What Is a Flight Simulator
A
flight simulator is a device that reproduce the dynamic response of an
aircraft in a real-time and interactive manner. Sophisticated mathematical
models in the flight simulation program represent all of the physical properties
of aircraft and ambient air. Which makes the flight simulator to act according
to the pilots input. The responds of the aircraft are represented by the
image, instrument readings and motion cue systems which can be seen or
felt by a human pilot.
Why Do We Want to Use Flight Simulators
Therere so many reasons that flight simulators with different level of fidelities are broadly used by military, airlines, researches and, of course, entertainment purpose. The low costs of money and time for training are usually the best reason military and airlines want to go for a state-of-art flight simulator. It is also much safer to use a flight simulator for training stall, malfunctions and emergency situations. A lot of situations you dont find them in real life, such as wind-shear, mechanical failures and some tactical situation; flight simulator provide more flexibility to simulates such conditions for accident investigation and military mission evaluation. Researchers also use flight simulator to review the design of an airplane in airplanes physical aspects and flight control/fly-by-wire logic before the aircraft is actually built. This will greatly reduce the cost of money and time for development cycle and the risk of aircraft testing. With the increased calculation power of PC, lots of flight simulation and the simulation of other vehicles games are found in the market. Flight simulation became a economical and available entertainment to every family.
How a Flight Sim Works
Conceptual Model (Mathematics Model)
Conceptual model works like the "brain" of the simulator, which "thinks" and "behaves" like the real airplane. Several sophisticated mathematics models make the system to simulate an aircraft. Based on those models, computer will calculates the aircrafts mass properties, aerodynamic forces and moments respect to aircrafts presenting attitude and position and predicts the accelerations for the next time instance. After the accelerations are obtained, the program integrates the accelerations over the time increment and gets the velocities. The program is therefore going through another iteration and integrates velocities into the displacement of the aircraft. By repeating this fashion and including the pilot in the loop, flight simulator is able to simulate the dynamic response of an aircraft in a real-time manner. The following diagram shows how the simulation is done.
Visual
Out-of-window
visual is one of the most important cueing for the pilot to sense the motion
of the aircraft. Modern technology can generate visual scenes which create
simulations of sufficient fidelity that their utility is considerable greater.
Out-of-window scenes of most modern flight simulators are done by the mean
of computer graphics which are similar to those used in video games. Objects
like buildings and runways are constructed by 3-D polygons. The positions
of those 3-D objects are defined in the visual database. The pilot eye
position will follow the movement of the aircraft while the simulator keeping
update aircrafts position in the "virtual space" by integrating
aircrafts velocities. Sophisticated computer graphing software will transfer
those 3-D polygons into 2-D drawing and project the image onto the screen.
The rate of this process is usually 60 times per second, which gives the
pilot a continuous animation.
Most full flight simulator equips with a rear projection visual system. The typical rear projection system includes projectors, a back project screen and a mirror. The visual image is projected onto the screen by the projects. The projectors need to be aligned for the overlap image. A high gain collimated mirror reflects the image to pilot's eyes and provides depth preception for the pilot.
Motion Cueing and Control Loading
Motion system provides more realism to the pilot by changing the gravity vectors at the flight compartment. Most of the state-of-the-art simulators equip with a 6 degree-of-freedom motion platform. The 6 hydraulic stands provide the pitching, rolling, yawing, heave, side ward and forward movement to the platform. Those motion cues make pilots to feel the maneuver of the aircraft for extra degree of realism. The motion cue is made possible by complex computer codes and mechanical mechanism. The aircraft acceleration vector (x, y, z, pitch, roll and yaw) from aerodynamic calculation is sending into the motion cueing codes. The motion cueing codes will command the hydraulic stands to move the flight compartment to appropriated attitude. Some maneuvers are difficult to simulate during the limited stroke the hydraulic stands can travel. However, human tend to adept to sustained yaw rate. If the sustained yawing is occur, the simulator will turn back slowly before it reach its physical limit and ready for next maneuver.
Control loading also provides important cue for the pilot. Pilot
relies on the stick force to control the airplane. The control loading
system combines with complex mechanical system and software. Position transducers
are placed to sense the stick position. Base on the stick position, the
control loading code will calculate the respective surface position. From
the surface position, aerodynamic moments on the hinge will be determined.
The aerodynamic hinge moment will be scaled according to the actual airplanes
rigging. The digital computer will tell how much the force will be send
to the particular axis of the stick by a means of pneumatic, magnetic or
friction mechanisms.
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