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Aircraft Simulators Simulators Simulators

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Aircraft Simulators Simulators Simulators Powered By Docstoc
					        Flight Simulators




 Aircraft Simulators




        GROUP 9:
Anderson, Ryan              1132309
Kolodziej, Claire           1132693
Kurji, Rahim                1126547
Ogilvie, Mark               1132008
Tan, Yong
Walladge, Terry             1133113



          Page 1 of 54
                                Flight Simulators




Flight simulators are a necessary part of pilot and flight training. They emulate
conditions encountered in normal flight both in calm and extreme weather
conditions. Modelling the flight of aeroplanes requires the critical parameters
of flight to be incorporated via many dynamical formulas and derivations. It
also includes allowing the simulator to adapt to motion created by the
simulator pilot. Allowing analysis of the development of flight simulators; future
possibilities and adaptations can be created to make the world of flight
simulators a permanent training tool.




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                                                        Flight Simulators




I. Contents
Aircraft Simulators..................................................................................................................... 1
II. Introduction........................................................................................................................... 5
1. History of Flight Simulators ................................................................................................... 6
2. Simulator types and training usage....................................................................................... 9
   2.1 Part Task Trainers .......................................................................................................... 10
   2.2 Flight Training Device .................................................................................................... 11
   2.3 Full Flight Simulators ..................................................................................................... 12
3. Systems Testing ................................................................................................................... 16
   3.2. Testing Existing Software and Hardware in New Environments.................................. 17
       3.2.1. Transferring Flight Control Systems ...................................................................... 17
       3.2.2. Testing Flight Systems in Extreme Environmental Conditions .............................. 18
   3.3. Testing New Software in Established Environments.................................................... 18
       3.3.1. Autopilot Development and Modification ............................................................ 18
       3.3.2. Flight Procedure Modification............................................................................... 20
       3.3.3. Emergency Procedure Testing............................................................................... 20
   3.4. Testing New Software Interfacing New Hardware....................................................... 22
       3.4.1. Military Applications.............................................................................................. 22
4. Cockpit Design ..................................................................................................................... 24
   4.1 Motion Base .................................................................................................................. 24
   4.2 Graphics and audio........................................................................................................ 25
   4.3 Flight Instruments and controls: ................................................................................... 27
   4.4 Interchangeable cab (ICAB) ........................................................................................... 29
5. The Working of a Flight Simulator....................................................................................... 30
   5.1 Coordinate Systems for Modelling................................................................................ 30
       5.1.1 Body Coordinates ................................................................................................... 31
       5.1.2 Wind Coordinates................................................................................................... 31
   5.2 Parameters of flight....................................................................................................... 32
   5.3 Flight environment variables: The atmosphere ............................................................ 32
       5.3.1 Flight environment parameters ............................................................................. 33
       5.3.2 Standard atmosphere............................................................................................. 33
       5.3.3 Background wind.................................................................................................... 33
       5.3.4 Turbulence.............................................................................................................. 34

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                                                      Flight Simulators


      5.3.5 Wind shear ............................................................................................................. 34
   5.4 Flight environment variables: The Earth ....................................................................... 35
      WGS-84............................................................................................................................ 35
   5.5 Flight control variables: The aerodynamic model ......................................................... 36
      Aerodynamic force .......................................................................................................... 36
      5.5.1 Aerodynamic moment............................................................................................ 37
   5.6 Flight control variables: The Propulsion model............................................................. 39
   5.7 Flight control variables: The Inertial model .................................................................. 41
   5.8 Equations of Motion...................................................................................................... 42
      5.8.1 Total Acceleration................................................................................................... 42
      5.8.2 Total Moment......................................................................................................... 42
      5.8.3 Structure Euler Angles ............................................................................................ 43
   5.9 Modelling Flight in a Simulator...................................................................................... 44
6. Limitations of flight simulators............................................................................................ 45
   6.1 Simulator Sickness......................................................................................................... 45
   6.2 Simulation of G forces ................................................................................................... 46
   6.3 Simulation of Radio Communications ........................................................................... 48
7. Future Flight Simulator Developments ............................................................................... 49
   7.1 Centrifuge-based Motion Flight Simulators .................................................................. 49
   7.2 Synchronized Real-time Radio Communications .......................................................... 51




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                                 Flight Simulators



II. Introduction

A necessary training tool for today’s pilots is to use a flight simulator. These
devices can incorporate many elements both dynamically and physically to
replicate almost exactly the conditions encountered in flight. Wether their
application for military applications or for use in training commercial aeroplane
pilots; they provide a safe platform to train prospective pilots. Whilst looking
into the vast history of flight simulators, this report aims to cover the extensive
use of flight simulators in pilots training, incorporating the vast number of
situations aeroplanes might encounter when in real flight. It also aims to look
at the systems involved in creating simulators and the ever increasing number
of new and improved software allowing for better control. Current shortfalls
and future possibilities are key issues which are addressed, as to be the
physical movements of the simulator. Finally taking into account the emulation
process and how this method simulates the surrounding environment.




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                                  Flight Simulators



1. History of Flight Simulators

The development of simulator flight began with the inception of rudimentary
aircraft being controlled on the ground. The element of wind by dragging the
simulator along the ground was the primary creator of situations which would
occur; mid flight. By harnessing this force and using the basic ground aircraft
the pilot was able to control the aircraft in particular by using the aileron,
elevator and rudder. Most of the education of flight was performed in a class
room where would be pilots were taught the basics of aircraft management,
and what would be presented to them in a danger situation.


In the year 1910 a simple yet effective simulator method was created. This
method was dubbed the “penguin system,” and was used in the French Ecole
de Combat. To create the simulation of taxiing the device was dragged along
the ground exposed to the elements, and hence rudder control was able to be
practised. “Short hops” were then introduced to introduce “elevator control.”
As this “hopping” process progressed the pilot would leave the ground, hence
creating real flight. The use of a “cut down Bleriot monoplane,” allowed the
“penguin system” to work.


As seen in figure 1, the pilot is simulating the “first truly synthetic flight training
device.” This incorporates the use of two cut in half barrels able to be
controlled by assistants on either side. The simulations created by this
method include the pitch and roll of the aircraft. To test the pilot’s ability to
control the aircraft in a real life flight he was required to “line up a reference
bar with the horizontal.”




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                                Flight Simulators




                                    Figure 1


The Sanders Teacher was another widely used method around the same time
period as the penguin system. This simulator involved placing a regularly
used aircraft on a universal joint, and exposing it to the wind. By testing the
pilot in this simulator, he was able to rotate and move as an aircraft in flight
would normally do.


To replicate the “less hazardous and less expensive” method of flying, the
Link Trainer was invented in 1929 by Edwin Link. “A pneumatic motion
platform” that was placed under a singular cockpit was used to reproduce the
movements of pitch, roll and yaw in the specific weather condition of cloud
flying. This was the birth of the first real flight simulators, as in World War 2,
10,000 Link Trainers were purchased by the US Air Force; and distributed to
the allied forces, to train their pilots in battle. A replica of this simulator is
shown in figure 2.




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                                Flight Simulators




                                    Figure 2


While the Link Trainer was effective in replicating the conditions pilots would
face in real flight, the introduction of the Celestial Navigation Trainer was the
first simulator to use analogue computers. This simulator was able to utilise
the dynamic equations which calculate flight, and turn it into the movement of
the chosen aircraft simulator. No real aircraft was necessary anymore to train
the pilot in flight; what was used was a huge structure (13.7m high) capable of
containing many pilots and crew who needed to be trained.


