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some data from the vertical axis. There are also disagreements
as to whether these translational cues are more
important that the rotational cue, or vice versa.
Since motion fidelity has not been thoroughly examined
in all axes, it is possible that some motion degrees of
freedom are redundant with the other simulator cues that
also allow motion perception. If a motion degree of
freedom is unnecessary, then a savings might be realized
as a result of the reduced complexity in the design,
development, and operation of flight simulators. If a
savings benefit is not chosen by a manufacturer, at least
an operator would know not to concentrate on tuning the
motion in an unnecessary degree of freedom.
An answer to “How much platform motion is enough?” is
likely to be vehicle and task dependent. Vehicles that rely
greatly on the pilot for stabilization, such as helicopters,
will have more stringent platform-motion requirements
than vehicles that do not depend on the pilot for stabilization.
As such, this report focuses on the former, more
stringent case.
Purpose of This Report
The purpose of this report is to develop reasonable
guidelines for the use of motion in helicopter simulations.
Areas in which weak guidance exists on how to employ
key motion cues will be strengthened. Specifically, it will
be first determined if yaw requirements are a natural
extension of pitch and roll requirements. Second, the
fidelity effects of vertical motion and their interaction with
visual cues in altitude control will be determined. Finally,
requirements for the relative magnitudes of roll and lateral
translational motion will be investigated.
Approach
Although platform-motion research has been conducted
previously, the approach used here is, perhaps, more
valid. There are several reasons for this greater validity.
First, the world’s largest displacement flight simulator
was used in all of the experiments. Use of this experimental
device allows selected flying tasks to be duplicated
faithfully. That is, the math model, the visual cues, and
the motion cues can be matched as a baseline, and then the
effects of altering motion can be subsequently determined.
Second, representative helicopter math models were used,
with one model identified from flight test. This
approach allows helicopter-specific requirements to be
determined. Third, highly experienced test pilots were used
as subjects, and their insightful comments allow confident
extrapolations from simulation to flight. Finally, the
results were corroborated with both objective and subjective
data. In most cases, enough data were collected to
allow the measures to be quantified statistically, an
advantage that limited facility-use time often does not
allow.
These methods should provide a high degree of confidence
in the results. They were applied in order to the yaw,
vertical, roll, and lateral translational degrees of freedom.
Motions in the yaw and vertical axes were examined first,
because these motions are the simplest. That is, the
gravity vector remains aligned relative to the cockpit for
these motions. Next, the coupled roll and lateral axes were
explored. These motions are coupled, since the gravity
vector rotates relative to the cockpit. The coupled pitch
and longitudinal axes have been left for future work;
however, the requirements in pitch and longitudinal are
not expected to differ substantially from those of roll and
lateral.
Contributions
1. The results indicate that yaw rotational platform
motion has no significant effect in hovering flight
simulation. For three tasks that broadly represented
hovering flight, the addition of yaw-rotational motion
yielded insignificant changes in pilot-vehicle positioning
performance, pilot control activity, pilots’
rating of required control compensation, and pilots’
opinion of motion fidelity.
2. Lateral translation of the motion platform has a
significant effect on hovering flight simulation. For
three tasks that broadly represent hovering flight, the
addition of lateral translational motion improved
pilot-vehicle positioning performance, reduced pilot
control activity, lowered pilot ratings of required
control compensation, and improved pilots’ opinions
of motion fidelity.
3. Lateral translation of the motion platform, plus
typical visual cues, made pilots believe that the
motion platform was rotating when it was not. That
is, pilots believed they were physically rotating when
the yaw platform degree of freedom was stationary. A
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Helicopter Flight Simulation Motion Platform Requirements(10)
