24, OpeRMayeER, R. W. and Muckter, F. A.: Performance
Measurement in Flight Simulation Studies, ALAA
Simulation for Aerospace Flight Conference pp. 58-
65. A Volume of Technical Papers Presented August
26-28, 1963.

ApvaMs, J. A.: The Role of Part-Task Simulators in
the Learning and Retention of Flying Skills. Avia-
tion Psychological Research-Reports of the 5th Conf.
for Aviation Psychol, Bad Godesberg, September
17-20, 1963.

Exsom, BE, R.: Problems of Simulated Flight Train-
ing for Pilots, Ibid. pp. 121-135.

25.

26.

18

27 Anon.: New Concepts of Training and Certification
of Airline Pilots, FAUSST VII, Working Paper
73.2.08; and Training of the Aircrew of Supersonic
Aircraft, FAUSST VII, Working Paper No. 7.12.02.,
Paris, February 3-7, 1969.

GasRiEL, R, F., Creamer, L, R., Carpenter, D. L.,
and Burrows, A. A.: Crew Performance as a Funce-
tion of Flight Duration (Fatigue) in an Operational
Simulator. 40th Annual Meet. Aerospace Med. Assoc.,
San Francisco, Cal., May 5-8, 1969.

28.


VARIATION OF ERROR
WITH MOTION CUES AND VEHICLE DYNAMICS

K
S(S + 10)

Ly
i
‘|=

ZZ
W224

MEAN SQUARE ERROR
MEAN SQUARE INPUT

tt

FIXED BASE |~—— MOVING BASE —>

HEAD AT Cg HEAD 3.5 ft
, ABOVE Cg

Ficure 8. Variation of Error with Motion Cues and Vehicle Dynamics

If similarities or differences between the two (a) Pilot ratings—Subjective pilot evalua-
types of responses are specified and determined, _ tion is still an accepted technique of assessing the
the degree of simulation fidelity or cue deficiency, interactions between a pilot and his aircraft, par-
respectively, can be established. There are four ticularly, in determining the handling qualities
different techniques available which may be use- of the vehicle, pilot performance, and the suit-
ful to the assessment of fidelity of simulation ability of an airplane for the mission, An
and transfer of training: example of this technique, which employs a 10-

12


before playing both hands together on the
piano. In this process, the student learns a
part of a task to a specified level of accuracy
and then is required to integrate the previously
learned tasks into the final entity. This prin-
ciple has long been applied to flying training.
Although Link Trainers, which were first used
to this end, are rather crude devices for instru-
ment flight training, they proved useful for
practicing navigation owing to the positive
transfer of learned behavior patterns from one
situation to the other. If the learned functions
disturb each other, negative transfer occurs.
On the basis of present evidence it appears
that flight simulators generally are very use-
ful, but that the amount of transfer of skill
from the simulator to the aircraft depends
upon a variety of factors which are still sub-
jects of experimental investigations.

III. The Purpose of Flight Simulators

In the course of this presentation, the topic
will be limited to the discussion of flight simu-
lators. Today, the use of flight simulators to
economize training and to cope with situations
which are difficult or impossible to reproduce is
recognized. Ground-based simulators are gen-
erally less expensive, easier to handle and to
maintain, independent of weather, and more
suitable for proficiency measurements than air-
craft. A simulator which reproduces the aero-
dynamic response of an aircraft with enough
realism is not only a valuable tool for practicing
newly acquired skills, but can also be used for
the study of man-machine relationships, stress
factors, human tolerances, and fatigue effects.
Proficiency measurements under realistic condi-
tions are necessary to determine the effectiveness
of man-machine links. Periodic checks are made
to evaluate proficiency in each of the many air-
crew activities for the purpose of detecting’
shortcomings in the system and of pinpointing
performance decrements due to overload of its
components. However, airborne measurements
of aircrew performance are limited by the extent
to which the aircraft can be equipped with re-
cording devices. Even if adequate criteria are
established and automated or computerized tech-
niques are available for recording and measuring
performance in flight, their application very
frequently appears inopportune because of inter-
ference with the actual crew duties. In addition,

the installation, maintenance, and calibration of
the instruments used in field tests or in combat
operations pose almost insurmountable difficulties
to the investigator. The impossibility of expos-
ing the astronauts to space conditions, for
example, left the simulator as the only means for
assessing their performance before the planned
missions in space and on the moon could be
undertaken.

In addition to meeting the training require-
ments, simulators have played an important role
in proficiency measurement. In studying the
possibility of using man as a backup for the
Mercury system, failure mode analyses were con-
ducted in order to determine the critical tasks of
the astronaut during the standard three-orbit
mission. The results of these analyses were then
checked by tasks in various simulators—the pro-
cedure trainer, the centrifuge and the aircraft—
and systems as well as procedure changes were
based on these test results.

The development of analog computers was in-
strumental for the construction of our present
day flight simulators; and computer technology
will further advance the improvements in simu-
lation. One of these advanced devices recently
on display is a fixed-base fighter/interceptor
simulator developed by the General Electric
Company, which shows the computer-generated
pictures of two aircraft on television. One of the
two aircraft is taxiing out of the hangar, taking
off, and flying on a programed course, while the
other one can be controlled by a joystick to follow,
intercept, or overtake the other aircraft. The
programs can be changed to meet various mission
requirements of these types of airplanes.

