Issues important in rotorcraft flight control are discussed. A perceptual description is suggested of what is believed to be the major issues in flight control. When the task is considered of a pilot controlling a helicopter in flight, the task is decomposed in several subtasks. These subtasks include: (1) the control of altitude, (2) the control of speed, (3) the control of heading, (4) the control of orientation, (5) the control of flight over obstacles, and (6) the control of flight to specified positions in the world. The first four subtasks can be considered to be primary control tasks as they are not dependent on any other subtasks. However, the latter two subtasks can be considered hierarchical tasks as they are dependent on other subtasks. For example, the task of flight control over obstacles can be decomposed as a task requiring the control of speed, altitude, and heading. Thus, incorrect control of altitude should result in poor control of flight over an obstacle

Andersen, George J.

English

NASA Technical Reports Server

N92-21474
AN INFORMAL ANALYSIS OF FLIGHT CONTROL TASKS
George J. Andersen
University of California
Riverside, California
An important theme of this workshop has been to bring together experts from several different
domains to discuss issues important in rotorcraft flight control. The experts have come from several
different domains including psychophysics, control theory, human factors, and engineering. One
goal of this workshop was to use interactions among the experts in these different domains as a way
to understand problems in flight control. While the majority of these interactions, in my opinion,
have been successful I believe that the workshop as a whole focussed to much on the specifics and
may have missed the big picture of how these different areas are relevant to flight control. In this
paper I will suggest a perceptual description of what I believe to be the major issues in flight control.
Although this opinion will be from the viewpoint of a psychophysicist I hope that it captures the
importance of some the issues from other research domains represented by others who attended the
workshop.
When one considers the task of a pilot controlling a helicopter in flight, we can decompose the
task in several subtasks. These subtasks include (1) the control of altitude, (2) the control of speed,
(3) the control of heading, (4) the control of orientation, (5) the control of flight over obstacles, and
(6) the control of flight to specified positions in the world. The first four subtasks can be considered
to be primary control tasks as they are not dependent on any other subtask. However, the latter two
subtasks can be considered hierarchical tasks as they are dependent on other subtasks. For example,
we can decompose the task of flight control over obstacles as a task requiring the control of speed,
altitude, and heading. Thus, incorrect control of altitude should result in poor control of flight over
an obstacle.
The following sections will discuss each of these task separately. Within this context the impor-
tance of possible perceptual information will be discussed.
1. The control of altitude.
Of all the tasks outlined above the control of altitude is one which has received the greatest
empirical investigation as a flight control task. Warren has proposed that splay rate (the change in
the angle formed by meridian lines converging at the horizon) is a useful source of information
whereas Owen has proposed that edge rate (the number of texture elements that pass a specific loca-
tion in the visual field) is a useful source of information. It is important to note that the effectiveness
of these sources of information are dependent on specific constraints present in the world. Specifi-
cally, splay rate is only useful if the meridian lines are parallel in the world. Edge rate requires that
texture elements be stochastically distributed evenly in the world. While the effectiveness of these
sources of information have been investigated in several studies, it is important to realize that they
also require that the world be flat and rigid. It is likely that for flight control over varying terrain
99 PRECEDING PAGE BLANK NOT FILMED
https://ntrs.nasa.gov/search.jsp?R=19920012231 2020-03-17T13:12:47+00:00Z
other sources of information, such as the slant of surfaces, the speed of translation, or the absolute
distances between the aircraft and points in the world be recovered.
2. The control of speed.
The control of speed is another task that has been studied extensively. The sources of information
that have been investigated for this task are edge rate and global optic flow rate. Again, it is impor-
tant to note that the use of these sources will only be effective if the simulated world is fiat and rigid.
For flight control over varying terrain it may be necessary to recover information for determining
altitude, slant of surfaces, and absolute distances to points in the world.
3. The control of heading.
There are two sources of information that have been proposed to be useful for the control of
heading--the focus of expansion (or the point of maximum divergence) and differential motion paral-
lax. Gibson was the first to suggest the usefulness of the focus of expansion and this has resulted in
many computational analyses (Lee, Perrone, Koenderink) which use this source to extract out other
characteristics of the environment (e.g. relative depth and time to contact). Differential motion paral-
lax (the different rates of velocity of points moving above and below a point of fixation) was pro-
posed by Cutting. A considerable body of research has been conducted to determine what informa-
tion is used by human observers. Johnston, White and Cummings found that subjects could not
determine the focus of expansion for displays simulating motion towards a frontal parallel surface.
Warren, found that subjects were accurate in determining heading for displays simulating motion to
a ground plane where the direction of looking was decoupled from the direction of motion. Regan
and Beverely, found that subjects could not determine the focus of expansion for displays simulating
