Effects of nonlinear flight control system elements on aircraft

This report presents the experimental method and results from a series of desktop simulation tests designed to investigate manual control characteristics of young and relatively inexperienced civil pilots (24 years average age and 66 hours flight experience). Subjects were asked to perform tasks during which they had to establish longitudinal control through pitch attitude shown on a primary flight display. A linear aircraft model coupled with nonlinear flight control system was used to produce realistic vehicle dynamics. Increased encroachment into nonlinear command gearing was found to make aggressive subjects resort to high levels of crossover regression. The combined effects of rate-limiting and nonlinear command gearing was observed only for demanding tasks during which over-control was a typical feature. The classical precision and bimodal models were used for an in-depth study of pilot dynamics observed during compensatory tasks. Model parameters were found through the definition of a constrained nonlinear optimisation problem. A single feedforward equalisation element was used for tracking tasks. It was found that subjects developed similar low frequency feedforward equalisations, whilst large inter-subject variations exist for high frequency equalisations. The resulting models also provided some insight into the Neal-Smith and Bandwidth handling qualities criteria. Actuator rate-limiting could not be directly correlated to any of the pilot model parameters.