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followed by a presentation of both the objective and
subjective results, which are summarized at the end.
Experimental Setup
There can be confusion when the words “yaw motion” are
used to describe a motion situation. This confusion arises
because the motion that occurs at the vehicle’s center of
mass is different from the motion experienced at the
pilot’s location. For instance, for the purposes here, when
a pilot sits forward of the yaw center of rotation, a vehicle
yawing motion produces both yaw and lateral translation
cues at the pilot’s location. Since the motion at the
pilot’s location is what the simulator is trying to reproduce,
all subsequent discussions of motion refer to pilotstation
motion. In addition, in this section, the word
“rotation” refers to orientation changes about the yaw
axis, and the word “translation” refers to sway motion in
the vehicle’s y body-axis.
Tasks
Three tasks were developed to represent a broad class of
situations in which both lateral-translational and yawrotational
motion cues may be useful in flight simulation.
Task 1 was a small-amplitude command task that allowed
for full math-model motion to be provided by the motion
system. Task 2 was a large-amplitude command task that
did not allow full math-model motion to be presented, for
the simulator cab rotational and longitudinal translational
limits would have been exceeded; however, it was
accompanied by strong rotational visual cues. Task 3 was
a disturbance-rejection task, which also allowed full mathmodel
motion to be provided by the motion system, but
with the pilot also controlling vehicle altitude.
Task 1: 15° yaw rotational capture
In the first task, the pilot controlled the vehicle only
about the yaw axis. The pilot was required to acquire
rapidly a north heading from 15° yaw rotational
offsets to either the east or west. This task allowed
for full math-model motion to be represented by the
motion system in all axes (rotational and translational).
An aircraft plan view, with the pilot’s
simulated position relative to the inertially fixed
center of mass (c.m.), is shown in figure 7.
The desired pilot-vehicle performance for the task was
to rapidly capture and stay within ±1° about north
with two overshoots or less. This 2° range was
visually demarcated by the sides of a vertical pole,
shown in the pilot’s forward field of view in figure 8.
The pilot’s reference on the aircraft for positioning
was a fixed vertical line centered on the head-up
display. Pilots performed six captures with each
motion configuration, alternating between initial west
and east directions. The repositionings from north to
the initial east or west initial positions were not part
of the task.
16
Figure 7. Pilot location in plan view.
Figure 8. Pilot’s visual scene in Tasks 1 and 3.
Figure 9. Pilot’s visual scene in Task 2.
Task 2: 180° hover turn
The second task required a 180° pedal turn over a
runway, which was to be performed in 10 sec. The
pilot again controlled the aircraft with the pedals
only, and the position of the c.m. remained fixed with
respect to Earth. This maneuver was taken from the
current U.S. Army rotary-wing design standard
(ref. 50) and, with one proviso, is representative of a
handling qualities maneuver performed for the
acceptance of military helicopters. However, in the
military acceptance maneuver, the pilot controls all
six degrees of freedom rather than one.
This maneuver did not allow for full math-model
motion, since the simulator cab cannot rotate 180°.
As a result, attenuated motion was used, as described
later. Desired performance was to stabilize at the end
of the turn to within ±3° and within 10 sec. Pilots
performed six 180° turns, always turning over the
same side of the runway to keep the visual scene
consistent for the set of turns. Figure 9 shows the
visual scene from the starting position.
Task 3: Yaw rotational regulation
The third task required the pilot to perform a rapid 9-ft
climb while attempting to maintain a constant
heading. This disturbance-rejection task was challenging,
because collective lever movement in the
unaugmented AH-64 model results in a substantial
yawing moment disturbance (because of engine
torque) that must be countered (rejected) by the pilot
with pedal inputs. This task allowed full vertical,
yaw-rotational, and lateral-translational motion at the
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Helicopter Flight Simulation Motion Platform Requirements(13)
