Report of the Second Piloted Aircraft Flight Control System - Acgsc.org

A SURVEY OF SUGGESTED MATHEMATICAL METHODS
FOR THE STUDY OF HUMAN PIWT'S RESPONSES
by EZRA S. KRENDEL
The Franklin Institute
Laboratories for Research and Development
Philadelphia, Pennsylvania
During the last decade considerable effort has been directed by
several laboratories, both in this country and in England, toward the
solution of the problem of rationally characterising the human operator
of various type8 of control equipment. The goal of this research has
been the determination of what might be called humen "transfer functions,"
where the term transfer function is used in a loose 8ense. In general,
the work has dealt with problems arising in gun directing situetione.
Although relatively little effort has been concetned with the study of
the guidance problems arising in the control of aircraft, the display and
aontrol problems for sighting system and aircraft have sufficient similarity
to make the suggested methods of study applicable to both problem.
The purpose of this paper is to state some of the pst suggestions for
appropriate ma thematical models to describe human operator performance,
and to present some of the current thinking at The rh-anklin Institute on
the problem.
The problem under discussion arises from the control situation
wherein an operator is attempting to orient a device so that a visually
perceived error may be minimized. Figure one represents this situation in
a simple tracking task which was Fnvestigated at The Franklin Institute.
The specification of the transfer functions in this figure is only for
explanatory effect. The humen element in this control system consiets of
the eye, which is the primary error sensing mechanism; the nerves, which
are the data transmission system; and the arm muscles which are the motor
system. It is, however, necessary to specify more about the situation.
Since the operator is largely non-linear, the stimulus must be carefully
-
specified. The visual signal can be characterized by the degree to which
the operator is able to predikt the stimulus. Close to perfect prediction
can be achieved either by having the future behavior of the signal disclosed
to the operator over a length of time greater than his reaction tlme plus -
movement time, or by conveying very little infomation in the visual stimulus
by presenting the useful past history of a signal the future of which
is determined simply from its past. ' Ekamples of the first type of easily
anticipated signal arise in the driving of an automobile; whereas an exemple
of the second type of predictable signal would be the tracking of a siapple
sine wave. The display which a gunner sees in his sights or which a pilot
sees when getting on target differs from the foregoing in thet the possible