Improved nonlinear design method for terrain-following flight control systems

An improved nonlinear control method is presented. This method adjusts the weights according to the magnitudes of the error and error rate. This method employs a correcting function α, which can be expressed as α=α₀ + K_α|E|/|E|_max; the symbols α, α₀, K_α, E, |E|_max have standard meanings, so they are not defined. As α is expressed in analytic form, it is easy to adjust the parameters of the controller according to the ITAE (integrated time absolute error) performance index and to optimize the design of the control system with high precision. This method is used to design a terrain following flight control system for a certain type of fighter and is compared with the traditional method. Simulation results show that: (1) the maximum terrain-following height error after 20 s is still about 20 m for the traditional method; (2) the maximum terrain-following height error after 5 s is only 0.4 m for our improved method.