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Sunday, June 1, 2003

Typhoon: Europe’s Finest

This multinational combat aircraft represents not only Europe’s best effort in air superiority, but also in fighter cockpit technology, designed to deliver extraordinary situational awareness minus an inordinate workload.

George Marsh

Many believe today’s manned combat aircraft will someday be dinosaurs, succeeded by unmanned air vehicles (UAVs). If so, the Eurofighter Typhoon, currently entering service, represents Europe’s ultimate effort in man-machine integration for aerial combat.

But such an accomplishment is just one among several tough challenges that the Typhoon program had to face. The multirole aircraft’s development was complicated by the need to provide different one- and two-crew variants for the four countries in the Eurofighter consortium–Britain, Germany, France and Spain–and for different upgrade paths during the aircraft’s anticipated quarter-century service span. On top of those obstacles was the challenge to meet different phased budgetary requirements. All in all, this was no small feat.

An advanced digital design backed by an architecture that is based on multiple data bus interconnection, shared data resources, and maximum software commonality provides the required flexibility for the Typhoon. And the aircraft’s designers used a high level of system integration and automation to secure a cockpit workload manageable by a single pilot. (The majority of the nearly 700 Eurofighters ordered so far will be single-seaters.) The key contributors to the integration and automation are:

  • An advanced control interface,

  • An automated fly-by-wire (FBW) system permitting "carefree" handling, and

  • A glass cockpit environment that facilitates rapid assimilation and input of data, both platform-related and tactical.

The Typhoon pilot can control the aircraft manually using a short conventionally located hands on throttle and stick (HOTAS) control column. Beyond its use to control the aircraft and its twin Eurojet EJ200 digitally controlled engines, the HOTAS has some 24 finger-tip functions for sensor and weapon control, defense aids management, communications handling, target manipulation and x/y cursor control. HOTAS is augmented by a Smiths Aerospace direct voice input (DVI) system, which permits voice selection of modes, radio and navaid management, checklist rundowns, display setups, and entry of data that is not flight safety critical. For example, to change a mode with DVI, the pilot merely says the word shown next to a button on a display menu. For verification of, say, a verbally fed data entry, corresponding text is scrolled along the bottom of the head-up display–a kind of instant proofreading.

A workload reduction tool, the DVI system is incorporated as a speaker-dependent recognition module in the Typhoon’s communications and audio management unit (CAMU). The module employs a frequency/time ratio that maps a person’s voice sound, and it converts audio input into command words. A filter diminishes aircraft noise. Pilots push the com switch to switch back and forth between external communications and DVI communications within the aircraft. The DVI is used during fairly routine operations and not during combat, when voice tone and inflection can change in periods of stress. Then the pilot uses the HOTAS.

Fly-by-Wire

A full-authority ACT (active control technology) digital FBW flight control system, developed by a German-led international team, signals Liebherr primary flight control actuators in response to pilot or automatic flight control system commands. Controlling the all-moving foreplanes (horizontal airfoils mounted near the aircraft’s nose), wing trailing-edge flaperons, rudder and airbrake, Typhoon’s FBW is described as carefree because it prevents excursions outside the permitted maneuver envelope and provides gust alleviation during high-alpha and other sustained extreme maneuvers.

The flight control system also compensates for the aircraft’s negative pitch stability, essential for combat agility. A digital flight control system (DFCS), developed by UK’s BAE Systems and EADS Germany, provides a high degree of automatic control. In addition to the usual modes, the DFCS incorporates an auto-recovery mode under which the aircraft makes an immediate return to straight and level after the pilot engages an emergency "panic" button.

Since fly-by-wire without manual reversion requires the highest integrity, the Typhoon is fitted with a quadruplex FBW flight control system. Each of the four FBW units comprises eight 68020 processors, as well as several application-specific integrated circuits (ASICs) for handling critical tasks. Each box connects to the main avionics system via a STANAG-3910 high-speed optical data bus. A STANAG-3838 link connects to other data buses, and various proprietary high-speed links provide the interconnections between boxes. Each FBW unit, including all necessary interfaces, weighs some 22 pounds (10 kg).