The simulator systems completely controlled by electronics became the sole
training method in the late 1960s. This new and improved system used
cameras and other devices to harness the conditions in the sky, and transfer
them to the simulator. These terrain images were capable of 10 degrees of
pitch, roll and yaw angle; used in 1964.


Progression for flight simulators increased rapidly from the year 1964 to the
present day. The introduction of hydraulic actuators in 1969, to redesigning
the look of the simulator in 1977, allowed for fast progression.


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                                Flight Simulators


2. Simulator types and training usage

Flight simulators are predominantly used for training purposes. Simulator
training is used to provide a means for crewmembers to gain the skills and
knowledge required to perform to a safe standard without the risk and cost of
actual flight training. Simulators provide an excellent environment for the
instruction, demonstration and practice of manoeuvres and procedures.


The level of training provided is dependent on the complexity of the simulator,
ranging from simple procedure training to military fighter training. Simulators
are categorised by their purpose, and fall in three main categories, Part Task
Trainers (PTT), Flight Training Devices (FTD) and Full Flight Simulators (FFS).


The benefits of flight simulators are widely accepted in pilot and crew training.
The most significant benefit is that the risk of a crash during training is
dramatically reduced if initial training occurs in a simulator. The simulator
allows the pilot to learn how to control the aircraft in a risk free environment,
and as such the pilot is more able to focus on ensuring the procedures and
manoeuvres are performed correctly. Simulators can also improve the quality
of training due to the ability to more closely instruct and communicate during
the training process.


Simulators also provide an excellent basis for pilot performance evaluation,
due to the inherent ability to monitor pilot response to a simulated event. A
simulator allows a great variety of system malfunctions and environmental
effects to be simulated, which can greatly improve the experience of a pilot in
dealing with rare and dangerous situations.


Flight simulators dramatically reduce the costs associated with the pilot
training. Even expensive level D simulators are significantly cheaper to
purchase and operate than the respective aircraft. This also means that less
noise and emissions are produced, reducing environmental impact.



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                                 Flight Simulators



2.1 Part Task Trainers

Part Task Trainers (PTT) are designed to simulate certain aspects of an
aircraft. Basic systems may be used to simply familiarise a new student with
the basic position and function of the aircraft controls, while more complex
systems may relate to specific features of a certain aircraft, such as the auto
pilot system. PTT systems aim to ensure that the pilot or crew know exactly
how an aspect of the aircraft is operated.


These systems are often computer based software with input hardware, and
hence are generally very cheap to purchase and operate in comparison to an
aircraft. PTT systems may also be full three dimensional systems and
demonstration areas, dependent on the type of training required. Figure 3
shows a typical part task trainer setup. The ability to learn a system in all
states of flight is also a distinct advantage, as it allows pilots to fully associate
themselves with a system without the risk of actual flight.




                     Figure 3 - A typical Part Task Trainer
Most training courses will include the use of a PTT in some form. In most
cases, a particular training lesson will be first theoretically taught, after which
the student will spend time in a simulator completing missions based on the
topic.




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                                Flight Simulators



2.2 Flight Training Device

A Flight Training Device (FTD) is a full scale replica of an aircraft cockpit,
including instruments, equipment and controls. The system also requires a
software system that represents the airplane in both ground and flight
conditions. These systems are used to familiarise the pilot with the
procedures and drills before they move to a full flight simulator. As such,
these systems vary significantly in complexity depending on the specific
requirements.


In order to be used for training purposes, these devices are certified by FAA
designations Level 1 through to Level 7. The lower level FTD’s represent
general cockpit layouts, and are hence not made with reference to a specific
aircraft. These systems lack motion and visual systems, and are most
generally used for early training. These systems may also be used for training
for low visibility conditions, where the pilot must recognise problems with only
instrument indication. Scenarios such as Dutch Roll recognition and correction
can also be taught in lower level FTDs. Higher levels have progressively more
realistic properties and hence can be used for more complex training
purposes. The cockpit design of these simulators replicates a specific plane.
Higher level systems have full visual and audio systems, as well as a complex
aerodynamics models. All flight systems function as they would in the real
aircraft, to the extent of changes in aerodynamics due to loading changes,
and the “sound of precipitation, windshield wipers, and other significant
airplane noises” (FAA, 1992).




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                                Flight Simulators




             Figure 4 - A level 5 FTD (image courtesy of CAE)



2.3 Full Flight Simulators

Full Flight Simulators (FFS) are very realistic devices that are intended to
completely simulate the flight environment. Full flight systems simulate all
aircraft subsystems, such as engines and hydraulics, while effects such as
aerodynamic noise and landing gear bumps while on the ground are also
present. Higher levels of FFSs feature movable cockpits in order to generate
realistic g-forces on the pilot. Due to the significant cost of producing and
running a FFS, they are generally reserved for training in very expensive
aircraft, such as commercial airliners, and for research usage.


In order to be used for training purposes, Full flight simulators are certified as
Level A through D simulators.


Level A simulators are the most generic form of a full flight simulator. These
simulators are not required to replicate a specific aircraft physically, and
hence are much more flexible than the more complex models.


Level B onwards simulators replicate exactly the layout and operation of a
specific aircraft. The parts used in the simulator are often identical to those
present in the relative aircraft. These simulators are often re-fitable to allow
different aircraft to be simulated by the same hardware.

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                                       Flight Simulators



      Level C and D simulators use a full six Degree of Freedom (6 Dof) movement
      in order to simulate the acceleration forces experienced during flight
      manoeuvres. An example of a 6 Dof simulator is shown is figure 6. Level D
      simulators have a higher degree of simulation fidelity than level C requires.
      Later models of these simulators are incredibly realistic in operation, able to
      simulate to high fidelity both physical occurrences such as turbulence as well
      as visual detail to the extent of shadows, sun glare effects and motion blur.
      This detail and accuracy allows high level simulators to be used for varying
      levels of Zero Flight Training (ZFT).          The basic requirements for FAA
      certification of Full Flight Simulators are described in figure 5.


Flight Simulators (AC 120-40B)
Simul Cont      Visual     Moti    Visual      Grou      Runway     Soun   Buffets      Radar
ator  rol       Scenes     on      Field of    nd        Contami    d
Level Load                         View        Hand      nates
      ing                          (Note       ing
                                   4.)         Pack
                                               age
A      Static   Night   3          45x30
                        Axis
B      Static   Night   3          45x30       Yes                         Yes
                        Axis
C      Static   Night & 6          75x30       Yes       Feel       Cock Yes
       &        Dusk    Axis                                        pit
       Dyna                                                         Noise
       mic
D      Static   Night,     6       75x30       Yes       Feel    & RealiCharacter Operat
       &        Dusk &     Axis                          See       stic istic,      ing
       Dyna     Day                                                Cock Complian Radar
       mic                                                         pit  ce          (Note
                                                                   NoiseStatemen 5)
                                                                        t&
                                                                        Test
                                                                        Required
      Figure 5 - Basic requirements for FAA certification of Full Flight Simulators
      (DOT/FAA, 2000)




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                                 Flight Simulators




     Figure 6 - A 737-300 Full Flight Simulator with 6 Dof movement


Zero flight training is a process where a pilot with experience in an aircraft is
able to train and achieve certification for another similar aircraft based purely
on simulator time, rather than actual flight time. ZFT training is used
extensively in cases where the aircraft is particularly expensive to operate,
and the operation and behaviour of the aircrafts are quite similar.


