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0.7. The two parameters that are used to then keep the
motion system within its displacement limits for a given
math model and task are K and w. To reduce simulator
motions, either K is reduced or w is increased. Achieving
the proper balance between these two possible ways of
reducing the motion, while trying to minimize a loss
in motion fidelity, is not well defined. The criterion
suggested by Sinacori and discussed in section 1 was used
to select the characteristics of the motion configurations.
To validate or modify the criterion, 10 sets of gains and
natural frequencies were chosen to span the criterion, as
shown in figure 38. The values for the filter are given in
table 3. Note that configurations V3 and V4, from
table 3, result in gain and phase-distortion coordinates of
[0.970, 45.0] and [0.795, 80.0], respectively. Although
these filters have unity gain at high frequencies (K = 1),
the dynamics of the high-pass filter cause the above
attenuations and phase distortions at 1 rad/sec, which is
the frequency used to plot the motion filters against the
criterion.
33
Figure 38. Motion configurations for vertical tracking.
Table 3. Motion-filter quantities for vertical tracking.
Vertical
Configuration K w
(rad/sec)
V1 1.000 0.010
V2 0.901 0.245
V3 1.000 0.521
V4 1.000 0.885
V5 0.650 0.245
V6 0.670 0.521
V7 0.300 0.245
V8 0.309 0.521
V9 0.377 0.885
V10 0.000 —
Procedure
For the pilot to rate the motion fidelity of each
configuration, a baseline was established for comparison.
The baseline specified that the pilots perform the task first
with 1:1 motion; this was a calibration run. Here, the
pilots were told that they had 1:1 motion, and that the
sensations they were feeling were to be interpreted as the
“actual aircraft.” The motion fidelity of all future configurations
was then compared to this 1:1 motion baseline
configuration. This testing procedure allowed immediate
back-to-back comparisons of the effects of motion
parameter changes. This procedure mitigates some of the
problems that occur in simulation fidelity experiments
that compare the actual aircraft to the simulation back-toback,
even when the events occur in the same day.
34
During the evaluations, the pilots had no knowledge of
the configuration changes, except when they were told of
the full-motion “calibration runs.” Still, the 1:1 motion
case (configuration V1 in table 3) was also evaluated;
during its evaluation, the pilot was not told he had the
1:1 configuration.
Pilots A and C completed all the configurations listed in
table 3 in one session, Pilot B completed all the configurations
in two sessions, and all of the configurations
were evaluated by all three pilots. Some configurations
were repeated if time permitted. For each configuration,
pilots assigned a motion-fidelity rating using the definitions
in figure 4. Then, the pilots answered questions
regarding the aircraft’s characteristics, their task performance,
and the compensation required to perform the task.
The pilots were also asked to estimate the relative use of
the motion and visual feedback cues.
Results
The results of Vertical Experiment I consist of objective
performance data and subjective fidelity ratings. Relevant
pilot comments will be added in the discussion of these
results.
Objective Performance Data
Again, compelling performance differences are shown
between full motion and no motion in figure 39
(configurations V1 and V10, respectively). For the
configuration V1 case, well damped, accurate bob-ups
were achieved with the vertical velocity remaining within
10 ft/sec; the vertical acceleration remained within 0.5 g,
and the collective stayed within 1.5 in. A drastic difference
is evident in the no-motion case (V10). Initially, the pilot
overshot the 85-ft desired altitude and then returned to the
starting point as he responded to the unfamiliar cues.
Since the acceleration feedback cue was the only cue that
changed from the full- to the no-motion case, part of the
pilot’s collective input must have been a result of that
cue. With the acceleration cue removed in the V10
configuration, the pilot had to adjust his compensation
based on the new set of cues. With time in the motionless
configuration, the performance improved, but even the
final repositioning took longer in the fixed-base case than
in the full-motion case. These differences have obvious
training implications, for the pilot must develop different
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Helicopter Flight Simulation Motion Platform Requirements(24)