Three large Smiths Aerospace color cathode ray tube (CRT) multifunction displays (MFDs) occupy the width of the instrument panel in front of the Typhoon pilot. Primary flight instrumentation, navigation, sensor, weapons, engine and systems data can be presented on any of the displays in various combinations. The pilot selects his preference using display soft keys.

The aim, however, is not to waste the impressive field of view the Typhoon affords its pilots from its raised cockpit position. So flight and tactical data also can be presented on the BAE Systems wide-angle head-up display (HUD) and via the pilot’s helmet-mounted symbology system (HMSS), which can present complex and TV-like imagery. Forward-looking infrared (FLIR) imagery can be shown on both the HUD and helmet-mounted display (HMD). The HMD incorporates a binocular CRT system with a wide (up-to-40-degree) field of view.

The HMSS, with a head tracking system, provides flight reference data, an energy cue and weapon aiming through the pilot’s visor. It allows target acquisition and engagement at large off-boresight angles. As well as being FLIR-capable, the system incorporates light intensification-based night vision.

For navigation Eurofighter relies on a mil-spec GPS receiver, supplemented by a laser gyro-based, inertial navigation system (INS) and accelerometer package that is accurate to within 1 nautical mile (nm) per hour of flight. Unintended contact with the ground is avoided by a terrain awareness warning system (TAWS) based on BAE Systems’ highly regarded TERPROM (terrain profile matching) technology linked with GPS, INS and radar altimeter. This combination also provides drift-free terrain-referenced navigation, plus passive terrain following and weapon aiming benefits during low-flying operations.

The TERPROM unit is based on a system in service with the Tornado combat aircraft. But the Typhoon system includes enhancements, such as extra warnings during TAWS recoveries, improved capability in fast dives, and built-in test functionality, all delivered through an extra 10,000 lines of Ada code. All-weather day/night landings are facilitated by the Typhoon’s microwave landing system.

Sensor Package

The European fighter has a sensor package that allows a rapid swing between the air-superiority and air-to-ground roles. Its ECR-90 Captor radar, developed by the Euroradar consortium–comprising BAE Systems in the UK, EADS in Germany, FIAR in Italy, and INDRA in Spain–is considered the jewel in the Eurofighter sensor crown. Since the system’s roots lie in the GEC Blue Vixen radar, installed in the Harrier vertical or short takeoff and landing (VSTOL) aircraft, BAE Systems was made the consortium leader.

This third-generation, coherent X-band (8-to-12-GHz) multimode pulse Doppler radar takes mechanical scanning about as far in capability as it can go. Use of a low inertia, non-counterbalanced planar (flat) antenna, driven in azimuth and elevation by four high-torque samarium-cobalt electric motors, ensures rapid scanning. This enables diverse operations, such as air target detection and ground mapping, to be interleaved. A traveling wave tube (TWT-vacuum tube used in wireless communications) develops the required microwave energy. Power and signal processing are such that Typhoon pilots can detect fighter-sized aircraft at well over 100 nm.

The Captor system is highly adaptive to prevailing circumstances. It can, for instance, "swing" automatically during a mission to long-range, look-up detection, for which a low pulse repetition frequency (PRF) is required. Or pilots can adjust for a high PRF that can be employed for close-range and look-down situations. Captor also can resist severe electronic jamming. Small wonder that half a million lines of software code (Ada to Mil-Std-2167A) are needed to make up its real-time control software.

Captor can track multiple targets while scanning. Data adaptive scanning enhances the tracking of selected targets while minimizing antenna movement. For close-in combat, the radar automatically tracks the single target of interest, to the high level of precision required for weapon delivery. The radar also can be slaved to the pilot’s helmet-mounted sight. Here the data is used to cue advanced short-range air-to-air missiles (ASRAAM) or other weapons.

