UWE Bristol Engineering showcase 2015

Sarah Parsons
BEng Electrical Engineering
Dr Hassan Nouri
An Investigation into Lightning Current Distribution in Helicopter Rotor Blades
Lightning is an atmospheric electrical phenomenon which presents multiple threats to aircraft safety. Across the world commercial and military helicopters are
frequently exposed to the threat of lightning strikes while performing in-flight operations.
Currently the only way to confidently assess the full effects of lightning on aircraft materials, structures and equipment is to carry out high and low level
current and voltage testing. This, as expected, can be expensive and time consuming and so in an ideal world assessments would be carried out using computer
modelling software, thus asking the following question:
Can computer modelling software be used to accurately and reliably determine the damaging effects of lightning as an alternative to expensive and time
consuming testing?
Project summary
By carrying out this investigation, although limited to
a particular helicopter tail rotor blade, it should be
possible to establish if computer modelling software
can be used as an accurate and reliable method for
assessing and understanding current distribution and
its heating effects, thus providing an alternative or
addition to testing.
Modeling and Simulation
2D INDCAL modelling software was
used to calculate the current
distribution within the blade. The
model had to be as representative of
the actual blade as possible. This
included identifying the material types,
sizes, thicknesses and resistivity’s.
High Current Testing
A series of tests whereby current, of
matching peak amplitudes to those
simulated in INDCAL, were injected into
the tip end of the blade, whilst
measuring the characteristics of the
current flow within each conductive
element.
Injected current levels included:
10kA, 20kA, 40kA, 80kA and 120kA.
High Speed Thermal Camera
A thermal camera (30fps) captured surface temperature as
current was injected into and passed through the blade.
Project Objectives
Utilise a computer modelling program to gather
analytical data
Conduct a series of physical lightning tests and
measure the results
Compare modelled analytical data with measured
results
Evaluate degree of accuracy and determine
whether the model accurately and reliably represents
the physical test
Project Conclusion
The tip end INDCAL model behaved in good linear
fashion between 10kA and 120kA injected current
and all modelled currents multiplied up
approximately proportionately. This modelled
behaviour was well reflected in the bench and
chamber tests when injecting current into all
conductive elements combined .
Simulated Results vs Measured Results
The peak currents measured by Rogowski coil 3 during high current chamber
testing were all within a 10% tolerance of the simulated peak currents predicted
by INDCAL within the erosion shield and lead weight added together.
The peak currents measured by Rogowski coil 1 during high current chamber
testing were within a 10% tolerance of the simulated peak currents predicted by
INDCAL within the tip end model containing 3 plies of carbon only.
The current injected into a helicopter rotor blade, or
any aircraft part, will always tend to find and utilise
the path of lowest impedance where inductance does
not play an important part. Depending on the
lightning strike location and the design, or lack of,
protective measures installed, breakdown of
materials and flashover to more conductive elements
can occur.