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Several types of flight simulators and flight training devices are used for pilot training. At the basic level, there are the comparatively simple Part-Task Trainers. These are used for training involving one or more aircraft systems. Also at the basic level are the Cockpit Procedures Trainers, which are used for practising drills and checks (e.g. pre-take off checks). At the other end of the scale are the Full Flight Simulators, which, in the most sophisticated versions, can move in all six degrees of freedom thanks to a six-jack motion platform and have wide-angle collimated visual displays.
The six degrees of motion that these Full Flight Simulators are capable of involve the three linear movements and the three rotations that are possible in three-dimensional motion (i.e. motion in air, water or a vacuum). These degrees of motion are yaw, pitch, roll, heave, surge and sway, although the latter three occasionally go by other names. Yaw moves the nose of the aircraft clockwise and anticlockwise; Pitch moves the nose up and down (these two motions are possible in a motor car); Roll is the classic "barrel roll" manoeuvre where one wing goes upward and the other downward. Heave, Surge and Sway are linear motions that occur with the aircraft remaining level and travelling in a straight line, with heave being and up and down motion (bouncing or bobbing), sway involving side to side motion, and surge involving speeding up and slowing down.
Flight simulators are used to train flight crews for normal operating procedures and also emergency procedures. For obvious reasons, the emergency procedures cannot be tested in flight. Flight simulators can be used to train for failures and malfunctions of the engine or systems, for example electrical systems, hydraulics, pressure, instruments, etc.
Because of their crucial role in emergency procedure training and training in general, flight simulators are subject to strict regulation and safety checks international. Air safety bodies such as the European Aviation Safety Agency and the US Federal Aviation Administration have to certify and test simulators to ensure that they meet the required standards for each category. Naturally, a Full Flight Simulator used for testing new avionic equipment has to meet much tighter criteria than a basic Cockpit Procedure Trainer. Commercial pilots can only log required training time in simulators that are certified by their controlling authority. For a simulator to be officially certified, the testers must be satisfied that its performance matches that of the airplane that is being simulated, according to the criteria required by the category that the flight simulator is intended to fit. These criteria are explained in test guides referred to as Approval Test Guides or Qualification Test Guides. Simulators can be classified as Level 1-7 flight training devices or Level A-D Full Flight simulators, with Level D Full Flight Simulators being the most sophisticated. Level D Full Flight Simulators are used for what are known in the industry as zero-flight-time conversions, where an experience pilot can obtain his/her type rating for a new variety of aircraft (provided it is similar to what the pilot is already qualified for, e.g. converting from a Boeing 757 to a Boeing 767) without having any "air time" until they make their first commercial flight – under close supervision.
A trainee pilot will probably encounter several types of flight simulator during his/her training. Firstly, system trainers are used to teach pilots how to operate various aircraft systems. After he/she has become confident and familiar with the aircraft systems, they will move on to cockpit procedures trainers, which are cockpit instruments, switches and other controls, and are used to train flight crews in the routine checks and drills. Trainee pilots and air crew may also be trained on other, more sophisticated simulators, with the highest level of these being the 'mini simulators'. These flight training devices may or may not have visual displays (if they do, the displays will not have the fidelity of the Full Flight Simulators), and they do not have any motion modelling.
A feature common to most simulators is an Instructor Operating Station (IOS). An IOS allows an instructor to create a condition that the trainee must cope with, whether routine or untoward. Depending on the instructor’s focus, he/she can set the simulator so the trainee has to cope with engine fires, malfunctioning landing gear, electrical faults, bad weather conditions (including lightning), oncoming aircraft, slippery runways, navigational system failures or any other situation that pilots and air crew have to be able to cope with. The instructor may be seated in the cockpit, either behind the pilot(s) or in the co-pilot’s seat, depending on whether a co-pilot is being trained or not.
A Full Flight Simulator is the ultimate in virtual reality, as every aspect of real flight is simulated with a very high level of realism, including motion. As the motion jacks can simulate all six degrees of freedom in motion, seatbelts must be worn in this type of flight simulator. However, simulating surge is often limited, so only the onset of acceleration (and the resultant G-forces experienced) can be mimicked so as to prevent the limits of the motion jack being exceeded.
Full Flight Simulators were once limited to multi-million dollar hydraulic devices and only found at the larger training centres, such as those of the major airlines. But nowadays, electric motion platforms have been perfected so they can be used in Full Flight Simulator at a lower cost than hydraulic systems. This has allowed Full Flight Simulators to be made and used for smaller aircraft at other training centres.
Flight simulators are used for research in various areas within the general aerospace field, with two of these areas being flight dynamics and human-machine interactions. The most expensive and sophisticated research flight simulator is the LAMARS simulator located at Wright-Patterson Air Force Base, Ohio. Built by Northrop for the Air Force Research Laboratory, this simulator has dome-mounted 360 degree visual displays and a large motion system with five degrees of freedom.
