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E FF E CTS OF AIR C R AFT N OI S E O N F LI GHT AND GROUND STRUCTU RE S J o hn S. M i xs o n , Wi ll i am H . M a yes , an d C o n r ad M. W i ll i s NASA Lan g ley Resear c h Cen t er SUMMARY Str u ctural vibr a ti o ns c ause d by air c raft no is e c an l ead t o dama ge o f th e stru c ture o r t o tra ns missi o n of n o is e an d vibrati o n th a t re d u c es the c om f o rt o f o c c u p ants. T his p ap e r d is c usses t h r e e e xampl e s involvi n g st r uc- tur a l res po nse t o air c raft ,noise . A co usti c l o ads measure d o n J e t-p o w e r e d STOL co nfigur a ti o ns a re p r e s e nt e d f o r e xt ern ally bl ow n and up per s u rf ac e bl o wn flap models rangin g in size fr o m a small la bor a to ry m o del up to a full-sca l e a ircr af t m o d el . Th e impl ica tio ns o f t he measured l o ads f o r pot en ti al ac o us ti c fa tig u e and ca b in n o ise a r e discussed. N o ise transmis- si o n c haracteristics o f li g h t airc r a f t st ructu r es are p resented. The relative im port ance o f n o ise transmissi o n pa t hs , such as fus el a g e s i d e wall and p rimar y s t ruc t ure , is es t i m a te d. Acc e le r a t i o n resp o nses o f a hist o ric b u i l ding and a r es l den ti a l h o me are p r esen t ed f or f l y o ver n o ise f r o m su b - s o ni c and s u p e r s o nic airc r a ft . Po ssi b le e f fec t s o n o ccu p an t c o mf ort a re as s essed. The r e sults f ro m t hese t hr e e examples sh o w that a ir craf t n o ise c an indu c e stru c tu r al _ esp o nses that ar e lar g e en o u g h to r e q uire c o nsider- atio n in t he d e s i gn or ope r atio n of t he a i r c raft .
IN T R ODUCTIO N N o ise g enera t ed b y a i rcraf t p r o paga te s i n to t h e a i rcraf t it s e lf and t h ro u g h t he a tmo s p here to s t ruc t ures o n t he gro und. I n t he a ir c r af t, t he n o ise c an genera t e vi br a t o ry s t r e ss e s t ha t l e ad to a co us t lc fa ti gu e, o r c an p r op a g a t e t h ro u g h f use l a g e walls an d caus e un co mf ort a b l y h ig h ca bi n n ois e l ev els . On t he g r o und , a i rcraf t n oi se can c ause b u i ld i ng v ib ra t i o ns t ha t m ay lead to da m a ge o r to in c reased disc o mf o rt o f t h e o ccupants.
Penal tie s ass o cia t ed wi t h n o ise ef f e cts o n aircraf t s t ruc t ur e s can tak e t he f o r m o f ex c ess wei ght re q ui r ed to pr ev en t f a t i g ue an d to lo we r n oi se l ev el s , o f mai n t enance re q u i r e d to r e pa i r fa t i g ue f a il ur e s , o r of p assen g er com - pl ain ts o f ex c essi v e n o ise. P e na l t i e s ass o c i a te d w it h n oi s e e ffe ct s o n gr o und s t ruc t ures c a n r a nge f rom un fav ora b l e p u b li ci ty to c o mmun it y a ct io ns ( s uch a s curfew s) t h a t r e strict t he use o f a irp o r t s . T o mi n im ize such • pen a l t ies , it i s i m po rt an t t o ass e ss p ossi b le no is e effe c ts ea r l y i n t he de vel o p m en t o f new ai r c r a ft t ypes, es p eci a ll y th o se w it h incr e as e d pe r fo r- n u an c e, s o t h at n ois e-redu ctlo n m e t h o ds can b e d e v elop e d .
I n t his paper, examp les o f n o ise e ffects are discussed fo r thre e c la ss es o f a i r c ra ft f o r which incr ea sed perf o r ma nce i s bein g s o u g h t . The topics di s cu s s e d are: ST O L a i rcr a f t acous ti c l o ads, l ig ht a i rcraf t n o i s e t r a nsm issio n, a nd b uilding resp o nse to air c raft n o ise. The e m p h as i s o f t he 51 3 I I
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i disc u ssi on i s on t he res p on s e o f t he s t ru ct ure t o t he noise. Im pl ic a ti ons o f t he r e s ul ts f or p o ssibl e s t ru ctu ral dama g e a nd o cc u p an t annoyance due t o noise are discussed.
