92 lines
2.3 KiB
C
92 lines
2.3 KiB
C
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/***************************************************************************
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TITLE: ls_gravity
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----------------------------------------------------------------------------
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FUNCTION: Gravity model for LaRCsim
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----------------------------------------------------------------------------
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MODULE STATUS: developmental
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----------------------------------------------------------------------------
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GENEALOGY: Created by Bruce Jackson on September 25, 1992.
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----------------------------------------------------------------------------
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DESIGNED BY: Bruce Jackson
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CODED BY: Bruce Jackson
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MAINTAINED BY: Bruce Jackson
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----------------------------------------------------------------------------
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MODIFICATION HISTORY:
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DATE PURPOSE BY
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940111 Changed include files to "ls_types.h" and
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"ls_constants.h" from "ls_eom.h"; also changed DATA types
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to SCALAR types. EBJ
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$Header$
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$Log$
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Revision 1.1 1997/05/29 00:09:56 curt
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Initial Flight Gear revision.
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* Revision 1.2 1994/01/11 18:50:35 bjax
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* Corrected include files (was ls_eom.h) and DATA types changed
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* to SCALARs. EBJ
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*
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* Revision 1.1 1992/12/30 13:18:46 bjax
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* Initial revision
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*
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----------------------------------------------------------------------------
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REFERENCES: Stevens, Brian L.; and Lewis, Frank L.: "Aircraft
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Control and Simulation", Wiley and Sons, 1992.
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ISBN 0-471-
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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 "ls_types.h"
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#include "ls_constants.h"
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#include <math.h>
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#define GM 1.4076431E16
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#define J2 1.08263E-3
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void ls_gravity( SCALAR radius, SCALAR lat, SCALAR *gravity )
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{
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SCALAR radius_ratio, rrsq, sinsqlat;
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radius_ratio = radius/EQUATORIAL_RADIUS;
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rrsq = radius_ratio*radius_ratio;
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sinsqlat = sin(lat)*sin(lat);
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*gravity = (GM/(radius*radius))
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*sqrt(2.25*rrsq*rrsq*J2*J2*(5*sinsqlat*sinsqlat -2*sinsqlat + 1)
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+ 3*rrsq*J2*(1 - 3*sinsqlat) + 1);
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}
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