Fastener modeling for lightning current assessment in aircraft fuel tank
Résumé
A large number of fasteners are used in an aircraft assembly, because the nonconducting protective paint makes them the only way to drive the current. The lightning current assessment in these fasteners is a challenge carried out by aircraft manufacturers for the lightning certification, but
they generally emphasize on modeling rather than tests which are expensive and time consuming. Despite this, few fastener models [1]-[4] have been proposed, and the uncertainties of their main parameter, a resistive parameter which represents contact resistances, result in inaccuracy of the models. In this paper, we propose to represent a fastener by a lumped resistance into a short wire, and apply the uncertainty model proposed in [5] : each lumped resistance has a stochastic value drawn from a probability distribution. We model a FDTD fuel tank using this fastener model, and perform measurements at various locations of the fuel tank during a lightning strike, with its current directly injected in a fastener. Our goal is to obtain confidence intervals of the current value using FDTD simulations. In order to achieve this, we perform several simulations with different
resistance values drawn from the uncertainty model. We observe that the modeling of the lightning attachment fastener requires specific attention, particularly regarding the current assessment close to this lightning injection point, so we analyze the sensitivity of several models and discuss them. In the case of the fuel tank, we question the use of extended copper foils as protection and show that the measured currents are well within the expectations of our approach,
proving its reliability for the lightning current
assessment.