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.i G E NE R AL AV IA T I ON C R AS H S A F ET Y P RO GR A M AT L A N G LE Y RESEAR CH C ENTER Rob e r t G . Thoms o n NASA Lang le y Resea r ch Cen te r SU _k RY The pu r p o se o f th e L an gl e y Re s e a r c h C e n ter c ra s h sa f e ty p rog ra m is t o "' supp o r t devel o pmen t o f t h e te chn o logy to d ef in e and dem o ns t ra te new s tr uc- t ural c o ncep t s f or i mp ro v e d crash s af e t y and o ccu p an t sur vi vabil i t y i n gene r al a v ia t i o n a ir craf t . Th e program i nv o lves t hre e basic ar e a s o f r esearch: full-scal e crash s i mula t i o n te s t ing , n o nl i n e ar s t ruc t ural anal- y s es necessary to pr e d i c t fa i lure m o d e s and c oll apse me chanisms o f t h e veh i cl e, and evalua tio n o f en e rgy abs or p t i o n c o nc e p t s for specif i c c om p o - nen t d e s ig n. B ot h analy ti cal and exp eri men t al m et hods ar e b e in g used to d e v el o p exper t ise i n t hese a rea s. Ana l ys e s i nclude bo t h s i mplif i ed pr o- cedures f or es t im a ti ng en erg y abs o rp t i o n ca p abil itie s and m ore complex c o mpu t er p rog r am s f o r analys i s of ge n er a l ai r f r am e r e spons e . Und er t h e c r a s h safe t y p rog ram , t hese analyses wil l b e d e v e l o p e d to pr o v i de t he des i gner wi t h me t h o ds f o r pr e dic ti n g acc ele ra tl ons , lo ad , and d i s p lacemen t his to rie s o f c o llaps i ng s t ruc t u re s. Ful l - scale t es t s o f t ypical s t ruc t ur e s as well as t es t s o n s t ruc t u ral c o mp o n e n t s ar e b e ing us e d to v er ify t he ana l - yses and to dem o ns tr a t e imp r oved des ig n c o ncep t s.
INTRODUCTION Techn o l og y f or pr ed i c t in g a i r c raft dyn a mic r e spo n se und er c ra s h l o a ds and o ccupan t b ehavi or durin g im p ac t i s b ein g d e v el op ed b y Lan gl ey R es e a r ch Cen t er (La R C) in a j o in t NASA / FAA c r ashw o r t hln e ss prog ra m . P ar t o f t he analy t ical and expe ri men t al p rog ram inc l ud e s e va l ua tl n g a ir frame , s e a t, and re st ra l n t - s y st e m c o nc e p t s f o r mitig a ti n g cr a sh l o a ds imp o s e d o n o ccup a n t s o f g eneral avia tio n a ir craf t . Th e m et h o ds us e d an d c o nc e p t s devel o ped fr o m t hese o n goi n g eff o r t s w ill mak e f eas lble f u t ur e ai r cra ft de s ig ns th a t wi ll en ha nce t h e de gre e o f surv i va bil i t y und er a crash c o n dit i o n w it h m in im um we ig h t an d c o s t p enal t i e s. Th e tot al p ro g ra m wi t h it s go a l o f im p r o v e d o ccupan t su r v lv a b i llt y fo ll o wi ng a n airp la n e acciden t is sh o wn in fig ur e 1 .
NASA' s r esp o ns lbilit y in t his J oi n t p r og ram i s sh o wn as shad e d bo x e s , t h e FAAts ro le as unshad e d bo xes , a nd j oint effort s a s c ro ssh at c h ed bo x ea.
• C r ashw o r t h l ness d esi g n t e chn o l ogy is divided in to t hree a r eas: env iron m e n t al , ai r fram e de s ig n , an d c o m p on e n t d e si g n. The env lr on m en t a l fac to r s c o ns i s t o f acqui ri n g an d e va l ua t in g ac t ua l fiel d c r ash d a t a a n d definin g a c r ash enve lo pe wi t hin wh i ch t h e i m p ac t p a r am eter s a llo w toler a bl e ac c elera t i o n le v els.
A i r f rame design has a t w of old o bjec ti ve: t o a sses s a nd apply cu r ren t, o n- th e- s h e l f, an a ly t ical m et h o ds to pred i ct s t ructu r _ l c o llapse ; a n d to devel o p and val l d _te a d vanced analy t ical t echniqu e s . N AS A' s pr im ary r o l e :' 36 9 i" ' ' " _" " " " " " ' " " , " , ' , L'_ r _ %_ _ " h 0 , : . _ , : , _ ' " I t , ! t : I -i .
in th e Joint pr o gra m i s t he deve l opmen t o f a dv an ced an a lyti c al t ec hniq ue s.
F ull- scale te s t s w il l be u sed to ve ¢ if y th e a n aly ti ca l pr e d i c tion._, as w ell a s to d emon s t ra t e i m p ro v ed cr a shw o r t hy d e s i g n c o ncep t s. A f a c ility f o r fr ee- f ll g h t cra sh t e sting o f f ul l-s ca le a i rcra ft st r u ct u re s a n d st r u c tu ral c om p on e nt s h a s b ee n d e v e lo pe d a t La R C. Ai r f ra me des ign als o in cl ud e s e valu a tion o f nov e l ; c rashworthy desi g n c on c epts and their effe c t on stru c tural c rashworthin e ss.
_ Co mp o n e n t de s i g n c o ns ists o f e x p l or ing t h e d e v elopm e nt o f new a n d inn ova - tiv e e n er gy- a b s o r bln g c on cep ts to imp r o ve p er fo r m a n ce of sea t s an d o cc up a nt : re st ra int syst e ms a s w ell a s th e d e sign of n on le th a l ca bi n int er io r s .
_, i ;, LaRC C R ASH SA FE TY P RO G R AM L T h e re sp on s ibi l itie s of La R C i n the air fr am e d e s ig n tec hn o l og y p o r tio n of t h e j oi n t p r og ram (see f ig . 2) can be d i v i ded i n to t hr e e p rogram e l eme n t s: _ full-scal e crash s i mula tio n te s ti n g, n o nl i n e a r crash i m pac t analys i s , an ..
,_ c rashw o r t hy d e s ig n c o nce pt s.
