At I/ITSEC 2014, FlightSafety International presented a paper that described what it claims is the collimated display with the largest field of view (FOV) ever built. While this system was not demonstrated on the trade show floor, the company did have a full collimated display set up as a helicopter simulator.
Collimated displays are highly desirable in aircraft simulation as they create an image that is focused at infinity. This creates a more realistic view out of the window and is very easy on the eyes. They can be designed for a single eyepoint (pilot) or two eyepoints and can even be done in 3D!
A collimated display can be based on front or back projection but features a curved screen to create a real image and an even larger curved mirror to reflect that image onto the screen and create a virtual image focused at infinity. The mirrors and screen need to be extremely high quality as any flaws are magnified in the system. The mirrors can be made of glass or stretched mylar. As a result, these are very expensive displays.
The simulator described in the paper presented by Chief Engineer Justin Knaplund, was created for the UH-1Y, a Marine Corps helicopter. Helicopters have one of the most demanding simulator requirements as pilots can see pretty far behind the airframe and they often have what are called “chin” windows that allow the pilot to have a look down capability – which is critical for landings.
The horizontal field-of-view (FOV) of traditional simulators is 220-degrees. If it could be increased to 270-degrees, it would allow training in a wedge formation. And if increased to 300-degrees, training for threat detection and surveillance of aft 380 like smoke or muzzle flashes can be simulated as well. In other words, the restrictions of the FOV limit the training scenarios.
The illustration shows the FOV of the pilots in the UH-1Y along with the coverage of the new 300-degree horizontal by 60-degree vertical collimated display. Note that the configuration of the collimated display also creates an area where there can be no image. Also note that it does not include views out of the chin and auxiliary windows, so FlightSafety added additional screens to include these views as well.
To design and build this display, FlightSafety chose to use a glass mirror instead of mylar as mylar would have to be spliced together to fill the full FOV and splices cannot be made today without being very visible. The glass mirrors must also be made in segments but the company developed new methods to assemble them with minimal visual impact.
FlightSafety also chose to use a back projection method, projecting on a screen that sits above the pilot’s head. In the graphic, the projector is on the top angled down to illuminate the screen. The instructor station is in the wedge-shaped section to the right.
FlightSafety is building two of these simulators as shown in the photo. The entire projection and screen assembly is hoisted on top of the cockpit and mirror assembly.
The company also reported on the contrast it is seeing in the display. Using an LCOS projector and a high contrast screen, it is able to achieve a high level of 13.5:1 (their goal was 8:1). The screen is a gray type that absorbs reflections form other parts of the screen and has a carefully matched diffusion gain coating to reduce scatter of light between the screen and mirror. The effective screen gain is near 1.0. The design of these screens is very complex as was partly explained in our Da-Lite interview on this topic. The company did not disclose the supplier of the screen or projectors. – Chris Chinnock