SYMBO L S Measu r emen t s were made i n U.S. Cus t omary Units , and are pre s en t ed i n both t he In t e r na ti onal Sys t em of Un it s (SI) and U.S. Cus t o ma ry Un it s.
d di ame t er of nozzle ex i t -- f frequency, Hz g accel e -at l on of grav i t y P root mean square o f t he f l uc t ua tl ng c o mp o nen t o f pre s sure E ro s q0 dyna m ic pressure o f t he eng i ne exhaus t fl o w a t t he n o zzle exi t U 0 vel ocit y o f t he eng i ne exhaus t f lo w a t t he n o zzle exit A Sb r eviat i on s : A MST advanced m ed i um STOL t rans p or t E BF ex t er na lly blown flap FPL flu ct ua ti n g pressure level OA _ - _ L overall flu ctu a ti n g p ressure level ms roo t m ean square SPL s o u nd pres s ure level ST O L s h ort (runway) take- o ff and land i n g USB upper s urface b l o wn Refe r en c e l eve l f o r FPL, O AFPL, and SPL is 2 0 _ Pa.
i • ST O L AIRCRAFT AC O USTIC LOADS • " Config ura ti ons and Sources In order t o ob t a i n STOL performance of Je t a i rc r af t using t he power ed - ll f t concep t , a par tl cular arrangemen t of t he aircraft componen t s has been deve l oped.
So m e f ea tures are i llus t ra t ed i n f i gure 1. Powered l l f t is ob t a i ned by defle ct i ng t he eng i ne exhaus t f l ow do wn ward us l v g wing and flaps. To ob t a i n , r s uc h int erac tio n, th e engin e must b e lo c at e d f o rward o f t he w ing , e it her und e r th e w in g (e xt er na ll y blo w n ) or ov er t he w ing ( upp er sur fa ce blown ). In bot h ii c a s es, th e di rec t i mp i ng e m e nt of the h i gh v el o ci t y , t u rb ulen t , e xh au st f lo w s ub jec ts t he w ing an d flap s to i nte n se fluc t ua ting l o a d s ( in t h e prese n ce o f 'i h igh stati c lo a ds and t e mp e rat u r e s) th a t m ay ca us e e x ce ssiv e ac ousti c f a ti g ue.
_ . _ T o mi ni mi z e r otation a l mom e nts wh e n o per atin g wi t h an e ngin e o u t , t he ST OL ai r- ' , l cr a f t' s engin e s a r e l o cate d n ea r e r to t he fusela ge than a r e c on ve nt i o nal a i r- _ :. craf t en g in e s. The lo ca tio n o f the e ngin e s i n a f o rward an d in bo ar d p o s it i o n < . e xp o s e s lar ge r ar e as o f t he fusela g e to mo re in t e ns e ac o us t ic pressur e s t han _-:_ c onventio nal l o ca tio ns . T h e s e h i gh ext ernal a c o us tic press u res may c a us e e xc e ssiv e in terior n o is e l e v e ls. I n add itio n , t h e e x terio r n oi s e of STOL i: }_ air c r a ft wh e n op era t in g in t h e p o w e r e d-l ift m o d e ( t a k e- of f and landin g) is • expec t e d to be of e x ten d e d d u ratio n a s we ll as a t hig h l e v e ls . The s e l o n g du r a - l . i: t io n s at hi g h l evel s in c re as e the li ke li hoo d of un f a vo ra ble n o i se effe c t s o n ! ! , the a ir c r a ft.