The activities in aeronautics closely related to
simulation include several steps, namely, re-
search, training, and operations (see Table I).
In the hardware research field, various models
are manufactured which simulate the charac-
teristics and functions of the final vehicle. Later,
the flight and handling characteristics of ad-
vanced systems and its major components are
determined through simulation. The last step
includes operational use; and it is in this phase
that the human element in the simulation process
becomes of prime importance. Simulators are
being used to determine the dynamic character-
istics of the human operator as a servo element.
There are significant implications as to man’s
capabilities to evaluate, control, and improve the



Physical identity alone is not enough to generate
motivation and acceptance. The question whether
danger must be involved in order to produce
fidelity is not easy to answer. Experience in the
training of the astronauts seems to indicate that
danger is not a necessary prerequisite for the
transfer of training.

In closing it is recommended that an optimum
degree of fidelity be provided in order to obtain
a maximum amount of transfer. In certain in-
stances, this can be achieved simply by part-task
simulation; in most cases, however, the use of
whole-task or even inflight flight simulators may
be optimal. This latter device can provide for

16

the highest degree of fidelity, but it is generally
the most complex, complicated, and expensive
type of simulator. For certain types of training,
for example SST pilot training, a combination
of ground-based whole-task and inflight simula-
tors will be used (Fig. 10).27 This approach is
straight forward by proceeding from the aircraft
which is apparently easier to handle than the
more difficult one. It is based on the best judg-
ments of qualified test pilots and on face validity.
A general scientific theory which accurately pre-
dicts the optimum degree of fidelity needed to
achieve the maximum of transfer in flight train-
ing has still to be developed.


90)
80

iC

Comparative evaluations o;
the centrifuge vimlation 2 50
and *ixed-base motion sys- %

| Fixed Bose Simutotor
Dynamic NADC Centrifuge Simutotor

. 40)
30
20] ox conrtene
10)
° Good Poor Unsotisfoctory

a Fixed Base Simulotor

ZA Oynomic NADC
<4 Centrifuge
Simulator

Ficure 4. Comparative Evaluations of the Centrifuge Simulation and Fixed-Base Motion Systems

experiment was to establish a two-modality pilot
function, which would allow predictions of the
effects of motion, motion washout, and simulator
fidelity. The initial phase consisted of a simple
hover task: the pilot had to roll-stabilize the
craft in the presence of disturbance input. The
experiment was so designed that the effects of
visual input as well as angular and linear ac-
celeration on pilot performance and dynamic
response could be determined. Figure 7 shows
the block diagram for this experiment including
the three feedback loops. The position of the
pilot’s head was varied to change the ratio of
linear to angular acceleration feedback. Three
sets of vehicle dynamics were used: K/S-
(S+10)=good, K/S(S+1)=moderate, and
K/S*=no roll damping. In addition, washout
time constants for both roll and lateral motion
were varied from 0.5 to 2 seconds.

One of the most important findings of this
experiment is presented in Figure 8 which shows
results from analysis of the two-input (disturb-
ance and command) data. The fixed-base data

are for the visual cues alone. As indicated, the
pilot operates with greater gain in the visual
mode but with less lead, and he utilizes the mo-
tion channels to develop the required lead. This
result quantifies previous intuitive notions and
observations regarding the beneficial effects of
motion cues.

4. Environmental Factors. The simulation of
environmental factors primarily concerns the
aerodynamic forces which act on the aircraft.
An experiment similar to that mentioned before
was conducted on the centrifuge simulating a
sweptwing transport in severe turbulence; and
its results were released in 1969.2? Several
of the pilots who participated noticed that the
centrifuge did not realistically represent such
factors as the pitch changes and the associated
control forces, the lack of trim stabilization, and
the representation of normal G-forces, although
the simulation generally was authentic. More-
over, the noise level in the cockpit was not
realistic and the lighting was sometimes discon-
certing, particularly when pictures were taken


results of a recent study concerning general
aviation cockpit display and control simulation,
made by FAA personnel at NAFEC in Atlantic
City, New Jersey, show that the use of improved
cockpit display and aids are especially beneficial
at an early stage of instrument training in the
simulator as well as in the aircraft. If visual
noise is present in the system, operator perform-
ance is temporarily disturbed. However, Briggs,
Fitts and Bahrick’ in 1956 established experi-
mentally that the degradation of performance
js not relevant for learning the visual task re-
quired for proficiency. This was recently con-
firmed by Hopkin, Poulter, and Whiteside® for
a flight simulator task performed by pilots with
a blinded retinal area. Since VFR provide the
pilot with continuous general orientation and a
feeling of security, it is only natural that the
critical maneuvers which are performed close to
the ground, namely, takeoff, approach, and Jand-
ing, should be done VFR in the simulator.

In 1967, Chase® evaluated a simulator display
system at the NASA Ames Research Center by
measuring pilot performance during landings.
He also compared the visual qualities of the TV
picture with “real world” conditions. Owing to
the limitations of the TV system used, the simu-
lation was not of high fidelity. Nevertheless, the
approaches were flown very similar to that in
actual flight, and the pilots even included the
so-called “duck-under” maneuver. Touchdown
distance was about the same as during aircraft
landings, but the simulated approach was made
at a higher rate of descent.

In order to provide systematic information
about the value of TV displays for research and
training, another study was initiated by the Man-
Machine Integration Branch at Ames using a
color TV system (General Precision Instruments,
Ltd.) in a fixed-base simulator. The task con-
sisted of simulated approaches and landings of
a DC-8 type aircraft by experienced airline cap-
tains. Performance measures included rate of
descent, flight path variations, and touchdown
accuracy in addition to the evaluation of the
fidelity of simulation by the pilots.