_ i Fu ll -Sca l e Cra s h Simu lation T e s ting i. , Th e full-scal e crash s imu la tio n te s ti n g i s bei n g d o ne a t La R C i n the -,i: Lan g le y im p ac t d ynam i cs r e sea r c h fac i l it y ( re f. I) sh o wn i n f ig ure 3 . Th i s _ , fa ci l ity i s the f o r me r L an g le y luna r lan di n g r e s e arc h fac i l ity th a t has bee n i , m o d i f ie d f o r free-f lig h t crash t es ti n g o f fu ll -s c a l e a i rcraf t str u ct u r es an d i_ _C s t ru ct ural com p o n e n t s under hig hly c o n t r o lled te s t co nd iti ons . The te s t v e hl- r --- ", i" cl e s ar e sus pe n d e d fr o m the g an t ry an d the n swun g pe n d ul u m fas h i o n an d re l e ased ,_ to s im ula t e fr e e-fll ght c r as h c o nd itio ns a t imp a ct.
i . / I"L _'_ Th e fac i l it y's b as i c g antr y s t ruc t ure i s 7 3 m (24 0 f t) h igh an d 122 m -'_ ( 4 00 f t ) lo n g supp o r te d b y t hree se t s o f i nc li ned l e g s sp rea d 8 1 m (26 7 f t ) _ : a p ar t a t the gro und an d 2 0 m ( 6 7 f t) a p a rt a t the 66-m ( 218- ft ) level. A _i; m o v ab le b r i d g e s pa ns the top a nd tra ve r ses t h e l e n gt h o f th e g a n t ry.
. _ -!!
.!_ Test method . - T he metho d for c r ash t e s .ti n g t he a i rcraft i s s ho wn p i c tori ally i n f i gur e 4. Th e aircraft i s suspended fr o m the to p o f the g an t ry b y tw o sw i n e c a bles an d i s d r awn b a ck a b ov e t h e im p a c t surface by a p ullb a ck c a ble. A n -_ umbi l i c a l ca b l e us ed f o r d ata a cqu i s itio n i s a ls o susp e nd e d fr om t h e t o p o £ the gan t ry a nd c o nn e cts to t he to p o f t he a i rcraf t . Th e t es t sequence i s i n iti a ted i_ ; whe n the a i rcraf t i s r e leased from th e pullback ca b le• T he a i rcraf t sw i ng s L : pen dulum s t yl e i nt o t h e im p a c t surface. The s w i ng c ab l e s ar e s epa rate d f r o m i : , _o t he a i r c ra ft by p yr ote chnics Ju st p r io r to i m p a ct, f r eei ng t h e a i r c raf t fr o m _-_ r es traint. T h e um bi l ica l cab le re ma i ns atta ch ed to t h e air c ra ft f or d a t a _ a cqu i s itio n , b ut it a ls o sep a r a tes b y p yr o tech ni cs b ef o re i t bec ome s ta ut dur in g skid o u t. Sin ce the separ a ti o n point is he l d r elati v el y fix ed near th e i mpa c t su rf ace , t he l en gt h o f the sw i n g ca bl es i s us e d to adjust t he f lig h t - p a t h an g le i " fr om 0 ° to 6 0 ° The h ei ght of t h e ai rcr a ft a b o ve the im p a c t s u rf a ce a t re leas e d e te r min e s t h e im pac t vel oci ty a nd c an be varie d to giv e imp act velo c ities from ; _ : 0 t o 2 6 . 8 m / s ( 60 mph). It is import a nt that, in th e s u spended position, th e ,, 370 ,'-- = ,,7C.
T ', t t
+ , !
for ce ve c tors of t he swing cabl e s and p u llba c k c abl e s act at 90 ° t o e ac h ot h er and pass throu g h the c ent e r of gravity o f th e a ir c r a ft . This is n ece ss a ry to c ontrol a ir c raf t pit c h r eac tion durin g th e s w in g ph a s e . Th e mov a bl e bri dge allows th e pullb ac k point to b e pos i tion e d a lon g th e ga ntry to i nsure this for ce r el a tion fo r v ar ious pullb ac k he i gh ts a nd s wl ng- c abl e l e n g t h s . The pit ch i ng v e lo c ity of th e a ir cra ft a t s w in g - ca bl e s e p arat io n c ontinu e s to c h a n ge th e pit c h a ttitud e of th e a i rcra ft du r in g th e f ree- fll g ht ph a s e of th e t e st . In th e i0 t e st s c ondu c t e d to d a t e, th e pit c h a ngl e c h a ng e du e to this c o nd iti on has n e v er b ee n grea t e r th a n 1 . 7 5° .
A t y pi c al air c raft s u spension s y stem w hich is d esi g ned sp e c i f i c a ll y f or , th e air c raft c onfigurat i on b e ing t es t e d is s h o wn in f ig u r e 5 . T h e s wing cab le s att ac h t o har d point s in th e ma in wing s pa r o f th e ai r cra f t s o that a l in e c o nn e c t in g t h e t w o ha r d poi n t s ( dashed li n e i n fi g ur e ) p asses d lre ct ly t h ro u g h t he aircraf t cen te r o f g ravi ty . The pull b ack ca b le a tt aches t o t hese sam e ha rd p o in t s ; t hus , it s f o rc e reac t i o n als o passes t hr o u g h the c e n te r o f g rav i ty.
Two s e t s of pi t ch ca bl es are a tt ach e d to t h e sw i n g ca b les 3 m ( 1 0 ft ) a bov e t he hard poin t s i n t he w i n g s and to ha rd po in t s i n t he fusela ge f or e and af t o f t he ai r cra ft c e n t e r o f g rav it y. Adjus tm e n t s in r o ll an g l e to a bo u t 30 ° can be made , wi t h o u t sac ri f i cin g c o n t rol , b y vary i n g t he l en gt h o f t h e sw i n g and pit ch ca b les.
Adjus t men t s in yaw an g l e to a bo u t 15 ° can b e made b y v a ryi n g t h e len gt h o f t he ca b l e s i n t h e p u llb ack ha r ness and t he p it ch ca bl es. Adjus tm en t s _ n pit ch to a bo u t 4 5 ° can b e ma d e by v aryin g t h e le n gt h o f t he pit ch ca bl es in t he fo re an d af t dir e c t i o ns. Lar g e r chan g es i n p i t ch , yaw , and r o ll r eq u i r e r _ es ig n and / o r re l o ca t i o n o f t h e hard p oi n ts in t h e ai r craf t . F o r ot h e r a i rc r af t c o nfi g ura- tio ns , t he h ard p o in t s m us t b e p r o p e r ly l o ca te d and a n e w sus p ens io n s ys t em mus t b e d e si g ned to m a int a i n t he sw i n g and p u llb ack ca bl es a t 90 ° to each ot her wi th t heir f o rce v e c to rs passin g t hr o u g h tl_ a ir craf t cen t e r o f g ravi t y.
