NASA Technical Memorandum 4598 X - 29 Flight Control System : Lessons Learned June 1994

Two X-29A aircraft were flown at the NASA Dryden Flight Research Center over a period of eight years. The airplanes' unique features are the forward-swept wing, variable incidence close-coupled canard and highly relaxed longitudinal static stability (up to 35-percent negative static margin at subsonic conditions). This paper describes the primary flight control system and significant modifications made to this system, flight test techniques used during envelope expansion, and results for the lowand high-angle-of-attack programs. Throughout the paper, lessons learned will be discussed to illustrate the problems associated with the implementation of complex flight control systems. 1. NOMENCLATURE ACC automatic camber control (flight control system mode) AOA angle of attack ARI aileron-to-rudder interconnect BMAX rudder pedal command gain maximum lift coefficient CF cost function CP constraint penalty DP design point FCS flight control system FFT fast Fourier transform g unit of acceleration, 32.2 ft/sec 2 G lim pitch stick limit gain pitch rate feedback gain pitch acceleration feedback gain normal acceleration feedback gain GAIN1 pitch axis g -compensation gain GH(s) open-loop transfer function GF1 symmetric flaperon gain factor GS1 strake flap gain factor GMAX pitch stick command gain GYCWSH rudder pedal-to-aileron washout filter time constant Hg chemical symbol for the element mercury HG(s) loop gain matrix I identity matrix ISA integrated servoactuator j K2 roll rate-to-aileron feedback gain K3 -to-aileron feedback gain K4 lateral acceleration-to-aileron feedback gain K13 lateral stick-to-aileron forward-loop gain K14 rudder pedal-to-aileron forward-loop gain K17 -to-rudder feedback gain K18 lateral acceleration-to-rudder feedback gain K27 lateral stick-to-rudder forward-loop gain LOF left outboard flaperon LVOT linear variable differential transducer M Mach number MIMO multi-input–multi-output n y lateral acceleration, g n z normal acceleration, g NACA National Advisory Committee for Aeronautics p roll rate, deg/sec P s static pressure, inHg PCE pilot compensation error PMAX lateral stick command gain q pitch rate, deg/sec Q c impact pressure, inHg r yaw rate, deg/sec RDM return difference matrix RM redundancy management RPE resonance peak error s Laplace transform variable Lmax