Flight Control Systems

Flight Control Systems By John Routledge

In previously developed aircraft flight control systems, it has been the airframers responsibility to fully define the system prior to it being put out to tender. However, in more recent flight control system developments, there has been a move towards an open period of system definition, where the system supplier has liaised closely with the customer to jointly develop the system definition. This has largely been driven by the reduction in time to market for new aircraft.

Improved by adopting a collaborative systems approach to engineering, there is now less duplication of effort.

Lucas Aerospace designs, manufactures and supplies advanced technology systems, products and services in the aerospace industry. Lucas Aerospace were chosen as contract leaders for the Indonesian IPTN N250 aircraft's Flight Control Systems, with complete responsibility for the control of the three axis fly-by-wire actuation system. Lucas Aerospace worked closely with IPTN at the start of the project to jointly define the requirements for the flight control systems. Drawing on aircraft level and equipment level expertise in this way produced a more complete system specification.

Benefits of this approach include all the requirements being understood by both customer and supplier; a cleaner customer/supplier interface; optimised system components, all leading to technologically advanced, but cost effective solution being engineered.

A number of lessons have also been learned from this project, mainly in the areas of customer/supplier management and in dealing with the difficulties in managing such a complex system In future projects, effective requirements management will be instrumental in controlling systems which are becoming ever more complex.

Historically, the provision of flight control systems has undergone a slow but steady development over the years.
In the early days systems were invariably mechanical. The pilot was directly linked to the control surfaces such that he could feel what was happening, This resulted in very simple systems. The aircraft manufacturer took responsibility for the design and manufacture of all the systems within the aircraft allowing an optimised and highly integrated design against their own requirements.

During the 1950's to 1960's, the increase in aircraft speeds and size resulted in the requirement for power flying controls. The power flying controls were complex, redundancy was required to achieve safety, hydraulic power sources had to be provided and artificial feel systems required to give the pilot tactile feedback he was used to. The huge increase in both complexity and technology forced a change of approach. Typically the aircraft manufacturer continued to be responsible for the system configuration and developed expertise in all areas of system design allowing them to define the configuration required and the major features of the component units. Equipment suppliers were used to design the equipment against the requirements and were only given responsibility for the detailed definition of the component units.

System complexity continued to increase, driven by the need to reduce aircraft weight and operating costs. Suppliers were given responsibility for larger systems e.g. secondary flight controls and increased responsibility for the configuration definition of other flight control units. This allowed a steady reduction in the level of aircraft manufacturer support necessary in the base technology areas.

Compressed project time scales started to drive the need for concurrent working in order to allow the airframe and equipment supplier to work together to jointly define the system configuration. The A300 Flap and Slat system are typical of the systems developed around this time.