Variable Stability Flight Simulator
Next Stage Development
P. W. Gibbens
D. P. Boyle
D. J. Auld
Department of Aeronautical Engineering
University of Sydney
Contents
1
2
3
4
5
6
7
8
Overview of the Variable Stability Flight Simulator .................................................................. 1
The Variable Stability Flight Simulation Facility in Detail ........................................................ 3
2.1
Simulator Platform .............................................................................................................. 3
2.2
Computer Systems .............................................................................................................. 5
2.2.1
Cranfield Connection .................................................................................................. 5
2.2.2
Simulation System Architecture ................................................................................. 5
2.3
Image Generation System ................................................................................................... 7
2.4
Hardware Control Systems ................................................................................................. 7
2.5
Software Modules ............................................................................................................... 8
2.5.1
Flight Simulation ........................................................................................................ 8
2.5.2
Instructor’s Station ...................................................................................................... 9
2.5.3
Variable Stability Module ......................................................................................... 11
2.5.4
Control Law Builder ................................................................................................. 12
Status of Simulator Implementation ......................................................................................... 13
3.1
Timeline for Development ................................................................................................ 14
Utility of the Facility................................................................................................................. 14
Benefits for Human Factors, Operational, and Safety and Accident Investigation .................. 15
Next Stage Development - Visual Projection System .............................................................. 17
6.1
Equipment Options ........................................................................................................... 19
Commercial Use and Facility Access ........................................Error! Bookmark not defined.
Contact Information .................................................................................................................. 21
Variable Stability Flight Simulator
Next Stage Development
1 Overview of the Variable Stability Flight Simulator
Commercial flight simulators are commonplace in the Aeronautical industry today. Aircraft
manufacturers, airline operators, training organisations, and research institutions utilise commercial
simulators for a wide range of purposes, including aircraft design and development, flight crew
training, human factors and safety investigation, and pure and applied research in the various fields
of aeronautical engineering and other disciplines.
However, commercial flight simulators are somewhat restrictive, in that they are designed to
provide a precisely reproduced simulation environment which is representative of a single specific
aircraft only. Considerable attention is paid to the detailed reconstruction of the cockpit and
various systems controls of the aircraft being simulated, as well as to the underlying flight
dynamics and associated motion-based simulation. This incurs large production costs, and hence
large purchasing and operating costs. The user of such a facility is thus constrained to a very
expensive simulation platform which reproduces the operational environment and flying handling
qualities of a single aircraft alone.
While this may not be a deterrent for airline operators, it is most definitely a severe drawback for
users whose primary purposes include human factors and safety investigation, and/or pure and
applied aeronautical research. Users in these categories require a relatively low-cost simulation
facility which is capable of generic reproduction of the flight operation environment, including
flying handling qualities, flight dynamic response, and cockpit primary instrumentation and
controls. In other words, such users require a simulation facility capable of reproducing the
operating environment for many different aircraft, at a low cost. Moreover, the operating
environment for any particular aircraft must also be reconfigurable, such that the simulation can
capture not only normal operational modes, but very abnormal situations as well. It is useless, for
example, attempting to simulate an aircraft’s response following the loss of a critical piece of
airframe, unless the simulation facility itself is capable of reproducing the dynamics the aircraft
would truly exhibit in such a situation.
This is critical particularly for accident investigation, human factors and safety investigations,
where the capability to reproduce and re-run a large number of widely varying scenarios is
paramount. From both an ergonomic (crew-operations and interaction) and flight dynamics
(aircraft handling and response) viewpoint, a generic and reconfigurable flight simulation facility
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can provide the insight required to fully understand a particular situation, incident, or sequence of
events in the operational environment. The use of a commercial simulator for a similar purpose can
often be either too costly or simply infeasible, due to an inability to reconfigure the simulation
parameters required to accurately reproduce an aircraft’s behaviour or response in unusual (or offdesign) circumstances and with unusual internal and external inputs. Since such design flight
envelope excursions are frequently encountered either immediately prior to, or during, an incident
which leads to safety investigation, the capability to accurately reproduce such excursions is
extremely important.
Perhaps more importantly, the ability to analyse “what-if” scenarios involving sequential variations
or failures in aircraft systems or airframes (and thus aircraft dynamic response and handling) is
made simple through a generic reconfigurable simulation facility. It may in fact be very difficult,
or impossible to perform the same analysis with commercial simulators, and such analysis is
certainly limited to a single aircraft type per commercial simulator.
