Unexpected encounters with degraded visual environments (DVE) pose a serious risk to rotary-wing aircraft. Due to the loss of outside visual references, pilots engaged in DVE become entirely reliant on cockpit displays and instrument information to land safely. Flight symbology systems have been accordingly developed which offer a set of symbolic cues meant to replace the pilot's lost visual cues. Prior to engaging in operational use, symbology systems must undergo a certification process in part comprised of tuning the display scaling (i.e. the manner in which physical states are scaled to units representable on the display). At present, tuning is conducted through trial-and-error according to the feedback of the test team, without applying quantitative rigor to the process. The premise of this investigation is therefore to prove the existence of a predictable relationship between display scaling and pilot response, and in doing so provide a quantifiable and defendable basis for the tuning process. An experiment is designed in which participants conduct a single-axis precision hover using a pared-down, non-conformal symbology system. During the experiment, three display scalings are varied: the acceleration cue scaling K a , the velocity cue scaling K v , and the position cue scaling K x . A fourth independent variable, Lead, is also considered, which represents the amount of velocity prediction afforded by the acceleration cue. The response is measured according to the root-mean-square (RMS) of the position error, the control activity, and the Bedford workload ratings. From the generated trends, suggested scaling and Lead levels are selected as those simultaneously resulting in low RMS, low control activity, and low workload: K x = 175 f t screen , K v ≈ 22 kts screen , K a = 15 f t s 2 screen , and Lead = 2-2.5 s. Participant control aggression is then captured through the maximum attitude excursion and the time taken to complete the precision hover in an attempt at explaining anomalous responses.iii
Rotorcraft symbology can provide pilots with the flight information necessary to replace the visual cues lost when operating in degraded visual environments. However, tuning symbology for effective use is a time-consuming process as it generally requires considerable in-flight testing and extensive trial and error. In this work, two experiments are conducted to assess how changes in the display scaling of a position–velocity–acceleration architectured symbology set affects pilot performance and workload. In the first experiment, participants attempt a modified single-axis precision hover using a simulated helicopter and nonconformal symbology set while display parameters relating to acceleration, velocity, and position cue scaling are varied. Performance is measured using the root mean square of the position error relative to a target location, and participant workload is assessed using their cyclic control activity and Bedford ratings. In the second experiment, an analytical pilot-in-the-loop simulation is conducted to validate the performance results obtained in the first experiment and to investigate the underlying system characteristics that contribute the observed trends. For the implemented symbology and Bell UH-1H model, the results from both experiments concur that a combination of low-to-mid range acceleration cue scaling and mid-to-high range position cue scaling enable strong performance without inflating workload. Results indicate an insensitivity to velocity vector scaling, likely due to the symbology architecture and nature of the control task. The results of these experiments establish a predictable relationship between display scaling and pilot response, which can aid in streamlining the tuning process for similarly-styled symbology, helicopter and task envelope combinations.
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