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repeated for the remaining configurations, V8 and V9; the
objective performance worsened as the phase distortion
increased. From the comments and ratings, configurations
V7, V8, and V9 were consistent with Sinacori’s hypothesized
boundaries (ref. 44). Therefore, regardless of the
phase distortion, a gain of 0.3 results in low fidelity.
Referring to the fixed-base configuration, V10, two pilots
said that they put the control input in the wrong direction
during the run. Pilots were generally stunned at the effects
of the total loss of motion. During the 1:1 calibration
runs, one pilot made a comment prior to the evaluations
that “The visual scene is so compelling at conveying the
error that it seems to primarily be a visual task . . . I
would expect the effects of motion to be minor.” Another
pilot commented after the fixed-base configuration “I have
never experienced such a dramatic disconnect from reality
as during that configuration, as compared to the fullmotion
case.” Thus, caution should be used when interpreting
a priori conjectures on the value of motion, even
when given by experienced test pilots with considerable
simulation experience.
Motion cues were certainly perceived by the pilots in all
but this fixed-based configuration. This is evident from
the performance and comments, but it is also consistent
with tests that have determined the vertical-acceleration
sensing threshold to be in the 0.09-0.27 ft/sec2 range
(ref. 19). This threshold was exceeded in all but the fixedbase
configuration.
Suggested Revision to Fidelity Criteria
Based on these results, a revision to the vertical axis of
Sinacori’s criterion is suggested in figure 51. Here, the
changes consist of lowering the gain required when the
phase distortion is low. The gain for the high-fidelity
region is reduced to account for the results of the V5
configuration. The medium-fidelity region has been
extended to a lower gain, but kept above that of the V7
configuration, which has a gain of 0.3. These suggestions
are consistent in trend with the data of Mitchell and Hart
(ref. 47), which indicated a preference for low-gain, low
phase-distortion motion over high-gain, high phasedistortion
motion. Also, the fidelity boundaries have been
rounded to account for the reduction in fidelity when a
gain attenuation is combined with phase distortion. The
determination of exactly where the rounding should begin
and end requires additional data.
Also, slight wording changes are suggested to the motionfidelity
definitions of figure 4 to alleviate the previously
mentioned difficulties in their use. The word “disorientation”
should be removed; it caused some pilots to shy
40
away from the low rating. Although a configuration may
have been objectionable, the pilots felt no disorientation.
The suggested rewording, as noted on figure 51, should
suffice, since any disorientation experienced would be
expected to receive an “objectionable” description.
Significant differences in measured performance and in
perceived fidelity were evident across these configurations.
The analytical model discussed in appendix B predicted a
performance decrease when the motion filter natural
frequency increased. However, the predicted bandwidths of
the primary loop did not differ by a factor of 1.5, which
was the general guideline suggested for determining
dissimilarity between motion configuration responses
(ref. 61). Although this analytical model is perhaps the
most reasonable available, this experiment demonstrated
that additional data are needed in order to continue its
refinement and validation.
Medium
Low
Ref. 44
Modified
Vertical axis
High
80
60
40
20
0
0.6 0.8 1.0
Gain @ 1 rad/sec
Phase distortion @ 1 rad/sec (deg)
0.0 0.2 0.4
High
Medium
Low
Motion sensations are not noticeably different from those of visual flight
Motion sensation differences are noticeable but not objectionable
Motion sensation differences are noticeable and objectionable
Figure 51. Suggested vertical criterion and fidelity definitions.
41
5. Vertical Experiment II:
Compensatory Tracking
Background
In Vertical Experiment I, the global performance effects of
motion-filter gain and natural frequency variations were
examined during tracking. In Vertical Experiment II, a
more detailed examination of the same filter variations
was conducted for a new task: key pilot-vehicle frequencyresponse
metrics were measured during combined tracking
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Helicopter Flight Simulation Motion Platform Requirements(28)
