## Subsystem Airdata Group

The subsystem Airdata Group from the Beaver model consists of four masked subsystem blocks: Atmosph, Airdata1, Airdata2, and Airdata3. The block Atmosph computes a number of atmospheric properties, Airdata1 computes the basic airdata variables, and Airdata2 and Airdata3 compute additional airdata (-related) variables.

The results from the masked subsystem Atmosph are needed by the three Airdata blocks, and the results from Airdata1 are needed by Airdata2 and Airdata3. For this reason, the block Atmosph has been located on the upper left side of the subsystem, Airdata1 has been located in the middle of the subsystem, and Airdata2 and Airdata3 have been located on the lower right side of the subsystem. The vertical shift is needed in order to be able to connect the outputvectors from the different blocks to the Outports on the right side of the subsystem Airdata Group.

Note: ICAO Standard Atmosphere is used for the atmosphere model. See for instance ref.[1] for details about that model.

### Inputvector: x

      x = [V alpha beta p q r psi theta phi xe ye H]'        (states)

      V    : true 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, relative to Earth-axes [m]               }
     {ye   : Y-coordinate, relative to Earth-axes [m]               }
      H    : altitude above sea level [m]

The curly braces denote state variables which are not needed by the masked subsystem blocks in the subsystem Airdata Group.

### Outputvectors: yatm, yad1, yad2, and yad3

      yatm = [rho ps T mu g]'                  (outputs from Atmosph)
      yad1 = [a M qdyn]'                      (outputs from Airdata1)
      yad2 = [qc Ve Vc]'                      (outputs from Airdata2)
      yad3 = [Tt Re Rc]'                      (outputs from Airdata3)

      rho  : air density [kg/m^3]
      ps   : static pressure [N/m^2]
      T    : air 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]

      qc   : impact pressure [N/m^2]
      Ve   : equivalent airspeed [m/s]
      Vc   : calibrated airspeed [m/s]

      Tt   : total temperature [K]
      Re   : Reynolds number per unit length [1/m]
      Rc   : Reynolds number with respect to mean aerodyn. chord [-]

### 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). This vector is needed by Airdata3. GM1 can be loaded into the workspace from file by running the utility DATLOAD. Run MODBUILD first if the datafile does not yet exist.

### References

1. Ruijgrok, G.J.J. Elements of airplane performance. Delft University Press, Delft, The Netherlands, 1993.