Flight simulator

A flight simulator is a system that tries to copy, or simulate, the experience of flying an aircraft. It is meant to be as realistic as possible. The different types of flight simulator range from computer based games up to full-size cockpit replicas mounted on hydraulic (or electromechanical) actuators, controlled by state of the art computer technology.

Use
Flight simulators are extensively used by the aviation industry for design and development and for the training of pilots and other flight deck crew in both civil and military aircraft.

Engineering simulators
Engineering flight simulators are also used by aerospace manufacturers for such tasks as:
 * development and testing of flight hardware. Simulation (emulation) and stimulation techniques can be used, the latter being where real hardware is fed artificially-generated or real signals (sTimulated) in order to make it work. Such signals can be electrical, RF, sonar and so forth, depending on the equipment to be tested.
 * development and testing of flight software. It is much safer to develop critical flight software on simulators or using simulation techniques, than development using aircraft in flight.
 * development and testing of aircraft systems. For electrical, hydraulic and flight control systems, full-size engineering rigs sometimes called 'Iron Birds' are used during the development of the aircraft and its systems.

World War I and on
A number of electro-mechanical devices were tried during World War I and thereafter. For example, learning to fire a machine gun requires that the pilot learn to lead targets, so a ground simulator was developed to teach this skill to new pilots. The best-known was the Link Trainer, produced by Edwin Link in Binghamton, New York USA and available from 1929. This had a pneumatic motion platform driven by bellows giving pitch, roll and yaw, on which a replica generic cockpit was mounted. It was designed for the teaching of Instrument (cloud) flying in a less hazardous and less expensive environment than the aircraft. After a period where not much interest was shown by professional aviation, the US Army Air Force purchased four Link Trainers in 1934 after a series of fatal accidents in instrument flight. The world flight simulation industry was born. Some 10,000 Link Trainers were used in the 1939-45 war to train new pilots of allied nations. They were still in use in several Air Forces into the 1960s and early 1970s.

The Celestial Navigation Trainer of 1941 was a massive structure 13.7 m (45 ft) high and capable of accommodating an entire bomber crew learning how to fly night missions. In the 1940s, analog computers were used to solve the equations of flight, resulting in the first electronic simulators.

Simulators in the civilian aviation industry
In 1948, Curtiss-Wright delivered a trainer for the Stratocruiser to Pan American, the first complete simulator owned by an airline. Although there was no motion modelling or visual display, the entire cockpit and instruments worked, and crews found it very effective. Full motion systems came in starting in the late 1950s.

The early visual systems used an actual small model of the terrain. A camera was "flown" over the model terrain and the picture displayed to the pilot. The camera responded to pilot control actions and the display changed in response. Naturally only limited areas of the ground were able to be simulated in this manner, usually just the area around an airport or, in military simulators, typical terrain and sometimes targets. The use of digital computers for flight simulation began in the 1960s.

In 1954, the Link Division of General Precision Inc. (later part of Singer Corporation and now part of L-3 Communications) developed a motion simulator which housed a cockpit within a metal framework. It provided 3 degrees (angle) of pitch, roll, and yaw, but by 1964 improved, compact versions increased this to 10 degrees angle. By 1969 airline simulators were developed where hydraulic actuators controlled each axis of motion, and simulators began to be built with six degrees of freedom (roll, pitch, yaw for angular motion and surge, heave and sway for longitudinal, vertical and lateral translation). Starting in 1977, airline simulators began adopting the modern "cab" configuration where computers are placed in the cockpit area (rather than in off-simulator racks), and equipment is accessed via a wraparound catwalk when the simulator motion system is inoperative.