In the simulator, flight scenarios are usually controlled by a training instructor.
The instructor generally sits behind the pilots inside the simulator, next to an
Instructor Operating Station (IOS). The IOS is an interface to the simulator,
allowing the instructor to cue a variety of events, ranging from environmental
inputs such as turbulence to malfunctions in various systems, as well as alter
the training scenario.




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                                Flight Simulators




   Figure 7 - The cockpit of a Full Flight Simulator. Note the Instructor
                Operating Station located behind the pilots.


The usage of flight simulators in military applications is becoming increasingly
common. This is primarily due to the ability to interface systems, such that the
simulator is able to not only simulate the flight environment, but also interface
with mission elements. New military simulation environments allow the
integration of flight simulators with allied forces, such as ground units. This
allows command units to make tactical decisions that can later be reviewed
after the exercise. Similarly, some commercial simulators are considering
traffic congestion, and using air traffic control to guide the pilot. Some
simulators can even be linked together to create a dynamic environment with
multiple aircraft. Sophisticated systems may also take terrain data in a
particular area from satellite imagery. While expensive, this detail can be
valuable in military training, and particularly before a real mission takes place.
This terrain detail can also be used to generate the probability of turbulence,
wind shear at low altitudes.




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                                Flight Simulators



3. Systems Testing

3.1 Introduction
The use of flight simulators is vital in the testing of new aircraft systems or in
the redesign of older aircraft, as it allows safe and inexpensive testing of the
various features. Often this testing is of one of three main modifications to the
design of an aircraft. The common modifications are new flight software, such
as a reconfigured auto pilot, new flight software to interface new hardware,
such as introducing a fly-by-wire system in to an existing aircraft, and
modifying software to manage new flight conditions, such as adaptive flight
controls for extreme weather conditions.




                    Figure 8 - Simulator hardware layout



The modified software can be installed at multiple levels in the system
dependant on its required function. For example modifications to the autopilot
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                                 Flight Simulators


would most likely be made in the input locations, providing input information in
the place of the yoke, pedals, throttle, and other flight controls. Where as
modification of the environment and aircraft design would take place within
the Simulator Flight Controller (Figure 8).


The use of simulated testing methods allows minor to radical changes to
flight systems to be tested extensively with out placing human occupants of
the aircraft at risk, or risking damage to the aircraft itself in untested situations
or flight configurations.



3.2. Testing Existing Software and Hardware in New Environments


In aviation it is important that aircraft respond as desired in all situations. The
testing of existing aircraft control systems in new environments like prototype
aircraft or extreme weather conditions is paramount to the performance and
safety of the aircraft.



3.2.1. Transferring Flight Control Systems


The transfer of a flight control system between different aircraft is a useful
option, as it removes the need to re-design an entire control system. However
aircraft with different performance characteristics may respond in an
undesirable manner with a control system that was not designed specifically
for that aircraft. This means that the system must be tested in its new
environment, and the use of a flight simulator makes it a relatively simple
procedure. The system is installed into the flight simulator and provides inputs
to the flight controls; the simulator’s software is modified to emulate the
performance of the new aircraft, and a simulation is run. The simulation
provides data that can be used to modify the existing software so that the
flight control system operates correctly in the new aircraft, thus saving the
time and money that would be required to test the system in a real aircraft.




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                                  Flight Simulators


3.2.2. Testing Flight Systems in Extreme Environmental Conditions

Extreme environmental conditions such as storms and large variations in
temperature and pressure pose a problem to the testing of flight systems.
These sorts of conditions are inherently dangerous to the aircraft and its’
occupants; hence it is desirable to test them in a simulated environment. The
flight simulator interface allows the implementation of extreme environments
on the aircraft, via modifications in the simulator’s software to reflect the
desired environmental conditions. Thus through testing using the flight
simulator, data can be gathered regarding the performance of the aircraft, and
hence the control system can be modified to maintain flight stability in adverse
conditions. With a number of tests in a variety of environmental conditions the
control system software can be modified to perform optimally in most
situations, allowing the aircraft to safely negotiate extreme weather and/or
temperature fluctuations.


3.3. Testing New Software in Established Environments


The implementation of new software in established environments is important
in optimising the method of controlling modern aircraft. This type of system
testing involves developing and operating improved autopilot systems, flight
procedure changes, and emergency flight systems. The updating of these
systems is vital to improving the controllability and safety of the aircraft, as
issues are found in the old systems that could cause problems during flight.



3.3.1. Autopilot Development and Modification

Autopilot development for aircraft currently operating requires a simple
phenomena mapping flight simulator, which is based on flight data taken from
recordings of aircraft flights.




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                                Flight Simulators




                             Figure 9 - Typical light
                                aircraft autopilot
The new autopilot system is installed in to the flight simulator and provides
input to the flight controls, the simulation is run and varying environmental
conditions are provided to the system, with the response of the autopilot to
these conditions recorded. From the recorded performance of the autopilot,
modifications are made to the autopilot to rectify any issues in its
programming. These simulations may be run multiple times to perfect the new
autopilot so that when it is installed into the flight computer of the aircraft it
has no issues that may compromise the aircraft’s performance. An example of
the implementation of these methods is in the design of advanced air traffic
management systems. This system communicates with air traffic control on
ground, and uses information on the position of other aircraft in the area to
determine a safe flight vector. Due to the complexity of the system it would be
inefficient to test this in flight as there are a large number of variables to be
controlled, and would require multiple aircraft to be flown for extended testing
periods. Hence a simulator is utilised, which allowed the system to be tested
in a multitude of situations. The simulator emulates a sector of airspace
surrounding an airport, containing aircraft at different altitudes and approach
vectors’, this information is relayed to the autopilot system which adjusts its
flight vector to avoid intrusion into the paths of the other aircraft. The
behaviour of the system was modified so that the autopilot functioned
correctly in all situations, but due to the highly variable nature of flights
manual override is still incorporated into the autopilot. This method is useful
as new software often behaves unpredictably in new situations, and
implementing an untested autopilot system in to a real aircraft for testing
places the occupants at risk if the system malfunctions.




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                                  Flight Simulators


3.3.2. Flight Procedure Modification

Changes in flight procedure such as cruising height or airport circuit layout
often can not be incorporated into an existing autopilot, as varying
atmospheric conditions alter the performance of the aircraft. In this case the
existing autopilot or control system is installed in the simulator, and provides
the inputs to the flight controls. As the simulation is run the effects of the new
flight procedure is monitored and recorded. From this data the control system
is modified so that the aircraft operates as desired under the new conditions.
Multiple simulations may be run to perfect the new system, which when
complete will be installed into the flight computer of the aircraft it was made
for. This method of modifying the system can be as simple as changing a
number of variables in the flight system, however with the risk involved in
aircraft flight, testing of these seemingly small alterations is important, before
the system is put into service.



3.3.3. Emergency Procedure Testing

Emergency procedures on aircraft are significant in the management of
incidents that could be fatal the human occupants or the aircraft. Emergency
situations such as stalling or spins have a large number of variables all with
major effects on the aircrafts handling. As situations like these might lead to
the aircraft crashing due to the unrecoverable nature of complex spins, testing
using real aircraft is avoided.




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                                Flight Simulators




                           Figure 10 - Inverted flat
                                    spin
                             (Due to stall during
The simulator allows the system’s response to this sort of event to be
inspected without risk, as the modifications to the system are complex and
may cause unpredictable results. The system is required to recover from
emergency situations when required, yet not interfere with the overall
operation of the aircraft and the use of a flight simulator allows this to be
tested, and issues fixed during the simulation.


