TECHNOLOGY BAE SYSTEMS’ TARANIS
In the first of a three-part series on aircraft designed and produced by BAE Systems, Mark Ayton provides an update on the unmanned Taranis technology demonstrator, one of the most advanced air vehicles ever flown
AIR International has previously covered the BAE Systems’ Taranis UAV on several occasions. Since the aircraft was last flown in 2015 not much has been reported on the system, though the story is by no means complete given its link with the UK Future Combat Air System (FCAS) ongoing with Team Tempest. Before reporting on the latest account of the Taranis programme it’s worth looking at the system one more time.
Taranis in depth
The configuration of Taranis was determined by the low-observable design which aims to avoid detection by radar and infrared systems. Its fundamental features are the clean blended wing and body, which exclude radar returns due to a lack of fins and a tail plane. Similarly, the highly swept wing, swept leading and trailing edge alignment of the planform, control surfaces, access panels and doors, internal stores carriage, a low-observable system, and not least a propulsion system that incorporates novel features from intake to exhaust are all design aspects that help to exclude radar returns and minimise the vehicle’s radar cross-section.
The wing, with a sharp leading edge and sweep of approximately 60°, eliminates potential large spiky radar returns which are normal to a leading edge over a very wide, 300°, critical frontal detection aspect. The greatest contributor of an aircraft’s frontal radar cross-section signature, and the one capable of swamping all other returns, is that created by the intake and engine face.
Dorsal positioning of the intake on Taranis is favourable, providing some shielding from radar and IR detection. Its highly raked intake, positioned well forward is conducive to achieving a long low radar cross-section installation. Radar absorbent material (RAM) treatments and/or radar blocker devices may be incorporated.
A further significant feature on Taranis is the absence of a boundary layer diverter, the latter being a problematic area for achieving minimal radar cross-section. The sharplipped triangular intake form, possibly a compromise between internal aerodynamic performance and low radar cross-section, and the complete intake duct have been the subject of full-scale signature reduction using the BAE Systems’ Nightjar test body on the Warton range.
Taranis is powered by a single Adour engine as used by the Hawk Advanced Jet Trainer, the most powerful version of which is the Mk951 rated at 6,500lb (28.9kN) thrust. Although not confirmed as the specific version for Taranis, the Mk951 incorporates full authority digital engine control, ideal for integration with the air vehicle’s flight control system.
Given that BAE Systems reckons the Taranis is of similar size to a Hawk, an Adour engine is likely to propel the air vehicle to a maximum airspeed of between Mach 0.7 and Mach 0.8 similar to that of the Hawk T2.
The letterbox shape of the engine nozzle blends well with the overall configuration and offers reduced rear-aspect radar crosssection, probably with a ‘bendy’ duct, that primarily minimises IR returns from hot engine parts and exhaust plume: the latter by mixing external air and hot exhaust gases. A complete propulsion rig was tested at Rolls-Royce’s Bristol facility.
In side elevation Taranis presents a somewhat tubby profile due to the high dorsal intake and deep lower body, whilst head-on, the significant depth and width of the lower fuselage is apparent. This stems from its major systems; engine, main undercarriage, airframe and mission systems and fuel tanks all of which need to be positioned close to the aircraft’s centre of gravity and within its relatively short body. It’s easy to see how the S-shaped ducts are readily integrated within this rotund body.
A nose boom with conventional air data sensors was fitted for early flight trials – a flight regime in which a minimal radar cross-section is of no consequence and was not present during phases two and three of flight-testing.
Two small air inlets on the upper surface are evident in the images released by BAE Systems, shown to be open on the ground and in low-speed flight, and are perhaps related to cooling or just possibly auxiliary air intakes. Clearly these would not be open in the low radar cross-section flight regime. A truly pragmatic approach to reduce the cost of this one-off demonstrator was adopted for the Taranis undercarriage, the undercarriage is an off -the-shelf system used by the JAS 39 Gripen fighter.
