A parameter identification self-adaptive control system

Abstract

dbstmcf-In a high-performance aircraft, c h a n g e s i n M a c h number, angle of attack, and altitude can cause a large variation i n t h e short-period transfer function. To provide the pilot with a constant pitch rate control characteristic, an airborne computer with inputs of elevator deflection angle and pitch rate is used to identify and track changes in the elevator effectiveness. Empirical equations are defined to approximate the aircraft time constant, damping factor, and natural frequency as functions of elevator effectiveness in three difference equations, which are iterated to model the aircraft. Parameters in the difference equations are systematically perturbed until the equation, which uses a value of elevator effectiveness intermediate between the values in the other two equations, also has the smallest mean-square error from the actual aircraft response. The value of elevator effectiveness in this intermediate equation is then presumed to be the same as that of the aircraft and is used to set the loop gain to a pre-determined suitable value. Simulation with an aircraft whose elevator effectiveness varied over a range of 240: 1 showed that the desired loop gain was maintained within a factor of two for both pilot command inputs and for random wind gust disturbances of a root-mean-square magnitude of 20 ftjs.