i_ii _i_ The t wo p o w ere d - l lf t s y s t e ms cu rre n t ly und er deve l op men t (exter nally b l ow n il f la p an d upper s urf ac e b l o: . n%f la p) a re fundam e n t ally d iffere n t f rom e ach o t h e r ' _ s o that aco u s t i c l o ads infor m ation o n o n e s y s tem may n nt ne c e ssa r ily a p pl y to _; . the other. Therefore, parall e l programs are underway o n bo t h EBF an d USB sys- i_ tem s to d eve l o p a c o us ti c loads i n for m a t io n t hro u gh me a s u reme n t s o n sma ll - scal e ;_ ' m o dels, l arge- s ca l e m ode ls , and fu ll - s ca l e aircraft i n f l ight. The ob j ective s !ii of the s e p rogr a ms ar e to d eve l op metho ds for pr e d ic t in g a c o us t i c lo a ds o n a ir - _il c raf t in flig h t ( us i n g mo d e l te s t s a n d scali ng la w s ) and to provi d e ac ou s ti c _'. l oa ds d a t a o n a c t ual a ir c r a f t fo r us e i n o ng oing d ev elo pme n t s . So m e re sul t s _ fr o m t h e s e re s ear c h p rogr ams a re prese n t e d i n the fo ll o wi ng dis cussi o n .
_ U SB F la p S t ud ie s j ', _ A c oust ic l o ads have been m e as ured on U SB c onf i g u rat i on s in clud ing small ::: l aboratory sc ale m od e ls , s ev e ral 8.9-kN ( 20 0 0 - 1 b) thru s t engine models, and a _: f ull s ize 220- kN (5 0 0 0 0-1b) t hrus t ai r c r a f t e n g i ne configuration. Prepara t i o ns _ a re u nd e rway t o men, sure a c ou s ti c lo a ds on t h e Y C-1 4 AMST ai rc r a f t . Co mpar is on s L:_ are p re s ente d in referen ce s 1 a n d 2 b etween re sul t s f r om s m al l-sca le mod el s , _L _ u sing ai r J e t s to sim u la t e engine e x ha u st, and fro m lar ge- sc ale mode l s ha vi ng _! a c t ua l J et engine s . In figure 2 , re s ul ts a re s hown fro m t e s t s of a full- sc ale i:' YC- 1 4 groun d test rig and a i / 4 -sc ale mo d el of t h a t gro u n d te s t. The full- sca le Y C -14 rig in c ludes a CF6 engine an d m any syste m s t hat are to be flown on the _! air c raft; t h e te s t i ncl u d ed c he c ko u t of s ever al f li ght s y s t e m s, in c luding the % fl o w - t u rning aer o d y namic p erformance of the f la p sy s t em a n d t he flu c t ua t ing ; pressure measuremen t s y s t em. The s c a l e mod e l us e s a 8.9-kN ( 20 0 0 -1b) t hru s t !: - :_ • engine and was designed to geo m etri c ally s c ale the important features of the °_ ful l -s c ale setup. The te s t s in c luded aerodyn a mi c meas u rements of f l ow turning i and thrust, so the acoustic loads results shown were measured on models that Li were operating in a flight-typ e power e d-llft c on di ti o n. In figure 2, overall = " flu c tuating pressur e levels at three positions on the flap and fuselage are :_ shown as a fun c ti o n of the average v e l oci ty o f the exhaust jet at the nozzle !, e xit. Full-scale data are taken from reference 2 . Figure 2 shows that the !: l eve ls o f th e acousti c loads are 135 to 160 dB o n the fuselage (gages 7 a n d 20) . _: a n d up t o 165 dB o n the w i ng (gage 3 4). Thes e l e vels are high en o ugh that %: " 515 [ s ubs t a nti a l eff or t will b e requir , _d t o p r ov i de satisfactory a cou sti c f a ti gu e ll fe an d interi o r noise envlronment'_. Fu ll-- scale results are a bo ut 3 d B hi gh er t h an m od el results, The overa)l a_,re_,me . tb.tween model and full-s c ale results shown in figure 2 is sufficiently good to give confidence that m od el r esults can b e used to predict f ull-scale charactcr ] stlcs . Addition a l a n a l y ses o f the results o btained on the I / 4-scale mode[ tests are underwa y f o r c o mparis o n with t h e full - scale m o del results. Current plans Include measurements o f ac o ustic l o a d s o n t h e wing, flaps, and fuselage of the YC-14 AMS T aircraft to determine a ctual flight levels and e_fects due to forward speed, and t o ob tain results f o r c o m pa ri so n with v a l u es predicted from ground tests. " EBF Studies Aco us tic loading information has bee n measured o n the thr e e EBF configur a- ti o ns shown in figure 3 (ref. 3). Data from the s m all-scale model and the TF34 m o del (using an 36-kN (8000-1b) thrust engine) are intended t o be used w ith scaling laws to provide predictions of acoustic loads f o r full-scale flight situations. Measurements on the YC-15 AMST aircraft are intended to aid the d evel o pment o f the scaling law prediction technique, and to pr o vide ac o ustic l o ads data in an aircraft flight situation for an EBF STOL c o nfigurati o n. Data from the s m all-scale model are compared with results fr o m the TF34 m o del in fi g ur e 4.