Around this time great strides were also made in display technology. In 1972 Singer-Link developed a collimating lens apparatus, using a curved mirror and beamsplitter, which projected Out of The cockpit Window (OTW) views to the pilot at a distant focus. These collimated monitors greatly improved the realism of flight simulation. However, each monitor only offered a field of view of 28 degrees and several were needed for a realistic field of view. In 1976 wider angle collimated monitors (e.g. ) were introduced, so-called 'WAC windows' standing for 'Wide Angle Collimated'. Finally, in 1982 the Rediffusion company of Crawley, UK, introduced the Wide-angle Infinity Display Equipment (WIDE) that used a curved mirror of large horizontal extent to allow distant-focus (collimated) viewing by side-by-side pilots in a seamless display. For details, see the entry under 'Collimation'. WIDE-type displays are now universal in the highest levels of Full Flight Simulators for aircraft where two pilots are seated side-by-side.

Flight simulators and flight training devices
Various categories of flight simulators and flight training devices are used for pilot training. These vary from relatively simple Part-Task Trainers (PTTs) that cover one or more aircraft systems, Cockpit Procedures Trainers (CPT) for practicing drills and checks, to so-called Full Flight Simulators (FFS). The higher levels of Full Flight Simulators have motion platforms capable of moving in all six degrees-of-freedom (6-DoF). They also have wide-angle high-fidelity collimated visual systems for displaying the outside world to the pilots under training. Medium to high-end simulators use a Control Loading System to provide realistic forces on the pilot controls. The simulator cabin containing the replica cockpit and visual system is mounted on a six-cylinder motion platform that, by moving the platform cylinder under computer control, gives the three linear movements and the three rotations that a freely moving body can experience. The three rotations are Pitch (nose up and down), Roll (one wing up, the other wing down) and Yaw (nose left and right). The three linear movements have a number of names depending on the area of engineering involved but in simulation they are called Heave (up and down), Sway (sideways left and right) and Surge (longitudinal acceleration and deceleration).

Flight simulators are used to train flight crews in normal and emergency operating procedures. Using simulators, pilots are able to train for situations that are unsafe in the aircraft itself. These situations include engine failures and failures or malfunctions of aircraft systems such as electrics, hydraulics, pressurization, flight instruments and so forth. System trainers are used to teach pilots how to operate various aircraft systems. Once pilots become familiar with the aircraft systems, they will transition to cockpit procedures trainers or CPTs. These are fixed-base devices (no motion platform) and are exact replicas of the cockpit instruments, switches and other controls. They are used to train flight crews in checks and drills and are part of a hierarchy of flight training devices (FTD). The higher level FTDs are 'mini simulators'. Some may also be equipped with visual systems. However, FTDs do not have motion platforms, though many have the fidelity of the Full Flight Simulators. Images of the surrounding environment is projected on displays outside of the cockpit for effect. A computer or computers are used to generate the images, which can be very accurate, and simulate the movements of the instruments. A full flight simulator (FFS) duplicates all aspects of the aircraft and its environment, including motion in all six degrees-of-freedom. Personnel in the simulator must wear seat belts as they do in the real aircraft. As the cylinders' travel in any simulator is limited, the motion system employs what is called 'acceleration onset cueing' that simulates initial accelerations well and then backs off the motion below the pilot's sensory threshold so that the cylinder limits are not exceeded.

Flight simulator use referenced in aviation incidents
Flight simulators have been referenced as having been used for training in security incidents involving real world aircraft. The 9/11 Commission in the US concluded in 2004 that those responsible for flying the planes into World Trade Center and Pentagon had used PC-based flight simulators for training.
 * In 1999, gamer Yuji Nishizawa briefly hijacked a Boeing 747 over Tokyo, fatally stabbing the pilot and flying within 1,000 feet of the ground before being subdued. Later the hijacker explained that he was a flight simulator fan who had wanted to try flying a real aircraft.


 * Zacarias Moussaoui was one of the hijackers involved in the September 11 attacks, and had flight-simulation software on his laptop computer when he was arrested. During the trial of Moussaoui it was revealed that he had used the Flight simulation software to improve his flying skills.


 * In 2005 through an open letter, Jack Thompson, a former attorney and anti-videogame activist, accused Microsoft of aiding terrorists in its popular Microsoft Flight Simulator series. His letter and the response from the industry was widely reported in the news media.