Some preliminary results, made available by
Mr. Sadoff, Chief of the Man-Machine Integra-
tion Branch, are shown in Figures 2 and 3.*
From Figure 2 it appears that the rates of de-

* Personal communication (1969).

scent were better controlled with the color dis-
play than with the black and white picture.

The pilots then rated the various displays ac-
cording to the fidelity of simulation on a subjec-
tive scale from 1 (real world) to 5 (poor fidelity).
The results obtained from four pilots are shown
in Figure 8. There is a progressive increase in
fidelity of simulation through the addition of
color and with the collimated visual image dis-
play. The pilots also commented that color re-
duced visual workload, made it easier to line up
with the runway, and that the collimated visual
image system facilitated altitude estimates dur-
ing the flare.

The implications of these findings are straight
forward. If we are training for IFR, the infor-
mation obtained from instruments should have
high priority. Visual noise may or may not be a
factor, depending upon the criticality of picture
clarity at the moment of decision. For VFR
operation, the ultimate goal is the “real-world”
display. Advanced TV display systems, used in
conjunction with properly designed collimated
visual image, should approach “real-world”
quality. There was subjective agreement on this
point by experienced airline pilots, and it was
quantitatively reflected by their performance.
Collimated TV pictures of this sort eliminate the
need for expensive projector systems, and they
can be used equally well for crew training.

2. Control and Kinesthetic Feedback. The
main problem in control simulation concerns the
precision and exactness with which the basic
form of the input-output relationship must be
reproduced. Pertinent experiments on this sub-
ject have shown that even a low fidelity in
part-task simulation provides for positive trans-
fer of proprioceptive feedback (see Ref. 1). This
means that the basic control movements can be
learned in a simulator, although the control sen-
sitivity may be altered, the direction of an indi-
cator may not exactly correspond to a specific
control movement, or the mathematical function
specifying these relationships may differ. How-
ever, it must be emphasized that these conclusions
are based almost entirely on continuous psycho-
motor responses and cannot be extended to apply
to whole-task procedural simulation.

If the control system characteristics are under
study, the situation is different. Because of the
close relationship between control system charac-
teristics and handling qualities, the vehicle con-



efficiency of complex systems—including his
own—under normal or the most unusual circum-
stances.

Specifically, our problem boils down to asking
how accurately any simulated task element, inter-
action, function, or situation should represent
that encountered in the real world. In order to
obtain a maximum return, or transfer of train-
ing, the following questions should be answered:

1. How “true” should be the visual input
which is presented to the pilot in simulated
situations?

2. How closely should the feedback from the
controls in the simulator resemble that of the
aircraft in order to elicit the desired response?

3. Are motion cues necessary for the simu-
lation of the operational characteristics of a
control system ?

4, What environmental factors should be in-
cluded in order to obtain valid results?

5. What measures are available to determine
quantitatively the effect which fidelity of simu-
lation has on the transfer of training?

FLIGHT CONTROL SIMULATOR USE IN DESIGN CYCLE

DESIGN REQUIREMENTS

DATA ON SPECIFIC
PROBLEMS.
PILOT TRAINING.

FINAL DESIGN REQUIREMENTS.
PROOF OF DESIGN ACCEPTABILITY

EQUIPMENT DEVELOPMENT

PILOT TRAINING CREW TRAINING

PILOT PROFICIENCY PROCEDURAL TRAINING.
DANGEROUS REGIMES NAVIGATION

RESOLUTION GF PROBLEMS J ALL WEATHER OPERATION

RESEARCH PRELIMINARY DESIGN

DETAILED DEVELOPMENT

FLIGHT TEST GPERATIONAL USE

TIME >

Taste I.

IV. Influence of Fidelity of Simulation on
Pilot Performance

1. Visual Input in Simulation. The fidelity
of the visual input required for simulation de-
pends to a large extent on the pilot’s task. For
IFR simulation, the flight instruments are the
more important components of the simulator,
since they may provide the pilot with more ac-
curate information than obtained from the ex-

Flight Control Simulator Use in Design Cycle

ternal visual field (Cooper 1963).> For example,
rate information can hardly be accurately per-
ceived by the pilot. If flight instruments are
designed to combine, integrate, or compute in-
formation, the pilot may find himself engaged
in a more or less complex tracking task. Thus,
care must be taken to present instrument infor-
mation with high fidelity ; otherwise, the purpose
of the simulation task may be defeated. The


e

Ny

n

2

10.

ni.

. CHASE,

REFERENCES

Apams, J. A.: Some Considerations in the Design
and Use of Dynamic Flight Simulators. Selected
Papers on Human Factors in the Design and Use of
Control Systems (Ed.: H. W. Sinaiko), pp. 88-114.
Dover Publications, Inc., N.¥., 1961.

. Saporr, Metvin and Harper, ©. W.: Piloted Flight

Simulator Research—A Critical Review. Aerospace
Engineering 21:50-63, 1962; and Savory, M.: Per-
sonal Communication (1969).

Westsr00K, C. B,: Background of Piloted Simulator
Development. The Role of Simulation in Space
Technology, Part B, pp. XI-1-XI-69, Virginia Poly-
technic Institute, August 17-26, 1964.

