Data from low-observability trials of Britain’s Taranis unmanned combat air vehicle (UCAV) demonstrator are set to feed into studies that could result in an Anglo-French UCAV in the 2030s.

A veil of strict secrecy still surrounds the Taranis program and its flight trials being conducted at the remote and still officially undisclosed Woomera test site in Southern Australia in late 2013 and early 2014.

Now the aircraft is back in the U.K. undergoing maintenance, ready for a possible third round of flight tests that could help inform a £120 million ($193 million) project to develop UCAV concepts and technologies concluded by French Defense Minister Jean-Yves Le Drian and former U.K. Defense Minister Philip Hammond as well as industrial partners from the two nations during the Farnborough air show.

Low-observable tests formed a second phase of flight trials for the aircraft conducted during the Australian summer in late 2013 and early 2014. BAE officials have revealed that the first round of trials, disclosed by the U.K. Defense Ministry and BAE Systems back in February, were partly used to verify a conformal air data system developed for the aircraft. The first phase saw the aircraft fitted with a large air-data probe on the nose. But in order to test the Taranis’s thermal and radar stealth characteristics, the probe was removed, the nose was cleaned up and “signature-controlled” antennae were added.

Changes also were made to the aircraft’s flight control software before it was taken through what company officials described as “realistic operational scenarios.”

Testing of sensors “was taken to a certain level” in the first two flight phases, said BAE Systems’ chief engineer of future combat air systems, Chris Garside. “Sensors were part of the original evaluation criteria, and we are currently discussing options for further trials with the defense ministry.”

Taranis uses high levels of automation throughout its specified mission. As well as making use of automated taxi, landing and takeoff profiles, it has been designed to fly a programmed path, generate an attack profile based on the targets it sees with its sensors and then engage.

If necessary, Taranis will produce a bomb damage assessment and re-attack. At every stage of the flight, the aircraft is capable of dealing with pop-up threats, indicating that it is fitted with electronic surveillance measures. It can also devise an alternate route to minimize exposure to air defenses.

While the automation is designed to reduce dependence on non-stealthy data links, the aircraft is programmed not to carry out any of those actions without the approval of a human controller. Detection, identification and geolocation of targets is passed back to the mission controller, who has to give positive consent before the vehicle will go into attack mode.

“During the sortie there is a level of action that the aircraft can decide on the best approach, but in respect of the rules of engagement, the system will always ensure there’s a ground commander in the loop,” Garside said.

BAE Systems was unwilling to disclose whether Taranis had been designed to avoid detection by VHF radar, although the planform—which has no edges or components that would be resonant at VHF—suggests that it is. 

Nor did engineers confirm or deny the use of thrust-vectoring in the yaw axis, although Garside did say that the four inlay surfaces above and below the wings would be locked out “in certain flight regimes,” and said that the solution to providing yaw control with only two elevons was “within the flight control software. This is a stealth aircraft, and stealth aircraft are by definition difficult to fly,” he said.

BAE Systems has previously demonstrated fluidic thrust- vectoring using the Demon UAV under the Flavir project, which it jointly conducted with Cranfield University in 2007.

Rolls-Royce’s defense division chief engineer for research and technology Conrad Banks noted that the Adour Mk.951 engine ran surge-free throughout the test program despite the complex inlet and exhaust system and the triangular inlet, which caused distortion and swirl in the inlet flow.

“The challenge was to fully embed and hide the gas turbine in the aircraft so you would not see any indication of an engine. That is essential, but that brings challenges, unusual airflow and aerodynamics. It had to be surge-free at all points of the flight envelope and cannot reduce performance,” explained Banks.

The engine was also challenged by much greater electrical and hydraulic loads than when used in the Hawk trainer.

Chris Boardman, managing director at BAE Systems Military Aircraft hinted that Taranis could form the basis of a future platform, describing it as being at a more “advanced stage of technology development than the Experimental Aircraft Program (EAP) had been to the current Eurofighter Typhoon.”

Few details are known about how extensive the Taranis trials have been. The U.K. Defense Ministry continues to refuse to divulge details on the number of flights or hours flown.