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pilot’s station. Desired performance was for the pilot
to acquire the new height as quickly as possible while
keeping the heading within ±1° of north. The same
visual scene was presented as in Task 1 (fig. 8), but
with the scene also indicating height variations as the
vehicle model changed altitude.
Simulated Vehicle Math Model
The math model represented an unaugmented AH-64
Apache helicopter in hover, which had been identified
from flight-test data and subsequently validated by several
AH-64 pilots (ref. 51). Equation (5) describes the vehicle
dynamics for the rotational y and vertical h degrees of
freedom:
17
˙˙
˙˙
˙
. . .
. . .
. . .
˙
˙
. .
. .
. .
y y
d
d
h
z
h
z
r
c
1 1
0 270 0 000 0 000
0 000 0 122 118
0 000 0 000 12 9
0 494 0 266
0 000 14 6
0 000 1 000
é
ë
êêêê
ù
û
úúúú
=
-
- -
-
é
ë
êêê
ù
û
úúú
é
ë
êêêê
ù
û
úúúú
+
é
ë
êêê
ù
û
úúú
é
ë
êê
ê
ù
û
úú
(5)
The collective position dc and pedal position dr are in
inches. The variable z1 was an additional state added to
approximate the effects of dynamic inflow (ref. 51). All
other vehicle states were kinematically related to the above
dynamics. So, in effect, the vehicle c.m. was constrained
to remain on a vertical axis fixed with respect to Earth for
all tasks. Although the tail rotor in an actual helicopter
produces both a side force and a moment about the c.m.,
only the moment was represented in this experiment, a
result of the fixed c.m. These vehicle constraints were
introduced to simplify the number of motion sensations
that had to be interpreted by the pilot. In addition, no
coordination of the gravity vector was required, for it
remained fixed relative to the pilot. No atmospheric
turbulence was present in any of the tasks. The collective
lever was used for Task 3 only.
The pilot was located 4.5 ft forward of the c.m., which
represents the AH-64 pilot location. Thus for this case,
math model rotational accelerations were accompanied by
lateral translational accelerations at the pilot’s station, and
rotational rates were accompanied by longitudinal accelerations
at the pilot’s station. Specifically, the accelerations
at the pilot’s station in this experiment were as
follows:
axp = -4.5y˙ 2 (6)
ayp = 4.5y˙˙ (7)
y˙˙ p = y˙˙ (8)
where the subscript p refers to the pilot’s station.
Simulator and Cockpit
The Vertical Motion Simulator, described in section 2,
was used. The mainframe-computer cycle time was 25
msec. The Evans and Sutherland CT5A visual system
provided the visual cues, and it had a math-model-tovisual-
image-generation delay of 86 msec (ref. 52). This
delay is typical of today’s flight simulators. The visual
field of view is shown in figure 10. The visual cues
40°
30°
20°
20° 60°
10°
-40°
-50°
-30°
-20°
-60° -40° -20°
-10°
40°
Figure 10. Cockpit visual field of view.
presented to the pilot did not vary and were always those
of the math model. These cues represented the pilot’s
physical offset of 4.5 ft forward of the vehicle’s c.m.
Conventional pedals and a left-hand collective lever were
used. The pedals had a travel of ±2.7 in, a breakout force
of 3.0 lb, a force gradient of 3 lb/in, and a damping ratio
of 0.5. The collective had a travel of ±5 in, no force
gradient, and the friction was adjustable by the pilot.
All cockpit instruments were disabled, which made the
visual scene and motion system cues the only primary
cues available to the pilot. Rotor and transmission noises
were present to mask the motion-system noise. Six
NASA Ames test pilots participated in Task 1, and five of
the same six participated in Tasks 2 and 3. All pilots had
extensive rotorcraft flight and simulation experience.
Motion System Configurations
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Helicopter Flight Simulation Motion Platform Requirements(14)
