Avionics Crown Typhoon Performance

It’s often been said that the appeal of aircraft comes from the dramatic combination of mechanical systems, aerodynamics, chemistry and electronics in a way that can stir the heart. Those lucky enough to see a Eurofighter Typhoon displayed at an air show will know what that means. But, more than ever, that show-stealing performance depends on the core electronic systems that give the aircraft its eyes and ears and the ability to remain under control throughout the most demanding maneuvers.

But Typhoon wasn’t built to impress air show audiences. Its swing role capability — of quickly changing among multiple roles in a single mission — make it one of the most advanced fighters in the world today.

Last May the order book for Typhoon stood at 638 aircraft from the four development partners (U.K., Germany, Spain and Italy), plus Austria. All 148 Tranche 1 aircraft are in the final stages of production and all four partner air forces now operate series production single-seaters to the Block 2 standard.

Typhoon is being made by a raft of international companies, including Alenia Aeronautica, BAE Systems, EADS Germany, EADS CASA, Smiths Aerospace and Selex. The aircraft are being manufactured in three tranches, or phases, which are themselves subdivided into batches and then blocks. The notation is quite complex because the numbers and letters are not always consecutive. For example, Tranche 1 is divided into Batch 1 and 2, each corresponding to one of two different levels of the weapon system specification. Batch 1 is further divided into Block 1, 1B and 1C. These blocks differ substantially, with improvements to the detail physical design, as might be expected for early production aircraft. The four blocks in Batch 2, (Blocks 2, 2B, 5 and 5A), feature a progressively more capable suite of software and electronic line replaceable units (LRUs), rather than changes to the physical design.

Among the updates planned or under way for Typhoon, many involve avionics systems. These include the new helmet-mounted sight, upgrades of the defensive aids subsystem (DASS) and development of a new phased array radar.

In avionics terms, the aircraft will always be young. According to Aloysius Rauen, chief executive of Eurofighter GmbH, "The simple fact is that Typhoon is a new generation aircraft and will continue to be new throughout its service life. Eurofighter partner industries are constantly employing the technologies required to ensure optimum performance in air-to-air and air-to-ground roles over the next 40 years."

Current Status

The first tranche of 148 aircraft and the second tranche of 254 aircraft (402 in total) have been under contract since the signing of the Tranche 2 production agreement on Dec. 14, 2004. As of May 2006 the UK Royal Air Force had 27 aircraft, the German Air Force 21, the Spanish Air Force 15 and the Italian Air Force 13. Total fleet time exceeds 12,000 hours.

These aircraft have production system package-2 (PSP 2) capability with the initial DASS, Multifunctional Information Distribution System (MIDS) data link, initial direct voice input (DVI) and sensor fusion.

Although the aircraft have been in service for some two years, they’ve been flying with initial operating capability (IOC). Once the full operational capability (FOC) has been achieved in late 2007, work will start on the extended operating capability (EOC), an ongoing series of enhancements. The main focus of FOC validation will be the testing of the new Eurofighter Typhoon pilot helmet. A critical element of the helmet is the BAE Systems helmet-mounted sight, which enables the pilot to simply look at the target to make an off-boresight kill. The fully binocular sight uses technology from around the world, including South Africa’s Denel, which supplies the helmet tracking system.

Test flights of FOC avionics are under way "to validate the systems’ performance in air-to-air and air-to-ground missions," says Rauen. The first flight with the FOC software took place in the summer of 2005 on the DA4 development aircraft from BAE’s Warton, UK, facility.

Initial flight testing of the Mk1 pilot helmet has already begun. Tests of the DASS are taking place in the UK, as well, in a dedicated electronic warfare (EW) facility to stimulate the equipment at various frequencies in an anechoic chamber. Recent successes include clearance of air-to-air, "carefree handling"–where the flight control system automatically limits parameters such as angle of attack, g force and roll rate to a safe level.

Sensor Fusion

On Typhoon, sensor fusion is achieved through the attack and identification system (AIS), which combines data from the major onboard sensors. It also can combine onboard sensor data with that received from offboard sensor platforms, such as airborne warning and control system (AWACS) E-3, joint surveillance target attack radar system (Joint STARS) E-8, and the airborne standoff radar (ASTOR) aircraft. And AIS can take data from other Typhoons via the MIDS, which includes Link 16.

AIS also integrates other functions such as the DASS, navigation and communications. It consists of an "avionic computer" and a navigation computer, which are linked via the STANAG 3910 data bus to other systems such as the Captor radar and the passive infrared airborne tracking equipment (PIRATE) system. The computers are identical and have a modular design based on Motorola’s 68020 CPUs with 68882 math coprocessors. In addition, several custom reduced instruction set computer (RISC) -based processors are used to accelerate floating point and matrix operations.

PIRATE gives Typhoon its passive detection system, which can be used when the Captor radar might give away Typhoon’s position and intentions. It’s provided by the EuroFirst consortium, headed by Thales Optronics.

