## Subsystem Aerodynamics Group (Beaver)

The subsystem Aerodynamics Group (Beaver) of the Beaver model contains blocks that determine the aerodynamic forces and moments for the 'Beaver' aircraft. The block Dimless first computes the non-dimensional rotational velocity components along the aircraft's body-axes. The dimensionless force and moment coefficients are then calculated in the block Aeromod (Beaver), which contains the actual (aircraft-dependent) aerodynamic model, and finally, the real values of these forces and moments are determined by the block FMdims.

As implied by its name, the subsystem Aerodynamics Group (Beaver) is only valid for the De Havilland DHC-2 'Beaver', using the aerodynamic model from ref.[1]. The internal structure of similar models for other aircraft may look entirely different. For instance, in this case the block Dimless is needed, because the dimensionless rotational velocities are used as helpvariables for the actual aerodynamic model in Aeromod, whereas aerodynamic models for other aircraft may require entirely different helpvariables.

For this reason, the internal structure of the subsystem Aerodynamics Group will always depend upon the aircraft model considered.

### Inputs: x, uaero, yad1

      x    = [V alpha beta p q r psi theta phi xe ye H]'     (states)
      uaero= [deltae deltaa deltar deltaf]' (aerodyn. control-inputs)
      yad1 = [a M qdyn]'                   (basic airdata variables,
                                                coming from Airdata1)

      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]                          }

      deltae: deflection of elevator [rad]
      deltaa: deflection of ailerons [rad]
      deltar: deflection of rudder [rad]
      deltaf: deflection of flaps [rad]

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

The variables which are not actually used by any of the masked subsystems Dimless, Aeromod (Beaver), and FMdims have been displayed between curly braces.

### Outputs: ydl, Caero, FMaero

      ydl   = [pb/2V qc/V rb/2V]'              (outputs from Dimless)
      Caero = [CXa CYa CZa Cla Cma Cna]'       (outputs from Aeromod)
      FMaero= [Xa Ya Za La Ma Na]'              (outputs from FMdims)

      CXa, CYa, CZa: dimensionless aerodynamic force coefficients
      Cla, Cma, Cna: dimensionless aerodynamic moment coefficients
      Xa, Ya, Za   : aerodynamic forces [N]
      La, Ma, Na   : aerodynamic moments [Nm]

### 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, it is needed by Dimless in order to extract geometrical data.
- AM: matrix with stability and control derivatives of the 'Beaver' (valid only for the nonlinear aerodynamic model of the DHC-2 'Beaver', see ref.[1]). This matrix is needed by Aeromod (Beaver).

AM and GM1 can be loaded into the workspace from datafile by running the utility DATLOAD. Run MODBUILD first if the datafile does not yet exist.

### References

1. R.T.H. Tjee and J.A. Mulder. Stability and Control Derivatives of the De Havilland DHC-2 "Beaver" aircraft. Report LR-556, Delft University of Technology, 1988.