## Autopilot model, subsystem Symmetrical autopilot modes

The subsystem Asymmetrical autopilot modes, which is part of the systems APILOT1, APILOT2, and APILOT3 contains the following control modes of the 'Beaver' autopilot:

- Pitch Attitude Hold (PAH), including turn compensation
- Altitude Hold (ALH), including turn compensation
- Altitude Select (ALS)
- symmetrical approach mode: Glideslope (GS)

The PAH mode is also used as inner-loop for ALH, ALS, and GS.

In Glideslope mode, a switch criterion is used to switch from the Glideslope-Armed phase, in which the aircraft is usually flying under ALH control, to Glideslope-Coupled. Note: for reasons of computing speed, GS has not been included in the system APILOT1.

The block Select symm. mode-controller signals separates the mode-switch settings from the inputvector ymode and reference signals from the inputvector yref for the symmetrical autopilot modes from the asymmetrical mode-switch settings and reference signals.

### More information

See the explanation of the subsystems Mode Controller and Reference Signals for more information about the inputvectors ymode and yref. See also the color definition table for the FDC toolbox and the subsystem Asymmetrical autopilot modes.

### References

For a detailed description of the 'Beaver' autopilot, refer to the FDC user-manual. More information can be found in the following references:

1. M.O. Rauw: A Simulink environment for Flight Dynamics and Control analysis - Application to the DHC-2 'Beaver' (PART II). MSc-thesis, Delft University of Technology, Faculty of Aerospace Engineering, Delft, The Netherlands, 1993.
2. P.N.H. Wever: Ontwerp en implementatie van de regelwetten van de De Havilland DHC-2 'Beaver' (in Dutch). MSc-thesis, Delft University of Technology, Faculty of Aerospace Engineering, Delft, The Netherlands, 1993.