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activity, lower pilot-rated compensation, and higher
pilot-rated motion fidelity.
3. Lateral translational platform motion combined with
visual yaw cues made pilots believe yaw platform
rotational motion was present when it was not. This
visual and motion cueing combination gave pilots a
strong sensation that both rotational and lateral
translational motions were present. It is believed that
more rapid vection was produced by the lateral
translational motion cue. Thus, for hovering flight
simulation, one should represent the lateral translational
acceleration cue, for it is important to all the
aspects of pilot-vehicle performance and pilot
opinion. The same point cannot be made for yaw-axis
rotational motion. As such, since many of today’s
hexapod motion platforms achieve both lateral
translational and yaw rotational motion with the same
set of limited-travel actuators, a high weighting
should be placed on representing the former cues
rather than the latter. An alternative to modifying
today’s hexapod motion platforms is to develop a new
simulator configuration that emphasizes limited
translational motion. Because lateral and vertical
translational motions are the most prevalent, placing
a cab on the end of a cantilevered arm that can rotate
in azimuth and elevation would provide these
motions. Different length arms could be used
depending on the vehicle capability, the evaluation
requirements, or both.
4. Vertical platform motion has a significant effect on
pilot-vehicle performance, control activity, and
motion fidelity. Pilots were surprised at the performance
results and at how their technique had to
change when all motion was removed. Two of the
three pilots made collective inputs in the wrong
direction when flying fixed base. Until the value of
vertical motion was demonstrated, pilot subjective
impressions were that the vertical task was primarily
visual. Thus, caution should be used when interpreting
piloted subjective impressions of the value of
motion. From these vertical-axis results, a revised
specification was developed that better correlated with
existing experimental results.
5. Vertical motion cues affected altitude estimation.
Pilots, when asked to double or halve their altitude,
had their performance significantly affected by vertical
platform motion. With vertical motion, pilots more
accurately doubled and halved their altitude. Until
now, it was generally accepted that steady-state
altitude estimation was derived from visual cues only.
A hypothesis is that the pilot estimates vehicle state
using all the available sensory inputs. As a part of
this, some significant weighting is applied to
acceleration cues that provide a component of the
pilot’s position estimate.
6. A specification for roll-lateral motion requirements
was developed. For a side-step task that exactly
reproduced motion and visual cues, significant
performance and opinion differences resulted as
motion was removed. A combination of translational
and rotational gain specifications provided a good
prediction of motion-fidelity ratings.
Recommendations for Future Work
1. Two additional degrees of freedom, pitch and surge,
should be examined. The results for these two coupled
axes are expected to be similar to those of
the coupled roll and lateral axes.
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2. The specification demarcations between high,
medium, and low fidelity were determined based on
the granularity of the points tested. Further efforts are
needed to determine the curves that divide the fidelity
regions more precisely.
3. Controlled experiments should be performed on
several representative hexapod platforms to quantify
the performance benefits of allowing increased motion
in the other axes when turning the yaw rotational
displacement off.
4. Continued attempts should be made to model the
pilot-vehicle system in the simulator environment.
Several unusual results, such as the performance
degradation with the addition of yaw rotational
motion and the improved estimation of height with
the addition of vertical motion have been shown here.
Future models need to account for these findings.
5. Does learning to fly a helicopter on a substandard or
suboptimal motion platform increase total training
costs, or does it pose a safety hazard? To answer these
questions, a careful transfer-of-training study needs to
be performed.
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Appendix A—Human Motion Sensing
Characteristics
Models of how the semicircular canals and the central
　
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