How do you design and validate a flight control law for a fly-by-wire aircraft?

Control law design process: Requirements definition (handling qualities specs, envelope protection needs), Linear design using classical (root locus, frequency response) or modern (LQR, H-infinity) methods, Nonlinear elements (limiters, blenders, gain schedules with Mach/altitude/config), Protection functions (AOA, g, bank angle limiting, departure prevention), and Robustness analysis (stability margins, parameter sensitivity). Validation includes: Linear analysis at grid of flight conditions, Nonlinear simulation across envelope including failures, Piloted simulation for handling qualities rating, Iron bird testing for system integration, and Flight test for final clearance. Documentation per DO-178C for software, ARP4754 for systems. Iteration between design, analysis, and piloted evaluation is essential. Process typically takes 3-5 years for new aircraft.