Planning the new build – base and display system

So, while I’m laid low with my ear infection, I’ve been planning. The two more important considerations at the moment are the overall dimensions / positioning of the shell, and the visual display system. You can’t separate these two unless you have so much room that you can afford to place a projector anywhere you like and still get a big enough image.

First up, I measured the dimensions of my build room and was disappointed to learn that they were a mere 3.6m x 2.6m. A full-scale B737 cockpit enclosure, for example, would almost entirely fill the room. I was planning on still being able to use it as an office as well as a sim-room. I would have to work with what I had, I decided.

Now, this project has always been about making a very generic cockpit that could be pressed into service for various different flying experiences, and the area I’ve been pitching at has always been ‘very light jet’, so I did some research into cockpit and cabin dimensions for these, and found – for example – that the classic Learjet 45 has a maximum cabin width of 1.65m. Much more do-able. So I ummed and ahed and played about in Visio and settled on a base area of 1.8m x 2.4m, which will take about 2/3 of the room. I then decided that there was no need for an instructor’s station or similar behind the main cockpit area; I wanted enough space to get in and maneuver into place, and potentially have enough space for two observers to sit, and that’s it. The floor plan I mocked up in Visio looks like this:

The white rectangles represent the existing console and pedestal structures, the seats are – well, seats. Or at least space for them. Black lines indicate the line of the windows and inner shell around the MIP. Finally, the green arc represents a projection screen and the blue arc a mirror – which bears some explaining.

Back in the beginning, I was planning on using a single 46″ LCD display as my external visuals. It wasn’t going to be full wraparound, but it should be good enough to get a feel for things. Something more elaborate was planned for a future phase. Well, that future phase has been brought forward, so something more elaborate is needed now.

Many – indeed, probably most – simmers use a projector as their primary visual display system. You can project this onto a screen erected in front of the cockpit – or even a wall. Some builders rear-project to avoid having to angle the projector and cause ‘keystoning’ – where the edges of the picture at the bottom are further out than the top, creating a trapezoidal image. Many simmers use a three-projector system with three flat screens joined together (left-front-right) with the left and right screens angled at 45 degrees or so, to get a very wide field of view (FOV) and a convincing front-side-view effect. Some use more – I have heard of systems with five or seven projectors to get individual side and rear-side views. Three is a common number because of the existence of the Matrox Triple-Head-2-Go, a hardware adapter box that lets you plug three displays into one side and one graphics card into the other, and have the card see all three displays as a single, joined display. Since MSFS performance decreases rapidly the more windows you have open, being able to have a very wide single window is a great advantage.

Some simmers use a curved projection screen, because this offers a smoother transitional effect especially when banking, but both curved and angled screens have the same problem – the image distorts due to the shape of the screen and the angle of the projector (with curved screens this is much more visible). In days of old, people used the manual or digital correction facilities of their projectors to fix this, but few projectors have the ability to correct for curved or dome-shaped screens. In recent years a piece of software called Sol7 has been developed that implements lots of correction algorithms at the display-driver level, and most curved-screen builders seem to use it; so many that the company that developed it, ImmersaView, has developed a special (and lower-priced) version of the software specifically for sim-builders.

Projection is a bit of black art, but one of the key factors in deciding on a projector is the throw ratio. This number, basically, says how large an image a given projector can display at a given distance from the screen. Short-throw projectors have wide lenses designed to spread the image over a short distance, so you could get an image a couple of meters wide from less than 2m away (0.61:1 seems to be the shortest throw ratio on the market right now). Most projectors also have a zoom lens so that you can blow up the picture and thus shorten the throw ratio.

Most cheap-ish projectors have a native resolution of 800×600 – which, by current standards, isn’t much. Over the years 1024×768 has become more affordable (I recall spending £3K on a 1024×768 capable projector for the office 9 years ago) but we’re still talking £500+. Widescreen 16:9 projectors are even more expensive. Full HD-capable projectors are at the top of the range and you would expect to pay at least £900 for one. A fair chunk of anyone’s cash, even by simmer standards.

As it happens, I have a projector already. It’s a Full HD 16:9 job with a native res of 1920×1080. The throw ratio is long (it was designed as a home theater projector, not a business unit) but I found a crafty way around that which I shall describe shortly. I had been using it as my day-to-day display in the living room, but decided to sacrifice it for the good of the project, and have now gone back to watching TV on the 46″ LCD I was going to use for the sim.

Because of the space limitations, I decided to go for rear-projection and put the screen as near to the windows of the enclosure as I could. Even so, the longest distance I could get between the wall and the screen would be 0.5m, and the maximum image size I could coax out of the projector at that distance would be 105cm wide. Not wide enough for a base that’s 1.8m wide. So, to increase the throw length I had available I decided to use a mirror. This is a common trick in projection. You need a so-called ‘first surface’ mirror – that is, the reflective coating is on the top surface of the mirror, not behind a layer of glass or plastic as on traditional mirrors, as this introduces distortion and ghosting into the image. The projector would sit inside the console, angled slightly up, and the mirror would  be placed against the wall in the right position and slightly angled down to correct the beam path onto the screen. Result – slightly more than double the throw length. Of course, the ratio ensures that this doesn’t double the size of the picture…

The problem with this was, when I did the maths, I still couldn’t get the image above 146cm, where I really needed 200cm. So I thought about it for a while and realised that while horizontal space was at a premium, vertical space was not. This led me to my current putative design for the visual display system, where the projector sits on the floor of the base, immediately ajacent to the wall. In front of its lens is a small mirror at 45 degrees to the beam; this reflects the beam directly up 1.7m or so, where it will encounter the main mirror, sized to cover the maximum size at that distance taking into account the angle (which distorts and lengthens the image vertically) – this will be an acrylic mirror and thus very light and flexible. The mirror will be curved to the same ratio as the screen to eliminate the keystoning due to the radius of the curve itself. It will be angled at a little more than 45 degrees in order to focus the beam slightly downwards and onto the final screen, which will itself be tilted back a few degrees to compensate. Lastly, Sol7 will be used to correct for the angles and the keystoning they introduce. With this system I can get a throw length of 2.5m and a zoomed display width of 210cm – more than enough.

The aspect ratio of the cockpit windows will be more like 2.35:1 (the so-called ‘Academy Ratio’ of cinemas) than 16:9, so I will end up with around 1920 x 800 pixels on the projected surface. This is more than enough, coupled with creative use of the MSFS negative-zoom feature, so get a FOV of around 120 degrees, which is more than adequate for my purposes.

The final touch – which I may not get around to immediately – is to cater for the windows directly to either side. One option is to build the windows so that they can be completely covered by the surface of a 24″ LCD monitor or a 30″ LCD TV, then simply put a left-right side view on each. Another is to cover the window with back-projection material and use a lower-res projector with a complex mirror system. Either way, this will require another dedicated PC to achieve a reasonable framerate. Something for Phase 2.5, I suspect.

I’m looking forward to getting started at the weekend, provided I meet my deadline to clear the sim-room. If this infection continues to clear up as it is now doing, that should be achieveable.

Lots of fun ahead!