Search Results

Lightning and static charging tests were performed on one transport aircraft radome and one small aircraft nose radome at the NASA Icing Research Tunnel (IRT), Lewis Research Center, Cleveland, Ohio. The primary purpose of these tests was to evaluate the effects of rain and icing conditions on the lightning protection effectiveness of segmented-type diverters. A secondary purpose was to evaluate the effects of static electrical charges deposited by rain and ice particles. The tests were performed under Task 2.4 of the Joint Program on Improving Lightning and Static Protection of Radomes. Fifty-four lightning tests were performed on two radomes to evaluate the effect of icing, precipitation drop size, and temperature on the ability of segmented diverters to prevent puncture of a radome skin and attachment to the internal radar antenna. Five of the tests resulted in radome puncture under icing conditions. One of the punctures occurred under rain without radome icing.

A companion paper in this conference gave an overview of the Joint Radome Programme results (paper 2322). This paper reports on experiments that were able to reproduce some features of the failures to radomes that had occurred in-flight despite passing ground based tests. The electric field environment reviewed in the programme suggested that for most lightning strikes a more realistic test was to use a destressed electrode and the slower high voltage waveform D, rather than a rod electrode and a faster waveform A. Moreover other recent work also reported at this conference by Drumm et al, suggested that segmented divertor strips require higher light up voltages for slower voltage gradient waveforms. Therefore a series of tests with this revised test configuration have been conducted on some A320 radomes supplied by DGA Toulon France equipped with segmented strips that had experienced in-flight failures.

Concern over severe lightning strikes to helicopters in the North Sea resulted in a UK Civil Aviation Authority sponsored research programme. The programme investigated the polarity of lightning strikes in this region by remote sensing with a view to determining the likelihood of severe positive strikes. It also investigated correlations of individual incidents with meteorological conditions and .the lightning detected by remote survey on the day of the strike. The study shows that the strikes to helicopters occur only in winter, possibly triggered by the helicopter itself. The proportion of positive strikes, believed to be on average more energetic than negative strikes, is higher than the World-wide average, particularly in winter. The meteorological investigation found that temperature and updraft parameters allowed a predictive algorithm for helicopter strikes to be constructed.

In the EU FULMEN collaborative project a series of experiments based on AEA Technology’s Hawker Hunter airframe have studied coupling of E and dE/dt threats. Currents and fields were applied using either a low level lightning current simulator to the whole airframe, or by injecting the threats more locally. Coupling could be measured in two apertures at opposite ends of the airframe, in which cables were routed both parallel and perpendicular to the current paths. The different configurations for measurement and test allowed the various coupling methods to be separately elucidated. Likely levels of E-field and d2B/dt2 coupled transients which could couple to internal equipment are discussed in relation to the present consensus of external environments.

The Joint Radome Programme was formed in February 1993 to investigate and research the effects of lightning and static electricity on aircraft radomes and dielectric fairings. Some preliminary results were presented at the Williamsberg Conference in 1995. Since then experiments have been completed that have recreated in the laboratory some of the features of in-flight failures; these have included both radome measles and punctures of radomes that had previously passed existing test methods. This paper gives an overview of some of the key results and the implications on test techniques.

AEA Technology is carrying out an ongoing programme of lightning simulation testing work on carbon composite ‘T-joints’. These typically represent skin to spar bolted interfaces, and the tests help to determine whether aircraft fuel tanks incorporating such structures are liable to produce sparks during a lightning attachment. For testing, the T-joints are integrated into a complex test rig that is intended to provide representative current flow during the simulation tests. The intention is that the current distribution in the T-joint should be similar to the current distribution on the equivalent part of the aircraft structure during a lightning attachment. A combined experimental testing and computational modelling work programme has been carried out in order to investigate how representative the test-rig current distribution is to that on a real aircraft. In the first part of this study the test rig itself is modelled using the 3D code ELECTRA.

DO160D/ED14D S 22 describes procedures for pin testing; they define a specific source impedance for the transient generator. This inevitably limits the maximum current that can be driven into a pin during a test. Sometimes this implied current limit has been questioned as being too high since s/c currents associated with Waveform 5A have a lot of energy and can damage components. This paper reports investigations into actual current levels that can occur particularly when transorbs installed for protection purposes become conducting. Theoretical estimates and results of experiments are described. For Waveforms 4 and 5, the currents can be estimated for simple circuit equations. In some circumstances the current limits could be set too low so the procedures need to be carefully reconsidered during DO160D testing.