Jaguar Flight Control Computer (FCC)

 The Jaguar was the result of an Anglo-French collaboration to develop an advanced training and strike aircraft, entering service with the Royal Air Force in 1973.
XX765 was withdrawn from RAF service to demonstrate the feasibility of Active Control Technology (ACT), under development by British Aerospace (BAe). The aircraft's normal control rods were replaced with a 'fly-by-wire' (FBW) control system, which used four independent computer-controlled electrical channels to relay instructions to the flight surfaces. The aircraft was further modified by fitting large leading edge strakes (wing extensions) to move the centre of lift forward and adding ballast to the rear fuselage to move the centre of gravity aft. This enhanced the lift and drag characteristics and made the tail plane more efficient thereby allowing smaller lighter engines with greater fuel efficiency to be used, decreasing overall weight by 15% thereby greatly enhancing aircraft manoeuvrability – important to the next generation of air superiority fighters.
Flight trials began in October 1981. Test pilots were impressed by the crisp control responses and smooth flight. The aerodynamic instability of the aircraft enhanced manoeuvrability, but the computer-controlled flight commands provided split-second corrections to compensate for the unstable configuration.

The aircraft first flew on 20 October 1981 and was the first aircraft to fly with an all digital FBW flight control system with no form of reversionary (back up) control. The test programme was completed in 1984 after 96 flights, having successfully demonstrated concepts which were subsequently incorporated into the Typhoon and Boeing 777 FBW flight control computers produced by the company.

This Flight Control Computer (FCC) was part of the FBW system developed to demonstrate the feasibility of Active Control Technology using an RAF Jaguar which was withdrawn from Service. The aircraft’s normal control rods were replaced with an Integrated Flight Control System FBW which used four of these independent FCCs to electrically relay instructions to the flight surfaces.

The duo-triplex actuation system was developed to drive the rudder, two taileron and two spoiler control surfaces. The five Powered Flying Control Units (PFCU) are essentially similar, with variations in valve ports, jack strokes and diameters. Each PFCU contains six flapper nozzle service valves which convert electrical inputs from the Flight Control Computers (FCC) and Actuator Drive and Monitor Computers (ADMC) into hydraulic signals which are then used to drive the actuators.

The actuation architecture requires 6 independent drive signals to each actuator, but the integrity objectives do not necessitate the cost and complexity of a full six lane system. The flight control system (FCS) is therefore essentially a quadruplex digital system with special facilities to provide the additional independent drives to the actuators. All mechanical rods downstream of the trim and feel units have been removed, thus there is no mechanical or independent back up reversion.

Quadruplex Position Sensors (QPS) are used to sense pilot control demands in terms of stick, pedal and trim inputs and quadruplex rate gyros sense aircraft pitch, roll and yaw rates. Four identical digital FCCs are used to process these signals together with those from other sensors. The resulting command signals are used to control the actuators. To convert the quadruplex signals from the FCCs into the sextuplex signals required by the actuators, the FCCs are supplemented by two Actuator Drive and Monitor Computers (ADMC).