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This hypothesis is rejected based on the following. To determine if whatever cue the yaw rotational platform motion might be providing was indeed being sensed, an additional motion configuration was evaluated on an ad hoc basis. That configuration simply reversed the sign in the yaw rotational platform motion command. So for math model rotations to the right, the visual scene correspondingly moved to the right, but the platform moved a symmetric amount to the left. This configuration was extremely disliked by all the pilots, some of whom experienced physical discomfort. Thus, what appears to be happening in the typical motion configuration (with correct motion signs) is that the yaw rotational platform motion cue is simply confirming the already compelling rotational cues that come from the visual scene. This conclusion is also supported by the earlier studies performed by the author (refs. 48, 49) in which the pilot was sitting at the rotational center. In that case, no translational cue was present, so the yaw rotational cue was redundant with the visual cue.
Table 2. Summary of yaw task results.
Translational/
Translational Rotational rotational interaction
Task: 1 2 3 1 2 3 1 2 3
Measure
Pilot-vehicle stability + + + + -o Control rate ++o oo-Compensation +o + ooo Fidelity ++ + ooo Translational reporting ++ o-x Rotational reporting o oxx
+: Significant improvement; +: marginal improvement; -: significant degradation; o: no effect; x: interaction.
In addition to these compelling visual cues, when lateral translational motion is present, its combination with the visual cues provides more than enough cues to cause the pilot to believe he is rotating when he is not physically rotating. When the yaw rotational platform cue is in the opposite direction, it is no longer providing confirmation, but it is instead providing conflict. Consistent with this explanation is the dictum “bad motion is worse than no motion” in that spurious motion cues destroy any vection that has been generated by the other motion and visual cues (ref. 9).
Earlier it was stated that Meiry’s yaw experiment (ref. 22) showed that the addition of rotational motion improved performance. It is possible that the difference in experi-mental setup between that experiment and the one reported here could account for the difference, although the results of Task 1 in the present study did agree with those of Meiry by showing a marginal improvement in perfor-mance. In Meiry’s experiment, pilots countered a consid-erable yaw rotational disturbance (white noise with a 15° rms), did not control a model representative of a helicopter (the model resulted in yaw rate proportional to pilot input at all frequencies), and the visual system was a line on an oscilloscope. So, with this deprived-cue visual system and with only a yaw rotational cue, yaw rotational motion might have helped. However, Meiry’s study did not determine if the lateral translational motion cue could An example of the dependency is shown in figure 34, which was generated by Cooper and Howlett (ref. 40). Loss of available motion in the longitudinal, lateral, and vertical axes also occurs for rotations about the yaw axis. Thus, users should disable yaw rotation and thereby gain additional benefits in axes that provide added value in flight simulation.
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