The Honeywell/ GEC-Marconi new-generation head-up display is about to enter flight-testing.
Guy Norris/PHOENIX
HONEYWELL AND GEC-Marconi Avionics' two-year old teaming arrangement to develop new-generation head-up-displays (HUDs) for business and regional aircraft is about to bear fruit, in the shape of the HUD-2020 destined for the Gulfstream IV, IV-SP and V.
Throughout January, the two companies have been working closely to integrate a pre-production system on Honeywell Business and Commuter Aviation System's GIV. The advanced HUD uses new symbology, including conformal approach and runway displays. Gulfstream, as launch customer, intends to use the HUD as the basis for an enhanced-vision cockpit to be available within two years.
If all goes well, the HUD will undergo the first of around 50 test flights in February. The team hopes that the flights will not produce any unpleasant surprises, as a generic version of the HUD-2020 has been put through its paces on the US avionics manufacturer's Cessna Citation III testbed, a process which began in April 1995.
Certification for Category II landing conditions on the GIV and GIV-SP is planned for the third quarter of 1996, with certification on the GV scheduled for 1997. Gulfstream, which is taking over the GIV HUD supplementary type-certification (STC) and "...rolling it into a GIV-SP STC for Cat II and GV for Cat II", will also have the programme lead for certification to Cat III - the ultimate aim of the HUD effort.
For Gulfstream, the development mainly offers improvements in safety and operating efficiency, both of which may boost future GIV and GV sales. In particular, the design potential of the HUD provides a platform for its planned enhanced-vision system, in which it will be augmented by forward-looking infra-red (FLIR) or a passive millimetre-wave (MMW) detection system.
"We are committed to go forward on an enhanced-vision programme," says Gulfstream HUD project manager Robert Morris. "We know our customer base traditionally operates from less-developed airports, so we want to give them the capability to operate from those airports at lower minima. You don't want to be circling the airport with your boss aboard while your competition is getting in with the airlines or other competitors' equipment," he says.
From a safety perspective, the Flight Safety Foundation suggests that, of more than 1,000 accidents, the presence of a HUD would have prevented around 31% of them. Honeywell believes that "black-hole" approaches, in particular, will be a safer proposition with "eyes out of the cockpit and all-round improved situational awareness".
INSIDE THE HUD
The most obvious, and possibly most innovative, features of the HUD-2020 include the large, 30 x 25¡, field-of-view of the GEC-Marconi Avionics combiner and the conformal symbology which it displays.
The compact CB-200 monochrome combiner and EO-200 electro-optical overhead unit, together with the HG-200 digital head up guidance computer, weigh only 23kg. Much of the saving comes from the advanced construction of the combiner. "The synthetic hologram system allows you to have a hard external surface on the combiner, which weighs only 140g instead of around 2.3kg for a normal glass combiner," says GEC-Marconi senior project leader, Martin Alpin. GEC is also looking at polycarbonate combiners for the future, which will reduce weight even more.
"This is a very efficient HUD system," claims Alpin, who says that 40% of the light gets through to the pilot's eye, compared with levels as low as 10% for some systems "...including some of ours", he adds. The glass layer, which is only 4mm thick, supports raster- scanned images for when MMW, FLIR or television systems are considered for enhanced-vision upgrades.
The combiner's large size enables the display to be less cluttered and gives the system the ability to project conformal symbology, even in high crosswinds.
At the heart of the system is the HG-200 head-up guidance computer containing redundant, fail-passive, Intel 80960CA 32-bit display processors which have "plenty of growth capability", according to Honeywell HUD-2020 technical leader, Dean Wilkins.
To fulfil future regulatory safety requirements for Cat IIIa capability, the system is also fitted with Intel 80386EX independent monitor processors.
To ensure easy operation with the GIV/GV avionics suite, the HUD-2020s are fully integrated with the SPZ-8000/8400/8500 avionics systems and HUD selections are integrated into the existing GIV/GV DC-884 display controllers in the GIV/GV. The HUD symbology is also complementary to the existing head-down electronic flight-instrumentation symbology.
Honeywell and Gulfstream jointly developed new symbology for the HUD covering all phases of the flight. "The flight-path vector [FPV] is the real key," says Wilkins. "It acts as an aiming point and tells you exactly where the aircraft is heading." The FPV is generated by a combination of data from the aircraft's global-positioning system (GPS) and inertial-reference system.
