Get documents about "oral Presentation outline
Document Sample
WF 16
EVALUATING THE BIRDSTRIKE THREAT
TO A1RCRAFT WTNDSITIELDSYSTEMS -
A PROBABILTSTIC APPROACH]
SpeelDan
Ralph
USAF
Flight Dynanlcs Laboratory
Wright-Patterson AFB, Ohio, USA
Fteure 1- The purpose of this report is to briefly describe and
illustrate a iecent effort to analyze lhe potential risk of birdstrlke
danage to an aircraft windshield system,
ligure 2 - This devetopnent affords us another weapon for use 1n our
bird \rar battles. The technique results ln predlctire the probability of
birdstrlke danage thru statlstlcal considerarion of 4 facrors: Number of
inpacts, bird \reight, impact velocity, and inpacr codponent strength,
Fieure 3 - The approach vhich v111 be taken 1n descrlbing thls tech-
nlque is to briefly describe rhe staristical inodel forDulatlon, descrlbe
the components of the node1, apply the technique and suinarlze the flndings
Figure 4 - The techflique was fonnulated by Dr. John Halpin, USAF,
during his efforts to assess the adequacy of vindshleld systeD blrdstrike
ptotection being designed lnto a new aircraft. Subsequent nodel dewelop-
nrent, analysis and docunentation were perfornred by the Universlty of
Dayton Research Insrirure (UDRI). The efforr at UDRI was sponsored by
the Air Force Flight Dynamics Laboratory, Princlpal lnvestigators at
UDRIwere: A. Belens, B. West, and M. Turetla.
Iigure 5 - Regardless of preventive neasures, birdsrrikes !1111 occur.
USAF experience is that there are abour 35 birdstrlkes per 100,000 fllght
hours. It is obvlously unrealistic to protecr againsr all 1eve1s of potenrial
birdstrikes, so the general approach, as you all nell know, is to pick a
?lotection 1eve1 vhich is felr to reasonably represent the rlsk to be en-
countered. Hotrever, once rhis desired protectlon level is esrablished,
we ltust consider tro questions: rrhrharhappens tf I hit a bigger bird ar
a slower speed or a sr0a11erbird at a higher speed?I and,'kow likely
is such an occurrence?rr The answers ao these tso questions are, of course,
a functlon of such things as geographical location, alrcraf! alrlrude,
alrcraft nission, and aircraft deslgn. An abiliry to aralytlcally assess
this rlsk to a tr:ansparency systen, from birdstrike hazards other than
those fohhich it was designed, is truly needed. Tr is this need which
plomptedthe nork being reported on coday.
I i g u r e 6 - l { h a t a r e lhe factors which influence qrhethe. a birdstrike
'iII result in danage ro t h e w i n d s h i e l d s y s t e r o ? I n t u l t i v e t y , the probability
of damage due to a single b i r d s t r i k e is a funcrion of the bird weieht. the
oral P r e s e n t a t i o n o u t l i n e for use a! the Birdstrike Cordnitree Europe Meeting
ln The H a g u e , N e r h e r l a n d s d.UTing 22-26 october 1979.
lnpact velocity, and the strength of the lnpact point. Carrying this intui-
tion one step further, the probability of birdstrike danage during a flighr
is then the probability of danage due to a single blrdstrike times the
expected nuDber of birdstrikes. It was hypotheslzed that if each of these
factors could be ldentlfted ln a statistical fashion, there should be
of Dathenatically conbtning thed.
Flgure 7 - The flode1 formulated by Dr. Halpin was based on the prenlse
that the expected nunber of birdstrikes can be predlcted and thar damaae
lrlll resutt when the kinetic energy fron a birdstrike is greater than sone
crltical tevel. It ras assuned that a velocity distribution for the air-
craft and 'eight distribution for the birds could be conbined ro predicr a
probability dlstrlbutlon for kinetic energy. By assuning lhat the abillty
of any given windshietd systern to defeat a birdstrike is essentialty related
to impact kinetic energy and impact location, we can ldentlfy the proportion
of the {indshi€ld systen which will be daraased as a functlon of birdstrike
ktnetlc energy 1eve1. Mathematically conblnlng the kinetic energy prob-
abifity distributton with the critical strength leve1 distribution vill
produce the probability of danage due to a single birdstrlke. combining
the expected nunber vith the probabillty of daoage yields the expected
nunber of damaging birdstrlkes.
