Field-of-View |
In order to achieve a realistic training environment, high quality visual feedback to the pilot is integral. The visual systems must be of a high resolution and a wide field-of-view, so that the person sitting in the simulator can be fully immersed into the flying experience.
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Field-of-View |
High-fidelity visual systems are capable of both day and night time views, with taxiway and full weather and ground environment control. The visual system should permit variations in runway lighting, airport and terrain characteristics and atmospheric conditions, as all of these factors can influence a pilot's decision making and flight performance while enroute and during visual approach and landing manoeuvres.
Various methods have been used in the pursuit of a quality visual system:-
These methods are often combined to ensure the ultimate visual system. The one aspect that they all share is that when done properly, they can be a very costly proposition!
 Six-degrees-of-freedom motion base with dome projection visual system. This system (in Amsterdam) uses a head-tracked 140°x 110° instantaneous field of view overlaid with a high resolution area of interest, providing an almost 360° field of regard. |
Domes
Historically, domes have been the visual system of choice when a 360 degree field-of-view is desired. There are many types of domes - some which use external projectors, others with internal projectors and combinations of the two. In all cases, the display surface is independent of the user's head position.
The major drawback to this approach is the cost involved in providing resolution over the entire area of the dome. The cost can be reduced by using a combination of high and low resolution images (which can be either computer generated or images from a TV model board system). High resolution images would be projected in key areas of interest and a low-resolution image, would be projected over the whole dome. The high resolution inset would be projected based on the pilot's head or eye position.
The cost effectiveness of this approach is greatly dependent on the cost of the hardware involved. Specifically, it will be cost effective if the cost of the additional image generators and fixed projects is more than the cost of the slaved projector.
Collimated Display Systems
In modern flight simulators used by major airlines and aerospace companies, visual scenes are displayed by means of display systems which are compatible with the computer generated image system. The result is an “out-of the-window” virtual image. For instance, if four displays are used, this gives the pilots a 106° by 36° field-of-view.
The display systems are located outside of the simulator cockpit and are mounted on the platform along with the cockpit. Typically, the display systems are 50 inches from the pilot’s eye, each presenting a nominal 48° width by 36° height field of view.
 Cockpit with three of the systems visible. |
 Arrows point to the display systems. |
 A Swissair 6-D-o-F simulator using a Projector Based Collimated Display system. |
Projector Based
In the photo on the right, the rounded section at the front of the simulator (left hand side) is the visual mirror, which wraps round the cockpit 180 Deg giving the Pilot, and Co-pilot an unobscured view all around.
The mirror is made from a reflective plastic
film, held in shape by a vacuum. The image itself is projected on to a
back projection screen above the pilot's head, by the 5 projectors which can
just be seen on the roof of the simulator, so the pilot is actually looking at a
reflection of the image. Due to the wonders of geometry this seems to be
infinity, ie. it does not look as though it is only a reflection of a picture on
a screen just a few feet away.
Monitor Based
Stand Alone System (Single Window)
Provides the user with a high quality view through a single window. The collimator frame is square as viewed from above and slightly oversized to allow greater head motion.
Juxtaposed with Channel Separation (Multiple Window)
Wider horizontal fields of view are possible by connecting several collimators together, side-by-side, with baffle(s) between the mirrors. This provides an inexpensive means of having a "continuous" scene across multiple systems. Baffles allow for less critical alignment tolerances and a simple monitor design, with remote capability for ease of alignment.
Juxtaposed with No Separation (Multiple Window)
Similar to the above system except without baffle(s) between collimators. Adjacent mirror and beamsplitter edges are aligned flush to present a "seamless" image across the scene. CRT images are overlapped using precise geometry control and alignment. This type of system is designed for the most demanding visual system requirements.
This approach has the display attached to the viewer's head, so computer imagery is seen based on the wearer's head motion. To enable the correct eye point and orientation to draw the imagery, a head tracker is used.
The key advantage with this approach is that only high resolution images are seen by the viewer, without the need for multiple area-of-interest projectors or large facilities to house them.
The problem with this approach is the weight and size of Head Mounted Displays. The trend however is for these items to reduce in size and systems are currently available which weigh about 1.8kg (4 pounds).