Chong-Sup Kim, Gi-Bong Hur, Byung-Moon Hwang, In-Je Cho and Seung-Jun Kim
International Journal of Aeronautical and Space Sicences, vol. 8, no. 1, pp.32-45, 2007

Abstract : The T-50 advanced supersonic jet trainer employs the Relaxed Static Stability (RSS) concept to improve the aerodynamic performance while the flight control system stabilizes the unstable aircraft and provides adequate handling qualities. The T-50 flight control laws employ a proportional-plus-integral type controller based on a dynamic inversion method in longitudinal axis and a proportional type controller based on a blended roll system with simple roll rate feedback and beta-betadot feedback system. These control laws are verified by flight tests with various maneuver set flight envelopes and the control laws are updated to resolve flight test issues. This paper describes several concepts of flight control laws used in T-50 to resolve those flight test issues. Control laws for solving the roll-off problem during pitch maneuver in asymmetric loading configurations, improving the departure resistance in negative angle of attack conditions and enhancing the fine tracking performance in air-to-air tracking maneuvers are described with flight test data.

Keyword : Relaxed static stability, Digital fly-by-wire flight control system, Angle-of-attack limiter, Departure resistance, Fine tacking performance