Despite Level D requirements already being well satisfied, visual systems for civil flight simulators continue to improve incrementally, driven by new capabilities developed primarily for consumer markets. Rick Adams looks at trends in projectors and image generators.

Of course, airline pilot training operations desire ever-improving realism. So long as it doesn’t cost more.

“There’s a balancing act,” says Ed Koharik, General Manager, Visual Systems, for FlightSafety International. “They would like to see more fidelity in the systems to be sure their training is optimal, but there’s a reluctance to pay for something that’s more than a Level D requirement. You get a little bit of a conflict between the training teams and the resourcing teams. A contracts person is looking at the requirement, where the operator might see a visual system that brings more fidelity but is going to be more costly.”

“Customers don’t want to pay for anything more than they need,” agrees Dave Fluegeman, Vice President, Simulation at Barco. “Our systems integration partners have a very specific set of requirements and they don’t want excessive over performance, weight, or size. The spaces for the projectors are proven, they’re designed in, they don’t want to alter that too much and change their formula too much, and we don’t want to cause them a lot of disruption from a mechanical engineering or thermal engineering perspective. We try to keep it within the same footprint, the same energy consumption, the power draw. Our challenge is to bring something to market that takes advantage of higher performance in a footprint that they can readily use without any disruptions.”

Cost-resistance aside, the inexorable advancements keep coming, largely thanks to enormous sums being invested by visualisation companies focused on the consumer electronics market (while also addressing the niche simulation customers).

Projectors: LED, Laser, or New HLD?

In the projector space, the lamp is dead. Long live solid-state illumination.

“The state of the art in projection is certainly centered around solid-state illumination, given the long lifetime of those illumination devices compared to lamps,” states Barco’s Fluegeman. “This allows the simulator to stay up for a lot longer, a lot more training time, less maintenance downtime.”

Lamps burn independently; no two lamps burn at the same rate, at the same degradation pattern, at the same loss of colour, he explains. “There’s just no consistency there. The potential for an imbalance in your colours and the lumens in a lamp-driven device is pretty high. You’re always swapping and calibrating. All of that equates to downtime.”

Solid state devices promise 20-50,000 hours of lifetime service, and can be digitally controlled – the degradation can be managed and balanced automatically.

“We have designed our last lamp projector,” Fluegeman emphasised. “Barco is implementing solid state devices across all our markets.” Barco offers both red-green-blue light emitting diode (RGB LED)-based projectors for simulation and laser-powered phosphor display projectors.

Airlines and independent training centres are seeking “depth of colours, stability of operations, overall higher resolutions, better performance, lower total cost of ownership, less downtime,” summarises Fluegeman. “The peak loading of simulators has only gotten tighter and tighter. The product has to be near bulletproof. No touch or low touch. Maintenance-free. With solid state, it’s a set it up and let it run type of approach.”

JVCKenwood Chief Engineer Rod Sterling is in agreement regarding solid state illumination, though JVC has gone all-in on laser. “A lamp is still cheaper than a laser illumination system to build,” he admits, but considering simulation ownership cost across five or 10 years, “laser makes sense.” The company will bring out its third generation Blue Essence laser phosphor simulation projector later this year. “Laser phosphor is getting more robust, smaller, more efficient,” notes Sterling.

An advantage of lasers compared with LEDs is stability in the light wave output, which can be managed down to zero lumens. If operating in night vision, it’s easier to set up a darker scene by turning the laser power down very, very low. But this is more for military training applications.

Certainly lasers offer much higher brightness, as much as 2-3,000 lumens (compared with 7-800 for LEDs) plus better contrast.

One primary difference is that laser phosphor uses mechanical devices – a phosphor wheel (a blue laser is directed through a yellow phosphor-embedded wheel and then into a colour wheel to get the spectrum of colours). There is therefore potential for failure of the mechanics. An LED projector has no moving parts except for fans.

Fluegeman says the output of current second-generation LED-based projectors is “right on the upper edge of the limits of the projector,” but “it’s acceptable. It passes. It gets certified. CAE has deployed hundreds of these units around the world and never had a challenge getting them certified.”