Aerodynamic control surfaces include upper and lower surface drag spoilers on the outer wing, which operate differentially port and starboard, to provide control yaw on this finless/rudderless configuration. Due to aerodynamic subtleties spoilers are not fully closed flush in flight. Large-span trailing edge elevons provide pitch and roll control. Edge alignment and edge and junction shaping minimise radar cross-section penalties. On the ground and without power these surfaces relax and give Taranis a distinctly droopy appearance. Proving this form of aerodynamic control was a prime purpose of the BAE Systems Raven demonstrator first flown in December 2003.
Flight demonstration trials of the Taranis air vehicle were flown at the Woomera Prohibited Area, a unique military test range covering nearly 124,000km2 (47,875 square miles) in northwest South Australia. By early 2016, BAE Systems had completed the third and final phase of flight demonstration trials.
Objectives for the flight-testing programme were demonstration of the air vehicle’s low radar cross-section, the so-called lowobservability capability, its ability to avoid shoot-down by either a surface-to-air or an air-to-air missile in contested airspace, autonomous operation in terms of a deep strike capability in a combat zone, and prove the ability to scale up some of the individual technologies amalgamated into Taranis air vehicle ZZ250.
During phases two and three, air vehicle ZZ250 was used to test as many facets of the technologies as possible. Results of the flight demonstrations were used to progress Team Taranis to a point at which the maturity of the technologies amalgamated or otherwise proved they were capabilities worthy of pursuing further.
Jointly funded by the UK government (70%) and UK industry (30%), the technology demonstrator is a UK-only programme developed by a six-party collaboration involving BAE Systems, Rolls-Royce, GE Aviation and QinetiQ, supported by the Defence Science and Technology Laboratory (DSTL) and the Defence Equipment and Support agency.
For BAE Systems, Taranis sits in an interesting place – by which the author is not referring to the hangar at Warton, its current home, but the conflict between which programme aspects can be discussed and those cannot. This information lockdown is care of the folks running the UK MoD. According to one programme manager, air vehicle ZZ250 contains some pretty cool stuff developed by the UK industry team, much of which has to remain undercover.
Stealthy by design, engineers had to verify the air vehicle met the radar cross-section criteria set by the government. To accomplish verification, the air vehicle spent some time at Warton’s radar cross-section range. Radar cross-section verification requires measurement from all aspects, which was the primary reason for supporting the air vehicle on three circular struts atop a turntable that enabled the vehicle to be spun through all aspects.
Air vehicle facts
Taranis is an intelligent system that builds on proven systems and control technology designed, built and tested successfully in earlier BAE Systems unmanned platforms.
It was designed by BAE System’s Warton-based design office.
DSTL had a big input in the design requirements of the air vehicle and the operational environment.
Design challenges included combining advanced low observability technologies into the design, integrating secure communications on to a stealthy autonomous vehicle, and mission sensor integration.
Airframe is a combination of metal and composite materials.
However, the Warton radar cross-section range comprises more than a turntable and a bunch of circular struts. The facility also has a hangar, but one of a different kind from the usual. Set on railway lines, the hangar is movable. When required, the test piece can be covered by moving the hangar to position overhead the turntable, and moved away from the test piece during testing.
When the Taranis air vehicle was under test, each of the three circular struts was shrouded by a large cone founded on the floor as part of the range gate process. Range gates are used to select a certain target for further processing: in this case, to range gate the hangar with the test piece in the foreground. Ground-based activities also included hardware-in-the-loop testing used to mimic flying in order to exercise fully all systems on board and execute the mission plan.
During phase one, the air vehicle was configured with antennas and a nose boom for flight sciences testing, verifying operation of the highly automated finless air vehicle and its flight characteristics. The onboard air data system provided sufficient data to deem the air vehicle airworthy, which meant that the nose boom could be removed for the followon phases.
Phases two and three involved testing the air vehicle in all three signature domains: infrared (across the aft aspect); radar (from all aspects); and communications (also from all aspects) for which the air vehicle was in a low-observable configuration without antennas and the boom to further reduce the radar cross.
Specifically, reduction of the amount of communication emissions in time and volume to and from the air vehicle was one aspect of phases two and three, as was air vehicle survivability, testing the group of technologies and systems designed to prevent shootdown across all three signature domains concurrently.
Prior to each flight, the air vehicle is uploaded with the mission plan containing every objective. Taranis has three flight modes available: automatic, the primary mode used for take-off, general flying and landing and the most common for much of the flight-testing; autonomous, used to accomplish the mission requirements; and manual, the back-up.