I ns tr umen t a t i o n.- Da t a g a t h eri n g f ro m t he full-scale crash te s t o f an a ir - c r af t is acc o mpl i sh e d w it h ex t e ns i v e ph otogr a p h i c c ov e r a g e , bot h in t e rior a nd ex t e r i or to t he f usela g e, u til lz i n g lo w- , m ed i u m-, an d hi g h-ra t e cameras and w it h o n bo a r d s t ra i n g a g es and acceler om e t ers. Th e pi ez o elec t r i c acc e l ero me t ers ( ran ge o f 250 g an d 2 to 5000 H z) a re t h e p ri mar y data- g enera tl n g i ns t r ument s.
A t y p ical accel erometer lay o u t f o r a te s t s p e c imen ex peri e ncin g z e r o yaw at i mp act i s sh own i n fi g ur e 6. C i rcles indica t e i ns tr u m e n t s po s it i o n e d to measu r e accel e ra t i o ns n o r m al to t he fusela g e ' s h or l _o n t al p lan e . D i am ond s r epresen t ins t ru me n t s p o s itio ned to m e asur e a cc el e cat io ns bot h in the n o rmal an d l o n gi - t ud i na l dir e c tio ns as sh o wn i n t h e f i g u r, . The side- vi ew sch emat ic a l s o sh o ws t w o du m mi e s o nb o ard t h e t es t spec ime n . _ l ere ha v e b e e n fr o m o n e to f o ur an t hr opomo rph i c d u mmi es (Na tio nal H ig hw j Traf fi c Safe t y A dmi n i s tr a t i o n Hy br i d ll ) o n bo ar d all fu ll -sca l e aircraft t ests c o nduc t ed to d a t e a t LaRC.
Sh own i n fi g ure 7 i s a sch emat ic o f a typ ica l o n bo ar d camera an d r e s t ra i n t - " s y s t e m arran g em en t . Th e fo rwa rd c amer a i s l o ca t ed in t he rad io c om pa rtme n t i n t he in s tr um e n t pa nel, t he re a r c am er a o n a re a r ins t ru m en t shelf , and t h e t w o s i de c a m e ras ar e cantil e vered o ff t he fuselag e . These ca m e ras are sh o ck resistan t and a r e mo unted in a can til ever fashi o n. There are appr o ximately 15 exteri o r c a meras used during a t e s t . The l o ca t i o n and framing r a t e o f t he s e cam e r a s a re disc u ssed in referenc e i . The re st r a l n t -sy st e m arrange m en t a nd t ype of re st r a i n t u s ed vary fr o m t e st I: o t e st .
Tests cond uct ed .- Full -sca le c ra sh testing o f air craft a nd a i rc r a ft co m po- n e nt s i s b e ing c ondu c t e d at LaRC t o d e t e rmine a s et of stru c tural d e sign cr a sh pa r am ete r s for wh i ch th e c abin a re a main t ains its st ructural int e grity t o t he d eg r ee that it s uppor t s a l i vabl e volum e throughout th e c rash s e _u e,,ce . Th ese s tru c tural c rash param e ter s w i ll be suppl e ment e d by FAA fi e ld c rash da ta t o form a ba sis f o r a rati on al c ra s h d esi gn env e l o p e . In additi o n, t he e xperi- m e n t al c rash t _st da t a w i ll b e us e d to as cer tain th e valid i ty o f an a lyti c al pr e di ct ions a nd to t e s t th e p e r f orman ce of improv e d stru c tur a l a nd s eat c on cepts < for c rashworthlness. The initial stages of th e c rash t e st program, f rom : _ F e bruary 19 7 4 to Jun e 1976, hav e b ee n c ondu cted us i ng i0 twln -e ngin e light air - ! c raf t i mpac tin g into a c on cre te s urf ace . -- A s u mmary of t he im p a c t p a ra meters a s so c iat ed with t he se i0 t e sts is sh o w n in figure 8 by the sha d ed bo x es. The flight-pat h angle w a s maintaine d a t -15 ° ! exce pt fo r t w o t e sts. These t w o t e st s ha d f l igh t -pa t h an g l e s of -3 0 ° and -4 5 ° .
J T he f lig h t - pa th v el o c ity h a s been hel d c o ns t a n t a t 2 6.8 m / s (60 mph) e xce pt for I_ I o n e te s t a t 13 .4 m / s ( 3 0 mph). T w o te s ts were performed with l a n di n g gear e xt e n d e d an d ar e in d i c ated by an asterisk . P osi t iv e angles of attack of 15° _! : a nd 3 0 ° were i n t rodu c ed in t wo t ests a t -15 ° f l ight-path angle. In a dditi o n, t w o tests were c ondu c t ed with neg at ive roll angles of 30 ° and 15°.
Fu t ure full-s c ale air c raft t es t s, shown in figure 8 by unshaded boxes, will ; , i nclu d e t w ln- en gl n e a ir c r a f t a t l o w er i mpa c t f l l ght -p ath an g l e s b u t h ig her ; _ impact v el o c iti e s (aircraft's s wing ve l ocity wi l l be a ugmen t ed w ith w i n g-mo un ted -!i ro c k e t m otor s ). I n add ition, three h ig h - an d t hree l o w - win g, sin g le - en gi ne a i r c raf t crash t e s t s are plan n e d , as well as s t ripped airframe t es ts o n f ield terr a in simulated by dirt. The ma trix of full-scale c rash testing is by no m eans co m plete and does not consider such secondary effects as aircraft sli d ing, overturning, cartwheeling, or tree and obstacle i m pact. However, the proposed crash tests should gener a te enough meaningful crash data to define si n gle- an d twin-englne structural crash test envelopes.
