Paul Lewis/NASHVILLE
The US military is preparing for a warfare revolution by forming the world's first digitised army early next century. At the head of this planned Army XXI will be the Boeing Sikorsky RAH-66 Comanche armed scout/attack helicopter.
Battlefield digitisation entails the fusing of a broad range of ground, airborne and space-based command, control, communication and intelligence-gathering systems. The strategy is to win the war by dominating and exploiting information. Comanche was designed as one of the main means by which to achieve this goal.
"This platform is not just another system - it's an asset with a multirole-ability to gain information dominance and then pass on that information to the critical command and control people, the intelligence people, to the manoeuvre elements and guys in fire support," says US Army RAH-66 programme manager, Brig Gen Joseph Bergantz.
Comanche will plug into a pan-military information exchange network and as such will be the first army helicopter to be fully conversant with a spectrum of different communication protocols. In addition to the US Army's Mil Std 188-220, it will be compatible with US Air Force AFAPD and US Navy/Marine Corps marine tactical protocol, as well as the Link 16 Joint Tactical Information Distribution System.
It will be able to interface with complementary surveillance systems, such as the Boeing E-3 Airborne Early Warning and Command System, Boeing RC-135 Rivet Joint and Northrop Grumman E-8 Joint Surveillance Target Attack Radar System (Joint-STARS), Raytheon RC-12 Guardrail electronic intelligence assets, as well as tactical strike aircraft, unmanned air vehicles and communication and positioning satellites.
"We're talking about joint forces," says Bergantz. "We're going to have communication systems to allow us to talk to, say, fighter aircraft and our Joint STARS sister up in the air with a God's eye view and share information back and forth. This is where the real potential for this thing will come about," he adds.
The key ingredient to make all this work is RAH-66's mission equipment package (MEP). In place of traditional federated "black boxes", the helicopter has two redundant mission computers and slot-in cards. The 190 or so electronic modules are solder-free and can easily be changed for repair, replacement or updating.
One example of this architectural approach is Comanche's Integrated Communication Navigation and Identification (ICNIA) system, which essentially acts as an inter-service calling card. ICNIA's different modules comprise Sincgars VHF-FM, VHF-AM AND UHF-AM Have Quick radios, identification friend or foe transponders, voice security and automated data communications hardware.
The TRW-designed Comanche system leverages off technology being developed for the Lockheed Martin/Boeing F-22 fighter. "A lot of the modules are common between what the F-22 has and what we're going to use. It's probably going to be the same architecture and systems used on the Joint Strike Fighter as TRW is on both teams," says Bergantz.
Comanche's two mission computers are linked to other MEP avionics and sensory systems via a network of fibre optic and conventional wire data buses. Included in this arterial loop is the new electro-optical sensor system (EOSS) under development by Lockheed Martin.
The nose-mounted EOSS mainly comprises two second-generation 8-12 micron forward looking infrared (FLIR) imagers for targeting and piloting. "These sensors can see about twice as far as current sensors and by the time you multiply the length and width you can really see four times the area," claims Art Linden, director of the Boeing Sikorsky RAH-66 joint programme office.
The night vision pilotage system (NVPS), the upper of the two EOSS turrets, also includes an image-intensified television. Both are linked to a Kaiser Electronics Helmet Integrated Display Sight System (HIDSS), which offers a wider 30 x 52í field view than the 30 x 40í binocular system employed on the Boeing AH-64 Apache. The RAH-66's 20mm gun turret is similarly slaved to the HIDSS.
Directly beneath NVPS is the larger electro-optical target acquisition and designation system (EOTADS), which can also act as a back-up piloting system. The stabilised turret in addition to housing the SADA I surveillance and search FLIR and a second solid-state television, accommodates a two-colour laser designator and rangefinder.
Comanche is not only able to see further with EOTADS, but will be much faster and more discerning about what it views with the use of an Aided Target Detection and Classification System (ATDC). The system will automatically scan an area and store image data and so minimise the time the helicopter is unmasked to hostile fire.
"Our issue was that covering so much more of the battlefield made it extremely unacceptable to keep the aircraft exposed that length of time. The ATDC with preprogrammed algorithms will classify targets, based on what the threat is and the range. All this can be displayed or transmitted back," says Linden.
