22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-4.10.1 (IL)

LONGITUDINAL ACTIVE STABILITY : KEY ISSUES FOR FUTURE LARGE TRANSPORT AIRCRAFT

F. Sauvinet
Aérospatiale-Matra Airbus, France

Keywords: stability, performance, weight, optimization

Aircraft optimization process pay a strong attention to weight and drag, especially for large aircraft that have severe cruise performance objectives. This paper shows how to reduce the tailplane size, using a concept of "active stability", i.e. reducing the aft CG margins provided an adequate system is always present to restore a same or even higher controllability level than conventionally "passively stable" aircraft. Modern flight control and autopilot systems do provide active stability whilst they are operating in non failure state. In order to take full benefit of active stability to reduce tailplane size, flight control system architecture must be designed in such a way that all the failure state including reversion to the backup mode provide active stability. The backup system is based on a simple feedback using a pitch rate gyrometer parallel to the normal flight control system. Several simulator sessions and test flight have been performed in order to validate the concept and prove that such design is viable. Information given by this flight test campaign show a very promising way, the aircraft with active stability system being very easy to fly at maximum aft CG, both in nominal non failure state and in backup mode simulation.

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