NASA full-scale crash test data.- Experiment a l acceleration time history d ata and structural damage assessment, generated fro m each of NASA's full-scale crash tes t s, are being analyzed for publication. The analyses consi d er the effects of varying one of the i m pact para m eters only, such as, fllght-p a th : v elo c it y , fllght- p ath angle, an gle o f a tta c k, o r roll. A r e pr e se n tati v e s e m p le _ , o f the t yp e o f da t a to be repo rt e d is presen t ed h erein for 1 of t h e i0 t es t s =_ s h own in fi gu r e 8 (n o mi nal t e s t c o n d it ions of 2 6. 8 m / s (60 mph) f ll gh t-pat h ve lo c ity, - 1 5 ° f ll gh t - p ath ang l e , zer o ang l e of a tt ac k, and zer o r ol l and y aw).
'T e : Figure 9 i s a se qu e n ce o f p h o t ograp hs t ak e n w i t h a 20 -fram e - per - s e c o n d i_ , . ca mer a d uring the sec o n d c r as h tes t. Ti m e be tw e e n fr a m es i s 0.0 5 sec o nd . T he s e qu e nc e cl e a rly sh o ws th e fr e e- fllght c o nd itio n of t h e t e s t a i rcra f t pr io r to f imp act at 2 6. 8 m / s (60 mph) an d a pitch a ngl e of - 1 2 ° . Th e str uc t ur a l da ma ge to t h e fus ela g e o cc urs dur i n g two imp act s: prim a ry imp act wh e n th e no se initi a lly imp ac ts th e ground surf ace (third fr a m e ) a nd s ec ond a ry im pac t whe n t h e ca bin sl a ms down on t o th e g round surf ace b eca u se of fus e l age ro ta tion : (fi fth fra me ). This s econ dary i m p ac t produce s t he mos t s evere no r m a l a ccel er- !_ a tfon s in the cabin ar e a. For this parti c ular test, stru c tura l d a m a g e w a s _ mod e r a t e with t h e ca b i n maintaining its li va ble v olume. Rivet s h ea r o cc P rr ed =: : 372
! : I I
J i , : in t he ca bi n a lo ng lin e s of o ver la pp in g s k in s hee t met a l and i n t er io r sti f f e ning s t r u cture. Bre a ks due to t h i s r i ve t shear appeared in t he r o of at t he m a in s p ar fra m e , a long t he win d ow l e d ge s , an d in t h e v i c inity o f t he d oor . Up on i m pac t, th e fo rwa rd f loor b ea ms a nd nos e w h e el we ll rot a t e d u pward ca using b uc klin g o f t he e n t i re no se , f i re wall , a n d f loo r beams in th e c o c k p it. T h e c o m bin at ion o f d o w nw ar d mom e ntum o f th e w ing s a nd th e imp act o f t h e m a in s par w it h t h e g r o u nd pr o d u ce d twi s ting o f t he m a in spar a nd loss o f win g dih e d ral a ngl e. In a dd ition, t he ca bin f loo r exper i e n ce d u p w ar d h eav in g o f th e fl oor b ea m s ca using ou t bo ar d s eat r ot a tio n. Gl a ss b rea k a g e w a s c on f in e d t o the pilot' s w in d s cr e e n a nd s i de wi n dow.
F our _presentatl v e sets of acceleration time histories, norm a l to the l on g itudinal axis, recor d e d d uri n g this full-scale crash test are presented in figures I0, 11, 12, an d 13. At the t op of each figure there is a _ide- v iew s c hem a tic locating the accelerometers ( d i a m o nd s y mbols) an d the four a n thropo- mo rp hic du m m ies (pilot, copilot, a nd two p a ssen g ers) of interest. Fi g u r es I0 a n d II a re t yp ical acceleration time histories while figures 12 an d 13 are acc e l e ra tio n time h i s to r ies w it h timed e v e n t s fro m ph ot o g raph i c data sup e r impo s ed o n t h e a cc eleratio n t r a c es.
F ig ur e i 0 pr e s e n t s a c c e l er a tio n tr ac e s at t w o di f fe r e n t l o ca tio ns norm a l to t he fl oo r beam o f t h e fuselage. The f i rs t acc e l e r omet er i s l o ca t ed a t t he i n iti a l p oi n t o f im pac t , firs t fuse l a g e frame. Acc e l er a tio n t race (2) i s af t o f t he f i rs t passenger and i s n ot affec t ed by t h e _ r l mary im pac t b u t by t he sec o nda r y i mpac t wh e n t h e cab i n c o mpar t men t slams o n to t he c o n t ac t surfa c e.
The fus el age d i r ec " v be l o w p o in t (2) c o n t ac t s t h e gr o und 0 .09 se co nd af te r ini ti al g r o und c o n L_ ' . (fif t h frame o f f ig . 9). F o r t h e n o se loc a tio n a t t h e f i rs t fuse l a ge fr ame ( t rac e ( 1 )) dur i n g t he fi r s t 0. 1 sec o nd af te r i m pac t , t he aircraf t exh i bi t s high ampli t ud e o s cill a to ry behavi o r caused by inl t la l i m pac t ( 1 2 0 g nega ti v e accel er a tio n ), the n reb o und ( 4 2 g p o s it iv e a c c el era t i o n) f o ll o w e d by an ot her im pac t (4 0 g nega t ive acc el era tio n) wh i ch is canc e l e d by t h e a ct i o n o f t he adjacen t s t ruc t u re as it c o n ti nu e s al o ng t he f l igh t pa t h. Al t h o ugh t h e o ec o nd a_ y im pa ct pr o duc e s t he m ost s e ver e n o r ma l acc e l e r a tio ns i n t h e c ab i n ar e a, t h e magn it udes o f t h e s e acce l era tio ns (22 g ne g a t ive and 50 g p o s iti v e ) a re s till substant i ally l o w e r t han t h o se o f t he n o s e ( i mpa ct p oi n t ) acc e l e ra tio n s and o ccur be t w e en 0 . 1 and 0 .2 se co nd a fte r primary im pac t .
