Nearly three years after it first flew, key aspects of the all-British Taranis UCAV (unmanned combat aerial vehicle) demonstrator remain classified. But further insights into the flight test program were revealed recently by three senior participants from BAE Systems, which is leading the effort. They spoke to the Royal Aeronautical Society’s Flight Test Group in London.
“Taranis has pushed the boundaries of technology, especially in autonomy, flight control, low observability and secure communications,” said Paddy Bourne, chief engineer. Although BAE Systems (Outdoor Exhibit 11) gained some prior experience in tail-less flight from the Corax, Kestrel and Raven small-scale experimental vehicles, the flight test progression of the Taranis campaign had to be very carefully designed on a safety-first basis, he explained.
In the first phase, the UCAV flew with a traditional flight test data boom and protruding blade antennas. But recordings from the low-observable flush-surface flight data system were recorded for comparison, and conformal antennas were gradually introduced. These low-observable features were fully introduced for phase two.
Bourne noted that actuation specialist Claverham Ltd was an important partner on the flight control system, while Cobham and QinetiQ contributed to the communications system. GE Aviation and the Triumph Group were involved with the flight systems. GE Fanuc and QinetiQ made inputs to the UCAV’s autonomy. Rolls-Royce was responsible for the modified Adour powerplant, and its exhaust system.
Flight test manager Jon Wiggall noted that although full certification was not required, a “fatality” (not literally, since it is unmanned) rate of one-in-a-million flight hours was specified. This was met by such features as a triplex flight control system, plus duplex hydraulics and electrical power generation. “We elected to fly over a sterile area, so we only had to prove that we could stay within it,” he added. That area was the very large Woomera Test Range in Australia, which also offered an integral runway and a benign electromagnetic environment.
The core flight test processes were the same as for a manned aircraft—expand the flight envelope from the middle towards the edges, by going slower and faster, higher and lower, Wiggall said. A Frequency and Bias Input (FBI) system that BAE Systems had used for Eurofighter Typhoon flight tests was used to program test maneuvers. But with no pilot on board, the progression between test points such as climb and descent angles and turn radii, had to be very carefully pre-planned. Unique additional considerations came into play—such as the possibility of the line-of-sight communications to the ground control station being ‘blanked’ by maneuvering. Another was the need to pre-arrange how to re-fly test points.
Taranis has three flight modes—automatic, autonomous and manual. Automatic is the equivalent of autopilot in a manned aircraft, with 3D following of waypoints, each of which has associated metadata for adjusting (for instance) speed, altitude and turn radius. The distance between waypoints determined the rate of adjustment. Wiggall showed a diagram of the second test flight, which had 47 waypoints. The waypoints also controlled angle-of-attack, g-force, and retraction or extension of the landing gear.
The autonomous mode is entered and exited from specified waypoints, and is where the UCAV “thinks for itself” according to Wiggall. His diagram showed a box of airspace within which the Taranis could self-navigate, with its sensor searching for targets such as vehicles or aircraft shelters. Upon finding a match according to pre-specified criteria, an image of the target is transmitted to the ground station for validation by the mission commander. If—and only if—that person approves, the UCAV then sets up an attack profile; provides battle damage assessment; and re-attacks if required and authorized.
Wiggall said that while the UCAV was searching in autonomous mode, the flight test team would insert “pop-up” threats such as a surface-to-air missile system, to determine whether it would self-navigate to avoid them.
Manual mode is a reversionary backup, designed to bring the UCAV home if something goes wrong. Wiggall said that it was never needed during the Taranis test flights, but was turned on for 90 seconds so that the test pilots could check whether it behaved as per the simulations.
“The first test flights were almost an anti-climax, because they were so like our simulations,” said Neil Dawson, chief test pilot. Each mission plan was rehearsed using hardware-in-the-loop—linking the ground station to the aircraft at Woomera. “We spent hours learning how to land, with the aircraft on jacks so that the undercarriage could be operated,” Dawson said.
The ground station was “crowded,’ he noted. In addition to the mission commander and the pilot, there was an aircraft systems operator, a sensor operator, a flight test engineer, a range safety officer and five “subject matter experts” for the propulsion, FCS, air data system; fuel system and hydraulics.
Dawson said that a chase aircraft was used on some test flights. Its pilot looked for leaks and venting from the UCAV. “We did have a microphone on the aircraft, so that we could detect engine or other vibrations in the ground station,” he added.
The trio that spoke at the RAeS were not authorized by the UK Ministry of Defence to discuss the third phase of Taranis flight tests, which was successfully completed in August 2015. He also said that a fourth phase may be conducted.
Just over £200 million ($290 million) has been spent by British industry and government on the Taranis program. Another £40 million is likely. Meanwhile, a separate outlay of £120 million by the British and French governments is now going toward a feasibility study for a Future Combat Air System (FCAS). This Anglo-French effort is now in its second year, and involves BAE Systems, Dassault Aviation, Rolls-Royce, Finmeccanica (e.g. the former Selex in the UK) and Thales. The British and French defense ministries are also involved.
Bourne said the FCAS study includes safety trades; airspace integration; levels of redundancy; diagnostics; communications; propulsion; armament; the regulatory regime; mission systems and ground control—“some of the things that can be very different in an unmanned system.” The study includes ethical as well as technical issues. “Man-in-the-loop is an important aspect,” Bourne added.
Last March, the British and French governments promised to fund the next phase of FCAS. This work would start next year, and aim to produce “operationally representative demonstrators” by 2025. There would be a technical review in 2020. Each nation will contribute about $1 billion.
BAE Systems Showing UCAV Scenarios Here
In the BAE Systems exhibition building here at Farnborough, the company is showing scenarios in which a UCAV (unmanned combat aerial vehicle) identifies and drops weapons on a target. Three screens display a tactical situation, a map-based overview, and the status of the UCAV (fuel state, weapons, etc.).
In a recent preview of the display, Drew Steele, operational requirements executive, future systems, BAE Systems, said that the aim was to show how manned and unmanned air platforms might work together. The UCAV takes off, and soon demonstrates how its “sense and avoid” system enables it to avoid conflicting traffic. It then sends a burst transmission of status data to the ground station, before hooking up with a manned tanker for a fully autonomous air-air-refueling (AAR).
After that, the UCAV goes into silent mode and detects some surface-to-air missile (SAM) sites. It compares their location with prior data that it has received from an E-3 AWACS over Link 16. It renews contact with the ground station so that the mission commander seated there, can review the target and grant permission to engage.
Some Typhoon manned combat jets are also airborne, armed with heavier and more versatile weapons. The UCAV strike on the SAMs should clear the way for them to enter the hostile area to engage other targets.
Steele emphasized that the various scenarios are open to discussion and debate. Might the tanker control the AAR of the UCAV? Might the Typhoon formation commander take control of the UCAV? There’s plenty still to decide, as the Anglo-French FCAS work continues. And it will likely be another 15 years, before the scenarios on view here, are actually played out for real.