Interplay Between Optic Flow, Pilot Workload and Control Response During Aggressive Approach to Hover Maneuvers for Three Vertical Lift Vehicle Models

Abstract

This work proposes a novel relationship between pilot workload and optic flow during visual approach-to-land maneuvers. A simulation experiment was conducted at NASA Ames Vertical Motion Simulator (VMS) to evaluate the workload associated with operating two candidate Army Future Vertical Lift (FVL) vehicles: a compound (coaxialrotor and push-prop) vehicle, and a tilt-rotor vehicle. The UH-60 was included in the evaluation as a baseline reference. Sixteen experienced military pilots flew aggressive visual approaches terminating in a hover while providing Bedford workload ratings in real time. No approach or hover guidance was displayed to the pilot. The out-the-window (OTW) environment (front and chin monitors) was digitally recorded and the optical flow of each video frame computed. Prior work identified a mathematical relationship between pilot workload and the combination of display error rate and stick rate during compensatory tracking tasks. The current work extends this relationship to visual landing approaches, where the pilot is hypothesized to track key optical variables that are available from the OTW scene. Hypothesizing that the visual approach is essentially a compensatory task, optical flow rate was combined with stick rate to compute Bedford workload estimates. Actual and estimated Bedford ratings are compared for the three aircraft models. Innovative contributions of this research include: 1) Optical flow from high resolution, high frame rate flight video is computed and analyzed for workload analysis; 2) A modelling technique is developed that produces workload estimates that closely matches actual pilot ratings; 3) A technique based on visual perceptual requirements allows optical flow to be employed in a tractable, effective manner; 4); Using a novel method, Bedford workload ratings were collected in real time without impinging on the flight task, enabling in-situ workload analysis. Lastly, the authors recently proposed a psychophysical approach which characterizes workload response for a given task in concise terms such as sensitivity to stimulus (Weber fraction), just-noticeable difference (JND), and dynamic range. This new methodology is applied to the workload results obtained for the three aircraft models and discussed, demonstrating how a psychophysical treatment to workload brings a different and relevant toolset for quantitatively examining human-machine performance.