To address these needs, the Department of Aeronautical Engineering at the University of Sydney is
developing a Variable Stability Flight Simulator Facility (VSFS). This is a generic tool capable of
providing reproduction of the dynamic flight characteristics of many widely differing aircraft types.
It aims to accurately reproduce the motions and handling qualities associated with these different
aircraft, while basing the simulation on an environment and platform that is adequate for such
generic representation. More importantly, the characteristics of any given aircraft can also be
changed in real time, allowing such properties as aircraft stability and controllability to be altered
while the aircraft is being flown.
This represents a unique opportunity to organisations involved in research and analysis of all
aspects of aviation operations. The benefits of a generic facility stem from its inherent
reconfigurability, and include the following:

It can be used to represent the flight characteristics of any aircraft through software
selection of various flight models,
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Use of glass cockpit principles permits the reconfiguration of engine and flight instrument
suites and layouts through software selection,
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The flight characteristics can be modified in real time by direct modification of the
aerodynamic parameters in the flight model (variable stability)

Control systems can be implemented, modified, enabled and disabled in real-time via a
software interface
This document outlines the structure and components of the VSFS, our plans for its development
and benefits of upgrading its visual systems. In order to realise its full potential in this regard,
substantial resources and effort are still required.
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2 The Variable Stability Flight Simulation Facility in Detail
The facility is based on a Link three-degree-of-freedom motion based flight simulator. Formerly a
Boeing 707 cockpit, the simulator is being upgraded to operate from a distributed Personal
Computer (PC) network. All original computer systems have been replaced by PCs. The visual
systems and analogue instruments have been replaced by computer generated graphic
representations. The PC system operates all simulation components including:
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Flight models
Out-of-window displays
Instrument displays
Control force feedback
Motion control system, and
Sound system
These systems operate in conjunction with one another to provide a powerful, generic,
reconfigurable simulation system with high-fidelity visual displays and dynamic response, and
unparalleled freedom to reproduce vastly differing operational environments for use in safety and
accident investigation, human factors and aeronautical research, and operational training.
In converting to new computing systems, our fundamental philosophy is to replace all B707
specific display instrumentation and flight characteristics with a generic system. This is based on
the use of “glass cockpit” principles using Cathode Ray Tubes (CRT’s) in the instrumentation panel
so that engine and flight instrumentation display arrangements can be tailored to specific aircraft in
software. Aircraft models can then be chosen from standard base configurations, for example,
multi-jet, turboprop, piston-prop, GA, etc, and then tailored to give specific flight characteristics for
aircraft to be represented in the simulation.
The following sections discuss the simulator system components
2.1 Simulator Platform
The base platform of the simulation facility is a former Link B707 Simulator. This simulator
comprises the following primary systems:
 a full scale B707 cockpit that is fully equipped with all flight controls,
 a hydraulically driven three degree-of-freedom motion base providing pitch, roll and heave
motions,
 hydraulically driven control loading systems for the two control stick axes and rudder
pedals,
 electrically driven trims and thrust reversers,
 dual collimators for display of forward looking outside world imagery.
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Figure 1: Simulator installation (starboard view)
Figure 2: Simulator installation (nose view)
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In addition, it has background infrastructure equipment including:
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Hydraulic pump and accumulators,
Instrument and control cabling,
Cabinets and housings.
Figure 1 and Figure 2 illustrate the simulator installation in its current stage of development.
Visible are the cockpit, hydraulic rams for the motion system (bottom) and collimators (atop nose).
Figure 2 also shows the throttle control equipment in the cockpit nose.
2.2 Computer Systems
The Link simulator was previously controlled by a predominantly analogue computer system of
1960’s vintage. Following acquisition, it was decided that the Department could not support this
aging equipment. It was decided, instead, to retrofit the simulator with more modern computer
hardware and software systems based on a network of PC’s, thus taking advantage of up-to-date
simulation and graphics technologies. More importantly, this affords a great degree of flexibility,
at a far reduced operating cost.
2.2.1 Cranfield Connection
The Department of Aeronautical Engineering has an agreement with the College of Aeronautics at
Cranfield University in the UK, covering the use of the Cranfield flight simulation architecture and
software. The agreement was initiated in order to implement well established simulation software
into the simulation facility without extensive developmental time lags, and to foster the
collaborative development of improved simulation features and operations.