Iigur:e 8 - Let's lake a brief exanination of how these terns can be
quantified. The flrst one is the expected nunber of strikes. The equation
is not new to those of you who have worked with this problen. D represents
the btrds per unit volune through vhich the aircraft is flying and AVT
represents rhe volurne sn,ept by the cornponent of concern. Ir is inportant
to note that in conpuling lhe values tor these terns, there is a necessity
to give ser:ious attenEion ro the environnent of concen. Ir nusr be rele-
vant to the specific problem being addressed and must be comon for each
of the terns. The expected nunber of danaging birdstrikes, as opposed to
lhe expected number of strikes, is then the expected nunber of strikes
tiines the probabilily that any one strike vi1l result in daMge. The prob-
abllity of a birdstrike causing danage is obtalned by an integration \rhich
considers the probability thac a specific klnetic energy w111 occur, and
t\e probrbility thar darage Li I I occur rr th ,L kjnetic erergy.
Figute 9 - It is this comJrucation of the probability of danage shlch
represents Dr. Halpin's major contriburion. l"l3rhenarically, this tern
relates the probability that a specific KE IJilI occur and the probability
that danage w111 result at this KE. It conblnes the bird welght disrri-
butlon, f(w), the inpact veloclry distribution, f(v), and determines rhe
probability that the resulttng kinetic energy will exceed the critical
value necessary to result in darnage.
Figure 10 - Let's now take a look at how this technlque was applied
to 3 situation vhich would seeD iepresentacive of the necessity to assess
the risk of birdstrike damage. lde have an exisrinA aircraft vhere mission
profiles are betng revised to inprove low-altitude proficiency. Those
r:esPonsible fo! flight safety were concerned with the inc.ease in bird-
strike risk due to the increased lov-altitude flying time. Infornation
\tas needed which they could use in considering both the effects of additional
flight tine in the birdstrike enviroomenr and the effects of improving
rtndshleld systen blrdstrlke resistance' In short' what is the blrdsttike
aiicraft due to increased lo\t_allitude flight tlne'
,f"t to ttl. crev and lhe
to reduce
ana vtrat noartications of the windshield svsten would be required
thls !lsk,
to use the
Ftsure 11 - We krow that there are four faclors required
upp.ouch: Ebe expected number of birdstrikes' the blrd ueisht
orol.iii".i"
ii"iiit"ir.", iire werocrrv of impact distribution and the $indshleld svsten
".."";ir' ar"i'rt".ron. Let's take a brief look at hor values were conputed
for these four Para0etels'
Birdstrlke
fisure 12 - Faclor 1, Expecteal i{unber of Birdstrtkes'
..-tF"t ,ni" speclfic alraraft were on hand so these were used arong
the
"iii-"p.r.ir.""r records of velocitv bv altirude band to establish
pe! 100,000 fllght hours --The equation
expectea ntortter of birdstrlkes
;ii;;; i;-;;;" .t .".."e. veiocltv and per:centas€ or r11sht time below
increased
i.OOO:.* so that it coulJ be used lo consider the effects of
low-altitude loisslons.
Fieure 13 - Iactor 2, Bird Weight Discribution' Birdscllke.re'otds
fo. .Eif"p."lfl" alrcraft were aaain used in esEabllshing the bird reight
of
aisttit"tion characterislics . rhe records shoq a sPeciftc quanlitv
A certain pe'centage of this
blrdstrikes occurring over a peraod of tine'
ouantltv was ldentlftable as to tvpe of bird' This racio of identiflable
assumeito exist for the entire quanritv'
l Bird $eight
i;;-;";h";
rhe r€surtlna
;;";;; ;;;; "." "".a co esrablish the welghr dlstribution'
""*ririi""-Jt".rrt"tion curve for rhis biril !,,elshr is as shown in the fisure.