F i gu r e ii pres e n t s ti me h i s tor y o f t h e averag e of fo ur ac c el e r omet e r s lo ca te d n orm al to t h e base o f t he f i rs t passen g e r se at (beh i nd t h e p ilot ) and t he n o r m al p el v l c acce l era tlo n time h i s to ry o f t he an t hr o p o m o rphic du m m y. Th e f i rs t passen g er ( 7 9 . 3 k g (1 7 5 ib)) was sea t e d i n a s t a ndard pass e n g er s_ a t and was res t r a i ned by a f l ve-p o ln t res t ra i n t sy ste m - l ap b elt , cr ot ch b elt, and t w o s ho uld e r harnesses. The a ve rag e s eat i up u t (a t t h e ba s e of t h e s eat ) p e aks at a bo u t 0 .0 8 seco nd after initia l impa c t. Ther e is some s imilarit y betwe e n t he av er ag e a cceler a tio n trace o f the seat base ( 3 ) a n d the fir s t p a ss en g er p el v ic trace (4) if o n e co ns iders t h at there i s a time la g of 0.02 s e co n d bet w ee n t h e trace s d ur ing wh ich the seat cu s hio n and dumm y com p ress. However, little e n er g y i s d i ss i pa ted by the s eat s tru c ture a s is e v ide n t in the smnll di f fe r e nc e i n ma x im u m a cceler a tio n pe a ks bet w een t he se at b a se (3) (5 4g positive ) an d t h e dum m y's pe l vis ( 4) (50 g ne gative).
In f i gure 12 , s i x normal acceler a t l on time history tr a c e s are pr e sented w it h tim e d e v ents f rom p h o togr a p hi c d a ta su p er im posed on t h e traces for corre- l a tio n a n d int erpre t a ti on. The s ix accelero m e t ers are spaced alon g th e f l o or bea m o f t he a i rcraf t fro m t he f i rs t fuselage frame t o t he rear of th e f i rs t p as se ng e r se a t ( s ee si d e- and t op-v lew i ns e r t). The r e sponse of i n iti a l ground con t ac t i s f el t i mmed i a t e l y a t t he f i rs t fra m e ( t race (i)) and i s seen t o pro- gr e ss r e a rw a rd t o t he fi re w al l ( t r a ce (3)) w it h di m i n i sh i n g int en sit y a nd wit h a s ll gh t t ime l ag ass o c i a t ed w it h t he r e arw a rd p ro gress io n o f t h e c o n t ac t sur- f a ce. M a i n sp a r gr o und c o n t a c t ( 0.0 5 s ec o nd) pr o duces a p o s it ive a c c e lera t i o n o r downward f o rce i n t he n o se o f t he aircraf t a nd sig nals t he i n iti a tio n o f cabin c o mpar t men t exc it a tio n. The in t ensi t y o f t h e accelera tio n peaks in t h e cabin c om par tm en t i s m ax im um in t he vicin it y o f t he mai n sp a r and d im in i shes pr o gress i vely fr o m t ha t p oi n t rea rw ard. The sec o nd a ry imp a c t due t o d o wnw a rd i fuselage r ot a t i o n pr o duces a neg a ti ve accelera tio n p ea k ( o r upward f o rc e ) i n !
t he cab i n c o mp a r t men t ( 60 g on t race ( 4 ), 4 0g o n t race (5)). The lo ss of w i ng I d i hedral angle and w i ng gr o und con t ac t have l itt le overall eff e c t on t he f u se- i lage resp o nse e xcep t f o r t he m ain spar t w i s t ing. The r i ve t sh ea r fa i lure o f t he fuselage i n t he r oo f a t t he main spar, 0.1 7 8 sec o nd af t er i mpac t , c o ncludes !
f u r t her s i gn i f i can t crash effec t s fel t i n t he a i rcraf t s t ruc t ure, i • !
Accelera tio n t ime h i s to ry t races o f the anthr o p o m o rph i c du m my a t t he f i rs t • passenger l o ca tio n and o f t he s e a t a t t he base o f each le g a r e sh o wn i n fig- ure 13 superimp o sed w it h tim ed even t s fro m ph oto g r aph i c da t a. I n iti a l gr o und c o n t ac t, i ndica t ed by zer o tlm e i n figure 13 , i s n ot fel t app r eci a b l y by t he f i rs t passenger. The f i rs t passenger begin s d o wnward and f orw ard motio n 0.06 sec o nd af t er i m pac t a t precisely t he tim e t ha t t he f ro n t and rear legs of i t he sea t f i rs t begin to rec o rd large l o cal i zed f o rces. The sea t t hen be gi ns to r ota te o ut bo a r d ( 0 . 0 6 9 se co nd) . The s hap es o f the p ulses o f th e tw o fr o n t se a t !
le g s a r e n e a r ly i den ti cal as are t h e shapes o f t he p u l se s o f t h e t w o r e ar s e a t le g s. The p r im ary pu l se i n to e ach le g ( t he tim e i n t erva l b e t we e n 0.0 7 to 0.09 sec o nd) has prac ti ca ll y t h e s a me p e ri o d but mu c h lo wer a mp l i t ud e i n t he r ear le g s o f t he sea t . Th i s pr im a r y p ulse i s exh ibit e d i n t he _ e l v ic r eg i on (tr ace ( 3)) o f th e d ummy 0 .0 25 sec on d l at er. F o r d et erm i n i ng a s in g l e acc e l e r- a t ion pu l se shape f or sea t eva l ua t l o n , i t appears t ha t t he simp le av e rag i n g of t h e inpu t s a t each leg a tt achmen t p oi n t ( f ig . 11) y l e l ds a sa ti sfac t ory r epre- sen t a t i o n. C o mpa ri s o n o f aisle leg to wind o w le g accelera tio ns i nd i c a t es t ha t t he aisle l e g ne g a t ive acce l era t i o n peaks during sea t r ot a tio n are high e r t han t he c o rresp o nding wind o w l e g peaks. This difference is du e to t he a i s le floo r s t ruc t ure im pa ct in g first and causing o u t b o ard sea t r ot a t i o n. A t t h e end of t he o u tbo ard sea t r ot a t i o n a p o s iti ve (d o wnwa r d) no rmal acce l era t l o n peak ( 7 0g an d 63g) o ccurs i n b ot h r ear se a t legs as t he du m my m o ves re a rw a rd i n t he se a t , and a t t he e nd of du m my f o rward p lt ch l n gD a l a rg e n e g a tive lo n git ud i n a l a ccel- era t i o n ( 7 0g o n t race (2)) o ccurs because of ti gh t en i ng of t he re st ra i n t system.
• (The n o rmal and l on gi t udinal du m my acce l era tlo n traces are taken re l atlve t o a l o cal du mm y c oo rdinate system perpendicu l ar and paral l e l t o the du m my ' s spine.)
Cabin l a t eral expansi o n ends a t 0.1 46 s e c o nd t wh l ch m a rks t he end of sign ifi c a n t sea t and dummy resp o nse. T h e c a b i n's l at era l e l a s tl c rec o very occurs by 0.306 sec o nd.
