Jul 13, 2008
By Robert Wall and Douglas Barrie
Britain’s Taranis unmanned combat air vehicle demonstrator will fly in 2010, with the French-led Neuron to follow in 2011. Both will use the same model of Rolls-Royce Adour engine – though ironically, propulsion is one area that is underfunded by both nations in terms of future development.
Europe will conceivably be in a position to begin fielding operational UCAVs toward the end of the next decade, but both programs already build on years of predominantly classified research and development.
The U.K. and France have been instrumental in pushing UCAV technology development in Europe; in Britain, through the BAE Systems-led Taranis project, while France has taken the lead on the multicountry Neuron UCAV demonstrator. Even with defense budget pressures in both countries, industry officials are confident their efforts will proceed.
In the U.K. a UCAV is a candidate to meet at least part of the air force’s Deep and Persistent Offensive Capability (DPOC), which is now assumed by the Defense Ministry to be entering service in 2018. For the Royal Air Force a UCAV would provide a first-day-of-war deep-strike capability against enemy air defense systems and time-sensitive targets using a platform capable of surviving in airspace defended by double-digit surface-to-air missile systems in the class of the Russian Almaz Antey S-400. A 24-hr. endurance capability is believed to be under study.
Taranis will take the U.K. a considerable way toward an operationally capable system. The effort is aimed at risk reduction in several areas, including signature control and flight performance. Beyond Taranis the ministry is looking at an as-yet-undefined assessment phase. Taranis is being run by the Defense Ministry’s Strategic UAV Experiment (Suave) team. Industry partners alongside BAE Systems are Rolls-Royce, Qinetiq and GE Aerospace.
The program, publicly launched in 2006, builds on classified low-observable and UCAV design work that started more than a decade ago. Taranis, says BAE Systems Suave project director Chris Allam, draws in part from the experience of the Testbed/Replica manned aircraft low-observable (LO) demonstrator program from the late 1990s in terms of airframe and systems integration. In terms of LO technology, Allam suggests that the “reasonable gap between the two mean things have moved on a bit.”
Another LO-related effort was the 4-5-year Nightjar program carried out by the Defense Ministry in conjunction with industry using BAE’s radar cross-section range at Warton. This is thought to have looked at specific elements of airframe design and performance related to LO signature. The Raven sub-scale demo program, first flown by BAE Systems in December 2003, provided valuable input in terms of development of control laws for an unstable tailless airframe.
The Taranis design was the culmination of several studies by the ministry and industry, a process that is continuing in support of developing an operational platform.
“The Taranis build program is going well, we’re effectively in mid-build, while avionics rigs are also up and running. We’ll start final assembly [at Warton] toward year-end.”
Taranis will undergo flight testing in 2010 with aims including examining the “operational utility” of aspects of the design, says Allam. Several research efforts are underway regarding autonomous operation of unmanned platforms in the DPOC role, including Qinetiq’s Surrogate program, which has used a BAC 1-11 test aircraft to act as a UCAV. One aim of the Taranis trials is to demonstrate the required level of autonomy, including a representative strike mission. Sensor and payload integration are also being addressed.
The Initial Gate approval – part of the ministry’s procurement process – is due in 2011. Allam suggests the industry and the ministry are looking at how to proceed with the program in the assessment phase. A “spiral development-type approach” is one option.
The Taranis design utilizes comparatively mature LO technology, thought to be baselined against the present generation of threat systems. In moving forward with the full development and acquisition – or off-the-shelf purchase – of an operational system, it must prove to be survivable against projected threat systems in the 2020s and beyond. With this in mind, the ministry is continuing to fund research into LO capabilities running in parallel with the Taranis project. The control portion covers not only the RF but the infrared spectrum, with work undertaken to examine reducing the engine signature in terms of the jet efflux. The engine intake and jet efflux nozzle have also received considerable focus.
The U.K. continues to pursue a dual-track approach to the acquisition of a UCAV, since it remains involved with the U.S. in examining the operational utility of such systems. While an off-the-shelf purchase remains an option, issues surrounding what London terms operational sovereignty could militate against purchasing a system from Washington.
While Taranis will fly using Rolls’s Adour 951, development of an operational UCAV could be accompanied by work on a new engine, or a project based on using a more advanced core than Adour’s.
Rolls-Royce had been pushing for an engine demonstrator project to run along with Taranis, but funding was lacking. The engine has a fundamental impact on the size of the UCAV, while some of the likely performance demands – both in loiter capability and power output for directed energy weapons – also drive a more-advanced propulsion solution.
The U.K. is pursuing development of high-power microwaves (HPMs) and laser weapons, with the UCAV certainly a clear candidate for an HPM payload.
The Rolls-Royce-Turbomeca relationship on Adour could yet continue in terms of UCAV propulsion. There have been suggestions that this could be an area of reemerging Anglo-French collaboration.
The six industrial partners involved in Neuron – Dassault Aviation, Saab, Alenia Aeronautica, EADS CASA, Ruag Aerospace of Switzerland and Hellenic Aerospace Industry – are also preparing to start production of their lone flight-test vehicle, now slated to undergo trials in 2011. The go-ahead for the production phase comes after months of validating technologies deemed critical to the operational concept.
Developers created 13 technology road maps in which to tackle key issues before production go-ahead. The bulk of those are now complete, with good results, says Neuron program manager Benoit Dussaugey, Dassault’s senior vice president for military sales and cooperation.
