Dual Loop PI^m PI^n Control for an Aileron Positioning

Aircraft control surfaces are subjected to uncertain design parameters and time–varying external disturbances related to aerodynamic loads. This paper presents a control formulation for their positioning based on a velocity/position dual loop, embedding an arbitrary order of integral actions determined through a simple linear design. The adoption of an appropriate high order integration aims to compensate for external disturbances, modeling uncertainties and the impact of some nonlinearities. Relevant design and implementation issues were also described, including windup mitigation and the use of an observer to compensate for out–of–band disturbances. After a numerical model validation comprising a Monte Carlo assessment of the combined uncertainties, the controller was verified experimentally. The test bench was made up of the aileron of a wind tunnel model, driven by an electric motor through a mildly tensioned timing belt transmission. The results of a significant test set are provided to demonstrate the effectiveness of such a controller against noteworthy design uncertainties, such as sliding friction, sensor failure, free play due to inadequate belt tension, and approximate design parameters.