A second use of the simulated environment in relation to emergencies is the
testing of emergency devices, including oxygen mask and other safety device
deployment, and system failures. Incorrect implementation of emergency
procedures in situations where they are not required could cause an
emergency rather than preventing one. The simulator allows the system
response   to   events   such   as   loss   of      hydraulic   control,   or   cabin
depressurisation, to be determined, and modified so that the system responds
correctly, and only when necessary to events of this type.




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3.4. Testing New Software Interfacing New Hardware


The use of updated hardware in modern aircraft is mainly limited to military
applications although it can be applied to commercial applications where
changes to an aircraft are required to improve safety or efficiency.



3.4.1. Military Applications


Due to the rapidly changing nature of technology in military applications,
upgrading hardware in aircraft is important to maintain superiority to
competitors. This can cause issues with control systems as the improved
hardware will have different performance characteristics to the original
configuration.


Hardware changes include the inclusion or modification of flight surface
actuators, avionic systems, threat detection systems, engine control systems
and weapon systems. All the previously stated changes require testing to
ensure that they perform as is required. However military aircraft are required
to operate in hostile airspace and testing new aircraft systems in hostile
regions is unsuitable, because of the risk to the aircraft, its occupants, and the
technology being tested.


A flight simulator allows modifications to be tested in an efficient manner,
before the system is used in a potentially dangerous situation. The simulator
also allows situations that would be hard to reproduce in reality, such as
bombing a hostile target or avoiding antiaircraft fire, to be easy implemented
in the simulator software.


In tests done on the V-22 osprey by the United States Air Force, a simulated
combat environment including hostile fighter aircraft, mobile SAM launchers,
support aircraft including two AH-1 cobra helicopters and a downed pilot
behind hostile borders, was developed.



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                               Flight Simulators




                            Figure 11 - V-22 Osprey



This would be impossible to implement in reality, however the simulated
environment allows the search and rescue capabilities of the V-22 to be
tested. Data was recorded involving the control systems ability to notify the
crew of imminent threats, and the overall performance of the V-22 in its flight
envelope. This data made it possible to make modifications to the flight
controller and also flight crew training, that would improve the performance of
the V-22 in future real life missions. The tests exposed issues with information
relay to the crew, discrepancies between the radar display and the actual
terrain, and troubles with the aerodynamic, flight control, and avionic systems,
that otherwise would have gone unnoticed until flight testing, which would
have meant extended delays in the development of the V-22’s search and
rescue capabilities.


Overall the use of the flight simulator environment reduces the costs involved
in the implementation of new hardware systems in existing military aircraft.




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                                Flight Simulators



4. Cockpit Design

An important aspect of many aircraft simulators is their ability to replicate real
life aircraft. There are a number of different design aspects that are used to
produce these models. Principle design features include the motion base,
ideally used to provide movement with six degrees of freedom, a graphics
system, designed to create a virtual replica of real environments, as well as
flight instruments and controls that provide realistic information and feedback
for the pilots and researchers. All these components are joined to create an
environment that looks and feels like the aircraft being simulated.



4.1 Motion Base

The motion base of a high-fidelity flight simulator ideally provides 6 degrees of
freedom, thereby technically allowing the full motion range of an aircraft. The
six degrees of freedom of an aircraft are in vertical, lateral and longitudinal
translation as well as the three rotational movements of pitch, roll and yaw. A
major problem in providing all six degrees of freedom is due to the large
volume of space required to make them effective for long periods of time.
Hence, these systems are best at replicating critical stages of flight such as
takeoff and landing. Figure 12 below shows the design of a NASA flight
simulator, showing the devices used to produce the six degrees of motion.




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                                Flight Simulators




               Figure 12 - Details of the VMS Motion Base


The NASA simulator seen in figure 12 above is housed in a ten story high
building to allow a large movement range of the system. The flexibility of this
particular system has been improved by allowing the cab to be mounted at 90
degrees from its usual orientation. This changes the axis of maximum motion,
thereby allowing a wider range of tests to be run.



4.2 Graphics and audio

The graphical display technology used in flight simulators to display the
aircraft surroundings varies greatly, as always, depending on the level of
detail and realism required. For simple simulators, these images are displayed
on nothing more than a standard television or computer screen. These
systems are easily setup and cheap to operate, but due to their simple design,
they are not adequate for top of the range simulators. More advanced visual
display systems reflect the images off a number of mirrors placed behind the
window of the cockpit. The use of this system results in a great improvement
in the overall realism of the view created, by creating an impression of a three
dimensional view for the pilots. This display technology also results in an
image display that varies depending on the angle from which it is viewed. As
the pilots head moves, the image will change. This also means that the pilot

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                                Flight Simulators


and copilot will see different images out of the same window of the cockpit at
the same time.


To further enhance the realism of the images produced, a wide range of visual
effects are able to be produced. These include shadows, sun glare and
motion blur, while accounting for reduced visibility due to fog as well as
raindrops on the windscreen. An example of such as setup is shown below in
figure 13, which is a simulator used to train pilots in the Boeing 777




               Figure 13 - The cockpit of a Boeing 777 flight simulator



Many simulators have large areas of the earth graphically modeled, able to be
displayed at different quality levels depending on the desired application.
NASA have modeled the entire globe at relatively low quality for use in their
aerospace simulators, while still having high graphical models of desired
areas and locations, including individual buildings and countryside, for use in
low level flights.


These advanced graphics systems are also backed up with sound simulation,
capable of reproducing all sounds audible in the cockpit. This includes sounds
produced due the aircraft itself, such as engine noise, as well as those which
would be produced by the surrounding environment such as wind and rain.
The simulated noises are produced by synchronizing a range of prerecorded
sounds with the computer system, allowing the sounds to vary with the aircraft
and environmental conditions.




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4.3 Flight Instruments and controls:


The type of simulator will determine the required detail of the flight
instruments and controls. In a training simulator, the cockpit is required to be
an exact replica of the real aircraft, whereas simulators designed for testing
and research often require much less attention to detail in the cockpit layout.


Training simulators are built using as many real flight instruments and controls
as possible. They will commonly use real throttle controls, control sticks,
switches, pedals, helmets and seats. The flight controls must accurately
measure the pilots input as well as provide realistic feedback. Just like the
rest of the simulator, the controls should respond just like they would in a real
aircraft in the given situations. The simulation system should be able to
incorporate different control stick setups and designs that are used in different
aircraft such as those for transport aircraft, fighter jets and helicopters. The
response characteristics of these controls and more can be altered to
simulate different aircraft often just by changing the governing computer
program.




   Wheel and Column        Center Stick             Side Stick

            Figure 14 - A range of different control sticks used


However, not all equipment can be replicated perfectly. Instruments such as
the altimeter, which rely on environmental pressure differences to determine
the aircrafts altitude, are not able to be implemented into the simulated
system. Therefore, the readouts for these instruments are determined by the

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simulators computer system. This information can either be used to drive
small servomotors in the altimeter or the desired output can be displayed on
an electronic display unit that replicates the visual appearance of the real
instrument. The use of these digital displays in flight simulators allows for
greater flexibility in the overall design as they can be used to replicate a wide
range of both analogue and electronic instruments. Providing these displays
reach the required standards, the same displays can be used to simulate a
range of different aircraft cockpits.