The agreement was established under a large equipment grant obtained from the University of
Sydney Major Equipment Grants Scheme. The grant covered a licence to use the Cranfield
simulation software, the purchase of instrumentation interfacing equipment and computer hardware
including a dedicated sound card, and three high power image generator (IG) cards.
2.2.2 Simulation System Architecture
A schematic of the simulation system is given in Figure 3. The system design comprises multiple
PC nodes connected via a dedicated Ethernet computer network. Each of the nodes runs a separate
software module dedicated to a particular simulation function. There are three key modules, The
core components of the system are;

Flight simulation core – This first PC node runs the core flight simulation which represents
the aircraft behaviour and response to control inputs.
o I/O: It houses the Input/Output card which interfaces the pilot control input
inceptors through a signal conditioning and multiplexing card. The input signals are
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used to drive the aircraft model, which communicates the aircraft state to the other
modules through the ethernet.
o Sound: It houses a sound card that generates engine and environmental noises that
are reproduced in the cockpit.
o Instrument Display: It houses a graphics card that generates flight and engine
instrument displays for presentation on CRT’s in the pilots instrument panel.
Image Generation – The second PC node runs the image generation software which drives
three Primary Image Barracuda image generation cards. These cards are currently driving
new full colour high resolution CRT displays through the existing collimator systems.
Planned upgrades involve utilization of a multiple projector/curved projection screen
system.
Instructor Station – The third PC node runs an instructor station that enables the following
functions
o Instructor/supervisor: The simulator instructor or operator can configure the
aircraft flight condition, systems status and environmental conditions,
o Navigation modes: The instructor or flight engineer can monitor or alter navigation
information and navigation display representations,
o Flight Information: A flight test mode can be configured that permits the
monitoring and recording of flight behaviour for post analysis.
Figure 3: Cranfield PC based flight simulation system architecture
The flexibility of the systems stems from the capability to add further software modules simply by
adding additional PC nodes to the Ethernet. These communicate with the flight simulation core to
receive current flight status or to update the aircraft flight characteristics or systems status. In
particular, specific modules that will be attached to the simulation are;
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Variable Stability module – modifies aircraft behaviour via GUI (Section 2.5),
Control Law Builder –implementats flight control laws via GUI (Section 2.5),
Motion Base and Force Feedback module – receives aircraft motion and control
information from the flight simulation core and drives the motion base and control force
feedback hydraulic systems (see Section 2.4).
2.3 Image Generation System
Image generation for the out-of-window displays is provided by Barracuda image generation (IG)
cards supplied by Primary Image Ltd. The system currently consists of three cards, which are used
to drive three video channels, providing forward and peripheral vision. A sample composite threechannel image is shown in Figure 4. The Barracuda is a high performance system providing image
resolution up to 1280x1024 pixels at refresh rates up to 115 Hz. The system achieves this
performance by storing a database of environment objects in memory on each IG card, thus
avoiding communication bottlenecks.
Figure 4: Sample image combined from 3 Barracuda image generation channels
Currently, the image generation system is implemented in separate channels driving two forward
facing collimated images and one peripheral image in the pilot’s side window. However, the
system is completely reconfigurable and expandable and can easily be adapted to projector and
screen based display system (Section 6). Image orientation is set in the driving software thus
allowing simple tailoring of image generation to display orientation.
2.4 Hardware Control Systems
One of the important features of the Variable Stability Flight Simulator as a teaching, analysis and
research tool is its capability to represent the sensitivity of the aircraft’s behaviour to changes in the
geometric and aerodynamic configuration of the aircraft. It achieves this through both the apparent
motion represented by the out-of-the-window displays, and through the simulated motion provided
by the motion base.
The replacement of the Link computer systems has necessitated the development of new interfaces
to the servovalves controlling the hydraulic actuators for the motion base and control loading (force
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feedback) systems. To this end, compatible analogue servo-controller cards have been purchased
from Moog Australia which provide a simple control interface to the existing hydraulic servovalves (also manufactured by Moog) and analogue actuator position sensors. With this control
equipment in place, the task of hydraulic control reduces to one of providing an analogue set-point
from a PC node equipped with a suitable digital to analogue converter (D/A) interface, and of
developing suitable control algorithms to run on that PC. This will constitute an additional PC node
on the network, running the control force feedback and motion control software modules. Figure 5
illustrates the hardware configuration of the hydraulic control loops.