Fieure 14 - Iaclor 3, Velocity Distribullon oPeraEional records
tor tt'Tfipeciflc alrcraft were used Eo esrablish the rePresentatiwe cumu-
pxofile shown in lhe figure' The equation
lattve velocltv dlsttlbutlon
i.r tt. "".". a11ows consideration of the effects on the overall distri-
flighls'
irif." ar'.."gt' increasing the quantitv of lo\t-altitude
Based-on prior birdstrlke
Fieure 15 - Iaclot 4, strength Distribution'
t""tiffi-t tnr" "i..i"i. ir"J"r'r!rd svsEem, strensth discribution plofile
a
ot tairure
""" *ip"*a by assunlng thal faltures vere representative
r.-" tiit.tf" .rle.gy f".'"f. Based on current \tindshield svsten sEate-of-the-
and wisi-
..a, i""f"ai"g operationaf consideratlons such as cosl' weight '
possible design nodificarions were eslablished' strength
iriity, " *ri*'.r
dlstrilutlon profiles for tfrese svsce' nodlficaEions uere estinated as sho!'n'
1et's see v'hat the
Noo that sll four iactors are rnatienatically defined'
technlque predlcted.
penetratldns for
llsure 16 - Predicted windshleld systen birdsttlke
Note thal thele are four different wersions
u r.offiroa ".. "r'.*-.
with,lultiP1e
"f .r"l,io""l the existing nlssion, anil lhe existing nission
i""i.t""." ;f lo\r-altltuAe flight;' Note also that thele ate 4 dJfferent
and.then 3 oodlfi-
r"i"i""" "t lhe windshield svsteo; the existinB svsten
cations of that o.lstlng systeE' Since I hawent t presented you with the
nbers
e x a c t n u ! $ e r s g h i c h \ ' e r e u s e d h a P p l y i n g t h e t e c h n l q u e t h e s p e c i f i c n usignificant
trends and the
have 1ltt1e oeanlng to you other ti1u"- tftut tnty shos
inprovenents attainable through any one of the sysren nodifications. DesiAn
o
otEions whlch will allou inpLemenLation f any one or tle noailt.ations are
currently being pursued. Final selection oi]1 be nade b! about mid-1980.
Figure 17 - But hoq realistic are rhese predicrions? A predicrion
technique such as this produces results which are only as realistlc as
are the inputs. ExaDining roode1 sensilivity ro lnputs reveated tha! resulrs
can vary quite significanrly. The approach used to get a measure of hov
realistic were the predicrions, rras ro rake a backlrard glance ar how,e11
this model would have predict€d losses over a ren-year period ending uirh
the current period. These loss predlcrions could then be compared wirh
the actual losses and hopefully rhe results would indicare sorne deAree
of realisn berween nodel and acrual results. Flight recor:ds for rne ren-
year period for this specific aircraft revealed rhar the canopy experienced
17 birdstrikes rirh roughly 6-8 of rhese being recorded as ,'failures.,'
The Findshield experienced 29 birdstrikes nith roughly 1-2 of rhese being
recorded as "failures.r' The "failures" were representative of Denerration
or signlficant fracture and parrial loss of a portton of the canopy.
Resufting probabiliries of failure were as shor"{r on the figure. Applying
the probibllistic rechnique for rhe sane rine period resulted in a p!e_
dicted probability of failure as shom. The correlarion between the actual
and the predicted qas rarher reassurang.