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• " N on linear C ras h Im p a ct A n al y sis The object i ve o f the analy ti ca l eff o r ts at L a RC is t o deve lo p the cap a b i l- i ty to predi c t t he n onl i ne a r geometr i c a nd ma ter ial beh avi or of s h eet-str i nger a ircraft structures subject to l a rge defor ma tions a nd t o demons t r a te this c a pa- : b il ity by determ i n i ng t h e plastic buckling and coll a pse response o f s u ch struc- tures t o im puls i ve l o a d i n g s. Tw o spec ifi c fi n i te-e l e m ent computer progr am s are J bei n g de v elo p ed wit h attent i on f ocused on m ode li ng concepts appli c abl e t o la rge p l as ti c de f orma ti ons o f real i s ti c a ircra f t s t ruc t ural co m ponen t s. These tw o programs are d i scussed i n t he follow i ng sections. O t her curren t compu t er pro- : gra m s a v ai lable for cr a sh w or t hy a nalys i s a re rev i e w ed in reference 2. This .
rev i e w de al s p rim a r i ly wi th m odel i ng concepts a nd the relative ca pa b iliti es and l im it a tions of nonl i ne a r co m pu t er progr a ms for a ppl i c ati on to l a rge p la st i c : defor m at ion s o f re a l i st i c veh i cle struc t ures.
. P LANS. - For sever al ye a rs L aR C has b een deve lopi ng a r at her s o ph isti ca t ed : _ p la s ti c a n a lys i s co m pu t er progr am (Pl a s ti c a nd L a rge Deflec ti on An a lys i s of N onl in ear _t ruc t ures) which i ncludes geo m e tri c a s w ell a s ma t e ria l n o nl i near iti es D _ ( r e fs. 3 and 4). This c om p ute r p r o gram f o r static f i n it e- e lem e n t ana lysis i s capab l e o f t rea ti ng pr o blems wh l c: i nclude bend i n g and membrane s t resses, t h i ck and thin a x l sy m me t r l c b od i es, gener a l t hr e e-d im ensi o n a l bo d i es, a nd la mina ted • -' c om p o s it es . The solu ti on p rocedure emb o d i es t he i n itia l st r ai n c o n c ep t which . : ' reduces t he n o nl l n _ ar ma terial a n a lysis to t he an a lysis o f a n el a s ti c b o dy o f i den ti cal shape and b o und a ry c o ng ltio ns, but w it h a n a dd itio n a l se t o f a ppl i ed " effec ti ve plas ti c loads. " The advan ta ge o f t h i s sol u tio n t echn i que i s t h at it .. i . does n o t require m o dif i ca t ion o f t he elemen t s t iffness mat rix at e a ch incr em en t al : lo a d step.
. _ ACT I O N. - A n onl i near dy nami c f i n ite -el eme n t c o m pu te r pr o gr am (Analyzer o f ?i C_rash T..ransien t s i n l__nel a s tl c o _rN_ o nllnear Response (CRASH i n ref. 5)) is being extended at LaRC t o mo re re a l i s t ic a ircr a f t shee t -s t r l nger s t ruc t ures. Me m brane ! e lem e n t s have b ee n added to t h e i n iti al truss and frame s im ulatl o n c apa b i l it y _ii t o p redict th e t rans i en t re s p o nse o f frame s w it h a nd w it hou t shee t cover in gs .
- _ Th i s new computer pr o gram u s e s d i rec t energy mi ni m i za t i o n to o b t a i n s o lu tio n s _ ra t her t han t he usu a l direc t st i ffness m e t hod wh i ch requires mo d i f i c atio ns o f , " t he i ni t ial st i ffne s s ma t ri x f o r plas ti c m a t er ia l bel _ v lo r .
_;i _ Anal yti cal and experimental r e sul ts. - These c om pu te r p r o gr am s ar e cu r re nt ly .' _ be i ng evalua t ed by co m p a r i son w it h experimen t al resul ts o n s o me s i mpl i f i ed _j . s t ruc t ure s . The s e structures a re sh o wn i n figure 1 4 i n t he o rder of increasing c om p l ex it y: an ax i al c om press io n of a clrcu l a _ cy ll nder , a t ubu l ar s t ruc t ure _:il c o mp o sed of 1 2 e l emen t s wi t h symm et r i c cr o ss _ c t l o ns J o ined a t c o mm o n rigid "_ J o in t s, a n a ngular f r am e co m posed of a sy mm etr i c a ngles a nd bulkhe a ds w ith no d a l v eccent r i c iti es a t t he rigid Joints, and t he sa m e angular fr am e covered with . sheet mat er ia l . S t atic a nd dyn ami c a n a lyses of t hese s t ruc t ures loa ded i n t o , t he large deflect io n pl a s ti c coll a p s e regi m e are be i ng c o nduc t ed w it h PLANS and _ : ACTION and are being compared w it h experimen t al d at a . L a rge deflec tio n s tati c analyses w i th corrobora ti ng experim e n t al r e su lt s, f or t he s im p li f i ed s t ru ct u r e s _ s ho wn i n f i gur e 1 4 , a re reported in reference 6.
_ Figure 1 5 i s a pho t ograph of the angul a r frame s t ruc t ure wb l ch me a sures : 1 . 5 m (5 f t ) i n length wit h a base 1 . 3 m by i m ( 4. 2 f t b y 3. 3 f t ) t apering F ,_ 3 75
. ORIGINAI} PA G E IS
_ : OF POORqUAI / I _
l
i I I to 0. 61 m b y 0 . 57 m (2 f t by 1.87 f t) a t t h e t ip. The frame is c ompos e d o f rigi d bu lkhea ds c onn ec ted lon_,tt t tdtnall y by 2 . 54 cm by 2 . 54 cm by 0 .1 6 c m ( 1 in .
b y 1 in. by 0. 062 5 in.) angle. A T-b e am mad e o f two riv e ted 2 . 5 4 c m by 2 .54 c m by 0. 2 4 c m (1 in. by 1 _n. by 0.0 9 4 in.) an_,l e s br_,c c, _ tile rear bulkhead with a ce nt e r T - b e am of t h e sam e d i m e n s i ons. S h o w n i n f i _ : ur o 16 i s a c h r o n olo g i cal s e qu e n ce of c omput e r de fo rmation patterns for the a n pular f ra m e l o a ded im p u l - s i vel y. Th e en d (sm a llest) bulkhead o f th e angular flame w as giv e n an Initlal lon g ltudln a l v e lo c ity at tim e z e ro of 13. 4 m / s (30 mph ) ; t he remaind e r of the f ra m e w a s k e pt a t r e st .