Engine start is a manual function, but from there on the air vehicle operates in automatic mode; it taxis to a holding point close to the runway and holds there until a take-off authorisation is received. Take-off is also an automatic function, as is transit to the area.
Once within the area, operation switches to autonomous mode. This is a neat capability. Taranis autonomously determines where to fly within the socalled search sector air space to acquire its assigned targets in accordance with the mission plan’s set constraints. Surveying an area with an imaging system, collecting, storing and relaying information back to a ground station is one example. Given the air vehicle knows its altitude, flight pattern and sensor footprint, the system could determine the number of images required to map an area fully.
Despite its autonomous capability, Taranis always operates with a two-person crew – a vehicle operator and a vehicle commander – supported by numerous technicians and flight-test engineers.
Phase two and three trials helped determine the limits of the existing technologies and what could be achieved with them. Consideration was then given to how the technologies were to be used.
Continuing with this example, once the mapping task was complete Taranis picked up a new tasking from the mission plan: for example, an attack profile involving the simulated release of a weapon (no weapons were carried), then holding off before receiving a command to return to the target area for a simulated battle damage assessment.
The three stages outlined for the mapping task above are normally undertaken by a combat ISTAR aircraft with very little continuous communication. By contrast, a current generation remotely piloted aircraft requires continuous communication to achieve the task in addition to a high bandwidth for video stream downlink and a complex exploitation capability to handle the data. Continuous uplink and downlinking makes that remotely piloted aircraft an emissions beacon.
Taranis, on the other hand, demonstrated how it could operate in simulated contested air space with minimal communication and use of greater automation in a combat zone. This is an advantageous capability, but one that’s also sensitive to all sides to which BAE Systems stressed that Taranis is not a demonstrator of a fully autonomous future weapons system.
The company says communication architecture is a key requirement for a manin- the-loop system like Taranis.
Now that air vehicle ZZ250 is parked up in a hangar at Warton in an airworthy anti-deterioration maintenance state, it’s worth reviewing what BAE Systems will do next, not just with its light grey, wedgeshaped aircraft, but also the technologies demonstrated by Taranis.
To understand the programmatic aspects, it’s best to review briefly the background of the Anglo-French FCAS programme. BAE Systems worked on the FCAS feasibility phase back in 2016, a phase created in the Lancaster House defence accord signed in November 2010. In 2012, BAE Systems conducted a small, demonstration phase, and also received the route signposting for a two-year funded feasibility programme following an Anglo- French summit at RAF Brize Norton in 2014.
Commitment to the FCAS programme was reconfirmed in the UK government’s 2015 Strategic Defence and Security Review (SDSR), with further commitment coming from the Anglo-French summit at Amiens in March 2016. Amiens confirmed the UK and France both wanted to transition to the next phase of FCAS in 2017. Both nations also wanted to launch a joint programme to build two operationally representative demonstrators by 2025, one for the UK and one for France. Collaborative in nature, the construct of this feasibility phase included national variance of a common core solution with recognition of the possible differing operational requirements of the two nations, and an assurance that the common core could handle the individual UK and French objectives.
The £200 million, two-year FCAS feasibility phase included £120 million for the joint programme and £80 million for national technology programmes. Six defence companies are involved, two for airframes, two for systems and two for engines.
From a practical perspective, the binational programme is based on systems and components produced by each of the six defence companies as contributions to the common core.
Design and development required an adaptable programme that recognised the likelihood of two national trials each individually feeding information into the common core as well.
€2 billion was committed by the two governments, with a technical review scheduled for 2020, aligned with the UK’s next SDSR.
For the UK, the FCAS programme seeks to meet the combat air capability requirements five to ten years beyond 2025. It also poses a conundrum. Does the programme seek to put a new air weapon system into service that operates in cooperation with Typhoon and F-35 in a manned-unmanned mix, or to prepare a Typhoon replacement for 2040?
There’s no reason why the programme cannot support both and keeping both options open will be essential to setting up physically an eventual new air weapon system programme.
