During the initial phase of a lightning strike attachment on an aircraft, fast current pulses (rise time approximately 100 ns, I(sub max) approximately few kA) were measured, which can create equipment upsets or disturbances. This threat, made of repetitive pulses and usually called 'multiple bursts', can be reproduced at the equipment interfaces assuming that the transfer function of the structure was determined. The normalized waveform H (10 kA - 100 ns rise time) is the reference for one of these pulses. The importance of the coaxial return path termination for the injection of the wave H is emphasized. According to the constitutive materials of the test bed, and the adaptation of the line, the natural oscillations of the structure and the internal coupling mechanisms can be modified. As a conclusion, various test configurations in relation with the nature of the test bed and the characteristics of the generator are detailed, for a more accurate ground simulation of the attachment phase

Cantaloube, M.

Emanuely, J. L.

English

NASA Technical Reports Server

INFLUENCE OF CONFIGURATION EFFECTS ON 
"MULTIPLE BURST" SIMULATION TESTING 
M -  CANTALOUBE J - L -  EMANUELY - 
CENTRE D'ESSAIS AERONAUTIQUE DE TOULOUSE 
23, avenue Henri Guillaumet 31056 - TOULOUSE CEDEX 
&ring the initial phaeie of a lightning 
etrike attaohment on an aircraft, fast 
current puleee (rise time J 100 ne, Iraxa 
few kA) have been measured, which can 
create equipment upeetm or dieturbancee. 
Thie threat, made of repetitive pulsea and 
usually called "multiple buret", can be 
reproduoed at the equiment interfaces 
aeeuming that the transfer function of the 
structure was determined. The normaliaed 
waveform H ( 1 0 M  - 100 ne rime tire) ie the 
reference for one of these puleee. 
Thie paper emphasizes the importance of the 
ooaxial return path termination for the 
injection of the wave H. According to the 
constitutive materials of the test-bed. and 
the adaptation of the line, the natural 
oecillatione of the structure and the 
internal coup1 in8 mechanire can be 
modified. Ae a oonclueion, various test 
configuratione in relation with the nature 
of c t e  test-bed and the characteristics of 
the generator are detailed, for a more 
accurate yzdund simulation of the 
attachment y1:aeir. 
I - INTRODUCTION 
The dooument GAB-AB 4L "ORANGE BOOK" 
euggeete the following soenrrio for the 
attachment prooeee : for eaoh attachment or 
reattachment, a eerie. of 20 pubes of 
current (waveform HI ie flowing in the 
external mtruoture with a repetition 
frequency between 20 and 100 kHz. It ie 
mentioned that 24 burets of 20 pulses 
(total of 480 puleee) can w o u r  in a 
lightning event during a total duration 
time of 2 e. 
The analymie of the reeulte of "in flight 
reamuremente" (TRANSALL - CV 580) made by 
the OWBRA ("Offioe National d'ltudes et de 
Reoherahee Akoepatialee" - FRANCE : in 
flisht prwramre eupported by the HOOD/DCA) 
eumeetm another eoenario [Ref. 1 1  : the 
multiple buret sequenoe oould only appear 2 
or 3 timer maximum during the lightning 
flash. and nr HAZUR explained in the ICOLSE 
88 oonferenoe of oSI.nXOHA that one 
attaohment only uae likely to w c u r  fur the 
etepped leadere. 
We can however notice that there la a 
coneeneue about the characteriatice of the 
waveform H, with the restriction that riae 
time of 60 ne have been recorded. 
Whatever the number of puleee, it ie clear 
that it rill be irpoeeible to drive n 
puleee of l burets on a whole aircraft ! 
It would require n x m Marx generator8 
from about 800 kv. euceeeively triggered. 
