AUTOMATIC FLIGHT CONTROL SYSTEM FOR THE ANGLO-ITALIAN EH101 HELICOPTER

The EH101 Helicopter is being developed by Westland Helicopters Ltd. and Agusta Spl to meet two widely differing primary roles, namely anti-submarine operations and passenger transport for Civil applications. The Automatic Flight Control System is designed to ensure that the helicopter will both meet the exacting safety standards necessary for the Civil role and successfully complete a mission when subjected to the severe environmental conditions encountered during naval operations. Following a brief review of the major design objectives, the paper presents a description of the AFCS configuration, which provides failure survival autostabilisation about cyclic and yaw axes, and a wide range of autopilot functions with reversionary processing capability. The system includes two computer units, each incorporating four microprocessors, two of one type and two of a dissimilar type, with the processing functions distributed to achieve a high degree of axis independence and to minimise the probability and consequences of common mode failures. The technology adopted for units of the system and special design features of the flight control computers, including monitoring and memory protection are discussed. Techniques adopted to ensure adequate protection of the system against the arduous environment conditions are discussed. Independent design teams in the UK and in Italy are producing software for the two different microprocessor types. The software development and control techniques are discussed in the paper which concludes with a brief discussion of the specialised rigs, simulators and flight trials equipment being developed to carry out the programme. The AFCS development is a joint Anglo-Italian programme, shared by Smiths Industries Aerospace & Defence Systems and Agust-OMI. This team is also developing the Electronic Flight Instrument System for the EH101.