About 1200 civilian Full Flight Simulators are in use around the world today, with the USA having the greatest number (550). The UK has 75 full flight simulators; China has 60, with Germany, Japan and France coming next with 50, 50 and 40 full flight simulators, respectively.
The leading manufacturers of civil (not military) Full Flight Simulators include FlightSafety International (FSI), Rockwell Collins and Opinicus in the USA, CAE Inc. and Mechtronix in Canada, Thales in France and the UK. Thales’ UK site is the ex-Rediffusion simulator factory at Crawley located near Gatwick airport. CAE seems to be the largest manufacturer of civilian Full Flight Simulators, having made 450 of the 1200 in use, wthi Thales (or its predecessor Rediffusion) and Flight Safety being the next most significant.
Flight simulators are a vital part of pilot and flight crew training, saving lives, money and time. Even the costliest Level D Full Flight Simulator costs much less for training a pilot than the same training provided in an actual aircraft, with a cost ration of 1:40 being reported for Level D simulator training compared to real-flight training in a Boeing 747 Jumbo.
Modern High-End Flight Simulators
Psychologists tell us that motion sickness is caused partially by conflicting cues between visual and motion stimuli. What is more, we tend to feel a change in motion before we see it – the G-forces begin acting on us before we actually move. This is one of the reasons that the most sophisticated commercial and military flight simulators use motion bases or platforms to provide kinaesthetic stimuli. But preventing motion sickness is not the only reason: motion cues are vital in instrument flying, e.g. night flying or flying in cloud. Most moving simulators use variants of the six-jack Stewart platform (known as hexapods) to mimic the motion of an actual aircraft. Hexapods use six hydraulic jacks (hence the name) to allow the training capsule to undergo yaw, pitch, roll, heave, sway and surge. Hexapods, can allow up to ±35 degrees of roll, yaw and pitch, and one metre of heave, sway and surge. Even though the hexapods can only provide a limited amount of these latter three types of motion, they are still highly realistic. This is because the human body’s motion sensors (in the inner ear, whole-body movement sensors and muscle and joint sensors) are very sensitive to acceleration and is less able to perceive constant linear motion. This is why instruments are vital when flying in cloud: you could be steadily heading downwards and not know it. The hexapod can simulate the onset of acceleration, which is enough to suggest the appropriate change in linear motion.
Once a simulator has made the trainee feel the initial acceleration, the platform movement is backed off so that the physical limits of the jacks are not exceeded and the jacks are then re-set to the neutral position ready for the next signal from the pilot or the simulator. This backing-off from the initial acceleration is performed automatically by the simulator computer and is known as the "washout phase". "Washout algorithms" are carefully designed to ensure that washout and the later re-set to about neutral so that those using the simulator cannot feel it – all they feel is the force of the initial acceleration, a process know as "acceleration-onset cueing". In this way, someone using the simulator will experience all the bodily sensations that would be felt in a high-speed manoeuvre while the cabin itself is merely bobbing and swaying up and down on a platform.
These high-level techniques for simulating motion are used in civilian Level D Full Flight Simulators in their military equivalents. One of these is the Desdemona system developed and built by European companies AMST Systemtechnik (Austria) and TNO Human Factors (the Netherlands). This simulator can mimic sustainable g-force simulation and almost unlimited rotational motion due to its gimballed cockpit mounted on a framework that can add vertical motion and a rotating platform. Across the Atlantic, the Vertical Motion Simulator at the NASA Ames Research Center south of San Francisco is capable of simulating 60 feet (+/- 30 ft) of heave. This heave system supports a horizontal beam with forty-foot rails, allowing the simulator cockpit to undergo lateral movement +/- 20 feet. Added to this, the Vertical Motion Simulator incorporates a hexapod platform mounted on the 40 ft beam. This platform is designed to fit several interchangeable cabins, allowing many aircraft types to be simulated, from blimps to the Space Shuttle, plus both military and civilian aircraft. When simulating the Space Shuttle, the Vertical Motion Simulator was used to research a longitudinal Pilot-Induced Oscillation (PIO) that occurred on an early Shuttle flight just before landing, and ultimately led to the elimination of the problem. The realistic motion capacity of the Vertical Motion Simulator was a key part of replicating the oscillation, and has also been critical in simulating and eliminating roll-upset accidents that were experienced in Boeing 737s.
Ride Simulators
Flight Simulators have their fun side, too. In theme parks such as the Disneyland parks and the Universal theme parks, you can find flight simulator technology used for rides that give park guests an experience of simulated flight or motion.
Some of the theme park style flight simulators include:
* Soarin' Over California (Disney's California Adventure), which uses an IMAX dome screen and a hang-glider simulation allowing the user to “fly” over to scenic places within California;
* Star Trek: The Experience (Las Vegas Hilton), which features the "Klingon Encounter" flight simulator complete with six degrees of freedom motion stimuli accompanying space battle scenes for the visual stimuli;
* Back To The Future: The Ride (Florida and Hollywood Universal Studios, currently closed), which used simulated DeLorean cars and a 70ft tall IMAX dome screen for the visual cues. |
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