Newert, F. D, and Prmrrzax P. E.: In-Flight Meas-
urement of Human Response Characteristics, AIAA
Flight Test, Simulation and Support Conference.
Paper No. 67-240. Cocoa Beach, Florida, Feb. 6-8,
1967.

. Coorer, G. E.: The Use of Piloted Flight Simulators

in Take-off and Landing Research. North Atlantic
Treaty Organization, Advisory Group for Aeronauti-
cal Research and Development, Report 430, Paris,
January 1963.

Onnivenos, R. J.: General Aviation Cockpit Display
and Control Simulation (Final Report), Depart-
ment of Transportation, Federal Aviation Adminis-
tration, National Aviation Facilities Experimental
Center, Report No. NA-68-48, Atlantic City, NwJ.,
October 1968.

Bricas, G. E., Frrrs, P. M., and Banrtcx, H. P.:
Transfer Effects from a Single to a Double Integral
Tracking System. AFPTRC Lackland AFB, Texas,
Research Report 'TN-56-135, December 1956.

. Hopkin, V. D., Pounrer, R. F., and Wuiresipe, T.

©. D.: Effects of a Blinded Retinal Area on Per-
formance of a Simulated Task. RAF Institute of
‘Aviation Medicine, R449, RAE Farnborough, Hants,
1968.

W. D.: Piloted Simulator Display System
Evaluation-Effective Resolution and Pilot Perform-
ancee in the Landing Approach. 8rd Ann. NASA-
University Conf. on Man Contr. NASA SP-144,
1967.

McPurrson, A.: A Piloted Simulator Study of a
Slender Wing Research Aircraft, (HP 115) Royal
Aircraft Establishment Technical Report 68068.
March 1968, Ministry of Tech., Farnborough, Hants.
Racranv, §., JR, CHamuers, R. M., Cnossm, R. J.,
and Hrrencock, L., Jn.: Simulation and Effects of
Severe Turbulence on Jet Airline Pilots. U.S. Naval
Air Development Center, Johnsville, Pa. NADC-
ML-6411, 13 August 1964.

17

12, Hrreucocx, L., Jz, and Morway, D, A.: A Dynamite
Simulation Study of the Swept-Wing Transport Air-
craft in Severe Turbulence. U.S. Naval Air Devel-
opment Center, NADRC-MR-6807, Johnsville, Pa.,
30 October 1968.

Corxrnpate, K, G. and Benson, A. J.: Physiological
and Psychological Factors Influencing Vehicle Simu-
lation, Vehicle Simulation for Training and Re-
search, R.A.F. Institute of Aviation Medicine, IAM
Report No. 442, Farnborough, Hants, March 1968.

Coormn, G. E. and Hanper, R. P., In: The Use of
Pilot Rating in the Evaluation of Aircraft Handling
Qualities, NASA Ames Research Center, Technical
Note, Moffett Field, Calif. 1969.

McRver, D. T. and Krenvet, BE. S.: Dynamic Re-
sponse of Human Operators, WADC-TR-56-524;
Dayton, Ohio, 1957.

Wasuizu, K. and Mrvastwa, K.: Controllability
Limit of a@ Human Pilot, ATAA Journal, Vol. 3,
No. 5, May 1965,

GeRaTHEWoHT, 8. J.: The Human Pilot in a@ Control
Loop. 5th Conf. Aviation Psychol. Bad Godesberg,
Germany, September 17-20, 1963.

McRumr, D. T. and Jex, H. R.: A System Analysis
Theory of Manual Control Displays. 8rd Ann.
NASA-University Conf. on Man Contr. NASA SP-
144, 1967.

Savory, Metvin: The Effects of Longitudinal Control-
System Dynamics on Pilot Opinion and Response
Characteristics as Determined from Flight Tests and
from Ground Simulator Studies. NASA Memo 10-
158A, October 1958.

Mupp, S.: Assessment of the Fidelity of Dynamic
Flight Simulators. Human Factors 10: 351-358,
1968.

Rotre, J. M. Hammert-Fraser, A, M., Pourrer,
R. F., and Smirs, E. M. B.: Pilot Response in Flight
and Simulated Flight. Vehicle Simulation for Train-
ing and Research. R.A.F. Institute of Aviation
Medicine, IAM Report No. 442, Farnborough, Hants,
March 1968.

Rurrett Smrrn, H. P., BaTeMan, S. C., GoLpsMITH,
R., Jackson, K. F., and Marrocxs, U. S.: Heart
Rate of Training Captains Engaged in Different
Activities, 40th Ann, Meeting, Aerospace Medical
Assn., San Francisco, Calif., May 5-8, 1969.
Sepa, H. A., Rocers, T. A., Duanx, T. D., Howpen,
G. R., and Smirx, J. R.: The Physiological Limita-
tions of Performance During Acceleration. Aero-
space Medicine 34 :48-55, 1963.

13.

14,

15.

16.

17.

18.

19.

20.

21.

22.

23,



FIDELITY OF SIMULATION (4 PILOTS)

"REALWORLD"
FIDELITY 1
2
3
4
POOR
FIDELITY 5 SCREEN
BLACK &
WHITE

Al

SCREEN TV MONITOR, TV MONITOR
COLOR BLACK AND COLOR
WHITE

Ficure 3. Fidelity of Simulation (4 pilots)

an unusual nose-up or nose-down position, pilots
may increase the deviations from normal attitude
alternately and thus induce uncontrollable oscil-
lations. Some of the pilots indicated that the
involuntary control movements” which occurred
were reflexes largely resulting from what they
had learned in transport flying training and
through experience. All of the pilots thought
that the two centrifuge runs improved their per-
formance. In general, the simulations were
much more realistic than the pilots had thought;
in particular, the negative G-portion was es-
pecially realistic and the turbulence conditions
seemed real. A comparative evaluation of the
centrifuge simulation and fixed-base motion sys-
tem is shown in Figure 4.

