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2.5° in excess of the Medium fidelity boundary. Still, the
boundary at 60° should remain, for both the work of
Stapleford et al. (ref. 26) and Bray (ref. 27) support it. If
Shirachi and Shirley had evaluated conditions with less
phase distortion, those conditions might have been
preferred.
In the translational axes, a “region of uncertainty” extends
into the Low fidelity region; this does not suggest an
inconsistency, however, because that area simply was not
evaluated by Jex et al. (ref. 43). However, a “delayed side
force” region cuts off an area in Medium fidelity. The
delayed-side-force region applies to the sway axis when
that axis is used to eliminate the specific force that arises
from platform roll. That region was not explored in
section 7, and it may merit additional examination.
However, the delayed-side-force region is certainly adequate
when trying to represent true math model cues, as shown
in the vertical experiments discussed in sections 4 and 5.
There is another inconsistency in the translational axis
when compared to the results of Cooper and Howlett
(ref. 40). The displacement of their simulator was clearly
limited as shown by their boundary “too much displacement.”
And their report states “Pilot criticism to motion
anomalies during returns from steady maneuvers still is a
problem.” So, their region of “best compromise” is likely
to be based on their simulator’s capability. It is interesting
to note that their rotational axis filter is well within
the High fidelity region. Since their platform is synergistic
(angular motion usurps translational motion and
vice versa), figure 80 suggests that they might relax their
angular motion in order to gain translational motion. This
change might allow both angular and translational axes to
be in the Medium fidelity region for some maneuvers,
rather than one in High and one in Low. The remaining
comparisons in figure 80 for the translational axes are
favorable. In general, the suggested criteria are reasonably
consistent with those of previous work.
65
Low fidelity
Shirachi-Shirley (ref. 42)
van Gool (39)
SS
Bray (24)
C
b b b
Cooper-Howlett (40)
SS
V
SS
0.0 0.2 0.4 0.6 0.8 1.0
0
20
40
Pitch/roll
60
80
100
High fidelity
Medium
fidelity
Rotational gain
Low fidelity
Medium
fidelity
High fidelity
Motion cues
inadequate
Cooper-Howlett (40)
Best
compromise
Cooper-Howlett (40)
Too much
displacement
Cooper-Howlett (40)
0.0 0.2 0.4 0.6 0.8 1.0
0
20
40
Phase error (deg) Phase error (deg)
Translational
60
80
100
Rotational gain
"Delayed side force"
Jex, et al. (41)
S
Stapleford, et al.
S
V
V
B
B
B
B
"Acceptable"
Jex, et al.
Region of
uncertainty
Jex, et al. (41)
Bray (27)
Jex, et al.
Too much
displacement
Jex, et al. (41)
"The leans"
Jex, et al. (4.1)
Bergeron (38)
Figure 80. Comparison of previous work with suggested criteria.
66
A General Method for Configuring Motion
Systems
Based on these experiments, on the experience attained in
their development, and on the discussion above, figure 81
suggests a step-by-step method for users who configure
motion systems. In figure 81, boxes that are dashed, and
underlined words in the boxes, represent suggested
additions to current practice as a result of the research
described in this report. This method is in contrast to the
current trial-and-error method that is often used by motiontuning
experts and in subjective pilot evaluations. A
recent improvement to the trial-and-error method has been
suggested through the use of an expert system by Grant
and Reid (refs. 68, 69). However, their method does not
explicitly use motion-fidelity criteria as does the method
proposed here.
First, the task needs to be analyzed to determine if
fundamental motion frequencies are present. Some tasks
have a predominant task frequency. For instance, nap-ofthe-
Earth flight over regularly varying terrain can
necessitate low-frequency heave cues (the frequency
determined by hill separation divided by vehicle forward
speed). In these instances, the motion-filter natural
frequency and gain should not be set independently in an
attempt to satisfy the motion-fidelity criteria. Otherwise,
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Helicopter Flight Simulation Motion Platform Requirements(42)