The Northrop Grumman programmed software uses memorised images scanned in from different angles to generate a match with objects captured by EOSS. In addition to identification and classification, the distance and co-ordinates of a potent threat can be calculated with the help of global positioning satellites for targeting.
Lockheed Martin's Longbow millimetre-wave radar has a similar classification capability, but ATDC has the advantage of being passive and providing better image clarity. "The ultimate solution will be to take FLIR, with low light TV and the radar image and do a fusion of all three. That will give you remarkable characteristics as each sensor sees things differently," adds Linden.
The US Army is provisionally intending to equip about one-third of its planned 1,292 Comanches with a development of the Longbow system. The fire control radar will feature 560mm (22in) diameter electronically scanned antenna, almost half the size of the APG-78's rotating array being retrofitted to the AH-64D Apache Longbow.
To conform with the RAH-66's overall low-observable design, the radar's mast-mounted housing is being remoulded to reduce the radar signature of the current Apache Longbow's doughnut-shaped rotodome. Windtunnel and model testing is under way of a new "truncated cone" type arrangement, which although slightly taller, will be more stealth-like.
Comanche's role as an information gatherer will require it to operate well forward of the army's mainbody, and survivability on a modern battlefield is critical. Reducing its radar, acoustic and infra-red signature accordingly has been the primary driver behind the helicopter's design. "We want to see without being seen," says Linden, who claims a radar signature for RAH-66 around 1/300th of current aircraft.
Critical design features, aside from passive sensors, include a low-noise shrouded tail rotor, suppressed infra-red engine exhaust, fully retractable landing gear, twin internal weapons bays and an airframe structure 58% comprised graphite, kevlar and glassfibre-reinforced plastic. Active defensive systems will include infra-red, laser and radar homing detectors.
Deployability has been another major criterion for Comanche designers. The RAH-66 will be able to self-deploy across the Atlantic, via the Azores, with two 1,700 litre (448 USgal) auxiliary long-range fuel tanks on external stores pylons. Preliminary work is under way to install 425 litre tanks to the side weapon bays (Flight International, 26 May-1 June)
A planned increase in the Comanche's maximum take-off weight to 5,845kg (12,880lb) will also increase the helicopter's maximum internal fuel load to 870kg and extend its endurance by 25% to 2.6h. "The army's design mission never required that we fill the tank and we designed it with a little bit of growth," says Linden.
These revised weights, with a wider 12.2m-diameter main rotor, will be incorporated into the first of five preproduction prototypes due to fly in May 2003. A $3.6 billion engineering and manufacturing development (EMD) contract is due to be awarded by March 2000, 19 months ahead of the previously revised timetable.
"It made sense to bring it forward because we were ready to enter into the full-scale development phase and the technology was there to demonstrate an earlier milestone exit criterion. It's a strong signal we're ready to get on with it and get closer to production," says Bergantz.
The move is tacit recognition that the initial demonstration/validation phase of the Comanche programme has been treading water for some time due to funding slippages. The initial prototype has clocked up close to 150h in flight validation time since early 1996, during which it reached 175kt (325km/h) in level flight, a ceiling of 9,500ft and 80í a second hover turns.
A second MEP test machine flew in March, but has been grounded grounded after logging only a few hours. It is not scheduled to fly again before 2001. "One of the things we have on our list is to get some more money to fly aircraft No 2 all of next year," says Linden.
EMD includes funding for eight preproduction RAH-66s which will be fielded by the US Army for digital experimentation. The Fort Hood-based 4th Infantry Division has been designated as Army XXI's inaugural digital unit in FY2000-1 and the parent 3rd Corps, the first digital corps from FY2004-5. This will include the 1st Cavalry Division, the first troop to receive Comanches.
Low-rate production deliveries will begin in 2006 with an initial 14 machines, progressively increasing to 72 a year by 2010-11. "Comanche will be a leap ahead of the Bell AH-58D Kiowa and AH-1 Cobra helicopters we're replacing in the light divisions. In terms of digital weapons systems and with the capability being brought to the fray, we'll be able to get information dominance," predicts Bergantz.
Source: Flight International
