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

There has been some work done at. The F'ranklin Institute on the
problem of studying human frequency response with the view in mind of
obtaining "transfer functions ,It on a project sponsored by the United
States Air ~orce.6,7,8 The method which this project has selected for
studying the human operatorts frequency response is the comparison of
the output spectral density to the spectral density of the visual input
using a random signal as the input. Such a comparison yields utleFul
informetion whether or not the human operator behaves in a lineer
fashion. Were a linear aystem under study, it can be ehom that the
amplitude part of the systemle frequency response is equal to the square
root of the ratio of the speotral density of the output to the spectral
density of the input. A complete description of the linear eyatem would
reqnlre the cross spectral density of the output and input so that
phase as well as amplitude characterietics could be specified. Since
the computation of the cross spectral density would have required twlce
as much work as the computation of spectral densities, it was decided
that only the amplitude response would be computed in the preliminary
experiments. The main purpoee of the preliminary experimente, the
apparatus for which was a simple compensatory position tracking device,
was to determine whether the foregoing input-output analysis was a
suitable method for analyzing the data of more ambitious experimente using
a dynamic flight simulator for a high speed jet fighter built by The
Franklin Institute Leboratories. The random input function was obtained
by constraining a pip on an oscilloscope to take positions on a horizontal
axis alternatively to the left and to the right of a vertical
fiducial line so that the number of zero crossings were described by a
Poisson distribution. In order to make the display somewhat less
predictable the amplitudes to the left and to the right were rtandamly
selected from a Gaussian population of the same mean and standard
deviation for amplitudes to the left and to the right. One of the underlying
reasons for selecting a random time series input was the belief
that the human operator is largely non-linear. This particuhr random
time series had a specitrum which was similar to the spectrum of atmoepheric
turbulence.
In order. to add psychological interkt to the investigation of the
applicability of the analytical procedures, three questions were examined.
Does the operator track the random input in a linear fashion? How does
his behavior change as a function of practice? How do different instructions
affect his response patterns? The question of linearity was
examined by comparing the amplitude frequency response for two subjects
when tracking a distribution whose mean absolute amplitude was one
centimeter and when tracking a distribution of mean absolute amplitude
equal to two centimeters. The effect of practice, i.e., time variation
of the system, was exambed by comparing the output of the two subjects
when naive and when hi.ghly trained in following a certain random input
signal. The effects of instructions to track for accuracy and of
instructions to track for speed were compared for two subjects in order