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pilots do not feel like they are falling or climbing when
the visual scene indicates they are falling or climbing.
Setting the motion-filter natural frequency should take
priority over setting the gain. The filter natural frequency
should be selected such that less than a 30° phase error at
that predominant task frequency exists. Then, the motion
gain can be selected by trying to maximize the criteria
shown in figure 78. Once these two parameters are
selected, the motion-filter configuration should be
evaluated with a pilot flying the task in simulation to
determine if simulator excursions reach their physical
limits. If the physical displacement limits are reached,
Start
Is motion fidelity acceptable?
Yes
Yes
No
No
Done
Evaluate to
determine if you are
within motion limits
Are there
fundamental motion
frequencies?
Adjust
task
Set motion gain and
natural frequency in
each axis per criteria
Set motion gain
per criteria
Task
Set motion system w
to give < 30° phase
error there
Figure 81. Method for configuring motion systems.
67
then the motion gain should be lowered until the ensuing
motion remains off the limits.
If fundamental motion frequencies do not exist, then the
gain and natural frequency of the motion filter can be set
independently. In this instance, the highest fidelity should
be sought in accordance with the criteria in figure 78.
Iteration with a pilot still needs to be performed to
determine the reachable fidelity level. At the end of either
of these paths, a certain achievable fidelity level will be
reached.
If the desired fidelity level cannot be achieved for a given
simulator’s displacement capability, then the user should
consider changing the task. Often the task is considered a
given and is treated as inviolate, since its origins may be
from flight test experience. However, trying to extrapolate
simulator results to flight when the simulator can only
duplicate the task with low fidelity will usually result in a
poor extrapolation.
Poor extrapolations from simulation to flight have
occurred frequently because of a control sensitivity that is
too high. Pilots improperly perceive vehicle sensitivity to
control stick inputs if tasks are not developed in concert
with a simulator’s displacement capability. Rather than
change the task, the simulator’s gain is reduced, which
gives the pilot a false reading of the true sensitivity.
If the process of developing a task is considered as a
feedback process with the attained simulator fidelity as a
performance metric, then modifying both the motion cues
and the task itself should be considered. It may be the only
method for achieving high simulation fidelity.
Extrapolations to flight can then be made with improved
confidence.
Generally, this method should serve as a useful guide for
configuring motion systems and for selecting tasks to
minimize differences between simulation and flight.
Although the method is iterative, it is possible that its
combination with the expert system ideas of Grant and
Reid (refs. 68, 69) might prove useful.
69
9. Conclusions
Summary
The five piloted helicopter simulation experiments
described in this report produced several important results.
Four of the six degrees of freedom were examined: roll,
yaw, lateral, and vertical. These experiments were
performed on the world’s largest displacement flight
simulator, making it possible to perform many of the
tasks with the motion and visual cues matching exactly.
Using these experiments as a baseline allowed the effects
of degraded motion cues to be examined.
Representative helicopter math models were used; in some
cases, the models were derived from flight test data.
Experienced test pilots were the experimental subjects, and
both objective and subjective data were employed in
developing the principal conclusions that follow.
1. Yaw rotational platform motion has no significant
effect on hovering flight simulation. The presence of
yaw platform rotational motion did not contribute to
significant improvements in pilot-vehicle performance,
control activity, pilot-rated compensation, or
pilot-rated motion fidelity.
2. Lateral translational platform motion has a significant
effect on hovering flight simulation. In contrast to
yaw rotational cues, the presence of lateral translational
motion did contribute to improvements in
pilot-vehicle performance, reductions in control
　
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