In-flight Lightning Strike Damage Assessment System

Final Report Summary - ILDAS (In-flight Lightning Strike Damage Assessment System)

ILDAS was a research project within the scope of aeronautics research of the Sixth Framework Programme (FP6) of the European Commission. The first objective of the ILDAS research project was to develop and validate a concept prototype of an ILDAS, capable of in-flight measurement of the parameters of lightning strikes. Such a system would give in due course better knowledge of these parameters that could be used to improve aircraft lighting protection. Based on the reconstructed attachment points and amplitudes of the in-flight lightning strike in real time, the second objective was to enable the development of tailored and efficient maintenance inspection procedures that must be applied after a recorded strike.

A number of sensors have been developed for ILDAS by the Technical University of Eindhoven and by ONERA, in order to evaluate possible sensor configurations capable of correctly measuring the lightning current. A specific H-field sensor has been developed capable of measuring both the high-frequency (HF) lightning strike signals as well as the associated low-frequency (LF) signals that characterise continuing current. Another specific sensor is a window sensor, which can possibly replace externally mounted fuselage sensors. Furthermore, a method for measuring the E-field behind a window has been evaluated in order to verify if it can replace an external fuselage E-field sensor. Several methods for determination of the continuing current were developed and evaluated.

In the frame of the ILDAS project, numerical methods have been proposed both for recovering the localisation of initial lightning attachment points (lightning scenario) and for the reconstruction of the return stroke current waveform, starting from the magnetic field components measured with different sensors on the structure.

Measurement aspects of the components have been considered during the ILDAS concept development and the performance has been verified during laboratory tests and tests on a test rig at the Cobham Lightning Laboratory in the United Kingdom. A further set of tests to an A320 aircraft at the Airbus site in Toulouse was made with an ILDAS sensor set and DADS system installed to study an actual installation of the system. While the main sensor set was designed around a largely aluminium alloy transport aircraft, there is interest in composites and rotor craft too so the current density characteristics arising from strikes to a composite helicopter were measured during some tests at Eurocopter in Donauwoerth.

A verification of the system was performed to confirm the system's measurement and data handling performance and to provide initial calibration values for the measurement chain. For each sensor, the effective area was determined, for each integrator the time constant was measured. For the electronics unit the band pass frequency of both the LF and HF channels was verified to be 160 mHz to 10 MHz, while the amplitude dynamic range was determined to be 96 dB when using the twin HF measurement channels. Download of 192 MiB of data from a single sensor assembly to the DADS took about twenty seconds. Tests were conducted for the case of an A320 plane and an EC135 type helicopter.

For most cases (15 out of 18) the correct attachment scenario has been predicted by the numerical method. The method failed in cases where H-field reported by several sensors had similar amplitudes leading to a ranking sensitive to discrepancies between tests and models. For left wingtip - right engine case, the method was unable to distinguish between several scenarios, as a consequence of a lack of refinement in the scenario profiles pre-established. One of the most satisfactory results is the capability of the method to discriminate between engine and landing gear attachment points. These results prove that the approach consisting in characterising a lightning scenario by a max H-field ranking and polarities is quite efficient.

The ILDAS project was an ambitious research programme aiming at validating the principle of an in-flight lightning strike measurement system. From that perspective, it can be stated that the project main objectives have been reached. Not only has the ILDAS system been specified and developed but its performance was verified during both a rig test campaign and an A320 ground test campaign. In conclusion, the principle of an in-flight lightning strike measurement system has been successfully validated. All the subsystems performed in an acceptable way. It was possible to measure aircraft skin currents resulting from a simulated strike. The measurements were of a sufficient quality to enable the determination of the entry / exit scenarios as well as the reconstruction of the injected current. After some necessary improvements to the prototype, it is likely that real lightning measurements will be performed within two or three years by fitting on a test aircraft during icing trials. The analysis of these data will benefit the industrial and scientific lightning community, improving the knowledge of the phenomenon and possibly leading to better-tailored lightning protection.

Final Report Summary - ILDAS (In-flight Lightning Strike Damage Assessment System)

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