 * Jermaine Lindsay, one of the four 7 July 2005 London bombings, may have used flight simulators to practice flying an airliner with an accusation that he was registered with a virtual airline. A person of the same name listed his nearest major airport as Heathrow and clocked up 30 hours in two months with a virtual airline. The website later denied the member's linking with the bombing, and indicated it was working with the Metropolitan Police to establish whether its former member was the bomber.  The website stated that it provides information about airlines and free add-on software for Microsoft Flight Simulator and does not provide flight instruction to its members.

Simulator and flight training device certifications
National Aviation Authorities (NAA) for civil aircraft such as the U.S. Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA), certify each category of simulators and test individual simulators within the approved categories. U.S. commercial pilots can only log required training time in simulators that are certified by the FAA and European pilots in simulators approved by EASA. In order for a simulator to be officially certified, it must be able to demonstrate that its performance matches that of the airplane that is being simulated to the fidelity required by the category of Flight Training Device (FTD) or Full Flight Simulator (FFS) to which it is designed and approved by the regulatory body. The testing requirements are detailed in test guides referred to as an Approval Test Guide (ATG) or Qualification Test Guide (QTG). Simulators are classified as Level 1-7 Flight Training Devices (FTD) or Level A-D full-flight simulators. The highest, most capable device is the Level D Full Flight Simulator. This can be used for so-called Zero Flight Time (ZFT) conversions of already-experienced pilots from one type of aircraft to a type with similar characteristics. In ZFT conversions, no aircraft time is needed and the pilot first flies the aircraft, under close supervision by a Training Captain, on a revenue flight.

Manufacturers
Civil Full Flight Simulators include FlightSafety International (FSI), Frasca International, Inc., Rockwell Collins, Opinicus in the USA, CAE Inc. and Mechtronix in Canada, Sim Industries in the Netherlands, Havelsan in Turkey and Thales Group in France and the UK, the UK site being the ex-Rediffusion simulator factory at Crawley, near Gatwick airport.There are currently about 1200 Full Flight Simulators in operation worldwide , of which about 550 are in the USA, 75 in the UK, 60 in China (PRC), 50 each in Germany and Japan, and 40 in France. Of these, some 450 were made by CAE, mainly in their Montreal factory, about 380 by Thales and its predecessors Rediffusion, (Singer) Link-Miles, and Thomson CSF, and about 280 by Flight Safety International. L-3 Communications operates a facility in Arlington, Texas which manufactures flight simulators for the military; the division (Link Simulation and Training) traces its legacy back to Link's original invention.

Flight simulators are also extensively used for research in various aerospace subjects, particularly in flight dynamics and man-machine interaction (MMI). Both regular and purpose-built research simulators are employed. They range from the simplest ones, which resemble video games, to very specific and extremely expensive designs such as LAMARS, installed at Wright-Patterson Air Force Base, Ohio. This was built by Northrop for the Air Force Research Laboratory (AFRL) and features a large scale five degrees of freedom motion system to a unique design and a 360 degree dome-mounted visual system.



Instructor operating stations
Most simulators have Instructor Operating Stations (IOS). At the IOS, an instructor can quickly create any normal and abnormal condition in the simulated aircraft or in the simulated external environment. This can range from engine fires, malfunctioning landing gear, electrical faults, storms, downbursts, lightning, oncoming aircraft, slippery runways, navigational system failures and countless other problems which the crew need to be familiar with and act upon. Many simulators allow the instructor to control the simulator from the cockpit, either from a console behind the pilot's seats, or, in some simulators, from the co-pilot's seat on sorties where a co-pilot is not being trained. Some simulators are equipped with PDA-like devices in which the instructor can fly in the co-pilot seat and control the events of the simulation, while not interfering with the lesson.

In the past full motion flight simulators had been limited to multi-million dollar hydraulic devices used at large training centers such as those provided by FlightSafety International, CAE, Alteon (a Boeing company) and at the training centers of the larger airlines. Recent advances in electric motion platforms have led to their use in Full Flight Simulators at these and other training centers and also permitted full motion simulation to be provided economically for much smaller aircraft including single-engine piston aircraft at training centers such as Flight Level Aviation.