motion towards a frontal parallel surface when a simulated eye fixation was included in the
transformation.
However, Reiger and Toet found that subjects could determine direction of heading for displays
simulating motion towards frontal parallel surfaces. In their research subjects were quite accurate
when the display simulated motion towards two overlapping transparent frontal parallel surfaces that
were separated in depth. However subjects were inaccurate when the display contained only a single
frontal parallel surface. Finally, work by cutting found that subjects could determine the direction of
heading for displays simulating motion through an array of poles that were positioned at varying
simulated depths from the observer. Although an initial inspection of the literature would suggest
that the results from several studies are contradictory, a closer inspection of these studies suggests an
interesting patternmthose studies that failed to fred good accuracy involved displays that did not
have variations in depth whereas those studies that found good accuracy did involve variations in
depth. This suggests that differential motion parallax, which is only effective if the display contains
variations in depth, may be the source of information used by human observers.
It is important to note that differential motion parallax and the focus of expansion can only be
extracted for rigid worlds. Constraints such as altitude, speed, or absolute distance are not required to
use either source of information.
100
4. Control of orientation.
The control of orientation has traditionally been decomposed into the control of roll (rotation
about the line of sight), pitch (rotation about the horizontal axis), and yaw (rotation about the vertical
axis). In order to accurately control roll and pitch there are two sources of information that could be
used---a change in the direction of the gravitoinertial vector, and a change in the horizon. The direc-
tion of the gravitoinertial vector can only be estimated by nonvisual sensory systems such as the
vestibular and kinesthetic systems. However, changes in the horizon can be determined by the visual
system. In order to control yaw information from the vestibular and visual systems can be used if the
rotation involves an acceleration of deceleration.
Another issue of importance for determining changes in orientation is the need to use a frame of
reference. A frame of reference (such as the frame in the rod and frame effect) can be viewed as
providing information regarding a false horizon.
An alternative way to consider the control of orientation is to describe orientation change as a
change in the position of the viewer with respect to the environment. This definition allows us to
consider orientation as an issue regarding locomotion in the world as opposed to rotation in the
world. I believe this def'mition is useful as it incorporates navigational issues (such as where am I
located on this map) which are extremely important for nap of the earth and low level flight. Incon-
sistencies between where you think you are when you look out of a cockpit and where you think you
are when viewing a map may lead to disorientation.
5. Control of flight over obstacles.
The control of flight over obstacles is an issue that has not received much attention. This is prob-
ably a result of the fact that accurate control of flight over obstacles requires the integration of sev-
eral sources of information. At a minimum it requires information regard!ng altitude, speed of
motion, and heading. In addition, it may require other information such as time to contact, absolute
distance to surfaces in the environment, the slant and elevation of the obstacle to be flown over, and
the location of the horizon. In many respects these sources of information may be interrelated. For
example, a misperception of where the horizon is located may result in a misperception of slant. This
could result in a misperception of elevation of the obstacle to be flown over which may have drastic
effects on the ability of a pilot to successfully fly a nap of the earth mission.
6. Control of flight to targets.
The control of flight to targets is another type of flight control task that has not received much
attention in the literature. There are two versions of this type of flight control that should be consid-
ered. One version involves the control of flight to a target that is visible from the outside scene. The
second version involves the control of flight to a specific target when the pilot can not see the target
in her field of view but has a map which indicates that location of the target in the world.
For the control of flight to a target visible from the outside scene there are several sources of
information that the pilot must use. The pilot must determine the difference between the current
heading of the helicopter and the desired heading to the target. In addition the pilot must determine
101
thecurrentspeedof travelin orderto produceanappropriatecontroladjustmentfor approach to the
target.
For the control of flight to a target not visible in the scene the pilot must navigate such that her
current position changes in accordance with a desired location in the world. This task not only
requires that the pilot's perceived location in space (from information in the visual world) match the
perceived location of the pilot's position on a map but also requires that the pilot correctly determine
the relative position of landmarks in the visual scene. Incorrectly perceiving the layout of these
landmarks most probably result in poor flight control through these landmarks.
One interesting issue regarding this flight control to a target is whether the pilot must recover the
spatial layout of the world in order to successfully perform this task. It may be that all that is neces-
sary to correctly perform this type of task is to recover the spatial layout of the landmarks rather than
the spatial layout of the world with the relative position of the landmarks nested in the layout of the
world.
102


An informal analysis of flight control tasks

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server