## Subsystem Airdata3

Airdata3 computes the total temperature Tt and Reynolds numbers Re and Rc. Actually, the Reynolds numbers are no 'airdata variables', but they are closely related. Also, they are very important in aerospace engineering, in particular for the evaluation of windtunnel experiments. The block Airdata3 is contained in the subsystem Airdata Group of the system Beaver. Other airdata (-related) variables are computed in the blocks Atmosph, Airdata1, and Airdata2, which also contained in the subsystem Airdata Group.

### Inputvectors: x, yatm, and yad1

      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)
      yad1 = [a M qdyn]'    (airdata variables, computed in Airdata1)

      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]                        }

     {a    : speed of sound [m/s]                                   }
      M    : Mach number [-]
     {qdyn : dynamic pressure [N/m^2]                               }

The inputvariables which are not actually used by Airdata3 have been displayed between curly braces.

### Outputvector: yad3

      yad3 = [Tt Re Rc]',

      Tt   : total temperature [K]
      Re   : Reynolds number per m [1/m]
      Rc   : Reynolds number (using the mean aerodynamic chord as
             characteristic length) [-]

### Parameters to be defined in the Matlab workspace

- GM1: vector with some important geometrical properties of the 'Beaver' aircraft, and the mass of the aircraft (which is assumed to be constant during the motions of interest). Here, the mean aerodynamic chord is needed, in order to find the Reynolds number Rc. GM1 can be loaded into the workspace from file by running the utility DATLOAD. Run MODBUILD first if the datafile does not yet exist.