Com p u ter predi c tions o f th e subs e qu e nt d e f o rmati o n pa t t e rns of t he angular . .
fra me obtain e d with th e PLANS c omputer program are sho w n in f igur e 16 fo r v a rious tim e s (in millis ec onds) after initial impact . Th e c omput e r pr e di ct ions in d ic at e no apprec i able co llapse of the first bay of the ang u lar fra m e fo r t he 13 .4 m / s ( 3 0 mph ) lo a ding. Plasti c stress e s and deformat i ons a r e p re s e nt, h ow eve r, i n t he first bay. In igur e 1 7 the fr a m e is loa de d imp u lsiv ely (at t he e nd bulkh ea d ) wi t h a n initi a l v e lo c ity of 89 .4 m / s ( 2 00 mph). T h e fr a m e , un der thi s loading c on d i t ion, e xp e ri e n ce s c oll a ps e i n th e first b a y i n 0. 7 0 milli- sec on d . Corrobor a tion of th e a n a lyti ca l pr e di c tions w ith e xp er im e nt a l d at a i s to b e a cc omplish e d by e xplosiv e ly loading th e a n g ul a r f r a m e in a seq uen c e of ex p erimental t e sts with ex plosiv e sheet , d e tonat e d with fus e cord. A s ch em a ti c a n d ph oto gr aph o f t he t e st s e tu p sho w in g th e angu la r f ram e po s ition ed vert i c a lly wit h the l oad ing on th e e nd bulkh ea d a r e giv e n in f i gure 1 8.
Cr a shworthy D e sign Con c epts T he final ar e a of r e s e arch in the crash safety program is th e de velopm e nt of c rashworthy d e sign c on c epts. Th e obje c tive here is to dev e lop stru c tura l c on c epts that improv e the en e rgy absorption chara c t e risti c s of a stru c ture either by mo d lfylng its stru c tural ass e mbly, c hanging the g e om e try of its e l e m e nts, or ad d ing spe c ifi c en e rgy absorption d evices to h e lp d issipat e k in et i c energ y . R ece n t e fforts in this r e s e ar c h area at LaRC have b e en c on ce ntrate d o n t he d evelopment of c rashworthy air c raft seat and restraint syst e ms. A user- oriente d c ompu t er pro g ram c alled SOMLA (S e at Occupant Mod e l-_i g ht Air c raft), de s c rib ed in r e f e r e n ce 7, is b e ing us e d to study seat and o cc upant r e sponse under c ras h loading c onditions. Th e computer program is bas e d on a t h r ee - d imensional o cc upant and s e at mod e l in whi c h th e o cc upa n t mod e l c onsists of i i rigid mass s e gm e nts. The seat model is composed of beam and m e mbran e _l e m e nts with provision for simulating plastic behavior by t he us e of plasti c hin ge s. ( S ee fig. 19. ) K erlfl c atlon e fforts of SO_A using LaRC full-s c a l e c rash te st d a t a hav e r e sulted in th e in c orporation of modifi c ations to allow for mo re r e alisti c simula t ion of s e at l e g loading and occupant / r e stralnt-system • i nt er fa ce.
A co mp a r ison o f SOMLA's c ompu t er pred i c tions with e xp er im e nt a l d a t a fr o m an ai rcr aft s ec tion d r op test is presented in figure 20. The ai rcr a ft s ect i on is a 1 . 5 m (5 ft) longltudin a l fus e l a g e s ec tion of a twln- e n g ln e a ir c r a f t b eg inning dir ec tly b e hind the pilot a nd c ontaining th e f irst ro w of p a s s e n ge rs .
(S ee f i g . 2 1.) Tbs solid curves in figure 2 0 are experimental a cce l e r at ion s fo r an ai s le seat l e g, a window s e a t l e g, and t h e p e lvis of t h e fir st pa sse n ge r
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i ( b eh i n d the p ilot). T he f t rct passenge r in se a ted in a s t a n d ard air c r aft pa ss eng e r s eat. The da sh ed c ur v e i s ttl e c o m pu t er pr e d i c ti o n of th e p e l v is r es po ns e for thc f i r st pa s s e n g e r ( 50 pe r cen t ile m a le a nthropomo r phic d umm y ) .
Th e pe a k m ag nit ud e and d u ra tion o f th e p e l v i s r e s p ons e sho w g oo d c o rr e l a tio n with t h e ex p erime n t a l da t a. ll owe v e r , t he e x p e r lmen_al da t a ,: x hiblt an i n iti a l n e g a tlve (u pw a rd) acc ele ra tion whi c h diminishes as the se a t , :ushlon c omp re sses, f ollo w e d b y a s ec ond neg a tivo p e a k a s th e o cc u pa nt is lo a d e d by th e s ea t f ra m e.
The f ailu re o f SOMLA to pred i ct t h is r espons e is du e to th e o cc upan t b e in g lo aded throu g h nod e points w hi c h ar c time Inv a riant .
T wo -d im e nsional c om p u ter g raph i c s of S O_R A 's seat , o cc u p a nt , and re s tra in t- " syst e m re s p ons e f o r th e ai rcraf t s ec tion dr o p t e st are s h o w n i n f i gure 22. The c om p ut er grap hi c s sho w th e o cc u pa nt c om pre ssin g th e s ea t c ushion a nd th e s lac kin g ( g ap p in g ) o f th e s ea t b e lt . No shou lder h ar n e ss wa s simu la t e d b eca us e o f th e ver ti ca l t e st c o nd ition and th e imm ed i a t e fl e xing of t he u pper p o r tion o f t he ai rcr a f t s ec tion, a r ti f i c iall y u n lo ad i n g t h e t e st d um m i e s' s h oul der ha r n e ss e s , a s s hown i n fig ur e 21 . C om pu ter gr ap hi c d is pl a ys, a s i ll ust ra te d in fig ur e 22 , a i d i n v i suall y i n t e r pre ti n g th e c o m bined motion s of th e s eat , occ u pa n t , and r e s t r aint sy s t e m d ur i ng the c rash se q uen c e; they are al s o helpful in verify in g mode li n g t ech ni ques an d dat a in p ut.