The demonstration method chosen by ihe 
C.E.A.T. oonsiate in determining tlle 
tranfer function of the varioun bundleb 
for a eingle excitation of a H pulse on 
the whole aircraft. and then to teat the 
inside equipments at low level ( 2000 V . )  
with the repetition rate specified 
(arbitrary waveform eyntheeizer + pulse 
amplifier). 
I1 - NATURAL RESONANCES 
lo) When etudyinp the data of in flight 
meaeuremente, we oan notice that natural 
reeonancee of the etructure are excited. 
For exemple, on the F 106 [NASA-Ref 21 the 
measurements of dD/dt show oacillatiorre at 
7 MHz and 21 1Mz (L = A / 2  = 14 m 4 Fr = 13 
MHn) and the dB/dt laade to 7 HHz only. The 
oecillation at 21 1Mz ie preponderant on 
the noee current. On the TRANSALL [Ref 31J 
the oscillation io about 5 HHz (very near 
to the fuselage reeonanoe of the aircraft). 
Neverthelesm, no information ie given about 
the damping faator of theee oacillatione. A 
theoretical analyeie with a 3 D code 
(Integral method) [Ref 4 1 ,  on model 
repreeenting the central part of the 
fueelage with ite 2 winge. ahowe the 
euperpoeition of two main reeonancee A 1 2  
and A / *  (lightning etrike from one wing tip 
to the other wing tip). 
In ehort : 
IReaonancel IN FLIGHT I 3D ?IODELING-_.-I 
I I I I 
I 
I 
I Wing I --- 1 A / b  - X / 2  I 
I Fueelagel X / 2  - 3x12 1 --- 
- I 
Table I : atrutural resonances 
https://ntrs.nasa.gov/search.jsp?R=19910023317 2020-03-17T15:04:59+00:00Z
2 O )  Classical test set-up for the ground 
simulation : 
A coaxial return path is built around the 
structure of the aircraft to ensure that 
the repartition of currents on the skin la 
the same as it  would be in free apace. 
during a lightning strike (Fig. 1) 
Pulse generator 
(wave H) 
1x1 1 - "ECUREUIL" helicopter 
In the frame of the joint venture 
Programme AFARP 17 (Anglo French 
Research Programme), Aeronautical 
different tests (CW - High voltage teat - 
High current inject ions) have been 
performed on the structure Of d 
helicopter (with large dielectric parte). 
A view of the teat set-up ia glven 0 t h  
fig. 2 ,  for the high current rn~ectlon 
phaeie. 
Figure 1 .  Usual test set-up 
To prevent parasite reflections. the 
inductance (uH/m) of the, transriaion 1 ine 
uill be as constant as possible. But the 
same question remains for the simulation 
what appropriate mismatchin8 must be 
recreated and how to reproduce the in 
flight osoillations ? 
It is obviouo that the induced effects on 
the internal wirings are strongly 
correlated to the possible oscillations and 
their damping factor. That'e why 2 
different values of load resletance W w e r e  
cho8en : 
- Fiist saze-: R = 0 (short-circuit = usual 
test siet-up configuration for v e r y  
high current inject ions) 
Travelling waves (f= c/41) are going 
to pile on the bi-exponential current 
delivered by the generator. The 
frequency speatrum of the normal ited 
uave H is strongly modified at the 
frequencies corre8ponding to 1 = X I 6  
and 1 = 3 A / 4  
- Second-cass R = Zo (characteristic 
impedanoe of the coaxial return. path) 
6xaept some discontinuitiee of the 
aircraft geometry, the line ie 
matched, and the natural atructural 
oscillations are not excited. The 
frequency mpectrum of the normalized 
wave H is not modified. 
