Wednesday, September 1, 2010
Rotorcraft Enhanced and Synthetic Vision
Enhanced vision (EV) and synthetic vision (SV) systems are becoming more common in rotary-wing as well as fixed-wing aircraft. The technologies are particularly valuable in helicopters, which fly much of the time at low altitude in the terrain. EV, typically based on IR sensors, gives the pilot a thermal image of the area in front of the aircraft, which is very compatible with human eyesight. SV is a computer-generated view of the landscape in front of the aircraft, using data from terrain and obstacle databases, the navigation solution, attitude information and other inputs. In helicopters SV is typically overlaid on the PFD, which also displays HUD-style flight guidance, while EV is presented on MFDs or small, dedicated displays within the pilot’s scan. Both technologies increase the pilot’s situational awareness while reducing pilot workload.
In the fixed-wing environment FAA has already granted operational credit when EV is used in combination with flight guidance on a HUD, in what’s known as an enhanced flight vision system (EFVS). RTCA is working with FAA to extend EFVS operational credit and to take initial steps toward credit for SV. But comparable credit has not yet been granted for head-down EV systems, the type used on helicopters. One way forward is to combine EV and SV so that real-time sensor data can help in detecting obstacles and painting them in the synthetic picture.
SV as it exists today has limits, said Gordon Pratt, Cobham Avionics vice president of business development. It is “not designed for zero/zero conditions or nap-of-the-earth flight by reference to the terrain,” he said. “It’s to keep you from hitting the ridgetop.”
Cobham’s SV-EFIS was certified on both rotary-wing and fixed-wing aircraft in 2003, Pratt said. It has now been approved on more than 740 fixed-wing aircraft and helicopters, including Bell, Eurocopter, Enstrom, AgustaWestland and MD Helicopters. The two- or four-screen system, which displays SV on the PFD and MFD, also includes H-TAWS and FMS. Traffic within the 70-degree SV field-of-view is also depicted on the synthetic display when interfaced to TCAS or TAS or when ADS-B is enabled. (Traffic on the MFD is visible a full 360 degrees.) H-TAWS and weather are also displayed on the MFD. Highway-in-the-sky (HITS) symbology provides a predictive flight director in the form of a series of concentric boxes on the PFD that the pilot flies through to keep on the flight path. The SV terrain database is accurate to six arc seconds worldwide. It is presented at six arc seconds on the MFD and 24 arc seconds on the PFD.
|The green boxes that frame the HITS route on the primary flight display lead the pilot along a pre-planned route to the destination. The ground track is shown in image on page 34. Cobham Avionics|
Tony Ashley, a DPS safety training officer in Del Rio, Texas, likes the ability to insert user waypoints and employ them with HITS. In a pursuit, for example, DPS communications operators can give pilots a lat/long for a patrol unit. The pilot programs the position as a waypoint, punches in “direct enter” to that waypoint and gets a HITS to that location. Another way to use it is if a pilot has to break off from a search orbit to refuel. Just save the last position as a waypoint, gas up, and when back in the air, punch in the last user waypoint. The system then gives HITS to the pilot’s last point in the search.
Although DPS helicopters wouldn’t take off under IMC conditions, SV is a wonderful tool under inadvertent IMC, Ashley said. “If you look at this thing, which is like a video game, it’s telling you which way is up—it looks like when you look outside,” if you could see anything outside. Where SV really pays, however, is on search orbits at 600 feet on “zero illumination” nights with no moon and heavy cloud cover, Ashley said. Even though you have goggles, you still don’t have very good clarity because there’s not enough illumination for the goggles to work. If the pilot is flying on instruments in a continuous right-hand orbit, it tends to be a little disorienting, especially in strong winds. So having HUD guidance and SV on the PFD “adds a great deal of safety,” Ashley said. The pilot can verify his orientation at a glance.
|Cobham Avionics’ highway-in-the-sky (HITS) tunnel (shown in green) is 400 feet wide by 320 feet high, spaced at 2,000-foot intervals. See page 35 for interior tunnel view. Cobham Avionics|
Chelton’s helicopter SV display differs little outwardly from the fixed-wing version, Pratt said. The main addition is the hover vector, a symbol set on the PFD and MFD that indicates the direction and velocity of a hover. Pilots use it to visualize drift over the ground and avoid brownout and whiteout accidents.
On the PFD below 30 knots ground speed the flight path marker changes to a “bull’s eye” display with a conventional attitude indicator overlaying the synthetic scene. Two concentric circles represent ground speed—the first, 10 knots and the second, 20 knots. As the pilot drift, a line grows out of the white dot at the center—in the 12 o’clock position—and ends in a gray dot somewhere off 12 o’clock, showing the speed and direction of drift. The pilot corrects to a static hover by centering the gray dot on the white dot. The hover display is also geo-referenced, so the pilot can also drop a marker, or temporary waypoint, and hover relative to it.
Garmin has introduced synthetic vision technology (SVT) specifically for helicopters as an option in its G500H product. The pictorial display on the helicopter side is very similar to that on the fixed-wing side. But the G500H synthetic picture on the PFD uses slightly different algorithms in the background, said Jessica Myers, manager of media relations. The synthetic presentation is driven off of a Garmin WAAS box, the GNS-430W or 530W, both of which include visual terrain advisory data. (The 530W is also capable of full Class B TAWS alerting.) Garmin’s helicopter SVT display does not use the HITS symbology simply because the ARINC 429 connection between the navigator and the G500H lacks sufficient bandwidth to transfer this information fast enough to the display. IR imagery can be shown on the MFD.
