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˙˙ ˙
φ=.45. φ+17. δlat (21)
˙= (22)vgsin φ
where v is the body-fixed velocity in the y direction (lateral). These equations represent a typical helicopter math model that is fully coordinated at the aircraft’s c.m., since no lateral aero-propulsive forces are present
(ay =.v˙ gsin φ). Actual helicopters have a drag owing to lateral translational velocity, and they also produce a side force at the rotor which contributes to a rolling moment. Each of these real-world effects causes uncoordinated flight during a side-step maneuver. This experiment used a fully coordinated model, since the objective was to examine the effects of uncoordinated simulation cues caused by simu-lator platform displacement limitations. Thus, these real-world effects were intentionally absent. So the model represented a vehicle in which only applied torques created rolling motion (similar to an AV-8B-like concept) with no drag owing to velocity (which is small near hover).
For the experiment, the pilot’s abdomen was located at the aircraft’s c.m. The roll-axis dynamics given above, when combined with the visual system delay of 60 msec, had satisfactory (Level 1) handling qualities as predicted by the U.S. Army’s Rotary Wing Handling Qualities Specification (ref. 50).
Simulator and Cockpit
The experiment again used the NASA Ames Vertical Motion Simulator, but only the roll and lateral axes. The lateral axis has ±20 ft of travel, and the roll axis has ±18° of displacement. The roll and lateral axis dynamic charac-teristics were dynamically tuned with feedforward filters in the motion software to synchronize the two axes as much as possible. For this experiment, each motion axis had an equivalent time delay of approximately 60 msec, as measured using techniques developed by Tischler and Cauffman (ref. 46). The cockpit was configured with a center stick only. No instruments were present, so the pilot had to extract all cues from the motion system, the visual system, and the inceptor (center-stick) dynamics. The center-stick dynamics were measured to be
δlat1 82
()s = (23)Flat 06. s2 + 2088 (. ) s + 82
where δ lat and Flat are the displacement and force, respectively, at the pilot’s grip.
For the visual system, the Evans and Sutherland ESIG 3000 image generator was used. The visual time delay was adjusted so that it was 60 msec in order to match the equivalent motion time delay in the roll and lateral axes. The simulator cab was the same as that used in section 4, so the field of view is that shown in figure 36.
Motion System Configurations
Figure 70 shows the relevant motion-platform drive laws. That is, the simulator-roll-angle command differed from the math model only by a gain (i.e., no frequency-dependent motion attenuation from a washout filter was present). The platform moved laterally to reduce the false lateral acceleration caused by platform roll angle. Only a gain was applied on this lateral translational platform command as well. In practice, both a gain and a high-pass filter are used, but these effects were not examined.
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