Allan Winn/DUBAI
Ever since the then-Hughes AH-64 Apache entered service with the US Army in 1984, it has been the benchmark against which other combat helicopters are measured. Since then, it has undergone two marque-name changes (first to McDonnell Douglas, then, more recently, to Boeing) and become the most prolific Western attack helicopter. In addition to 827 Apaches delivered to the US Army, well over 100 have gone to export customers Egypt, Greece, Israel, Saudi Arabia and the United Arab Emirates.
Periodic upgrades have kept the Apache competitive with more recent designs such as the Eurocopter Tiger: the most comprehensive of these has been the revision to AH-64D specification, which involves a major upgrade to the helicopter's systems and incorporates the ability to carry the Northrop Grumman Longbow millimetre-wave fire-control radar and Lockheed Martin Hellfire missiles. All US Army AH-64As are being upgraded to this -D specification, and the AH-64D has been chosen by the Netherlands and the UK (where the Westland-assembled version with Rolls-Royce Turboméca RTM322 engines will be known as the WAH-64).
Not all -D models will be fitted with the mast-mounted Longbow radar: the Netherlands, for instance, is not taking the radar, and the radar-equipped version is not yet cleared for export to some parts of the world. Thus, when the AH-64D was exhibited at the Dubai air show in November 1997, it was without the distinctive mast "mushroom": it was in this form that Flight International was invited to sample the latest machine and, in particular, to try out its new targeting and designation systems.
SIGNIFICANT CHANGES
Much has changed since we last flew in an Apache, in 1989. Then, the outstanding performance and exemplary handling of the AH-64 were of as much interest as the mission systems. The outstanding memories of that earlier acquaintance are of the perfectly balanced, weighted and harmonised flying controls, and of the comparative ease of acquiring and locking on to a target with television or infra-red sensors.
Apart from the "mushroom", when fitted, the most obvious visual differences in the newer machine are the much-enlarged forward avionics bays, which now flare out from the nose and extend aft to finish just behind the stub wings. These large composite fairings hold the avionics for the target-acquisition and designating system (TADS) and the pilot's night-vision system (PNVS), both produced by Lockheed Martin, as well as the compressor for the avionics environmental-control system. The lower right-hand fairing eases access to the cockpits.
The avionics are based around a 1553B databus and 32-bit processors. By using a three-channel architecture instead of a single channel, there is enough redundancy to meet the objective of retaining combat capability even if a processor is lost - whereas the A model was susceptible to a single-point failure. Boeing demonstration pilot, Jim Adkins says that the previous system was equipped with 13 different processors using nine different software languages: everything on the 1553B bus uses the ADA programming language.
There have been similar improvements in the navigation system. The -A model has a Litton Doppler-based heading- and attitude-reference system, which, says Adkins, "can drift about 20ft [6m]/min and still be in spec". Such systems need to be updated frequently by overflying known reference points, but the inertial-navigation/global-positioning system (GPS) now used does not need that overflying for reference. Using the "government key" in the GPS means, says Adkins, that the system is generally accurate to within 10m.
ACCURACY
As a part of the demonstration to Flight International, the Apache was asked to return to a waypoint (a tree in the generally featureless landscape some 30km (16nm) outside Dubai) which had been entered into the system during a flight the previous day: the system brought the helicopter to within 20m of the tree.
The accuracy given by this enhanced navigation system to the "hover-hold" capability is such that, in 20min of exercises using the TADS to identify and track various targets in the vicinity of this tree, there was no perceptible drift. Altitude hold in the hover, at up to 1,500ft (450m) above ground level, is managed through the radar altimeter. In flight, altitude is governed barometrically.
The -D model, like the later -A models, has two General Electric T700-701C turboshafts with a maximum continuous rating of 1,410kW (1,890shp) each and an emergency rating for single-engine operation of 1,450kW. This gives the -D a single-engine flyaway capability at a weight of 7,305kg in conditions of 50íC at sea level (the maximum take-off weight with full fuel for a ferry mission is 10,110kg).
More significantly, for combat duties - with full internal fuel, two crew, 16 Hellfire missiles and 19 70mm rockets with multi-purpose submunitions (weighing 12.25kg each), 600 rounds of high-explosive 30mm ammunition for the chin-mounted chain gun and one 870litre external fuel tank, (giving an all-up weight of 9,000kg) - the AH-64D has a combat radius of 305km with 30min on station and 20min reserves.
The real advances incorporated in the AH-64D, however, are in its fighting capability - largely through improvements to its mission systems. To the crew (pilot in the rear seat, co-pilot/gunner in front) the most obvious visual difference is in the two enlarged (150 x 150mm) colour multi-function displays (MFDs) facing each, and the comparative lack of clutter. The number of cockpit switches is reduced from some 1,200 in the older model to 200 in the -D. The aim with the new displays, says Adkins, is "-to manage information by exception". An improved data modem allows the crew two-way communication and targeting transfer with other Apaches and ground control, and to link with other airborne control platforms such as the E-8 Joint Surveillance Target Attack Radar System.
The data-transfer unit (DTU) in the rear cockpit uses a data cartridge which occupies a space of just 20 x 100 x 150mm. This cartridge can be updated by a battle-planning station on the ground with targets, routes, etc, and then plugged into the aircraft. It can store ten routes, each using up to 99 waypoints, 50 known threats or targets, 15 boundary lines, 12 engagement areas, six primary fire zones and one no-fire zone. Through it, the weapons system can be configured with, for instance, laser or weapons codes. "Somebody else can programme all that for me and give it to me," says Adkins. The cartridge can also store during flight the co-ordinates of up to 100 targets which have been shot at and, as before, there is also a video recorder.
The DTU, says Adkins, "allows any one individual [in an Apache fleet] to become a battle commander and to run other aircraft. Anything on the data cartridge can be transmitted to another aircraft." Also, he says, "somebody else can designate a target and hand it over to me - even without a radar on my own machine, I can take a radar target". All the transmissions by the system can be made as databursts using a rate of 16,000bits/s.
The DTU has non-combat roles as well. It stores data on all maintenance-related difficulties experienced during a flight, including malfunctions which correct themselves during the flight, all on a time-log basis.
CLEAR AND LOGICAL
All the combat functions of this and other systems are presented to the co-pilot/gunner in a clear and logical way, with virtually all the controls based on either the buttons of the MFDs or on the hand-grips. Essentially, the MFD buttons are used to select modes on the displays, and the hand-grip switches, buttons and "coolie-hat" knobs are used to control the sensors and weapons.
The TADS sensors are for daylight, a television camera with narrow (0° 50') and wide (4° 0') fields of view, direct-view optics with 4° and 18° fields of view, with laser spot-tracker and designator and, for night, a forward-looking infra-red (FLIR) sensor with fields of view of 3° 6', 10° 6' and 50° .
The television and FLIR outputs can be brought up on either of the MFDs, as can the navigation and targeting information.
The output from the FLIR can also be used as a back-up source for the head-slaved PNVS should the latter's own wide-field-of-view sensor be disabled. Both the FLIR and television images are exceptionally clear on the big displays and, on the greatest-available magnification, clear details of targets at distances of a kilometre or more are easily discerned.
While the hand-grip controls fall easily to hand, and are nicely geared and positive in action, it would take a good few hours of ground-school (and a lot of airborne practice against realistic military targets) for a co-pilot gunner to become thoroughly proficient with their use to the point where reactions were automatic. Certainly, a session of just over 30min aloft can give only a quick introduction to - but a very clear indication of the potential of - the enormous capabilities of the systems. There is no doubt that they are extremely impressive.
Source: Flight International
