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and disturbance regulation. This procedure allowed for the
influence of the motion-filter changes to be examined
simultaneously for these two important piloting tasks.
The task and experimental apparatus are first described.
Then, objective pilot-vehicle performance metrics and
subjective motion-fidelity ratings are discussed.
Experimental Setup
Task
Figure 52 shows the display presented to the pilot. The
object was to null the error between the moving target
aircraft and the horizontal dashed line that was fixed to the
pilot’s aircraft.
A system block diagram depicting how the error developed
is shown in figure 53. Two external inputs were used in a
scheme similar to that developed by Stapleford et al.
(ref. 26).
Target Aircraft
Fixed horizontal line
e
Figure 52. Pilot’s display for vertical compensatory
tracking.
ih dc
dc
d
dc
tot
h
filt
+
+
+
Aircraft
–
e
h
sim
h h
Pilot
h
dc tot
(s)
1
s2
Motion
hardware
Motion
filter
Visual
hardware
Figure 53. Vertical compensatory loop.
The target was driven by a sum-of-sines (SOS) input, and
the vehicle was disturbed by a separate SOS input that
was summed with the pilot’s collective position. These
SOS’s were as follows:
i t t t
t t
t t
t
h ( ) . sin( . ) . sin( . )
. sin( . ) . sin( . )
. sin( . ) . sin( . )
. sin( . )
= +
+ +
+ +
+
2 573 0 15 2 202 0 34
1 563 0 64 0 923 1 13
0 411 2 05 0 150 3 56
0 040 6 32 feet
(16)
dcdt t t
t t
t t
t
( ) . sin( . ) . sin( . )
. sin( . ) . sin( . )
. sin( . ) . sin( . )
. sin( . )
= +
+ +
+ +
+
0 029 0 28 0 058 0 49
0 999 0 80 0 167 1 50
0 209 2 67 0 201 4 63
0 148 8 50 inches of collective
(17)
Each component of each SOS completed an integral
number of cycles in the task time-length of 204.8 sec.
A warm-up period of 10 sec preceded the run, and a cooldown
period of 3 sec followed the run. To prevent the
pilot from separating target motion from disturbance
motion, the disturbance input, dcd, was selected so that its
resulting altitude spectral content (when filtered by the
vehicle dynamics) matched the target shaping function
(refs. 26, 41). If the pilot is able to separate the target
motion (which is sensed only visually) from the disturbance
motion (which is sensed visually and vestibularly),
previous research has shown that pilots may alter their
behavior and potentially ignore the motion cues when
nulling the target motion (ref. 26). The above spectral
matching is an attempt to prevent this behavior.
The above shaping function was determined empirically.
The compromised result of this shaping was that the
highest frequency component of the target input was
below the simulator’s visible threshold of 3–4 arc min,
and the lowest component of the disturbance input was
below the vestibular translational acceleration detection
threshold of 0.01 g’s (ref. 28). As shown in figure 53,
the pilot received two external cues for use in zeroing the
target error, e: a visual cue, and a motion cue. The
dynamics between the pilot input and these cues are
discussed in the sections that follow; however, only the
block labeled “motion filter” was modified in this experiment.
The details of these blocks will be described later.
Although the pilot was instructed to null the displayed
error constantly, the desired performance for the task was
to keep the error within one-half the height of the target
vertical tail for half of the run length. The target was
placed 100 ft in front of the aircraft, and the height of the
vertical tail was 3 ft.
42
Simulated Vehicle Math Model
The vertical-axis dynamics were the same as for Vertical
Experiment I given by equation (11). Again, only this
single degree of freedom was modeled, and the pilot
controlled this degree of freedom with a collective lever in
the cockpit.
Simulator and Cockpit
The simulator and cockpit were also the same as for
Vertical Experiment I. All flight instruments were again
disabled. Six NASA Ames test pilots participated (three of
the six being the same three who participated in Vertical
Experiment I), hereinafter referred to as pilots A–F. All
pilots had extensive rotorcraft flight and simulation
experience.
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Helicopter Flight Simulation Motion Platform Requirements(29)
