Flight control system

The flight control system model includes the pilot’s controls, mechanical linkages, actuation system and control rods; it also includes any augmentation through feedback control and hence will, in general, encompass the sensors, computing element and any additional actuation in parallel and/or in series with those driven by the mechanical inputs from the pilot. This description corresponds to the classical layout found in most contemporary helicopters. Discussion on the modelling requirements for full authority, digital, active control systems are not covered in this book. We refer to Fig. 3.36 as we develop the model of the flight control system, from the rotors through to the cockpit controls – the cyclic, collective and pedals. In the following analysis, the cockpit controls are represented by the variable n, with appropriate subscripts; in all cases,

0 < n < 1 (3.278)

with the positive sense defined by a positive increase in the corresponding rotor blade angle (see Fig. 3.36). The automatic flight control system (AFCS) is usually made up of stability and control augmentation system (SCAS) functions, applied through series actuators, and autopilot functions applied through parallel actuators. In this section we consider only the modelling of the SCAS.