DESIGN DEVELOPMENT AND FLIGHT EVALUATION OF AN ADVANCED DIGITAL FLIGHT CONTROL SYSTEM

An Advanced Digital Fight Control System (ADFCS) has been designed, installed in a prototype Apache Helicopter and flight tested. The ADFCS consists of a redundant set of 1750A microprocessor based computers and sensors supplied by Honeywell. This system controls a set of direct drive valve secondary actuators which drive the mechanical input valves on the aircraft primary actuators supplied by Bertea. The system is commanded from the CPG seat by means of side-arm-controllers with four-axis control capability. An advanced set of control laws designed to reduce pilot workload have been programmed into the computers. The aircraft flew for the first time in December 1985 with control laws which were designed to produce decoupled flying characteristics in hover and lowspeed flight conditions. Flight testing was successfully concluded in June 1986 and the workload reduction potential of control axis decoupling was demonstrated. As the development progressed, another set of control laws were incorporated which were designed to cover the full Apache envelope. This version included several control modes. The system transitions automatically between the control modes with no manual switching required. The first flight with the full envelope control laws was made in November of 1986. To date, the potential of control law concepts such as velocity vector management, auto-moding, self-trimming, hover position hold, turn-coordination in cruise and envelope control in reducing the pilot workload has been demonstrated. The ADFCS system on this aircraft is continuing to evolve during 1987 with refinement of the control laws providing engineering lessons applicable to future aircraft developments such as LHX.