3. Motion Simulation. The importance of
providing motion information for the specific
ranges of vehicle dynamics has long been recog-
nized. From the pilot’s point of view, motion
adds realism and either helps or hinders the
execution of his task. Motion becomes distract-

ing when it disturbs the pilot physically, as is the
case during high G-forces on the centrifuge (see
Fig. 5). Useful cues produced through motion
do assist the pilot and improve his performance.
‘An example, which illustrates how the motion
cues help the pilot to control a simulated aircraft
following abrupt asymmetry due to engine fail-
ure, is shown in Figure 6. Marked improvements
can be seen in the excursions of bank angle, side-
slip, rudder, and side force (see Ref. 5).

The rotation simulators of the Link Trainer
type have limitations due to rotational travel.
By incorporating an initial movement into the
simulator and then “washing out” the motion but
continuing it on the instruments, a very effective
simulation of motion is obtained. In order to
understand better the effects of motion inputs
on the pilot, a study was conducted by Systems
Technology, Inc., using the Ames Six-Degree-
of-Freedom Simulator.* The purpose of the

* Personal communication (1969).



AM 69-24

FIDELITY OF SIMULATION AND TRANSFER OF —
TRAINING: A REVIEW OF THE PROBLEM

by
Siegfried J. Gerathewohl, Ph.D.

Approved by Released by

Sterne ® en\ehhe Z wo

P. V. Srecet, M.D.

Srantey R. Mouuzr, M.D.
Feprrat Air Surcron

Crrer, Arromepican ApriicaTons
Division

December 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



FIXED COCKPIT

MOVING COCKPIT

BANK Apo
AILERON iMate — Da ade tncmatinnane
SIDESLIP APPA ee

LIMIT ~~~
YAW RATE a ao ~
RUDDER LOA ze
SIDE FORCE A AP AA
LIMIT ae
TIME TIME

EFFECT OF COCKPIT MOTION ON PILOT CONTROLLABILITY
FOLLOWING ABRUPT ENGINE FAILURE

Ficure 6. Effect of Cockpit Motion on Pilot Controllability Following Abrupt Engine Failure

free of unwanted motion because of the restric-
tions imposed by the physical dimensions. The
actual displacements in flight can be in the order
of hundreds of feet, whereas those in the simu-
lator are in the order of a few feet. Therefore,
the Flight Simulator for Advanced Aircraft at
Ames has a side-to-side displacement of +50
feet in order to simulate yaw in case of outer
engine failure, and the designer still considers
this marginal.* But even under normal flight
conditions there are shortcomings due to inac-
curacies in aerodynamic representation. Al-
though the pilots were able to fly the six-degrees-
of-freedom. Aero Flight research simulator,
which represents the Handley-Page 115 slender-
wing aircraft, they particularly disliked the
“normal acceleration” cue and felt it reduced the
realism of the simulation (see Ref. 10). With
the cockpit fixed or with pitch attitude and side-
slip motion, the simulator did not feel like the
real HP 115, regardless of the other features
available to the pilot. When the motion cues
were realistic, the nature of the external visual

* Personal communication (1969).

10

background was not very important. Of the six
degrees of freedom of motion simulated, pitch
and roll attitude cues proved most pertinent, al-
though there always was a spurious sensation of
side force during the bank, which is not present
in actual flight. Roll washout (by gradually
restoring the cockpit to wings-level position) was
used to overcome this particular deficiency.

One of the difficulties of the realistic presenta-
tion of the environment concerns the size of the
objects on the ground. Ideally, they should be
presented at a scale which allows a large enough
area to be pictured without loss of detail. Norm-
ally, a scale of the order of 1: 2000 is used for
most models which are suitable for take-off and
landing studies. This means that a house on the
model needs to be made only 0.2 of an inch high.
The total size of the area and the scale depends
primarily on the purpose of the experiment and
the variables under study, since the eye is able to
fill in details so that some kind of perceptual
equivalent exists (Corkindale and Benson 1968).
For the simulation of three-dimensional objects
in space, the use of holograms may prove more
realistic.


STABILIZER “Of

—14 10 SEC

DEFLECTION, 90 _———+r Wt
8s, DEG | gL
STICK FORCE 257 n . 4
Fs, L8 ° on rte
-25 L
or —PILOT TERMINATED RUN DAMPER FAILED

5
PITCH ANGLE °
6, DEG

pif yet egy —

[ TRACKING STARTED pamper FAILED TRACKING STARTED
ADAPTATION COMPLETED

“7

5

+10

normal = #
ACCELERATION 2
Ans @ °
Pitcuing = '0
VELOCITY, @, ©
DEG/SEC "19
PITCHING 20

ACCELERATION 0
6, DEG/SEC? 209

Ficure 5. Example of Pilot Loss of Control in Centrifuge (damper failure)

inside the cab. Experiments with the Ames
Five-Degree-of Freedom Flight Simulator also
indicated that, as the number of degrees gf-mo-

tion increased, it became more difficult to main-
tain a natural flight environment (see Ref. 5).
One of the problems is to keep the simulation



