A study to measure and compare pilot time delay when using a space shuttle rotational hand controller and a more conventional control stick was conducted at NASA Ames Research Center's Dryden Flight Research Facility. The space shuttle controller has a palm pivot in the pitch axis. The more conventional controller used was a general-purpose engineering simulator stick that has a pivot length between that of a typical aircraft center stick and a sidestick. Measurements of the pilot's effective time delay were obtained through a first-order, closed-loop, compensatory tracking task in pitch. The tasks were implemented through a space shuttle cockpit simulator and a critical task tester device. The study consisted of 450 data runs with four test pilots and one nonpilot, and used three control stick configurations and two system delays. Results showed that the heavier conventional stick had the lowest pilot effective time delays associated with it, whereas the shuttle and light conventional sticks each had similar higher pilot time delay characteristics. It was also determined that each control stick showed an increase in pilot time delay when the total system delay was increased

Bartoli, A. G.

Berry, D. T.

Privoznik, C. M.

English

NASA Technical Reports Server

MEASUREMENTS OF PILOT TIME DELAY AS INFLUENCED BY CONTROLLER 
CHARACTERISTICS AND VEHICLE TIME DELAYS 
Cynthia M. Privoznik, Donald T. Berry, and Adrian G. Bartoli 
NASA Ames Research Center 
Dryden Flight Research Facility 
P.O. Box 273 
Edwards, California 93523 
ABSTRACT 
A study to measure and compare pilot time delay when using a space 
shuttle rotational hand controller and a more conventional control stick was 
conducted at NASA Ames Research Center's Dryden Flight Research Facility. 
The space shuttle controller has a palm pivot in the pitch axis. The more 
conventional controller used was a general-purpose engineering simulator 
stick that has a pivot length between that of a typical aircraft center stick 
and a sidestick. Measurements of the pilot's effective time delay were 
obtained through a first-order, closed-loop, compensatory tracking task in 
pitch. The tasks were implemented through a space shuttle cockpit simulator 
and a critical task tester device. The study consisted of 450 data runs with 
four test pilots and one nonpilot, and used three control stick configura-
tions and two system delays. Results showed that the heavier conventional 
stick had the lowest pilot effective time delays associated with it, whereas 
the shuttle and light conventional sticks each had similar higher pilot time 
delay characteristics. It was also determined that each control stick showed 
an increase in pilot time delay when the total system delay was increased. 
NOMENCLATURE 
CTT critical task tester 
e base of natural system of logarithms (2.718) 
controlled element constant 
j imaginary number 
operator describing function constant 
s LaPlace operator 
SHARP Summer High School Apprentice Research Program 
controlled element 
operator describing function 
210 
https://ntrs.nasa.gov/search.jsp?R=19850006191 2020-03-22T17:47:47+00:00Z
inverse time constant, rad/sec 
inverse time constant at critical time 
total system delay, sec 
pilot effective time delay, sec 
w frequency 
INTRODUCTION 
The space shuttle control stick is different than a conventional air-
craft stick in that it has a palm pivot in the pitch axis and is essentially 
a wrist rotation controller. A conventional controller has a longer p i vot 
length and a more translational movement. Because of this difference there 
is an interest in how this may affect pilot time delay. Past studies con-
ducted by Systems Technology Incorporated (refs. 1 and 2) have shown a dif-
ference in pilot effective time delay due to manipulator characteristics and 
the order of the controlled element. Total system time delays, which consist 
of pilot and vehicle system delays, are critical parameters in aircraf t han-
dling qualities. For example, pilot-induced oscillations can be encountered 
in critical tasks such as landing and inflight refueling when excessive time 
delays exist. The pilot's effective time delay can be an important component 
of the total system time delay when the pilot is in the loop. In some cir-
cumstances small changes in vehicle system time delays result in large 
changes in flying qualities (ref. 3). 
In a study performed at NASA Ames Research Center's Dryden Flight 
Research Facility, a critical task tester (CTT) was used to obtain pilot 