Typhoon’s radar can track, identify and prioritize some 20 air targets simultaneously. An auto-attack mode reduces pilot workload. In this mode, the radar and the DFCS join forces to fly Typhoon under autopilot control to a selected target.

Air-to-surface modes include beam mapping, sea and surface search, ground moving target indication (GMTI), spot mapping and surface ranging. A synthetic aperture radar (SAR) mode presents ground objects in high definition–to about 1 meter (3.3 feet) in Tranche (or Block) 1 Eurofighter deliveries, improving to a third of a meter (1 foot) in Tranche 2 aircraft. The Captor system can automatically select the modes, or the pilot can do so manually, using the HOTAS control.

Identification friend or foe (IFF) capability–developed by Raytheon’s UK division with EADS Germany, Italy’s MID and Spain’s Enosa–comprises an interrogator and Mode S transponder. Designed for NATO interoperability, it is compatible with the IFF Mk XII standard and is upgradeable to future standards. Captor also employs pattern recognition techniques–jet-exhaust spectra, radar cross-section signatures, etc.– to identify aircraft not responding with IFF. The radar is unusual in having three (rather than two) parallel operating signal and data processing channels, both for survivability and to confer resistance to electronic countermeasures. The third channel is used in a jamming scenario for sidelobe nulling, interference blanking and jammer classification. Electronics for Captor are highly modular, comprising some 61 shop replaceable items and six line-replaceable units (LRUs) to ensure quick maintenance turn arounds and simple upgrade paths.

Software upgrades are planned for the mechanically scanned radar, as are hardware upgrades involving a progressive shift from existing electronics to more economical off-the-shelf components.

Enhanced Radar Planned

For even greater scanning speed and multimode operation, the UK, France and Germany have been collaborating on an airborne multimode solid state active array radar (AMSAR), intended eventually to replace both the Captor on Typhoon and the passive phased array radar used on the French Rafale fighter. Following demonstration of a trial array made up of 144 microwave monolithic integrated circuit (MMIC) modules, the contracting partners have been working on a full-scale 1,000-plus module unit.

Eurofighter’s radome is a complex glass-reinforced plastic (GRP) structure manufactured to close tolerances. It includes layers of frequency-selective surface (FSS) materials, comprising metallic micro-arrays that absorb all frequencies outside the band of the aircraft’s own radar. The radome, of course, must remain transparent to the radar to reduce the Typhoon’s frontal radar cross-sectional area and hence its detectability.

Radar-absorbent materials coat wing leading edges, intake edges and interior rudder surrounds, and other significantly reflective structure. Overall, radar returns from Typhoon are said to be four times less intense than from the Tornado combat jet currently in service.

Passive PIRATE

For more stealthy operations and to complement the radar, the Typhoon is equipped with a second-generation infrared system, dubbed PIRATE (passive infrared airborne tracking equipment), developed by the Thales Optronics-led EuroFirst consortium. Mounted on the fuselage’s port side forward of the windscreen, this sensor, like the radar, is dual-mode.

In the air-to-air role, it provides a passive target detection and tracking system referred to as infrared search and track (IRST). Scanning in two spectral bands, 3-to-5- and 8-to-11-micron, the high-sensitivity, supercooled sensor detects targets at ranges typically up to 50 nm. A stabilized mount, along with a high-precision control system and advanced signal processing, ensure clear imagery that is directed to a display of choice: MFD, HUD or helmet-mounted display.

Eurofighter officials claim PIRATE can scan up to 200 targets simultaneously. PIRATE’s operating modes include multiple target track (MTT), single target track (STT), single target track ident (STTI), sector acquisition and slaved acquisition. In STTI mode, imagery is presented with the highest possible resolution so that targets can be identified visually. In sector acquisition mode, a volume of space is scanned under the direction of another on-board sensor such as Captor. In slaved acquisition mode PIRATE is slaved to off-board sensors such as those carried on intelligence gathering aircraft like AWACS (Airborne Warning and Control System), ASTOR (Airborne Standoff Radar) and JSTARS (Joint Surveillance and Target Attack Radar System). In either case, when the target is found, the system automatically designates it and switches to STT. Once an identified target is within weapon range, the pilot can use PIRATE to cue a missile.