COMPARISON OF TOUCHDOWN RATES OF DESCENT FOR COLOR
AND BLACK AND WHITE DISPLAY CONFIGURATIONS

COLOR
“0 t= MEAN
1
wy 30
2
4
s
8 20
3
ve
S
>
(s
& 10
>
nf
&
0 123 45 67

h, ft/sec

trol system should be simulated with high fidelity.
This will reveal the actual balance or lack of
balance between control sensitivity and control
power input. If the actual control system cannot
be simulated, a variable feel system should be
provided. At least, the simulator control system
should have no adverse characteristics, such as
friction, lag, or dead band. While the simulator
should accurately represent the short period ve-
hicle dynamics and the essential control system
characteristics, it has been found that its value
is not a direct function of the degree of sophisti-
cation (see Ref. 5). However, experience with
the Aero Flight simulator by Perry and Naish
(1964) suggests that kinesthetic cues used for
control may be at least as important as the visual
cues (McPherson 1968).*°

An outstanding example of the use of the
simulator for studies of proprioceptive feedback
is the turbulence experiment which was con-
ducted by Ragland" in 1963/1964 on the human

0

BLACK AND WHITE

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Ficure 2. Comparison of Touchdown Rates of Descent for Color and Black and White Display Configurations

10

centrifuge at Johnsville. The purpose of the
experiment was (1) to determine whether physi-
cal events, which led to a 25,000-foot dive of a
United Airlines 720 and which were retained on
the flight recorder, could be reproduced by the
centrifuge, and (2) what effects detrimental to
the safe control of the aircraft. were experienced
by the pilots. The turbulence produced accelera-
tions ranging from +3.5g to —2g at a random
frequency of about 1 Hertz. The pilot and co-
pilot of the United Airlines aircraft participated
in the experiment. They pronounced the fidelity
of simulation excellent. Eight more pilots who
also took part adjudged it realistic, based on
their own. experience of turbulence.

The most interesting finding of the study was
a “kinesthetic illusion” of climb or dive after
rapidly changing G-forces, which sometimes
causes the pilot to move his controls in the wrong
direction. By responding to a strong kinesthetic
illusion of climb or dive after correcting from


FLIGHT CONTROL SYSTEM
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Ficure 1. Flight Control System Simulation

Examples of whole-task simulators are the
space flight simulators which were used by the
astronauts for the simulation of the Mercury,
Gemini, and Apollo missions.

Another grouping of simulators is that in
fixed-base or stationary and moving-base or
dynamic simulators. The first group mostly
consists of cockpits of aircraft or facilities, in
which a pilot or an aircrew can familiarize
itself with the flight instruments, their arrange-
ment, and certain operating procedures in the
absence of dynamic and motion cues. These
cues are available in the moving base simulator.
In order to obtain dynamic responses of the
pilot or the vehicle, cockpits of aircraft and
entire space capsules have been placed on
wheels, gimbals, pulleys, or air bearings. Need-
less to say, a simulator does not produce tasks
or environmental conditions which are identi-

cal to that encountered in the “real world”, it
merely represents them to a degree neces-
sary for the intended purpose. There is a
certain type of dynamic simulator, however,
which approaches reality in aviation as closely
as possible, namely, the in-flight flight simu-
lator. The variable stability aircraft is a
most realistic flight simulator when properly
used. An example of such a device is the T-33
variable stability airplane operated by the
Cornell Aeronautical Laboratory in Buffalo,
New York.t

Transfer of training—Transfer of training
is a concept which derives both from learning
theory and from practice. In both instances
it has been shown that skills acquired in a
particular situation can be successfully trans-
ferred to a similar situation. A well-known
example is to practice each hand separately


point numerical rating scale, is the so-called
Cooper-Scale developed by G. E. Cooper at the
NASA Ames Research Center.* As a general
rule, each pilot judges the suitability of any set
of aircraft characteristics in terms of his own
skill and experience, and in terms of the required
operations and circumstances as defined in the
experiment. Correspondingly, the pilot’s usual
approach to the assessment of simulator fidelity
involves the judging of accuracy of simulation
by means of pilot comments and ratings. Em-
pirically, a simulator is thought to have high
fidelity if the pilot ratings are satisfactory and
comments favorable. Although the pilot makes
his judgments in quantitative terms, his ratings
are obviously subjective and predominantly based
on face validity. It has therefore been suggested
that a confidence factor be added, which deter-
mines the ratio of information available to the
pilot in the simulation situation to the informa-
tion required to derive a realistic pilot rating
(see Ref. 13). Useful as it may be for judging
fidelity, a strictly subjective method does not
provide the type of information required for
measuring transfer of training.

(b) Pilot transfer functions—The — suc-
cess in correlating handling characteristics of
aircraft with human response characteristics has
resulted in adequate human transfer or describ-
ing functions. These functions are mathematical
expressions of the input-output relationship of
the human operator in a control system.’ ** 17 1
An example of a simplified model of a flight
control system transfer characteristic is shown in
Figure 9. Y, is the pilot describing function
made up of pilot gain (K,), his reaction time
delay (e-r), and his lead (Tz). S indicates the
Laplace transform operator. In one study of
this kind, the parameters K, (gain) and Ty,
(lead) have been related quantitatively to pilot
opinion concerning aircraft landing performance
ranging from “satisfactory” to “unacceptable.”””
This concept calls for a model-matching proce-
dure, in which the dynamics of a given vehicle
are represented in the form of equations of mo-
tion to be matched or approximated by the simu-
lator. Analytically, a simulator is considered to
have fidelity to the extent that the simulator
model generates an output that falls within
standard engineering tolerances of the parent
model. Mudd? (1968) has amended this ap-
proach by proposing an adaptive contro] system

13

for immediate discrepancy recording. The basic
concept of his theory is that pilots can evaluate
the fidelity of dynamic flight simulators in terms
of psychomotoric responses. If a means for re-
cording such responses can be provided, deficien-
cies of simulation in terms of specific aircraft
motion can be objectively determined. The
“control-recorded discrepancy technique” would
generate a subjective error signal in a form suit-
able for analysis by control system methods, par-
ticularly those developed for model reference
self adaptive systems. The relative magnitude
of the error signal generated by the pilot would
then provide a direct measure of simulation
fidelity.