UK combat air
BAE Systems supported the government in its review of the Combat Air Strategy during late 2017 and this led to the Tempest announcement at the 2018 Farnborough International Airshow. Taranis was the blueprint for how a group of companies with technologies and a vision of the future could come together to work with the UK government to mature the technologies to a point where it and industry are happy to move forward into the production phase. Taranis was significant in two ways: investment, and the technological challenge of designing and maturing critical design technology and best acquiring that capability, based on the results.
Determining how the Royal Air Force and Royal Navy will potentially train with a future air vehicle is a key point of BAE Systems’ ongoing work. How will the operational use of a UAV that for 95% of the time will operate for training manifest itself when you’ve got a force mix of manned and unmanned?
December 17, 2003 First flight of the BAE Systems Raven used to prove novel aerodynamic flight control and autonomous operation.
December 2005 Defence Industrial Strategy programme announced by the government to ensure the UK has the technology to go it alone on military UAVs.
December 2006 The joint funded contract was placed in December 2006. Originally valued at £124.5 million, the contract was uplifted under separate approvals to £185 million, and extended to accommodate an additional programme of work with a wider scope.
December 2008 Air vehicle final assembly started.
July 12, 2010 A superficially complete airframe was rolled-out to the media at Warton.
March–May 2012 Clandestine radar cross-section testing conducted on the outdoor range at Warton, mostly at night due to the sensitivity of the aircraft’s design.
June 19, 2012 Taranis was placed on display during a media event at Warton. The aircraft was about to start extensive ground testing, including the first engine run and pre-flight preparation.
Early 2013 Air vehicle configured for flight sciences testing.
April–May 2013 Low-speed taxi trials were undertaken at Warton.
May 18, 2013 Taranis technology demonstrator ZZ250 transported to Woomera on board RAF C-17A ZZ173 from Warton.
July 2013 High-speed taxi trials held at Woomera.
August 10, 2013 The first flight took place from the Woomera test facility at 8.09am and lasted approximately 15 minutes.
August 17, 2013 Second flight involved the retraction of the undercarriage for the first time while airborne.
October 2013 MoD confirmed the first flight had taken place and trials were continuing.
Early 2014 Air vehicle configured for low-observability testing.
February 5, 2014 BAE Systems announced the cost of the programme to date as £185 million.
Spring 2014 Start of the second flight demonstration phase.
Autumn 2015 Start of the third flight demonstration phase.
BAE Systems is part of a UK working group that includes the Military Aviation Authority and the Civil Aviation Authority (for administration of the civil aviation regulation component) whose first major test will be the certification of the Protector UAV in UK airspace for RAF service entry; Protector will be the first CAA-qualified unmanned vehicle.
As such, Protector is core to how the UK progresses to routine UAV operations in UK airspace. This is a large programme of ongoing work, and some of the key technologies used by Taranis are evolving, such as sense and avoid and autonomous operation, which BAE Systems must now progress further and ultimately demonstrate.
It’s fair to say that the level of capability demonstrated by the Taranis air vehicle can be classed as world-beating. It is equipped with some cool stuff and stands as an example of how BAE Systems and its programme teammates successfully manufactured an advanced air vehicle system in quite a short timescale that concluded with a successful flight demonstration programme.
Science under the covers
Taranis is shaped to achieve specular scattering of radar waves such that they bounce off the structure; the fuselage shape and articulation is formed to minimise the returns to the radar. The entire fuselage form achieves that by minimising the number of features dubbed bounce structures; the ones that reflect most of the energy of the radar wave back to source. More specifically facets, control surfaces, leading and trailing edges are arranged in such a way to direct radar wave reflections just a few angles; in engineering terms this is known as planform alignment and seeks to reduce the air vehicle’s detectability at every other angle than the few mentioned above.
Radar waves occupy various frequency bands within the electromagnetic spectrum, and to date American aeronautical engineers designing stealth aircraft such as the F-117 Knighthawk, B-2 Spirit, F-22 Raptor and F-35 Lightning II have created materials with an ever greater ability to absorb electromagnetic waves. Absorption depends on two properties: one to store electrical energy (permittivity) and one to store magnetic energy (permeability). These properties are dependent on the existence of electric or magnetic dipoles at the atomic, molecular or the crystal lattice levels. Dipoles are pairs of equal and oppositely charged or magnetised poles separated by a distance, and crystal lattice is the symmetrical three-dimensional arrangement of atoms inside a crystal.
