Practical aspects of flight control systems design

An aircraft´s flight envelope will usually be described in terms of Mach number to cover velocity and air compressibility effects, and altitude to cover air temperature and density effects. In order for the design of control laws to cover such an envelope, it is necessary to select a grid of operating points for which design is to be carried out. This results in a set of localised controllers for the operating points. As described so far, the design task is over a two-dimensional envelope, however, a third dimension covering aircraft angle-of-attack needs to be considered, in order to address the effects of aerodynamic nonlinearity and control surface trimming capability. The localised controller designs need to be linked together to cover the flight envelope. This can usually be satisfactorily achieved by using gain scheduling to produce a set of control laws. Various considerations are discussed