FiCgg lq - Ue have a risk assessnenr technique which is avaitabte
for use in rhe conrinuing bird wa! bartle. The technique is sensitive
to bird density, bird relghr, inpac! vetoclty, and inpact area strength
distributions, This sensitiwiry has borh negative and positive inptlca-
tions. On the negarive slde ir pernits eirher accidental or inrentional
bias to distort the resulrs. On rhe posirive side ir pernrits consideration
of specific alterations to the inpur dara and rhus, atlows recoAnltton ot
the overall problen conplexlry. The abitiry ro derive Ehe prerequisite
distributions fron operalional dara inproves confldence in the resulEing
risk assessnent as rhese distributions, if selected vith cale, can rruly
represent the speciflc operarional enwironnent of conceh. ApplicaEaons
where all foui distributions nusr be hyporhesized, such as foi a new aircraft
in a nev role, rhus inwolve the highest risk of inproper interpretarion
of results. Applications involvlne tower rlsk in interprering the resutrs
are those where fever distributions nusr be hyporhesized, as opposed ro
derived fron operational data. For exaDple, chansing operating locarlons
with a given aircraf! and nission profile or changins nission profile
without changing aircraft or operating locarion. Inwestisations have shoLn
r\at the sensi' iviLy of the 'F.nniquo can be reduced. if ;esired, rhroLsh
future 'nodel developnenrs, Unrit such ilevelopnent is acconplish;d, hovever,
it is felt that the technlque does hawe current applicarlon providing
reallstic disrributions for rhe,:our factors are establistred-represenrrng
a comon operarionsl environnent of concern.
BACKUP FIGURES
A. Characterisric disrribution shapes. Weighr and velocity distri-
butlon are of rhe l,Ielbufl typei str:enarh dlsrriburion is of 1in€ar
B. Conputarion of probabiliry density funcrion of impacting kinetic
t t
IJ
=
- > c>
z z ,
<oo
i3=?
I
I ;FeE
I 6 * o
o 7o -- u.- ' 1
4 3
q- ; : J <
!u a- e,4 vt
lz
&,
3
|JI
r'4)
e L,
v, (J
o at,
4
ao
e co
r! I
T &, ro
o
o 4
z o o-
I
f UI vt
e l!
d
f
lll ttt
o ur
4
D
LJ o
z
lI| t!
c\..,
e{
alt I
}].,1
i \,r
n<
\v]
Cl
z
o
F
J
f
=
d,
o
t ! r ! 3 2
z i =; o
J 6 0 =
= u r O ;
d 2 ,= i I 5 : t
,
= e e et
u l = J J < ur
x S H3 =
d
Y
; o O D
o
; ; = = d t!
o o a o a
-
=
; -z= =
l
-
= Z Ha ;
4 .
- s r u J
o
co = A ,
z a
F
3
3 b c/,
tll
d >-
> F F . i ' ;
=
rtl =
3 a 5 ;E
o v. F g E ' - k
o
U-
€ = a r =
< - J a : ( , ' . ,
llr F > - = 4 1 ! u1 3
=
= <1-.+= =
e , < n E
)
.J
9 E = > - - ,
o 6 o= - 6- x * --=-P
z =
z.
c H =
d - e . = f i 2< o =
Y
(., z. - o - > - X E
z. = 6 8 s 1
- E j 3 E
, o 9 z - =
+-===
= H 5 a
v
tll
oz
, . - ; = + f
E o h 6 (9
3 = 4 = l!
-t
E
c
o
tlt I
z a z
{J ttl ul
=
UI o r/t
v,
Itt
z llr
tt,
vl
z o
g
4 o Y
vl
D (J
I IJ
ul e,
I tlt
o o
G
ra o
tl,l
o
o
d,
CL
ltl
d
tlt
z
I I I I
ra
IJI
Y
&, r/l
r,) |ll
o e
&
o
CO t!
F
(,
-t
IL
()
z
lrl d,
(., f
o
z IIT LLr Y,
ttl ()
o &,
f F
t!
I
ttl E ; E
o ; z o E
= rrj Y tl,l
Y
o5
= d .
& F F
(J
d. E
z
(n z 3 2 )-
q-
atl
o
e, I
= 6
= E v ll,
o tlt
t ! J
F
d
II
I
tu
o() o tl,l
> I o x
I IJJ tll
= F x
tL = < i J €
6
3 e
ro
4
o
.
O O
F
co a
ur
e
o o
5
9- o
o d,
o-
o o
z
o z
tr
F l.! z
E ;
J z
d. z.
D L'.t, = =
co z
= z F _ :z
d (J co r-
o
It
L!
Y
E
E =
>- :-: =
J z -i -3 .. Lr-
E E
IJ z. r-rr -
o
@ = <
LTJI t- trJ - F CE !r-
5 c ) < O
o e.
=
=
e. z
)
tr 9 > c o
o . .
d
o-
E .
