Honeywell has been exploring synthetic-vision system (SVS) technology for the helicopter cockpit, but the display concept will bear little resemblance to the system the company unveiled last summer for fixed-wing applications.
HAI Convention News sat in on an in-flight sneak preview of what Honeywell calls its integrated primary flight display (IPFD) for helicopters, which is also being demonstrated here in the Orange County Convention Center exhibit hall at Booth No. 2801. “This is a true research project, aimed specifically at reducing the helicopter accident rate, not a warmed-over fixed-wing application,” said Sergio Cecutta, electronic displays product manager for Honeywell. He noted that helicopters and airplanes “are two different animals,” with dissimilar flight characteristics and control laws.
Honeywell introduced its fixed-wing IPFD–primary flight guidance symbology overlaid on a synthetic-vision terrain presentation–at the Farnborough airshow last July. It was, Honeywell said, the first “forward fit” (as opposed to retrofit) high-end SVS product on the market. The Phoenix company was also first to market with a helicopter-specific terrain avoidance warning system, the H-EGPWS (helicopter-
enhanced ground proximity warning system). The H-EGPWS terrain database, caution alerts and warnings are incorporated in the helicopter IPFD now under development.
Explaining why Honeywell is studying SVS now, Cecutta cited the need to provide helicopter pilots with greater situational awareness in all weather conditions and at night, requirements the H-IPFD is being designed to fill. “Every month there is a fatal helicopter CFIT accident in the U.S [civil and military],” he noted, pointing to a chart illustrating the high percentage of such mishaps arising from visual obscuration of terrain or water. He added that a GPS-based synthetic-vision system with a high-resolution terrain database combined with essential flight parameter information is showing a potential to make all rotary-wing flight equivalent to a “severe clear” day.
However, he continued, the helicopter presents vastly different SVS and PFD programming challenges than an airplane. First, helicopters routinely assume pitch attitudes that would be absurd in fixed-wing flight, especially negative pitch on takeoff and climb. Then there is the often-seen large differential between pitch and vertical flight path, and between heading and track. Throw in hover, steep approaches, low-altitude and low-speed operation and a whole new set of display parameters need to be developed.
While night-vision goggles (NVG) and infrared enhanced-vision systems (EVS) gain increasing use along with radar for real-time out-the-window visual enhancement, Cecutta said sensor-only systems have limitations. “No magic sensor sees through all particulates at all temperatures in all flight conditions,” he said. To provide the level of precision required for low-level flight in marginal visibility, Honeywell has tightened the resolution of its helicopter terrain database, from 24 arc-seconds in the fixed-wing application to six arc-seconds for rotorcraft. The result is a crisper, more realistic presentation of the environment ahead.
The helicopter terrain database differs from that in the fixed-wing SVS primarily in resolution. Contour lines are plotted much closer together. “Think of a topographic map with contour lines for every 10 feet of elevation instead of 50 feet,” explained Thea Feyereisen, Honeywell advanced vision systems program manager. Also, the helicopter display retains full resolution throughout its distance range, whereas the fixed-wing system degrades with distance. The helicopter database can offer more precision in part because it will cover a smaller area compared with the worldwide database of the fixed-wing version. The helicopter IPFD coverage will be offered in regional blocks, the size of about what two sectional navigation charts would cover, Cecutta predicted.
Honeywell will provide worldwide helo EGPWS database coverage with six arc-second global detail, however. It will contain more than 108,000 obstacles 100 feet and higher, including Gulf of Mexico and North Sea oil rigs. Obstacles as low as 100 feet in the U.S. and Caribbean will be updated from NOAA every 56 days. The developmental system now being flown in a Honeywell AStar also accepts pilot inputs of obstacles and waypoint designations using GPS lat-long coordinates.
As currently configured, the Honeywell helicopter IPFD is using a blended navigation solution with GPS, VOR and inertial inputs. No forward-looking IR sensor is included at present, but one might be added in a future production version. The production equipment will be NVG lighting-compatible. Honeywell is thinking in terms of both OEM and retrofit applications. Cecutta said the helicopter IPDF is “two to three years out as a marketable product. As for price, it’s too early for a cost estimate.”
February 19 turned out to be a perfect day to demonstrate the H-IPDF in the air, with a 3,000-foot overcast ceiling and seven-mile visibility except in the numerous rain showers dotting the Valley of the Sun outside Phoenix. The demonstration aircraft, which is also the system development platform, is one of the first AStars, built in 1979 as an Aerospatiale AS 350. N350FD has been used for several Honeywell STC programs, including conversion to the LTS101 turboshaft engine. Test pilot and tour guide Tom Frazier, director of Honeywell’s aerospace flight operations from the Deer Valley Airport (DVT) in north Phoenix, used the weather to give a real-time demonstration of the SVS accuracy vis à vis the real world outside.
One of the rain squalls, with about a half-mile visibility inside, happened to be right over a local landmark, Pinnacle Peak. From five miles west, the 500-foot crag was invisible but showed up in its actual shape on the IPFD along with a neighboring outcrop and the saddle between them. Frazier kept the PFD flight-path marker glued to the top of the peak as the AStar bored into the murk. The helo passed Pinnacle Peak level with its top and about 200 feet away, just as the head-down display said it would.
Next, Frazier headed west toward a practice helo landing pad marked visually by a circle of whitewashed tires and entered as a waypoint in the IPFD database. At about four miles from the pad, a round helipad symbol became visible on the display. With the flight-path marker planted on it, the IFPD showed an increasing approach path angle to the pad as range decreased. At his selected descent angle, Frazier started down, the pad still not visible to the unaided eye. At about a half mile, the circle of tires came into sight, out from among the surrounding desert vegetation as Frazier decelerated and transitioned into a hover.
A particularly useful (and potentially life-saving) feature of the helicopter IPDF is a set of unusual- attitude recovery cues on a decluttered display with arrows pointing in the direction of proper cyclic control inputs. Frazier put the AStar into a severe enough attitude to activate the feature, which gives a hard-to-misinterpret “This Way Up” (or Down) command.
He then demonstrated a low pitch angle, about 10 degrees nosedown, combined with a steep upward flight path during climbout, a rather unnerving PFD picture to a fixed-wing pilot with no helo experience. “You don’t see that in your airplane, do you?” Frazier asked. Meanwhile, the SVS background continued to match the view out the front window.
The SVS scene is color coded by altitude msl, much as on a sectional chart.