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mental compensation between the two cases. No data were
taken when returning to the full-motion case for recalibration,
but pilots commented that relearning the full-motion
configuration was easy and natural.
Figures 40 through 49 show phase-plane portraits for each
motion configuration. Each portrait shows three runs, one
for each pilot, using his best performance run if an evaluation
was repeated. Both the bob-up and bob-down are
shown. These plots show how the motion changes
affected the pilot’s ability to capture the upper desired
point smoothly. Ideally, these plots should be welldamped
and approximately oval.
Figure 40 indicates that some overshoots were present for
the full-motion condition, but overall the trajectories were
well damped and smooth. There was reasonably precise
control about the 85-ft altitude point, with one instance of
a pilot not arresting the vertical velocity soon enough,
which caused a position overshoot. Little change in
performance, or perhaps a slight improvement, is noted
for the slight motion changes of configuration V2 in
figure 41.
The high-gain, moderate phase-distortion case of
configuration V3 in figure 42 still produces well-damped
trajectories on ascents. The acceleration cues for this
configuration lead the math model by 90° at 0.52 rad/sec.
If the motion between the ascents and descents were sinusoidal,
the frequency of the maneuver would be approximately
2 rad/sec. This value is approximated by letting
h = 80 + 5sinwt (13)
h˙ = 5wcoswt (14)
˙ / sec / sec hmax = 10 ft Þw = 2 rad (15)
For the initial phase of the maneuver, therefore, the
motion cues would be accurate, but the subsequent
stabilization at a particular altitude would produce some
miscues, for lower frequency content would be present.
Pilots seemed to have more difficulty in returning to the
starting point than in the first two configurations;
however, this repositioning was not officially part of the
evaluations. For the high-gain and high-phase-distortion
case of configuration V4 in figure 43, the overshoots were
more prominent, and the overall control was much less
precise.
35
70
75
80
85
90
Altitude, ft
-15
-10
-5
0
5
10
Vert. vel., ft/sec
-30
-20
-10
0
10
20
Vert. accn., ft/sec2
0 50 100
-3
-2
-1
0
1
2
Collective, in
Time, sec
70
75
80
85
90
Altitude, ft
-15
-10
-5
0
5
10
Vert. vel., ft/sec
-30
-20
-10
0
10
20
Vert. accn., ft/sec2
0 50 100
-3
-2
-1
0
1
2
Collective, in
Time, sec
Figure 39. Altitude control: full motion versus no motion.
36
-20 -10 0 10 20
70
75
80
85
90
Vertical velocity, ft/sec
Altitude, ft
Figure 40. Phase-plane portrait for configuration V1.
-20 -10 0 10 20
70
75
80
85
90
Vertical velocity, ft/sec
Altitude, ft
Figure 41. Phase plane portrait for configuration V2.
-20 -10 0 10 20
70
75
80
85
90
Vertical velocity, ft/sec
Altitude, ft
Figure 42. Phase-plane portrait for configuration V3.
-20 -10 0 10 20
70
75
80
85
90
Vertical velocity, ft/sec
Altitude, ft
Figure 43. Phase-plane portrait for configuration V4.
For the medium-gain, low-phase-distortion case of
configuration V5 in figure 44, the bob-up trajectories
show good performance, with the trajectories being
similar to those of the full-motion case, or at least similar
to those of the V2 case. The gain is lowered to 65% of
full motion for the V5 configuration.
Increasing the phase distortion from configuration V5 to
configuration V6 caused a slight reduction in the precision
around the desired stationkeeping point with a few undershoots
of the ascent point as shown in figure 45. The gain
reduction in going from V3 to V6 does not appear to
degrade performance significantly.
The low-gain, low-phase-distortion case, configuration V7
in figure 46, resulted in less precision with more over- and
undershoots than in the previous configurations. Here the
gain is at 30% of full motion at high frequencies.
Performance definitely decreases when the gain drops from
0.65 in configuration V5 to 0.3 in V7.
The precision in V7 also appears worse than in the V4
　
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