L!
= J
:ZI
\,/1 \./,\
z
= -)
J :z
3t, F
o o
(J z L!
=
o )<
F o-
-
o
(/t
= N
F f ttl
atl e
rn D
F (,
tn tl-
--,----.lb--
llJ
:z
d,
z. a/l
=
z o
lJ- e,
E
co
= =
= f c)r
, =
o
z
-
z.
o
e .
2
o
z
a/t
tlr
F
z . =
o Y.
v z z . = E
=
4 t,/^t
z.
:- ..r
( - ) r - < o
r^ o =.= 6 o =
co
o rJ >-
u- i-- { L,r
o =
co
-)
v ( -
< O
) 1
;
o O <
u, !2. o a q J
7
= e, F <
tlJ O 6 tlr
co co A aoi
= t > > o') fl ?ft =
Z. E. = tr)
= < =
'-t =
)
-
9 ! < = :) < (-)
5 o o- <
z u- <Q t-
z r!
o
rll
c o - : -
LJJ O < l > F llt
(J ttl
I 4
rlt llr
o- o-
x
lII
x ,lt
;
III
\'/1
ur (J
Y :-
e, *
\_1 =
(3
e
?
vt a
o ll| =si =
&, o z . a ' = ' < -
P P ( ' O E T H
co , 2 . . - : v t 4
= € , ! = 6 =
v e = ; - a
I! o ; z > E ) U LP= H- b
oo : - z >
z d i . , f i 9 i
o - = = e . - i -
- g E = = EE
vl
E :) " S "E ?E 3 ? F E
L, I l l
lo
o
4
lrJ
v,
6
g llr
u
f
o
IL
b-.4r-.
: ! !
= 5 =
z ' o 8
z O r o
o A
2
a 2
; 9
< F
3 =
* J J
F 7. ,
\ N..,,= G;
. a <z uJ
tt1 :Ef J
tr
I ottt
J a E t t r Y ( / l F J a \
o- Y H s t < - = :
CL a = fr 72
z = =oz Eg =:: 2 5
o
e{ -
t f o
= ; = z 9 : : o o
< ; o E i l ; UJ
e.
J u r J ! n Z <
f
i o o o o
u-
-
L' z
o
o
e,
o
ur
G
CO
d,
4
4 at v!
|lI
Y
o
l (J
a
ul F
e,
r^ o
4,
.tl o
4 z z
o ltl'
e
z o
ao z
o 3tl
o o f
ro =
F co e c, )
co
Itl
o
&,
tll
CO
=
vl
a
d,
tJl
tt
=
L l I 6
4 z o
o tll o I tr
g
IL I lll tlt
z I
|lI a
(J
o
atl
o
z
|lI 4 e,
lr1 x
ttl ro
IJ
f i d
tll
,
ci e) \ 3
o
F
9
t!
o
z
t{t
ltr
o
f
F
F
F
It
at,
tlj
Y
u,
|J co
d. d,
F
.tl F
o I U
d,
co
t! o !.1_
F
L,, rll
l!. ltt
o r> tt, F
Il.
&, o e, o '----=-
rlt
co ll o a/l ti
E I!
o l>
d,
:)
z tlr o o
U
o
lft
d,
o llt
e,
ii
l 5
I l::
F IIJ -l
I
IIJ
u,
o- IJT
v
z - t 5
x
lu d,
o lo-
F
F la (\a
- ttl
o 4
IJJ ttr
&. a. 4
co o )
o
I I lJ-
s d
d u
t Y
r - O
U u
f
p (
F
c , 4
F
t ! o - =
ul
c l'l :zo
J z
lrl
&,2
- F <
< 4
z |lr LIl
o 9 t d[
t
O ( J
orz
- 4
f
o t 3 o =
e, d <
4 -
vt o f r t-
o | ! F
6 -
=
6 { = = ;
I t e
- <
I
ul
o
L . , *
f - a
| r t l ,
& +
o : e ,
z
o
v
C
o
at)
ilu
) z
; =
- o
N o o - G
d , 4 o u.r
u . O
ao ao t!