Another type of display being incorporated into simulators are the head-up
displays (HUD’s). This type of display is primarily used in military aircraft, as
the information is displayed on screens in between the pilot’s eye and the
window. This allows the pilots to view vital information without the need to
remove their eyes from their immediate environment. The idea of the HUD is
also being incorporated into the helmets of the pilots, making the display like a
lense of a pair of glasses, allowing the information to be viewed, independent
of the direction the pilot is looking. The display can be used during bad
weather, especially for poor visibility, to show the pilot guidance information
needed to land. The use of these displays in simulators allows pilots to
familiarize themselves with this technology in a safe and secure environment.
An example of the helmet mounted display can be seen in figure 15 below.




                          Figure 15 - Helmet Mounted
                                Display (HMD)




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4.4 Interchangeable cab (ICAB)

The ICAB is a design idea being used by NASA for its aerospace simulators.
This design allows the cab, or cockpit, of the simulator to be removed from the
motion base. This gives NASA the option to test multiple vehicles, using a
single motion base and without having to redesign the cockpit. All that is
required is that they change the cab that is fitted to the only motion base.


Other fixed-base labs are used during the set-up of an ICAB, allowing all parts
of simulation to be tested except for the motion. This ensures that the system
is operating as desired, before it is fitted to the motion base. Therefore,
multiple setups can be tested, whilst still only using a single motion base. This
is critical when cutting down space, time and money required for experiments
and thereby increasing the efficiency of the system.




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5. The Working of a Flight Simulator
The primary aim of using a flight simulator is to have a system that can
accurately replicate the flight of an aircraft in real time without the expense or
danger of actually putting an aircraft in to flight. In order to do this the designer
of the flight simulator must take in to account all the real time variables that an
aircrafts flight is parameterized by.
This section will take a brief look at the parameters of flight that have to be
considered in order to emulate real time flight in a simulator.




5.1 Coordinate Systems for Modelling
Before the specifics of the simulator can be discusses it is crucial to define a
reference on which the parameters of the simulator will be applied. The most
important reference is the craft itself, more importantly the complete
description of the orientation of the craft is a fundamental reference. The
simplest coordinate system in use today is a fixed coordinate system with the
body (the aircraft) as the point of reference




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5.1.1 Body Coordinates

The non-inertial body coordinate system is fixed in both origin and
orientation to the moving craft. The craft is assumed to be rigid.
The orientation of the body coordinate axes is fixed in the shape of
body.

      •    The x-axis points through the nose of the craft.
      •    The y-axis points to the right of the x-axis (facing in the pilot's direction of
           view), perpendicular to the x-axis.
      •    The z-axis points down through the bottom the craft, perpendicular to the xy
           plane and satisfying the RH rule.

Translational Degrees of Freedom.                Translations are defined by moving along
these axes by distances x, y, and z from the origin.
Rotational Degrees of Freedom. Rotations are defined by the Euler angles P, Q,
R or Φ, Θ, Ψ. They are:
P or Φ Roll about the x-axis

Q or Θ Pitch about the y-axis

R or Ψ Yaw about the z-axis




5.1.2 Wind Coordinates

The non-inertial wind coordinate system has its origin fixed in
the rigid aircraft. The coordinate system orientation is defined
relative to the craft's velocity V.


The orientation of the wind coordinate axes is fixed by the
velocity V.


  •       The x-axis points in the direction of V.
  •       The y-axis points to the right of the x-axis (facing in the direction of V),
          perpendicular to the x-axis.
  •       The z-axis points perpendicular to the xy plane in whatever way needed to
          satisfy the RH rule with respect to the x- and y-axes.




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Translational Degrees of Freedom.          Translations are defined by moving along
these axes by distances x, y, and z from the origin.

Rotational Degrees of Freedom. Rotations are defined by the Euler angles Φ, γ, χ.
They are:


Φ Bank angle about the x-axis

γ Flight path about the y-axis

χ Heading angle about the z-axis


5.2 Parameters of flight
As an aircraft flies through the air in real time its flight will be influenced 3
major factors. First and most importantly the environment in which it flies. This
will include the not only the atmospheric conditions but where on earth it is
actually flying ( the gravitational field) its exact location will also affect the
navigational instrumentation on board and this is another factor that has to be
taken into account. The second factor that will affect the flight regime will be
the aircraft itself, in other words the design of the aircraft. In this ‘factor’ we
are considering firstly the aerodynamic model of the aircraft secondly the
thrust that the aircraft can generate and thirdly the inertial forces that the
aircraft experiences in flight. The last factors that will affect the flight of the
aircraft are the common laws of physics. In other words the input of the other
two factors will be filtered through the ‘equations of motion’ of the aircraft and
result in a real time flight model.
**In order to construct an accurate simulator it is imperative that we
understand these factors and consequently find a way to model these
characteristics. **

5.3 Flight environment variables: The atmosphere
One of the key requirements of any simulator is the ability of the simulator to
accurately replicate a flying environment in real time. Even if all other flight
parameters of flight have been replicated to perfection if the environment in
which the aircraft is flying cannot be replicated the functionality of the
simulator is rendered useless.



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5.3.1 Flight environment parameters
The mission profile of any aircraft will take it through several key stages and
hence environments. These stages include;
   •   Taxi/ takeoff
   •   Climb
   •   Cruise
   •   Descend/ Loiter
   •   Land

Even though the stage of flight may vary it is only the value of the variables
that will change and not the variables themselves. Now although the list of
variables may not be absolute it serves as a list of fundamental variables that
have to be considered when designing the simulator. The variables can be
considered as blocks that have inputs and corresponding outputs. The inputs
would be influenced by the stage of flight of the aircraft and the output would
be calculated through standard aeronautical knowledge and the given input,
hence providing raw data for the simulated flight characteristics.

5.3.2 Standard atmosphere
The standard atmosphere would take into account the air parameters at the
current altitude. The input to this block would be the current altitude above
the Mean Sea Level in meters. From here the processor could use simple
interpolation from stored data tables to provide the static pressure (p in Pa),
the outside air temperature (T in K), the air density (ρ in kg/m3) and the speed
of sound (a in m/s).

5.3.3 Background wind
Background wind plays a critical role in the handling and trimming of the
aircraft in flight. This block would capture the effects of time varying
background winds which are encountered in weather condition such as wind
shears and thermals. Inputs would have to include the source of the wind
relative to an inertial frame as well as the orientation of the aircraft relative to
this frame of reference. The output to this block would include the wind
velocity components again relative to this frame and the acceleration
components of the wind forces to create a dynamic model.

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5.3.4 Turbulence
Continuous wind turbulence can be generated in a simulator using a Von
Kármán velocity filter.The Von Kármán Wind Turbulence Model uses the Von
Kármán spectral representation to add turbulence to the model by passing
band-limited white noise through appropriate forming filters. This is the way
turbulence is simulated in the Matlab Aerospace Blockset. The block would be
parameterized by the sample time for the white noise sources. Inputs to the
block would include the wind velocity vectors the current altitude of the aircraft
and the background velocity of the model.
The output with be a 3D vector describing the turbulence vector. It is
important to note that the Von Karman turbulence filter applies to the
longitudinal, lateral and vertical components of turbulence and hence uses 3
white noise sources. Thus the background wind vector and aircraft altitude are
critical factors that are needed in the calculation of turbulence.

5.3.5 Wind shear
The wind shear affects the pitch and the yaw. The pitch rate due to wind
shear can be computed using equation 1 and the yaw rate by equation 2.


