Computers

The computation performed by the data processing part of an AFCS may be simple or complex depending on the type of system and degree of augmentation provided. Many older systems based around an analogue computer are still in operation, some of which provide limited outer loop modes such as height hold and automatic transitions. More modern and sophisticated systems such as fully capable autopilots suited for single pilot IFR operations and FBW installations require the flexibility and ease of control law implementation offered by digital computers. Some of the more common functions of the computer are:

• Amplification. To increase the signal strength from the sensor to a level high enough to be effective at the output stage.

• Integration. To derive synthetic attitude information from a rate gyro signal or translation rate from acceleration.

• Differentiation. To derive synthetic rate information from a vertical gyro signal.

• Summation. To generate an error signal by comparison of the pilot demand with the output from the appropriate sensor or to blend angular rate and attitude feedback signals.

• Limiting. To contain the effect of certain parameter changes within predetermined limits or to contain the effect of sub-system failures.

• Shaping. To adapt the control strategy and handling qualities to suit the particular mission phase.

• Programming. To produce a precise manoeuvre, such as an automatic transition, in the absence of positional data.

• Blending. The use of a particular parameter, such as airspeed, to modify the gain or functioning of an AFCS feature.

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