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While composites deliver weight savings compared with traditional aluminium aircraft structures, there are trade-offs to consider in other areas of performance and capability, particularly around lightning protection.
The highly conductive nature of aluminium means that lightning strikes measuring up to 200,000A can be quickly conducted on their journey from cloud to ground or cloud to cloud. But with extensive use of carbon-fibre outer skins, more thought has to be given to accommodating that path without resultant voltage surges causing damage to safety-critical systems.
That’s why engineers at Rolls-Royce subsidiary Controls and Data Services are working with Raytheon UK to develop components that would provide aircraft electronics and wiring with a more efficient device to protect against lightning strikes.
The project is exploring the use of the high-temperature resistant silicon carbide to make Current Limiting Diodes (CLDs), a new kind of protection device which stands to reduce the amount of electrical energy traditional suppressors have to deal with during a lightning strike. The CLDs will be able to absorb much of the electrical energy that dampening devices would otherwise have to channel during a lightning strike.
“These silicon carbide CLDs are highly resistive to the excessive surges that lightning strikes can bring,” said Greg Wells, chief of research and technology at Controls and Data Services. “The devices would be located on the printed circuit boards that go into the control cards of engine control units. We have tested batches of CLDs with simulated lightning strikes at our labs and they have performed very well.”
Project partner Raytheon runs a silicon carbide production plant at Glenrothes in Fife. Jennifer Walls, portfolio manager of integrated power solutions at Raytheon, said the material has remarkable temperature resistance characteristics but, owing to its hardness properties, processing is complex.
“We’ve been working with silicon carbide for over 10 years,” she said. “There are challenges around manufacturing as it’s very different from normal silicon substrate. We’ve built up experience in how best to process the material, and how to get the best yield. That’s a major part of what we are bringing to the project.”
The aim of the project is to develop a silicon carbide CLD for use on civil aircraft. “At the moment we are concentrating on engine control systems,” said Wells. “But the technology could also be exploited on other aircraft units that could be affected by lightning strikes.
“We believe we can come up with a commercial product. But we need to look at how we can physically integrate the components into existing systems.”