In figure 4, values of the di m ensionless fluctuating pressure level (FPL) are presented as a function of Strouhal number. Data for two flap settings are shown at two positions on the flaps. The data for the TF34 model include engine exhaust velocities ranging f_om a _ch number of 0.33 to 0. 5 9. The fact that these data all fall within the narrow dotted region indicates that FPL and Strouhal number are appropriate dlm_usi_, u less quantities to a ccount for the effects of velocity on FPL and f_equency. The figure shows that for three of the four conditions there is good a_lreemeLltbetween the results from the small- scale model (nozzle diameter of 5.08 em (2 I n.)) and from the TF34 engine (nozzle diameter of 96.52 cm (38 in.)). This agree..lentsug_;ests that acoustic loads can b e scaled, at least over the range of variables represented by these two tests.
An indi c ation of the magnitude of the acousti c loads on the EBF configu r a- t ion is given in figure 5. 1,,this i f _<u,e, o' , ,erallfluctuating pressure levels (OAFPL) are shown for seven tra n sdu_-er._;, two f lap positions repr e senting expe c ted fligh t positions, and five e.gin e exhau . ';tv,,lo c lti e s c overing the range from low to full engine power. Exami n at i o n ,,f th , _ tabl e (note the four cir c l e d v a lues) shows that the pressure lew , lx ra_,.e from 1 4 3 dB to 16 3 dB. Previous experien c e with a c oustic f atigue of t:ttu_turL, s :_u£_ests that when levels are in • the 140-dB range, some a c oustit- fat i).,-,, r,a',' he rxpe c ted, and when the levels rise to the 160-dB ran}, e , sub.;ta_tLa } l,rul, lut, m may be a nticipated.
Est i m a t e s o f the inter i o r t_t, l s, , l_,v,, ] : ; t ha t m i _'.h t be expect e d o n pa sse ng e r- c a rr yi ng versi o ns of both the EBF a u,1 the, l l:_l,, air t ,,alt have been made us i ng da t a su c h as ar e shown in f|_,,_1,,,,; ; ' ;_l_d '_ , u_d t . ur_ t mt sid e wall n o ise redu c tion t e c hnology. These estlmat_ , s _:u_ ) ,_,st lhat n , -,w ,Ivv e ]opments either in redu cti on o f exterior n oi s e level : _ o_ ] . imI,_,,v_,_,,,._ ,, l l,,,_ela);_ sidewall n oi se r e ducti o n are needed t o provide a :; ; _t i _ ;f act_,, .... al, i. _,, , i:,_ , e.vlr o nment.
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_ ,: I i I | ' i , ' j , _ I , J c ;II T A I R A L AFq N O ISE T RANSMISSION ) ; J " "" Test Des c ription :_ , Flight measurements o f interi o r noise in light a ircraft (refs. 4 a n d 5) _:: ' , : , h a v e sh o wn that the I t :w, l t_ art, hi},h enough that nois e redu c tion efforts ar e i) . neede d to provid e a noise enviromnent tha t is c omfortable and similar to the : 1 environment that passengers have come to expect f r om their experiences in .... ',!: mo d ern Jet a i r craft . I n ord e r to car r y out noi s e re duc ti o n, it is ne c essary to " ? kn o w t h e sources of the no i se and the transmission pr o perties of c u rrent air- o _ . c raft structures, btudles on light aircraft (refs. 6 and 7) have suggested that , / propellers and engines are important noise sour c es, a nd that p o ssible noise : ' ii tr ans m issio n paths Inc ] ude the exter i or a ir an d f us e la ge s ide wal l (referre d to i , J ! herein as the "airborne" path) and the primary structure (referred to herein : _; , as the "structureborne" path) through whi_n interior noi s e is tra n smitted in the ) ! form of structural vibration that may originate, for example, in the engine.
