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no fidelity differences should exist when, in fact, they do
exist. In addition, the model is incomplete, for it does not
account for the gain on motion platform acceleration.
To summarize, a credible analytical model does not yet
exist for flight simulation. More experimental data are
needed to develop and refine the model further. The experiments
that have been performed to date are discussed next.
Experimental Motion Research. Many previous
experiments have contributed toward the development of
motion-fidelity requirements. Although some of the data
from these previous studies may be correlated, differences
in visual and motion systems, tasks, and vehicle dynamics
typically prevent the consistent understanding and
development of motion-fidelity criteria. Below, key results
of both rotational and translational experiments are
presented.
Experimental Rotational Criteria. Stapleford
et al. examined the effects of roll and roll-lateral motion
on a pilot’s ability to track a target during a disturbance
(ref. 26). Using both a tracking and a disturbance input,
some key aspects of how the pilot closes the visual and
motion feedback loops were presented. They suggested
that angular cues be accurate in the 0.5–10 rad/sec range;
however, “accurate” was not precisely defined.
Bergeron evaluated the effects of attenuating only the
motion filter gain in the angular degrees of freedom
(ref. 38). For the highly stabilized vehicle that was
simulated, the results suggested that motion has no effect
on the performance of single-axis stabilization tasks.
Motion effects became evident only when simultaneous
control of two angular axes was required. Presenting as
little as 25% of the full motion produced results
comparable to those for full motion.
In the Netherlands, van Gool suggested that second-order
pitch and roll high-pass filters with break frequencies of
0.5 rad/sec appear adequate (ref. 39). This result was for
stabilizing the pitch and roll attitude of a DC-9 on
approach. Both the high-frequency gain and damping ratio
of the motion filter were unity in all of van Gool’s
motion configurations.
Cooper and Howlett examined five tasks with a helicopter
model in an attempt to determine motion fidelity requirements
for a particular six-degrees-of-freedom hexapod
motion platform (ref. 40). They made the point that to
achieve maximum results from a simulator, the structure
and values of the high-pass motion filters need to be
tailored for the task while staying within the platform
excursion limits. Although motion amplitude can be
reduced by either reducing the motion filter gain or the
time-constant, their experience had been that it was better
to use the combination of both rather than reducing only
the time-constant. Their tentative conclusion was that it
was best to use a gain of 0.8 in pitch and roll with a timeconstant
of 4 sec.
Using a fixed-wing model, the effects of roll-only motion
were examined by Jex et al. (ref. 41). Their recommendation
was to provide the pilot with accurate roll-rate
motion cues at frequencies above 0.5–1.0 rad/sec with a
first-order high-pass filter. A filter time-constant of
2–3 sec was recommended. Here, the word “accurate”
included the allowance of a 0.5–0.7 gain on the filter.
Not providing the initial full roll-rate cue was deemed
acceptable.
Shirachi and Shirley used a model of a Boeing 367
transport for a disturbance-rejection task in roll (ref. 42).
The simulator motion platform had sufficient lateral
translational displacement to coordinate the rolling
maneuvers. The results suggested that if the highfrequency
gain on the roll high-pass filter was lower than
about 0.5 performance would approach that of no motion.
8
This gain limitation was deemed acceptable with a secondorder
high-pass filter break frequency of 0.7 rad/sec.
Bray found that for a large transport aircraft with full roll
gain, motion filter break frequencies of 0.5 rad/sec caused
slight contradictions in the visual and roll motions
(ref. 27). Increasing the break frequency to 1.0 or
1.4 rad/sec resulted in a reduction of some pilots’ ability
to stabilize the Dutch roll motions.
Experimental Translational Criteria. Fewer
experiments have examined translational motion than
rotational motion. Cooper and Howlett (ref. 40) suggested
a lateral translational-axis fidelity criterion, as shown in
figure 3. Second-order filters were used with a hexapod
platform capable of ±5 ft of lateral translation. The
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Helicopter Flight Simulation Motion Platform Requirements(8)