                          (1)


                         (2)
The wind shear block is an important factor to have when considering the
angular rate effects caused by the variation in time/space of the background
wind /turbulence velocities. The inputs for its calculation would include the
wind acceleration vector the turbulence vector and the velocity of the aircraft.
A suitable output would be the wind angular rates.




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5.4 Flight environment variables: The Earth
WGS-84
Of equal importance to identify flying the conditions the craft is flying in is to
fully describe the orientation of the craft and its position relative to a reference
coordinate system.
Currently in use in open source simulators is the WGS-84 earth model. This
block computes the earth’s radius and gravity at its current location using the
WGS- 84 earth model coefficients.


It is also important to note that
current open source simulators
use     the    right-handed   (RH)
Cartesian coordinate systems.
The right-hand rule establishes
the     x-y-z     sequence      of
coordinate axes
The variable inputs to this
block         would    be      the
geographical position given by
the aircrafts longitude, latitude
and altitude. The outputs would
be the meridian radius the normal radius and the equivalent radius as well as
the gravitational constant at that point. These parameters can be calculated
using the following mathematical relationships.




The WGS 84 constants include;




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Φ represents the latitude of the aircrafts current location.

5.5 Flight control variables: The aerodynamic model

Given the atmospheric model (i.e.
the environment in which the
aircraft will fly) the next most
important factor is to define the
aerodynamic parameters of the
aircraft    itself.     In    terms        of
aerodynamics there are several
key components of flight. The
aircraft    aerodynamics           can    be
modelled      in      terms   of    blocks;
dynamic variables as inputs and force vectors as outputs. The aerodynamics
of the aircraft can be sub divided into two distinct groups: aerodynamic force
and aerodynamic moment.

Aerodynamic force
In order to calculate the force that acts on the airframe of an aircraft, a block is
needed that takes into account the aerodynamic force coefficients and the
dynamic pressure. The block will be parameterized by the wing reference
area.
Inputs to this block would include the drag coefficient (CD) the side force
coefficient (CY) the lift coefficient (CL) the dynamic pressure (q) and a vector
fully describing the wind velocity. This vector would be characterized by the
airspeed the angle of attack and the slide slip angle.

FORCE COEFFICIENTS
Lift coefficient



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Drag coefficient




Side force coefficient




The equations above are the textbook standard for calculating the coefficients
needed.
The forces are calculated using the following expressions:




The output to this block would be a vector describing the aerodynamic forces
on the body.

5.5.1 Aerodynamic moment
The aerodynamic moment is another key component when considering the
aerodynamic forces on the airframe. In this case the aero dynamic moment
coefficients and dynamic pressure have to be taken into account. This block
will be parameterized by the following factors;
   1. Mean aerodynamic chord- the reference chord with respect to which pitch
       moment coefficients will be computed
   2. Wing span- the reference wing span with respect to which the roll and yaw
       moment coefficient will be computed
   3. Wing reference area- the reference area with respect to which the moment
       coefficients will be computed




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MOMENT COEFFICIENTS
Pitch moment




Roll moment




Yaw moment




The aerodynamic moment block would use the following inputs; the roll
moment coefficient, the pitch moment coefficient and the yaw moment
coefficient as well as the dynamic pressure. The following equations would be
used to calculate the aerodynamic moments.




Note: it is important to note that the defining the parameters of the block is
crucial before the inputs to the block can be defined. The roll moment, pitch
moment and yaw moment are defined with respect to the aerodynamic centre
of the wing and hence the current aerodynamic centre must be defined first
before the block will have a useful output.
Details on the calculation of the force and moment coefficients can be found
with the references.




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5.6 Flight control variables: The Propulsion model
Modelling the aircrafts thrust is crucial in defining the overall response of the
craft when the pilot changes the throttle. However it is important to note that
when we consider the overall propulsion of the aircraft it includes more
variables than simply the overall change in thrust. Depending on the accuracy
some if not all the variable listed below has to be taken into consideration.
Once again the propulsion model can be modelled as a block with parameter
that constrain the block and inputs which are user controlled in the simulator
and an output which manifests itself as the response of the aircraft in the
simulator environment.
The general aviation system is a block system that can be used to model the
propulsion system for a fixed pitch propeller. At this stage we shall limit the
analysis of the system to fixed pitch propeller d aircraft. Key parameters of
this block would include:
    •   The initial engine speed
    •   The engine speed data points (i.e. its RPM as a vector)
    •   The manifold pressure
    •   A fuel flow look up table
    •   A power look up table
    •   The sea level pressure
    •   The sea level temperature
    •   The advanced ratio (j)
    •   The coefficient of thrust
    •   The coefficient of power
    •   The propeller radius
    •   The propellers moment of inertia
    •   The engines moment of inertia (the moment of inertia of the rotating part of
        the engine)


With these parameters defined the block is sufficiently constrained to compute the
relevant output for a range of given inputs.
Inputs to this block would include
   •    Throttle level


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   •   Mixture
   •   Ignition (on or off)
   •   Atmospheric pressure
   •   Atmospheric temperature
   •   Air density
   •   Wind velocity vector (as calculated earlier)


With these variables as the inputs the simulators core processor would be able to
process the propeller thrust and propeller moment. This in turn would then be
translated to motion (depending on what category of simulator was in use to either
physical movement of the simulator cabin or movement on the window display.
In general the propulsion block is used to compute the forces and moment that are
applied to the aircraft. These forces will depend on the engine control inputs,
atmospheric conditions, altitude and airspeed. In real flying conditions these
variables are present and ever changing, however in the simulator they have to be
defined in order to simulate true flying conditions as accurately as possible.




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5.7 Flight control variables: The Inertial model
Ultimately the simulator processor will rely not only on the environmental
inputs but on the definition of the craft itself. As an aircraft fly’s its burns off
fuel constantly changing is weight and more importantly its centre of gravity.
In real time flight the pilot can feel this as the angle of attack changes,
however in simulated flight this is not an innate parameter and has to be
modelled. This is where the inertial model plays a pivotal role in the overall
success of the aircraft simulator.
The inertial block of the simulator integrates the fuel consumption of the
aircraft to obtain the aircrafts inertia parameters. That is its mass centre of
gravity location and its moment of inertia.
However as always, the block has to be constrained by various parameters, in
order to ensure its congruence to real time flight.
In real time flight the following parameters would constrain the way in which
the centre of gravity of the aircraft would change as fuel was burn off and
hence must be considered when constructing the simulator, in particular when
constraining the way in which the simulators processor interprets the flight
model.
Key parameters include:
   •      Initial fuel mass
              o   How much fuel did the aircraft start off with
   •      Empty mass
              o   The mass of the aircraft without any fuel
   •      Gross mass
              o   The aircraft mass with a full tank of fuel
   •      The centre of gravities location (gross weight)
   •      The empty moment of inertia
   •      The gross moment of inertia

With these parameters constraining the block and with the fuel consumption
rate as the input, there is sufficient information to calculate the aircrafts
current mass , the centre of gravities position and the moment of inertia
vector.      The inertia parameters are computed using linear interpolation

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between the empty and the gross aircraft inertia parameters based on the
aircrafts current mass. This can then be fed in to the simulators process and
give the desired simulated effect.

5.8 Equations of Motion
In real time flight the laws of physics apply unconditionally. In order for the
pilot flying in the aircraft to get the feeling that he is really flying the craft these
laws have to be replicated with the highest precision using all the pre
calculated variables. In essence all the blocks which were formulated earlier
are brought together using the standard equations of motion.
The equations of motion are a set of differential equations that fully describe
the dynamics of the aircraft, in other words they are the basis of the simulator.
The simulator uses these equations to ‘determine’ how the aircraft will
respond to different inputs form the operator and the change in parameters.

