Electrical or avionic equipment needs to be protected against
the transients induced in the wiring, to avoid damage, misleading
information or system interrupt.
An important part of the design and qualification process is to
understand the magnitude/type of transients, so that the equipment
can be appropriately protected against them. There are two ways in
which this can be done:
- Perform a full vehicle test at low level (between 1kA and 10kA
typically) and measure the induced transients on the wiring.
- Perform an analysis of the installed wiring and lightning
current paths in order to predict the transient levels on the
Frequently both approaches are combined.
Full Vehicle Testing
Cobham offer full vehicle tests at customer premises, in a
programme of testing which could extend typically over a couple of
weeks. A return conductor cage is constructed around the aircraft.
This is designed to allow different lightning attachment scenarios
and current paths to be simulated.
A current generator typically capable of 1kA-2kA is used,
although a transportable 10kA generator is sometimes preferred.
Current pulses at this level are applied to the aircraft, whilst
remote measurements are made of cable harness currents and
individual wire pin voltages, concentrating especially on the more
critical systems and more exposed harnesses.
We can also provide support in helping identify the most useful
and effective measurements to make, and in interpreting the
Cobham's experience of aircraft test and measurements provides
an insight into lightning induced effects and their avoidance; this
experience underpins the consultancy support provided to our
Our experience is supplemented by our in-house software tools,
in particular the INDCAL program. This is a 2D modelling program
ideally suited to solving current distribution and induced voltage
problems in structures such as aircraft fuselages and wings.
INDCAL's results are used in support of design or certification
by determining the transients induced in wiring, to allow them to
be compared to the transient protection of the connected
The approach also helps to identify optimum and cost-effective
lightning protection in the installation of electrical/avionic