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The Neal-Smith criterion for handling qualities analysis of highly augmented aircraft is rewritten in terms of H∞ norms. The pitch attitude control is solved in the framework of an H∞ problem by the model matching technique to yield H∞-control pilot models. The obtained H∞ closed-loop transfer function satisfies the Neal-Smith criterion quite well, and the required pilot compensation is clearly exhibited in the H∞-control pilot model. Surveying all the flight configurations in the work by Neal and Smith, an attempt is made at pursuing the pilot compensation indices that correlate well with pilot ratings.

An experiment was conducted to seek the models of the human pilot controlling a vehicle with time-varying dynamics manually. In the experiment the human pilot controlled basic first-order linear time-varying controlled elements in a compensatory closed-loop fashion for step and random inputs. The analysis of the experimental data has found that for the step input case the human pilot can be modeled as a stationary proportional-plus-integral controller, whereas for the random input case a stationary model with constant coefficients cannot describe the pilot's control behavior sufficiently well. A nonstationary time series analysis suggests that the human pilot's control behavior for the random input case is also time-varying; adapting his characteristics to the changing controlled element dynamics in such a manner that the error and output spectral characteristics do not make appreciable changes with respect to time.