effective time delay (Tp) values for the shuttle stick and a more conven-
tional stick. The experiment used two system time delays. Variations in the 
values of Tp are used to show how the shuttle stick compares to a more con-
ventional control stick and what effect the total system delay has on the 
pilot's effective time delay. 
At the completion of this experiment, the equipment was available for the 
NASA Summer High School Apprentice Research Program (SHARP). A high school 
student in a science and engineering program measured operator time delay for 
a diverse group of subjects, mostly SHARP students. Results as a function of 
background and flying experience are briefly summarized in this paper. 
DESCRIPTION OF EQUIPMENT 
Three control stick configurations were used in this study with the 
shuttle cockpit simulator in the Ames Dryden simulation laboratory. One con-
figuration was a space shuttle stick, which is a three-degree-of - freedom 
rotational manipulator with nonlinear gearing. The other two configurations 
used a more conventional general-purpose engineering simulation stick with 
two different spring constants. All sticks were center mounted. The 
211 
L 
general-purpose stick was used in a variety of engineering simulators and 
r epresented a compromise among a broad range of stick characteristics. It 
had two degrees of freedom and linear gearing; however it had a pivot point 
between that of a typical aircraft center stick and a sidestick. This 
general-purpose stick was tested first with a stiff set of springs and was 
designated the heavy conventional stick. Later, a softer set of springs was 
i nstalled to obtain the light conventional stick. The designations light, 
heavy, and conventional are only relative, however, since the force gradients 
are lighter and pivot arms are shorter for this stick than that used in most 
aircraft center sticks. For stick characteristics see table 1 and figures 1, 
2, and 3. 
The control stick signal that is processed through the cockpit simulator 
is operated with a 40-msec frame time and is sent through the CTT. The total 
inherent time delay between the pilot input and the CTT was 46 msec; 20 msec 
was due to the average sampling delay of the 40 msec frame time, and 26 msec 
was due to the computation time. 
The CTT uses a first-order compensatory tracking task with an unstable 
controlled element: 
Yc = KcAf(s - A) 
where A is the inverse time constant. Under these conditions it can be 
assumed that the operator can be described by: 
where Tp is the pilot's effective time delay. Figure 4 shows the block dia-
gram and root locus of these elements using a first-order Pade' approximation 
for the e-TpS term. A is increased as a function of time and error magni-
tude, making the system more unstable until control is lost. The value of A 
at that critical point approximates the reciprocal of the operator's effec-
t ive time delay, AC = 1/Tp. This simplified summary is based on more detailed 
explanations of the critical tracking task theory which includes systems with 
additional system delays. These explanations can be found in references 1 
and 2. 
The pitch indicator is displayed on an oscilloscope as a horizontal bar 
t hat moves vertically in pitch. The AC values are read directly from a volt-
meter. Figures 5 and 6 show the setup of the equipment. 
TEST PROCEDURE 
The test subjects for this study included four test pilots and one non-
pilot engineer. All of the subjects were orientated to the experimental 
setup through a series of trial runs. 
A series of 15 runs for each of the three stick conf igurations was con-
ducted. Adding runs with a system delay of 250 msec brought the total number 
2 12 
of runs for each of the five test sUbjects to 90. The Ac values were recorded 
for each run, and the average for the 15 runs was computed for each case. The 
Ac values, which were read directly off the voltmeter, contained the 46 msec 
inherent time delay but did not contain the added system delay of 250 msec 
when it was applied. A time delay of 250 msec was chosen to simulate the 
total system delay nearer to the value of the space shuttle. The total aver-
age AC value from each set of 15 runs was converted to time delay and the 
46 msec computational delay was subtracted from it to obtain the pilot's total 
effective time delay. 
RESULTS AND DISCUSSION 
Figure 7 shows the averaged Tp values for each subject and the total 
average for all the sUbjects; these averages are denoted by solid bars. The 