(c) Physiologic measurements—There is a
possibility of determining simulator fidelity by
comparing physiologie data obtained in the
simulator and during flight. Among others Rolfe
and cowokers”* used heart rate and respiratory
rate to compare pilot response during flight in
the Hunter T-7 aircraft and in the simulator
with and without pitch motion. Of the two
criteria used, heart rate was more indicative of
the similarities and differences between tasks and
conditions. In addition, control performance
data were valuable in comparing simulator and
flight response. By and large, there were no
significant differences for either heart rate or
respiratory rate between simulation and the
various types of flight involved in this study.

During the past years, Ruffell Smith and
coworkers” studied airline captains charged with
the conversion training of pilots for Comets,
Tridents, Vanguard, and Viscount type aircraft.
The investigators compared physiologic responses
recorded in regular line flying to stress produced
by three kinds of training; namely, simulator
training, involving all phases of “flight”, base
training involving takeoff and landing, and line
training which followed the simulator phase and
included base work.

The heart rate was considered a stress index
and recorded in 12 training captains. The high-
est heart rates were found during base training,
followed in descending order by simulator work,
line flying, and line training.

The human centrifuge has long been used as
a flight simulator to study physiologic functions
under acceleration stress.?* Now Melton (1969)
has proposed that the aeromedical factors asso-
ciated with stress flying and flight training,



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FAA SST PILOT TRAINING

Ficure 10. FAA SST Pilot Training Plan

flight recording, computing, and data processing
systems. Moreover, the elements, components,
and functions to be measured have been defined,
and it is known how to do it. In its most com-
plex mode, the pilot’s task of flying or “flight
management” is characterized by the integration
of information gathering, communicating, deci-
sion making, and direct control. If one even-
tually succeeds in measuring the functions which
determine pilot proficiency in the aircraft, it
will be possible to provide for the degree of
fidelity required for its true simulation.

V. Summary and Conclusions

In general, it can be stated that the amount of
transfer expected to occur in flight simulator
application seems to be proportional to the degree
of fidelity provided. Although part-task simu-
lators are usually less expensive and of lower
fidelity than whole-task simulators, they can be
very useful for the learning of specific tasks.

15

However, their shortcomings, as clearly demon-
strated by Adams®* can be traced back to the
lack of fidelity, particularly in simulating
motion.

It seems that the whole-task flight simulator
derives its advantages as a training device pri-
marily from the incorporation of motion cues, if
the addition of complex motion vectors increases
the fidelity of the simulation and does not result
in spurious stimuli. The various perceptual
phenomena, physiological effects, and perform-
ance changes observed in complex simulators
indicate that it is the psychologic, physiologic,
and operational realism which determine fidelity
in simulation and not face validity based on
physical similarity of the devices.

There are two additional factors which must
be mentioned in this context, namely, motivation
and danger. Elsom* has pointed out that a
certain degree of stress is necessary in order to
motivate the pilot who works in the simulator.



FIDELITY OF SIMULATION AND TRANSFER OF TRAINING

I. Introduction

In 1957, Jack A. Adams, who was at that time
with the Air Force Personnel and Training Re-
search Center at Lackland Air Force Base, Texas,
wrote a chapter about “Fidelity of Simulation
and Transfer of Training” in an article entitled
“Some Considerations in the Design and Use of
Dynamic Flight Simulators” Although he
dealt primarily with flight simulators used by
the USAF at that time, his report deals with
fundamental knowledge and, therefore, has a
much wider application.

Results of a number of piloted simulator in-
vestigations were critically reviewed by Sadoff
and Harper in 19622 Comparative appraisals,
obtained in various ground-based simulators and
in flight, were used by the two authors to deter-

mine the degree of simulator sophistication re-

quired for the evaluation of handling qualities
and specific control problem research on conven-
tional and advanced vehicles.

In 1964, Westbrook reviewed the development
of piloted simulators, primarily that in the
United States, and he gave 278 references on this
subject. He listed 68 ground simulators, which
do not include the simple cockpit-computer
simulators and the so-called “iron bird” simu-
lators used in the development of the flight con-
trol systems of a given vehicle. The number of
in-flight simulators given by Westbrook was 32.
Figure 1 shows a logical grouping. There are
certainly more flight simulators of various de-
grees of sophistication available in the United
States toady. Twelve different types alone are
described in the new NASA Ames brochure.

In this review, some of the results obtained
from newer studies will be presented. The
examples and studies which will be discussed are
mainly from investigations conducted within the

Lecture presented at the AGARD-NATO Course on
Advanced Operational Aviation Medicine from 9-27 June
1969 at the Institute of Aviation Medicine, Furstenfeld-
bruck, Germany.

civilian sector of simulator research that is,
within the FAA and NASA. Nevertheless, they
are so closely related to operational problems
that they equally apply to Air Force and other
weapon systems problems.