Other sensors can include radar warning receivers (RWR), laser warning receiver (LWR) and a missile approach warner (MAW), integrated within an advanced defensive aids subsystem (DASS). This airframe-integrated system (no external pods needed), developed by the Euro-DASS consortium led by BAE Systems, includes the following:

  • A wideband (below 100-MHz to 10-GHz) 360-degree scanning RWR and active jammer, with antennas at each wingtip and on the fuselage;

  • Pulse Doppler-based MAW sensors on wing leading edges and tailcone; and

  • An LWR in front of the cockpit, plus (on RAF aircraft) expendable towed radar decoys.

Threats can be identified by comparing their signatures with those stored in an extensive threat library. Due to budgetary constraints, not all the subscribing nations are to have the full DASS. The UK and Spain, for example, are the only nations to have the laser warning receiver. In its eventual, fully developed form, DASS will be able to detect, identify and prioritize threats, and then respond with active countermeasures, all without pilot intervention.

Chaff and flare dispensers can be fitted in Typhoon’s flight control surface actuator fairings at the rear of the wing. "Jaff" capability involves the illumination of the chaff by the active jamming system, enhancing the chaff’s effectiveness.

For even greater situational awareness, Typhoon pilots have available sensor fusion techniques and networking with other platforms, including other Typhoons. Utilizing all available sensors to best advantage, an attack and identification system (AIS) permits identification of threats at over 150 nm, followed by target acquisition and prioritization at up to 100 nm. AIS carries out the cross-checking, freeing Typhoon pilots from the need to assess conflicting data that can arise from separately used sensors.

A high-capacity multifunctional information distribution system (MIDS) digital data link is used to gather off-board data from air, land and naval assets as appropriate. The system, developed by the EuroMIDS consortium (including Data Link Solutions in the United States), presents a comprehensive tactical environment on the MFDs. Typhoon pilots, therefore, don’t need to assemble the necessary information from various independent sources. The system further lightens pilot workload by providing automatic emissions control (EMCON) during periods of stealthy operation.

AIS comprises an avionic computer and a navigation computer. These identical-hardware computers, developed under Teldix leadership, are each based on Motorola 68020 central processing units (CPUs) with 68882 math coprocessors, together with RISC-based processors to facilitate floating point and matrix computations.

The Typhoon includes a Smiths utilities management system (UMS), which provides stores management functions, including weapons arming and release.

Communications

A consortium led by Rohde and Schwarz GmbH (Germany) provides the Typhoon’s secure, jam-resistant VHF/UHF communications. The NATO-interoperable system supports open and encrypted communication and features low probability of detection and exploitation via the SATURN (second-generation, anti-jam tactical UHF radio for NATO) system and NATO encryption algorithms.

The CAMU integrates not only the various communications boxes, under rational central control, but also digital video interface and audio synthesis modules. The latter, provided by Spain’s Enosa, enables some 200 stored warning messages to be replayed in either a male or female voice on request.

Debriefing, training and post-incident analysis are supported by a video and voice recorder (VVR) from Computing Devices, backed up by a crash survivable recorder provided by BAE Systems (previously GEC-Marconi Elmer). General Dynamics UK contributed a central warnings panel and other technology for the VVR, a high-resolution cockpit system that places a record of HUD video, head-down displays, pilot voice and digital data bus information on a TEAC recorder.

The following facilitates Typhoon’s maintenance in the field:

  • Organizing the electronics into shop and line replaceable units,

  • Built-in test facilities, and

  • Reportedly the first integrated structural health and usage monitoring system (HUMS) to be incorporated in a fixed-wing combat aircraft.

