D-Joints manages lightning strike action

Clean Sky 2’s D-Joints (Design of innovative composite hybrid joints with electromagnetic compatibility) project has successfully tested and validated two types of joint technologies developed under Clean Sky 2’s C-Joints project to protect aircraft from lightning strikes. The joints ensure that an aircraft’s external panels or structures, when made from composite material, are connected in a way that ensures that if hit by lightning, the electrical charge can be conducted safely between panels along the length of the aircraft, preventing damage or safety concerns.

This was not an issue in the days when aircraft were made of entirely metal construction – the electric charge of a lightning strike could be channelled towards the trailing edges of the aircraft and safely discharged. However, with the increased use of composite material, managing a lightning strike becomes more complex.

The lightning strike challenge for composites
The two technologies successfully developed in the C-Joint project, tufting (an industrial stitching process, applied using robotics, whereby a thin copper thread is sewn through a composite panel to facilitate electrical conductivity), and thermal spraying (a process developed at TWI Limited whereby metal particles are sprayed onto composites to provide metallic connections that can carry energy between composite-composite panels, and between composite-to-metal panels) solve this specific challenge.

The purpose of D-Joints was to put the C-Joint technologies to the test, validate their effectiveness, and then incorporate the results into a ‘sizing tool’.

This is a user-friendly software tool for engineers which helps them quickly specify the technical parameters, material characteristics and size of joints that are required when designing aircraft external panels and structures that require embedded protection from lightning strikes.

“The tufting and thermal spraying technologies were tested and validated for electromagnetic compatibility testing at demonstrator level, on the nose section of the Evektor EV-55 aircraft.” said Sonia de la Cierva, Project Officer at Clean Aviation.

The nose section demonstrator was tested in a relevant environment where it was subjected to simulated lightning strike conditions. Results indicated that these new technologies provided effective protection to aerostructures in the event of a strike, as well as protection from the indirect effects of lightning (from the electromagnetic fields that lightning generates). This was confirmed through successful assessment using a technique known as ‘High-Intensity Radiated Field’ ground tests. Learnings from the project were integrated into the sizing tool.

Environmental advantages
Though the project’s main focus was on lightning strike protection, the results also have clear environmental benefits. The sizing tool will assist designers in determining the appropriate size and shape of joints needed when designing integrated composite structures with Lightning Strike Protection (LSP), thereby saving weight, reducing fuel consumption and thereby cutting emissions. The tool also accelerates the time-to-market due to elimination of time-consuming design review iterations required to develop and produce joints. It does this by enabling the designer to quickly specify the most appropriate type of material combination that can be used for a particular joint.

“A further deliverable, encapsulating the compiled test outcomes and assessment of the environmental benefits is currently in progress,” says Clean Aviation’s de la Cierva. “This will take the form of a summary document that classifies the benefits of the investigated technologies with evaluations of their cost and weight reduction.” 

D-JOINTS ran from May 2020 until December 2022 with an EU budget of €468 000. The project was coordinated by TWI Limited and supported by Cranfield University and Brunel University’s Composites Centre. The Topic Manager was Evektor of the Czech Republic.