Figure 5: PC controlled analogue control loops for motion and force feedback actuation
2.5 Software Modules
2.5.1 Flight Simulation
The Cranfield flight simulation software is the core of the simulator. It comprises simulation
programs covering a range of aircraft types, including Boeing 747, Jetstream 100 and Cessna 172.
These contain models of control input suites and flight instrument panel displays that are intrinsic
to these aircraft types. An example instrument display is given in Figure 6.
In producing a generic simulator, each one of these basic “types” is being made conformable by
integration with a Variable Stability module. This allows the representation of other aircraft of the
same type to be implemented rapidly, using the same or modified instrument representations.
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The Simulator cockpit, being a fully equipped jet transport, contains all primary and secondary
flight control inputs and switchgear that are required for representation of the turbo-prop, pistonprop and General Aviation (GA) aircraft types. This hardware suite is thus compatible with the
philosophy of simulator reconfigurability through software.
Figure 6: Boeing 747 flight instrument display
2.5.2 Instructor’s Station
The instructor’s station controls the status of the simulation. Its functions include
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Start, pause and stop simulation,
Selection and setting of flight condition, system and autopilot parameters,
Selection of instrument, control, engine and system failure modes,
Selection of weather conditions such as turbulence, wind, visibility and lighting.
The instructor’s station operates in either of two basic modes, displaying either
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Navigation mode: a map with the aircraft track, navigation aids and airports,
Flight data mode: a selection of time histories of the aircraft state variables.
The navigation mode and selection options are illustrated in Figure 7. The flight data mode is
illustrated in Figure 8.
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Figure 7: Instructors station navigation mode showing flight condition, failure and weather options
Figure 8: Instructors station flight test data recording mode
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2.5.3 Variable Stability Module
The variable stability module is designed to enable modification of the aircraft flight characteristics
in real time. It presents the operator with displays of the current aerodynamic characteristics and
inertia properties. These can be modified graphically by moving control points on a curve for
strongly state dependent parameters, or by numerical specification for constant parameters. The
new selections can be downloaded into the flight simulation by selection of an icon. The simulation
immediately takes on the new characteristics. The interface also interrogates the flight simulation
for its current state and analyses the instantaneous stability and handling characteristics of the
aircraft. These are continually re-analysed. A sample of the variable stability interface is given in
Figure 9.
The main utility features of this module are;
 Teaching: permits demonstration of the effects of changes in the primary aerodynamic and
inertial characteristics of the aircraft on its stability and handling qualities,
 Research: investigation of human responses and crew performance to changes in aircraft
behaviour while subjected to various workloads,
 Industry: investigation of unplanned aerodynamic changes on aircraft behaviour and crew
action in reconstructing the sequence of events surrounding incidents.
Figure 9: Variable stability module interface
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2.5.4 Control Law Builder
The control law builder is designed to provide the capability for an operator to implement a
stability augmentation or autopilot control system using a simple block diagram interface. The
graphical interface provides numerous options of standard control system components which can be
interconnected by dragging a line between input and output ports. Inputs can be selected from a
pull-down list of aircraft state variables representing feedback from flight sensors. Outputs of the
control loops can be selected from a list of standard aircraft control effectors, for example, control
surface actuator commands, throttle commands, flap setting etc. A sample of the variable stability
interface is given in Figure 10.
The main utility features of this module are;
 Teaching: permits demonstration of the effects of control laws, and illustration of practical
control implementation issues,
 Research: investigation of crew reaction to control system operations and crew assessment
of different control implementations. Assessment of various control design techniques,
 Industry: investigation of aircraft behaviour resulting from failure or malfunction of control
system components.
Figure 10: Control law builder module interface
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3 Status of Simulator Implementation
The Variable Stability Flight Simulator facility constitutes the integration of the computer,
software, electronic and hardware systems detailed in Section 2. Progress in implementing each of
these components is at various stages, with different priorities assigned to each. The status of each
component is listed below in priority order.
Site Infrastructure
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Installation of the Simulator cockpit and motion base is complete,
Laboratory space, computer cabinet placement and cabling layout is complete,
Pump-house construction is complete,
Hydraulic pump installation and hydraulic connection is imminent,
Hydraulic pump electrical connection ASAP after pump installation in pump-house,
Air conditioning plant being specified, installation ASAP.
Electrical Systems Fitting and Connection
The interfacing of electrical systems is a high priority from a hardware perspective.