In order to study the characteristics of these two noise transmission paths, a "" _'_ light aircraft fuselage was set up and tested in the reverberation chamber of i _ o k _ii ' the L angley aircraft noise reduction laboratory, as s hown in figure 6. A sound _ i_ field was generated by speakers, and the c hamber c haracteristics provided a ! " "_ reverberant uniform noise field over the c o mplete exterior of the fuselage.
• _ T hree mi croph o nes in the chamber ( sh own i n f i g. 6) w e r e u s ed to me asu re t h e _o°_:l" _: n oi s e f i e ld exterior to the fuselage. Re ad ing s from t h e s e three m i c rophone s o f du r ing t esting were nearly the same, indicating that the exterior noise field "[" was uniform. Noise was measured inside t he fuselage by the two mlcropho_es E- _,_ s hown i n figure 6 for the reverberant noise fie ld to d eter m ine ai rbor n e n oi s e.
-_ ( o ¢_i_ N oise transmitted through the structureborne path was determined by a ttaching _ _,:. a me c h a ni c a l shaker to t he engine supp o rt str uc t u re a t the front of the a ir c r a ft i_il and t a king measurements with the two microphones inside the fuselage with no _. _ exterior noise fie].d. A broadband spectrum, having nearly c onstant level over '_" _:" t h e frequency ran_,e fr o m about i00 l lz t o I000 Hz f o r the mechanical i n put and i_," fr o m about i00 to 4000 }|z for the acoustic input, was used.
.- j ! A_rborne and Structureborne Transmission ; Some results fr o m t hcs ( _ tests are shown in figure 7, where interior noise L i : l evels measured with e : ; t_, r i , ,rnoise alone and with v i bration input alone are _:. sh o wn. The data show. in I i _ure 7 indicate that the interior noise level SPL _:°_i'_ var i es w i th either c xt ( ,rlo r noise lev e l or mechani ca l input in a l i near trend _o i with 45° slope. Bas_,d on the lo_,_arlthmlcscales used in these figure_, this !: . : I : " result indicat e s that the interior noise level is a linear fun c tion of either ; -_ : ._._ . exterior n o ise, or mech,:._lc,'_] v i bration input. This r e sult was antici p ated and _, . _ _- in d icates that ana l v[|c_ t ] pro ). ,,r a m, , 3 fo r predi c tion an d c o ntr o l of interior n o ise _' ! can be b a sed on tr:tctal,l_, Ilt_t . ;tl relations. The graph o f interior noise as a ,I[ fun c ti o n of exte r i¢,t no i se i nd i cates that the interior l ev els are ab o ut 21 dB . n : " _o ; l o wer than the e xtet h,r l,'v u ls, indicating that the fus e lage is pro v ._ding a : _[ ' i"'":: :$ ' ) significant ov, : r n l ] u,,,; - ,¢, r_.d. c t|on (averaged over frequency and the various '.i / " / of the fusela,;e :, , d,.w:,l! ,,,,i , ,, . . i . det;irable a n d miFht be accomplished by means transmitting struc t ure:; _mch a , ' _ windows and sidewall p anels). Further reducti o n of analytical method,_; t t : .prim t: , ,, the distributio n of mass, stiffness, and i.... .: . dam p ing while re t a i .in_: mi_imt t m _t,i_ht.
: _ " ! ' 517 ! ....'!!:.'F ; . Fi g u re 7 a lso shows th a t v i b r a tio n inpu t s ar e an e f fi c i e nt m ec ha n ism o f : interior nois e g e n e r a t i on. For exa mpl e , 8.9 N ( 2 ib) of vibration for c e input _ results in a n int e rior nois e l e vel of a bout 8 2 dB . The exterior noise l e vel io : re q ui r e d to in d u ce 8 2 dB of interio r nois e is a bout 103 dB. This result s ugg e sts _ " t h at int e rior nois e re sulting from v ib ra tions t ra nsmitt e d t h rough stru c tur a l ! " p a t h s (f r om vibr a tion so urce s in the e ngin e , fo r ex a mpl e ) c an be signifi c ant.
