Flight Simulations
Various categories of flight simulations 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 simulations (FFS). The higher levels of Full Flight simulations 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 simulations use a Control Loading System to provide realistic forces on the pilot controls. The simulations 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 simulations are used to train flight crews in normal and emergency operating procedures. Using simulations, 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 simulations'. Some may also be equipped with visual systems. However, FTDs do not have motion platforms, though many have the fidelity of the Full Flight simulations. 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.
About Flight Simulations
Large Amplitude Multi-mode Aerospace Research simulations (LAMARS)A full flight simulations (FFS) duplicates all aspects of the aircraft and its environment, including motion in all six degrees-of-freedom. Personnel in the simulations must wear seat belts as they do in the real aircraft. As the cylinders' travel in any simulations 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.
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 simulations and test individual simulations within the approved categories. U.S. commercial pilots can only log required training time in simulations that are certified by the FAA and European pilots in simulations approved by EASA. In order for a simulations 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 simulations (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). simulations are classified as Level 1-7 Flight Training Devices (FTD) or Level A-D full-flight simulations. The highest, most capable device is the Level D Full Flight simulations. 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.
High-end commercial and military flight simulations 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 simulations 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.
More about Flight Simulations
Flight Simulations platformed These limited angular and linear movements (or "throws") do not inhibit the realism of motion cueing imparted to the simulations 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 simulations 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 ("simulations sickness") due to the cue-mismatch compared to the real world.
In a motion-based simulations, 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 simulations 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 simulations 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 simulations and their military counterparts.
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