Flight simulators are an essential element in individual pilot as well as flight crew training. They save time, money and lives. The cost of operating even an expensive Level D Full Flight Simulator is many times less than if the training was to be on the aircraft itself and a cost ratio of some 1:40 has been reported for Level D simulator training compared to the cost of training in a real Boeing 747 aircraft.

Modern high-end flight simulators
High-end commercial and military flight simulators incorporate motion bases or platforms to provide cues of real motion. These are important to complement the visual cues (see below) and are vital when visual cues are poor such as at night or in reduced visibility or, in cloud, non-existent. The majority of simulators with motion platforms use variants of the six cylinder Stewart platform to generate motion cues. These platforms are also known as Hexapods. Stewart used an interlinked array of six hydraulic cylinders to provide accelerations in all six degrees of freedom. Motion bases using modern Stewart based hexapod platforms can provide about +/- 35 degrees of the three rotations pitch, roll and yaw, and about one metre of the three linear movements heave, sway and surge.

These limited angular and linear movements (or "throws") do not inhibit the realism of motion cueing imparted to the simulator crew. This is because the human sensors of body motion are more sensitive to acceleration rather than steady-state movement and a six cylinder platform can produce such initial accelerations in all six DoF. The body motion sensors include the vestibular (inner ear, semicircular canals and otoliths), muscle-and joint sensors, and sensors of whole body movements. Furthermore, because acceleration precedes displacement, the human brain senses motion cues before the visual cues that follow. These human motion sensors have low-motion thresholds below which no motion is sensed and this is important to the way that simulator motion platforms are programmed (and also explains why instruments are needed for safe cloud flying). In the real world, after conditioning to the particular environment (in this case aircraft motions), the brain is subconsciously used to receiving a motion cue before noticing the associated change in the visual scene. If motion cues are not present to back up the visual, some disorientation can result ("simulator sickness") due to the cue-mismatch compared to the real world.

In a motion-based simulator, after the initial acceleration, the platform movement is backed off so that the physical limits of the cylinders are not exceeded and the cylinders are then re-set to the neutral position ready for the next acceleration cue. The backing-off from the initial acceleration is carried out automatically through the simulator computer and is called the "washout phase". Carefully-designed "washout algorithms" are used to ensure that washout and the later re-set to about neutral is carried out below the human motion thresholds mentioned above and so is not sensed by the simulator crew, who just sense the initial acceleration. This process is called "acceleration-onset cueing" and fortunately matches the way the sensors of body motion work. This is why aircraft manoeuvre at, say, 300 knots, can be effectively simulated in a replica cabin that itself does not move except in a controlled way through its motion platform. These are the techniques that are used in civil Level D flight simulators and their military counterparts.

The NASA Ames Research Center in "Silicon Valley" south of San Francisco operates the Vertical Motion Simulator. This has a very large-throw motion system with 60 feet (+/- 30 ft) of vertical movement (heave). The heave system supports a horizontal beam on which are mounted rails of length 40 feet, allowing lateral movement of a simulator cab of +/- 20 feet. A conventional 6-degree of freedom hexapod platform is mounted on the 40 ft beam, and an interchangeable cabin is mounted on the hexapod platform. This design permits quick switching of different aircraft cabins. Simulations have ranged from blimps, commercial and military aircraft to the Space Shuttle. In the case of the Space Shuttle, the large Vertical Motion Simulator was used to investigate a longitudinal pilot-induced oscillation (PIO) that occurred on an early Shuttle flight just before landing. After identification of the problem on the VMS, it was used to try different longitudinal control algorithms and recommend the best for use in the Shuttle programme. After this exercise, no similar Shuttle PIO has occurred. The ability to simulate realistic motion cues was considered important in reproducing the PIO and attempts on a non-motion simulator were not successful (a similar pattern exists in simulating the roll-upset accidents to a number of early Boeing 737 aircraft, where a motion-based simulator is needed to replicate the conditions).

