## Subsystem Gravity

Gravity computes the gravitational force components along the aircraft's body axes. The acceleration of gravity, g, is extracted from the outputvector of Atmosph. The outputs from Gravity are sent to the block FMsort.

### Inputvectors: x and yatm

      x    = [V alpha beta p q r psi theta phi xe ye H]'     (states)
      yatm = [rho ps T mu g]'   (atmospheric properties, computed in
                                                   the block Atmosph)

     {V    : airspeed [m/s]                                         }
     {alpha: angle of attack [rad]                                  }
     {beta : sideslip angle [rad]                                   }
     {p    : roll rate [rad/s]                                      }
     {q    : pitch rate [rad/s]                                     }
     {r    : yaw rate [rad/s]                                       }
     {psi  : yaw angle [rad]                                        }
      theta: pitch angle [rad]
      phi  : roll angle [rad]
     {xe   : x-coordinate in Earth-fixed reference frame [m]        }
     {ye   : y-coordinate ''     ''          ''      ''  [m]        }
     {H    : altitude above sea-level [m]                           }

     {rho  : airdensity [kg/m^3]                                    }
     {ps   : static pressure [N/m^2]                                }
     {T    : temperature [K]                                        }
     {mu   : dynamic viscosity [kg/(m*s)]                           }
      g    : acceleration of gravity [m/s^2]

The inputsignals which are not actually used by Gravity have been put between curly braces.

### Outputvector: Fgrav

      Fgrav = [Xgr Ygr Zgr]'.

      Xgr, Ygr, Zgr: gravity force components along the aircraft's
                     body-axes [N].

### Parameters to be defined in the Matlab Workspace.

GM1: vector with some important geometrical properties of the 'Beaver' aircraft, and its mass (which is assumed to be constant during the motions of interest). Here, the mass m is extracted from GM1. The vector GM1 can be loaded into the workspace from file by running the utility DATLOAD. Run MODBUILD first if the datafile does not yet exist.