  99         SCALAR  radius_ratio, rrsq, sinsqlat;
 100
 101         radius_ratio = radius/EQUATORIAL_RADIUS;
 102         rrsq = radius_ratio*radius_ratio;
 103         sinsqlat = sin(lat)*sin(lat);
 104         *gravity = (GM/(radius*radius))
 105                 *sqrt(2.25*rrsq*rrsq*J2*J2*(5*sinsqlat*sinsqlat -2*sinsqlat + 1)
 106                                 + 3*rrsq*J2*(1 - 3*sinsqlat) + 1);
 107
 108 }