The problem of determining cruise-dash trajectories is examined for the case of time-fuel optimization using a linear combination of time and fuel as the performance index. These trajectories consist of a transient arc followed by a steady-state arc. For cases where the steady-state arc is flown with full throttle the associated skeletal transient trajectories are also flown with full throttle, and approach the cruise-dash points monotonically in an asymptotic fashion. When the steady-state arc is flown at an intermediate throttle setting, the transient trajectories follow a singular control law and exhibit a complex structure that is different from the full-throttle transients. Singular transients in the vicinity of singular cruise-dash points are confined to a bounded singular surface. In state-space these trajectories trace out asymptotic spirals on the singular surface as they approach the steady-state arc. If the initial operating point lies outside the singular surface, then the transient trajectories are composites consisting of a full-throttle or zero-throttle segment flown until the singular surface is met, followed by a singular segment that fairs into the cruise-dash point. Addressing the question of optimality of the steady-state arc, it was found that although steady-state cruise fails a Jacobi-type condition, steady-state cruise-dash can satisfy this condition if the emphasis on time is sufficiently large. The outcome of the Jacobi-type test appears to be connected with the eigenstructure of the linearized state-adjoint system. / PH. D.

The objective of this research effort was to identify opportunities and demonstrate methods to reduce aircraft crew member cognitive workload (CWL) by reducing short-term memory (STM) demand. Two experiments qualitatively and quantitatively compared memory loading as a function of stimulus class. Experiment 1 employed a dual-task paradigm where the primary task was compensatory tracking used to load STM and the secondary task was item recognition using the Sternberg paradigm. Experiment 2 employed a singletask paradigm using a modified version of the Sternberg task. Digits, letters, colors, words, and geometrical shapes were tested as memory-set (MSET) items in the Sternberg task. Recognition latency and error rate served as objective measures of STM performance while the Subjective Workload Assessment Technique (SWAT) was employed as a Subjective second measure. Root Mean Square error was used to gauge tracking performance. Analyses of the experiments' results revealed that recognition latency and SWAT ratings Statistically varied as functions of stimulus class, MSET size, and the interaction between stimulus class and MSET size. Error rate was not statistically different across stimulus class or MSET size. Post-hoc analyses found SWAT to be a more sensitive STM measurement instrument than recognition latency or error rate. No statistically significant degree of secondary task intrusion on the tracking task was found. In addition to the commonly used classes of digits and letters, this research demonstrated that colors, words, and geometrical shapes could also be utilized as MSET items in short-term memory workload investigations. This research has, more importantly, provided further support for the vital link between STM demand and perceived workload. The main conclusion of this research is that stimulus class optimization can be a feasible method for reducing STM demand. Differences in processing rate among stimulus classes are large enough to impact visual display design. For many context-specific applications, it should be possible to determine the most efficient stimulus class in which to portray the needed information. The findings of this research are especially applicable in situations of elevated STM demand (e.g., aviation systems operations). In general, however, the results provide helpful information for visual display designers. / Ph. D.