 Interfacing B707 transducers with PC data acquisition equipment and software - half
complete.
 Fitting of CRT’s into instrument panel – half complete
 Retrofitting of large CRT’s into collimators (temporary) – one collimator is complete
.
PC System and Simulation Flight Models
The PC system, core flight simulation software, flight models, instrument displays and sound
system are operating in a mockup situation, awaiting readiness of the simulator. With cabling
virtually complete, the PC system and simulation system installation in the Simulator facility is
imminent. Flight models are ready for immediate implementation.
Out-of-Window-Display Systems
The collimators (one at this stage) have been retrofitted with new large screen high resolution
colour monitors, thus upgrading the graphic capability of the simulator to full colour daytime
operation via the Primary Image IG system (Section 2.3). These monitors use standard VGA
interfaces and will connect immediately to the IG graphics cards.
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Control Force Feedback and Motion Control System
The control force feedback and motion systems will utilize the existing hydraulic actuator system
and Moog hydraulic servo valve system. New electronic control systems have been purchased
from Moog Australia (see Section 2.4) for the control of the servo-actuators. These will be
implemented in due course. Control force and motion base control algorithms need to be
developed.
The priority is to implement the control force feedback system first (6-12 months), followed by the
motion system (12-18 months).
3.1 Timeline for Development
Component
Projected completion date
Base system (Cockpit, PC system, software)
July 2000 (firm)
Control force feedback (control loading) system
June 2001
Hydraulic motion system
Visual projection system (See Section 6)
December 2001
July 2001 (Option 2) OR
December 2001 (Option 3)
Depending on funding
4 Utility of the Facility
The utility of the Variable Stability Flight Simulator facility is wide and varying. From pure
research in the various fields of aeronautical engineering to investigations into crew management
and human factors in varying operational situations, this facility provides an unparalleled
opportunity and capability for research institutions and industry alike. In particular it is the perfect
environment to host endeavours in research, teaching, training and analysis by Universities and
collaborating industry and government bodies.
The major applications of the VSFS facility are listed below for each of the areas of interest for
research institutions and industry or government organisations.
Research
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Flight Mechanics
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Real-time aerodynamic parameter identification techniques,
Real-time state estimation and data fusion techniques,
Terrain Aided Navigation techniques,
Robust, optimal and nonlinear flight control methodologies,
Fault detection and isolation in flight sensor and control systems.
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Human Factors
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Vestibular function,
Visual perception,
Situational awareness,
Crew performance and cockpit interaction,
Cockpit ergonomics,
Factors influencing operational efficiency
Training and Operations
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Crew and cockpit management, interaction, and efficiency
Development and optimisation of training methodology and technique
Effects of flight stability on turbulence sensitivity
Effect of turbulence intensity on crew workload
Effects of rapidly changing flight situation on operational performance and associated
operational requirements issues
Industry
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Aircraft dynamic performance during design flight envelope excursions
Aircraft/Crew handling issues in off-design flight conditions
Flight Path Reconstruction techniques
Accident investigation and reconstruction
Critical event sequencing
Industry Support (Commercial) 1
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Accident investigation
Supplemental training
A-priori training
5 Benefits for Human Factors, Operational, and Safety and Accident
Investigation
The benefits for investigation into human factors, safety and accidents offered by the Variable
Stability Flight Simulation Facility are numerous and wide-ranging. The most obvious benefits
have already been outlined in the preceding overview. However, several points are worthy of
elaboration, and illustration by way of example is warranted.
The primary benefit of the VSFS facility for these kinds of investigation lies in the fact that it
enables repeated, accurate, low-cost reproduction of the operational environment under widely
varying scenarios. Such variations can include flight conditions, in terms of both aircraft
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infidelities and external influences, as well as real-time variations in the aircraft response to
disturbances (again internal or external) and faults which may occur.
Standard simulation facilities may enable minimal reconfiguration (such as weight redistribution
and associated centre of gravity movement over a small range), but are unable to reproduce the
flight environment following a substantial change in aircraft parameters; for example, loss of part
of the airframe or a control surface/s.
For example, an aircraft may suffer birdstrike on takeoff which destroys an engine and causes
damage to the nacelle and surrounding structure. A commercial simulator would only be capable
of simulating the shutdown of the affected engine. It could not model the associated drag increase
and various force and moment variations acting on the aircraft as a result of the damage to the
nacelle and surrounding structure. The fully reconfigurable VSFS accurately reproduces such
secondary effects, and indeed allows any similar effects to be simulated in real-time, while the
aircraft is being flown. This kind of detail can well mean the difference between an accurate
reproduction of the course of events leading to a particular incident or accident, and a suspect
simulation of the same events where few of the true contributing factors have been included.
