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Sensor fusion

Advanced man-machine interface techniques such as combined HMD and voice control promise to ease the pilot's workload

Substantially more effort has been expended in the development of the Typhoon's "man-machine interface" than Eurofighter had originally estimated. But the result is a cockpit that is highly automated and easy to use.

As demonstrated by project pilot Craig Penrice, in British Aerospace's Active Cockpit flight simulator, the aircraft seems deceptively simple to operate: "Start the APU at the bottom of the ladder, climb up, plug the data storage 'brick' in, fire up, strap in, push the throttles to idle, close the canopy and you're ready."

Information on the displays and operation of the controls are tailored to the phase of flight, from take-off, through navigation to combat, and back to landing. "The cockpit philosophy is to provide all the information needed - when it is needed," says Penrice. Sensor data are fused into a single picture and systems "housekeeping" is automated to allow the pilot to concentrate on tactics.

Behind the cockpit controls and displays is a network of distributed processors linked by multiple databuses. A single digital databus was not adequate, so the Eurofighter has several electrical, or "copper", buses and two high-speed fibre-optic, or "glass", buses. The glass bus has 20 times the throughput of the copper bus.

Dual-redundant copper buses connect elements of the cockpit, flight control, utilities control, armament and defensive aids systems. They also control the flow of data on the dual-redundant avionic and attack glass buses. This "distributed intelligence" architecture provides for "graceful degradation" with failures, says Eurofighter's Martin Friemer.

The utilities control system is a major contributor to reduced pilot workload, as it automates control, monitoring and fault detection for the aircraft's general systems, including electrics, hydraulics, fuel, environmental control, secondary power and landing gear. Each "utility" is digitally controlled and linked via databus to the cockpit and other systems.

The avionics system, meanwhile, is grouped into subsystems ranging from attack and identification to integrated monitoring and recording. The high-integrity armament control system is designed so that no single fault will cause or prevent the release of any stores. The navigation subsystem provides an automatic landing capability as well as combining laser inertial and satellite navigation.

The attack and identification system is at the heart of the Typhoon's combat capability. It is here, in the attack computer, that data from the radar, infrared search and track (IRST) sensor, identification friend or foe interrogator, and electronic support measures (ESM) system - and, via datalink, from offboard sources - are merged to produce a single tactical picture for display to the pilot.

"The sensor fusion process produces a unique track of a single target which may be reported by several sensors simultaneously, each one providing a subset of target attributes which are compiled to produce an as complete as possible view of the target," Friemer says. Algorithms weigh the reliability of each report before merging them to produce a fused target identity and priority.

The Typhoon's primary sensor is the ECR90 multi-mode pulse-Doppler radar, supplied by a Marconi/Fiar/Dasa/Indra team. Described as "third generation", the ECR90 represents a bridge between conventional mechanically scanned (M-scan) and advanced electronically scanned (E-scan) radars.

"We are very conscious of developing a mechanically scanned in the age of electronic scanning, but it is too early for E-scan," believes John Roulston, technical director of Marconi Electronic Systems' Avionics group. "We did not want a first-generation E-scan versus an end-generation M-scan radar."

Instead, the ECR90 incorporates improvements which increase performance beyond that of current radars. "Everything is a little better, and it adds up to a whole lot more," Roulston says. The biggest advance is "data-adaptive scanning". This allows the target tracking function to take control of the antenna scan pattern. In track-while-scan mode, as the radar continues to search for new targets, the antenna can "jump" to update information on targets that are already in the track file.

Data-adaptive scanning requires a lightweight low-inertia antenna, with a "very special" drive system, he says, adding: "The speed with which the antenna moves is awesome." The agility of the radar is such that interleaved air-to-surface and air-to-air operation is possible, Roulston says.

The ECR90 is highly automated, to reduce pilot workload. In air-to-air modes, the radar automatically selects the appropriate waveform - high, medium or low pulse-repetition frequency - as it scans, and automatically tracks all targets in its search volume. Threat identification and prioritisation are also automatic.

Air-to-air modes are being developed first, and will be incorporated in the initial operational capability (IOC) standard aircraft. These include multi-target track while scan, raid assessment, non-co-operative target recognition and close-range combat functions.

Air-to-ground modes will be added with the full operational capability (FOC) standard aircraft. These include Doppler beam-sharpened ground mapping for navigation and targeting, and synthetic-aperture radar ground imaging for reconnaissance.

Basic radar performance has been demonstrated. "We have no problems against the specification," says Roulston. "Air-to-air detection range is superb in all weather conditions." There will be no hardware changes from IOC to FOC standard. "The only difference will be software," he says.

Under development by a Fiar/Pilkington team, the IRST will provide a passive adjunct to the radar. Mounted below the windscreen on the left side of the fuselage, this sensor has two modes: scanning IRST and imaging forward-looking infrared (FLIR). The system also operates in two wavebands: 3Ám and 11Ám.

IRST target data is fed to the attack computer for fusion with other sensor inputs. Modes include multi-target track while scan, automatic prioritisation, kinematic ranging and identification (in single-target track mode). FLIR imagery can be displayed in the cockpit for use as a flying and landing aid. Development of the IRST lags that of the radar, and the system will not be installed until FOC.

Initial aircraft will also lack the defensive aids subsystem (DASS), under development by a Marconi/Elettronica/Indra team. The DASS provides integrated ESM and electronic countermeasures (ECM), with missile warning and, on some aircraft, laser warning.