Such material is generally referred to as RAM, which tend to be composite in nature and made of a matrix material and a filler. Matrix is dielectric in nature meaning it’s an electrical insulator such that electric charges do not flow through the material, and therefore provides considerable permittivity and negligible permeability.
Given the Taranis is designed with stealth capability, its surfaces appear to be a lowobservable coatings system. Closer inspection of edges around the air vehicle show a visibly different band, a so-called edge treatment.
This is likely to comprise an arrangement that suppresses edge waves (those emitted by surface currents when a surface edge is struck) by slowing surface current transition, and two means of absorbing electromagnetic energy; currents to suppress travelling waves (those that travel along a surface and bounce offedges in a specular manner) and incident radar waves to suppress edge diff raction.
Just what’s in the edge arrangement is not clear. In cross-sectional terms, think of the edge as a triangular wedge comprising a lightweight honeycomb material impregnated with an electrical energy impeding material probably at a level of concentration that increases toward the inner base, thereby decreasing the level of impedance to the wedge’s subsurface. Edge radar-wave- generated current transition is therefore slowed down and electromagnetic energy is absorbed. Consequently, the effect of the edge treatment is a drop in the air vehicle’s radar cross-section, especially abnormal angles.
Nobody outside of BAE Systems and the greater MoD agencies running Taranis knows what lies beyond the air inlet. Taranis is powered by a single Rolls-Royce Adour series turbofan engine, a successful motor used by the BAE Systems’ Hawk trainer.
The inlet is positioned on the air vehicle’s upper surface and triangular in forward elevation; its form is designed to minimise the radar cross-section of the inlet. Early images of Taranis supplied by BAE Systems had the inlet blackened out to prevent visual acquisition of the internal shape and form.
BAE Systems’ engineers have used two longitudinal curved S-shaped ducts coated with RAM material, one to the front of the engine and one aft. Use of the S-shaped ducts prevent visual or radar wave acquisition of the front or back of the engine.
Such an arrangement helps to reduce the radar cross-section of the inlet and duct (the curved duct causes radar waves to bounce multiple times) and the RAM material absorbs significant amounts of electromagnetic energy. Edge treatment is visible on the Taranis engine inlet.
Taranis might use a composite skin with non-directional woven fibre cured into the skin to prevent electromagnetic energy from varying with angle. Stealth framer Lockheed Martin is known to have developed a method for growing cylindrical carbon molecules called carbon nanotubes (CNT) on various materials including ceramic, fibre and metal. Fibres infused with CNT can absorb or reflect radar waves and provide pathways for the surface currents explained earlier.
BAE Systems has also paid attention to the effect of the engine exhaust on the air vehicle’s radar cross-section. When radar waves enter an engine exhaust from behind, they tend to exit in the same direction; those striking the edges of the nozzle are diff racted in the same direction, in the same way returns from trailing wing and tail edges do. As a consequence, the aircraft’s radar cross-section across the aft aspect is increased. BAE Systems’ engineers designed Taranis with a narrow engine exhaust positioned on the upper surface, inset from the trailing edges, with edge treatment, while its position in azimuth is obscured by the wings that extend past the exhaust. The exhaust arrangement is colloquially referred to as the pillar box which has a diverter in the very aft section that looks to be triangular in planform, suggesting the exhaust is channelled through a narrow outlet on both the left and right sides.
Engineers appear to have also designed the Taranis air vehicle with broadband stealth characteristics. How? By eliminating surfaces that cause what’s termed resonant behaviour, hence the lack of a tail. Resonant behaviour occurs when the air vehicle or a component of the air vehicle’s dimensions are close to the radar wavelength by a magnitude between a half and ten, a behaviour that increases the radar cross-section of the air vehicle.
BAE Systems’ engineers also designed the air vehicle with all of its edges in the horizontal plane, and aligned with the leading edges. Furthermore, the air vehicle’s profile comprises an upper and lower surface, both gently curved and joined at an acute angle, thereby limiting the angles of specular reflections. Upper and lower surface curves vary in both direction and radius to form a fuselage with sufficient depth to house the Adour engine.