Hi folks -- a little history … where I am quite sure that some of the “older heads” (sorry, I mean “more experienced professionals”) will, no doubt, recognize, and probably be able to offer similar, although, hopefully, not terribly diverse comments …
Early on in the development of visual system attachments to flight simulation, the Out-The-Window (OTW) imagery was decidedly “primitive.” Initially, the visual scenes were filmed during an approach to a specific airport, and then developed onto something like 50mm movie film which was projected directly in front of the simulator on a screen, and that visual scene was laterally adjusted (left/right) so that only one pilot would see the projected scene without any angular variance. Unfortunately, the other pilot would see that same visual scene at such an incorrect angle (depending on the distance between the 2 pilot seats) that this arrangement often led to the fact that flying the airplane from the not-optimized pilot’s seat was virtually impossible.
This method was soon seen to be fraught with problems – the major one being that when the film broke and was repaired – it turned out that final approach eventually became “shorter and shorter;” and the quality of the film image was eventually eroded due to the regular exposure to the bright projection light. This method evolved into the TV camera method, where the pilots actually “flew” a miniaturized television camera over what was essentially an “HO Gauge” model railroad board onto which was built a miniature airport, with runways, taxiways, and terminals – along with some surrounding features that sometimes included the edges of an adjacent town or city. The same direct projection issues were also present with this system, but the troubles with the film methods were exchanged for trouble with having pilots crash the TV camera into trees or buildings and the limitation of a maximum one 360-degree turn in either direction without necessitating a subsequent turn in the opposite direction later or run the inevitable disconnect of the cable from the camera, instantly providing a dark screen.
A break-through in the advancement of computer technology, resulted in the “CGI,” or computer generated image. A system of Cathode Ray Tube (CRT) visual displays was constructed to provide each pilot his/her own OTW display that could be viewed without any angular variance. Both pilots were seeing the identical OTW display – but the visual scene was limited to the size of the CRT screen. Not much time passed before the horizontal field of view was expanded for each pilot through adding an additional, side-mounted CRT to the left of the Captain’s primary CRT, and to the right of the FO’s primary CRT – expanding the horizontal scene for each pilot, again limited by the size of each additional CRT. Basically only night scenes were available, with some later versions providing a reasonably decent version of a dusk scene. Relatively soon thereafter, again as a result of computer technology advancement, and CRT screen advancements, the visual industry developed the ability to display full daylight scenes. However, each pilot was still limited to his/her own individual display – even expanded with the additional side-mounted CRT.
In the middle to late 1970’s, three significant specific occurrences were designed and implemented, where each was to have a significant effect on the art/science of simulation (AND simulation really IS both an ART and a SCIENCE):
The first was the development and adoption of a technical aspect of visual system presentation, called “collimation,” a word derived from the concept of "co-linear," that provides the imagery of the OTW scene viewed by the pilots to appear at a focal distance approaching infinity, where both pilots (seated side-by-side) are able to view the visual scene simultaneously without noticing any angular errors or distortions. This principle is used in Full Flight Simulators (FFS) to display imagery of the OTW scene to the pilots seated in the in the simulator when the pilot seats are properly located and adjusted.
The second, was a very serious effort to determine the degree to which the newest advancements in computer technology as applied to simulation could be seriously considered to not just supplement airplane training for pilots, but perhaps to completely replace airplane training. This official proposal was carefully considered and would be authorized strictly on the basis of adopting and successfully demonstrating the accuracy of these computer and simulation viability advancements; and if successfully implemented, would have the most significant effect on pilot training since Orville and Wilbur first tested the concept of flight. Undoubtedly, this was very likely THE most significant step, taken by a regulatory authority, with respect to pilot training and checking – and has now become a rather routine occurrence.
The third, was the development of a visual system that was to be mounted on top of the simulator cab, projecting a full color daylight, dusk, or night scene image, as desired, onto a transparent screen, also mounted on top of the simulator cab, which was to be viewed by the simulator occupants via a front mounted reflective surface (initially very tightly stretched very reflective Mylar film – later some attempts to use actual mirrors) mounted on the front of the simulator cab, so as to move with that cab, and providing the occupants of the simulator a completely unobstructed, reflective view of the back of the roof-mounted, transparent screen, and providing that scene through 150 degrees of horizontal viewing angle and almost 50 degrees of vertical viewing angle. The significance was that this reflective surface was curved, both horizontally and vertically – eventually making mirror installations exceptionally heavy, which had negative impacts on the ability of the motion system to effectively deal with the overall weight of the simulator system. However, this concept allowed cross-cockpit viewing of the entire projected visual scene for both pilots simultaneously. This breakthrough was developed by Rediffusion Simulation, at Crawly, England and their visual department in Arlington, Texas, and was first sold to an enterprising and motivated small airline in South Florida, called “Air Florida,” the same airline that later became famous, not for their foresight in simulation – but for another, much more noteworthy, though tragically negative, occurrence.
This new approach to visual system display technology eventually exploded into a rapid advancement of the type and quality of the screen onto which the scenes were projected, the reflectivity of the “mirror” surface, and the technical issues regarding weight, mounting methods, the number of visual projectors used – enabling a wider horizontal visual scene from the original 150 degrees up to what today approaches “wing tip to wing tip” horizontal and 60 degrees vertical fields of view. Because of the curvature of both the back-projected screen and the reflective surface from which the pilots are able to “see” the visual scene, and the now long-adopted collimation functions, today the OTW scene is viewed by both pilots at a distant focus (which approaches infinity) rather than at the focal distance of a screen onto which is projected that same visual scene.
Because of the fact that the benefits of the technology that makes up modern-day simulation are at least primarily focused on, and borders on being exclusively focused on, the pilots being trained or evaluated, the visual scene optics are adjusted specifically for those pilot occupants. Anyone not located at either of those pilot positions – and that includes the instructor or evaluator – may, at times, find that their inner ear (subject to the motion cues provided by the motion system) may not be completely “in-sync” with what images are transmitted from the eyes to that portion of the brain that is processing those external cues regarding position and position change – called movement or motion. Sometimes, persons on board a simulator may experience what is vertigo or motion sickness – either or both to varying degrees. While there is a reason that we have and use the word “individual,” it is, nonetheless, quite rare that a person occupying either of the pilot seats will experience any such anomaly – predicated, of course, on the fact that the simulator is producing all of those input cues designed to be provided to those pilots (i.e., motion, visual scene, and instrument response) within the established parameters outlined in the regulatory documents for qualification of that particular simulator.
As I attempted to point out in my last, hastily written, post I attempted to point out that the latency issue, while certainly important, has been able to be pushed toward a faster and faster rate of system performance such that a latency problem is not usually something that crops up frequently. Of course, malfunctions or wear, may, at times complicate the latency that is required. The current regulatory requirement in the US, according to Part 60 (presuming I have the latest, most current version – as I know there is another change that is currently working its way through the governmental bureaucracy) calls for a latency of not more than 150 ms for Level C and D simulators – where, as I pointed out, the latest simulator standards document published by ICAO (their Document 9625) the identical language contained in the FAA regulation for its description, the latency value for motion, visual, and instrument response is shown to be not more than 100 ms. However, as I’ve indicated, there are some simulators where aspects of latency approach 20-50 ms – that is an almost unbelievably short period of time – and there is almost no way that such latency could be recognized, even sub-conscientiously.
Last edited by AirRabbit; 11th June 2014 at 20:54.