Defensive Aids

The DASS is supplied by the EuroDASS consortium, led by EADS Defence Electronics and including Selex (a 75 percent Finmeccanica and 25 percent BAE Systems joint venture), Elettronica in Italy and Indra in Spain.

DASS comprises an integrated radar warner, electronic surveillance measures (ESM), a laser threat and missile approach warning system, an electronic countermeasures system (ECM), towed decoys, jammers and other sensors and avionics. All the DASS subsystems are managed by a single, central self-protection computer. DASS displays situational awareness information to the pilot, including the location of radar and surface-to-air missile sites.

DASS is the first integrated electronic warfare system on a military aircraft. It is installed inside the airframe, rather than bolted on as a pod. It’s fully automated to reduce pilot workload and will defend the aircraft without pilot action. According to Andy Lumb, avionics product manager at BAE Systems, "The feedback from our flight trials and the customer is that it is one of the best and most powerful DASS systems they’ve ever seen."

Part of the DASS system is a deployable towed decoy. Trials are ongoing and BAE Systems expects to deliver it next year. "We think we have a world’s first of deploying the decoy at Mach 1.4 and towing it up to Mach 1.8," says Lumb.

Flight Control

BAE Systems provides the digital flight control system (DFCS), the head-up display (HUD), the terrain awareness warning system (TAWS) and the ECR-90 Captor radar–considered the jewel in the crown of the Typhoon’s sensor suite.

Dave Short, BAE Systems’ avionics integration manager for Typhoon, describes the aircraft’s recovery modes. "If the pilot is disoriented, he presses one button and the aircraft autorecovers into straight and level flight." The second, auto low speed recovery system, he explains, "comes in if the aircraft flies at too low a speed, such that control may be lost." The pilot gets a warning before it engages.

"These recovery modes are specific to Typhoon because it’s such an agile aircraft," says Lumb. "It’s inherently an unstable platform. The DFCS is the only means whereby the aircraft stays in the air. Typhoon’s agility results in unique and unparalleled dynamic performance and the DFCS prevents the aircraft from getting into critical situations."

Earlier this year, EADS concluded tests of the DFCS’s auto low speed recovery system and disorientation recovery system in Jever, north Germany. These upgrades to the DFCS are needed because Typhoon has relaxed stability in pitch and is therefore capable of severe maneuvering, possibly to the extent that the pilot loses situational awareness. Recovery of the aircraft from these high-risk situations can be automatic or initiated by the pilot.

The HUD is the first "risk class 1," or high-integrity, head-up display which has been put on a military jet, according to Lumb. "It’s to keep the pilot’s eyes looking out of the cockpit as much as possible, not looking at the switches and displays inside the cockpit, We present data on the HUD that has to have 100 percent integrity."

"In previous aircraft, crew have had to cross-check with information elsewhere in the cockpit," Lumb says. "The Typhoon pilot can rely 100 percent on the HUD information. It’s performing very well."

Radar

Captor is a third-generation coherent X-band (8- to 12-GHz) multimode system developed from GEC’s Harrier FA.2 Blue Vixen system. Selex leads the EuroRADAR consortium that developed the sensor. Partners include Indra, Galileo Avionica of Italy, and EADS SEE of Germany.

The real-time control software, written in Ada to Mil-Std 2167A, has half a million lines of code. The radar is highly modular, comprising some 61 shop replaceable items (SRIs) and six LRUs.

Captor operates in three fundamental modes–long-range air-to-air, close-range visual and air-to-surface. In many cases it automatically selects how it will operate.

For example, for long-range look-up detection, Captor may select a low pulse repetition frequency, but for look-down operation a high pulse repetition frequency will normally be used. For simultaneous all-aspect detection, a medium rate will be employed.

Captor can automatically initiate track while scan, and it employs data adaptive scanning to improve the tracking of selected targets while minimizing unnecessary movement of the radar.

For close-in combat, Captor will automatically adjust its mode for a high-precision single attack. It can be slaved to the helmet mounted sight so that it can guide air-to-air weaponry such as the advanced short range air-to-air missile (ASRAAM).

Air-to-surface modes include beam mapping, sea and surface search, ground movement target information, spot mapping and surface ranging. The synthetic aperture radar (SAR) mode in Tranche 1 aircraft gives high resolution.

Although Captor has a mechanically steered array, the use of a low- inertia, non-counterbalanced antenna with four high-torque, high-precision, samarium-cobalt motors gives extremely high scanning speeds. However, for even better performance a stationary, electronically scanned array is needed. This is a major item on the roadmap for future capability upgrades.

AESA Upgrade

In 1993 a 50/50 Anglo-French project was launched called the airborne multimode solid state, active array radar (AMSAR) to provide an advanced radar for Typhoon and Rafale. Germany joined later.

This has evolved into the Captor active electronically scanned array radar (CAESAR), the first airborne operational tests of which took place over the UK in February of 2006. Development and funding are by EuroRADAR. CEASAR will introduce active electronically scanned array (AESA) technology to Captor while retaining much of the original hardware.