data obtained from the runs with no added time delay (46 msec Td) is on the 
left and the data for the 250 msec added system delay run (296 msec Td) is 
on the right for each stick. Based on the total average for all the test 
subjects, the heavy conventional control stick had the lowest Tp values with 
and without added system delay. The shuttle and the light conventional 
manipulator had similar Tp values. The shuttle and light conventional sticks 
both had the same Tp (200 msec) value for runs with no added system delay. 
On runs with added system delay, the shuttle stick Tp was slightly higher 
than with the light conventional stick. Scatter can be seen in the data in 
figure 7 but the trends with any given pilot look very consistent. 
The changes in Tp values for each control stick because of added system 
delay are evident in figure 7. In every case the subject's effective time 
delay increased with an added system delay of 250 msec. On the average, the 
shuttle controller showed the most change: 70 msec. For the heavy conven-
tional stick the average increase in sUbject delay was 50 msec. The average 
increase for the light conventional stick was 60 msec. 
These data show that the changes in pilot time delay due to differences 
in manipulator characteristics are much less than the changes in pilot time 
delay due to differences in total system time delay. This is consistent with 
previous results (fig. 8). These data are unpublished results obtained under 
NASA Contract NAS2-4405 with Systems Technology, Incorporated. The data show 
very small changes in Tp for a first-order controlled element as the gradient 
for a pencil controller changes from a rigid (force) stick to a free (uncon-
strained) stick. However, for a second-order controlled element, the Tp is 
much larger and more sensitive to stick force gradient. Figure 9 presents 
the results of the Ames Dryden experiment in a format similar to that in 
figure 8. Figures 8 and 9 cannot be directly compared because of the dif-
ferences in controller geometry, gradient, and controlled element time delay. 
However, some observations on gross trends are valid. The increase in Tp for 
the second-order controlled element (Yc ' fig. 8) can be attributed to the 
additional mental processing the pilot must perform to compensate for the 
213 
integrator lag. The time delay in the controlled elements of figure 9 would 
also require pilot compensation (or lead); an increase, therefore, in Tp 
would be expected. The change in pilot time delay for this experiment is not 
as large as that seen in figure 8. However, the variation in stick gradient 
for this experiment is not nearly as extreme as that used in figure 8. Per-
haps even more significant is the difference in compensation required for the 
time delay compared to the integrator. 
The secondary experiment conducted by a SHARP student was done in a 
similar manner to that of the primary experiment except that only one control 
stick configuration was used (the light Ames Dryden stick); the subjects 
included SHARP students and some adults. None of the subjects were profes-
sional pilots, although some were amateur pilots. The results of this experi-
ment are summarized in figures 10 and 11. Figure 10 compares results of the 
secondary and primary experiments, and indicates that previous piloting 
experience did not affect the pilot's time delay; nonpilots, amateur pilots, 
and professional pilots scored alike. The student investigator, a video game 
enthusiast, correlated the results with video game playing experience. These 
results are shown in figure 11, and improvements in the raw score are shown 
as the number of video games played per week increased. 
Although these data are insufficient to be statistically conclusive, they 
do suggest some interesting speculation. For example, the indication that 
pilot time delay is affected by video game experience, but not real-world 
piloting experience, suggests that laboratory setups that are too "game-like" 
may not give the same results as an operational environment. This, however, 
does not impair the usefulness of laboratory results in establishing trends 
and measuring differences. 
CONCLUDING REMARKS 
The space shuttle manipulator controller and a more conventional con-
troller with two different force gradients were evaluated in the pitch axis 
using a first-order, closed-loop, compensatory tracking task implemented 
through a critical task tester device. Five test subjects performed a total 
