A Theoretical Framework Unifying Handling Qualities, Workload, Stability and Control

Abstract

The concepts and principle developed in this work offer a novel and integrative approach for exploring fundamental issues surrounding pilot performance, handling qualities (HQs), and workload. Fundamental laws of sensory perception are extended to multi-input sensing, showing that multiple sensory inputs add logarithmically. It is proposed rather than being just a sensational response, a pilot’s perception of workload is a skill that is acquired and used for the purpose of modulating system stability (i.e., phase margin) during a tracking task. Evidence is presented indicating than an operator perceives workload and behaves such that workload is linearly related to phase margin (PM). It is also shown that this behavior associated with PM linearization serves to reduce workload. PM-workload linearization would enable a straightforward transformation of workload to PM, allowing PM to be set by the pilot to facilitate loop control. A perceptual transformation of the variables available to the pilot (control activity, error) couples with the behavioral conditioning to complete the linearization between PM and sensed workload. Two contrasting sets of experimental data were used to examine pilot response, indicating that pilot compensation is conducted via both frequency modulation (lead-lag) and temporal modulation (pure time delay). HQ sensing is treated as multi-input perception, where time delay and the lead-lag ratio are the stimuli for compensation sensing, and tracking error is the stimulus for performance sensing. A HQ metric arising from the logarithmic addition of these two sensations is shown to yield promising results. A cost function representing pilot behavioral objectives is developed that serves to modulate the following four items: 1) Tracking error; 2) Workload; 3) Linearity between workload and PM; and 4) Setting a reference PM. The pilot cost function was implemented in an optimal pilot which produced pilot time delay and pilot compensation estimates that closely matched the actual pilot data.