Europe demonstrates technological maturity in unmanned flying

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The jet fighter takes off from Le Tubé Air Base in Istres, France.It makes a sharp turn to the left and enters the assigned flight corridor over the Mediterranean Sea. The speed reaches the maximum of mach 0.85. But suddenly the stealth plane suffers a sudden and unplanned loss of communication with the pilots control system. It doesn’t seem to become them, sitting comfortably reclined in front of displays and panels

 

This could have been the maiden voyage of Neuron, Europe’s Unmanned Air Vehicle (UAV) demonstrator. The first flight is planned for the year 2012. The unmanned aircraft is designed to fly without communication with the two pilots on the ground.

 

– The reliability and characteristics of radio communication as well as placement of the antennas on the body of the aircraft leads to periodic loss of communication, says Jesper Tordenlid, one of the technical managers at Saab Aerosystems in Linköping, Sweden. The design of the control system takes this into account. The interface needs to be robust and the behavior of the aircraft predictable.

Contributing with ten years of experience

The French company Dassault Aviation is the prime contractor of the Neuron project and Saab Aerosystems is one of the five partner companies. Saab has explored the collaboration and behaviour of pilots and air traffic control operators when flying unmanned aircraft and how to apply the rules and regulations from aviation authorities. Saab’s technical development projects, trials, simulations and large role plays the last ten years are valuable sources of knowledge to the Neuron project.

– These experiences have taught us about requirements and has led to the development of a scalable system design for use with small unmanned helicopters as well as large jet fighters like this, says Jesper Tordenlid.

Neuron is a European project involving six nations. The objectives are to develop strategic technologies and gather experiences in the European aviation sector. The project result is not a product but a demonstrator of European know-how. One of the goals is to position European companies as possible prime contractors in future UAV development projects.

Neuron UAV – Facts and figures
Length:

Wingspan:

Weight empty:

Weight fully loaded:

Engines:
10 m

12.5 m

4,500 kg

6,000 kg

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Saab Aerosystems from Sweden is developing the central parts of the aircraft body, the avionics computers and software, the fuel system and the flight safety critical part of the control station on the ground. A philosophy in the Neuron project has been to use Commercial Off-The-Shelf (COTS) components to a large extent, preferably from European suppliers. Saab Aerosystems found that Hectronic’s principles to reuse embedded building blocks was a good match.

– We needed a robust system platform for the safety critical parts. One of Hectronic’s advantageous assets is the amount of functional parts to choose from and integrate to realize our vision of the system. As a result of that the project progressed fast and can rely on already verified functional blocks.

Designing according to RTCA DO-254 and DO-178

Jesper Tordenlid is technically responsible for the safety critical parts in the control station on the ground. He describes his experiences from working with Hectronic.

– We had a vision on what to accomplish, rather than a complete design. That vision was brought to Erik and Kjell at Hectronic. Together with Hectronic we discussed the visions and explored the possibilities during meetings in Uppsala. The conclusion was a design that matched Hectronic’s experiences and our knowledge on what’s needed for the future. It was a creative collaboration.

The cooperation proceeded and requirements were analyzed and made concrete. One major source of requirements in the project was RTCA DO-254, which is a standard for hardware in the aviation industry. The corresponding standard for software is RTCA DO-178. These standards make a separation of system parts into classes depending on impact on flight safety. The most safety critical parts are class A and the least are class D. Well thought-out system design simplifies development without reducing safety.

– It was crucial to properly break down the system and identify critical parts, partly to reduce costs. We tried to isolate and minimize the safety critical parts.

Proving reliability

It’s up to the development teams to prove reliability levels in the system required by DO-254. There are always design rules to rely upon but seldom any correct answers. The formal document of proof to the authorities, the Description of Function, in this case 2000 pages, contains numerous and extensive technical discussions, scenarios, alternative scenarios and consequences.

Hectronic’s strategy to reuse designs, in small or large parts, has advantages when it comes to proving reliability. Ethernet controllers, power supply and the H6046 ETX module are all examples of existing building blocks that were used in the project design. It’s easier to maintain and prove system reliability if the parts included are well-tried. It was an argument used in the document Description of Function.
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The H6046 ETX computer module from Hectronic was used in the control system on the ground. The computer module is based on a low power Intel® Atom™ processor and the Intel® System Controller Hub US15W. H6046 has soldered memory, optional conformal coating and will be available in extended/industrial temperature range later this year making it ideal for rugged applications in harsh environments.

The highest safety class according to DO-254 and DO-178 for any part of the system is B. It was possible to limit class B safety requirements to the software in the computer module that is used to communicate commands from the pilots to the aircraft.

Hectronic was the system integrator, developed the carrier board, the enclosure and supplied the project with the H6046 ETX computer module. Most parts of the system are class D in terms of safety according to DO-254 but numerous design measures had to be taken to support the class B category computer modules developed by Saab Avitronics, a company in the Saab Group.

Milling the enclosure for EMC protection

Communication to, from and between the B class computer modules needed to be isolated and protected. No complex components were allowed in the communication paths, only discrete ones. The power supply is designed to withstand malfunction without cutting power to both computer boards at the same time.

– All the data and every command passing through the system are protected using checksums until reaching the safety critical computer boards where unpacked.

Strict requirements applied for protection against electromagnetic disturbance, both internally and externally, for the safety critical computer modules especially. Some engineering creativity was needed for maximum EMC protection. Guido Kats, Mechanical Engineer at Hectronic decided to go for a solution where the enclosure was milled out from an aluminium block. He was able to introduce separate compartments for every hardware block, even separate parts of the carrier board.

– The monitor cables were placed in a vertical compartment leading to the connectors on the board. We placed copper strips in a pattern protecting each functional block on the carrier board to prevent leakage. This is more or less the best EMC protection possible, says Guido Kats.
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The carrier board with the Hectronic H6046 ETX computer module mounted to left and the two, redundant flight safety critical computer modules to the right. The golden metal strips separate functional blocks on the board. The aluminium enclosure is milled in compartments with walls that meet the metal strips when the carrier board is mounted in the enclosure. The design is for EMC protection.

Milling the enclosure brought further advantages. Cooling ribs were quite simply milled on the back of the enclosure. Heat spreaders were unnecessary since the metal thickness easily could be adjusted to come in contact with the processor surface on the H6046 computer module.

Keys to success

Ambitious goals and genuine determination were keys to success. System development and integration, production documents and formal documentation required by DO-254 was completed during three spring months in 2009.

– I have enjoyed, and I am enjoying cooperating with Hectronic personnel due to their genuine commitment, says Jesper Tordenlid. When promises are made all the efforts are put into keeping them.
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The system to monitor and control the flight from the ground is safety critical. Two redundant units communicate with the aircraft. Two redundant system units are used in the control station.

Two prototypes of the system to be used in the control station on the ground in the Neuron project have been delivered. Ten or so systems will follow. The European project Neuron weren’t about developing a product but the means to learn about the technology and international cooperation within the field of UAV.

In the year 2012 there will be quite a few European engineers at Dassault, in the five partner companies and their subcontractors keeping their fingers crossed as the Neuron Unmanned Air Vehicle leaves the airbase in France. Great efforts have been put into fulfilling the goal to show that European competences and resources are able to develop what’s needed for safe future unmanned air traffic.

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