Figure 2. "ECUREUIL" Helicopter 
in the coaxial return path ( Z o = 6 0 f i )  
The comparison is performed for the 
eingle wire L4 located in the aluminium 
tail, between the rear rotor and the 
equipment bay (length = 10 m = 33 ft) 
Table 11. presents in time and frequency 
domains the characterletice of the 
induced levels (for I inJected = 1 kA 
waveform HI101 
_ _ _ _ _ _ ~  
I aMXIAL iOfXNCIR3JIT I SHORTCIRCUIT I 
I KTUFU4 I VOLT- I a J ~  I 
I ODWFIGUUH. I I I 
I I L4 voc I L4 I e c  I 
I I I I 
IMax Levolllhin Fr.llhx Levelllhin Fr.1 I 
I Hatched I 1 8 o V  I 7,(yllrzl I A 16-1ZfU~ I 
I R = 6 0 )  I 1 2 2  H h l  I 22nhz I 
I l 4 . 3 B ~ I  15.- I 
I Short I 230 v I 7.8cYuI 1 . 5 A  I6 ,YPu I 
I Circuit I I12 nhzl 112 thz I 
I 
I11 COUPLING ON TYPICAL YIRES 
FOR BOTH CONFIGURATIONS (short 
circuit load and matched load) 
To quantify the importance of the 
rssishve load R ,  this paragraph 
summarizes the results achieved on 3 
d i f f erent test -beds 
37-2 
Table 1I.Induced levels on the line LL 
(101) for  I inJected = 1 kA (H/10) 
Resonances of the structure of the 
helicopter : ( 1  = 16 m = 52 It1 
A / *  = 4.3 nHz 
x / Z  = 0.6 "2 
3 A / 4  = 12.5 "2 
- -  
*Resonances of the wire L& (I= loo = 33 ft) 
A / 4  = 7 . 8  mi2 
3A/4 = 22.  m z  
In teble 2 and fie.6bwe can notice that : 
- The maximum levels are measured in the 
short-cirauit coaxial return path (the 
ratio is however < 2 )  - The energy at the frequency 
corrempondinR to ,k/2 of the structure is 
very low ( 8 , L  MHZ) - Resonances at the quarterwave length 
and 3 X  /4 of the structure are strong 
but the coupling on the line at these 
frequencies is only clear on the short 
circuit current. - Same level of enerey correapondlng to 
x / 4  and 3 x  /4 of the wire itself for 
both configurations. (we can notice that 
the capacitance of the line decreases 
the frqqrrency OC the resonance) 
- The transfer fonctione Vco/IznJ are 
different according to the load R .  
(Fig. 1 
short circuit Line = extrema for 
A / 4  and 3 X / &  of the structure and. 
A / & ,  31/4 of the wire itself. 
catched line = extrema only for 
A/& and 3 x / 4  of the wire itself 
The mouroe impedanaes Z.= Voo/Iac of the 
generator equivalent to the cable are the 
same for both oonfiguratione ( f i g . 6 d .  
It varies from ln to 3 0 0 n  *between 50 kHz 
and W r ,  and can increase 10 k R  for the 
resonances mentioned above. This parameter, 
dependent on the pornition of the wire in 
the mtructure, is not depending on the test 
condition [Remark : for P + 0, Z*+ ohmic 
resistanoe of the rirel 
In short, the frequency responses can be 
simplified as follow: 
I inj  
SHORT CIRCUIT P CURRENT 
t% OPEN CIRCUIT 
VOLTAGE 
Figure 3. Transfer functions 
for a rim io an shdniu strwt- 
(-rt circuit currmnt - open circuit wltese) 
Charaateristlcs : L = 5m (16ft) 
Z.= 20 mf2.o 
R tot61 = i6 Sn 
Figure 4. Wing "VCC" 
in ttm coaxial return path 
On a sinele wire loaated in the center 
part of the wing 'E field not 
signiliaant), the followang levels have 
been measured for Iin] = 1 M  (H/10) 
I awUu I ORUCIIQlIT I s l o n C l I Q l I 1  I 
I mm I UOLTIIB I ammn I 
IOMFIrn. I Uocl  I r  I 
I I I 
I I(lu h l  I
I e6OA 128Um&l I I J h  1 -=SI& I 
I td  -30 us _I I 8.5 ~hz I
I I I I I3 A Ibi-ew.wuc I 
I It: 0 . n  I 2 9 W p d r l  In,  0rill.I tm = 8 us I 
I I 8.5 lhz I I I t d  =30w I 
1- l l ln  hue1 Ibi-axpo.- I 
In, orcill. I 
Table I11 : Induced levels on a wire 
(L = 5.) located an the center part of 
the carbon fiber wing (without mesh) for 
Iinj-1kA (H/lO) 
We can notice here. that no excitation 
corresponding to the natural reaonances 
of the structure (wing) is visible, 
contrary to the case of the helicopter 
part in aluainium. The only rcmonance 
measured A S  the one of the wire itself 
(8.5 1M2) 
So, in this oase, the test configuration 
hae no inlluenoe on the induaed levels. 