i _ C ont r o l o f su c h stru c t u r e born e n ois e might b e a cc omplished by ,s e of vibr a tion i' isolati o n d e vi ce s such as s h o c k mounts or int e gral d a mping t rea tm e nts in th e e ngine s upp o r t st r u c tur e .
i :i RE S PON S E OF BUILDINGS TO AIR C RAFT N O ISE _ r Study Plan ; ;; T h e a ir p o r t co m mu n it y n oi s e p rob l e m h as b een a majo r concern of airp o rt ! t p lann er s and t he ai r c r a f t m a nu f ac t u rer s and o pe r a tors for ma ny years. This _:_ co n cer n w a s hig h li g ht e d with th e pr o posed in t rodu c t ion o f th e Concorde super- i_!; soni c transport servi c e into t his c ountry. A major publi c c on c ern was expressed i_ in the enviro n mental impa c t state m ent (ref. 8) about the expe c ted Con c orde noise- °i_ i induc e d vibr a t ory r e s p o ns e of hi s t or ic b u i ld i n gs and h om es near the airp o r t i n _ , t e rm s o f s tr uc t u r al da m a ge and a nnoy anc e. A s a resul t o f t h i s c o n c e rn, me a sure- _ : me n t s of n olse- l nd uc ed bu il di n g vibration s hav e been co n d u c ted by Lang l ey ! _ R esea r c h Cen t e r n ear t h e Du l l e s In t erna t ional Airport as p a rt o f th e t otal !__ .% Department of Transpor t a t ion progra m of assess m ent of Con c orde.
The approa c h to the assess m en t of Con c orde nolse-lnduced building vibrations / i_' in vo l v es t he f o llow i n g st ep s: ( i ) me a s u reme n t o f vibr a t ory resp o nse of windows, _. f l oor s , an d w alls o f s e lec t e d bui ldi ng s , in cl uding hi s t ori c al one s ; ( 2 ) d e v el op- _,.:_ m eri t of f unc tio nal r e la t i o n sh ip s ("signatures") b e twee n the vibrat i on r es ponse _i_ o f b u i l di n g e l em en t s a n d th e range of outdoor a n d / o r in doo r n o ise levels asso c i - _. a t e d w ith even ts of i nte r e st; ( 3 ) c omp a ri s o n of t he C o nc o rde-indu c ed r e spon s e . _i _ wit h the respo n se as so c ia t e d with oth e r a ir c r a f t as well a s with c ommon d omestic . , i e v en t s a n d / or c riter i a. It s hould b e noted that c riteria ar e not well est a b - _ fi s he d part ic ularly w it h respe c t to building da m age.
- '_ T e s t Si t e D escrip t io n t -_{: F i g u re 8 is a map of th e D ulles Intern a tional A i rport and s urrounding !-- ' I_ c o m m u nity are as . A ls o s ho w n o n t h e m a p a re t h e n ominal depa r ture fl i ght p a ths _ _ of C on co rde a n d th e loca tion s of the t est s i tes w h ere stru c tural resp o nse wa s , m easu r ed . The t est s i t es i ncl ude one his t ori c buil d ing (Sully Plantation) w h ich if _ is loca ted o n t h e a irpor t bo u nd a ry a bou t 2 . 2 km (1.4 miles) f r o m the end o f t he _-_ cl os e s t run w ay. A ls o m on i tored were t h r ee r esident i al houses of families who i _i had r e g istered c o m pla i nts c on c erned with bu i lding vlbtations due to Concorde operat i ons. These hou s es, lo c a t ed in Montgomery County, Maryland, range from : a bo ut 2 1 to 32 km (13.1 to 19.9 miles) from th e airport.
_ : 51 8 i ( ' t Win do w a nd Wall Res pon se Sampl e vibra to ry r es pons e data and asso c ia te d ou t door n o is e l e v e ls are p r ese n ted in figur e s 9 an d i0. T he fun c ti o nal relati o nship b et w ee n t h e m e asure d vi b ra t i o n r es pon se o f a win do w an d wall o f Sully Plan t ation is sh o wn i n fi g - ur e 9 f o r t he rang e o f o utd oo r SPL m e asur ed d uring t ak e - o ff o p e ra t i o ns o f C o nc o rd e and su b s on ic ai rcr a f t (refs . 9 and i 0 ) . The da ta cluste r a b o ut a sing l e l ine and sh o w a l in e ar r e l a t i o nsh i p b e t we e n resp o nse and n oi se l evel.
