During the design of an aircraft it becomes necessary to predict the aircraft handling qualities. Previously, this has been done through the use of pilot opinion ratings of similar vehicles. However, it is desirable to develop more objective means of predicting handling qualities which also do not require the expensive flight testing or simulation necessary to obtain pilot ratings directly. An analysis of the closed-loop pilot-airframe system is performed, utilizing the linear human-pilot transfer function in conjunction with conventional servoanalysis techniques. Boundaries are developed on aircraft frequency and damping ratio for "good" longitudinal short-period control. The lateral phugoid mode is also investigated and the conclusion reached is that this mode cannot be controlled in a manner resulting in "good" pilot ratings. Comparison of the results obtained for the longitudinal short-period mode with experimental data indicates that the analysis is valid. Experimental data is lacking for comparison in the case of the lateral phugoid mode. / M.S.

In this thesis, A nonlinear methodology for the control of the highly maneuverable, high performance aircraft HARV (F-18) is studied by using sliding-mode control (SMC). This control law, which takes a continuous function when the input constraints are not considered, satisfies the reachability condition by which concerned states are driven to their sliding surfaces. Especially, this SMC is generalized for the so-called (square) uncoupled multi-input multi-output (MIMO) system by the use of error dynamics and applied directly to the nonlinear aircraft system without linearizing the system. For the practical application of the SMC to aircraft with input constraints, two control schemes are used, considering that variations of pitch rate q directly affect variations of the angle of attack. The first scheme consists of an ��-q control for the fast response. The second scheme consists an a-control for making the output approach its sliding surface slowly by setting boundary layers and adjusting reachable speeds to the sliding surface. Robustness to parameter uncertainties and disturbances is also studied for the SMC. Especially, when the effect of parameter uncertainties is severe, then multiple boundary layers are set in the neighborhood of sliding surface, in which different reachable speeds to the sliding surface are used to sustain the concerned state within the boundary layer and to reduce the effect of chattering. / Graduation date: 1994