which are identical. (Pig.3b) 
This renult is Cundamentally different 
rror the previous one cancernang the 
aluminium struature of the UCURHUIL (5 
I11 1) 
It's important to look at the waveform of 
the induced short circuit current 
(Fig.5): the injeoted waveform is a 
O.l/4ws wave and the induoed wave is a 
8/60vs wave. The oar- fiber akin acts 
ae an integrator (let order filter with 
fc 10 kHz) ,  which leadm to an important 
delay between the two waveform peake : 
ICC = KJVw.dt 
37-3 
The ratio of the extrema (Fig. 5 )  of the 
values of Voc and ISC has no physical 
meaninq. Only the integral 1/6/Voc .Icc dt 
can be interpreted as the maximum energy 
that the wire will be able to deliver on O 
terminal l o a d .  
Figure 5. Iinjected current 
Isc and Voc waveforms 
I11 2-2- Carbon fiber wing covered by 
an aluminium meeh : 
The same wing (as in & 111.2.1.) was 
covered by d mesh : 2s = 3 m n . D  
The total resistanoe of the wing Rt=7.8 mCL 
I I O A I I C I l l l l I T  UDLTIISE I SHXT C W I T  [IIPPMT I 
I I I I 
I I U D E l  Isc I 
I Ilk Lml I I k L M l I I a n & r n  I 
I ban. I I L.F.= 6 U I 4 A. I I 
I 114 U Fb& I H.F.= E U.1 I b = & t s  I 
I I 8.5 Ihz I I I t d = a L s  I 
I 1- I 1- I I 
I I I L.F.= 6 U.1 I I 
I 12.9 V P J I  H.F.= 6 U.1 3,s A. I I 
I E= 0 A 18,s Mu I I r t . = 8 y  I 
I 1- I 1- I I 
I I I I I t d = -  I 
Table IV : Induced levels on a eingle wire 
(5m) in the center part of the wing aovered 
by alumesh (rave H/10). 
By compariaon of the tables 111, IV and 
Fig. 8 we notice the following important 
resulta : - Same internal behaviour of the wing, 
whiahever the aoaxial return load is 
used. The transfer funations are given 
below : the shielding effect of the mesh 
is only evident below 1 IMn on the 
voltase transfer function (-lode). We 
have to bear in mind that the main 
reamon far the use of a meDh is the 
Proteotion of the fuel tank Uainet the 
direct effect. (burning through) and not 
to achieve high attenuation levels. 
A summary of the typical transfer 
functions on wire in a carbon fiber 
structure is Elven below : 
- - -  with mesh 
__ W I  rhout mesh 
-3WB 
SHORT C I R C U I T  
-5WB "\\ CURRENT 
- 6 W B t  F e n  Hz 
-2WB iN CIRCUIT 
- 30dB VOLfAGLi 
-----f 
F s n t k  
The shielding effect of the meah is 
about -10 dE between 1 0  khz and 1 plllz 
(Fig. 9 )  
IU- INFLUENCE OF THE ELECTRIC 
FIELD ASSOCIATED TO THE 
CURRENT 
A high voltage senerator ie neceeeary to 
inject the current waveform. So, an 
important electric fied raiees in the 
coaxial return. The previous analyses 
were performed on wires located in areas 
where the electric field was 
insignificant. that means without any 
effect. 