Moreover, the true aircraft behaviour can be vastly different once ALL contributing factors have
been correctly included in the simulation.
There are any number of similar situations that may arise as causes of serious safety incidents or
accidents. There are infinitely many possibilities, and this is indeed the case even where certain
contributing factors of a particular incident may be known, but the larger, wholistic picture remains
to be investigated.
From the large-scale and dramatic, such as a loss of control or partial loss of aircraft structure, to
the minor and arguably insignificant, such as an inoperative or erroneous cockpit indication, ALL
potential factors must be addressed in any thorough investigation involving human interaction and
safety issues. All of these possibilities can be easily investigated with the VSFS through repeated
and varied simulations because of the reconfigurability of the facility. This is simply not possible
with a commercial simulation facility.
The VSFS will be equipped with several cockpit recording devices, both video and audio, and the
fact that the entire simulation is PC-based enables easy recording of every event during a given
simulation, from the aircraft response and control inputs, to pilot reaction and visual cues and
perception.
This is also important with respect to the issue of repeatability and reconfigurability. When
assessing the various aspects of human factors which contribute to pilot reaction, such as visual
perception, situational awareness, and vestibular function to name a few, it is essential that the
simulation environment be capable of both exact reproduction and subtle variations when
continually re-running a particular scenario. Again, a commercial facility could well provide some
of the various stimuli which the flight crew may experience, such as cockpit indications and initial
(but limited) aircraft motion. However the true, complete picture of what the crew face in a given
situation cannot possibly be repeated if the requirements for that situation exceed the operating
capability of the simulation facility.
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For example, in a commercial simulator, the crew may well heed warnings of a nacelle overheat
alarm coupled with wildly fluctuating engine instrumentation readings. One can rest assured,
though, that their reaction to this situation would be vastly different if, in the VSFS facility, such
warnings and readings were coupled with the true dynamic response accompanying the real cause
of the situation - a complete detachment of the engine! Such a simulation is impossible with a
commercial facility, and suggested crew reactions to a given scenario would remain exactly that mere postulation.
Such melodramatic examples are not required to highlight the benefits of the VSFS facility. The
ability to provide repeatable, widely-varying scenarios with true dynamic response and real-time
interaction and recording in a cost-effective environment places the VSFS facility in a class of its
own for human factors, safety, and accident investigation and research.
6 Next Stage Development - Visual Projection System
Without doubt the most important element of any simulation is the external (out-of-window) visual
system and display/s. This is by far the most crucial simulation component from the perspective of
human perception and realism. Since the primary goal of the VSFS facility in terms of human
factors issues is accurate reproduction of the various stimuli and factors affecting perception and
performance in the operational environment, it is critical that the facility be equipped with the best
possible visual system.
The system that will be implemented is, unfortunately, limited by available funding. The next stage
of development of the system is aimed at generating far more realistic immersion in the simulation
environment by implementing a visual projection of the outside world images.
The current system uses a normal computer monitor mounted in a collimator. This produces an
image not unlike the visuals produced in older commercial simulators like the early Boeing 747, or
the Hercules C130-E. The only improvement in image quality over the old raster displays (or
monochrome “multiple green dot” images) comes from the fact that the external “world-view” is
actually produced by state-of-the-art computer graphics imagery which gives a textured, full-colour
image of the surrounding scenery.
The pilot views this scene as a collimated (mirrored) image, which appears “at infinity” (that is to
say, as it would appear to a person viewing the scene from the window of a real aircraft). However,
this collimated image is correct only if the pilot is looking directly forward out of the window in
front of him/her. If the pilot looks at a wider angle through the window in front, or if he/she looks
out another window (for example the co-pilot’s window), the image seen becomes vastly distorted.
The view they would receive from the real aircraft if looking out the same window in the same
direction would be much different.
This is critical from a human factors perspective, because the pilot’s brain perceives this
inconsistency, and the pilot is then immediately reminded of the fact that he/she is in fact sitting in
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a simulated environment. The secondary effects of this can be wide-ranging, but the bottom line is
that their reactions to stimuli become different as a direct result of this loss of realism. Research
quality is thus compromised, because the true “cause-and-effect” nature of the operational
environment in terms of human perception and reaction has been flooded with inaccuracies and
contaminants.