The field-of-view is about 33 degrees lateral by 44 degrees vertical. The helicopter SVT uses six-arc second data and has slightly higher resolution than Garmin’s fixed-wing SVT, which uses nine-arc second data. The G500H’s PFD display supports six-arc second data. Airports are indicated by little signs with their designators. The extended runway centerline is pilot-selectable from 500 feet to 10 nm. The SVT can also show traffic targets as dots on the PFD.
|Max-Viz offers its EVS-1500, which supplies dual fields-of-view with optical zoom. Max-Viz|
A screen shot of a prototype version of SmartView for helicopters shows an approach to Deer Valley Airport near Phoenix. The synthetic terrain depiction is overlaid on the PFD. “Super-sized” landing zone and helipad symbols are shown in the upper part of the display. In the lower portion is an HSI with partial compass, range ring of distance-to-go and a top-down view of the landing pad. The SV terrain has a “dimpled” texture which helps to give the pilot a sense of height and motion.
IR-based EVS systems are also readily available for helicopters, displayed head-down on an MFD, primary navigation display, or a small, dedicated display. Max-Viz and FLIR Systems offer a range of products. The Max-Viz EVS-1500, for example, provides dual fields-of-view with optical zoom. It is the only optical-zoom, dual-FOV sensor in the industry, said Bob Yerex, vice president of sales and marketing. The pilot can select a 53- or 30-degree field-of-view, depending on the situation. If the pilot chooses 30 degrees, the lens physically moves and the pixels are compressed, increasing resolution, Yerex said. A digital zoom, by contrast, basically “blows up the pixels,” he said.
One way to use the dual FOV is on an instrument approach, Yerex continued. On the interception leg, the pilot could use the wider FOV. As soon as he intercepts the localizer and turns inbound, the pilot would go to the narrower FOV. Then, when coming in for the landing, he could switch back to the wider FOV to pick up anything off in the periphery. The EVS-1500 has been approved on multiple Bell, Eurocopter, Sikorsky and AgustaWestland models.
FLIR Systems’ EVS product is the EVS3, launched three to four years ago and approved on the MD900 and in process on several MD and Eurocopter models. The EVS3 is available in three fixed FOVs—20 degrees, 35 degrees and 46 degrees, explained Jim McGowen, vice president of FLIR Systems’ Personal Vision Systems unit. It is the first EVS aviation product to hit the market at under $15,000, he added.
The Next Step
The next step, developers agree, is to combine real-time sensor input with the synthetic image of the outside world. Companies are experimenting with IR, millimeter-wave radar and lidar sensors to complement SV, which is typically limited by its dependence on GPS and terrain/obstacle databases. But IR, the most popular choice so far, is limited as well. It can’t penetrate heavy weather such as dense fog, Pratt pointed out. Nor could it help to identify the runway when the tarmac and adjacent ground are covered with snow. If one could engineer a blend of SV and EV, the pilot at a certain point relative to the runway could “determine which bias—SV or EV—is favored” and tune the display accordingly, he said. At about 2,500 feet AGL, for example, where the radar altimeter comes into effect, would be a good point to enhance synthetic vision on the PFD in a heads-down environment, said Greg Schmidt, Cobham business development manager.
Rockwell Collins’ Pro Line Fusion avionics system will provide enhanced vision and synthetic vision on the HUD (though not in blended form) for corporate jets. Another way of combining the two technologies is to extract obstacle data gathered by the real-time sensor and display it on the SV overlay presented head-down on the PFD. Military-driven research has employed millimeter-wave radar, lidar and IR sensors in combination with SV in an effort to solve the brownout problem.
Honeywell, as part of the U.S. military’s Sandblaster research program, overlaid sensor data from a 94-GHz millimeter-wave radar on a terrain database, presenting obstacles such as wires and trucks in the approach to a landing area on the SV display shown on the PFD.
CAE is developing an Augmented Visionics System (AVS) that combines input from a lidar or IR sensor with SV on a PFD or helmet-mounted display. In an AVS demonstration in January 2010, the company used a lidar sensor to scan the terrain in a FOV 30 degrees horizontal by 60 degrees vertical in front of the aircraft in order to see through brownout and detect obstacles that can’t be seen with the naked eye, explained Adolfo Klassen, CAE’s chief technology officer. CAE added a PFD display to a Bell 412 for the demo. The high-definition display supported a database resolution of five to six arc seconds. After the demo, the flight data was also played back on Thales’ Top Owl helmet mounted display.
In the AVS application, sensor data is processed and presented on a SV display overlaid on the PFD. It is not a target recognition system, Klassen advised. The pilot would not see a clear picture of a truck, for example. Basically the system paints in a block showing the orientation, size and exact location of the obstacle. But “we’re updating the synthetic view in real time,” he said. In actual use, the AVS real-time sensor data would probably augment imagery of a mission area that had been collected by satellites or UAV overflights. The AVS sensor data can be temporarily or permanently added to the application’s terrain and obstacle database.
With today’s technology the AVS system would allow a helicopter flying at 140–180 knots to see an obstacle on the display 200 meters ahead. The goal is to maintain a safe warning distance at speeds of up to 240 knots. CAE is refining the algorithms that process the incoming sensor data and productizing the system.
Cobham also is working on combining EV and SV, Pratt said. This would add the benefits of a real-time sensor for detection of wires or obstacles like trucks on the runway. The company is already able to display an image from an IR camera on the EFIS. Pratt envisions a combination of infrared-based EV and SV on an MFD. But there’s a lot of certification and human factors work that has to occur before such a solution is certifiable, he added.