Simulators

One area experiencing rapid growth in the use of computers in recent years is simulation. Simulations are used for training in procedures that would be too dangerous or expensive to perform in real life. Some simulations are even used for routine and repetitious tasks. As computers become more powerful, the variety of things that they can imitate becomes larger, and the accuracy of the simulations is better.

Aviation was among the first fields to use simulation. Today, military and airline pilots spend much of their time interacting with the computers that are flying the airplane. Computers have taken over both the mundane and the most difficult piloting tasks. The mundane tasks are automated because in many cases they are more distracting than they are worth. The difficult tasks are automated to increase efficiency and safety. The pilot of an aircraft approaching a busy terminal area with a low, thick cloud cover need not hand-fly the instrument landing procedure when a computer is on board carrying all the information necessary for the task and programmed to follow all the steps in order without making a mistake.

Even with good autopilots and computers, human pilots must still monitor the systems and be ready to recognize failures and take over the controls. Pilots of highly automated aircraft have training that involves all of the computer systems. They must be put into situations where events occur that might not happen in years of routine flight so that they can see how they and their systems react. Most of these situations are dangerous: engine fires, hail storms, and electrical failures, for example. It is not sensible or possible to put pilots and multi-million dollar aircraft at risk for training purposes. Fortunately, for every computer advance that makes the cockpit more automated, there is an advance that makes it easier to create an artificial environment for training that is closer to reality. Simulations of real airplanes are now of such high fidelity that a pilot training on them can legally log actual flying time.

Simulators of aircraft are of two types: fixed-base and motion-base. The main purpose of a fixed-base simulator is to enable a student to practice complex procedures in a specialized environment. Many part-task trainers exist for the trainee to concentrate on one set of events or components, such as the interface to the computer systems. At the high end of the scale of fixed-base simulators is a stationary version of the forward area of an airliner cockpit.

As desktop computers become more powerful and graphics capability increases, procedures trainers can be created out of one computer system. The simulator can configure itself to be a different airplane in a few seconds. In contrast, current simulators, both fixed-and motion-base, would have to be rebuilt to represent a different airplane. There is research underway to take advantage of improved hardware and software by enabling a larger simulator to simulate several cockpits using very big displays to show instruments graphically.

Motion-base simulators are much different. The hallmark of the very best motion-base simulators is the complete cockpit. Every instrument, lever, and control in the cockpit is exactly the same as on the aircraft. In most cases, the equipment is on the same maintenance and replacement schedule as that in real airplanes. This means that when an airline pilot comes to his airline's simulator center for transition or recurrent training, there is complete carryover back to operations.

From the outside, a motion-base simulator looks like a box on stilts. The box contains the cockpit and the instructor's stations. The stilts are hydraulically actuated pistons that can move the box in response to control inputs by the pilot. In the earlier days of these simulators, they only operated on three axes. So, the feel was close, but not quite right. Currently, most motion-base simulators move with six degrees of freedom. They can mix roll and yaw, pitch and roll, and so on, in order to give the pilots a more realistic feel. This improvement is due to advances in computer technology.

On top of the front of the cockpit are image generators connected to computers in an adjacent machine room. The image generators place scenes on the windows of the cockpit. Full-color, daylight imaging is available, but very expensive. Many airlines opt for dusk/dark imaging. The outside scene appears to be well after sunset. Buildings are in ghostly light, cars have their lights on, forests are shades of greys. Aside from making the simulator less costly, it also forces pilots to practice in what is the most common time of day for accidents: twilight.

Inside the cockpit, the flight deck from the forward bulkhead (where the door to the cabin would be in a real airplane) to the nose is a precise copy of the actual aircraft. Just off the flight deck is a rectangular room containing a workstation for the instructor and a maintenance terminal for the software and hardware technicians. These technicians work in three shifts. The simulators are in use twenty-four hours a day. Time not used by the owner airline can be rented out to another airline's crews and instructors. A typical motion-base simulator has several different computer systems to create artificial reality. The main computer is often a 32-bit word-size machine, like the average desktop. FORTRAN programs reside in this computer to analyze control inputs and send commands to the hydraulics and the instruments. The commands travel on an ARINC 429 serial data bus — the standard bus in actual commercial aircraft. Another system drives displays and handles input and output to the instructor's station. Three large cabinets of image generation hardware—one for the front generators, one for each side—complete the system.

The best thing about the simulator is that it can do some things that would be impossible in real life. It can return the simulation to a marked point for repetitive practice, say at 2,438 kilometers (8,000 feet) and 24 kilometers (15 miles) from the runway. After a few keystrokes, the entire airplane is transported from the landing point back up into the air. The movement of the simulation can be frozen at any point and then resumed at that point. An approach to landing in instrument conditions can be run a few feet at a time for teaching purposes.

The pilots who do the training emphasize to their students that they should treat the simulator just like a real airplane. That way they can get the maximum benefit from the training. In fact, the simulator makes it easy to maintain the illusion. Sitting on the simulated ramp in Indianapolis, for example, pilots can see the terminal building and the lights of cars going by on Interstate 70 in the distance. Beginning to taxi to the active runway, the building moves out of view and the taxiway lights pass by the windows. The runway is a dark ribbon bordered by its rows of lights.

Pilots are not the only ones trained for complex tasks using simulation. Nuclear reactor operators, air traffic controllers, and astronauts are all able to take advantage of computer power to create a virtual world that allows them to practice their occupation safely and cheaply.

see also Artificial Intelligence; Robotics; Simulation; Virtual Reality; Virtual Reality in Education.

James E. Tomayko

Bibliography

Campbell-Kelly, Martin, and William Aspray. Computer: A History of the Information Machine. New York: Basic Books, 1996.

Ceruzzi, Paul E. "Advances in Simulation, Testing, and Control." In Beyond the Limits: Flight Enters the Computer Age. Boston: MIT Press, 1989.

sim·u·la·tor / ˈsimyəˌlātər/ • n. a machine with a similar set of controls designed to provide a realistic imitation of the operation of a vehicle, aircraft, or other complex system, used for training purposes. ∎  (also simulator program) a program enabling a computer to execute programs written for a different computer.

simulator Any system that performs a simulation. It is normally a system dedicated for some period to performing a specific simulation, as distinct from, say, the case where a simulation program is executed as a normal job on some general-purpose computer. Simulators often employ either special-purpose hardware or hardware components from the system that is simulated.