Bot h t he C o nc or de n oi se leve l s and i nduced res po nses exceed t he l evels due to su bso nic a i r c raf t by a bo u t I0 d B o r a f a ctor of 3 . A l so, th e respon se of t he _ wall is l o we r t han t h e w i nd o w which w o u l d b e expec t ed because o f t he l a rg er ma s s and s ti ffness o f t he wal l . O f p ar t icula r s ig ni fi canc e i s t he fac t t ha t t he v i br a to ry r esp o nse i s a f unc t i o n o f pr e ssu re a mp l it ude and v i r t ua ll y i nde p enden t o f a i rc r af t t ype. Thus _ t h e i n f erence of re f erences 8 and 1 1 t ha t C o nc or de- i nduced b u il d i n g res po nse w ill b e g rea t er b ecause o f t he lo w-f r e q uen c y c o n t en t o f t he C o n co rd e spec t r u m i s n ot supp o r t ed by t he da t a sh own i n fi g ure 9.
Sample vib ra to ry r es po nse da t a obt a i ned i n t he r e s i den ti al c o mmun itie s o f M o n t g o mer y C o un t y (re f . 1 2) a r e sh own i n f igu r e 1 0 f o r b o t h C o n co rd e and su b - s o nic t ake- o ff o pera tio ns fo r t es t s ite 3. A func tio na l r e lat io nsh i p b e t ween t he vib ra to ry resp o nse and n oi se le v e l s s i m i lar t o t h o se obt a i ned a t t he Sully Plan t a tio n is a g a i n ob ser v e d. Bot h t he n oi se le v els and vibra tio n res po nse due to C o nc or de a r e higher t han t h e levels ass o c i a t ed w it h su b s o n i c a i rcraf t op e r a- t i o ns. H o wever , t h e d i f f erence b e t w e en t he max i mu m l e vels of no i s e and v ib ra- tio n f o r C o nc o rd e and f o r t h e s ubs o nic aircra ft i s a b o u t 2 6 dB o r a f acto r o f 23.
The reas o n f or t he g rea ter di f feren c e b e t ween r esponses of C o nc o rd e and o f su b s o ni c ai r craf t a t t h i s l o ca t i o n as c o mpa r ed w it h t h o se m e asur e d cl o s er to t he a ir p ort a t Sully P lan t a tio n i s b e li eved to b e due t o d iff e r ences i n a irc raf t o pera t i o nal pr o cedures .
Th e li nea r res po nse rel a t i o nsh i p ob ser ved in fig u r es 9 and 1 0 i s s i gn i f ic an t in t ha t it n ot o nly g ives t he a b s o lu t e res po nse of t he a ir craf t a s rec o rded b u t ena b les ex t rap o la tio n to ot her runwa y c ases , f l yov e r d i s t an c es , or h o use l o ca- tio ns if a n o ise da t a b ase i s a v ai labl e. Th e acce l era t ion l e v e l s i ndu c e d b y th e air c raf t a r e sh own to b e h ig h en o u g h to c aus e small ob jec ts to ra tt le , p erhaps r esu lti ng i n increas e d ann o yance.
C ON C L U DING RE_ L% RKS This pa pe r pr e s e nt s thr ee ex amp l es o f s it u a t ion s wh e re st ru c tur al r es pon se s ar e cau sed by aircraft nois e . Acoustic loads measur e d on e x ternally blown and upp e r s urfa ce b l own flap S T OL c onfigurations are shown to be suffici e n t ly hi gh t ha t acou s tic fatigu e and cabin nois e r e quire c ar e ful c onsid e ration f or po ss ible c omm e r c ia l applica t ions. Laboratory studie s of the noise transmission into a i li g ht ai r c raft fu sel age i ndicate that interior no i s e can enter the fu s elage thr o ug h bot h t he f usela ge si de wall tran s m i ss io n path an d t h e pr i mary st ruc t u r e (v i brat i on) tran s m i ss i on path. Ac c elerat i ons mea s ured on the window s and wall s of a h is toric building and a residential home indicate that noise f ro m a s uper- s on ic a i rcraft causes acceleration l e vels high enou g h to b e perceptible b y o cc upants, and that the no i se and vibration levels due to the su p erson i c aircraft 51 9 a re h i ghe r t h a n t ho s e due t o sub s o nic a i rc raft by a l arge enough fa c t or t o p resen t a clear con t r a s t t ha t dr a ws a tt en ti on t o t he s u p e rson i c ai rcr aft .