But, more senerally, the extrapolation 
of the signals to the threat (Dl10 + D 
-and H / 1 0  + H) requires a precise 
analyeis to separate the electric 
coupling from the magnetic coupling. 
This is particularly true for the 
wirings exposed under open structures 
(dielectric fairings) . The two test 
set-up above mentionned lead to a 
different electric aoupling. 
matched coaxial return : 
The values of E and d W d t on the 
extradoe of the wing are constant along 
the coaxial return. An idea of the 
levels i s  given below for HI10 wave - ( 1  
kA 1 
E E + 120 w / m  
[r E = k l  I 
t 4 ~ v / m / p  
37-4 
Short-oirouit aoaxial return : 
The valurs of B and dB/dt are not constant _ _ _ _  ~ 
m y  more along the line : maximum at the 
entrj -0 at the end of the line. The 
folloriw diaararmm 8hor the raveforme 
reoorded at the input of the transmission 
line (for H / l O )  ; 
3W/m4~3 c- -A . 
For a teat at H level (10 M), the order of 
magnitude of dWdt im loqB V/r /m,  clome to 
the value8 of in flight measuremente 
IRef.31 Although it ia controlled by the 
ourrent parameter, the simulation In a 
oosxial return Hives a proper electrical 
exoitrtion, by oolparimon rith the levele 
enawnterrd in free mpaoe (excitation not 
yet normalired) 
RE)URI : A temt oonfiguration oan help, i n  
S O I ~  oases. to determine the type of 
oouplinm (E or I) and thug enablee the 
extrapolation method : by areating a 8eCOnd 
ara ohannel at the end of the coaxial 
roturn, the eleotrio field iw maintained 
till the oonneotion of thim sap (feu W) 
and then a nemative dWdt is appearing, 
t h u  I and Dl/dt are pomitivr. An 
invermion of polarity on the induced 
voltaae, due to the mubmequent effeata of E 
ana I 1a vimible. 
u - coNcLusIoN 
Thim paper remind. ua of the influence of 
the type of return load umed (matched or 
rhort oirouit) on the levrla and frequency 
mpeatrum of the induord transients. 
Aooordiau to the nature of the struoture, a 
temt aonfiguration is more muitablc to 
reoreate the real thrmat. 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I m a  
1- 
I 
I khu* I S t ~ ~ t u r e  I (In fli&t)I Extrgolatim rnpd I 
I I I I -Simrt Circuitor I 
I I i !mctclmd cDy(i.I return1 
I I u~ I A/4 I hdifformntly) 1 
I c r b o n I  I 3X/4 I Extrgolatla, : see I 
I I (with or I I I I rt c w  
Iuithout I I t - m c i r c u i t a  I 
I rrh) I I l u t e k d  coy(i.1 mturnl 
I I F u M ~ ~  I I(idiffo~ntb) I 
I I I I trtr&tial: u I 
I I I I lad c g .  
I I I I -  lo malyu,acordird 
I I I Itnth~vntityd I 
I c v h  I Mol. I I l O u t i a , O f  rtd I 
I rtd I Ilircrdt I Sr b 11-1 Iputsn lcamni rn t  I 
I I I Ipuibilitiu far tha I 
I I I IruLiutia,Ofthr I 
I I I trt-hd. I 
I I I bm*r. I lest Y t - w  
I 
The generator muat be able to in)ect 
the norraliaed ourrent waveform. That's 
why the C . E . A . T .  hae given the fOllOWlng 
opecif~oations for i t a  new facilities. 