AMST Systemtechnik (Austria) and TNO Human Factors (the Netherlands) have developed the Desdemona flight simulation system for the Netherlands-based research organisation TNO. This large scale simulator provides unlimited rotation via a gimballed cockpit. The gimbal sub-system is supported by a framework which adds vertical motion. Furthermore, this framework is mounted on a large rotating platform with an adjustable radius. The Desdemona simulator is designed to provide sustainable g-force simulation with unlimited rotational freedom.

Flight simulators at home
Crude flight simulators were among the first types of programs to be developed for early personal computers. Bruce Artwick's subLOGIC simulators were well-known for the functionality they managed to get onto 8-bit machines. Key computer game technologies such as 3D graphics, online play, and modding were first showcased in combat flight simulators such as Red Baron II and European Air War. The game world in flight simulators is often based on the real world. However, they are often confined to one part of the game world by invisible boundaries. In some games, the aircraft simply halts in midair, while other games force the player to turn around. However, many games solve this boundary problem by wrapping the game world as a sphere.

Although these games strive for a great deal of realism, they often simplify or abstract certain elements to reach a wider audience. Many modern fighter aircraft have hundreds of controls, and flight simulator games usually simplify these controls drastically. Further, certain maneuvers can knock a pilot unconscious or rip their aircraft apart, but games do not always implement these concerns.

A popular type of flight simulator are combat flight simulators, which simulate combat air operations from the pilot and crew's point of view. Combat flight simulation titles are more numerous than civilian flight simulators due to variety of subject matter available and market demand.

In the early 2000s, even home entertainment flight simulators had become so realistic that after the events of September 11, 2001, some journalists and experts speculated that the hijackers might have gained enough knowledge to steer a passenger airliner from packages such as Microsoft Flight Simulator. Microsoft, while rebutting such criticisms, delayed the release of the 2002 version of its hallmark simulator to delete the World Trade Center from its New York scenery and even supplied a patch to delete the towers retroactively from earlier versions of the sim.

The advent of flight simulators as home video game entertainment has prompted many users to become "airplane designers" for these systems. As such, they may create both military or commercial airline airplanes, and they may even use names of real life airlines, as long as they don't make profits out of their designs. Many other home flight simulator users create fictional airlines, or virtual versions of real-world airlines, so called virtual airlines. These modifications to a simulation generally add to the simulation's realism and often grant a significantly expanded playing experience, with new situations and content. In some cases, a simulation is taken much further in regards to its features than was envisioned or intended by its original developers. Falcon 4.0 is an example of such modification; "modders" have created whole new warzones, along with the ability to fly hundreds of different aircraft, as opposed to the single original flyable airframe.

One way that users of flight simulation software engage is through the internet. Virtual pilots and virtual air traffic controllers take part in an online flying experience which attempts to simulate real-world aviation to a high degree. There are several networks where this sort of play is possible, the most popular ones being VATSIM and IVAO. Virtual Skies provides a low barrier of entry allowing any level member to fly or control without worrying if something goes wrong. Virtual Skies covers mainly UK & USA VATSIM and is generally regarded to have better coverage of the virtual North America and Great Britain, while IVAO's pilots and controllers generally fly and control the virtual Europe, Africa and South America. IVAO's ATC certification process is not as strict as VATSIM's, which allows for a greater number of controllers to be available, but guarantees their proficiency to a lesser degree than VATSIM. Both networks receive anywhere from 300 to 900 ATC and pilot connections, depending on the time of day.

Much rarer but still notable are flight simulators available for various game consoles. The most notable of these were Pilotwings, made available for the Super Nintendo, the sequel Pilotwings 64 for the Nintendo 64 and the Ace Combat series on PlayStation 1&2. The very rare Sky Odyssey is yet another example of console flight simulators. Due to the restrictive nature of a game console's ability to simulate environments properly in general and the processing limitations of these systems in particular, game console-based flight simulators tend to be simplistic and have a more arcade-like feel to them. While generally not as complex as PC based simulators, console flight simulators can still be enjoyable to play, though their 'simulation' status is disputed by many in the flight simulation community.

