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motion platform is reduced relative to the model (and thus
the visual scene). This requires less lateral travel, since
less lean-due-to-roll motion is present. In the second
method, less than the full amount of lateral translational
motion required for coordination is used. The purpose of
his study was to investigate the trade-off between these
two options.
Experimental Setup
Task
Constant-altitude lateral side steps were performed between
two points 20 ft apart. A positioning sight in the visual
scene allowed pilots to use parallax to determine their
positioning error precisely. The desired positioning
performance standard was ±3 ft about the desired hover
point (which was 20 ft away), and the adequate performance
standard was ±8 ft. The task had to be completed in
less than 10 sec for desired performance and in less than
15 sec for adequate performance. Pilots pressed an event
marker on the center stick when they felt they had acquired
the station-keeping point. They were instructed that pushing
this button meant that they were within the position
error for desired performance, and that they believed they
would remain within the desired performance standard.
Simulated Vehicle Math Model
The math model had only two degrees of freedom. Altitude
remained constant at 25 ft; heading, pitch, and
longitudinal position remained constant at zero. Pilots
controlled the vehicle with lateral displacements of a
center stick only. The equations for motion were
˙f˙ = -4.5f˙ +1.7dlat (21)
v˙ = gsin f (22)
where v is the body-fixed velocity in the y direction
(lateral). These equations represent a typical helicopter
math model that is fully coordinated at the aircraft’s
c.m., since no lateral aero-propulsive forces are present
( ay = v˙ - gsin f). Actual helicopters have a drag owing to
lateral translational velocity, and they also produce a side
force at the rotor which contributes to a rolling moment.
Each of these real-world effects causes uncoordinated flight
during a side-step maneuver. This experiment used a fully
coordinated model, since the objective was to examine the
effects of uncoordinated simulation cues caused by simulator
platform displacement limitations. Thus, these realworld
effects were intentionally absent. So the model
represented a vehicle in which only applied torques created
rolling motion (similar to an AV-8B-like concept) with
no drag owing to velocity (which is small near hover).
For the experiment, the pilot’s abdomen was located at the
aircraft’s c.m. The roll-axis dynamics given above, when
combined with the visual system delay of 60 msec, had
56
satisfactory (Level 1) handling qualities as predicted by
the U.S. Army’s Rotary Wing Handling Qualities
Specification (ref. 50).
Simulator and Cockpit
The experiment again used the NASA Ames Vertical
Motion Simulator, but only the roll and lateral axes. The
lateral axis has ±20 ft of travel, and the roll axis has ±18°
of displacement. The roll and lateral axis dynamic characteristics
were dynamically tuned with feedforward filters in
the motion software to synchronize the two axes as much
as possible. For this experiment, each motion axis had an
equivalent time delay of approximately 60 msec, as
measured using techniques developed by Tischler and
Cauffman (ref. 46). The cockpit was configured with a
center stick only. No instruments were present, so the
pilot had to extract all cues from the motion system, the
visual system, and the inceptor (center-stick) dynamics.
The center-stick dynamics were measured to be
dlat
Flat
s
s s
( )
. ( . )
=
+ +
1
0 6
8
2 0 8 8 8
2
2 2 (23)
where dlat and Flat are the displacement and force,
respectively, at the pilot’s grip.
For the visual system, the Evans and Sutherland ESIG
3000 image generator was used. The visual time delay was
adjusted so that it was 60 msec in order to match the
equivalent motion time delay in the roll and lateral axes.
The simulator cab was the same as that used in section 4,
so the field of view is that shown in figure 36.
Motion System Configurations
Figure 70 shows the relevant motion-platform drive laws.
That is, the simulator-roll-angle command differed from
the math model only by a gain (i.e., no frequencydependent
motion attenuation from a washout filter was
present). The platform moved laterally to reduce the false
lateral acceleration caused by platform roll angle. Only a
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Helicopter Flight Simulation Motion Platform Requirements(37)
