Developing an In-flight Lightning Strike Damage Assessment System (ILDAS)

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Developing an In-flight Lightning Strike Damage
Assessment System(ILDAS)

• V. Stelmashuk, C.V.Nguyen
• Eindhoven University of Technology,
• The Netherlands

TLE2008 Workshop University of Corsica, Corte,
France June 23-27, 2008
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Background
Commercial passenger aircraft are on average
struck by lightning once a year. The effects of
lightning on aircraft and helicopters are minimal
for low amplitude strikes, but higher-amplitude
strikes may result in expensive delays and
important repair and maintenance. To be able to
design appropriate lightning protection,
fixed-wing aircraft and helicopter manufacturers
have a strong need for a good definition of the
threat that lightning poses to aircraft.
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The Project
The In-flight Lightning Strike Damage Assessment
System (ILDAS) is a research project within the
scope of Aeronautics Research of the 6th
Framework Programme of the European Commission,
which has started in October 2006 and will end in
March 2009. Aim is to develop and validate an
efficient prototype of a system capable of
in-flight measurement of the current waveform and
reconstruction of the path of lightning current.
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Objectives
Two high level objectives of ILDAS 1.
Characterisation of the lightning strike for a
better design and certification of
aircraft. 2. A near-real-time indication of the
lightning strike for maintenance team.
Inverse Method
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ILDAS preliminary system architecture
H-field sensors were chosen for current density
measurements and an E-field sensor will be used
for triggering of the measuring process.
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Requirements for sensor configuration

• For the numerical tool developers
• - Surface sensors (instead of internal sensors
  on cables)
• - Sensors on planar surfaces or having high
  radius of curvature as fuselage
• - Sensors on the main lightning paths
• - Large number of sensors, spread over the
  aircraft
• - Sensor redundancy if one sensor is missing or
  not working
• - etc.
• For manufacturers
• Companies and maintenance teams
• Sensor developers
• Requirements come from different partners and are
  sometimes in contradiction

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Lightning Current Waveform
Typical waveform associated with a lightning
strike acquired through earlier measurement
campaigns
The complicated waveform (broad frequency band
and large dynamic range) requires the use of
different sensors to be combined into one device.
continuing current solid state sensors
bursts and strokes inductive sensors based on
Faradays law
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Lightning current characteristic
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Solid State Sensors
The continuing current value is important,
because of its large action integral and
possible damage at the attachment point.

• Difficulties
• high amplitude of stroke current will lead to
  saturation of solid state sensors
• the associated fields around the fuselage and
  the wings are small, below the
• Earth magnetic field (even for 500 A)

Sensor type Sensor type Sensor type
GMR AMR Hall
Frequency band 0 - 200 kHz for the tested sample, available with response 0 - 1 MHz 0 - 200 kHz for tested sample, 0 - 1 MHz, depending on the type 0 - 5 kHz for tested sample, typical up to 5.6 kHz
Sensitivity 0.03 mV/V/A/m for tested sample, max 0.225 mV/V/A/m depending on the type 0.02 mV/V/A/m for tested sample, max 0.04 mV/V/A/m depending on the type 0.26 mV/A/m for tested sample (gain 5, Vcc5.6 V), typical 0.05 mV/A/m for gain 1
Hysteresis 2 - 15 , type dependent 0.1 no hysteresis known
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Inductive Sensors
Different coils have to be constructed for
multiple bursts, return stroke and subsequent
stroke waveforms separately
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(No Transcript)
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Window Sensor
The sensors geometry is designed to captures the
magnetic field penetrating trough the window. The
sensor output is proportional to the magnetic
field H that would have existed at the outside of
the fuselage without the window.
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A mathematical expression for the magnetic field
penetrating a circular opening in an infinite
conductive plane H. Kaden, Wirbelströme und
Schirmung in der Nachrichtentechnik, Berlin
Springer, 1959, 2nd ed.
with H0 the strength of the magnetic field
parallel to the plane, r0 the radius of the hole,
r the distance to the centre of the hole, ? the
angle between axis perpendicular to the plane and
r.
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Testing window sensor
Simplified model of fuselage
M 810-10 H calc. 7.6 10-10 H
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Window Field Mapping (measurements)
GMR sensor NVE AA002-02E
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Window sensor tested by Culham with simulated
lightning. The current was injected on the nose
refuelling probe and extracted on the underside
of the rear fuselage.
The slight additional droop is caused by the lack
of the active integrator
Position of instrumented window
The window sensor output reproduces the injected
current with good suppression of noise
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Passive integrator
The passive integrator is the first step in the
signal processing and has a number of
functions 1. terminate the signal cable into
its characteristic impedance 2. filter the
signal and limit the dynamics to an
acceptable level for the subsequent
electronics 3. act as determining element in the
composite integrator frequency
characteristic 4. filter the signal against any
unwanted interference outside the frequency
band of interest
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Triggering
E-field sensors will be used for triggering
only Trigger criteria If the E-field peak
amplitude exceeds 100 kV/m more then 1 ms and if
during the next 100 ms a short E-field peak with
amplitude more then 11 kV/m is detected, then a
direct lightning strike is taking place.
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Lightning spot location on the fuselage
Location of the lightning spots on a BAC 1-11
aircraft
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Possible sensor locations
Current paths for main lightning scenarios
including wings
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Reconstruction of lightning current

• A numerical method will be developed for the
  reconstruction of lightning current
• by calculations from a set of surface field
  measurements recorded during a
• lightning strike. Several types of information
  but also levels of accuracy will be
• provided by the numerical analysis of
  measurements.
• Some rough analysis will be done during the
  flight to identify the initial entry and exit
  points of the lightning channel, but also to make
  an estimation of the maximum current intensity.
• Analysis will be performed at ground, on a
  distant server, with the objective to reconstruct
  the lightning current waveforms according to
  different numerical methods (inverse method,
  transfer functions,).
• - minimum number sensors on appropriated
  positions
• - specific characteristics (frequency band,
  data sampling, amplitude
• measurement or time-derivative
  measurements,)

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Conclusion

• For most of the measurements copper coil plus
  integrator is the best option,
• especially for the initiation phase and the
  large-amplitude strikes.
• The continuing current is of interest, because of
  its large action integral and
• possible damage to the attachment point.

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Further Exploitation

• Two major phases are foreseen
• Further development of the ILDAS on-board
  subsystems dedicated to a specific aircraft on
  which ILDAS will be actually flown possibly a
  prototype aircraft.
• Sensors for other dedicated locations should be
  developed, along with specific required
  interfaces to the ILDAS.
• 2. Start with an extensive business case study
  in order to be sure that actual application to an
  operational fleet will be overall cost effective.
• Further industrialization for serial production
  and final certification are part of this final
  phase.