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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.
Kroll g*Klat
f fplat Yplat
Figure 70. Motion platform logic for roll/lateral task.
As such, the cues felt by the pilot were all in phase with
the visual scene. Usually, this is not the case, because
high-pass (washout) filters introduce a distortion between
not only the motion and visual cues, but also between
motion cue axes.
For small angles, the motion system mechanization of
figure 70 results in a false lateral specific force given by
ayplat g Klat Kroll = ( -1) f (24)
Thus, as expected, decreasing lateral translational gain
increases the false cue. However, for a given Klat, increasing
the roll gain, Kroll, also increases the false lateral
translational cue. So, increasing the roll gain improves
the fidelity of the roll acceleration cue, but if the subsequent
lateral translational motion is not coordinated, the
improvement comes at the expense of increasing the false
lateral translational cue.
Table 4 shows the combinations of roll and lateral
translational motion gains that were tested. Figure 71
shows these combinations with arrows indicating predicted
fidelity trends for the variations in the motion gains. As
Kroll increases, the fidelity of roll accelerations and rates
would increase, but at a given Klat, coordination would
decrease, as the leans resulting from roll would increase.
From the earlier equation for ayplat, the false lateral
specific force for a given roll attitude decreases along the
diagonal.
Table 4. Motion gains tested for roll/lateral experiment.
Klat Kroll
0.0 0.0
0.4 0.2
0.4 0.4
0.4 0.6
0.6 0.2
0.6 0.4
0.6 0.6
0.8 0.2
0.8 0.4
0.8 0.6
1.0 1.0
57
1.0
Increasing roll fidelity
Increasing
coordination
0.8
0.6
0.4
0.2
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Kroll
Klat
Figure 71. Configurations and fidelity effects for roll/lateral
experiment.
Procedure
Three test pilots participated in the study. The pilots were
from NASA Ames, the Federal Aviation Administration,
and Lockheed-Martin. All pilots had significant flight and
simulation experience. The NASA and the FAA pilot had
extensive helicopter experience, and the Lockheed Martin
pilot had experience in hovering jet aircraft.
Pilots practiced with a motion configuration selected
randomly at the beginning of each test period. During the
trials, each of the three pilots evaluated the configurations
in a random order. Pilots rated each configuration after
performing the task with that configuration three times.
Pilots subjectively evaluated the configurations in two
categories: motion fidelity and handling qualities. For
motion fidelity, they used the scale developed by Sinacori
(ref. 44), but with the modifications suggested in Vertical
Experiment I. The scale is shown in table 5. To rate the
handling qualities, the Cooper-Harper scale was used
(ref. 53). An overview of the scale is given in
appendix D.
Table 5. Revised motion fidelity scale.
Fidelity rating Definition
High Motion sensations are like
those of flight
Medium Motion sensations are
noticeably different from
flight, but not objectionable
Low Motion sensations are
noticeably different from
flight and are objectionable
Results
Objective Performance Data
Again, compelling performance differences occurred
between full motion and no motion, as shown in
figure 72. The solid lines in the figure represent full
motion (Kroll = Klat = 1), and the dotted lines represent no
motion. When transitioning from full to no motion,
performance degraded, and the magnitude and rate of
control inputs increased. Pilot-vehicle performance degradation
typically becomes more marked as the dependency
on the pilot for control and stabilization increases. The
magnitude and rate of control input increases, because the
pilot is now trying to extract vehicle state information
kinesthetically (via sensing position and forces in the
limb-manipulator system), since the platform cues that
supplied lead information directly (from vehicle acceleration)
are now missing. These tendencies are consistent
with the other studies in this report.
Figure 73 illustrates how overall positioning performance
varied with the configurations. Pilots assigned numerical
values to designate performance levels: a 1 for desired
performance; a 2 for adequate performance; and a 3 for
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Helicopter Flight Simulation Motion Platform Requirements(38)
