Indirect Lightning Effects Evaluation of an F/A-18E/F

The F/A-18E/F aircraft are now being constructed with a skin of largely composite material. With this new configuration, the Navy required that the aircraft be evaluated for lightning vulnerability. The test was performed at the Navy Patuxent (Pax) River (MD) facility during the spring of 2001.

The test was conducted in accordance with MIL-STD-464 using the test configuration shown above. Current was pulsed into the aircraft and returned via a unique coaxial return path. The current waveform was produced with a moderate capacitor bank (1.65 μF) discharged with a crowbar switch used to attain the double exponential waveform. A matrix of circuits were evaluated with both flight critical and mission essential systems considered as highest priority test points. The test was conducted with two current path configurations. The first path was the normal nose-to-tail path and the second was nose-to-wing, which included the wingtip-mounted AIM-9 missile. The missile was required since it is part of normal aircraft operations. After the impulse test phase, the aircraft systems were then induced with the ‘direct drive’ current evaluation, which scales to full threat lightning level. The test results are to be used for the evaluation of the aircraft’s lightning vulnerability and will be compared to tests performed on the F/A-18A aircraft at Sandia National Laboratories. Data acquisition during the lightning simulation test was automated via a Data Acquisition and Processing System. The system automatically corrected the waveform information by removing instrumentation-unique characteristics. Noise and field measurements assured that the recorded signals were not produced by extraneous influences. Preliminary results indicated high magnetic fields on the interior of the aircraft due to the composite skin on the bay doors and by the simulated lightning currents being transfer to the aircraft (sub)structure, as expected. Details of the test setup, instrumentation, aircraft preparation, and test results are presented in this paper.