In October, Barco will introduce a third-gen product – the FL40 – that “has a lot more headroom in terms of performance. Our partners can double the lumens and still get more performance out of it. So they’re not running the projector at maximum performance and have to figure out tricks to try to make the contrast better or to make it a little brighter.” The FL40 will use a hybrid solution incorporating a Phillips ColorSpark High Lumen Density (HLD) rod to replace the green LED. (The HLD rod is basically an aggregation of LEDs in a tube. Phillips is still working on the red and blue HLD variants.)

The hybrid approach, Fluegeman claims, will yield about 2,500 lumens, or up to three times the output of the current LED projectors. “It gives the simulator configurators a lot more breathing room, a lot more flexibility in how to operate the projector or how they manage the content in the image generator (IG) side of things. It just takes some of the restrictions off the system integrator from a design perspective,” notes Fluegeman.

“Nothing is perfect,” he adds. “Every systems integrator has to take a projector and compensate for its shortcomings.”

JVC incorporates a technique they call “pixelshift” to improve the resolution of lower-cost imagers with some minor hardware and firmware changes. “For the first 60 Hz,” Sterling explains, “you image the panel resolution. Then with an optical shift plate you can shift the image half a pixel – up and down, left and right – and then flash the image again.” He said this effectively doubles the precision while still writing at 60 Hz without any flicker. Also, “if updating the panel at 120 Hz, you can put real data in that frame, not interpolated but intelligent data where it belongs. This helps with smear, readability and static resolution as well.” He estimates the resolution improvement at about 50-70%.

Pushing Pixels

Dennis Hartley, Principal Systems Engineer for Rockwell Collins, a long-time leader in IG technology, says, “We’re usually not too concerned with the illuminator technology. Though we do have preference for the laser projectors; they’re a little brighter and their dynamic range is a little higher than the LED. What the IG cares about is how many pixels it has to drive.”

The industry standard has shifted from 1080p HD (High Definition) projection with about 2 million pixels (2 megapixels) to 2560x1600 WQXGA at 4 megapixels. The next step will be what is referred to as 4K, which is actually about 8.8 megapixels. By 2020, more than half of US households are expected to have 4K-capable televisions. Even the camera in the new smart phone I purchased recently incorporates 4K resolution.

“If you are driving an HD projector, WQXGA is 2.2 times at the same update rate of 60 Hz,” notes Hartley. “If now you step up to a 4K projector, that’s a 4X increase in pixel processing. It puts more of a burden on the IG being able to process all those pixels.”

He adds that Rockwell is attempting to build modularity into their systems capabilities so they can offer a lower cost system that drives an HD or WQXGA projector or increase it to a 4K projector.

FlightSafety’s Koharik says, “Native 4K is now becoming a standard, and I think you’ll see projector manufacturers in the future bringing out 8K. A native 8K is going to improve it even more, but again at a cost.”

“The projector technology is going to be key, whether it be resolution or higher frame rates reducing the smear for dynamic scenes,” he adds. “No matter how good your databases look, how much detail you put into them, if the projectors are not capable of providing that in front of the operator it doesn’t do you any good.”

He hopes to see improvements in the cost of IGs, taking advantage of commercial off-the-shelf (COTS) solutions and “maybe less customisation, focus more on the software, applications and content to get the level of training required.”

FlightSafety engineers have developed an IG capable of delivering a true 120 Hz frame rate with a single channel. Previously, some manufacturers had run two channels to achieve 120. “With a single channel, we keep the cost down for the customer but provide added performance,” Koharik told CAT. The new system addresses visual cues the pilots see when closer to the ground and reduces smear effect, particularly on the aircraft’s final approach.

The 120 Hz single channel is incorporated into a new Embraer E2 full flight simulator with collimated glass display, which will be installed later this year at FlightSafety’s training centre in Paris, France. Koharik declares: “I would challenge any other commercial provider to have a capability anywhere near what we have delivered on that system.”

Published in CAT issue 4/2018