Numerical Assessment in Aeronautics for Electromagnetic Environmental Effects

Introduction And Background

Modern aircrafts have become increasingly dependent on electronic equipment to control its systems. This has led to new safety concerns with respect to their immunity levels against EM hazards and, in consequence, their assessment by aircraft manufacturers. Besides, the variety of potential EMI sources are increasing dramatically due to the appearing of new artificial sources in addition to the natural ones. This situation is aggravated by the pervasive use of composite materials in aircraft structure: CFC, CFRC, CFRP, etc. These materials, lighter and stronger from the mechanical point of view, are poorer conductors than metals and therefore have lower shielding capabilities.

From the EMC point of view, the main EM threats for an AV can be summarized as follows:

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  Lightning Indirect Effects (LIE): 0 to ~50 MHz: Indirect effects are caused by the electric current flowing through the structure and internal wiring as a consequence of the impact of a lightning strike. This is, undoubtedly, the most important threat to onboard electronic equipment, becoming critical for aircrafts mostly made of CFCs (Meyer et al., 2008) like, for instance, modern UAVs.

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  High Intensity Radiated Fields (HIRF): 0 to ~100 MHz: This threat is caused by artificial intentional or unintentional, external or internal RF sources. These are constantly increasing in number: TV, mobile networks (3G/4G/5G), radars, navigation satellite systems, etc. and may couple to cables and equipment, potentially causing malfunction for high field levels.

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  Electromagnetic Pulses (EMP) of Nuclear or Non-Nuclear Origin: 0-100 MHz: Most of current non-nuclear low-level electromagnetic pulse generators are not capable of radiating enough EM energy to produce a significant damage. However, novel devices are appearing, which are able to involve much higher power levels with extremely short durations. These modern weapons, also named E-bombs, are becoming cheaper and susceptible of being used in terrorist acts. They can wreak havoc on computers and networks, yielding temporary disruptive effects (Radasky et al., 2004; Radasky, 2014).

In all these cases, as a result of the exposition to the EM hazard, transient currents will flow along the aircraft surface, creating EM fields which penetrate into the fuselage through apertures such as windows, or by diffusion through parts made of poorly conducting materials (Figure 1). Inside the aircraft, these transients induce currents to the EWIS, which, in turn, couple to equipment, potentially compromising their safe operation or even creating permanent damage.

Several aviation incidents, reported in the last quarter of the past century, triggered the attention of aviation agencies to include strict EMC requirements for the airworthiness certification processes of AVs during their whole life-cycle. Before a newly developed AV model is permitted to operate, it must get a certificate of airworthiness issued by an aviation regulatory authority. For instance, in civil aviation, the regulatory authority is the EASA in the EU, or the FAA in the US. Within the EMC context, certification methods are mainly based on experimental tests and the guidelines provided in several standardized documents and certification guides: Eurocae ED-105/SAE-ARP5416; SAE-ARP5415; Eurocae ED-107/SAE-ARP5583; MIL-STD-202; MIL-STD-461;EUROCAE ED-14/RTCA/DO-160, MIL-STD-464, STANAG 4370, etc..

Figure 1.

Typical EM Hazard in aeronautics. Reprinted from (Cabello, 2017d)