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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 Background
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V. Stelmashuk, C.V.Nguyen
Eindhoven University of Technology,
University of Corsica, Corte, France June 23-27, 2008
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.
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.
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
H-field sensors were chosen for current density measurements and an E-field sensor will be used for triggering of the measuring process.
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.
solid state sensors
bursts and strokes:
inductive sensors based on Faraday’s law
The continuing current value is important, because of its large action
integral and possible damage at the attachment point.
H magnetic field
time constant of integrator
For pick-up coil with sensitive area NA = 10-2 m2, integrator with time constant = 400 s for 0 dB gain and H = 104 A/m, the integrator output for a magnetic field H equal to 2.5 V.Inductive Sensors
Different coils have to be constructed for multiple bursts,
return stroke and subsequent stroke waveforms separately
The sensor’s 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.
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, υ the angle between axis perpendicular to the plane and r.
Simplified model of fuselage
M = 8*10-10 H
calc.: 7.6 *10-10 H
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
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
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
E-field sensors will be used for triggering only
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.
Location of the lightning spots on a BAC 1-11 aircraft
Current paths for main lightning scenarios including wings
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.
- minimum number sensors on appropriated positions
- specific characteristics (frequency band, data sampling, amplitude
measurement or time-derivative measurements,…)
especially for the initiation phase and the large-amplitude strikes.
possible damage to the attachment point.
Two major phases are foreseen:
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.