5.8.1 Total Acceleration
The acceleration applied to the airframe as a result of the aircrafts
aerodynamics and propulsion gives the simulator a bearing of the airframes
total acceleration. In open source code simulators the inputs to this block
would simply be the aerodynamic force vector derived earlier, the propulsion
vector and the mass of the aircraft.
Computed simply the equation below, the output to the simulators processor
would simply be the acceleration vector. This intern would be processes to
modify the panel readings and the orientation of the craft on screen




5.8.2 Total Moment
Just as the force block calculated the overall forces on the aircraft, the
moment block computes the moments applied to the airframe using
aerodynamic inputs and propulsion inputs. The principles are the same as the
force block however with the moment block the following parameters will
apply.

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   •   The aerodynamic force application point must be specified.
   •   The propulsion force application point must be specified.

Unlike in real time flight where there is only one point where this force could
possibly act given that the laws of physics are universal with a computer
simulated flight model, if these points are not specified the model would not
work as the processor would have no reference to apple the relevant forcer
vectors.
Inputs to this block would include all the force and moment vectors previously
defined as well as the crafts centre gravity.
The moments in the craft can be calculated simply by




5.8.3 Structure Euler Angles
Given that the aircraft has 6 degrees of freedom in real flight and the simulator
is trying to emulate this as best it can, the angular rate of the aircraft must be
obtained
This section of simulation control begins to go beyond the scope of this paper,
nevertheless the principle of emulating the system remain the same.
In the case of the Euler angles the angular rates would have to be treated as
inputs and the Euler ands as outputs.
The angles can be calculated in part by the equation below.




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5.9 Modelling Flight in a Simulator
This section of the report has aimed at giving the reader an insight into the
variables that the designer of the simulator must consider when trying
emulating flight in real time. The truth of the matter though is that this is only
the first step in creating a fully operational simulator. Once flight can be
defined mathematically the arduous task of physically simulating flight in a
ground based simulator still has to be tackled. The following section of the
report will look at the physical simulator itself and their key features




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6. Limitations of flight simulators
The development of the flight simulator is an important development in the
history of aeronautical engineering. It allows the novice to handle and pilot
various types of aircraft in a simulated environment, which is usually too
dangerous to perform in the real world without any prior experience or training.
However, flight simulators are at the same time far from a perfect technology.
Various imperfections and shortcomings still exist which may pose problems
and limitations to how well flight simulators can fulfil their intended purposes.
To develop a more complete understanding of flight simulator technology,
their limitations must be discussed as well.


As different types of flight simulators have been designed for various
purposes, the types of problem encountered, and their respective causes and
effects differ as well. Research has been carried out into the typical limitations
faced by two fields of application of flight simulators, namely pilot training, and
flight simulators for electronic entertainment purposes.



6.1 Simulator Sickness

Virtual Reality (also known as Virtual Environment or VE) technology shows
many promising applications, and is used intensively in flight simulators due to
their intrinsic nature. A potential threat to using this technology is the mild to
severe discomfort that some users experience during or after a VE session.
Similar effects have been observed with flight and driving simulators. The
simulator sickness literature forms a solid background for the study of
sickness in virtual environments and many of the findings may be directly
applicable. Forty factors, which may be associated with simulator sickness in
virtual environments, have been identified.


Although there is debate as to the exact cause or causes of simulator
sickness, a primary suspected cause is inconsistent information about body
orientation and motion received by the different senses, known as the cue

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conflict theory, as documented by Kolasinki (1995). For example, the visual
system may perceive that the body is moving rapidly, while the vestibular
system perceives that the body is stationary. Inconsistent, non-natural
information within a single sense has also been prominent among suggested
causes.


Although a large contingent of researchers believe the cue conflict theory
explains simulator sickness, an alternative theory was reviewed as well. Forty
factors shown or believed to influence the occurrence or severity of simulator
sickness were identified.


To emphasize the significance of simulator sickness, Crowley (1987)
identified four important consequences: aversion to and/or decreased
simulator use, compromised training, ground safety and flight safety.
Ineffective simulator use may result from pilots who have undergone such
symptoms and are hence unwilling to repeat the experience. Training may be
compromised in one of two ways. First, simulator sickness can potentially
distract the pilot during the session, interfering with the training process;
second, pilots may train themselves to develop behaviours to mitigate motion
sickness in the simulator which, if transferred to actual aircraft, may be
detrimental. Ground safety in terms of exiting the simulator or driving away
from the site may also be jeopardized by after effects from the motion
sickness effects of the simulator. These effects and adopted behaviours can
be potentially undesirable or dangerous when pilots turn to operating actual
aircraft.




6.2 Simulation of G forces

Another one of more important limitations of current flight simulators is the
usage of a motion base. While a motion base imparts sensation to the trainee
pilot of aircraft orientation and position, it has the drawback of being unable to
simulate gravity forces, which are generated when a real-world aircraft

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undergoes acceleration. Generally speaking, pilots of commercial passenger
aircraft do not experience any significant G-forces while piloting their vehicle,
since 60 degrees, which causes 2G of force, is the maximum banking angle to
minimize the discomfort of passengers in commercial airplane flight.




           Figure: G-forces corresponding to Angle of Banking
                                  Source from
    http://www.aerospaceweb.org/question/performance/q0146.shtml


However, pilots who operate fighter aircraft will usually take at least 4G in
their flight, and this is a phenomenon difficult to replicate in flight simulators,
as the machine is stationary and not in a state of acceleration. There are
several shortcomings to this. First, the flight simulator is unable to fully
replicate situations which will occur when the pilot operates an actual aircraft,
which decreases the effectiveness of the simulation. Secondly, G-forces at
higher magnitudes have considerable effects on the human body; high G-
force can force blood into the lower part of body and then cause local hypoxia
in higher parts of the body such as the brain. Such a condition can easily
induce tunnel vision or the pilot blacking out and losing consciousness. For


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this reason, most flight simulators that rely on a motion base to simulate
motion and are hence unable to reproduce G-forces are inadequate to provide
a pilot with fighter aircraft training; for example, in actual combat manoeuvres,
G-forces can cause a pilot's arm to feel four times as heavy, in addition to the
above-mentioned problems. Strictly speaking, current simulators are suitable
to not military tactical flight but the instrument flight or emergency training.



6.3 Simulation of Radio Communications

One of the widely recognized deficiencies of fight simulators is the current
state in the art of realistic radio communications. Currently, the way such
simulations are handled is by a pilot instructor/evaluator (I/E), who has the
role of operating the simulator and observing the performance of the trainee
pilot while at the same time carrying out such communications with the trainee.
This   is   a   vastly   simplified    representation   of   the      real-world   radio
communications that a pilot faces when operating an actual aircraft, and does
not even begin to approach the challenges of hearing, acknowledging and
adequately responding to radio communications with multiple operators and
other pilots within a real-world environment.


According to Longridge et al 2001, information was collected from 29 I/Es
from 14 AQP airlines, including seven major, one cargo, four regional, and
two foreign airlines in an attempt to determine the magnitude and extent of
this issue. I/Es were queried about their simulation of different events,
including   ATC    (tower,    approach/departure,       en   route)     and   company
communications (dispatch, ramp, maintenance, flight attendants) to own
aircraft, ATC communications to and from other aircraft or ground vehicles
(the so-called party line), as well as visual representation of other traffic.