CAESAR was tested in a three-hour flight on a BAC 1-11 test bed aircraft, during which it engaged air targets and demonstrated performance advantages. Further flight trials are scheduled for the latter half of 2006. CEASAR is expected to be fitted to Tranche 3 Typhoons.

"Captor has a mechanical scanner, and it has taken that technology about as far as it can go," Short says. "When the development contracts were placed on Eurofighter, it was by far the better option, rather than the emerging technology of phased array. In the early 1980s, when we were putting the technology together for the radar, we made a risk-based decision."

"In the early 1990s, when the radar was finally specified, phased array was more of a twinkle in somebody’s eye, rather than a technology that could be put into production," Lumb adds. "Even now it’s still in its very early days. But Typhoon will benefit in the future."

For example, the phased array will allow control of emitted energy by fast frequency hopping. This allows transmissions to be hidden in background noise, reducing the possibility of monitoring and spoofing, leading to a low probability of interception (LPI). Also peak power can be traded against resolution to further reduce LPI.

Captor hardware is complete, but there may be some software "tweaks" in the Tranche 1 aircraft related to flight test feedback and performance, Short says. There are future developments in radar integration with the Meteor (missile) program. Meteor is a beyond visual range, air-to-air weapon which will be part of the EOC. Although Meteor has its own radar used to seek its targets, initial target detection will be with Typhoon’s Captor.

One of the most often discussed innovations of the Typhoon is its voice recognition technology–known as the direct voice input system–developed by Smiths Aerospace under subcontract to General Dynamics.

According to Alan Raine, Smiths Aerospace vice president of European military original equipment accounts, the company provides the module and the algorithms for incorporation within the cockpit audio management unit. "We’re putting an upgrade through at the moment, adding some algorithm changes. These are being tested in Spain and we’re getting very good feedback."

To be an effective component of the flight deck controls, the speech recognition system must perform reliably on the great majority of occasions, and become trusted by the pilots. "The Smiths Aerospace system successfully reaches the desired recognition rate, and maintains a good level of performance through high speed, high-g maneuvers," Raine says. This is where the real challenge lies, he explains, as the pilot’s voice changes under high g loading and high stress. "The effectiveness and reliability of the Eurofighter system is perhaps best shown by the enthusiasm among its pilot users, who are now actively suggesting extensions to the use of voice on the flight deck."

Voice Input Algorithms

Smiths is adding more modern algorithms, such as spectral shape analysis and a cosine transform. Nevertheless, despite increases in performance, "the DVI is never likely to take on safety critical functions, such as firing commands," Raine says.

The control philosophy on Typhoon is "voice, throttle and stick" (VTAS) with the DVI system controlling around 26 functions, such as display and radio frequency selection, navaid management, checklist rundown and data entry. Raine says, "The real advantage is reducing pilot workload, not taking on those safety critical functions."

Active matrix liquid crystal displays (AMLCDs) were specified quite early in the Typhoon program, when they were new to fighter aircraft. "We moved from bespoke ruggedized glass, taking something from a commercial process and making it rugged by adding heater planes, ruggedization planes, etc.," Raine says. "We made best use of commercial technology."

The Typhoon displays are among the most advanced to be found in any aircraft, asserts Smiths. One interesting feature is "intelligent" keypads. The keys have built-in legends that change as the role of the aircraft changes, keeping the screen uncluttered. Screen formats are not contained within the displays, which are driven by the computer symbol generator. When a particular mode is selected by the pilot, the key function may change. The legends appropriate to key function are automatically selected and displayed by the computer.

Smiths provides the mission data loader recorder, the portable data store and the bulk storage device, as well. According to Raine, Smiths is now "putting through an upgrade to the portable data store, which doubles the capacity in Tranche 2." This meets all the requirements that Smiths sees going forward, he says. "People are using more and more data these days, not less."

Innovative Support

One of the main objectives of the Eurofighter program is to cut maintenance and support costs. Smiths participates in the Industrial Exchange and repair service, which will shortly be extended to 2009. Then the participating nations will choose their support philosophy. "You can drive huge efficiencies in support if you align the motivations of the supply chain, making use of its ability to be innovative in support," Raine says. "It lines up very tightly with through-life capability management, helping support the equipment more efficiently and upgrade it as time goes by."

Selex, Thales and Smiths have teamed to offer "total support services," providing a broader scope of support and consolidating the capabilities of the companies in this area, says Raine. "Whatever the individual nations choose to have the service look like from the outside, I believe that the core service will be based on these new ideas–pooling and rationalizing resources, aligning incentives within the supply chain to drive out costs and improving availability."

"With mature systems we’re taking 30 percent out of support costs, and

I can’t see why that would be any different for Eurofighter," Raine adds. "We can make up-front savings by changing how the service is defined. The cost of a weapon system is focused on the support phase rather than the acquisition phase."