# llarx eenerator ( 8  etages of 100 kV) 
with low internal inductance I. < 2 VH 
arid a cosxisl output Z = 6 0 n  ) 
Two biexponential waver will be 
possible : 
-H . ImaxslO ItA t m  = fb0,lOOnsl 
-D/2 . (with arorbar) 
t if2 = 4 us 
Imax = 50 kA tm= l ~ s  t 1 f 2  = 35 )le 
The result0 of the V.C.C. (Voilure 
Composite Carbon = Carbon Composite Uins) 
oome from a joint programme C.E.A.T. 1 
AHROSPATIALB / DASSAULT AVIATION supported 
by DCAC and DGAf DCAefSTTE 
06y = Ihrrrrtiaa firinl. & I'rki. t icn Civile 
gypcAi/snt = Lil&tioa -de  plu I ' k n m t  . 
Olmtlaa &r Conrbutiam - t igus.  bm1n 
ruhiqn &s ri1iEOrvliutiarr *t E I u i p a n t s  
Adrmutiqur. 
37-5 
, 
Coaxial return matched. 
1 ) - 7  7.IF.I  
- 1 - 2 3  7W-I 
C D - % S  a--z 
a) Source impedance Zg=Voc/lsc of the generator equivalent to the wire L 4  
( Coaxial return i n  short c ircuit  or matched) 
/ coaxial return matched. 
/. .I 
i 
-4 
10' 40 ' 4 0  
b )  Transfer function Voc/linj for the w l re  L4 
(2 different coaxial return loads). 
FIGURE 6 : SINGLE W I R E  BETWEEN THE TAIL ROTOR AND THE EQUIPMENT BAY 
OF THE HELICOPTER 'ECUREUIL' FROM AEROSPATIALE (As 355). 
37-6 
-m 5 C I I  
t 
- - --- 
Coaxial return matched. / -.- - L - - & v J o V  . . ' -  d e n ?  
(Coaxlal return i n  short-circuit or matched) 
a)Source impedance Zg=Voc/lsc of the generator equivalent to the w i re  B2A 
4 1D 1 
Coaxial return in  short-circuit. I 
--.+.-L-.L.-L. ... : 
4044 ,205 106 
- . . L ..I.L--io*, 
1Q?,,Z/89 I2 LS :a . -  
aD 
Coaxial return matched. F % - e  
b) Transfer function Voc/linj for the w i re  B2A 
( 2  different coaxial return loads). 
-A-.lo.l.-.~og- J . ' *  ' 
FIGURE 7 : COMPOSITE CARBON WING (VCC) WITHOUT MESH. 
37-7 
Coax lal  return I n  short-clrcult. 
CI - .4 . . )L .L I  
- - ,  1 . . . , . . . . I - -1 
10 10' 10' 10' luam 
i?S/W/OO 0921'16 
,ob . . -,--"; - . - * - - . - I  - 
8)Source Impedance Zg=Voc/lsc of the generator equivalent to the wire B2A 
(Coaxlal return I n  short-clrcult or matched) 
7 Coaxial return i n  short-circuit. A 
Coaxial roturn matched. 
I . . . . _  . I  . . . , v  - I I . I _ _ -  
b) Trfnsfer - t *  func- I =  1 6  110 * 1 
( 2  different coaxlal return loads). 
s 
i 
IM 
FIOURE 8 : COtlPOSITE CARBON WING (VCC) WITH flESH. 
37-0 
9 
r 
1 1  1 VCC wing without mesh 
-- - 44 dd 
I ,... I . , I I .L.I . I ,I v , , . , . .yI , * I  , . , , ." 
Coaxial return in  short-circuit. 
1 *... I , . . 1-1 . . . I . . 1 I .. 
(104 40 -rO 6 %* 1 .  .h I 
Coaxial return matched. 
Transfer function Voc/lsc for the wire B2A of the carbone wing 
wtth and without mesh for both values of return load. 
FIGURE 9 
37-9 


Influence of configuration effects on multiple burst simulation testing

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