Flight Control Actuator

FARL demonstrated their Fly-by-Light system (in which fibre-optic cables are used instead of wires to pass signals between aircraft electronics boxes) at the 1980 SBAC show held at Farnborough. Following this they were approached by Airship Industries who were attempting to enter the military market, for which an airship is ideally suited for early warning, coastal surveillance and other long duration roles. The original system involved cables and pulleys and gave a heavy pilot workload as a result. Having realised that some form of electronic flight control system was required they ran into another problem that the airship was largely fabricated of non-conducting material and that the electrical cables would give dangerous lightning conductors.

FARL proposed the novel fibre-optic system which also included a highly innovative electrical actuator. The GEC Avionics design team was led by Consultants Staff Ellis and Peter Keay with Paul Buckingham, Trevor Hall, Dave Larner and Phil Lamb of FARL assisting. In January 1983 Marconi Avionics (FARL) signed a contract with Airship Industries Limited to design and build a prototype optically signalled FCS for the SKS600 airship. Delivery of the system was made in September 1983. The maiden flight was made on October 23 1988 fly-by-light by Airship Industries' chief test pilot Dave Burns at the company's US facility in Weeksville, North Carolina.

The major features of the FCS are:
● Fibre optic data transmission between the Flight Control Computer (FCC) and Actuator Drive Unit (ADU) to provide electrical isolation. Single fibres are to be used with data transmitted using Manchester encoding with MIL-STD-1553 format. Two independent supplies are provided.
● A duplicate system with pilot changeover in the event of a failure.
● An electrical actuator incorporating two dc servo motors with integral gear box The Actuator Drive Unit contains all the actuator electronics and fibre optic interface.
● A microprocessor-based Flight Control Computer.

The fibre optic cable used was a single optical fibre produced by GEC Optical Fibres Ltd and packaged by AEI Cables Ltd. Twelve fibre optic links are used within the Airship Flight Control System (FCS). These links handle all the data transmission between the Flight Control Computer (FCC) and Actuator Drive Units (ADU); the FCC being mounted in the gondola and the ADU are mounted within the surfaces on the rear of the Airship.

Eight of the twelve fibre optic links within the Airship FCS carry all surface position information from the FCC to the ADU and are therefore a vital part of the FCS. The remaining four fibre optic links transmit the status information from each ADU to the FCC for diagnosis.