Decay Rate and Workload: Elemental Bases of HQRs and PIO Ratings

A quantitative understanding of the perceptual elements of handling qualities rating brings us to the heart of pilot control. In previous work it was shown that pilot induced oscillation ratings (PIORs) were a strong linear function of the closed loop dominant mode decay rate of the modeled pilot-vehicle system. While PIORs are based solely on the degree that oscillation degrades the task, the handling qualities rating (HQR) scale employs aggregate performance criteria and three apparently distinct sensations: workload, compensation, and controllability. However, in practice the pilot must modulate control in real time based on an instantaneous sense of performance. It is incumbent to model these four perceptions if the objective is to reproduce the manner and resolution with which the pilot assigns HQRs. The current work examines the same offset landing task that was conducted in two separate piloted studies: 1) Flight, using the Calspan variable stability NT-33A aircraft, and 2) Fixed and motion-based simulation, using the NASA Vertical Motion Simulator (VMS). The substantial difference in actual pilot ratings between the inflight and simulation studies was unexpected and hitherto could not be accounted for. The perception-based theory developed herein predicted pilot ratings that matched well the two studies’ ratings. It is demonstrated how acceleration washout (employed in most motion simulators) could impede the vestibular system from sensing decay rate and require the visual system to be used for primary control. A biomechanical feedback model is developed that computes dynamic limb tension from the neuromuscular system which is then integrated with the feel system to produce a stick force disturbance in response to aircraft motion. This model is flight-data-validated, and the neuromuscular mode’s decay rate was used as a metric to successfully predict the occurrence of roll ratchet (a higher frequency PIO phenomenon).