A special emphasis has been placed on LO technologies. Although some team partners, such as Dassault and Saab, have already dabbled in low-observable shaping and materials – including applications on combat aircraft – Neuron is aiming at a level of stealth not attempted before in continental Europe. In part, it was only when development started that engineers realized how every design choice can impact stealthiness. Eight of the 13 technology efforts were related to radar and infrared low-observability.
For instance, Saab has built a model of the front forward-fuselage and the landing gear door for measurement at the outdoor radar cross-section facility in Linkoping. The emitter is about 500 meters from the test specimen and therefore provides good radar return data, Dussaugey indicates.
Alenia is doing similar work. The company is assigned the window for the electro-optical sensor. Unlike on the F-35 Joint Strike Fighter, which features a protruding sensor window, Neuron designers have opted for one basically flush with the fuselage. The Italians also have run tests on a partial weapons bay door to gauge whether radar returns are meeting specifications.
Last year, Dassault ran tests of the leading and training edges of the air vehicle. Dussaugey says results were good, but the company is pursuing upgrades to further improve LO performance.
A key element of Neuron is the engine intake, which features radar-absorbing material. Tests are being evaluated.
Preliminary design reviews for almost all Neuron systems have now been completed and developers are in the final stages of defining interface control documents so team members can proceed with detailed design activities and production. Orders for long-lead items are likely to be on contract by year-end to begin the process of turning the €400-million ($628-million) undertaking – which kicked off in 2004 and went to contract in February 2006 – from concept to reality.
The airframe shape has been largely frozen for well over a year, with only tweaks being applied. The vehicle is expected to be 9.3 meters (30.5 ft.) long and have a 12.5-meter wingspan. Maximum takeoff weight will be 5,000-6,500 kg. (11,000-14,300 lb.). Top speed is Mach 0.85, with 12-hr. endurance. Composites will feature heavily in the design.
The air vehicle will sport four control surfaces and two weapon bays, each sized for a Mk.82 bomb. Beyond the electro-optical sensor, it will be fitted with a line-of-sight data link, but no synthetic aperture radar or radar-warning receiver (although there will be provision for one).
Infrared signature suppression is also a watchword for engineers. Designing the exhaust assembly was another major technology demonstration area and a full-scale demonstrator was built. The first run of the Adour engine is due this month; the exhaust assembly is to be added a few months later. It includes a masking plate to shield the infrared signature from the ground. Engineers will be scrutinizing thermal and dynamic strains on the exhaust assembly during those trials. HAI built the full-scale nozzle from alloys since composites were deemed too costly.
The airframe and engine team also has worked closely to ensure that the S-shaped inlet to mask the turbojet’s fan doesn’t starve the engine of vital airflow. A series of wind tunnel tests has been completed with an inlet distortion grid to mimic the airflow impact on the inlet.
Coming trials will be done in three steps, first just running the powerplant, then adding the distortion grid and nozzle, and then the masking plate. Dassaugey notes that this gradual process should make it easier to get flight clearance approval from authorities.
System software also features heavily in the design. One technology road map dealt with validating the open architecture approach, which should allow companies to modify code for a subsystem they are developing without requiring the rewrite of the entire system software – the team settled on the Arinc 653 software design standard. Saab is writing the core underlying computer software, with a first version expected by early 2009.
Dassault is responsible for the fly-by-wire flight control software, which the company is adapting from its Falcon 7X long-range business jet. The Falcon 7X has greater redundancy than the Rafale fighter’s fly-by-wire system, and with only one flight-test article, developers want as much safety margin as possible.
In fact, Neuron’s airworthiness safety standard should be almost as good as that of the European Aviation Safety Agency’s or FAA’s requirement for commercial aircraft, Dassaugey says. Avionics, hydraulics and electrical systems will be fully redundant to meet JAR 23 civil airworthiness requirements.
As developers build the program, concern about loss of the lone vehicle is weighing on them heavily. In particular, Neuron officials realize what a significant setback EADS suffered when its Barracuda UCAV demonstrator crashed, and are mindful of the magnitude of Lockheed Martin’s loss of the Polecat stealth endurance UAV. One lesson gleaned from Polecat is to design a more flexible flight termination system. If a flight has to be terminated but the problem can still be resolved before the vehicle crashes, Neuron operators will have the ability to retake control of the UCAV. Since most of the flight tests will be in sparsely inhabited areas, the flight termination process will also be gradual, rather than directly commanding the vehicle to fly into the ground or sea.
Aircraft autonomy – another key design driver – will also reflect the design-to-cost approach. Unlike existing UAV programs, which tend to be personnel intensive, Neuron will nominally require only a small ground staff. Controllers will merely provide waypoint updates, allowing the vehicle to replan its route automatically, taking into account programmed threat information. Planners think this approach, which parallels work on other UCAV programs, will allow the vehicle to be controlled by just two individuals – and might even permit several vehicles to be handled by the same team.
With the basic design process coming to its end, the Neuron team is getting ready to reduce the core team of 100-150 personnel now operating at Dassault’s St. Cloud headquarters outside of Paris and standing up the “virtual plateau.” This will have engineers working at their dispersed sites. The core team will likely be reduced by half within a year.
Although Neuron is not designed to be an operationally representative system – it is about three-quarters the scale of what a future production model would probably require – attention will nevertheless be on the flight-test program. Those trials will commence at the facility in Istres, France, where the vehicle also will be assembled. They will then move to Sweden, for LO trials and weapons release, before finishing up in Italy. Radar testing at different frequencies will take place in Rennes, France. Stealth measurements will be performed after a few flights, in part to assess the impact of flight operations on the radar cross-section. Flight trials will run around 18 months.
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July 14, 2008 at 8:51 pm