9t=
< 6 =
=<x
= 6 6 u,l
= O a r
4
f
(9
z
o
z
o = TT
;l_
ul
:) o ,>l-, €
o q ) n
e o F
r O
4 J ; od.
3 o <
o ; =
c,o -J
L4
u ( - r
o z <
o 2
ut
F O
< F
(!t d -
rrr O t
a o
o < ltl
d
)
r-L
o
tt
>:-
t--2.
<co<
=<ou
=co=
=o(-)
=oa (J
z.
va
iz. = =
z. z.
d
t!
z = r
o l! r
F
llr
p o E ;
l
ro = g o = H=
d,
? < ; = uO
t E;J; |l.tUJ-
c)F
>-.,d
6 ; 9 9 >
E F < z a sZ
o J , a 9 o
z
gl
=
:-
; "
tlt
;
J\
<=
4 G z < ,
C t r . gZ . -
r/!
rf
;=35
5E;"
*:a r/t
ul
4
f
zF o
=1
5>
3sE
Eets
ci
a
=
at, =
z tlt
v,
o v, =
.i
o o
e, o J
tlt
r E -
ttl
ul ru o .i
D
z
rll
o- z =
tt, CL 4 =
1I|
4 o UI
z.
tr
Ln
F x
I o r/\
o
rll
.^ \t1
e, = 4 u -
o- tt,
z =tr E ! = 5
o
v!
3
, E g=- = ;
=
r,t1
-E--
r,h ^
=
(a
>< =
N i,
><
.^
=
=
= X x x rJJ
x :
t!
O 6
do
- c {
B N
!t
v, ol j |tl o
o l
z a
=
F1 C L - o i f
9 : i ;
ct
zt l
u l e e :
= Il
rtt
|.)
tll
e
(/|l e
f
J
u,rI f Jt a
(^l J
llrl l!
t/tl @ ot ..
<l o.
t!
ol o
I
Jl
I
o O
u.
=l r
utl
@
€
ul
6 . el =
ol o. e,
O i r =
;- FI ;
3l :
ol vr
o
U | j I C o
rJ.r 4
c ? . o
-ll
6l o
co
=l 4
o v t = o
lrl
y t ! c
$l r
ol o
I
dl
lll
4, = t u=r { i
v
"l =
g N
o
r l F
= t t r
=
F 5l s
l c ,
llt
e
t
co i/t uJl a o
J (,1l
fl LL
E4--
F
x
trt
a-
=
o
I UI
o
z ur
= z
o o
EI
F o I
f o
e,
IJ
f
6 z o
6= (L
|/I
o
F
rl|
e,
< u l . llt
o ;v lfo o < t 9 Z o
- rJ,l o z o
F
r ; ;
- -
: f s I
?
J < F z
e o ul , t t r (
o raa= d,
Z u u l.)
2A>- = 2 "
=
llt
oo-;; < o o =
F a ; O
=
6 i=g; F- 1 t - =
f tt i . o = - 6
( z :e3I z
lu uJ lrl
9
c i ! i ! <
e
z
O } U U a e 4< 4 < =
ltl
ttl
rlt
ooss a
lt-
f
o : : = =
o
tlt
i E <E =
Z < r
o
rJt
@
z oaao tlt
e o o o o ur
e
IJJ
d,
:E
(,
rtl
o
1I,
o
ttr o
o o
o o o
vl
z
o
u o ';i E
z
l .=>:z
, z
z
o F
. 6 : :
f =
I
e
tr!
o
3XA€pebPueo .-.....
eaJV
aluBrnJgo /ii!lqeqoJd
l0 -----
a^tlplnutn3 tll
g
eeue.lnrsorilrlrqeqor6
1o a^rlslnun3-
N0un€ |0 lLn |8v80ud tlvrnwnJ
| uts tA o
t!
z.q V
= z o
> - v =
L : - / 6
u^,= F
a- z ,., :4
--: E ) IJJI
v-l-
coS < di't >
< c _ r Yr >lcr) ---- =t)<
\-.)- e Y' =l'\
=
O- O_ 8--o
:z
o-
ao
lfJ
d.
:)
o
t!
