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Successful lightning protection design is important for the CargoLifter CL 160 large non-rigid transport airship. Non-rigid airships, like balloons, have few hard structures so alternative means need to be designed to collect and conduct lightning currents. The helium lifting gas ionizes at one third the field intensity required for air so spark formation in ambient electric fields is more likely to originate inside a helium filled envelope than in the air outside of it. Protection development is being accomplished by a combination of high voltage strike attachment tests on scale models, and numerical analyses of electric fields.

Numerical simulation of indirect effects of lightning on a multibranched engine control wiring harness set was developed using the MHARNESS* simulation code. Electrical parameters of the harnesses and subassemblies were measured and entered into the analytical model. Results of the analytical model for bundle current distribution and harness attenuation for a lightning pulse were compared against actual test data. Close correlation was obtained in most branches. Further work to optimize the model and add sensor and actuator loads will be conducted in the near future, and sensitivity analysis will be performed on various harness parameters and bonding impedance.

It is well known that the shape of a conductor in an ambient electric field will act to enhance the maximum field levels and can in fact cause an air breakdown condition. This geometry can also have an effect on the type of breakdown that occurs, for example a corona discharge versus an arc discharge. Hermstein [1] has done an investigation into the conditions necessary for arc propagation instead of corona breakdown for the case of two electrodes with a forced potential between them. He used spherically shaped electrodes and he computed the electric field between them to determine the conditions necessary for arcing to occur as opposed to corona. The purpose of this study is to determine if the Hermstein results apply for the case of a floating electrode, or metal object, immersed in a static electric field.

In this paper the interaction of the High Intensity Radio Frequency (HIRF) environment with aircraft is described. This environment is assuming more importance because of the use of composite materials and low level semiconductor technology which performs critical functions. Experimental coupling results are presented and discussed for induced cable currents at low frequencies, and for internal fields at high frequencies. A major portion of the paper is used to describe numerical techniques which can be used to solve the coupling problem.