A first finding was that the method of simulating radio communications is
indeed almost exclusively I/E role-play, where the I/E issues instructions and
responds from his station directly behind the crew. I/Es were asked to indicate
their allocation of time and effort between running the simulation, simulating

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radio communications, instructing and observing. According to the survey,
I/Es spend about 50 percent their time and effort observing, twenty percent
each role-playing radio communications and operating the simulator, and less
than ten percent instructing. As expected, I/Es indicated that their workload is
consistently higher for training and in the simulator than in the actual aircraft
with real communications minus the need to operate a simulator at the same
time. On the other hand, they feel that the communications workload of the
pilots is significantly reduced. One I/E indicate that even the manual workload
of pilots is reduced, because “[p]pilots are not normally given a chart
frequency, nor do they need to redial a new frequency to communicate.” The
surveyed I/Es emphasized the importance of radio communications simulation
in order to effectively teaching such skills as (new) ATC procedures, Crew
Resource Management (CRM) and situation awareness. The overall
importance of radio communications is perceived highest in the terminal
environment. I/Es concern with simulating radio communications may have
best been     summarized by the I/E who stated: “Without         communication
simulation, when the pilot trainee finally arrives in the ‘real world,’ he must
add another      component…This new (additional) component can             really
complicate line flying.”



7. Future Flight Simulator Developments


Despite their widespread usage in multiple areas of aeronautics, the
usefulness of flight simulator technology is still hampered by several
shortcomings and limitations as discussed earlier. Research is continually in
progress to improve upon the scope and application of flight simulators, with a
few of the newest developments discussed here.



7.1 Centrifuge-based Motion Flight Simulators




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As its name implies, a centrifuge-based motion flight simulator uses a
centrifuge to simulate motion instead of a motion base in an attempt to
reproduce the G-forces encountered in actual flight. While various models of
such flight simulators have already been experimented and produced by
several companies, the basic operating principle behind the centrifuge-based
flight simulator is essentially the same. The cockpit of the flight simulator is
fixed at one end of an arm with a counterweight at the other end of the arm,
which is split in half like bicycle forks. The arm revolves around a central pivot,
supported by a vertical column in a spherical room.


When the simulation starts, the arm is vertical and will begin to rotate, with the
cockpit at the top counter-rotating to keep it stationary. As the simulated
aircraft encounters a force, the arm moves outwards to simulate the amount
of force, and the orientation of the cockpit will change to represent the
direction of the force.




          Model 2015-C Human Centrifuge, by Wyle Laboratories
                                  Source from
http://www.wylelabs.com/products/aeromedicaltrainingequipmentandfacilities/
                          dynamicflightsimulators.html


Several such flight simulators are already in use; for example, the model
produced by Wyle Laboratories, as shown in the above figure, are purportedly
already used by the Royal Canadian Air Force for pilot training. Manufacturer
claims are that such flight simulators are more realistic than fixed-
base/motion-based simulators, which are mostly unable to replicate G-forces.

                                  Page 50 of 54
                                 Flight Simulators




7.2 Synchronized Real-time Radio Communications

As discussed earlier, real-time radio communications continues to be one of
the major problems plaguing the effectiveness of flight simulators for pilot
training purposes. Given all the evidence of the problems posed, it is not
surprising that both airlines and simulator industry are striving to improve the
realism of simulated radio communications. As documented by Longridge et
al, 2001, one of the most operationally realistic efforts produced to date is
United Airlines’ Interactive Real Time Audio System (IRAS). By using field
recordings of actual air traffic control communications, including both
communications to own and to and from other aircraft with controller voices
dubbed with the individual instructors' voices, pilots undergoing simulator
training are fed with the most realistic radio communications possible.
Unfortunately the system is no longer operational due to high scenario-
development, integration and instructor-training costs.


Again according to Longridge et al, CAE, a Canadian simulation manufacturer
has developed the Ground Air Traffic Environment System (GATES) after a
request from a foreign airline to provide a visual representation of traffic in the
airport terminal environment. It quickly became apparent that correlated and
meaningful radio communications would have to be an essential component
of such traffic representation if realism is to be maintained. The
instructor/evaluator (I/E) still provides all ATC communications to one airplane,
however. It is reported that several foreign airlines, training facilities and even
military are currently equipping their simulators with GATES. Lufthansa and
the   German     ATC    organization    Deutsche     Flugsicherung    (DFS)    are
collaborating on Joint Operational Incidents Training (JOINT). Up to eight
Lufthansa simulators can be linked to two DFS ATC control sector simulators,
resulting in highly effective recurrent training of both pilots and controllers.
Each ATC simulator consists of a controller work station with a radar display

                                  Page 51 of 54
                                 Flight Simulators


showing the simulated airplanes flown by the flight simulator crews as well as
other airplanes sharing the same airspace operated by a pseudo pilot sitting
at a connected computer station.


A   similar,   multi-linking   concept   to   simulate   authentic   multiple-end
communications has also been explored by Environmental Tectonics
Corporation, with its development of the Battle Space system. By
electronically linking multiple pilots in different flight simulators together in a
shared virtual environment, the system sends and receives information from
the connected flight simulators to create a real-time common situation for all
trainee pilots involved.




                                   Page 52 of 54
                                Flight Simulators


References:

2. Federal Aviation Administration, Airplane
Flight Training Device Qualification, Advisory
Circular 120-45A, 5 February 1992.


http://gabbai.com/academic/the-art-of-flight-simulation/


www.faa.gov/safety/programs_initiatives/aircraft_aviation/nsp/flight_training/fa
qs/media/Sim_Levels.doc


http://www.atlantissi.com/products/ftd/


http://www.cae.com/www2004/Products_and_Services/Civil_Simulation_and_
Training/Simulation_Equipment/Simfinity/ipt.shtml


http://www.pprune.org/forums/archive/index.php/t-271935.html


http://72.14.253.104/search?q=cache:R_pkIPdRa2MJ:www.airweb.faa.gov/Re
gulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/5b7322950dd10f6b8
62569ba006f60aa/%24FILE/Appx1.pdf+FAA+Appx1.pdf&hl=en&ct=clnk&cd=
3&gl=au


http://www.faa.gov/safety/programs_initiatives/aircraft_aviation/nsp/


http://ffc.arc.nasa.gov/vms/vms.html


Kolasinski EM 1995, 'Simulator Sickness in Virtual Environments', U.S. Army
Research Institute, Technical Report 1027


Crowley, JS 1987, ‘Simulator sickness: A problem for Army aviation', Aviation,
Space, and Environmental Medicine, vol. 58 no. 4, pp. 355-357



                                 Page 53 of 54
                                Flight Simulators


Scott J 2003, 'Bank Angle and G's', Aerospaceweb.org, viewed 30 September
2007 <http://www.aerospaceweb.org/question/performance/q0146.shtml>


Longridge T, Burki-Cohen J, Go TH, Kendra AJ 2001, 'Simulator Fidelity
Considerations for Training and Evaluation of Today's Airline Pilots', in
Proceedings of the 11th International Symposium on Aviation Psychology,
Columbus, OH: The Ohio State University Press


www.wylelabs.com 2003, 'Dynamic Flight Simulators', viewed 29 September
2007
<http://www.wylelabs.com/products/aeromedicaltrainingequipmentandfacilities
/dynamicflightsimulators.html




                                 Page 54 of 54

				
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