The purpose of upgrading the visual system is thus to maximize the quality of the simulation
environment and the “immersion” of the pilot into that environment for human factors, safety, and
operational investigations and research. To eliminate the problems with a collimated visual system
outlined above, the proposed visual system for the VSFS comprises a projection system with a
curved external screen. This is a set of three or more projectors, not unlike those used in office
presentations with PCs, which project an image out onto a curved screen located some short
distance (2-3 metres) from the cockpit windows. These arrangements project a continuous image
covering a 40 degree vertical by up to 180 degree horizontal forward view from the cockpit (see
options in Figure 11).
Figure 11: Out-of-window display projection options
The aim of such a system is to produce a seemless and continuous view of the outside world, so
that primary and peripheral visual cues are all accurately represented in the simulation. This means
that the pilots can look out on a high-fidelity outside world image which appears almost exactly the
way it would were they seated in the real aircraft. The complete outside image ensures that the
realism of the simulation is not annihilated by visual inconsistencies that remind the pilots that they
are actually in a simulator. Obviously this completeness is related to the horizontal coverage of the
display. From Figure 11, it can be seen that a 120 degree horizontal image gives rise to incomplete
and inconsistent peripheral visual cues, while the 180 degree horizontal image gives complete
coverage from the pilot’s eye point in the cockpit.
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The new visual projection system has several variables that affect the quality of the visual image
created. These include image pixel density, field of view, lenses, and image continuity. The more
pixels per image, the more realistic and detailed the external image appears. The more projectors
used, the wider the field of view. Special lenses are required to account for projection on the
curved screen.
Image continuity at the junctions of the projected images may affect the realism created. Low end
(office quality) LCD projectors suffer from variations in image intensity and colour spectrum
differences from projector to projector and hence result in inconsistencies at the junctions between
adjacent images (an effect similar to that seen in Figure 4). Higher level projectors tailored
specifically for simulation are available, but are far more expensive. These permit edge blending
compensation in software for intensity, colour differences and alignment (e.g. SEOS optiblend).
Low end projectors may also produce image distortions. These occur because low end projectors
are made to project onto a flat screen and hence do not compensate for the change in perspective as
the angular disposition of objects in the image becomes large. Adjoining images may therefore
present an object with different and therefore inconsistent perspectives. An example is a runway
which appears to bend when crossing an image boundary (a little of this effect is visible at the
boundary of the left and middle images in Figure 4). High end projection systems provide software
compensation to account for image transformation to a curved screen, thus providing consistent
perspective and seemless projection (e.g. SEOS mercator).
The choice of projection and computer equipment for the final visual system governs the choice for
each of these variables, and in turn, the quality of the final visual image. Obviously, the higher the
fidelity of the image, the more detailed the required equipment, and the higher the cost. The
various equipment options are listed below, together with the associated technical details of the
resultant image in terms of the variables discussed above.
6.1 Equipment Options
1.
2.
3.
4.
3 LCD projectors/Wide-Angle (WA) lenses and curved screen
4 LCD projectors/WA lenses, additional Barracuda graphics card and curved screen
3 SEOS LCD projectors with edge blending, distortion correction and curved screen
3 SEOS LCD projectors with edge blending, distortion correction and concave reflective
screen (SEOS PANORAMA)
Options 1 and 2 involve in-house integration of the multiple projectors and construction of the
concave screen. These options use LCD projectors typically used in office presentations. There is
no edge blending capability available with this option. High end models are required to enable
control of edge bowing and colour and contrast to minimize alignment errors where images meet.
Option 3 is a commercially available system manufactured by SEOS. It uses coupled Barco LCD
projectors that permit edge blending and distortion correction using SEOS optiblend and mercator
software. Option 4 provides the same capability with a SEOS Panorama reflective screen, thus
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collimating the single continuous image at infinity. The reflective screen also serves to provide
additional immersion and depth sensation.
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7 Contact Information
Peter Gibbens
Tel: 02 9351 7350
Email: pwg@aero.usyd.edu.au
David Boyle
Tel: 02 9351 7160
Email: dpb@aero.usyd.edu.au
Douglass Auld
Tel: 02 9351 7336
Email: douga@aero.usyd.edu.au
Postal address:
Department of Aeronautical Engineering
Building J07
University of Sydney
NSW 2006
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