AEA Technology is carrying out an ongoing programme of lightning simulation testing work on carbon composite ‘T-joints’. These typically represent skin to spar bolted interfaces, and the tests help to determine whether aircraft fuel tanks incorporating such structures are liable to produce sparks during a lightning attachment.
For testing, the T-joints are integrated into a complex test rig that is intended to provide representative current flow during the simulation tests. The intention is that the current distribution in the T-joint should be similar to the current distribution on the equivalent part of the aircraft structure during a lightning attachment.
A combined experimental testing and computational modelling work programme has been carried out in order to investigate how representative the test-rig current distribution is to that on a real aircraft. In the first part of this study the test rig itself is modelled using the 3D code ELECTRA. This is a mesh network code which solves Maxwell’s equations in the low frequency domain, and which has already undergone validation for some lightning applications. The predictions of current distribution from ELECTRA are compared with the experimental measurements. The exercise is carried out both for all-metallic components, and for carbon composite components. The good correlation obtained between the prediction and measurement provides further confidence in the use of the code.
Following this validation exercise a model is created of a lightning attachment to the skin of a composite wing box in order to determine the current distribution in the skin, spars and ribs. In this way a comparison between an inflight lightning strike current distribution and that achieved in the test rig can be compared.
This programme of work has been funded by the UK Defence Procurement Agency.