Where lightning strikes twice

I recently penned an article on here about some of the research I have been involved with in Wales and some people asked for a few more details about the Morgan-Botti Lightning Lab (MBLL) at Cardiff University / Prifysgol Caerdydd , so here is some extra information about the lab, and why the study of Lightning Direct Effects (LDE) is so vital.

Many people may not know, but on average, a standard commercial plane will be hit by lightning about once per year, so it’s really important we understand the results of this, and what mitigations can be put in place.

This is one of the main research topics for the MBLL, which is an amazing facility, and is the only one of its kind that is University based. The £2.4m facility is capable of generating controlled lightning with currents up to 200,000 amps, more than five times that of an average lightning strike.

A lightning speed explanation of LDE

Without delving too deep into the mechanics of lightning itself, there are 4 main waveforms, A, B, C & D, which are as follows;

 ·         'A' component (first return stroke): Peak current of 200kA, with an action integral no less than 2x106 A2s and delivered within 500µs

·         'B' component (intermediate current): 10 Coulomb charge delivered at an average current of 2kA

·         'C' component (continuing current): 200 Coulomb total charge delivered at a constant DC current of 200-800A

·         'D' component: (subsequent return stroke): Peak current of 100kA, with an action integral no less than 0.25x106 A2s and delivered within 500µs

The MBLL is capable of delivering most of these, which makes it one of only a handful worldwide with such power – literally!

Why is this important?

Well, that is a great question, and the answer lies in the proterties of the materials.

Up to the most recent aircraft, most commercial planes were constructed mainly of metal - aluminium. The study of how lightning interacts with metal, where the arcs occur, and how to safely dissipate the raw power is quite mature.

With metallic aircraft, the structure is almost independent from systems. In addition, it provides free of charge;

·         Grounding, bonding…

·         Current return

·         Protection against lightning strikes

With the advent of lower weight aircraft structures, such as those built using Carbon Fibre-Reinforced Plastic (CFRP), the studies are at a newer stage, and in fact the numerical simulation required in early airframe design is significantly more complex.

With a CFRP fuselage, which is not conductive, structure is NO LONGER independent from systems and becomes vulnerable to electrical aggression, which means we need to;

·         Analyse the detailed electrical services formerly provided for free by the metallic structure

·         Understand new dependencies between systems and structures

In addition, we need to design and manufacture;

·         Replacement systems for services formerly offered by the structure, including the miles of cabling around the inside of the body

·         New systems, for new functionalities, made necessary by the material evolution roadmaps

 A simplistic video example

This video, which was shot at the MBLL shows this in very simple terms. It shows a toy metal aircraft and an equivalent plastic one, both being hit by a generated lightning strike.

Did you spot the difference?

Of course, it goes without saying that today’s commercial aircraft are not toys, and don’t react this way, but it is a good analogy of the problem for simulation. How do you prove, for certification purposes, that you know how lightning will react against a specific material?

There are several solutions in the real world, some involved adding metallic elements into the paint, to provide a mesh, or pathway for the lightning to travel safely and others include adding metal plates in specific areas to help the arcs travel safely.

This is why the MBLL and those who work there are so important to this aspect of safe air travel.

Now for some fun...

Of course, if you take a machine that generates lightning, and a group of students, some fun will always be had, and the following videos show what happens when you throw in some “normal objects” into the mix.

A Computer Mouse being hit by lightning

An Unfortunate Santa

Thanks

Many thanks to A. Manu Haddad , the team and for the videos, Cardiff University’s Morgan-Botti Lightning Laboratory, which were filmed by Phil Leichauer and Chris Stone.

Also, a special mention to one of the people from that initial team whom I am very proud to have followed his progress through Airbus. Rhys Phillips , from being a research engineer in the Lightning, Electrostatics & EMH team, to now a leader in the Airbus / Google Digital Transformation space, oh and in the middle somewhere he has managed to fit it an IET Medal winner, Podcast presenter, STEM ambassador and Jazz superstar!