Homebuilt cockpits
Often referred to as Simpits, home cockpit building is a common hobby among simulator pilots. Simpits range in complexity from a single computer, with some effort to create a permanent area for simulation, through to complete cockpit reconstruction projects utilizing multiple systems. The growth in home cockpit complexity and realism has been further fueled by the opening up of the simulation software packages with published SDKs (Software Development Kits) now common.

The push for higher realism in desktop simulation, often fueled by real pilots looking to practice cheaply at home, has led to a wide array of suppliers growing up to satisfy the demand. Hardware is available from a variety of commercial sources ranging from yokes, throttles and pedals, through to radios, lights and complete instruments. This home use hardware is rarely certified for flight training, so the hours spent practicing in the simpit will not count towards a pilot's hours. However it is widely utilized as an unofficial training aid, allowing realistic procedures practice, as well as the opportunity to complete visual or IMC approaches prior to a real world flight. This can help make a pilot's real-world flight time safer and more productive. Professional opinion is divided about how effective this home simulation can be against real world flight, and this has been a subject of debate in popular flying magazines such as 'Pilot' through 2007.

For those wishing more than a desktop simulator, replica panels are commercially available mimicking those found in a modern airliners such as a Boeing or Airbus. These panels will either fit into a real cockpit section, which some large scale home simulators are built into, or will be mounted in a home constructed cockpit frame, normally made from wood. With most modern airliners now using Glass Cockpit type displays it is relatively simple to replicate the displays in software, outputting them via multi head graphics cards or networked PCs to cheaply available LCD monitors mounted behind the panel. To the casual observer it can be hard to tell a home built static simulator and a commercial one apart.

In addition, companies who now build FTDs (Flight Training Devices) for leisure and Flight Training have developed replica cockpits. One company in New Zealand has launched Flight Experience based worldwide which offers an exact replica of a 737-800NG to the public. So far they have locations in Australia, New Zealand and Singapore and under the guidance of real flight instructors you can take off, fly and land at hundreds of airports and use the same SOPs (Standard Operating Procedures) as the airlines (www.flightexperience.com)



Where commercial panels or controls do not exist, simulator builders will often create their own out of wood or similar easily worked materials. Another common route for sourcing the specific hardware needed in a simulator, and one used by the commercial sector as well, is to obtain a real component from a scrapyard and convert it for PC input. Interface hardware for these home-made controls is directly available from commercial suppliers, or can be obtained by dismantling cheap joysticks or similar components and rewiring them. Some home builds will even incorporate motion platforms, although unlike commercial simulators these are normally more limited in motion, and often rely on electrical motors as opposed to hydraulics.

Beyond the hardware of home cockpits, most flight simulator software can simulate modern aircraft systems to a very high standard in addition to the basic flight dynamics, providing accurate recreations of, among others, the FMC (Flight Management Computer), autopilot and engine management systems. With additional hardware and add-in software this may be extended further, for example into a fully functional overhead panel requiring real-world check lists to be followed for engine start-up and flight with a full flight deck crew.

Space flight simulators
As space is a natural extension of airspace, space flight simulators may be treated as an extension of flight simulators' genre. There is a considerable interdependence between those two kinds of simulators, as some flight simulators feature spacecraft as an extension and some space flight simulators may feature realistic atmospheric flight simulation engines.

Popular home flight simulator software
Popular flight simulators for home computers include:
 * Google Earth flight simulator can be activated by pressing Ctrl-Alt-A
 * Rise of Flight: The First Great Air War new generation combat flight simulator of World War I
 * Microsoft Space Simulator
 * Microsoft Flight Simulator Series - its latest installment (Microsoft Flight Simulator X) now includes space as an area to be discovered, with a payware space shuttle available.
 * Orbiter, a freeware space flight simulator
 * ''Space Shuttle Mission 2007, Includes several missions flown by several space shuttle.
 * X-Plane, also includes a Space Shuttle and Mars flight simulators
 * YS Flight Simulation 2000, a freeware flight simulator
 * FlightGear, an open source flight simulator