During take-off, for example, the HUD displays FPV lateral command to maintain the runway centreline during the roll. In this case, the HG-200 computer is taking signals from the instrument-landing-system's localiser to establish the centreline. A set of damped, closed-loop control laws have been written to prevent runway overshoots.
INSTANTANEOUS INDICATION
In flight, the HUD displays flight-director commands based on the FPV. This means that the pilot receives an instantaneous indication of where the aircraft is going, rather than having to integrate separate guidance cues from the standard aircraft reference, which only provides pitch and roll attitude information. "It brings the pilot more into the loop. He's now more aware of the motion and dynamic velocity of the aircraft," according to Honeywell engineering development test pilot, David Maahs.
The HUD really comes into its own on the approach, when the inputs from a range of sensors, including inertial navigation, GPS and the flight-management system, combine to give almost complete situational awareness. During a demonstration of the system to Flight International, the location of the destination airfield (the former Williams AFB, Arizona) was picked out clearly on the HUD at around 37km (20nm) range. The airfield was represented by a conformal rectangle with the extended runway centreline projecting towards the aircraft.
The conformal symbolic airport and runway gives the pilot a quick orientation to the landing area before normal visual sighting during an instrument approach. As the aircraft descends through 350ft (100m), the symbol representing the airfield narrows to converge into the shape of the runway. The symbolic runway (representing a 45m-wide strip) is aligned and adjusted to the elevation and direction of the real runway and is drawn with reference to the instrument-landing system. "Our goal is to have this generated by the FMS eventually," says Wilkins.
A patented symbology set gives cues to deviation on finals. "This is a first for a HUD," says Rolly McFarlin, Honeywell eastern regional marketing manager. The symbols take the form of short stripes, aligned with the runway and are arranged either side of the extended centreline.
"We flattened the symbols out to make it into a three-dimensional image," says McFarlin. The symbols relate to 1¡ deviations and they adjust with reference to the surface of the Earth.
The HUD symbology includes a glide-slope and flight path angle selectable between +9.5°. "It's like a built-in VASI [visual-approach slope indicator]", says McFarlin. Honeywell and GEC believe that the feature "...dramatically enhances night 'black-hole' approach safety", because it provides the crew to develop 'pseudo'-glide-slopes at airports not equipped for precision approaches.
Other symbology provides an instant display of aircraft acceleration and energy states. A speed-error tape rises above the "wing" of the FPV if the current speed is faster than the target or set speed, and drops below if the speed falls. An arrow slides up and down the speed tape to provide a cue to longitudinal acceleration along the flight path. "This has become an excellent visual cue to set power," says Maahs, who adds that it was scaled to be a potential flight path-angle cue.
More than 30 pilots who have flown with the pre-production HUD report that the symbology allows precise control of airspeed and glide path. The instantaneous acceleration cue and FPV will also allow the pilot to "...sense a windshear far before the wind shear computer warning", says Honeywell.
The HUD is also integrated with the traffic-alert and collision-avoidance system (TCAS), and displays resolution advisories and guidance. Because these are projected on the HUD, this enables the pilot to maintain a view of the outside world while making TCAS-commanded manoeuvres.
FUTURE GROWTH
Gulfstream believes that certification to Cat IIIa may be achievable by as soon as December 1996, if it can successfully combine a cooled FLIR enhanced-vision system with the HUD. "By the end of 1996 we intend to be well on our way to Cat IIIa minimas, if not already certificated," says Morris.
Gulfstream believes that a cooled FLIR system, possibly supplanted at a later stage by a passive MMW system, will be adequate for Cat IIIa. Honeywell, meanwhile, is pursuing a programme to develop an uncooled FLIR sensor for business aircraft, which would be integrated with the HUD.
Honeywell plans to use existing technology derived from its military business and believes that the uncooled alternative would be a cheaper solution. "We're pursuing something that would simply turn night into day. The Honeywell system will be cheaper and we intend to put it into a Citation testbed in 1996," says Wilkins.
In the meantime, Gulfstream expects to be fitting the HUD to "one in every four or five [aircraft] off the production line", says Morris. The HUD-2020 will be offered as a standard option on the GIV, GIV-SP and GV at around $400,000 installed.
Source: Flight International