"The ESM and ECM are fully integrated," says Marconi's Roulston. "In most other aircraft they are separate systems, but in the Eurofighter they share common processing and other elements." The ESM warns the pilot of threats, analyses detected signals, supplies data for sensor fusion and cues the ECM, which includes onboard and offboard jamming as well as underwing chaff and flare dispensers.

The jamming sources, including towed decoys, are housed in wingtip pods. The decoy is reeled out on a Kevlar cable which includes a fibre-optic connection between the device and the onboard signal generator. "The decoy provides a special type of jamming, for use against a special type of missile," he says. In flight tests, the aircraft has been manoeuvred and flown supersonically with the decoy deployed. The device is jettisoned after use.

Mounted in the tail, the missile warning system is an active pulse-Doppler radar. It was judged that passive ultraviolet sensors would not be ready in time for the Eurofighter's entry into service, Roulston says. A laser warning system, with sensors under the nose, will be fitted to RAF aircraft only.

Completing the sensor suite is the datalink - otherwise known as the Multifunction Information Distribution System (MIDS). This uses the Link 16 secure, jam-resistant, datalink and a low-volume terminal under development by the multinational MIDSCo consortium.

Back in the Active Cockpit simulator, Penrice demonstrates the real-life utility of sensor fusion and systems automation. The Typhoon cockpit provides information to the pilot on a head-up display (HUD), three multifunction head-down displays (MHDDs) and a helmet-mounted display (HMD). In addition, there is a datalink message panel below the HUD and a warning panel on the right glareshield.

Control is via switches on the throttles and stick and direct voice input (DVI) - a combination dubbed "voice, throttle and stick" (VTS) control. There are also keys on the display bezels and left glareshield - their function depends on flight phase and display format, and is conveyed to the pilot by illuminated labels which change in response to what Eurofighter calls "intelligent moding".

Tailoring the controls and displays to mission requirements and pilot preferences allows the information available to be limited to that needed for each phase of flight. There are 21 display formats, but only five or six are available in each flight phase, says Penrice. The pilot selects the default options during mission planning.

Supplied by a Marconi/Teldix team, the wide field-of-view HUD has a single-element holographic combiner with minimal support structure. Both symbology and FLIR imagery can be displayed. On a panel below the HUD are the radio selectors, engine and fuel indicators and MIDS display. This presents datalink messages and allows the pilot to compose messages by voice or glareshield data-entry keyboard.

In the production Typhoon, the three colour MHDDs will be 150mm-square liquid-crystal displays (LCDs). A typical set-up would have the pilot awareness format on the centre display, flanked by attack and systems formats on the left and right displays, respectively. The pilot awareness display is a "god's eye" view showing the complete tactical situation overlaid on a digital moving map.

System synoptics allow the pilot to control aircraft subsystems via "soft" keys on the right-hand display. If a system fails, the primary cause is highlighted and the consequences to mission performance and flight safety outlined. In an emergency, a "fridge door" get-home instrument can be unfolded from the right glare-shield. This 75mm LCD shows airspeed, altitude and other vital information, including bearing to the nearest airfield.

Sensor fusion comes into its own on the attack display, which presents correlated target information. The shape, colour and content of each target symbol tells the pilot where the data came from. If there is conflicting information, the symbol will alternate between possibilities. The pilot can override the computer-assigned identification, Penrice says.

Using a "mouse" on the throttles to control an X/Y cursor on the display, the pilot can select a target, change range scale or adjust sensor coverage. Default settings for each phase of flight are preloaded during mission planning, but radar and IRST scan volumes can be changed separately or together, by cursor - or by voice.

In Penrice's opinion, DVI and the HMD "are the big leap in capability with this aircraft". Voice control "allows the pilot to do everything he can do with his fingers" - with a few exceptions, such as launching weapons. The helmet, meanwhile, provides night vision enhancement and allows off-boresight target acquisition and weapon aiming.

The interactive voice capability resides in the communications and audio management unit (CAMU), supplied by a Computing Devices-led team. The CAMU controls and routes audio between pilot and radios, and includes modules for voice warning generation and speech recognition. This allows the unit to provide digitised voice responses to spoken commands.

The pilot's voice template is recorded on his mission data storage "brick" - "A one hour job," says Penrice. The speech recognition module, supplied by Smiths Industries, can handle up to 200 words, but is looking for one of only 26 at the start. Each word recognised leads to a subset of words that can follow, a "noding" technique that improves recognition performance. Recognised words are displayed on the HUD for confirmation.

DVI will be used in the Eurofighter for data entry and non-safety-critical functions such as display, radio and target selection. "The pilot will be able to use DVI to assign targets to his wingmen via datalink," says Penrice.

Combined with the HMD, DVI will allow the pilot to track a target visually and designate it by voice. This will even be possible in darkness, as integrated into the helmet are two night vision enhancement (NVE) cameras, video images from which are projected on to the visor, along with flight reference and weapon aiming symbology.

Supplied by a Marconi/Alenia team, the HMD provides a 30í x 40í binocular field of view. Head tracking is optical, using a pattern of light-emitting diodes on the helmet. The NVE cameras are enclosed in the helmet, either side of the pilot's head, and do not have to be jettisoned before ejection.

Flight information, including an energy cue, is displayed whenever the pilot is looking outside the canopy bow. The target designation box is always displayed, allowing the pilot to "look through" the cockpit to keep track of a target during manoeuvres.

The helmet is part of the new aircrew equipment developed for the Eurofighter. This includes an anti-g suit with pressure breathing, designed to provide a "relaxed" 9g capability, Penrice says. While air combat in the Typhoon is unlikely to be relaxing, it promises to be low workload compared to today's fighters.

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