C O NCL U DING REMARKS Langley Resear c h Cen t er (LaRC) has initiated a c rash safe t y program that will lea d to the development of te c hnology to define and de m ons t ra t e new stru c - tur a l c onc ep t s f o r i m p ro v e d cr as h safe t y and oc c upan t survi va bility in g ene ral a viation aircraft. This te c hnology will m ake possible the integration of crashworthy structural design concepts into general aviation design methods.
The technology will include airframe, seat, and restr a lnt-system concepts that will dissipate energy and properly restrain the occupants within the cabin interior. The current efforts at LaRC are focused on developing improved air- craft components needed for crash protection, and both improved seat and restraint syste m s are being considered as well as structural airfra m e modifica- tions. The dynamic nonlinear behavior of these co m ponents is being a nalytically evaluated to determine their dynamic response and to verify design modifications in structural crushing efficiency. In particular, that portion of the aircraft which surrounds the cabin area is being studied to determine m ethods of effec- tively dissipating crushing loads from three different vector directions while maintaining c abin integrity. Seats and restraint systems with d ec eleration devi c es incorporated are being studied that will absorb energy, remain firmly a ttached to the cabin floor, and adequately restrain the o c cupant fro m impact with the c abin interior. Full-s c ale mockups of structural c omponents are being used to verify a nd provide c orroboration to the analytical design methods.
In the development of aircraft design c riteria, a set of des i gn crash p aram e t er s ar e t o b e de t er min e d fr om both F AA f i e l d da t a a n d L aRC st r uct ural cr ash te st d ata . Th e st r u c tur a l cra sh t e st data will In c h, d e c ontroll e d c r a sh e s a t ve lo c iti e s c om para bl e w i t h th e stall v el o c ity o f most g e ne ra l a vi at ion a i r - craft. Clos e c oo pera tion w i t h oth e r gov er nment a l age n c i e s is b e in g maint a in e d to p r ovid e inpu t s for hum a n tol e r a n ce c rit e ri a c on c erning th e m ag ni t ud e a nd
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d u r aLion of d ec e leration le v els a nd f o r realistic c r as h d ata on s u r v ivablll t y.
Devel o pment o f rellable cr a shw o r t hl n es_ d e sign method_ and analytical tech- ni q ues f o r effe ct i v e c rash pr ot e ction o f g e n e r al a v _a tl on a ir craft _s the f i n a l goa l of the L aR C cras h s af e t y p rogram .
RE F ERENCES • i . V au_;han, Vict o r L., Jr .; a nd A l faro- B o u , Emi li o: I m p act D y n ami cs R ese a rch Faci li ty f o r F u l l -S c a le A irc raft C ra s h T est ing. NASA TN D-81 7 9, 19 7 6.
2 . M c lv o r, I vo r K.: M od eling an d S im u lation as A pp lie d t o Veh i c le S t ru ct ur e s and E x te r i o rs. V e hi c le Safety Research Inte g ra t ion Sym po sium, _ R ep. N o . DOT H S-8 2 0 306, U.S. Dep. Transp., May 19 7 3, p p. 5-18.
L _ 3. Arm e n, H ., J r.; P ifko, A.; an d Le v ln e , H . S.: Finit e Ele m en t Analysis o f Stru c tures in the Plasti c Ran g e. NASA C R -1649, 19 7 1.
[ 4. Pif k m , A.; Levlne, H. S.; Armen, H ., Jr.; and Levy, A.: Plans - A Fini te _ E le m ent P rog r am for N o n l in e ar Ana l y s i s of S t r uctures . P aper 7 4 - WA / PVP-6, : America n S o c . M ec h. En g ., N o v. 197 4.
; 5 . M el o s h, R o be r t J. : Ca r-B ar r l er I m p ac t Resp on se of a C o mputer S im u late d M us tan g . Rep. No. DOT-HS-Og I -I-12 5 -A, U .S. Dep. Transp., Mar. 19 7 2.
6 . Al far o-Bo u , E .; Ha yduk , R . J .; Th o m son, R . G.; a n d V a ug han, V. L., Jr.: Sim u lation of Air c raf t Crash an d I ts Vali d ation. Air c r a ft Cra s hworthlne ss , Ke nnet h Sa c zals k l, Geor g e T. Singley Ill, Walter D. Pilke y , a nd Ronal d L. Hust on, eds ., Univ . Press o f V ir g ini a , c .197 5 , pp . 4 85- 497.
7. Laanane n , Dav id H.: Developme n t of a S cie n t if ic Ba s i s fo r Analy s is of :- A_ x c r af t S eati n g Sy ste m s . Rep . No. F AA -R D- 7 4 -13 0 , J an ua ry 1 9 75 .
":,' 37 8 I I C RAS H WORT H iN ES SD EsI GN AI R F R AME DL S I GN ..__ T ECHNOLO G Y TEcftNOIO GY ] T ECHNOLOGY | TECHNOLOGYj ACTUALCR AS H _CURRENT ANAtYT I CAL_
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CRASH SIMULATION T E STING 'J E LEM E N TS ' .. ' ' , ' _"_ I .
A CRA',--;HWORTHY DESIGN CONCEPTS NONL I NEAR (:RASH IMPACT ANALYS I S Figure 2.- Elements of LaRC cras h sa f ety program.
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Figure 4. - AlrcLa[t crash test method.
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Figur e 6.- Ac c eIerometer layout for a syrm n etrte crash test (no yaw).
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3 82 I r I ; : ,I_ F i gure 9.- Sequence of photographs taken I during full-scale crash tests. 0.05 second between frames.
g u nit s o 1 21 120I- 42 80 35 [ - 120 ) L .... _ t ......... L_.__.I ...... .i ....... L . __I .... i I 0 .02 , 04 .0 6 .0 8 .10 .12 .1 4 .1 6 I A CCELER A T I ON . TI ME, s e c g un it s • oL : , 0 . 06 .08 .I0 .12 .1 4 .16-- . 1 8 .20 TI M E, se c Figure 10.- N ormal acce l eration traces from two e x treme points on floor beam.
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STATIC DYNAMIC _ , _ ANA L YSIS ANALYSIS Figur e 14 . - S im plified s t ructures us e d to corrob or at e experi m en t al d a ta wlth t heore ti cal predi c t ions.
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