of 450 data runs using the three control stick configurations with a total 
system delay of 46 and 296 msec. The data indicate that the heavy conven-
tional controller had the lowest effective pilot time delay values associated 
with it, with and without the added system delay. The shuttle and light con-
ventional controllers had similar pilot time delay characteristics. Each 
control stick experiment showed an increase in pilot time delay when there 
was an increase in total delay. 
Changes in pilot time delay because of increases in system time delay were 
much more significant than changes because of manipulator characteristics. 
A secondary experiment using the critical task tester indicated that the 
pilot time delay is unaffected by previous piloting experience but is influ-
enced by video game experience. 
214 
_ __ I 
------ -- -- -
REFERENCES 
1. Jex, H. R.; McDonnell, J. D.; and Phatak, A. v.: A "Critical" Track-
ing Task for Man-Machine Research Related to the Operator's Effective 
Delay Time, Part I: Theory and Experiments with a First-Order 
Divergent Controlled Element. NASA CR-616, 1966. 
2. MCDonnell, J. D.; and Jex, H. R.: A "Critical" Tracking Task for Man-
Machine Research Related to the Operator's Effective Delay Time, 
Part II: Experimental Effects of System Input Spectra, Control Stick 
Stiffness, and Controlled Element Order. NASA CR-674, 1967. 
3. Berry, Donald T.; Powers, Bruce G.; Szalai, Kenneth J.; and Wilson, R. J.: 
In-Flight Evaluation of Control System Pure Time Delays. J. Aircraft, 
vol. 19, no. 4, Apr. 1982, pp. 318-323. 
Table 1 Control stick 
characteristics 
Characteristics 
Shuttle stick 
Breakout, in-lb 
Travel, deg 
Gradient, in-lb/deg 
Pivot point, in* 
pitch 
1 .2 
±19.5 
1.2 
o 
Heavy conventional stick 
Breakout, in-lb 
At stop, lb 
Travel, in 
Gradient, lb/in 
Pivot point, in* 
0.5 
11 .0 
±2.0 
5.3 
7.0 
Light conventional stick 
Breakout, lb 
At stop, lb 
Travel, in 
Gradient, lb/in 
pivot point, in* 
0.5 
6.5 
±2.0 
3.0 
7.0 
*Measured from middle of palm 
point on control stick. 
21 5 
ECN 249Z2A 
Figure 1. Space shuttle rotational hand controller • 
.. , 
!. f I f ( 
'- -
ECN 24919A 
Figure 2. Conventional control stick. 
21 6 
I 
J 
F 
12 Shuttle 
10 
Stick 
8 ,..-,..--
voltage 6 
- --,,--- Conventional output 
4 
2 
o 2 4 6 8 10 12 14 16 18 20 
Shuttle stick deflection, deg 
o .5 1.0 1.5 2.0 
Conventional stick deflection, in t • 
. ' 
Figure 3. pitch axis stick shaping. 
.' 
. 
. 
Displayed Pilot 
Input + error 
Negative feedback 
Controlled 
element 
KcA Output 
y C = -(S---A) t--..._--. 
, 
System Is stable within 
pilot gain levels 
t = 0 
System Is being 
driven more unstable for 
time > 0 
At critical point 
system is unstable 
jw 
time = time critical, 
Tp = 1/Acrltical 
jw 
Figure 4. Critical task tester block diagram and 
root locus. 
21 7 
OFFSEl ). LIMIT 
CONTROl 
SLOW LOST 
). SCORE NORf,lAL POWER 
\) 
" "" 
METER 
AOJUST DISPlAY MonON 
snc)( METER Vtlll 
",," LOCAL LOCAL GND 
• 
REIolOlE REIIOTE 
ECN 24923A 
Figure 5. Critical task tester. 
ECN 24924A 
Figure 6. simulator cockpit. 
218 
,. 
Shuttle 
o Pilot 1 
o Pilot 2 
o Pilot 3 
l:::. Pilot 4 
o Engineer 
.30 
Heavy 
conventional 
Light 
conventional -- Average 
.25 
Pilot 
effective .20 
time delay (T p) . 
sec 
.15 
.10 
.046 .296 .046 .296 .046 .296 
Total system delay (T d) ' sec 
Figure 7. Summary of pilot time delay results • 
. 5 
.4 
Pilot time .3 
delay (Tp). 
sec 
.2 
.1 
Kc A Y - - -~ c - (s - A) O----------L -o 
Free 
stick 
Force 
stick 
o Zero Infinite 
Stick gradient. force/deflection 
Figure 8. pilot time delays for pencil 
controller. 
21 9 
.5 
.4 
Pilot time .3 
delay (Tp). 
sec 
.2 
.1 
K e -0.296s 
c 
r Ye == (s - A) o----_-Q..., 
-----0 
cr-----D------o 
\ K e -0.046s L Y == ~c-;-_:-;-_ 
c (s - A) 
OL--~--------~------~~ 
Shuttle Light Heavy 
rotational conventional conventional 
hand controller 
Stick gradient. force/deflection 
Figure 9. Pilot time delays for 
shuttle and conventional control 
sticks. 
4.0.-
3.6 t-
3.2 t-
2.8 I-
2.4 t-
Raw score 
I.e· 2.0 t-
1/sec 1.6 t-
1.2 r-
.8 r-
.4 r-
0 
Amateur pilots Nonpilots Professional 
pilots 
Previous flying skill 
Figure 10. Raw scores as a function 
of flying skill. 
2 20 
5.0 
4.0 
Raw score 3.0 
AC' 
1/sec 2.0 
1.0 
o 3 6 9 12 15 18 21 24 27 
Video games played, per week 
Figure 11. Raw scores as a function 
of video games played. 
221 


Measurements of Pilot Time Delay as Influenced by Controller Characteristics and Vehicles Time Delays

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