Stress monitoring sensors at 20 points in the airframe send data, collected 16 times a second, to a central processing and data storage unit. Data from sensors in the EJ200 engines are similarly collected. Extracting from the Mil-Std-1553 data bus data on aircraft systems, flight performance and structural wear, the HUMS enables maintenance personnel to home in on incipient conditions before they can become problems.

Six digital data buses, two of which are fiber optic, provide the interconnecting backbone of the Typhoon’s avionics system. The high-speed fiber optic buses complement Mil-Std-1553 technology operating at standard speed. AIM GmbH’s E2-HLBA (high level bus analyzer) supports the monitoring of four dual-redundant STANAG-3910 buses with frame check sequence (FCS) protocol implementation plus eight STANAG-3838 (Mil-Std-1553B) dual-redundant data buses directly from the aircraft. Delivered to Alenia’s Cacelle plant for aircraft testing, the data acquisition system makes available real-time monitoring and an archive of all stored, general data bus traffic (GDT). Multiple portable workstations can be connected to the E2-HLBA via an Ethernet hub, and each one can store up to 1,000 selected data parameters in an engineering-unit-converted format requested uniquely by each workstation operator.

Not all the Typhoon’s capabilities described here are available from day one. Full functionality will evolve in production software packages (PSPs), with full sensor and sensor fusion capabilities, for instance, expected with PSP-3 in about 2005 or 2006.

Air-to-ground modes and full digital flight control system capability will likewise be achieved in the later stages. Despite the inevitable difficulties of multinational collaboration, Europe should have a highly capable combat system by the end of this decade. Eurofighter Typhoon, with its ability to survive in intense combat environments, will let little stand in its way–especially being armed with its 27-mm Mauser cannon and some 14,330 pounds (6,500 kg) of under-wing munitions. These can include combinations of the Meteor beyond-visual-range air-to-air missiles (BVRAAM) currently under development, advanced medium-range air-to-air missiles (AMRAAMs), ASRAAMs, antiradar missiles (ARMs), Storm Shadow cruise missiles, antiarmour and antiship missiles, and Paveway III guided bombs, all of which can mounted to a total of 13 external stores stations.

As test pilot Christian Worning put it, "Eurofighter Typhoon is fast, with a top speed of Mach 2. It’s highly computerized, making it not only easy for pilots to fly but also adaptable to new technology. And it’s versatile, geared primarily for air-to-air combat but with air-to-ground attacking ability. In short, about the ultimate in manned combat aircraft."

Typhoon Acronyms

Because this story contains more than the usual amount of acronyms, we provide this list for your quick reference.

  • ACT - active control technology

  • AMRAAM - advanced medium-range air-to-air missile

  • AMSAR - airborne multimode solid state active array radar

  • ARM - antiradar missile

  • ASIC - application-specific integrated circuits

  • ASRAAM - airborne short-range air-to-air missile

  • BVRAAM - beyond visual range air-to-air missile

  • CAMU - communications and audio management unit

  • DASS - defensive aids subsystem

  • DFCS - digital flight control system

  • DVI - direct voice input

  • EMCON - emissions control

  • FBW - fly-by-wire

  • FCS - frame check sequence

  • FSS - frequency selective surface

  • GDT - general data bus traffic

  • GMTI - ground moving target indicator

  • GRP - glass-reinforced plastic

  • HMD - helmet-mounted display

  • HMSS - helmet-mounted symbology system

  • HOTAS - hands on throttle and stick

  • IRST - infrared search and track

  • MAW - missile approach warning

  • MIDS - multifunctional information distribution system

  • MMIC - microwave monolithic integrated circuit

  • PIRATE - passive infrared airborne tracking equipment

  • PRF - pulse repetition frequency

  • RWR - radar warning receiver

  • SAR - synthetic aperture radar

  • STT - single target track

  • STTI - single target track ident

  • TERPROM - terrain profile matching

  • TWT - traveling wave tube

  • UMS - utilities management system

  • VVR - video and voice recorder

 

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