1) Field of the Disclosure
The disclosure relates generally to lightning strike testing systems and methods, and more particularly, to lightning direct effects (LDE) testing systems and methods for testing test articles for aircraft structures.
2) Description of Related Art
Composite materials are used in manufacturing various structures of aircraft, including fuselage, wings, tail sections, skin panels, and other structures. A challenge to the use of composite structures, as compared to metal structures, is their susceptibility to the effects of lightning. Composite materials are less conductive than metal materials, and structures made of composite materials may have difficulty dissipating electric charge or energy from a lightning strike, as quickly or efficiently as structures made of metal materials. Lightning strikes to aircraft are of concern because they may result in electrical arcs or heating sufficient to ignite vaporous fuel mixtures.
Aircraft manufacturers design and continually test their aircraft for lightning strike protection. Physical damage to an aircraft occurring at an attachment point of a lightning strike, or arc, and more generally, damage caused by conduction of current into a structure is typically referred to as “lightning direct effects (LDE)”. Compliance with applicable regulatory agency requirements for protection against lightning strikes or lightning events requires lightning direct effects (LDE) testing for certification. LDE testing systems and methods typically use a test article, which may be in the form of a model or a component of the aircraft structure, and subject the test article to an energy discharge that simulates and/or generates the lightning strike, or arc. For example, LDE testing systems and methods may use a lightning strike simulator.
Known LDE testing systems and methods typically include testing criteria for passing or failing based on a comparison of an optical signature of sparking or hot particle ejection observed at a test article, such as a composite test article, and an optical signature of a reference sparker that is tuned to release a minimum ignition energy (MIE) of greater than, or equal to, 200 μJ (microjoules), the applicable standard for compliance according to the Federal Aviation Administration (FAA). However, the observed sparking or hot particle ejection at a composite test article repeatedly indicates that the spectral signature of those events are toward the lower end of the visual spectrum, i.e. a reddish-yellow color, while the reference sparker emitted light is on the upper end of the spectrum, i.e. a bluish-purple color. This is due to differences in the nature of light production in these two systems. Moreover, the reference sparker of such known LDE testing systems and methods may be dependent on environmental factors, such as relative humidity, ambient temperature, cosmic rays, and other environmental factors.
In addition, known LDE testing systems and methods typically involve subjective review by users of digital photographic images taken during lightning direct effects (LDE) testing, to determine a light intensity at a spark location on a test article. However, such subjective review may be prone to error and may result in delays in testing, as additional LDE tests may be required if there are inaccurate results.
Further, such known LDE testing systems and methods may be based on calibration of a camera used to take images of a reference sparker, and may require frequent calibration of the camera used to take the images of the reference sparker and the observed sparking or hot particle ejection. The difficulties with such known LDE testing systems and methods arise from a variability in producing a reference sparker image and frequent camera calibrations and settings. In addition, it may be difficult to obtain a repeatable and reliable reference sparker using such known LDE testing systems and methods.
Accordingly, there is a need in the art for an improved lightning direct effects (LDE) testing system and an improved lightning direct effects (LDE) testing method that are repeatable, accurate, automated, programmable, reliable, fast, and simple to set up and use, and that eliminate frequent camera calibration of the camera used to take images of a spark and a reference light source, and that provide advantages over known systems and methods.