REFER EN CE S 1 . M o rt on, J e ff rey B .; Rav il a n d, J . K; Ca t a lan o, G . D .; an d Her li ng, W . W .: : Inve stig a ti ons o f Scalin g Laws f o r Je t Im p i n g emen t . P o wered-L i f t i: Aer ody na m i cs and Aco us ti cs, N AS A SP- 4 0 6 , 19 7 6, pp. 44 5- 4 63.
i_ 2. S u ssnmn, M. B.; Hark o nen, D. L.; and Reed, J B.: U S B Env i r o nmen t Measu r e- _[ m en ts B a s ed on F u ll-Sc al e St a tic En g ine Gro und T e s ts • AI AAPa p er :" No . 7 6-624 , J ul y 1 9 7 6• _ ' 3. Sch o en st er, J a m es A.; W i ll i s, C o nra d M .; Schr o eder, J am es C.; a nd i_ M i xs o n, J ohn S•: Ac ou s tlc -L o ads Research f o r Po wered- Li f t C o nfig u r at i o n s .
_i P o we r ed-L i f t A er o dynamic s and Ac o us ti cs, NASA SP- 406 , 19 76 , pp. 4 29- 44 3.
_ ' 4 H ow le tt, Ja mes T.; W il l i ams , Lo us l e H.; C at her i nes, Jo h n J. ; a nd J ha, : Sun i l K .: Me a suremen t , A nalys i s, a n d P red ictio n o f Ai rcraf t I n t er io r I : , No i se. AIA A P a p er N o . 76-551, Jul y 19 7 6.
_ 5. G i l b e rt , G or d o n: Ca b in N o ise L e ve ls . B us. & C o mme r . Av l a t ., J u l y 1 9 7 6, ? pp . 80- 8 2, 84 , 86 .
._ 6 . C a t he rin e s , John J.; an d _ y e s, William H. : I n t e ri o r N o i se L e ve ls of Tw o _ P ro p eller-Driven Li g ht Air cr a f t. N A S A TM X -727 1 6 , 1 97 5.
: 7 Ca t h er in e s, J o hn J ; and Jha, S un l l K . : S ourc e s an d Ch a rac t er i s ti cs o f ' I n t er i or N oi se i n Ge n er a l A v iatio n Ai r c r a f t . NA S A TMX-7 28 39, 1 9 7 6.
',_ 8 . C o nc o r d e Su p ers o n i c T r a nsp o r t A i r c ra f t. Fin a l E nv i r o nmen ta l Im pa ct _ St a t em ent - Vo lume I. FAA, Sept• 19 7 5 .
_ii:: 9. S t aff , L a ngley Res e a rch C e n t e r: C o nc o rd e No lse-Induced B u i ld i ng V ib rat ion s _ : . f o r Sull y P l antation, C hanti lly, Vi rg inia. NA S A TM X- 7 3919 , 1976.
'J i 0. S t a ff, L a n g ley Res ea rch C e n te r : C o ncord e No is e -I nduc e d B uildin g Vibra t io ns, i=!_ Su l l y P l a n tat i o n - R e p o rt No. 2 , C ha n ti l ly, Vi rgi nia . NASA TM X -73926, . ? 19 76.
• I_ _!! i i . W esler, J. E. : C ompa r ativ e Noi se a nd St ruc t ur al V ib r a t ion Leve ls F r om " C on c o rde and S ub s o n i c Ai rc raf t . Pro ceed ing s of th e Technic a l Prog r a m , i , N O I S EXP O - Nat io na l N o i se and V i b r ation Co n tr o l C on fere n ce, c .197 5 , pp. 344 - 3 50 .
1 2 . St af f, L a ng l ey R ese a rc h C e nt er: C on co rde Noi se -I nd uc ed Bu il d i ng V i br ati ons, i" Mont g om er y County, Ma r yland - R e port No. 3 . NASA TM X-7 3 94 7 , 1976.
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