IL. Definitions

In order to establish a common basis of under-
standing, in particular with those not familiar
with the terminology used in this discussion, the
key expressions of this subject will be defined:

Fidelity—Fidelity is defined in this context
as the degree to which a device accurately
reproduces a specific effect.

Simulator—A simulator is a device or a
facility which represents a machine, system, or
environment and their functions under cer-
tain—mostly well specified and controlled—
conditions. Examples of the various types of
simulators are equipment simulators (eg., the
F-111 simulator and other piloted simulators
in which a human operator performs a control
task) ; environment simulators (eg., the lunar
surface simulator) ; situation simulators (eg.,
simulation of turbulence, attack, approach, or
landing); condition simulators (eg. IFR,
VFR, night or daylight, zero-G) ; and proce-
dure or mission simulators (e.g., for combat,
space flight, SST flight profile).

Simulators have been categorized as “part-
task” and “whole-task” simulators. A  part-
task simulator is defined as a device which
represents only specific characteristics or func-
tions of the task, such as radar observation,
navigation, or fire control. An illustration of
a part-task simulation is the pilot’s job to
position a target return in the center of a
radar scope. In contrast, whole-task simula-
tion has been defined as the “deliberate effort
to achieve complete representation of equip-
ment characteristics and in-flight mission fac-
tors”. The latter include the environmental
factors which are thought to be important.



Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va, 22151.


BLOCK DIAGRAM OF MULTIMODALITY PILOT MODEL AND SIMULATION EXPERIMENT

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Another “environmental” factor, namely dan-
ger, cannot be simulated on the ground. It is
present, however, with the inflight flight simu-
lator.

By and large, it can be stated that whole-task
and inflight flight simulators provide the greatest
variety of factors in regard to the aerodynamic
and the ground environment. They have their
real potential in the fidelity with which they can
be used to represent the environmental conditions
in the area of greatest interest. Some short-
comings—such as spurious motions, lack of
gross movements, high washout and reduced di-
mensions—must be accepted even in modern
ground-based simulators. Naturally, the inflight
flight simulator provides the highest fidelity of
the aerodynamic environment.

5. Quantitative Assessment of Fidelity. Al-
though simulators are widely used for research,
development, and training purposes, quantitative
information about the degree of fidelity needed

11

to produce the desired amount of transfer is
scarce. Training simulators are employed today
with the assumption that if the trainer accurately
reproduces the characteristics of the aircraft, and
if the task of operating the trainer resembles
that in the air, enough transfer of training will
occur. The validity of this assumption is known
as “face validity” which may not be dependable.
A better estimate of the validity of a training
device can be obtained by quantitatively assessing
the fidelity of the simulator and the resulting
transfer effect.

A valid evaluation technique of simulation
should employ means for measuring those aspects
of a situation which are relevant to the set of
responses involved in the system being simulated.
Moreover, the evaluation of fidelity necessary for
simulation should apply measures for the ex-
tent to which a simular elicits behavioral and
physiological responses or sets of responses other-
wise produced by the operational environment.



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Fiaure 9, System Block Diagram

previously studied on the centrifuge and in flight,
be studied for comparative purposes in the Link
GAT-1. It is thought that the physiologic func-
tions may be sensitive to the amount of stress
provided by the GAT-1 and that the change of
the physiological functions due to the stress may
reflect, the degree of fidelity present in this type
of flight simulator.*

Recently, Gabriel, Creamer, Carpenter, and
Burrows used the U.S. Navy S-2 Operational
Flight Trainer, a rather realistic weapon system
simulator, to investigate the behavioral and
physiological effects of workload on the flight
crew. In all, over 70 different variables were
measured in 16 volunteer subjects during expo-
sure to low and high workloads. While the
psychological functions and performance were
affected but slightly, most physiological param-
eters including heart rate, respiration rate and
basal skin resistance yielded statistically signifi-
cant differences between high and low workloads.
The experimenters believe that the equipment
and methods used for the acquisition and inter-
pretation of their data seem promising as tools
in the investigation of fatigue.

(d) Proficiency measurements—Finally, it is
suggested to use proficiency measurements for the

* Personal communication (1969).

14

assessment of simulator fidelity. The assumption
is that if one succeeds in objectively measuring
pilot performance during actual flight, the results
can then be related to the simulator. In order
to do this, one first has to record actual pilot
performances during parts of the mission, such
as preflight checkout, taxiing, takeoff, . cruise,
ete., and for the entire mission; and one must.
then “construct” an “ideal” mission based on
zero error scores and minimum deviations from
an idealized pilot describing (transfer) function.
It is not quite clear, however, how accurately
this can be done today, but it appears that “pro-
ficiency” comparisons of this sort will be helpful
in assessing the fidelity of simulators. The main
problems yet to be solved are to agree upon the
essential criteria measures, to develop precise
measuring scales and systems which do not inter-
fere with cockpit duties, and to apply meaningful
standards of determining pilot proficiency
equally valid to the flying and to the simulated
condition. Six years ago, Obermayer and
Muckler** summed up the dilemma as follows:

“Unfortunately, in the case of the selection

of performance measurement for flight simu-

lation studies, all of the measurement deci-
sion problems remain unsolved.”

Undoubtedly, progress has been made since

then particularly through the use of advanced