flightgear/src/FDM/JSBSim/FGRotation.cpp

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 Module:       FGRotation.cpp
 Author:       Jon Berndt
 Date started: 12/02/98
 Purpose:      Integrates the rotational EOM
 Called by:    FGFDMExec

 ------------- Copyright (C) 1999  Jon S. Berndt (jsb@hal-pc.org) -------------

 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
 Foundation; either version 2 of the License, or (at your option) any later
 version.

 This program is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 details.

 You should have received a copy of the GNU General Public License along with
 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 Place - Suite 330, Boston, MA  02111-1307, USA.

 Further information about the GNU General Public License can also be found on
 the world wide web at http://www.gnu.org.

FUNCTIONAL DESCRIPTION
--------------------------------------------------------------------------------
This class integrates the rotational EOM.

HISTORY
--------------------------------------------------------------------------------
12/02/98   JSB   Created

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
COMMENTS, REFERENCES,  and NOTES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[1] Cooke, Zyda, Pratt, and McGhee, "NPSNET: Flight Simulation Dynamic Modeling
    Using Quaternions", Presence, Vol. 1, No. 4, pp. 404-420  Naval Postgraduate
    School, January 1994
[2] D. M. Henderson, "Euler Angles, Quaternions, and Transformation Matrices",
    JSC 12960, July 1977
[3] Richard E. McFarland, "A Standard Kinematic Model for Flight Simulation at
    NASA-Ames", NASA CR-2497, January 1975
[4] Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics",
    Wiley & Sons, 1979 ISBN 0-471-03032-5
[5] Bernard Etkin, "Dynamics of Flight, Stability and Control", Wiley & Sons,
    1982 ISBN 0-471-08936-2

  The order of rotations used in this class corresponds to a 3-2-1 sequence,
  or Y-P-R, or Z-Y-X, if you prefer.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

#include "FGRotation.h"
#include "FGAtmosphere.h"
#include "FGState.h"
#include "FGFDMExec.h"
#include "FGFCS.h"
#include "FGAircraft.h"
#include "FGMassBalance.h"
#include "FGTranslation.h"
#include "FGPosition.h"
#include "FGAuxiliary.h"
#include "FGOutput.h"

static const char *IdSrc = "$Id$";
static const char *IdHdr = ID_ROTATION;

extern short debug_lvl;

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/


FGRotation::FGRotation(FGFDMExec* fdmex) : FGModel(fdmex),
        vPQR(3),
        vPQRdot(3),
        vMoments(3),
        vEuler(3),
        vEulerRates(3),
	vlastPQRdot(3)
{
  Name = "FGRotation";
  cTht=cPhi=cPsi=1.0;
  sTht=sPhi=sPsi=0.0;

  if (debug_lvl & 2) cout << "Instantiated: " << Name << endl;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

FGRotation::~FGRotation()
{
  if (debug_lvl & 2) cout << "Destroyed:    FGRotation" << endl;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

bool FGRotation::Run(void)
{
  float L2, N1;
  float tTheta;

  if (!FGModel::Run()) {
    GetState();

    L2 = vMoments(eL) + Ixz*vPQR(eP)*vPQR(eQ) - (Izz-Iyy)*vPQR(eR)*vPQR(eQ);
    N1 = vMoments(eN) - (Iyy-Ixx)*vPQR(eP)*vPQR(eQ) - Ixz*vPQR(eR)*vPQR(eQ);

    vPQRdot(eP) = (L2*Izz - N1*Ixz) / (Ixx*Izz - Ixz*Ixz);
    vPQRdot(eQ) = (vMoments(eM) - (Ixx-Izz)*vPQR(eP)*vPQR(eR) - Ixz*(vPQR(eP)*vPQR(eP) - vPQR(eR)*vPQR(eR)))/Iyy;
    vPQRdot(eR) = (N1*Ixx + L2*Ixz) / (Ixx*Izz - Ixz*Ixz);

    vPQR += dt*rate*(vlastPQRdot + vPQRdot)/2.0;

    State->IntegrateQuat(vPQR, rate);
    State->CalcMatrices();
    vEuler = State->CalcEuler();

    cTht = cos(vEuler(eTht));   sTht = sin(vEuler(eTht));
    cPhi = cos(vEuler(ePhi));   sPhi = sin(vEuler(ePhi));
    cPsi = cos(vEuler(ePsi));   sPsi = sin(vEuler(ePsi));

    vEulerRates(eTht) = vPQR(2)*cPhi - vPQR(3)*sPhi;
    if (cTht != 0.0) {
      tTheta = sTht/cTht;       // what's cheaper: / or tan() ?
      vEulerRates(ePhi) = vPQR(1) + (vPQR(2)*sPhi + vPQR(3)*cPhi)*tTheta;
      vEulerRates(ePsi) = (vPQR(2)*sPhi + vPQR(3)*cPhi)/cTht;
    }

    vlastPQRdot = vPQRdot;

    if (debug_lvl > 1) Debug();

    return false;
  } else {
    return true;
  }
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

void FGRotation::GetState(void)
{
  dt = State->Getdt();
  vMoments = Aircraft->GetMoments();

  Ixx = MassBalance->GetIxx();
  Iyy = MassBalance->GetIyy();
  Izz = MassBalance->GetIzz();
  Ixz = MassBalance->GetIxz();
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

void FGRotation::Debug(void)
{
  if (debug_lvl & 16) { // Sanity check variables
    if (fabs(vPQR(eP)) > 100)
      cout << "FGRotation::P (Roll Rate) out of bounds: " << vPQR(eP) << endl;
    if (fabs(vPQR(eQ)) > 100)
      cout << "FGRotation::Q (Pitch Rate) out of bounds: " << vPQR(eQ) << endl;
    if (fabs(vPQR(eR)) > 100)
      cout << "FGRotation::R (Yaw Rate) out of bounds: " << vPQR(eR) << endl;
  }
}